Mn3O4/activated carbon nanocomposites for adsorptive removal of methylene blue

Recently, the recycling and reuse of biomass wastes to produce valuable materials have garnered significant attention due to their substantial economic and environmental benefits. In this study, spent coffee grounds (SCGs) were utilized to prepare nanocomposites through a one-pot carbonization approach under optimal conditions of 550 °C, 2 h, and 1:0.5 mass ratio of SCGs to MnSO4·H2O. The produced Mn3O4/activated carbon nanocomposites (Mn3O4/AC) were employed for adsorption studies of methylene blue (MB). The mechanism of Mn3O4/AC formation was comprehensively elucidated, and its morphological and structural features were determined by XRD, SEM, FTIR, TEM, and BET methods. Batch experiments were performed to examine the effect of different parameters on the adsorptive removal of MB. The findings have demonstrated a maximum uptake of Mn3O4/AC for MB at 77.02 mg g−1. The most appropriate models for predicting the adsorption kinetics and equilibrium data were determined to be the pseudo-first-order kinetic model and the Freundlich isotherm, respectively. Furthermore, the composite exhibited remarkable reusability and stability, retaining over 90% of MB removal efficiency even after undergoing five cycles of reuse. The adsorption mechanism of the dye was clarified based on the physical properties of the adsorbent, including stacking interactions, pore-filling, hydrogen bonding, and electrostatic interactions. The Mn3O4/AC composite holds promise for future investigations concerning wastewater-containing dyes.