Bi-template effect of a vegetal system on the synthesis of alkaline-earth tungstate nanocrystals
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-Zhang Zhu and Qing-Sheng Wua) Department of Chemistry, Tongji University, Shanghai 200092, People’s Republic of China (Received 29 May 2008; accepted 8 August 2008)
The MBS (mung bean sprouts) vegetal system, with its high penetrability, high selectivity, and space restriction, was explored to control nanocrystal synthesis. We found that the inside and outside of MBS have different structures and ion transformation properties. Two nanocrystals with distinct morphology, the nanorod and the nanosphere, were grown on the outer surface and the inner stem wall of MBS, respectively. The two XWO4 (X = Ca,Sr,Ba) nanocrystals were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and Fourier transform infrared (FTIR). The FTIR spectra of nanoproducts were different from bulk products due to the nano-size effect. A presumable mechanism was also determined. This work benefits the application of nanotungstates.
I. INTRODUCTION
Concerning the manufacturing capacity of biology, people generally think of nucleic acids, proteins, and other bio-macromolecules with incredibly complex sequence and superstructure. However, the status of inorganic minerals is nothing less than that organic substance mentioned above. Both human bones and natural pearls are often fine products for their perfect structure and performance.1 The exploration and simulation of the biomimetic process has been a focus of materials research in recent years.2 Nature uses organic molecules to control and direct the crystallization of biominerals with special orientation, texture, and morphology under normal ambient conditions.3 Furthermore, biominerals are organized from the nanoscopic to the macroscopic scale to form structures with hierarchical long-range order.4,5 Inspired by the formation of biomaterials, many studies have been carried out to control the choice of polymorph and the morphology of minerals in the lab.6–9 Over the past few decades, templates of organism structures have attracted a lot of attention,10,11 such as tobacco mosaic virus,12 silica algae,13 and so on. Most methods using biotemplates to synthesize well-defined nanostructures or superstructures,14 however, are performed under harsh conditions with relatively high temperatures or extreme pH values, or followed by a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0072 J. Mater. Res., Vol. 24, No. 2, Feb 2009
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complicated procedures, or else they require other modifiers. Few ordered nanocrystals were produced in a heterogeneous environment at ambient temperature and pressure and at a pH value close to neutral without additives. MBS, the sprout form of the mung bean, a traditional vegetable in China and Southeast Asia, and largely cultivated in many developing countries, is an ideal biological template. MBS is extremely inexpensive, remaining stable at temperatures between 0 C and 35 C and at pH 4–10. It consists of large amounts of cellulose, protein, and mo
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