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

摘要

In this study, an effective low-temperature method was developed, for the first time, for the synthesis of bismuth titanate nanobelts by using Na_2Ti_3O_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_2Ti_3O_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_2O_3 whereas the interior was converted to TiO_2(B), forming TiO_2(B)@Bi_2O_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_4Ti_3O_(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_4Ti_3O_(12). Such a structural evolution was man ifested 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. Photolumi-nescence 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.