Ag-doping on ZnO support mediated by bio-analytes rich in ascorbic acid for photocatalytic degradation of dipyrone drug

Abstract

The analytes such as ascorbic acid (AA) present in Sechium edule were extracted (294 mg AA kg^-1 fruit) in an aqueous media for its potential application for Ag-doping onto wurtzite ZnO. The bandgap of ZnO was decreased to 2.85 eV at the optimal Ag-loading of 1.18% (w/w) against 3.13 eV for the control catalyst without using the analytes and, the commercial AA only could reduce the bandgap to 2.91 eV. The saturation photo-electrochemical current density (46.68 mA cm^-2) at E_anode ≥ 0.31 V vs. Ag/AgCl was almost double than pristine ZnO under visible light illumination (λ_mean = 525 nm, 18 K lux) and, the current density was insignificant in the dark. The doped catalyst exhibited the maximum 79.5% degradation (71% COD removal) of an anti-analgesic drug, dipyrone (100 μg L^-1 dipyrone, catalyst 100 mg L^-1) resulted from the formation of O₂^•- radical (g-factor of 2.002-2.008) and paramagnetic oxygen vacancies (g-factor of 2.020) and, no effect of dye-sensitization was noted. The highest quantum yield was found to be 34.7%. The catalyst loss was 6% after the fourth cycle and the dipyrone degradation was reduced to 70.8%.

Keywords: Band gap reduction; Bio-inspired doping; Pharmaceutical wastewater; Photocurrent; Sechium edule; ZnO support.