CRYSTAL GROWTH & DESIGN
Hydrothermal Synthesis and Characterization of Alkaline-Earth Metal Phenylphosphonate Nanostructures
2007 VOL. 7, NO. 5 895-899
Li-Li Gao, Shu-Yan Song, Jian-Fang Ma,* and Jin Yang Key Lab for Polyoxometalate Science, Department of Chemistry, Northeast Normal UniVersity, Changchun 130024, People’s Republic of China ReceiVed September 26, 2006; ReVised Manuscript ReceiVed January 18, 2007
ABSTRACT: A simple hydrothermal method has been designed for the synthesis of the nanorods of alkaline-earth metal phenylphosphonates Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca or Sr) in the presence of surfactants cetyltrimethylammonium bromide or sodium dodecyl sulfate at pH 6.0. Rod-shaped nanocrystals, nanocubes, and hexagonal nanocrystals of the Ba(HO3PPh)2 have also been prepared separately. The possible growth mechanisms of these nanocrystals were elucidated in detail. Mesoporous nanorods of Ca2P2O7 possessing a large surface area and high thermal stability were obtained by removing the organic part of Ca(HO3PPh)2 nanorods at 700 °C. X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, electron diffraction, and Brunauer-Emmett-Teller surface area were used to characterize these materials. Introduction In recent years, metal phosphonates, which are a rich class of inorganic-organic hybrid materials, have undergone significant expansion due to their potential application in catalysis, ion exchange, proton conductivity, sorbent, sensors, intercalation chemistry, etc.1 In general, current work has centered on their composite properties and the possibility of tuning their chemistry, including the effects of a wide variety of organophosphonate ligands and different metal atoms to the crystal structure and their characters. However, interests in controlling the size and the morphology have not extended appreciably to material chemists. Cao et al. have reported the synthesis of two series of divalent metal phosphonates, M(O3PR)‚H2O (M ) Mg, Mn, Zn, Ca, or Cd; R ) n-alkyl, aryl group) and M(HO3PR)2 (M ) Ca), some of which single crystals have been obtained and the crystal structures have been determined.2 These crystalline layered compounds, in which the metal-oxygen layers are similar to their inorganic counterparts but are separated by insulating alkyl or aryl groups,3 exhibit some attractive properties, such as high thermal stability, resistance to oxidation, high selectivity to a series of ions and molecules, and convenience for chemical modifications.4 However, many of the properties of these hybrid materials that can integrate inorganic and organic characteristics within a single molecular composite not only rely on their chemical composition and crystal structure but also are affected by their size, surface chemistry, and morphology.5 It is well-known that nanoscale materials often offer larger surface areas than those of solid or bulk forms, and also, a lot of interesting and new phenomena are associated with nanometer-sized structures.6 The synthesis of one-dimensional (1D) nanostructures would offer great opportunities to explore their unexpected properties and lead to the construction of nanoscale devices;7 for example, welldefined 1D ZnO nanostructures are applicable to optoelectronic nanoscale devices such as nanolasers,8 gas sensors,9 transistors,10 and nanoresonators.11 Among a variety of methods to fabricate anisotropic nanostructures, e.g., tubes, wires, rods, cubes, dendrites, disks, etc.,12-15 by hydrothermal methods, many starting materials can undergo quite unexpected reactions, which * To whom correspondence should be addressed. E-mail: jianfangma@ yahoo.com.cn.
are often accompanied by the formation of nanoscopic morphologies that are not accessible by classical routes.16 In our previous study, the nanorods of cobalt6a and lanthanide phenylphosphonates1e have been reported, but to the best of our knowledge, little attention has been paid to the nanostructures of alkaline-earth metal phenylphosphonates. Recently, the chemistry of calcium phosphonate has stimulated great interest due to their use as phosphonate-based drugs for diagnosis and therapy for bone diseases and also for calcium metabolism.17 Application of calcium phenylphosphonate for the surface treatment of calcerous stones is currently under investigation.17 In this work, we systematically studied the syntheses of alkalineearth metal phenylphosphonate Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca, Sr, or Ba) nanocrystals under low-temperature hydrothermal conditions, using surfactants cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS). It is found that the heating times have a great influence on the morphologies of Ba(HO3PPh)2. In addition, Ca(HO3PPh)2 nanorods can be converted to the pyrophosphate by heating without altering the 1D morphology. Experimental Section All chemical reagents were of analytical grade and used as received without further purification. Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca or Sr) nanorods were prepared by a low-temperature hydrothermal method for 48 h but with different heating times for Ba(HO3PPh)2. In a typical procedure, a solution of 0.40 mmol of MCl2 and 0.14 g of SDS in 5 mL of distilled water was added to a solution of 0.40 mmol of phenylphosphonic acid in 5 mL of distilled water. After stirring for about 40 min, the pH was adjusted to 6.0 using aqueous solution of NaOH. The resulting suspension was transferred into a stainless steel autoclave with a Teflon liner of 23 mL capacity and heated in an oven at 100 °C for 48 h. After the autoclave was air-cooled to room temperature unaided, the resulting white precipitate was filtered and washed with distilled water and absolute ethanol and finally dried under vacuum at 60 °C for 4 h. The typical procedure when using CTAB was as follows: A solution of 0.40 mmol of phenylphosphonic acid and 0.14 g of CTAB in 5 mL of distilled water was added to a solution of 0.40 mmol of MCl2 in 5 mL of distilled water. Then, the procedure was the same as that using SDS above. X-ray powder diffraction (XRD) patterns of the samples were collected on a Rigaku Dmax 2000 X-ray diffractometer with graphite monochromatized Cu KR radiation (λ ) 0.154 nm) and 2θ ranging from 4 to 60°. Transmission electron microscopy (TEM) and high-
10.1021/cg0606491 CCC: $37.00 © 2007 American Chemical Society Published on Web 03/15/2007
896 Crystal Growth & Design, Vol. 7, No. 5, 2007
Gao et al.
Figure 1. XRD patterns of the metal phenylphosphonates: (a) simulated XRD powder pattern of Mg(O3PPh)‚H2O, (b) Mg(O3PPh)‚ H2O nanorods, (c) simulated XRD powder pattern of Ca(HO3PPh)2, (d) Ca(HO3PPh)2 nanorods, and (e) Sr(HO3PPh)2 nanorods. Figure 3. TEM images of Mg(O3PPh)‚H2O (a) in the absence of surfactants, (b and c) using CTAB (insets show the HRTEM and the SAED pattern), and (c) using SDS.
Figure 2. XRD patterns of Ba(HO3PPh)2 nanocrystals formed with different reaction times: (a) rod-shaped nanocrystals for 6 h, (b) hexagonal nanocrystals for 48 h, and (c) nanocubes for 60 h. resolution (HR) TEM were recorded on a Hitachi model H-800 transmission electron microscope, using an accelerating voltage of 200 kV. Elemental analyses were obtained from an inductively coupled plasma-atomic emission spectrometry, Labtest Equipment Co. model 710 Plasmas. Brunauer-Emmett-Teller (BET) surface area and pore diameter were measured on a Quantachrome NOVA 1000 Ver.6.11 system at 77.4 K.
Figure 4. TEM images of the products obtained (a and b) Ca(HO3PPh)2 nanorods using CTAB (insets show the HRTEM and the SAED pattern), (c) Ca(HO3PPh)2 nanorods using SDS, (d) Sr(HO3PPh)2 nanorods using CTAB, and (e) Sr(HO3PPh)2 nanorods using SDS.
Results and Discussion A family of alkaline-earth metal phenylphosphonate Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca, Sr, or Ba) nanostructures was synthesized via a hydrothermal process at 100 °C in the presence of surfactants of CTAB or SDS. All of these phenylphosphonate compounds are not soluble in water at pH values higher than 2. The crystal structures of Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca, Sr, or Ba) have been reported. Mg(O3PPh)‚H2O was orthorhombic: space group, Pmn21; Z ) 2; a ) 5.61(1) Å; b ) 14.28(2) Å; and c ) 4.82(1) Å.18 M(HO3PPh)2 (M ) Ca,17 Sr,3c or Ba3b) were all monoclinic space group C2/c with similar lattice constants. The XRD patterns of the samples are shown in Figures 1b,d,e and 2, respectively. Both of the reflection peaks of the Mg(O3PPh)‚H2O and Ca(HO3PPh)2 nanorods are all in good agreement with their simulated XRD powder patterns (Figure 1a,c), saying that they are the target compounds. The above-mentioned results can be further confirmed by TEM in which the solid samples were mounted on a copper mesh with a dispersion treatment. Typical TEM images of the Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca or Sr) nanorods using CTAB and SDS are shown in Figures 3 and 4. However,
Figure 5. TEM images of Ba(HO3PPh)2 prepared with different heating times: (a) 6, (b) 48, and (c) 60 h.
in the absence of surfactants, the irregular solids of the compounds were obtained (Figure 3a and Figures S1 and S2 in the Supporting Information). It can be seen that these products display a rodlike morphology with a width in the range of 6080 nm. Figure 5a shows that the Ba(HO3PPh)2 prepared by heating for 6 h are rod-shaped nanocrystals. However, when the reaction time was extended from 48 to 60 h, the morphology of Ba(HO3PPh)2 was changed from hexagonal nanocrystals to nanocubes (Figure 5b,c). More details about the structure of nanorods were investigated using HRTEM and the selected area electron diffraction. The HRTEM and SAED images (inset of Figure 3c) of the Mg(O3PC6H5)‚H2O nanorods show that the obtained nanorods are
Alkaline-Earth Metal Phenylphosphonate Nanostructures
Figure 6. (a) Inorganic polymeric layer of Mg(O3PPh)‚H2O, (b) lamellar structure of Mg(O3PPh)‚H2O, (c) inorganic polymeric layer of Ca(HO3PPh)2, and (d) lamellar structure of Ca(HO3PPh)2.
Chart 1. Effect of Surfactant on the Growth Process of Mg(O3PC6H5)‚H2O Nanorods
structurally uniform with a clear resolved interplanar spacing of about 14.3 Å, which corresponds to (010) planes, and the growth direction of nanorods is along the c-axis. Chart 1 illustrates the effect of surfactants on the growth process of Mg(O3PC6H5)‚H2O nanorods. Mg(O3PC6H5)‚H2O exhibits a lamellar structure with alternate Mg-O3P layer and phenyl layer.18 The hydrophobic groups of the surfactants connect to the top and bottom phenyl layers of Mg(O3PC6H5)‚H2O with van der Waals forces, which can efficiently prevent the particle from growing along the direction perpendicular to the layers. However, in the side of the lamellar structure, the hydrophilic Mg-O3P layer and hydrophobic phenyl layer stack alternatively; thus, no stable protecting shell of surfactants can be formed. The growth of Mg(O3PC6H5)‚H2O nanorods along the c-axis rather than the a-axis may be determined by its highly anisotropic character along the c-axis. The structure of the inorganic polymeric Mg-O3P layer is shown in Figure 6a.18 Each magnesium ion is coordinated by five phosphonate oxygen atoms and one water molecule. Each phosphonate group is coordinated to four magnesium ions. The two-dimensional polymeric structure may be described as columns built up of alternate magnesium and phosphonate ions, extending along the c-axis, and each column is linked to two neighboring columns. So, the anisotropic character along the c-axis is apparently different from that along the a-axis. From a kinetic perspective, the activation energy for the [001] direction of growth of Mg(O3PC6H5)‚H2O is lower than that of growth along the a-axis. This means a higher growth rate along the c-axis and a lower
Crystal Growth & Design, Vol. 7, No. 5, 2007 897
one along the a-axis to form Mg(O3PC6H5)‚H2O nanorods that grow preferentially along the [001] direction.19 Ca(HO3PPh)2 is monoclinic with lattice constants a ) 31.5414 (7) Å, b ) 5.6696(1) Å, c ) 7.7985(5) Å, and β ) 101.755 (1)°.17 The HRTEM image of a selected area from a single Ca(HO3PPh)2 nanorods is shown in Figure 4b. The HRTEM image of the nanorod shows a fringe spacing (ca. 15.8 Å), which corresponds to the interlayer spacing of the (200) planes, and the SAED patterns shown in Figure 4b suggest that the (001) planes are oriented parallel to the nanorod growth axis, indicating that the growth direction of nanorods is along the c-axis. The clear lattice fringes together with the SAED pattern confirm that these nanorods are single crystalline. Ca(HO3PPh)2 and Sr(HO3PPh)2 exhibit a typical lamellar structure like Mg(O3PC6H5)‚H2O, so the growth mechanism of Mg(O3PC6H5)‚H2O nanorods can also be applicable to them. As shown in Figure 6c,d, the calcium ion is eight-coordinated by oxygen atoms from the phosphonate groups in distorted dodecahedron fashion. In the bc-plane, the metal atoms are separated by about 5.67 Å along the b-direction and 4.09 Å in the c-direction. Along the c-axis, calcium atoms are arranged in the form of a zigzag chain and the adjacent calcium atoms in the chain are bridged by oxygen atoms, which created four-membered rings.3b So, the anisotropic characteristic along the c-axis is different from that along the b-axis. The anisotropic structural feature of Ca(HO3PPh)2 provides the base for the anisotropic growth of the nanocrystal. From a kinetic perspective, the activation energy for the [001] direction of growth of Ca(HO3PPh)2 is lower than that of growth along the b-axis. This means a higher growth rate along the c-axis and a lower one along the a- and b-axes to form Ca(HO3PPh)2 nanorods that grow preferentially along the [001] direction. An interesting phenomenon for Ba(HO3PPh)2 is that the morphologies are dependent on the reaction time. The growth process for Ba(HO3PPh)2 is in agreement with the three distinguishable stages of the shape evolution of CdSe nanocrystals.20 At the beginning of the experiment, the monomer concentration in the bulk solution is high and the chemical potential of the monomers in the bulk solution is significantly higher than that in the stagnant solution at any facets of the crystals. So, the anisotropy character of the crystal structure plays an important role in determining the morphology from kinetics factors. This means the limited amount of monomers mainly diffuses into the quick growth of the unique facets, especially the (001) facet, which leads to the formation of rodshaped nanocrystals (Figure 5a). With the reaction proceeding, the monomer concentration drops to a certain level and the overall chemical potential gradient between the bulk solution and the different facets decreases. Therefore, the monomers are difficult to diffuse to the (001) facet as compared to the other facets leading to the monomers being shared by three dimensions. As a result, the crystals grow to hexagonal nanocrystals (Figure 5b). Consequently, the monomers move on the crystal from one dimension to the other two dimensions in an intraparticle manner because of the internal chemical potential gradient. As a result, the short axis grows significantly and the aspect ratio of nanocrystal decreases to nearly one, resulting in nanocubes at last (Figure 5c). Because the solubility product constant of Ca(HO3PPh)2 is much larger than that of Ba(HO3PPh)2, the monomer concentration in the solution of Ca(HO3PPh)2 is much higher than that of Ba(HO3PPh)2 under the same condition. Even in the final growth stage of Ca(HO3PPh)2, the chemical potential of the monomers in the solution is still
898 Crystal Growth & Design, Vol. 7, No. 5, 2007
Gao et al.
0.7-1.0 P/P0 (Figure 8). The measurement shows that these nanorods have mesopores with an average diameter of ca. 10 nm (Figure S3), and the BET surface area is 141.45 m2/g. Until now, many studies have been conducted on the preparation of various porous nanomaterials including nanoporous films and nanotubule arrays by the methods of sol-gel process,22 anodization,23 and electrodeposition.24 The process presented here offers an effective method for the synthesis of porous nanorods, which could possibly be used for applications in catalysis, electrolysis, and sensor arrays. High surface areas should serve to increase reactivity and sensitivity. In addition, the porous characteristics of nanorods should be thermally stable because the sample was prepared at 700 °C. Conclusion
Figure 7. XRD pattern and TEM image of Ca2P2O7 prepared by heating Ca(HO3PPh)2 nanorods.
Figure 8. N2 adsorption-desorption isotherm for Ca2P2O7.
relatively high, and this results in the formation of a 1D nanostructure for Ca(HO3PPh)2. After the Ca(HO3PPh)2 nanorods were heated at 700 °C in the air for 2 h, the nanorods could be transformed into crystalline Ca2P2O71f without altering the 1D morphology and many holes formed in the nanorods (Figures 7b,c). All of the reflections of the XRD (Figure 7a) patterns can be readily indexed to a pure tetragonal phase of Ca2P2O7 [space group, P41 (no. 76)] with lattice constants a ) 6.684 Å and c ) 24.14 Å (JCPDS 712123). Elemental analysis can further confirm the elemental composition of the compounds in expected stoichiometric proportions; obsd (%): Ca, 31.97; P, 24.01; calcd (%): Ca, 31.55, P, 24.38. The width of calcinated Ca2P2O7 nanorods (220-230 nm) is enlarged from the width of Ca(HO3PPh)2 nanorods (60-80 nm) because of the thermal expansion. The holes in crystalline Ca2P2O7 are formed due to the release of the organic part of the Ca(HO3PPh)2 (Figure 7d). The hollow nature of the Ca2P2O7 was further confirmed by measurement of the pore size distribution, which was obtained by nitrogen adsorption-desorption isotherm and Barrett-Joyner-Halenda (BJH) methods. The isotherms are of type IV in the BDDT classification,21 with a hysteresis loop observed in the range of
In summary, the nanostructures of alkaline-earth metal phenylphosphonates Mg(O3PPh)‚H2O and M(HO3PPh)2 (M ) Ca, Sr, or Ba) were synthesized by a facile hydrothermal method. The morphologies of the Ba(HO3PPh)2 are strongly dependent on the heating time. Through the control of the reaction time, rod-shaped nanocrystals, nanocubes, and hexagonal nanocrystals of Ba(HO3PPh)2 have been obtained, respectively. Mesoporous nanorods of Ca2P2O7 with an average diameter of 10 nm and a BET surface area of 141.45 m2/g were successfully prepared by heating Ca(HO3PPh)2 nanorods at 700 °C. On the basis of experimental results, the possible growth mechanisms are discussed. This may provide a useful guide for future design and synthesis of other nanomaterials. These new nanomaterials of alkaline-earth metal phenlyphosphonates are believed to be valuable for new possibilities in many research areas. Acknowledgment. We thank the National Natural Science Foundation of China (no. 20471014), Program for New Century Excellent Talents in Chinese University (NCET-05-0320), the Fok Ying Tung Education Foundation, and the Analysis and Testing Foundation of Northeast Normal University for support. TEM work was performed by Dr. L.-H. Ge in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Crystal Data of Mg(O3PPh)‚H2O, M(HO3PPh)2 (MdCa, Sr), and Ba(HO3PPh)2 were obtained from Prof. G. Cao, A. H. Mahmoudkhani, and A. Clearfield, respectively. Supporting Information Available: TEM images of the Ca(HO3PPh)2 and Sr(HO3PPh)2 prepared in the absence of surfactants (Figures S1 and S2) and pore size distribution curve for Ca2P2O7 (Figure S3). This material is available free of charge via the Internet at http:// pubs.acs.org.
References (1) (a) Alberti, G. In ComprehensiVe Supramolecular Chemistry; Alberti, G., Bein, T., Eds.; Pergamon Press: New York, 1996; Vol. 7, p 151. (b) Clearfield, A. Chem. Mater. 1998, 10, 2801. (c) Dines, M. B.; DiGiacomo, P. M. Inorg. Chem. 1981, 20, 92. (d) Song, J. L.; Prosvirin, A. V.; Zhao, H. H.; Mao, J. G. Eur. J. Inorg. Chem. 2004, 3706. (e) Song, S. Y.; Ma, J. F.; Yang, J.; Cao, M. H.; Zhang, H. J.; Wang, H. S.; Yang, K. Y. Inorg. Chem. 2006, 45, 1201. (f) Lima, C. B. A.; Airoldi, C. Solid State Sci. 2002, 4, 1321. (2) Cao, G.; Lee, H.; Lynch, V. M.; Mallouk, T. E. Inorg. Chem. 1990, 29, 11. (3) (a) Zhang, Y. P.; Clearfield, A. Inorg. Chem. 1992, 31, 2821. (b) Poojary, D. M.; Zhang, B.; Cabeza, A.; Aranda, M. A. G.; Bruque, S.; Clearfield, A. J. Mater. Chem. 1996, 6, 639. (c) Mahmoudkhani, A. H.; Langer, V.; Smrcok, L. Solid State Sci. 2002, 4, 873. (4) (a) Prevot, V.; Forano, C.; Besse, J. P. J. Mater. Chem. 1999, 9, 155. (b) Ruiz, V. O.; Dias, S. P.; Gushikem, Y.; Bruns, R. E.; Airoldi, C. J. Solid State Chem. 2004, 177, 675.
Alkaline-Earth Metal Phenylphosphonate Nanostructures (5) (a) Zhu, Y. C.; Bando, Y.; Xue, D. F.; Golberg, D. AdV. Mater. 2004, 16, 831. (b) Bonchio, M.; Carraro, M.; Scorrano, G.; Bagno, A. AdV. Synth. Catal. 2004, 346, 648. (c) Johnson, C. J.; Edler, K. J.; Mann, S.; Murphy, C. J. J. Mater. Chem. 2002, 12, 2909. (6) (a) Song, S. Y.; Ma, J. F.; Yang, J.; Cao, M. H.; Li, K. C. Inorg. Chem. 2005, 44, 2140. (b) Wang, X. D.; Summers, C. J.; Wang, Z. L. Nano Lett. 2004, 4, 423. (c) Xia, Y. N.; Yang, P. D.; Sun, Y. G.; Wu, Y. Y.; Mayers, B.; Gates, B.; Yin, Y. D.; Kim, F.; Yan, H. Q. AdV. Mater. 2003, 15, 353. (7) (a) Vayssieres, L.; Beermann, N.; Lindquist, S. E.; Hagfeldt, A. Chem. Mater. 2001, 13, 233. (b) Zhang, Z.; Ramanath, G.; Ajavan, P. M.; Goldberg, D.; Bando, Y. Adv. Mater. 2001, 13, 197. (c) Hatzor, A.; Weiss, P. S. Science 2001, 291, 1019. (d) Wang, Z. L.; Gao, R. P.; Gole, J. L.; Stout, J. D. Adv. Mater. 2000, 12, 1938. (e) Li, M.; Schnablegger, H.; Mann, S. Nature 1999, 402, 393. (f) Rao, C. N. R.; Govindaraj, A.; Deepak, F. L.; Gunari, N. A.; Nath, M. Appl. Phys. Lett. 2001, 78, 1853. (g) Lu, Q. Y.; Gao, F.; Komarneni, S. J. Am. Chem. Soc. 2004, 126, 54. (8) Huang, M.; Mao, S.; Feick, H.; Yan, H.; Wu, Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. Science 2001, 292, 1897. (9) Comini, E.; Faglia, G.; Sberveglier, G.; Pan, Z.; Wang, Z. L. Appl. Phys. Lett. 2002, 81, 1869. (10) Arnold, M. S.; Avouris, P.; Pan, Z. W.; Wang, Z. L. J. Phys. Chem. B 2003, 107, 659. (11) (a) Shi, L.; Hao, Q.; Yu, C.; Mingo, N.; Kong, X.; Wang, Z. L. Appl. Phys. Lett. 2004, 84, 2638. (b) Cheng, B.; Shi, W. S.; Russell-Tanner, J. M.; Zhang, L.; Samulski, E. T. Inorg. Chem. 2006, 45, 1208. (12) (a) Goldberger, J.; He, R.; Zhang, Y. F.; Lee, S.; Yan, H. Q.; Chol, H. J.; Yang, P. D. Nature 2003, 422, 599. (b) Liu, Z.; Zhang, D.; Han, S.; Li, C.; Lei, B.; Lu, W.; Fang, J.; Zhou, C. J. Am. Chem. Soc. 2005, 127, 6. (c) Kang, Z. H.; Wang, E. B.; Gao, L.; Lian, S. Y.; Jian, M.; Hu, C. W.; Xu, L. J. Am. Chem. Soc. 2003, 125, 13652. (13) (a) Liu, B.; Zeng, H. C. J. Am. Chem. Soc. 2004, 126, 8124. (b) Yang, H. G.; Zeng, H. C. Angew. Chem., Int. Ed. 2004, 43, 5930. (c) Wang, X.; Li, Y. D. Chem. Eur. J. 2003, 9, 5627. (d) Wang, X.; Li, Y. D. Chem. Eur. J. 2003, 9, 300. (e) Wang, X.; Li, Y. D. Angew. Chem., Int. Ed. 2002, 41, 4790. (14) (a) Li, X. D.; Gao, H. S.; Murphy, C. J.; Gou, L. F. Nano Lett. 2004, 4, 1903. (b) Yu, D. B.; Yam, V. W. W. J. Am. Chem. Soc. 2004, 126, 13200. (c) Im, S. H.; Lee, Y. T.; Wiley, B.; Xia, Y. N. Angew. Chem., Int. Ed. 2005, 44, 2154. (d) Woo, K.; Lee, H. J.; Ahn, J. P.; Park, Y. S. Adv. Mater. 2003, 15, 1761.
Crystal Growth & Design, Vol. 7, No. 5, 2007 899 (15) (a) Sun, X. P.; Dong, S. J.; Wang, E. K. Angew. Chem., Int. Ed. 2004, 43, 6360. (b) Li, F.; Ding, Y.; Gao, P. X.; Xin, X. Q.; Wang, Z. L. Angew. Chem., Int. Ed. 2004, 43, 5238. (c) Shi, W. D.; Wang, C.; Wang, H. S.; Zhang, H. J. J. Cryst. Growth 2006, 6, 915. (16) Tang, B.; Zhuo, L.; Ge, J.; Niu, J.; Shi, Z. Inorg. Chem. 2005, 44, 2568. (17) Mahmoudkhani, A. H.; Langer, V. Solid State Sci. 2001, 3, 519. (18) (a) Cunningham, D.; Hennelly, P. J. D.; Deeney, T. Inorg. Chim. Acta 1979, 37, 95. (b) Cao, G.; Lee, H.; Lynch, V. M.; Mallouk, T. E. Inorg. Chem. 1988, 27, 2781. (c) Cao, G.; Lee, H.; Lynch, V. M.; Mallouk, T. E. Solid State Ionics 1988, 26, 63. (19) Fang, Y. P.; Xu, A. W.; Song, R. Q.; Zhang, H. X.; You, L. P.; Yu, J. C.; Liu, H. Q. J. Am. Chem. Soc. 2003, 51, 16025. (20) Peng, Z. A.; Peng, X. G. J. Am. Chem. Soc. 2001, 123, 1389. (21) (a) Gregg, S. J.; Sing, K. S. W. Adsorption, Surface Area and Porosity, 2nd ed.; Academic Press: New York, 1982; p 4. (b) Go´mezAlca´ntara, M. d. M.; Cabeza, A.; Moreno-Real, L.; Aranda, M. A.; Clearfield, A. Microporous Mesoporous Mater. 2006, 88, 293. (c) Subbiah, A.; Pyle, D.; Rowland, A.; Huang, J.; Narayanan, R. A.; Thiyagarajan, P.; Zon´, J.; Clearfield, A. J. Am. Chem. Soc. 2005, 127, 10826. (d) Kruk, M.; Jaroniec, M. Chem. Mater. 2001, 13, 3169. (e) Wang, Z.; Heising, J. M.; Clearfield, A. J. Am. Chem. Soc. 2003, 125, 10375. (22) (a) Lakshmi, B. B.; Dorhout, P. K.; Martin, C. R. Chem. Mater. 1997, 9, 857. (b) Chu, S. Z.; Wada, K.; Inoue, S.; Todoroki, S. Chem. Mater. 2002, 14, 266. (c) Chu, S. Z.; Wada, K.; Inoue, S. AdV. Mater. 2002, 23, 1752. (d) Chu, S. Z.; Wada, K.; Inoue, S.; Todoroki, S. J. Electrom. Soc. 2002, 149, B321. (e) Meng, Q. B.; Fu, C. H.; Einaga, Y.; Gu, Z. Z.; Fujishima, A.; Sato, O. Chem. Mater. 2002, 14, 83. (23) (a) Mor, G. K.; Carvalho, M. A.; Varghese, O. K.; Pishko, M. V.; Grimes, C. A. J. Mater. Res. 2004, 19, 628. (b) Miller, D.; MamicheAfara, S.; Dignam, M. J.; Moskovits, M. Chem. Phys. Lett. 1983, 100, 236. (c) Chu, S. Z.; Inoue, S.; Wada, K.; Hishita, S.; Kurashima, K. J. Electrochem. Soc. 2005, 152, B116. (24) (a) Ishikawa, Y.; Matsumoto, Y. Electrochim. Acta 2001, 46, 2819. (b) Peiro´, M.; Brillas, E.; Peral, J.; Dome`nech, X.; Ayllo´n, J. A. J. Mater. Chem. 2002, 12, 2769. (c) Chu, S. Z.; Inoue, S.; Wada, K.; Li, D.; Jun, S. Langmuir 2005, 21, 8035.
CG0606491
