Synthesis of polymer functionalized spent coffee-based porous carbon for efficient dye adsorption

This study reports the development of a sustainable polymer-functionalized adsorbent (SCAC-g-PSPA) prepared by grafting 3-sulfopropyl methacrylate potassium salt onto spent coffee-derived activated carbon. The material was comprehensively characterized by SEM, XRD, FTIR, BET, TGA, and XPS, confirming successful surface functionalization, polymer loading (∼8.5 wt%), and enhanced physicochemical properties. Compared to the unmodified SCAC and intermediate SCAC-g-MPS, the final composite exhibited a markedly higher adsorption capacity for methylene blue (MB), achieving 430.64 mg/g under optimized conditions. Adsorption followed the Freundlich isotherm and Elovich kinetic models, indicating adsorption on a heterogeneous surface with multiple active sites, without implying a specific chemisorption mechanism. Mechanistic validation using FTIR and XPS confirmed that electrostatic attraction and n–π interactions drive the uptake of the dye. Recyclability tests demonstrated excellent durability, with SCAC-g-PSPA retaining more than 90 % efficiency after five adsorption–desorption cycles and showing no significant polymer degradation. These results highlight the combined benefits of waste valorization, polymer functionalization, and robust reusability, establishing SCAC-g-PSPA as a cost-effective and sustainable adsorbent for wastewater treatment applications.