Biochar doping of synthesized mordenite improves adsorption and oxidation in As(III) removal: Experiments and DFT calculations.

In this study, a composite material was synthesized through the co-pyrolysis of biochar doped with synthetic mordenite. The adsorption experiments conducted with BC@ASM on As(III) facilitated the determination of the optimal mass ratio of 20:1 (ASM: Yak dung) and a pyrolysis temperature of 500 °C. The adsorption properties of ASM and BC@ASM were examined through batch adsorption experiments and a range of characterization techniques. And the reaction mechanism was further elucidated by DFT calculations, revealing the essential difference in the adsorption of As(III) by ASM and BC@ASM. The adsorption kinetics of As(III) were found to align with both the pseudo-second-order and Elovich kinetic models, while the isothermal adsorption was consistent with the Freundlich model. The maximum theoretical adsorption capacities were determined to be 371.9 mg/g and 449.6 mg/g, respectively. When the initial concentration of arsenite (As(III)) is 100 mg/L, the optimal dosage of synthetic mordenite is determined to be between 6 and 8 g/L, while the optimal dosage of the composite material ranges from 5 to 6 g/L. The composite material demonstrated significant resistance to fluctuations in pH. Within the pH range of 2-12, the removal efficiency is sustained between 78.3% and 88.7%. Furthermore, the adsorption capacity exhibited minimal sensitivity to the presence of anions such as chloride (Cl⁻), nitrate (NO₃⁻), bicarbonate (HCO₃⁻), and sulfate (SO₄⁻) in the surrounding environment. In addition, BC@ASM facilitated the formation of arsenite-tannic acid complexes, which markedly improved its adsorption capacity for arsenite. In conclusion, the composite material presents a viable approach for addressing arsenic contamination in aquatic environments, while the foundational data offers a novel perspective for the remediation of metallic pollutants.