Guest-host interactions of a rigid organic molecule in porous silica frameworks
Abstract
Molecular-level interactions at organic–inorganic interfaces play crucial roles in many fields including catalysis, drug delivery, and geological mineral precipitation in the presence of organic matter. To seek insights into organic–inorganic interactions in porous framework materials, we investigated the phase evolution and energetics of confinement of a rigid organic guest, N,N,N-trimethyl-1-adamantammonium iodide (TMAAI), in inorganic porous silica frameworks (SSZ-24, MCM-41, and SBA-15) as a function of pore size (0.8 nm to 20.0 nm). We used hydrofluoric acid solution calorimetry to obtain the enthalpies of interaction between silica framework materials and TMAAI, and the values range from −56 to −177 kJ per mole of TMAAI. The phase evolution as a function of pore size was investigated by X-ray diffraction, IR, thermogravimetric differential scanning calorimetry, and solid-state NMR. The results suggest the existence of three types of inclusion depending on the pore size of the framework: single-molecule confinement in a small pore, multiple-molecule confinement/adsorption of an amorphous and possibly mobile assemblage of molecules near the pore walls, and nanocrystal confinement in the pore interior. These changes in structure probably represent equilibrium and minimize the free energy of the system for each pore size, as indicated by trends in the enthalpy of interaction and differential scanning calorimetry profiles, as well as the reversible changes in structure and mobility seen by variable temperature NMR.
Additional Information
© 2014 National Academy of Sciences. Contributed by Alexandra Navrotsky, December 23, 2013 (sent for review October 23, 2013). This work is supported as part of the Center of Nanoscale Control of Geologic CO2, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under Award DE-AC02-05CH11231. The NMR facility at California Institute of Technology (Caltech) was supported by the National Science Foundation (NSF) under Grant 9724240, partially supported by the Materials Research Science and Engineering Centers Program of the NSF under Award DMR-520565, and the US DOE, Office of Energy Efficiency and Renewable Energy, through the Hydrogen, Fuel Cells and Infrastructure Technologies Program under Contract DE-AI-01-05EE11105 (Jet Propulsion Laboratory–Caltech). Author contributions: D.W., S.I.Z., and A.N. designed research; D.W. and S.-J.H. performed research; D.W., S.-J.H., S.I.Z., and A.N. contributed new reagents/analytic tools; D.W., S.-J.H., S.I.Z., and A.N. analyzed data; and D.W. and A.N. wrote the paper. The authors declare no conflict of interest.Attached Files
Published - PNAS-2014-Wu-1720-5.pdf
Supplemental Material - pnas.201323989SI.pdf
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Additional details
- PMCID
- PMC3918769
- Eprint ID
- 44195
- Resolver ID
- CaltechAUTHORS:20140307-132612925
- DE-AC02-05CH11231
- Department of Energy (DOE)
- DMR-9724240
- NSF
- DMR-520565
- NSF
- DE-AI-01-05EE11105
- Department of Energy (DOE)
- Created
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2014-03-10Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field