Novel Mg-doped pyro-hydrochars as methylene blue adsorbents: Adsorption behavior and mechanism

In this study, Mg-based pyro-hydrochars derived from waste grape pomace (Mg-GP), corn cob (Mg-CC), and Miscanthus x giganteus (Mg-MIS) were successfully prepared applying one-step hydrothermal carbonization followed by pyrolysis. The structural characteristics and surface analysis of the prepared materials were characterized by various techniques, while its adsorption ability was examined through remediation of methylene blue (MB) under batch adsorption experiments. The obtained results revealed that pyro-hydrochars are highly effective adsorbents of MB with achieved capacities of 289.65 mg g(-1), 262.30 mg g(-1), and 232.48 mg g(-1) for Mg-GP, Mg-CC and Mg-MIS, respectively. The binding of MB to the surface on either of the tested material was achieved by a complex mechanism that unifies electro-static interaction, hydrogen bonding, pi-pi interaction, surface complexation, and ion-exchange mechanism. The kinetic study display that the adsorption process onto used Mg-doped pyro-hydrochars is favorable and follows pseudo-second order kinetics, while the isotherm equilibriums were determined by Sips isotherm model. Tested materials can be effectively reused for at least 3 cycles, with minimal loss of efficiency. Overall, findings from this work promote Mg-doped pyro-hydrochars form different precursors as promising, sustainable, and efficient adsorbents of MB from polluted wastewaters.