Cerium oxide: synthesis, brief characterization, and optimization of the photocatalytic activity against phenazopyridine in an aqueous solution.

Water pollution by antibiotics is a global crisis, and its risk is critically more severe due to the explosive use of these drug compounds. A critical effective removal method to diminish this risk is heterogeneous photocatalysis and optimizing the conditions to reach higher mineralization efficiency. CeO anoparticles (NPs) were synthesized and characterized by X-ray diffraction (XRD), UV-Vis diffuse reflection spectroscopy (DRS), and Fourier transform infrared spectroscopy (FTIR) techniques. A cubic structural crystallite phase was detected that had crystallite sizes of 17.9 and 16.7 nm estimated by the Scherrer and Williamson-Hall models. A typical FTIR absorption band for the Ce-O stretching absorption has appeared at 554 cm. Based on DRS data and the Kubelka-Munk and Tauc models, Eg values of 2.80, 3.06, 3.12, and 3.13 eV were obtained for n-values of 1/2, 2, 3/2, and 3, respectively. pHpzc of CeO NPs was about 5.7. The direct photolysis and surface adsorption processes have no critical role in phenazopyridine (PP) removal by appearing with 2.7 and 6.7% removal efficiencies, respectively. Due to the highest photocatalytic activity of CeO NPs toward PP, the effects of the critical operating variable on the activity were evaluated, and the optimal conditions were as catalyst dose, 0.7 g/L; pH, 6; irradiation time, 90 min; and C, 20 ppm. The Hinshelwood kinetics equation plot was y =  - 6.6442 - 0.4677x (r = 0.9296), in which its slope as the rate constant of the photodegradation process was 0.4677 min (corresponding to a t value of 1.48 min).