Adsorption of arsenite by core–shell K-OMS-2@UiO-66 microspheres: performance and mechanism

Abstract

Arsenite (As(III)) is more toxic and more difficult to remove from water than arsenate (As(V)). A new nano core–shell-structured K-OMS-2@UiO-66 (K-OMS-2, formula KMn₈O₁₆·nH₂O) was fabricated via a facile one-step oxidation–coprecipitation method for enhanced As(III) removal. Results showed that the maximal adsorption capacity of As(III) achieved was 180.10 mg g⁻¹. The as-synthesized K-OMS-2@UiO-66 adsorbent functions excellently across a broad pH range of 1.5 to 10.0, and the residual concentrations of As(III) can drop under 10.0 μg L⁻¹. Based on XPS and FTIR measurements, it is proposed that the removal mechanism was mainly controlled through a synergistic interaction of surface complexation and hydrogen bonding. As(III) was sorbed onto the surface of the sorbent by Zr–O bonds and Mn–O bonds. Mn(IV) and Mn(III) in K-OMS-2@UiO-66 effectively oxidized As(III) to As(V). Then, some negatively charged As(V) were adsorbed at the positive sites of the adsorbent through electrostatic attraction, while others formed bidentate complexes with the Zr–O bonds. This study develops an attractive sorbent for As(III) removal from contaminated water and has a facile and low-cost synthesis process, good As(III) sorption performance, and reusability.