Fabrication of porous and visible light active ZnO nanorods and ZnO@TiO2 core-shell photocatalysts for self-cleaning applications

Highly transparent and self-cleaning ZnO nanorods (NRs) and ZnO@TiO2 core-shell (CS) nanoarrays were fabricated using the sol-gel dip-coating technique. TiO2 nanoparticles (NPs) were coated as a shell layer over the hydrothermally grown ZnO NRs. The number of shell layers on the ZnO NRs was varied by modulating the number of dipping cycles from 1 to 3 to optimize their transmittance. The optimized CS nanoarrays with two dipping cycles display a 2% enhancement of optical transmission compared to the ZnO NRs. In addition, superhydrophilicity (contact angle similar to of 12 degrees) stimulates the self-cleaning nature of the thin films. A water contact angle of 12 degrees was noted for the ZnO@TiO2: 2 cycle sample, indicating their superhydrophilic nature. Moreover, the photocatalytic activity of the pristine ZnO NRs and ZnO@TiO2 CS nanoarrays was tested under UV and direct sunlight through the dye degradation of methylene blue (MB). Based upon the TiO2 morphology and accessibility of the ZnO@TiO2 heterojunction interface, CS nanoarrays with two shell layers exhibit the highest degree of dye photodegradation efficiency of 68.72% and 91% under sunlight and UV light irradiation, respectively. The CS nanoarrays demonstrate medium sunlight and excellent UV-light-driven photocatalytic activity. Our findings suggest that the ZnO@TiO2 CS nanoarrays are potential photocatalysts for dye degradation and self-cleaning applications in solar cell coverings.