The role of thermal annealing in controlling morphology, crystal structure and adherence of dip coated TiO2 film on glass and its photocatalytic activity

In this paper, sol-gel technique with dip coating was used to prepare photocatalytic TiO2 coatings on glass plates. Effect of different calcination temperatures of 400, 500, 600 and 700 °C on the photocatalytic activity of TiO2 coatings was investigated in de-colorization of methylene blue under UV-A irradiations in a batch reactor. The highest methylene blue degradation was achieved by the coating calcined at 500 °C. Lower and higher calcination temperatures had lower activity in degradation of methylene blue. The TiO2 coating calcined at 500 °C removed almost 90% of initial methylene blue while other coatings barley removed 30% of dye after 400 min of UV irradiations. XRD, FESEM, FTIR, EDX and TEM showed that the calcination temperature had a great influence on crystalline structure of TiO2 coatings. The coating calcined at 400 °C indicated mixed phase of anatase and rutile but with increasing the calcination temperature to 500 °C, crystalline phase transformed from mixed phase to pure phase of anatase. The TiO2 crystallites were small and highly dispersed in 500 °C calcined coating compared to other calcination temperatures. The sample calcined at 500 °C had a uniform morphology with smooth coating of small nanoparticles without any crack. Adhesion of TiO2 coatings on glass plates was investigated by atomic absorption of treated wastewater and sonication weight loss of TiO2 coatings. The amount of Ti leached from studied coatings was negligible and the 500 °C calcined coating showed the lowest weight loss after sonication. The effect of pH of wastewater, initial concentration of methylene blue and number of TiO2 coated glass plates was evaluated in decolorization of methylene blue using the TiO2 coating calcined at 500 °C.