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

MOF-derived Fe/Ni@C marigold-like nanosheets as heterogeneous electro-Fenton cathode for efficient antibiotic oxytetracycline degradation

The widespread occurrence of organic antibiotic pollution in the environment and the associated harmful effects necessitate effective treatment method. Heterogeneous electro-Fenton (hetero-EF) has been regarded as one of the most promising techniques towards organic pollutant removal. However, the preparation of efficient cathode still remains challenging. Herein, a novel metal-organic framework (MOF)-derived Fe/Ni@C marigold-like nanosheets were fabricated successfully for the degradation of oxytetracycline (OTC) by serving as the hetero-EF cathode. The FeNi3@C (Fe/Ni molar ratio of 1:3) based hetero-EF system exhibited 8.2 times faster OTC removal rate than that of anodic oxidation and possessed many advantages such as excellent OTC degradation efficiency (95.4% within 90 min), broad environmental adaptability (satisfactory treatment performance for multiple antibiotics under various actual water matrixes), good stability and reusability, and significant toxicity reduction. The superior hetero-EF catalytic performance was mainly attributed to: 1) porous carbon and Ni existence were both conducive to the in-situ generation of H2O2 from dissolved O2; 2) the synergistic effects of bimetals together with electron transfer from the cathode promoted the regeneration of ≡ FeII/NiII, thereby accelerating the production of reactive oxygen species; 3) the unique nanosheet structure derived from the precursor two-dimensional Fe-Ni MOFs enhanced the accessibility of active sites. This work presented a promising hetero-EF cathode for the electrocatalytic treatment of antibiotic-containing wastewaters.

A carbon felt cathode modified by acidic oxidised carbon nanotubes for the high H2O2 generation and its application in electro-Fenton

Herein, a carbon felt (CF) cathode modified by the acidic oxidised carbon nanotubes (OCNTs) exhibited a high yield of the H2O2 generation in electro-Fenton. Rotating disk electrode (RDE) measurements showed that the selective generation of H2O2 occurred on the CF cathode coated by OCNTs (OCNTs/CF), which was attributed to the high amount of oxygen-containing functional groups in OCNTs. Moreover, the pollutant degradation efficiency could almost reach 100% within 60 min in electro-Fenton with OCNTs/CF as the cathode. Furthermore, the pollutant removal efficiency was kept constant after five consecutive cycles, indicating the high stability of OCNTs/CF cathode. Besides, the hydrophilicity of OCNTs/CF cathode was significantly enhanced owing to the abundant oxygen-contained functional groups on the surface of the OCNTs/CF cathode, which facilitated the mass transfer between the OCNTs/CF cathode and the reactants in the bulk solution. To reveal the possible mechanism in electro-Fenton equipped with the OCNTs/CF cathode, quenching experiments and electron paramagnetic resonance (EPR) investigations were further conducted. This work provided valuable insights into the fabrication of the non-metallic cathode with a high ability towards H2O2 generation in electro-Fenton for efficient pollutant removal.

Advancements in electrochemical technologies for the removal of fluoroquinolone antibiotics in wastewater: A review

In recent times, the need to make water safer and cleaner through the elimination of recalcitrant pharmaceutical residues has been the aim of many studies. Fluoroquinolone antibiotics such as ciprofloxacin, norfloxacin, enrofloxacin, and levofloxacin are among the commonly detected pharmaceuticals in wastewater. Since the presence of these pharmaceuticals in water bodies poses serious risks to living organisms, it is vital to adopt effective wastewater treatment techniques for their complete removal. Electrochemical technologies such as photoelectrocatalysis, electro-Fenton, electrocoagulation, and electrochemical oxidation have been established as techniques capable of the complete removal of organics including pharmaceuticals from wastewater. Hence, this review presents discussions on the recent progress (literature within 2018-2022) in the applications of common electrochemical processes for the degradation of fluoroquinolone antibiotics from wastewater. The fundamentals of these processes are highlighted while the results obtained using the processes are critically discussed. Furthermore, the inherent advantages and limitations of these processes in the mineralization of fluoroquinolone antibiotics are clearly emphasized. Additionally, appropriate recommendations are made toward improving electrochemical technologies for the complete removal of these pharmaceuticals with minimal energy consumption. Therefore, this review will serve as a bedrock for future researchers concerned with wastewater treatments to make informed decisions in the selection of suitable electrochemical techniques for the removal of pharmaceuticals from wastewater.

Two-dimensional manganese-iron bimetallic MOF-74 for electro-Fenton degradation of sulfamethoxazole

This study reported a novel application of Mn_0.67Fe_0.33-MOF-74 with two-dimensional (2D) morphology grown on carbon felt as a cathode for efficiently removing antibiotic sulfamethoxazole in the heterogeneous electro-Fenton system. Characterization demonstrated the successful synthesis of bimetallic MOF-74 by a simple one-step method. Electrochemical detection showed that the second metal addition and morphological change improved the electrochemical activity of the electrode and contributed to pollutant degradation. At pH 3 and 30 mA of current, the degradation efficiency of SMX reached 96% with 12.09 mg L^-1 H₂O₂ and 0.21 mM ·OH detected in the system after 90 min. During the reaction, electron transfer between ≡Fe^II/III and ≡Mn^II/III promoted divalent metal ions regeneration, which ensured the continuation of the Fenton reaction. Two-dimensional structures exposed more active sites favoring ·OH production. The pathway of sulfamethoxazole degradation and the reaction mechanisms were proposed based on the intermediates identification by LC-MS and radical capture results. High degradation rates were still observed in tap and river water, revealing the potential of Mn_0.67Fe_0.33-MOF-74@CF for practical applications. This study provides a simple MOF-based cathode synthesis method, which enhances our understanding of constructing efficient electrocatalytic cathodes based on morphological design and multi-metal strategies.

Degradation of emerging pollutants on bifunctional ZnFeV LDH@graphite felt cathode through prominent catalytic activity in heterogeneous electrocatalytic processes

The heterogeneous Electro-Fenton (EF) process is a promising wastewater treatment technology that can generate onsite H₂O₂, and operate in a wide pH range without generating a metal sludge. However, the heterogeneous EF process needs bifunctional cathode electrodes that can have high activity in 2e^- oxygen reduction reaction and H₂O₂ decomposition. Herein, ZnFeV layered double hydroxide (LDH), as a heterogeneous catalyst, was coated on the graphite felt (ZnFeV LDH@GF) cathode using the electrophoretic deposition method. ZnFeV LDH@GF cathode was able to generate 59.8 ± 5.9 mg L^-1 H₂O₂ in 90 min under a constant supply of O₂. EF process with ZnFeV LDH@GF cathode exhibited 89.8 ± 6.8% removal efficiency for pharmaceutical (ciprofloxacin) at neutral pH. Remarkably, the apparent reaction rate constant (k_app) of the ZnFeV LDH@GF-EF was 2.14 times that of the EF process with pristine GF. ZnFeV LDH coating increased the hydroxyl radical (^•OH) production of the EF process from 1.74 mM to 3.65 mM. The pathway of ^•OH production is thought to be a single electron transfer from redox couples of Fe²⁺/Fe³⁺ and [Formula: see text] to H₂O₂. After 10 reuse cycles, the ZnFeV LDH@GF cathode retained 90.2% of its efficiency. Eight intermediate compounds were identified by GC-MS including cyclic compounds and aliphatic compounds.

Challenges and Future Roadmaps in Heterogeneous Electro-Fenton Process for Wastewater Treatment

The efficiency of heterogeneous electro-Fenton technology on the degradation of recalcitrant organic pollutants in wastewater is glaringly obvious. This green technology can be effectively harnessed for addressing ever-increasing water-related challenges. Due to its outstanding performance, eco-friendliness, easy automation, and operability over a wide range of pH, it has garnered significant attention from different wastewater treatment research communities. This review paper briefly discusses the principal mechanism of the electro-Fenton process, the crucial properties of a highly efficient heterogeneous catalyst, the heterogeneous electro-Fenton system enabled with Fe-functionalized cathodic materials, and its essential operating parameters. Moreover, the authors comprehensively explored the major challenges that prevent the commercialization of the electro-Fenton process and propose future research pathways to countervail those disconcerting challenges. Synthesizing heterogeneous catalysts by application of advanced materials for maximizing their reusability and stability, the full realization of H₂O₂ activation mechanism, conduction of life-cycle assessment to explore environmental footprints and potential adverse effects of side-products, scale-up from lab-scale to industrial scale, and better reactor design, fabrication of electrodes with state-of-the-art technologies, using the electro-Fenton process for treatment of biological contaminants, application of different effective cells in the electro-Fenton process, hybridization of the electro-Fenton with other wastewater treatments technologies and full-scale analysis of economic costs are key recommendations which deserve considerable scholarly attention. Finally, it concludes that by implementing all the abovementioned gaps, the commercialization of electro-Fenton technology would be a realistic goal.

Insight into advanced oxidation processes for the degradation of fluoroquinolone antibiotics: Removal, mechanism, and influencing factors

The enrichment and transport of antibiotics in the environments pose many potential hazards to aquatic animals and humans, which has become one of the public health challenges worldwide. As a widely used class of antibiotics, fluoroquinolones (FQs) generally accumulated in the environments as traditional sewage treatment plants cannot completely remove them. Advanced oxidation processes (AOPs) have been shown to be a promising method for the abatement of antibiotic contamination. In this review, influencing factors and relevant mechanisms of FQs removal by various AOPs were summarized. Compared with other AOPs, photocatalytic ozone may be considered as a cost-effective method for degrading FQs. Finally, the benefits and application restrictions of AOPs were discussed, along with proposed research directions to provide new insights into the control of FQs pollutant via AOPs in practical applications.

Remediation of pharmaceutical pollutants using graphene-based materials - A review on operating conditions, mechanism and toxicology

Graphene is a high surface area special carbon compound with exceptional biological, electronic and mechanical properties. Graphene-based materials are potential components used in water treatment on different modes and processes. Ibuprofen and ciprofloxacin are two commonly found pharmaceutical contaminants discharged into water bodies from industrial, domestic and hospital sources. Their concentration levels in water bodies are reported in the range of 1 μg/L to 6.5 mg/L and 0.050-100 μg/L respectively. Their toxic effects pose very high risk to the inhabiting organisms. Their ability to resist biodegradation and capacity to bioaccumulate makes the conventional methods less effective in removal. In the present article, treatment of these compounds via three methods, adsorption, photocatalytic degradation and electro-fenton reactions using graphene-based materials along with the methods adopted for synthesis and treatment are reviewed. The uptakes obtained by graphene-derived adsorbents are presented along with the optimal operating conditions. Studies reported complete removal of ibuprofen from wastewater was achieved at 7 pH for 60 min using graphene membrane as adsorbent and uptake of 99% of ciprofloxacin was exhibited for graphene nanoplates/boron nitrate aerogel at a pH of 7 and 60 min. The reduced graphene oxide surface exhibits higher affinity to light adsorption which leads to the formation of photo generated electrons. The future perspectives for improved applications of graphene-based materials and the research gap currently existing are highlighted.

Mn doping improves in-situ H2O2 generation and activation in electro-Fenton process by Fe/Mn@CC cathode using high-temperature shock technique

Fe/Mn@carbon cloth (CC) was successfully fabricated through high-temperature shock (HTS) technique and used as cathode modification in heterogeneous electro-Fenton (hetero-EF) process for methylisothiazolinone (MIT) degradation. The nanocrystalline on Fe/Mn@CC electrode is doped with Fe and Mn oxides and coated with carbon layer, which could markedly enhance the electrocatalysis with high electro-chemical active area and low resistance. Fe/Mn@CC modified cathode can efficiently in-situ produce and activate H₂O₂, showing high electrocatalytic activity to MIT degradation. The 95.2% MIT degradation with in 100 min were achieved under the condition of 30 mA current, 0.75 L min^-1 aeration intensity and initial pH = 3. Based on the CV curves and stability test, the high degradation activity revealed the kinetically beneficial regeneration of Fe^II/Mn^II in Fe/Mn@CC and activation of H₂O₂. The electron transfer between Fe^II/III and Mn^II/III, together with the direct Fe^II/Mn^II regeneration on the cathode, could markedly promote the H₂O₂ utilization, and eventually lead to MIT degradation.

Recent progress in Fenton/Fenton-like reactions for the removal of antibiotics in aqueous environments

The frequent use of antibiotics allows them to enter aqueous environments via wastewater, and many types of antibiotics accumulate in the environment due to difficult degradation, causing a threat to environmental health. It is crucial to adopt effective technical means to remove antibiotics in aqueous environments. The Fenton reaction, as an effective organic pollution treatment technology, is particularly suitable for the treatment of antibiotics, and at present, it is one of the most promising advanced oxidation technologies. Specifically, rapid Fenton oxidation, which features high removal efficiency, thorough reactions, negligible secondary pollution, etc., has led to many studies on using the Fenton reaction to degrade antibiotics. This paper summarizes recent progress on the removal of antibiotics in aqueous environments by Fenton and Fenton-like reactions. First, the applications of various Fenton and Fenton-like oxidation technologies to the removal of antibiotics are summarized; then, the advantages and disadvantages of these technologies are further summarized. Compared with Fenton oxidation, Fenton-like oxidations exhibit milder reaction conditions, wider application ranges, great reduction in economic costs, and great improved cycle times, in addition to simple and easy recycling of the catalyst. Finally, based on the above analysis, we discuss the potential for the removal of antibiotics under different application scenarios. This review will enable the selection of a suitable Fenton system to treat antibiotics according to practical conditions and will also aid the development of more advanced Fenton technologies for removing antibiotics and other organic pollutants.

Tannic acid-Fe complex derivative-modified electrode with pH regulating function for environmental remediation by electro-Fenton process

A heterogeneous electro-Fenton (hetero-EF) system can effectively broaden the applicable pH range, although the decreased electrogeneration efficiency of H₂O₂ at elevated pH (especially neutral conditions) is unfavorable for the efficient removal of organic pollutants. Herein, a tannic acid-Fe complex derivative-modified carbon felt (TFD@CF) cathode was prepared for hetero-EF treatment of organic pollutants over a wide pH range. Interestingly, the as-prepared hetero-EF cathode could act as a pH regulator that acidified the solution over a wide pH range. As expected, the TFD@CF cathode exhibited excellent hetero-EF activity for the removal of diverse organic pollutants (such as methyl orange, methylene blue, sulfamerazine, bisphenol A and 2,4-dichlorophenoxyacetic acid) at neutral and even alkaline pH (removal efficiency >90 %). A total of 2.98 kWh kg^-1 COD^-1 with 83.2 % COD removal could be achieved by the TFD@CF cathode for the treatment of actual textile dyeing secondary wastewater. Electrochemical characterizations proved that the TFD@CF cathode had excellent electrochemical properties with improved electron transfer ability and a well-pronounced Fe(III) electroreductive response. Meanwhile, more acidic groups were newly generated during the electrochemical reaction (an increase of 30.1 %), thus dissociating more H⁺ into solution. The identification of reactive oxygen species suggested that OH and ¹O₂ could be responsible for the removal of organic pollutants in the TFD@CF EF system. These interesting findings may provide new insights into the design of multifunctional hetero-EF cathodes for the removal of refractory organic pollutants.

Anthraquinone (AQS)/polyaniline (PANI) modified carbon felt (CF) cathode for selective H2O2 generation and efficient pollutant removal in electro-Fenton

A novel binder-free anthraquinone (AQS)/polyaniline (PANI) modified carbon felt (CF) cathode for selective H₂O₂ generation and efficient pollutant removal in electro-Fenton was fabricated by CV electro-deposition method. AQS, the oxygen reduction reaction (ORR) catalyst, was immobilized by the PANI film, which contributed to the obtained high stability of the AQS/PANI@CF cathode. The concentration of the electro-generated H₂O₂ on AQS/PANI@CF cathode (83.3 μmol L^-1) was about 10 times higher than that of the bare CF cathode. And the high yield of H₂O₂ was attributed to the catalytic reduction of O₂ by AQS to generate more superoxide radical (O₂^•-), which combined with H⁺ to form H₂O₂. Additionally, the rhodamine B (RhB) degradation efficiency reached 98.8% within 60 min with the AQS/PANI@CF served as the cathode with high stability and good repeatability. The main generated reactive radicals were determined by the quenching experiments and the electron paramagnetic resonance (EPR) tests. Besides, a plausible mechanism of the AQS/PANI@CF cathode applied electro-Fenton process was proposed. This work provided a reliable reference for the subsequent investigations of the binder-free cathode with high performance and stability.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe₂O₄/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm^-2, pH 3, 50 mgTTZ L^-1, and 50 mM of Na₂SO₄, respectively. By radical quenching test, , ¹O₂, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe₂O₄/CF cathode. The reusability and stability test showed that the highly efficient CoFe₂O₄/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

Enhanced electron transfer and hydrogen peroxide activation capacity with N, P-codoped carbon encapsulated CeO2 in heterogeneous electro-Fenton process

Designing catalysts that can effectively activate oxygen and hydrogen peroxide is a huge challenge in electro-Fenton (EF) process. Considering the superior ability of electrons transport and activation of H₂O₂, ceria encapsulated with N, P-codoped carbon material was a promising catalyst for EF reaction. Herein, CeO₂-NPC_T^X (where T and X represented the calcination temperature and the initial mass of CeO₂, respectively) materials were synthesized via pyrolysis process and used as catalysts to degrade ciprofloxacin (CIP) in EF process. The results indicated that CeO₂-NPC₁₀₀₀¹⁰⁰ catalyst had good degradation performance under the optimal conditions. Compared with CeO₂ and CeO₂-NC₁₀₀₀¹⁰⁰ catalysts, CeO₂-NPC₁₀₀₀¹⁰⁰ catalyst had more content of graphite N and more oxygen vacancies, which were beneficial to activation of oxygen and hydrogen peroxide. Scavenging experiments and electron paramagnetic resonance analysis confirmed ·O₂^- and ·OH were the main reactive oxygen species in the CIP degradation process. And three logical degradation routes of CIP were given. In addition, CeO₂-NPC₁₀₀₀¹⁰⁰ catalyst still had good stability after three times of continuous operation, and presented good universality for the treatment of a variety of antibiotic wastewaters. Finally, a convincing mechanism in the EF system with CeO₂-NPC₁₀₀₀¹⁰⁰ for CIP degradation was proposed.

Two-Dimensional Nanomaterials for the Removal of Pharmaceuticals from Wastewater: A Critical Review

The removal of pharmaceuticals from wastewater is critical due to their considerable risk on ecosystems and human health. Additionally, they are resistant to conventional chemical and biological remediation methods. Two-dimensional nanomaterials are a promising approach to face this challenge due to their combination of high surface areas, high electrical conductivities, and partially optical transparency. This review discusses the state-of-the-art concerning their use as adsorbents, oxidation catalysts or photocatalysts, and electrochemical catalysts for water treatment purposes. The bibliographic search bases upon academic databases including articles published until August 2021. Regarding adsorption, high removal capacities (>200 mg g−1) and short equilibrium times (<30 min) are reported for molybdenum disulfide, metal-organic frameworks, MXenes, and graphene oxide/magnetite nanocomposites, attributed to a strong adsorbate-adsorbent chemical interaction. Concerning photocatalysis, MXenes and carbon nitride heterostructures show enhanced charge carriers separation, favoring the generation of reactive oxygen species to degrade most pharmaceuticals. Peroxymonosulfate activation via pure or photo-assisted catalytic oxidation is promising to completely degrade many compounds in less than 30 min. Future work should be focused on the exploration of greener synthesis methods, regeneration, and recycling at the end-of-life of two-dimensional materials towards their successful large-scale production and application.

FeIIFeIII layered double hydroxide modified carbon felt cathode for removal of ciprofloxacin in electro-Fenton process

The disadvantages of limited working pH range and poor stability have hindered the practical application of traditional electro-Fenton process. In this research, a novel heterogeneous electro-Fenton (HEF) process with Fe^IIFe^III layered double hydroxide/carbon felt (Fe^IIFe^III LDH/CF) as cathode was developed for the rapid destruction of ciprofloxacin (CIP) in bulk solution. Effects of crucial influencing factors (initial pH, current intensity) on CIP degradation were investigated. Results indicated that Fe^IIFe^III LDH/CF cathode was efficient for CIP degradation (88.11%). Furthermore, CIP degradation performance in HEF could remain stable over wide range of pH (pH 3-9). The catalytic degradation of CIP in HEF process might be a combined effect of homogeneous EF reaction, anodic oxidation, and surface catalysis process via≡Fe^II/≡Fe^III cycle. Possible degradation pathways were proposed. The results suggested that Fe^IIFe^III LDH/CF cathode showed great application potential for CIP degradation.

Enhanced electro-Fenton catalytic performance with in-situ grown Ce/Fe@NPC-GF as self-standing cathode: Fabrication, influence factors and mechanism

Heterogeneous electro-Fenton (E-F) is considered as an attractive technique for efficient removal of refractory organic pollutants in wastewater. The regeneration of Fe^II and catalyst reusability are key issues for effective and sustainable degradation. Developing binder-free iron phase/carbon composite cathode is a feasible strategy. In this work, the stable Ce/Fe-nanoporous carbon modified graphite felt electrode (Ce/Fe@NPC-GF) was fabricated using in situ solvothermal method and subsequent carbonization treatment, which worked as the cathode in a heterogeneous electro-Fenton system to degrade sulfamethoxazole. The electrocatalytic activity was significantly improved with doping of Ce. It was found that mesoporous Ce/Fe@NPC-GF cathode demonstrated high oxygen reduction activity and low resistance. The co-existence of Fe^Ⅱ/Fe^Ⅲ and Ce^Ⅲ/Ce^Ⅳ redox couples enhanced remarkably interfacial electron transfer, promoting in-situ H₂O₂ generation and decomposition, sequentially boosting the production of reactive radicals (·OH and ·O₂^-). Under 20 mA and pH 3, Sulfamethoxazole (SMX) was basically degraded in 120 min, and the removal rate was satisfactory in wide pH (2-6). After 8 cycles, the electrode could still maintain high stability and outstanding catalytic capacity. This work displayed a novel in-situ preparation method of composite cathode with excellent catalytic performance in E-F system, which offered inspiration for developing efficient heterogeneous electro-Fenton cathode material.

Graphene family for hydrogen peroxide production in electrochemical system

The development of carbon-based materials to catalyze two-electron (2e^-) pathway of oxygen reduction reaction (ORR) offers great potential for hydrogen peroxide (H₂O₂) production. As a class of novel two-dimensional (2D) carbon materials, graphene and its derivatives have raised increasing attention as excellent noble-metal-free catalysts in 2e ORR due to their unique structure, physical and chemical properties. This review focuses on the synthesis of main graphene family members and graphene based electrodes, as well as their applications for H₂O₂ generation in electrochemical systems. We describe the functions of the graphene family in electrochemical systems, such as accelerating electron transfer and increasing oxygen transfer for cathodes in electrochemical systems, aiming to reveal the enhancement mechanisms of graphene and its derivatives on H₂O₂ production. Furthermore, the challenges and prospects for graphene family used as catalyst for H₂O₂ production in the future are also proposed.

Graphene-Based Composites as Catalysts for the Degradation of Pharmaceuticals

The incessant release of pharmaceuticals into the aquatic environment continues to be a subject of increasing concern. This is because of the growing demand for potable water sources and the potential health hazards which these pollutants pose to aquatic animals and humans. The inability of conventional water treatment systems to remove these compounds creates the need for new treatment systems in order to deal with these class of compounds. This review focuses on advanced oxidation processes that employ graphene-based composites as catalysts for the degradation of pharmaceuticals. These composites have been identified to possess enhanced catalytic activity due to increased surface area and reduced charge carrier recombination. The techniques employed in synthesizing these composites have been explored and five different advanced oxidation processes-direct degradation process, chemical oxidation process, photocatalysis, electrocatalyis processes and sonocatalytic/sono-photocatalytic processes-have been studied in terms of their enhanced catalytic activity. Finally, a comparative analysis of the processes that employ graphene-based composites was done in terms of process efficiency, reaction rate, mineralization efficiency and time required to achieve 90% degradation.

A WO3/PPy/ACF modified electrode in electrochemical system for simultaneous removal of heavy metal ion Cu2+ and organic acid

Heavy metal ions and organic acids are common pollutants in electroplating wastewater. Effective and economic treatment of such wastewater needs novel technologies. In this study, WO₃/PPy-1/ACF electrode was prepared using a hydrothermal modification method and it has large specific area (788.27 m² g^-1), high areal capacitance (2.58 F cm^-2 under 5 mA cm^-2 charge and discharge) and excellent conductivity. The modified electrode was used in an electrochemical system with activated carbon fiber felt (ACF) as counter electrode. The system simultaneously and successfully removed 97.8 % Cu²⁺ and 80.1 % citric acid (CA) from a simulated electroplating wastewater (typically 100 mg L^-1 Cu²⁺ and 800 mg L^-1 CA) in five- hour optimized operation. The influence of operating parameters (circulating inflow rate, applied voltage and influent pH) on the treatment performance was compared. There is interplay between Cu²⁺ reductive deposition and CA oxidation. The synergetic electrochemical treatment mechanism involves formation of hydrogen peroxide, free radicals, and catalytic effect of Cu species was proposed. This electrochemical system which is low-cost, easy to operate and highly efficient, may be applicable in treating acid-wash or electroplating wastewater, containing heavy-metal ions and organic acids.

Graphene-Modified Composites and Electrodes and Their Potential Applications in the Electro-Fenton Process

In recent years, graphene-based materials have been identified as an emerging and promising new material in electro-Fenton, with the potential to form highly efficient metal-free catalysts that can be employed in the removal of contaminants from water, conserving precious water resources. In this review, the recent applications of graphene-based materials in electro-Fenton are described and discussed. Initially, homogenous and heterogenous electro-Fenton methods are briefly introduced, highlighting the importance of the generation of H2O2 from the two-electron reduction of dissolved oxygen and its catalysed decomposition to produce reactive and oxidising hydroxy radicals. Next, the promising applications of graphene-based electrodes in promoting this two-electron oxygen reduction reaction are considered and this is followed by an account of the various graphene-based materials that have been used successfully to give highly efficient graphene-based cathodes in electro-Fenton. In particular, graphene-based composites that have been combined with other carbonaceous materials, doped with nitrogen, formed as highly porous aerogels, three-dimensional materials and porous gas diffusion electrodes, used as supports for iron oxides and functionalised with ferrocene and employed in the more effective heterogeneous electro-Fenton, are all reviewed. It is perfectly clear that graphene-based materials have the potential to degrade and mineralise dyes, pharmaceutical compounds, antibiotics, phenolic compounds and show tremendous potential in electro-Fenton and other advanced oxidation processes.

A review of graphene-based nanomaterials for removal of antibiotics from aqueous environments

Antibiotics as emerging pharmaceutical pollutants have seriously not only threatened human life and animal health security, but also caused environmental pollution. It has drawn enormous attention and research interests in the study of antibiotics removal from aqueous environments. Graphene, an interesting one-atom-thick, 2D single-layer carbon sheet with sp² hybridized carbon atoms, has become an important agent for removal of antibiotic, owing to its unique physiochemical properties. Recently, a variety of graphene-based nanomaterials (GNMs) are reported to efficiently remove antibiotics from aqueous solutions by different technologies. In this review, we summarize different structure and properties of GNMs for the removal of antibiotics by adsorption. Meanwhile, advanced oxidation processes (AOPs), such as photocatalysis, Fenton process, ozonation, sulfate radical and combined AOPs by the aid of GNMs are summarized. Finally, the opportunities and challenges on the future scope of GNMs for removal of antibiotics from aqueous environments are proposed.