Encapsulation and Release Characteristics of Carbon Dioxide in alpha-Cyclodextrin

摘要

Encapsulation and release of carbon dioxide (CO_2) into and from alpha-cyclodextrin (alpha-CD) was studied.Initial moisture content of alpha-CD and CO_2 pressure were found to have affected the encapsulation behavior.The increase of CO_2 pressure has constantly accelerated the encapsulation rates and increased the maximum inclusion ratio,whereas the increase of initial moisture content showed no consistent effect.The saturated alpha-CD solution produced the inclusion complex crystal of similar inclusion ratio to solid alpha-CD.The release characteristics of inclusion complexes were also monitored at various relative humidities at 25 deg C.Predominantly,increase in storage humidity accelerated the release of CO_2.The inclusion complex crystal prepared from saturated alpha-CD solution showed the most stable release characteristic at all storage humidities investigated.The encapsulation and the release characteristics were analyzed using the first-order reaction equation and the Avrami's equation respectively,in order to estimate the rate processes of encapsulation and release.The FT-IR spectra of inclusion complexes presented an absorption band at wavenumber around 2338 cm~(-1),indicating CO_2 molecules resided inside the alpha-CD cavities in gaseous state rather than being bound to the hydroxyl groups of alpha-CD.Powder X-ray diffractometry was carried out to investigate the crystal lattice structure of alpha-CD and inclusion complexes.Scanning electron microscopy was also performed for morphological examination.