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[Display omitted] • A novel enhanced As(III) removal process, MIL-53(Fe)/sulfite, was developed. • As(III) removal was through a combination of oxidation and adsorption. • As(III) oxidation relied on the powerful Fe(IV) and SO 4 •− generated from SO 5 •−. • Oxidation product As(V) was adsorbed by forming monodentate complexes. • Procedure to realize the purification of real arsenic-spiked water was proposed. Iron based metal–organic frameworks (Fe-MOFs) have garnered international interest as a novel and promising category of adsorbent materials for the elimination of arsenic from neutral waters. Nevertheless, their practical implementation is constrained by their inadequate adsorption capacity for aqueous arsenite (As(III)), a prevalent arsenic species found in acidic environments such as acid mine drainage. Herein, a novel oxidation-adsorption process to effectively purify As(III)-contaminated water is constructed by combining the MIL-53(Fe) of high acid resistance with sulfite (S(IV)). Notably, the adsorption capacity of the MIL-53(Fe)/S(IV) process for As(III) at pH 3.5 reached 86.4 mg g−1, surpassing the values achieved by MIL-53(Fe) alone by 21.6 times for As(III) and 1.62 times for As(V) (oxidized As(III)). During the oxidation process, MIL-53(Fe) effectively activated S(IV), leading to the formation of the crucial intermediate SO 5 •−, which then underwent two distinct pathways to respectively generate Fe(IV) and SO 4 •−, accounting for rapid oxidation of As(III). In the adsorption process, the S(IV) activation (i.e., complexation and electron transfer) on the MIL-53(Fe) surface created additional adsorption sites by dredging the pores and altering the electron cloud distribution within the adsorbent. Furthermore, As(V) trended to form monodentate complexes with surface Fe (e.g., Fe O As bond) in the MIL-53(Fe)/S(IV) process. Notably, this oxidative removal process demonstrated reliable performance in complex water matrices and practical arsenic-contaminated waters. Overall, this study presents a promising strategy to enhance the efficacy of Fe-MOFs for the removal of As(III). [ABSTRACT FROM AUTHOR]

• The catalyst possessed excellent separation ability and recyclability. • HSM-N-Cu/S(IV) system could effectively oxidize As(III) at circumneutral pH. • SO 4 − was suggested as the reactive oxidant responsible for As(III) oxidation. • The apparent reaction rate constant of SO 4 − production reached 1.81 ± 0.12 M−1 s−1. • k value of SO 5 −+As(III) → As(IV) + SO 5 2− was first calculated as 2.6 × 106 M−1 s−1. In heterogeneous reactions, efficient solid–liquid separation of catalyst from water after oxidation is a significant approach to reduce possible secondary pollution of aquatic environments. In this work, a hollow-structured self-floating copper-loaded catalyst (HSM-N-Cu) was fabricated using copper ammonia complexes and hollow glass microsphere as the copper source and supporter, respectively. The SEM, TEM, BET, XPS, and XRD characterization results suggested ideal specific surface area and stability of HSM-N-Cu. The prepared HSM-N-Cu in conjunction with sulfite have been successfully applied for As(III) oxidation in near-neutral conditions. In general, HSM-N-Cu effectively activating S(IV) process involved Cu(II)/Cu(I) conversion and chain reactions of oxysulfur radicals, where the S(IV) acted as a complexing ligand to Cu(II) surface and precursor of oxysulfur radicals. SO 4 − was verified as the dominant contributor to As(III) oxidation, the apparent reaction rate constant (k obs ') for SO 4 − generation was 1.81 ± 0.12 M−1 s−1, and the reaction rate constant (k 12) of SO 5 − + As(III) → As(IV) + SO 5 2− was first calculated as 2.6 × 106 M−1 s−1 by kinetic study. The apparent activation energy (E a) was 48.6 ± 0.1 kJ mol−1 at 100 mg L−1 HSM-N-Cu. Additionally, self-floating HSM-N-Cu could be easily separated, and its great stability was proven after six-cycle test. Furthermore, the HSM-N-Cu/S(IV) system can work effectively in broad range of geochemical conditions. In summary, the established process is feasible for remediation of As(III)-contaminated water, the collection of self-floating catalysts by surface separation from water provides a new idea to reduce secondary pollution of water by catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Promoted removal of arsenic by ZIF-67/sulfite than ZIF-67 is achieved. • Fast As(III) removal is through an integration of oxidation and adsorption. • SO 4 − is responsible for As(III) oxidation in solution and on catalyst surface. • The sulfite activation by ZIF-67 provides extra sites for As(III,V) adsorption. • Operating parameters of ZIF-67/sulfite system for arsenic removal are optimized. Elimination of As(III) from water has gotten more attention in comparison with As(V) due to its higher mobility and toxicity. In this work, we provide an effective method by integrating a cobalt-based metal–organic framework ZIF-67 and sulfite (S(IV)) to purify As(III)-laden water. The coupled oxidation with adsorption process (i.e., As(III) removal by ZIF-67/S(IV)) surpasses a divided preoxidation-adsorption process (i.e., As(V) removal by ZIF-67) for arsenic removal from the multi-component water containing various coexisting anions. Herein, the mechanism investigation corroborated that the S(IV) plays dual roles as a complexing ligand and a precursor of oxysulfur radicals. The enhanced As(III) removal is attributed to the S(IV) activation on the ZIF-67 surface via various reactions (e.g., surface complexation and intramolecular electron transfer), which not only generates SO 4 − radicals for rapid oxidation of As(III) to As(V), but also provides more adsorption sites for the immobilization of the oxidized product (As(V)). Furthermore, the combined process can rapidly treat arsenic in the realistic contaminated water from 242 to 7 μg L−1 within 15 min, directly meeting the provisional maximum contaminant level (<10 μg L−1). Overall, the proposed work may aid the rational design of S(IV) mediated oxidation-adsorption process to remove arsenic from a variety of contaminated waters. [ABSTRACT FROM AUTHOR]

[Display omitted] • La 2 (CO 3) 3 /CoFe 2 O 4 /biochar (LCB) was synthesized by a hydrothermal process. • LCB/PMS system was established to remove P(III) in one step. • LCB/PMS exhibited satisfactory removal rate of P(III) in a wide pH range. • SO 4 •- played a critical role in the oxidation process. • Different types of phosphorus could be rapidly removed by LCB/PMS. Phosphite [P(III)], an emerging eutrophication pollutant, has attracted limited attention in recent years. Owing to the higher solubility and resistance to biotransformation of P(III), oxidation of P(III) to phosphate [P(V)] is considered to be necessary to enhance P(III) removal. Herein, an efficient and regenerable magnetic La 2 (CO 3) 3 /CoFe 2 O 4 /biochar composite (LCB) was constructed through a facile one-pot hydrothermal method to treat phosphite-laden wastewater. LCB coupled with peroxymonosulfate (PMS) exhibited satisfactory P(III) removal performance through a one-step process for simultaneous oxidation and adsorption of P(III). The adsorption capacity of LCB/PMS for P(III) (71.94 mg/g) was much higher than that of LCB. LCB/PMS system showed high P(III) removal efficiency of 96.62 %, wide pH ranging from 4.0 to 9.0, and good reusability. It also worked well in the existence of anions and humic acid. The quenching experiments and electron spin resonance tests (ESR) revealed the critical role of SO 4 •- in the P(III) oxidation process. Characterization results demonstrated that electrostatic attraction and ligand exchange were responsible for P(III)/P(V) adsorption. Moreover, LCB/PMS system presented desirable performance in eliminating a series of typical organic and inorganic phosphorus. The LCB/PMS system provides a promising and sustainable technology for the purification of P(III)-contaminated water. [ABSTRACT FROM AUTHOR]

• A photo-enhanced removal of As(III) and Cu(II) was achieved. • As(III) removal was through a combination of photooxidation and coprecipation. • As(III) photooxidation relied on the formation of the Cu(II)–As(III) complex. • As(III) complexed with Cu(II) is photooxidized via direct electron transfer. • Procedures to realize the light-enhanced water's purification were proposed. Arsenic and copper causing water pollution is a worldwide problem, and simultaneously achieving water decontamination from arsenic and copper is immensely attractive. In this study, an economical and eco-friendly light-enhanced removal system was proposed to simultaneously alleviate water contamination from arsenic and copper, where nascent copper hydroxides (CHO) acted as nano-absorbers and electron acceptors for As(III) removal. According to the mechanism studies, the nascent CHO effectively capture As(III) forming surface Cu(II)–As(III) complex (formation constant, log K f1 = 6.0). Then, light induced the ligand-to-metal charge transfer (LMCT) from As(III) to Cu(II) inside the Cu(II)–As(III) complex, thus leading to both As(III) oxidation and Cu(II) reduction under anoxic conditions. The quantum yield of As(III) photooxidation at 365 nm was ascertained as (2.3 ± 0.2) × 10−2. The final photoproducts can be easily recycled as stabilized Cu(II)–As(V) complex and deposit. Real sunlight-driven photooxidation of As(III) in the presence of CHO and As(III) photooxidation to As(V) in solid Cu(II)–As(III) complex were also confirmed, which implying the promising application in practical water treatment. Accordingly, the oxygen-independent and light-enhanced removal of arsenic and copper can help develop recovery strategies for copper and arsenic. [ABSTRACT FROM AUTHOR]