Preparation and study of adsorbents based on silica nanoparticles and β-cyclodextrin
Abstract
The work is devoted to the preparation and study of new functional materials with a chiral structure
for sorption and chromatographic technologies used for the separation and concentration of organic compounds, including isomers of various types and optically active compounds. To obtain a composite adsorbent, silicon dioxide nanoparticles (butasil) were modified with unsubstituted β-cyclodextrin, and then they were applied on a silica support Chromaton N-AW. Also an adsorbent with silicon dioxide nanoparticles without cyclodextrin was also obtained. Using low-temperature nitrogen adsorption, the geometric characteristics of both adsorbents were determined. The study of the adsorption properties of adsorbents with respect to pairs of organic compounds of various nature was carried out by gas chromatography. From the obtained temperature dependences of the Henry adsorption constants, the thermodynamic characteristics of adsorption for the studied compounds were calculated. It was found that for both studied adsorbents, the values of specific surface areas are close and significantly differ from the corresponding values for butasil (176.4 m2/g) and solid support (2-4 m2/g). The modification of butasil nanoparticles with β-cyclodextrin seems to lead to a slight increase in the specific surface area and pore volume of the Bsil/CD adsorbent compared to the Bsil adsorbent due to intramolecular cavities. Based on the values of the thermodynamic characteristics of adsorption, it was concluded that, in the case of the Bsil/CD adsorbent, for the molecules of the studied adsorbates, a guest – host complexation is detected. In this case, for cyclic and bicyclic structures, difficulty is observed with inclusion in the cavity. Further, for alkanols, both outer-sphere and intra-sphere complexation is possible.
A possible structure of silicon dioxide nanoparticles modified with unsubstituted β-cyclodextrin was
proposed based on the obtained data. In the proposed structure, butyl fragments on the particle surface play the role of «guests» and are included in the macrocyclic cavities of cyclodextrin molecules. Thus, butyl
fragments on the particle surface act as anchor groups orienting macrocyclic molecules. The resulting orientation
of cyclodextrin molecules is favorable for the formation of complexes of different stability with enantiomeric
molecules, which is showed in high enantioselectivity for terpenes (limonene, camphene, pinene).
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References
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