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• Cl− efficiently enhanced oxidative degradation of TBP by PMS. • Unexpected halogenated organics were identified during the degradation of TBP. • Time-dependent transformation of TBP by PMS/Cl− process was investigated. • Consider first before treating salty TBP wastewater by PMS oxidation process. Nowadays, increasing attention has been paid on the peroxymonosulfate (PMS) in situ oxidation for environmental decontamination. Chloride ion (Cl−) could directly react with PMS to produce some reactive halogen agents via non-radical pathways. In present study, the degradation kinetics of 2,4,6-tribromophenol (TBP) and the total organic carbon (TOC) removal by adding PMS in salty wastewater were inspected. TBP could effectively degraded by PMS in salty wastewater over the pH range of 3.0−7.0, and the degradation ratio increased with the pH of reaction solution. Positive effects of Cl− concentration (1−100 mM) on TBP degradation kinetics were also examined. Moreover, the oxidation products and their evolution with reaction time were conducted in order to further evaluate the environmental benefits with co-existence of PMS and Cl−. Instead of complete mineralization, TBP was mainly transformed to new halogenated products which also have long half-lives. The chlorination of TBP is the dominant pathway in the presence of Cl−, since the main oxidant (HOCl) played an important role. The formation of undesirable halogenated products provides that adding PMS into salty wastewater might not be an unexpected proposal for TBP depletion involving of the attendance of chloride. [ABSTRACT FROM AUTHOR]

Abstract: Orange II (Org II), one of the most common used azo dyes, was taken as a model to investigate the effects of chloride ion on dye decoloration in cobalt/peroxymonosulfate (Co/PMS) system. A significant decrease in the rate of Org II decoloration was observed upon addition of Cl− (0.05–10mM), but further addition of Cl− (>50mM) apparently accelerated dyes degradation. This dual effect of chloride on dyes bleaching was also observed as other halide ions (e.g. Br−, I−) or other azo dyes were present in Co/PMS system. In the Co-free PMS solutions, the observed first-order rate constant always exponentially increased with the chloride content. The reactive chlorine species generated from chloride oxidation by PMS should be responsible for this non-radical mechanism for dye decoloration, however, these rapid decoloration of Org II as chloride ion was present, did not readily lead to much mineralization. Therefore, this finding may have significant technical implications for utilizing Co/PMS regent to detoxify chloride-rich azo dyes wastewater. [Copyright &y& Elsevier]

Iron-based catalysts have been demonstrated to activate peroxymonosulfate (PMS) to generate reactive radicals, which is however limited by their complex preparation process, high costs and inefficiency for practical applications. Herein we obtain spent LiFePO 4 (SLFP), with powerful catalytic capacity by a simple one-step treatment of the retired LiFePO 4 cathode material, for PMS activation to decontaminate organic pollutants. Lithium defects and oxygen vacancies in SLFP play critical roles for PMS utilization, further confirmed by density functional theory (DFT) calculations. SLFP materials rapidly adsorb PMS, and the surface PMS is activated by Fe(II) to generate radicals, with •OH playing a major role for the degradation of organics after multi-step reactions. The SLFP/PMS process is finally validated for ability to remove organic contaminants and potential environmental application. • SLFP was an old but vigorous PMS activator for decontamination. • Surface defects of SLFP play a key role in PMS activation. • Quenching experiment and DFT calculation were used to reveal mechanism. • This proposed SLFP/PMS process was environmental benign. [ABSTRACT FROM AUTHOR]

• The addition of Mo greatly facilitated the reduction of Cu2+ and Fe3+. • Mo enables Fe(II)/PMS to efficiently degrade and mineralize 4-chlorophenol. • Mo does not react with PMS, thus improving the utilization efficiency of PMS. • Tungsten (W) could also accelerate the conversion of Fe3+ to Fe2+. • Strategies in boosting PMS activation should be analyzed on a case by case basis. The interaction of reductive metal ions and peroxymonosulfate (PMS) is necessary for the generation of sulfate radials (SO 4 −), however, this process is greatly restrained by the sluggish reduction of high-valent metal ions. Here we report that commercially available reductive metal (Mo or W) powders are capable of unlocking this kinetic constraint. The reduction of Fe(III) to Fe(II), decomposition of PMS, and degradation/mineralization of 4-chlorophenol (4-CP) are all accelerated in the Mo/Fe2+/PMS process at a very low Fe2+/PMS ratio (Fe2+/PMS = 1/10). In such an accelerated system, common adverse effects of natural water constituents such as chloride and humic acid are largely mitigated. According to the fluorescence measurement and scavenging tests, sulfate and hydroxyl radicals dominate in Mo/Fe2+/PMS process. The addition of Mo or W is further confirmed to favor Cu2+/PMS process, but this is not the case for other metal ions (Mn2+, Ni2+, Ce3+ and Co2+). Reductive zero-valence and four-valence active sites (Mo0 and Mo4+; W0 and W4+) play key roles in overall redox reaction. Overall, our present work provides an alternative route for expediting redox cycling of transition metals in advanced oxidation processes, without useless consumption of PMS and increase of total organic carbon. [ABSTRACT FROM AUTHOR]

• 2-Br-4-CP and 2-Cl-4-BP could be effectively degraded in the PMS/X− system. • The release of endogenic X was determined by the initial level of exogenic X−. • 2-Br-4-CP is more easily degraded/mineralized, in line with theoretical prediction. • The importance of endogenic X position on pollutant transformation is emphasized. Transformation of halogenated organics in advanced oxidation processes (AOPs) have been extensively investigated, however, there is little information about the fate of polyhalogenated pollutants (-Cl, -Br coexist) particularly while exogenic halides (X−, Cl− or Br−) are present. Herein, the oxidation of isomeric compounds of 2-bromo-4-chlorophenol (2-Br-4-CP) and 2-chloro-4-bromophenol (2-Cl-4-BP) were comparatively investigated in the presence of peroxymonosulfate (PMS) and various concentrations of exogenic Cl− or Br−. Both 2-Br-4-CP and 2-Cl-4-BP could be efficiently degraded and gradually mineralized in the PMS/X− systems. Based on Gas Chromatography-Mass Spectrometer (GC–MS) data, different chlorinated products and brominated products were identified in the PMS/X− systems during the degradation of two compounds. The release of endogenic X was determined by the initial level of exogenic X−, where the low initial exogenic X− resulted in a high AOX accumulation. Endogenic halogen seems more liable to release in PMS/Br− system than PMS/X− system. The faster degradation rate and higher mineralization degree of 2-Br-4-CP than 2-Cl-4-BP were successfully predicted by frontier orbital theory and mulliken atomic charge distribution. The importance of the position of halogen atoms on dehalogenation, halogenation and degradation processes is emphasized. These findings also demonstrate the necessity of 1) monitoring the X− levels in wastewater prior to application of PMS-based oxidation processes and 2) precise identification of halogen position in byproducts analysis for predicting their fates. [ABSTRACT FROM AUTHOR]

• The addition of MoS 2 greatly accelerated the conversion of Fe(III) to Fe(II). • MoS 2 enables Fe(II)/PMS to efficiently degrade halogenated organic pollutants. • The unsaturated S on the fresh MoS 2 was found to assist in PMS decomposition. • The used or rinsed MoS 2 still exhibited excellent recyclability and reactivity. Despite the success of Fe(II)/peroxymonsulfate (PMS) process in detoxifying organic pollutants, its intrinsic drawback of sluggish Fe(III) conversion to Fe(II) limits its large-scale practical application. Here we report that commercial MoS 2 , a common metal sulfide, can be used to unlock this kinetic constrain. Addition of MoS 2 greatly accelerates the reduction of Fe(III) to Fe(II), decomposition of PMS, and thus results in enhanced degradation efficiency of 2,4,6-trichlorophenol (TCP) (>95%) and other biorefractory halogenated organic compounds within 30 min. Mass spectroscopy data indicate that TCP can be destructed into low-molecular-weight organic acids, manifesting its powerful oxidation capacity of MoS 2 -assisted Fe(II)/PMS process. Once the Fe(III) in aqueous solution is stabilized by its organic or inorganic ligands, the boosting effects of MoS 2 are largely inhibited and less than 80% of TCP is degraded. Sulfate radicals and hydroxyl radicals are identified as the dominant reactive oxidants in the MoS 2 /Fe(II)/PMS process by radical scavenging tests. The unsaturated S on the fresh MoS 2 surface and the exposed Mo(IV) sites are supposed to react with PMS and Fe(III) in the aqueous solution, respectively. No iron oxides and Mo oxides are detected in X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) measurement, indicating the accelerated Fe(II)/PMS process mainly occurs in the homogeneous solution. MoS 2 exhibits excellent recyclability and sustainable reactivity for the degradation of TCP after 5 consecutive runs. Overall, the present study provides a novel strategy to overcome the rate-limiting step of Fe(III)/Fe(II) that is commonly challenging Fe-based advanced oxidation processes (AOPs) and enable Fe(II)/PMS as efficient as typical Co(II)/PMS. [ABSTRACT FROM AUTHOR]