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Highlights • Metribuzin solutions treated by AO-H 2 O 2 , EF and PEF with a BDD/air-diffusion cell. • Two kinetic stages in EF and PEF: uncomplexed and Fe(III)-complexed herbicide. • Overall mineralization by all methods is ensured at current densities ≥100 mA cm−2. • PEF as the best method: total combustion of 0.523 mM metribuzin at pH 3.0 in 420 min. • Heteroaromatic, dimeric and aliphatic by-products degraded by BDD(OH) and OH. Abstract This article reports the electrochemical degradation of the herbicide metribuzin (MTZ) in sulfate medium by advanced oxidation processes like anodic oxidation with electrogenerated H 2 O 2 (AO-H 2 O 2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF). A boron-doped diamond (BDD) anode was combined with an air-diffusion cathode with ability to produce H 2 O 2. Unprecedented overall combustion was feasible by all methods at a constant current density (j) ≥100.0 mA cm−2. The total organic carbon (TOC) removal achieved by AO-H 2 O 2 was independent from pH within the range 3.0–9.0, whereas the oscillatory dependence of the pseudo-first-order MTZ decay rate constant with this variable was ascribed to adsorption on the BDD surface. In EF and PEF at pH 3.0, 0.50 mM Fe2+ was determined as optimum catalyst content and the MTZ removal showed two consecutive pseudo-first-order kinetic stages. These were related to the fast reaction of the target molecule with OH formed from Fenton's reaction, followed by a slower attack of physisorbed BDD(OH) onto Fe(III)-MTZ complexes. The effect of j and MTZ content on decay kinetics and TOC removal was examined. PEF was the best treatment due to the decomposition of photoactive intermediates by UVA radiation, yielding total mineralization of a 0.523 mM herbicide solution after 420 min of electrolysis at 100.0 mA cm−2. A thorough reaction pathway for MTZ degradation is proposed from the sixteen heteroaromatic by-products and three aliphatic molecules identified by GC–MS and LC-MS/MS. Oxalic and oxamic acids were detected as final carboxylic acids by ion-exclusion HPLC. [ABSTRACT FROM AUTHOR]

Highlights • Poor BHA and DOC decays in simulated matrix and urban wastewater by EC with Fe|Fe cell. • Active chlorine formed in simulated matrix accelerates BHA decay in EO-H 2 O 2. • Large mineralization of BHA in simulated matrix by EF and PEF with BDD/air-diffusion cell. • Growing mineralization in urban wastewater at pH 7.9: EO-H 2 O 2 < EF < PEF, greater with BDD. • Better performance of EF and PEF in urban wastewater at pH 3.0 by greater generation of OH. Abstract This work compares the removal of butylated hydroxyanisole (BHA), a ubiquitous antioxidant in food and pharmaceuticals, from water either by electrocoagulation (EC) with an Fe|Fe cell or H 2 O 2 -based electrochemical advanced oxidation processes like electrochemical oxidation (EO-H 2 O 2), electro-Fenton (EF) and photoelectro-Fenton (PEF) with an air-diffusion cathode. BHA degradation by EC was very poor, whereas the dissolved organic carbon (DOC) was more effectively abated in urban wastewater. The effect of pH, number of Fe|Fe pairs and current on the EC performance was examined. The additive was also slowly degraded by EO-H 2 O 2 with a RuO 2 -based or BDD anode in 50 mM Na 2 SO 4 solution. In the simulated matrix, BHA decay by EO-H 2 O 2 was substantially enhanced owing to active chlorine generation from anodic oxidation of Cl−, whereas the OH-mediated oxidation at the BDD surface accounted for DOC decay. In EF and PEF, the OH produced in the bulk upgraded the mineralization, primordially using BDD. In raw urban wastewater at natural pH 7.9, the time course of BHA and DOC contents was affected by NOM oxidation, being accelerated in the order: EO-H 2 O 2 < EF < PEF. The quickest decontamination of urban wastewater occurred in PEF at pH 3.0, because of the higher amounts of OH in the bulk along with UVA photolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural iron ore (IO) as the PMS activator for pollutants degradation. • Fast destruction of organics (dyes and antibiotics) by the WS 2 /IO/PMS system. • Kinetic fitting verified the crucial role of WS 2 in the catalytic reaction. • Exposed W4+, S2− species in WS 2 boost Fe3+/Fe2+ redox cycles during PMS activation. • Proposed mechanism insights for reactive species generation. The seek for efficient and low-cost heterogeneous catalysts for peroxymonosulfate (PMS) activation holds great promise in the treatment of organic contaminants. Natural iron ore (IO) has been identified as a potential catalyst due to its low environmental risk and cost-savings. Herein, the commercial tungsten sulfide (WS 2) was employed to significantly enhance the performance of IO towards PMS activation (WS 2 /IO/PMS) for the removal of pollutants. This system demonstrated remarkable performance, with >98.2% removal of organic pollutants in 60 min, including dyes and antibiotics, under the optimized conditions of 0.50 g/L IO, 0.10 g/L WS 2 , 2.0 mM PMS, and initial pH 6.0. The apparent degradation rate constant (k) of Acid Orange 7 (AO7) in WS 2 /IO/PMS system (0.073 min−1) was about 30.4-fold and 104.3-fold higher than that of in WS 2 /PMS system (0.0024 min−1) and IO/PMS system (0.0007 min−1), respectively. Mechanism insights revealed the crucial role of WS 2 in boosting the degradation kinetics in the WS 2 /IO/PMS system. The exposed W4+ or S2− species on WS 2 surface were the dominant reactive sites responsible for the promotion of Fe3+/Fe2+ redox cycles and subsequently the PMS activation. Importantly, the electrochemical analysis demonstrates that the iron ions released from IO were prone to adsorb onto the WS 2 surface, forming active Fe species with high oxidative potential, which remarkably accelerated the electron transfer for Fe2+ regeneration, thereby enhancing PMS activation to generate reactive oxygen species like hydroxyl radicals (OH), sulfate radicals (SO 4 −) and superoxide radicals (O 2 −). Furthermore, the practicability of WS 2 /IO/PMS system was validated by treating various pollutants and investigating the interference of coexisting anions in water. Overall, this study provides a green and advanced strategy to enhance the PMS activation by natural iron ore for efficient water decontamination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nf-MSCF exhibits a remarkable piezocatalysis efficiency of removing 98% of RhB in 4 min under ultrasound. • Nafion layer of Nf-MSCF greatly enhanced the structural stability under sonication. • Nafion layer of Nf-MSCF enhanced adsorption of cationic organic substrates. • The removal mechanism for RhB of Nf-MSCF was proposed. • The piezoelectric voltage was simulated by COMSOL Multiphysics and measured in the experiment. The piezocatalytic effect is a promising approach for the efficient degradation of organic pollutants. However, directly dispersing such catalysts in aqueous media introduces other issues including media purification (since it constitutes a secondary pollutant), and catalyst recyclability. In this work, a highly recyclable hierarchical composite material, MoS 2 decorated onto carbon felt with further coated by Nafion (Nf-MSCF), was demonstrated to be an efficient piezocatalyst for organic pollutants degradation. The hierarchical Nf-MSCF catalyst structure designed in this way exhibited strong piezocatalytic performance as well as stability and durability. It achieved a high efficiency of removing 98% of Rhodamine B (RhB) pollutants in water after 4 min under ultrasound and this efficiency was maintained even after 300 min of ultrasound. Such excellent properties were attributed to the combined effects of high piezocatalytic activity of MoS 2 nanosheets, high specific surface area of carbon felt, and improved cation adsorption as well as stability resulting from surface modification by the Nafion layer. The reactive oxygen species generated was verified and analyzed by electron spin resonance measurements and radical trapping experiments. The Zeta potentials were measured to confirm the more negatively charged surface brought about by Nafion modification. Finally, combining COMSOL Multiphysics simulation and piezoelectric voltage measurement with energy band theory, the possible piezocatalytic mechanism of the structure was proposed. This work provides a facile strategy to prepare recyclable and high efficiency piezocatalysts, and further promotes the practical applications of piezocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • HClO reacts with H 2 O 2 to generate 1O 2 in EF-Fere-HClO process. • The steady-state concentration of •OH decreased with increasing Cl– content. • The yield of •OH via Fenton-like reaction between HClO and Fe2+ is inefficient. • Contaminants' structure affects the performance of EF-Fere-HClO process. • The accumulation of toxic chlorinated intermediates causes new environmental concerns. The speciation of reactive species and the degradation of pollutants during Fered-Fenton (EF-Fere) treatment of industrial wastewater are strongly affected by chloride ions (Cl−). The generation of active chlorine at the anode has been considered as the main positive effect of Cl– since it can contribute to pollutants degradation, however, the detrimental effects of Cl− were largely neglected. In this study, for the first time, the double-edged roles of Cl– in Fered-Fenton treatment of high salinity wastewater were systematically investigated. First, HClO can act as the scavenger of H 2 O 2 , thereby inhibiting the production of •OH from Fenton's reaction. The steady-state concentration of •OH was only 1.0 × 10-13 M in the presence of 142.5 mM Cl–, being much lower than that of the conventional EF-Fere (8.3 × 10-13 M). The formation of singlet oxygen (1O 2) via this scavenging reaction was confirmed by the electron paramagnetic resonance (EPR) test, but it can hardly contribute to furfuryl alcohol (FFA) decay due to its fast deactivation in water. The dominant roles of •OH and HClO in pollutants degradation during Cl–-mediated EF-Fere process (EF-Fere-HClO) were disclosed, the performance highly depends on the structure of target pollutants. The selective oxidation by HClO can efficiently destroy some electron-rich compounds, whereas the degradation of many electron-deficient contaminants still relies on the •OH-mediated pathway. Besides, the generation of toxic chlorinated intermediates from HClO-mediated oxidation can cause new environmental concerns. Finally, the treatment of industrial wastewater was performed to guide the practical application of the EF-Fere-HClO process. [ABSTRACT FROM AUTHOR]