Journal article
Guest–host interactions of a rigid organic molecule in porous silica frameworks
Proceedings of the National Academy of Sciences - PNAS, Vol.111(5), pp.1720-1725
02/04/2014
Handle:
https://hdl.handle.net/2376/116149
PMCID: PMC3918769
PMID: 24449886
Abstract
Confinement of molecules in nanoscale pores is important in both science and technology. This paper reports a systematic analysis of the structural, thermodynamic, and dynamic behavior on confinement of a rigid organic molecule in a series of silica frameworks with different pore sizes (0.8 to 20.0 nm). The comprehensive data set enables the strength of guest–host interactions to be calculated; structure, phase, and dynamics of confined guests in pores of various diameters to be analyzed; and different types of inclusion to be described. The evolution from single-molecule confinement to multimolecule adsorption/confinement to nanocrystal confinement is documented. This provides a conceptual model linking confinement on various length scales.
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.
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Details
- Title
- Guest–host interactions of a rigid organic molecule in porous silica frameworks
- Creators
- Di Wu - Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU)Son-Jong Hwang - Division of Chemistry and Chemical EngineeringStacey I Zones - Catalyst Department, Chevron Energy Technology Company, RichmondAlexandra Navrotsky - Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit (NEAT ORU)
- Publication Details
- Proceedings of the National Academy of Sciences - PNAS, Vol.111(5), pp.1720-1725
- Academic Unit
- Chemical Engineering and Bioengineering, School of
- Publisher
- National Academy of Sciences
- Identifiers
- 99900547746501842
- Language
- English
- Resource Type
- Journal article