- Email: [email protected]
The synthesis of calcium carbonate microparticles with multiple morphologies through self-assembly method
The Synthesis of Calcium Carbonate Microparticles with Multiple Morphologies through Self-assembly Method Guang Yuan, Xiaofeng Chen, Xian Li, Qiming Liang, Guohou Miao, Bo Yuan PII: DOI: Reference:
S0032-5910(15)00525-2 doi: 10.1016/j.powtec.2015.06.066 PTEC 11110
To appear in:
Powder Technology
Received date: Revised date: Accepted date:
30 November 2014 17 June 2015 28 June 2015
Please cite this article as: Guang Yuan, Xiaofeng Chen, Xian Li, Qiming Liang, Guohou Miao, Bo Yuan, The Synthesis of Calcium Carbonate Microparticles with Multiple Morphologies through Self-assembly Method, Powder Technology (2015), doi: 10.1016/j.powtec.2015.06.066
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT The Synthesis of Calcium Carbonate Microparticles with Multiple Morphologies through Self-assembly Method
School of Materials Science and Engineering, South China University of Technology, Guangzhou
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1.
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Guang Yuan1, 2*, Xiaofeng Chen1, 2*, Xian Li1, 2, Qiming Liang1, 2, Guohou Miao1, 2, Bo Yuan1,2
510641, China. 2.
National Engineering Research Center for Tissue Restoration and Reconstruction, Guangzhou
NU
510006, China.
MA
Abstract：Taking advantage of the biocompability and biodegradability of calcium carbonate, a simple method was introduced to synthesize the calcium carbonate microparticles with different morphologies,
D
including hollow (H-Calcium), flower-like (P-Calcium) and peanut-like (P-Calcium). The possible
TE
formation mechanisms of these kinds of calcium carbonate microparticles were discussed in this study.
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Initially, the aminopropyltriethoxysilane (APTES) was possibly hydrolyzed, and octa(aminopropylsilsesquioxane) (R-NH3+) was obtained. The R-NH3+ might guide the CaCO3 nanoparticles to
AC
form multiple calcium carbonate microparticles in aqueous phase because of their positive potential. Furthermore, the final treatments were very essential to obtain the calcium carbonate microparticles with satisfactory shape with this method. The XRD and FTIR results revealed the components and crystalline phase of these products. The morphologies were characterized by SEM and TEM. Furthermore, the potential value of these kinds of microparticles was discussed. Keyword: Calcium carbonate, Mineralization, Microstructure, Microparticles.
—— *Corresponding author. Tel: +8613924193905 E-mail address: [email protected]
1
ACCEPTED MANUSCRIPT Introduction Calcium carbonate was a kind of material with good biocompatibility and suitable biodegradation
IP
T
rate [1-3]. There are different crystalline phases existed in calcium carbonate, such as calcite, aragonite
SC R
and vaterite. The interactions between CaCO3 species and proteins were very important [5-8]. Masahiro and his colleagues have studied the encapsulation of protein through the phase transition of calcium carbonate, from vaterite to calcite
[5]
. And some kinds of calcium carbonate biominerals which
NU
contained different proteins possessed some unique properties [9-10].
MA
Taking advantage of the pH sensitivity and other excellent properties of calcium carbonate, a simple method was reported to obtain multiple morphologies of calcium carbonate microparticles in
TE
Materials and Methods
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this paper.
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Materials: APTES and calcium chloride dihydrate (CaCl2·H2O) were purchased from the Aladdin Chemical Reagent Co., Ltd. Ammonia water was purchased from the Sinopharm Chemical Reagent Co.,
AC
Ltd. Ethanol was bought from the KeLong Chemical Reagent Co., Ltd. Deionized water was produced by our own laboratory. Synthesis of calcium carbonate microparticles with multiple morphologies: Solution I was a mixed solution by NH3·H2O and ethanol with the volume ratio of 1:3. 0.120g CaCl2·2H2O, 1.1ml aminopropyltriethoxysilane (APTES) and 9.0ml ethanol were mixed to obtain solution II. Solution II (5ml) was added into solution I (80ml) under stirring to obtain solution III. Then, solution III was stirred for 10h at room temperature. Afterward, solution III was placed in the fuming cupboard to absorb CO2 in the air. The white sediment was collected by centrifugation. Finally, the precipitates were treated with different measurements that were described as follows. 2
ACCEPTED MANUSCRIPT The precipitates were divided into three groups, group A, group B and group C. Certain amount of deionized water was added into these precipitates. Precipitates in group A and group B were collected
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by centrifugation after being standing for 6h at room temperature. After that, precipitate in group B was
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placed in deionized water for 7days at room temperature. And, precipitates in group C were stirred for 6h with a certain amount of deionized water at room temperature. Then, precipitates in group C were collected by centrifugation. All these samples by centrifugation were washed 3 times with deionized
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water. Finally, products of white powders in these groups were obtained after freeze-drying. The
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product of group A, group B and group C were named H-Calcium, F-Calcium and P-Calcium, respectively.
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Characterization: The X-ray diffraction (XRD) measurements of these products were realized by
TE
using D8 ADVANCE (German Bruker) diffractometer with Ni-filtered, Cu Kα1 target,
= 1.54183 Å at
CE P
40 kV and 40 mA. Samples were scanned from 2 =5º to 80º with a step size of 0.02º and a scanning speed of 0.1s per step. The surface morphologies of these different microparticles were characterized
AC
by using NOVA NANOSEM 430 (Netherlands) instrument after coated with gold by using a sputter coater. The transmission electron microscopy (TEM) images were carried out by using the JEM-2100HR (JEOL) instrument. The Fourier Transform Infrared Spectrometer (FTIR) results were recorded in the range of 400-4000 cm-1 by using Lambda950 (PerkinElmer Co., LTD. USA). Results Through this method, which was depicted in the experimental section, three kinds of CaCO3 microparticles were synthesized. SEM (Figure.1) images showed the different morphologies of these microparticles. FTIR and XRD results of these microparticles were listed in Fig. 2. The differences of morphologies among three products were revealed from the SEM images 3
ACCEPTED MANUSCRIPT (Fig.1). The microstructure of H-calcium, F-Calcium and P-Calcium were hollowed (Fig.1A and a), flower-like (Figure. 1B and b) and peanut-like (Fig.1C and c), respectively. It was shown from Fig.1B
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and b that F-Calcium was formed by many diamond-like particles. The component of diamond-like
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particles was confirmed by XRD and FTIR.
Fig.2a showed FTIR results of three microparticles. Absorption peaks at 1467cm-1, 876cm-1 and 712cm-1 were the absorption peaks of CO32-. Absorption peaks at 2512cm-1 and 1797cm-1 could confirm
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the presence of calcium carbonate. Absorption peaks of H-Calcium at 1087cm-1 and 745cm-1 showed
MA
the presence of vaterite polymorph, according to Gunawan Hadiko and his colleagues [2]. It was seen that absorption peak at 745 cm-1 was disappeared in the FTIR image (Fig.2a) of P-Calcium. These
D
results demonstrated that the crystal-phase of calcium carbonate microparticles was converted, from
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vaterite to calcite. The peaks at 1030cm-1 and 1130cm-1 were corresponding to the absorption peaks of
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Si-O bond in R-NH3+ [11]. Compared with the FTIR results of Dazhou Zhao and his colleagues [12], the peak at 712cm-1 in our work showed that the H-Calcium and F-Calcium was not pure vaterite. XRD
AC
results (Fig.2b) of H-Calcium and F-Calcium could further validate this conclusion. The diffraction peaks of the H-Calcium at approximately 25º, 27ºand 33º indicated the existence of vaterite, while the peaks at approximately 30º indicated the existence of calcite[5],[13]. These results confirmed that the components of H-Calcium and F-Calcium were not pure vaterite. Diffraction peaks at approximately 25º, 27ºand 33º were disappeared in P-Calcium. Overall, from the FTIR and XRD results, we can conclude that the components of these products were calcium carbonate. H-Calcium and F-Calcium were composed of vaterite and calcite, while P-Calcium was composed of calcite. Discussion In this research, a possible formation mechanism of three different CaCO3 microparticles was 4
ACCEPTED MANUSCRIPT proposed (Fig.3A). At first, APTES was hydrolyzed to obtain octa(aminopropylsilsesquioxane) (R-NH3+). CO2 was reacted with NH3·H2O to obtain HCO3- and CO32-. The incorporation of R-NH3+ to
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Ca2+, CO32- and HCO3- ions give rise to the precursor of calcium carbonate crystal. Then the amorphous
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calcium carbonate (ACC) was generated [13] following the combination of Ca2+ and CO32-. After being treated with water, heating and standing, HCO3- was decorticated into CO2 and CO32-. CO32- continued to react with Ca2+ to form CaCO3 nanoparticles. At the same time, ACC transformed to crystal phase
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under these conditions. This phenomenon that some organisms could produce stable amorphous
MA
calcium carbonate (ACC) and the ACC functioned as a transient precursor of more stable crystalline phase was proposed by Steve Weiner and his colleagues [2], [14]. The calcium carbonate nanoparticles
D
were combined with R-NH3+. Then, CO2 was encased to obtain hollow microspheres (H-Calcium).
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Within stirring treatment, CO2 was escaped and the R-NH3+ bond to the CaCO3 nanoparticles to obtain
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the peanut-like microparticles (P-Calcium) attributing to mechanics effects. FTIR (Fig.3B) and XRD (Fig.3C) results of intermediate product showed that the intermediate product was not any kind of
AC
calcium carbonate crystal. XRD result (Fig.3C) showed that the intermediate product was under the amorphous state. In Fig.3B, peaks at 1570cm-1, 1498cm-1, 861cm-1, 694cm-1 showed the existence of CO32-. Peaks at 1030cm-1 and 1130cm-1 were absorption peaks of Si-O bond in R-NH3+. The peaks at 2933cm-1 was corresponding to the absorption peaks of -CH2- and peaks at 3349cm-1 was the absorption peaks of -NH3+. The content of Si element in H-Calcium was estimated to be 4.96 wt. % by using the Energy Dispersive X-ray Detector (EDX). These results confirmed the existence of R-NH3+ and could also validate the possible mechanism. The formation mechanism of F-Calcium was possibly because of the surface mineralization of CaCO3 microparticles. Fig.4 was the SEM and TEM images that showed the possible formation 5
ACCEPTED MANUSCRIPT process. Fig.4a showed the morphology of the material that was kept standing in water for 6h at room temperature. Fig.4b displayed the morphology of material that was further treated in water for 3days at
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T
room temperature. These treatments was handled for observing the formation process of F-Calcium
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microparticles. The image (Fig.4c) demonstrated that the F-Calcium was formed. The surface potential of H-Calcium (In deionized water) was analyzed by using the Zeta-potential Analyzer (Shimazduo, Japan), and the result was about +14mV. It could be concluded from these results that the most possible
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formation mechanism were as follows. In water, the vaterite on the surface of calcium carbonate
MA
microparticles was converted to calcite which was attracted to the surface of calcium carbonate microparticles with positive potential. Then the calcite was covered on the surface of CaCO3
D
microparticles. Finally, flower-like microparticles (F-Calcium) were formed. TEM images of
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F-Calcium (Fig.4d and Fig.4d-1) showed the detail characteristic information. XRD and FTIR results
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(Fig.2) of F-Calcium revealed that the component of F-Calcium was not pure calcite, which also composed of vaterite. These results could also confirm the possible formation process of F-Calcium.
AC
Furthermore, these CaCO3 microparticles with different crystal-phase might have the potential value for acting as the drug carries in therapy field in the future. F-Calcium microparticles might be used to encapsulate some unique protein for preparing some unique materials with different functions. Conclusions In this work, a simple method to synthesize CaCO3 microparticles was described. Three kinds of calcium carbonate microparticles were prepared through the different final treatments by using this method. A beautiful flower-like microsphere was obtained by the surface mineralization of calcium carbonate microparticles. Moreover, the possible formation mechanisms of these microparticles were discussed, and this possible mechanisms might be used to synthesize other kinds of microparticles by 6
ACCEPTED MANUSCRIPT using other materials. Acknowledgments
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This work was supported by the Key Project of the National Natural Science Foundation of China
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(Grant No.50830101), the National 973 project of China (2011CB606204), National Natural Science Foundation of China (Grant No.51202069, 51172073), Research Fund for the Doctoral Program of Higher Education of China (Grant No.20110172110002), the Fundamental Research Funds for the
NU
Central Universities (Grant No.2014ZM0009) and National Nature Science Foundation of China
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(Grant No.51202069). References
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[1] Hadiko, G., et al., Synthesis of hollow calcium carbonate particles by the bubble templating method.
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Materials Letters (2005) 59 (19–20), 2519.
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[2] Addadi, L., et al., Taking Advantage of Disorder: Amorphous Calcium Carbonate and Its Roles in Biomineralization. Advanced Materials (2003) 15 (12), 959.
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[3] Fakhrullin, R. F., et al., Magnetically responsive calcium carbonate microcrystals. ACS applied materials & interfaces (2009) 1 (9), 1847. [4] Fujiwara, M., et al., Encapsulation of Proteins into CaCO3by Phase Transition from Vaterite to Calcite. Crystal Growth & Design (2010) 10 (9), 4030. [5] Xu, A.-W., et al., Polymorph Switching of Calcium Carbonate Crystals by Polymer‐Controlled Crystallization. Journal of Materials Chemistry (2007) 17 (5), 415. [6] Wang, S.-S., and Xu, A.-W., Amorphous Calcium Carbonate Stabilized by a Flexible Biomimetic Polymer Inspired by Marine Mussels.
Crystal Growth & Design (2013) 13 (5), 1937.
[7] Guo, X.-H., et al., Crystallization of Calcium Carbonate Mineral with Hierarchical Structures in 7
ACCEPTED MANUSCRIPT DMF Solution under Control of Poly (ethylene glycol)-b-poly (l-glutamic acid): Effects of Crystallization Temperature and Polymer Concentration. Crystal Growth and Design (2008) 8 (4),
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1233.
Crystal growth & design
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[8] Qiao, L., et al., Special vaterite found in freshwater lackluster pearls. (2007) 7 (2), 275.
[9] Aizenberg, J., et al., Calcitic microlenses as part of the photoreceptor system in brittlestars. Nature
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(2001) 412 (6849), 819.
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[10] Rao, M. S., Kinetics and Mechanism of the Transformation of Vaterite to Calcite. Bulletin of the Chemical Society of Japan (1973) 46, 1414.
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[11] Zhang, L.; Abbenhuis, H. C. L.; Yang, Q.; Wang, Y.-M.; Magusin, P. C. M. M.; Mezari, B.; van
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Santen, R. A.; Li, C. Angewandte Chemie 2007, 119, (26), 5091-5094.
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[12] Zhao, D., et al., Synthesis of template-free hollow vaterite CaCO3 microspheres in the H2O/EG system. Materials Letters (2013) 104, 28.
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[13] Shen, Q.; Wei, H.; et al, Properties of amorphous calcium carbonate and the template action of vaterite spheres. Journal of Physical Chemistry B 2006, 110, (7), 2994-3000. [14] Raz, S., et al., The Transient Phase of Amorphous Calcium Carbonate in Sea Urchin Larval Spicules: The Involvement of Proteins and Magnesium Ions in Its Formation and Stabilization. Advanced Functional Materials, 2003. 13(6): p. 480-486. Appendices
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ACCEPTED MANUSCRIPT
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Figure 1. The SEM images of these different products. Image A, B and C showed the microstructure of H-Calcium, F-Calcium and P-Calcium. Image a, image b and image c were the magnified images of
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image A, B and C.
Figure 2.The FTIR (image a) and X-ray diffraction (image b) results of these microparticles.
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ACCEPTED MANUSCRIPT
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Figure 3. The possible formation mechanism of these CaCO3 microparticles. Image A showed the main
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possible mechanism of this method. Image B was the FTIR result of middle product, C was the XRD
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result of middle product, D was the SEM image of P-Calcium and E was the SEM image of H-Calcium.
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(The middle product was obtained by centrifugation before the final treatments.)
Figure 4. The SEM images of the F-Calcium formation process, and the TEM images of F-Calcium. Image a, b and c was corresponding to the beginning, forming, and ending time during the F-Calcium formation process. Images d and d-1 were the TEM images of F-Calcium (Image d-2 was the electron diffraction image of F-Calcium).
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ACCEPTED MANUSCRIPT
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Grpahical Abstract
Highlights: A facile method was used to synthesize these different kinds of microparticles. The formation process of the F-Calcium was recorded through the SEM images. 11
ACCEPTED MANUSCRIPT The formation mechanisms of these microparticles were discussed.
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These mechanisms might be used to fabricate other microparticles.
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S0032-5910(15)00525-2 doi: 10.1016/j.powtec.2015.06.066 PTEC 11110
To appear in:
Powder Technology
Received date: Revised date: Accepted date:
30 November 2014 17 June 2015 28 June 2015
Please cite this article as: Guang Yuan, Xiaofeng Chen, Xian Li, Qiming Liang, Guohou Miao, Bo Yuan, The Synthesis of Calcium Carbonate Microparticles with Multiple Morphologies through Self-assembly Method, Powder Technology (2015), doi: 10.1016/j.powtec.2015.06.066
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT The Synthesis of Calcium Carbonate Microparticles with Multiple Morphologies through Self-assembly Method
School of Materials Science and Engineering, South China University of Technology, Guangzhou
SC R
1.
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T
Guang Yuan1, 2*, Xiaofeng Chen1, 2*, Xian Li1, 2, Qiming Liang1, 2, Guohou Miao1, 2, Bo Yuan1,2
510641, China. 2.
National Engineering Research Center for Tissue Restoration and Reconstruction, Guangzhou
NU
510006, China.
MA
Abstract：Taking advantage of the biocompability and biodegradability of calcium carbonate, a simple method was introduced to synthesize the calcium carbonate microparticles with different morphologies,
D
including hollow (H-Calcium), flower-like (P-Calcium) and peanut-like (P-Calcium). The possible
TE
formation mechanisms of these kinds of calcium carbonate microparticles were discussed in this study.
CE P
Initially, the aminopropyltriethoxysilane (APTES) was possibly hydrolyzed, and octa(aminopropylsilsesquioxane) (R-NH3+) was obtained. The R-NH3+ might guide the CaCO3 nanoparticles to
AC
form multiple calcium carbonate microparticles in aqueous phase because of their positive potential. Furthermore, the final treatments were very essential to obtain the calcium carbonate microparticles with satisfactory shape with this method. The XRD and FTIR results revealed the components and crystalline phase of these products. The morphologies were characterized by SEM and TEM. Furthermore, the potential value of these kinds of microparticles was discussed. Keyword: Calcium carbonate, Mineralization, Microstructure, Microparticles.
—— *Corresponding author. Tel: +8613924193905 E-mail address: [email protected]
1
ACCEPTED MANUSCRIPT Introduction Calcium carbonate was a kind of material with good biocompatibility and suitable biodegradation
IP
T
rate [1-3]. There are different crystalline phases existed in calcium carbonate, such as calcite, aragonite
SC R
and vaterite. The interactions between CaCO3 species and proteins were very important [5-8]. Masahiro and his colleagues have studied the encapsulation of protein through the phase transition of calcium carbonate, from vaterite to calcite
[5]
. And some kinds of calcium carbonate biominerals which
NU
contained different proteins possessed some unique properties [9-10].
MA
Taking advantage of the pH sensitivity and other excellent properties of calcium carbonate, a simple method was reported to obtain multiple morphologies of calcium carbonate microparticles in
TE
Materials and Methods
D
this paper.
CE P
Materials: APTES and calcium chloride dihydrate (CaCl2·H2O) were purchased from the Aladdin Chemical Reagent Co., Ltd. Ammonia water was purchased from the Sinopharm Chemical Reagent Co.,
AC
Ltd. Ethanol was bought from the KeLong Chemical Reagent Co., Ltd. Deionized water was produced by our own laboratory. Synthesis of calcium carbonate microparticles with multiple morphologies: Solution I was a mixed solution by NH3·H2O and ethanol with the volume ratio of 1:3. 0.120g CaCl2·2H2O, 1.1ml aminopropyltriethoxysilane (APTES) and 9.0ml ethanol were mixed to obtain solution II. Solution II (5ml) was added into solution I (80ml) under stirring to obtain solution III. Then, solution III was stirred for 10h at room temperature. Afterward, solution III was placed in the fuming cupboard to absorb CO2 in the air. The white sediment was collected by centrifugation. Finally, the precipitates were treated with different measurements that were described as follows. 2
ACCEPTED MANUSCRIPT The precipitates were divided into three groups, group A, group B and group C. Certain amount of deionized water was added into these precipitates. Precipitates in group A and group B were collected
IP
T
by centrifugation after being standing for 6h at room temperature. After that, precipitate in group B was
SC R
placed in deionized water for 7days at room temperature. And, precipitates in group C were stirred for 6h with a certain amount of deionized water at room temperature. Then, precipitates in group C were collected by centrifugation. All these samples by centrifugation were washed 3 times with deionized
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water. Finally, products of white powders in these groups were obtained after freeze-drying. The
MA
product of group A, group B and group C were named H-Calcium, F-Calcium and P-Calcium, respectively.
D
Characterization: The X-ray diffraction (XRD) measurements of these products were realized by
TE
using D8 ADVANCE (German Bruker) diffractometer with Ni-filtered, Cu Kα1 target,
= 1.54183 Å at
CE P
40 kV and 40 mA. Samples were scanned from 2 =5º to 80º with a step size of 0.02º and a scanning speed of 0.1s per step. The surface morphologies of these different microparticles were characterized
AC
by using NOVA NANOSEM 430 (Netherlands) instrument after coated with gold by using a sputter coater. The transmission electron microscopy (TEM) images were carried out by using the JEM-2100HR (JEOL) instrument. The Fourier Transform Infrared Spectrometer (FTIR) results were recorded in the range of 400-4000 cm-1 by using Lambda950 (PerkinElmer Co., LTD. USA). Results Through this method, which was depicted in the experimental section, three kinds of CaCO3 microparticles were synthesized. SEM (Figure.1) images showed the different morphologies of these microparticles. FTIR and XRD results of these microparticles were listed in Fig. 2. The differences of morphologies among three products were revealed from the SEM images 3
ACCEPTED MANUSCRIPT (Fig.1). The microstructure of H-calcium, F-Calcium and P-Calcium were hollowed (Fig.1A and a), flower-like (Figure. 1B and b) and peanut-like (Fig.1C and c), respectively. It was shown from Fig.1B
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T
and b that F-Calcium was formed by many diamond-like particles. The component of diamond-like
SC R
particles was confirmed by XRD and FTIR.
Fig.2a showed FTIR results of three microparticles. Absorption peaks at 1467cm-1, 876cm-1 and 712cm-1 were the absorption peaks of CO32-. Absorption peaks at 2512cm-1 and 1797cm-1 could confirm
NU
the presence of calcium carbonate. Absorption peaks of H-Calcium at 1087cm-1 and 745cm-1 showed
MA
the presence of vaterite polymorph, according to Gunawan Hadiko and his colleagues [2]. It was seen that absorption peak at 745 cm-1 was disappeared in the FTIR image (Fig.2a) of P-Calcium. These
D
results demonstrated that the crystal-phase of calcium carbonate microparticles was converted, from
TE
vaterite to calcite. The peaks at 1030cm-1 and 1130cm-1 were corresponding to the absorption peaks of
CE P
Si-O bond in R-NH3+ [11]. Compared with the FTIR results of Dazhou Zhao and his colleagues [12], the peak at 712cm-1 in our work showed that the H-Calcium and F-Calcium was not pure vaterite. XRD
AC
results (Fig.2b) of H-Calcium and F-Calcium could further validate this conclusion. The diffraction peaks of the H-Calcium at approximately 25º, 27ºand 33º indicated the existence of vaterite, while the peaks at approximately 30º indicated the existence of calcite[5],[13]. These results confirmed that the components of H-Calcium and F-Calcium were not pure vaterite. Diffraction peaks at approximately 25º, 27ºand 33º were disappeared in P-Calcium. Overall, from the FTIR and XRD results, we can conclude that the components of these products were calcium carbonate. H-Calcium and F-Calcium were composed of vaterite and calcite, while P-Calcium was composed of calcite. Discussion In this research, a possible formation mechanism of three different CaCO3 microparticles was 4
ACCEPTED MANUSCRIPT proposed (Fig.3A). At first, APTES was hydrolyzed to obtain octa(aminopropylsilsesquioxane) (R-NH3+). CO2 was reacted with NH3·H2O to obtain HCO3- and CO32-. The incorporation of R-NH3+ to
IP
T
Ca2+, CO32- and HCO3- ions give rise to the precursor of calcium carbonate crystal. Then the amorphous
SC R
calcium carbonate (ACC) was generated [13] following the combination of Ca2+ and CO32-. After being treated with water, heating and standing, HCO3- was decorticated into CO2 and CO32-. CO32- continued to react with Ca2+ to form CaCO3 nanoparticles. At the same time, ACC transformed to crystal phase
NU
under these conditions. This phenomenon that some organisms could produce stable amorphous
MA
calcium carbonate (ACC) and the ACC functioned as a transient precursor of more stable crystalline phase was proposed by Steve Weiner and his colleagues [2], [14]. The calcium carbonate nanoparticles
D
were combined with R-NH3+. Then, CO2 was encased to obtain hollow microspheres (H-Calcium).
TE
Within stirring treatment, CO2 was escaped and the R-NH3+ bond to the CaCO3 nanoparticles to obtain
CE P
the peanut-like microparticles (P-Calcium) attributing to mechanics effects. FTIR (Fig.3B) and XRD (Fig.3C) results of intermediate product showed that the intermediate product was not any kind of
AC
calcium carbonate crystal. XRD result (Fig.3C) showed that the intermediate product was under the amorphous state. In Fig.3B, peaks at 1570cm-1, 1498cm-1, 861cm-1, 694cm-1 showed the existence of CO32-. Peaks at 1030cm-1 and 1130cm-1 were absorption peaks of Si-O bond in R-NH3+. The peaks at 2933cm-1 was corresponding to the absorption peaks of -CH2- and peaks at 3349cm-1 was the absorption peaks of -NH3+. The content of Si element in H-Calcium was estimated to be 4.96 wt. % by using the Energy Dispersive X-ray Detector (EDX). These results confirmed the existence of R-NH3+ and could also validate the possible mechanism. The formation mechanism of F-Calcium was possibly because of the surface mineralization of CaCO3 microparticles. Fig.4 was the SEM and TEM images that showed the possible formation 5
ACCEPTED MANUSCRIPT process. Fig.4a showed the morphology of the material that was kept standing in water for 6h at room temperature. Fig.4b displayed the morphology of material that was further treated in water for 3days at
IP
T
room temperature. These treatments was handled for observing the formation process of F-Calcium
SC R
microparticles. The image (Fig.4c) demonstrated that the F-Calcium was formed. The surface potential of H-Calcium (In deionized water) was analyzed by using the Zeta-potential Analyzer (Shimazduo, Japan), and the result was about +14mV. It could be concluded from these results that the most possible
NU
formation mechanism were as follows. In water, the vaterite on the surface of calcium carbonate
MA
microparticles was converted to calcite which was attracted to the surface of calcium carbonate microparticles with positive potential. Then the calcite was covered on the surface of CaCO3
D
microparticles. Finally, flower-like microparticles (F-Calcium) were formed. TEM images of
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F-Calcium (Fig.4d and Fig.4d-1) showed the detail characteristic information. XRD and FTIR results
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(Fig.2) of F-Calcium revealed that the component of F-Calcium was not pure calcite, which also composed of vaterite. These results could also confirm the possible formation process of F-Calcium.
AC
Furthermore, these CaCO3 microparticles with different crystal-phase might have the potential value for acting as the drug carries in therapy field in the future. F-Calcium microparticles might be used to encapsulate some unique protein for preparing some unique materials with different functions. Conclusions In this work, a simple method to synthesize CaCO3 microparticles was described. Three kinds of calcium carbonate microparticles were prepared through the different final treatments by using this method. A beautiful flower-like microsphere was obtained by the surface mineralization of calcium carbonate microparticles. Moreover, the possible formation mechanisms of these microparticles were discussed, and this possible mechanisms might be used to synthesize other kinds of microparticles by 6
ACCEPTED MANUSCRIPT using other materials. Acknowledgments
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T
This work was supported by the Key Project of the National Natural Science Foundation of China
SC R
(Grant No.50830101), the National 973 project of China (2011CB606204), National Natural Science Foundation of China (Grant No.51202069, 51172073), Research Fund for the Doctoral Program of Higher Education of China (Grant No.20110172110002), the Fundamental Research Funds for the
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Central Universities (Grant No.2014ZM0009) and National Nature Science Foundation of China
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(Grant No.51202069). References
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[3] Fakhrullin, R. F., et al., Magnetically responsive calcium carbonate microcrystals. ACS applied materials & interfaces (2009) 1 (9), 1847. [4] Fujiwara, M., et al., Encapsulation of Proteins into CaCO3by Phase Transition from Vaterite to Calcite. Crystal Growth & Design (2010) 10 (9), 4030. [5] Xu, A.-W., et al., Polymorph Switching of Calcium Carbonate Crystals by Polymer‐Controlled Crystallization. Journal of Materials Chemistry (2007) 17 (5), 415. [6] Wang, S.-S., and Xu, A.-W., Amorphous Calcium Carbonate Stabilized by a Flexible Biomimetic Polymer Inspired by Marine Mussels.
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ACCEPTED MANUSCRIPT DMF Solution under Control of Poly (ethylene glycol)-b-poly (l-glutamic acid): Effects of Crystallization Temperature and Polymer Concentration. Crystal Growth and Design (2008) 8 (4),
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[8] Qiao, L., et al., Special vaterite found in freshwater lackluster pearls. (2007) 7 (2), 275.
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(2001) 412 (6849), 819.
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[10] Rao, M. S., Kinetics and Mechanism of the Transformation of Vaterite to Calcite. Bulletin of the Chemical Society of Japan (1973) 46, 1414.
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[11] Zhang, L.; Abbenhuis, H. C. L.; Yang, Q.; Wang, Y.-M.; Magusin, P. C. M. M.; Mezari, B.; van
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Santen, R. A.; Li, C. Angewandte Chemie 2007, 119, (26), 5091-5094.
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[12] Zhao, D., et al., Synthesis of template-free hollow vaterite CaCO3 microspheres in the H2O/EG system. Materials Letters (2013) 104, 28.
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[13] Shen, Q.; Wei, H.; et al, Properties of amorphous calcium carbonate and the template action of vaterite spheres. Journal of Physical Chemistry B 2006, 110, (7), 2994-3000. [14] Raz, S., et al., The Transient Phase of Amorphous Calcium Carbonate in Sea Urchin Larval Spicules: The Involvement of Proteins and Magnesium Ions in Its Formation and Stabilization. Advanced Functional Materials, 2003. 13(6): p. 480-486. Appendices
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Figure 1. The SEM images of these different products. Image A, B and C showed the microstructure of H-Calcium, F-Calcium and P-Calcium. Image a, image b and image c were the magnified images of
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image A, B and C.
Figure 2.The FTIR (image a) and X-ray diffraction (image b) results of these microparticles.
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Figure 3. The possible formation mechanism of these CaCO3 microparticles. Image A showed the main
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possible mechanism of this method. Image B was the FTIR result of middle product, C was the XRD
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result of middle product, D was the SEM image of P-Calcium and E was the SEM image of H-Calcium.
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(The middle product was obtained by centrifugation before the final treatments.)
Figure 4. The SEM images of the F-Calcium formation process, and the TEM images of F-Calcium. Image a, b and c was corresponding to the beginning, forming, and ending time during the F-Calcium formation process. Images d and d-1 were the TEM images of F-Calcium (Image d-2 was the electron diffraction image of F-Calcium).
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Grpahical Abstract
Highlights: A facile method was used to synthesize these different kinds of microparticles. The formation process of the F-Calcium was recorded through the SEM images. 11
ACCEPTED MANUSCRIPT The formation mechanisms of these microparticles were discussed.
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These mechanisms might be used to fabricate other microparticles.
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