Ultrahigh-porosity peony-like magnesium oxide for the superior adsorption of arsenic (III) and arsenic (V) from aqueous solutions

Solidification of soluble arsenic from water has been one of the major challenges in global water management, with the urgent need for new adsorbent development. Therefore, ultrahigh-porosity MgO adsorbent (i.e., M400, M500, M600) was prepared by dehydration and calcination methods at different temperatures (400, 500, 600 °C). The adsorbents have peony-like folds with ultrahigh-specific surface areas of up to 228 m²/g with highly crystal structures compared to the existing MgO. Various promising capabilities were observed for the three MgO adsorbents with the best performance belonging to M600, i.e., wide optimal pH range (2−10), good stability, ultrahigh capacities (629 and 654 mg/g), excellent interference-tolerance and good reusability after five cycles, which are superior to the earlier reported values for arsenic (III) and arsenic (V) adsorption. Adsorption mechanisms were described well with the chemical adsorption (i.e., complexation, electrostatic, and H-bonding interaction between arsenic species and homogeneous MgO monolayers) and the endothermic nature of the process. Column adsorption tests using natural water were also conducted, resulting in excellent 36.53 and 39.87-fold pore volumes of pure water with no detectable arsenic (III) and arsenic (V) concentrations. The reported materials' significant capacity and reusability, coupled with the simple synthesis and promising practical applicability, indicate they would generally offer an environmentally sustainable and high efficiency for decontaminating arsenic-containing water in real-world applications.