Superhydrophilicity of photocatalytic ZnO/SnO2 heterostructure for self-cleaning applications

Abstract

Sol–gel spin coating technique was used to deposit thin films of ZnO, SnO2, and ZnO/SnO2 on a borosilicate glass substrate. The films were characterized using XRD, FESEM, EDX, HRTEM, AFM, UV-Vis spectrophotometer, and contact angle meter. X-ray diffraction confirms the presence of both hexagonal wurtzite and tetragonal phase of ZnO and SnO2 respectively in ZnO/SnO2. Wettability studies reveal that ZnO/SnO2 film is superhydrophilic with water contact angle of 3.4°. The photocatalytic performance of the films is evaluated by measuring the degradation of an aqueous solution of methylene blue, methyl orange, and their mixture. The degradation of stearic acid adsorbed on the film’s surface is measured by tracking the water contact angle after UV irradiation as a function of time. The excellent photocatalytic activity of ZnO/SnO2 thin films is attributed to formation of type-II heterostructure between ZnO and SnO2, which inhibits the charge recombination between photogenerated electrons and holes. The ZnO/SnO2 shows good photocatalytic activity after five recycling runs. ZnO/SnO2 thin films being excellent photocatalyst along with its superhydrophilic nature will have potential application in self-cleaning and antifogging.