Heterogeneous electro-Fenton treatment of clofibric acid with an Fe₃O₄-loaded bifunctional carbon felt cathode via different anode types

Heterogeneous electro-Fenton treatment of clofibric acid with an Fe₃O₄-loaded bifunctional carbon felt cathode via different anode types | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Heterogeneous electro-Fenton treatment of clofibric acid with an Fe₃O₄-loaded bifunctional carbon felt cathode via different anode types Titus Otamayomi Moses, Doğan Çirmi, Yalçın Fidan, Belgin Gözmen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6965557/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Dec, 2025 Read the published version in Journal of Applied Electrochemistry → Version 1 posted 11 You are reading this latest preprint version Abstract Pharmaceutical pollutants like clofibric acid (CFA) pose significant threats to aquatic ecosystems and human health. In this study, a bifunctional cathode was synthesized by loading Fe 3 O 4 nanoparticles onto a carbon felt cathode using solvothermal method. The characterizations of CF@Fe 3 O 4 were performed using FESEM, CV and EIS. The developed CF@Fe 3 O 4 cathode was then evaluated in heterogeneous electro-Fenton (HEF) application in clofibric acid (CFA) oxidation at different current and pH values using Pt and BDD anodes. The CF@Fe 3 O 4 electrode accelerated electron transfer, minimizing mass transport limitations, enhancing CFA degradation. The CF@Fe 3 O 4 / Pt electrode pair exhibited 75% mineralization following 3 h of HEF treatment, whereas the BDD anode exhibited 78% mineralization at 50 mA. Both values outperformed the homogenous EF process with CF in terms of effectiveness. Radical scavenging experiments proved • OH as the dominant reactive species, with contributions from O 2 •- and SO 4 •- . Mineralization remained high (>85%) across pH 3–8, due to enhanced oxidation of intermediate products via BDD( • OH) and electron transfer mechanisms, while degradation slowed at higher currents. The CF@Fe 3 O 4 /BDD combination consistently outperformed Pt in terms of both degradation kinetics and energy efficiency. Here we show that even after 5 reuses, the CF@Fe 3 O 4 cathode/BDD anode pair can effectively remove persistent organic pollutants without pH limitation and with an environmentally friendly process without any significant performance loss. CF@Fe3O4 Heterogeneous electro-Fenton Clofibric acid BDD anode Carbon felt EAOPs Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Aquatic creatures and human health are seriously threatened by the presence of pharmaceutical chemicals and their metabolites in aquatic systems. The dearth of knowledge regarding the durability and ecotoxicity of the majority of these chemicals is concerning. An active metabolite of the common lipid regulator clofibrate is clofibric acid (CFA). Because CFA is a structural isomer of the herbicide mecoprop, it was also the first medication found in an aquatic environment [ 1 ]. Clofibric acid is continuously found in surface and groundwater due to its chemical stability (greater than 21 years) and resistance to conventional biological and physicochemical remediation techniques [ 2 , 3 ]. Hence, the designation of CFA as a persistent organic pollutant (POP), necessitating the development of innovative remediation strategies [ 4 , 5 ]. Numerous persistent organic pollutants (POPs) in wastewater are degraded by electrochemical advanced oxidation processes (EAOPs), particularly the electro-Fenton (EF) process, which turns them into less hazardous or biodegradable by-products [ 6 – 9 ]. By combining electrochemical and Fenton chemistry to produce hydroxyl radicals in situ through the cathodic reduction of oxygen to hydrogen peroxide (H 2 O 2 ) in Eq. (1), the EF process is a noteworthy breakthrough. According to Fenton's reaction (Eq. (2)), ferrous ions subsequently activate H 2 O 2 [ 10 ]. Eq. (3) describes the electrochemical conversion of Fe 3+ ions to Fe 2+ , formed in the Fenton reaction [ 11 ]. The process is characterized as an electrocatalytic system, as Fe 2+ is being regenerated in the medium [ 12 ]. As a strong oxidizing agent (E o ( • OH/H 2 O) = 2.80 V vs. SHE), the generated • OH reacts non-selectively with organic molecules, causing them to mineralize [ 13 ]. O 2 + 2H + + 2e − → H 2 O 2 (1) Fe 2+ + H 2 O 2 → Fe 3+ + OH – + • OH (2) Fe 3+ + e − → Fe 2+ (3) Critical parameters in the EF process are revealed as electrode material, current density, pH, distance between electrodes and O 2 /air supply rate [ 14 , 15 ]. Since its inception in the mid-20th century, the EF process has undergone continuous modification in response to the growing complexity and variety of pollutants present in industrial effluents. These refinements underscore how crucial it is within the broader context of advanced oxidation techniques and environmental sustainability [ 5 , 8 , 16 , 17 ]. Heterogeneous EF processes have been studied in diverse systems, incorporating a wide range of materials, including natural minerals, different metal oxides, zero-valent metals, composite structures with reduced graphene oxide (rGO), graphene oxide (GO), metal organic frameworks (MOFs), etc., because Fe(II) ions cannot be recovered after the process [ 18 – 21 ]. Recent years have seen the development of electrodes that enable both H 2 O 2 generation and activation in heterogeneous electro-Fenton (HEF) applications [ 22 ]. Deng et al. [ 8 ] summarized different strategies that can enhance electron transfer control and mass transport control to improve Fe 3+ /Fe 2+ conversion in the EF process. The formation of both carbon and metal-based active sites is important to ensure the Fe 3+ / Fe 2+ cycle through electron transfer. Recent developments in electrodes for HEF processes have brought attention to the use of a variety of catalysts that increase process efficiency by reducing sludge generation, increasing catalyst reusability, and expanding operating pH ranges (e.g., pH 3–8). For example, immobilization of layered double hydroxides (LDHs) such as Fe II Fe III , CuFeV have become increasingly popular as cathodes because of their extensive surface areas, sites of activity that generate catalytic effects, and their chemical stability [ 6 , 24 – 25 ]. Furthermore, researchers reported that the active sites offered by the CoFe 2 O 4 [ 26 , 27 ] and MoS 2 [ 28 ] loaded on carbon felt or carbon fiber paper enhance the oxidation of different contaminants while promoting the Fe 3+ /Fe 2+ transformation. Magnetite (Fe 3 O 4 ) nanoparticles have low toxicity, easy synthesis conditions and most importantly, can be easily separated from solution due to their magnetic properties, making them a good catalyst for HEF. Electron mobility in the spinel structure of magnetite, which consists of Fe II and Fe III , is quite high [ 29 ]. In order to prevent agglomeration of Fe 3 O 4 structure [ 30 ], effective mineralization of organic pollutants in a wider pH range was achieved in HEF process by using GO, rGO or multiwalled carbon nanotubes (MWCN) bases [ 7 , 31 – 33 ]. However, mass transfer is of great importance in enhancing the interaction of catalysts dispersed in solution with H 2 O 2 formed on the cathode surface. Camcıoğlu et al. [ 7 ] reported effective mineralization compared to the homogeneous EF process by using rGO / Fe 3 O 4 /CB@CF electrode in the oxidation of busulfan. According to this study, carbon compounds with high conductivity made it easier to activate H 2 O 2 and assist the Fe 3+ /Fe 2+ cycle. Chen et al. [ 34 ] performed the efficient mineralization of ceftriaxone sodium using Fe 0 -Fe 3 O 4 /CeO 2 /C composite cathode. the CeO 2 structure within the electrode framework accelerated electron transfer at the catalyst interface due to the Ce 4+ /Ce 3+ redox cycle and facilitated the production of hydroxyl radicals due to the iron/cerium synergistic effect. In this study, 1) magnetite (Fe 3 O 4 ) nanoparticles were loaded onto the activated carbon felt surface by solvothermal method. 2) CF@Fe 3 O 4 cathode characterization was carried out using analytical and electroanalytical techniques. 3) CF@Fe 3 O 4 cathode was tested against Pt and BDD anode in the oxidation of low biodegradable clofibric acid in the HEF process. 4) Determination of reactive oxygen species responsible for CFA oxidation and the effect of pH on the HEF process were revealed. In summary, this investigation seeks to thoroughly explore the use of HEF process in the degradation of CFA, drawing on both conventional and innovative research methodologies. Experimental sections Materials Experimental details are provided in the supplementary materials document including the chemicals used and the properties of the electrodes (Text S1.1), the preparation of CF@Fe 3 O 4 cathode and characterization methods (Text S1.2, Text S1.3), homogenous and heterogonous electro-Fenton procedures (Text S1.4), formulas used to determine CFA degradation / mineralization, and characterization methods and analytical tools (Text S1. 5). Results and discussion Characterization of Fe 3 O 4 and CF@Fe 3 O 4 cathode SEM images of Fe 3 O 4 nanoparticles scattered on the carbon felt surface were depicted in different magnification rates at Fig. 1 a-c. Magnetite NPs show a very small distribution in the range of 7–17 nm, but clustered as a result of agglomeration. The crystal structure of the Fe 3 O 4 NPs in powder form was examined by XRD analysis (Fig. 1 d). The diffraction peaks observed at 18.12° (111), 30.07° (220), 35.43° (311), 43.10° (400), 53.44° (422), 57.03° (511), and 62.65° (440) correspond to the standard cubic spinel group (PDF 19–0629) [ 35 , 36 ]. Crystallite size (D) was determined as 15.3 nm. This is a value compatible with the size of the clusters observed in the SEM images. Electrochemical performances of the cathode materials To investigate the oxygen reduction reaction (ORR) performance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted for bare carbon felt (CF) and Fe 3 O 4 -coated carbon felt (CF@Fe 3 O 4 ) electrodes 0.1 M Na 2 SO 4 electrolyte under N 2 and O 2 -saturated conditions. Figure 2 a presents the CV curves of the bare CF electrode. Under both N 2 and O 2 atmospheres, the electrode predominantly exhibited double-layer capacitive behavior, and no distinct redox peaks were observed. Only a slight increase in current density was recorded under O₂ saturation, indicating that the bare CF possesses very limited electrocatalytic activity toward ORR. Figure 2 b displays the CV profiles of the CF@Fe 3 O 4 electrode. In the N 2 -saturated environment, the redox peaks observed in the CV curves confirm the intrinsic electrochemical activity of the Fe 3 O 4 coating. Under O 2 -saturated conditions, a significant increase in current density compared to the N₂ environment was observed. A sharp cathodic peak appearing around − 0.5 V (vs. Ag/AgCl) indicates active ORR kinetics on the Fe 3 O 4 -coated surface. These findings reveal that the Fe 3 O 4 coating not only facilitates efficient electron transfer at the electrode–electrolyte interface but also enhances ORR activity [ 9 ]. Furthermore, the increase in cathodic current density under the oxygen atmosphere suggests a potential pathway for the two-electron reduction of O 2 to form H 2 O 2 [ 37 ], indicating that the CF@Fe 3 O 4 electrode is a promising catalytic material for EF applications. Electrochemical impedance spectroscopy (EIS) was employed to further investigate the interfacial charge transfer characteristics of the electrodes. Figure 2 c shows the Nyquist plots of the CF@Fe 3 O 4 electrode under N 2 and O 2 -saturated conditions. Under a nitrogen atmosphere, the electrode exhibited a large semicircle, indicative of high charge transfer resistance (Rct) and sluggish reaction kinetics. In contrast, under oxygen saturation, the semicircle became significantly smaller, indicating a substantial reduction in Rct and enhanced interfacial charge transfer efficiency [ 38 ]. The pronounced differences between the N 2 and O 2 environments confirm that the presence of oxygen significantly improves the electrochemical performance of the CF@Fe 3 O 4 electrode. Homogenous and heterogeneous electro-Fenton treatment of cofibric acid Clofibric acid was oxidized using CF and CF@Fe 3 O 4 cathodes against a Pt anode at constant currents of 50, 100, and 300 mA (Fig. 3 ). In the EF process carried out with CF / Pt electrode pair, H 2 O 2 formed due to O 2 reduction at the cathode forms • OH radicals according to the Fenton reaction with Fe 2+ ions in the solution. Fe 3+ ions formed in the solution are transported to the cathode surface and reduced. When CF@Fe 3 O 4 / Pt electrode pair is used, H 2 O 2 reacts with immobilized ≡Fe II and ≡Fe III on the bifunctional cathode surface and forms • OH radicals, while there is no need for iron ions to be transported for the Fe 3+ / Fe 2+ cycle. Homogeneous • OH radicals in bulk solution are responsible for CFA degradation. The contribution of semi-adsorbed heterogeneous • OH radicals (M( • OH)) formed by the oxidation of water on the Pt anode surface is lower due to its low O 2 evolution overpotential (1.6 V vs. SHE) [ 39 ]. ≡Fe II + H 2 O 2 → Fe III + OH − + • OH (4) ≡Fe III + H 2 O 2 → Fe II + HO 2 • + H + (5) ≡Fe III + e − → Fe II (6) CFA degradation was shown to occur quite rapidly at 50 mA, constant current for both homogenous and heterogeneous EF processes (Fig. 3 a, 3 b). On the other hand, degradation slowed as the applied current level grew. The pseudo-first-order rate constant value for CFA oxidation in the homogenous EF processes decreased from 0.1184 to 0.0469 min −1 as the applied current was increased from 50 mA to 300 mA (Table S1 ). Because the bifunctional cathode enhanced electron transfer and removed the necessity for mass transfer, CFA deterioration happened more quickly in the HEF process. With a rate constant of 0.2266 min −1 at 50 mA, the most efficient degradation was accomplished; at 300 mA, the rate dropped to 0.0695 min −1 . Figures 4 a and 4 b showed the homogeneous and heterogeneous processes that resulted from mineralization. Mineralization rates were 64.5% and 76.2%, respectively, following 3 and 5 h of electrochemical treatment, with CFA 50 mA producing the most efficient degradation in homogeneous EF (Fig. 4 a). Mineralization efficiency decreased by around 50% when the current was increased from 50 mA to 100 mA. Rapidly generated H 2 O 2 and associated • OH radicals were consumed during CFA degradation at the applied high current values because of several parasitic reactions (Eqs. (7–11)) [ 40 ]. Also, previous studies determined that the production of less readily oxidized byproducts, including short-chain carboxylic acids, occurs at high currents [ 41 ]. Consequently, there was a notable reduction in the mineralization and degradation of CFA. 2H 2 O + 2e − → H 2 + 2OH − (7) 2H 2 O → O 2 + 4H + + 4e − (8) ≡Fe 2+ + • OH → ≡Fe 3+ + OH − (9) H 2 O 2 + • OH → H 2 O + HO 2 • (10) HO 2 • + • OH → H 2 O + O 2 (11) The elimination of TOC from the CFA solution was 73.9% and 81.8%, respectively, following 3 and 5 h of treatment with the CF@Fe 3 O 4 cathode at 50 mA. TOC removal efficiency dropped to 54.5% and 69.2%, respectively, at the same time values with a constant current of 100 mA. Mineralization efficiency was found to be relatively low at 300 mA. The mineralization current efficiency (MCE) parameter is used to show the efficiency of the electrical energy used for mineralization. The MCE value was obtained higher in both systems at 50 mA and 3 h due to more effective degradation and mineralization of degradation products. At high current values, the MCE values ​​​​decreased significantly due to the increase in parasitic reactions and the formation of by-products that make mineralization difficult. While the MCE values ​​​​obtained for 3 and 5 h in the HEF process at 50 mA were 29.2 and 19.5%, respectively, it was observed that these values ​​​​were higher compared to homogeneous EF (27.2 and 19.3%) (Table S1 ). BDD anode produces a higher amount of semi-adsorbed • OH radicals on its surface (Eq. (12)) than Pt due to its high O 2 evolution overpotential (2.2 V vs. SHE) [ 42 ]. Although EF is a cathodic process, both cathodic and anodic reactions drive degradation and mineralization in the undivided cell when BDD is utilized as the anode [ 43 ]. CFA degradation and mineralization were investigated at 50, 100 and 300 mA current values ​​using CF@Fe 3 O 4 / BDD electrode pair and the results are shown in Fig. 5 . BDD + H 2 O → BDD( • OH) + H + + e − (12) It is observed that CFA degrades quite quickly with a constant current of 50 mA, with 99% of it, degraded in about 20 min. However, CFA degradation slowed as a result of the current increment. 100% degradation happens in 40 min with a 100 mA current, and 92% degradation is reached after 50 min with a 300 mA current (Fig. 5 a). Heterogeneous BDD( • OH) generation rises with increasing applied current, but it has also been observed to oxidize H 2 O 2 on the BDD anode surface (Eq. (13)) [ 43 ]. H 2 O 2 → O 2 + 2H + + 2e − (13) The initial pH value is one of the factors influencing the procedure. Wastewater often has a pH value that is almost neutral or basic [ 44 ]. Because of this, clofibric acid degradation was carried out at various pH levels while maintaining a constant current of 100 mA. As indicated in Fig. 5 b that the fastest degradation is at pH 3 and the CFA degradation slows down with increasing initial pH. The reaction rates of aromatic weak acids such as clofibric acid with homogeneous • OH radicals can vary considerably depending on the ionization state of the molecule. Clofibric acid has a pK a value of 3.18. For example, in this instance, the CFA aqueous solution ionizes 40% at pH 3 and 99.8% at pH 6. The aromatic ring in the unionized form may be more susceptible to electrophilic attack by • OH because it has more electron density. In the ionized CFA form, the molecule is negatively charged, which can make the electrophilic • OH attack somewhat more difficult due to electrostatic repulsion. The impact of reactive oxygen species (ROS), which are in charge of oxidizing organic pollutants, can differ depending on the process, electrode, and catalyst used. Different radical scavengers were used to determine the ROS effective in CFA degradation by the HEF process (Fig. 5 c). The reaction rate constants of EtOH with • OH and SO 4 •− radicals were determined as 1.2–2.8 × 10 9 M −1 s −1 and 1.6–7.7 × 10 7 M −1 s −1 , respectively. TBA has a lower reaction rate constant (k = 4.0–9.1 × 10 5 M −1 s −1 ) with SO 4 •− radicals than EtOH, and it is regarded as a • OH radical scavenger (k = 3.8–7.6 × 10 8 M −1 s −1 ). Additionally, pBQ is utilized as an inhibitor for the O 2 •− radical due to its rapid reaction (k = 1.1 × 10 9 M −1 s −1 ) with this ROS [ 21 ]. It is produced from Eqs. (4) and (12) that the ROS primarily responsible for CFA degradation are hydroxyl radicals generated by the heterogeneous Fenton reaction and the application of BDD( • OH) anode, respectively. Furthermore, HO 2 • / O 2 •− species produced as a result of the Fenton-like reaction in Eq. (5) are figured out to contribute to the degradation of CFA. Consequently, in the presence of EtOH, TBA, and pBQ, the apparent rate constant of CFA dropped from 0.1020 min −1 to 0.0149, 0.0164, and 0.0310 min −1 , respectively. Also, after five cycles, it was found that the CF@Fe 3 O 4 cathode's reusability in the CFA degradation by HEF process did not significantly alter its performance (Fig. 5 d). Figure 6 a illustrate the effect of applied current on mineralization ​with the CF@Fe 3 O 4 / BDD electrode pair. While there was a minor increase in mineralization at 50 mA current in comparison to the Pt anode results, the majority of the increase occurred at 100 and 300 mA. As the current increases in anodic oxidation, more BDD( • OH) is produced. Additionally, the Fe + 3 /Fe 2+ cycle on the electrode surface is facilitated by the rise in current. While CFA degradation slows down, these two encouraging developments also promote the oxidation of degradation products, which leads to a notable increase in mineralization. The multi-step oxidation route of organic pollutants in the HEF process is the cause of higher mineralization with increasing current but decreased degradation. The increased mineralization could be thought to have happened as a result of easier mass transfer of the breakdown products from the solution to the BDD anode surface. While the homogeneous • OH contribution was high in the first two hours, BDD( • OH) played a dominant role in mineralization through electron transfer in the subsequent periods, according to Olvera-Vargas et al. [ 44 ] calculation of the effect of homogeneous • OH and heterogeneous BDD( • OH) radicals on mineralization in the EF process conducted with BDD anode. In the EF process, oxidation products of small molecular weight carboxylic acids react very slowly with homogeneous • OH and easily undergo mineralization via electron transfer on the BDD surface [ 45 , 46 ]. The difference in mineralization was quite small, even though the CFA solution degraded more quickly at pH 3 than at pH 6 and 8 at 100 mA current. At all pH levels, 85% and higher mineralization was attained after 3 h treatment at 100 mA (Fig. 6 b). In this case, as discussed before, BDD supports the effect of anode on decomposition mineralization. Examining the MCE results in Table S1 , it is evident that the CF@Fe 3 O 4 / BDD electrode pair provides high mineralization with higher energy efficiency. After 3 h treatment, CFA mineralization was above 77% due to the HEF process conducted at 50, 100, and 300 mA. The MCE values for these currents were found to be 32.74%, 18.05%, and 6.18%, respectively. Conclusion This study aimed to immobilize the Fe 3 O 4 NPs catalyst, which plays a major role in electrocatalytic production of • OH radical in the HEF process, on the activated CF surface and to use it independently of pH in organic pollutant oxidation. While 100% degradation of CFA was achieved under mild conditions, high TOC removal was achieved with high mineralization current efficiency with the CF@Fe 3 O 4 / BDD electrode pair. High TOC removals were achieved at different pH values ​​by developing the bifunctional cathode. In addition, the fact that the CF@Fe 3 O 4 cathode has the same efficiency in CFA degradation after 5 reuses is promising in terms of being an environmentally friendly process without adding external reagents. The heterogeneous EF system enabled effective degradation and mineralization of the target pollutant, clofibric acid, under mild conditions with low Fe 3 O 4 loading. Since the Fe ion concentration leaching from the CF@Fe3O4 cathode surface to the solution during use is extremely low compared to the amounts used in the homogeneous EF method, secondary pollution is not caused by this method. The process was efficient, pH-independent, and did not cause secondary pollution. The dominant oxidant was determined to be the hydroxyl radical ( • OH), although superoxide radicals (O 2 •− ) also contributed to the oxidation mechanism. Declarations Acknowledgements This study is supported by Mersin University Scientific Research Projects Coordination Unit. Project Number: 2023-1-TP2-4902 Author contributions Titus Otamayomi Moses: Investigation, Conceptualization, Methodology, Data curation, Writing – original draft. Doğan Çirmi: Conceptualization, Visualization, Methodology, Writing-review & editing. Yalçın Fidan: Methodology. Belgin Gözmen: Methodology, Supervision, Project administration. Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 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1","display":"","copyAsset":false,"role":"figure","size":379094,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e at different magnifications (a-c), and XRD pattern of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e powder (d).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/e527d2d69a10154b1b938072.png"},{"id":94197114,"identity":"6576be6a-c71f-4b22-8464-49b9d1eda2cb","added_by":"auto","created_at":"2025-10-23 13:19:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":112760,"visible":true,"origin":"","legend":"\u003cp\u003eCV curves of (a) bare CF, (b) CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and (c) electrochemical impedance spectra of CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/314ed20eecf4c6a633729d62.png"},{"id":94197115,"identity":"413690a4-88fd-4523-8026-b46a10b7e374","added_by":"auto","created_at":"2025-10-23 13:19:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":206709,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of current on CFA degradation using CF (a), and CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (b). Experimental conditions: [CFA]\u003csub\u003e0\u003c/sub\u003e= 0.23 mM, [Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e] = 50 mM, V = 0.2 L, pH = 3, [Fe\u003csup\u003e2+\u003c/sup\u003e] = 0.1 mM.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/762cfd0ee3df5ca6783d8aa8.png"},{"id":94196837,"identity":"8fe4d395-f765-4737-9a0c-b909404e52b4","added_by":"auto","created_at":"2025-10-23 13:11:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":222348,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of current on CFA mineralization using CF (a), and CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (b). Experimental conditions: [CFA]\u003csub\u003e0\u003c/sub\u003e= 0.23 mM, [Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e] = 50 mM, V = 0.2 L, pH = 3, [Fe\u003csup\u003e2+\u003c/sup\u003e] = 0.1 mM.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/9da28d51bc6e1a996533eee8.png"},{"id":94195932,"identity":"6d9a9331-cfcb-421b-a072-d4a8480fa173","added_by":"auto","created_at":"2025-10-23 13:03:05","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":263173,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of current (a), pH (b), and radical scavengers (c) on CFA mineralization using CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / BDD pair; Recycle tests on CFA degradation at 100 mA (d). Experimental conditions: [CFA]\u003csub\u003e0\u003c/sub\u003e= 0.23 mM, [Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e] = 50 mM, V = 0.2 L.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/a963a63ce8da397c85c734c3.png"},{"id":94195936,"identity":"96c18be8-3dd4-485b-8bfc-8fa807c52073","added_by":"auto","created_at":"2025-10-23 13:03:05","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":339691,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of current (a), and initial pH (b) on CFA mineralization using CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / BDD pair at 100 mA. Experimental conditions: [CFA]\u003csub\u003e0\u003c/sub\u003e= 0.23 mM, [Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e] = 50 mM, V = 0.2 L.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/abc672b9c54bc97c4d5f198a.png"},{"id":99172349,"identity":"5f955c21-ab33-4483-bd01-15b526f11ec1","added_by":"auto","created_at":"2025-12-29 16:08:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2231317,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/c4efa73d-2ff1-4c0e-9c46-d06aeb6df3ae.pdf"},{"id":94195927,"identity":"17cf4291-f54e-4175-b561-fd28947ccc6d","added_by":"auto","created_at":"2025-10-23 13:03:05","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":19678,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-6965557/v1/0c923f68a9097aed5c54b40c.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Heterogeneous electro-Fenton treatment of clofibric acid with an Fe₃O₄-loaded bifunctional carbon felt cathode via different anode types","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAquatic creatures and human health are seriously threatened by the presence of pharmaceutical chemicals and their metabolites in aquatic systems. The dearth of knowledge regarding the durability and ecotoxicity of the majority of these chemicals is concerning. An active metabolite of the common lipid regulator clofibrate is clofibric acid (CFA). Because CFA is a structural isomer of the herbicide mecoprop, it was also the first medication found in an aquatic environment [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Clofibric acid is continuously found in surface and groundwater due to its chemical stability (greater than 21 years) and resistance to conventional biological and physicochemical remediation techniques [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Hence, the designation of CFA as a persistent organic pollutant (POP), necessitating the development of innovative remediation strategies [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eNumerous persistent organic pollutants (POPs) in wastewater are degraded by electrochemical advanced oxidation processes (EAOPs), particularly the electro-Fenton (EF) process, which turns them into less hazardous or biodegradable by-products [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. By combining electrochemical and Fenton chemistry to produce hydroxyl radicals in situ through the cathodic reduction of oxygen to hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) in Eq.\u0026nbsp;(1), the EF process is a noteworthy breakthrough. According to Fenton's reaction (Eq.\u0026nbsp;(2)), ferrous ions subsequently activate H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Eq.\u0026nbsp;(3) describes the electrochemical conversion of Fe\u003csup\u003e3+\u003c/sup\u003e ions to Fe\u003csup\u003e2+\u003c/sup\u003e, formed in the Fenton reaction [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The process is characterized as an electrocatalytic system, as Fe\u003csup\u003e2+\u003c/sup\u003e is being regenerated in the medium [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. As a strong oxidizing agent (E\u003csup\u003eo\u003c/sup\u003e (\u003csup\u003e\u0026bull;\u003c/sup\u003eOH/H\u003csub\u003e2\u003c/sub\u003eO)\u0026thinsp;=\u0026thinsp;2.80 V vs. SHE), the generated \u003csup\u003e\u0026bull;\u003c/sup\u003eOH reacts non-selectively with organic molecules, causing them to mineralize [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2H\u003csup\u003e+\u003c/sup\u003e + 2e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (1)\u003c/p\u003e\u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026rarr; Fe\u003csup\u003e3+\u003c/sup\u003e + OH\u003csup\u003e\u0026ndash;\u003c/sup\u003e + \u003csup\u003e\u0026bull;\u003c/sup\u003eOH (2)\u003c/p\u003e\u003cp\u003eFe\u003csup\u003e3+\u003c/sup\u003e + e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; Fe\u003csup\u003e2+\u003c/sup\u003e (3)\u003c/p\u003e\u003cp\u003eCritical parameters in the EF process are revealed as electrode material, current density, pH, distance between electrodes and O\u003csub\u003e2\u003c/sub\u003e/air supply rate [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Since its inception in the mid-20th century, the EF process has undergone continuous modification in response to the growing complexity and variety of pollutants present in industrial effluents. These refinements underscore how crucial it is within the broader context of advanced oxidation techniques and environmental sustainability [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHeterogeneous EF processes have been studied in diverse systems, incorporating a wide range of materials, including natural minerals, different metal oxides, zero-valent metals, composite structures with reduced graphene oxide (rGO), graphene oxide (GO), metal organic frameworks (MOFs), etc., because Fe(II) ions cannot be recovered after the process [\u003cspan additionalcitationids=\"CR19 CR20\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Recent years have seen the development of electrodes that enable both H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e generation and activation in heterogeneous electro-Fenton (HEF) applications [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Deng et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] summarized different strategies that can enhance electron transfer control and mass transport control to improve Fe\u003csup\u003e3+\u003c/sup\u003e/Fe\u003csup\u003e2+\u003c/sup\u003e conversion in the EF process. The formation of both carbon and metal-based active sites is important to ensure the Fe\u003csup\u003e3+\u003c/sup\u003e / Fe\u003csup\u003e2+\u003c/sup\u003e cycle through electron transfer. Recent developments in electrodes for HEF processes have brought attention to the use of a variety of catalysts that increase process efficiency by reducing sludge generation, increasing catalyst reusability, and expanding operating pH ranges (e.g., pH 3\u0026ndash;8). For example, immobilization of layered double hydroxides (LDHs) such as Fe\u003csup\u003eII\u003c/sup\u003eFe\u003csup\u003eIII\u003c/sup\u003e, CuFeV have become increasingly popular as cathodes because of their extensive surface areas, sites of activity that generate catalytic effects, and their chemical stability [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Furthermore, researchers reported that the active sites offered by the CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] and MoS\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] loaded on carbon felt or carbon fiber paper enhance the oxidation of different contaminants while promoting the Fe\u003csup\u003e3+\u003c/sup\u003e/Fe\u003csup\u003e2+\u003c/sup\u003e transformation.\u003c/p\u003e\u003cp\u003eMagnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) nanoparticles have low toxicity, easy synthesis conditions and most importantly, can be easily separated from solution due to their magnetic properties, making them a good catalyst for HEF. Electron mobility in the spinel structure of magnetite, which consists of Fe\u003csup\u003eII\u003c/sup\u003e and Fe\u003csup\u003eIII\u003c/sup\u003e, is quite high [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In order to prevent agglomeration of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e structure [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], effective mineralization of organic pollutants in a wider pH range was achieved in HEF process by using GO, rGO or multiwalled carbon nanotubes (MWCN) bases [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. However, mass transfer is of great importance in enhancing the interaction of catalysts dispersed in solution with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e formed on the cathode surface. Camcıoğlu et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] reported effective mineralization compared to the homogeneous EF process by using rGO / Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CB@CF electrode in the oxidation of busulfan. According to this study, carbon compounds with high conductivity made it easier to activate H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and assist the Fe\u003csup\u003e3+\u003c/sup\u003e/Fe\u003csup\u003e2+\u003c/sup\u003e cycle. Chen et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] performed the efficient mineralization of ceftriaxone sodium using Fe\u003csup\u003e0\u003c/sup\u003e-Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/CeO\u003csub\u003e2\u003c/sub\u003e/C composite cathode. the CeO\u003csub\u003e2\u003c/sub\u003e structure within the electrode framework accelerated electron transfer at the catalyst interface due to the Ce\u003csup\u003e4+\u003c/sup\u003e/Ce\u003csup\u003e3+\u003c/sup\u003e redox cycle and facilitated the production of hydroxyl radicals due to the iron/cerium synergistic effect.\u003c/p\u003e\u003cp\u003eIn this study, 1) magnetite (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) nanoparticles were loaded onto the activated carbon felt surface by solvothermal method. 2) CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode characterization was carried out using analytical and electroanalytical techniques. 3) CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode was tested against Pt and BDD anode in the oxidation of low biodegradable clofibric acid in the HEF process. 4) Determination of reactive oxygen species responsible for CFA oxidation and the effect of pH on the HEF process were revealed. In summary, this investigation seeks to thoroughly explore the use of HEF process in the degradation of CFA, drawing on both conventional and innovative research methodologies.\u003c/p\u003e"},{"header":"Experimental sections","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eMaterials\u003c/h2\u003e\u003cp\u003eExperimental details are provided in the supplementary materials document including the chemicals used and the properties of the electrodes (Text S1.1), the preparation of CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode and characterization methods (Text S1.2, Text S1.3), homogenous and heterogonous electro-Fenton procedures (Text S1.4), formulas used to determine CFA degradation / mineralization, and characterization methods and analytical tools (Text S1. 5).\u003c/p\u003e\u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003eCharacterization of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode\u003c/h2\u003e\u003cp\u003eSEM images of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles scattered on the carbon felt surface were depicted in different magnification rates at Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-c. Magnetite NPs show a very small distribution in the range of 7\u0026ndash;17 nm, but clustered as a result of agglomeration. The crystal structure of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs in powder form was examined by XRD analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). The diffraction peaks observed at 18.12\u0026deg; (111), 30.07\u0026deg; (220), 35.43\u0026deg; (311), 43.10\u0026deg; (400), 53.44\u0026deg; (422), 57.03\u0026deg; (511), and 62.65\u0026deg; (440) correspond to the standard cubic spinel group (PDF 19\u0026ndash;0629) [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Crystallite size (D) was determined as 15.3 nm. This is a value compatible with the size of the clusters observed in the SEM images.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eElectrochemical performances of the cathode materials\u003c/h3\u003e\n\u003cp\u003eTo investigate the oxygen reduction reaction (ORR) performance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted for bare carbon felt (CF) and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-coated carbon felt (CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) electrodes 0.1 M Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte under N\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e-saturated conditions. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea presents the CV curves of the bare CF electrode. Under both N\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e atmospheres, the electrode predominantly exhibited double-layer capacitive behavior, and no distinct redox peaks were observed. Only a slight increase in current density was recorded under O₂ saturation, indicating that the bare CF possesses very limited electrocatalytic activity toward ORR.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb displays the CV profiles of the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode. In the N\u003csub\u003e2\u003c/sub\u003e-saturated environment, the redox peaks observed in the CV curves confirm the intrinsic electrochemical activity of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e coating. Under O\u003csub\u003e2\u003c/sub\u003e-saturated conditions, a significant increase in current density compared to the N₂ environment was observed. A sharp cathodic peak appearing around \u0026minus;\u0026thinsp;0.5 V (vs. Ag/AgCl) indicates active ORR kinetics on the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e -coated surface. These findings reveal that the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e coating not only facilitates efficient electron transfer at the electrode\u0026ndash;electrolyte interface but also enhances ORR activity [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Furthermore, the increase in cathodic current density under the oxygen atmosphere suggests a potential pathway for the two-electron reduction of O\u003csub\u003e2\u003c/sub\u003e to form H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], indicating that the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode is a promising catalytic material for EF applications.\u003c/p\u003e\u003cp\u003eElectrochemical impedance spectroscopy (EIS) was employed to further investigate the interfacial charge transfer characteristics of the electrodes. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec shows the Nyquist plots of the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode under N\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e-saturated conditions. Under a nitrogen atmosphere, the electrode exhibited a large semicircle, indicative of high charge transfer resistance (Rct) and sluggish reaction kinetics. In contrast, under oxygen saturation, the semicircle became significantly smaller, indicating a substantial reduction in Rct and enhanced interfacial charge transfer efficiency [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. The pronounced differences between the N\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e environments confirm that the presence of oxygen significantly improves the electrochemical performance of the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode.\u003c/p\u003e\n\u003ch3\u003eHomogenous and heterogeneous electro-Fenton treatment of cofibric acid\u003c/h3\u003e\n\u003cp\u003eClofibric acid was oxidized using CF and CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathodes against a Pt anode at constant currents of 50, 100, and 300 mA (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In the EF process carried out with CF / Pt electrode pair, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e formed due to O\u003csub\u003e2\u003c/sub\u003e reduction at the cathode forms \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals according to the Fenton reaction with Fe\u003csup\u003e2+\u003c/sup\u003e ions in the solution. Fe\u003csup\u003e3+\u003c/sup\u003e ions formed in the solution are transported to the cathode surface and reduced. When CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / Pt electrode pair is used, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e reacts with immobilized \u0026equiv;Fe\u003csup\u003eII\u003c/sup\u003e and \u0026equiv;Fe\u003csup\u003eIII\u003c/sup\u003e on the bifunctional cathode surface and forms \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals, while there is no need for iron ions to be transported for the Fe\u003csup\u003e3+\u003c/sup\u003e / Fe\u003csup\u003e2+\u003c/sup\u003e cycle. Homogeneous \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals in bulk solution are responsible for CFA degradation. The contribution of semi-adsorbed heterogeneous \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals (M(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH)) formed by the oxidation of water on the Pt anode surface is lower due to its low O\u003csub\u003e2\u003c/sub\u003e evolution overpotential (1.6 V vs. SHE) [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u0026equiv;Fe\u003csup\u003eII\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026rarr; Fe\u003csup\u003eIII\u003c/sup\u003e + OH\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026thinsp;+\u0026thinsp;\u003csup\u003e\u0026bull;\u003c/sup\u003eOH (4)\u003c/p\u003e\u003cp\u003e\u0026equiv;Fe\u003csup\u003eIII\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026rarr; Fe\u003csup\u003eII\u003c/sup\u003e + HO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u003c/sup\u003e\u0026thinsp;+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e (5)\u003c/p\u003e\u003cp\u003e\u0026equiv;Fe\u003csup\u003eIII\u003c/sup\u003e + e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; Fe\u003csup\u003eII\u003c/sup\u003e (6)\u003c/p\u003e\u003cp\u003eCFA degradation was shown to occur quite rapidly at 50 mA, constant current for both homogenous and heterogeneous EF processes (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). On the other hand, degradation slowed as the applied current level grew. The pseudo-first-order rate constant value for CFA oxidation in the homogenous EF processes decreased from 0.1184 to 0.0469 min\u003csup\u003e\u0026minus;1\u003c/sup\u003e as the applied current was increased from 50 mA to 300 mA (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Because the bifunctional cathode enhanced electron transfer and removed the necessity for mass transfer, CFA deterioration happened more quickly in the HEF process. With a rate constant of 0.2266 min\u003csup\u003e\u0026minus;1\u003c/sup\u003e at 50 mA, the most efficient degradation was accomplished; at 300 mA, the rate dropped to 0.0695 min\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb showed the homogeneous and heterogeneous processes that resulted from mineralization. Mineralization rates were 64.5% and 76.2%, respectively, following 3 and 5 h of electrochemical treatment, with CFA 50 mA producing the most efficient degradation in homogeneous EF (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Mineralization efficiency decreased by around 50% when the current was increased from 50 mA to 100 mA.\u003c/p\u003e\u003cp\u003eRapidly generated H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and associated \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals were consumed during CFA degradation at the applied high current values because of several parasitic reactions (Eqs.\u0026nbsp;(7\u0026ndash;11)) [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Also, previous studies determined that the production of less readily oxidized byproducts, including short-chain carboxylic acids, occurs at high currents [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Consequently, there was a notable reduction in the mineralization and degradation of CFA.\u003c/p\u003e\u003cp\u003e2H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;2e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (7)\u003c/p\u003e\u003cp\u003e2H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; O\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;4H\u003csup\u003e+\u003c/sup\u003e + 4e\u003csup\u003e\u0026minus;\u003c/sup\u003e (8)\u003c/p\u003e\u003cp\u003e\u0026equiv;Fe\u003csup\u003e2+\u003c/sup\u003e + \u003csup\u003e\u0026bull;\u003c/sup\u003eOH \u0026rarr; \u0026equiv;Fe\u003csup\u003e3+\u003c/sup\u003e + OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (9)\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;\u003csup\u003e\u0026bull;\u003c/sup\u003eOH \u0026rarr; H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;HO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u003c/sup\u003e (10)\u003c/h2\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003eHO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u003c/sup\u003e\u0026thinsp;+\u0026thinsp;\u003csup\u003e\u0026bull;\u003c/sup\u003eOH \u0026rarr; H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;O\u003csub\u003e2\u003c/sub\u003e (11)\u003c/h2\u003e\u003cp\u003eThe elimination of TOC from the CFA solution was 73.9% and 81.8%, respectively, following 3 and 5 h of treatment with the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode at 50 mA. TOC removal efficiency dropped to 54.5% and 69.2%, respectively, at the same time values with a constant current of 100 mA. Mineralization efficiency was found to be relatively low at 300 mA.\u003c/p\u003e\u003cp\u003eThe mineralization current efficiency (MCE) parameter is used to show the efficiency of the electrical energy used for mineralization. The MCE value was obtained higher in both systems at 50 mA and 3 h due to more effective degradation and mineralization of degradation products. At high current values, the MCE values ​​​​decreased significantly due to the increase in parasitic reactions and the formation of by-products that make mineralization difficult. While the MCE values ​​​​obtained for 3 and 5 h in the HEF process at 50 mA were 29.2 and 19.5%, respectively, it was observed that these values ​​​​were higher compared to homogeneous EF (27.2 and 19.3%) (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eBDD anode produces a higher amount of semi-adsorbed \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals on its surface (Eq.\u0026nbsp;(12)) than Pt due to its high O\u003csub\u003e2\u003c/sub\u003e evolution overpotential (2.2 V vs. SHE) [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Although EF is a cathodic process, both cathodic and anodic reactions drive degradation and mineralization in the undivided cell when BDD is utilized as the anode [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. CFA degradation and mineralization were investigated at 50, 100 and 300 mA current values ​​using CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / BDD electrode pair and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eBDD\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; BDD(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH)\u0026thinsp;+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e + e\u003csup\u003e\u0026minus;\u003c/sup\u003e (12)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIt is observed that CFA degrades quite quickly with a constant current of 50 mA, with 99% of it, degraded in about 20 min. However, CFA degradation slowed as a result of the current increment. 100% degradation happens in 40 min with a 100 mA current, and 92% degradation is reached after 50 min with a 300 mA current (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Heterogeneous BDD(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH) generation rises with increasing applied current, but it has also been observed to oxidize H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e on the BDD anode surface (Eq.\u0026nbsp;(13)) [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u0026rarr; O\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2H\u003csup\u003e+\u003c/sup\u003e + 2e\u003csup\u003e\u0026minus;\u003c/sup\u003e (13)\u003c/p\u003e\u003cp\u003eThe initial pH value is one of the factors influencing the procedure. Wastewater often has a pH value that is almost neutral or basic [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Because of this, clofibric acid degradation was carried out at various pH levels while maintaining a constant current of 100 mA. As indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb that the fastest degradation is at pH 3 and the CFA degradation slows down with increasing initial pH. The reaction rates of aromatic weak acids such as clofibric acid with homogeneous \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radicals can vary considerably depending on the ionization state of the molecule. Clofibric acid has a pK\u003csub\u003ea\u003c/sub\u003e value of 3.18. For example, in this instance, the CFA aqueous solution ionizes 40% at pH 3 and 99.8% at pH 6. The aromatic ring in the unionized form may be more susceptible to electrophilic attack by \u003csup\u003e\u0026bull;\u003c/sup\u003eOH because it has more electron density. In the ionized CFA form, the molecule is negatively charged, which can make the electrophilic \u003csup\u003e\u0026bull;\u003c/sup\u003eOH attack somewhat more difficult due to electrostatic repulsion.\u003c/p\u003e\u003cp\u003eThe impact of reactive oxygen species (ROS), which are in charge of oxidizing organic pollutants, can differ depending on the process, electrode, and catalyst used. Different radical scavengers were used to determine the ROS effective in CFA degradation by the HEF process (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). The reaction rate constants of EtOH with \u003csup\u003e\u0026bull;\u003c/sup\u003eOH and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e radicals were determined as 1.2\u0026ndash;2.8 \u0026times; 10\u003csup\u003e9\u003c/sup\u003e M\u003csup\u003e\u0026minus;1\u003c/sup\u003es\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 1.6\u0026ndash;7.7 \u0026times; 10\u003csup\u003e7\u003c/sup\u003e M\u003csup\u003e\u0026minus;1\u003c/sup\u003es\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. TBA has a lower reaction rate constant (k\u0026thinsp;=\u0026thinsp;4.0\u0026ndash;9.1 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e M\u003csup\u003e\u0026minus;1\u003c/sup\u003es\u003csup\u003e\u0026minus;1\u003c/sup\u003e) with SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e radicals than EtOH, and it is regarded as a \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radical scavenger (k\u0026thinsp;=\u0026thinsp;3.8\u0026ndash;7.6 \u0026times; 10\u003csup\u003e8\u003c/sup\u003e M\u003csup\u003e\u0026minus;1\u003c/sup\u003es\u003csup\u003e\u0026minus;1\u003c/sup\u003e). Additionally, pBQ is utilized as an inhibitor for the O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e radical due to its rapid reaction (k\u0026thinsp;=\u0026thinsp;1.1 \u0026times; 10\u003csup\u003e9\u003c/sup\u003e M\u003csup\u003e\u0026minus;1\u003c/sup\u003es\u003csup\u003e\u0026minus;1\u003c/sup\u003e) with this ROS [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. It is produced from Eqs.\u0026nbsp;(4) and (12) that the ROS primarily responsible for CFA degradation are hydroxyl radicals generated by the heterogeneous Fenton reaction and the application of BDD(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH) anode, respectively. Furthermore, HO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u003c/sup\u003e / O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e species produced as a result of the Fenton-like reaction in Eq.\u0026nbsp;(5) are figured out to contribute to the degradation of CFA. Consequently, in the presence of EtOH, TBA, and pBQ, the apparent rate constant of CFA dropped from 0.1020 min\u003csup\u003e\u0026minus;1\u003c/sup\u003e to 0.0149, 0.0164, and 0.0310 min\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. Also, after five cycles, it was found that the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode's reusability in the CFA degradation by HEF process did not significantly alter its performance (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed).\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea illustrate the effect of applied current on mineralization ​with the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / BDD electrode pair. While there was a minor increase in mineralization at 50 mA current in comparison to the Pt anode results, the majority of the increase occurred at 100 and 300 mA. As the current increases in anodic oxidation, more BDD(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH) is produced. Additionally, the Fe\u003csup\u003e+\u0026thinsp;3\u003c/sup\u003e/Fe\u003csup\u003e2+\u003c/sup\u003e cycle on the electrode surface is facilitated by the rise in current. While CFA degradation slows down, these two encouraging developments also promote the oxidation of degradation products, which leads to a notable increase in mineralization. The multi-step oxidation route of organic pollutants in the HEF process is the cause of higher mineralization with increasing current but decreased degradation. The increased mineralization could be thought to have happened as a result of easier mass transfer of the breakdown products from the solution to the BDD anode surface. While the homogeneous \u003csup\u003e\u0026bull;\u003c/sup\u003eOH contribution was high in the first two hours, BDD(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH) played a dominant role in mineralization through electron transfer in the subsequent periods, according to Olvera-Vargas et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] calculation of the effect of homogeneous \u003csup\u003e\u0026bull;\u003c/sup\u003eOH and heterogeneous BDD(\u003csup\u003e\u0026bull;\u003c/sup\u003eOH) radicals on mineralization in the EF process conducted with BDD anode. In the EF process, oxidation products of small molecular weight carboxylic acids react very slowly with homogeneous \u003csup\u003e\u0026bull;\u003c/sup\u003eOH and easily undergo mineralization via electron transfer on the BDD surface [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe difference in mineralization was quite small, even though the CFA solution degraded more quickly at pH 3 than at pH 6 and 8 at 100 mA current. At all pH levels, 85% and higher mineralization was attained after 3 h treatment at 100 mA (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). In this case, as discussed before, BDD supports the effect of anode on decomposition mineralization.\u003c/p\u003e\u003cp\u003eExamining the MCE results in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e, it is evident that the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / BDD electrode pair provides high mineralization with higher energy efficiency. After 3 h treatment, CFA mineralization was above 77% due to the HEF process conducted at 50, 100, and 300 mA. The MCE values for these currents were found to be 32.74%, 18.05%, and 6.18%, respectively.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study aimed to immobilize the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs catalyst, which plays a major role in electrocatalytic production of \u003csup\u003e\u0026bull;\u003c/sup\u003eOH radical in the HEF process, on the activated CF surface and to use it independently of pH in organic pollutant oxidation. While 100% degradation of CFA was achieved under mild conditions, high TOC removal was achieved with high mineralization current efficiency with the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / BDD electrode pair. High TOC removals were achieved at different pH values ​​by developing the bifunctional cathode. In addition, the fact that the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode has the same efficiency in CFA degradation after 5 reuses is promising in terms of being an environmentally friendly process without adding external reagents. The heterogeneous EF system enabled effective degradation and mineralization of the target pollutant, clofibric acid, under mild conditions with low Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e loading. Since the Fe ion concentration leaching from the CF@Fe3O4 cathode surface to the solution during use is extremely low compared to the amounts used in the homogeneous EF method, secondary pollution is not caused by this method. The process was efficient, pH-independent, and did not cause secondary pollution. The dominant oxidant was determined to be the hydroxyl radical (\u003csup\u003e\u0026bull;\u003c/sup\u003eOH), although superoxide radicals (O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u0026minus;\u003c/sup\u003e) also contributed to the oxidation mechanism.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study is supported by Mersin University Scientific Research Projects Coordination Unit. Project Number: 2023-1-TP2-4902\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTitus Otamayomi Moses: Investigation, Conceptualization, Methodology, Data curation, Writing – original draft. Doğan Çirmi: Conceptualization, Visualization, Methodology, Writing-review \u0026amp; editing. Yalçın Fidan: Methodology. Belgin Gözmen: Methodology, Supervision, Project administration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis manuscript has not been previously published, is not currently submited for review to any other journal, and will not be submited elsewhere before a decision is made by this journal. All images used in the Table of Contents Graphic are original and contain no copyright-protected material. All co-authors are aware of and have approved the submission.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eK\u0026uuml;mmerer, K., Pharmaceuticals in the Environment: Sources, Fate, Effects and Risks, ed. by K. K\u0026uuml;mmerer (Springer, New York, 2008) pp. 3-21. https://doi.org/10.1007/978-3-540-74664-5\u003c/li\u003e\n\u003cli\u003ePetrovic M, Eljarrat E, Lopez de Alda MJ, Barcel\u0026oacute; D (2004) Endocrine disrupting compounds and other emerging contaminants in the environment: A survey on new monitoring strategies and occurrence data. Anal Bioanal Chem, 378:549\u0026ndash;562. https://doi.org/10.1007/s00216-003-2184-7\u003c/li\u003e\n\u003cli\u003eEmblidge JP, DeLorenzo ME (2006) Preliminary risk assessment of the lipid-regulating pharmaceutical clofibric acid, for three estuarine species. 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Chem Eng J 183:124\u0026ndash;134, https://doi.org/10.1016/j.cej.2011.12.042\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-applied-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jach","sideBox":"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)","snPcode":"10800","submissionUrl":"https://submission.nature.com/new-submission/10800/3","title":"Journal of Applied Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"CF@Fe3O4, Heterogeneous electro-Fenton, Clofibric acid, BDD anode, Carbon felt, EAOPs","lastPublishedDoi":"10.21203/rs.3.rs-6965557/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6965557/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePharmaceutical pollutants like clofibric acid (CFA) pose significant threats to aquatic ecosystems and human health. In this study, a bifunctional cathode was synthesized by loading Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles onto a carbon felt cathode using solvothermal method. The characterizations of CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were performed using FESEM, CV and EIS. The developed CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode was then evaluated in heterogeneous electro-Fenton (HEF) application in clofibric acid (CFA) oxidation at different current and pH values using Pt and BDD anodes. The CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode accelerated electron transfer, minimizing mass transport limitations, enhancing CFA degradation. The CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e / Pt electrode pair exhibited 75% mineralization following 3 h of HEF treatment, whereas the BDD anode exhibited 78% mineralization at 50 mA. Both values outperformed the homogenous EF process with CF in terms of effectiveness. Radical scavenging experiments proved \u003csup\u003e•\u003c/sup\u003eOH as the dominant reactive species, with contributions from O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e•-\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e•-\u003c/sup\u003e. Mineralization remained high (\u0026gt;85%) across pH 3–8, due to enhanced oxidation of intermediate products via BDD(\u003csup\u003e•\u003c/sup\u003eOH) and electron transfer mechanisms, while degradation slowed at higher currents. The CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/BDD combination consistently outperformed Pt in terms of both degradation kinetics and energy efficiency. Here we show that even after 5 reuses, the CF@Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode/BDD anode pair can effectively remove persistent organic pollutants without pH limitation and with an environmentally friendly process without any significant performance loss.\u003c/p\u003e","manuscriptTitle":"Heterogeneous electro-Fenton treatment of clofibric acid with an Fe₃O₄-loaded bifunctional carbon felt cathode via different anode types","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-23 13:03:00","doi":"10.21203/rs.3.rs-6965557/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-01T17:31:57+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-27T04:22:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"46571033771426445279985820147261849675","date":"2025-10-22T07:22:45+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-07T06:16:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"239368736172836109978071952691262520842","date":"2025-08-18T23:17:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"277473152829927340848227200183777492682","date":"2025-08-18T12:26:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"175044688367108528631647802374842994286","date":"2025-08-14T14:20:19+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-14T05:19:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-26T03:26:45+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-25T13:58:12+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Electrochemistry","date":"2025-06-24T11:55:28+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-applied-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jach","sideBox":"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)","snPcode":"10800","submissionUrl":"https://submission.nature.com/new-submission/10800/3","title":"Journal of Applied Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"9239e33b-d71c-42ca-a247-0139da73cd54","owner":[],"postedDate":"October 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-29T16:01:56+00:00","versionOfRecord":{"articleIdentity":"rs-6965557","link":"https://doi.org/10.1007/s10800-025-02400-3","journal":{"identity":"journal-of-applied-electrochemistry","isVorOnly":false,"title":"Journal of Applied Electrochemistry"},"publishedOn":"2025-12-26 15:58:00","publishedOnDateReadable":"December 26th, 2025"},"versionCreatedAt":"2025-10-23 13:03:00","video":"","vorDoi":"10.1007/s10800-025-02400-3","vorDoiUrl":"https://doi.org/10.1007/s10800-025-02400-3","workflowStages":[]},"version":"v1","identity":"rs-6965557","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6965557","identity":"rs-6965557","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}