Enhancement of photocatalytic properties of TiO2 for NO photo-oxidation by optimized sol-gel synthesis

TiO2 samples were prepared by the sol-gel method applying a factorial design in order to improve the photocatalytic properties of the semiconductor oxide for the nitric oxide (NO) photo-oxidation reaction. The temperature of calcination and the amount of alcohol and acid used in the course of the sol-gel reaction were selected as critical experimental variables. As the products of the factorial design, 27 TiO2 samples were obtained and characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, diffuse reflectance spectroscopy, and adsorption-desorption N-2 isotherms. The photocatalytic activity of the TiO2 samples was evaluated in the NO photo-oxidation reaction under UV irradiation. The conversion degree of NO reached by each sample was associated with its physicochemical properties, finding a stronger dependence with the temperature of calcination and morphology of the samples. Different photocatalytic reaction parameters were modified such as mass of photocatalyst, irradiance, flow rate of gas, and relative humidity in order to evaluate their effect in the constants of velocity and adsorption. The TiO2 sample with the highest photocatalytic activity was exposed under different experimental conditions to evaluate its selectivity for the formation of innocuous nitrate ions as final product of the NO photo-oxidation reaction.