The Effect of Zn Doping to TiO₂Thin Film Band Gap and Photocatalytic Performance: Experiment and Density Functional Theory Simulation

Methylene blue (MB), a prevalent organic dye, continues to be extensively used and released into the environment, threatening aquatic life. In this experiment, TiO2 thin films doped with Zn were synthesized and studied as photocatalysts for wastewater treatment to remove MB from the water. The thin films were made by the simple dip coating method. It was found that the addition of Zn as doping (10 v/v%) reduced the band gap of the TiO2 thin film and increased the calcination temperature. The lowest band gap obtained in our experiment was 3.03 eV, which is close to that of the pure TiO2 thin film band gap of 3.2 eV. With a Zn content of 10 v/v % and a calcination temperature of 500 °C, the decrease in band gap was due to the change in the electronic structure of TiO2, which was confirmed by X-ray diffraction (XRD) measurement and also due to the growth of the anatase phase of TiO2, which was confirmed by Fourier transform infrared spectroscopy (FTIR) measurement. A density functional theory simulation also confirmed the decrease in the band gap. The photocatalytic activity was also conducted and showed that TiO2 with doping of Zn (10 v/v%) at a calcination temperature of 400 °C had the highest photocatalytic activity of 89.47% MB removal after five hours of soaking under sunlight.