Removal of Trace Arsenite through Simultaneous Photocatalytic Oxidation and Adsorption by Magnetic Fe₃O₄@PpPDA@TiO₂ Core–Shell Nanoparticles

Efficient removal of trace arsenites [As(III)] in groundwater is a big challenge worldwide. In this study, magnetic Fe3O4@poly(p-phenylenediamine)@TiO2 (Fe3O4@PpPDA@TiO2) core–shell nanoparticles were synthesized for As(III) ions removal via the photocatalytic oxidation–adsorption process. Under dark conditions, the As(III) adsorption on the as-synthesized core–shell nanoparticles obeyed the pseudo-second-order kinetic model and reached adsorption equilibrium within 45 min with a removal efficiency of 36.5%. Under visible-light irradiation, approximately 92% of As(III) ions were transformed into relatively low-toxic As(V) ions via the Fe3O4@PpPDA@TiO2 core–shell nanoparticles, and the arsenic removal efficiency increased dramatically to about 81% owing to As(V) ions being simultaneously adsorbed on the nanocomposite surfaces. The photocatalytic oxidation mechanisms were attributed to the synergism of photogenerated holes, hydroxyl radicals, and superoxide radicals. The as-synthesized Fe3O4@PpPDA@TiO2 core–shell nanoparticles are potentially useful in purifying the trace As(III)-contaminated groundwater owing to their easy magnetic separation, high optical quantum efficiency, and visible-light photocatalytic activity.