Highly aligned, vertically oriented TiO2 nanotube arrays formed by electrochemical anodization have been extensively investigated in the recent times because of various potential applications such as in solar cells, hydrogen generation, CO2 reduction, gas sensors and as biocompatible material. The as prepared nanotubes, however, are amorphous and require a thermal annealing process to achieve the desired crystallographic phase. Here we report a simple solvothermal technique by which the crystallinity of the nanotube arrays can be tailored at temperatures around 200 °C to achieve the anatase phase without destroying the tubular morphology. In this alcohol-based solvothermal process, the crystalhnity can be enhanced by changing the solvent from methanol to isobutanol and the sample treated with isobutanol for 2 h shows crystallinity and strain comparable to that of a sample annealed in a conventional furnace at 550 °C. A mechanism for the solvothermal crystallization and the enhancement of crystalhnity has been proposed. Furthermore, the gas sensing measurements on solvothermally treated samples have been performed with 1000 ppm methane which showed higher room temperature sensitivity compared to that of conventionally annealed sample.
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