Molecular level investigations of (organo)clays
Abstract
This medium allocation proposal aims at continue our research efforts enabled by previous allocations SNIC 2017/1-369 and SNIC 2016/1-375, investigating the molecular organization and mobility of small inorganic solutes and organics in smectite interlayers (i.e. in lamellar pores between 1nm thick clay layers) of (organo-)clay nanocomposites. Smectite clays have a layered structure and an extremely high surface area, enabling intercalation of large quantities of molecular substances leading to nanomaterials with novel and/or improved properties compared to a simple isotropic mixtures.
Our ultimate goal is to improve our understanding of the main interactions controlling intercalation and surface adsorption of water, CO2 and organics to clay mineral surfaces. Using primarily classical molecular dynamics simulations we will study adsorption and interaction behavior of clay minerals with a range of organic molecules, covering a selected range of functional groups (initially alcohols and amines), using methods developed during our previous (and ongoing) work of similarly hydrated systems, such as calculation of theoretical XRD diffractograms, vibrational powerspectra as well as free energy perturbation and umbrella sampling methods, see:
Holmboe+Bourg, J. Phys. Chem. C 2014, 118, 1001−1013
doi: dx.doi.org/10.1021/jp408884g
Tinnacher+Holmboe et al, 2016 Geo. et Cosm. Acta 177 (2016) 130–149
doi: 10.1016/j.gca.2015.12.010
Tournassat+Holmboe et al, 2016, Clays and Clay Min. 64, 4, 374–388
doi: 10.1346/CCMN.2016.0640403
Hellrup+Holmboe et al, Langmuir 2016, 32, 13214−13225
doi:10.1021/acs.langmuir.6b01967
Holmboe et al., Langmuir 2016, 32, 12732−12740
doi: 10.1021/acs.langmuir.6b03008
Yang+Holmboe, Journal of Chem. Phys. 2017, 147, 084705
doi: 10.1063/1.4992001
Yeşilbaş+Holmboe+Boily, ACS Earth Space Chem. 2018, 2, 38−47
doi: 10.1021/acsearthspacechem.7b00103
Yeşilbaş+Holmboe+Boily, Trapping and release of atmospheric carbon dioxide by clays, Recently accepted to Environmental Science: Nano, RSC.
Our group at Umeå University have implemented two clay-specific forcefields, Clayff (Cygan, 2004) and the charmm-like INTERFACE ff (Heinz, 2005, 2013) for Gromacs, and have prior experience of OPLS/aa, gaff and charmm’s general ff for organic molecules. As an initial benchmarking study, we are studying i) smectite solvation (of clay surfaces + counter-cations) of pure alcohol and mixed water/alcohol mixtures, to find the dependence on clay basal spacings versus loading, to aid interpretation of experimental XRD diffraction data on the corresponding systems (by subsequent calculation of structure factors and 1D XRD modeling). These simulations are also be performed for other layered materials such as graphene and graphite oxide, for which a vast amount of experimental XRD data already exists.
In another project we address ion-exchange reactions of the natural occurring cations in clays (Na+, Ca2+, K+) with small tertiary amines and lipids like CTAB, since they are known to undergo intercalation, replacing the existing cations. The motivation for this subproject is the potential applications of hydrophobic clay interlayers with tunable pore size.
