Low Alkali Bottom-Up Synthesis of Titanate Nanotubes Using a Peroxo Titanium Complex Ion Precursor for Photocatalysis

Titanate nanotubes (TNTs) have attracted significant attention as functional materials in various fields for their photocatalytic properties. However, their synthesis method, which requires high alkali concentrations, limits their preparation and application. Here, we applied a peroxo titanium complex as a precursor for low alkali synthesis of titanate nanotubes to design appropriate inorganic nanostructures through a controlled bottom-up synthesis route for photocatalyst applications. The use of peroxo titanium complexes could minimize the number of alkaline species used for the synthesis of nanostructured titanates, which is advantageous for the mass production of nanostructured titania powders. The complex ions were prepared by the ionization of titanium hydride powder in the presence of hydrogen peroxide and a sodium hydroxide mixed solution, in which a minimum concentration of 1.5 M NaOH was required. This concentration is 87.5% lower than that of the traditional method. Sodium titanate was synthesized by heating the prepared peroxo titanium complex ion precursor at 100 °C for 12 h without additional input of NaOH. The sodium titanate possessed layers of sheetlike structures 100 nm in width. Further ion exchange phenomenon via a distilled water washing procedure had resulted in the formation of tubelike structures 10 nm in diameter rather than sheetlike structures. The transformation into nanotube structures occurs by the reduction of the lepidocrocite titanate interlayer. It was verified by a reduced amount of sodium and the formation of Ti–O–H bonds in the structures. By the photocatalytic decolorization test of dye molecules, the decolorization rate of the synthesized TNTs (95.8%) was higher than that of pristine TNTs (75.8%) under solar light for 360 min. These findings show not only that the process is a lower environmental impact method than the previous synthesis method but also that the current method contributes to the development of highly functionalized materials for photochemical applications.