# Efficient Peroxymonosulfate Activation by Metallic Copper in TiO2-CaTiO3-Cu2O-Cu Anodes for Electrocatalytic Degradation of Organic Pollutants

Fida Tanos, Elissa Makhoul, Amr Nada, Maged Bekheet, Eddy Petit, Antonio

Razzouk, Geoffroy Lesage, Marc Cretin, Mikhael Bechelany

► To cite this version:

Fida Tanos, Elissa Makhoul, Amr Nada, Maged Bekheet, Eddy Petit, et al., Efficient Peroxymono-sulfate Activation by Metallic Copper in TiO2-CaTiO3-Cu2O-Cu Anodes for Electrocatalytic Degra-dation of Organic Pollutants. Advanced Energy and Sustainability Research, 2024, 5, pp.2400102. 10.1002/aesr.202400102 . hal-04817990

HAL Id: hal-04817990

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Submitted on 9 Jul 2025

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# Efficient Peroxymonosulfate Activation by Metallic Copper in TiO₂-CaTiO₃-Cu₂O-Cu Anodes for Electrocatalytic Degradation of Organic Pollutants

Fida Tanos, Elissa Makhoul, Amr A. Nada, Maged F. Bekheet, Eddy Petit, Antonio Razzouk, Geoffroy Lesage, Marc Cretin, and Mikhael Bechelany*

The development of heterogeneous electrodes with high conductivity and electrocatalytic activity is a crucial goal. Achieving this using a simple and low-cost method is essential for wastewater purification by anodic oxidation combined with peroxymonosulfate (PMS). Herein, TiO₂-CaTiO₃(CTO)-Cu₂O-Cu heterojunction electrodes are prepared by mixing CaCu₃Ti₄O₁₂ with different amounts of graphene oxide (GO). The different mixtures are pressed into pellets and sintered under inert atmosphere at 1100 °C for 3 h. The obtained pellets are used as anodes for PMS activation in the electrocatalysis. The efficiency of paracetamol (PCM) removal reaches its maximum (93%) after 90 min using the CTO-Cu-5GO electrode in a solution containing 10 ppm PCM, 210 mL sodium sulfate, and 0.5 mM PMS. The higher amount of metallic copper in this anode promotes the generation of radicals to effectively degrade PCM. In optimal conditions (1.2 V versus Ag/AgCl, 1 mM PMS, and 10 ppm PCM), PCM is completely removed in 45 min. According to the quenching test results, *O₂⁻* and *OH*⁻ are the radicals generated during PCM degradation, and *O₂⁻* plays the main role. In this work, insights are provided into the rational combination of different metal oxides with TiO₂ as a heterostructure electrode to ensure high mineralization of pharmaceuticals by electrocatalysis.

## 1. Introduction

Modernization and industrial development have led to an increase in freshwater consumption worldwide.[1,2] In recent years, it is has become clear that water shortage poses a risk

to the maintainability of human culture.[3] Moreover, the uncontrolled discharge of many pollutants into aquatic sources has serious environmental consequences.[2] Most of these pollutants are known as emerging contaminants that are increasingly detected in water samples.[4,5] Exposure to emerging contaminants, even at low concentrations, can have harmful impacts on the environment and human health.[6,7] Pharmaceutical pollutants have received growing attention because they are potential bioactive chemicals that are resistant to degradation and are highly persistent in wastewater, groundwater, and surface water.[4,8,9] Paracetamol (PCM), also known as acetaminophen, is considered the most significant emerging contaminant due to its wide use in human and veterinary medicine.[10-12] The inadequate treatment of these effluents results in PCM presence in surface water and also in drinking water.[10,13]

Therefore, it is important to develop adequate treatment processes with proper filtration and purification to ensure the emerging contaminant effective removal.[14] Conventional methods are inefficient in removing pharmaceutical pollutants due to the toxicity, chemical characteristics, and varying concentrations (ng L⁻¹ to µg L⁻¹) of these

F. Tanos, E. Makhoul, A. A. Nada, E. Petit, G. Lesage, M. Cretin, M. Bechelany
Institut Européen des Membranes, IEM, UMR 5635, Univ Montpellier, ENSCM
Centre National de la Recherche Scientifique (CNRS)
Place Eugène Bataillon, Montpellier 34095, France
E-mail: mikhael.bechelany@umontpellier.fr

A. A. Nada
Department of Analysis and Evaluation
Egyptian Petroleum Research Institute
Cairo 11727, Egypt

M. F. Bekheet
Technische Universität Berlin, Faculty III Process Sciences, Institute of Materials Science and Technology, Chair of Advanced Ceramic Materials
Straße des 17. Juni 135, Berlin 10623, Germany

A. Razzouk
Laboratoire d'Analyses Chimiques, Faculty of Sciences
LAC—Lebanese University
Jdeidet 90656, Lebanon

M. Bechelany
Functional Materials Group
Gulf University for Science and Technology (GUST)
Mubarak Al-Abdullah 32093, Kuwait

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aesr.202400102.

© 2024 The Author(s). Advanced Energy and Sustainability Research published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/aesr.202400102
compounds.[5,11,15] This means that more powerful technologies must be developed to ensure the mineralization of these difficult-to-remove pollutants before their final discharge.[6,10]

Several advanced oxidation processes (AOPs)[14,16] are gaining great attention for the removal of pharmaceuticals in water through the generation of effective reactive species, such as hydroxyl (·OH), sulfate (·SO₄⁻), and superoxide (·O₂⁻) radicals.[5,17] Specifically, electrocatalysis offers the benefits of easy operation, high degradation efficiency, environmental friendliness, and absence of secondary pollution.[18–23] In an electrocatalytic process, electrical energy is converted to chemical energy[24,25] that contributes to the generation reactive oxygen species to oxidize recalcitrant contaminants and form CO₂ and H₂O.[20,25–27] Different studies have shown that electrocatalysis performance is influenced by various factors, such as type of anode and electrolyte, applied power, pH, anode surface, and drug concentration.[28]

A fundamental issue in electrocatalysis is the selection of suitable anode materials to boost the electrochemical reaction efficiency to increase the degradation rate.[18,19,29,30] Among the possible electrodes, titanium dioxide (TiO₂) is characterized by high chemical resistance, low cost, and environmental friendliness. However, its low electrical conductivity and wide-bandgap energy (3.2 eV) limit its electrocatalytic performance.[12,20,31] To overcome these drawbacks, heterostructures could be created by combining multi-metal oxides.[22] Ramanavicius et al.[32] showed the efficiency and advantages of titanium-oxide-based heterostructures for sensor applications.

The application of multi-metal oxide anodes has been investigated especially due to their superior electrical conductivity and durability.[26,33,34] For instance, calcium titanate (CaTiO₃) has been used as electrocatalyst due to its catalytic activity, abundance, electronic structure, and electron mobility.[35–38] TiO₂ and CaTiO₃ can be coupled to modify inactive anodes, leading to a major improvement in the design of stable electrocatalytic systems.[39,40]

To further enhance the electrocatalytic activity of TiO₂ anodes, significant efforts have been made in constructing metal/metal oxide anodes by improving the conductivity of metal oxides.[41] Metallic copper (Cu) is one of the most promising candidates owing to its high abundance, low cost, high activity, and multiple oxidation states (i.e., Cu⁰, Cu⁺, and Cu²⁺).[42] Recently, metallic Cu and p-type Cu₂O have been tested due to their excellent electrocatalytic properties.[43–46] Pingzhou et al. synthesized Ti–SnO₂–Sb and Ti–SnO₂–Cu electrodes by thermal decomposition. Their electrochemical characterization showed that copper presence in the Ti–SnO₂–Cu electrode improved stability and corrosion resistance compared with the Ti–SnO₂–Sb electrode.[47]

Peroxymonosulfate (PMS)-based AOPs also have been extensively studied to degrade pharmaceutical pollutants for environmental remediation.[48–50] PMS can be activated to produce highly reactive oxygen species (e.g., ·OH, ·SO₄⁻, and ·O₂⁻) and displays high catalysis activity.[49,51] Recently, Cu-based catalysts have been proposed as promising candidates for PMS activation due to their previously described characteristics.[48,51,52] Indeed,[52,53] the Cu²⁺/Cu⁺ redox cycle is considered the key point for the continuous production of reactive species through PMS activation.[54,55] Researchers have also combined electrocatalysis with PMS activation by Cu species to form an

electrocatalysis/Cu⁺/PMS system to facilitate the effective mineralization of organic compounds.[56] Panpan et al. introduced Cu in LaMnO₃ perovskite to promote PMS activation for sulfamethoxazole removal. The Cu-doped LaMnO₃ catalyst led to the complete removal of sulfamethoxazole in 60 min compared with 60% by pure LaMnO₃. The excellent efficiency in the Cu–LaMnO₃–PMS system was explained by the regulation of the produced reactive oxygen species, such as ·OH, ·SO₄⁻, and ·O₂⁻ radicals.[49]

However, the metal on the electrode surface easily degrades in water, which may affect the anode activity. To overcome this drawback, carbon materials, such as graphene oxide (GO), have been introduced to stabilize the active metal on the electrode surface.[57] The development of graphene/metal oxide electrocatalysts has been extensively studied to mitigate the metal oxide easy degradation and also due to their electrochemical properties and large surface area.[19,58] Among the different carbon materials, graphene and GO display excellent conductivity, fast electronic transport rate, and 2D structure.[59,60] Therefore, metal oxide–graphene–metal nanocomposites might become promising candidate as anodes for electrocatalysis and also as catalysts for PMS activation.

This work combined different material types to fabricate TiO₂–CaTiO₃–Cu₂O–Cu heterojunction electrodes: CaTiO₃ perovskite, TiO₂, Cu₂O (metal oxide), and metallic Cu. Additionally, CuO reduction into Cu₂O and Cu was improved via GO decomposition under nitrogen. The obtained electrodes were used for the first time as electrocatalyst for PCM degradation. The CaTiO₃–TiO₂–Cu₂O–Cu composite anodes were synthesized using a one-step sintering process. First, CaCu₃Ti₄O₁₂ (CCTO) powder was prepared using the solid-state method and then mixed with different GO amounts and pressed into pellets. The obtained pellets were sintered under nitrogen to obtain a mixture of TiO₂, CaTiO₃, Cu₂O, and Cu through the decomposition of CCTO composites. During sintering, GO oxidation changed the Cu₂O–Cu weight fraction and the growth direction of metallic Cu. The morphology and composition of the obtained electrodes were studied. The anodes were electrochemically characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Then, the electrocatalytic efficiency of the anode materials for PCM removal was investigated. In addition, the process conditions, including initial concentration of PCM, applied potential, and PMS concentration, were optimized.

## 2. Results and Discussion

### 2.1. Characterization of the Prepared Electrodes

The pure CCTO phase was obtained using a mixture of CuO powder, TiO₂, and CaCO₃. Then, the CCTO precursor was used for the synthesis of electrocatalysts with different GO amounts. Four pellets were obtained after sintering under nitrogen at 1100 °C for 3 h, followed by dry polishing of the surface. The resulting electrodes were labeled CTO–Cu, CTO–Cu–1GO, CTO–Cu–3GO, and CTO–Cu–5GO in function of the amount of GO × wt% = 0, 1, 3, and 5%, respectively. CTO was used to indicate the TiO₂ and CaTiO₃ phases, whereas Cu defined the
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Visual representation of the synthesis of CTO-Cu-GO electrocatalysts.</figcaption></figure>

Cu₂O and Cu metal phases. **Figure 1** illustrates the different steps of the synthesis of CTO-Cu-GO electrodes.

GO effect on the morphology of the CTO-Cu-GO electrodes was investigated using SEM. GO addition did not affect the morphology of the CTO-Cu-GO samples compared with the pure CTO-Cu sample (Figure S2, Supporting Information). In addition, the electrode composition and the elemental distribution were evaluated by SEM coupled with EDX (Figure 2, Supporting Information). The elemental mapping demonstrated the presence of Ca, Cu, Ti, and O elements in the CTO-Cu and CTO-Cu-GO samples, confirming the effectiveness of the preparation method. Additionally, we observe a distribution of Cu on the surface of all the samples. The amount of Cu metal in each pellet will be determined in the subsequent results.

Various studies have demonstrated the atomic-scale distribution in composites, providing significant insights into their microstructure and properties. For instance, Luong et al. examined the micro- and nanoscale morphology, atomic structure, and elemental distribution in perovskite CaTi₁-xFexO₃-δ.[61] However, in our case, the presence of four distinct phases makes it considerably more challenging to individually distinguish and attribute properties to each phase. The complexity arises from the intricate intermixing and overlapping of phases at the atomic level, which can obscure clear identification and separation.

XRD was used to determine the phase composition and crystallinity of the samples. Rietveld refinement of the powder XRD data was performed to obtain insights into the weight fraction of the crystalline phases, crystallite size, and microstrain in the

<figure><img src="image_3.png" /><figcaption>**Figure 2.** SEM-EDX mapping of the CTO-Cu, CTO-Cu-1GO, CTO-Cu-3GO, and CTO-Cu-5GO electrodes.</figcaption></figure>
CTO-Cu-GO electrodes following sintering under nitrogen. The plots of the final Rietveld refinement cycle for the XRD data of CTO-Cu, CTO-Cu-1GO, CTO-Cu-3GO, and CTO-Cu-5GO samples (Figure 3a-d) showed that in all samples, the main crystalline phase was TiO₂ rutile (PDF #021-1276), characterized by its intensive reflection at 27.4°.[62] The XRD reflections of orthorhombic CaTiO₃ (PDF #042-0423), cubic Cu₂O (PDF #005-0667), and cubic metallic Cu (PDF #004-0836) were also detected in all samples. The absence of XRD reflections associated with GO or any other carbon/carbide phases, including carbon monoxide that might be released from carboxyl groups in the GO structure, in all XRD patterns indicates a significant transformation during sintering. This implies that the original carbonaceous components, such as GO, and their potential decomposition products, were not present or were present in quantities below the detection limit of the XRD technique. These results indicate that the obtained ceramics are primarily composed of four phases with a heterostructure composition of TiO₂-CaTiO₃-Cu₂O-Cu.

The weight fraction of the four distinct crystalline phases, determined by Rietveld refinement, varied in each pellet based on the initial amount of GO (Figure 4). The results confirmed that TiO₂ rutile was the main phase (40–45 wt%) in all compounds. At high GO percentages (3% and 5%), the weight fraction

of Cu species (Cu₂O and metallic Cu) increased significantly compared with pure CTO-Cu and the CTO-Cu-1GO pellet. In the CTO-Cu-3GO sample, Cu²⁺ was mainly reduced into Cu⁺ ions with ≈29.2 wt% of Cu₂O phase. The 5% of GO in the CTO-Cu-5GO sample induced the reduction of Cu²⁺ into Cu⁰ to form ≈12.9 wt% of metallic Cu phase, which was the highest amount of metallic Cu in all tested samples. In fact, during GO decomposition at high temperatures and under an inert atmosphere (nitrogen), CuO was reduced to Cu₂O and metallic Cu, in agreement with other studies.[63–65] It has been reported that during CO oxidation, different transition metals can be reduced and released through the decomposition of carbon-based materials.[66,67]

Microstrains and crystallite size were also analyzed by Rietveld refinements (Figure 4b,c). The highest microstrain values (20–23 nm for all samples) were observed for the Cu₂O phase due to its smallest crystallite size. For metallic Cu, the mean crystallite size ranged between 54 and 66 nm, and the highest value was obtained with the CTO-Cu-5GO pellet. Therefore, lower microstrain values are observed for metallic Cu than for the Cu₂O phase. These findings are in agreement with a previous study showing that an increase in crystallite size may lead to a reduction in microstrain, attributed to the enhanced ordering of atoms within the crystal lattice.[68]

<figure><img src="image_4.png" /><figcaption>**Figure 3.** Rietveld refinement fitting profiles of the a) CTO-Cu, b) CTO-Cu-1GO, c) CTO-Cu-3GO, and d) CTO-Cu-5GO electrodes after 3 h sintering (1100 °C under nitrogen atmosphere).</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Figure 4.** a) Weight fractions and the Rietveld refinement parameters. b) Microstrain and c) crystal size of the formed crystalline phases extracted from the Rietveld refinement analysis of the ex situ XRD patterns of the indicated samples.</figcaption></figure>

Next, the decomposition mechanism of CCTO and GO and their conversion into the TiO₂-CaTiO₃-Cu₂O-Cu heterojunction ceramic composite under nitrogen were investigated by thermal analysis. The TGA curves, obtained during the heating of pure CCTO and the CCTO-Cu-5GO sample, showed two stages. The first covered the two regions from 584 to 860 °C, with low mass loss (≈1% and 1.5% for CTO-Cu and CCTO-Cu-5GO, respectively). The second stage was observed at temperatures between 860 and 1100 °C and included the main weight loss (≈2.7% and 3.5% for the CTO-Cu and CTO-Cu-5GO, respectively) (Figure 5a). The second stage was accompanied by two endothermic peaks at ≈1030 and 1100 °C in the DTA curves of both samples (Figure 5b,c). In addition, a third endothermic peak was detected at 1057 °C during the cooling step. The in situ MS spectra collected during heating revealed that the weight loss during the two stages was accompanied by the release of CO₂ (m/z = 44) and C (m/z = 12) (Figure 5d,e). This can be attributed to PVA thermal decomposition and GO oxidation during the thermal decomposition of CCTO. The MS signals attributed to C and CO₂ gases were higher in the CTO-Cu-5GO than in the CTO-Cu sample, confirming GO oxidation in the CTO-Cu-5GO sample. In fact, GO includes different oxygen-containing functional groups, such as hydroxyl, epoxy, and carboxyl groups. During thermal decomposition at elevated temperatures, these functional groups break down, causing chemical transformations in the GO structure. This process liberates volatile species (e.g., H₂O and CO₂) and gaseous atomic carbon (m/z = 12) through cleavage of carbon-oxygen bonds in various functional groups. However, the observed mass loss for both samples in both stages was higher than the amount of PVA and GO in the samples, indicating CCTO decomposition. This was confirmed by the endothermic peaks at ≈1030 and 1100 °C and the evolution of O₂ gas (m/z = 32) due to the reduction of CuO into Cu₂O and metallic Cu phases. These results suggest that in the presence of nitrogen, CCTO is decomposed in two steps: i) decomposition into CaTiO₃, CuO, and TiO₂ and then ii) reduction of CuO into Cu₂O and Cu. The higher intensity of the MS signal of O₂ gas (Figure 5f) in the CTO-Cu-5GO sample than in the pure CTO-Cu sample suggests the formation of higher amounts of Cu₂O and metallic Cu phases in the pellet containing 5% of GO. During the holding step at 1100 °C for 3 h, no weight loss, endothermic/exothermic peaks, and MS

signals for CO₂ and C were observed. This confirmed the complete decomposition of CCTO and GO before the holding step. However, the holding step for 3 h was necessary to sinter the resulting phase compositions under nitrogen. These results confirmed the decomposition process occurring in CCTO ceramics at 1100 °C under nitrogen for 3 h.[69] in good agreement with previous studies.[70-72] During cooling process to room temperature, the metastable Cu₂O phase usually tends to reoxidize to CuO in air; however, as the sintering took place under nitrogen, this phase was reduced into metallic Cu. Thus, a small mass loss accompanied by a strong endothermic peak and evolution of O₂ gas was observed during the cooling step at 1057 °C. The decomposition of the CCTO phase during the thermal analysis experiments was confirmed by XRD analysis of the recovered powder samples. Indeed, the recovered samples consisted of three phases: TiO₂ rutile, CaTiO₃, and Cu₂O (Figure S3, Supporting Information). Although no metallic Cu phase was observed in the two recovered samples, the alumina crucibles used for the measurements became black after the TGA experiments, suggesting the diffusion of the metallic Cu phase into the crucibles due to its low melting point (1085 °C). This was confirmed by determining the weight fractions of the crystalline phases in the samples by Rietveld refinement of the XRD data. This showed that the recovered CTO-Cu sample contained 40.9 wt% TiO₂, 26.9 wt% CaTiO₃, and 32.3 wt% Cu₂O, and the recovered CTO-Cu-5GO sample included 47.2 wt% TiO₂, 42 wt% CaTiO₃, and 10.8 wt% Cu₂O. According to the chemical formula of CCTO, the full decomposition of this phase should yield 40.6 wt% TiO₂, 23 wt% CaTiO₃, and 36.4 wt% Cu₂O. The amount of metallic Cu diffused in the alumina crucible can be predicted from the difference between the expected and determined weight fractions of Cu₂O in the recovered samples. Accordingly, 4.1 and 25.6 wt% of Cu₂O were reduced into metallic Cu in CTO-Cu and CTO-Cu-5GO, respectively. These results confirmed that the thermal decomposition of GO promotes the reduction of Cu₂O into metallic Cu.

## 2.2. Electrochemical Performance of CTO-Cu-GO Electrodes

The catalytic efficacy of the prepared electrodes was initially assessed by comparing their electrochemical behavior by CV (1M KOH electrolyte and scan rate of 25 mV s⁻¹). The pure
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /><figcaption>**Figure 5.** Results of the thermal analysis. a) TGA curves. b) TGA-DTA curves for the CTO-Cu sample. c) TGA-DTA curves for the CTO-Cu-5GO sample. d) TGA-MS spectra of the outlet CO₂ gas from the decomposition of the materials. TGA-MS spectra e) for C and f) for O₂ evolution during the TGA of the CTO-Cu and CTO-Cu-5GO pellets.</figcaption></figure>

CTO-Cu electrode and the sample with 1% GO displayed lower current compared with the anodes with 3% and 5% GO (Figure 6a). Notably, the CTO-Cu-5GO composite electrode exhibited exceptional electrochemical performance compared with all other electrodes. Therefore, addition of 1% of GO was insufficient to improve the electrocatalytic properties of the resulting composite, while 5% of GO effectively promoted the catalytic activity. The two anodic peaks at ≈0.56 and ≈0.89 V were assigned to Cu→Cu₂O and Cu, Cu₂O→CuO

transitions, respectively.[73] Therefore, the redox peaks registered were related to Cu species. Considering the weight fraction of Cu species obtained from the Rietveld refinement, the CTO-Cu samples with 3% and 5% of GO included the highest amount of Cu₂O and metallic Cu phases. The greater intensity of their redox peaks could be related to this high concentration. The CTO-Cu-5GO electrode had the highest quantity of metallic Cu, which is beneficial for improving the redox reactions and catalytic activity.
<figure><img src="image_12.png" /><figcaption>**Figure 6.** a) CV results for the pure CTO-Cu and CTO-Cu-1GO, CTO-Cu-3GO and CTO-Cu-5GO electrodes in 1M KOH at the scan rate of 25 mV s⁻¹.
b) Nyquist plots for the electrodes without and with different amounts of GO. c) Cyclic voltammograms in 10 mM K₄[Fe(CN)₆] at a scan rate of 50 mV s⁻¹.
d–g) Cyclic voltammograms recorded in 10 mM K₄[Fe(CN)₆] at different scan rates: d) CTO-Cu, e) CTO-Cu-1GO, f) CTO-Cu-3GO, and g) CTO-Cu-5GO.
h) Plot of Iₚₐ versus √v for the indicated electrodes.</figcaption></figure>

Then, EIS was carried out to analyze the resistive and charge-transfer properties of the different anodes using a Nyquist plot. The diameter of the semicircle in the EIS curves serves as an indicator of the electrode charge-transfer resistance.[³⁴,⁷⁴] The obtained data were fitted using the ZView software and the representative equivalent electrical circuit $R_Ω + Q_{CPE}/R_{ct}$, where $R_Ω$ is the electrolyte resistance, $Q_{CPE}$ is the constant phase element, and $R_{ct}$ is the charge-transfer resistance. The largest semicircle diameter was obtained for the pure CTO-Cu electrode, and it significantly and progressively decreased with the increasing GO amount (Figure 6b). CTO-Cu-5GO showed the smallest arc radius, indicative of low resistance. In the quantitative analysis (Table 1), the calculated $R_{ct}$ value of the CTO-Cu-5GO electrode was much lower than that of the other samples, revealing the stronger electron-transfer capability of CTO-Cu-5GO. The substantial quantity of metallic Cu in this sample underscores Cu role in reducing resistance, resulting in a highly conductive

electrode. This effectively improved the electrocatalytic activity of the CTO-Cu-5GO electrode, in line with the CV result. This remarkable change in the electrochemical properties proves the importance of combining TiO₂ with metal-metal oxides by forming heterojunction composites.

As the electrochemical reactions during anodic oxidation are surface reactions, it was interesting to determine the ESA of the samples. The interaction between the electrode surface and the analyte compound strongly depends on the anode ESA.[⁷⁵] Therefore, the ESA was determined by CV in 10 mM K₄[Fe(CN)₆] and 1M KCl as electroactive species and electrolyte solution, respectively. The measurements were registered between -0.3 and 0.3 eV at a scan rate of 50 mV s⁻¹. Most studies chose the Fe(CN)₆³⁻/₄⁻ redox couple due to its classification as a surface sensitive and not oxide-sensitive redox system.[⁷⁶] The cyclic voltammograms (Figure 6c) showed that the CTO-Cu-5GO electrode resulted in a larger current response
<table><caption>**Table 1.** Summary of the electrochemical parameters obtained for the CTO-Cu, CTO-Cu-1GO, CTO-Cu-3GO, and CTO-Cu-5GO electrodes.</caption><thead><tr><th rowspan="2">Electrode</th><th colspan="1">EIS study</th><th colspan="3">Randles-Sevcik study</th></tr><tr><th>R<sub>ct</sub> [Ω]</th><th>Linear correlation [r<sup>2</sup>]</th><th>Slope</th><th>Electroactive surface area [cm<sup>2</sup>] at different ν</th></tr></thead><tbody><tr><td>CTO-Cu</td><td>1189 ± 7</td><td>0.997 ± 0.003</td><td>0.0130 ± 0.0002</td><td>1.75 ± 0.03</td></tr><tr><td>CTO-Cu-1GO</td><td>868 ± 9</td><td>0.998 ± 0.002</td><td>0.0150 ± 0.0001</td><td>2.01 ± 0.03</td></tr><tr><td>CTO-Cu-3GO</td><td>105 ± 3</td><td>0.993 ± 0.003</td><td>0.0391 ± 0.0010</td><td>5.26 ± 0.02</td></tr><tr><td>CTO-Cu-5GO</td><td>49 ± 4</td><td>0.989 ± 0.002</td><td>0.0737 ± 0.0015</td><td>9.92 ± 0.03</td></tr></tbody></table>

toward the Fe(II)/Fe(III) couple compared with pure CTO-Cu and CTO-Cu with 1% and 3% GO. Then, the same parameters were held constant, and the cyclic voltammograms of the different electrodes were recorded at scan rates between 10 and 100 mV s⁻¹. The cyclic voltammograms at different scan rates (Figure 6d-g) showed that the currents associated with the oxidation and reduction peaks of all electrodes (CTO-Cu and CTO-Cu-GO samples) increased when the scan rate moved from 10 to 100 mV s⁻¹. This acceleration in speed was accompanied by a modest shift in both anodic and cathodic peak potentials, showing that in the CTO-Cu-GO electrodes, a redox reaction was involved in the surface-bound electron transfer. The scan rate influence on the CV response of the fabricated electrodes to the Fe(CN)₆³⁻/⁴⁻ couple was exploited to calculate the effective surface area. The graphs of the maximum anodic peak current (I<sub>pa</sub>) in function of the scan rate square root (√ν) (Figure 6h) showed a linear correlation between I<sub>pa</sub> and √ν with a straight line, indicating that the Fe(II)/Fe(III) redox couple has diffused on the electrode surface.[77] The active surface area was calculated using the slope value of the linear equation of I<sub>pa</sub> versus √ν (see the Randles-Sevcik equation, Equation (3)). The obtained values (Table 1) indicated that the ESA was highest in the CTO-Cu-5GO sample, providing the effective reduction induced with the decomposition of 5% of GO by increasing the amount of metallic Cu compared with the other samples. The geometrical surface area of the CTO-Cu-5GO electrode was 1 cm², while the active surface was 9.92 cm². Altogether, these results proved the electrocatalytic activity of the heterostructure composite with TiO₂-based material modified with metallic Cu.

To summarize, the morphology of the samples was not affected by GO presence, as evidenced by the SEM-EDX analysis. The XRD analysis indicated that Cu reduction was influenced by GO addition and that CTO-Cu-5GO contained the highest amount of metallic Cu. The TGA results suggested that CCTO decomposition in a nitrogen atmosphere occurs in two steps: i) decomposition into CaTiO₃, CuO, and TiO₂, followed by ii) reduction of CuO to Cu₂O and Cu. The higher concentration of metallic Cu in CTO-Cu-5GO and the combination of TiO₂ with metal-metal oxides significantly enhanced conductivity, redox reactions, and catalytic activity, as confirmed by the CV and EIS results.

## 2.3. Electrocatalytic Degradation Experiments

The electrochemical activities of the as-prepared CTO-Cu-GO anodes were compared by evaluating the electrocatalytic degradation of PCM. The experiments were carried out with a fixed

potential of 1.5 V versus Ag/AgCl, in a beaker containing 10 ppm PCM (initial concentration), 0.5 mM PMS (active component), and 210 mL of 50 mM Na₂SO₄ (electrolyte). The removal efficiency was improved significantly by GO addition in the composites (Figure 7a,b). Indeed, after 90 min, PCM degradation rates were 40% and 48% using the CTO-Cu and the CTO-Cu-1GO electrodes, respectively, compared with 88% and 93% in the presence of CTO-Cu-3GO and CTO-Cu-5GO, respectively. In addition, the fastest degradation kinetics was obtained with the CTO-Cu-5GO electrode. This confirmed that the high amount of metallic Cu promoted during the decomposition of 5% GO in the CTO-Cu-5GO composite strongly influences PCM degradation efficiency. The CTO-Cu-5GO composite electrode performed better because metallic Cu with high conductivity enhanced its electrocatalytic performance.[34] This electrode had the largest ESA. Moreover, its higher electroactivity improved the charge-transfer process of the target contaminants to the electrode surface with high electron-transfer ability. This effectively boosts the anodic oxidation of PCM on the catalyst surface. These findings underscore the significance of the heterojunction composite in efficiently promoting the electrocatalytic reaction for pollutant removal. We examined the impact of CaTiO₃ and TiO₂ on electrocatalysis degradation. Figure S4, Supporting Information, shows a degradation of 52% and 20% of PCM after 4 h using CaTiO₃ and TiO₂ pellets, respectively. Comparing the effectiveness of these catalysts with our own confirms the importance of combining TiO₂, CaTiO₃, Cu metal, and Cu₂O.

The differences in electrochemical properties and PCM degradation efficiency between CTO-Cu-3GO and CTO-Cu-5GO were minimal. Consequently, we chose to limit the graphene content to 5% GO to maintain the lowest necessary amount.

### 2.3.1. Effect of Different Systems on PCM Removal

Various systems were used to investigate PMS role in PCM degradation during the electrocatalytic process using the CTO-Cu-5GO electrode. No PCM degradation was detected after 90 min using PMS or CTO-Cu-5GO alone (Figure 7c). Similarly, the PMS/CTO-Cu-5GO and electrocatalysis/CTO-Cu-5GO systems showed a low degradation efficiency. The catalyst alone could not activate PMS, and it was difficult to effectively remove PCM during anodic oxidation without adding PMS. Conversely, the electrocatalysis-CTO-Cu-5GO-PMS system exhibited the highest removal efficiency (93% of PCM). A considerable improvement in the catalysis performance was observed by combining PMS, as a sulfate-radical-based AOP (persulfate
<figure><img src="image_13.png" /><figcaption>**Figure 7.** a) Normalized concentration decay in function of time for PCM electrocatalytic degradation using the CTO-Cu-5GO electrode, 1.5 V, 0.5 mM PMS solution, 10 ppm PCM, and 50 mM Na₂SO₄ as electrolyte. b) PCM removal efficiency. c) Comparison of PCM catalytic degradation in different systems. d) Effect of the applied voltage on PCM degradation. e) Influence of PMS concentration on PCM removal efficiency. f) Effect of the initial concentration of PCM. g) PCM degradation in optimized and not-optimized conditions using the CTO-Cu-5GO anode. h) Comparison of the removal efficiency in different conditions: potential = 1.5 V versus 1.2 V; CₚMS = 0.5 mM versus 1 mM; and CₚCM = 10 ppm in both conditions, i) V. fischeri luminescence inhibition (5 min exposure) during PCM electrocatalytic degradation.</figcaption></figure>

(PS)-AOP), to electrocatalysis with the CTO-Cu-5GO anode. The Cu species in the CTO-Cu-5GO composite were very effective in activating PMS to generate radicals. In addition, anodic oxidation is considered an activator in PS-AOPs, leading to an increase in the quantity of reactive oxygen species to ensure the complete removal of pollutants. Therefore, the electrocatalysis-CTO-Cu-5GO-PMS system achieved the elimination of PCM with satisfactory efficiency, suggesting the existence of synergistic effects.

### 2.3.2. Influence of Operational Parameters on PCM Degradation in the Electrocatalysis-CTO-Cu-5GO-PMS System

The electrocatalytic efficiency of PCM removal was further improved by optimizing the experimental operating conditions.[78]

The effects of applied potential, PMS concentration, and initial PCM concentration were studied by conducting experiments with the CTO-Cu-5GO electrode. PCM removal speed increased when the applied potential was increased from 0.5 to 1.2 V, but not between 1.2 and 2 V (Figure 7d). Therefore, the catalytic activity of CTO-Cu-5GO was favored in this range. Remarkably, the difference in the removal efficiency at 1.2 V was negligible compared with 1.5 V. In both cases, 93% of PCM was eliminated. Hence, opting for 1.2 V is more advantageous in terms of minimizing energy consumption throughout the process. At 2 V, the removal efficiency was slightly inhibited, possibly due to the competitive reactions between anodic oxidation and PMS activation at high voltage to limit radical generation.[56] A second reason could be related to the occurrence of other side reactions,
such as the oxygen evolution reaction, leading to competitive
reactions between water splitting and organic oxidation that
decrease PCM degradation rate.[20]

The PMS precursor as an active component is an important factor in PCM degradation, and its concentration directly affects the generation of reactive oxygen species. PCM removal efficiency increased from 81% to 100% after 90 min when PMS concentration was increased from 0.25 to 1 mM (Figure 7e). This indicated that the removal rate depends on the amount of PMS added (0.25–1 mM range). Conversely, in the presence of 2 mM PMS, the removal speed was remarkably reduced. Excess PMS can promote unfavorable radical consumption, leading to radical–radical reactions before the radical–organic reactions and consequently to a decrease in the available number of oxidizing species for PCM degradation.[79,80] PMS at 1 mM concentration showed a synergistic effect with electrolysis to produce a high number of radicals upon the application of voltage, leading to acceleration of the interaction between this radicals and PCM molecules to ensure their complete degradation into CO₂ and H₂O.[56]

When using 0.5 mM PMS and 1.5 V (Figure 7f), PCM degrada-
dation rates at 90 min were 100% and 93% when the initial PCM
concentration was 5 and 10 ppm, respectively. With higher initial
PCM concentrations, the removal efficiency gradually decreased,
which was attributed to the insufficient number of radicals
generated on the CTO-Cu-5GO electrode surface. When the
concentration of organic compounds increases, more time is
required for degradation due the lack of radicals compared to
the large number of molecules. Furthermore, at high concentra-
tion of PCM, more intermediates might be produced on the
anode surface that consume a certain number of reactive oxygen
species, thus explaining the decreased degradation efficiency at
90 min.[34]

These results indicate the need to select the appropriate PMS dose and potential range to optimize the efficiency of PCM removal while limiting energy consumption and chemical quantity. These findings indicated that an applied potential of 1.2 V versus Ag/AgCl and 1 mM of PMS were the optimal conditions. However, the initial concentration of 10 ppm PCM (and not 5 ppm) will be used to facilitate comparisons with previous studies. When using these optimal parameters and the CTO-Cu-5GO electrode, PCM was completely removed in only 45 min, compared to 93% after 90 min with 1.5 V and 0.5 mM PMS (Figure 7g–h).

To achieve the goal of wastewater treatment, which is to
reduce the presence of harmful substances, it was crucial to
investigate the toxicity of PCM and the by-products that
remained in the solution. Initially, the addition of PCM
resulted in a 65.5% inhibition of Vibrio fischeri biolumines-
cence (Figure 7i). After 10 min of PCM degradation, inhibition
increased to 89.4%, indicating the formation of harmful by-
products, such as p-BQ, benzaldehyde, and benzoic acid.
After 90 min of electrocatalysis, bioluminescence inhibition
decreased to ≈7%, suggesting the breakdown of these hazard-
ous intermediate by-products into less harmful chemicals.
Finally, after 10 h, luminescence inhibition was minimal,
indicating the complete decomposition of PCM and its
by-products into nontoxic compounds.

2.3.3. Detection of Reactive Species in the Electrocatalysis/
CTO-Cu-5GO/PMS System

Quenching experiments were carried out to identify the radicals involved in PCM electrocatalytic degradation: TBA and MeOH to inhibit the action of ·OH and both ·OH and ·SO₄⁻ radicals, respectively, and p-BQ for ·O₂⁻ radicals. No significant effect was observed when TBA was added: the removal efficiency remained unchanged (100%), indicating that the system did not produce ·OH (Figure 8a). Upon introduction of MeOH, the removal efficiency decreased from 100% to 80%, indicating the existence of ·SO₄⁻ species in the system. After addition of p-BQ, the removal efficiency decreased from 100% to less than 5%. This suggests that ·O₂⁻ radicals are the primary species responsible for PCM degradation in the presence of PMS. Therefore, both ·O₂⁻ and ·SO₄⁻ were involved, but ·O₂⁻ played the major role during PCM degradation.

2.3.4. Stability Tests

The same CTO-Cu-5GO electrode was used for five cycles of PCM degradation in the optimal electrocatalytic conditions, to evaluate its reusability. After the first cycle, the catalytic capacity of the CTO-Cu-5GO electrode decreased (removal efficiency from 100% in the first cycle to ≈50% afterward) and remained almost unchanged in the next cycles (Figure 8b). To understand this decrease in catalytic activity after reuse, XPS analysis was performed to evaluate the transformation and the valence state at the surface of the used CTO-Cu-5GO electrode compared with a fresh CTO-Cu-5GO electrode. The XPS survey of the CTO-Cu-5GO electrode before and after use showed that all the elements were present in both samples (Figure 8c). This indicates the maintenance of the heterostructure of TiO₂-CaTiO₃-Cu₂O-Cu after its reuse. The high-resolution XPS spectra of Cu2p revealed the same peaks in the used electrode and the fresh electrode (Figure 8d). However, the Cu⁺/Cu⁰ peaks had shifted slightly to a higher binding energy, indicating the formation of high-valence Cu species. In other words, some of Cu⁺/Cu⁰ were converted into Cu²⁺. Therefore, during the electrocatalytic process, part of the high amount of metallic Cu was oxidized into CuO. This decreased the electrode conductivity and affected the efficiency of PCM removal.[81] In addition, Cu⁰ oxidation in the presence of PMS induces the formation of more Cu⁺ ions that play a major role in PMS activation to generate radicals. However, this reaction is limited at low amounts of metallic Cu, leading to the generation of fewer ·O₂⁻ and ·OH radicals for PCM degradation. To overcome this limitation, the used electrode was treated under nitrogen at 1100 °C for 3 h and the obtained CTO-Cu-5GO pellet was used to remove PCM in the same conditions as before. Complete PCM removal was achieved in 60 min, like when using a fresh electrode (Figure 8b). Therefore, the thermal treatment under nitrogen is a solution to regenerate the catalytic activity of CTO-Cu-5GO by reducing the CuO phase formed on the electrode surface to metallic Cu at a similar high amount as obtained in the fresh CTO-Cu-5GO electrode. A second solution could be electrochemical regeneration. In addition, a previous study showed that using the atomic layer deposition technique to coat
<figure><img src="image_14.png" /><figcaption>**Figure 8.** a) Effects of radical scavengers on PCM removal (1.2 V versus Ag/AgCl; $C_{PMS}$ = 1 mM; $C_{PCM}$ = 10 ppm) using the CTO-Cu-5GO electrode. b) PCM removal efficiency with the CTO-Cu-5GO electrode during five cycles and after regeneration. c) Full survey XPS spectra of CTO-Cu-5GO before and after degradation. d) Cu2p peaks of the fresh and used CTO-Cu-5GO electrode.</figcaption></figure>

<table><caption>**Table 2.** Comparison of the effectiveness of various anodes in the electrocatalytic removal of paracetamol.</caption><thead><tr><th>Pollutant</th><th>C<sub>pollutant</sub><br>[mg L<sup>-1</sup>]</th><th>Anode material</th><th>Current or voltage</th><th>Solution<br>volume [mL]</th><th>pH</th><th>Degradation<br>time</th><th>Removal<br>efficiency [%]</th><th>Reference</th></tr></thead><tbody><tr><td>Paracetamol</td><td>10</td><td>Porous CCTO-30</td><td>1.5 V</td><td>210</td><td>7</td><td>90</td><td>100</td><td>[22]</td></tr><tr><td>Paracetamol</td><td>10</td><td>CCTO-N<sub>2</sub> (CaTiO<sub>3</sub>/TiO<sub>2</sub> rutile/Cu<sub>2</sub>O)</td><td>1.5 V</td><td>210</td><td>7</td><td>180</td><td>100</td><td>[70]</td></tr><tr><td>Paracetamol</td><td>15</td><td>Foam Ti/TiOx material</td><td>5 mA cm<sup>-2</sup></td><td>300</td><td>7</td><td>120</td><td>100</td><td>[88]</td></tr><tr><td>Paracetamol</td><td>10</td><td>CTO-Cu-5GO</td><td>1.5 V</td><td>210</td><td>7</td><td>45</td><td>100</td><td>This work</td></tr></tbody></table>

the catalyst surface with $Al_2O_3$ effectively improves the stability of the heterostructure catalyst.[82]

To assess the performance of the CTO-Cu-5GO electrode, **Table 2** provides a comparison with other anodes of similar composition for PCM removal. This comparison shows that the controlled decomposition of CCTO perovskite via GO reduction produces a composite electrocatalyst capable of achieving complete removal in a short time (45 min), compared to other electrodes. This makes it a promising anode for electrochemical wastewater treatment.

The enhanced effectiveness is attributed to the higher conductivity of the Cu metal phase, which improves PMS activation.

### 3. Conclusions

In this work, CTO-Cu-GO electrocatalysts were synthesized using CCTO and different amounts of GO as precursors by high-temperature sintering under inert nitrogen atmosphere for 3 h. The XRD results showed that sintering under nitrogen allowed the formation of a heterostructure composite of $TiO_2-CaTiO_3-Cu_2O-Cu$ in all samples. The increase in GO amount promoted the reduction of $Cu_2O$ to metallic Cu and CTO-Cu-5GO showed the highest amount of Cu metal. The TGA-MS method provided good insights into the decomposition mechanism of CCTO and GO at high temperatures under an
inert nitrogen atmosphere. CCTO decomposed in two steps, the first leading to the formation of $TiO_2$, $CaTiO_3$, and CuO and the second leading to the reduction of CuO to $Cu_2O$ and Cu. The higher intensity of the MS signal of $O_2$ gas in the sample containing 5% of GO confirmed the formation of more metallic Cu in CTO-Cu-5GO compared with the pure CTO-Cu sample. The electrochemical characteristics indicated that the CTO-Cu-5GO electrode displayed significant catalytic activity, excellent conductivity, and a substantial ESA compared with all the other electrodes. PCM removal by electrocatalytic degradation was studied using the prepared electrodes as anode and PMS activation. Using the CTO-Cu-5GO anode 93% of PCM was degraded after 90 min. In the optimal conditions (1.2 V versus Ag/AgCl, initial PMS concentration of 1 mM and initial PCM concentration of 10 ppm), complete PCM removal was achieved in 45 min. The reduction of CuO to metallic Cu is a crucial mechanism to increase the material effectiveness as anode. This reduction process plays a pivotal role by promoting efficient electron transfer and exerting a positive influence on surface reactivity. Consequently, these improvements are anticipated to contribute significantly to the overall performance of the material as an anode in the intended application, enhancing its ability to facilitate electrochemical reactions and optimize the efficiency of the anodic oxidation to remove organic contaminants. However, PCM removal rate decreased to 50% after one reuse due to the oxidation of metallic Cu to CuO. The electrode regeneration by thermal treatment overcame this limitation by reducing the CuO formed on the electrode surface to metallic Cu. Therefore, the CTO-Cu-5GO heterostructure electrode with high conductivity is a promising candidate for the anodic oxidation of organic pollutants in wastewater. However, the electrode stability needs to be optimized using a simple and fast method to improve its reusability.

## 4. Experimental Section

**Chemicals:** Titanium (IV) oxide ($TiO_2$, CAS number: 13463-67-7, 99.5%, Sigma Aldrich), calcium carbonate ($CaCO_3$, CAS number: 471-34-1, 99.95-100.05%, Sigma Aldrich), and copper (II) oxide (CuO, CAS number: 1317-38-0, 99.7%, Alfa Aesar) were used to synthesize the CCTO powder. Graphite (CAS number: 7782-42-5, graphite powder <20 µm, synthetic), sulfuric acid ($H_2SO_4$, CAS number: 7664-93-9, 99.99%), phosphoric acid ($H_3PO_4$, CAS number: 7664-38-2, 99.99%), potassium permanganate ($KMnO_4$, CAS number: 7722-64-7, 99.0%), hydrochloric acid (HCl, CAS number: 7647-01-0, 37%), and absolute ethanol (CAS number: 64-17-5) (all from Sigma Aldrich) were used to exfoliate GO. Poly (vinyl alcohol) (PVA, CAS number: 9002-89-5, 99%, Sigma Aldrich) was used as organic binder for pellet preparation. Potassium hydroxide (KOH, CAS number: 1310-58-3, ≥85%), sodium sulfate ($Na_2SO_4$, CAS number: 7757-82-6, ≥99.0%), and potassium chloride (KCl, CAS number: 7447-40-7, 99.0-100.5%) were purchased from Sigma Aldrich as electrolytes. Potassium hexacyanoferrate (III) ($K_3[Fe(CN)_6]$, CAS number: 13 746-66-2, ≥99.0%, Sigma Aldrich) was used for the determination of the pellet electroactive surface. $OXONE$ monopersulfate ($KHSO_3$ 0.5$KHSO_4$·0.5$K_2SO_4$, CAS number: 70 693-62-8) and PCM ($CH_3CONHC_6H_4OH$, CAS number: 103-90-2, BioXtra, ≥99.0%), from Sigma Aldrich, were used as active component and target pharmaceutical pollutant for electrocatalytic degradation, respectively. All chemicals were used without additional purification.

**GO Synthesis:** GO was synthesized by oxidizing graphite using a modified Hummer's method.[83] Briefly, graphite powder (3.0 g) and a mixture of concentrated $H_2SO_4/H_3PO_4$ (9:1) solution were combined in a beaker and stirred mechanically for 5 min. Subsequently, 18 g of

$KMnO_4$ was slowly introduced into the solution and stirred vigorously for 12 h. Then, 3 mL of $H_2O_2$ was gradually added to the solution while stirring magnetically for about 1 h. The resulting mixture was centrifuged at 6000 rpm for 10 min, and the precipitates were washed successively with 30% HCl, distilled water (to remove the acid), and ethanol. The washed GO was dried in an oven at 50 °C for 24 h to yield the pure exfoliated GO powder as verified in our previous work.[84] The formation of GO was verified by X-Ray diffraction (XRD) and Raman measurements as shown in Figure S1, Supporting Information. The XRD pattern of GO, depicted in Figure S1a, Supporting Information, shows a prominent (001) reflection at 10°. Additionally, a broad reflection at 42.2° was associated with the (100) plane. These reflections were characteristic of the pure GO structure. Raman spectroscopy (Figure S1b, Supporting Information) distinctly displayed two strong bands between 1000 and 1800 cm⁻¹, corresponding to the D and G bands specific to GO.

**Preparation of Pure Calcium Copper Titanate:** CCTO powder was synthesized through a solid-state reaction using a stoichiometric ratio of $TiO_2$, $CaCO_3$, and CuO as precursors. In a typical procedure, the mixture underwent ball milling in an alumina jar ($Al_2O_3$) with a precursors-to-alumina ball ratio of 1:9 and a rotation speed of 350 rpm for 5 h. Then, the homogeneous powder was calcined in a muffle furnace under ambient atmosphere at 900 °C for 3 h (constant heating and cooling rate of 5 °C min⁻¹). This thermal treatment was used to obtain the pure phase CCTO powder.

**Preparation of Electrodes with Different GO Amounts:** The nanocrystalline CCTO and different amounts (x) of GO (x wt% = 1, 3, and 5%) were used as precursors to prepare the electrodes. Briefly, the CCTO powder was granulated without and with different GO amounts in a mortar with two drops of 0.5 wt% PVA as binder. PVA served as an organic binder in the formation of the pellet, ensuring that it will not have a reducing effect due to the minimal quantity used (only 2 drops). The mixtures were pressed by a hydraulic press at 5T into 10 mm diameter and ≈2.3 mm thick pellets. The obtained pellets were sintered in an inert nitrogen atmosphere at 1100 °C for 3 h (heating and cooling ramp rates set at 2 °C min⁻¹). Sintering under nitrogen atmosphere resulted in CCTO decomposition,[84] as described in Equation (1)

$$CaCu_3Ti_4O_{12} \rightarrow CaTiO_3 + 3TiO_2 + 1.5Cu_2O \quad (1)$$

In the presence of GO, Equation (2) is added to reactions described in Equation (1).

$$CuO \rightarrow Cu + O_2 \quad (2)$$

The resulting electrodes were named CTO-Cu, CTO-Cu-1GO, CTO-Cu-3GO, and CTO-Cu-5GO in function of the amount of GO × wt% = 0, 1, 3, and 5%, respectively. CTO was used to indicate the $TiO_2$ and $CaTiO_3$ phases, whereas Cu defined the $Cu_2O$ and Cu metal phases. Before the electrochemical tests, the electrode surface was dry-polished with emery paper (grit number #600).

**Physical and Chemical Characterization of the Prepared Electrodes:** The surface morphology of the materials was examined using a Hitachi S4800 scanning electron microscope (SEM). Elemental mapping was done with a Zeiss EVO HD15 microscope coupled with an Oxford X-MaxN energy-dispersive X-Ray (EDX) detector. The crystalline phase of the composites was analyzed using a PANalytical Xpert-PRO diffractometer, paired with an Xcelerator detector and employing Ni-filtered Cu radiation with a wavelength of 1.54 Å (scan step size = 0.0020889° step⁻¹, time per step = 200.660 s step⁻¹, and 2θ = 20°-80°). The crystalline phase composition was determined by Rietveld refinement using the FULLPROF software,[85] with the instrument resolution function derived from the structure refinement of a silicon standard. Raman spectra were recorded using dispersive techniques.

**Thermogravimetric analysis (TGA) and differential thermal analysis (DTA)** were performed in an nitrogen atmosphere with a flow rate of 200 mL min⁻¹ and a heating rate of 5 K min⁻¹ using an STA 409 PC LUXX thermal analyzer (Netzsch, Germany) coupled to an OMNi Star GSD 320 mass spectrometer (Pfeiffer Vacuum, Germany). The elemental composition on the pellet surface was determined using X-Ray
photoelectron spectroscopy (XPS) and a monochromatic X-Ray source (Al-Kα, 1486.6 eV—resolution full width at half maximum (FWHM) 0.45 eV).

**Electrochemical Experiments:** Electrochemical measurements were carried out using a Solartron SI 1287 galvanostatic-potentiostat with a three-electrode configuration. The working electrodes were CTO-Cu pellets with different GO amounts, the counter electrode was platinum wire, and the reference electrode was Ag/AgCl. To examine the oxidation and reduction potentials of the semiconductor materials, CV was performed with 1M KOH as supporting electrolyte. The electrode charge transport resistance was assessed by EIS across a frequency range from 0.01 Hz to 105 MHz, and a voltage bias with 10 mV amplitude.

The electroactive surface area (ESA) was determined by CV in a solution of 1.0 M KCl and 10 mM K₃[Fe(CN)₆]. The curves were recorded at various scan rates (10–100 mV s⁻¹) within a potential range of -0.3–0.3 V versus Ag/AgCl. The ESA was quantified using the Randles–Sevcik equation (Equation (3)) [86]

$$I_p = 2.69 \times 10^5 AD^{1/2} n^{3/2} \gamma^{1/2} C \quad (3)$$

where *I*<sub>p</sub> denotes the peak current (in amperes), *n* represents the number of transferred electrons (*n* = 1), *A* is the electrode ESA (in cm²), *D* is the diffusion coefficient of [Fe(CN)₆]³⁻ (7.60 × 10⁻⁶ cm² s⁻¹), *C* is the concentration of [Fe(CN)₆]³⁻ in the solution (specifically, 1 × 10⁻⁵ mol cm⁻³), and is the scan rate. Before each measurement, all electrolytes were degassed with pure argon for 30 min to remove the dissolved O₂.

**Electrocatalytic System for PCM Degradation:** PCM removal by electrocatalysis was performed at room temperature using a three-electrode system. The applied potential was controlled using a Versatast3 potentiostat in chronoamperometry mode. The working electrode consisted of the prepared CTO-Cu anodes (without/with GO at different concentrations) with a surface area of 1 cm². A platinum plate (5 × 5 mm) and Ag/AgCl were the counter electrode and the reference electrode, respectively. The separation distance between anode and cathode was set at 3 cm, and the potential remained fixed at 1.5 V throughout the entire degradation process. The reaction was carried out in a glass beaker reactor with 10 ppm PCM, 0.5 mM PMS as active component, and 50 mM Na₂SO₄ as electrolyte in 210 mL of deionized water. Before electrolysis, argon gas was bubbled for 30 min to remove the dissolved O₂. The solution was mechanically stirred throughout the experiment, and 1 mL fractions were collected at specified time points using a disposable syringe and filtered.

**Analytical Procedures:** The high-performance liquid chromatography-mass spectrometry (HPLC-MS) system included a Waters 2695 pump, an autosampler with a 20 µl loop, a Waters 2695 Separation Module (HPLC), and a Waters Micromass Quattro Micro Mass Spectrometer equipped with electrospray ionization (Wythenshawe, Manchester, UK). For the separation process, a C18 XSelect HSS T3 column (length = 100 mm, internal diameter = 2.1 mm, and 2.5 µm particle size) from Waters was used. The column temperature was maintained at 25 °C. The mobile phase was composed of a mixture of 97% buffer A (0.1% formic acid in HPLC-grade water) and 3% buffer B (HPLC-grade acetonitrile with 0.1% formic acid). The measurement and run times for the process were set at 3 min, and a constant flow rate was maintained. The triple quadrupole MS, coupled to the HPLC instrument, was done in the positive electrospray ionization mode. The MS parameters were fine-tuned to improve ionization for optimal sensitivity. The detection settings were adjusted as follows: capillary potential was set to 3.5 kV, cone potential was set at 25 V, collision energy was maintained at 20 V, source temperature was set to 120 °C, desolvation temperature was set at 450 °C, desolvation gas flow was set at 450 L h⁻¹, and cone gas flow was set at 50 L h⁻¹. Nitrogen (99.5% purity) served as the nebulizer gas. The HPLC-MS data were used to calculate PCM removal efficiency using Equation (4) [22]

$$\text{Removal efficiency (\%)} = \frac{(C_0 - C)}{C_0} \times 100 \quad (4)$$

where C₀ (mg L⁻¹) is PCM concentration at time = 0, and C (mg L⁻¹) is PCM concentration in the solution at different time points during electrocatalysis.

**Scavenger Studies:** Experiments involving radical trapping with scavengers were carried out to identify the reactive species implicated in PCM mineralization in the electrocatalysis system. Three scavengers were added to different solutions: 6.6 mM of p-benzoquinone (p-BQ) to quench O₂⁻, 660 mM M tert-butyl alcohol (TBA) for scavenging *OH* and *SO₄*⁻, and 660 mM methanol (MeOH) to target *OH* radicals.

**Toxicity Tests:** To evaluate the acute toxicity of PCM and its intermediate by-products formed during degradation, a bioluminescence inhibition assay was used to quantify changes in luminescence in the marine bacterium V. fischeri (LCK 487 strain). Bacterial luminescence was quantified using a Microtox Model 500 Analyzer from Modern Water Inc. (UK), equipped with the MicrotoxOmni software for comprehensive data analysis. First, 5 mL of reagent diluent was added to allow V. fischeri reconstitution at 5 °C, leading to luminescence emission. Then, the reagent was stabilized by transferring 200 µL of the solution to the cuvettes at 15 °C for 15 min. V. fischeri bacteria were activated by adding 22% NaCl solution to the mixture to dilute to 0.27% the initial sample concentration. This dilution was selected to increase the bioluminescence measurement sensitivity and the detection of acute toxicity, even at extremely low concentrations of toxic compounds. In fact, the presence of toxic elements can decrease V. fischeri activity and thus, their luminescence. V. fischeri luminescence inhibition rate was calculated using Equation (5) [87]

$$I(t) (\%) = \left( 1 - \frac{LU(t)}{R(t) \times LU(0)} \right) \times 100 \quad (5)$$

where LU(t) is the luminescence intensity emitted by V. fischeri after 5 min or 15 min of exposure to the sample, LU(0) is the initial luminescence intensity before adding the sample, and R(t) is the correction term. In the absence of toxicity, luminescence naturally decreased overtime due to the environmental conditions. Therefore, it was essential to compensate for errors arising from these factors by considering the luminescence variability, R(t), in a control solution (MilliQ water and NaCl). This corrected term was calculated using Equation (6) [87]

$$R(t) = \frac{LU0(t)}{LU0(0)} \quad (6)$$

where LU0(t) denotes the luminescence intensity emitted by V. fischeri after 5 or 15 min of exposure to the control solution (MilliQ water and NaCl), and LU0(0) is the initial luminescence intensity before addition of the control solution.

## Supporting Information

Supporting Information is available from the Wiley Online Library or from the author.

## Acknowledgements

The authors would like to thank Delf Kober (TU Berlin) for TGA measurements.

## Conflict of Interest

The authors declare no conflict of interest.

## Author Contributions

**Fida Tanos:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Methodology (equal); Writing—original draft (lead). **Elissa Makhoul:** Conceptualization (equal); Data curation (equal); Formal analysis (equal); Validation (equal); Writing—original draft (supporting); Writing—review and editing (equal). **Amr A. Nada:** Conceptualization
(equal); Data curation (equal); Validation (equal); Writing—review and editing (equal). **Maged F. Bekheet**: Data curation (equal); Formal analysis (equal); Resources (equal); Validation (equal); Writing—review and editing (equal). **Eddy Petit**: Data curation (equal); Formal analysis (equal); Validation (equal); Writing—review and editing (equal). **Antonio Razzouk**: Conceptualization (equal); Resources (equal); Supervision (equal); Validation (equal); Writing—review and editing (equal). **Geoffroy Lesage**: Data curation (equal); Formal analysis (equal); Resources (equal); Supervision (equal); Writing—review and editing (equal). **Marc Cretin**: Conceptualization (lead); Formal analysis (equal); Resources (equal); Supervision (equal); Validation (equal); Writing—review and editing (equal). **Mikhael Bechelany**: Conceptualization (equal); Funding acquisition (lead); Project administration (lead); Supervision (equal); Validation (equal); Writing—review and editing (equal).

## Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## Keywords

emerging contaminants, electrocatalysis, metallic copper, peroxymonosulfate, water treatment

Received: April 2, 2024

Revised: July 6, 2024

Published online: August 1, 2024

[1] S. M. Sathe, I. Chakraborty, B. K. Dubey, M. M. Ghangrekar, *Environ. Res.* **2022**, *204*, 112135.

[2] F. Vale, C. A. Sousa, H. Sousa, L. Santos, M. Simões, *J. Clean. Prod.* **2022**, *347*, 131244.

[3] R. Sivaranjanee, P. Senthil Kumar, R. Saravanan, M. Govarthanan, *Chemosphere* **2022**, *294*, 133779.

[4] S. Khan, *Environ. Res.* **2022**, *207*, 112609.

[5] M. Tobajas, C. Belver, J. J. Rodriguez, *Chem. Eng. J.* **2017**, *309*, 596.

[6] V. Muelas-Ramos, M. Peñas-Garzón, J. J. Rodriguez, J. Bedia, C. Belver, *Sep. Purif. Technol.* **2022**, *297*, 121442.

[7] K. Noguera-Oviedo, D. S. Aga, *J. Hazard. Mater.* **2016**, *316*, 242.

[8] J. Rivera-Utrilla, M. Sánchez-Polo, M. A. Ferro-García, G. Prados-Joya, R. Ocampo-Pérez, *Chemosphere* **2013**, *93*, 1268.

[9] G. F. Birch, D. S. Drage, K. Thompson, G. Eaglesham, J. F. Mueller, *Mar. Pollut. Bull.* **2015**, *97*, 56.

[10] M. Pacheco-Álvarez, R. Picos Benítez, O. M. Rodríguez-Narváez, E. Brillas, J. M. Peralta-Hernández, *Chemosphere* **2022**, *303*, 134883.

[11] M. G. Alalm, A. Tawfik, S. Ookawara, *J. Environ. Chem. Eng.* **2015**, *3*, 46.

[12] F. Tanos, A. Razzouk, G. Lesage, M. Cretin, M. Bechelany, *ChemSusChem* **2023**, *17*, e202301139.

[13] H. N. Phong Vo, G. K. Le, T. M. Hong Nguyen, X.-T. Bui, K. H. Nguyen, E. R. Rene, T. D. H. Vo, N.-D. Thanh Cao, R. Mohan, *Chemosphere* **2019**, *236*, 124391.

[14] M. K. Shahid, A. Kashif, A. Fuwad, Y. Choi, *Coord. Chem. Rev.* **2021**, *442*, 213993.

[15] A. Rempel, J. P. Gutkoski, M. T. Nazari, G. N. Biolchi, B. Biduski, H. Treichel, L. M. Colla, *J. Water Process Eng.* **2022**, *46*, 102616.

[16] Y. Akhi, M. Irani, M. E. Olya, *J. Taiwan Inst. Chem. Eng.* **2016**, *63*, 327.

[17] S. Balu, C. Chuaicham, V. Balakumar, S. Rajendran, K. Sasaki, K. Sekar, A. Maruthapillai, *Chemosphere* **2022**, *298*, 134311.

[18] W. Nabgan, M. Saeed, A. A. Jalil, B. Nabgan, Y. Gambo, M. W. Ali, M. Ikram, A. A. Fauzi, A. H. K. Owgi, I. Hussain, A. A. Thahe, X. Hu, N. S. Hassan, A. Sherryna, A. Kadier, M. Y. Mohamud, *Environ. Res.* **2022**, *210*, 112975.

[19] Q. Zhang, B. X. Wang, Y. L. Zhou, J. Hong, Y. B. Yu, *J. Phys. Chem. Solids* **2022**, *161*, 110443.

[20] J.-C. Wu, Y.-H. Chuang, S. Y. H. Liou, Q. Li, C.-H. Hou, *J. Hazard. Mater.* **2022**, *429*, 128328.

[21] Y. Niu, Y. Yin, R. Xu, Z. Yang, J. Wang, D. Xu, Y. Yuan, J. Han, H. Wang, *Chemosphere* **2022**, *297*, 134146.

[22] E. Makhoul, F. Tanos, M. F. Bekheet, W. Riedel, E. Petit, R. Viter, I. Tepliakova, A. Ramanavicius, A. Razzouk, G. Lesage, M. Cretin, M. Boulos, D. Cornu, M. Bechelany, *Environ. Sci. Nano* **2023**, *10*, 3156.

[23] E. Makhoul, M. Boulos, M. Cretin, G. Lesage, P. Miele, D. Cornu, M. Bechelany, *Nanomaterials* **2023**, *13*, 2119.

[24] T. Chouki, M. Machreki, J. Topić, L. Butinar, P. Stefanov, E. Jez, J. S. Summers, M. Valant, A. Fait, S. Emin, *Catalysts* **2022**, *12*, 269.

[25] P. Khare, R. K. Patel, S. Sharan, R. Shankar, in *Advanced Oxidation Processes for Effluent Treatment Plants*, **2021**, pp. 137–160.

[26] S. A. Bomfim, A. R. Dória, I. M. D. Gonzaga, R. V. M. Oliveira, L. P. C. Romão, G. R. Salazar-Banda, L. F. R. Ferreira, K. I. B. Eguiluz, *Chemosphere* **2022**, *299*, 134350.

[27] B. A. Marinho, L. Suhadolnik, B. Likozar, M. Huš, Ž. Marinko, M. Čeh, *J. Clean. Prod.* **2022**, *343*, 131061.

[28] S. Ghasemi, F. Nabizadeh Chianeh, *SSRN Electron.* **J. 2022**.

[29] B. Shi, L. Zhang, H. Sun, J. Ren, H. Wang, H. Tang, Z. Bian, *Chemosphere* **2022**, *304*, 135258.

[30] J. Zhang, Y. Zhao, Y. Liu, C. Zhu, B. Wang, L. Zhang, G. Li, H. Wu, C. Liu, Y. Li, J. Ren, C. Shao, X. Zhang, *J. Alloys Compd.* **2022**, *902*, 163723.

[31] P. Kaur, Y. Park, M. Sillanpää, M. A. Imteaz, *J. Clean. Prod.* **2021**, *313*, 127915.

[32] S. Ramanavicius, A. Ramanavicius, *Sensors* **2020**, *20*, 6833.

[33] I. Pouladvand, S. K. Asl, M. G. Hoseini, M. Rezvani, *J. Sol-Gel Sci. Technol.* **2019**, *89*, 553.

[34] C. Ma, Y. Zhang, *Sep. Purif. Technol.* **2021**, *258*, 118024.

[35] M. Zhang, G. Jeerh, P. Zou, R. Lan, M. Wang, H. Wang, S. Tao, *Mater. Today* **2021**, *49*, 351.

[36] L. Chen, Y. Zhang, C. Ma, *Chem. Eng. J.* **2020**, *393*, 124514.

[37] X. Li, H. Zhao, J. Liang, Y. Luo, G. Chen, X. Shi, S. Lu, S. Gao, J. Hu, Q. Liu, X. Sun, *J. Mater. Chem. A* **2021**, *9*, 6650.

[38] Y. Zhang, Z. Jin, L. Chen, J. Wang, *Materials* **2019**, *12*, 511.

[39] J. Lin, J. Hu, C. Qiu, H. Huang, L. Chen, Y. Xie, Z. Zhang, H. Lin, X. Wang, *Catal. Sci. Technol.* **2019**, *9*, 336.

[40] J. Yang, C. Shi, Y. Dong, H. Su, H. Sun, Y. Guo, S. Yin, *J. Colloid Interface Sci.* **2022**, *605*, 373.

[41] R. Li, J. Xu, R. Zeng, Q. Pan, T. Tang, W. Luo, *J. Power Sources* **2020**, *457*, 228058.

[42] Z. Wei, D. Feng, J. Li, Y. Lin, H. Zhang, *Chem. Eng. J.* **2022**, *427*, 131659.

[43] Y. Wei, W. He, P. Sun, J. Yin, X. Deng, X. Xu, *Appl. Surf. Sci.* **2019**, *476*, 966.

[44] Q. Song, S. Zhang, X. Hou, J. Li, L. Yang, X. Liu, M. Li, *J. Hazard. Mater.* **2022**, *438*, 129455.

[45] B. Long, H. Yang, M. Li, M.-S. Balogun, W. Mai, G. Ouyang, Y. Tong, P. Tsiakaras, S. Song, *Appl. Catal. B Environ.* **2019**, *243*, 365.

[46] P. Muthukumar, P. S. Kumar, S. P. Anthony, *Mater. Res. Express* **2018**, *6*, 025518.

[47] P. Duan, X. Hu, Z. Ji, X. Yang, Z. Sun, *Chemosphere* **2018**, *212*, 594.

[48] W. Zheng, Y. Liu, W. Liu, H. Ji, F. Li, C. Shen, X. Fang, X. Li, X. Duan, *Water Res.* **2021**, *194*, 116961.

[49] P. Gao, X. Tian, W. Fu, Y. Wang, Y. Nie, C. Yang, Y. Deng, *J. Hazard. Mater.* **2021**, *411*, 125163.

[50] J. Cao, S. Sun, X. Li, Z. Yang, W. Xiong, Y. Wu, M. Jia, Y. Zhou, C. Zhou, Y. Zhang, *Chem. Eng. J.* **2020**, *382*, 122802.

[51] Y. Yang, S. Yu, Y. Zong, R. Wu, J. Feng, T. Wei, Y. Ren, *J. Environ. Chem. Eng.* **2022**, *10*, 108113.
[52] T. Liu, K. Yin, N. Li, H. Liu, J. Chen, X. Zhou, Y. Zhang, *Chem. Eng. J.* **2022**, *427*, 131741.

[53] Q. Zhang, X. Sun, Y. Dang, J.-J. Zhu, Y. Zhao, X. Xu, Y. Zhou, *J. Hazard. Mater.* **2022**, *424*, 127651.

[54] J. Yang, R. Huang, L. Wang, D. Luo, C. Wang, *J. Environ. Chem. Eng.* **2022**, *10*, 107606.

[55] T. Chen, Z. Zhu, H. Zhang, Y. Qiu, D. Yin, G. Zhao, *ACS Appl. Mater. Interfaces* **2020**, *12*, 42790.

[56] C. Bai, G. Yang, S. Zhang, S. Deng, Y. Zhang, C. Chen, J. He, M. Xu, L. Long, *Chem. Eng. J.* **2021**, *423*, 130284.

[57] J. Wang, S. Wang, Z. Zhang, C. Wang, *J. Environ. Manage.* **2020**, *276*, 111357.

[58] S. Asim, Y. Zhu, M. Rana, J. Yin, M. W. Shah, Y. Li, C. Wang, *Chemosphere* **2017**, *169*, 651.

[59] T. Hong, F. Tao, J. Lin, W. Ding, M. Lan, *J. Solid State Chem.* **2015**, *228*, 174.

[60] S. Dayana Priyadharshini, S. Manikandan, R. Kiruthiga, U. Rednam, P. S. Babu, R. Subbaiya, N. Karmegam, W. Kim, M. Govarthanan, *Environ. Pollut.* **2022**, *306*, 119377.

[61] J. Luong, X. Wang, A. Tsung, N. Humphrey, H. Guo, B. X. Lam, S. Mallikarjun Sharada, W. J. Bowman, *ACS Appl. Nano Mater.* **2023**, *6*, 1620.

[62] F. Duquet, A. A. Nada, M. Rivallin, F. Rouessac, C. Villeneuve-Faure, S. Roualdes, *Catalysts* **2021**, *11*, 1228.

[63] S. Kawrani, M. Boulos, M. F. Bekheet, R. Viter, A. A. Nada, W. Riedel, S. Roualdes, D. Cornu, M. Bechelany, *Appl. Surf. Sci.* **2020**, *516*, 146051.

[64] Y. Qu, Y. Du, G. Fan, J. Xin, Y. Liu, P. Xie, S. You, Z. Zhang, K. Sun, R. Fan, *J. Alloys Compd.* **2019**, *771*, 699.

[65] E. Makhoul, F. Tanos, M. F. Bekheet, W. Riedel, E. Petit, G. Lesage, M. Cretin, M. Boulos, D. Cornu, M. Bechelany, *Appl. Mater. Today* **2023**, *35*, 101983.

[66] M. F. Bekheet, G. Miehe, C. Fasel, A. Gurlo, R. Riedel, *Dalton Trans.* **2012**, *41*, 3374.

[67] M. F. Bekheet, L. Schlicker, A. Doran, K. Siemensmeyer, A. Gurlo, *Dalton Trans.* **2018**, *47*, 2727.

[68] R. Djafar, K. Boumchedda, A. Chaouchi, D. Fasquelle, K. Sedda, S. Brahimi, K. Khalfaoui, M. Bououdina, *Mater. Chem. Phys.* **2020**, *256*, 123706.

[69] F. Moura, A. Z. Simões, R. C. Deus, M. R. Silva, J. A. Varela, E. Longo, *Ceram. Int.* **2013**, *39*, 3499.

[70] R. Schmidt, M. C. Stennett, N. C. Hyatt, J. Pokorny, J. Prado-Gonjal, M. Li, D. C. Sinclair, *J. Eur. Ceram. Soc.* **2012**, *32*, 3313.

[71] J. Zhao, J. Liu, G. Ma, *Ceram. Int.* **2012**, *38*, 1221.

[72] T. B. Adams, D. C. Sinclair, A. R. West, *J. Am. Ceram. Soc.* **2006**.

[73] Y. Deng, A. D. Handoko, Y. Du, S. Xi, B. S. Yeo, *ACS Catal.* **2016**, *6*, 2473.

[74] G. Dong, K. Lang, Y. Gao, W. Zhang, D. Guo, J. Li, D.-F. Chai, L. Jing, Z. Zhang, Y. Wang, *J. Colloid Interface Sci.* **2022**, *608*, 2921.

[75] V. B. Patil, S. J. Malode, S. N. Mangasuli, S. M. Tuwar, K. Mondal, N. P. Shetti, *Micromachines* **2022**, *13*, 1166.

[76] D. Salinas-Torres, F. Huerta, F. Montilla, E. Morallón, *Electrochim. Acta* **2011**, *56*, 2464.

[77] L. Jaber, A. Elgamouz, A.-N. Kawde, *Arab. J. Chem.* **2022**, *15*, 104303.

[78] R. Xie, X. Meng, P. Sun, J. Niu, W. Jiang, L. Bottomley, D. Li, Y. Chen, *J. Crittenden, Appl. Catal. B Environ.* **2017**, *203*, 515.

[79] X. Du, X. Bai, L. Xu, L. Yang, P. Jin, *Chem. Eng. J.* **2020**, *384*, 123245.

[80] C. Qi, X. Liu, J. Ma, C. Lin, X. Li, H. Zhang, *Chemosphere* **2016**, *151*, 280.

[81] S. Mao, X. Sun, H. Qi, Z. Sun, *Sci. Tot. Environ.* **2021**, *793*, 148492.

[82] J. Lu, B. Fu, M. C. Kung, G. Xiao, J. W. Elam, H. H. Kung, P. C. Stair, *Science* **2012**, *335*, 1205.

[83] H. Belaid, S. Nagarajan, C. Teyssier, C. Barou, J. Barés, S. Balme, H. Garay, V. Huon, D. Cornu, V. Cavaillès, M. Bechelany, *Mater. Sci. Eng. C* **2020**, *110*, 110595.

[84] F. Tanos, E. Makhoul, A. A. Nada, M. F. Bekheet, W. Riedel, S. Kawrani, H. Belaid, E. Petit, R. Viter, V. Fedorenko, A. Ramanavicius, M. Boulos, D. Cornu, A. Razzouk, G. Lesage, M. Cretin, M. Bechelany, *Appl. Surf. Sci.* **2024**, *656*, 159698.

[85] J. Rodriguez-Carvajal, *Newsletter* **2001**, *26*, 12.

[86] T. X. H. Le, C. Charmette, M. Bechelany, M. Cretin, *Electrochim. Acta* **2016**, *188*, 378.

[87] T. X. H. Le, T. V. Nguyen, Z. A. Yacouba, L. Zoungrana, F. Avril, E. Petit, J. Mendret, V. Bonniol, M. Bechelany, S. Lacour, G. Lesage, M. Cretin, *Chemosphere* **2016**, *161*, 308.

[88] J. Ma, C. Trellu, N. Oturan, S. Raffy, M. A. Oturan, *Appl. Catal. B Environ.* **2022**, *317*, 121736.