Probing the Core–Shell Organization of Nanoconfined Methane in Cylindrical Silica Pores Using In Situ Small-Angle Neutron Scattering and Molecular Dynamics Simulations

Journal Article · Tue Sep 15 00:00:00 EDT 2020 · Energy and Fuels

DOI:https://doi.org/10.1021/acs.energyfuels.0c02237· OSTI ID:1721721

Mohammed, Sohaib ^[1]; Liu, Meishen ^[2]; Liu, Yun ^[3]; Gadikota, Greeshma ^[2]

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1. Cornell Univ., Ithaca, NY (United States); University of Utah
2. Cornell Univ., Ithaca, NY (United States)
3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)

Determining the structure of nanoconfined fluids is essential for predicting the fate of these fluids in subsurface geologic formations with nanoporous features and for engineering novel nanoporous materials for storing compressed gases. In this study, we probe the structure of nanoconfined methane at pressures in the range of 15–100 bar using in situ small-angle neutron scattering (SANS) measurements and molecular dynamics (MD) simulations. The structure of methane is probed in MCM-41 and SBA-15 with cylindrical pores and diameters of 3.3 and 6.8 nm, respectively. In situ SANS measurements and MD simulations showed that the confined methane molecules are organized in a core–shell structure, with the shell arising from the adsorption of methane molecules on the silica surface. The shell thicknesses of the adsorbed deuterated methane (CD4) molecules in MCM-41 obtained by SANS measurements are 1.4 ± 0.5, 2.1 ± 0.1, 3.2 ± 0.8, 4.0 ± 0.3, and 6.0 ± 0.7 Å at equilibrated pressures of 15.6, 35.6, 55.5, 73.3, and 95.7 bar, respectively. The shell thicknesses of the adsorbed CD4 layer in SBA-15 pores are 2.7 ± 0.5, 4.3 ± 0.7, 6.6 ± 0.7, 10.2 ± 0.3, and 14.6 ± 0.8 Å at equilibrated pressures of 15.5, 32.7, 52.4, 70, and 99.5 bar, respectively. These experimental results are in close agreement with the results predicted from MD simulations. Adsorption of methane molecules on the silica surfaces is primarily driven by van der Waals interactions between the methane molecules and the hydroxyl groups on the silica surface, while electrostatic interactions play a minor role. In conclusion, the experimental and simulation approaches described in this study provide fundamental insights into the organization of confined gases using methane as a specific example in the context of compressed fluid storage in natural and engineered materials for adaptive energy use.

• Research Organization: Univ. of Utah, Salt Lake City, UT (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0019285
• OSTI ID: 1721721
• Journal Information: Energy and Fuels, Journal Name: Energy and Fuels Journal Issue: 12 Vol. 34; ISSN 0887-0624
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
Adsorption
Fluids
Hydrocarbons
Molecules
Silica