A unique three-dimensional photocatalytic structure consisting of highly crystalline Na₂Ti₃O₇ whiskers grown from a NaCl Flux

Highly crystalline and oriented Na₂Ti₃O₇ whiskers were successfully and directly grown on a metallic titanium mesh using a NaCl flux cooling method for application to semiconducting photocatalysis. Specifically, unique three-dimensional photocatalytic materials were fabricated by converting a titanium mesh into a Na₂Ti₃O₇ tubular mesh consisting of highly oriented whiskers. The formation mechanism of the oriented Na₂Ti₃O₇ whiskers was investigated using field emission scanning electron microscopy, energy-dispersive X-ray spectrometry, and X-ray diffraction. From these results, the following conclusions could be confirmed. First, a titanium oxide layer was formed on the Ti wire surface by thermal oxidation. Since this oxide layer acts as a protective layer to thermal energy, the wire shape was maintained during Na ₂Ti₃O₇ whisker growth. Next, highly oriented Na₂Ti₃O₇ whiskers were directly grown on the titanium oxide layer. During whisker growth, Ti was radially supplied from the bulk of the Ti mesh to the inner surface of the TiO₂ layer. Finally, the Ti wire structure transitioned into a tubular structure consisting of Na₂Ti₃O₇ whiskers. During the fabrication process, the Ti wire was dissolved by the NaCl flux, and the dissolved Ti ions reacted with O and Na ions to form TiO₂ and Na₂Ti ₃O₇ layers. As a result, oriented and highly crystalline Na₂Ti₃O₇ whiskers were directly grown on the TiO₂ layer. The Ti wire was completely dissolved in this reaction system. Furthermore, the photocatalytic activities of the tubular mesh consisting of Na₂Ti₃O₇ whiskers were confirmed by the photocatalytic degradation of a fluoroalkylsilane self-assembled monolayer and trichloroethylene under ultraviolet light irradiation. The whisker mesh developed herein exhibited good photocatalytic properties under ultraviolet light irradiation.