Synthesis of activated carbon from spent tea leaves for aspirin removal

Adsorption capacity of activated carbon prepared from spent tea leaves (STL-AC) for the removal of aspirin from aqueous solution was investigated in this study. Preliminary studies have shown that treatment with phosphoric acid (H3PO4) increased removal efficiency of STL-AC. Characterizations on STL-AC revealed excellent textural properties (1200 m(2).g(-1), 51% mesoporosity), as well as distinctive surface chemistry (1.08 mmol.g(-1) and 0.54 mmol.g(-1) for acidic and basic oxygenated groups, pH(pzc) = 2.02). Maximum removal efficiency of aspirin observed was 94.28% after 60 min when the initial concentration was 100 mg.L-1, 0.5 g of adsorbent used, pH 3 and at a temperature of 30 degrees C. The adsorption data were well fitted to the Freundlich isotherm model and obeyed the pseudo-second order kinetics model. The adsorption of aspirin onto STL-AC was exothermic in nature (Delta H-circle minus = - 13.808 kJ.mol(-1)) and had a negative entropy change, Delta S-circle minus(- 41A44 J.mol(-1)). A negative Gibbs free energy, Delta G(circle minus) was obtained indicating feasibility and spontaneity of the adsorption process. The adsorption capacity of AC-STL (178.57 mg.g(-1)) is considerably high compared to most adsorbents synthesized from various sources, due to the well-defined textural properties coupled with surface chemistry of STL-AC which favors aspirin adsorption. The results demonstrate the potential of STL-AC as aspirin adsorbent. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.