KOH-activated biochar and chitosan composites for efficient adsorption of industrial dye pollutants

[Display omitted] •A novel biochar (CHKBC) co-modified with KOH and chitosan was synthesized.•KOH activation significantly increased the loading of chitosan on biochar surface.•CHKBC showed strong adsorption for methylene blue in various environments.•Adsorption mechanisms were revealed by various characterization methods. The treatment of dye pollutants remains a challenge in the current management of the water environment. In this study, an innovative biochar material co-modified with KOH and chitosan was synthesized. The morphology and physicochemical properties of the modified biochar material were assessed by SEM, FTIR, XPS, XRD, and thermogravimetric analyses. The results revealed a significant enhancement in chitosan loading due to the pretreatment of biochar with KOH. The co-modified biochar with KOH and chitosan (CHKBC) exhibited an enriched composition of functional groups such as − COOH, −NH2, and − OH, leading to a substantial increase in the maximum adsorption of MB by the biochar from 8.83 mg g−1 to 62.04 mg g−1, a 7.03-fold increase. The excellent adsorption performance of CHKBC for MB was maintained at different solution temperature (288–––318 K) and pH (5–––11) conditions. The main adsorption mechanisms of MB removal by CHKBC involved ion exchange, pore filling, electrostatic attraction, π - π interactions, and hydrogen bonding. Overall, CHKBC has higher chitosan loading, more uniform chitosan distribution, and better adsorption efficiency of MB. It is a promising adsorption material with low cost and a simple production process.