The effect of Mg²⁺ incorporation on the structure of calcium carbonate clusters: investigation by the anharmonic downward distortion following method

Abstract

Mg 2+ is considered to play an important role in the formation of calcium carbonate polymorphs; however, how it affects polymorph selection during the early stages of CaCO3 formation is not yet well understood. In the present study, in order to clarify the effect of Mg 2+ on the nucleation of calcium carbonate polymorphs, the stable structures of anhydrous additivefree and Mg-containing calcium carbonate clusters are derived using the anharmonic downward distortion following method, based on quantum chemical calculation. Optimization is performed at the B3LYP/6-31+G(d) level and the solvent effect is induced by the self-consistent reaction field method using the conductor-like polarized continuum calculation model. Calculation results show that incorporating Mg 2+ into clusters can change the clusters' stable configuration. In case of dimers and trimers, a Mg ion strongly prefers to locate at the centre of the clusters, which suggests that Mg is easy to incorporate into the clusters once it is released from its tight hydration shell. Notably, structures similar to the crystalline phase appear when only four CaCO3 units aggregate into the cluster: in the stable structure of the additive-free CaCO3 tetramer, the arrangement of Ca and CO3 ions is almost the same as that of the calcite structure, while the structure of the Mg-containing CaCO3 tetramer resembles the aragonite structure in the way that CO3 ions are stacked. These results indicate that Mg can play a key role in aragonite formation not only by inhibiting calcite growth but also by directly promoting aragonite nucleation in the early stages of CaCO3 formation.

Role of Impurities in the Kinetic Persistence of Amorphous Calcium Carbonate: A Nanoscopic Dynamics View

“…This surprising phenomenon was common in all the amorphous carbonates examined in the present study (Supporting Information Figure S8b). The local order of amorphous carbonates has been studied by different authors both experimentally ,− and computationally ,− to elucidate the mechanisms of polymorph selection and crystallization. However, it is clear from our results that structural studies alone miss important information, in particular the dynamic characteristics such as those provided here which gives a more complete and rich picture of the physics behind the crystallization process of the amorphous systems.…”

The synthesis of polyaspartic acid derivative PASP-Im and investigation of its scale inhibition performance and mechanism in industrial circulating water

“…Non-local hybrid density functional B3LYP with the basis set 6-31 G of the Gaussian 09 program was adopted to conduct the complete optimization of the PASP-Im molecule. 20,21 The inhibition behavior of the PASP-Im additive was studied by a computational analysis based on the density functional theory (DFT). 22 3.…”

Controlling nucleation and growth of nano-CaCO3 via CO2 sequestration by a calcium alkoxide solution to produce nanocomposites for drug delivery applications

“…However these methods usually lead to quite poly-disperse particles and to the best of our knowledge never with particle size below 20 nm. Most promising for further diminution of the particle size have recently been proposed to be, on one hand, the addition of smaller and higher charged ions [39], causing enhanced surface charge of the particles, and, on the other hand, the uptake of carbon dioxide gas by solution of calcium organic derivatives in less polar medium [40]. For the latter approach, we considered the precursor calcium ethoxide most promising, since it immediately transforms on contact with humid atmosphere into large oligo-nuclear oxo-ethoxide species, like Ca 6 O 2 (OC 2 H 5 ) 8 (C 2 H 5 OH) 14 [41], and is potentially capable of facilitating the nucleation process, according to theoretical predictions [7].…”