Effective elimination of malachite green from solutions by functionalized hydrochar derived from co-hydrothermal carbonization of bamboo and polyvinyl chloride with ammonium persulfate assistance

The high-value use of waste biomass and plastics is crucial for green development and environmental protection. Herein, an efficient hydrochar material (BPS-Na) was synthesized via co-hydrothermal carbonization (co-HTC) of bamboo powder, polyvinyl chloride (PVC), and ammonium persulfate (APS) followed by NaOH activation, and applied to uptake malachite green (MG) from water solutions. The focus was on elucidating the function of APS in modulating the physicochemical characteristics and removal performance of the resulting hydrochar. Compared with the hydrochar (BP-Na) prepared without adding APS, the incorporation of APS slightly enlarged the specific surface area (11.10 vs. 10.17 m 2 ·g −1 ) and total pore volume (0.014 vs. 0.016 cm 3 ·g −1 ), but significantly enhanced the oxygen content from 25.75% to 32.87% and mesopore volume, while reducing the carbon content from 62.53% to 52.35%. Adsorption experiments revealed that the uptake of MG by both BP-Na and BPS-Na followed a monolayer chemisorption mechanism and was endothermic. Notably, the removal ability of BPS-Na at 298 K significantly exceeded that of BP-Na (1181.69 vs. 348.52 mg·g −1 ) and many previously reported hydrochar-based adsorbents. This is mainly ascribed to the enriched O-containing functional groups, particularly carboxylate groups, on BPS-Na, which has been confirmed by XPS and FTIR analyses. Furthermore, the effective adsorption of MG by both BP-Na and BPS-Na is achieved through multiple mechanisms, including hydrogen bonding, electrostatic interactions, ion exchange, and π-π stacking interactions. This work demonstrates a novel and effective APS-assisted co-HTC approach that not only enables the synergistic valorization of waste biomass and PVC but also provides a potent method for tailoring surface chemistry to achieve superior performance in cationic dye removal, advancing beyond conventional co-HTC systems.