Synthesis and characterization of ZnO–Ce nanophotocatalyst and their application for the removal of dye (Reactive red 198) by degradation process: Kinetics, thermodynamics and experimental design

In this study, Ce-doped ZnO, an effective photocatalyst, was synthesized via combustion method using different weight percentages (wt.%) of Cerium. The synthesized photocatalyst was used to remove reactive red 198 from the aqueous solution. In the present work, the photocatalytic activity of ZnO nanoparticles was investigated by doping different weight percentages of Cerium (0.4 w% and 0.2w%). The photocatalyst was then characterized by XRD, FTIR, SEM, DRS, TOC and, EDX analyses. According to the results, 0.2 w% Cerium doped ZnO showed better performance than 0.4 w% Cerium doped ZnO. In addition, the central composite design was used to evaluate the influential variables on the elimination of dye from an aqueous solution. The optimal values of effective factors such as photocatalyst dose, pH and initial dye concentration while 0.4 w% Ce:ZnO was used as photocatalyst were obtained 0.12 g.L−1, 6.5 and, 3.18 g.L−1 respectively. While these factors were obtained for 0.2 w% Ce:ZnO photocatalyst 0.16 g.L−1, 6.5 and 3.18 g.L−1, respectively. Moreover, the kinetic aspects of the elimination of reactive red 198 from an aqueous solution were investigated using the pseudo-first-order model. Since to study the process efficiency, it is necessary to find the optimal parameters and flow regime inside the reactor, so the hydrodynamics of the reactor were analyzed through the residence time distribution. Also, from the value obtained for the Reynolds number, it can be concluded that the internal flow of the reactor was laminar. Additionally, from the thermodynamic study of the Reactive red 198 degradation process using 0.2 w% Ce:ZnO and 0.4 w% Ce:ZnO photocatalysts, the adiabatic temperature of 678.54 and 474.19 °C were calculated, respectively. By increasing the temperature of the degradation process up to 40 °C, the dye removal efficiency for 0.2 w% Ce-doped ZnO and 0.4 w% Ce-doped ZnO photocatalysts reached to 96% and 58%, respectively.