Optimization and modeling of efficient photocatalytic TiO2-ZnO composite preparation parameters by response surface methodology

Abstract

The major focus of this work is the design and optimization of the preparation conditions of binary titanium dioxide-zinc oxide (TiO2-ZnO) composite using response surface methodology (RSM). Calcination temperature and ZnO weight percent (%) with respect to TiO2 were chosen as the key parameters for optimizing the preparation conditions. The evaluation of photocatalytic nitrogen oxides (NOx) removal efficiency was selected for modeling the RSM. Thirteen factorial design runs were first generated with one replicate and 5 center points in order to perform all the experiments. The experimental results on NOx removal efficiency for the composites calcined at 747, 602, and 558 °C containing 5.48%, 3.48%, and 2.1% of ZnO with respect to the weight of TiO2, designated as MaxT(Z%), MedT(Z%) and MinT(Z%) respectively, agree well with RSM predictions. The response coefficient difference between experimental and RSM results of MaxT(Z%), MedT(Z%), and MinT(Z%) were approximately 0.019, 0.044, and 0.11, respectively. The microstructural and optical properties as well the surface composition of MaxT(Z%), MedT(Z%), and MinT(Z%) were evaluated by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS), respectively. The results from the photodecomposition of NOx gas under illuminated UV-light confirmed that the TiO2-ZnO prepared with a 2.1 wt% of ZnO and calcined at 558 °C witnessed the best photocatalytic activity and the reasons for the excellent performance are corroborated with XRD, XPS, and DRS results. This study provides a simple and systematic approach for the optimization and modeling of the binary composite preparation for achieving enhanced photoactivity.