Characterization of brookite thin film deposited by spin coating method with green sol-gel route

• Main Author: Johari, Nur Dalilah
• Format: Thesis
• Language: English; English
• Published: 2022
• Subjects: T Technology (General); TP Chemical technology
• Online Access: http://eprints.utem.edu.my/id/eprint/26913/1/Characterization%20of%20brookite%20thin%20film%20deposited%20by%20spin%20coating%20method%20with%20green%20sol-gel%20route.pdf; http://eprints.utem.edu.my/id/eprint/26913/2/Characterization%20of%20brookite%20thin%20film%20deposited%20by%20spin%20coating%20method%20with%20green%20sol-gel%20route.pdf; http://eprints.utem.edu.my/id/eprint/26913/; https://plh.utem.edu.my/cgi-bin/koha/opac-detail.pl?biblionumber=122095

Brookite thin film is one of the great interests as a photocatalyst for water treatment in photocatalytic applications. Brookite has several advantages, but its applicability has been mainly limited because of the inability to synthesize brookite in pure phase due to its high purity and large surface area. One way to overcome such limitation is to establish the brookite phase by optimizing the synthesizing technique and sol-gel formulation. The current study was focused on the comparative deposition methods between dip and spin coating in order to evaluate the brookite phase. The green sol used was made free from solvent as an attempt for a green sol–gel route. The heat treatment temperature is varied and fixed at 200°C, 300°C, 400°C and 500°C for 3 h. The produced thin films were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). Results showed that deposition methods influence the type of phase formation and crystallinity. TiO2 thin films via dip coating composed of anatase (101) at 2θ = 25° and rutile (110) at 2θ = 27° while spin coating produce single brookite (111) at 2θ = 31°. The crystallite size of brookite thin film was larger (47.9 nm and 58.4 nm) compared to dip coating (5.0 nm to 28.8 nm). Raman shows that the TiO2 thin film via dip and spin coating has a mixture of anatase, rutile and brookite. SEM analysis shows that the brookite thin film deposited via spin coating produced uniform and crack free coating at 200°C and 300°C. Brookite thin film had a crack coating with a width of 3.1 μm at 400°C and 1.5 μm at 500°C. In comparison to the TiO2 thin film deposited via dip coating, which had a dense coating and cracks ranging in width from 0.4 μm to 4.3 μm. The coating thickness of brookite thin films via spin coating was in the range of 350.6 nm to 618.7 nm and TiO2 thin films via dip coating was in the range of 320.5 nm to 1005.9 nm. TEM analysis on the films deposited via spin coating confirmed the presence of only brookite crystallites with lattice fringes of 0.28 nm compared to films via dip coating, which show anatase with lattice fringes of 0.35 nm and rutile with lattice fringes of 0.33 nm. FTIR results shows the TiO2 thin film obtained via dip and spin coating contained the hydroxyl group on the surface of thin film. Next, the properties of brookite thin films via spin coating, which is band gap energy were in the range of 3.37 eV to 3.90 eV at 200°C to 500°C. The water contact angle of brookite thin films via spin coating was between 11.79° to 19.64° at 200°C to 500°C. The degradation of methylene blue shows the brookite thin film at 300°C and 200°C exhibit the highest degradation of methylene blue under UV light (67.7% and 63.0% after 4 h) and visible light (97.8% and 95.4% after 4 h) irradiation, respectively. The larger crystallite size (47.9 nm and 58.4 nm) and lower band gap energy value (3.37 eV) influenced the degradation of methylene blue. Thus, from the results, the brookite thin film coating was shown to be more effective in the degradation of methylene blue under visible light irradiation compared to under UV light irradiation in decomposing water contaminants by transforming them into benign substances.