Enhanced visible photocatalytic performance of un-doped TiO2 nanoparticles thin films through modifying the substrate surface roughness

Abstract

Titanium oxide (TiO2) has been widely utilized for application in environmental pollution due to its unique properties. However, large bandgap (3.2 eV) and low surface area of bulk TiO2 are the main properties that limit its photocatalytic applications. In this work, a thin layer of TiO2 (<200 nm) nanoparticles (NPs) on mechanically roughened glass substrates is deposited by a simple sol-gel method followed by a dip-coating process along with fast heating and sintering. The effect of substrate surface roughness on the morphology, hydrophilicity, and optical properties which results in a more electron-hole generation and consequently improved photocatalytic activity was investigated by different characterization techniques. The TiO2 layer on the roughest substrate (RMS = 76.90 nm) showed the smallest average NP size (3 nm) with the highest surface roughness (RMS = 121.00 nm) and hydrophilicity (74.5%) as well as strong optical absorption. This sample photodegraded the pollutant with an efficiency of 85% at a rate of 0.0054 min−1 under the illumination of the vis-light emitting diode (LED)-based source (440 and 590 nm). Therefore, an enhanced photocatalytic activity accompanied by recyclability was achieved by modifying the substrate surface roughness and thermal treatment in the process of synthesis. Conclusively, intrinsic defects and grain boundaries appear which behave as active areas for charge transfer in the photocatalytic process under visible irradiation. This research may provide an insight into the fabrication of highly efficient photocatalysts based on commonly used wide band gap materials to work in the absence of UV light.