Thiamine-functionalized magnetic coffee-derived carbon for efficient methylene blue removal: Synthesis, mechanism, and performance evaluation

This study reports the development of a magnetically retrievable and surface-functionalized activated carbon derived from spent coffee grounds (SCG) for the adsorption of methylene blue (MB) from aqueous solutions. The SCG was carbonized and chemically activated, followed by incorporation of Fe₃O₄ nanoparticles and functionalization with thiamine to yield the MSCAC@TA nanocomposite. Characterization using FTIR, SEM, XPS, TGA, BET, and zeta potential analysis confirmed successful integration of surface functional groups, magnetic domains, and enhanced porosity. The composite achieved a maximum MB removal efficiency of 93.14 % under optimal conditions. Adsorption equilibrium data fit best with the Langmuir isotherm (qₘₐₓ = 211.54 mg/g), indicating monolayer coverage. While the Elovich kinetic model suggested surface heterogeneity and strong dye–adsorbent interactions, the thermodynamic parameters (ΔH° = –21.96 kJ/mol) indicated physisorption predominance. Reusability tests demonstrated a 90.1 % retention in removal efficiency after five cycles. These results suggest MSCAC@TA offers a promising, low-cost route for dye remediation, though further studies in real wastewater matrices are needed to validate broader applicability.