Bismuth titanate nanobelts through a low-temperature nanoscale solid-state reaction

Abstract In this study, an effective low-temperature method was developed, for the first time, for the synthesis of bismuth titanate nanobelts by using Na 2 Ti 3 O 7 nanobelts as the reactants and templates. The experimental procedure was based on ion substitution followed by a nanoscale solid-state reaction. In the first step, Na 2 Ti 3 O 7 nanobelts were soaked in a bismuth nitrate solution where ion substitution at the nanobelt surfaces led to the formation of a bismuth compound overlayer. The resulting bismuth-modified nanobelts were then subject to a calcination process at controlled temperatures. At the calcination temperature of 400 °C, the top layer was converted to Bi 2 O 3 whereas the interior was converted to TiO 2 (B), forming TiO 2 (B)@Bi 2 O 3 core–shell nanobelts. When the calcination temperature was increased to 450 °C, a metastable interphase Bi 20 TiO 32 was produced on the nanobelt surface whereas the interior structure remained virtually unchanged, and the nanobelts now exhibited a TiO 2 (B)@Bi 20 TiO 32 core–shell structure. At calcination temperatures higher than 550 °C, the shell of the nanobelts became Bi 4 Ti 3 O 12 . At even higher temperatures (600–700 °C), no TiO 2 (B) was found and the nanobelts exhibited single-crystalline characteristics that were consistent with those of Bi 4 Ti 3 O 12 . Such a structural evolution was manifested in X-ray diffraction, Raman and Fourier transform infrared spectroscopic measurements, and scanning electron microscopic and transmission electron microscopic studies showed that the belt-like surface morphology was maintained without any apparent distortion or destruction. A mechanism based on nanoscale solid-state reactions was proposed to account for the structural evolution. Photoluminescence measurements showed that the core–shell nanobelts exhibited a markedly suppressed emission intensity, suggesting impeded recombination of photogenerated carriers as compared to the single-phase counterparts. Such a unique feature was found to be beneficiary to photocatalysis, as exemplified by the photodegradation of methyl orange under UV irradiation, where TiO 2 (B)@Bi 20 TiO 32 core–shell nanobelts were found to exhibit the best performance among the series.