Phase-controlled Crystallization Of ACC In Ethanol-water Binary Solvents

As the precursor of crystalline biogenic minerals in organisms, amorphous calcium carbonate (ACC) has been found playing an important role in the crystallization of CaCO3. In recent years, reseaches about how the organics make effects on the ions in solutions when crystallizing have been studied,the same as researches about the interaction and structure match between organics and mineral, however, the effect of organics on the precursor phase (ACC) has been ignored.In this thesis, we use the sensitively Fourier Transform Infrared Spectrum (FTIR) to monitor the whole process of ACC crystallization as mainline, then X-ray Diffraction (XRD) and Scanning Electronic Microscopy (SEM) were chosen to characterize the change of each crystal phase. The evolution of amorphous calcium carbonate (ACC) into crystals in ethanol/water binary solvents under ambient temperature was investigated; the increasing ratio of ethanol could lead to a dramatic change in the polymorph from calcite to aragonite. However, when poly (allylamine hydrochloride)(PAH) was added in the binary solution at the appropriate ratio of ethanol, almost pure vaterite could be obtained, which has a specific morphological variation (from hollow microspheres to cloud-like). At last, we change the type of polyeletrolyte additive to study the effects of the negative ones on ACC crystallization, and we found the polymer acrylic acid (PAAs) has fancy effect on inhibition crystallization of ACC in solutions.This study provides an alternative polymorphic route for the CaCO3mineral by using the evolution of ACC in different solvent environments, which provides some useful clues for understanding the amorphous precursor theory. In addition, this simple mild phase-controlled synthetic method could be scaled up as a green chemistry route for the industrial production of different polymorphs of inorganics.