Uniform coating of TiO2 nanoparticles using biotemplates for photocatalytic wastewater treatment

Immobilization of TiO₂ particles over substrates like glass can facilitate the separation after photocatalytic runs. Photocatalytic activity of TiO₂ coatings is related to its morphology, crystallography, optical properties and adherence of the coating. Biotemplates, including animal-based and herbal-based templates are inexpensive, biocompatible and abundant and can control the quality of TiO₂ coating. In this study the effects of biotemplates such as agar, gelatin, and starch on the physiochemical properties of TiO₂ coatings were investigated. Synthesized coatings were characterized by XRD, BET, FESEM, TEM, FTIR, EDX, and UV-Vis DRS analyses. The results showed that using biotemplates reduces the TiO₂ crystallite size. Template-free TiO₂ had 30 nm crystallite size, but using templates like agar decreased the size to 18 nm. Moreover, the addition of biotemplates decreased the thickness of TiO₂ coatings compared to template free coating. And the use of biotemplates also limits the pore size distribution and increases BET surface area. According to EDX, TiO₂ coating with agar indicated a uniform Ti distribution and crack-free homogenous morphology. TEM analysis of agar-templated TiO₂ film showed a uniform morphology of TiO₂ particles with average particle size of 20 nm. The UV-Vis DRS also confirmed a reduction in the band gap of TiO₂ after the introduction of biotemplates. The study of the photocatalytic performance of samples showed that agar-templated TiO₂ coating was able to remove 62.4% of methylene blue, while the coatings synthesized with gelatin and starch were just able to remove 42.77% and 35%, respectively. The TiO₂ coating with agar was studied at different pH values and different initial methylene blue concentrations as well. The stability test of agar-templated TiO₂ coating after four runs indicated just 5% of activity lost.