Adsorption of crystal violet from wastewater using alkaline-modified pomelo peel-derived biochar

The purpose of this study is to investigate the optimal preparation conditions for alkali-modified pomelo peel biochar and to clarify its adsorption process towards crystal violet (CV). The pyrolysis temperature and the alkali-to-carbon ratio of pomelo peel raw materials with varying epidermal layers were evaluated and optimized. Several characterization techniques demonstrated that alkaline modification enhances the adsorption performance of biochar by modifying its pore structure and functional group composition. Notably, the biochar, derived from the outer epidermis of pomelo, modified with an alkali-to-carbon ratio of 2:1 at 900 °C (KC2), exhibited significant adsorption capacity through mechanisms such as pore filling, hydrogen bonding, π-π interactions, electrostatic interactions, and functional groups including C[dbnd]C and C[sbnd]O[sbnd]C. The Freundlich isotherm and the pseudo-second-order kinetic model were determined to be the most appropriate for describing the equilibrium data. Accordingly, KC2 exhibited a maximum adsorption capacity of 805.69 mg/g, which significantly exceeded that of biochar derived from pomelo peel with a basic outer epidermis pyrolyzed at 900 °C (BC-GOP900, 586.7 mg/g). This study ultimately concluded that utilizing pomelo peel biochar, particularly KC2, represents an innovative strategy to address pollution caused by CV while effectively repurposing agricultural waste.