PNAS: Scientists Reveal Details of Ethanol onto Calcite

The interactions between simple organic molecules and inorganic surfaces of nanoparticles get ubiquitously involved in biomineralization, contaminant and nutrient transport in soils and aquifers, and CO2 transport and carbonate formation in nature and selective catalysis, oil recovery, self-assembly of colloidal nanoparticles, and CO2 capture and sequestration in technogical processes.

 Di Wu and Alexandra Navrotsky from Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit, University of California, in a paper in the Proceedings of the National Academy of Sciences of the United States of America Scientific Journal (Published on March 25, 2015), reveal in detail the interactions of ethanol on calcite.
Calcite, the most stable calcium carbonate polymorph, is common and abundant carbonate in nature. Ethanol, a colorless volatile flammable liquid, is readily produced by the natural  or engieerined fermentation of sugars. Ethanol, a simple chain-like polar molecule, is a representative of hydroxyl containing organic ligands.The  ethanol-nanocalcite organic–inorganic system, seemingly simple  yet complex in physiochemistry, represent typical phenomena in nature and engineering processes in industry.
 Di Wu and Alexandra Navrotsky found that there is a stepwise, yet gradually and continuously evolved energetics from weak associating to strong bonding to classical capping, with a rich energetics of organic–nanoparticles binding as a function of molecular coverage for ethanol–nanocalcite system.  Namely, a series adsorption events as a function of coverage occur when the ethanol molecules are adsorbed onto the surface of nanocalcite. First, ethanol molecules are strongly chemisorbed on active sites on fresh nanocalcite surfaces. Then.  an ethanol monolayer is formed by major chemical binding through its polar hydroxyl group to the calcite surface. After that, more ethanol molecules are adsorbed, or say self-assemblied, onto the surface of nanocalcite by very weak, near-zero energy, physisorption in this way the hydrophobic ends of the ethanol molecules interact only weakly with the next layer of adsorbing ethanol. Accordingly, there is a spatial gap with low ethanol density between the monolayer and subsequent adsorbed ethanol molecules.
 Such evolved energetics and accordingly an ordered assembly of ethanol, or say a capping layer, on calcite nanoparticles provide deep insights into continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers. Such findings can help material and catalysis scientists well understand. finely use chemical reactions,and  control the nucleation and growth of nanocrystals on organic ligand-capped surfaces, to as to design and fabricate advanced  functional nanomaterials and industrial catalysts. The  fundamental thermodynamic study also gives important clues to understand many natural geological processes and biological-environmental conditions. 
                                                                                                                                                                                                                                                (QYIM & AMSC. Edited and Reported by CHZ)



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