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For eliminating organic pollutants from wastewater, Fe 0 or Fe 0 -composites as catalyst for peroxymonosulfate (PMS) activation have attracted increasing attention in advanced oxidation processes. In this work, a novel Fe 0 -montmorillonite composites (Fe-Mt-C-H 2 ) have been prepared by thermal reduction and used as an activator for PMS to remove bisphenol A (BPA). The removal efficiency of BPA (25 mg·L −1 ) and total organic carbon (TOC) were 99.3% and 70.6%, respectively, in the presence of Fe-Mt-C-H 2 (0.4 g·L −1 ) and PMS (1 mM) at pH of 3. Electron paramagnetic resonance (EPR) spectroscopy and radical scavenger studies demonstrated that superoxide radical (O 2 − ) and singlet oxygen ( 1 O 2 ) were the crucial reactive oxygen species (ROS) in the Fe-Mt-C-H 2 /PMS system rather than sulfate (SO 4 − ) and hydroxyl radical (·OH). Besides, it was found that pH had a great influence on the catalytic oxidation rate of BPA and the Fe-Mt-C-H 2 exhibited best catalytic performance and reusability at initial pH of 3. Furthermore, the constituents of the iron surface oxidation layer at different initial pH were investigated with X-ray photoelectron spectroscopy studies, which indicated that the major constituents were Fe 3 O 4 in acidic solution and contained α-Fe 2 O 3 , FeO and FeSO 4 (s) in alkaline or neutral solution. The findings of this study provide new insights into the activation mechanism of PMS by Fe 0 -composites and exhibit a promising application of Fe-Mt-C-H 2 in wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • LDH and kaolin would affect the stability of PSNPs in aquatic environment. • IS and pH played significant roles in both homoaggregation and heteroaggregation. • Electrostatic interaction was the dominant force of PSNPs-minerals heteroaggregation. • DLVO theory and DFT calculations were used to elucidate the interaction mechanism. The transport, fate, and toxic effects of nanoplastics (NPs) would be affected by various environmental factors. In this study, the aggregation behaviors of polystyrene nanoplastics (PSNPs) with or without the presence of oppositely charged minerals (Mg/Al layered double hydroxides (LDH) and kaolin) in aqueous phase were investigated through settling experiment, and the influencing factors including pH and ionic strength (IS) were also analyzed systematically. Our results revealed that pH had a negligible effect on the fate of individual PSNPs under natural aquatic conditions, while high IS would cause homoaggregation. The positively charged LDH decreased the stability of PSNPs, while negatively charged kaolin had a weak effect on it, suggesting that electrostatic interaction was directly related to the stability of PSNPs in aquatic environment. Further experiments of PSNPs with other metal oxides with different surface charges (Al 2 O 3 and SiO 2) confirmed the importance of electrostatic interaction for PSNPs-minerals heteroaggregation. Transmission electron microscopic (TEM), Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and Density function theory (DFT) calculations were combined for the first time to explain the heteroaggregation mechanism, demonstrating that there were expected to exist hydrogen bond and van der Waals interaction in addition to the dominant force of electrostatic interaction. Our findings are expected to shed light on the environmental behavior of PSNPs in a complex aquatic environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • PMS activation by CoFe-LDH was improved by compounding with biochar. • Biochar acted as the catalyst carrier and electron mediator. • Reducing functional groups in biochar facilitated Co(III) and Fe(III) reduction. Efficient and low-cost catalysts for peroxymonosulfate (PMS) activation are needed for pollution prevention and environmental remediation. In this work, PMS activation by CoFe layered double hydroxide (CoFe-LDH) was promoted by compositing with biochar (BC). The characterization and catalytic performance of BC, CoFe-LDH, and BC@CoFe-LDH composite (BC-LDH) were investigated. The results indicated that BC could act as a catalyst carrier and electron mediator, which improved the physicochemical properties of CoFe-LDH and promoted the redox cycle of transition metals. The redox-active moieties (RAMs) of BC, especially the reduced functional groups (e.g., phenolic –OH), played an important role in the reduction of Co(III) and Fe(III). Remarkably, benefiting from the synergistic effect between BC and CoFe-LDH, the resulting BC-LDH exhibited excellent catalytic activity and stability for PMS activation. More reactive oxygen species (ROS) were produced in BC-LDH/PMS system. As a result, 100% of dimethyl phthalate (DMP, 10 mg L−1) degradation efficiency was achieved within 60 min in BC-LDH/PMS system, while only 62% in CoFe-LDH/PMS system. The intermediates of DMP degradation were identified and the degradation pathways were proposed. Our findings are expected to provide new insights into the rational design and application of BC materials and transition metals/PMS system for environmental remediation. [ABSTRACT FROM AUTHOR]