A critical review on the recent progress of synthesizing techniques and fabrication of TiO2-based nanotubes photocatalysts

• TiO2 nanotubes photocatalyst for environmental application is reviewed.
• Progress of three main approaches used to synthesize TiO2 nanotubes is summarized.
• Influencing factors of hydrothermal synthesis are demonstrated.
• Recent works on various modification methods on TiO2 nanotubes are discussed.
• Catalyst enhancement through the modifications of TiO2 nanotubes is highlighted.

One-dimensional titanium dioxide (TiO2)-based nanotubes have attracted great interest to be used as photocatalysts in the field of environmental applications. Three main approaches via template-assisted, electrochemical anodic oxidation and alkaline hydrothermal treatment used to prepare the nanostructured TiO2-based nanotubes are reviewed. The parameters that affect the formation of TiO2-based nanotubes via hydrothermal method such as phases and particle sizes of starting materials, types and concentrations of alkaline solution, temperature and duration of hydrothermal treatment, ultrasonication- and microwave-assisted hydrothermal synthesis, acid washing and calcination have been reviewed in details. This paper also discussed the possible crystal structure and formation mechanism of TiO2-based nanotubes via alkaline hydrothermal treatment. In addition, the recent research progress on the structural modification of TiO2-based nanotubes to be used as photocatalysts is summarized in this review. Modification strategies investigated include metal nanoparticles deposition, single- and co-doping of metal ions/non-metal ions, coupled with other semiconductors to form binary composites and hybrid with carbon nanomaterials.

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