Self-cleaning thin films with controlled optical properties based on WO3-rGO

Abstract

The study investigates the self-cleaning and anti-reflectance properties of thin films based on tungsten oxide (WO3) and reduced graphene oxide (rGO) deposited by spraying stable dispersions of sol-gel powders. Two routes were employed: (Route 1) highly crystalline WO3 powder (annealed at 550 °C for 3 h) was mixed with commercial rGO powder in the dispersion and (Route 2) rGO was directly added to the WO3 precursor system to obtain a WO3-rGO sol-gel composite powder (further on annealed at 100 °C for 3 h). Both powders contain WO3 and rGO as confirmed by FTIR and XRD analyses. By milling the pristine WO3 (Route 1) with rGO, more stable dispersions could be obtained using sodium dodecylsulfate (SDS). The hydrophobic surfactant tail bonds to the rGO and the electrostatic repulsion between the anionic heads prevent the flakes agglomeration. In Route 2, the dispersions are not well stabilized by SDS as the anionic head and the WO3 “grafted” on the rGO are both negatively charged, thus repulsions can be expected. This leads to agglomerates formed on the thin films surface that affect the thin films’ UV-VIS transmittance and reflectance but increase their efficiency in methylene blue removal through adsorption. Overall, however, the films obtained following Route 1 proved more uniform, crystalline and superhydrophilic, while maintaining comparable stability in the photocatalysis conditions, and comparable efficiency in methylene blue removal: 25% after 8 h of irradiation with 10% UV + 90% VIS light, having the global irradiance of 34 W/m2.