The environmental mobility of As and Sb, which are hazardous to ecosystems and human health, depends on their oxidation state and interactions with mineral surfaces. Although boehmite (γ-AlOOH) is commonly used to adsorb oxyanionic contaminants, the relationships among its synthesis conditions, surface structure, and oxidation-state-dependent As and Sb adsorption mechanisms remain poorly understood. We hypothesized that hydrothermal synthesis conditions can be tuned to produce hierarchical mesoporous boehmite with optimized surface properties and that metalloid oxidation state governs adsorption mechanisms on this well-defined mineral surface. We optimized a one-pot hydrothermal method for synthesizing boehmite by systematically varying the pH, temperature, aging time, and aluminum concentrations, forming a plate-stacked spherical morphology with a high surface area and large pore volume. Adsorption isotherms revealed maximum As(III), As(V), and Sb(V) sorption capacities at pH 5/9 of 59.5/66.4, 38.1/13.5, and 54.6/16.0 mg/g, respectively. In contrast, the Sb(III) uptake (13 mg/g) was lowest at pH 5 but increased markedly at pH 9 because valentinite (Sb 2 O 3 ) precipitated. Synchrotron-based spectroscopic analyses demonstrated that As(III/V) and Sb(V) form inner-sphere complexes with surface hydroxyl groups, whereas Sb(III) interacts mainly through weaker outer-sphere associations with negligible Al coordination. Molecular-scale structural interpretation further revealed that As(III) and As(V) form bidentate binuclear corner-sharing complexes on the boehmite surface, whereas Sb(V) forms both bidentate edge- and corner-sharing geometries. Therefore, metalloid adsorption was governed by oxidation-state-dependent surface complexation mechanisms, highlighting that efficiently removing As and Sb requires solution conditions tailored to each species. This study provides mechanistic insights into redox-dependent metalloid adsorption and demonstrates hydrothermally engineered boehmite as a high-capacity adsorbent among pristine aluminum oxyhydroxides without post-modification for metalloid remediation in complex aqueous systems. • Hydrothermal boehmite shows high surface area and mesoporosity. • As(III/V) and Sb(V) form inner-sphere complexes on boehmite. • Sb(III) adsorbs mainly via weaker outer-sphere interactions. • Redox state governs adsorption behavior and environmental mobility. • XAS, XPS, and FT-IR analyses reveal detailed adsorption mechanisms.
Kang et al. (Wed,) studied this question.