Preparation And Properties Of Insulating Titanium Dioxide Nanostructured Coatings

TiO2 nanotube coating is playing an important role in fields that self-cleaning, anti-fog, electrochromic devices and photocatalysis, etc. due to its nanotube structure with large specific surface area and its outstanding physic and chemical properties. In order to prepared TiO2 coating with good integrated performance, single-layer Ti films were deposited onto the glass substrates at room temperature by magnetron sputtering and anodized into TiO2 nanotube coating in ethylene glycol containing 0.75wt% NH4F and 3vo1% H2O under voltage 8-60 V, followed by being annealed at 450 ℃. The crystal structure, morphology and thickness of the prepared coatings were studied via X-ray diffractometry (XRD), scanning electron microscopy (SEM) and surface profiler respectively. The optical property of coatings and the change in concentration for organic solution were investigated by UV-Vis spectrophotometer. The photocatalytic activity of the prepared TiO2 coatings was evaluated by decomposing methylene blue solution (MB) under high pressure mercury lamp irradiation. The wettability of coatings and the adhesion between coatings and substrates were detected by contact angle meter and scratch tester respectively.The structure studies show that: 1) Homogeneous TiO2 nanotube coatings without residual metal Ti underneath the nanotubes are obtained successfully by anodizing Ti films deposited onto isolating substrates at room temperature at 8-40 V. The coating anodized at 8 V presents irregular nanotube structure and the average diameter of the tubes are range from 20-70 nm; The coatings anodized at 15 V and 20 V present ordered nanotube structure and the average diameter of tubes are 25 nm and 27 nm respectively; Nanotube structure appears inner the coating anodized at 40 V while its surface morphology are regular nanopore with average diameter about 44 nm. 2) Only anatase was obtained in the TiO2 nanotube coatings anodized at 8-40 V after being annealed at 450 ℃ and the anatase is preferred orientation in (101) crystal face; The higher the voltage in anodization is, the more apparent the preferred orientation will be.The properties studies show that: 1) The nanotube coatings anodized at 15～20V present the highest transmittance and are higher than those reported in literatures. They are completely transparent and the average transmittance in visible region (λ=400～800 nm) is about 100% when the thickness of coatings are about 378-514 nm; the transmittance can reach as high as 96～97% when the thickness of coatings increase to 1.25～1.33 μm. Besides, the transmittances of the prepared transparent TiO2 nanotube coatings at λ=400 nm are about 97% when the thickness are about 378～514 nm and 81～86% at 1.25～1.33 μm. 2) The wettability of TiO2 nanotube coatings can be changed by changing voltage during anodization. The prepared coatings anodized at 8-20 V are hydrophobic and the contact angle are 137～139°. 3) The prepared coatings have good photocatalytic performance for methylene blue. The photo-induced decomposition rate of methylene blue solution can reach 70% in 3 hours and reaction rate constant κ can be 0.42 h-1 by the nanotube coatings with area of 1×1 cm2 and thickness about 1.2 μm, while the constant κ for self-photocatalysis is only about 0.08 h-1. 4) The TiO2 nanotube coatings anodized at 8-40 V have a good adhesion to the substrates and the adhesion load are about 2.9-6.5 N.