Controlled Mineralization of Barium Carbonate Mesocrystals in a

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Controlled Mineralization of Barium Carbonate Mesocrystals in a Mixed Solvent and at the Air/Solution Interface Using a Double Hydrophilic Block Copolymer as a Crystal Modifier Xiao-Hui Guo and Shu-Hong Yu*

CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 2 354-359

DiVision of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemistry, UniVersity of Science and Technology of China, Hefei 230026, P. R. China ReceiVed August 29, 2006; ReVised Manuscript ReceiVed NoVember 9, 2006

ABSTRACT: Mineralization and crystallization of barium carbonate mesocrystals with various shapes and complex form using double hydrophilic block copolymers (DHBCs) as crystal growth modifiers in a mixed solvent composed of N,N-dimethylformamide (DMF) and deionized water (DIW) have been systematically investigated. The effects of polymer concentration, solvent, and the volume ratio of a mixed solvent on the controlled crystallization of BaCO3 mesocrystals have been examined. Shuttle-like BaCO3 rods with different sizes and ratios of average length (L) to maximum diameter (D) can be obtained by simply altering polymer concentration in the mixed solvent. In addition, complex hierarchical shuttle-like aggregated structures can be formed at the air/ solution interface that were dramatically different from the structure obtained in bulk solution. This crystallization method in a mixed solvent containing a crystal growth modifier represents a simple but versatile route to achieve unique synergic effects on manipulation of the morphology and preferential orientation growth of BaCO3 mineral both in bulk solution and at the air/solution interface, which can be extended for shape control over other minerals or inorganic-organic hybrid materials. 1. Introduction Biomimetic synthesis of minerals with complex and fine morphology and structure through the self-assembly of nanobuilding blocks have attracted more and more attention in recent years.1 Recently, so-called mesocrystal has emerged as usually an intermediate built up with individual nanocrystals that have a common crystallographic register, which makes a mesocrystal scatter like a single crystal.2 The building units of mesocrystals can be spherical or nonspherical, which offers new possibilities of superstructure formation due to the anisotropic particle shape of the nanobuilding units.2 Barium carbonate (BaCO3) as a common mineral has some important applications in industry for producing barium salts, pigment, optical glass, ceramic, electric condensers, and barium ferrite.3 Moreover, it was used to act as a precursor for producing superconductor and ceramic materials.4,5 Previous investigations also demonstrated that the specific surface area, morphology, size, purity, and so on can affect the performance of BaCO3.6 Thus, controlled synthesis of BaCO3 crystals has attracted much interest. Various kinds of BaCO3 crystals with morphologies such as candy-like, needle-like, or olivary-like have been prepared by using a double-jet feed semibatch technique.6 Sondi et al. have obtained similar spherical and rod structures of BaCO3 crystals with the aid of urease enzyme-catalyzed reaction.7 In addition, BaCO3 crystals obtained with distinct morphologies either through adding different crystal growth modifiers or within the template of reversed micelles have been reported.8 Different organic additives or templates have been intensively used for controlled growth of carbonate minerals,9 such as Langmuir films,10 ultrathin organic films,11 selfassembled monolayers,12 varied soluble additives like synthetic peptides,13 dendrimers,14 and common polymer.15 In recent years, a class of so-called double hydrophilic block copolymers (DHBCs) has been developed as crystal growth modifiers.16 These polymers consist of a hydrophilic polyelectrolyte domain and a noninteracting hydrophilic block, and they have shown remarkable influence on the morphogenesis of a

Figure 1. XRD patterns of BaCO3 crystals obtained from the solvents with different volume ratios of DMF/DIW (v/v) in the presence of polymer: (a) 0/6; (b) 1/5; (c) 1/1; (d) 2/1; (e) 5/1; (f) 10/1. The concentrations of polymer and barium chloride were 1.0 g L-1 and 10 mM, respectively.

huge number of inorganic materials.1c-f,17,18 For example, helical BaCO3 nanofibers,18 concentric circled pattern of BaCO3 rods,17e and CaCO3 pancakes 17d can be mineralized in the presence of DHBCs. The nucleation and growth experiments of many carbonate crystals are often carried out in aqueous solution; however, some carbonates can also be crystallized at the air/solution interface. Different and entirely unexpected CaCO3 aggregated structures were observed at the air/water interface or liquid/liquid interface.19-21 A kind of hemispherical vaterite and needle-like aragonite were selectively synthesized in supersaturated calcium bicarbonate solution at the air/water interface in the presence of poly(ethylene imines).22 Recently, we have synthesized multilayered CaCO3 crystals with controlled stratification at the air/water interface in the presence of DHBCs.23

10.1021/cg060575t CCC: $37.00 © 2007 American Chemical Society Published on Web 01/13/2007

Controlled Mineralization of BaCO3 Mesocrystals

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Table 1. The Summary of Length, Thickness, and Aspect Ratio of BaCO3 Particles Produced in Mixed Solvents with Different Volume Ratios of DMF/DIW (v/v)a pure DIW

1/5

δ ) 164∼246 nm

δavg ) 209 nm a/b ) 0.85

1/1 Lavg ) 35.3 µm D ) 1.71 µm Ravg ) 20.62

2/1

5/1

10/1

Lmin ) 3.12 µm Lmax ) 28 µm D ) 1.18 µm

Lmin ) 3.24 µm Lmax ) 33.4 µm D ) 0.94 µm

Lmin ) 2.7 µm Lmax ) 8 µm D ) 3.26 µm

Rmin ) 2.65

Rmin ) 3.46

Rmin ) 0.83

Rmax ) 23.81

Rmax ) 35.70

Rmax ) 2.45

a

δ represents the thickness of flake-shaped samples, a and b represent the length magnitude of tetracorner-shaped flake structures along two axes perpendicular to each other, and R ) L/D denotes the aspect ratios of the length (L) to the average diameter (D) for the rod-shaped particles.

It should be pointed out that crystallization of minerals like CaCO3 and BaCO3 was mainly carried out in deionized water (DIW), and the mineralization reactions in nonaqueous solution such as alcohol, ethanol, isopropanol, and diethylene glycol have been rarely explored.24 Recently, crystallization in usual aqueous solution has been extended to nonaqueous solvent25 or mixed solvent.26 The result demonstrated that DHBC-controlled crystallization in mixed solution can lead to entirely new effects as in the case of synthesis of highly monodisperse vaterite microspheres in a mixed solvent of N,N-dimethylformamide (DMF) and water under control of an artificial double hydrophilic block copolymer (DHBC) called poly(ethylene glycol)b-poly(L-glutamic acid).26 Up till now, polymer-controlled crystallization in a mixed solvent and at the air/solution interface has been rarely studied. In this paper, we present a systematic study on biomimetic synthesis of shuttle-like or thin flake-like BaCO3 mesocrystals with controlled shapes and sizes by a gas-liquid diffusion reaction using a macrocycle-coupled block copolymer, so-called poly(ethylene glycol)-b-poly(1,4,7,10,13,16-hexaazacyclooctadecan ethylene imine),27 as a crystal modifier in a mixed solution of N,N-dimethylformamide (DMF) and deionized water (DIW). The synergic effect of DHBCs and a mixed solvent on the growth of BaCO3 and further investigation on the crystallization for morphogenesis of complex superstructures at the air/solution interface will be demonstrated. 2. Experimental Section Materials. A block copolymer containing a poly(ethylene glycol)b-poly(1,4,7,10,13,16-hexaazacyclooctadecan ethylene imine) (PEG ) 5000 g mol-1, Mw of macrocycle ) 500 g mol-1), namely, macrocycle (PEG-b-hexacyclen) was synthesized as described elsewhere.27 The polymer was purified by exhaustive before use in the crystallization of BaCO3. Ammonium carbonate, barium chloride, and N,N-bimethylformamide (DMF) were obtained from chemical reagent company of Shanghai, and deionized water (DIW) was obtained from Millipore simplicity 185 types (18.2 Ω‚cm-1). All chemical reagents obtained were used without further purification. Crystallization Experiments. The biomimetic crystallization of BaCO3 was carried out in glass bottles with volume 5-15 mL, which were put in a closed desiccator at room temperature (20 ( 3 °C). Stock aqueous solution of BaCl2 (0.1 M) was freshly prepared in DIW. Polymer (5 mg) was added into 5 mL of DMF or DMF/DIW in a glass bottle, and stirred continuously to dissolve completely so as to contain 1 g L-1 polymer in solution; the pH of the solution was adjusted to a desired pH by using dilute HCl or NaOH. After that, 500 µL of BaCl2 solution (0.1 M) was injected into the glass bottles containing 5 mL of polymer solution under vigorous stirring. This gives a final BaCO3 concentration of 10 mM. The bottle was then covered with Parafilm, which was punched with three needle holes, and placed in a larger desiccator. Three small glass bottles (10 mL) of crushed ammonium carbonate were also covered with Parafilm punched with four needle holes and placed at the bottom of the desiccator. After different periods of time, the Parafilm was removed, and the precipitate deposited on

Figure 2. SEM images of BaCO3 crystals obtained in a mixed solvent with different volume ratios of VDMF/VDIW (v/v): (a) pure DIW; (b) 1/5; (c) 1/1; (d) 2/1; (e) magnified SEM image of panel d; (f) 5/1; (g) 10/1; (h) magnified SEM image of panel g. [Ba2+] ) 10 mM; [polymer] ) 1.0 g L-1. All samples were obtained by mineralization for 5 days at ambient temperature. the glass slice was rinsed with DIW and ethanol and allowed to dry at room temperature. Time-dependent crystallization experiments were carried out by taking out the small pieces of glass substrates at different time intervals from the bottom of bottles in order to stop the reaction for examination. The precipitates were collected and washed with DIW and dried in air for further characterization. The concentration of polymer used varied from 0.25 to 2.0 g L-1; the concentration of BaCl2 was kept at 10 mM. Characterization. The samples were characterized by X-ray diffraction pattern (XRD), recorded on a (Philips X’Pert Pro Super) X-ray powder diffractometer with Cu KR radiation (λ ) 1.541 874 Å). Scanning electron microscopy (SEM) analysis was performed on a KYKY-1010B microscope and a field emission SEM microscope (JSM6700F). Transmission electron microscope (TEM) imaging and selected area electron diffraction pattern (SAED) were performed with a H-800 electron microscope operating at 200 kV. In addition, high-resolution transmission electron microscopy (HRTEM) was performed on a JEOL2010 high-resolution transmission electron microscope at an accelerating voltage of 200 kV. For TEM analysis, samples deposited on the glass slice in the bottle were taken out from reaction solution and washed with DIW and ethanol, and then the sample was transferred into a small centrifugal tube with ethanol and subsequently subjected to ultrasonic treatment for several minutes; finally these samples obtained were used for TEM or HRTEM observation. Thermogravimetric analysis (TGA) was carried out on a Diamond TG/DTA thermal analyzer (Perkin-Elmer Corporation) with a heating rate of 10 °C‚min-1 in nitrogen atmosphere.

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Figure 3. (a) TEM image of an individual BaCO3 rod and (b) HRTEM image taken from the panel a image (left corner insert is the electron diffraction pattern). The sample was obtained from the solvents with a volume ratio of DMF/DIW ) 10/1 (v/v). [Ba2+] ) 10 mM; [polymer] ) 1.0 g L-1.

3. Results and Discussion 3.1. Morphogenesis of BaCO3 Crystals in Mixed Solvent of DMF/DIW. A series of experiments for crystallization of BaCO3 were done in mixed solvent with varied volume ratio of DMF to DIW. All BaCO3 samples obtained in mixed solvents with different volume ratios of VDMF/VDIW can be indexed as pure witherite phase (BaCO3, orthorhombic, space group Pmcn, a ) 6.43, b ) 5.31, c ) 8.90 Å, JCPDS 45-1471). The exposing faces are (011), (002), (111), (102), (020), (013), etc. Figure 1 shows that all BaCO3 samples obtained in mixed solution are crystalline. With increase of the volume ratio of VDMF/VDIW up to 10/1 and 5/1, all the diffraction peaks tend to broaden compared with those occurring in lowered DMF content, indicating the small crystalline sizes and the preferential orientation. BaCO3 crystals with distinct morphologies were obtained by altering the volume ratios of DMF to DIW, and as shown in Figure 2. While pure DIW was used as mineralization media, thin flake-shape BaCO3 crystals with irregular multiple sharp corners were produced in aqueous solution (Figure 2a), and the yield of BaCO3 samples was very high. However, the crystal shape changes dramatically when the mineralization reaction happens in a mixed solvent such as DMF and DIW. With the volume content of DMF in mixed solvent kept as VDMF/VDIW ) 1:5, a kind of tetracorner star-like BaCO3 crystals with thin flake structure was generated (Figure 2b, also see Supporting Information, Figure S1). Dramatic shape change occurs if the volume ratios of DMF to DIW continue increasing up to 1 or higher than 1, resulting in the formation of more elongated rods with two sharp tips (Figure 2c-h), which have similar shape to that previously produced by enzyme-assistant precipitation reaction.7 In addition, the yield of BaCO3 particles deposited on the glass substrate gradually increased as the volume ratio of DMF to DIW increased. Moreover, it is obvious to see that elongated rods tend to form raft-like assemblies when the volume ratio VDMF/VDIW ) 10:1. The detailed results on sizes and shapes of BaCO3 particles obtained in the case of variable volume ratio of DMF to DIW are summarized in Table 1. The results suggested that the introduction of a solvent DMF in a polymer-controlled crystallization process played a crucial role in the crystallization of BaCO3 mineral with remarkable differences as those results usually obtained in pure water,15a which is also similar to that found recently in the case of mineralization of CaCO3 mineral in a mixed solvent system.26 In the DMF/DIW mixed solution system, solvent with different volume ratio will have significant influence on the polymer’s solution properties, including the polymer conformation, resulting in different aggregate conformation of polymer in mixed

Figure 4. SEM images of BaCO3 particles obtained in a mixed solution of VDMF/VDIW ) 10:1 (v/v) after mineralization for 4 days at ambient temperature in the presence of different polymer concentrations: (a) 0.25; (b) 0.5; (c) 1.0; (d) 2.0 g L-1. [Ba2+] ) 10 mM.

Figure 5. The relationship of the ratio of the average length (L) to diameter maximum (D) available of the BaCO3 shuttle-like crystals (L/D) vs the polymer concentration [polymer] (g L-1). The crystallization reaction takes place in DMF/DIW ) 10/1 (v/v) mixed solution.

solvent and differences in inducing directed orientation growth of a mineral.28 To further confirm the crystal structure and growth orientation of BaCO3 formed in DMF/DIW mixed solution, TEM and SAED patterns taken on a tip of a single rod obtained under conditions shown in Figure 1f are shown in Figure 3. Lattice fringes with spacing of 3.64 Å were observed, corresponding to that of the (102) plane. The results suggested that the rod axis is along the b-axis, which is perpendicular to the [102] direction. The broadening features of the sample shown in Figure 1f implied that the rods could be composed of primary nanoparticles with a size of about 30-40 nm according to the Scherrer equation, even though the rod scattered like a single crystal (insert in Figure 3b). The results suggested the BaCO3 rods are so-called mesocrystals as recently reviewed by Co¨lfen and Antonietti.2 A series of experiments were performed in order to further investigate the influence of polymer concentration on the size and shape in a mixed solvent. At first, when the polymer concentration was 0.25 g L-1 in a mixed solvent of VDMF/VDIW ) 10:1, shuttle-like BaCO3 rods were observed (Figure 4a). With the polymer concentration increased to 0.5 and 1.0 g L-1, the shuttle-like BaCO3 crystals become more uniform, and they tend

Controlled Mineralization of BaCO3 Mesocrystals

Figure 6. SEM images (a-e) of the BaCO3 crystals formed at the air/solution interface after mineralization for 2 days at ambient temperature, VDMF/VDIW ) 2:1 (v/v), [Ba2+] ) 10 mM, [polymer] ) 1 g L-1: (a) SEM of fiber-like structures; (b, c) magnified SEM images of the fiber-like structures in panel a; (d, e) FE-SEM images of the BaCO3 crystals obtained after ultrasonic treatment for several minutes. Panel f shows a TEM image of a BaCO3 nanoflake falling off the backbone of the fibers shown in panel c. Panel g shows the HRTEM image and panel h the electron diffraction pattern taken on the marked area shown in panel f along [2h00] direction.

to assemble in an orderly way by parallel alignment along the same crystallization orientation (Figure 4b,c). However, upon further increase of the polymer concentration to 2.0 g L-1, the particles tend to form rod-like aggregated structures still, but each rod branches out at two tips of the shuttle-like aggregate structures (Figure 4d). The XRD patterns clearly show that all samples obtained under varied polymer concentration from 0.25 to 2 g L-1 are pure witherite phase (see Supporting Information, Figure S2). All the diffraction peaks become broader, and the diffraction intensities of (111) and (102) peaks tend to become weaker with increasing polymer concentration from 0.25 to 1 g L-1. It has to be noted that the size and length of BaCO3 crystals obtained in mixed solvent changed accordingly with the variation of polymer concentration. The ratio of the average length (L) to the maximum diameter of the rod (D) of the four kinds of shuttle-like BaCO3 is dependent on the polymer concentration, and the relationship is shown in Figure 5, indicating that the ratio of L/D tends to gradually increase and then drop with the polymer concentration increase; as the polymer concentration reaches 0.5 g L-1, the ratio of L/D can reach a maximum value, then subsequently continue to decrease with polymer concentration increasing. The balance of the selective adsorption of the functional groups on the specific crystal faces and the electrostatic stabilization provided by the hydrophilic blocks in this mixed solution system will determine the final BaCO3 growth mode. Previously, it has been shown that the surface patterns of the cleavage planes indicated that the (011), (002), and (111) faces are negative, but the (110) and (020) are positive.18 Therefore, unlike in the case of using negative phosphonated block copolymer,18 positively charged -NH3+ groups here tend to selectively adsorb on those negative faces such as (011), (002),

Crystal Growth & Design, Vol. 7, No. 2, 2007 357

Figure 7. Typical SEM images (a-c) of the BaCO3 crystals formed at the air/solution interface in DMF/DIW mixed solvent after mineralization for 2 days at ambient temperature with VDMF/VDIW ) 5:1 (v/v), [Ba2+] ) 10 mM, and [polymer] ) 1.0 g L-1. Panel d shows a TEM image of thin flakes obtained after ultrasonic treatment for several minutes; panel e shows HRTEM images (left corner insert is ED pattern taken on thin flake along [020] direction).

Figure 8. SEM images of BaCO3 crystals formed at the air/solution interface in DMF/DIW mixed solvent after mineralization for 2 days at ambient temperature: VDMF/VDIW ) 10:1 (v/v); [Ba2+] ) 10 mM; [polymer] ) 1.0 g L-1.

and (111) faces and can also provide a selective steric stabilization of these faces as reported previously in the case of mineralization of CaCO3.17d Thus, (020) and (110) faces could have the fastest growth rate and finally will diminish resulting in the formation of thinner shutter-like rods with two sharp ends. When the polymer concentration is low (0.25 g L-1), the selective adsorption and stabilization will act, but net repulsion is still evident; thus these will result in the formation of uniform shuttle-like crystals (Figure 4a). Upon further increase of the polymer concentration to 0.5 g L-1, the optimal selective adsorption and the electrostatic stabilization, as well as the net repulsion interaction, could be provided, resulting in the formation of much elongated BaCO3 rods with the highest aspect ratio (Figure 4b). However, as the polymer concentration increases to higher than 1.0 g L-1, the interaction effects including the enhanced electrostatic effects, steric repulsion, and also gluing effects among the polymer-stabilized nanoparticles, as well as the selective electrostatic adsorption on the specific crystal face, could result in limited and also preferential growth. When the polymer concentration is 2.0 g L-1, increasing strong

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Figure 9. Schematic illustration of the formation of multiple hierarchical shuttle-like BaCO3 superstructures obtained at the air/solution interface in DMF/DIW mixed solvents: (a) BaCO3 rods grown under control of polymer by crystallization and transformation from polymer-stabilized amorphous nanoparticles and with polymer preferential adsorption on specific faces of the rods; (b, c) the self-assembly of mesoscale intermediates into raft-like structures; (d) the formation of intermediate shuttle-like hierarchical aggregates with flakes sitting on the backbone; (e) the formation of the hierarchical shuttle-like superstructures after the Ostwald ripening process.

interaction of the polymer with the crystals and a high polymer content in the particles will result in the morphology more dispersed as in the case of polymer-controlled growth of BaCrO4 mineral.29 In addition, several factors such as attractive forces due to van der Waals forces, which are in range of the steric stabilization layers around the rods, directed aggregation, and oriented attachment of the rods side by side with each other along the same crystallographic axis, can minimize the surface energy of the particles, resulting in the formation of the raftlike arrangement and the fusion of the rods as shown in Figure 4c,d. The aggregation of the rods into bundle-like structures tends to splay out at the ends (Figure 4d). This strong tendency to form rods with splaying ends could fit the scenario as found for the formation of peanuts or dumbbells30-32 and are described as the product of a stopped-growth and crystal-branching process.32 3.2. Crystallization and Morphogenesis of BaCO3 Mesocrystals at the Air/Solution Interface in a Mixed Solvent. Besides the formation of BaCO3 crystals in bulk solution, there is also floating product at the air/solution interface as reported previously in other cases.19-23 The SEM image in Figure 6a shows that similar fibrous BaCO3 structures were obtained as those found in the bulk solution after crystallization for 2 days at the air/solution interface in a mixed solvent of VDMF/VDIW ) 2:1. The length of the fiber reaches as much as 200-300 µm, and the diameter is about 10 µm, which is much longer and thicker than that of crystals found in the bulk solution (Figure 6a). However, detailed observation indicated that these fiberlike structures were actually bundle-like with sawtooth-shaped hierarchical structures (Figure 6b,c). There are many nanoflakes attaching and sitting on the backbone of the fibers. These nanoflakes were found to be adnascent and distributed around the backbone along the same oriented direction. After ultrasonic treatment of the sample, all attached nanoflakes fall off the backbone of the fibers (Figure 6d), and the surfaces of the shuttle like fiber bundles are very rough and consist of smaller shuttlelike structures, which are parallel to each other and align along the same axial crystallographic orientation (Figure 6e,f). All the nanoflakes tend to align along the axis of the shuttle-like rods. High-resolution transmission electron microscope (HRTEM) showed lattice spacings of 2.66 Å corresponding to that for (020) plane, which are perpendicular to (102) plane, suggesting that the raft-like particle was preferentially grown along the b-axis (Figure 6g). In addition, the HRTEM image showed that the lattice fringes are not completely continuous; there are amorphous BaCO3 nanoparticles present between two nanoparticles that have the same orientation. In addition, the electron diffraction pattern taken on the flake-like aggregates scattered like single crystalline material. Furthermore, the XRD pattern shows a broadening feature again, and calculation by the Scherrer equation gives the particle size about 40-50 nm (see Supporting Information, Figure S3a). All these results indicate that the BaCO3 microparticles are in fact mesocrystals, and they

are also formed via the directed self-organization of the nanobuilding blocks along the same crystallographic orientation.2 Variation of the volume ratio of DMF to DIW dramatically changes the morphologies of the fiber-like superstructures formed at the air/solution interface accordingly. When the volume ratio of DMF/DIW was equal to 5/1, gingili staff-like BaCO3 crystals formed at the air/solution interface (Figure 7a,b). A magnified SEM image shows that a typical gingili staff-like BaCO3 fiber is constructed from many highly oriented attached cushaw-seed-like particles (Figure 7c), implying the formation of mesocrystals. A HRTEM image of an individual thin flake (Figure 7d) showed the clear lattice spacings of 4.42 Å, corresponding to that of (002) plane (Figure 7e). Again, amorphous phase particles between two nanoparticles were observed (Figure 7e). The electron diffraction pattern taken along [020] showed that the particle is single crystalline (insert in Figure 7e). The broadening diffraction peaks in the XRD pattern implied that these flakes consisted of smaller nanoparticles with a size of about 40 nm, which was calculated via the Scherrer equation (see Supporting Information, Figure S3b), suggesting that the larger gingili staff-like rods are also in fact mesocrystals, which are comprised of nano-building blocks in a self-organized fashion.2 Upon further increase of the volume ratio of DMF to DIW to 10/1, bundle-like aggregates with more dendritic structures formed at the air/solution interface (Figure 8). Therefore, the superstructure of BaCO3 formed at the air/solution interface was also strongly related to the composition of the mixed solvent. In order to reveal the dramatic difference of the morphology formed at the air/solution interface and in bulk solution, the products collected from the interface and those precipitated from the bulk solution in a mixed solution of VDMF/VDIW ) 5:1 were examined using the TGA technique (see Supporting Information, Figure S4). The results suggested that the sample collected at the air/solution interface has more included polymer than that precipitated from the bulk solution, implying that the crystallization situation at the air/solution interface and in the bulk solution is quite different from that reported previously on the variation of the interaction fashion of the polymer and specific crystal faces of a mineral.22,23 Furthermore, the interfacial tension of different mixed solutions may also influence the formation of the special interface phenomena during the mineralizaton process.20a,23 Based on the above analysis, a possible growth mechanism for the formation of the hierarchical shuttle-like BaCO3 superstructure at the air/solution interface is schematically shown in Figure 9. First, the BaCO3 rods grow under control of polymer through frequently observed crystallization and transformation from polymer-stabilized amorphous nanoparticles, and the polymer additives were selectively absorbed on the backbone of rods (Figure 9a). Then, directed aggregation, fusion, and growth of the rods occurred to form intermediate raft-like

Controlled Mineralization of BaCO3 Mesocrystals

aggregates, a kind of mesocrystals (Figure 9b,c), as confirmed by the HRTEM and XRD analysis, which is similar to that found previously on the crystallization of CaCO3 mineral.33 Consequently, the hierarchical aggregates (Figure 9d) formed through the subsequent subnucleation of building block flakes formed on the backbone of aggregated rods at the air/solution interface via a highly orientated and adnascent mode. Finally, the hierarchical shuttle-shaped mesocrystals formed after undergoing the Ostwald ripening process (Figure 9e). 4. Conclusion In summary, biomimetic mineralization of BaCO3 minerals with various shapes and complex form in a mixed solvent made of DMF and DIW, as well as at the air/solution interface, has been systematically examined. The effects of polymer concentration, solvent, and the volume ratio of a mixed solvent on the controlled crystallization of BaCO3 have been investigated. The results demonstrate that the morphogenesis of BaCO3 crystals can be realized by simply tuning the volume ratio of DMF and DIW under control of a crystal growth modifier, showing the versatile ability and flexibility of this new reaction media for control over the morphology of minerals. Shuttle-like BaCO3 rods with different sizes and ratio values of the average length (L) to the maximum diameter (D) can be obtained by simply altering polymer concentration in the mixed solvent. In addition, the complex hierarchical shuttle-like aggregated structures can be formed at the air/solution interface, which were dramatically different from those obtained in bulk solution. The results indicate that the synergic effects by a combination of a mixed solvent with a suitable polymer make it possible and quite flexible to manipulate the morphology and preferential orientation growth of BaCO3 mineral both in bulk solution and at the air/solution interface. The present results, together with previous findings,20a,22,23,26 demonstrate that the crystallization method by a combination of additives with a gas(air)/solution interface in a solution (mixed solvent) provide a new way for shape control over other minerals or inorganic-organic hybrid materials. Acknowledgment. S.-H.Y. acknowledges the special funding support from the Centurial Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China (NSFC, Nos. 20325104, 20321101, 50372065, and 20671085) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, the Specialized Research Fund for the Doctoral Program (SRFDP) of Higher Education State Education Ministry, and the Partner-Group of the Chinese Academy of Sciences-the Max Planck Society. Supporting Information Available: TEM images, XRD patterns, and TG analysis. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) (a) Mann, S. Angew. Chem., Int. Ed. 2000, 39, 3392. (b) Estroff, L. A.; Hamilton, A. D. Chem. Mater. 2001, 13, 3227, (c) Yu, S. H.; Co¨lfen, H. J. Mater. Chem. 2004, 14, 2414. (d) Yu, S. H.; Co¨lfen, H. MRS Bull. 2005, 30, 727. (e) Yu, S. H.; Chen, S. F. Curr. Nanosci. 2006, 2, 81. (f) Co¨lfen, H. Top. Curr. Chem. 2007, 271, 1. (g) Imai, H. Top. Curr. Chem. 2007, 270, 43. (h) Yu, S. H. Top. Curr. Chem. 2007, 271, 79. (i) Niederberger, M.; Co¨lfen, H. Phys. Chem. Chem. Phys. 2006, 8, 3271. (2) Co¨lfen, H.; Antonietti, M. Angew. Chem., Int. Ed. 2005, 44, 5576. (3) Macketta, J. J. Encyclopedia of Chemical Processing and Design; Marcel Dekker: New York, 1977; p 51. (4) Allen, B. F.; Faulk, N. M.; Lin, S. C.; Semiat, R.; Luss, D.; Richardson, J. T. AIChE Symp. Ser. 1994, 88, 76.

Crystal Growth & Design, Vol. 7, No. 2, 2007 359 (5) Formica, J. P.; Forster, K.; Richardson, J. T.; Luss, D. AIChE Symp. Ser. 1994, 88, 1. (6) Chen, P. C.; Cheng, G. Y.; Kou, M. H.; Shia, P. Y.; Chung, P. O. J. Cryst. Growth 2001, 226, 458. (7) Sondi, I.; Matijevic, E. Chem. Mater. 2003, 15, 1322. (8) (a) Kuang, D.; Xu, A. W.; Fang, Y. P.; Ou, H. D.; Liu, H. Q. J. Crystal Growth. 2002, 244, 379. (b) Huo, J. C.; Liu, S. X.; Yang, D. M.; Wang, H. B. Chin. J. Struct. Chem. 2005, 24, 1290. (c) Karagiozov, C.; Montchilova, D. Chem. Eng. Process. 2005, 44, 115. (9) Co¨lfen, H. Curr. Opin. Colloid Interface Sci. 2003, 8, 23. (10) (a) Mann, S.; Heywood, B. R.; Rajam, S.; Birchall, S. J. D. Nature 1988, 334, 692. (b) Ahn, D. J.; Berman, A.; Charych, D. J. Phys. Chem. 1996, 100, 12455. (c) Litvin, A. L.; Valiyaveettil, S.; Kaplan, D. L.; Mann, S. AdV. Mater. 1997, 9, 124. (11) Archibald, D. D.; Qadri, S. B.; Gaber, B. P. Langmuir 1996, 12, 538. (12) (a) Kuther, J.; Nelles, G.; Seshadri, R.; Schaub, M.; Butt, H. J.; Tremel, W. Chem.sEur. J. 1998, 4, 1834. (b) Aizenberg, J.; Black, A. J.; Whitesides, G. M. Nature 1999, 398, 495. (c) Aizenberg, J.; Black, A. J.; Whitesides, G. M. J. Am. Chem. Soc. 1999, 121, 4500. (13) DeOliveira, D. B.; Lauren, R. A. J. Am. Chem. Soc. 1997, 119, 10627. (14) (a) Naka, K.; Tanaka, Y.; Chujo, Y.; Ito, Y. Chem. Commun. 1999, 1931. (b) See a review and references therein: Naka, N. Top. Curr. Chem. 2003, 228, 141. (15) (a) Yu, S. H.; Co¨lfen, H.; Xu, A. W.; Dong, W. F. Cryst. Growth Des. 2004, 4, 33. (b) Han, J. T.; Xu, X.; Kim, D. H.; Cho, K. Chem. Mater. 2005, 17, 136. (16) (a) Sedla´k, M.; Antonietti, M.; Co¨lfen, H. Macromol. Chem. Phys. 1998, 199, 247. (b) Co¨lfen, H.; Antonietti, M. Langmuir 1998, 14, 582. (c) Co¨lfen, H. Macromol. Rapid Commun. 2001, 22, 219. (17) (a) Taubert, A.; Glasser, G.; Palms, D. Langmuir 2002, 18, 4488. (b) Robinson, K. L.; Weaver, J. V. M.; Armes, S. P.; Marti, E. D.; Meldrum, F. C. J. Mater. Chem. 2002, 12, 890. (c) Zhang, D. B.; Qi, L. M.; Ma, J. M.; Cheng, H. M. Chem. Mater. 2002, 14, 2450. (d) Chen, S. F.; Yu, S. H.; Wang, T. X.; Jiang, J.; Co¨lfen, H.; Yu, B. AdV. Mater. 2005, 17, 1461. (e) Wang, T. X.; Xu, A. W.; Co¨lfen, H. Angew. Chem., Int. Ed. 2006, 45, 4451. (18) Yu, S. H.; Co¨lfen, H.; Tauer, K.; Antoietti, M. Nat. Mater. 2005, 4, 51. (19) Hashmi, S. M.; Wickman, H.; Weitz, D. A. Phys. ReV. E 2005, 72, 041605. (20) (a) Rudloff, J.; Co¨lfen, H. Langmuir 2004, 20, 991. (b) Walsh, D.; Boanini, E.; Tanaka, J.; Mann, S. J. Mater. Chem. 2005, 15, 1043. (c) Rautaray, D.; Banpurkar, A.; Sainkar, S. R.; Limaye, A. V.; Pavaskar, N. R.; Ogale, S. B.; Sastry, M. AdV. Mater. 2003, 15, 1273. (d) DiMasi, E.; Patel, V. M.; Sivakumar, M.; Olszta, M. J.; Yang, Y. P.; Gower, L. B. Langmuir, 2002, 18, 8902. (21) (a) Hadiko, G.; Han, Y. S.; Fu, M. J. Mater. Lett. 2005, 59, 2519. (b) Han, Y. S.; Hadiko, G.; Fu, M. J. Chem. Lett. 2005, 34, 152. (22) Park, H. K.; Lee, I.; Kim, K. Chem. Commun. 2004, 24. (23) Gao, Y. X.; Yu, S. H.; Guo, X. H. Langmuir 2006, 22, 6125. (24) (a) Manoli, F.; Dalas, E. J. Cryst. Growth 2000, 218, 359. (b) Qi, L. M.; Ma, J. M. Chem. J. Chin. UniV. 2002, 23, 1595. (25) (a) Dickinson, S. R.; Mcgrath, K. M. J. Mater. Chem. 2003, 13, 928. (b) Falini, G.; Gazzano, M.; Ripamonti, A. Chem. Commun. 1996, 1037. (c) Seo, K. S.; Han, C.; Wee, J. H.; Park, J. K.; Ahn, J. W. J. Cryst. Growth 2005, 276, 680. (d) Chen, S. F.; Yu, S. H.; Yu, B. Chem.sEur. J. 2004, 10, 3050. (e) Chen, S. F.; Yu, S. H.; Jiang, J.; Li, F. Q.; Liu, Y. K. Chem. Mater. 2006, 18, 122. (26) Guo, X. H.; Yu, S. H.; Cai, G. B. Angew. Chem., Int. Ed. 2006, 45, 3977. (27) Sedla´k, M.; Co¨lfen, H. Macromol. Chem. Phys. 2001, 202, 587. (28) Choi, C. S.; Kim, Y. W. Biomaterials. 2000, 21, 213. (29) Yu, S. H.; Co¨lfen, H.; Antonietti, M. Chem.sEur. J. 2002, 8, 2937. (30) (a) Co¨lfen, H.; Antonietti, M. Langmuir 1998, 14, 582. (b) Co¨lfen, H.; Qi, L. M. Chem.sEur. J. 2001, 7, 106. (31) (a) Qi, L. M.; Co¨lfen, H.; Antonietti, M. Angew. Chem., Int. Ed. 2000, 39, 604. (b) Qi, L. M.; Co¨lfen, H.; Antonietti, M. Chem. Mater. 2000, 12, 2392. (32) (a) Kniep, R.; Busch, S. Angew. Chem., Int. Ed. 1996, 35, 2624. (b) Busch, S.; Dolhaine, H.; DuChesne, A.; Heinz, S.; Hochrein, O.; Laeri, F.; Podebrad, O.; Vietze, U.; Weiland, T.; Kniep, R. Eur. J. Inorg. Chem. 1999, 10, 1643. (c) Co¨lfen, H. Habilitation thesis, Potsdam, Germany, 2001. (33) (a) Xu, A. W.; Antonietti, M.; Co¨lfen, H.; Fang, Y. P. AdV. Funct. Mater. 2006, 16, 903. (b) Wohlrab, S.; Antonietti, M.; Co¨lfen, H. Chem.sEur. J. 2005, 11, 2903.

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