Oriented Nanocrystal Mosaic in Monodispersed CaCO3 Microspheres

Article pubs.acs.org/crystal

Oriented Nanocrystal Mosaic in Monodispersed CaCO3 Microspheres with Functional Organic Molecules Hiroaki Imai,* Natsuki Tochimoto, Yuichi Nishino, Yoko Takezawa, and Yuya Oaki Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan S Supporting Information *

ABSTRACT: Monodispersed microspheres of vaterite CaCO3 with a diameter adjusted to the range of 1−10 μm were produced through an amorphous intermediate with polystyrene sulfate. Whereas the microspheres were composed of nanocrystals with a diameter of ca. 20 nm covered with the organic polymer, the crystallographic direction of the entire sphere was evaluated to be macroscopically uniform from its single-crystalline features on polarization anisotropy and morphological evolution into a hexagonal shape with an additional growth process. A particular mosaic with a radially grown backbone structure consisting of oriented nanocrystals was suggested to exist in the microspheres from the electron diffraction patterns. The rigid mosaic framework was covered with a flexible organic component. Thus, various functional organic molecules including hydrophilic and hydrophobic dyes were successfully introduced into the microspheres due to the amphiphilic nature of the organic phase.

■

INTRODUCTION Biominerals are known to be inorganic/organic composites with hierarchically organized structures from nanoscopic to macroscopic scales.1 The architectures and formation processes of biominerals provide considerable inspirations in the field of materials chemistry, leading to new fabrication techniques and the development of novel functionalities. In recent years, most CaCO3-based biominerals were revealed to have a hierarchical architecture composed of oriented nanometric crystals.2,3 These specific nanostructures are categorized as a kind of mesocrystal, that is, mesostructured crystals composed of oriented nanoscale units.4 A wide variety of mesocrystals have been artificially produced by the self-assembly of nanoscale particles and self-organized crystal growth in aqueous solution systems containing soluble organic species.5,6 Particularly, CaCO3-based mesocrystals have attracted attention as a typical structure of real biominerals. The addition of polyelectrolytes and gel matrices is known to affect the crystal growth drastically as a modifier.6−15 The presence of acidic polymers, such as poly(acrylic acid) (PAA),6 poly(aspartic acid),14 and polystyrene sulfonate (PSS),15 has been reported to be highly effective for the construction of mesostructured CaCO3. The gel matrix was also reported to promote the formation of mesocrystal structures. Although the polymer-mediated assembly of nanocrystals and polymer-modulated crystal growth has been proposed to be involved in the formation process of mesocrystals, the detailed mechanism for the construction of © 2012 American Chemical Society

the sophisticated nanostructures has not been sufficiently clarified due to the high complexity of the structure and processes. Recently, well-defined microspheres of CaCO3 nanoparticles were produced in solution systems containing PAA,16 PSS,17 and double hydrophilic block copolymers.18 In these cases, the polymers stabilized the metastable phase and promoted the aggregation of nanoparticles. The formation process and the internal structure have been revealed although these spheres were regarded as simple aggregates of nanocrystals. Here, we found that monodispersed microspheres having an oriented nanocrystal mosaic interior could be obtained through the crystal growth of CaCO3 with PSS under a specific condition. If the microspheres, like mesocrystals, consisted of regularly arranged building units, a new type of isotropically shaped crystal with an anisotropic nature would be scientifically and technologically interesting. From the standpoint of the exploration of their function, CaCO3-based mesocrystals have been hardly studied for practical applications. On the other hand, the mesocrystal is a candidate new family of host materials because most CaCO3based biominerals are particularly colored with organic molecules. Hosts for functional organic molecules including Received: October 1, 2011 Revised: December 13, 2011 Published: January 4, 2012 876

dx.doi.org/10.1021/cg201301x | Cryst. Growth Des. 2012, 12, 876−882

Crystal Growth & Design

Article

Figure 1. SEM images of typical microspheres. Monodispersed spheres with a diameter of ca. 4 μm were produced with 1.0 g/dm3 at pH 11 (a, b). The cross-sectional views of the microspheres (c, d) were observed after the removal of the organic polymers with an NaClO solution.

Figure 2. TEM images of a sliced sample of a typical microsphere (a, b). The electron diffraction pattern (c) from the square of the inset. The dark field image (d) with the diffraction from the circle in (c).

compounds,21 and sol−gel-derived mesoporous materials.22 Because mesocrystals have an interspatial organic domain

dyes and medical drugs have been widely developed using various inorganic materials, such as zeolites,19 clays,20 layered 877



Article

Figure 3. Variation of polarization microscope images (a) and XRD patterns (b) of the microspheres with prolongation of the reaction time. Actual micrographs are located at the center of eight polarized micrographs in (a). Repetition of light and dark of the polarized images was observed with rotation of the sample every 45°.

stable calcite. On the other hand, the PSS-mediated vaterite spheres were stable in water for a long time. The crystalline grains composing the microspheres were clearly observed after the decomposition of the organic phase by using an NaClO solution (Figure S3 in Supporting Information). Moreover, the size and the volume of the pores as an interspace among the nanoscale grains were drastically increased by the treatment. These facts indicate that the vaterite nanocrystals were covered with the organic polymer. Vaterite microspheres have already been reported to be formed in the presence of PAA, PSS, and a block copolymer.16−18 As mentioned in previous reports, the polymer stabilized the metastable phase and promoted the aggregation of nanoparticles. The microspheres have been regarded as a random aggregate of vaterite nanoparticles. In the present study, however, we focused on the specific internal mosaic structure of the vaterite microspheres. Figure 2 shows TEM images of a sliced sample of a microsphere. We observed a mosaic structure consisting of nanocrystals of ca. 20 nm which were randomly arranged in the nanometer-scale region. Interestingly, however, the broken ring pattern of electron diffraction obtained from a micrometer-scale area exhibited 6-fold symmetry. For example, the diffraction rings of (110) and (114) were composed of six bright and six dark segments. This means that the crystallographic direction of the nanocrystals in the mosaic was not random and was roughly arranged in the same orientation. The dark-field image indicates the presence of radial branches consisting of nanocrystals having a similar orientation in the microsphere. The iso-

consisting of crystals and polymers, various guest molecules can be introduced in the interspace.23 In the present study, we demonstrated a particular nanocrystal mosaic in the monodispersed microspheres of vaterite produced with PSS. The specific crystalline structure of oriented vaterite nanoparticles was prepared through an amorphous phase. Moreover, the nanocomposite with an oriented architecture was shown to be applicable as a new family of host materials for functional guest molecules due to its rigid framework in combination with a flexible organic domain.

■

RESULTS AND DISCUSSION Formation of Vaterite Microspheres Having a Mosaic Internal Structure. As shown in Figure 1, well-defined microspheres in the range of 1−10 μm in diameter were produced in 24 h after mixing of a calcium solution and a carbonate solution containing 1.0 g/dm3 PSS. We successfully tuned the diameter of the microspheres by the varying the pH of the mixed solution and the stirring rate (Figure S1 in Supporting Information). In the SEM images of the cross section and the surface, the microspheres were found to consist of small particles with a diameter of ca. 20 nm. According to the XRD patterns, the microspheres were assigned to be pure vaterite (Figure S2 in Supporting Information). The crystalline size (∼18 nm) estimated from the broadened diffraction peak with the Scherrer equation was almost the same as that observed in the SEM images. In the absence of PSS, the metastable vaterite particles, which were produced at a high degree of supersaturation in the initial stage of the precipitation, gradually changed into rhombohedrons of thermodynamically 878



Article

Figure 4. SEM images of typical hexagonal-shaped samples after the additional growth. The hexagonal-shaped crystal (a) was composed of small hexagonal units (b). The cross-sectional images (c, d) indicate that the hexagon was produced from the microsphere with the oriented growth of a bunch of rods consisting of nanograins.

oriented rods was roughly estimated to be about 60°. Because sharpened XRD peaks of vaterite were obtained from the resultant crystals, the nanoscale units are expected be arranged in the same crystallographic orientation. These results support the presence of iso-oriented nanograins in the mosaic of the original spheres. Introduction of Functional Molecules into the Mosaic. Figure 5 shows actual macroscopic and fluorescent images of the vaterite microspheres colored with R6G and Ru(bpy)3. The vaterite microspheres were easily colorized by immersion in ethanol solutions of not only hydrophilic but also hydrophobic dyes. When the dye molecules were previously mixed into the carbonate and PSS solution, the monodispersed microspheres were deeply colored. As a control experiment, we confirmed that the dye molecules that simply attached onto calcite particles were quickly washed out with ethanol. Moreover, the coloration of the vaterite microspheres was not observed after removal of PSS with the NaClO treatment. Fluorescent microscope images (Figure 5b) indicate that the dye molecules were homogeneously contained in the microspheres with the premixed solution, whereas the molecules were localized in the surface layer with the postimmersion method. The photoluminescence (PL) spectra of the dyes were more similar to those in ethanol solution than those of the solid samples (Figure 5c). Furthermore, the PL intensity of the colored microspheres was much higher than that of the solid powder. These facts suggest that the dye molecules were located in the PSS phase covering vaterite nanoparticles in the mosaic. Because both hydrophilic and hydrophobic dyes were stably trapped in the microspheres, the organic phase acted as an amphiphilic agent for the guest molecules. Figure 6 shows the photoisomerization behavior of AB molecules in the monodispersed vaterite microspheres. It is generally known that the absorption bands around 325 and 435 nm correspond to the π−π* and ν−π* transitions of NN in AB molecules, respectively.25 These two specific bands were clearly observed after their introduction into the mosaic

oriented branches as a backbone of the mosaic appeared to be covered with randomly oriented nanocrystals. Figure 3a shows polarization microscope images of the microsphere between crossed nicols. Repetition of light and dark of the image was observed with rotation of the sample every 45°, indicating that the core part in the microsphere had a single crystalline structure. The bright part of the initially grown microspheres was limited at the central part (Figure 3a), while the apparent particle size changed from ∼1 to ∼4 μm. The ratio of the bright core in the sphere increased with increasing the crystallinity evaluated from the intensity of XRD peaks by prolongation of the reaction time to 24 h (Figure 3b). These results indicate that the initially produced microspheres are composed of an amorphous phase containing a small vaterite core. Finally, the microspheres were entirely composed of vaterite through the crystal growth from the center of the spheres. The polarization micrographs suggest that the optical property of the entire microspheres obtained in 24 h was similar to that of a single crystal. These facts support the presence of iso-oriented branches consisting of vaterite nanocrystals in the mosaic. On the other hand, bright polarization images were always observed regardless of the angle on the microspheres obtained without PSS (Figure S2c in Supporting Information), indicating that the sample was polycrystal. Development of the Microspheres. Our research group reported that the crystal phase and orientation of original CaCO3 crystals prepared with polyelectrolyte developed with additional growth under a moderate supersaturated condition.24 This technique is useful to clarify the crystallographic structure of the tiny original crystal. Figure 4 shows SEM images of typical hexagonal aggregates of vaterite obtained from the microspheres with the additional growth. The hexagonal plates were composed of small hexagonal units oriented in almost the same direction (Figure 4b). From the images of the fracture cross-section (Figure 4c,d), the nanograins developed into the oriented rods. The deviation angle of each main bundle of the 879



Article

Figure 5. Actual macroscopic images, fluorescent images, and PL spectra of the vaterite microspheres colored with R6G and Ru(bpy)3.

reactions were achieved with irradiation of light, and further irradiation did not result in spectral changes. We demonstrated the reversible switching between trans and cis forms with the alternative irradiation of UV and visible lights. The photoisomerization reaction was smoothly achieved in the mosaic of the vaterite microspheres. Formation Process of Vaterite Microspheres Having a Specific Mosaic Structure. Figure 7a shows the specific features of the vaterite microspheres observed in the SEM and polarization microscope images. The equator line dividing the microsphere was found on the surface of most products (lift in Figure 7a). We commonly observed diphycercal branches in the fracture cross-section (middle in Figure 7a) and the polarization micrographs (right in Figure 7a). According to the darkfield image, iso-oriented branches (Figure 2d) were present in the radially grown spheres. As described in the previous section, the vaterite nanocrystals grew from the center of a noncrystalline precursor phase. Figure 7b shows a schematic illustration of the formation process of the microspheres. The crystalline CaCO3 has been reported to be transformed from amorphous calcium carbonate (ACC).26 The polyelectrolyte, PSS, strongly binds free Ca2+ ions in a solution and PSS−Ca2+ complex is then formed. The complex could act as a precursor of the amorphous

Figure 6. Variation of UV−vis spectra of AB-incorporated microspheres under UV (365 nm) and visible light irradiations.

structure of the microspheres. The trans-to-cis transformation resulted in a remarkable decrease in the 325 band and a slight increase in the 435 nm band. The trans isomers of AB molecules were changed to cis after irradiation with UV light at 365 nm within 3 min of the irradiation, and then cis-to-trans transformation conversely took place with the subsequent irradiation with visible light for 1 min. The photoisomerization 880



Article

Figure 7. (a) Side views of the microsphere in SEM (left: appearance, middle: fractured cross-section) and polarization microscope (right) images. (b) A schematic illustration of the formation process of the microsphere. An amorphous sphere (pink sphere) having a vaterite core is formed (i). Main branches consisting of oriented nanocrystals (gray grains) grow in the amorphous sphere (ii, iii). Main branches are then covered with randomly oriented nanocrystals (black and white grains) (iv). concentration of sulfonate groups contained in the PSS chains was estimated to be varied from 1.2 to 4.8 mM. After the mixing, the solution was stirred for 60 s and kept for several hours. The pH value of the mixed solution was adjusted from 8 to 12 by addition of HCl or NaOH. In order to introduce dye molecules previously, rhodamine 6G (R6G) and ruthenium trisbipyridine (Ru(bpy)3) were added into the carbonate solution before mixing. The concentration of the dye molecules was adjusted to be 0.04 mM. Anionic dyes (R6G, Ru(bpy)3) and hydrophobic dye (azobenzene (AB)) were also introduced into the CaCO3−PSS composites by a subsequent process. The resultant powder was immersed in a 0.2 mM ethanol solution of anionic dyes or a 10 mM ethanol solution of AB. The vessel was then put in a sonic bath for 30 min and maintained at 25 °C for 180 min. The dyecontaining samples were extensively washed with ethanol to remove excess dye molecules and were then powdered for characterization. Absorption spectra in ultraviolet−visible region were obtained with diffuse reflectance mode (Jasco V-560). The PL spectra were measured at room temperature with a Shimadzu RF-5300PC spectro-fluorophotometer. Additional growth of the resultant crystals was performed in a 20 mM CaCl2 solution by introduction of CO2. Vessels containing 40 cm3 of the precursor solution and substrates were covered with a polymer film with several pinholes. Two vessels were placed in a 600 cm3 desiccator filled with CO2 generated by the decomposition of 1.0 g of (NH4)2CO3 at 25 °C. The organic components included in the products were extracted by immersion in a 5 wt % NaClO aqueous solution for 12 h and then washing the sample extensively with purified water. The morphology of the products was characterized using a fieldemission scanning electron microscope (FESEM, Hitachi S-4700) and a field-emission transmission electron microscope (FETEM, FEI Tecnai F20). Optical, cross-polarized, and fluorescent images of the calcite prisms were taken by an epifluorescence microscope equipped with polarizers (Olympus BX-51-FL). The X-ray diffraction (XRD) patterns were recorded using Rigaku MiniFlex II with Cu Kα radiation. The pore-size distribution was evaluated from nitrogen adsorption− desorption isotherms obtained with Miromeritics Tristar 3000.

intermediates. In the initial stage of the precipitation reaction, an amorphous microsphere including a small vaterite core was formed with PSS. The presence of PSS prevents the random growth of nanocrystals and stabilizes the metastable vaterite phase. On the other hand, PAA was reported to promote the formation of calcite due to the affinity of the polymer chain.6c Thus, dendritic vaterite consisting of iso-oriented nanocrystals is formed from the core with the growth of the ACC sphere with PSS. The crystalline part dominates in the entire sphere in the progressive stage. Finally, a mosaic structure is achieved with the main branches covered with randomly oriented nanocrystals. The microspheres having the iso-oriented backbone could exhibit similar properties to those of single crystal.

■

CONCLUSION

■

EXPERIMENTAL PROCEDURES

We succeeded in the preparation of monodispersed vaterite microspheres consisting of a specific nanocrystal mosaic. The diameter of the microsphere was highly tuned in the range between 1 and 10 μm. Nanocrystals ca. 20 nm in size made up the oriented architectures in the mosaic with the incorporation of organic polymers. The single-crystalline features of the polarization anisotropy and morphology after an additional growth process indicated that the mosaic structure was regarded as a kind of mesocrystal. Cationic and hydrophobic organic molecules were introduced into the organic phase of the microspheres due to the amphiphilic nature. Since the mosaic structure provides a soft and flexible nanospace with a rigid framework, the introduction of various guest molecules and the smooth photochemical reaction would be allowed in the interspatial organic phase. In consequence, monodispersed microspheres with a specific crystalline framework and a flexible organic domain have potential as a new family of host materials.

■

We prepared CaCO3 crystals by using a simple mixing method of two solutions at room temperature. Typically, 16 cm3 of 1 M CaCl2 solution was added to 500 cm3 of 16 mM Na2CO3 ([Ca2+] ∼ 32 mM, [CO32−] ∼ 16 mM) solution containing PSS (Mw: 70 000). The concentration of PSS was varied in the range of 0 and 1.0 g/dm3. The

ASSOCIATED CONTENT

S Supporting Information *

The detailed data including SEM images of the microspheres prepared under various pH and stirring rate, SEM, polarized 881



Article

(15) (a) Kawaguchi, H.; Hirai, H.; Sakai, K.; Sera, S.; Nakajima, T.; Ebisawa, Y.; Koyama, K. Colloid Polym. Sci. 1992, 270, 1176. (b) Geng, X.; Liu, L.; Jiang, J.; Yu, S. H. Cryst. Growth Des. 2010, 10, 3448. (c) Wang, T. X.; Cölfen, H.; Antonietti, M. J. Am. Chem. Soc. 2005, 127, 3246. (d) Wang, T. X.; Antonietti, M.; Cölfen, H. Chem.−Eur. J. 2006, 12, 5722. (16) Naka, K.; Huang, S. C.; Chujo, Y. Langmuir 2006, 22, 7760. (17) (a) Lei, M.; Tang, W. H.; Gao, L. Z.; Li, P. G.; Yu, J. G. J. Cryst. Growth 2006, 294, 358. (b) Tang, H.; Yu, J.; Zhao, X.; Ng, D. H. L. J. Alloys Compd. 2007, 463, 343. (18) Guo, X. H.; Yu, S. H.; Cai, G. B. Angew. Chem., Int. Ed. 2006, 45, 3977. (19) (a) Calzaferri, G.; Huber, S.; Maas, H.; Minkowski, C. Angew. Chem., Int. Ed. 2003, 42, 3732. (b) Ozin, G. A.; Kuperman, A.; Stein, A. Angew. Chem., Int. Ed. Engl. 1989, 28, 359. (20) Ogawa, M.; Kuroda, K. Chem. Rev. 1995, 95, 399. (21) (a) Ogawa, M.; Kuroda, K. Bull. Chem. Soc. Jpn. 1997, 70, 2593. (b) Hata, H.; Kimura, T.; Ogawa, M.; Sugahara, Y.; Kuroda, K. J. SolGel Sci. Technol. 2000, 19, 543. (22) (a) Kapoor, M. P.; Inagaki, S. Bull. Chem. Soc. Jpn. 2006, 79, 1463. (b) Moller, K.; Bein, T. Chem. Mater. 1998, 10, 2950. (c) Schöllhorn, R. Chem. Mater. 1996, 8, 1747. (23) Oaki, Y.; Imai, H. Bull. Chem. Soc. Jpn. 2009, 82, 613. (24) Kotachi, A.; Imai, H. Chem. Lett. 2006, 35, 204. (25) (a) Bujdák, J.; Iyi, N.; Fujita, T. J. Colloid Interface Sci. 2003, 262, 282. (b) Fujita, T.; Iyi, N.; Klapyta, Z. Mater. Res. Bull. 1998, 33, 1693. (c) Iyi, N.; Kurashima, K.; Fujita, T. Chem. Mater. 2002, 14, 583. (26) (a) Aizenberg, J.; Muller, D. A.; Grazul, J. L.; Hamann, D. R. Science 2003, 299, 1205. (b) Politi, Y.; Arad, T.; Kleon, E.; Weiner, S.; Addadi, L. Science 2004, 306, 1161.

microscope images and XRD patterns of precipitates, and SEM images and pore-size distribution of the microspheres. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

■

ACKNOWLEDGMENTS This work was partially supported by a Grant-in-Aid for Scientific Research (No. 22107010) on Innovative Areas of “Fusion Materials: Creative Development of Materials and Exploration of Their Function through Molecular Control” (area no. 2206) from the Ministry of Education, Culture, Sports, Science and Technology from Japan Society of the Promotion of Science.

■

REFERENCES

(1) (a) Mann, S. Nature 1988, 332, 119. (b) Addadi, L.; Weiner, S. Angew. Chem., Int. Ed. Engl. 1992, 31, 153. (c) Mann, S. Nature 1993, 365, 499. (d) Mann, S. Biomineralization Principles and Concepts in Bioinorganic Materials Chemistry; Compton, R. G., Davies, S. G., , Evans, J., Eds.; Oxford University Press: Oxford, U. K., 2001. (e) Sumper, M.; Brunner, E. Adv. Funct. Mater. 2006, 16, 17. (f) Handbook of Biomineralization; Bäuerlein, E., Behrens, P., Epple, M., Eds.; Wiley-VCH: Weinheim, Germany; 2007. (2) (a) Oaki, Y.; Kotachi, A.; Miura, T.; Imai, H. Adv. Funct. Mater. 2006, 16, 1633. (b) Oaki, Y.; Imai, H. Small 2006, 2, 66. (3) Oaki, Y.; Imai, H. Angew. Chem., Int. Ed. 2005, 44, 6571. (4) (a) Cölfen, H.; Mann, S. Angew. Chem., Int. Ed. 2003, 42, 2350. (b) Cölfen, H.; Antonietti, M. Angew. Chem., Int. Ed. 2005, 44, 5576. (c) Niederberger, M.; Cölfen, H. Phys. Chem. Phys. Chem. 2006, 8, 3271. (d) Zhou, L.; O’Brien, P. Small 2008, 4, 1566. (e) Song, R. Q.; Cölfen, H. Adv. Mater. 2010, 22, 1301. (5) (a) Mann, S. Nature 1993, 365, 499. (b) Stupp, S. I.; Braun, P. V. Science 1997, 277, 1242. (c) Kato, T. Adv. Mater. 2000, 12, 1543. (d) Kato, T.; Sugawara, A.; Hosoda, N. Adv. Mater. 2002, 14, 869. (e) Yu, S.-H.; Cölfen, H. J. Mater. Chem. 2004, 14, 2124. (f) Imai, H.; Oaki, Y.; Kotachi, A. Bull. Chem. Soc. Jpn. 2006, 79, 1834. (g) Xu, A.W.; Ma, Y.; Cölfen, H. J. Mater. Chem. 2007, 17, 415. (h) Meldrum, F. C.; Cölfen, H. Chem. Rev. 2008, 108, 4332. (i) Sommerdijk, N. A. J. M.; de With, G. Chem. Rev. 2008, 108, 4499. (j) Mann, S. Nat. Mater. 2009, 8, 781. (k) Kato, T.; Sakamoto, T.; Nishimura, T. MRS Bull. 2010, 35, 127. (l) Imai, H.; Oaki, Y. MRS Bull. 2010, 35, 138. (6) (a) Yu, S. H.; Antonietti, M.; Cölfen, H.; Hartmann, J. Nano Lett. 2003, 3, 379. (b) Imai, H.; Terada, T.; Yamabi, S. Chem. Commun. 2003, 484. (c) Kotachi, A.; Miura, T.; Imai, H. Chem. Mater. 2004, 16, 3191. (d) Yang, H. G.; Zeng, H. C. Angew. Chem., Int. Ed. 2004, 43, 5390. (e) Oaki, Y.; Imai, H. Adv. Funct. Mater. 2005, 15, 1407. (f) Oaki, Y.; Imai, H. Chem. Commun. 2005, 6011. (g) Oaki, Y.; Hayashi, S.; Imai, H. Chem. Commun. 2007, 2841. (h) Xu, A. W.; Antonietti, M.; Yu, S. H.; Cölfen, H. Adv. Mater. 2008, 20, 1333. (7) Zhan, J.; Lin, H. P.; Mou, C. Y. Adv. Mater. 2003, 15, 621. (8) Grassmann, O.; Müllerand, G.; Löbmann, P. Chem. Mater. 2002, 14, 4530. (9) Yang, D.; Qi, L.; Ma, J. Chem. Commun. 2003, 1180. (10) Garcia-Ruiz, J. M. J. Cryst. Growth 1983, 73, 251. (11) Terada, T.; Yamabi, S.; Imai, H. J. Cryst. Growth 2003, 253, 435. (12) Estroff, L. A.; Addadi, L.; Weiner, S.; Hamilton, A. D. Org. Biomol. Chem. 2004, 2, 137. (13) (a) Grassmann, O.; Neder, R. B.; Putnis, A.; Löbmann, P. Am. Mineral. 2003, 88, 647. (b) Grassmann, O.; Löbmann, P. Chem.Eur. J. 2003, 9, 1310. (c) Grassmann, O.; Löbmann, P. Biomaterials 2004, 25, 277. (14) Gower, L.; Odom, D. J. J. Cryst. Growth 2000, 210, 719. 882


Oriented Nanocrystal Mosaic in Monodispersed CaCO3 Microspheres

Recommend Documents