Diclofenac degradation in water by FeCeOx catalyzed H2O2: Influencing factors, mechanism and pathways

Non-radical oxidation driven by iron-based materials without energy assistance in wastewater treatment

Chemical oxidation is extensively utilized to mitigate the impact of organic pollutants in wastewater. The non-radical oxidation driven by iron-based materials is noted for its environmental friendliness and resistance to wastewater matrix, and it is a promising approach for practical wastewater treatment. However, the complexity of heterogeneous systems and the diversity of evolutionary pathways make the mechanisms of non-radical oxidation driven by iron-based materials elusive. This work provides a systematic review of various non-radical oxidation systems driven by iron-based materials, including singlet oxygen (1O2), reactive iron species (RFeS), and interfacial electron transfer. The unique mechanisms by which iron-based materials activate different oxidants (ozone, hydrogen peroxide, persulfate, periodate, and peracetic acid) to produce non-radical oxidation are described. The roles of active sites and the unique structures of iron-based materials in facilitating non-radical oxidation are discussed. Commonly employed identification methods in wastewater treatment are compared, such as quenching, chemical probes, spectroscopy, mass spectrometry, and electrochemical testing. According to the process of iron-based materials driving non-radical oxidation to remove organic pollutants, the driving factors at different stages are summarized. Finally, challenges and countermeasures are proposed in terms of mechanism exploration, detection methods and practical applications of non-radical oxidation driven by iron-based materials. This work provides valuable insights for understanding and developing non-radical oxidation systems.

Nanoscale zero-valent iron/biochar composites containing persistent free radicals (PFRs) for degradation of p-nitrophenol

Despite the vital roles of Fe0/biochar composites in the Fenton-like systems for eliminating pollutants that have been recognized, the contributions of persistent free radicals (PFRs) of carbon-based materials are typically overlooked. In this study, the high-PFR-containing biochar nanoiron composites were prepared (nZVI/500), and the in situ generation of hydroxyl radicals (·OH) and degradation of p-nitrophenol (PNP) were investigated. The results showed that nZVI/500 could effectively remove PNP in solution within the pH range of 3-8. Quantitative experiments of ·OH presented that, compared with low PFRs-containing composites, nZVI/500 could generate 64.6 µM ·OH in 60 min without any extra energy consumption. Mechanistic studies revealed that (1) both PFRs and Fe0 are able to utilize dissolved oxygen to generate H2O2 in situ; (2) PFRs can promote the cycling of Fe3+/Fe2+ in the system due to their strong electron exchange ability; and (3) PFRs directly transfer electrons to H2O2; therefore, the presence of PFRs accelerates the generation of ·OH in the system and facilitates the removal of PNP. This study provides an important theoretical basis and technical reference for expanding the application of PFR-rich carbon-based materials to remove environmental pollutants.

Singlet oxygen: Properties, generation, detection, and environmental applications

Singlet oxygen (1O2) is molecular oxygen in the excited state with high energy and electrophilic properties. It is widely found in nature, and its important role is gradually extending from chemical syntheses and medical techniques to environmental remediation. However, there exist ambiguities and controversies regarding detection methods, generation pathways, and reaction mechanisms which have hindered the understanding and applications of 1O2. For example, the inaccurate detection of 1O2 has led to an overestimation of its role in pollutant degradation. The difficulty in detecting multiple intermediate species obscures the mechanism of 1O2 production. The applications of 1O2 in environmental remediation have also not been comprehensively commented on. To fill these knowledge gaps, this paper systematically discussed the properties and generation of 1O2, reviewed the state-of-the-art detection methods for 1O2 and long-standing controversies in the catalytic systems. Future opportunities and challenges were also discussed regarding the applications of 1O2 in the degradation of pollutants dissolved in water and volatilized in the atmosphere, the disinfection of drinking water, the gas/solid sterilization, and the self-cleaning of filter membranes. This review is expected to provide a better understanding of 1O2-based advanced oxidation processes and practical applications in the environmental protection of 1O2.

Impacts of Organic Emerging Contaminants (Erythromycin, Ibuprofen, and Diclofenac) on the Performance of a Membrane Bioreactor Treating Urban Wastewater: A Heterotrophic Kinetic Investigation

The occurrence of emerging organic contaminants, such as pharmaceuticals, is a growing global concern. In this research, for a membrane bioreactor (MBR) laboratory plant operating at a hydraulic retention time (HRT) of 24 h, fed with real urban wastewater, the heterotrophic biomass behaviour was analysed for two concentrations of erythromycin, ibuprofen, and diclofenac. The concentrations studied for the first phase were erythromycin 0.576 mg L-1, ibuprofen 0.056 mg L-1, and diclofenac 0.948 mg L-1. For Phase 2, the concentrations were increased to erythromycin 1.440 mg L-1, ibuprofen 0.140 mg L-1, and diclofenac 2.370 mg L-1. Heterotrophic biomass was affected and inhibited by the presence of pharmaceutical compounds in both phases. The system response to low concentrations of pharmaceutical compounds occurred in the initial phase of plant doping. Under these operating conditions, there was a gradual decrease in the concentration of mixed liquor suspended solids and the removal of chemical oxygen demand of the system, as it was not able to absorb the effect produced by the pharmaceutical compounds added in both phases.

Bifunctional catalytic degradation of diclofenac over Cu-Pd co-modified sponge iron-based trimetal: Parameter optimization

Currently, the pharmaceutical and personal care products (PPCPs) have posed great challenge to advanced oxidation techniques (AOTs). In this study, we decorated sponge iron (s-Fe⁰) with Cu and Pd (s-Fe⁰-Cu-Pd) and further optimized the synthesis parameters with a response surface method (RSM) to rapidly degrade diclofenac sodium (DCF). Under the RSM-optimized conditions of Fe: Cu: Pd = 100: 4.23: 0.10, initial solution pH of 5.13, and input dosage of 38.8 g/L, 99% removal of DCF could be obtained after 60 min of reaction. Moreover, the morphological structure of trimetal was characterized with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS). Electron spin resonance (ESR) signals have also been applied to capture reactive hydrogen atoms (H*), superoxygen anions, hydroxyl radicals, and single state oxygen (¹O₂). Furthermore, the variations of DCF and its selective degradation products over a series of s-Fe⁰-based bi(tri)metals have been compared. Additionally, the degradation mechanism of DCF has also been explored. To our best knowledge, this is the first report revealing the selective dechlorination of DCF with low toxicity over Pd-Cu co-doped s-Fe⁰ trimetal.

The efficient degradation of diclofenac by ferrate and peroxymonosulfate: performances, mechanisms, and toxicity assessment

In this study, the degradation efficiency and reaction mechanisms of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, by the combination of ferrate (Fe(VI) and peroxymonosulfate (PMS) (Fe(VI)/PMS) were systematically investigated. The higher degradation efficiency of DCF in Fe(VI)/PMS system can be obtained than that in alone persulfate (PS), Fe(VI), PMS, or the Fe(VI)/PS process at pH 6.0. DCF was efficiently removed in Fe(VI)/PMS process within a wide range of pH values from 4.0 to 8.0, with higher degradation efficiency in acidic conditions. The increasing reaction temperature (10 to 30 ℃), Fe(VI) dose (6.25 to 100 µM), or PMS concentration (50 to 1000 µM) significantly enhanced the DCF degradation. The existences of HCO₃¯, Cl¯, and humic acid (HA) obviously inhibited the DCF removal. Electron paramagnetic resonance (EPR), free radical quenching, and probing experiments confirmed the existence of sulfate radicals (SO₄^•¯), hydroxyl radicals (^•OH), and Fe(V)/ Fe(IV), which are responsible for DCF degradation in Fe(VI)/PMS system. The variations of TOC removal ratio reveal that the adsorption of organics with ferric particles, formed in the reduction of Fe(VI), also were functioned in the removal process. Sixteen DCF transformation byproducts were identified by UPLC-QTOF/MS, and the toxicity variation was evaluated. Consequently, eight reaction pathways for DCF degradation were proposed. This study provides theoretical basis for the utilization of Fe(VI)/PMS process.

CeO2 modified carbon nanotube electrified membrane for the removal of antibiotics

Electrified carbon nanotube membranes (ECM) are used as electroactive porous materials for the degradation of micropollutants. It integrated design of both electrochemical processes and filtration functions. In this study, CeO₂ modified carbon nanotube electrified membrane (CeO₂@CNT membrane) was prepared and activate NaClO towards degradation of antibiotics. As CeO₂ with face-centered cubic (Fcc) fluorite structure was loaded onto the CNT sidewalls, the CeO₂@CNT membrane showed a higher over potential and a smaller equivalent polarization resistance compared to ECM. More reactive oxygen species (ROS) and reactive chlorine species (RCS) were generated by CeO₂@CNT membrane due to faster electron transfer at the solid-liquid interface. Thus, the removal efficiencies of DCF, SMX, CIP, TC and CBZ were more than 91.2%, 91.3%, 94.4%, 99.3% and 89.4% by the CeO₂@CNT membrane with NaClO, respetively. And the apparent reaction rate constant (k) of the CeO₂@CNT membrane was 2.9 times of that of ECM. The selective capping experiments and density functional theory (DFT) calculation showed that the oxygen vacancies of CeO₂ contributed to the generation of ‧OH, and the generation of ClO‧ and ‧O₂^- would mainly occur on Lewis acid sites of CeO₂. In addition, the CeO₂@CNT membrane showed a reasonable stability to treat actual water samples and reduced disinfection byproducts (DBPs) formation, suggesting that it can potentially be combined with the conventional chlorine disinfection to degrade antibiotics in water.

Highly efficient visible light photocatalysis of Nix Zn1-x Fe2O4 (x= 0, 0.3, 0.7) nanoparticles: Diclofenac degradation mechanism and eco-toxicity

Pharmaceuticals and personal care products occupy a predominant position with respect to both utility and release into the ecosystem, thereby contributing to environmental pollution at alarming rates. Of the several methods identified to minimize the concentration of PPCPs, nanomaterial based photocatalysis seems to be a potential alternative for it being highly economical and eco-friendly. In this study, we synthesized Nickel zinc ferrite (Ni-ZF) [Ni_x Zn_1-x Fe₂O₄ (x = 0, 0.3, 0.7)] nanoparticles with an average diameter of ∼400 nm by a co-precipitation method towards diclofenac degradation. The composite showed greater degrees of crystallinity devoid of any impurities. Nearly complete DCF degradation (∼99%) was achieved after 50 min reaction time with the nanoparticles at pH 7 for an initial DCF concentration of 50 mg/L. The degradation process followed a pseudo first-order rate law with the rate constant of 0.1657 min^{- 1}. Microbial toxicity and phytotoxicity studies demonstrated negligible toxicity imposed by the contaminated water treated with the prepared composite, suggesting it as a promising photocatalyst benefitting in all aspects.

Synergistic adsorption and degradation of diclofenac by zero-valent iron modified spent bleaching earth carbon: Mechanism and toxicity assessment

Diclofenac (DCF) is a drug compound that exists widely in water bodies, which may pose a threat to the ecological environment. In this study, spent bleaching earth (SBE) was pyrolyzed, modified with cetyltrimethylammonium bromide (CTAB) and loaded with zero-valent iron (nZVI) to obtain CTAB-SBE@C-nZVI. The effects of CTAB concentration, Fe⁰ loading, CTAB-SBE@C-nZVI dosage, and initial pH value on the removal efficiency of DCF were studied. The results showed that the DCF removal efficiency could reach a maximum of 87.0% with 2.0 g/L dosage of the optimal material, which was prepared under the conditions of 30 mmol/L CTAB concentration, 25% Fe⁰ loading, and initial pH 5. It indicated that the strong adsorption of the material and the reduction effect of nZVI can achieve high-efficiency removal of DCF. Based on the detected reaction intermediate products, four possible degradation paths were inferred. The toxicity assessment of DCF and its intermediates manifested that the degradation of DCF by CTAB-SBE@C-nZVI was a process of gradual dechlorination and toxicity reduction. CTAB-SBE@C-nZVI displayed excellent DCF removal efficiency, good stability and environmental friendliness, achieving wastes treat wastes and exhibiting good prospects.

Diclofenac degradation by activating peroxydisulfate via well-dispersed GO/Cu2O nano-composite

Owing to high treatment efficiency under neutral condition and no extra energy required, copper-mediated activation of persulfate (PS) has been widely used for the degradation of refractory organic pollutants in water. The dispersion stability of copper nanoparticle in water, however, remains a great challenge. Meanwhile, chemical oxidative modification of graphene oxide (GO) can improve the dispersion stability of GO in water. In this paper, cuprous oxide (Cu₂O) was deposited on the surface of GO. GO/Cu₂O nano-composites with different mass ratios, i.e., m(GO):m(Cu₂O) of 1:2, 1:5, 1:10, and 1:25, were prepared. When m(GO):m(Cu₂O) was 1:2, the amount of GO/Cu₂O nano-composite was 1.00 g/L and C_PDS:C_DCF was 15:1, and the catalytic degradation rate of diclofenac (DCF) was up to 90%. Corresponding physicochemical properties of the resulting samples were comprehensively characterized by using SEM, TEM, XRD, Raman, FT-IR, and XPS. DCF degradation by activating peroxydisulfate (PDS) via GO/Cu₂O nano-composite was also investigated in detail. It is found that the synergistic effect, namely GO adsorption and multivalent copper ion electron transfer, makes GO/Cu₂O nano-composite reveal higher reactivity. Moreover, GO/Cu₂O nano-composite possesses good stability in consecutive cycling test. EPR analyses shows that ·OH and SO₄^·- radicals are involved in DCF degradation. It is indicated that the DCF degradation process contain hydroxylation and the cleavage of C-N bond, which is explored by GC-MS. In our research, well-dispersed GO/Cu₂O nano-composite with high capacity and good cycling stability was fabricated successfully. Compared with pure Cu₂O nanoparticle, GO/Cu₂O nano-composite exhibits the better performance for DCF removal. A novel well-dispersed cuprous oxide (Cu₂O) deposited on surface of GO was fabricated with high catalytic performance. Its heterogeneous activation of peroxydisulfate (PDS) for diclofenac (DCF) degradation was investigated. GO/Cu₂O nano-composite was proved high capacity and good cycling stability. Meanwhile, the possible DCF degradation pathway was explored. Compared with pure Cu₂O nanoparticle, GO/Cu₂O nano-composite exhibits better performance for DCF removal.

When bimetallic oxides and their complexes meet Fenton-like process

The heterogeneous Fenton-like reaction is an advanced oxidation process, which is widely recognized for its efficient removal of recalcitrant organic contaminants. In recent years, the construction of efficient and reusable heterogeneous Fenton-like catalysts has been extensively investigated. Recently, the use of bimetallic oxides and their complexes as catalysts for Fenton-like reaction has attracted intense attention due to their high catalytic performance and excellent stability over a wide pH range. In this article, the fundamental mechanisms of Fenton-like reactions were briefly introduced. The important reports on bimetallic oxides and their complexes are classified in detail, which are mainly divided into Fe-based and Fe-free bimetallic catalysts. We then focused in depth on the performance of their respective applications in Fenton-like reactions. Special consideration has been given to the respective contributions and synergistic mechanisms of the two metals in catalysts. Overall, it is concluded that synergistic effect of the two metals in the bimetallic catalyst can boost the utilization of hydrogen peroxide, provide adequate accessible active sites, which are all beneficial to improve catalytic performance. Finally, the current challenges in this field were proposed. Our review is expected to provide help for the application of bimetallic oxides and their complexes.

Enhanced degradation of complex organic compounds in wastewater using different novel continuous flow non - Thermal pulsed corona plasma discharge reactors

The presence of pharmaceutically active compounds (PhAcs) in water bodies is a major concern due to their persistence, biological activity, and detrimental environmental effects. The present study focuses on the application of pulsed corona plasma technology to degrade such compounds. Three different plasma reactors, namely, sequential flow plasma reactor (SFR), continuous flow top discharge plasma reactor (TDPR) and continuous flow side discharge plasma reactor (SDPR), are designed and fabricated for their performance evaluation with respect to PhAC degradation. In all the reactors, wastewater was discharged as fine droplets for better interaction between the reactive oxidizing species (ROS) generated in the system and the pollutants. Enhanced degradation of the selected pharmaceutical compounds, i.e., diclofenac (DCF) and verapamil hydrochloride (VPL), is achieved with decreased treatment time and lower energy consumption. In SFR reactor water was recycled, whereas in continuous flow reactors hydraulic retention times (HRTs) were varied. The degradation efficiency of DCF (1 mg/L) and VPL (1 mg/L) was 99 % in SDPR, at HRTs of 9 and 12 min, respectively. Deposited energies (SFR- 71 W, TDPR - 92 W, SDPR- 51 W) varied due to the difference in reactor geometries. In the SDPR reactor, 99 % degradation of mixed pollutants with an initial concentration of 10 mg/L was achieved, at a HRT of 21 min. With an input power of 51 W, good energy efficiency (EEO) of 3.8 kWh/m³ and high yield (G) of 256.2 mg/kWh were obtained. . Nitrate formation was reduced by 73.2 % in TDPR and 85.0% in SDPR (32.1-8.6 mg/L) as compared to SFR (32.1 mg/L). The operating cost estimated was 0.71 $/m³, 0.80 $/m³ and 0.67 $/m³ for SFR, TDPR and SDPR, respectively. The results clearly indicate that the continuous flow reactor with side discharge is a viable alternative to traditional plasma reactors.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Mechanistic investigations on the removal of diclofenac sodium by UV/S2O82-/Fe2+, UV/HSO5-/Fe2+ and UV/H2O2/Fe2+-based advanced oxidation processes

This study reports the comparative removal of an emerging contaminant diclofenac sodium (DCF) by UV-254 nm-based advanced oxidation processes (AOPs), i.e. UV/S₂O₈^2-/Fe²⁺, UV/HSO₅^-/Fe²⁺ and UV/H₂O₂/Fe²⁺ processes. The results demonstrated that by applying [DCF]₀ = 0.30 mM and [H₂O₂]₀ = [S₂O₈^2-]₀ = [HSO₅^-]₀ = 3 mM, k_app values were 0.082, 0.166, 0.221, 0.485 and 2.014 min^-1 for UV-only, UV/Fe²⁺, UV/H₂O₂/Fe²⁺, UV/S₂O₈^2-/Fe²⁺ and UV/HSO₅^-/Fe²⁺ processes, respectively. At different [DCF]₀ from 0.30 to 0.90 mM, the degradation rate was increased from 0.01 mM min^-1 to 0.12 mM min^-1, while the corresponding k_app values were decreased from 2.01 min^-1 to 1.04 min^-1. The removal performance of the applied AOP was significantly influenced by the presence of natural water contaminants (NO₃^-, Cl^-, HCO₃^-, SO₄^2- and humic acid (HA)) and [pH]₀. The inhibition of these natural water contaminants on the removal of DCF by UV/HSO₅-/Fe²⁺ process was in the order of HA > NO₂^- > SO₄^2- > HCO₃^- ≈ Cl^- > NO₃^-. Furthermore, seven (07) degradation products (DPs) of DCF were explored by UPLC-MS/MS and accordingly degradation pathways of DCF were suggested. The practical applications of the proposed AOPs towards the removal of DCF were further strengthened by calculating total organic carbon removal and toxicity assessment.

Insights into the mechanism of hydrogen peroxide activation with biochar produced from anaerobically digested residues at different pyrolysis temperatures for the degradation of BTEXS

The disposal of large amounts of biogas residue from anaerobically digested waste is a burden on environment protection. Porous biochars (BCs) were synthesized from biogas residue at three pyrolysis temperatures (300 °C, 550 °C, and 800 °C) and used to catalyze H₂O₂ for the degradation of benzene, toluene, ethylbenzene, xylene isomers (ortho, para, and meta), and styrene (BTEXS) to develop a new use for biogas residues. The prepared BCs were characterized through scanning electron microscopy, Brunauer-Emmett-Teller method, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. Results showed that BC800/H₂O₂ had the highest BTEXS degradation performance over 6 h. The degradation kinetic data were most consistent with the pseudo-second-order model. The different catalytic effect of the three BCs pyrolyzed at different temperatures were attributed to the dominant active sites (C-O/C-OH/C=C/C=O groups, pyridinic N, and graphitic N) that induced the production of reactive oxygen species (ROS). ROS-quenching experiments indicated that the degradation of BTEXS by BC300/H₂O₂, BC550/H₂O₂, and BC800/H₂O₂ involved ∙OH, ∙O₂^-, and ¹O₂. ∙OH was the dominant ROS in BC300/H₂O₂ and BC550/H₂O₂, and ¹O₂ was the dominant ROS in BC800/H₂O₂. Our findings provided new insight into the different catalytic mechanisms for BC production at different pyrolysis temperatures and demonstrated that a porous BC catalyst with high utilization value could be prepared from biogas residue and could hold considerable potential for application in BTEXS treatment in the future.

Effective treatment of hospital wastewater with high-concentration diclofenac and ibuprofen using a promising technology based on degradation reaction catalyzed by Fe0 under microwave irradiation

Real hospital wastewater was effectively treated by a promising technology based on degradation reaction catalyzed by Fe⁰ under microwave irradiation in this work. Fe⁰ powders were synthesized and characterized by different techniques, resulting in a single-phase sample with spherical particles. Optimum experimental conditions were determined by a central composite rotatable design combined with a response surface methodology, resulting in 96.8% of chemical oxygen demand reduction and 100% organic carbon removal, after applying MW power of 780 W and Fe⁰ dosage of 0.36 g L^-1 for 60 min. Amongst the several organic compounds identified in the wastewater sample, diclofenac and ibuprofen were present in higher concentrations; therefore, they were set as target pollutants. Both compounds were completely degraded in 35 min of reaction time. Their plausible degradation pathways were investigated and proposed. Overall, the method developed in this work effectively removed high concentrations of pharmaceuticals in hospital wastewater.

Carbon coating enhances single-electron oxygen reduction reaction on nZVI surface for oxidative degradation of nitrobenzene

Research on the in-situ generation of hydrogen peroxide (H₂O₂) using nano zero-valent iron (nZVI) has received more and more attention in recent years. However, the low utilization rate of nZVI, strict production conditions, and high energy consumption limit the application of this technology in actual environmental pollution remediation. In this study, carbon-coated nZVI (Fe⁰@C) was used to synthesize H₂O₂ in situ and realize the mineralization of nitrobenzene (NB). The results showed that the composite removed 91% of NB through adsorption, reduction, and oxidation within 120 min, of which oxidation accounts for 42.92%. Not only that, the composite material could achieve effective mineralization of NB under the wide pH range of 3-7. Quantitative experiments of hydroxyl radicals (HO) showed that the composite could generate 185.64 μM HO in 120 min without any extra energy consumption. The carbon-coated structure effectively inhibits the formation of the passivation layer on the surface of the nZVI, thereby ensuring the high activity of the Fe⁰. In addition, the carbon coating strengthens the sequential single-electron transfer process by changing the oxygen reduction pathway on the surface of the nZVI, so that the Fe⁰ can efficiently generate HO through the superoxide radical (O₂^-) pathway under neutral conditions. This study provides a fundamental understanding of the in-situ synthesis of H₂O₂ to mineralize NB by carbon-coated nZVI.

Defect Engineering on a Ti4O7 Electrode by Ce3+ Doping for the Efficient Electrooxidation of Perfluorooctanesulfonate

Defect engineering in an electrocatalyst, such as doping, has the potential to significantly enhance its catalytic activity and stability. Herein, we report the use of a defect engineering strategy to enhance the electrochemical reactivity of Ti₄O₇ through Ce³⁺ doping (1-3 at. %), resulting in the significantly accelerated interfacial charge transfer and yielding a 37-129% increase in the anodic production of the hydroxyl radical (OH^•). The Ce³⁺-doped Ti₄O₇ electrodes, [(Ti_1-xCe_x)₄O₇], also exhibited a more stable electrocatalytic activity than the pristine Ti₄O₇ electrode so as to facilitate the long-term operation. Furthermore, (Ti_1-xCe_x)₄O₇ electrodes were also shown to effectively mineralize perfluorooctanesulfonate (PFOS) in electrooxidation processes in both a trace-concentration river water sample and a simulated preconcentration waste stream sample. A 3 at. % dopant amount of Ce³⁺ resulted in a PFOS oxidation rate 2.4× greater than that of the pristine Ti₄O₇ electrode. X-ray photoelectron spectroscopy results suggest that Ce³⁺ doping created surficial oxygen vacancies that may be responsible for the enhanced electrochemical reactivity and stability of the (Ti_1-xCe_x)₄O₇ electrodes. Results of this study provide insights into the defect engineering strategy for boosting the electrochemical performance of the Ti₄O₇ electrode with a robust reactivity and stability.

Performance indicators for a holistic evaluation of catalyst-based degradation-A case study of selected pharmaceuticals and personal care products (PPCPs)

Considerable efforts have been made to develop effective and sustainable catalysts, e.g., carbon-/biochar-based catalyst, for the decontamination of organic pollutants in water/wastewater. Most of the published studies evaluated the catalytic performance mainly upon degradation efficiency of parent compounds; however, comprehensive and field-relevant performance assessment is still in need. This review critically analysed the performance indicators for carbon-/biochar-based catalytic degradation from the perspectives of: (1) degradation of parent compounds, i.e., concentrations, kinetics, reactive oxidative species (ROS) analysis, and residual oxidant concentration; (2) formation of intermediates and by-products, i.e., intermediates analysis, evolution of inorganic ions, and total organic carbon (TOC); and (3) impact assessment of treated samples, i.e., toxicity evolution, disinfection effect, and biodegradability test. Five most frequently detected pharmaceuticals and personal care products (PPCPs) (sulfamethoxazole, carbamazepine, ibuprofen, diclofenac, and acetaminophen) were selected as a case study to articulate the performance indicators for a holistic evaluation of carbon-/biochar-based catalytic degradation. This review also encourages the development of alternative performance indicators to facilitate the rational design of catalysts in future studies.

Heterogeneous Photo-Fenton Catalytic Degradation of Practical Pharmaceutical Wastewater by Modified Attapulgite Supported Multi-Metal Oxides

Chemical synthetic pharmaceutical wastewater has characteristics of high concentration, high toxicity and poor biodegradability, so it is difficult to directly biodegrade. We used acid modified attapulgite (ATP) supported Fe-Mn-Cu polymetallic oxide as catalyst for multi-phase Fenton-like ultraviolet photocatalytic oxidation (photo-Fenton) treatment with actual chemical synthetic pharmaceutical wastewater as the treatment object. The results showed that at the initial pH of 2.0, light distance of 20 cm, and catalyst dosage and hydrogen peroxide concentration of 10.0 g/L and 0.5 mol/L respectively, the COD removal rate of wastewater reached 65% and BOD5/COD increased to 0.387 when the reaction lasted for 180 min. The results of gas chromatography-mass spectrometry (GC-MS) indicated that Fenton-like reaction with Fe-Mn-Cu@ATP had good catalytic potential and significant synergistic effect, and could remove almost all heterocycle compounds well. 3D-EEM (3D electron microscope) fluorescence spectra showed that the fluorescence intensity decreased significantly during catalytic degradation, and the UV humus-like and fulvic acid were effectively removed. The degradation efficiency of the nanocomposite only decreased by 5.8% after repeated use for 6 cycles. It seems appropriate to use this process as a pre-treatment for actual pharmaceutical wastewater to facilitate further biological treatment.

Electrochemical oxidation of diclofenac on CNT and M/CNT modified electrodes

Successful electrochemical oxidation of diclofenac, a non-steroidal anti-inflammatory drug considered as an emerging pollutant, was investigated on CNT, Pt/CNT and Ru/CNT modified electrodes based on Carbon Toray in aqueous media.

Degradation of BTEXS with stable and pH-insensitive iron-manganese modified biochar from post pyrolysis

An efficient iron-manganese modified biochar (FMBC) was successfully synthesized as a heterogeneous Fenton-like catalyst through easy post-modification and applied for degradation of benzene, toluene, ethylbenzene, xylene isomers (ortho, para, and meta), and styrene (BTEXS) in the presence of H₂O₂. The catalyst was characterized by Brunauer-Emmett-Teller method, scanning electron microscopy, and X-ray photoelectron spectrometry. The effects of H₂O₂ concentration, FMBC dose, and initial pH on BTEXS degradation were also investigated. Results showed that degradation efficiency of FMBC for individual BTEXS varied from 83.05% to 94.12% in 3 h. Kinetic analysis showed that a first-order kinetic model with respect to BTEXS concentration could be used to explain the BTEXS degradation for FMBC/H₂O₂ system. The degradation reaction was more suitable in a wide pH range (3-10) than those in previous studies, thereby overcoming the low-efficiency problem of conventional Fenton reaction at high pH. Moreover, the doses of FMBC and H₂O₂ are a crucial factor affecting BTEXS degradation. Radical scavenger experiments revealed that ∙OH, ∙O₂^-, and ¹O₂ participated in the degradation process, and ∙OH was the major contributor. The synthesized catalyst is durable with stable BTEXS removal efficiency after seven consecutive cycles. The removal efficiency of BTEXS by FMBC in produced water reached 93.23% in 12 h, indicating FMBC has practical value.

Removal of Diclofenac in Wastewater Using Biosorption and Advanced Oxidation Techniques: Comparative Results

Wastewater treatment is a topic of primary interest with regard to the environment. Diclofenac is a common analgesic drug often detected in wastewater and surface water. In this paper, three commonly available agrifood waste types (artichoke agrowaste, olive-mill residues, and citrus waste) were reused as sorbents of diclofenac present in aqueous effluents. Citrus-waste biomass for a dose of 2 g·L−1 allowed for removing 99.7% of diclofenac present in the initial sample, with a sorption capacity of 9 mg of adsorbed diclofenac for each gram of used biomass. The respective values obtained for olive-mill residues and artichoke agrowaste were around 4.15 mg·g−1. Advanced oxidation processes with UV/H2O2 and UV/HOCl were shown to be effective treatments for the elimination of diclofenac. A significant reduction in chemical oxygen demand (COD; 40–48%) was also achieved with these oxidation treatments. Despite the lesser effectiveness of the sorption process, it should be considered that the reuse and valorization of these lignocellulosic agrifood residues would facilitate the fostering of a circular economy.

Oxidation of diclofenac by birnessite: Identification of products and proposed transformation pathway

Diclofenac (DCF), a widely used non-steroidal anti-inflammatory, reacted readily with birnessite under mild conditions, and the pseudo first order kinetic constants achieved 8.84 × 10^-2 hr^-1. Five products of DCF including an iminoquinone product (2,5-iminoquinone-diclofenac) and four dimer products were observed and identified by tandem mass spectrometry during the reaction. Meanwhile, 2,5-iminoquinone-diclofenac was identified to be the major product, accounting for 83.09% of the transformed DCF. According to the results of spectroscopic Mn(III) trapping experiments and X-ray Photoelectron Spectroscopy, Mn(IV) contained in birnessite solid was consumed and mainly converted into Mn(III) during reaction process, which proved that the removal of DCF by birnessite was through oxidation. Based on the identified products of DCF and the changes of Mn valence state in birnessite solid, a tentative transformation pathway of DCF was proposed.

The obvious advantage of amino-functionalized metal-organic frameworks: As a persulfate activator for bisphenol F degradation

In this study, two iron-based metal-organic framework compounds (MOFs), were used and compared as catalysts for persulfate (PS) activation to degrade bisphenol F (BPF). The outstanding advantage of using amino-functionalized MOFs in the catalytic system was verified under different reaction conditions, and the mechanism was explored. The results indicated that NH₂-MIL-101(Fe)/PS system not only had a wide pH application range, but also possessed an excellent catalytic performance towards interference from the coexisting anions and humic acid. Density functional theory (DFT) calculations showed that, compared with MIL-101(Fe), the -NH₂ modification could significantly improve the electronic conductivity of NH₂-MIL-101(Fe) by enhancing its Fermi level (-4.28 eV) and binding energy to PS (-1.19 eV). The free radical quenching experiments were combined with electron paramagnetic resonance (EPR) confirmed that free radicals (SO₄^-, OH, O₂^-) worked together with the non-radical (¹O₂) reaction to remove 91% BPF within 40 min in the NH₂-MIL-101(Fe)/PS system. The two proposed BPF degradation pathway were related to hydroxylation, oxidation and ring cracking. The toxicity of the BPF degradation intermediates as well as its final products were also evaluated.

Ce-based catalysts used in advanced oxidation processes for organic wastewater treatment: A review

Refractory organic pollutants in water threaten human health and environmental safety, and advanced oxidation processes (AOPs) are effective for the degradation of these pollutants. Catalysts play vital role in AOPs, and Ce-based catalysts have exhibited excellent performance. Recently, the development and application of Ce-based catalysts in various AOPs have been reported. Our study conducts the first review in this rapid growing field. This paper clarifies the variety and properties of Ce-based catalysts. Their applications in different AOP systems (catalytic ozonation, photodegradation, Fenton-like reactions, sulfate radical-based AOPs, and catalytic sonochemistry) are discussed. Different Ce-based catalysts suit different reaction systems and produce different active radicals. Finally, future research directions of Ce-based catalysts in AOP systems are suggested.

Can Cu2ZnSnS4 nanoparticles be used as heterogeneous catalysts for sulfadiazine degradation?

As a quaternary copper-based semiconductor, Cu₂ZnSnS₄ (CZTS) is drawing growing attention and is anticipated as a promising photocatalyst, thanks to its large absorption coefficient, exceptional photostability, and theoretical power conversion efficiency. However, CZTS has never been used as an activator of H₂O₂ for the degradation of refractory organic pollutants. In this study, the synthesis of CZTS nanoparticles obtained with diverse morphologies and crystallinities using solvents of deionized water (CZTS-W) and ethylene glycol (CZTS-EG) was examined in the activation of H₂O₂ to degrade sulfadiazine (SDZ). The results revealed that CZTS coupled with H₂O₂ could be an effective system for the degradation of SDZ. Compared to CZTS-EG, CZTS-W presented higher reusability in consecutive cycles with negligible leaching of copper. Reactive oxygen species quenching tests and electron paramagnetic resonance analyses illustrated that •O₂^-, •OH, and ¹O₂ contributed to the degradation of SDZ, and ¹O₂ prevailed over •O₂^- and •OH. The mechanistic investigation showed that efficient degradation could be associated to the effective recycling of Cu(II)/Cu(I) and low-valent/high-valent sulfur. Also, the degradation pathways of SDZ have been proposed through the detection of intermediate products. This study manifests that CZTS synthesized using deionized water is encouraging for the elimination of organic pollutants.

Fabrication of vessel-like biochar-based heterojunction photocatalyst Bi2S3/BiOBr/BC for diclofenac removal under visible LED light irradiation: Mechanistic investigation and intermediates analysis

In this work, a novel, economical and effective vessel-like biochar-based photocatalyst Bi₂S₃/BiOBr/BC was synthesized by a facile one-pot solvothermal method for the first time. A series of characterization analyses demonstrated the successful preparation of photocatalyst Bi₂S₃/BiOBr/BC. Furthermore, diclofenac (DCF) as the target contaminant was applied to elucidate the enhanced photocatalytic performance (93.65%, 40 min) under energy-saving visible LED light irradiation. Comparison experiments among different photocatalysts and photoelectrochemical tests results illustrated that excellent photocatalytic performance of Bi₂S₃/BiOBr/BC 10% might be attributed to the electrons transfer of biochar and higher charge separation efficiency of heterojunction structure. Besides, lower electrical energy per order value indicated photocatalyst/visible LED light system was more energy-saving. Proper photocatalyst dosage (0.6 g/L) and relatively acidic water environment (pH = 5.0) would be beneficial to DCF photodegrdation by Bi₂S₃/BiOBr/BC. Good reusability and stability of Bi₂S₃/BiOBr/BC were verified via five consecutive recycle experiments. Furthermore, the role of active species was determined through trapping experiments and O₂- and h⁺ dominated the photodegradation reaction to mineralize DCF molecules. Eleven main intermediates and four possible photodegradation pathways were proposed by HRMS analysis. Accordingly, photocatalyst Bi₂S₃/BiOBr/BC would provide potential technical support for emerging pollutant removal in water matrix.

Efficient degradation of sodium diclofenac via heterogeneous Fenton reaction boosted by Pd/Fe@Fe3O4 nanoparticles derived from bio-recovered palladium

Dehalogenation of emerging pollutants has attracted worldwide attention. In this study, novel bio-Pd/Fe@Fe₃O₄ nanoparticles (NPs) were proposed to boost the heterogeneous Fenton reaction for degradation of sodium diclofenac (DCF). Specifically, Enterococcus faecalis (E. faecalis) was employed to achieve bio-recovered palladium (bio-Pd). Results showed that expected preparation of bio-Pd/Fe@Fe₃O₄ NPs was confirmed by various characterization techniques. The prepared bio-Pd/Fe@Fe₃O₄ NPs were spherical morphology with average size of 9 nm. Under the optimum conditions, the removal efficiency of 10 mg/L DCF in 20 min and 40 min reached as high as 94.69% and 99.65%, respectively. The dechlorination and mineralization efficiencies of DCF were 85.16% and 59.21% in 120 min, respectively. The main degradation pathway of DCF was complete mineralization with the final products CO₂, chloride ions and H₂O. The improvement of dechlorination efficiency was ascribed to the accelerated corrosion of nano zero valent iron (nZVI) by Pd/Fe galvanic effect and the rise of active hydrogen. Meanwhile, more ferrous ions were released into this solution, resulting in the higher heterogeneous Fenton reaction rate driven by bio-Pd/Fe@Fe₃O₄ NPs. Therefore, the findings suggested that bio-Pd/Fe@Fe₃O₄ NPs were effective catalysts for DCF dechlorination and mineralization. The work provided a novel strategy for degradation of halogen-containing environmental pollutants.

New insight into the mechanism of peroxymonosulfate activation by nanoscaled lead-based spinel for organic matters degradation: A singlet oxygen-dominated oxidation process

Crystalline iron-based nanoparticles with spinel structure have received great attention for catalyzing peroxymonosulfate (PMS). This study introduces lead ferrite (PbFe₂O₄) as a novel, simple, and efficient catalyst to activate PMS for the degradation of organic contaminants in aqueous solution. The results indicated that, under pH 9.0, nearly 100% of 10 μM thionine was removed in 20 min. Operation factors, including pH, oxidant concentrations, catalyst dosage, and coexisting ions, were investigated and found to be influential for the thionine removal. PbFe₂O₄ showed higher catalytic activity and lower ions leaching than well-crystallized lead oxide (PbO) and ferric oxide (Fe₂O₃). The results from the characterization of the PbFe₂O₄ with X-ray diffraction (XRD) before and after reaction suggested that the structure and properties of the catalyst kept stable, and the recovered catalyst exhibited good catalytic performance during the recycling batch experiments. Free radical quenching experiments and electron paramagnetic resonance (EPR) spectra revealed that singlet-oxygen (¹O₂) is the dominant active oxygen species rather than sulfate radical for thionine degradation in PbFe₂O₄/PMS system. Meanwhile, the possible pathways of ¹O₂ generation were proposed: the redox reaction between Pb(Ⅳ)/Pb(II) and PMS may play an key role in PMS activation. This study provides an interesting insight in PMS activation by the high-efficient non-radical process, and the PbFe₂O₄ could be as efficient and recyclable heterogeneous catalyst for organic degradation.

Degradation kinetics and mechanism of diclofenac by UV/peracetic acid

In this work, the degradation kinetics and mechanism of diclofenac (DCF) by UV/peracetic acid (PAA) was investigated.

A High-Efficiency CuO/CeO2 Catalyst for Diclofenac Degradation in Fenton-Like System

An efficient Fenton-like catalyst CuO/CeO₂ was synthesized using ultrasonic impregnation and used to remove diclofenac from water. The catalyst was characterized by N₂ adsorption-desorption, SEM-EDS, XRD, HRTEM, Raman, and XPS analyses. Results showed that CuO/CeO₂ possessed large surface area, high porosity, and fine elements dispersion. Cu was loaded in CeO₂, which increased the oxygen vacancies. The exposed crystal face of CeO₂ (200) was beneficial to the catalytic activity. The diclofenac removal experiment showed that there was a synergistic effect between CuO and CeO₂, which might be caused by more oxygen vacancies generation and electronic interactions between Cu and Ce species. The experimental conditions were optimized, including pH, catalyst and H₂O₂ dosages, and 86.62% diclofenac removal was achieved. Diclofenac oxidation by ·OH and adsorbed oxygen species was the main mechanism for its removal in this Fenton-like system.

Magnetic Fe3O4/multi-walled carbon nanotubes materials for a highly efficient depletion of diclofenac by catalytic wet peroxideoxidation

The aim of this work is to synthesize a magnetic magnetite/multi-walled carbon nanotube (Fe₃O₄/MWCNT) catalyst by a method combining co-precipitation and hydrothermal treatments for the efficient removal of diclofenac (DCF) by catalytic wet peroxide oxidation (CWPO). The support (MWCNTs) shows a moderate-large surface area and good adsorption capacity, leading to the improvement of the magnetite (Fe₃O₄) dispersion on its surface. The response surface methodology (RSM) was applied in order to find out the effect of the reaction parameters on DCF removal, allowing to establish the optimum operating conditions (T = 60 °C, [H₂O₂]₀ = 2.7 mM, [catalyst] = 1.0 g L^-1). The optimum CWPO experiment showed an outstanding catalytic activity at non-modified pH solution (6.7), obtaining a 95% of DCF removal after 3 h reaction time; this high efficiency can be attributed to the synergistic effect of the iron-based catalyst with the high quantity of ^•OH radicals generated on the surface of the catalyst. In addition, the Fe₃O₄/MWCNT material exhibited good reusability along three consecutive reaction cycles, finding a pollutant removal close to 95% in each cycle of 3 h reaction time. Additionally, a degradation mechanism pathway was proposed for the removal of DCF by CWPO. The versatility of the material was finally demonstrated in the treatment of different environmentally relevant aqueous matrices (a wastewater treatment plant effluent, surface water, and hospital wastewater), obtaining an effective reduction in the ecotoxicity values.

Rapid in situ microwave synthesis of Fe3O4@MIL-100(Fe) for aqueous diclofenac sodium removal through integrated adsorption and photodegradation

Metal-Organic Frameworks (MOFs) are efficient adsorbent and catalyst, however, the prepare of MOFs can be extremely time consuming. The rapid in situ microwave synthesis process offers the possibility of MOFs to a large-scale application. In this study, Fe₃O₄@MIL-100(Fe) was rapidly prepared via microwave in 30 min using Fe₃O₄ as metal precursor and applied as the adsorbent and photocatalyst to remove diclofenac sodium (DCF) from water. Fe₃O₄@MIL-100(Fe) exhibited an excellent adsorption effect to DCF with the maximum adsorption capacities of 400 mg/L. The presence of H₂O₂ could promote the removal of DCF during photocatalytic process. Approximately 99.4% of the DCF was removed in Fe₃O₄@MIL-100(Fe)/vis/H₂O₂ system via adsorption removal and consequent photocatalytic degradation. The high efficiency was attributed to the large BET surface area (1244.62 m²/g) and abundant iron metal sites (Fe(III) and Fe(II)) of Fe₃O₄@MIL-100(Fe). The adsorptive, photocatalytic property of Fe₃O₄@MIL-100(Fe) and the Fenton-like reaction were the main mechanisms for DCF removal. TOC analyzer was served to assess the mineralization of solutions treated by Fe₃O₄@MIL-100(Fe)/vis/H₂O₂ in 12 h. High elimination of TOC (87.8%) was observed during the DCF mineralization process. In addition, the major products were illuminated using HPLC-Q-TOF-MS and DCF degradation pathways were also proposed.

Novel Fenton-like system (Mg/Fe-O2) for degradation of 4-chlorophenol

A novel heterogeneous Fenton-like system (Mg/Fe-O₂) which could directly convert oxygen (O₂) to hydrogen peroxide/hydroxyl radicals (H₂O₂/^•OH) was developed and used to degrade 4-chlorophenol. The Mg/Fe bimetallic particles were prepared by chemical displacement process and characterized by XRD, SEM and TEM. The in situ continuous production of H₂O₂/^•OH and the effect of the mole ratio of Mg to Fe in the Mg/Fe bimetallic particles and the operating parameters on the degradation 4-chlorophenol in Mg/Fe-O₂ system were investigated in detail. It was found that the Mg/Fe bimetallic particles with the mole ratio of Mg to Fe of 32:1 had the best performance for the 4-chlorophenol degradation and the maximum cumulative concentration of H₂O₂, the degradation efficiency of 4-chlorophenol and the removal efficiency of TOC in Mg/Fe-O₂ system were 34.5 mg/L, 100% and 91.8%, respectively, at pH 3, O₂ flow rate 400 mL/min, dosage of Mg/Fe bimetallic particles 2 g/L, 4-chlorophenol initial concentration 50 mg/L and reaction time 60 min. It was revealed by radical scavenging experiments that ^•OH, particularly the surface-bound ^•OH, were the predominant reactive oxygen species in Mg/Fe-O₂ system for the degradation of 4-chlorophenol. The main intermediates of 4-chlorophenol degradation were detected by high-resolution liquid chromatography equipped with time-of-flight mass spectrometry (HRLC-ToF-MS) and ion chromatography (IC). Based the results of control experiments and the electrochemical tests, the possible pathway and mechanism of 4-chlorophenol degradation in Mg/Fe-O₂ system were tentatively proposed.

Diclofenac removal by pyrite-Fenton process: Performance in batch and fixed-bed continuous flow systems

This study provides experimental results from batch and column studies to investigate diclofenac degradation by pyrite-Fenton process under variable chemical conditions (e.g., pyrite loading). Batch experiments show that diclofenac removal increased with increasing hydrogen peroxide and pyrite concentration. On the other hand, the addition of organic chelating agents such as citrate had an adverse effect on diclofenac removal by pyrite-Fenton process in batch systems due to scavenging effect of these agents for hydroxyl radicals. Batch results showed a direct correlation between the rate of diclofenac degradation and the rate of iron dissolution from pyrite, suggesting that diclofenac removal by pyrite-Fenton process was mainly controlled by solution phase hydroxyl radical attack on aromatic structure. Column experiments show that the effluent diclofenac concentration initially reached a peak value, and then sharply decreased to zero at higher pore volumes. The initial diclofenac breakthrough coincided well with the highest Fe(II) concentration observed in the breakthrough curve, implying that the generation of excess Fe(II) had a detrimental effect on removal efficiency due to scavenging effect of excess Fe(II) for hydroxyl radicals. The column system continued to function with 100% diclofenac removal efficiency when the effluent Fe(II) concentration decreased to a level at which the scavenging effect was minimized.

FeNiCeOx ternary catalyst prepared by ultrasonic impregnation method for diclofenac removal in Fenton-like system

FeNiCeO_x was firstly prepared by ultrasonic impregnation method and used to remove diclofenac in a Fenton-like system. The catalytic activity was improved successfully by doping Ni into FeCeO_x. The diclofenac removal efficiency reached 97.9% after 30 min reaction. The surface morphology and properties of FeNiCeO_x were characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman and X-ray photoelectron spectroscopy (XPS) analyses. FeNiCeO_x in this paper had larger specific surface area than those prepared by other methods, which was attributed to the cavitation effect and hot-spot effect during the ultrasonic synthesis process. Low crystallinity of Fe₂O₃ and NiO showed by characterization could lead to high interaction of Fe and Ni ions with support of CeO₂. They substituted Ce in CeO₂, caused lattice contraction and formed more oxygen vacancies, which favoured the catalytic reaction. Meanwhile, Fe and Ce ions both had redox cycles of Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺, which facilitated the electron transfer in the reaction. The synergistic effect among Fe, Ni and Ce might lead to better catalytic performance of FeNiCeO_x than any binary metal oxides constituted from the above three elements. Finally, the potential mechanism of diclofenac removal in FeNiCeO_x-H₂O₂ system is proposed.

Catalytic oxidation of diclofenac by hydroxylamine-enhanced Cu nanoparticles and the efficient neutral heterogeneous-homogeneous reactive copper cycle

This study has demonstrated that hydroxylamine (HA) could greatly enhance Cu nanoparticles (nCu) in activating molecular oxygen and significantly elevate the diclofenac (DCF) degradation rate about two orders of magnitude in neutral circumstances. Effects of several important parameters on the DCF degradation such as nCu loading, HA dosage, pH and reaction temperature were investigated in the nCu/HA/O₂ system. Multiple examinations revealed that the reactive Cu(III) species instead of OH• would be predominant in the nCu/HA/O₂ system, despite their similar DCF degradation pathways. Based on a HA-enhanced copper cycle depending on the pristine Cu⁰@Cu(I) (hydro)oxides core-shell structure, the heterogeneous-homogeneous reaction mechanism was proposed. It included solid-liquid interfacial and bulk reactions, e.g. heterogeneous activation of O₂ by Cu(I) to produce H₂O₂ and homogeneous Cu(I)-catalytic generation of Cu(III) from H₂O₂. Further quantitative investigation of the main reactive species in the cycle revealed that the Cu(I) regeneration instead of the O₂ activation would be rate-limited. Besides, nCu could be recycled to effectively degrade DCF in four consecutive cycles in the raw neural nCu/HA/O₂ system. It suggested that the nCu/HA/O₂ system with a more efficient copper cycle would be a good alternative Fenton-like system in treating neutral recalcitrant organic wastewaters.

Enhanced catalytic degradation by using RGO-Ce/WO3 nanosheets modified CF as electro-Fenton cathode: Influence factors, reaction mechanism and pathways

Development of an efficient cathode in advanced oxidation process is an important challenge. In this work, we synthesized a low-cost, high-catalytic-active and stable reduced graphene oxide (RGO)-Ce/WO₃ nanosheets (RCW) to modify carbon felt (CF) as cathode to degrade ciprofloxacin (CIP) in electro-Fenton process. Compared to traditional heterogeneous electro-Fenton process, carbon black was substituted by RGO and poly tetra fluoroethylene was avoided to be used as binder. We found that RCW/CF cathode reached about 100% degradation efficiency of CIP after 1 h and 98.55% mineralization degree after 8 h. Meanwhile, it had a very high current density, about 2.5 times that of CF. RCW/CF cathode produced more O₂^-, H₂O₂ and OH via one-electron reduction process (O₂→O₂- →H₂O₂). The modified cathode kept a stable performance for high CIP degradation efficiency during 5 cycles. The introduction of RGO could promote electron transfer, and the adding of Ce into the WO₃ lattice provided superior conditions for the adsorption and activation of oxygen molecules, thus promoting the formation of active oxygen species on the surface of RCW. This novel RCW/CF composite is an efficient and promising electrode for removal of CIP in the wastewater.

Degradation of emerging contaminants by Co (III) ions in situ generated on anode surface in aqueous solution

Cobalt ion is an environmental contaminant in general. But interestingly, it can also be used to degrade some refractory organic contaminants in water by mediated electrochemical oxidation process (MEOP) based on Co (III). MEOP is a very promising technology, and it can recycling use the mediator ions, Co (III), to degrade refractory organic contaminants in water. However, previous studies for this technology mainly conducted in strong acidic medium, the oxidation ability of this process for emerging contaminants near neutral pH condition was still unclear. Therefore, this study evaluated the emerging contaminants removal and mineralization efficiency of the MEOP-Co (III) around neutral pH, and investigated systematically the influence of series of operating parameters, including initial Co (II) concentration, current density, initial pH, electrolyte, and anions. Results from these studies indicated that the MEOP-Co (III) had a fairly good contaminants removal and mineralization ability for sulfamethoxazole, tetracycline, carbamazepine, diclofenac, and phenol at neutral pH. Besides, no radical was detected in MEOP-Co (III), and the main oxidizing substance was Co (III) ions, which was generated on anode surface. The addition of CO₃^2-/HCO₃^- could weaken the oxidation ability of MEOP-Co (III), while Cl^- and PO₄^3- could enhance the system's oxidation ability. Moreover, a reasonable energy consumption was achieved in MEOP-Co (III), and the highest electric energy per order (EE/O) value was 2.4 kWh·m^-3 in this study.

Heterogeneous activation of persulfate by Co3O4-CeO2 catalyst for diclofenac removal

A series of Co₃O₄-CeO₂ mixed metal oxides were synthesized by co-precipitation method and successfully used to activate persulfate for diclofenac removal. The effects of Co:Ce mole ratio, calcination temperature and calcination time on the catalytic activities were investigated. Results showed that the activity of Co₃O₄-CeO₂ catalysts increased with Co:Ce mole ratio from 1:9 to 7:3, and decreased with the calcination temperature from 300 to 800 °C. 90% diclofenac was removed with Co₇Ce₃-300-1 catalyst (Co:Ce = 7:3, calcinated at 300 °C for 1 h) after 15 min. Moreover, short calcination time and low temperature resulted in smaller crystallite size, more structural defects, more active crystal surfaces and larger surface area of the catalyst, which led to higher removal efficiency of diclofenac. The high ratios of Co²⁺/Co³⁺, Ce³⁺/Ce⁴⁺ and O_ads/O_latt were very important to enhance the catalytic activity. Finally, a potential reaction mechanism was proposed based on characterization of the fresh and spent catalysts.

Visible-light-driven photocatalytic degradation of diclofenac by carbon quantum dots modified porous g-C3N4: Mechanisms, degradation pathway and DFT calculation

Metal-free photocatalysts have attracted growing concern in recent years. In this work, a new class of carbon quantum dots (CQDs) modified porous graphitic carbon nitride (g-C₃N₄) is synthesized via a facile polymerization method. With the optimal CQDs loading, the CQDs modified g-C₃N₄ exhibits ∼15 times higher degradation kinetic towards diclofenac (DCF) than that of pure g-C₃N₄. The enhanced photocatalytic activity can be ascribed to the improved separation of charge carriers as well as the tuned band structure. Moreover, a photosensitation-like mechanism is proposed to elucidate the photo-generated electrons transfer and reactive radicals formation. CQDs are anchored to g-C₃N₄ surface via C-O bond, which provide channels for the preferential transfer of photo-excited electrons on DCF molecule to the conduction band of g-C₃N₄. Superoxide radical (·O₂^-) dominates the degradation of DCF, while holes (h⁺) show a negligible contribution. Density functional theory (DFT) calculation successfully predicts that the sites on DCF molecule with high Fukui index (f⁰) are preferable to be attacked by radicals. DCF degradation pathway mainly includes ring hydroxylation, ring closure and C-N bond cleavage processes. Acute toxicity estimation indicates the formation of less toxic intermediates/products compared to DCF after photocatalysis. Moreover, the hybrid photocatalysts exhibit good reusability in five consecutive cycles. This work not only proposes a deep insight into photosensitation-like mechanism in the photocatalysis system by using C₃N₄-based materials, but also develops new photocatalysts for potential application on removal of emerging organic pollutants from waters and wastewaters.

Advanced oxidation and adsorptive bubble separation of dyes using MnO2-coated Fe3O4 nanocomposite

In this study, MnO₂-coated Fe₃O₄ nanocomposite (Fe₃O₄@MnO₂) was utilized to decompose H₂O₂ to remove dyes via advanced oxidation processes and adsorptive bubble separation (advanced ABS system). The combination of H₂O₂ and Fe₃O₄@MnO₂ generated bubbles and formed a stable foam layer in the presence of a surfactant; sodium dodecyl sulfate (SDS) or cetyltrimethylammonium chloride (CTAC), separating dye from the solution. On the basis of radical quenching experiments, electron paramagnetic resonance and X-ray photoelectron spectroscopy analyses, it was confirmed that the MnO₂ shell of catalyst was reduced to Mn₂O₃ by H₂O₂, generating radicals and oxygen gas for the removal of dyes. In the advanced ABS system, ∙OH and ¹O₂ were the main radical species and the O₂ concentrations of 0.34 and 0.71 mM were increased in the solution and headspace, respectively. The advanced ABS system demonstrated a high removal efficiency of methylene blue (MB) (99.0%) and the removal rate increased with increasing amounts of components (H₂O₂, catalyst and SDS). Also, the advanced ABS system maintained high removal efficiency of MB at a wide pH range of 3-9. In addition to the anionic surfactant of SDS, CTAC was applied as a cationic surfactant for the advanced ABS of anionic dyes. Lastly, the scale-up system was applied to remediate dye-contaminated river water and industrial wastewater for possible practical applications.

Photocatalytical degradation of diclofenac by Ag-BiOI-rGO: Kinetics, mechanisms and pathways

A novel ternary nanocomposite photocatalyst, Ag-BiOI- reduced graphene oxide (rGO), driven by visible light was successfully synthesized with hydrothermal strategy. XRD, SEM, TEM, HRTEM, EDS, raman spectroscopy, XPS, DRS, photocurrent and EIS analysis were employed to characterize all synthesized compounds. Compared to pure BiOI, Ag-BiOI and BiOI-rGO, the 5 mol% Ag-BiOI-rGO 5 wt% displayed superior photocatalytic capability with complete removal of diclofenac (10.0 μg mL^-1) in 80 min under visible light. The characterization results indicated that the addition of Ag and rGO enhanced the charge separation and suppressed the recombination of photogenerated electrons and holes, which upgraded the ability of Ag-BiOI-rGO to degrade diclofenac compared with BiOI. Six reaction intermediates of diclofenac were detected by LC-MS/MS, subsequently, two degradation routes were proposed. This work provides a promising strategy to fabricate more effective photocatalysts to deal with organic pollutants in wastewater.