Sustainable Bio-Adsorbent Generated from Coffee Waste for Dual Application in Heavy Metal and Dye Removal

Heavy metal and dye contamination from industrial wastewater present substantial dangers to both ecological systems and human well-being. This study explores the upcycling of Coffee Powder Trimmings (CPT), a biomass waste rich in oxygen-containing functional groups, for water remediation. CPT was first used to adsorb Cu2+ and Fe3+ ions, then pyrolyzed at 750 °C to form metal oxide biochar composites (Cu/CB and Fe/CB). Characterization confirmed the formation of CuO and Fe3O4 particles and the retention of key adsorption functionalities. The materials were evaluated for methylene blue (MB) removal across pH levels, various water bodies, and multiple reuse cycles. CPT effectively removed >95% of Cu2+ and Fe3+ via chelation, while Fe/CB achieved up to 97.8% MB removal due to synergistic π–π, hydrogen bonding, and coordination interactions. Both biochars retained high performance after five cycles, with Fe/CB maintaining 86.88% efficiency. These results highlight CPT-derived biochar as a sustainable, low-cost adsorbent for dual removal of heavy metals and dyes.