Synergistic effect of TiO2@SiO2 coatings for photocatalytic treatment of dyes-based wastewater

In this research, TiO2 and SiO2 sols were prepared from precursor of titanium and silicon in an acetic acid-water mixture with no further chemicals to make the sol-gel method as green as possible. The TiO2 sol was heated at 40 ℃ or 50 ℃ during preparation to study the effect of temperature over its stability and photocatalytic ability. Dip-coating technique was employed for fabrication of bare TiO2 and multilayer silica-titania coatings over glass substrate. The stability of prepared sols over aging was assessed through DLS. The structural and morphological analysis of coatings was made through x-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The photocatalytic ability of coatings was tested by photodegradation of rhodamine B (RhB) dye under UV irradiance (λ = 365 nm). DLS revealed a reduction in shelf life of heat treated TiO2 sols with respect to sols produce at ambient temperature. XRD confirmed the formation of crystalline anatase phase TiO2 nanoparticles with an average crystalline size of 5 nm, and average particle size in the range of tens to hundreds of nanometers (evolving with aging) as provided by DLS, indicating strong agglomeration. The heating effect of TiO2 sol improved the photocatalytic ability of coatings thanks to accelerate hydrolysis reactions, producing a larger amount of crystallites. TiO2@SiO2 coatings showed a crack-less and uniform morphology with 100 % photocatalytic degradation of RhB in the tested conditions and a kinetic constant of 0.01392 min-1, compared to 92 % efficiency and 0.00827 min-1 of bare TiO2 coatings, respectively. Overall, the optimization of sol-gel parameters and composite material selection in TiO2 based coatings can lead to more effective photocatalysts for environmental cleanup.