Affiliation: | aDepartment of Chemistry, National Chung Hsing University, Taichung 402, Taiwan, ROC bDepartment of Applied Chemistry, Providence University, Shalu, Taichung Hsien 433, Taiwan, ROC cDepartment of Chemistry, Chinese Culture University, Taipei 111, Taiwan, ROC dCenter for Measurement Standards, Industrial Technology Research Institute, Hsinchu 300, Taiwan, ROC |
Abstract: | In situ preparation of polypyrrole (Ppy) by photo-polymerization coated on a quartz crystal microbalance (QCM) as a low humidity sensor was reported. Different concentrations of Ppy films say 0 wt.% (as blank), 0.1, 1, and 10 wt.% were investigated to measure humidity concentrations between 14.7 and 5412.5 ppmv. The adsorption/desorption behavior was also examined at humidity concentration 510.2 ppmv. The sensitivities of 0, 0.1 and 1 wt.% Ppy films at 51.5 ppmv were 0.143, 0.219 and 0.427, respectively. For 1 wt.% Ppy, the highest sensitivity was obtained. The slope and correlation coefficients (R2) for 1 wt.% Ppy at the ranges of 14.7–898.6 ppmv were 0.0646 and 0.9909, respectively. A series of molecular simulations have been carried out to calculate bond energy for the water molecule interaction with Ppy, which was found to be 3 kcal/mol indicating the existence of hydrogen bonding during the sorption process. Based on Langmuir isotherm adsorption assumption, for 0.1 and 1 wt.% Ppy films, the association constants were 2606.30 and 5792.98, respectively. This larger association constant for 1 wt.% Ppy film explains higher sensitivity. |