Synthesis of Wetland Plant-Based Biochar for Aqueous Cr(VI) Adsorption

Due to its advantages in specific surface area and oxygen-containing functional groups, biochar was often utilized for water pollution control. In this study, biochar was prepared from three types of wetland plants—Lotus Leaf, Arundo donax L., and Canna indica L. through slow pyrolysis. This biochar was utilized to adsorb Cr(VI) from wastewater, and the adsorption performance of the biochar under different pyrolysis temperatures and KOH modification ratios was investigated. The experimental results of biochar preparation demonstrated that under the pyrolysis of 500 °C and the lotus leaf powder/KOH mass ratio of 1:3, the prepared biochar (LBC-500(1:3)) exhibited the optimal adsorption capacity for Cr(VI) at a concentration of 50 mg·L−1, with an adsorption capacity reaching up to 27.88 mg·g−1. The optimal pH for Cr(VI) adsorption by LBC-500(1:3) was 3, with an adsorption capacity of 32.14 mg·g−1 at this pH. When the dosage amounted to 60 mg, LBC-500(1:3) demonstrated its highest adsorption capacity for Cr(VI), achieving a maximum of 19.39 mg·g−1. When the initial concentration peaked at 80 mg·L−1, the adsorption capacity was able to attain a value of 34.80 mg·g−1. Characterization analyses of the biochar prior to and subsequent to adsorption were conducted to elucidate the adsorption mechanisms of biochar for Cr(VI). The results revealed that the primary removal mechanisms of LBC-500(1:3) for Cr(VI) were coordination, electrostatic adsorption, and pore filling. The analysis of adsorption kinetics and isotherms revealed that the biochar predominantly adsorbed the Cr(VI) through monomolecular layer chemisorption. Adsorption thermodynamics results demonstrated that the adsorption process of the biochar was a spontaneous endothermic reaction. This study provides new insights and technical support for water pollution control, which holds significant environmental importance and application value.