Studies on the Gas Sensing Properties of Calixarenes

• Main Authors: Chiang, Chun-Yi, 江俊毅
• Other Authors: Liu, Chin-Hsin
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/42500848086603691036

碩士 === 國立臺灣科技大學 === 化學工程系 === 90 === Calix[n]arene with n=4,6,8 (denoted as CA[n]), and with —H, -iso-propyl, -tert-butyl, -CH2N(CH3)2, -CH2COOH groups at para- positions were utilized as sensing materials for various volatile organic compounds (VOCs), and were investigated with quartz crystal micro- balance (QCM) technique. Results show that both the amount of VOCs molecules adsorbed and the response speed increase with the number of rings, and the effects of substituted group can be summarized as following: (1)Non-polar substituents: with —H groups at para-positions, the amount of adsorption is least, due to the “shallowness” of the cavity, while with either -iso-propyl or -tert-butyl groups at para-positions, much higher adsorptivities are observed towards non-polar VOCs, such as benzenes, and -tert-butyl is better than -iso-propyl in this aspect, due to larger van der Waal forces. However, in the case of CA[4], those with -tert-butyl groups would adsorb less VOCs molecules than those with -iso-propyl groups, due to the steric-hindrance effect of the bulkier -tert-butyl group that would block the smaller opening of the CA[4] cavity. (2)Polar substituents: Excellent gas adsorptivities towards acids and amines are observed when substituents are -CH2N(CH3)2 and -CH2COOH, respectively; mainly due to acid-base interactions. In this study, we studied the effects of the cavity size and substituents on the sensitivity and selectivity of calix[n]arenes towards VOCs. A two-step sorption model, combing Langmuir and Henry models, is also presented.