Low-temperature synthesis of ribbon-like orthorhombic NaNbO₃ fibers and their photocatalytic activities for H₂ evolution

Ribbon-like orthorhombic NaNbO₃ fibers were successfully prepared by combining a traditional hydrothermal method with post-heat treatment at a low annealing temperature. In the hydrothermal reaction process, it was found that magnetic stirring could improve the fiber structure of the final NaNbO₃. Furthermore, the effects of different post-heat treatment conditions on the morphology and crystallinity of the product were investigated. Interestingly, results showed that a low temperature (300°C), by prolonging the post-heat treatment time (6 h), would promote predominant oriented growth on the (101) and (020) crystal faces in NaNbO₃ fibers, which possessed few defects and cracks. The photocatalytic activity of the fibers was also evaluated by H₂ evolution from an aqueous methanol solution. It was found that a sample undergoing post-heat treatment conditions of 300°C for 6 h exhibited higher photocatalytic activity compared with a sample undergoing post-heat treatment conditions of 600°C for 2 h. This is also the first example where different sacrificial reagents were employed to investigate the H₂ evolution efficiency of NaNbO₃ fibers.