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      Energies of the adsorption of functional groups to calcium carbonate polymorphs: the importance of -OH and -COOH groups.

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          Abstract

          The adsorption behavior of calcium carbonate is an important factor in many processes in nature, industry, and biological systems. We determined and compared the adsorption energies for a series of small molecules of different sizes and polarities (i.e., water, several alcohols, and acetic acid) on three synthetic CaCO3 polymorphs (calcite, aragonite, and vaterite). We measured isosteric heats of adsorption from vapor adsorption isotherms for 273 < T < 293 K, and we used XRD and SEM to confirm that samples did not change phase during the experiments. Density functional calculations and molecular dynamics simulations complemented the experimental results and aided interpretation. Alcohols with molecular mass greater than that of methanol bind more strongly to the calcium carbonate polymorphs than water and acetic acid. The adsorption energies for the alcohols are typical of chemisorption and indicate alcohol displacement of water from calcium carbonate surfaces. This explains why organisms favor biomolecules that contain alcohol functional groups (-OH) to control which polymorph they use, the crystal face and orientation, and the particle shape and size in biomineralization processes. This new insight is also very useful in understanding organic molecule adsorption mechanisms in soils, sediments, and rocks, which is important for predicting the behavior of mineral-fluid interactions when the challenge is to remediate contaminated groundwater aquifers or to produce oil and gas from reservoirs.

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          Author and article information

          Journal
          Langmuir
          Langmuir : the ACS journal of surfaces and colloids
          American Chemical Society (ACS)
          1520-5827
          0743-7463
          Sep 03 2013
          : 29
          : 35
          Affiliations
          [1 ] Nano-Science Center, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark. denisokr@nano.ku.dk
          Article
          10.1021/la402305x
          23919655
          fa67e6f2-ec86-4195-aca9-d2139526887a
          History

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