Weak localized electrons enhance electronic coherence for efficient photocatalytic uranium removal from nuclear wastewater

Domain: chemistry
Published: 2026-02-27
Editorial outcome: major_revision

Abstract
Photocatalytic uranium removal from nuclear wastewater is a promising strategy for radionuclide mitigation, yet its practical deployment is greatly hampered by inefficient charge separation of electron-hole pairs in photocatalytic systems, which critically limits the generation of reactive oxygen species essential for uranium precipitation. Herein, we propose a approach that leverages weakly localized electrons to enhance electronic coherence in fluorine-functionalized covalent organic frameworks, thereby strengthening charge separation and promoting directional electron transport for greatly boosting photocatalytic uranium removal from nuclear wastewater. We demonstrate that the partial fluorination in covalent organic frameworks induce weak electron localization and strong electronic coherence, which delivers a record-high solar-to-chemicals conversion efficiency of 1.52% and achieves 100% uranium removal efficiency within the pH range of 3-6, outperforming non-fluorinated (0.31%) and over-fluorinated (0.85%) counterparts. More importantly, a self-designed flow-type reactor achieves 99% uranium removal efficiency and superior U processing capacity of 281.3 gm-2 day-1 under natural sunlight, significantly surpassing reported photocatalytic systems and meeting World Health Organization discharge limits. Mechanism investigation reveal that the partial fluorination enhanced electronic coherence improves photogenerated carrier transport and reparation for accelerating reactive oxygen species synthesis, thereby promoting uranium removal from nuclear wastewater.

Introduction
Nuclear power is regarded as a promising new energy to substitute fossil fuels.1,2 Uranium is the most principal nuclear fuel to trigger the nuclear fission reaction in the process of nuclear power utilization.3,4 However, the nuclear wastewater is ineluctably generated during the operation of nuclear power plants and the mining process of nuclear mines, which destroy soil, water sources and ecosystems.5,6 The tradition physical adsorption method for uranium removal from nuclear wastewater suffers from weak adsorption interaction between uranium ions and adsorbents, leading to an unsatisfactory removal efficiency of uranium ion.7,8 Although chemical adsorption method can efficiently adsorb uranium ions from nuclear wastewater,9,10 difficult post desorption of uranium ion usually results in low repetition rates of adsorbents.11,12

Photocatalytic uranium removal technology, by generating H2O2 or •O2⁻ to react with UO22+ for forming uranyl superoxide (UO2(O2)•xH2O) precipitates,13,14 exhibits prospects for uranium ion removal from nuclear wastewater due to its low cost,15,16 high removal efficiency and no post-treatment desorption.17,18 Over the past decades, various photocatalytic materials, such as metal oxides, metal sulfides and organic semiconductors, have been explored for uranium extraction from nuclear wastewater,19,20 which primarily focus on generating reactive oxygen species (ROS) to convert UO22+ into stable uranyl superoxide precipitates.21,22 However, metal oxide and sulfide-based photocatalysts often suffer from weak light absorption in the visible spectrum, poor stability under harsh wastewater conditions and complex synthetic processes.23,24 Covalent organic frameworks (COFs), are considered as efficient photocatalysts for uranium removal because its unique donor-acceptor (D-A) structure provides a new platform for the photosynthesis of ROS, including H2O2, •O2⁻, and •OH, via oxygen reduction reaction (ORR) and water oxidation reaction (WOR) process for the photosynthesis of UO2(O2)•xH2O precipitates from nuclear wastewater.25,26 However, adverse photogenerated carrier recombination usually occurs in COFs during photocatalytic uranium removal processes, leading to low solar-to-chemical conversion and unsatisfactory uranium removal efficiency.27,28

Herein, we report a strategy that leverages the manipulation of local electron distribution to enhance electronic coherence, for the purpose of strengthening directional carrier transport and substantially improving photogenerated electron-hole separation, which boosts photocatalytic uranium removal from nuclear wastewater. The fluorine atom with strong electronegativity was introduced as an electron-regulating motif to modulate the local electron distribution in COF molecules and locally align energy levels, which reinforces electronically coherent transport along the preferred pathways. Our systematic investigations reveal that the TAPT-TPA-2F COF, featuring weak electron localization characteristics, endows enhanced electronic coherence. This electronic modulation effect not only facilitates intraframework directional electron transfer from the donor to acceptor moieties but also effectively mitigates electron-hole pair recombination. The as-made TAPT-TPA-2F COFs deliver a high solar-to-chemical conversion efficiency of 1.52% and achieve 100% uranium removal efficiency, far exceeding those of reported photocatalytic materials. Notably, the TAPT-TPA-2F-based flow reactor achieves a benchmark processing U efficiency of 281.3 g m-2 day-1 under natural sunlight, surpassing state-of-the-art systems and fulfilling World Health Organization (WHO) safety criteria, highlighting its strong application potential for nuclear wastewater treatment.

Results
Design strategy of F regulated local electron distribution in COFs. Photoexcited electron transport from electron donor unit to electron acceptor unit is desirable during the photocatalytic process. Accurately manipulating directional electron transfer through regulating electron localization can hinder the recombination of electron-hole pairs (Fig. 1a-b). To validate this concept, we investigate the regulatory role of electron localization in tailoring electronic coherence within COFs, which in turn enhances directional charge transport. 1,3,5-tris-(4-aminophenyl) triazine (TAPT) and terephthalaldehyde (TPA) were selected as molecular modules for constructing TAPT-TPA COFs. Molecular simulation results reveal that the electron donor and acceptor moieties are spatially segregated within the TAPT and TPA building blocks of the COFs. This spatial segregation in turn establishes intrinsically electronically coherent directional donor–acceptor (D–A) transport pathways, which facilitate the directional migration of photogenerated electrons from the TAPT (donor) to TPA (acceptor) moieties. Furthermore, fluorine atoms with strong electronegativity are employed to modulate the locally asymmetric electronic density distribution within the acceptor moieties (Fig. 1c–e). This structural engineering strategy preserves the frontier-orbital overlap between donor and acceptor units and meantime maintaining phase matching along the dominant coherent charge-transport pathway, thereby promoting constructive interference that further enhancing directional charge separation and transport. Partial fluorination in TAPT-TPA-2F COFs induce asymmetric electron localization and reinforce electron coherent for promoting directionally electron transfer (Fig. 1f-h). In contrast, relative to the TAPT-TPA-2F COFs, excessive fluorination in the TAPT-TPA-4F COF induces isotropic electronic over-localization, which generates multiple phase-mismatched charge transport pathways and ultimately impairs the efficiency of coherent charge transport (Fig. 1b). Consequently, oxygen molecules adsorbed on the electron acceptor unit are reduced to H2O2 or ·O2-, which subsequently react with enriched UO22+ to form stable UO2(O2)·xH2O precipitate (Supplementary Fig. 1).29

Molecular structure and chemical bond characterization. The powder X-ray diffraction (PXRD) techniques were carried out to investigate the crystal structure of different COFs. The peaks at 2θ=2.7, 4.9, 5.6, 7.3 and 26° in the XRD pattern of TAPT-TPA-2F COFs correspond to their (100), (110), (200), (210) and (001) crystal facets (Supplementary Fig. 2-4), consistent with simulated A-A stacking structure (Supplementary Fig. 5-7). High-resolution TEM (HRTEM) images of TAPT-TPA, TAPT-TPA-2F and TAPT-TPA-4F reveal well-defined periodic porosity with an apparent pore size of ~3.0 nm, and the resolved lattice fringes can be indexed to the (100) plane (Supplementary Fig. 8). Solid-state 13C NMR spectra of TAPT-TPA-2F COFs show that the chemical shift, located at around 150 ppm, corresponds to aromatic carbon atoms bonded to fluorine atoms (C-F bonds), indicating successful incorporation of fluorine into TAPT-TPA-2F COFs and TAPT-TPA-4F COFs. The chemical shift, located at 168 ppm, is attributed to C=N imine bonds, indicating the formation of C=N imine bond connected COFs (Supplementary Fig. 9-11).30 Fourier-transform infrared (FT-IR) spectra of TAPT-TPA-2F COFs show the vibrational peak, located at around 689 cm-1, corresponds to C-F chemical bond (Supplementary Fig. 12-15). Raman spectra of TAPT-TPA-2F COFs show a strong peak at 1620 cm-1, ascribed to the imine bond (C=N), indicating the synthesis of imine bond connected COFs (Supplementary Fig. 16).31 N2 adsorption–desorption analysis verify that the incorporation of fluorine atoms does not compromise the porous architecture of COFs (Supplementary Fig. 17-18).

Enhanced electronic coherence and exciton dissociation facilitated by weak electron localization. Ultrafast transient absorption (TA) spectra reveal that TAPT-TPA-2F COFs exhibit a significantly prolonged carrier lifetime (τ = 35.16 ps) relative to TAPT-TPA-4F COFs (17.63 ps) and TAPT-TPA COFs (6.32 ps), demonstrating that they exhibit the higher spatial electron-hole separation efficiency (Fig. 2a-2c, Supplementary Fig. 19-24). Both TAPT-TPA-2F and TAPT-TPA-4F COFs exhibit the pronounced built-in electric fields under illumination (Fig. 2d-2f). TAPT-TPA-2F COFs attains the contact potential difference (CPD) plateau more rapidly than TAPT-TPA-4F COFs (Fig. 2g-2i), which is indicative of a faster photoresponse (Supplementary Fig. 25-27). This result further confirms the intrinsically superior charge separation efficiency and carrier mobility of TAPT-TPA-2F COFs.32 Furthermore, the temperature-dependent photoluminescence measurements demonstrate that TAPT-TPA-2F COFs exhibit the lowest exciton binding energy (Eₑ = 43.82 meV), which is markedly lower than those of TAPT-TPA-4F COFs (55.17 meV) and TAPT-TPA COFs (104.64 meV). These findings collectively confirm that enhanced electronic coherence promotes efficient exciton dissociation (Supplementary Fig. 28-30).

Positron annihilation lifetime spectroscopy reveal that TAPT-TPA-2F COFs have a shorter positron lifetime than TAPT-TPA-4F COFs, indicating its higher electron density (Supplementary Fig. 31, Supplementary Table 1). This electron-rich environment is favorable for enhancing photocatalytic performance by effectively facilitating photogenerated electron separation and transfer. Transient fluorescence spectra of TAPT-TPA-2F COFs show that their decay lifetime is t1=2.1 ns and t2=203.5 ns, significantly higher than those of TAPT-TPA COFs (t1=1.3 and t2=39.9) and TAPT-TPA-4F COFs (t1=1.4 and t2=68.9) (Supplementary Fig. 32 and Table 2), further suggesting that partial fluorination–induced directional charge delocalization and coherent charge-transport channels in TAPT-TPA-2F COFs facilitate more efficient photogenerated electron–hole pair separation. Meanwhile, TAPT-TPA-2F COFs also exhibit superior photoelectric conversion performance relative to TAPT-TPA-4F COFs and TAPT-TPA COFs, indicating its excellent electron transport capability (Supplementary Fig. 33-35).

Photocatalytic uranium removal. To assess the photocatalytic uranium removal performance, all COFs were used for photocatalytic uranium removal at optimal condition of pH=4 (Supplementary Fig. 36 and 37). The as-made TAPT-TPA-2F COFs exhibit a 100% uranium removal efficiency and high uranium removal rate of 0.76% min-1, which is higher than those of TAPT-TPA COFs (0.45% min-1), TAPT-TPA-4F COFs (0.5% min-1) (Supplementary Fig. 38) and reported photocatalytic materials (Supplementary Table 3). Time-dependent uranium deposition curve shows that the precipitated amount of uranium is increased with light illumination duration, confirming the contribution of light radiation for U(VI) reduction (Supplementary Fig. 39). In addition, we demonstrate that TAPT-TPA-2F COFs also exhibits higher photocatalytic uranium efficiency than TAPT-TPA COFs and TAPT-TPA-4F COFs under natural water (pH = 6.1), neutral (pH = 7) and alkaline (pH = 8.2) condition (Supplementary Fig. 40-42). The as-made TAPT-TPA-2F COFs exhibit a high solar-to-chemical conversion (SCC) efficiency of 1.52%, which is 4.8 and 1.8 times higher than TAPT-TPA COFs (0.31%) and TAPT-TPA-4F COFs (0.85%) respectively, as well as significantly higher than those reported photocatalytic materials (Fig. 3a, Supplementary Fig. 43 and Supplementary Table 4). The apparent quantum efficiency (AQE) profile shows that the maximum AQE of TAPT-TPA-2F COFs is 19.7% under 380 nm-wavelength light radiation (Supplementary Fig. 44). Besides, we find that the introduction of F atom did not significantly alter the energy level structure of three COFs, indicating that the enhancement of photocatalytic performance is contributed from electronic coherence effect (Supplementary Fig. 45-48).

We find that the adsorption kinetic of UO22+ over all samples follows the pseudo-first-order kinetic model (Supplementary Fig. 49-51, Supplementary Table 5). The uranium adsorption over TAPT-TPA-2F COFs follows Langmuir monolayer adsorption model (Supplementary Fig. 52-55, Supplementary Table 6), which is conductive to the reaction of UO22+ and ROS to form uranyl superoxide complexes (Supplementary Fig. 56-57).33 To evaluate the feasibility of large-scale and continuous uranium removal, we constructed a flow-type TAPT-TPA-2F COFs-based photocatalytic system (Fig. 3b). This system achieves a high uranium removal efficiency of 99% even under the ultra-low UO22+ concentrations (1ppm) (Fig. 3c), which is below the WHO discharge limit of 30 ppb. More importantly, it delivers a benchmark nuclear wastewater processing capacity of 281.3 g U m-2 day-1, significantly surpassing previously reported photocatalytic systems and demonstrating strong potential for scalable application. Furthermore, cycling tests confirm the excellent reusability and operational stability of TAPT-TPA-2F COFs over multiple runs (Fig. 3d). PXRD profiles of TAPT-TPA-2F COFs used for uranium removal reveals integrity of porous structure, which confirm that the crystal structure and chemical bond of TAPT-TPA-2F COFs were not disrupted during the uranium removal process (Supplementary Fig. 58).

Photocatalytic mechanism. To reveal the essential relationship between electronic coherence and photocatalytic uranium removal performance, both experimental and DFT calculations were carried out. Chemical probe transfer experimental results show that the concentration of H2O2 and ·O2- over TAPT-TPA-2F COFs is 492.5 μmol L-1 and 1501.1 μmol L-1, respectively, significantly higher than those of TAPT-TPA COFs (The concentration of H2O2 and ·O2- is 148.1 mol L-1 and 210.8 mol L-1, respectively) and TAPT-TPA-4F COFs (The concentration of H2O2 and ·O2- is 365.6 mol L-1 and 730.4 mol L-1, respectively) (Supplementary Fig. 59 and 60), which is consistent with the electron paramagnetic resonance (EPR) results (Supplementary Fig. 61). The molecular dynamics simulation results reveal that the introduction of F atom can significantly promote the adsorption of UO22+ over TAPT-TPA-2F COFs and TAPT-TPA-4F COFs, which accelerates the reaction of UO22+ and ROS for the formation of uranyl superoxide (Supplementary Fig. 62 and 63).

DFT calculation reveals that the strong electronegativity of F atom regulates the electron localization distribution (Supplementary Fig. 64-66). TAPT-TPA COFs exhibit a completely delocalized electron distribution, accompanied by the disorderly electron transfer, resulting in severe photogenerated carrier recombination. For TAPT-TPA-2F COFs, the F atom with strong electronegativity induces the asymmetric electron cloud distribution, facilitating the direct photogenerated electron transport from bonding to antibonding orbitals during photocatalysis.34 In addition, TAPT-TPA-2F COFs exhibit a lower p-band center (1.47 eV) and higher density of states near the Fermi level relative to TAPT-TPA-4F COFs (p-band center of 1.81 eV) (Fig. 4a-b), which can decrease the overlap between the C 2p and F 2p orbitals (10.10%) in TAPT-TPA-2F COFs relative to TAPT-TPA-4F COFs (The overlap between the C 2p and F 2p orbitals is 20.97% ). These results can prevent the excessive electron localization for enhancing the electron transfer (Fig. 4c-d).35 Thus, TAPT-TPA-2F COFs with weak electron localization exhibit excellent electron-hole separation efficiency for enhancing photocatalytic uranium removal. The fluorination-induced local energy level engineering not only guides electron transfer pathways toward acceptor moieties but also strengthens electronic coherence, which in turn boosts directional electron transport and improves electron–hole separation dynamics. For TAPT-TPA-2F COFs, the partial fluorination-triggered weakening of electron localization contributes to enhanced electronic coherence, alongside favorable modulation of directional electron mobility and band alignment.36 In contrast, excessive localization in TAPT-TPA-4F COFs decrease the energy band density near the Fermi level and impedes directional transport of photogenerated carriers (Fig. 4e). Therefore, the partial fluorination of TAPT-TPA-2F COFs is more suitable for enhancing electronic coherence and enabling photogenerated electron-hole separation, which promote photocatalytic uranium removal performance.

Methods
Materials. 1,3,5-tris-(4-aminophenyl)triazine (TAPT), n-BuOH, o-dichlorobenzene, acetic acid, terephthalaldehyde (TPA), 2,5-difluoroterephthalaldehyde (TPA-2F) and 2,3,5,6-tetrafluoroterephthalaldehyde (TPA-4F) were purchased from Energy Chemical Co., Ltd, Shanghai Bide Pharmaceutical Technology Co., Ltd.,

Synthesis of TAPT-TPA COFs. The TAPT-TPA COFs were synthesized by acetic acid catalyzed Schiff base reaction of TAPT and TPA organic precursor. Typically, 35 mg of TAPT organic precursor and 22 mg of TPA organic precursor were added into the Pyrex tube. Then, 3 mL mixture of o-dichlorobenzene/n-BuOH (Volume ratio=1:1) was added into the above Pyrex tube, followed by ultrasound for 5 min. Subsequently, 0.1 mL of acetic acid solution (6 M) was added into the above solution. The solution was frozen in liquid nitrogen and then degassed, followed by sealing the Pyrex tube. And then, the Pyrex tube was transferred into oven at 120 ℃ for 3 d. Finally, the TAPT-TPA COFs was filtered, washed and dried. The synthesis process of TAPT-TPA-2F COFs and TAPT-TPA-4F COFs is the same as that of TAPT-TPA COFs, except that TPA organic precursor is replaced with TPA-2F organic precursor and TPA-4F organic precursor, respectively.

Photocatalytic removal of uranium. In a typical photocatalytic experiment, 10 mg of COFs and 5 mL of 0.01 M UO22+ stock solution were added to a 100 mL single-neck flask and diluted to 50 mL with deionized water. The suspension was transferred into a reactor, and the pH was adjusted using 0.1 M NaOH or HCl. Before irradiation, the reactor was bubbled with N2 in the dark for 120 min to remove dissolved oxygen and reach adsorption–desorption equilibrium. A 300 W Xe lamp (Microsolar 300, Beijing Perfectlight) was used as the light source, with a lamp-to-sample distance of 10 cm, an illumination intensity of 100 W cm-2 at the reactor surface, and a cut-off filter (λ > 420 nm) applied during irradiation. During the reaction, aliquots were withdrawn at defined intervals and analyzed by ICP-MS to determine the UO22+ concentration.

Construction of the flow-type quartz microreactor. The flow-type quartz microreactor channel with a width and length of 5 mm and 50 mm, respectively, was built. The photocatalyst was immobilized into the channel using 5% Nafion, and the device was reinforced to prevent the leakage. Simulated nuclear wastewater was introduced through a peristaltic pump at flow rates of 1 mL min-1 and 5 mL min-1. The flow-type microreactor enables continuous photocatalytic uranium removal under illumination, with the natural sunlight intensity measured at 650 W m-2 and its spectral distribution recorded during operation (Supplementary Fig. 67 and 68).

The determination of the SCC efficiency. The SCC efficiency was determined using the equation:
SCC(%) = (ΔG0×nH2O2/∙O2−) / (P×S×t) ×100%
Herein, the standard Gibbs free energy change (ΔG0) of photocatalytic H2O2/·O2⁻ production is 117.000 kJ mol-1 and 31.84 kJ mol-1, nH2O2/·O2⁻ is the photocatalytic H2O2/·O2⁻ yield (mol), P is the input light radiation power (1000 W m-2), S is the light irradiated area (about 1 × 10-4 m2) and t is the reaction time (s).

Structural characterization. Powder X-ray diffraction patterns were collected on a Rigaku D/max2400 diffractometer using Cu Kα radiation (λ = 1.5418 Å) to assess the crystallinity and structural features of the COFs. X-ray photoelectron spectroscopy measurements were performed with a monochromated Al Kα source (200 W; Thermo ESCALAB 250) to analyze the surface chemical states and bonding environments, complemented by solid-state NMR spectroscopy (Bruker AVANCE III 600M) for framework-level structural information. Sample morphologies were examined by transmission electron microscopy (TEM, Tecnai G2 F20 S-Twin). Time-resolved photoluminescence decay profiles were recorded using a fluorescence lifetime spectrophotometer (FLS1000/FSS). Electron paramagnetic resonance (EPR) spectra were obtained on a Bruker EMXPLUS 10/12 spectrometer. UV–vis diffuse reflectance spectra were measured on a Shimadzu UV-3600 spectrophotometer equipped with a diffuse-reflectance accessory, using BaSO4 as the reflectance standard, to determine the optical absorption characteristics and estimate band gaps.

DFT calculation. DFT computations were conducted using the Cambridge Sequential Total Energy Package (CASTEP, version 19.1.1). Electron–ion interactions were described with the projector-augmented wave (PAW) approach, and exchange–correlation effects were treated within the generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) functional. A plane-wave basis set was employed with a kinetic-energy cutoff of 700 eV. To account for on-site Coulomb interactions of localized Zn 3d states, a GGA+U scheme was applied with an effective Hubbard parameter of U_eff = 8.5 eV. Self-consistent field (SCF) cycles were converged to 1 × 10-6 eV in total energy. Brillouin-zone integrations used a 1 × 1 × 1 (Γ-point) k-point mesh together with Gaussian smearing (σ = 0.05 eV). Geometry optimizations were performed using a damped molecular-dynamics algorithm until the residual forces on all atoms were below 0.01 eV Å-1.

Molecular dynamic simulation. The simulation system was constructed by placing the COF model in a cubic periodic cell (8.0 nm × 8.0 nm × 8.0 nm), corresponding to an initial density of ~0.0510 g cm-3. The structure was pre-equilibrated using a five-cycle annealing protocol. The COF was then solvated in an explicit aqueous environment containing 5,000 water molecules and 8 uranyl ions. Charge neutrality was maintained by adding Na+ or Cl- counterions as needed. To reduce computational cost, the uranyl concentration was set to 0.09 mol L-1. Initial configurations were generated with Packmol. All MD simulations were performed using LAMMPS with the consistent valence force field (CVFF). Partial charges for the COFs building units were derived from restrained electrostatic potential (RESP) fitting based on quantum-chemical calculations in an implicit solvation model at the B3LYP/6-31G* level (Gaussian 09), with the charge fitting carried out using Multiwfn.

The MD workflow comprised: (i) energy minimization to relieve unfavorable contacts; (ii) a 200 ps NVT run at 300 K with initial velocities assigned from a Maxwell–Boltzmann distribution; (iii) a 2 ns NPT equilibration; and (iv) 10 ns production NPT simulations for independent sampling in each case. A 2.0 fs integration time step was used throughout. Temperature was regulated by a velocity-rescaling thermostat (relaxation time 0.1 ps), and pressure was controlled isotropically using the Berendsen barostat (target pressure 10⁵ Pa, time constant 1.0 ps). Long-range electrostatics were evaluated with the particle–mesh Ewald method under periodic boundary conditions in all three dimensions.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors report that weak localized electron-induced quantum constructive interference significantly enhances the photocatalytic removal of uranium from nuclear wastewater using covalent organic frameworks (COFs). The data presented are comprehensive and the interpretations are robust. However, before final acceptance, the authors should address the following minor issues:\n1. The manuscript currently reports uranium removal efficiencies and rates, yet lacks quantitative data demonstrating the relationship between illumination duration and the absolute mass of uranium precipitated.\n2. Comprehensive evaluation of the photocatalytic performance across different illumination wavelengths (e.g., ultraviolet vs. visible) is missing. It would be helpful if the authors could provide comparative experiments under various wavelengths to clarify the spectral responsiveness of the photocatalyst.\n3. Although the authors mention that uranium is removed in the form of UO₂(O₂)·xH₂O precipitates, no direct experimental characterization (e.g., XRD or FTIR) is presented to confirm their composition and stability. It is recommended to include these data to validate the exact chemical structure and stability of the uranium precipitates.\n4. The authors mention that uranium adsorption follows the Langmuir model, yet detailed parameters (e.g., maximum adsorption capacity Qmax and adsorption constant KL) are not provided. These parameters should be clearly reported and discussed to comprehensively characterize the material's uranium removal capacity.\n5. While cycling tests have been performed, structural analyses (such as PXRD or XPS) comparing the photocatalyst before and after long-term operation are missing. Including these analyses would convincingly demonstrate the long-term stability and robustness of the material.\n6. Please clearly specify the illumination intensity and spectral distribution of the natural sunlight used in flow reactor experiments to ensure experimental reproducibility.", "reviewer_2": "The manuscript presents an innovative strategy of leveraging weak electron localization to trigger constructive quantum interference (CQI) in fluorine-functionalized COFs for efficient photocatalytic uranium removal from nuclear wastewater. The partially fluorinated TAPT-TPA-2F COF achieves a record-high solar-to-chemical conversion efficiency and nearly 100% uranium removal. A flow-type reactor demonstrates remarkable scalability and stability. The mechanistic insights supported by ultrafast spectroscopy, surface photovoltage microscopy, positron annihilation lifetime spectroscopy, and DFT calculations are convincing and impactful. This work represents a significant advance in the field of photocatalysis and nuclear wastewater treatment. I have a few questions show below.\n1. Please provide comparative kinetic plots for uranium removal (e.g., pseudo-first-order fitting with rate constants) of TAPT-TPA, TAPT-TPA-2F, and TAPT-TPA-4F, to better illustrate the advantage of partial fluorination.\n2. In addition to recycling tests, PXRD or FT-IR spectra of the catalyst after multiple cycles would strengthen the claim of structural robustness.\n3. While H2O2 and •O2- quantifications are convincing, it would be helpful to include one additional radical scavenger experiment to further support the identification of dominant reactive species.\n4. A short test using U(VI) spiked in tap water or natural water (instead of simulated solutions) would highlight the practical anti-interference capability of the catalyst.\n5. Since COFs often exhibit tunable porosity that may influence uranium uptake, it would be useful to provide the BET surface area and pore size distribution (N2 adsorption–desorption) for TAPT-TPA, TAPT-TPA-2F, and TAPT-TPA-4F.\n6. UV–vis DRS results are provided; however, Tauc plot fittings for all samples should be included in the Supplementary Information to clearly indicate the band gap values.\n7. All photocatalytic uranium removal tests are reported at pH ≈ 4. Could the authors briefly show removal efficiency at one or two additional pH values (e.g., neutral pH), to demonstrate robustness under different conditions?\n8. The Methods section describes the irradiation setup, but the exact optical path (e.g., distance between Xe lamp and reactor, light intensity at the sample surface, use of cut-off filters) is not fully specified. Could the authors provide these details to improve reproducibility?\n9. Could the authors include a comparison to demonstrate that the superior photocatalytic activity is indeed ROS-driven rather than dominated by surface adsorption differences?\n10. The Figure 1 b, c and d should be further modified to clearly show the changes in structure.", "reviewer_3": "This study by Xu et al. presents a novel strategy that utilizes weakly localized electrons to induce constructive quantum interference (CQI) in fluorine-functionalized covalent organic frameworks (COFs), thereby enhancing charge separation and directional electron transfer for highly efficient photocatalytic uranium removal. The material TAPT-TPA-2F demonstrates a record-high solar-to-chemical conversion (SCC) efficiency of 1.52%, along with outstanding uranium extraction performance and cycling stability. The manuscript is well-organized and clearly written. The authors provided comprehensive experimental evidence to support the improved charge separation, extended carrier lifetime, and proposed photocatalytic mechanism in TAPT-TPA-2F, which strengthening the study. However, I think one most important point that is the basis of this paper are not sufficiently discussed, which is how the CQI and DQI happens in TAPT-TPA-2F and TAPT-TPA-4F respectively. This concept was novel and interesting to bridge the quantum chemical phenomena with photocatalysis. Such important point should be demonstrated clearly before the manuscript can be considered for acceptance. The following are my detailed comments:\n1. As mentioned in the manuscript, the electron transfer from donor to acceptor in a directed manner, how exactly do the fluorine atoms modulate the local electron distribution of the acceptor? what are the difference with 2F and 4F? Why does the aligned energy levels can promote directional electron transfer with CQI? How does CQI involves? In literature, the QI effect commonly discussed with wavefunctions of the quantum particles and the transmission curves, does the directional electron transfer between donor and acceptor has phase changes when COFs with 2F and 4F?\n2. Fig.1a is not clear enough. What do the curves in the central region mean? Are they intended to depict wavefunctions? Why does constructive interference promote disordered transmission?\n3. How does TAPT-TPA-2F reaches the contact potential difference (CPD) plateau more rapidly than TAPT-TPA-4F? I don’t see too much difference between Fig. 2h and 2i.\n4. Why does the longer decay lifetime in transient fluorescence spectra suggest the reduced electron localization in TAPT-TPA-2F COFs facilitates the CQI-mediated suppression of electron-hole recombination?\n5. The TAPT-TPA-2F exhibit a record-high SCC conversion efficiency of 1.52%. How about the quantum efficiency under certain wavelength of irradiation？Usually high SCC efficiency come along with high quantum efficiency.\n6. For the LUMO and HOMO electron cloud distribution in Supplementary Fig. 58 does not show much difference between TAPT-TPA-2F and TAPT-TPA-4F, I think it cannot support the claim that it facilitates the directional transfer and separation of photogenerated carriers."}, "author_response": "Response: We appreciate your constructive comments. We have revised the manuscript and marked in red colour. The responded point-by-point as follows.\nQ1: The manuscript currently reports uranium removal efficiencies and rates, yet lacks quantitative data demonstrating the relationship between illumination duration and the absolute mass of uranium precipitated.\nR1: Thanks for your valuable comment. Time-dependent uranium precipitation data have been supplemented in the revised manuscript, which shows the positive correlation between illumination duration and the absolute mass of precipitated uranium.\nWe have added the Supplementary Fig. 37 in the revised manuscript. The manuscript was revised and marked with red color in line 180-182.\nRevision: “Time-resolved quantification result further shows that the absolute amount of precipitated uranium increases steadily with illumination duration, confirming the continuous contribution of prolonged irradiation to U(VI) reduction (Supplementary Fig. 37).” (Please see line 180-182 of revised manuscript)\nSupplementary Fig. 37 | Uranium extraction capacity of different catalysts over time. Time-dependent uranium extraction capacity of TAPT–TPA–2F, TAPT–TPA–4F, and TAPT–TPA COFs.\nQ2: Comprehensive evaluation of the photocatalytic performance across different illumination wavelengths (e.g., ultraviolet vs. visible) is missing. It would be helpful if the authors could provide comparative experiments under various wavelengths to clarify the spectral responsiveness of the photocatalyst.\nR2: Thanks for your valuable suggestion. We have provided the apparent quantum efficiency (AQE) of photocatalytic performance under different excitation wavelengths, showing that the maximum AQE of TAPT-TPA-2F COFs is 19.7% under the 380 nm-1 wavelength light radiation.\nWe have added the Supplementary Fig. 42 in the revised manuscript. The manuscript was revised and marked with red color in line 190-192.\nRevision: “The apparent quantum efficiency (AQE) profile shows that the maximum AQE of TAPT-TPA-2F COFs is 19.7% under the condition of 380 nm wavelength light radiation (Supplementary Fig. 42).” (Please see line 190-192 of revised manuscript)\nSupplementary Fig. 42 | Apparent quantum efficiency (AQE) and optical absorption spectrum. Wavelength-dependent AQE and corresponding absorption spectrum of TAPT–TPA–2F COFs.\nQ3: Although the authors mention that uranium is removed in the form of UO (O )·xH O precipitates, no direct experimental characterization (e.g., XRD or FTIR) is presented to confirm their composition and stability. It is recommended to include these data to validate the exact chemical structure and stability of the uranium precipitates.\nR3: Thanks for your valuable suggestion. XRD and XPS were carried out to study the composition and stability of uranium precipitates, showing that the uranium precipitates is UO (O )·xH O.\nWe have added the Supplementary Fig. 54-55 in the revised manuscript. The manuscript was revised and marked with red color in line 199-201.\nRevision: “which is conductive to the reaction of UO 2+ and ROS to form uranyl superoxide complexes for the uranium removal from nuclear wastewater (Supplementary Fig. 54-55).” (Please see line 199-201 of revised manuscript)\nSupplementary Fig. 55 | XPS of uranium species after multiple photocatalytic cycles. High-resolution U 4f XPS spectra of the recovered products after multiple photocatalytic cycles.\nQ4: The authors mention that uranium adsorption follows the Langmuir model, yet detailed parameters (e.g., maximum adsorption capacity Q and adsorption constant KL) are not provided. These parameters should be clearly reported and discussed to comprehensively characterize the material's uranium removal capacity.\nR4: Thanks for your valuable comment. The Langmuir adsorption parameters (Qmax and K L) have been calculated, showing that the maximum adsorption capacity (Qmax) and adsorption constant (KL) are 970.1 mg g-1 and 0.06042, respectively.\nWe have added the Supplementary Table 5-6 in the revised manuscript. The manuscript was revised and marked with red color in line 196-199.\nRevision: “We find that the adsorption kinetic of UO 2+ over all samples follows the pseudo-first-order kinetic model (Supplementary Fig. 47-49, Supplementary Table 5). The uranium adsorption over TAPT-TPA-2F COFs follows Langmuir monolayer adsorption model (Supplementary Fig. 50-53, Supplementary Table 6)” (Please see line 196-199 of revised manuscript)\nModels Adsorbents Qe cal Qe exp k R2\n(mg g-1) (mg g-1)\npseudo-first-order TAPT-TPA-2F 970.10 269.8 0.06042 0.92025\nTAPT-TPA-4F 1037.58 355.1 0.05017 0.8711\nTAPT-TPA 372.07 157.0 0.04688 0.94065\npseudo-second-order TAPT-TPA-2F -- 269.8 1.854×10-4 0.0248\nTAPT-TPA-4F -- 355.1 1.473×10-4 0.0547\nTAPT-TPA -- 157.0 9.061×10-4 0.3008\nSupplementary Table 6. The specific parameters of isotherm models.\nModels Adsorbents Temperature Qm K R2\n(K) (mg g-1)\nLangmuire TAPT-TPA-2F 298 261.8 3.82×10-3 0.98647\n308 487.8 2.05×10-3 0.92952\n318 621.1 1.61×10-3 0.90816\nFreundlich TAPT-TPA-2F 298 -- 0.45399 0.46408\n308 -- 0.94569 0.38439\n318 -- 1.25937 0.36568\nDubinin- TAPT-TPA-2F 298 176.17 0.01037 0.67716\nRadushkevich 308 159.97 0.01032 0.61547\n318 176.17 0.01003 0.60827\nQ5: While cycling tests have been performed, structural analyses (such as PXRD or XPS) comparing the photocatalyst before and after long-term operation are missing. Including these analyses would convincingly demonstrate the long-term stability and robustness of the material.\nR5: Thanks for your valuable comment. PXRD pattern shows that the crystalline structure of TAPT-TPA-2F COFs after reaction is consistent with that before the reaction, indicating its high crystal structure stability.\nWe have added the Supplementary Fig. 56. The manuscript was revised and marked with red color in line 209-212.\nRevision: “PXRD profiles of TAPT-TPA-2F COFs used for uranium removal reveals integrity of porous structure, which confirm that the crystal structure and chemical bond of TAPT-TPA-2F COFs were not disrupted during the uranium removal process (Supplementary Fig. 56).” (Please see line 209-212 of revised manuscript)\nQ6: Please clearly specify the illumination intensity and spectral distribution of the natural sunlight used in flow reactor experiments to ensure experimental reproducibility.\nR6: Thanks for your valuable comment. The variation of natural light intensity over time is from 8:00 to 17:00. The spectral distribution of the natural sunlight was shown in Supplementary Fig. 66.\nWe have added the Supplementary Fig. 65-66 in the revised manuscript. The manuscript was revised and marked with red color in line 311-319.\nRevision: “Construction of the flow-type quartz microreactor. The flow-type quartz microreactor channel with a width and length of 5 mm and 50 mm, respectively, was built. The photocatalyst was immobilized into the channel using 5% Nafion, and the device was reinforced to prevent leakage. Simulated nuclear wastewater was introduced through a peristaltic pump at flow rates of 1 mL min-1 and 5 mL min-1. The flow-type microreactor enables continuous photocatalytic uranium removal under illumination, with the natural sunlight intensity measured at 650 W m-2 and its spectral distribution recorded during operation (Supplementary Fig. 65 and 66)” (Please see line 311-319 of revised manuscript)\nSupplementary Fig. 65 | Solar irradiance under natural sunlight. Variation of solar intensity with time during daytime under natural illumination conditions.\nOverall comments: The manuscript presents an innovative strategy of leveraging weak electron localization to trigger constructive quantum interference (CQI) in fluorine-functionalized COFs for efficient photocatalytic uranium removal from nuclear wastewater. The partially fluorinated TAPT-TPA-2F COF achieves a record-high solar-to-chemical conversion efficiency and nearly 100% uranium removal. A flow-type reactor demonstrates remarkable scalability and stability. The mechanistic insights supported by ultrafast spectroscopy, surface photovoltage microscopy, positron annihilation lifetime spectroscopy, and DFT calculations are convincing and impactful. This work represents a significant advance in the field of photocatalysis and nuclear wastewater treatment. I have a few questions show below.\nResponse: Thank you for your valuable comment. We have revised the manuscript and marked in red colour. The responded point-by-point as follows.\nQ1: Please provide comparative kinetic plots for uranium removal (e.g., pseudo-first-order fitting with rate constants) of TAPT-TPA, TAPT-TPA-2F, and TAPT-TPA-4F, to better illustrate the advantage of partial fluorination.\nR1: Thanks for your valuable comment. The different kinetic fitting models were used to evaluate uranium adsorption, showing that the adsorption kinetic of UO 2+ over all samples follows the pseudo-first-order kinetic model. The fitting parameters are shown in Table 5.\nWe have added the Supplementary Fig. 47-49 in the revised manuscript. The manuscript was revised and marked with red color in line 196-197.\nRevision: “We find that the adsorption kinetic of UO 2+ over all samples follows the pseudo-first-order kinetic model (Supplementary Fig. 47-49, Supplementary Table 5).” (Please see line 196-197 of revised manuscript)\nSupplementary Fig. 47 | Time-resolved U(VI) adsorption kinetics. U(VI) adsorption capacity of TAPT-TPA-2F, TAPT-TPA-4F and TAPT-TPA COFs as a function of time, with fitting curves based on the pseudo-second-order kinetic model (T = 298 K, UO 2+ = 100 ppm, 2\npH = 4).\n2\n= 4).\nSupplementary Table 5. The specific parameters of kinetics models.\nModels Adsorbents Qe cal Qe exp k R2\n(mg g-1) (mg g-1)\npseudo-first-order TAPT-TPA-2F 970.10 269.8 0.06042 0.92025\nTAPT-TPA-4F 1037.58 355.1 0.05017 0.8711\nTAPT-TPA 372.07 157.0 0.04688 0.94065\npseudo-second-order TAPT-TPA-2F -- 269.8 1.854×10-4 0.0248\nTAPT-TPA-4F -- 355.1 1.473×10-4 0.0547\nTAPT-TPA -- 157.0 9.061×10-4 0.3008\nQ2: In addition to recycling tests, PXRD or FT-IR spectra of the catalyst after multiple cycles would strengthen the claim of structural robustness.\nR2: Thanks for your valuable comment. Powder X-ray diffraction (PXRD) measurements were employed to characterize the crystal structure of TAPT-TPA-2F COFs following multiple cycles of photocatalytic uranium extraction, which validated the retention of the material’s crystalline integrity.\nWe have added the Supplementary Fig. 56 in the revised manuscript. The manuscript was revised and marked with red color in line 209-212.\nRevision: “PXRD profiles of TAPT-TPA-2F COFs used for uranium removal reveal integrity of porous structure, which confirm that the crystal structure and chemical bond of TAPT-TPA-2F COFs were not disrupted during the uranium removal process (Supplementary Fig. 56).” (Please see line 209-212 of revised manuscript)\nQ3: While H O and •O - quantifications are convincing, it would be helpful to include one additional radical scavenger experiment to further support the identification of dominant reactive species.\nR3: Thanks for your valuable suggestion. The radical scavenger experimental was performed, showing that ·O - and H O are the dominant reactive species.\n2 2 2\nWe have added the Supplementary Fig. 57 in the revised manuscript. The manuscript was revised and marked with red color in line 222-228.\nRevision: “Chemical probe transfer experimental show that the concentration of H O 2 2\nand •O - over TAPT-TPA-2F COFs is 492.5 μmol L-1 and 1501.1 μmol L-1, respectively, significantly higher than those of TAPT-TPA COFs (The concentration of H O and ·O - 2 2 2\nis 148.1 mol L-1 and 210.8 mol L-1 respectively) and TAPT-TPA-4F COFs (The concentration of H O and ·O - is 365.6 mol L-1 and 730.4 mol L-1, respectively) 2 2 2\n(Supplementary Fig. 57 and 58)” (Please see line 222-228 of revised manuscript)\nSupplementary Fig. 57 | Reactive species generated. Chemical probe method was used to identify reactive species produced by TAPT-TPA-2F COFs in solution during photocatalysis.\nQ4: A short test using U(VI) spiked in tap water or natural water (instead of simulated solutions) would highlight the practical anti-interference capability of the catalyst.\nWe have added the Supplementary Fig. 38. The manuscript was revised and marked with red color in line 183-186.\nRevision: “In addition, we demonstrate that TAPT-TPA-2F COFs also exhibit high photocatalytic uranium efficiency relative to TAPT-TPA COFs and TAPT-TPA-4F COFs under neutral (pH=7) and alkaline (pH=8.2) condition (Supplementary Fig. 38-40).” (Please see line 183-186 of revised manuscript)\nSupplementary Fig. 38 | Uranium removal efficiency in natural water over time. Time-dependent uranium removal performance of TAPT–TPA–2F, TAPT–TPA–4F, and TAPT–TPA COFs under dark and light conditions.\nQ5: Since COFs often exhibit tunable porosity that may influence uranium uptake, it would be useful to provide the BET surface area and pore size distribution (N 2\nadsorption–desorption) for TAPT-TPA, TAPT-TPA-2F, and TAPT-TPA-4F.\nR5: Thanks for your valuable suggestion. The N adsorption–desorption measurements 2\nwas carried out. The BET surface areas and pore size distributions of TAPT-TPA COFs, TAPT-TPA-2F COFs, and TAPT-TPA-4F COFs are shown in Supplementary Fig. 16.\nWe have added the Supplementary Fig. 16 in the revised manuscript. The manuscript was revised and marked with red color in line 131-132.\nRevision: “N adsorption–desorption analysis confirms that fluorine introduction 2\nleaves the pore structure essentially unchanged (Supplementary Fig. 16).” (Please see line 131-132 of revised manuscript)\nQ6: UV–vis DRS results are provided; however, Tauc plot fittings for all samples should be included in the Supplementary Information to clearly indicate the band gap values.\nR6: Thanks for your valuable suggestion. The Tauc plots of TAPT-TPA COFs, TAPT-TPA-2F COFs, and TAPT-TPA-4F COFs have been provided in the revised manuscript, showing that the band gap of TAPT-TPA COFs, TAPT-TPA-2F COFs, and TAPT-TPA-4F COFs are 2.41 eV, 2.49 3V, and 2.54 eV respectively.\nWe have added the Supplementary Fig. 44 in the revised manuscipt. The manuscript was revised and marked with red color in line 192-195.\nRevision: “In addition, the similar band gaps of three COFs further confirm that the performance enhancement is mainly from the contribution of the electron transfer related to F atom (Supplementary Fig. 43-46).” (Please see line 192-195 of revised manuscript)\nSupplementary Fig. 44 | Optical band gap analysis. Optical band gaps of TAPT-TPA-2F, TAPT-TPA-4F and TAPT-TPA COFs determined from UV-Vis absorption data using Tauc plots.\nR7: Thanks for your valuable suggestion. Photocatalytic uranium removal experimental was performed under the conditions of pH = 7 and pH = 8.2, showing that TAPT-TPA-2F COFs also exhibit high photocatalytic uranium efficiency relative to TAPT-TPA COFs and TAPT-TPA-4F COFs under neutral and alkaline condition.\nWe have added the Supplementary Fig. 39-40 in the revised manuscript. The manuscript was revised and marked with red color in line 183-186.\nRevision: “In addition, we demonstrate that TAPT-TPA-2F COFs also exhibits high photocatalytic uranium efficiency relative to TAPT-TPA COFs and TAPT-TPA-4F COFs under neutral (pH=7) and alkaline (pH=8.2) condition (Supplementary Fig. 38-40).” (Please see line 183-186 of revised manuscript)\nSupplementary Fig. 39 | Uranium removal efficiency at pH = 7. Time-dependent uranium removal performance of TAPT–TPA–2F, TAPT–TPA–4F, and TAPT–TPA COFs under neutral conditions.\nQ8: The Methods section describes the irradiation setup, but the exact optical path (e.g., distance between Xe lamp and reactor, light intensity at the sample surface, use of cut-off filters) is not fully specified. Could the authors provide these details to improve reproducibility?\nR8: Thanks for your valuable comment. More experimental informations have been provided in the methods section of the revised manuscript.\nThe manuscript was revised and marked with red color in line 300-310.\nRevision: “Photocatalytic removal of uranium. In a typical photocatalytic experiment, 10 mg of COFs and 5 mL of 0.01 M UO 2+ stock solution were added to a 100 mL 2\nsingle-neck flask and diluted to 50 mL with deionized water. The suspension was transferred into a reactor, and the pH was adjusted using 0.1 M NaOH or HCl. Before irradiation, the reactor was bubbled with N in the dark for 120 min to remove dissolved 2\noxygen and reach adsorption–desorption equilibrium. A 300 W Xe lamp (Microsolar 300, Beijing Perfectlight) was used as the light source, with a lamp-to-sample distance of 10 cm, an illumination intensity of 100 W cm-2 at the reactor surface, and a cut-off filter (λ > 420 nm) applied during irradiation. During the reaction, aliquots were withdrawn at defined intervals and analyzed by ICP-MS to determine the UO 2+ 2\nconcentration.” (Please see line 300-310 of revised manuscript)\nQ9: Could the authors include a comparison to demonstrate that the superior photocatalytic activity is indeed ROS-driven rather than dominated by surface adsorption differences?\nR9: Thanks for your valuable comment. Under dark conditions, the surface adsorption dominates uranium removal from solution. TAPT-TPA-4F COFs exhibits a higher uranium adsorption capacity than TAPT-TPA-2F COFs and TAPT-TPA COFs. Under light irradiation condition. Reactive oxygen species (ROS) dominates uranium removal from solution. TAPT-TPA-2F COFs exhibits a higher uranium adsorption capacity than TAPT-TPA-4F COFs and TAPT-TPA COFs. The uranium adsorption capacity can be neglected relative to ROS driven uranium removal. The above results provided a powerful evidence for ROS-driven uranium removal from solution.\nQ10: The Figure 1 b, c and d should be further modified to clearly show the changes in structure.\nR10: Thanks for your valuable comment. We have revised the Figure 1b–d and emphasized the structural differences among TAPT-TPA COFs, TAPT-TPA-2F COFs, and TAPT-TPA-4F COFs.\nOverall comments: This study by Xu et al. presents a novel strategy that utilizes weakly localized electrons to induce constructive quantum interference (CQI) in fluorine-functionalized covalent organic frameworks (COFs), thereby enhancing charge separation and directional electron transfer for highly efficient photocatalytic uranium removal. The material TAPT-TPA-2F demonstrates a record-high solar-to-chemical conversion (SCC) efficiency of 1.52%, along with outstanding uranium extraction performance and cycling stability. The manuscript is well-organized and clearly written. The authors provided comprehensive experimental evidence to support the improved charge separation, extended carrier lifetime, and proposed photocatalytic mechanism in TAPT-TPA-2F, which strengthening the study. However, I think one most important point that is the basis of this paper are not sufficiently discussed, which is how the CQI and DQI happens in TAPT-TPA-2F and TAPT-TPA-4F respectively. This concept was novel and interesting to bridge the quantum chemical phenomena with photocatalysis. Such important point should be demonstrated clearly before the manuscript can be considered for acceptance. The following are my detailed comments:\nResponse: Thanks for your valuable comment. We believe the mechanisms of weak electron localization and electronic coherence are better suited to elucidating the underlying origins of enhanced photocatalytic activity. A detailed elaboration on these mechanisms is presented as follows: the introduction of F atom into TAPT-TPA-2F COFs and TAPT-TPA-4F COFs induces and electronic coherence owing to its intrinsic strong electronegativity, which is beneficial for promoting electron transport and enhancing photocatalytic performance. Besides, relative to TAPT-TPA-4F COFs, TAPT-TPA-2F COFs with partial fluorination exhibits weak electron localization and directional charge delocalization effects, thereby constructing directional charge transport channels within the molecular framework. This structural modulation facilitates efficient ordered electron transfer, ultimately yielding a remarkable enhancement in photocatalytic activity.\nThe manuscript was revised and marked with red color in line 86-87.\nRevision: “To validate this concept, we focus on how electron localization modulates electronic coherence in COFs” (Revised manuscript, Line 86-87).\nQ1: As mentioned in the manuscript, the electron transfer from donor to acceptor in a directed manner, a) how exactly do the fluorine atoms modulate the local electron distribution of the acceptor? b) what are the difference with 2F and 4F? c) Why does the aligned energy levels can promote directional electron transfer with CQI? d) How does CQI involves? In literature, the QI effect commonly discussed with wavefunctions of the quantum particles and the transmission curves, e) does the directional electron transfer between donor and acceptor has phase changes when COFs with 2F and 4F?\nR1: Thanks for your valuable comments. We have provided a more detailed explanation regarding the above issues.\na) Fluorine-induced modulation of local electronic structure. The incorporation of fluorine (F) atoms into the electron acceptor units of covalent organic frameworks (COFs) triggers localized electron distribution within the benzene ring moiety, 1\nattributed to the strong electronegativity of F atoms. This electronic effect disrupts the in-plane symmetry of electron distribution in the electron acceptor units, thereby generating intrinsic anisotropic potential wells.\nb) Distinction between 2F and 4F. In TAPT–TPA–2F COFs, partial fluorination induces asymmetric electron localization within the electron acceptor moieties. This structural modification preserves adequate orbital overlap between donor and acceptor components while facilitating a predominant single coherent charge transport pathway from the electron donor units to the electron acceptor unit. In TAPT–TPA–4F COFs, the excessive fluorination causes isotropic over-localization. This over-localization impedes coherent charge delocalization and leads to stronger dephasing and less efficient transport.\nc) Why energy-level alignment promotes directional transfer. The partial fluorination of COFs optimizes energy level configurations of electron donor unit and electron acceptor unit, thereby enabling favorable alignment between their energy levels and orbital symmetries. Under such a tailored electronic configuration, electrons undergo delocalization from electron donor segments to electron acceptor units while sustaining electronic coherence along the predominant charge transport pathway. This synergistic effect of energy-level matching coupled with electronic anisotropic localization strengthens coherent donor–acceptor interfacial coupling, thereby facilitating efficient directional electron transfer.\nd) How does CQI involves? The mechanisms of weak electron localization and electronic coherence are more suitable for elucidating the fundamental origins of the enhanced photocatalytic activity. In our system, quantum constructive interference (CQI) emerges as a microscopic manifestation of this coherent transport rather than an independent effect. Partial fluorination of the TAPT-TPA-2F COF induces weak electron localization and strengthens electronic coherence, arising from the intrinsic strong electronegativity of fluorine atoms and the resulting asymmetric local potential, which preserves frontier-orbital overlap and phase matching along the dominant donor–acceptor transport pathways and thereby favours CQI-enhanced intraframework electron transport. Concomitantly, the electronic coherence and CQI-assisted charge transport within the TAPT-TPA-2F COF endow it with prolonged photogenerated carrier lifetimes, reduced exciton binding energy, and an enhanced surface photovoltage (SPV) response.\ne) On phase changes between 2F and 4F systems. Regarding the phase changes between the 2F (TAPT-TPA-2F) and 4F (TAPT-TPA-4F) COF systems, density functional theory (DFT) calculations consistently reveal no significant phase variation between the two systems. The mechanisms of weak electron localization and electronic coherence are more robust and mechanistically plausible in elucidating the fundamental origins of the enhanced photocatalytic activity of fluorinated COFs. This is because the subtle modulation of fluorination degree (2F vs. 4F) primarily tunes the electronic cloud distribution and conjugated π-system delocalization extent of the COFs photocatalyst, thereby regulating the electronic localization effect and coherence, rather than inducing significant phase transitions or phase mismatches between donor-acceptor units. We have revised the manuscript.\nWe have revised the Fig. 1. The manuscript has been revised and marked with red color 1\nin line 86-87, 92-95 and line 102-106.\nRevision: “To validate this concept, we focus on how electron localization modulates electronic coherence in COFs” (Please see line 86-87 of revised manuscript)\n“This spatial segregation in turn establishes intrinsically electronically coherent directional donor–acceptor (D–A) transport pathways, which facilitate the directional migration of photogenerated electrons from the TAPT (donor) to TPA (acceptor) moieties.” (Please see line 92-95 of revised manuscript)\n“In contrast, relative to the TAPT-TPA-2F COFs, excessive fluorination in the TAPT-TPA-4F COF induces isotropic electronic over-localization, which generates multiple phase-mismatched charge transport pathways and ultimately impairs the efficiency of coherent charge transport (Fig. 1b).” (Please see line 102-106 of revised manuscript)\nFig. 1│ Molecular design of weak-electron-localization. (a) Schematic diagram of enhanced electronic coherence promoting directional electron transfer. (b) Molecular structure of TAPT-TPA COFs, (c) TAPT-TPA-2F COFs and (d) TAPT-TPA-4F COFs. (e-g) Surface electrostatic potentials of (e) TAPT-TPA-2F COFs, (f) TAPT-TPA-4F COFs and (g) TAPT-TPA COFs.\nQ2: a) Fig.1a is not clear enough. What do the curves in the central region mean? b) Are they intended to depict wavefunctions? c) Why does constructive interference promote disordered transmission?\nR2: Thanks for your valuable comments.\n1\na) We have revised the Fig. 1a and clarified its meaning in the caption and main text.\nb) The curves in the central region are explicitly described as schematic representations of coherent versus incoherent charge-transport pathways, rather than ab initio wavefunctions.\nc) The partial fluorination in TAPT-TPA-2F COFs induces directional charge delocalization and preserves donor-acceptor orbital overlap and maintains phase alignment, forming a directional charge transport channel within the COFs framework, which can promote electron ordered transmission, rather than disordered transmission.\nWe have revised the Fig. 1. The manuscript has been revised and marked with red color in line 86-87, 92-95 and line 102-106.\nRevision: “To validate this concept, we focus on how electron localization modulates electronic coherence in COFs” (Please see line 86-87 of revised manuscript)\n“This spatial segregation in turn establishes intrinsically electronically coherent directional donor–acceptor (D–A) transport pathways, which facilitate the directional migration of photogenerated electrons from the TAPT (donor) to TPA (acceptor) moieties.” (Please see line 92-95 of revised manuscript)\n“In contrast, relative to the TAPT-TPA-2F COFs, excessive fluorination in the TAPT-TPA-4F COF induces isotropic electronic over-localization, which generates multiple phase-mismatched charge transport pathways and ultimately impairs the efficiency of coherent charge transport (Fig. 1b).” (Please see line 102-106 of revised manuscript)\nQ3: How does TAPT-TPA-2F reaches the contact potential difference (CPD) plateau more rapidly than TAPT-TPA-4F? I don’t see too much difference between Fig. 2h and 2i.\nR3: Thanks for your valuable comment. Time-dependent contact potential difference (CPD) demonstrate that the photogenerated charge response time of TAPT-TPA-2F COFs is 9 s, which is markedly shorter than that of TAPT-TPA-4F COFs (14 s). This result reveals that TAPT-TPA-2F COFs attains the CPD plateau more rapidly, reflecting enhanced kinetics of photogenerated charge transfer.\nWe have added the Supplementary Fig. 23-24. The manuscript was revised and marked with red color in line 138-142.\nRevision: “TAPT-TPA-2F COFs attains the contact potential difference (CPD) plateau more rapidly than TAPT-TPA-4F COFs (Fig. 2g-2i), which is indicative of a faster photoresponse (Supplementary Fig. 23-25). This result further confirms the intrinsically superior charge separation efficiency and carrier mobility of TAPT-TPA-2F COFs.” (Please see line 138-142 of revised manuscript)\nSupplementary Fig. 24 | Differential surface photovoltage profiling. Differential CPD profiles of TAPT-TPA-4F COFs under continuous light illumination, measured by surface photovoltage microscopy.\nQ4: Why does the longer decay lifetime in transient fluorescence spectra suggest the reduced electron localization in TAPT-TPA-2F COFs facilitates the CQI-mediated suppression of electron-hole recombination?\nR4: Thanks for your valuable comment, which prompts us to clarify the intrinsic correlation between the transient fluorescence decay lifetime, electron localization, and electron-hole separation in TAPT-TPA-2F COFs.\nIn transient fluorescence spectroscopy, the decay lifetime of photogenerated excitons (electron-hole pairs) is a direct manifestation of their separation and recombination dynamics: a longer decay lifetime typically indicates suppressed recombination and more efficient spatial separation of photogenerated charge carriers. Specifically, the partial fluorination of TAPT-TPA-2F COFs induces directional charge delocalization, forming a directional charge transport channel within the COFs framework, which can promote the separation of photogenerated electron-hole pairs. Consequently, the efficient photogenerated carriers separation is directly reflected in the longer fluorescence decay lifetime of TAPT-TPA-2F COFs.\nRevision: “further suggesting that partial fluorination–induced directional charge delocalization and coherent charge-transport channels in TAPT-TPA-2F COFs facilitate more efficient photogenerated electron–hole pair separation.” (Please see line 155-158 of revised manuscript)\nQ5: The TAPT-TPA-2F exhibit a record-high SCC conversion efficiency of 1.52%. How about the quantum efficiency under certain wavelength of irradiation? Usually high SCC efficiency come along with high quantum efficiency.\nR5: Thanks for your valuable comment. The apparent quantum efficiency (AQE) of photocatalytic performance was investigated under different excitation wavelengths, showing that the maximum AQE of TAPT-TPA-2F COFs is 19.7% under the condition of 380 nm wavelength light radiation.\nWe have added the Supplementary Fig. 42. The manuscript was revised and marked with red color in line 188-190.\nRevision: “The apparent quantum efficiency (AQE) profile shows that the maximum AQE of TAPT-TPA-2F COFs is 19.7% under the condition of 380 nm wavelength light radiation (Supplementary Fig. 42).” (Please see line 188-190 of revised manuscript)\nSupplementary Fig. 42 | Apparent quantum efficiency (AQE) and optical absorption spectrum. Wavelength-dependent AQE and corresponding absorption spectrum of TAPT–TPA–2F COFs.\nQ6: For the LUMO and HOMO electron cloud distribution in Supplementary Fig. 58 does not show much difference between TAPT-TPA-2F and TAPT-TPA-4F, I think it cannot support the claim that it facilitates the directional transfer and separation of photogenerated carriers.\nR6: Thanks for your valuable comment. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are primarily intended to characterize the band gap structure of photocatalysts, but they are not capable of adequately reflecting the electronic transport properties. We have revised the relevant claim accordingly and removed this section from the revised manuscript.\nOverall comments: The authors have properly addressed my concerns. It can be accepted now.\nResponse: We thank the reviewer for the positive comment and are pleased that all concerns have been addressed.\nTo Reviewer 2:\nOverall comments: I think it may be accepted.\nResponse: Thank you for your positive evaluation. We appreciate your time and constructive comments, and we are pleased that our revisions have properly addressed your concerns.\nTo Reviewer 3:\nOverall comments: I think most of my concerns have been well addressed. This manuscript could be published. But I have some minor suggestions:\nResponse: We sincerely thank the reviewer for the positive evaluation and for acknowledging that our major concerns have been addressed. We appreciate the additional minor suggestions and have revised the manuscript accordingly.\nQ1: In the abstract and conclusion part, the author should make it clear what conditions the 100% uranium removal achieved. Because in supplementary Fig. 39 and 40, it doesn’t show 100% removal. Also, the author should indicate what the pH value for natural water. It’s a little bit strange that the COF can achieve 100% removal efficiency in natural water while the pH = 7 water can not.\nR1: Thanks for your valuable comment. We have revised the Abstract and Conclusion to explicitly specify that 100% uranium removal was achieved across the pH range of 3-6, and that the tested natural water had a pH of 6.1. We have also aligned the wording with the corresponding datasets shown in Supplementary Fig. 40.\nWe have revised Supplementary Fig. 40 in the revised manuscript. The manuscript was revised and marked with red color in line 24-25, 187 and 277-278.\nRevision: “achieves 100% uranium removal efficiency within the pH range of 3-6,” (Please see line 24-25 of revised manuscript)\n“In addition, we demonstrate that TAPT-TPA-2F COFs also exhibits higher photocatalytic uranium efficiency than TAPT-TPA COFs and TAPT-TPA-4F COFs under natural water (pH = 6.1),…” (Please see line 187 of revised manuscript)\n“nearly 100% uranium removal within the pH range of 3-6,” (Please see line 277-278 of revised manuscript)\nSupplementary Fig. 40 | Uranium removal efficiency in natural water over time. Time-dependent uranium removal performance of TAPT–TPA–2F, TAPT–TPA–4F, and TAPT–TPA COFs under dark and light conditions.\nQ2: For supplementary Fig. 16, how does these data be calculated? Porous materials’ surface areas or pore volumes usually come along with the gas sorption isotherms, we cannot just provide the statistical data.\nR2: Thanks for your valuable comment. We have added the N adsorption-desorption 2\n(BET) isotherms in Supplementary Fig. 17-18 to support the reported textural parameters.\nWe have added Supplementary Fig. 18 in the revised manuscript.\nSupplementary Fig. 18 | Molecular structural characterization. N adsorption-desorption 2\nisotherms of TAPT-TPA, TAPT-TPA–2F and TAPT-TPA-4F."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have properly addressed my concerns. It can be accepted now.", "reviewer_2": "I think it may be accepted", "reviewer_3": "I think most of my concerns have been well addressed. This manuscript could be published. But I have some minor suggestions:\n1. In the abstract and conclusion part, the author should make it clear what conditions the 100% uranium removal achieved. Because in supplementary Fig. 39 and 40, it doesn’t show 100% removal. Also, the author should indicate what the pH value for natural water. It’s a little bit strange that the COF can achieve 100% removal efficiency in natural water while the pH=7 water can not.\n2. For supplementary Fig. 16, how does these data be calculated? Porous materials’ surface areas or pore volumes usually come along with the gas sorption isotherms, we cannot just provide the statistical data."}, "author_response": "Response: We sincerely thank the reviewer for the positive evaluation and for acknowledging that our major concerns have been addressed. We appreciate the additional minor suggestions and have revised the manuscript accordingly.\nQ1: In the abstract and conclusion part, the author should make it clear what conditions the 100% uranium removal achieved. Because in supplementary Fig. 39 and 40, it doesn’t show 100% removal. Also, the author should indicate what the pH value for natural water. It’s a little bit strange that the COF can achieve 100% removal efficiency in natural water while the pH = 7 water can not.\nR1: Thanks for your valuable comment. We have revised the Abstract and Conclusion to explicitly specify that 100% uranium removal was achieved across the pH range of 3-6, and that the tested natural water had a pH of 6.1. We have also aligned the wording with the corresponding datasets shown in Supplementary Fig. 40.\nWe have revised Supplementary Fig. 40 in the revised manuscript. The manuscript was revised and marked with red color in line 24-25, 187 and 277-278.\nRevision: “achieves 100% uranium removal efficiency within the pH range of 3-6,” (Please see line 24-25 of revised manuscript)\n“In addition, we demonstrate that TAPT-TPA-2F COFs also exhibits higher photocatalytic uranium efficiency than TAPT-TPA COFs and TAPT-TPA-4F COFs under natural water (pH = 6.1),…” (Please see line 187 of revised manuscript)\n“nearly 100% uranium removal within the pH range of 3-6,” (Please see line 277-278 of revised manuscript)\nSupplementary Fig. 40 | Uranium removal efficiency in natural water over time. Time-dependent uranium removal performance of TAPT–TPA–2F, TAPT–TPA–4F, and TAPT–TPA COFs under dark and light conditions.\nQ2: For supplementary Fig. 16, how does these data be calculated? Porous materials’ surface areas or pore volumes usually come along with the gas sorption isotherms, we cannot just provide the statistical data.\nR2: Thanks for your valuable comment. We have added the N adsorption-desorption 2\n(BET) isotherms in Supplementary Fig. 17-18 to support the reported textural parameters.\nWe have added Supplementary Fig. 18 in the revised manuscript.\nSupplementary Fig. 18 | Molecular structural characterization. N adsorption-desorption 2\nisotherms of TAPT-TPA, TAPT-TPA–2F and TAPT-TPA-4F."}, {"round": 3, "reviewer_comments": {"reviewer_3": "I think all my concerns have been well addressed. This work could be published now."}, "author_response": ""}]

Decision letter