Micro-nanostructured Δ-Bi₂O₃ with surface oxygen vacancies as superior adsorbents for SeO_x ²⁻ ions

Removal of the toxic selenium compounds, selenite (SeO₃ ²⁻) and selenate (SeO₄ ²⁻), from contaminated water is imperative for environmental protection in both developing and industrialized countries. Providing high selectivity adsorbents to the target ions is a big challenge. Here we report that micro sphere-like δ-Bi₂O₃ (MS-δ-Bi₂O₃) with surface oxygen vacancy defects can capture hypertoxic SeO_x ²⁻ anions from aqueous solutions with superior capacity and fast uptake rate. High capture selectivity to SeO₃ ²⁻ anions is observed, since the O atoms of SeO₃ ²⁻ anions fill the oxygen vacancies on the (111) facet of δ-Bi₂O₃ forming a stable complex structure. This mechanism is distinctly different from other known mechanisms for anion removal, and implies that we may utilize surface defects as highly efficient and selective sites to capture specific toxic species. Thus, we present a new route here to design superior adsorbents for toxic ions.