Turning Waste into Value: Comparative Synthesis of Activated Carbon from Non-Recyclable Polystyrene, Corn Stalks and Coffee Grounds

This study investigates the synthesis of activated carbon (AC) from two distinct waste derived feed stocks: coffee grounds (CG) and a mixture of non-recyclable polystyrene (PS) with corn stalks (CS) for the first time. The results of study show that the CG precursor applied the hydrothermal carbonization (HTC) at 240 °C for 5 h followed by KOH activation at 650°C, while the PS–CS mixture was subjected to pyrolysis at 500 °C for 1.5 h and activated at 750 °C. Interestingly, despite the milder treatment conditions, CGderived carbon achieved a good BET surface area of 914.83 m² g⁻¹, comparable to that of PS–CS-derived carbon (976.34 m² g⁻¹). The superior pore development in the CG sample is attributed to its high oxygen and nitrogen content, which facilitates dehydration, decarboxylation, and the formation of micropores during HTC. In contrast, PS requires higher activation temperature due to its aromatic and oxygen-deficient nature, although copyrolysis with CS promotes synergistic gas evolution and pore widening. These findings highlight that feed stock composition strongly dictates process parameters and pore characteristics, providing insights for designing sustainable routes to produce high performance activated carbon from diverse waste materials.