Mechanisms of CaCO3 nucleation from solutions that depend on multistage pathways and the existence of species far more complex than simple ions or ion pairs have recently been proposed. Herein, we provide a tightly coupled theoretical and experimental study on the pathways that precede the initial stages of CaCO3 nucleation. Starting from molecular simulations, we succeed in correctly predicting bulk thermodynamic quantities and experimental data, including equilibrium constants, titration curves, and detailed x-ray absorption spectra taken from the supersaturated CaCO3 solutions. The picture that emerges is in complete agreement with classical views of cluster populations in which ions and ion pairs dominate, with the concomitant free energy landscapes following classical nucleation theory.
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We acknowledge D. Gebauer for providing us with titration data, J. Gale for technical discussions about our theoretical approach, S. Kathmann for useful discussions on nucleation, and J. A. van Bokhoven for helpful discussions. We also thank R. Wetter and C. Frieh for providing technical support during the beamtime and for the construction of all in situ setups. Funding: PMF and MM simulations were performed at the Pacific Northwest National Laboratory (PNNL) with support from the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Division of Material Sciences and Engineering. The solution model and theoretical XANES calculations were supported by the DOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences. AVBMC simulations were supported through an award from the NSF (CHE-1265849). All measurements were performed at the PHOENIX beamline at the Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. S.P. acknowledges funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 290605 (PSIFELLOW/COFUND). J.M.X. acknowledges funding from the Swiss National Science Foundation (grant no. 200021_157148). DFT simulations were performed within the Materials Synthesis and Simulation Across Scales (MS3) Initiative through the Laboratory Research and Development Program at PNNL. E.O.F. acknowledges the Alternate Sponsored Fellow program at PNNL where he spent 3 months during this project and a University of Minnesota Doctoral Dissertation Fellowship. The PMF calculations used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the DOE, Office of Science under contract no. DE-AC02-05CH11231. A portion of the research (XANES calculations) was performed at the Environmental Molecular Sciences Laboratory, which is a DOE Office of Science User Facility; all other calculations were performed using PNNL’s Institutional Computing resources. The AVBMC simulations used resources of the Minnesota Supercomputing Institute. PNNL is a multiprogram national laboratory operated for the DOE by Battelle under contract no. DE-AC05-76RL01830.
Copyright © 2018 The Authors.