Fabrication and characterization of hybrid micro/nano-structured hydrophilic titania coatings deposited by suspension flame spraying

Nanostructured titania coatings have been a research focus for many years owing to their excellent photocatalytic activity. The major persistent challenge yet is development of competitive deposition techniques for fabricating the nanostructured coatings. Here we report a novel deposition approach by flame spraying the mixtures of nano titania-contained suspension and micron-sized titania powders feedstock. Promising hybrid micro/nano-structured TiO2 coatings comprising micron-sized splats (50–80 μm) and nano particles (10–40 nm) were successfully produced. Anatase-rutile ratio and proportion of the nanostructures in the coatings can be tailored in a wide range depending on the concentration of nano TiO2 particles (10–30 nm in size) in the starting suspension. Up to 30 wt.% of anatase in the coatings was achieved. The hybrid micro-/nano-structured TiO2 coatings exhibit super-hydrophilic performances (∼0° contact angle). Effect of the suspension concentration (concentration of the nano titania particles in the suspension) on the microstructure and mechanical properties of the coatings was also investigated. Compared to the coating deposited using the suspension alone, the hybrid micro/nano-structured TiO2 coatings exhibited markedly enhanced adhesive strength (by up to 1.8 times) and microhardness (by 9 times). The behavior between the TiO2 particles with micro- and nano-sizes was also elucidated.