Highly efficient cu2+ adsorption using oxygen-plasma-modified activated carbon derived from coffee grounds

Abstract

Activated carbon derived from agricultural biomass has emerged as a promising adsorbent for heavy metal removal due to its low cost, environmental sustainability, and tunable surface properties. In this study, activated carbon was synthesized from waste coffee grounds via anaerobic pyrolysis at different temperatures (400–650 °C), followed by oxygen plasma surface modification. The physicochemical characteristics of the materials were investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and wettability measurements. Porous structures were more pronounced at lower pyrolysis temperatures (400–450 °C), while XRD patterns revealed the evolution of amorphous carbon with broad diffraction peaks around 20° and 25°. Oxygen plasma treatment significantly improved surface hydrophilicity, reducing the water contact angle from 67.95° to 0° after 1 min treatment. Adsorption experiments showed that the sample pyrolyzed at 450 °C and plasma-treated for 1 min exhibited the best Cu2+ removal among untreated samples, achieving a removal efficiency of 34.14% and an adsorption capacity of 33.39 mg g−1 within 20 min. Remarkably, chemical activation using KOH followed by secondary pyrolysis and plasma treatment greatly enhanced adsorption performance. The optimized material achieved complete Cu2+ removal with a high adsorption capacity of ~416.31 mg g−1 within 20 min. These findings demonstrate that the synergistic combination of chemical activation and plasma modification is an effective strategy for developing high-performance biomass-derived carbon adsorbents for rapid heavy metal removal.