Effect of heat treatment temperature on the structural, morphological, optical and water contact angle properties of brookite TiO2 thin film deposited via green sol–gel route for photocatalytic activity

Brookite has only been utilized a few times and is always a by-product of TiO2. There have been few studies on the preparation of brookite coatings till recently with the existence of solvent. In this study, the structural, morphological, optical and water contact angle properties of brookite thin films deposited via green sol–gel route (without the use of a solvent) were reported. The TiO2 coatings were deposited on a glass substrate via a spin coating method at various temperatures (200 °C, 300 °C, 400 °C and 500 °C). X-ray diffraction analysis revealed the formation of brookite (111) and (023) at 200 °C, 300 °C and 400 °C with an average crystallite size of 7.8 to 58.4 nm. Raman analysis affirmed the brookite presence. Fourier Transform Infra-Red analysis also reveals that brookite thin film exhibits Ti–O–Ti bonding at 400–800 cm−1. A uniform surface of brookite coating was observed at low temperature with an average thicknesses of 350.6 to 618.7 nm. The band gap energy was in the range of 3.37 to 3.90 eV. The water contact angle for brookite coating shows hydrophilic properties throughout all temperatures. The photocatalytic degradation efficiency of methylene blue attributed to the higher crystallinity of brookite thin film heated at 300 °C is of 97.8% after 240 min under visible light.