Synthesis of ZnO nanorods on TiO2 and ZnO inverse opal structures prepared via thermal-atomic layer deposition and hydrothermal growth for photocatalytic applications

Industrial pollutants, including synthetic dyes and organic compounds, pose serious environmental risks, making efficient remediation methods crucial. In this study, opal templates were fabricated using the Evaporation Induced Confined Area Assembly (EICAA) method, where polystyrene nanospheres (300 nm) were precisely assembled on silicon wafers. Subsequently, ZnO and TiO₂ layers were deposited onto the templates using thermal ALD. The polystyrene templates were then removed via calcination at 500 °C. Hydrothermal synthesis was employed to grow ZnO nanorods on the prepared structures. Comprehensive characterization was conducted using TG/DTA/DTG, SEM-EDX, XRD, Raman spectroscopy, UV–Vis spectrophotometry, and photoluminescence analysis. The results showed that the samples exhibited a well-ordered, crystalline inverse opal structure with vertically aligned nanorods on their surface. The photocatalytic performance of the samples was evaluated through the degradation of methylene blue and 4-nitrophenol under UV and visible light irradiation.

Photocatalytic tests revealed that ZnO inverse opals exhibited higher photocatalytic activity than TiO₂ inverse opals. The growth of ZnO nanorods on TiO₂ inverse opals significantly improved their activity, owing to the formation of a micro p-n junction between TiO₂ and ZnO, which enhanced electron-hole separation and reduced recombination rates. ZnO nanorods on ZnO inverse opals demonstrated overall higher activity, benefiting from their increased surface area and charge transport properties. These findings highlight ZnO-based photocatalysts as promising for the degradation of various pollutants, demonstrating potential for environmental remediation applications.