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• Co-HTC of PVC and bamboo was employed to prepare high-efficiency adsorbent. • The contents of hydroxyl and carboxyl groups of hydrochar increased during Co-HTC. • Adsorption capacity of MB on hydrochar produced by addition of PVC increased significantly. • Electrostatic and hydrogen-bonding interactions are the main mechanisms. Polyvinyl chloride (PVC) was blended into bamboo powder during co-hydrothermal carbonization (Co-HTC) to understand the effects on the physicochemical properties and adsorbing ability of hydrochar. The properties of hydrochar were characterized by Zeta potential, elemental analyses, BET, FTIR, XPS, Boehm titration and SEM. The addition of PVC into bamboo in Co-HTC decreased the BET area, and pore volume and radius of hydrochar, but increased the contents of surface hydroxyl and carboxyl groups. The adsorption ability of hydrochar produced by addition of PVC at 473 K over methylene blue (MB) increased significantly. The main adsorption mechanism was electrostatic attraction by –N(CH 3) 2 + of MB and carboxylate of hydrochar, and hydrogen-bonding interaction through N atom of phenothiazine in MB and C–OH of hydrochar. Thus, Co-HTC offers a facile, green and economical alternative for conversion of waste into high-value adsorbents. [ABSTRACT FROM AUTHOR]