Removal of PFOA and PFOS from aqueous solutions using activated carbon produced from Vitis vinifera leaf litter

Abstract

The removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from aqueous solutions using agro-waste biomass of Vitis vinifera (grape) leaf litter was studied. Activated carbons were produced from the biomass and chemical activation achieved by using phosphoric acid (H3PO4) and potassium hydroxide (KOH) for the modification of the carbons’ surface morphology. Activated carbons were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy and Brunauer–Emmett–Teller (BET) in order to understand removal mechanisms of the contaminants by activated carbons. The effect of solution concentration, pH, adsorbent dosage, contact time and temperature was evaluated to optimize the removal efficiency of activated carbons. Adsorption isotherm models were used to analyse the equilibrium data obtained, and kinetic models were applied to study sorption mechanisms. The results fitted well into Freundlich isotherm with both AC-KOH and AC-H3PO4 having high K f values. Maximum adsorption capacities for AC-H3PO4 were 78.90 and 75.13 mg/g for PFOA and PFOS, respectively. Equilibrium was reached before 60 min on both adsorbents, and thermodynamic studies indicated that the process was exothermic and spontaneous. Surface morphology showed the abundance of microspores (>60%) with BET total surface area of 295.488 and 158.67 m2/g for AC-H3PO4 and AC-KOH activated carbons, respectively. Removal efficiencies were 95 and 90% for PFOA using AC-H3PO4 and AC-KOH, respectively; corresponding values for PFOS were 94 and 88%. Adsorbents’ removal capacities depended on the physicochemical characteristics of adsorbents.