2006 Fiscal Year Final Research Report Summary
Structural study of hydrated ions in confinement
| Project/Area Number |
17550023
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | Fukuoka University |
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Principal Investigator |
YAMAGUCHI Toshio Fukuoka University, Faculty of Science, Professor, 理学部, 教授 (70158111)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Nanometer pore / hydrated ion / microscopic structure / MCM-41 / Activated carbon / Aqueous electrolyte solutions / Hydrogen bonding / Acetonitrile |
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| Research Abstract |
In this study, the structure and dynamics of water, methanol, acetonitrile, and several aqueous electrolyte solutions confined in well-controlled MCM-41 with hydrophilic surface and activated carbon fibers with hydrophobic surface have been investigated by differential scanning calorimetry, FTIR, X-ray diffraction and quasi-elalstic neutron scattering.
(1) For MCM-41 C10(pore diameter 21 Å), C14(28 Å), and C18(37 Å), monolayered water are strongly bound to the surface silanol groups (SiOH) with an O-O distance of 2.6 Å, resulting in distorted hydrogen bonding network in capillary-condensed water. The translational diffusion coefficients of water molecules decrease with decreasing pore size and were found to be about half to bulk water.
(2) Methanol molecules confined in MCM-41 C10 and C14 form strong hydrogen bonds with the silanol groups. The structure and dynamics of the methanol molecules on the surface show little dependency on pore size and temperature. On the other hand, capillary-condensed methanol molecules form a chain-like structure as in bulk, but its hydrogen-boned network is very distorted.
(3) Acetonitrile molecule confined in MCM-41 C14 interact with the surface silanol groups by dipole-dipole interactions with an N-O distance of about 3 Å. Translational diffusion of acetonitrile molecules in the pores is more retarded than that in bulk, and its activation energy was found to be about 7-12 kJ/mol, much smaller than that of water.
(4) Capillary-condensed heavy water confined in MCM-41 C10 has shown a dynamical cross-over at around 229 K from low-density water to high-density water.
(5) The aqueous electrolyte solutions confined in MCM-41 C10, C14, C18, and ACF showed a decrease in melting point with lowering surface charge density of ions. The structure of the first hydration shell of the ions is similar to that in bulk.
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