Colloids and Surfaces A: Physicochemical and Engineering Aspects
Biomimetic synthesis of hollow microspheres of calcium carbonate crystals in the presence of polymer and surfactant
Graphical abstract
From the experimental results, the growth mechanism of hollow CaCO3 microspheres was speculated upon. Hypothetical mechanism of hollow CaCO3 microspheres formation is illustrated in this figure. PVP could interact strongly with anionic SDS to form PVP–SDS complex micelles with long chains intermingling in the headgroup region of the SDS micelles. SDS could provide the nucleation sites for the crystallization of CaCO3 owing to the interaction of SDS and Ca2+. Not only PVP–SDS complex micelles could be formed, but also free surfactant micelles could exist in the solution.
Highlights
► Hollow CaCO3 microspheres were synthesized by the precipitation reaction method. ► PVP and SDS were employed as a template for the controlled growth of CaCO3. ► A hypothetical mechanism of hollow CaCO3 microspheres formation was illustrated. ► This method is a useful route for the biomimetic mineralization materials.
Introduction
Modern technologies require innovation approaches for complex materials with excellent properties. It is well-known that biomineralization is an elaborate process that produces biominerals with complex and fascinating morphologies as well as superior mechanical properties [1], [2], [3]. The controlled synthesis of inorganic materials of specific size and morphology is a key aspect in fields as diverse as modern materials, catalysis, medicine, electronics, ceramics, pigments and cosmetics [4], [5]. Hollow CaCO3 particles with nanometer to micrometer dimensions represent an important class of materials because their unique structural, optical and surface properties may lead them to a wide range of application [6], [7], [8]. The strategy of using organic templates or modifiers with complex functional patterns to control the nucleation, growth, and alignment of inorganic crystals has been widely adopted for the biomimetic synthesis of inorganic materials with complex form [9], [10]. A number of studies have been carried out to elucidate the effect of various organic molecules on the crystallization of inorganic crystals [11], [12], [13]. As widely and efficiently used processing additives in industrial end products, the various surfactants aroused the particular interest in the crystallization process of inorganic species [14], [15]. The use of polymer–surfactant supramolecular systems for the control of inorganic crystallization has become an area of intense research activity in recent years [16], [17], [18], [19]. Although the influence of uncharged polymers [20], [21], [22], anionic surfactants, or the polymer–surfactant mixtures [23], [24], [25] on the crystallization process of inorganic crystals have been investigated, nevertheless, the aqueous systems containing polymer–surfactant mixtures have not been used for the research of crystallization and aggregation behavior of calcium carbonate [26]. In this work, hollow CaCO3 microspheres were successfully synthesized using sodium carbonate and calcium chloride through precipitation reaction at room temperature. Polyvinylpyrrolidone (PVP) and sodium dodecyl sulfonate (SDS) were employed together as template for the controlled growth of hollow CaCO3 microspheres. The effect of the concentration of SDS on the crystallization and aggregation of CaCO3 was investigated and discussed. The PVP–SDS complex micelles played a key role in controlling the growth of biominerals.
Section snippets
Chemicals
Polyvinylpyrrolidone (PVP) and sodium dodecyl sulfonate (SDS) were obtained from Beijing Chemical Factory (China). Na2CO3 and CaCl2·2H2O were brought from Shenyang Chemical Reagent Factory. All chemicals were of analytical grade and used without further purification. The water used in this work was distilled water made in our laboratory.
Preparation
0.1 M of Na2CO3 solution with 10 g/L of PVP and SDS, and 0.1 M of CaCl2 solution with certain concentration of SDS were prepared beforehand. Then, CaCO3 crystals
Morphology of the synthesized CaCO3 crystals
Fig. 1 shows the typical FESEM images of CaCO3 hollow spherical particles obtained in the reaction. It exhibited that the mean diameter of the hollow spheres ranged from 2 to 3 μm. It can be seen that CaCO3 microspheres with coarse surfaces were obtained (Fig. 1(a)). The magnified image shows that the hollow sphere with an opening hole is composed of nano-sized crystallites. The mean wall thickness was around 400 nm. The hollow structure of the product was further confirmed by TEM (see Fig. 1(b)).
Conclusions
In summary, hollow CaCO3 microspheres have been synthesized successfully in the presence of PVP and SDS using a facile precipitation method. The PVP–SDS complex micelles were the nucleating centers and serves as spherical template to generate hollow spheres of CaCO3 crystals in the reaction system. The PVP–SDS complex micelles could control the nucleation, growth, and aggregation of CaCO3 crystalline particles. However, the concentration of SDS plays an important role in influencing the
Acknowledgements
This research was financed by the National Natural Science Foundation of China (21077041) and supported by “the Twelfth Five” Science Technology Research of Jilin Education Hall. The authors also would like to thank Jilin Normal University for supplying the various instruments used in this study
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