Controlled Synthesis of Different Morphologies of BaWO4 Crystals through Biomembrane/Organic-Addition Supramolecule Templates Jinku Liu,† Qingsheng Wu,*,† and Yaping Ding‡
CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 2 445-449
Department of Chemistry, Tongji University, Shanghai 200092, and Department of Chemistry, Shanghai University, Shanghai 200436, China Received June 21, 2004;
Revised Manuscript Received August 28, 2004
ABSTRACT: By the employment of supramolecule templates composed of biomembrane and organic reagents, control over the morphologies and sizes of BaWO4 crystals has been successfully achieved, and a series of flower-like, spherelike, fasciculus-like, and other morphologies of BaWO4 were obtained at room temperature. Most of the morphologies are reported for the first time. Furthermore, the control rule of supramolecule templates was also discussed. This method may satisfy the requirements of materials of various morphologies and sizes by using different supramolecule templates, and provide significant theoretical reference to the controlled synthesis of other crystals. 1. Introduction Synthesis of inorganic crystals with a specific size and morphology has recently attracted a lot of interest because of their potential in the design of new materials and devices in various fields such as catalysis, medicine, electronics, ceramics, pigments, cosmetics,1-6 etc., especially because the size and morphology of these materials can be designed according to the requirements of the devices, and the rules of controlled synthesis could be grasped, which have important value for the practical application of materials.7-11 Barium tungstate can be used in a variety of fields such as electrooptics and microwave ceramics.12 This material has also attracted interest in basic research, because of its high-pressure phase transformation,13 and BaWO4 with a scheelite structure (tetragonal phase) is an important material in the electrooptical industry due to its emission of blue luminescence.14-16 BaWO4 is also a potential material for designing all solid-state lasers emitting radiation in a specific spectral region. Due to its extensive applications, much research has been reported on the synthesis of the BaWO4 crystal.6,17-24 However, so far no control on the crystal’s morphology and size has been achieved at mild conditions, so it is difficult to design the material morphologies according to its practical applications. In this study, a novel control-synthesis method using a supramolecule template is first developed. The bioactive eggshell membrane is used as a basic template and organic reagents as a cooperative template, and the two templates interact to form a supramolecule template through a nonchemical bonding effect. With the supramolecule templates, the control synthesis is achieved over the morphologies and sizes of BaWO4 crystals which have changed from a polyhedron morphology of the barium tungstate crystal to special morphologies such as flower-like morphology, anchorlike morphology, double-taper-like morphology, spheri* To whom correspondence should be addressed. +8602165982287; E-mail:
[email protected]. † Tongji University. ‡ Shanghai University.
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cal morphology, fasciculus-like morphology, etc., under mild conditions. These results may provide some references to the controlled synthesis and the practical application of other inorganic materials. 2. Experimental Section The eggshell membrane was obtained from fresh eggshell, the outer shell of which was removed and then washed with deionized water. It was fastened in a reactor to separate it into two horizontal compartments, to which were added 25 mL of 0.1 mol/L Na2WO4 solution and 25 mL of 0.1 mol/L BaCl2 solution, respectively. Then the organic reagent was added to both compartments. The additive reagents were L-ascorbic acid, n-dodecanethiol (C12H25SH), ethylenediamine [(CH2NH2)2], polyformaldehyde, and β-cyclodextrin. The pH values of the solutions in both sides were modulated to 10 by KOH solution except for the solution containing (CH2NH2)2 as additive reagent. Then the system was kept at room temperature for 10 h. Thereafter the solution containing products was centrifugally separated, and washed in turn with deionized water and absolute alcohol to obtain BaWO4 products. All used reagents, BaCl2, sodium tungstate (Na2WO4‚2H2O), KOH, L-ascorbic acid, n-dodecanethiol, ethylenediamine, β-cyclodextrin, and polyformaldehyde, were analytic grade purity. The structures of the obtained samples were characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD) using a Shimadzu XD-3A diffractometer with graphite-monochromatized Cu KR radiation (50 kV, 100 mA). The microstructures and morphologies were analyzed with a Philips XL-30E scanning electron microscope.
3. Results and Discussion When the eggshell membrane was used as a template in the absence of organic additive reagents (the pH value of the reaction solutions was modulated to 10 by KOH solution), the morphology of the product shown in Figure 1A was obtained. It had a polyhedron morphology with about 6 µm length in the axes. When n-dodecanethiol, β-cyclodextrin, ethylenediamine, Lascorbic acid, and polyformaldehyde were added to the system, the products were transformed into a flowerlike morphology (Figure 1B), double-taper-like morphology (Figure 1C), anchor-like morphology (Figure 1D), sphere-like morphology (Figure 1E), and fasciculus-like
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Figure 1. SEM morphologies of the products (A, no additive reagents; B, adding 0.05 g of 0.01 mol/L n-dodecanethiol; C, adding 0.04 g of 0.01 mol/L β-cyclodextrin; D, adding 0.015 g of 0.01 mol/L ethylenediamine; E, adding 0.044 g of 0.01 mol/L L-ascorbic acid; F, adding 0.0075 g of polyformaldehyde).
Figure 3. FT-IR spectra of the products (A, no additive reagents; B, adding 0.05 g of n-dodecanethiol; C, adding 0.04 g of β-cyclodextrin; D, adding 0.015 g of ethylenediamine; E, adding 0.044 g of L-ascorbic acid; F, adding 0.0075 g of polyformaldehyde). Figure 2. XRD patterns of the products (A, no additive reagents; B, adding 0.05 g of n-dodecanethiol; C, adding 0.04 g of β-cyclodextrin; D, adding 0.015 g of ethylenediamine; E, adding 0.044 g of L-ascorbic acid; F, adding 0.0075 g of polyformaldehyde).
morphology (Figure 1F) in sequence, and the morphologies in Figure 1B,C,E,F are reported for the first time. The size and morphology of each product were comparatively uniform. This indicates that the morphologies of the crystal were controlled under the cooperation of the eggshell membrane and the additive reagents, and the control of crystal morphology and structure was modulated very well. This made it impossible to design the shape and size of materials according to their practical applications. All the products have the same crystal structure despite their different morphologies. The XRD patterns are shown in Figure 2, in which all the peaks from XRD could be indexed according to the tetragonal-phase BaWO4. The shapes of the diffraction peaks suggest that the products were well crystallized. No obvious impurities could be detected. The cell constants were calculated to be a ) 5.61 Å and c ) 12.71 Å, which are consistent with the literature data (JCPDS, 8-457). The products were a scheelite tetragonal structure with high purity and crystallization.
The FT-IR spectra of the products provide an accessorial explanation to the products’ structures. Products of the same crystal structure should have approximate absorption spectra. The FT-IR spectra in Figure 3 show that the absorption peaks appearing at 800 and 1450 cm-1 are the typical FT-IR absorption peaks of WO42of scheelite tetragonal structure. The FT-IR peaks of all products were approximately identical; that is to say, although the shapes of the crystals were different, the structure of the crystals belongs to the same type. 4. Discussion of Conditions 4.1. Effect of Reaction Time. The product obtained in the presence of polyformaldehyde was chosen as a research object because of its rather complicated fasciculus-like morphology. As shown in Figure 4A, “axes” of fasciculi with one end loose and the other end spiculate formed after 1 h of aging. The axes were 3.5 µm long. At an aging time of 4 h, the other end of the products grew to loose flake bundles; at the same time, the length also increased (Figure 4B arrow). If the aging time was further increased to 6 h, the two ends of the products continued to grow and the thinner fasciculi formed as shown in Figure 4C. After 10 h of aging,
Synthesis of Different Morphologies of BaWO4
Figure 4. SEM morphologies of the products at different reaction times (A, 1 h; B, 4 h; C, 6 h; D, 10 h).
Figure 5. SEM morphologies of the products at different concentrations of polyformaldehyde (A, 0; B, 0.06 g/L; C, 0.012 g/L; D, 0.024 g/L).
Figure 4D showed the fasciculi became thicker and a little longer. This result indicates that an axis of fasciculus products formed at first, and then both sides grew gradually to loose flake bundles along the axis direction. Products with different morphologies could be obtained at different reaction times, so we could choose the reaction time freely according to our requirements. 4.2. Effect of Additive Reagents. The effects of the additive agents on the formation of BaWO4 crystals with different morphologies were investigated. The organic agents were crucial to the control of crystal morphologies. When n-dodecanethiol (C12H25SH) was used, flowerlike products about 15 µm in size were obtained whose component petals were small crystals about 5 µm in size as shown in Figure 1B. These petals were almost
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identical to the products shown in Figure 1A. This indicated that the products in Figure 1A accumulated together comparatively tightly to form products with flower-like morphology in Figure 1B, only a little smoother on their surface. When β-cyclodextrin was added to the system, the products shown in Figure 1C were obtained, and they seemed to form by elongation of the products in Figure 1A. Compared with the products in Figure 1A, they were smooth at the surface and spiculate at both ends, but still reserved the morphology of a polyhedron. They were about 15 µm long and 2 µm wide in the middle part, more like a double taper. In the presence of ethylenediamine as additive reagent, anchor-like products with comparatively uniform size, 15 µm long, were obtained as shown in Figure 1D. There were two symmetrical protuberances in the middle and transverse veins at both sides of the protuberances. With L-ascorbic acid as the additive reagent, the polyhedron morphology of barium tungstate completely disappeared and spherical particles about 180 nm in diameter were obtained. The morphology was quite regular, and the size was also uniform as observed in Figure 1E. The use of polyformaldehyde made the obtained morphology in Figure 1F completely different from that in Figure 1A. These products radiated at both ends, just like fasciculi. Different additive reagents have different functional groups, so their tropistic inducing effects on the crystal are different. We speculate the rules may be as follows: (1) There are various groups in different additive reagents, so their effects on the growth of products are also different.1 n-Dodecanethiol molecules containing more -HS cannot dissolve in water, so they interact with and adhere to the surface of the eggshell membrane by such nonchemical effects as hydrogen bonding, meanwhile interlacing themselves together. β-Cyclodextrin contains more -OH. Ethylenediamine contains -NH2. L-Ascorbic acid contains -OH and -COOH. Polyformaldehyde contains more -C-O-. The polarity of these functional groups in increasing order is -SH < EnDashC-O- < NH < EnDashOH < -COOH. The polarity of the group is greater, the sorption from the crystal surface is greater, and the tropistic inducing effect on the crystal is also stronger; thus, the effect on morphology is greater. (2) The more groups which have tropistic inducing effects on the crystal that are contained in the additive reagents, the greater effect they have on the morphology of the crystal. (3) Except for functional groups, the length and structure of the carbon chains in each additive reagent also have effects on the tropistic growth of the crystal. The chainlike additive
Figure 6. SEM morphologies of the products (A, adding polyformaldehyde in the absence of eggshell membrane) and eggshell membrane (B).
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reagents often easily generate products with a larger ratio of length to width, whereas the cyclic additive reagents often easily generate sphere or sphere-like products. 4.3. Effect of the Concentration of the Additive Reagent. The effects of the additive reagent concentration on the formation of different BaWO4 crystals were also studied, and an example is the preparation of fasciculus-like morphology products that were obtained in the presence of polyformaldehyde. Patterns of products obtained with different additive reagent concentrations are shown in Figure 5. In the absence of polyformaldehyde, regular polyhedrons formed as shown in Figure 5A. When the concentration of polyformaldehyde was 0.06 g/L, there was a big change in the morphology. Figure 5B shows that the obtained products had only one loose end, and were about 18 µm long, basically consistent with the length of fasciculus-like products with two loose ends. When the concentration was increased to 0.012 g/L, the fasciculus-like morphology products began to appear in Figure 5C. When the concentration was further increased to 0.024 g/L, almost all the products had a fasciculus-like morphology with a little immaturity as shown in Figure 5D. When the concentration was increased to 0.03 g/L, fasciculus-like morphology products were obtained as shown in Figure 1F. The result shows that the products whose one end had loose flake bundles formed at lower polyformaldehyde concentration, another end began to form loose flake bundles with an increase of concentration, and further increasing the concentration made the fasciculus-like products thicker and mature. This indicates that the concentration of additive reagent would influence the orientating inducing effects on crystal growth. 4.4. Effect of the Eggshell Membrane. The eggshell membrane also has an effect on the formation of crystals. Experiment reveals that crystals with the morphology shown in Figure 6A are obtained when polyformaldehyde is added to the reaction system in the absence of eggshell membrane, different from that obtained in the presence of eggshell membrane. The eggshell membrane has two roles in the formation of BaWO4 crystals with various morphologies; one is it controls the transport of reaction ions due to its semipermeable structure, and the other is it controls the growth of crystals. Figure 6B shows a typical scanning electron microscopy (SEM) image of the eggshell membrane that is a microporous network with diameters of 1.5-10 µm composed of complecting protein fibers with an average diameter of about 2 µm. The eggshell membrane mainly contains collagen, glycoprotein, and proteoglycan.25 The latter two macromolecules contain ionic hydrophilic and hydrophobic domains. The hydrophilic ends may adsorb Ba2+ ions and provide suitable sites for the nucleation and growth of BaWO4 crystals. The intermolecular and intramolecular nonchemical effects on the macromolecules and cooperative reagents, such as hydrogen-bonding and electrostatic effects, could orientate the macromolecules and cooperative reagents so that they could direct the growth of crystals and control the shape of the products.26 4.5. Effect of pH Values. Experiments reveal that the suitable pH range is 8-12 with which products with
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higher purity can be obtained. Lower pH values result in the formation of tungsten oxide, whereas higher pH values (pH > 12) would accelerate the hydrolyzation of eggshell membrane, leading to the failure of experimentation. A pH value of 10 was chosen as the experimental pH value in this paper. 5. Conclusion BaWO4 crystals with different morphologies have been successfully prepared using novel supramolecule templates at mild conditions. The morphologies of the crystals were well controlled, they were of uniform shape and size, and most of the morphologies are reported for the first time. Because of the extensive applications of barium tungstate in fields such as ceramic and luminescence materials etc., the preparation of various morphologies may have an advantage in the exploitation of the products’ application value and the design of the materials’ sizes and morphologies according to their practical requirements. The control over the materials’ morphologies could be realized using different supramolecule templates by changing the organic reagents. In this paper we provide a novel idea of using supramolecule templates to control the materials’ morphologies, which can be applied for the controlled synthesis of other materials besides barium tungstate. Acknowledgment. This work was supported by the National Natural Science Foundation of China (No. 20131030, No. 20471042) and the Nano Foundation of Shanghai (No. 0259nm021, No. 0452nm075). References (1) Yu, S. H.; Co¨lfen, H.; Antonietti, M. Chem.sEur. J. 2002, 8, 2937. (2) Sun, X. M.; Li. Y. D. Chem.sEur. J. 2003, 9, 2229. (3) Li, M.; Schnablegger, H.; Mann, S. Nature 1999, 402, 393. (4) Peng, Q.; Dong, Y. J.; Li, Y. D. Angew. Chem., Int. Ed. 2003, 42, 3027. (5) Yu, S. H.; Markus, A.; Co¨lfen, Helmut; Hartmann, J. Nano Lett. 2003, 3, 379. (6) Shi, H. T.; Qi, L. M.; Ma, J. M.; Cheng, H. M. J. Am. Chem. Soc. 2003, 125, 3450. (7) Hu, X. L.; Zhu, Y. J. Langmuir 2004, 20, 1521. (8) Rautaray, D.; Ahmad, A.; Sastry, M. J. Am. Chem. Soc. 2003, 125, 14656. (9) Tian, Z. R.; Voigt, J. A.; Liu, J.; Mckenzie, B.; Mcdermott, M. J. J. Am. Chem. Soc. 2002, 124, 12954. (10) Rautaray, D.; Sinha, K.; Shankar, S. S.; Adyanthaya, S. D.; Sastry M. Chem. Mater. 2004, 16, 1356. (11) Liao, H. W.; Wang, Y. F.; Lihnju, X. M.; Li, Y. D.; Qian, Y. T. Chem. Mater. 2000, 12, 2819. (12) Kima, J. S.; Kima, J. W.; Cheona, C. I.; Kimb, Y. S.; Nahmc, S.; Byunc, J. D. J. Eur. Ceram. Soc. 2001, 21, 2599. (13) Jayaraman, A.; Battlogg, B.; Van Uitert, L. G. Phys. Rev. B 1983, 28, 4774. (14) Baseive, T. T.; Sobol, A. A.; Voronko, Y.; Zverev, P. G. Opt. Mater. 2000, 15, 205. (15) Blasse, G.; Schipper, W. J. Phys. Status Solidi A 1974, 25, K163. (16) Blasse, G.; Dirksen, G. J. J. Solid State Chem. 1981, 36, 124. (17) Shi, H. T.; Qi, L. M.; Ma, J. M.; Cheng, H. M. Chem. Commun. 2002, 1704. (18) Kwan, S.; Kim, F.; Akana, J.; Yang, P. D. Chem. Commun. 2001, 447. (19) Roy, B. N.; Roy, M. R. Cryst. Res. Technol. 1981, 16, 1267. (20) Fujita, T.; Yamaoka, S.; Fukunaga, O. Mater. Res. Bull. 1974, 9, 141.
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