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

Abstract

Removal of pharmaceutical waste, aspirin (ASA) in an 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 BET technique measured the surface area of the adsorbent. The activated carbon derived from coffee waste modified by H3PO4 (AC-HCW) 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 to the adsorption procedure. In the batch adsorption test, the highest removal efficiency found was 98.02% in 30 min and 95% in 60 min when used AC-HCW and AC-CW, respectively. The optimum conditions for removing aspirin from aqueous solution were 1000 mg/L of initial concentration ASA, pH 4 and a temperature of 30 °C and 0.5 g of AC-HCW and 0.6 g AC-CW adsorbents. The experimental data for adsorption of aspirin were well fitted into the Langmuir isotherm model and obeyed the pseudo-second-order kinetics model. The adsorption of aspirin onto AC-HCW and AC-CW was exothermic, with enthalpy change ΔH°= −0.182 kJ/mol and −0.216 kJ/mol, ΔS° was 0.072 J/mol −0.004 J/mol, which indicates a decrease in randomness at the adsorbent surface/aspirin solution interface, respectively. In addition, a negative Gibbs free energy ΔG° was obtained, indicating the feasibility and spontaneity of the adsorption process. For this study, the coffee waste modified by H3PO4 is considered a promising adsorbent, and It could be employed as a low-cost alternative to commercial activated carbon in removing aspirin in aqueous solutions.