Photocatalytic degradation of malathion using Zn²⁺-doped TiO₂ nanoparticles: statistical analysis and optimization of operating parameters

A Zn²⁺-doped TiO₂ is successfully synthesized by a facile photodeposition method and used in the catalytic photo-degradation of organophosphorus pesticide, malathion. The obtained photocatalysts are characterized in detail by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD results confirm the formation of the anatase and rutile phases for the Zn²⁺-doped TiO₂ nanoparticles, with crystallite sizes of 12.9 nm. Zn²⁺-doped TiO₂ that was synthesized by 3.0%wt Zn doping at 200 °C exhibited the best photocatalytic activity. 60 sets of experiments were conducted using response surface methodology (RSM) by adjusting five operating parameters, i.e. initial malathion concentration, catalyst dose, pH, reaction time at five levels and presence or absence of UV light. The analysis revealed that all considered parameters are significant in the degradation process in their linear terms. The optimum values of the variables were found to be 177.59 mg/L, 0.99 g/L, 10.99 and 81.04 min for initial malathion concentration, catalyst dose, pH and reaction time, respectively, under UV irradiation (UV ON). Under the optimized conditions, the experimental values of degradation and mineralization were 98 and 74%, respectively. Moreover, the effects of competing anions and H₂O₂ on photocatalyst process were also investigated.