N-doped TiO2 nanosheets for photocatalytic degradation and mineralization of diazinon under simulated solar irradiation: Optimization and modeling using a response surface methodology

The nitrogen doped TiO2 (N-TiO2) was synthesized via a facile hydrothermal method using titanium (IV) butoxide as a titanium precursor and urea as a dopant source. The catalyst was characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD), surface area (BET method) and band gap energy by diffuse reflectance spectroscopy (DRS). N-TiO2 is a mesoporous nanocrystal sheet with the mean pore diameter of 14.9 nm, specific surface area of 66.3 m2/g, crystallite size of 27 nm, and band gap energy of 2.83 eV. Response surface methodology (RSM) with central composite design (CCD) was utilized for the modeling and optimization of the operational photodegradation variables such as pH, catalyst loading, initial diazinon concentration, and irradiation time. Under the optimum conditions established, the performance of 85% and 63% for degradation and mineralization of diazinon were experimentally reached, respectively. Moreover, the obtained quadratic model showed high correlation (R2 = 0.95 (degradation) and R2 = 0.928 (mineralization)) between the predicted and experimental values. It was found that all the selected variables had an important effect on diazinon removal.