Preparation of MnO2 modified winter melon-derived biochar for enhanced adsorption of U(VI) from aqueous solution

Abstract

This work synthesized MnO2 modified winter melon-derived biochar (MnO2@WBC) using potassium permanganate oxidation/hydrothermal method for uranium(VI) removal. The factors influencing uranium(VI) adsorption by MnO2@WBC, including pH, adsorbent dosage, time, temperature, and initial U(VI) concentration were explored. The material’s performance was characterized, and the underlying mechanism of U(VI) removal was analyzed using various techniques. The characterization results indicated that the MnO2@WBC exhibited excellent dispersibility, suggesting that MnO2 effectively prevented WBC aggregation and enhanced the reactive surface area, and providing more active sites that can effectively promote the complexation and adsorption of U(VI). The process suggested a dominant role for chemical adsorption. The Freundlich isotherm model demonstrated a high degree of alignment with the observed adsorption behavior, indicating a predominantly multilayer adsorption process. Thermodynamic studies indicated that adsorption was a spontaneous endothermic process. The XPS analysis demonstrated that the adsorption process was primarily due to the formation of stable complexes with C–O, Mn–O–H and C=O. The results demonstrated that MnO2@WBC effectively removed U(VI), achieving a maximum adsorption capacity of 240.86 mg g−1 at a pH of 5.0. These findings provided a theoretical basis for the treatment of wastewater contaminated with U(VI).