Structural modifications and thermodynamic characteristics of calcite growth during interaction with biomolecular glycine: new insights into biogenesis

Abstract

Extensive studies have led to a common understanding of how organic molecules affect the phase, morphology and crystal structure of carbonate minerals. However, further analyses of crystal structures and the unique thermal decomposition characteristics of calcite affected by glycine have rarely been reported. Here, glycine was added as an additive to investigate the biomimetic mineralization of calcites at different glycine concentrations and pH values by virtue of the titration method. The sample characteristics were first analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and laser grain size analysis to investigate the morphology, crystal structure and grain size distribution, respectively. The results indicate that the precipitates are calcites, although SEM and XRD analyses indicated significant differences regarding surface morphology, cell density and cell volume. In addition, taking into account the complexation of Ca2+ with glycine, the samples removed from the precipitation system at different time intervals also confirm the presence of vaterite. More importantly, comparative studies of thermal decomposition between calcites under different conditions were carefully investigated using thermogravimetric analysis at different heating rates of 5, 10, 20, and 30 °C min−1 from 100 to 1000 °C. The kinetic parameters of average activation energy (E) and pre-exponential factor (A) were calculated by the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods to verify that the calcite has a lower crystallinity, activation energy and enthalpy change (ΔH) with glycine incorporation. Thus, this study provides important new insight into the effects of glycine in inducing the biomimetic mineralization of calcite, especially the crystal structural and thermodynamic characteristics.