Removal of aspirin in aqueous using activated carbon derived from spent tea leaves

Abstract

Aspirin is one of the most consumed drugs which can be found in aquatic environment. Even though the concentration is in trace amount, it may bring adverse impacts to human and environments. This study was conducted to i) synthesize and characterize activated carbon derived from spent tea leaves (AC-STL); ii) determine the effects of various parameters on the removal of aspirin by batch adsorption; iii) determine the adsorption isotherm, kinetic and thermodynamic behavior of the adsorption. Several types of adsorbent were synthesized such as raw spent tea leaves, untreated AC-STL, H3PO4 treated AC-STL, ZnCl2 treated AC-STL and K2CO3 treated AC-STL. In a screening test for the best adsorbent to remove aspirin in aqueous, H3PO4 treated activated carbon derived from spent tea leaves (H3PO4-AC-STL) have the highest removal efficiency, thus it was used for further studies. H3PO4-AC-STL was characterized in terms of surface morphology, porosity and functional group using Field Emission Scanning Electron Microscopy, Micromeritics instrument and Fourier Transform Infrared Spectroscopy respectively. Batch study was conducted for H3PO4-AC-STL. The adsorption capacity was found to be dependent on reaction time, initial aspirin concentration, adsorbent dosage, pH and temperature. The highest removal efficiency observed was 94.28% after 60 minutes when the initial concentration was 100 mg/L, 0.5 g of adsorbent used, pH 3 and at a temperature of 30°C. The experimental data for adsorption of aspirin were well fitted into Freundlich isotherm model and obeyed pseudo-second order kinetics model. The adsorption of aspirin onto H3PO4-AC-STL was exothermic in nature (ΔH° = -13.808 kJ/mol) and have a negative entropy change, ΔS° (-41.444 J/mol). A negative Gibbs free energy, ΔG° was obtained indicating feasibility and spontaneity of the adsorption process. In conclusion, H3PO4-AC-STL could be employed as a low cost alternative to commercial activated in removal of aspirin in aqueous.