Removal of malachite green by in-situ N-doped biochar derived from wheat bran: kinetics, isotherms, and adsorption mechanism study

Abstract

The biomass-based adsorbents offer a promising solution for wastewater decolorization owing to their superior specific surface area, low-budget, high adsorption capacities, and environmental sustainability. In this work, wheat bran (WB) was used as raw material for the production of in situ N-doped biochar through a molten salt template method, and the adsorption characteristics of Malachite Green (MG) onto biochars prepared from WB by immersing and non-immersing (BC–NaK and BC–NaK-n) in the mixed salt solution (NaCl and KCl) were investigated. The experimental results indicated that the adsorption capacity of MG onto the BC–NaK was significantly better than BC–NaK-n, which was attributed to the rich functional groups and well-developed pore structure of BC–NaK. The adsorption equilibrium data of MG onto the BC–NaK was fitted well to Sips and Koble-Corrigan isotherm models and adsorption process of MG was spontaneous and endothermic. Meanwhile, the pseudo-second-order model was successfully applied to depict the adsorption process of MG. Furthermore, the adsorption of MG onto BC–NaK was primarily regulated by H-bonding, π–π interaction, hydrophobic interaction, electrostatic interaction. The maximum saturated adsorption capacity of the BC–NaK was 880.14 ± 9.35 mg g⁻¹ at 298 K, further demonstrating that biochar prepared from wheat bran provided a long-term development strategy for dye wastewater treatment.