Titanate nanotube thin films with enhanced thermal stability and high-transparency prepared from additive-free sols

Titanate nanotubes were synthesized from TiO2 in alkaline medium by a conventional hydrothermal method (150 °C, 4.7 bar). To obtain hydrogen titanates, the as-prepared sodium titanates were treated with either HCl or H3PO4 aqueous solutions. A simple synthesis procedure was devised for stable titanate nanotube sols without using any additives. These highly stable ethanolic sols can readily be used to prepare transparent titanate nanotube thin films of high quality. The resulting samples were studied by X-ray diffraction, N2-sorption measurements, Raman spectroscopy, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. The comparative results of using two kinds of acids shed light on the superior thermal stability of the H3PO4-treated titanate nanotubes (P-TNTs). X-ray photoelectron spectroscopy revealed that P-TNTs contains P in the near-surface region and the thermal stability was enhanced even at a low (∼0.5 at%) concentration of P. After calcination at 500 °C, the specific surface areas of the HCl- and H3PO4-treated samples were 153 and 244 m2 g−1, respectively. The effects of H3PO4 treatment on the structure, morphology and porosity of titanate nanotubes are discussed.

Graphical AbstractTEM picture (left) shows P-TNTs with diameters about 5–6 nm. Inset shows a stable titanate nanotube sol illuminated by a 532 nm laser beam. Due to the presence of the nanoparticles the way of the light is visible in the sol.Figure optionsDownload as PowerPoint slideCross sectional SEM picture (right) as well as ellipsometry revealed the formation of optical quality P-TNT films with thicknesses below 50 nm.Highlights
► H3PO4 treatment led to TNTs with high surface area even after calcination at 500 °C.
► H3PO4-treated TNTs preserved their nanotube morphology up to 500 °C.
► Stable TNT sols can be prepared by the peptization of TNT gels.
► High-transparency TNT thin films of high quality were fabricated.