Deep eutectic solvent-assisted valorization of bamboo biomass into functional biochar for sustainable wastewater treatment

A sustainable and environmentally benign approach was developed to valorize Phyllostachys edulis bamboo biomass into functional biochar (DESChar) via deep eutectic solvent (DES)-assisted solvothermal carbonization. Unlike previous reports that focus on DESs for biomass pretreatment, this study uniquely uses a carboxylic acid-based DES both as reaction medium and chemical activator in a one-pot synthesis of DESChar. The DES-induced reorganization of bamboo structure led to the formation of spherical carbon microspheres with high surface area and abundant functional groups. The optimized DESChar exhibited outstanding adsorption capacities of 850.14  mg/g for malachite green (MG) and 259.94  mg/g for rhodamine B (RB), surpassing many conventional adsorbents. Structural and compositional analyses confirmed its aromatic, and porous framework enriched with carboxyl and hydroxyl groups. Adsorption kinetics followed a pseudo-second-order model, and the thermodynamics indicated a spontaneous, and endothermic chemisorption process. Mechanistic insights supported by Zeta potential, XPS, and thermodynamic data revealed that electrostatic, hydrogen bonding, and π-π stacking interactions dominate the adsorption process. The DESChar also showed strong selectivity toward cationic dyes in mixed systems, high ion tolerance, and excellent reusability. An economic assessment further supported the feasibility of the preparation strategy. This study not only demonstrates a DES-enabled route to functional biochar from bamboo but also contributes to advancing sustainable separation technologies for wastewater treatment.