Tuning wettability of TiO2 thin film by photocatalytic deposition of 3D flower- and hedgehog-like Au nano- and microstructures

Highlights: • Two-steps photocatalytic deposition method was used to synthesize hierarchical Au micro- and nanostructures. • The prepared Au-TiO₂ hybrid structured surface exhibits a superhydrophilic state with a CA below 5°. • An extremely water-repellency (with CA > 163°) was achieved after the modification of Au-TiO₂ surface by ODP-SAM. • The photocatalytic decomposition of OPD-SAM on TiO₂ allows a superhydrophilic-superhydrophobic patterning. We propose a two-steps photocatalytic deposition method to synthesize hierarchical Au nano- and microstructures on TiO₂ surface. While the first deposition leads to the formation of flower-like Au microstructures on a highly active TiO₂ thin film, needle-like sharp Au nanostructures are grown on the former Au microstructures after the second deposition. TiO₂ surface decorated with hierarchical Au structures exhibits a superhydrophilic state with a contact angle (CA) below 5°. After the modification of Au-TiO₂ surface by octadecyl-phosphonic acid (ODP)-self-assembly monolayer (SAM), an extreme water-repellency (with CA > 163°) is achieved which retains its stability even after multiple low-high temperature cycles. The spatially controlled photocatalytic decomposition of OPD-SAM on TiO₂ thin film allows a superhydrophilic-superhydrophobic patterning which may open lot of application avenues in microfluidics, oil-water separation including in water harvesting technologies.