Complete defluorination of PFASs via photocatalytic reduction in water

Domain: chemistry
Published: 2026-02-23
Editorial outcome: major_revision

Abstract
The environmental persistence of per- and polyfluoroalkyl substances (PFASs), driven by the exceptional stability of their C–F bonds, presents a formidable challenge for remediation. Herein, we report the 5,10,15,20-tetraphenyl(4-aminophenyl)porphyrin (TAPP) aggregates as visible-light-driven photocatalysts capable of achieving almost-100% defluorination of PFASs without chemical additives. Central to this process is the ultra-stable TAPP radical species (TAPP•), which exhibits a lifetime exceeding 7 days under ambient conditions. Under visible-light irradiation, TAPP• generates reductive electrons with a potential of −2.68 V NHE, enabling injection into the C–F antibonding orbitals to initiate defluorination. The exceptional stability of TAPP• arises from intramolecular charge delocalization mediated by the synergistic overlap between the lone-pair electrons distribution of the amino groups and the highest occupied molecular orbital. This work develops a steady radical strategy that leverages charge-delocalization to engineer photocatalysts with highly reductive electron, offering an approach to address persistent environmental contaminants.

Introduction
Per- and polyfluoroalkyl substances (PFASs) consist of fully or partially fluorinated alkyl chains, exhibiting daunting stability and bioaccumulation. PFASs pose significant environmental and health challenges due to their ubiquitous distribution and persistence. Thereinto, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are the most prevalent PFASs found in numerous water sources1. In 2024, the World Health Organization cancer agency classified PFOA as carcinogenic to humans and PFOS as possibly carcinogenic2. Regulations on PFASs are gradually stricter, with latest drinking water quality standards (GB5749–2022) in China suggesting concentration limits of 40 ppt for PFOA and 80 ppt for PFOS, while the United States set compulsory maximum levels of 4.0 ppt for both. Water treatment facilities and fluorochemical industries face mounting pressure to comply with these restrictions.

The exceptional stability of PFAS arises from robust carbon-fluorine (C-F) bonds (bond energy: 536 kJ mol−1)3 and fluorine’s high electronegativity. Together, these properties promote a stable, three-dimensional helical conformation (Fig. 1a). This structure creates a static electron shielding effect around the carbon atoms, effectively protecting the carbon chain from nucleophilic attack and rendering PFAS extremely refractory to remediation. To quantify the challenge, we calculated the total energy and relative energy of PFOS and its defluorinated counterpart. Based on these calculations (Supplementary Tables 1 and 2), the reduction potential for PFOS was inferred to be −2.37 V vs. NHE. This highly negative value indicates that strong reductants are essential for degradation. Furthermore, PFAS remediation faces dual challenges: (i) Ultra-low trace concentrations (often parts-per-trillion) hinder efficient enrichment from contaminated matrices, and (ii) inherent amphiphilicity drives conflicted environmental behavior-hydrophilic heads promote aqueous mobility while superhydrophobic perfluorinated chains strongly adsorb to solids, impeding both separation and degradation processes.

Current defluorination methods, such as sonolysis4, advanced reduction processes5 and thermal desorption6,7, are effective only for high PFAS concentrations. These methods necessitate auxiliary conditions, including high–energy inputs (electricity8, sonication9, UV10,11) and additives (sulfite12, iodide13) to enhance the generation of aqueous electrons (e −) and reactive species. Their high operational costs and stringent conditions hinder practical implementation. Consequently, the field prioritizes green remediation strategies capable of complete mineralization without toxic byproducts. While single-excitation photoredox catalysis fails to cleave robust C–F bonds in PFASs, tandem photoexcitation—leveraging two-photon absorption14,15—has emerged to overcome the limited redox potential of visible-light photocatalysis. This approach enables solar-driven activation of recalcitrant bonds through consecutive photoexcitation. However, the nanosecond-scale lifetime of transient radicals necessitates abundant sacrificial reductants (e.g., γ-terpinene) to sustain electron flux for efficient defluorination16.

Our laboratory has published many works highlighting that porphyrin-based supramolecular assemblies act as effective photocatalysts for H₂ evolution and CO₂ reduction17–19, their photogenerated electrons lack the requisite reducing potential for C–F bond cleavage in PFAS. To overcome this limitation, we turned to a two-photon excitation strategy. Inspired by our previous success in manipulating localized hole orbitals in organic semiconductors to generate two-photon-driven carriers20, we rationally tailored the frontier orbital energies and electronic structures of these porphyrin systems. This design enhances the generation of highly reducing electrons capable of driving demanding reductive transformations.

Benefiting from past fundamental advantages, we address the challenging remediation of PFAS through the rational design of TAPP supramolecular aggregates, which enable complete visible-light-driven PFAS defluorination without chemical additives. Density functional theory (DFT) and spectroscopic studies demonstrate that TAPP generates ultra-stable radical species (TAPP•, lifetime > 1 week) via synergistic overlap between the lone-pair electrons of its amino side chains and the porphyrin’s highest occupied molecular orbital (HOMO). This stable TAPP• enables consecutive photoexcitation to yield high-energy electrons (−2.68 V vs. NHE). Mechanistic investigations confirm direct electron injection into C–F antibonding orbitals, achieving quantitative defluorination of PFASs at environmentally relevant concentrations (0.1 ppm). Field trials in natural water systems and outdoor environments validate the catalyst’s robustness under ambient conditions, establishing a scalable framework for mitigating PFAS contamination. This work advances a molecular engineering paradigm that integrates supramolecular charge delocalization with photocatalytic potency, offering a potential pathway to degrade recalcitrant pollutants.

Results
Photoexcitation Produces Stable TAPP•
The proposed consecutive photoexcitation process for high-energy electrons generated, as illustrated in Fig. 1b, operates through three critical stages: (1) Upon visible light irradiation, TAPP undergoes primary electron excitation from the highest unoccupied crystal orbital (HOCO) to the lowest unoccupied crystal orbital (LUCO). (2) Concomitant delocalization of lone-pair electrons from peripheral -NH2 groups stabilizes the resulting TAPP radical species (TAPP•). (3) Continuous visible light irradiation triggering electron transition to higher-energy LUCO+1 orbital in TAPP• and generates an unprecedented reduction potential of −2.68 V vs NHE20. This potential surpasses the standard reduction threshold of PFOS (Ered = −2.37 V) by 310 mV, thermodynamically enabling direct C-F bond dissociation through single-electron transfer processes. Crystallographic, spectroscopic, and density functional theory (DFT) analyses collectively validate this mechanistic pathway.

To comprehensively validate the molecular structure and substituent integration, we employed a multi-technique spectroscopic approach. Vibrational spectroscopy provides chemical fingerprints: Fourier transform infrared spectroscopy (FTIR) analysis identifies characteristic N-H stretching modes at 3300–3500 cm-1, with peaks revealing distinct symmetric (3420 cm-1) and asymmetric (3380 cm-1) vibration components of the -NH2 substituents (Supplementary Fig. 1a)21. X-ray photoelectron spectroscopy (XPS) depth profiling resolves the electronic environment of nitrogen species, where the N 1s core-level spectrum (Supplementary Fig. 1b) exhibits two resolved components at 399.0 eV and 397.2 eV representing pyrrolic N and amine N, respectively. This multimodal structural verification establishes a robust foundation for subsequent electronic behavior analysis.

Ordered molecular assembly is essential to enhance exciton dissociation efficiency and facilitate rapid migration of photogenerated carriers to catalytic sites for efficient redox reactions with PFAS.16 In TAPP, synergistic π-π and van der Waals interactions drive the formation of π-stacked aggregates. Powder X-ray diffraction (XRD) confirms the crystalline structure of TAPP aggregates (Fig. 1c). Pawley refinement determined the symmetry and lattice parameters (Supplementary Table 3), while DFT-optimized atomic coordinates resolved the molecular stacking configuration. We utilized spherical aberration-corrected cryogenic transmission electron microscopy (cryo-TEM) for crystalline structural analysis. The aggregates form uniform nanoparticles with catalytically active surfaces. Cryo-TEM lattice imaging resolved intersecting (144) and (213) facets at an interplanar angle of 82°—consistent with the PXRD-refined crystal structure (Supplementary Fig. 2). Furthermore, we identified an ordered (0 0 2) stacking plane with a periodicity of 9.8 Å (corresponding to the molecular length of TAPP) and an interplanar spacing of 3.2 Å (Fig. 1d), directly visualizing π-π stacked TAPP assemblies. The concomitant suppression of photoluminescence (PL) emission indicates effective inhibition of electron-hole recombination within this ordered lattice (Supplementary Figs. 3 and 4). Photoelectrochemical measurements provide corroborating evidence: a 16-fold increase in photocurrent density and a 245% enhancement in surface photo voltage collectively demonstrate optimized carrier transport dynamics in the crystalline phase (Supplementary Fig. 3a, b). This phenomenon arises from periodic molecular stacking, which minimizes defect states and ensures unimpeded charge transfer to reactive centers.

The frontier molecular orbital architecture of TAPP dictates its photoexcited charge-transfer dynamics. As demonstrated in Supplementary Fig. 5, the HOMO, HOMO-2, and HOMO-3 orbitals localize predominantly on peripheral -NH2 groups, while the lowest unoccupied molecular orbitals (LUMO/LUMO+1) reside on the porphyrin macrocycle (Fig. 2a). This molecular orbital architecture determines hole accumulation on amino side chains and electron population within the polypyrrolic π-system under visible light excitation, inducing asymmetric charge separation. Time-dependent density functional theory (TDDFT) further revealed the influence of orbital distribution on electron-hole separation dynamics. The results show >85% hole density overlaps with nitrogen lone-pair orbitals (Fig. 2c, Supplementary Fig. 6), establishing robust spin-orbit coupling that enables lone-pair delocalization and stabilizes the TAPP• radical. The persistence of this stabilized radical enables sequential secondary excitation to the high-energy TAPP•* state under low irradiance (non-laser light source), providing access to ultra high reduction potentials.

To elucidate the structure-dependent frontier orbital modulation in porphyrin systems, we engineered peripheral substituents with divergent electronic character: TAPP featuring strong electron-donating amino groups (−NH2) was comparatively studied against tetra(4-cyanophenyl)porphyrin (TCyPP) bearing electron-withdrawing cyano groups (-CN) and benchmarked by unsubstituted tetraphenylporphyrin (TPP) as an electronic benchmark (Supplementary Figs. 7 and 8). This systematic design decouples substituent electronic effects from core porphyrin properties: -NH2 groups lower orbital energy in peripheral sidechains via electron-donating conjugation, while -CN groups elevate orbital energy through electron-withdrawing conjugation.

FTIR validated the structural integrity of all porphyrin aggregates, confirming retention of functional group signatures after assembly (Supplementary Fig. 9). UV-vis spectroscopy further demonstrated broad visible-light harvesting capabilities (Supplementary Figs. 10–12). Crucially, a stark contrast emerges in frontier orbital distribution: whereas TAPP exhibits amino-dominated hole localization in its HOMO (Fig. 2b, Supplementary Fig. 13), the cyano-functionalized analogue TCyPP inverts this configuration—electron-withdrawing -CN groups dominate the lowest unoccupied orbitals (LUMO/LUMO+1). This electronic reversal precipitates directional electron transfer upon photoexcitation, with TD-DFT simulations demonstrating migration of electron density from pyrrolic nitrogen to peripheral cyano groups (Fig. 2c, Supplementary Fig. 14). Consequently, the constrained electron localization at cyano sites impedes lone-pair delocalization, thereby suppressing stable radical formation in TCyPP. This atomic-scale orbital engineering dictates divergent fates of peripheral lone-pair electrons: delocalization across the conjugated framework in TAPP versus localization within sidechains in TCyPP, directly modulating porphyrin radical generation efficiency.

Experimental validation via integrated electron paramagnetic resonance (EPR) and cyclic voltammetry confirms TAPP's exceptional radical-stabilization capacity. Transient sextet EPR signals in cyano-functionalized TCyPP and TPP decay completely within 3 minutes due to photobleaching (Supplementary Fig. 15), while TAPP exhibits persistent singlet-state resonance (g = 2.007) under visible light irradiation (λ ≥ 420 nm, 100 mW cm-2), confirming stable TAPP• radical formation (Fig. 2d)22. In situ EPR kinetic analysis reveals rapid photogeneration (τrise = 16 min) and slow decay (τ1/2 = 20 min) of TAPP• in solution, retaining 46% residual radical population after 30 minutes (Fig. 2e, Supplementary Figs. 16 and 17). To circumvent quenching of solution-phase TAPP• by dissolved O2 and H2O2, solid-state TAPP• radicals were investigated. Their stability arises from crystallographic confinement effects, wherein π-π stacking interactions generate a protective lattice environment that spatially isolates unpaired electrons. The solid-state TAPP• radical exhibits unprecedented environmental stability under ambient conditions (Fig. 2f). After undergoing 24-hour ambient diffuse light, the solid samples maintained their spin signal integrity with a remarkably low variance of ±5% in EPR intensity over an 8-day storage period in air (25 °C, 40–60% relative humidity; Supplementary Fig. 18). Notably, this stability surpasses conventional organic radicals (e.g., Mes-Acr• typically quenches within 100 ps14 and the lifetime of PDI•- is 160 ps in solution23).

The exceptional kinetic persistence of the TAPP• radical—maintaining 46% population after 30 minutes in solution and almost negligible attenuation over eight days in air—establishes the foundational platform for sequential photoactivation. Its prolonged lifetime enables continuous harvesting of visible photons (λ ≥ 420 nm) during extended irradiation, while covalent p-π hybridization between amino groups and the porphyrin core localizes unpaired electrons at nitrogen sites, creating a metastable reservoir primed for secondary excitation. Electrochemical interrogation corroborates this resilience through two fully reversible single-electron transfers (–1.03 V and –1.45 V vs NHE, Supplementary Figs. 19 and 20)24, confirming operational stability under aqueous redox cycling.

The absorption peaks of TAPP, TAPP•, and TAPP•* were identified by combining the experiment with TDDFT. Time-resolved spectral dynamics map the sequential charge-transfer cascade: attenuation of the Soret band (400–450 nm) signals ground-state depletion, followed by transient absorption at 450–650 nm marking TAPP• accumulation, and culminating in a 764 nm signature of the high-energy TAPP•* state (Supplementary Fig. 21)25. Crucially, this three-stage trajectory (TAPP→TAPP•→TAPP•*) emerges exclusively under visible-light irradiation, circumventing energy-intensive UV inputs. Thermodynamic validation via TD-DFT quantifies the TAPP•* excited-state reduction potential at –2.68 V vs NHE (Supplementary Notes 1-2), generating a 310 mV driving force relative to PFOS reduction (–2.37 V vs NHE). The synergy between TAPP•’s kinetic persistence (τ1/2 = 20 min) and TAPP•*’s thermodynamic superiority enables concerted C–F bond cleavage—achieving efficient defluorination unattainable with transient radical species.

Photocatalysis PFASs defluorination
The photocatalytic defluorination mechanism of PFOS involves photoexcited electrons with sufficient energy from TAPP cleaving C-F bonds through consecutive photoexcitation processes. Systematic evaluation of TAPP’s defluorination efficiency (deF%) was conducted under standardized conditions: 0.1 ppm PFAS concentration, 0.2 g L⁻¹ catalyst loading, and additive-free aqueous systems. Prior to irradiation, an adsorption equilibrium was established via 6-hour dark-phase preconditioning, with liquid chromatography-tandem mass spectrometry (LC-MS/MS) monitoring real-time PFOS concentrations. No significant desorption of PFOS was observed under irradiation.

TAPP aggregates exhibited exceptional adsorption capacity (Supplementary Fig. 22), achieving complete PFOS removal within 1 hour across a broad concentration range (0.1–50 ppm; Supplementary Fig. 23). Notably, no fluoride ions were detected in solution at this adsorption equilibrium stage. Subsequent irradiation with visible light (λ ≥ 420 nm) triggered gradual fluoride ions accumulation (Supplementary Fig. 24). After 48 hours, fluoride release equivalent to the theoretical maximum from adsorbed PFOS was quantified (0.10 ± 0.01 ppm; Fig. 3a and Supplementary Figs. 25 and 26), confirming photocatalytic defluorination of PFOS contaminants over TAPP aggregates. Of note, the IC analysis detected a peak corresponding to formate, which increased over time alongside fluorine ions. However, its concentration remained consistently below the method detection limit, preventing reliable quantification. In the absence of TAPP aggregates photocatalyst, PFOS exhibited negligible defluorination under identical experimental conditions, emphasizing that conventional photocatalytic processes (e.g. UV direct photolysis) are insufficient for PFOS degradation (Supplementary Fig. 27). The defluorination efficiency of PFOS showed negligible variation (<5% difference) when comparing visible-light (λ ≥ 420 nm) and full-spectrum irradiation (300-800 nm) (Fig. 3b). This wavelength-independent behavior stems from TAPP’s narrow bandgap (1.25 eV) and broad spectral absorption, enabling efficient production of high energy electron across the visible spectrum (Supplementary Fig. 10).

The concentration dependence of PFOS levels (0.1–1 ppm) is shown in Fig. 3c, indicating defluorination decreases with increasing initial PFOS concentration. Comparative analysis of four representative PFAS compounds highlighted higher defluorination rates for perfluoroalkyl sulfonates (PFSAs: OBS, PFOS) versus perfluorocarboxylates (PFCAs: PFOA, PFdeA) (Fig. 3d). This superior PFSAs degradation efficiency contrasts markedly with conventional alkaline thermal treatment (NaOH/DMSO), which achieves >90% defluorination for PFOA in 24 h but less than 1% for PFOS in 150 h26. Additionally, while UVC photocatalysis achieves 25% defluorination for PFCAs like PFOA, they demonstrate ≤5% efficiency for PFSAs such as PFOS under anaerobic conditions27 —a limitation rooted in the electron-withdrawing sulfonate group’s capacity to stabilize radical intermediates. Remarkably, TAPP’s consecutive photoexcitation mechanism overcomes this challenge, achieving 99.8% defluorination for both PFOS (C8F17SO3⁻) within 48 h through controlled reductive electron transfer (−2.68 V vs NHE). This efficacy originates from TAPP•‘s photogenerated electrons that bypass conventional oxidation bottlenecks, instead directly targeting the perfluoroalkyl chain’s high-energy σ*(C-F) orbitals via electron injection. Cyclic experiments spanning 240 hours demonstrated TAPP’s robust durability, maintaining >90% defluorination efficiency across five consecutive cycles (Fig. 3e). XRD (Supplementary Figs. 28 and 29) confirmed preserved crystallinity and structural integrity post-reaction, with no detectable phase transitions.

Reactive species identification through scavenging experiments (Fig. 3f) revealed electron-mediated C-F bond cleavage as the dominant pathway. Complete inhibition of defluorination (deF% <5%) by AgNO3 unambiguously demonstrated photogenerated electrons’ pivotal role, while isopropyl alcohol (IPA) showed partial inhibition (~22% efficiency loss), suggesting minor •OH radical contribution. Methanol’s negligible impact (<3% efficiency change) excluded holes as active participants, aligning with reported reductive degradation mechanisms for sulfonated PFAS.

TOF-SIMS detected no residual PFOS on the photocatalyst surface post-reaction (Supplementary Fig. 30). Furthermore, 19F NMR investigations (Supplementary Fig. 31) shows that PFOS signal gradually decreased and disappeared with 48 h, confirming the defluorination of PFOS. Consistently, LC-MS/MS revealed no detectable PFOS signal in the post-reaction solution (Supplementary Figs 32–35). The terminal products of complete defluorination (Supplementary Fig. 32a, b) are identified as formate, oxalate, and lactate (quantified by HPLC and IC, Supplementary Fig. 36), suggesting complete degradation through sequential defluorination and carbon chain cleavage28. Further analysis of PFOS degradation byproducts at the early-stage intermediates (~10% defluorination, Supplementary Fig. 37) revealed the presence of short-chain perfluorocarboxylic acids (e.g., CF3CH2COO⁻) and fluorinated compounds (e.g., CF3CF2CF2CF2CF=CF, CF3CF2CF2⁻). The identification of intermediates with three or more carbons supports a direct defluorination mechanism, rather than conventional stepwise chain shortening mechanism26,29.

These findings demonstrate that TAPP’s photogenerated electrons selectively engage with the high-energy σ*(C-F) orbitals of PFOS through direct electron injection. Based on the electronic configuration of PFOS, the reductive electrons predominantly populate the antibonding σ* orbital of its LUMO, which spans the perfluorinated carbon tail. This electron transfer destabilizes the molecular framework by elongating the C-C backbone, thereby unwinding PFOS’s helical conformation and disrupting its static electrostatic shielding30. The increased internuclear distance between adjacent fluorine atoms weakens C-F bonds, facilitating their cleavage31. Mechanistic integration in Fig. 3g delineates the defluorination and mineralization process of PFOS.

Photoexcited Electrons from TAPP• Mediate C–F Cleavage
Operando XPS analysis reveals dynamic fluorine chemical state evolution during PFOS photodegradation. Upon TAPP adsorption, the F 1s binding energy exhibits a 0.60 eV downward shift (Supplementary Figs. 38 and 39), indicative of interfacial electron redistribution driven by electrostatic interactions between TAPP and PFOS. The interfacial charge characteristics of TAPP aggregates revealed a pronounced positive zeta potential of +48.7 in aqueous suspension (Supplementary Fig. 40), establishing strong electrostatic complementarity with anionic PFOS molecules. Real-time zeta potential monitoring during PFOS adsorption demonstrated rapid surface charge reversal: within 180 s of exposure to 10 ppm PFOS solution, the potential shifted from +50.1 mV to -9.3 mV. This dramatic charge inversion provides direct evidence of ultrafast PFAS adsorption, achieving sub-minute surficial accumulation.

Visible-light irradiation further reduces F 1s binding energy by 0.45 eV, corresponding to photoelectron injection into C–F bond32. Moreover, Hirshfeld surface analysis via the Independent Gradient Model based on Hirshfeld partition (IGMH) reveals critical non-covalent interactions governing TAPP-PFOS adsorption (Fig. 4a). Distinct electrostatic complementarity and H-bond emerges between PFOS’s anionic sulfonic acid group (−SO3⁻) and TAPP’s protonated amino moieties (−NH3⁺). Concurrently, the perfluorocarbon chain engages the porphyrin plane through extensive van der Waals contacts due to fluorine’s enhanced polarizability. Significant atomic charge redistribution further corroborates wavefunction overlap between TAPP and PFOS, facilitating electron delocalization across the interface33. These results confirm an efficient electron transfer channel between TAPP and PFOS, which overcoming PFOS recalcitrance and enabling electron injection into C–F σ* orbitals. The robust interfacial interaction between TAPP aggregates and PFAS directs preferential electron transfer from photoexcited TAPP to PFAS over competing electron scavengers, as evidenced by EPR studies (Supplementary Fig. 41). While superoxide anion radicals (•O2⁻) can form via oxygen reduction by TAPP-derived photoelectrons (a competing pathway reducing defluorination efficiency), EPR analysis revealed complete suppression of the characteristic DMPO-OOH adduct signal (indicative of •O2⁻ generation) upon introducing 1 ppm PFOS under identical irradiation conditions. This distinct signal disappearance quantitatively demonstrates PFOS’s priority in capturing conduction-band electrons.

Femtosecond transient absorption spectroscopy (fs-TAS) delineates interfacial charge transfer dynamics in TAPP during PFOS defluorination. The transient absorption kinetics under 400 nm excitation (Fig. 4b and Supplementary Fig. 42) revealed two ground-state bleach (GSB) signals at 480 nm (Soret band) and 600 nm (Q band)34. The long-lived stimulated emission (SE) peak at 670 nm indicated excited-state electron relaxation. Notably, short-lived excited-state absorption (ESA) at 760 nm is aligned with the persistent photoproduct absorption (PA) at 740 nm in UV-Vis-NIR spectra referring to the second excited state (TAPP•*). The suppression of SE and ESA signals in the TAPP/PFOS system unequivocally underscores efficient interfacial electron transfer.

Triexponential fitting in Fig. 4c revealed three distinct phases—ultrafast phonon relaxation (τ1 = 52.3 ps), excitation annihilation within the band gap (τ2 = 243.9 ps), and triplet-pair decay (τ3 = 1852.3 ps)35,36. Further calculations show that the average lifetime (τave) is 1557.2 ps. Remarkably, the TAPP/PFOS system exhibited a drastically shortened lifetime τave = 0.4 ps—a 99.97% reduction—providing definitive evidence of rapid charge transfer to PFOS. In summary, the mechanism of high-energy photoexcited electrons-driven C–F bond cleavage in PFOS proceeds through three key stages (Fig. 4d): (1) targeted adsorption via dual van der Waals and electrostatic interactions, (2) sequential electron excitation generating high-energy reductive states, and (3) concerted reductive/oxidative degradation pathways achieving complete defluorination. This approach establishes a framework for designing advanced photocatalytic systems.

Environmental suitability assessment
The environmental adaptability of TAPP was systematically evaluated to bridge laboratory-scale efficiency with practical application requirements. A pilot-scale photocatalytic reactor (Fig. 5a), designed to mimic conventional wastewater treatment workflows, achieved complete (100%) PFOS defluorination within three days under natural solar irradiation, demonstrating its scalability under real-world conditions. To further assess interference from environmental matrices, three representative water systems were tested (Fig. 5b): municipal tap water (containing residual disinfectants and inorganic ions), natural organic matter (NOM, from Suwannee River), and soluble inorganic matter (IOM, 1 ppm K⁺ and 10 ppm Na⁺). Remarkably, TAPP retained full defluorination efficiency in NOM-laden systems, highlighting its robustness and anti-interference to organic co-contaminants. For IOM and tap water matrices, however, complete defluorination required extended treatment durations (60 h), likely due to ionic competition from K⁺/Na⁺ reducing PFOS adsorption via electrostatic screening and the formation of electroneutral PFOS-cation complexes, which hindered interfacial congregation on TAPP’s surface.

TAPP exhibits exceptional stability and energy efficiency, eliminating reliance on exogenous oxidants (e.g., peroxydisulfate) and artificial UV irradiation. As quantified in Fig. 5c and Supplementary Table 4, the solar-driven system reduces energy consumption by 90–98% relative to conventional photocatalysis. Comparative analysis reveals TAPP-mediated PFAS defluorination operates at 3.99 kWh/m³, outperforming all reported light-activated catalytic systems. Notably, this represents >96% energy savings compared to technologies achieving ≥50% defluorination efficiency. While CdS nanocrystals demonstrate near-complete defluorination, their prohibitive energy demand (139 kWh/m³) and cadmium toxicity preclude practical environmental deployment. The synergy of solar autonomy, chemical independence, ultra-low energy requirements, and non-toxic heavy metal properties of TAPP organic semiconductors establishes TAPP as a scalable, economical solution for PFAS remediation in resource-constrained settings.

In conclusion, the recalcitrant C-F bond cleavage constitutes the core challenge in PFAS remediation37,38. Here, we engineer air-stable TAPP• radicals (>7-day persistence) through molecular orbital synergy—where amino lone-pair electrons delocalize via π-conjugation/HOMO overlap upon photoexcitation. Subsequent photoactivation of these radicals generates highly reductive electrons (-2.68 V vs NHE) that selectively cleave C-F bonds in adsorbed PFOS via direct electron transfer. By achieving solar-powered defluorination without sacrificial reagents or energy-intensive infrastructure, this approach offers insights for sustainable PFAS destruction under ambient conditions. Furthermore, this study provided a feasible molecular engineering paradigm for generating high-energy photoexcited electrons, suggesting potential for demanding photocatalytic reductions such as hydrodehalogenation.

Methods
Chemicals and photocatalysts synthesis
All the chemicals were AR grade and used as received. Heptadecafluorooctanesulfonic acid potassium salt (98%, PFOS-K) and sodium p-perfluorous nonenoxybenzene sulfonate (98%, OBS-Na) were purchased from J & K, used as the source of pollutant PFOS and OBS, respectively. 13C4-PFOS were purchased from Wellington Laboratories (Guelph, Ontario, Canada), with concentration 50 μg ml-1 in methanol and was added to the sample to make a concentration of 0.05 ppm. PFOA and PFdeA was 98% from Meryer. 5,10,15,20-tetraphenyl (4-aminophenyl) porphyrin (98%, TAPP), tetraphenylporphyrin (98%, TPP) and meso-Tetra(4-cyanobenzyl)porphine (98%, TCyPP) was purchased from Bidepharm. Aluminum trichloride (99%) and methanol were purchased from Aladdin. Chloroform and dimethylformamide were both from Adams. NOM from Suwannee River (2R101N reference sample) was legally purchased from the International Humic Substances Society (IHSS).

The synthesis of porphyrin derivatives was conducted through a straightforward method, in which TAPP (0.20 g, 0.15 mmol) was dissolved in CHCl3/DMF (60 ml/15 ml) and a methanol solution of AlCl3 (0.07 g, 5.5 mM). The mixture was refluxed at 80°C under nitrogen protection for 24 h and then rotary evaporated to concentrate. The residue solution was added dropwise into 100 ml DIW and aged for 1 h. The precipitation was centrifuged and washed with DIW several times to obtain purple powder (yield: 63%). TPP aggregates (yield: 70%) were obtained through a similar process without the addition of DMF and methanol, while TCyPP aggregates (yield: 65%) used DMF as the only solvent in the first step.

Characterisation and analytic methods
Powder XRD were obtained by Rigaku D/max-2400 X-ray diffractometer using a Cu Kα1 (λ = 1.5418 Å) at 40 kV and 200 mA. XPS spectrum was measured by ESCALAB 250Xi equipped with an Al target. Cryo-electron microscopy (cryo-EM) was conducted by Thermo Fisher Scientific Titan Krios with K3 Summit Direct Electron Detector equipped with a GIF quantum energy filter. Fourier transform infrared (FT-IR) spectra were obtained using a Bruker V70 FTIR spectrometer. Water contact angle data were acquired from a DMe-211 Plus of Kyowa Interface Science Co, Ltd. at ambient conditions. UV-Vis diffuse reflectance spectroscopy was collected by a Hitachi U-3010 spectrophotometer. The surface potential was evaluated through Zeta potential (Horiba SZ-100). For the adsorption kinetics, 0.02 g L−1 of the sample was dispersed in a 10 ppm PFOS solution (pH = 4.2), and 0.5 mL of the sample was collected at specific intervals of time. The degradation experiments were performed in triplicate and error bars represent to standard deviation. The fluorine ion and formate were measured by ion chromatography (Metrohm 831, Switzerland) with a conductivity detector equipped with an A Supp 5 250/4.0 column, and sodium carbonate/sodium bicarbonate as mobile phase (Supplementary Figs. 46 and 47). Oxalate acid and lactic acid was measured by HPLC (Supplementary Figs. 48 and 49). LC-MS/MS analyses were performed using Shimadzu LCMS-8060 triple Quadrupole MS (LC-MS/MS), coupled to Shim-pack GIST Phenyl-Hexyl (2 mm ID X 100 mm) (Supplementary Figs. 50–52). Detailed analytical procedures are described in Supplementary Note 3 and Supplementary Table 5. Time of flight secondary ion mass spectrometry (TOF–SIM, TOFSIMS 5–100, ION–TOF GmbH) equipped with Bi3+ ion beam was used to analyse the photocatalyst surface.

Photocatalysis treatment
Photocatalytic degradation experiments were carried out in a 50 ml quartz tube containing PFASs aqueous solution, with a photocatalyst concentration of 0.2 g L−1 and no cocatalysts or additives. To ensure environmental relevance and practical applicability, the initial concentration was set at 0.1 ppm. A 500W Xenon lamp, placed at the center of the water–cooling tube, is used as light source with light intensity of 70 mW cm−2. For those experiments with visible light, a 420 nm filter was added (Supplementary Fig. 44). Each mixed suspension was stirred under dark conditions for 6 h to reach the adsorption equilibrium. For the outdoor experiment, 0.5 L 0.1 ppm PFOS with 0.2 g L−1 photocatalyst was filled in a reactor (Supplementary Fig. 45, size: 20 × 20 × 3 cm) and a pump was used to keep the internal recycling.

During fixed intervals of time, 2 ml samples were taken out and passed through 0.2 μm syringe filter to remove the solid for subsequent analysis. The degradation experiments were performed in triplicate and error bars represent to standard deviation. The fluorine ion and formate were measured by ion chromatography (Metrohm 831, Switzerland) with a conductivity detector equipped with an A Supp 5 250/4.0 column, and sodium carbonate/sodium bicarbonate as mobile phase (Supplementary Figs. 46 and 47). Oxalate acid and lactic acid was measured by HPLC (Supplementary Figs. 48 and 49). LC-MS/MS analyses were performed using Shimadzu LCMS-8060 triple Quadrupole MS (LC-MS/MS), coupled to Shim-pack GIST Phenyl-Hexyl (2 mm ID X 100 mm) (Supplementary Figs. 50–52). Detailed analytical procedures are described in Supplementary Note 3 and Supplementary Table 5. Time of flight secondary ion mass spectrometry (TOF–SIM, TOFSIMS 5–100, ION–TOF GmbH) equipped with Bi3+ ion beam was used to analyse the photocatalyst surface.

Theoretical calculations
The HOMO–LUMO analysis was performed using Gauss 16W. The states of structure and the vibration frequency calculations were carried out by the B3LYP functional and 6–31G(d) basis set, using water as an implicit solvent to simulate solution effects. All the atomic coordinates of DFT calculation has been provided in Supplementary Data 1–3. Time–dependent density functional theory (TDDFT) was performed by the CAM–B3LYP/6–311G(d) to simulate the adsorption spectra. The PFOS adsorption of the TAPP model was simulated, and the supercell of TAPP was illustrated using the Material Studio programs. The final structure and total energy of STAPP–PFOS were optimized using Dmol3 module of Material Studio 202039,40. Multiwfn 3.7 program was used to analyze the adsorptive interaction of TAPP for PFOS and visualized through VMD 1.9.3 program41,42.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study presents a highly innovative approach to PFOS degradation using a stable porphyrin radical (TAPP•) photocatalyst under ambient conditions. The authors provide compelling mechanism insights into how intramolecular charge delocalization of porphyrin endows exceptional stability of TAPP• (> 7 days) and a remarkable reduction potential of −2.68 V vs. NHE. The achievement of complete defluorination without chemical additives or external heating represents a potential paradigm shift in PFASs treatments. All in all, this is a meaningful work with comprehensive characterizations and detailed discussions, offering an insightful PFASs remediation technology. I would like to recommend publication of this manuscript in Nature Communications after addressing the following comments.\n1. Given by reported PFASs defluorination study, most of the defluorination routes require alkaline conditions. How does TAPP avoid OH- dependency? I wonder what is the initial pH of the defluorination test.\n2. Please provide post-reaction SEM or TEM image of TAPP aggregates to verify the catalyst integrity.\n3. The abbreviations are suggested to be standardized, using either TDDFT or TD-DFT.\n4. In the section of “High-Energy Photoexcited Electrons from TAPP• Mediate C–F Bond Cleavage in PFOS”, the F1s of XPS directly provide electron transfer between TAPP-PFOS. How about the other elements? Please include complementary analyses (N1s, S2p spectra) to confirm TAPP-PFOS interaction.\n5. The authors emphasized TAPP is “visible light driven” and “sunlight driven”. The wavelength range of the light source is suggested to be provided.\n6. I noticed that the authors compared four different types of PFASs. Why were they chosen? Are they common and representative of environmental-relevant?\n7. The outdoor experiment is impressive, but the details of the experiment are expected to be provided. What is the size of the reactor and the loading of photocatalysts?\n8. Data Presentation: eg., In Fig. 5a, the x-axis label “time” is overlapped to the frame; Fig. 3d (C8F17SOK vs. correct C8F17SO3K); Line 40, the “totalenergy” should be corrected to “total energy”.\n9. Fig. 3c suggests incomplete defluorination of 0.2 ppm PFOS within the tested timeframe. Does extending the reaction duration enable complete defluorination at this concentration? Additionally, why the minimal defluorination is observed at 0.3 ppm PFOS, compared with 0.1, 0.2, 0.5 and 1 ppm.", "reviewer_2": "The authors present an interesting and promising study on the complete defluorination of PFOS. The manuscript is well-written and employs a range of advanced analytical techniques and modeling approaches to investigate the underlying mechanism.\nHowever, before the manuscript can be considered for publication, several important points need to be addressed to strengthen the evidence for complete PFOS defluorination:\n1.Experimental Details:\nSome key experimental details are lacking:\n(a) In the adsorption experiments, the authors mention stirring the suspension under dark conditions. Please clarify how the stirring was performed. Was stirring also applied during photodegradation? If a magnetic stirrer was used, it is important to consider potential contamination from Teflon-coated stir bars, which could introduce fluorine.\n(b) The manuscript lacks detailed information on the analytical procedures for PFAS detection by LC-MS/MS. The authors should provide descriptions of the quality assurance and quality control (QA/QC) protocols used, including method detection limits, calibration strategies, and recovery tests.\n2.Adsorption and Desorption:\nThe manuscript states that PFOS was adsorbed onto TAPP aggregates; however, no information is provided on desorption. To accurately determine the degradation efficiency of PFOS or PFASs, desorption experiments should be conducted to distinguish between adsorbed and degraded fractions.\n3.Reaction Pathway and Analytical Evidence:\n(a) The TOF-SIMS analysis appears to show a variety of intermediate products even in the untreated samples (Figure S24), raising questions about background signals and sample handling.\n(b) As mentioned above, desorption should be conducted prior to intermediate analysis to ensure that the reported products are from actual degradation.\n(c) The use of ¹⁹F NMR would provide strong, direct evidence of fluorine removal and should be considered to complement the LC/MS and TOF-SIMS data.\n(d) The manuscript states that the final degradation products include formate, oxalate, and lactate. Given that formate, oxalate, and lactate are commonly detectable by IC or HPLC, the authors are encouraged to quantify these species pre- and post-treatment. Such data would provide compelling evidence to support the extent of PFOS mineralization.\n4.LC/MS Data Interpretation:\nThe authors mention that LC/MS analysis of PFOS degradation byproducts suggests the presence of early-stage intermediates (~10% defluorination), such as short-chain perfluorocarboxylic acids (e.g., CF₃CH₂COO⁻) and fluorinated compounds (e.g., CF₃CF₂CF₂CF₂CF=CF, CF₃CF₂CF₂⁻). However, this alone is not sufficient evidence of complete degradation, especially in the absence of post-treatment LC/MS data. Furthermore, TOF-SIMS results suggest that many of these intermediates may already be present prior to treatment.\n5. For defluorination of various PFASs, PFSAs generally exhibit much higher defluorination efficiency than PFCAs. This trend contrasts with results obtained using hydrated electrons, which have an even stronger reduction potential (~ –2.9 V vs. NHE), where PFOA typically undergoes greater defluorination than PFOS. The reasons for this discrepancy are not yet fully understood. Could it be related to PFSAs being more readily adsorbed by TAPP aggregates?\nIn Supplementary Figure 6, nitrogen atoms are missing from the cyano groups in TCyPP structure.\nIn summary, while the study is of high interest, further experimental clarification and additional quantitative data are needed to robustly support the claim of complete PFOS defluorination.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Response to the reviewers’ comments\nManuscript Title: Complete defluorination of PFASs via photocatalytic reduction in water\nManuscript Number: NCOMMS-25-47396-T\nAuthor: Meichi Chong 1, Qixin Zhou 1, Jingyi Xu 1, Zhaohui Wu 1, Enwei Zhu 1, Wenlu Li 1,\nLing Zhang 1, Yan Guo 2* and Yongfa Zhu 1*\n[The reviewer comments are shown in italic; responses are in blue; all revisions in the main\ntext and supplementary information are highlighted in red]\nEditor’s Suggestion:\nComment from the editor: This is optional, but the work might benefit from some additional\ncomments on Supramolecular Photocatalysts, for example in your recent paper\n(https://doi.org/10.1002/anie.202405962) you demonstrated that this family of the catalysts\nshow exceptional increase in photocatalytic performance, perhaps highlighting this aspect\nwould not only broaden the scope of the work (thereby attracting the attention of researchers\nthat are working in other areas, not just PFAS degradation) but also explain the motivation\nbehind the catalyst selection As I said earlier, this is just a recommendation, and I leave it up\nto you to decide. I am happy to discuss more, if needed.\nResponse: We sincerely appreciate the editorial team's constructive feedback. Our laboratory\nhas published many works highlighting that supramolecular photocatalysts, such as porphyrin-\nbased supramolecular, exhibit exceptional photocatalytic performance in H evolution (Adv.\n2\n2025, 11.1).\nOur motivation for selecting TAPP aggregates stems from past fundamental advantages. Their\nability to generate long-lived, high-energy photoexcited electrons is not only crucial for the\nchallenging PFASs remediation but also suggests their broad potential for driving other\ndemanding photocatalytic reductions. We have now added a sentence in the introduction to\nbriefly mention this context and included a discussion in the conclusion section to highlight\nhow this work extends the application of supramolecular photocatalysts.\nRevised in Manuscript:\n(Manuscript Page 3) While we have shown that porphyrin-based supramolecular assemblies\nact as effective photocatalysts for H₂ evolution and CO₂ reduction,17-19 their photogenerated\nelectrons lack the requisite reducing potential for C–F bond cleavage in PFAS. To overcome\nthis limitation, we turned to a two-photon excitation strategy. Inspired by our previous success\nin manipulating localized hole orbitals in organic semiconductors to generate two-photon-\ndriven carriers,20 we rationally tailored the frontier orbital energies and electronic structures of\nthese porphyrin systems. This design enhances the generation of highly reducing electrons\ncapable of driving demanding reductive transformations.\n(Manuscript Page 21) Furthermore, this study provided a feasible molecular engineering\nparadigm for generating high-energy photoexcited electrons, suggesting potential for\ndemanding photocatalytic reductions such as hydrodehalogenation.\nRef.\n17. Jing, J., J. Yang, Z. Zhang, and Y. Zhu, Supramolecular Zinc Porphyrin Photocatalyst with\nStrong Reduction Ability and Robust Built‐In Electric Field for Highly Efficient Hydrogen\nProduction. Advanced Energy Materials. 11(29), (2021).\n18. Xu, J., et al., Efficient Photocatalytic Hydrogen and Oxygen Evolution by Side-Group\nEngineered Benzodiimidazole Oligomers with Strong Built-in Electric Fields and Short-\nRange Crystallinity. Angew Chem Int Ed Engl. 61(45): p. e202212243, (2022).\n19. Xu, J., et al., Guiding electron transfer for selective C H photoproduction from CO .\n2 6 2\nChem. (2024).\npotentials under visible light. Chem. 10(4): p. 1252-1267, (2024).\nReviewer #1\nGeneral comment: This study presents a highly innovative approach to PFOS degradation\nusing a stable porphyrin radical (TAPP•) photocatalyst under ambient conditions. The authors\nprovide compelling mechanism insights into how intramolecular charge delocalization of\nporphyrin endows exceptional stability of TAPP• (> 7 days) and a remarkable reduction\npotential of −2.68 V vs. NHE. The achievement of complete defluorination without chemical\nadditives or external heating represents a potential paradigm shift in PFASs treatments. All in\nall, this is a meaningful work with comprehensive characterizations and detailed discussions,\noffering an insightful PFASs remediation technology. I would like to recommend publication\nof this manuscript in Nature Communications after addressing the following comments.\nResponse: We thank reviewer 1 for his positive comments on the manuscript and are grateful\nto reviewer 1 for giving us the opportunity to revise and clarify experimental details.\nComment 1: Given by reported PFASs defluorination study, most of the defluorination routes\nrequire alkaline conditions. How does TAPP avoid OH- dependency? I wonder what is the\ninitial pH of the defluorination test.\nResponse: Thank you for the helpful comment. In our experiment conditions, the pH values\nvaried with the PFOS concentration, ranging from approximately 6.5 for 0.1 ppm to 4.4 for 1\nppm. These initial environments are neutral to weakly acidic, as detailed in the revised\nSupplementary Figure 42. We agree that alkaline conditions are crucial in many reported\nsystems, such as UV/sulfite processes, where they facilitate the generation of hydrated\nelectrons and ensure PFASs are in anionic form for better contact with catalysts.\nIn contrast, the TAPP-photocatalysis system in our study operates differently. Highly reductive\nelectrons are generated through the consecutive photoexcitation of TAPP aggregates, a\nmechanism distinct from the generation of hydrated electrons. Besides, as shown in\nSupplementary Figure 20, TAPP aggregates exhibit a remarkable intrinsic adsorption capacity\nof PFOS without pH modification. The peripheral amino groups on TAPP act as Lewis basic\nsites that interact strongly with anionic PFOS, providing strong interaction between the\npollutant and the catalyst. This dual contribution of electronic excitation and intimate contact\nenables efficient defluorination under neutral to mildly acidic conditions, without the need for\nalkaline adjustment or co-catalysts.\nSupplementary Figure 42. The pH value in different PFOS concentrations.\n(Supplementary Page 48) “The pH values varied with the PFOS concentration, ranging\nfrom approximately 6.5 for 0.1 ppm to 4.4 for 1 ppm. The initial environments are neutral to\nweakly acidic”\nComment 2: Please provide post-reaction SEM or TEM image of TAPP aggregates to verify\nthe catalyst integrity.\nResponse: Thank you for the comments. In response, the TEM image of post-reaction TAPP\naggregates was added in the Supplementary Figure 43 (TEM of fresh sample: Supplementary\nFigure 2), which shows no significant morphological change compared to the pre-reaction\nsample. Besides, XRD measurement was performed in Supplementary Figure 23, which\nundoubtedly confirmed the structural integrity of reacted TAPP aggregates. The XRD patterns\nremain consistent before and after the reaction, supporting the stability of TAPP aggregates\nunder the photocatalytic conditions used in this work.\nSupplementary Figure 2. Crystal structure analysis. (a) Transmission electron microscopy\n(TEM) images\nSupplementary Figure 43. Transmission electron microscopy (TEM) images of post-reaction\nTAPP aggregates.\nSupplementary Figure 23. XRD measurement of fresh and post-reaction TAPP aggregates.\nComment 3: The abbreviations are suggested to be standardized, using either TDDFT or TD-\nDFT.\nResponse: Thank you for this correction. We appreciate the reminder and have now\nstandardized the abbreviation to “TDDFT” throughout the manuscript. The relevant sentence\non Page 8 has been modified accordingly:\nComment 4: In the section of “High-Energy Photoexcited Electrons from TAPP• Mediate C–\nF Bond Cleavage in PFOS”, the F1s of XPS directly provide electron transfer between\nTAPPPFOS. How about the other elements? Please include complementary analyses (N1s, S2p\nspectra) to confirm TAPP-PFOS interaction.\nResponse: Thank you for the helpful advice. As recommended, the XPS analyses (C1s, N1s\nand S2p) of pristine PFOS and TAPP-adsorbed PFOS were included in Supplementary Figure\n29. These results consistently support the interaction between PFOS and TAPP aggregates. The\nappearance and shift of the -CF signal to lower binding energy in the C 1s spectrum suggest\n2\nthe successful adsorption of PFOS. Furthermore, the N 1s spectrum shows a significant shift\nto higher binding energy for the terminal amino groups of TAPP. Conversely, the S 2p\nspectrum exhibits notable changes and a shift to lower binding energy, attributed to hydrogen\nbonding between the sulphonate groups of PFOS and -NH group of TAPP.\nSupplementary Figure 29. X-ray photoelectron spectroscopy (XPS) tracking of chemical states\nduring photocatalytic PFOS adsorption: (a) C 1s, (b) N 1s, (c) S 2p.\n(Supplementary Page 37) “The adsorption interaction proved by XPS spectroscopy was\nconsistent. Likewise, as depicted in the Supplementary Figure 28, the presence and movement\nto lower energy of a -CF signal in the C 1s spectrum suggests the successful adsorption of\narisen in the terminal amino group of TAPP. Conversely, a significant shift to lower binding\nenergy was observed in the S 2p spectrum, attributed to electrostatic interaction between the\nsulphonate groups of PFOS and -NH group of TAPP.”\nThe wavelength range of the light source is suggested to be provided.\nResponse: We appreciate the reviewer’s suggestion. In response, we have included the\nemission spectrum of the Xe lamp (Supplementary Figure 44) used in our experiments. As\ndescribed in the Methods section, a 420 nm cut-off filter was applied to block wavelengths\nbelow 420 nm, ensuring irradiation was confined to visible light with wavelengths above 420\nnm.\nSupplementary Figure 44. The spectrum of Xe lamp and Xe lamp with 420 nm cut-off.\nComment 6: I noticed that the authors compared four different types of PFASs. Why were they\nchosen? Are they common and representative of environmental-relevant?\nResponse: We appreciate the reviewer for raising this important point. The four PFASs\nselected for this study- PFOA, PFOS, PFDeA and OBS- are indeed representative both legacy\nand emerging PFASs.\nPFOA and PFOS are two of the most widely detected PFASs, usually used in packaging,\nfirefighting foams and cookware industries. Their significant environmental persistence and\ntoxicity are well-established. In fact, the International Agency for Research on Cancer (IARC)\nhas classified PFOA as carcinogenic to humans (Group 1) and PFOS as possibly carcinogenic\n(Group 2B) as of 2024. PFDeA, a long-chain perfluoroalkyl acid, is often found in outdoor\ntextiles and cosmetics. OBS, an increasingly used substitute for PFOS, shares similar refractory\ncharacteristics due to its C-F bonds. Thus, the selected PFASs encompass both classic and\nemerging pollutants with environmental significance, supporting the relevance of our study.\nThe environmental concentration of PFOS, PFOA and OBS in water is typically from 15 to\n500 ppt (ng/L) (Environmental Sciences Europe, 2021, 33.1: 6), while PFDeA is often found\nat 40 to 80 ppt (Environmental research, 2023, 237: 117036.). The PFASs concentrations could\nbe higher (ppb to ppm levels) in populated areas (American Journal of Industrial Medicine,\n2023, 66.5: 379-39, Scientific Reports, 2025, 15.1: 16241.). Considering the experimental\ndetection limitations, systematic evaluation of TAPP's defluorination performance (deF%) was\nconducted under standardized conditions: 0.1 ppm PFAS concentration 0.2 g L⁻¹ catalyst\nloading.\nComment 7: The outdoor experiment is impressive, but the details of the experiment are\nexpected to be provided. What is the size of the reactor and the loading of\nphotocatalysts?\nResponse: Thank you for your positive evaluation and detailed comments. To further\ndemonstrate the scalability of the outdoor reactor, we provided a detailed dimension figure of\nthe reactor in Supplementary Figure 49. The size of the reactor was 20 x 20 x 3 cm and the\nphotocatalyst loading was 0.2 g L–1.\nWe revised the manuscript accordingly on Page 24:\n(Manuscript Page 24) “For the outdoor experiment, 0.5 L 0.1 ppm PFOS with 0.2 g L–1\nphotocatalyst was filled in a reactor (Supplement Figure 49, size: 20 × 20 × 3 cm) and a pump\nwas used to keep the internal recycling.”\nSupplementary Figure 49. Detailed dimensions of the outdoor reactor.\nComment 8: Data Presentation: e.g., In Fig. 5a, the x-axis label “time” is overlapped to the\nframe; Fig. 3d (C F SOK vs. correct C F SO K); Line 40, the “totalenergy” should be\n8 17 8 17 3\ncorrected to “total energy”.\nResponse: We appreciate your attention to detail, which has greatly improved the accuracy of\nour manuscript. We have corrected them in the revised manuscript:\nFig. 5a. Comprehensive assessment of TAPP-mediated PFOS remediation under\nenvironmentally relevant conditions.\nFig. 3a. Photocatalysis PFASs Defluorination of substrate scope analysis of polyfluoroalkyl\nsubstances ([PFAS] = 0.1 ppm, catalyst loading = 0.2 g L–1)\n(Manuscript Line 40) “To quantify the challenge, we calculated the total energy and\nrelative energy of PFOS and its defluorinated counterpart.”\nComment 9: Fig. 3c suggests incomplete defluorination of 0.2 ppm PFOS within the tested\ntimeframe. Does extending the reaction duration enable complete defluorination at this\nconcentration? Additionally, why the minimal defluorination is observed at 0.3 ppm PFOS,\ncompared with 0.1, 0.2, 0.5 and 1 ppm.\nResponse: We thank the reviewer for the insightful comments regarding the defluorination\nefficiency at different PFOS concentrations. For the first question, we conducted additional\nexperiments by extending the reaction time under the 0.2 ppm PFOS condition. As shown in\nthe revised Supplement Figure 45, complete defluorination was achieved within 72 h.\nRegarding the apparent minimal defluorination efficiency at 0.3 ppm PFOS, we apologize for\nany confusion caused by the original figure. The defluorination efficiency at 0.3 ppm is not the\nlowest among the tested concentrations. Instead, the efficiencies from 0.3 ppm to 1 ppm are\nrelatively similar. This phenomenon likely reflects the complex balance between adsorption\nand degradation processes, potentially influenced by factors such as mass transfer and\ncompetitive adsorption of intermediates. However, as we do not yet have conclusive\nmechanistic evidence to support a definitive explanation, we have removed the defluorination\nefficiency curve from the revised figure to avoid possible misinterpretation.\nSupplement Figure 45. Photocatalysis PFOS defluorination of 0.2 ppm PFOS (full spectra).\n(Supplementary Page 51) “Complete defluorination was achieved within 72 h for the 0.2\nppm PFOS condition.”\nFig. 3c. Concentration-dependent defluorination efficiency under full-spectrum illumination\n(PFOS: 0.1–1 ppm)\n(Manuscript Page 13) “The concentration dependence of PFOS levels (0.1–1 ppm) is\nshown in Fig. 3c, indicating defluorination decreases with increasing initial PFOS\nconcentration.”\nReviewer #2 :\nGeneral comment: The authors present an interesting and promising study on the complete\ndefluorination of PFOS. The manuscript is well-written and employs a range of advanced\nanalytical techniques and modeling approaches to investigate the underlying mechanism.\nHowever, before the manuscript can be considered for publication, several important points\nneed to be addressed to strengthen the evidence for complete PFOS defluorination:\nResponse: We thank reviewer 2 for his positive comments on the manuscript and are grateful\nto reviewer 2 for giving us the opportunity to revise and clarify experimental details.\nComment 1:.Experimental Details:\nSome key experimental details are lacking:\nComment 1(a): In the adsorption experiments, the authors mention stirring the suspension\n the suspension\nunder dark conditions. Please clarify how the stirring was performed. Was stirring also applied\nduring photodegradation? If a magnetic stirrer was used, it is important to consider potential\ncontamination from Teflon-coated stir bars, which could introduce fluorine.\nResponse: Thank you for raising the important point about the potential fluorine contamination.\nReviewer 2's consideration further improved the manuscript. In the both adsorption (dark) and\nphotodegradation experiments, each mixed suspension was stirred at a constant rate of 380 rpm\nusing a digital magnetic stirrer with PTFE-coated bar.\nThe possibility of potential fluorine contamination from PTFE-coat stir bars was systematically\ninvestigated through a series of control experiments. Control experiments detected no fluoride\nrelease attributable to the stirrer under these conditions (Supplementary Figure 21).\nConsequently, observed PFOS defluorination is exclusively ascribed to the heterogeneous\nphotocatalytic activity of TAPP aggregates. We have added the following discussion to the\nrevised version:\nSupplementary Figure 21. Defluorination of 0.1 ppm PFOS in the presence of porphyrin\nderivatives.\n(Supplementary Page 28) “A series of control experiments systematically excluded\nalternative degradation pathways:\n(i) Control experiment with PFOS under irradiation without photocatalysts (Fig. 3b)\nshowed negligible fluoride ion release, effectively ruling out defluorination from direct\nphotolysis or mechanical degradation induced by the stirring process.\n(ii) Control experiment with TAPP aggregates under irradiation but in the absence of PFOS\n(Supplementary Fig. 21) was conducted. No detectable fluoride ions were released in\nthis scenario, which excludes the PTFE stir bar as a notable fluorine source.\nThese results unambiguously demonstrate that PFOS defluorination observed in our study is\nexclusively attributable to the heterogenous photocatalytic activity of TAPP aggregates.”\nComment 1(b): The manuscript lacks detailed information on the analytical procedures for\nPFAS detection by LC-MS/MS. The authors should provide descriptions of the quality\nassurance and quality control (QA/QC) protocols used, including method detection limits,\ncalibration strategies, and recovery tests.\nResponse: We thank the reviewers for the insightful suggestion. We have now included a\ndetailed description of the LC-MS/MS analytical procedures and the corresponding quality\nassurance/quality control (QA/QC) in the revised Supplementary Note 3:\n(Manuscript Page 24) “LC-MS/MS analyses were performed using Shimadzu LCMS-\n8060 triple Quadrupole MS (LC-MS/MS), coupled to Shim-pack GIST Phenyl-Hexyl (2 mm\nID X 100 mm). Detailed analytical procedures are described in Supplementary Note 3.”\n(Supplementary Note 3 on Page S60) “The quantification of PFOS was conducted by\nShimadzu LCMS-8060 triple Quadrupole MS (LC-MS/MS), coupled to Shim-pack GIST\nPhenyl-Hexyl (2 mm ID X 100 mm). A delay column (Shim-pack XR-ODS, 3 mm X 50 mm)\nwas installed to account for potential background PFASs contamination from the system and\nlaboratory consumables. Column temperature was set as 40˚C. The mobile phase consisted of\n(phase A) 5 mmol L-1 ammonium acetate and acetonitrile (phase B). The flow rate of mobile\nphase was 0.2 mL min-1, with a gradient elution program: 90% phase A for 1 min, 90-70%\nphase A for 2 min, 70-35% phase A for 11 min, 35-2% phase A for 0.1 min, 2-90% phase A\nfor 3 min and 90% phase A for 2.9 min. PFOS were quantified by negative electrospray\nionization (ESI) mode via selected reaction monitoring (SRM). The ESI source conditions were\nas follows: gas flow 5 L min-1, 300˚C. The SRM transitions for PFOS were 499.0  79.8 at a\ncollision energy (CE) of 62. 13C -PFOS was used as an internal standard (IS) at a concentration\n4\nof 0.05 ppm in all samples, with the transition m/z 503.0  79.8 at a CE of 60.\nA six-point calibration (Supplementary Figure 51) was performed, ranging from 0.01 ppm\n(mg L-1) to 0.1 ppm, with r2 values of 0.9993. The method detection limit (MDL) was 0.01\nppm (mg L-1) while the injection volume is 10 μL. For QA/QC, recovery tests were conducted\nat three concentrations (0.01, 0.05 and 0.075 ppm) in triplicate. The measured recoveries\nranged from 94 to 98%, with relative standard deviations (RSDs) below 5%, confirming the\nhigh accuracy and precision. These details of recovery data are provided in Supplementary\nTable S5.”\nSupplementary Figure 51. LC-MS/MS calibration curves for PFOS.\nTable S5. Recovery tests results of LC-MS/MS.\nConcentration (ppm) Sample Area ratio (A/A ) RSD (%) Recovery (%)\nIS\n1st 0.267028\n0.01 2nd 0.253952 2.53 95.1\n3rd 0.252507\n1st 1.256363\n0.05 2nd 1.345136 4.08 94.4\n3rd 1.386216\n1st 2.031128\n0.075 2nd 2.154476 2.44 98.5\n3rd 2.076634\nComment 2:.Adsorption and Desorption:\nThe manuscript states that PFOS was adsorbed onto TAPP aggregates; however, no\ninformation is provided on desorption. To accurately determine the degradation efficiency of\nPFOS or PFASs, desorption experiments should be conducted to distinguish between adsorbed\nand degraded fractions.\nResponse: We thank the reviewer for raising this important point, which has prompted us to\nprovide further clarification in the revised manuscript. Our experimental results demonstrate\nthat TAPP aggregates exhibit strong adsorption capacity for PFOS, achieving nearly complete\nremoval from the solution across the tested concentration range (0.1 to 10 ppm). This high\nadsorption efficiency is primarily attributed to van der Waals interactions between TAPP and\nPFOS, as discussed on page 16 of the manuscript.\nAs rightly emphasized by the reviewer, understanding the desorption behavior is essential\nto accurately distinguish between adsorption and degradation. In response, we have conducted\nadditional experiments to evaluate the potential desorption of PFOS under irradiation. The\nconcentration of PFOS in the solution was monitored using LC/MS, and the results\n(Supplementary Figure 22) indicate no significant desorption of PFOS during the process.\nInstead, the degradation of PFOS was quantitatively confirmed through the stoichiometric\nrelease of fluoride ions, with a fluoride ion recovery rate reaching up to 99.8%, as measured\nby ion chromatography (Fig. 3a). This high recovery rate further indicates that PFOS adsorbed\nonto TAPP aggregates is effectively degraded rather than undergoing desorption.\nThe following statement has been added to the revised Supplementary Information:\nSupplementary Figure 22. Removal and defluorination of PFOS by TAPP aggregates (0.1 ppm\nPFOS, [photocatalyst] = 0.2 g L-1, full spectra)\nFig 3a. Fluoride ion and intermediates quantification via ion chromatography (IC) during\nvisible-light-driven PFOS degradation.\n(Supplementary Page 30) “Following dark adsorption equilibrium, the concentration of\nPFOS decreased from an initial 0.1 ppm to 0.015 ppm, achieving a 98.5% removal rate. The\nconcentration of PFOS in the solution was monitored using LC/MS throughout the\nphotoirradiation process (Supplementary Figure 22), revealing no significant desorption of\nPFOS from the photocatalyst. Concurrently, the incessant release of fluoride ions (F⁻) was\nmeasured, serving as direct evidence that the removal of PFOS is primarily due to degradation\nrather than adsorption”\nComment 3: Reaction Pathway and Analytical Evidence:\nComment 3(a): The TOF-SIMS analysis appears to show a variety of intermediate products\neven in the untreated samples (Figure S24), raising questions about background signals and\nsample handling.\nResponse:\nWe are very grateful to the reviewer for raising this important point. We sincerely apologize\nfor the lack of clarity in our original presentation of the TOF-SIMS data, which may have led\nto misinterpretation.\nAs the reviewer rightly implies, TOF-SIMS is a surface-sensitive technique that operates via a\nhigh-energy primary ion beam, which sputters and ionizes species from the surface of a solid\nsample. This process inherently fragments the surface material, and signals originating from\nthe intrinsic photocatalyst can appear in the untreated sample (like fresh TAPP aggregates).\nTherefore, the resulting spectrum is naturally dominated by signals intrinsic to the\nphotocatalyst material itself.\nIn our initial submission, displaying the full m/z range unfortunately included these intrinsic\nfragment peaks, which obscured the critical signals from adsorbed species such as PFOS and\nfluoride ions. We agree with the reviewer that this was not ideal and diluted the central message.\nAs shown in Figure R1, the spectrum of the post-adsorption (before light irradiation) showed\na significant peak of intact PFOS- (m/z = 498.9297) and its characteristic fragment, F- (m/z\n=18.9990), confirming its adsorption. After photocatalytic reaction, the PFOS signal vanished,\nand distinct new peaks emerged exclusively on the surface of the reacted TAPP aggregates,\nincluding C H O ⁻ (m/z = 148.9985), C H O ⁻ (m/z = 74.9851). These observations confirm\n4 5 6 2 3 3\nthat the detected ions are not from background signals.\nFigure R1. Negative ion TOF-SIMS spectrum of reacted, post-adsorption and fresh TAPP\naggregates.\nBesides, we would also like to clarify that TOF-SIMS was mainly employed to confirm the\nremoval of PFOS from the photocatalyst surface. Accordingly, the Supplementary Figure 24\nwas modified to better reflect this purpose. In contrast, the identification of the intermediate\nwas primarily based on LC-MS/MS analysis (detailed in our response to Comment 4).\nTherefore, the proposed degradation mechanism (Fig. 3g) highlights the intermediate detected\nby LC-MS/MS.\nTo improve clarity, we have revised the manuscript as follows:\nSupplementary Figure 24 Negative ion TOF-SIMS spectrum of reacted TAPP aggregates (0.1\nppm PFOS degradation reaction after 48 h with visible light irradiation), post-adsorption TAPP\naggregates and fresh TAPP aggregates.\n(Manuscript Page 15) “TOF-SIMS detected no residual PFOS on the photocatalyst surface\npost-reaction (Fig. S24). Consistently, LC-MS/MS revealed no detectable PFOS signal (Fig.\nS25c) in the post-reaction solution. Instead, the terminal products of complete defluorination\n(Fig. S25a-b) are identified as formate, oxalate, and lactate, suggesting complete degradation\nthrough sequential defluorination and carbon chain cleavage28. Further analysis of PFOS\ndegradation byproducts at the early-stage intermediates (~10% defluorination, Fig. S26)\nrevealed the presence of short-chain perfluorocarboxylic acids (e.g., CF CH COO⁻) and\n3 2\nfluorinated compounds (e.g., CF CF CF CF CF=CF, CF CF CF ⁻). The identification of\n3 2 2 2 3 2 2\nintermediates with three or more carbons supports a direct defluorination mechanism, rather\nthan conventional stepwise chain shortening mechanism26, 29”\n(Manuscript Page 24) “Time of flight secondary ion mass spectrometry (TOF–SIM, TOF\nSIMS 5–100, ION–TOF GmbH) equipped with Bi3+ ion beam was used to analyse the\nphotocatalyst surface.”\nFig. 3g Proposed PFOS degradation pathway via sequential C–F bond cleavage and\ndegradation. The yellow highlight represents LC-MS/MS-detected products.\nWe believe these revisions provide a much clearer and more accurate interpretation of our data,\nand we thank the reviewer again for their insightful comment, which has significantly improved\nthis section of the paper.\nComment 3(b): As mentioned above, desorption should be conducted prior to intermediate\nanalysis to ensure that the reported products are from actual degradation.\nResponse: We appreciate the reviewer’s thoughtful comment regarding the necessity of\ndesorption before intermediate analysis. We appoloize again for the misleading expression in\nthe original manuscript. As outlined in our response to Comment 2, we have carefully\nconsidered the potential impact of adsorption on the observed results. However, no significant\ndesorption of PFOS was detected under irradiation. Additionally, we have clarified in the\nrevised manuscript that no residual PFOS on the photocatalyst surface was detected after the\nreaction, as confirmed by TOF-SIMS analysis.\nLC-MS/MS analysis, which was the primary method for identifying the degradation\nintermediates, provided a comprehensive overview of the degradation pathway. To address the\nconcern about desorption, we performed a 15-minute sonication desorption step followed by\nLC-MS/MS analysis (Supplementary Figure 26). No additional signals were observed in the\ndesorbed solution and majority of the intermediate peaks weakened, likely due to further\ndegradation or volatilization of the terminal products.\nSupplementary Figure 26. LC-MS of the complete defluorination sample after 15 min of\nsonication desorption. (0.1 ppm PFOS under 48 h visible light irradiation). (a) range m/z=80-\n160, (b) range m/z=180-250 and (c) range m/z = 400-550.\n(Manuscript Page 15) “Consistently, no detectable PFOS signal was observed from the\npost-reaction solution (Fig. S25c) or in the solution after 15 min of sonication desorption (Fig.\nS26c). The terminal products from complete defluorination (Fig. S25a-b) are identified as\nformate, oxalate, and lactate, suggesting complete degradation through sequential\ndefluorination and carbon chain cleavage28.”\nComment 3(c): The use of ¹⁹F NMR would provide strong, direct evidence of fluorine removal\nand should be considered to complement the LC/MS and TOF-SIMS data.\nResponse: Thank you for the construction suggestion. We fully agree that 19F NMR could\nprovide valuable evidence for fluorine analysis. We indeed attempted this approach, however,\nfluorine NMR typically requires relatively high analyte concentration (often in the millimolar\nrange, e.g., >500 ppm PFOS), as noted in prior reports (Progress in nuclear magnetic\nresonance spectroscopy, 70, 25-49, Journal of hazardous materials letters 2 (2021): 100023).\nIn our study, the PFAS concentrations were intentionally set as trace levels, which better reflect\nenvironmentally relevant conditions (ppb to ppt). Under these concentrations, as well as even\n10 ppm PFOS, no discernible NMR signals could be observed (Supplementary Figure. 46).\nWe have added the corresponding discussion in the revised supplementary:\nSupplementary Figure. 46. Liquid state of 19F NMR spectroscopy of 400 μl sample (a) added\nin 100 μl D O and (b) added in 100 μl CDCl .\n2 2\n(Supplementary Page 52) “In 19F NMR, the reaction solution and 10 ppm PFOS shows no\ndetectable signals due to the inherently low sensitivity of NMR.”\nComment 3(d): The manuscript states that the final degradation products include formate,\noxalate, and lactate. Given that formate, oxalate, and lactate are commonly detectable by IC\nor HPLC, the authors are encouraged to quantify these species pre- and posttreatment. Such\ndata would provide compelling evidence to support the extent of PFOS mineralization.\nResponse: We appreciate the insightful suggestions to quantify potential products. As shown\nin Fig. 3a, the IC analysis did detect a peak corresponding to formate, which increased over\ntime alongside fluorine ions. However, its concentration remained consistently below the\nmethod detection limit (Supplementary Figure 37, Limit of detection: 0.1 ppm), preventing\nreliable quantification. Similarly, we attempted to quantify oxalate (Supplementary Figure 38,\nLimit of detection: 1 ppm) and lactate (Supplementary Figure 39, Limit of detection: 0.4 ppm)\nusing HPLC, but the trace-level concentrations fell below the reliable quantification range of\nour analytical method under the experimental conditions.\nImportantly, considering that the initial PFOS concentration was only 0.1 ppm, the expected\nconcentrations of carbon-containing products are far below not only the instrument detection\nlimits but also the level of background carbon contamination and analytical fluctuations (e.g.,\n0.1 ppm PFOS totally converted to lactic acid is approximately 0.048 ppm). Due to PFASs\ntoxicity at extremely low concentrations, the quantitative detection of these PFASs\ncontaminants and degraded products is always a significant challenge for related studies. (npj\nClean Water 8.1 (2025): 41., ES&T 53.5 (2019): 2731-2738) Therefore, while we are not able\nto quantitatively confirm the presence of these products, the most reliable and definitive\nevidence for PFOS degradation in our system remains the stoichiometry release of fluorine ion,\nwhich can be measured accurately.\nWe have included a note in the revised manuscript to clarify this limitation and to state that\ntheir low concentrations hindered the quantitative tracking of minor organic intermediates.\n(Manuscript Page 12) “Of noted, the IC analysis detected a peak corresponding to formate,\nwhich increased over time alongside fluorine ions. However, its concentration remained\nconsistently below the method detection limit, preventing reliable quantification.”\nSupplementary Figure 37. Standard calibration curve of oxalate by ion chromatography (LOD:\n0.1 ppm).\nSupplementary Figure 38. Standard calibration curve of oxalate acid by HPLC (LOD: 1 ppm).\nOperational conditions for HPLC: 0.05% H PO /methanol (97/3, v/v); flow rate: 0.5 mL min-\n3 3\n1 and detection wavelength 215 nm. Injection volume: 50 μL.\nSupplementary Figure 39. Standard calibration curve of lactic acid by HPLC (LOD: 0.4 ppm).\nOperational conditions for HPLC: mobile phase: 0.1% H PO /methanol (97.5/2.5, v/v), flow\n3 3\nrate: 0.5 mL min-1 and detection wavelength 210 nm. Injection volume: 20 μL.\n(Supplementary Page 47) “We attempted to quantify oxalate (Supplementary Figure 38,\nLimit of detection: 1 ppm) and lactate (Supplementary Figure 39, Limit of detection: 0.4 ppm)\nusing HPLC, but the trace-level concentrations fell below the reliable quantification range of\nour analytical method under the experimental conditions. Due to PFASs toxicity at extremely\nlow concentrations, the quantitative detection of these PFASs contaminants and degraded\nproducts is always a significant challenge for related studies5, 6.”\nComment 4:.LC/MS Data Interpretation:\nThe authors mention that LC/MS analysis of PFOS degradation byproducts suggests the\npresence of early-stage intermediates (~10% defluorination), such as short-chain\nperfluorocarboxylic acids (e.g., CF₃CH₂COO⁻) and fluorinated compounds (e.g.,\nCF₃CF₂CF₂CF₂CF=CF, CF₃CF₂CF₂⁻). However, this alone is not sufficient evidence of\ncomplete degradation, especially in the absence of post-treatment LC/MS data. Furthermore,\nTOFSIMS results suggest that many of these intermediates may already be present prior to\ntreatment.\nResponse: We thank the reviewer for raising these critical points that improve the clarity and\nrobustness of this work. As addressed in response to Comments 3a and 3b, we apologize for\nany confusion caused by TOF-SIMS demonstration. The complex signals from the fragments\nof TAPP aggregates could have interfered the TOF-SIMS analysis.\nTo clarify, we have now ensured a cleaner presentation of LC-MS/MS data. Post-treatment\nLC-MS analysis for complete defluorination of 0.1 ppm PFOS under visible light is provided\nin Supplementary Figure 25. The presence of small organic acids, such as formate, oxalate and\nlactate in the final reaction solution, further supports the complete degradation of PFOS.\nFor more information regarding the LC-MS/MS analysis, we used the NIST20, mzCloud\nOffline PFAS Reference 2024 and mzCloud Offline PFAS Autoprocess 2024 databases for\nLC-MS/MS analysis. For species not present in these libraries, we calculated exact masses for\npredicted formulas based on plausible degradation pathways (Science,2022, 377, 839-845). MS\ndata for several short-chain fluoride intermediates (including CF CF=CFO-, CFOCFH- and\n2 2\nSupplementary Figure 25. LC-MS of terminal products under complete defluorination (0.1\nppm PFOS under 48 h visible light irradiation). (a) range m/z=80-160, (b) range m/z=180-250\nand (c) range m/z = 400-550.\nSupplementary Figure 47 MS spectra of several fluoride intermediates corresponding to LC-\nMS of early-stage intermediates for ~10% defluorination.\nSupplementary Figure 48 MS/MS spectra of intermediates corresponding to LC-MS of\ncomplete defluorination.\nComment 5:. For defluorination of various PFASs, PFSAs generally exhibit much higher\ndefluorination efficiency than PFCAs. This trend contrasts with results obtained using\nhydrated electrons, which have an even stronger reduction potential (~ –2.9 V vs. NHE), where\nPFOA typically undergoes greater defluorination than PFOS. The reasons for this discrepancy\nare not yet fully understood. Could it be related to PFSAs being more readily adsorbed by\nTAPP aggregates?\nResponse: Thank you for your raising this constructive question regarding the contrasting\ndefluorination trends in different reductive systems. As the reviewer pointed out, hydrated\nelectrons typically show greater defluorination of PFOA compared to PFOS. This is often\nattributed to the higher stability of the sulfonate functional group.\nIn contrast, our photocatalytic system exhibits a different trend, with PFOS exhibiting higher\ndefluorination efficiency than PFOA. This discrepancy is due to the stronger affinity and\nadsorption strength between TAPP aggregates and PFSA molecules. As shown in\nSupplementary Figure 31, the maximum adsorption capacity of PFOS (62.54 mg g-1 h-1)exceeds that of PFOA (51.05 mg g-1 h-1). The sulfonate group in PFOS is more acidic and\nreadily ionized than the carboxyl group in PFOA, allowing it to form stronger ionic interactions\nwith the amino-functionalized TAPP aggregates. This stronger adsorption not only enhances\nthe surface concentration of PFOS on the catalyst but also facilitates more efficient interfacial\nelectron transfer, ultimately leading to higher defluorination efficiency.\nThe related discussion in the revised Supplementary has been added:\nSupplementary Figure 31. Kinetic adsorption capacity of 50 ppm PFASs on TAPP aggregates\n( [photocatalysts] = 0.2 g L-1).\n(Supplementary Page 37) “TAPP aggregates showed minor adsorption capacity to PFOA.\nThe maximum adsorption capacity was calculated to be 62.54 mg PFOS g-1 h-1 and 51.05 mg\nPFOA g-1 h-1.”\nComment 6: In Supplementary Figure 6, nitrogen atoms are missing from the cyano groups in\nTCyPP structure.\nResponse: Thank you for your kindly reminder. The structure of TCyPP in Supplementary\nFigure 6 has been corrected.\nSupplementary Figure 6. Molecular structure of TAPP, TPP and TCyPP.\nIn summary, while the study is of high interest, further experimental clarification\nand additional quantitative data are needed to robustly support the claim of complete PFOS\ndefluorination.\nResponse: Thank you for the positive evaluation to our work. We hope to have answered all\nyour questions here. If we unintentionally left something out, we shall revise that if you point\nout.\nReviewer #3\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This\nis part of the Nature Communications initiative to facilitate training in peer review and to\nprovide appropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We thank the reviewer 3 for the constructive comments and suggestions, which\nhave greatly improved our manuscript."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have diligently revised and improved the manuscript in accordance with the requirements, and I endorse this manuscript for publication in Nature Communications.", "reviewer_2": "The authors have made substantial efforts and addressed several of the earlier concerns. However, some issues remain that require further clarification. Please see below:\n1. On Supplementary Page 30, the authors state:\n“Following dark adsorption equilibrium, the concentration of PFOS decreased from an initial 0.1 ppm to 0.015 ppm, achieving a 98.5% removal rate. The concentration of PFOS in the solution was monitored using LC/MS throughout the photoirradiation process (Supplementary Figure 22), revealing no significant desorption of PFOS from the photocatalyst. Concurrently, the incessant release of fluoride ions (F⁻) was measured, serving as direct evidence that the removal of PFOS is primarily due to degradation rather than adsorption.”\nThe authors mention that desorption was monitored throughout the photoirradiation process. However, it remains unclear whether sonication is an appropriate method for desorption. The authors should perform a control experiment (without light irradiation) to verify that the sonication treatment alone can completely desorb PFOS from the TAPP aggregates. This control would help confirm that the observed PFOS disappearance is indeed due to degradation rather than incomplete desorption.\n2. \"In Figure R1: Negative ion TOF-SIM spectrum of reacted, post adsorption and fresh aggregates\"\nWhy does the reacted sample still show an F⁻ signal? According to the authors, the system achieved 100% defluorination, so F⁻ should not be detected. Since TOF-SIMS is a surface-sensitive technique for analyzing solid samples, the presence of F⁻—especially with an intensity comparable to that observed after dark adsorption—is unexpected and requires further clarification.\n3. I am not fully convinced by the authors’ response regarding the detection of the final products, including formate, oxalate, and lactate. The authors emphasize that they used an initial PFOS concentration of 0.1 ppm, and thus the concentrations of these products were below the LOD. However, according to the manuscript, the authors also conducted experiments at higher PFOS concentrations (0.1–1 ppm) and investigated the reusability of the TAPP aggregate system. These experiments showed complete defluorination even at higher PFOS concentrations over longer reaction periods. Therefore, the detection limit should not be a limiting factor, as the final products could be detectable under such conditions. Unlike 19F NMR, where a higher concentration (e.g., 10 ppm) is still challenging, using HPLC for product analysis at 1–10 ppm PFOS degradation should allow reliable detection of these low-molecular-weight organic acids.\nAdditionally, 10 ppm PFOS may be hard for 19F NMR, but 10 ppm PFOA should be cleared to see from 19F NMR（https://pubs.acs.org/doi/10.1021/acsnanoscienceau.3c00022）. Since author also investigated PFOA, it would be alternative way to explain the transformation of PFAS from the system.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Response to the reviewers’ comments\nManuscript Title: Complete defluorination of PFASs via photocatalytic reduction in water\nManuscript Number: NCOMMS-25-47396B\nAuthor: Meichi Chong 1, Qixin Zhou 1, Jingyi Xu 1, Zhaohui Wu 1, Enwei Zhu 1, Wenlu Li 1,\nLing Zhang 1, Yan Guo 2* and Yongfa Zhu 1*\n[The reviewer comments are shown in italic; responses are in blue; all revisions in the main\ntext and supplementary information are highlighted in red]\nReviewer #1:\nThe authors have diligently revised and improved the manuscript in accordance with the\nrequirements, and I endorse this manuscript for publication in Nature Communications.\nResponse: We appreciate the reviewer for the kind review of our work\nReviewer #2:\nThe authors have made substantial efforts and addressed several of the earlier concerns.\nHowever, some issues remain that require further clarification. Please see below:\n1. On Supplementary Page 30, the authors state:\n“Following dark adsorption equilibrium, the concentration of PFOS decreased from an initial\n0.1 ppm to 0.015 ppm, achieving a 98.5% removal rate. The concentration of PFOS in the\nsolution was monitored using LC/MS throughout the photoirradiation process (Supplementary\nFigure 22), revealing no significant desorption of PFOS from the photocatalyst. Concurrently,\nthe incessant release of fluoride ions (F⁻) was measured, serving as direct evidence that the\nremoval of PFOS is primarily due to degradation rather than adsorption.”\nThe authors mention that desorption was monitored throughout the photoirradiation process.\nHowever, it remains unclear whether sonication is an appropriate method for desorption.\nThe authors should perform a control experiment (without light irradiation) to verify that the\nsonication treatment alone can completely desorb PFOS from the TAPP aggregates. This\ncontrol would help confirm that the observed PFOS disappearance is indeed due to\ndegradation rather than incomplete desorption.\nResponse: We thank the reviewer for this valuable suggestion regrading to completely\ndesorption. We acknowledge that sonication treatment alone may not ensure complete\ndesorption of PFOS. To address this concern, we conducted a systematic control experiment\nrelated to PFOS desorption.\nSpecifically, 0.1 ppm PFOS solution containing 0.2 g L-1 TAPP aggregates was stirred for 1 h\nunder dark conditions to reach adsorption equilibrium. The suspension was then divided into\nfive groups subjected to different desorption treatments:\n(a) No treatment (blank).\n(b) Sonication for 1 h.\n(c) Heating at 80˚C for 3 h.\n(d) Adjusting pH to 10 using 10 M NaOH followed by heating at 80˚C for 3 h.\n(e) Addition of 50% acetonitrile (v/v =50/50) to dissolve TAPP aggregates.\nEach sample was filtered through a 0.22 µm PES syringe filter before LC-MS/MS\nquantification analysis. The results show that TAPP aggregates adsorbed PFOS completely (>\n99.5%), while mechanical or thermal treatment caused only minor desorption (< 0.2%). In\ncontrast, as TAPP aggregates are soluble in acetonitrile, majority of PFOS was recovered (99.38\n± 0.61%) when acetonitrile was added.\nFigure R1. Adsorption under 0.1 ppm PFOS (100 ppb) and desorption performance during\ndifferent treatment.\nAccordingly, we employed this dissolution-based method to ensure complete desorption in the\nreacted samples. A mixture containing 50% reacted solution (with 0.2 g L-1 photocatalysts) and\n50% acetonitrile (50/50, v/v) was analyzed by LC-MS/MS. As shown in Fig. S26c, no PFOS\nsignal was detected, confirming that the disappearance of PFOS is not due to incomplete\ndesorption.\nWe have replaced the corresponding discussion in the revised supplementary:\n(Manuscript Page 15) “Consistently, no detectable PFOS signal was observed from the\npost-reaction solution (Fig. S26c and Fig. S27c).”\n(Supplementary Page 34) “To verify the absence of adsorbed PFOS, the reacted solution\n(with 0.2 g L-1 photocatalysts) was mixed with an equal volume of acetonitrile (50/50, v/v).\nThis treatment ensures the complete release of any adsorbed species due to the solubility of\nTAPP aggregates in acetonitrile. LC-MS/MS analysis of the mixture confirmed that no PFOS\nwas detected after 48 h irradiation.”\nSupplementary Figure 27. LC-MS/MS of the complete defluorination sample. (0.1 ppm PFOS\nunder 48 h visible light irradiation). (a) range m/z=80-160, (b) range m/z=180-250 and (c)\nrange m/z = 400-550. The sample was prepared with reacted aqueous sample solution and\nacetonitrile (50/50, v/v).\n2. \"In Figure R1: Negative ion TOF-SIM spectrum of reacted, post adsorption and fresh\naggregates\"\nWhy does the reacted sample still show an F⁻ signal? According to the authors, the system\nachieved 100% defluorination, so F⁻ should not be detected. Since TOF-SIMS is a surface-\nsensitive technique for analyzing solid samples, the presence of F⁻—especially with an intensity\ncomparable to that observed after dark adsorption—is unexpected and requires further\nclarification.\nResponse: We thank the reviewer for this insightful question. The complete defluorination of\nPFOS was confirmed by ion chromatography (IC), which quantified the total fluoride ions\nreleased into the aqueous phase. As noted in the manuscript, TOF-SIMS analysis was primarily\nperformed to examine the removal of PFOS from the photocatalyst surface, rather than to\nquantify fluoride ions.\nTo response your concern, we would like to clarify that TOF-SIMS samples (solid phase) were\nprepared by centrifuging the reacted suspension (14000 rpm, 10 min) to separate the\nphotocatalysts from the solution, followed by pouring out the supernatant and drying at 60˚C.\nTherefore, the F⁻ signals are attributed to unavoidable residual F⁻ on the surface from the\nvestigial moisture and do not contradict the 100% defluorination determined by IC.\nRegarding the relatively high intensity (× 105 counts) of F⁻, it is important to emphasize that\nTOF-SIMS signal intensity does not directly correlate with the actual amount of fluoride.\nThe detected signal depends strongly on matrix effects, ionization efficiency, and specific ion\nyields of the substrate. The F⁻ signals on the post adsorption sample originated from PFOS fragment,\nwhich may differ in ionization efficiency from the residual fluoride on the reacted sample.\nTherefore, the two F⁻ signals cannot be directly compared.\nMoreover, TOF-SIMS is an extremely surface-sensitive technique and even trace residues of\nfluoride generate detectable F⁻ signals. To further illustrate this point, two TAPP aggregate\nsamples (0.2 g L-1) were dispersed in 2.5 ppt and 25 ppt F⁻ solutions (corresponding to 0.004%\nand 0.04% of the total fluoride ions produced from 0.1 ppm PFOS defluorination, respectively),\nfollowed by centrifugation and drying at 60˚C. Despite such extremely low concentration (Fig.\nR2), both samples produced pronounced F⁻ signals (× 105 counts) in the TOF-SIMS spectra.\nTherefore, even though TAPP aggerates might partially adsorb F⁻ ions, the adsorption rate\nshould be minor—far below 0.04% of total fluoride ions produced from 0.1 ppm PFOS\ndefluorination.\nFigure R2. Negative ion TOF-SIMS spectrum of F- adsorbed TAPP aggregates.\n3. I am not fully convinced by the authors’ response regarding the detection of the final products,\nincluding formate, oxalate, and lactate. The authors emphasize that they used an initial PFOS\nconcentration of 0.1 ppm, and thus the concentrations of these products were below the LOD.\nHowever, according to the manuscript, the authors also conducted experiments at higher PFOS\nconcentrations (0.1–1 ppm) and investigated the reusability of the TAPP aggregate system.\nThese experiments showed complete defluorination even at higher PFOS concentrations over\nlonger reaction periods. Therefore, the detection limit should not be a limiting factor, as the\nfinal products could be detectable under such conditions. Unlike 19F NMR, where a higher\nconcentration (e.g., 10 ppm) is still challenging, using HPLC for product analysis at 1–10 ppm\nPFOS degradation should allow reliable detection of these low-molecular-weight organic\nacids.\nResponse: We thank the reviewer for the thoughtful comment. Indeed, we performed\nphotocatalytic degradation experiments at various PFOS concentrations up to 1 ppm and the\nobserved that the defluorination efficiency decreased as the PFOS concentration increased.\nWhen the initial PFOS concentration was10 ppm, negligible defluorination was observed after\n7 days.\nIn response to the reviewer’s suggestion, we carefully re-examined the reaction solutions under\n0.2 ppm PFOS using HPLC and ion chromatography to detect low-molecular-weight organic\nacids. As shown in Fig. S29, the concentration of lactic, oxalic, formic acids gradually\nincreased with the release of F⁻. However, several factors should be considered during\nquantitative determination of these small organic acids.\nFirst, HPLC analysis for small organic acids relied on UV absorption at 210 nm, where lactic\nand oxalic acids exhibit weak absorbance. In addition, the photocatalytic degradation matrix is\ncomplex, containing various intermediates and organic residues that introduce substantial\nbaseline noise and UV adsorption, leading to signal fluctuations in quantification.\nSecond, trace organic residues originating from the photocatalyst synthesis may contribute\nbackground signals that are comparable to the expected product levels. In addition, the total\norganic carbon (TOC) of the deionized water and distilled water (Watsons) used in this study\nwas 0.811 ± 0.073 ppm and 0.739 ± 0.011 ppm, respectively, which is on the same order\nof magnitude as the theoretical concentrations of the expected products. These pervasive\ncarbon impurities may partially contribute to the detected signals, leading to an overestimation\nof the concentrations of these small organic acids.\nWe have added the corresponding discussion in the revised supplementary:\nSupplementary Figure 29. Development of intermediate concentrations during PFOS\ndefluorination. (0.2 ppm PFOS, photocatalyst loading = 0.2 g L–1) Blue lines: measured by\nHPLC. Purple lines: measured by IC.\n(Manuscript Page 15) “The terminal products of complete defluorination (Fig. S26a-b)\nare identified as formate, oxalate, and lactate (quantified by HPLC and IC, Fig.S29), suggesting\ncomplete degradation through sequential defluorination and carbon chain cleavage28.”\n(Supplementary Page 36) “To investigate the formation of intermediates, the\nconcentrations of lactic and oxalic acids were quantified using HPLC, while fluoride ions and\nformic acid were analyzed by IC. As shown in Fig. S29, the concentrations of these small\norganic acids increased concurrently with the release of F⁻.\nHowever, there are several factors may affect the accuracy of quantifying small organic\nacids. The low products concentration (less than 0.8 ppm) and the presence of trace organic\nimpurities in the system introduce notable analytical uncertainty. The total organic carbon of\nDIW (0.811 ± 0.073 ppm) and residual organics from photocatalyst synthesis are comparable\nto the expected products levels, which may lead to overestimation of small organic acids\nconcentrations.”\n4.Additionally, 10 ppm PFOS may be hard for 19F NMR, but 10 ppm PFOA should be\ncleared to see from 19F NMR\n（https://pubs.acs.org/doi/10.1021/acsnanoscienceau.3c00022）. Since author also\ninvestigated PFOA, it would be alternative way to explain the transformation of PFAS from\nthe system.\nResponse: We sincerely thank the reviewer for the valuable suggestion and the helpful\nreference provided. The cited work employed a highly sensitive setup-564 MHz on a Bruker\n600-MHz Avance NEO with a 5 mm triple resonance cryoprobe without proton decoupling.\nSuch cryogenic probe systems are known to provide approximately one order of magnitude\nhigher signal-to-noise ratio compared with conventional room-temperature probes.\nTherefore, we conducted the 19F NMR measurements using the same model of equipment\nunder comparable conditions. As shown in Fig. S25, 100 ppm PFOS exhibited a characteristic\n19F NMR signal at -80.76 ppm, corresponding to the terminal -CF . However, when the\n3\nconcentration decreased to 10 ppm or below, an additional dominant peak emerged at -119.6\nppm. Two possible explanations are considered for this observation:\n(a) Instrumental contamination: PFASs are ubiquitous (e.g. PTFE pipeline) and can be\nintroduced from inherent equipment. Therefore, the emerged signal may attribute to the\nfluoride pollutants. However, the 19F NMR of blank sample (90% DIW + 10% D O)\n2\nshowed no significant peak, excluding this possibility.\n(b) Concentration effect: At high concentrations, PFOS molecules tend to aggregate above\nthe critical micellar concentration (CMC), which in turn affects the observed 19F NMR\nsignals (similar behavior was reported for PFOA, Journal of Molecular Liquids 283\n(2019): 45-50.). Intermolecular interactions and diffuse coefficient in various\nconcentration may show significant influence of 19F NMR spectra.\nNevertheless, the current 19F NMR data alone are insufficient to unambiguously elucidate these\nresults. Further systematic studies are requisite to explain this interesting concentration-\ndependent behavior, and we wish to have a deep and thorough study to explore it in our future\nwork.\nFurthermore, for the photocatalytic samples, 20 % acetonitrile was additionally added to\ndissolve the photocatalyst and exclude adsorption effects. The 19F signals gradually decreased\nwith irradiation time and complete disappeared within 48 h, further confirming the\ndefluorination.\nThe corresponding discussion have been included in the revised supplementary:\nSupplementary Figure 25. 19F spectra of PFOS solutions at various concentration and during\nphotocatalytic reaction (0 to 48 h). The data was collected at a relaxation delay time of 8 s\nand 512 scans for 1 to 100 ppm PFOS, 1024 scans for 0.1 ppm PFOS.\n(Manuscript Page 15) “Furthermore, 19F NMR investigations (Fig. S25) shows that PFOS\nsignal gradually decreased and disappeared with 48 h, confirming the defluorination of PFOS.”\n(Supplementary Page 33) “Further 19F NMR investigations were performed to study\nPFOS transformation. Samples were prepared in 90% aqueous sample solution and 10% D O\n2\n(v/v) with D-trifluoroacetic acid as a chemical shift reference (-75.51 ppm), and 20%\nacetonitrile was additionally added to dissolve the photocatalyst and exclude adsorption effects\nfor the photocatalytic samples. The 19F NMR were acquired using a Bruker 600-MHz Avance\nNEO (AV-HD-600X) with a 5 mm triple resonance cryoprobe without proton decoupling, at a\nrelaxation delay time of 8 s and 512 -1024 scans depending on the concentration.\nThe results revealed two distinct sets of signals, possibly associated with the critical\nmicellar concentration (CMC)5, 6. Above the CMC, PFOS favor an aggregation form rather than\nmonomer form, resulting to the different intermolecular interactions and diffusion coefficient.\nDuring the photocatalytic process, peaks corresponding to PFOS decreased progressively and\ndisappeared within 48 h, confirming the defluorination of PFOS.”\nReviewer #3:\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This\nis part of the Nature Communications initiative to facilitate training in peer review and to\nprovide appropriate recognition for Early Career Researchers who co-review manuscripts.\nResponse: We are grateful to the reviewer for their constructive comments that significantly\nimproved the quality of our manuscript."}, {"round": 3, "reviewer_comments": {"reviewer_2": "The authors have made an excellent effort to address our concerns. I am happy to recommend publication of the manuscript.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": ""}]

Decision letter