The photodegradation of oxytetracycline by Degussa P25-TiO₂/Fe⁰/ZnO ternary chain heterojunction in the presence of persulfate under visible light irradiation: The optimization and kinetic study

Degussa P25-TiO₂/ZnO was impregnated with (Fe (NO₃)₃·9H₂O) solution to give a ternary chain heterojunction of P25-TiO₂/1.5 wt% Fe⁰/ZnO (denoted as P25/Fe⁰/ZnO) (Gap Energy, Eg = 2.84 eV). The obtained nanocomposite was used in the presence of K₂S₂O₈ for the degradation of oxytetracycline (OTC) in an aqueous solution under visible-light irradiation. The response surface methodology (RSM) was employed to understand the effects of catalyst dosage, pH, and K₂S₂O₈ on OTC degradation. The RSM could correlate the experimental value of OTC degradation with the predicted values. The best OTC degradation efficiency (89.3 %) was obtained with 0.28 g/L of P25/Fe⁰/ZnO at 3.02 mg/L of [K₂S₂O₈] and pH 7.5 for 120 min. The superior performance of the catalytic system was attributed to the attraction effects between the negative charge on the catalyst surface and the positive charge on the dimethylammonium functional group on OTC at pH = 7.5. The OTC adsorption rate on P25/Fe⁰/ZnO was investigated using the linear form of the pseudo-second-order kinetic model. The heterogeneous nature of the catalyst was studied by a hot filtration test. Finally, the generated products of photocatalytic degradation were determined using GC–MS analysis, and the oxidation route and an acceptable mechanism were suggested.