Crystallization habit of calcium carbonate in presence of sodium dodecyl sulfate and/or polypyrrolidone

Transcription

1 Journal of Crystal Growth 260 (2004) Crystallization habit of calcium carbonate in presence of sodium dodecyl sulfate and/or polypyrrolidone Hao Wei a, Qiang Shen b, *, Ying Zhao a, Dujin Wang a, *, Duanfu Xu a a State Key Laboratory of Polymer Physics & Chemistry, Joint Laboratory of Polymer Science and Materials, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing , China b Key Laboratory for Colloid and Interface Chemistry of Education Ministry, Shandong University, Ji nan , China Received 14 July 2003; accepted 7 September 2003 Communicated by M. Schieber Abstract The synthesis of calcium carbonate (CaCO 3 ) crystals from aqueous solutions containing sodium dodecyl sulfate (SDS), poly(n-vinyl-1-pyrrolidone) (PVP) or SDS/PVP complexes has been performed through a slow titration method. It was found that aragonite and calcite coexisted in the prepared crystals. The formation of aragonite in the precipitation systems without magnesium ions indicates that at ambient temperature ca C, initially formed amorphous CaCO 3 could also transfer into aragonite in the sedimentary phase, which indicates the controlling factor of organic additives in the nucleation and growth process of CaCO 3 crystals. The appearance of hexagonal crystals in the suspensible phase confirmed the hexagonal crystallization cell of vaterite, and revealed the colloidal-dispersion function of the SDS/PVP complex in the crystallization process of CaCO 3. r 2003 Elsevier B.V. All rights reserved. PACS: Dn; Aj; Kj Keywords: B1. Aragonite; B1. Calcium carbonate; B1. Calcite; B1. Poly(vinyl pyrrolidone); B1. Sodium dodecyl sulfate 1. Introduction Biological materials have unique structures and morphologies, which acquire much better performance than the relatively crude minerals. More than 60 kinds of inorganic minerals have been found in various organisms. For example, CaCO 3 / *Corresponding author. Tel.: ; fax: addresses: qshen@sdu.edu.cn (Q. Shen), djwang@iccas.ac.cn (D. Wang). protein hybrids in mollusk shells have superior mechanical properties, which arouse in scientists great interest in understanding natural biomineralization process [1 3]. CaCO 3 is one of the most common biological minerals and has polymorphs of calcite, aragonite, and to a less extent amorphous state, vaterite or monohydrate in calcareous structures of organisms [4]. All of the size, habit and aggregation state of these polymorphic species in each calcareous structure are different and exhibit specific characteristics. This is possible due to the controlling effect of organic matrix over /$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi: /j.jcrysgro 转载

2 546 H. Wei et al. / Journal of Crystal Growth 260 (2004) morphology, composition and spatial organization of CaCO 3. A number of studies [5 9] have been carried out to elucidate the effect of various organic molecules on the CaCO 3 morphology. Recently, it was reported that mechanism of interaction of calcium carbonate with an organic molecule depends on size, ionic charge and structure of additive molecules [10 11]. Small molecules with high charge density preferentially interact electrostatically with charged lateral faces and highenergy tips of the growing crystals, while rigid polymers require a structural fit with ionic structure of a particular crystal face for efficient interaction. As widely and efficiently used processing additives in industrial end products, the anion surfactants aroused the particular interest in the growth of calcium carbonate. However, difficulties in understanding their role arise not only because of theoretical problems in the thermodynamic treatment of solid liquid system [12] but also because of the ability of surfactants to form a variety of supermolecular structures (micelles, nick-line, vesicles, etc.) in the solution. In recent years, people have made a great process in the effect of anionic surfactants on crystallization process and controlled polymorph of inorganic materials [13 17]. It has been shown that surfactants can influence one or several crystallization steps (nucleation, crystal growth, aggregation) and, as a consequence, can control the formation of crystal phase, which does not usually formed under natural environments. In addition, surfactant aggregations have been used as microreactors for the preparation of specific morphologies, sizes or new crystal structures of inorganic [18 20] or organic [21,22] materials. The aim of the present study was to investigate the influence of sodium dodecyl sulfate (SDS), a most commonly used anionic surfactant, on the crystal and growth of CaCO 3. As the cocomponent of SDS in industrial application, the effect of poly(n-vinyl-1-pyrrolidone) (PVP) on CaCO 3 crystallization was also investigated. At last, a possible mechanism was proposed for the influence of SDS, PVP and SDS/PVP over CaCO 3 crystallization habit. 2. Experimental procedure 2.1. Chemicals and CaCO 3 synthesis All chemicals, CaCl 2,Na 2 CO 3, SDS and PVP (molecular weighte30,000 g/mol) are of analytical grade and used without further purification. Doubly deionized water was used to prepare aqueous CaCl 2 and Na 2 CO 3 solutions just before each experiment. In all cases, calcium carbonate was precipitated by titrating 0.1 M CaCl 2 at the speed of 1.0 ml/min into 300 ml beaker containing equal volume of 0.1 M Na 2 CO 3, and the samples were incubated for 24 h. Either used singly or combining with SDS, PVP was added into both aqueous CaCl 2 and Na 2 CO 3 solutions; while SDS was only added into Na 2 CO 3 solution before experiments. During the precipitation and incubation process, the reactive systems were kept at 2671 C. At the end of each crystallization experiment, the precipitated solids were collected by filtering through cellulose nitrate/acetate membrane filters (0.2 mm), rinsed three times with doubly deionized water. Finally, the CaCO 3 crystals were dried in vacuous desiccator cabinet at 40 C for at least 24 h, and used for measurements Characterization All samples were Au-coated prior to examination by a Hitachi S-4300 scanning electron microscope (SEM), fitted with a field emission source and operating at an accelerating voltage of 15 kv. For transmission electron microscopy (TEM) studies, the samples were dispersed in water under nearly 5 min of untrasonic waves and then deposited on a carbon film supported by a copper grid. The TEM images and corresponding electron diffraction patterns were recorded by a Hitachi H-800 electron microscope. X-ray diffraction (XRD) patterns were collected on a Rigaku D/max-2400 powder X-ray diffractometer with Cu Ka radiation (40 kv, 120 ma). A 0.02 step and 2y range from 20 to 40 were selected to analyze the crystal structure and orientation. Micro-IR spectra measurements were performed on a Nicolet

3 H. Wei et al. / Journal of Crystal Growth 260 (2004) Magna-750 IR spectrometer, with scanning times of 100, and resolution of 4 cm Results and discussion In order to eliminate the possible existence of amorphous and metastable phases of CaCO 3, CaCl 2 solution was slowly dropped into the Na 2 CO 3 solution, and the incubation lasted 24 h [23]. Fig. 1 shows the SEM pictures of CaCO 3 particles obtained in the absence and presence of SDS, PVP or SDS/PVP complex. Fig. 2 provides the corresponding XRD results. crystallization morphology and crystal phase, in accordance with our previous report [28]. According to Ostwald s rule [29], the least stable phase (amorphous CaCO 3 ) with the highest solubility is formed preferentially in the solution, then it is transformed within a few minutes to calcite, vaterite or aragonite under different 3.1. Influence of PVP on the crystalline CaCO 3 In the presence of PVP, the crystalline CaCO 3 showed hexahedron or pseudo-sphere (Fig. 1a), similar to the control sample (Fig. 1b). Corresponding XRD spectra results indicated that the particles were mixed with calcite and vaterite, in good agreement with literatures [24 27]. That is to say, PVP alone has no obvious effect on CaCO 3 Fig 2. XRD pattern of calcium carbonate prepared from different systems: (a) deionized water; (b) 100 g/l PVP; (c) mol/l SDS; and (d) 100 g/l PVP mol/l SDS. Fig. 1. SEM micrographs of calcium carbonate prepared from different systems. (A) Deionized water; (B) 100 g/l PVP; (C) mol/l SDS; and (D) 100 g/l PVP mol/l SDS.

4 548 H. Wei et al. / Journal of Crystal Growth 260 (2004) conditions [30]. The crystalline state and lifetime of these polymorphic phase mainly depend on the interaction between the additives and the nuclei face, and the assemblies of the additives in aqueous solution [31]. Nonionic polymer PVP cannot absorb on the crystal face and control the transformation of amorphous CaCO 3 to other crystalline phase through electrostatic interaction or other weak interactions. So a conclusion can be drawn that PVP alone has no effect on CaCO 3 crystallization Influence of SDS and SDS/PVP complex on the crystallization of CaCO 3 However, in the systems of SDS or SDS/PVP, anion surfactant SDS can strongly interact with Fig. 3. Micro-IR spectra of crystalline CaCO 3 grown in the presence of 100 g/l PVP mol/l SDS. Peaks at 879 (v 2 )/ 713 cm 1 (v 4 ) and 1083 (v 1 )/858 cm 1 (v 2 ) correspond to calcite and aragonite, respectively [34,35]. the crystal faces of CaCO 3 after nuclei formation, and will inevitably influence the transformation process (Figs. 1c and d). The effect depends on the concentration and specific mode of aggregation of surfactant in the bulk solution and at the crystal/ solution interface [32]. The XRD diffraction measurements confirm that the CaCO 3 particles were the mixture of calcite and aragonite in the sedimentary phase both in the SDS and the SDS/ PVP complex system (Figs. 2c and d). The micro- IR measurements further confirmed the coexistence of calcite and aragonite (Fig. 3). It should be emphasized that aragonite herein was synthesized at room temperature, not high temperature, and magnesium was needed. Such phenomena often occur in some biomineralization process, with the presence of acidic proteins or magnesium ions. In the presence of SDS, the aggregates of nanometer-sized crystals of CaCO 3 were formed without evident shape. In contrast with the SDS system, flat sheet and flower-shaped crystals of CaCO 3 were obtained in the SDS/PVP system. The magnified SEM image shown in Fig. 4a indicates that the flower-shaped crystals were composed of nano-sized hexagonal platelets. The TEM measurements show clearly hexagonal crystal of CaCO 3 (Fig. 4b). It was found that the crystal does not have uniform thickness along the main crystal axis, though the selected area electron diffraction (SAED) patterns indicate that the crystal is a perfect single crystal with the symmetry of hexagonal system. The existence of relatively dark diffraction spots in the SAED patterns also Fig. 4. (A) SEM images of the precipitated CaCO 3 crystal in the presence of PVP/SDS complex; and (B) TEM image of an isolated hexagonal crystal from the same system. The inset is the corresponding SAED patterns.

5 H. Wei et al. / Journal of Crystal Growth 260 (2004) indicates the un-uniform thickness of the hexagonal crystals. Similar results were also reported by Dupont [33,34], who observed the hexagonal texture of the synthetic CaCO 3 crystals directly by both SEM and TEM. It should be pointed out that although the hexagonal particles were very large (>5 mm), their extremely small thickness supplied sufficient contrast for the TEM imaging. It is well-known that the crystallinity of CaCO 3 depends primarily upon the degree of molecule organization and lattice matching between the nucleating organic matrix and the presence of additive [35]. In the present work, the SDS concentration exceeds the critical micelle concentration [32], so micelles were formed in solution, which play a role of organic matrix for CaCO 3 mineralization. After the amorphous nuclei of CaCO 3 formed, the micelle will preferentially absorb the homo-charged calcium plane of CaCO 3 and induce growth of crystallite. The homocharged calcium planes of vaterite are (0 0 1) and (1 0 0) crystalline plane, while that of calcite are the (0 1 2) and (0 0 1), and of aragonite (0 0 1) [36]. The coexistence of calcite and aragonite is attributed to that the solid/liquid surface can better match with homo-charged calcium plant of calcite and aragonite. On the other hand, this interaction between SDS and the (0 0 1) plane of CaCO 3 crystal inhibits the crystal growth in this direction and this results in formation of little trigonal crystal. With increase in the concentration of amorphous CaCO 3, more and more nuclei are absorbed on the micelle surface, and slowly aggregate into big particles [37]. In the pure SDS system, micelles were separately distributed, so it is difficult for CaCO 3 crystallites to aggregate to regular shape and only particles of CaCO 3 without evident shape were obtained. However, according to current model of surfactant polymer complexes [38], addition of PVP in the SDS system leads to the formation of a pearlnecklace type of structure, for the macromolecular wraps around the micelles. As a result, the small trigonal crystal aggregates into hexagon plane which could randomly aggregate into floretshaped crystals. Fig. 5 illustrates the possible mechanism for the formation of hexagonal single crystal of CaCO 3. Fig. 5. Schematic illustration for the formation of hexagonal single crystals of CaCO Conclusion SDS and SDS/PVP complexes can strongly influence the crystal morphology, texture and polymorphic structure of calcium carbonate crystals grown from aqueous solutions at room temperature, while there is no influence of PVP on the crystallization behavior. The coexistence of aragonite and calcite in both systems SDS and SDS/PVP, and the flat sheet and flower-shaped crystals of CaCO 3 were obtained in the SDS/PVP system while aggregates of nanometer-sized crystals of CaCO 3 without evidence shape were obtained in SDS system. Acknowledgements This work was supported by the National Natural Science Foundation of China [ ] and the Foundation from the State Key Laboratory of Polymer Physics and Chemistry [01-B-08]. References [1] J.D. Currey, J.D. Talor, J. Zool. London 173 (1974) 395. [2] J.D. Currey, A.J. Kohn, J. Mater. Sci. 11 (1976) [3] J.D. Currey, J. Zool. London 180 (1976) 445. [4] N. Watabe, Crystal Growth of Calcium Carbonate in the Invertebrates: In: B.R. Pamplin (Ed.), Progress in Crystal Growth and Characterization, Vol. 4, Pergamon Press, Oxford, London, Edinburgh, New York, Paris, Frankfurt, 1981, pp (and reference therein). [5] S. Mann, Nature 332 (1988) 119. [6] G. Xu, N. Yao, I.A. Akasay, J.T. Groves, J. Am. Chem. Soc. 120 (1998) [7] H. C.olfen, L. Qi, Chem. Eur. J. 7 (2001) 106. [8] L. Balogh, D.A. Tomalia, J. Am. Chem. Soc. 120 (1998) 7355.

6 550 H. Wei et al. / Journal of Crystal Growth 260 (2004) [9] K. Esumi, A. Suzuki, K. Usui, K. Torigoe, Langmuir 16 (2000) [10] G. Falini, M. Gazzano, A. Ripamonti, Adv. Mater. 6 (1994) 46. [11] G. Falini, S. Albeck, S. Weiner, L. Addadi, Science 271 (1996) 67. [12] J.P. Canselier, J. Dispers. Sci. Technol. 14 (1993) 625. [13] D. $ Skrti!c, N. Filipovi!c-Vincekovi!c, J. Crystal Growth 88 (1988) 313. [14] D. $ Skrti!c, N. Filipovi!c-Vincekovi!c, H. F.uredi-Milhofer, J. Crystal Growth 114 (1991) 118. [15] D. $ Skrti!c, N. Filipovi!c-Vincekovi!c, R. Babi!c-Ivanci!c, L. Tu$sek-Bomi!c, J. Crystal Growth 133 (1993) 189. [16] L. Tunik, L. Addadi, N. Garti, H. F.uredi-Milhofer, J. Crystal Growth 167 (1996) 748. [17] M.J.J.M. Van Kemenade, P.L. De Bruyn, Colloids Surf. 36 (1989) 359. [18] M.P. Pileni, J. Tanori, A. Filankembl, Colloids Surf. A (1997) 561. [19] M.P. Pileni, Langmuir 13 (1997) [20] D. Walsh, S. Mann, Nature 377 (1995) 320. [21] J. Yano, H. F.uredi-Milhofer, E. Wachtel, N. Garti, Langmuir 16 (2000) [22] H. F.uredi-Milhofer, A. Kamyshny, N. Garti, J. Crystal Growth 198/199 (1999) [23] M. Kitamura, J. Colloid Interface Sci. 236 (2001) 318. [24] J. K.uther, W. Tremel, Thin Solid Films (1998) 554. [25] J. K.uther, R. Seshadri, W. Tremel, J. Mater. Chem. 8 (3) (1998) 641. [26] G. Falini, S. Albeck, S. Weiner, L. Addadi, Science 271 (1996) 67 (and references therein). [27] K. Naka, Y. Tanaka, Y. Chujo, Langmuir 18 (2002) [28] H. Wei, Q. Shen, Y. Zhao, D.-J. Wang, D.-F. Xu, J. Crystal Growth 250 (2003) 516. [29] O. S.ohnel, J. Garside, Precipitation: Basic Principles and Industrial Applications, Butterworth-Heinemann, Oxford, 1992, p [30] H. Elfil, H. Roques, Desalination 137 (2001) 177. [31] R.H. Brigid, S. Mann, Adv. Mater. 6 (1) (1994) 9. [32] M. Bujan, M. Sikiri!c, N. Filipovi!c-Vincekovi!c, N. Vdovi!c, N. Garti, H. F.uredi-Milhofer, Langmuir 17 (2001) [33] L. Dupont, F. Portemer, M. Figlarz, J. Mater. Chem. 7 (5) (1997) 797 (and reference therein). [34] G. Falini, S. Ablbeck, S. Weiner, L. Addadi, Science 271 (1996) 67 (and reference therein). [35] M.J. Lochhead, S.R. Letellier, V. Vogel, J. Phys. Chem. B 101 (1997) [36] G. Fanili, S. Fermani, M. Gazzano, A. Ripamionti, Chem. Eur. J. 4 (1998) [37] A.E. Nielsen, In: R. Belcher, L. Gordon (Eds.), Kinetics of Precipitation in Vol. 18 of the International Series of Monographs on Analytical Chemistry, Pergamon Press, Oxford, London, Edinburgh, New York, Paris, Frankfurt, 1964, p. 40. [38] M.F. Britta, K. Bengt, Langmuir 16 (2000) 5987.