MorphologiesControlled Synthesis and Optical Properties of Bismuth Tungstate Nanocrystals by a LowTemperature Molten Salt Method
Lijin Xie, Junfeng Ma,1'* Jun Zhou, and Zhongqiang Zhao
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266003, China
Hua Tian, Yonggang Wang, Jiantao Tao, and Xiaoyi Zhu
Institute of Materials Science and Engineering, Ocean University of China, Qingdao 266003, China
Well-crystallized bismuth tungstate (Bi2W06) powders with different morphologies were successfully synthesized via a low-temperature molten salt method. The powders were characterized by X-ray diffraction, transmission electron microscopy, and UV-Vis, respectively. It was found that the variation of morphology of the obtained Bi2W06 powder mainly depends on the different reaction temperatures and the weight ratio of LiN03-NaN03 salt to precursor. In addition, the UV-Visible absorption spectra showed that the synthesized powders had strong light absorption properties not only in the ultraviolet light but also in the visible light region.
I. Introduction
Since the discovery of carbon nanotube by Iijima in 1991,1 the synthesis of crystals with specific size and morphology has recently attracted considerable interest,2 4 especially because the size and morphology of these materials can be designed according to the requirements of the devices, which have important value for the practical application of materials.5 9 Many research results have been reported on the synthesis of crystals with different morphologies, such as ZnO nanowires/'nanorods obtained by vapor-liquid—solid growth,10 feather-like BaW04 superstructure in reverse micelle,1 PbCr04 nanorods and nano-particles synthesized by using different surfactants and organic additives,12 and CaW04 crystals with different morphologies prepared by a supramolecular template method.13 Unfortunately, most of these methods need high-reaction temperature, tedious procedures, or complex equipment. Therefore, it is still highly desirable to develop an efficient, simple method to control crystal morphologies.
Tungstates have been extensively studied in the past century, especially their very interesting luminescence and structural properties and electro-optical applications.14 18 Among these tungstates, B¡2W06 (BWO) has been attracting increasing attention because of its ferroelectric piezoelectricity, pyroelectric-ity, catalytic behavior, and a non-linear dielectric susceptibility. In recent years, the photocatalytic reaction has attracted much interest owing to energy and environmental issues.19 21 BWO is also a photocatalyst with good visible-light photocatalytic activity.2 BWO was conventionally prepared by a high-temperature solid-state reaction (ca. 700°C). Various improved synthesis methods for this material have also been reported including the
I. Baílalo contributing editor
Manuscript No. 21144. Received November 11, 2005; approved December 15, 2005. +Author to whom correspondence should be addressed, e-mail: majf(a>mail.ouc.edu.cn institute of Materials Science & Engineering, Ocean University of China, Qingdao. China.
hydro thermal process and slow the cooling method using borate fluxes.23'24
In our previous work, we have successfully synthesized LiNiV04 and (Sn0.25,Tio.75)02 nanocrystals by a low-temperature molten salt (LTMS) method.25'26 In present study, we use this simple, inexpensive and versatile technique for the synthesis of highly crystallized BWO powders with no need for any template, surfactant, organic solvent, and high-temperature treatment. Morphologies of BWO powders could be controlled
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