Thin Films for Self-Cleaning and Energy Efficiency

Abstract

In this research work, nano level multilayered transparent thin films of ZnO, Ag and TiO2 were synthesized by physical vapor deposition (sputtering) for combined applications of self-cleaning and energy efficient smart glasses. These “self-cleaning and low- ɛ” (SCALE) coatings can be applied on window surfaces to make them heat insulated and self-cleaning. The coatings were separately made from ZnO and TiO2 nanoparticles which act as a self-cleaning layer and Ag nanoparticles were added in these coatings for low emissivity, hence energy efficiency. Also, thin films of TiO2 and ZnO were deposited on soda lime glass (SLG) via Spray Pyrolysis to evaluate the self-cleaning properties. TiO2 and ZnO sol was prepared via sol-gel synthesis. SEM images shows the nanoparticles size range from 15 to 30 nm with a good nano size distribution. X-ray diffraction (XRD) results confirmed the presence of both ZnO and Ag in the thin films produced by sputtering and the presence of ZnO thin films produced by Spray Pyrolysis. Atomic force microscopy (AFM) images showed maximum surface coverage and enhanced surface roughness by nanoparticles deposited as a result of sputtering and Spray Pyrolysis. Contact angle shows varying nature of the prepared samples and surface roughness of the thin films prepared by Sputtering and Spray Pyrolysis. UV-Vis-NIR spectroscopy showed reflectance up to 90% in IR region of solar spectrum by the optimized coating produced by sputtering by combining ZnO and Ag, and TiO2 and Ag. Then for the samples prepared by Sputtering and Spray Pyrolysis, band gap was calculated using UV-Vis Spectroscopy and the results showed that the prepared thin films were highly transparent in visible region of solar spectrum. Self-cleaning ability of prepared samples was tested by degradation of an organic dye rhodamine B. The SCALE nano coatings provide a cost efficient and novel alternative by giving two properties of self-cleaning and energy efficiency in a single assembly and the thin films prepared by Spray Pyrolysis can be employed as efficient coatings on glass for self-cleaning properties.