Direct Synthesis of Hollow Vaterite Nanospheres from Amorphous Calcium Carbonate Nanoparticles via Phase Transformation

Abstract

A new and simple method for preparation of hollow calcium carbonate nanospheres under mild conditions is developed. Hollow vaterite nanospheres are achieved by water-induced phase transformation of poly(4-sodium styrene sulfonate)-stabilized amorphous calcium carbonate (PSS−ACC) in water−ethanol solution at room temperature. It is found that the sizes of the resulting hollow-structured nanospheres can be easily regulated by the content of PSS and the phase transformation can be greatly affected by the ratio of water to ethanol in the mixed solvent. A combination effect of PSS and water is emphasized in this formation process. It is important to control the amounts of PSS and water in the experiments so that a large scale of hollow vaterite nanospheres with different sizes can be achieved. We suggest that the PSS−ACC particles use themselves as the templates to form the new crystallized shells, and its mechanism is also discussed.

Synthesis of Submicrometer Calcium Carbonate Particles from Inorganic Salts Using Linear Polymers as Crystallization Modifiers

“…In our case, this series of events (i.e., adhesion to the surface followed by breaking away leaving a patch of material on the surface and a hole on the particle) is not present. Cai et al 9 reported the formation of hollow vaterite nanospheres from amorphous calcium carbonate solid particles, controlled by the presence of PSS and water. On applying a much simpler experimental protocol than Cai et al, 9 we did not observe holes in the vaterite particles prepared in the presence of PSS.…”

“…Under such conditions, freshly precipitated calcium carbonate can then be redissolved in a process governed by equilibrium displacement towards the formation of Ca II /PAA complexes at certain points on the particles, eventually resulting in a hole, which will ultimately serve as a release valve for the high concentration of PAA inside the particle. 9 This process is also favored by the osmotic pressure imbalance that evolves from a combination of osmotic flow and concentration changes. This is not observed in the presence of PSS because of its weaker interaction with Ca 2+ cations as compared to PAA.…”

“…1 Although calcium carbonate is an abundant naturally occurring mineral already largely used in the polymer industry, recently the clever manipulation of particle size and its effects on the material properties has attracted considerable attention. [2][3][4][5][6][7][8][9][10][11][12] Nano-and micrometer calcium carbonate particles can be synthesized by a variety of methods, including controlled gas diffusion, colloidal/microemulsion systems, sonochemistry, hydrothermal synthesis, etc. The simplest approach consists of the precipitation of calcium carbonate from solutions containing inorganic salts as a source of calcium(II) and carbonate ions.…”

“…These include metallic ions, surfactants, 10,13 biopolymers, 2,[14][15][16] and synthetic polymers. [2][3][4][5][6]9,[17][18][19][20][21][22][23][24][25] Indeed, crystallization control is a critical requirement in the synthesis of many important materials.…”

“…One common feature of polymers able to control the crystallization of calcium carbonate, such as poly(styrene sulfonate) 5,9,23 and poly(acrylic acid), 4,17,18,[26][27][28] is that they are anionic (or contain anionic segments) and are therefore capable of interacting with calcium(II) ions and with the crystal surface itself.…”