Insight into the adsorption and oxidation activity of a ZnO/piezoelectric quartz core-shell for enhanced decontamination of ibuprofen: Steric, energetic, and oxidation studies

A natural piezoelectric quartz core was coated with environmentally friendly ZnO nanoparticles (GZn/PQz) for enhanced decontamination of ibuprofen (IBF) by adsorption and advanced oxidation. The adsorption properties were described based on the monolayer model of one energy site. The steric studies demonstrated a decline in active site density (Nm) and the saturation adsorption capacities (Qsat) with increasing temperature, and the best values were achieved at 25 °C (Nm = 38.42 mg/g and Qsat = 145.6 mg/g). The number of adsorbed IBF molecules (n) (>3 and <4) suggested the uptake of 3 or 4 IBF molecules per receptor site in a vertical orientation and by a multimolecular mechanism. The adsorption energy values (−7.93 to −9.5 kJ/mol) suggest physical uptake processes. The thermodynamic functions reflected the exothermic and spontaneous properties of the reactions. GZn/PQz achieved IBF (50 mg/L) oxidation percentages of 100%, 93.8%, and 100% after 80 min (photocatalyst), 360 min (piezoelectric catalyst), and 40 min (piezo-photocatalyst), respectively. Hydroxyl radicals and superoxide radicals are essential oxidizing species during the oxidation of IBF by GZn/PQz. Based on the detected intermediate compounds, the oxidation pathway of IBF by GZn/PQz involved hydroxylation, decarboxylation/demethylation, and ring-opening processes.