Favorably Adjusting the Oxygen Species over Fe-Mn Binary Oxide Sorbent by Directional Etching for Arsenic Oxidation and Adsorption

In this study, raw and etched Fe-Mn binary oxide sorbents were prepared via the coprecipitation method to explore the catalytic oxidation and adsorption of As2O3. The oxidation and adsorption capacities for As2O3 were investigated at different temperatures, citric acid etching concentrations, and O2 concentrations. Compared with the raw sorbent, the sorbents etched with citric acid show excellent arsenic adsorption and oxidation capacities. As confirmed by scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) studies, etching increased the number of oxygen vacancies and specific surface area. Oxygen temperature programming desorption (O2-TPD) characterization showed that the oxygen vacancy structure enhanced the instability and fluidity of the lattice oxygen, promoting arsenic adsorption and oxidation. Hydrogen temperature programmed reduction (H2-TPR) characterization indicated that citric acid etching facilitated the oxidation of the sorbent. In addition, density functional theory (DFT) calculations also confirmed that etching facilitated arsenic adsorption by altering the adsorption energies of the sorbents.