Removal of aspirin from aqueous solution using phosphoric acid - modified coffee waste adsorbent

Abstract

Removal of pharmaceutical waste, aspirin (ASA) in aqueous solution was investigated using activated carbon derived from coffee waste(CW). Activated carbon was prepared by using phosphoric acid as a chemical activating agent. Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the functional groups on the surface of the adsorbents. The surface area of the adsorbent was measured by BET technique. The activated carbon derived from coffee waste modified by H3PO4 was observed to have a larger surface area than AC-CW. The states of the adsorption operations are controlled by the effect of initial ASA concentration, adsorbent dose, contact time, temperature and pH adjacent on the adsorption procedure. In the batch adsorption test, the highest removal efficiency found was 98.02% in 30 minutes and 95% in 60 minutes when used H3PO4 - ACCW and AC-CW respectively. The optimum conditions for removal of aspirin from aqueous solution was found to be at 1000 mg/L of initial concentration ASA , pH 4 and at a temperature of 30°C and 0.5 g of H3PO4 - AC-CW and 0.6g AC-CW adsorbents. The experimental data for adsorption of aspirin were well fitted into Langmuir isotherm model and obeyed pseudo-second order kinetics model. The adsorption of aspirin onto H3PO4- AC-CW and AC-CW were exothermic in nature, with enthalpy change AH° = - 0.182 kJ/mol and -0.216 kJ/mol, AS0 was 0.072 J/mol -0.004 J/mol , which indicates a decrease in randomness at the adsorbent surface/aspirin solution interface, respectively. A negative Gibbs free energy AG° was obtained indicating feasibility and spontaneity of the adsorption process. For this study, the coffee waste modified by H3PO4 modified is considered as promising adsorbent and it could be employed as a low cost alternative to commercial activated in removal of aspirin in aqueous solutions.