Hollow structured copper-loaded self-floating catalyst in sulfite-induced oxidation of arsenic(III) at neutral pH: Kinetics and mechanisms investigation

[Display omitted] •The catalyst possessed excellent separation ability and recyclability.•HSM-N-Cu/S(IV) system could effectively oxidize As(III) at circumneutral pH.•SO4− was suggested as the reactive oxidant responsible for As(III) oxidation.•The apparent reaction rate constant of SO4− production reached 1.81 ± 0.12 M−1 s−1.•k value of SO5−+As(III) → As(IV) + SO52− 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. SO4− was verified as the dominant contributor to As(III) oxidation, the apparent reaction rate constant (kobs’) for SO4− generation was 1.81 ± 0.12 M−1 s−1, and the reaction rate constant (k12) of SO5− + As(III) → As(IV) + SO52− was first calculated as 2.6 × 106 M−1 s−1 by kinetic study. The apparent activation energy (Ea) 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.