CO ₂ adsorption on pristine Cu-laden biomass-derived hydrochar

Abstract The circular reuse of biowaste materials offers a promising pathway for creating environmentally sustainable CO 2 adsorbents. Pristine hydrochars derived from waste biomass provide a sustainable and affordable solution for CO 2 capture, eliminating the need for energy-demanding activation or chemical functionalization. In this study, we investigate the CO 2 adsorption performance of hydrochars synthesized via hydrothermal carbonization of copper-contaminated switchgrass. Unlike numerous biomass-based adsorbents previously reported, the hydrochars examined here are utilized without post-synthesis activation or chemical treatment, offering a low-energy, simplified approach to CO 2 capture. Using thermogravimetric analysis (TGA), the hydrochar produced at 220 °C for 6 h exhibited the highest CO 2 uptake of 0.38 ± 0.02 mmol g −1 (16.52 ± 0.78 mg g −1 ) at 30 °C, a remarkable value considering the material’s low specific surface area of 21.8 m 2 g −1 . To further investigate adsorption kinetics, pseudo-first-order, pseudo-second-order, and Avrami kinetic models were applied. The Avrami model provided the best fit, assuming different adsorption mechanisms co-exist. Furthermore, cyclic adsorption–desorption tests on HC-2h at 50 °C with 100%vol of CO 2 demonstrated a gradual decrease in capacity over three cycles (from 10.43 ± 0.70 to 7.67 ± 0.65 mg g −1 ), revealing partial capacity for regeneration and moderate stability. The research outcomes establish an initial stage for the ongoing development of hydrochars derived from contaminated biomass waste as a potential CO 2 adsorbent and open new avenues for integrating such materials into circular carbon management strategies where captured CO 2 may be valorized through utilization pathways.