Electrochemical oxidation and advanced oxidation processes using a 3D hexagonal Co3O4 array anode for 4-nitrophenol decomposition coupled with simultaneous CO2 conversion to liquid fuels via a flower-like CuO cathode

Graphene/MoS2-assisted alum sludge electrode induces selective oxidation for organophosphorus pesticides degradation: Co-oxidation and detoxification mechanism

Designing an electrode that can generate abundant free radicals and 1O2, which can effectively degrade and detoxify organophosphorus pesticides (OPPs) through a co-oxidation pathway, is important. In this study, we prepared a electrode GO/MoS2@AS by supporting MoS2 on alum sludge (AS) under graphene oxide (GO) nanoconfinement. The results show that the dominant role of 1O2 at the cathode and •OHads at the anode for degradation, in addition to the involvement of 1O2 in the cathodic degradation mechanism, can be attributed to the abundant precursor •O2- and H2O2. Furthermore, calculations using density functional theory and toxicity prediction of products show that the energy (∆E) requirements of •OHfree to break the C-O bond of the pyridine ring and phosphate group are higher than that required for 1O2, and this non-radical oxidation plays a key role in detoxification. In contrast, accelerating ring opening and oxidation processes are attributed to radical oxidation. Above all, the cathodic detoxification is more effective than anodic detoxification. Three prevalent OPPs, chlorpyrifos, glyphosate, and trichlorfon, were degraded in the GO/MoS2@AS system by over 90 %, with mineralization rates of 76.66 %, 85.46 %, and 82.18 %, respectively. This study provides insights into the co-oxidation degradation and detoxification mechanism mediated by 1O2 and •OHfree.

Sn/Sb-assisted alum sludge electrodes for eliminating hydrophilic organic pollutants in self-produced H2O2 electro-Fenton system: Insights into the co-oxidation mediated by 1O2 and •OH(ads)

Few reports have focused on using particle electrodes with polar adsorbent properties in heterogeneous electro-Fenton (EF) system to improve the degradation of hydrophilic organic pollutants (HLOPs). In this study, a hydrophilic electrode Sn-Sb/AS was prepared by supporting metals Sn and Sb on alum sludge (AS), which can effectively degrade 91.68%, 92.54%, 89.62%, and 96.24% of the four types of HLOPs, chlorpyrifos (CPF), atrazine (ATZ), diuron (DIU), and glyphosate (PMG), respectively, within 40 min. The mineralization rates were 82.37%, 78.93%, 73.98%, and 85.65% for CPF, ATZ, DIU, and PMG, respectively. Based on the analysis of Electron Paramagnetic Resonance test, quenching test, and identified anthracene endoperoxide, the degradation at the cathode was attributed to non-radical oxidation via interaction with 1O2. In contrast, the anodic oxidation occurred via direct electron transfer at the anode and/or oxidation via interaction with adsorbed •OH (•OHads) around the particle electrodes. Furthermore, the reaction sites were calculated by Density functional theory (DFT) and Fukui function, corresponding to the electrophilic attack (fA-) of 1O2 and anodic direct oxidation, besides, the radical attack (fA0) of •OH(ads). Herein, this study proposes a targeted elimination strategy for HLOPs in wastewater treatment using particle electrodes with polar adsorbent properties in EF system.

Research Progress of Ozone/Peroxymonosulfate Advanced Oxidation Technology for Degrading Antibiotics in Drinking Water and Wastewater Effluent: A Review

Nowadays, antibiotics are widely used, increasing the risk of contamination of the water body and further threatening human health. The traditional water treatment process is less efficient in degrading antibiotics, and the advanced oxidation process (AOPs) is cleaner and more efficient than the traditional biochemical degradation process. The combined ozone/peroxymonosulfate (PMS) advanced oxidation process (O3/PMS) based on sulfate radical (SO4•-) and hydroxyl radical (•OH) has developed rapidly in recent years. The O3/PMS process has become one of the most effective ways to treat antibiotic wastewater. The reaction mechanism of O3/PMS was reviewed in this paper, and the research and application progress of the O3/PMS process in the degradation of antibiotics in drinking water and wastewater effluent were evaluated. The operation characteristics and current application range of the process were summarized, which has a certain reference value for further research on O3/PMS process.

Sea Urchin-like NiCo2O4 Catalyst Activated Peroxymonosulfate for Degradation of Phenol: Performance and Mechanism

How to efficiently activate peroxymonosulfate (PMS) in a complex water matrix to degrade organic pollutants still needs greater efforts, and cobalt-based bimetallic nanomaterials are desirable catalysts. In this paper, sea urchin-like NiCo2O4 nanomaterials were successfully prepared and comprehensively characterized for their structural, morphological and chemical properties via techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), among others. The sea urchin-like NiCo2O4 nanomaterials exhibited remarkable catalytic performance in activating PMS to degrade phenol. Within the NiCo2O4/PMS system, the removal rate of phenol (50 mg L-1, 250 mL) reached 100% after 45 min, with a reaction rate constant k of 0.091 min-1, which was 1.4-times higher than that of the monometallic compound Co3O4/PMS system. The outstanding catalytic activity of sea urchin-like NiCo2O4 primarily arises from the synergistic effect between Ni and Co ions. Additionally, a comprehensive analysis of key parameters influencing the catalytic activity of the sea urchin-like NiCo2O4/PMS system, including reaction temperature, initial pH of solution, initial concentration, catalyst and PMS dosages and coexisting anions (HCO3-, Cl-, NO3- and humic acid), was conducted. Cycling experiments show that the material has good chemical stability. Electron paramagnetic resonance (EPR) and quenching experiments verified that both radical activation (SO4•-, •OH, O2•-) and nonradical activation (1O2) are present in the NiCo2O4/PMS system. Finally, the possible degradation pathways in the NiCo2O4/PMS system were proposed based on gas chromatography-mass spectrometry (GC-MS). Favorably, sea urchin-like NiCo2O4-activated PMS is a promising technology for environmental treatment and the remediation of phenol-induced water pollution problems.

SnS2/MWNTs/sponge electrode combined with plasma dielectric barrier discharge catalytic system: CO2 reduction and pollutant degradation

SnS2 nanosheets combined with multi-walled carbon nanotubes (MWNTs) were made into sponge electrodes which were used for CO2 reduction reaction (CO2RR) in dielectric barrier discharges (DBD) system. The amounts of formate and formaldehyde produced by CO2 reduction with SnS2/MWNTs/sponge electrode were 299.52 and 31.62 μmol h-1, which were higher than that of MWNTs/sponge electrodes. The addition of pollutants had different degrees of inhibitory effect on CO2 reduction, among which addition of bisphenol A (BPA) had the smallest effect that the degradation rate of BPA was 94.37% and the C1 products remained 204.43 μmol after 60 min discharge. The mechanism of CO2RR was studied by quencher experiment, and the main contribution order of the active substance in DBD system for CO2RR is: H+>e->·OH>·O2-. It was found that the degradation process of pollutants consumed H+ and e- in solution, thereby inhibiting CO2RR. Generally, the SnS2/MWNTs/sponge electrode provided a reference for the design of catalysts for CO2 reduction and pollutant degradation in plasma gas-liquid system.

An Integrated Electrochemical System for Synergistic Cathodic Nitrate Reduction and Anodic Sulfite Oxidation

Electrochemical reduction of nitrate has broad application prospects. However, in traditional electrochemical reduction of nitrate, the low value of oxygen produced by the anodic oxygen evolution reaction and the high overpotential limit its application. Seeking a more valuable and faster anodic reaction to form a cathode-anode integrated system with nitrate reaction can effectively accelerate the reaction rate of the cathode and anode, and improve the utilization of electrical energy. Sulfite, as a pollutant after wet desulfurization, has faster reaction kinetics in its oxidation reaction compared to the oxygen evolution reaction. Therefore, this study proposes an integrated cathodic nitrate reduction and anodic sulfite oxidation system. The effect of operating parameters (cathode potential, initial NO₃^--N concentration, and initial SO₃^2--S concentration) on the integrated system was studied. Under the optimal operating parameters, the nitrate reduction rate in the integrated system reached 93.26% within 1 h, and the sulfite oxidation rate reached 94.64%. Compared with the nitrate reduction rate (91.26%) and sulfite oxidation rate (53.33%) in the separate system, the integrated system had a significant synergistic effect. This work provides a reference for solving nitrate and sulfite pollution, and promotes the application and development of electrochemical cathode-anode integrated technology.

Three-dimensional structured electrode for electrocatalytic organic wastewater purification: Design, mechanism and role

Considering the growing need in decentralized water treatment, the application of electrocatalytic processes (EP) to achieve organic wastewater purification will be dominant in the near future due to high efficiency, small reactor assembly as well as the flexibility of operation and management. The catalytic performance of electrode materials determines the development of this technology. Among them, the unique three-dimensional (3D) structure electrode shows better performance than two-dimensional (2D) electrode in increasing mass transfer, enhancing adsorption and exposing more active sites. Hence, this review starts with the introduction of definition, classification, advantages and disadvantages of 3D electrode materials. Then a critical discussion on the design and construction of 3D electrode materials for organic wastewater purification application is provided. Next, the removal mechanism of organic pollutants on the surface of 3D electrode, the role of 3D structure, the design of reactor with 3D electrode, the conversion and toxicity of degradation products, electrode energy efficiency, stability and cost, are comprehensively reviewed. At last, current challenges and future perspectives for the development of 3D electrode materials are addressed. We deem that this review will provide a valuable insight into the design and application of 3D electrodes in environmental water purification.

Electro-reduction Induced Fast Metal Redox Cycle on Co3O4-CuO@CNTs/Copper Foam Cathode for Enhanced Fenton-like Reaction

In this study, free-standing Co₃O₄-CuO/CF electrodes are synthesized via an electrodeposition-annealing process and then protected by dip-coated carbon nanotubes (CNTs). The obtained Co₃O₄-CuO@CNTs/CF is employed as cathode to activate peroxymonosulfate (PMS) for the degradation of Bisphenol A (BPA) in an electrochemical system. The electrochemical assistant (EA) plays a critical role to accelerate metal redox by donating electrons sustainably, and the fast regeneration of Co²⁺/Cu⁺ could be achieved to promote chemical-catalysis for PMS activation, which is proved via the pre-electroreduction treatment. The rate constant of Co₃O₄-CuO@CNTs/CF/PMS system with EA is ∼ 4.4 times compared to the system without EA. It also exhibits an excellent stability, which could still remove over 90% of BPA after eight cycles in 45 min. In addition, the coating of CNTs could decrease leaching of metals effectively. According to quenching tests and electron spin-resonance spectroscopy (ESR), the presence of EA could enhance the radical route by producing more SO₄^•- and •OH greatly, which is also proved by much faster degradation of carbamazepine (CBZ) and atrazine (ATZ) than that without EA. This work reveals activation mechanism of PMS in the electrochemical system, and provides an effective strategy to achieve the fast metal redox cycle for effective and long-term pollutant degradation.

Coupling Value-Added Anodic Reactions with Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction features a promising approach to realize carbon neutrality. However, its competitiveness is limited by the sluggish oxygen evolution reaction (OER) at anode, which consumes a large portion of energy. Coupling value-added anodic reactions with CO₂ electroreduction has been emerging as a promising strategy in recent years to enhance the full-cell energy efficiency and produce valuable chemicals at both cathode and anode of the electrolyzer. This review briefly summarizes recent progresses on the electrocatalytic CO₂ reduction, and the economic feasibility of different CO₂ electrolysis systems is discussed. Then a comprehensive summary of recent advances in the coupled electrolysis of CO₂ and potential value-added anodic reactions is provided, with special focus on the specific cell designs. Finally, current challenges and future opportunities for the coupled electrolysis systems are proposed, which are targeted to facilitate progress in this field and push the CO₂ electrolyzers to a more practical level.

Sensitive detection of 4-nitrophenol based on pyridine diketopyrrolopyrrole-functionalized graphene oxide direct electrochemical sensor

For highly sensitive detection of 4-nitrophenol (4-NP) in the environment, a novel pyridine diketopyrrolopyrrole-functionalized graphene oxide (PDPP-GO) composite was constructed for the first time by an improved Hummers' method. Herein, PDPP was completely dissolved in sulfuric acid (6 mol L^-1) and reacted with GO, promoting PDPP evenly adhering to the GO surface. Moreover, the specific surface area increased from 15.51 to 22.033 m² g^-1. Infrared spectroscopy and X-ray photoelectron spectroscopy simultaneously demonstrated that PDPP was bound to GO by the strong intermolecular hydrogen bonding and π-π stacking conjugation. During the cyclic voltammetry test, the PDPP-GO coated glassy carbon electrode (PDPP-GO/GCE) direct electrochemical sensor gave expression to the best electrocatalytic activity for 4-nitrophenol detection than GO/GCE and bare GCE. Under optimization conditions, the as-prepared PDPP-GO/GCE sensor brought out remarkable sensitivities of 18.54 (0.5-50 μM) and 6.61 μA μM^-1 cm^-2 (50-163 μM) in the linear detection of 4-NP. Besides, a low detection limit of 0.10 μM, reliable long-term stability, excellent selectivity, and reproducibility were obtained. In the real sample test, the PDPP-GO/GCE demonstrated sensitive and reliable determination.

Bicarbonate enhanced heterogeneous activation of peroxymonosulfate by copper ferrite nanoparticles for the efficient degradation of refractory organic contaminants in water

Nowadays, the treatment of residual refractory organic contaminants (ROCs) is a huge challenge for environmental remediation. In this study, a potential process is provided by copper ferrite catalyst (CuFe₂O₄) activated peroxymonosulfate (PMS, HSO₅^-) in the bicarbonate (HCO₃^-) enhanced system for efficient removal of Acid Orange 7 (AO7), 2,4-dichlorophenol, phenol and methyl orange (MO) in water. The impact of key reaction parameters, water quality components, main reactive oxygen species (ROS), probable degradation mechanism, rational degradation pathways and catalyst stability were systematically investigated. A 95.0% AO7 (C₀ = 100 mg L^-1) removal was achieved at initial pH (pH₀) of 5.9 ± 0.1 (natural pH), CuFe₂O₄ dosage of 0.15 g L^-1, PMS concentration of 0.98 mM, HCO₃^- concentration of 2 mM, and reaction time of 30 min. Both sulfate radical (SO₄^-•) and hydroxyl radical (^•OH) on the surface of catalyst were proved as the predominant radical species through radical quenching experiments and electron paramagnetic resonance (EPR) analysis. The buffer nature of HCO₃^- was partially contributed for the enhanced degradation of AO7 under CuFe₂O₄/PMS/HCO₃^- system. Importantly, according to ¹³C nuclear magnetic resonance (NMR) and EPR analysis, the positive effect of bicarbonate may be mainly attributed to the formation of peroxymonocarbonate (HCO₄^-), which may enhance the generation of ^•OH. The magnetic CuFe₂O₄ particles can be well recycled and the leaching concentration of Cu was acceptable (<1 mg L^-1). Considering the widespread presence of bicarbonate in water environment, this work may provide a safe, efficient, and sustainable technique for the elimination of ROCs from practical complex wastewater.

Energy-efficient electrochemical treatment of paracetamol using a PbO2 anode based on pulse electrodeposition strategy: Kinetics, energy consumption and mechanism

The purpose of this research is to study the pulse electrochemical oxidation of paracetamol (PCT) using a novel PbO₂ anode based on pulse electrodeposition strategy (PbO₂-PE). The pulse electrodeposition strategy used to prepare a PbO₂ anode resulted in rougher surface, higher directional specificity of β(101) and more redox couples of Pb⁴⁺/Pb²⁺. Additionally, the oxygen evolution potential (OEP) and charge transfer resistance were also improved. When compared to direct current electrochemical oxidation process, pulse electrolysis in had a slightly higher PCT removal efficiency and active species (·OH and active chlorine) production, while 72.04% of energy consumption was saved. The effects of operating parameters on PCT degradation efficiency and specific energy consumption were studied. The findings suggested that the pulse electrochemical oxidation of PCT followed a pseudo-first-order kinetic model, with PCT removal reaching 98.63% after 60 min of electrolysis under optimal conditions. Possible mechanisms describing reaction pathways for PCT were also proposed. Finally, combinating with the economic feasibility and safety evaluation, we could conclude that pulse electrolysis with a PbO₂-PE electrode was a promising option for improving the practicability of electrochemical treatment for refractory organic wastewater.

Integrating adsorption and in situ advanced oxidation for the treatment of organic wastewater by 3D carbon aerogel embedded with Fe-doped carbonitrides

Wastewater containing organic pollutants with high toxicity and poor biodegradability poses a considerable threat to human health and the ecosystem. Although adsorption and advanced oxidation processes (AOPs) are currently the most widely used technologies for wastewater treatment, limitations of these two independent processes make the treatment effect unsatisfactory. Herein, a system of integrating adsorption and subsequent in situ AOPs is established by a 3D carbon aerogel embedded with Fe-doped carbonitrides (Fe-NC/CAG). The SEM and BET analysis demonstrate that Fe-NC/CAG possesses porous structures with a specific surface area of 518.7 m²/g. The XRD result indicates the formation of Fe⁰ and Fe₃O₄ in Fe-NC/CAG. The impacts of operational parameters such as Fe-NC/CAG dosage, pollutants concentration, temperature, initial pH, and inorganic ions on the adsorption efficiency are investigated. The adsorption kinetics is predominantly based on the pseudo-second-order model. After adsorbing organic pollutants, the Fe-NC/CAG is immersed in peroxymonosulfate (PMS) solution. The adsorbed pollutants are in situ degraded by PMS-based AOPs, leading to the regeneration of Fe-NC/CAG. At optimum conditions, the integrating process established by Fe-NC/CAG achieves over 90% removal of antibiotics, phenolics, and dyes as well as keeps stable performance even after 6 cycles. This integrating adsorption and AOPs system is expected to open up a rich field for wastewater treatment.

Ecofriendly Green Synthesis of Copper (II) Oxide Nanoparticles Using Corchorus olitorus Leaves (Molokhaia) Extract and Their Application for the Environmental Remediation of Direct Violet Dye via Advanced Oxidation Process

In this research, copper (II) oxide nanoparticles were prepared by an ecofriendly green method using the extract of corchorus olitorus leaves (Molokhaia) as a surfactant, capping and anti-agglomeration agent. The ecofriendly green CuO NPs were characterized using different chemical and physical techniques and the results confirmed the formation of monoclinic tenorite CuO nanoparticles with an average particle size of 12 nm and BET surface area of 11.1 m²/g. The eco-friendly green CuO NPs were used in environmental remediation for the efficient catalytic degradation of direct violet dye via advanced oxidation process (AOP) in presence of H₂O₂. The impact of AOP environmental parameters affecting the degradation process was investigated. Moreover, the catalytic degradation of the direct violet dye using the ecofriendly green CuO NPs was studied kinetically and thermodynamically and the results showed that the catalytic degradation process agreed well with the pseudo-second-order kinetic model and the process was spontaneous and endothermic in nature. Finally, high catalytic degradation of the direct violet dye was observed when the eco-friendly prepared green CuO NPs were placed in real water samples.

Synergistically interactive P-Co-N bonding states in cobalt phosphide-decorated covalent organic frameworks for enhanced photocatalytic hydrogen evolution

Non-noble materials with high efficiency and stability are essential for renewable energy applications. Herein, cobalt phosphide nanoparticles-decorated covalent organic frameworks (CTF-CoP) are synthesized via an in situ self-assembly method combined with the calcination process. In such a configuration, an intimate interaction between CoP and CTF matrix is gained through the Co-N chemical bonds, which not only significantly enhance the recyclability of CoP nanoparticles but also significantly improve the charge separation efficiency. Besides, the synergistically interactive P^δ--Co^δ+-N^δ- states induced by the polarization effect of N-anchoring sites benefit for the adsorption and dissociation of water molecules in CTF-CoP. Consequently, CTF-CoP exhibits a higher photocatalytic hydrogen evolution rate (261.7 μmol g^-1 h^-1) and better durability as compared with the physically fixed CTF/CoP composite (64.8 μmol g^-1 h^-1) and even the noble metal-based CTF-Pt (191.3 μmol g^-1 h^-1). This work provides an avenue to construct highly stable non-noble photocatalyst for energy conversion and also emphasizes the potential of CTFs in constructing efficient heterojunctions.

Anthraquinone acted as a catalyst for the removal of triphenylmethane dye containing tertiary amino group: Characteristics and mechanism

Herein, we found that anthraquinone (AQ) acted as a catalyst for the rapid and effective removal of triphenylmethane dye containing tertiary amino group (TDAG). Results showed that AQ had an enhanced catalytic reactivity towards the removal of TDAG compared to hydro-quinone, which was further proved and explained using density functional theory (DFT) calculations. AQs could achieve a TDAG removal efficiency and rate of approximately 100% and 0.3583 min^-1, respectively, within 20 min. Quenching experiments and electron paramagnetic resonance (EPR) tests indicated that the superoxide radical (O₂^•-) generated through the catalytic reduction of an oxygen molecule (O₂) by AQ contributed to the effective removal of the TDAG. In addition, it was found that the electrophilic attack of the O₂^•- radical on the TDAG was the driving force for the dye degradation process. Decreasing the pH led to protonation of the substituted group of AG, which resulted in formation of an electron deficient center in the TDAG molecule (TDAG-EDC⁺) through delocalization of the π electron. Therefore, the possibility of the electrophilic attack for the dye by the negative O₂^•- radical was significantly enhanced. This study revealed that the H⁺ and the O₂^•- generated by the catalytic reduction of O₂ have synergistic effects that led to a significant increase in the dye removal rate and efficiency, which were higher than those obtained through persulfate oxidation.

Efficient electro-catalyzed PMS activation on a Fe-ZIF-8 based BTNAs/Ti anode: An in-depth investigation on anodic catalytic behavior

Phenanthrene (PHE), mainly released from coal tar and petroleum distillation, is an important kind of prevalent polycyclic aromatic hydrocarbons (PAHs) contamination in China (up to 2.38 ± 0.02 mg/kg in soil and 8668 ng/L in surface water) and other countries in the world. Metal-organic frameworks (MOFs) show promising application prospects in the decontamination field, however, suffering from the intrinsic fragility and fine powder forms. Therefore, macroscopic MOFs architecture-sandwich-like Fe-ZIF-8/blue TiO₂ nanotube arrays (BTNAs)/Ti substrate (FBTT) anode with strong interfacial bonding (Fe-O-Ti and Fe-2-MIM-Ti coordination) was constructed using innovative in situ growth, condensation-crystallization-deposition, and pyrolysis methods, aiming at exploring the feasibility of MOFs-based anode/peroxymonosulfate (PMS) mediated PHE elimination, revealing the in-depth mechanisms, simultaneously overcoming the intrinsic drawbacks of MOFs. The FBTT-4 (doping content of 30 %) efficiently degraded PHE by 90.01 % and 74.5 % within 10 min at 350 μg/L and 3 mg/L, respectively, mediated by the ^·OH compared to the SO₄^·-, ¹O₂, and O₂^·-. Post-optimized range of anodic potential enabled (i) anodic oxidation, (ii) activation of water and PMS molecules to produce active species, (iii) capture of electrons in reactants to reduce Fe³⁺/Ti⁴⁺ to Fe²⁺/Ti³⁺, maintaining the proportion of Fe/Ti with low valence and thus stable PMS activation capacity, and (iv) regulation of the Fe/Ti d-band center to modulate the anode adsorption capacity. The further increment in anodic potential could promote "dark photocatalysis" with a Z-scheme-like mechanism. Thus, it is proposed that the development of macroscopic MOFs-based anode, especially those with small band gaps, represents vast potentials in electrocatalytic contamination elimination. Simultaneously, the MOFs-based anode is expected to fully exploit their catalytic capacities and solve their intrinsic defects as well.

Electro-Induced Carbon Nanotube Discrete Electrodes for Sustainable Persulfate Activation

In electrochemical advanced oxidation processes (EAOPs), the rate-limiting step is the mass transfer of pollutants to the electrodes due to the limited active surface areas. To this end, we established a three-dimensional (3D) EAOP system by coupling conventional graphite electrodes with dispersed carbon nanotubes (CNTs). The electrodes (particularly the anode) induced electric field spontaneously polarized CNTs into dispersed reactive particle electrodes (CNT-PEs) in the solution, which remarkably promoted electrochemical activation of peroxydisulfate (PDS) to generate surface CNT-PDS* complexes and surface-bound radicals (SBRs). Based on the excited potential (E_CNT-PEs) at different positions in the 3D electric field, CNT-PEs were activated into three states. (i) E_CNT-PEs < E_organic, CNT-PEs are chemically inert toward DCP oxidation; (ii) E_organic < E_CNT-PEs < E_water, CNT-PEs will oxidize DCP via an electron-transfer process (ETP); (iii) E_CNT-PEs > E_water, both CNT-PDS* complexes and the anode will oxidize water to produce SBRs. Thus, DCP could be oxidized by CNT-PDS* complexes via ETP to form polychlorophenols on the CNT surface, causing rapid deactivation of the micro-electrodes. In contrast, SBRs attack DCP directly into chloride ions and hydroxylated products, maintaining the surface cleanliness and activity of CNT-PEs for long-term operations.

Heterogeneous Metal-Activated Persulfate and Electrochemically Activated Persulfate: A Review

The problem of organic pollution in wastewater is an important challenge due to its negative impact on the aquatic environment and human health. This review provides an outline of the research status for a sulfate-based advanced oxidation process in the removal of organic pollutants from water. The progress for metal catalyst activation and electrochemical activation is summarized including the use of catalyst-activated peroxymonosulfate (PMS) and peroxydisulfate (PDS) to generate hydroxyl radicals and sulfate radicals to degrade pollutants in water. This review covers mainly single metal (e.g., cobalt, copper, iron and manganese) and mixed metal catalyst activation as well as electrochemical activation in recent years. The leaching of metal ions in transition metal catalysts, the application of mixed metals, and the combination with the electrochemical process are summarized. The research and development process of the electrochemical activation process for the degradation of the main pollutants is also described in detail.

Controllable States and Porosity of Cu-Carbon for CO2 Electroreduction to Hydrocarbons

The electrocatalytic carbon dioxide reduction reaction (CO₂ RR) to value-added chemical products is an effective strategy for both greenhouse effect mitigation and high-density energy storage. However, controllable manipulation of the oxidation state and porous structure of Cu-carbon based catalysts to achieve high selectivity and current density for a particular product remains very challenging. Herein, a strategy derived from Cu-based metal-organic frameworks (MOFs) for the synthesis of controllable oxidation states and porous structure of Cu-carbon (Cu-pC, Cu₂ O-pC, and Cu₂ O/Cu-pC) is demonstrated. By regulating oxygen partial pressure during the annealing process, the valence state of the Cu and mesoporous structures of surrounding carbon are changed, leads to the different selectivity of products. Cu₂ O/CuO-pC with the higher oxidation state exhibits FE_C2H4 of 65.12% and a partial current density of -578 mA cm^-2 , while the Cu₂ O-pC shows the FE_CH4 over 55% and a partial current density exceeding -438 mA cm^-2 . Experimental and theoretical studies indicate that porous carbon-coated Cu₂ O structures favor the CH₄ pathway and inhibit the hydrogen evolution reaction. This work provides an effective strategy for exploring the influence of the various valence states of Cu and mesoporous carbon structures on the selectivity of CH₄ and C₂ H₄ products in CO₂ RR.

Rapid purification of As(III) in water using iron-manganese composite oxide coupled with sulfite: Importance of the SO5•- radicals

Manganese (Mn)-containing composite metal adsorbents are very effective at removing arsenite (As(III)) from contaminated water, however, the low removal speed and oxidation efficiency have limited their further application. In this study, a nonhomogeneous catalytic oxidation-adsorption system was constructed by coupling iron-manganese composite oxide (FeMnO_x) with sulfite (S(IV)) to enhance the recovery of oxidative capacity and accelerate the removal of As(III). Experimental results showed that the FeMnO_x/S(IV) system decreased the As(III) concentration from 1079 to <10 µg/L within 10 min and almost completely oxidized As(III) to As(V). In contrast, FeMnO_x alone removed only 82.4% of As(III) within 30 min, and 60.0% of the adsorbed As(III) was not oxidized. Meanwhile, the adsorption capacity of FeMnO_x/S(IV) system for As(III) was considerably higher than that of the only-FeMnO_x system (76.5 > 46.3 mg/g). The efficient and fast As(III) removal was attributed to the SO₅^•- radical generated by S(IV) acting as the driving force for the redox cycle between As(III) and Mn(II/III/IV). Several environmental factors (e.g., solution pH and inorganic anions) and the reusability and practicality of FeMnO_x were systematically investigated, and the results further confirmed the superiority of the FeMnO_x/S(IV) system in As(III) removal. In particular, the proposed FeMnO_x nanocellulose aerogel effectively purified arsenic-contaminated groundwater using a fixed-bed column. Thus, FeMnO_x-S(IV) coupling is very promising for the purification of arsenic-contaminated water bodies.

Remediation of pesticides using TiO2 based photocatalytic strategies: A review

Nowadays, pesticides are regarded as the most dangerous of the various organic pollutants, posing substantial environmental and human threats worldwide. Pesticide contamination has become one of the most crucial environmental issues due to its bio-persistence and bioaccumulation. Different conventional methods are being utilized for pesticide removal, yet pesticides are thought to be significantly present in the environment. The development and application of sophisticated wastewater treatment methods are being pursued to remove contaminants effectively, particularly pesticides. In the past several decades, nanoscience and nanotechnology have emerged as essential tools for the identification, removal, and mineralization of persistent pesticides by employing advanced nanomaterials such as pristine titanium dioxide (TiO₂), doped TiO₂, nanocomposites (NCs) TiO₂, and ternary nanocomposites (TNCs) TiO₂ by advanced oxidation processes (AOPs). Advancement in the characteristics of TiO₂ by doping, co-doping, construction of NCs and TNCs has contributed to the dramatic efficiency up-gradation by reducing band gap, solar active photocatalyst, enhancing PCA, high photostability, chemically inertness and multiple time reusability. Based on previous literature, utilizing La-TiO₂ NCs photocatalyst, the mineralization of pesticide (imidacloprid) attained up to 98.17% that is almost 40-53% greater than pristine TiO₂. The present review attempt to discuss the recent research performed on TiO₂ based nanoparticles (NPs) and NCs for photocatalytic mineralization of various pesticides. The basic mechanism of TiO₂ photocatalysis, types of reactors used for photocatalysis, and optimized experimental conditions of TiO₂ for pesticides mineralization are discussed.

Defective MOFs-based electrocatalytic self-cleaning membrane for wastewater reclamation: Enhanced antibiotics removal, membrane fouling control and mechanisms

In order to resolve the poor antibiotics rejection and serious fouling of ultrafiltration (UF) membrane during municipal wastewater reclamation, a novel anodic membrane (defective UiO-66 (D-UiO-66)/Graphite/Polyvinylidene fluoride (PVDF)) with high pure water flux (596.1 L•h ^- 1•m ^- 2•bar^-1) was fabricated by incorporating defective zirconium based metal-organic framework (D-UiO-66) and conductive graphite particles into PVDF matrix and applied in the coupling of electro-oxidation and membrane filtration process. Compared to the other anodic membranes (i.e., Graphite/PVDF and UiO-66/Graphite/PVDF), D-UiO-66/Graphite/PVDF possesses superior anti-fouling and self-cleaning abilities (flux recovery=100%, model foulant: bovine serum albumin) in both intermittent and continuous supply of electric field under current density of 0.01 mA/cm²; moreover, efficient antibiotics (tetracycline, norfloxacin, tylosin and sulfamethoxazole) removal (> 96.6%) and bactericidal efficiency against E. coli and S. aureus (100%) were achieved simultaneously without the addition of chemical reagents due to the higher electrocatalytic activity of anodic membrane for oxidation of pollutants by •OH and •O₂^- free radicals. Three degradation pathways of antibiotics were proposed and the self-cleaning mechanism of membrane was dominated by the synergy of the partial mineralization and the reduced fouling potential of foulants after oxidation as revealed by the increase in hydrophilicity, and decrease in negative charge and molecular weight. The fabricated membrane also presents excellent electrochemical stability, separation and self-cleaning performance for treatment of municipal secondary effluent during long-term filtration with low electric energy consumption, which is promising in wastewater reclamation.

The Potential Strategies of ZnIn2S4-Based Photocatalysts for the Enhanced Hydrogen Evolution Reaction

Photocatalysis is a potential strategy to solve energy and environmental problems. The development of new sustainable photocatalysts is a current topic in the field of photocatalysis. ZnIn2S4, a visible light-responsive photocatalyst, has attracted extensive research interest in recent years. Due to its suitable band gap, strong chemical stability, durability, and easy synthesis, it is expected to become a new hot spot in the field of photocatalysis in the near future. This mini-review presents a comprehensive summary of the modulation strategies to effectively improve the photocatalytic activity of ZnIn2S4 such as morphology and structural engineering, defects engineering, doping engineering, and heterojunction engineering. This review aims to provide reference to the proof-of-concept design of highly active ZnIn2S4-based photocatalysts for the enhanced hydrogen evolution reaction.

Construction of a new type of three-dimensional honeycomb-structure anode in microbial electrochemical systems for energy harvesting and pollutant removal

Electrode materials occupy most of the construction cost of the microbial electrochemical system (MES), and the low mechanical strength and poor electrochemical performance of the commonly used traditional carbon-based materials restrict the promotion and application of this technology. In this study, polymer-based three-dimensional (3D) honeycomb-structure (HS) materials with good mechanical properties were used as supporting materials. Graphene (GR), carbon nanotube (CNT), and polypyrrole (PPy) was separately chosen as a surface conductivity coating layer for preparing MES anodes. The introduction of GR, CNT, and PPy on HS increased surface roughness, hydrophilicity, O and N content, electrochemically active surface area, and decreased charge transfer internal resistance, which promoted the adhesion of microorganisms on their surface and enhanced the extracellular electron transfer process at the electrode/microbe interface. The CNT-HS anode system got the better maximal power density (1700.7 ± 149.0 mW/m²) of the three modified anode systems and 3.60 times that of MES using CC (471.8 ± 27.2 mW/m²) as the anode. The accelerated reactions of the redox species in the outer cell membrane, the promoted electron shuttle secretion, and the enhanced abundance of the tricarboxylic acid cycle-related functional genes in biofilm led to better performance of the CNT-HS anode system. The CNT-HS anode system also exhibited long-term operational stability (>6 months) and a good chemical oxygen demand degradation effect. Furthermore, CNT-HS material exhibited its cost advantage, and its projected cost is estimated to be about $1.8/m², much lower than the currently used MES anodes ($8.2-548.2/m²). Considering the good mechanical properties, simple preparation process, low manufacturing cost, long-term stability, excellent bio-electrochemical performance, and good pollutant removal ability, HS-based anode has promising potential for high-performance MES in applications.

Hydroxyl radicals in anodic oxidation systems: generation, identification and quantification

Anodic oxidation has emerged as a promising treatment technology for the removal of a broad range of organic pollutants from wastewaters. Hydroxyl radicals are the primary species generated in anodic oxidation systems to oxidize organics. In this review, the methods of identifying hydroxyl radicals and the existing debates and misunderstandings regarding the validity of experimental results are discussed. Consideration is given to the methods of quantification of hydroxyl radicals in anodic oxidation systems with particular attention to approaches used to compare the electrochemical performance of different anodes. In addition, we describe recent progress in understanding the mechanisms of hydroxyl radical generation at the surface of most commonly used anodes and the utilization of hydroxyl radical in typical electrochemical reactors. This review shows that the key challenges facing anodic oxidation technology are related to i) the elimination of mistakes in identifying hydroxyl radicals, ii) the establishment of an effective hydroxyl radical quantification method, iii) the development of cost effective anode materials with high corrosion resistance and high electrochemical activity and iv) the optimization of electrochemical reactor design to maximise the utilization efficiency of hydroxyl radicals.

Mineralization of cyanides via a novel Electro-Fenton system generating •OH and •O2. WATER RESEARCH 2022;209:117890. [PMID: 34856430 DOI: 10.1016/j.watres.2021.117890]

Traditional methods of cyanides' (CN-) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO-) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2-. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2- were simultaneously generated and 92.9% of free cyanides were transformed into NO3- within 120 min. No low-toxic CNO- intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN- was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2- via nucleophilic addition to quickly form NO3-, preventing the formation of CNO- and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.

Targeted degradation of refractory organic compounds in wastewaters based on molecular imprinting catalysts

Efficient removal of low-concentration refractory pollutants is a crucial problem to ensuring water safety. The use of heterogeneous catalysis of molecular imprinting technology combined with traditional catalysts is a promising method to improve removal efficiency. Presently, the research into molecular imprinting targeting catalysts focuses mainly on material preparation and performance optimization. However, more researchers are investigating other applications of imprinting materials. This review provides recent progress in photocatalyst preparation, electrocatalyst, and Fenton-like catalysts synthesized by molecular imprinting. The principle and control points of target catalysts prepared by precipitation polymerization (PP) and surface molecular imprinting (S-MIP) are introduced. Also, the application of imprinted catalysts in targeted degradation of drugs, pesticides, environmental hormones, and other refractory pollutants is summarized. In addition, the reusability and stability of imprinted catalyst in water treatment are discussed, and the possible ecotoxicity risk is analyzed. Finally, we appraised the prospects, challenges, and opportunities of imprinted catalysts in the advanced oxidation process. This paper provides a reference for the targeted degradation of refractory pollutants and the preparation of targeted catalysts.

Review on application of perylene diimide (PDI)-based materials in environment: Pollutant detection and degradation

Environment pollution is getting serious and various poisonous contaminants with chemical durability, biotoxicity and bioaccumulation have been widespreadly discovered in municipal wastewaters and surface water. The detection and removal of pollutants show great significance for the protection of human health and other organisms. Due to its distinctive physical and chemical properties, perylene diimide (PDI) has received widespread attention from different research fields, especially in the area of environment. In this review, a comprehensive summary of the development of PDI-based materials in fluorescence detection and advanced oxidation technology for environment was introduced. Firstly, we chiefly presented the recent progress about the synthesis of PDI and PDI-based nanomaterials. Then, their application in fluorescence detection for environment was presented and categorized, principally including the detection of heavy metal ions, harmful anions and organic contaminants in the environment. In addition, the application of PDI and PDI-based materials in different advanced oxidation technologies for environment, such as photocatalysis, photoelectrocatalysis, Fenton and Fenton-like reaction and persulfate activation, was also summarized. At last, the challenges and future prospects of PDI-based materials in environmental applications were discussed. This review focuses on presenting the practical applications of PDI and PDI-based materials as fluorescent probes or catalysts (especially photocatalysts) in the detection of hazardous substances or catalytic elimination of organic contaminants. The contents are aimed at supplying the researchers with a deeper understanding of PDI and PDI-based materials and encouraging their further development in environmental applications.

Selective and Adjustable Removal of Phenolic Compounds from Water by Biquaternary Ammonium Polyacrylonitrile Fibers

A series of biquaternary ammonium-functionalized fibers were developed to efficiently realize selective removal of phenolic compounds from water. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to determine the successful preparation of functionalized fibers. Scanning electron microscopy, X-ray diffraction (XRD) patterns, and elemental analysis were used to analyze the microstructure and composition. First, the adsorption result shows that a fiber with a three-carbon alkyl chain (PAN_BQAS-3F) has the maximum adsorption capacity for 2,4-dinitrophenol (2,4-DNP) (406 mg g^-1). Electrostatic attraction and π-π interaction are the main forces in adsorption. The adsorption kinetics studies display that PAN_BQAS-3F can rapidly adsorb 2,4-DNP in 10 min and achieve equilibrium within 20 min. The adsorption process of 2,4-DNP by PAN_BQAS-3F follows the Langmuir model, demonstrating that the process is more consistent with monolayer adsorption. What is more, the adsorbent PAN_BQAS-3F can be reused after 10 adsorption/desorption cycles and still maintains an excellent removal rate (99%). Otherwise, PAN_BQAS-3F was used in a continuous flow process and exhibited a removal rate of more than 96%, which certifies that PAN_BQAS-3F is an excellent adsorbent and can be utilized in practice.

Flow anodic oxidation: Towards high-efficiency removal of aqueous contaminants by adsorbed hydroxyl radicals at 1.5 V vs SHE

Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising water treatment alternative but major breakthroughs are still needed in order for EAOPs to be competitive with traditional treatment technologies in terms of energy cost. Most existing studies have been conducted at high potentials to generate the powerful hydroxyl radical oxidant (aqueous •OH). While adsorbed hydroxyl radicals (OH*) may form at a much lower energy cost, their possible utilization is limited due to the poor mass transfer of this highly reactive species on solid electrodes. In this report, we describe a novel flow anode system using 4-16 μm Magnéli phase titanium suboxide particles as the anode material which enables the generation of a high steady state •OH concentration (5.4 × 10^-12 mol m^-2) at only 1.5 V (vs SHE) in a dilute electrolyte (5 mM KH₂PO₄). The energy cost of removal per order of selected water contaminants (tetracycline and orange II in this study) using the flow anode is 1.5--6.7 Wh m^-3, which is 1 - 4 orders of magnitude lower than that of existing techniques. The anode material used demonstrates great stability with the configuration readily scaled up. The results of this study provide new insight into a high efficiency, low cost water treatment technology for organic contaminant degradation.

In situ chloride-mediated synthesis of TiO2 thin film photoanode with enhanced photoelectrochemical activity for carbamazepine oxidation coupled with simultaneous cathodic H2 production and CO2 conversion to fuels

This study investigated the simultaneous photoelectrochemical (PEC) degradation of carbamazepine (CBZ), reduction of CO₂ and production of H₂ using a TiO₂ thin film as photoanode and Ag plate as cathode. The photoanode was fabricated using sequential hydrothermal and calcination processes. The use of chloride during the hydrothermal process enhanced formation of oxygen vacancies and defects on the TiO₂ surface. Calcination not only further strengthened those features but also enhanced the crystallinity and anatase/rutile ratio, endowing the TiO₂ photoanode with superior PEC capacity. Characterization of physicochemical and PEC properties revealed that photogenerated electrons-holes were rapidly generated and efficiently separated on the TiO₂ surface during the PEC process. Hydroxyl radicals were the main active species responsible for anodic oxidation of carbamazepine, while hydrogen radicals and carbon dioxide radical anions mediated CO₂ reduction and H₂ production in the cathodic process. This work confirms the suitability of the prepared TiO₂ photoanode for PEC degradation of organic pollutants coupled with CO₂ reduction and H₂ production.

Microwave-Assisted Synthesis of CuO Nanoparticles Using Cordia africana Lam. Leaf Extract for 4-Nitrophenol Reduction

Copper-oxide-based nanomaterials play an important role as a low-cost alternative to nanoparticles of precious metals for the catalytic reduction of 4-nitrophenols. In this study, CuO nanoparticles were synthesized by a microwave-assisted method using Cordia africana Lam. leaf extract for reduction or stabilization processes. The synthesized CuO nanoparticles (NPs) were characterized using X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The analysis indicated that nanocrystals of the monoclinic CuO phase having a cluster of agglomerated morphology with a crystallite size of about 9 nm were synthesized. We also evaluated the catalytic performance of CuO NPs against 4-nitrophenol (4-NP) reduction. The catalyst has shown excellent performance completing the reaction within 12 min. Furthermore, the performance of CuO NPs synthesized at different pH values was investigated, and results indicated that the one synthesized at pH 7 reduced 4-NP effectively in shorter minutes compared to those obtained at higher pH values. The CuO NPs synthesized using Cordia africana Lam. leaf extract exhibited a better reducing capacity with an activity parameter constant of 75.8 min−1·g−1. Thus, CuO synthesized using Cordia africana Lam. holds a potential application for the catalytic conversion of nitroarene compounds into aminoarene.

Synergistic multiple active species driven fast estrone oxidation by δ-MnO2 in the existence of methanol

Endocrine-disrupting chemicals (EDCs) cause serious threats to human health. Five types of MnO₂ were synthesized and characterized. They exhibited different removal performances for three EDCs, i.e., estrone (E1), ethynylestradiol (EE2) and bisphenol A (BPA). Only δ-MnO₂ can completely remove E1 within 120 min at pH 3.0. Free Mn (III) was determined at the beginning of the reaction and participated in the EDCs removal process. Electron spin resonance (ESR) indicated that δ-MnO₂ could produce superoxide anions (·O₂^-) and singlet oxygen (¹O₂) in the existence of methanol. The reactive oxygen species (ROS) quenching experiments showed ¹O₂ have certain contribution to the E1 removal by δ-MnO₂. The source of ROS is mainly the lattice oxygen from δ-MnO₂, and can be replenished through the layer structure destruction caused by the reaction between Mn(III) and E1. The ROS dependent EDCs removal by δ-MnO₂ leads to a deep understanding on this well-known oxidant.

Effective Visible Light-Driven Photocatalytic Degradation of Ciprofloxacin over Flower-like Fe3O4/Bi2WO6 Composites

Photocatalytic degradation of organic pollution is a vital path to deal with environmental problems. Here, a direct Z-scheme 2D/2D heterojunction of a Fe₃O₄/Bi₂WO₆ photocatalyst is fabricated for the degradation of ciprofloxacin by a self-assembly strategy. Furthermore, to characterize the morphology of the obtained composite photocatalysts, various kinds of characterization methods were employed like XRD, XPS, SEM, and TEM. It is indicated that the flower-like photocatalyst is composed of nanosheets. Comparable photocatalysts were prepared by controlling the hydrothermal temperature and the iron content. In the photocatalytic degradation of ciprofloxacin (CIP) in water, under visible light irradiation, FB-180 (synthesized at 180 °C with 4% iron content) presents approximately 99.7% degradation efficiency in only 15 min. Meanwhile, during photocatalytic degradation reactions, the Fe₃O₄/Bi₂WO₆ heterojunction also displayed excellent stability, which still kept above 90% degradation efficiency after five consecutive cycles. UV-Vis DRS and M-S analyses showed that the Fe₃O₄/Bi₂WO₆ catalyst has a strong visible light absorption capacity and the transfer pathway of photo-induced charge carriers. PL, EIS, and TPR showed that Fe₃O₄/Bi₂WO₆ has an efficient separation and transfer rate of the photo-generated carriers. ESR analysis proved that the superoxide radical (^•O₂ ^-) and hydroxyl radical (^•OH) play a major role in the Fe₃O₄/Bi₂WO₆ photocatalytic system. This special 2D/2D heterojunction we proposed may have huge potential for marine pollution treatment by photocatalysis degradation with dramatically boosted activities.

A novel electrochemical oxidation-methanogenesis system for simultaneously degrading antibiotics and reducing CO2 to CH4 with low energy costs

A novel electrochemical oxidation-methanogenesis (EO-M) system was proposed for the first time to simultaneously achieve antibiotic degradation and a bioelectrochemical conversion of CO₂ to CH₄ with low energy costs. A dual-chamber system was installed with an antimony-doped tin oxide anode (Ti/SnO₂-Sb) for the electrocatalytic generation of hydroxyl radicals to degrade ciprofloxacin (CIP), and a CO₂-reducing methanogenic biocathode was enriched based on a three-dimensional (3D) graphitized granular activated carbon (GGAC) for microbial electromethanogenesis. The anode achieved removal efficiencies as high as 99.99% and 90.53% for CIP (14 mL, 50 mg L^-1) and the chemical oxygen demand (COD, 89 mg L^-1), respectively. The biocathode was rapidly enriched within 15 days and exhibited a methane production rate that stabilized at 15.12 ± 1.82 m³ m^-3 d^-1; additionally, the cathodic coulombic efficiency reached 71.76 ± 17.24%. The energy consumption of CIP degradation was reduced by 3.03 Wh L^-1 compared to that of a single electrochemical oxidation system due to the lower cathodic overpotential of CO₂ bioelectrochemical reduction in the EO-M system. A detailed analysis of the biofilm evolution in the 3D biocathode during the start-up process demonstrated that the enhanced absorption of extracellular polymeric substances by the GGAC cathode accelerated the enrichment of methanogens and induced the formation of methanogens with a large number of flagella. An analysis of the microbial community showed that a high relative abundance of Methanobacterium movens could promote a flagella-mediated direct electron transfer of the biocathode, eventually reducing the cathodic overpotential and energy costs of the EO-M system.

Carbon nanofibers supported Co/Ag bimetallic nanoparticles for heterogeneous activation of peroxymonosulfate and efficient oxidation of amoxicillin

The carbon nanofibers supported Co/Ag bimetallic nanoparticles (Co@CNFs-Ag) were synthesized for heterogeneous activation of peroxymonosulfate and efficient oxidation of amoxicillin in this work. Co nanoparticles with a diameter of 20-30 nm were encapsulated in the carbon nanofibers to reduce the loss of Co during the preparation and catalysis processes. Ag nanoparticles (5-10 nm) were distributed on the surface of CNFs. Complete removal of amoxicillin could be achieved within 30 min by Co@CNFs-Ag activated peroxymonosulfate system. The high catalytic performance could be attributed to the large aspect ratio (> 10,000) of the carbon nanofibers and the mutual reaction of the Co/Ag bimetallic nanoparticles with peroxymonosulfate. The optimal mass ratio of oxidant and catalyst was 10 and the optimized pH was 7. Co@CNFs-Ag exhibited stable catalytic activity and minimal metal leakage over a period of 5 cycles. The activation energy of the system was 29.51 kJ/mol derived by the Arrhenius equation. Both hydroxyl and sulfate radicals contributed to amoxicillin degradation and the latter were key to the degradation. Finally, the reaction mechanism of bimetallic synergistic catalytic system and possible amoxicillin degradation pathways were elucidated. The results of this study provide novel insights for application of sulfate radical-based advanced oxidation processes in environmental remediation.