Application Of Advanced Oxidation Processes Research Articles

Innovative carbon materials from lignocellulosic wastes for electrochemical hydrogen peroxide production: Bridging biomass conversion and material properties

This study aims to assess the electrochemical generation of hydrogen peroxide and hydroxyl radicals (*OH) using carbon cathodes synthesized from three different lignocellulosic residues, Phragmites australis (PA), Cladium mariscus (CM) and Typha domingensis (TD). These vegetal species are commonly used in natural wetlands and phytoremediation processes and can accumulate recalcitrant pollutants within these treatment processes, generating a waste that should be properly managed. To convert these residues into valuable carbon materials, they underwent hydrothermal carbonization (HTC) followed by either chemical activation with KOH or pyrolysis at 1000 ºC. The best results were obtained with chemically activated materials, yielding a maximum H2O2 concentration of 313 mg L−1 with the carbon cathode produced from PA. The specific surface area, oxygenated functional groups and presence of structural defects in carbonous structures, were key parameters related to a good performance as catalysts towards the 2e- Oxygen Reduction Reaction (ORR). It was also demonstrated, in comparison with previous studies, that the presence of heavy metals in the structure of the lignocellulosic residue enhanced the decomposition of H2O2 into *OH. However, in the study of the degradation of a model organic contaminant as methylene blue (MB), it was shown that these *OH were not the main contributors to degradation, as direct H2O2 chemical degradation and adsorption on the carbon materials played the most significant role. Therefore, the outstanding capacity of these lignocellulosic residues as catalysts for the electrogeneration of H2O2 was confirmed, suggesting their potential future application in advanced oxidation processes for water decontamination.

Activation of peracetic acid by a magnetic biochar-ferrospinel AFe2O4 (A = Cu, Co, or Mn) nanocomposite for the degradation of carbamazepine − A comparative and mechanistic study

Peracetic acid (PAA)-based advanced oxidation processes (AOPs) are promising technologies for the efficient treatment of persistent contaminants in wastewater. In this study, three different magnetic biochar (BC)-ferrospinel AFe2O4 (A = Cu, Co, or Mn) nanocomposites were synthesized through a combined sol–gel/pyrolysis process for the activation of PAA to degrade carbamazepine (CBZ). The following order of efficiency was observed for CBZ degradation in the presence of PAA: BC-CoFe2O4 (100 %) > BC-MnFe2O4 (7 %) ≈ BC-CuFe2O4 (7 %). In addition, 0.8 mM PAA, 0.3 g/L catalyst, nearly neutral pH, and 333 K were identified as the optimal operating parameters for the degradation of 1 mg/L CBZ in the BC-CoFe2O4/PAA system. Mechanistic studies revealed that CH3C(O)OO radicals are the dominant active species for the degradation of CBZ in the BC-CoFe2O4/PAA system, and the continuous conversion of Co(II) to Co(III) in this system is responsible for the generation of these radicals. In addition, the water matrices (e.g., humic acid (20 mg/L), NaCl (0.05 M), and NaNO3 (0.01 M)) played negligible roles in the degradation of CBZ in the BC-CoFe2O4/PAA system. This system exhibited highly selective and reactive degradation of organic pollutants with electron-rich groups (e.g., CBZ (0.36 min−1), sulfamethoxazole (0.12 min−1), and diclofenac (0.28 min−1)). Furthermore, the degradation products of CBZ were identified, and possible degradation pathways and toxicity of these transformation products were proposed. The BC-CoFe2O4/PAA system demonstrated outstanding degradation performance in dynamic systems and real wastewater treatment applications. This study describes the performance of an efficient and easy-to-separate catalyst for the activation of PAA. This study facilitates the development and application of PAA-based AOPs for wastewater treatment.

New insight into wastewater treatment by activation of sulfite with humic acid under visible light irradiation

Sulfite (S(IV)), as an alternative to persulfate, has demonstrated its cost-effectiveness and environmentally friendly nature, garnering increasing attention in Advanced Oxidation Processes (AOPs). Dissolved organic matter (DOM) commonly occurred in diverse environments and was often regarded as an interfering factor in sulfite-based AOPs. However, less attention has been paid to the promotion of the activation of sulfite by excited DOM, which could produce various reactive intermediates. The study focused on the activation of sulfite using visible light (VL) - excited humic acid (HA) to efficiently degrade many common organic pollutants, which was better than peroxydisulfate (PDS) and peroxymonosulfate (PMS) systems. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that the triplet states of HA (3HA*) activated sulfite through energy transfer, resulting in the production of SO4•−, O2•−, and 1O2. The most significant active species found in the degradation of roxarsone (ROX) was 1O2, which was a non-radical pathway and exhibits high selectivity for pollutant degradation. This non-radical pathway was not commonly observed in traditional sulfite-based AOPs. Additionally, the coexistence of various inorganic anions, such as NO3−, Cl−, SO42−, CO32−, and PO43−, had little effect on the degradation of ROX. Furthermore, DOM from different natural water demonstrated efficient activation of S(IV) under light conditions, opening up new possibilities for applying sulfite-based advanced oxidation to the remediation of organic pollution in diverse sites and water bodies. In summary, this research offered promising insights into the potential application of sulfite-based AOPs, facilitated by photo-excited HA, as a new strategy for efficiently degrading organic pollutants in various environmental settings.

2D Cobalt-carbon–nitrogen loaded 3D Prussian blue analogues enhances peroxymonosulfate activation for bisphenol A Degradation: Singlet oxygen dominated nonradical pathway

Singlet oxygen (1O2) dominated peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) is an effective technology for the removal of electron-rich organic contaminants. However, the highly selective generation of 1O2 is limited by the development of catalysts. Herein, a two-dimensional (2D) cobalt-carbon–nitrogen loaded three-dimensional (3D) Prussian blue analogue (CoCN@PBA-P) material was synthesized by the one-step method using hematite with different morphologies as the precursor. The two atomically dispersed Co sites in three CoCN@PBA-P were demonstrated that could effectively activate PMS to degrade bisphenol A (BPA) in different and complex environmental backgrounds. The quenching, probe quantitative, and EPR results indicated the dominant role of 1O2 in CoCN@PBA-P/PMS system, and the steady-state concentration of 1O2 can achieve 4.0 × 10-9-1.3 × 10-8 M. Importantly, the role of Co as the active site was verified by screening experiments, and the mechanism of CoCN@PBA-P activate PMS was revealed by experimentally and theoretically, and the pathway to generate 1O2 is *HSO5→*SO4+OH–→*SO4+*OH→*O→1O2 (* represents that the species is bound to the active site). Finally, the analysis of degradation intermediates and their toxicity showed that the whole process is harmless to the environment. This work provides a new perspective to the design of 2D@3D materials and their application in PMS-based AOPs.

3D hollow cobalt/carbon fiber-like PMS activator for dynamic carbamazepine degradation: promotional effect and reaction mechanism

Finding effective and practical ways to remove contaminants in the water is a challenging problem, therefore, the construction of recyclable materials has been paid attention to in the practical application of advanced oxidation processes. A three-dimensional hollow tubular surface-loaded cobalt/cotton carbon fiber composite (Co-CCF-600) is successfully prepared by carbonization, which can effectively activate PMS to degrade CBZ. The synthetic Co-CCF-600 degrades 93.47% of CBZ within 60 min. It is worth noting that Co-CCF-600 has good stability and high catalytic activity after 5 cycles, which is attributed to the synergy between Co species (Co0 and CoO) and CCF. In addition, both radical and non-radical processes contribute to the degradation of CBZ, and SO4•− plays a dominant role. After a 118 h wastewater degradation experiment, the Co-CCF-600/PMS system still maintains high degradation efficiency and stability. Overall, this study provides an environmentally friendly, low-cost cobalt/carbon fiber material for the removal of CBZ in wastewater and provides a practical solution for environmental remediation.

Co-Fe bimetallic oxides derived from Prussian blue analogs to activate peracetic acid for eliminating sulfamethazine: Contribution and identification of radical species

Peracetic acid (PAA), as a disinfectant with powerful oxidation and exceptional antimicrobial efficiency, has gained considerable attention for its application in advanced oxidation processes (AOPs). However, leaching of metal ions and low recovery efficiency limited the application of heterogeneous AOPs. Herein, we synthesized a CoFe bimetallic oxide (Co-Fe-O) derived from Prussian blue analogs to serve as an activator for PAA, efficiently eliminating sulfamethazine (SMZ) in a wide pH range (5–9). Electron paramagnetic resonance and quenching test revealed the coexistence of radical species in the system, and R-O· were the main factors of SMZ elimination. The steady-state model evaluation showed that 3.1 × 10−14 M R-O· and 2.05 × 10−14 M ·OH existed in the system. CoFe bimetallic synergies expedite the generation of radical species. Based on density functional theory, the aniline ring and heterocyclic ring of SMZ were regarded as the susceptible sites for radical attack and electron transfer. Furthermore, the elimination pathway of SMZ was proposed by combining the results of intermediate products. Additionally, the toxicity of SMZ and intermediates as well as the reaction conditions, water matrices, stability, and oxidation capacity of Co-Fe-O/PAA were subjected to evaluation. Results indicate that the Co-Fe-O/PAA system has significant application potential in the elimination of micropollutants.

Olive mill waste bio-based catalyst application in advanced oxidation processes for wastewater treatment

This study explores the physicochemical capacities of solid wastes from olive oil mills (olive stone, OS, and olive pomace, OP), in obtaining catalysts to be applied in heterogeneous Fenton and persulfate processes. Through physicochemical treatments and the impregnation of iron by hydrothermal deposition and wetness impregnation (WI) different catalysts were produced, tested and characterized. The olive mill wastewater (OMW) studied in this work is a synthetic solution with five phenolic compounds to mimic the real effluent. The removal efficiency of phenolic acids and organic load (COD) present in this type of effluent was evaluated. In the treatment of synthetic wastewater, almost 100% COD was removed using OS and OP-FeWI as catalysts in the heterogeneous Fenton process. In the sulfate radical-based reaction, the 3,4–Dihydroxybenzoic acid was slightly more degradable than other phenolic acids which confirms the selectivity of sulfate radicals. The materials subject to thermal processes revealed an interesting adsorption capacity. This procedure not only reduces the environmental impact of OMW, but also promotes the implementation of new circular economy approaches.

Simultaneous Degradation, Dehalogenation, and Detoxification of Halogenated Antibiotics by Carbon Dioxide Radical Anions

Despite the extensive application of advanced oxidation processes (AOPs) in water treatment, the efficiency of AOPs in eliminating various emerging contaminants such as halogenated antibiotics is constrained by a number of factors. Halogen moieties exhibit strong resistance to oxidative radicals, affecting the dehalogenation and detoxification efficiencies. To address these limitations of AOPs, advanced reduction processes (ARPs) have been proposed. Herein, a novel nucleophilic reductant—namely, the carbon dioxide radical anion (CO2•-)—is introduced for the simultaneous degradation, dehalogenation, and detoxification of florfenicol (FF), a typical halogenated antibiotic. The results demonstrate that FF is completely eliminated by CO2•-, with approximately 100% of Cl- and 46% of F- released after 120 min of treatment. Simultaneous detoxification is observed, which exhibits a linear response to the release of free inorganic halogen ions (R2 = 0.97, p < 0.01). The formation of halogen-free products is the primary reason for the superior detoxification performance of this method, in comparison with conventional hydroxyl-radical-based AOPs. Products identification and density functional theory (DFT) calculations reveal the underlying dehalogenation mechanism, in which the chlorine moiety of FF is more susceptible than other moieties to nucleophilic attack by CO2•-. Moreover, CO2•--based ARPs exhibit superior dehalogenation efficiencies (> 75%) in degrading a series of halogenated antibiotics, including chloramphenicol (CAP), thiamphenicol (THA), diclofenac (DLF), triclosan (TCS), and ciprofloxacin (CIP). The system shows high tolerance to the pH of the solution and the presence of natural water constituents, and demonstrates an excellent degradation performance in actual groundwater, indicating the strong application potential of CO2•--based ARPs in real life. Overall, this study elucidates the feasibility of CO2•- for the simultaneous degradation, dehalogenation, and detoxification of halogenated antibiotics and provides a promising method for their regulation during water or wastewater treatment.

Highly efficient micropollutant decomposition by ultrathin amorphous cobalt-iron oxide nanosheets in peroxymonosulfate-mediated membrane-confined catalysis

Applications of advanced oxidation processes (AOPs) in water treatment require addressing technological challenges such as developing low-cost techniques for nanocatalyst synthesis, overcoming mass transfer limitations, and enhancing the yield of reactive oxygen species (ROS). This study employs a simple sodium borohydride (NaBH4)-based reduction technique for synthesizing ultrathin amorphous cobalt-iron oxide nanosheets (A/Co3-Fe ONS) to activate peroxymonosulfate (PMS). These nanosheets were found to outperform crystalline nanosheets due to their abundant reactive sites, oxygen vacancies, and capability to produce ROS through O–O and S–O bond cleavage. Due to the nanoconfinement effect, converting A/Co3-Fe ONS into a lamellar membrane significantly enhances reactivity and efficacy (1290 times) compared to batch PMS-mediated AOP reactors. Quenching experiments, solid-state and solution-based electron paramagnetic resonance (EPR) spectroscopy facilitated delineation of the reaction mechanisms involving both radical and nonradical pathways. Finally, the A/CoFeOx membrane achieved efficient removal (>95 %) of various organic micropollutants (OMPs), ultrafast destruction (318 ms), and excellent stability (48 h) through redox-recycling facilitated by the redox-potential difference and oxygen vacancies. This strategy offers a low-temperature cost-effective alternative and may be considered for scale-up in water treatment.

Highly efficient peroxymonosulfate activation by Fe[sbnd]Co bimetallic modified metal-organic frameworks-derived polyhedron with enriched oxygen vacancy for tetracycline degradation

It is important to propose a targeted solution strategy for the rate-limiting step in peroxymonosulfate activation in order to promote its wider application in advanced oxidation processes. In this study, a novel catalyst with FeCo bimetal doping, rich oxygen vacancy and porous polyhedral structure was prepared by using Fe, Co-doped Metal-Organic Framework as the precursor, which strategically enhanced the abundance and stability of active sites and promoted the adsorption of contaminates and PMS molecules. The M-450 (oxygen vacancy-rich)/PMS system demonstrated superior catalytic activity and interference resistance, in which 100 % of TC could be removed within 5 min. The corresponding reaction rate constant is 1.119 min−1, which is much higher than that of M-0 (without oxygen vacancy). Moreover, a series of studies proved that nonradical pathway (singlet oxygen) accompanied free radicals (sulfate radicals and hydroxyl radicals) collectively contributed to the tetracycline degradation. This study provides new ideas for the design and improvement of the functional catalyst for application in sulfate radicals based advanced oxidation processes.

Electrochemical activation of peracetic acid with activated carbon fiber cathode for sulfamethoxazole elimination: Long-lasting catalytic performance and mechanism

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) could generate various radicals with low by-product generation, making them a vital technology in the remediation of organic pollution. Maintaining the activity and continuous operation of catalytic systems in water treatment processes was a highly challenging research topic. Herein, the electrochemical process with an activated carbon fiber (E-ACF) cathode was devised to boost the activation of PAA (E-ACF-PAA) for persistent elimination of organics. Compared to other commonly used electrodes, the ACF cathode displayed superior PAA activation ability and higher sulfamethoxazole (SMX) removal. The applied cathodic electric field could protect ACF from PAA oxidation, maintaining its long-term catalytic ability over 50 cycles. Based on radical quenching studies, the EPR test, and the estimation of radical contribution, the E-ACF-PAA process was identified as a radical dominant system. Importantly, isolated chamber experiments proved that PAA was mainly decomposed on the cathode to produce hydroxyl radicals (OH) for SMX degradation, while the anode played a negligible role. According to toxicity prediction and algae growth tests, the degradation products were harmless to the aquatic ecology. Remarkably, continuous flow experiments over a 24 h and different water matrix tests have also proven applicability in practical scenarios. This work provided novel insights into the electrochemical activation of PAA and further expanded the potential applications of PAA-based AOPs in the remediation of organic pollution.

Metal-free catalysts with local fluorination regulation for peroxymonosulfate activation: Nearly 100 % singlet oxygen production for selective degradation of aqueous organic pollutants

Generating singlet oxygen (1O2) via activating peroxymonosulfate (PMS) is crucial for the selective removal of organic pollutants in aquatic environments. However, achieving efficient and selective conversion of PMS into 1O2 without consuming energy or metals remains a significant challenge. In this study, graphite phase carbon nitride (g-C3N4) was locally fluorinated via a simple polymerization method. The local fluorinated g-C3N4 (FCN) was used as a metal-free catalyst to activate PMS, enabling highly efficient degradation of 4-chlorophenol (100 %) and detoxification. The FCN/PMS system demonstrates exceptional selectivity for electron-rich pollutants, functions effectively across a broad pH range (2–10), and exhibits remarkable interference resistances to background scavenging ions and natural organic compounds. Furthermore, quenching experiments, probe tests, electron paramagnetic spin resonance measurements, electrochemical characterizations, and theoretical calculations demonstrated that 1O2 was the only reactive species in the catalytic process. Local fluorination regulated the electronic structure of g-C3N4, juxtaposing electron-rich fluorine with electron-deficient carbon dual active sites. This modification alters the electron transfer direction between PMS and g-C3N4, allowing for nearly 100 % selective generation of 1O2via dual electron transfer channels without the need for energy or metals. This study provides a new strategy for designing metal-free heterogeneous catalysts to selectively generate 1O2 in a green way and can facilitate the wider applications of advanced oxidation processes for water purification.

A Systematic Review of Contaminants of Concern in Uganda: Occurrence, Sources, Potential Risks, and Removal Strategies

Contaminants of concern (CoCs) pose significant threats to Uganda’s ecosystems and public health, particularly in the face of rapid urbanization, industrial expansion, and intensified agriculture. This systematic review comprehensively analyzed Uganda’s CoC landscape, addressing imminent challenges that endanger the country’s ecosystems and public health. CoCs, originating from urban, industrial, and agricultural activities, encompass a wide range of substances, including pharmaceuticals, personal care products, pesticides, industrial chemicals, heavy metals, radionuclides, biotoxins, disinfection byproducts, hydrocarbons, and microplastics. This review identified the major drivers of CoC dispersion, particularly wastewater and improper waste disposal practices. From an initial pool of 887 articles collected from reputable databases such as PubMed, African Journal Online (AJOL), Web of Science, Science Direct, and Google Scholar, 177 pertinent studies were extracted. The literature review pointed to the presence of 57 pharmaceutical residues and personal care products, along with 38 pesticide residues and 12 heavy metals, across various environmental matrices, such as wastewater, groundwater, seawater, rainwater, surface water, drinking water, and pharmaceutical effluents. CoC concentrations displayed significant levels exceeding established regulations, varying based on the specific locations, compounds, and matrices. This review underscores potential ecological and health consequences associated with CoCs, including antibiotic resistance, endocrine disruption, and carcinogenicity. Inefficiencies in traditional wastewater treatment methods, coupled with inadequate sanitation practices in certain areas, exacerbate the contamination of Uganda’s aquatic environments, intensifying environmental and health concerns. To address these challenges, advanced oxidation processes (AOPs) emerge as promising and efficient alternatives for CoC degradation and the prevention of environmental pollution. Notably, no prior studies have explored the management and mitigation of these contaminants through AOP application within various aqueous matrices in Uganda. This review emphasizes the necessity of specific regulations, improved data collection, and public awareness campaigns, offering recommendations for advanced wastewater treatment implementation, the adoption of sustainable agricultural practices, and the enforcement of source control measures. Furthermore, it highlights the significance of further research to bridge knowledge gaps and devise effective policies and interventions. Ultimately, this comprehensive analysis equips readers, policymakers, and regulators with vital knowledge for informed decision-making, policy development, and the protection of public health and the environment.

Synergetic multiple free radicals lower the organohalide conversion barrier and potentiate effective contaminant mineralization

Here we investigated the synergetic multiple free radicals (atomic hydrogen (H*), superoxide anion (•O2−), and hydroxyl radicals (•OH)) in enhancing removal efficiencies of the halogen organic pollutants, such as p-chlorophenol (4-CP). A TiO2 photoanode and a palladium and carbon layer co-modified Cu/Cu2O/CuO (CuxO@C/Pd) photocathode were combined to construct a photoelectrocatalytic platform that enabled the synchronous production of multiple free radicals. It was found that the conversion and mineralization rates of 4-CP were up to ∼0.044 min−1 and ∼71.3% respectively, representing an increase of ∼4.3 times and ∼2.1 times compared to conventional •OH mediated oxidation. Theoretical calculations and experiments indicated that the conversion barrier of 4-CP was significantly reduced through the redox synergies of H* and •OH and the simultaneous nucleophilic-electrophilic addition of •O2− effectively inhibited the accumulation of benzoquinone intermediates. This work is beneficial for the study and application of advanced oxidation processes mediated by multiple free radicals.

Exploring a chemical input free advanced oxidation process based on nanobubble technology to treat organic micropollutants

Advanced oxidation processes (AOPs) are increasingly applied in water and wastewater treatment, but their energy consumption and chemical use may hinder their further implementation in a changing world. This study investigated the feasibility and mechanisms involved in a chemical-free nanobubble-based AOP for treating organic micropollutants in both synthetic and real water matrices. The removal efficiency of the model micropollutant Rhodamine B (RhB) by oxygen nanobubble AOP (98%) was significantly higher than for air (73%) and nitrogen nanobubbles (69%). The treatment performance was not significantly affected by pH (3–10) and the presence of ions (Ca2+, Mg2+, HCO3−, and Cl−). Although a higher initial concentration of RhB (10 mg/L) led to a slower treatment process when compared to lower initial concentrations (0.1 and 1 mg/L), the final removal performance reached a similar level (∼98%) between 100 and 500 min. The coexistence of organic matter (humic acid, HA) resulted in a much lower reduction (70%) in the RhB removal rate. Both qualitative and quantitative analysis of reactive oxygen species (ROSs) using fluorescent probe, electron spin resonance, and quenching experiments demonstrated that the contributions of ROSs in RhB degradation followed the order: hydroxyl radical (•OH) > superoxide radical (•O2−) > singlet oxygen (1O2). The cascade degradation reactions for RhB were identified which involve N-de-ethylation, hydroxylation, chromophore cleavage, opening-ring and final mineralisation processes. Moreover, the treatment of real water samples spiked with RhB, including natural lake water and secondary effluent from a sewage works, still showed considerable removals of the dye (75.3%–90.8%), supporting its practical feasibility. Overall, the results benefit future research and application of chemical free nanobubble-based AOP for water and wastewater treatment.

MOF-derived 2D Co@C nanosheet membrane with enhanced catalytic activity: Mechanism and stability insights

Two-dimensional (2D) metal-organic frameworks (MOFs) membranes have recently gained attention as novel material membranes for advanced oxidation processes (AOPs). Nonetheless, the susceptibility of 2D MOFs to reactive oxygen species (ROS) limits 2D MOF membranes’ effectiveness in AOPs. In this study, we introduce a novel approach, fabricating a 2D Co-MOF-derived nanosheet membrane (referred to as Co@C NS), assembled from pyrolyzed and exfoliated Co-MOF nanosheets, for the activation of peroxymonosulfate (PMS) in the removal of bisphenol A (BPA). Crucially, the synthesis process involves the pyrolysis of a carbon layer, serving as a protective barrier. This barrier effectively prevents the release of Co ions, ensuring the long-term structural and catalytic stability of the Co@C NS membrane. Notably, the membrane exhibits remarkable capabilities in discriminating between natural organic matter (NOM) and BPA through size exclusion, significantly mitigating the impact of NOM competition for ROS. Additionally, our study demonstrates an exceptional removal efficiency, achieving 100% BPA removal at an ultrahigh permeance of 1100 L m−2 h−1 bar−1, corresponding to an exceedingly short retention time of 0.14 s. Our mechanistic investigation reveals the involvement of singlet oxygen and sulfate radicals in the removal of BPA within the nanochannels, facilitated by the nanoconfinement effect. This study introduces valuable strategies for the development of 2D MOF-derived nanosheet membranes characterized by high catalytic activity and excellent stability, underlining their practical potential in AOP applications.

FeS and Fe3O4 Co-modified biochar to build a highly resistant advanced oxidation process system for quinclorac degradation in irrigation water

Advanced oxidation processes (AOPs), based on sulfate radical (SO4·-) produced by peroxymonosulfate (PMS), can effectively mineralize refractory organic pollutants. However, the coexistence of anions and natural organic matters in actual wastewater prevents the application of AOPs. A simple one-step method was used to prepare FeS/Fe3O4 co-modified biochar materials (FFB) that could activate PMS to degrade quinclorac (QNC) with a removal rate of 100%, even exhibiting optimum degradation of QNC reached 99.31% in irrigation water, demonstrating excellent anti-interference performance for co-existing anions and natural organic matter. Meanwhile, ecotoxicity analysis showed that the toxicity of degradation intermediates was lower than that of QNC. Characterization results demonstrated the even distribution of FeS and Fe3O4 onto biochar, supplying abundant Fe2+ to activate PMS producing reactive oxygen species (ROS), while the generated Fe3+ after reactive continue to be reduced with sulfur species to promote the cycle of Fe2+/Fe3+. The coexistence of ·OH, SO4·-, 1O2, and O2·- in the FFB/PMS-QNC system suggest the possession of two pathway with free radical and non-free radical pathways to degrade QNC. The density functional theory (DFT) was used to analyze the adsorption sites and adsorption energy of PMS, as well as the differential charge density, which further proved the generation of SO4·-, O2·- and 1O2. In addition, the electrochemical test results showed that electron transfer also played an important role in the degradation of QNC. This study provides a feasible approach for the removal of organic pollutants in actual water.

Regulating the peroxymonosulfate activation on N doped δ-MnO2 nanosheets for tetracycline degradation: N species as the degradation pathways switcher to convert radical to nonradical

Although the free radical pathway can obtain high organic degradation efficiency during advanced oxidation processes, it is difficult to cater the diverse degradation environment due to the coexistence of various interference. Here, the δ-MnO2 nanosheets are prepared to regulate the reactive oxidation species converting from radical-dominated to nonradical-dominated through the nitrogen doped operation in a gentle mechanical stirring method. The optimal 0.5 N-MnO2 materials present 91.2 % TC degradation efficiency in the presence of peroxymonosulfate (PMS) with the apparent rate constant is 0.63 min−1, which is 1.66 and 4.2 times higher than that of in δ-MnO2/PMS (0.38 min−1) and alone PMS (0.15 min−1) systems,respectively. Radicals quenching experiments, electron paramagnetic resonance spectra and competing kinetics experiments indicate that the δ-MnO2 nanosheets promote PMS decomposition with attaining a high radical (SO4·-, ·OH and ·O2–) oxidation path contribution (74.5 %) for TC degradation. Meanwhile, the doping of N species and electrons contribute to the generation of 1O2, allowing the whole reactive system dominated by a nonradical species (e- and 1O2) pathway (80.3 %). Importantly, electrochemical tests verify the participation of electrons and the electrons transfer from TC to the 0.5 N-MnO2 surface for PMS activation via 0.5 N-MnO2-PMS* surface complex. Overall, it is practical to cater the specific application of advanced oxidation processes through N as the degradation pathways switcher.

Photocatalytic degradation of chlorinated organic pollutants by ZnS@ZIF-8 composite through hydrogen peroxide generation by activating dioxygen under simulated sunlight irradiation

Photocatalytic hydrogen peroxide (H2O2) production and its application in advanced oxidation processes (AOPs) are regarded as low-cost and environmentally friendly wastewater treatment processes. Herein, by modifying a small amount of sulphide on the zeolitic imidazolate framework-8 (ZIF-8), a ZnS@ZIF-8 composite and used for photocatalytic H2O2 production to degrade chlorinated organic pollutants under simulated sunlight (SSL). ZnS@ZIF-8 composite could enhance the separation of photo-induced charge carriers, promote electron transfer from zinc sulphide (ZnS) to ZIF-8, which exhibited good selectivity for the two-electron oxygen reduction reaction (2e--ORR) and two-electron water oxidation (2e--WOR) pathways. Based on oxygen (O2) activation, the developed ZnS@ZIF-8/O2/SSL system could achieve 6.43 mmol/L H2O2 production within 150 min, which was approximately 8.66 and 10.36 times higher than that of the ZnS/O2/SSL and ZIF-8/O2/SSL systems, respectively. In the ZnS@ZIF-8/O2/SSL system, the ORR, WOR and H2O2 photolysis led to the generation of hydroxyl radical (•OH), while the photochemical behavior of ZnS in ZnS@ZIF-8 composite resulted in the generation of active hydrogen (*H). Benefitting from the high concentration of H2O2 and the coexistence of redox species in the ZnS@ZIF-8/O2/SSL system, various chlorinated organic pollutants could be dechlorinated and mineralized. In addition, a possible mechanism for photocatalytic H2O2 production was also proposed. Importantly, the proposed process did not involve an additional sacrificial agent or Fenton-like catalysts. This work provides insights into the potential application of ZnS@ZIF-8 composite for H2O2 production and wastewater treatment.

Reduced TiO2 nanotube arrays as environmental catalysts that enable advanced oxidation processes: A mini review

Advanced oxidation processes (AOPs) that utilize heterogeneous catalysts are an engaging and compelling technology for treating emerging contaminants in water and wastewater. Substantial efforts have been devoted to developing cost-effective and environmentally benign materials for application in AOPs. Reduced TiO2 nanotube arrays (r-TNAs) have recently emerged as promising environmental materials for efficiently mitigating persistent organic pollutants (POPs) resistant to conventional biological treatment. r-TNAs possess distinct electrical, optical, and catalytic features, including superior conductivity and solar light absorption due to structural defects involving oxygen vacancies and Ti3+ states. Moreover, their well-organized open channel structures provide a substantial surface area, facilitating the efficient mass transfer of reactants and products. Notably, r-TNAs can be grown directly on the substrate without using organic adhesives or binders, which improves their mechanical and chemical durability and facilitates their repeated use. This article represents the pioneering comprehensive review of r-TNAs in AOP applications. We introduce an electrochemical anodization technique to fabricate TNAs and summarizes the reduction methods employed in r-TNA synthesis. We also elucidate the appealing attributes of r-TNAs and explore their applications in emerging AOPs, including persulfate activation, electrocatalysis, and photo(electro)catalysis. Finally, we outline critical challenges and provide insights into future prospects for the development of AOP systems based on r-TNAs.