Enhanced visible light photocatalytic activity of nanostructured SiO2-TiO2 thin films through optimizing thickness

Thin films of silicon dioxide-titanium dioxide (SiO2-TiO2) with different thicknesses were deposited by a simple dip-coating method in a repetition behavior followed by heating processes. Choosing the optimum thickness is accounted as an approach for improving photocatalytic and hydrophilicity properties of a thin film. The obtained results from FESEM and AFM characterizations showed that with increasing thickness, the surface roughness increases from 3.089 nm to 132.8 nm. The XRD patterns indicate the presence of anatase phase for the SiO2-TiO2 thin film. Optical measurements were used to calculate thickness, generation rate of photocarriers, band gap, and refractive index of the samples. Decrease of band gap with increasing thickness makes the layer more proper for photocatalytic activity under visible light. It is obtained that the generation rate of carriers has the highest value (17.16 x 10(24) m(-3)s(-1)) for the thickness of 336 nm. PL spectra for the thickness of 336 nm confirmed the presence of defects which reduce the recombination rate and improve charge carrier separation. XPS was used to distinguish the chemical composition. Variation of defect concentrations, number of grain boundaries, and surface roughness with thickness were considered as the main parameters affecting the photocatalytic performance. The highest photodegradation was obtained for 336 nm thick film under illumination of visible light (100% degradation of 40 ml solution of 10 mg l-1 methylene blue (MB)). This research provides a systematic study on the structural and optical properties of the different thick SiO2-TiO2 films with goal of enhancing photocatalytic activity in the visible light region.

Automated summary

This study focuses on the preparation of silicon dioxide-titanium dioxide (SiO2-TiO2) thin films with different thicknesses using a dip-coating method. The aim is to improve the photocatalytic and hydrophilicity properties of the film by optimizing the thickness. The results show that increasing the thickness leads to higher surface roughness and a decrease in band gap, making the film more suitable for photocatalytic activity in visible light. The presence of defects in the 336 nm thick film also contributes to the improved charge carrier separation. XPS analysis is used to determine the chemical composition and the main parameters affecting photocatalytic performance, such as defect concentrations, grain boundaries, and surface roughness. The 336 nm thick film exhibits the highest photodegradation rate under visible light. This research provides valuable insights into the structural and optical properties of SiO2-TiO2 thin films for enhanced photocatalytic activity in the visible light region.