Novel Chemical Strategies for Gas Sensing and Separations

Detection of trace gases are relevant for environmental, combustion and health-related applications. Resistive semiconducting metal oxide sensing platforms are extensively studied for gas detection. Two important aspects of gas sensing are enhancing sensitivity and selectivity. Mixtures of WO 3 and Cr2O3 in varying weight ratios as well as adjacent alignment of these two powders were both examined as possible designs for NO-selective sensor. Studies focused on resistance measurements toward NO and CO at 300&;A sensor platform with n-type In2O3 and p-type NiO placed side by side was developed for the detection of trace NH3 . Our focus was to develop an ammonia sensor with ppb sensitivity, with possible application in breath analysis. With low concentrations of NH 3 (< 100 ppb), the change in resistance with NiO was anomalous at 300°C, the resistance decreased and then gradually increased over tens of minutes before decreasing again to reach the baseline. In situ diffuse reflectance infrared spectroscopy exhibited a band at 1267 cm-1, which was assigned to O2- and the change in intensity of this band with time mirrored the transient change in resistance with 1 ppm NH3 at 300°C, indicating that NH 3 chemisorption was correlated with the O2- species. Taking advantage of the transient resistance decrease of NiO with NH3, and combining the In2O3 and NiO allowed selectivity enhancement towards NH3 at concentrations as low as 100 ppb. Interference to CO, NOx and humidity were studied by selecting a suitable combination of both oxides, the response to CO at <10 ppm could be negated. Similarly, with NO at <10 ppb, there was minimal sensor response. The sensor was used to analyze NH3 mixed into human breath at 10- 1000 ppb concentrations. Water had to be completely removed from the breath via a moisture trap, since water interfered with the NH3 chemisorption chemistry. Potential applications of this sensor platform in breath analysis are discussed.;Chemical absorption by aqueous amine solution and membrane gas separation are the leading technologies for CO2 capture. A simple, fast, and robust method was developed for assessing the effect of SO2 on CO2 absorption with monoethanolamine (MEA) solution by Horizontal Attenuated Total Reflectance (HATR) monitoring. This method aims at monitoring the influence of SO2 on CO2 absorption process by MEA, and obtaining information on speciation, concentration and kinetics. First, the absorption bands observed during CO2 reaction with MEA was assigned to characteristic vibration modes. Then, CO2 absorption in the presence of SO2 was studied. The chemical speciation was evaluated by kinetic measurements and tentative solutions were examined for quantitative analysis. The present study used concentrations of SO2 that can be observed in a typical flue gas stream after the power plant desulfurization process. Speciation of the MEA/PZ blends was analyzed by the HATR spectrum and the influence of PZ on CO2 uptake by MEA was examined. As an application of IR spectroscopy for practical samples, the SO2 effect on an amine based polymer membrane was assessed. In the presence of SO 2, the individual amine carrier was studied by transmission FTIR and the membrane was studied by ATR FTIR.;A strategy for growing CHA zeolite membrane on polymer support and demonstrating its viability for CO2/N2 separation was reported. CHA zeolite nanocrystals were synthesized by interzeolite conversion of H-form zeolite Y nanocrystals. A rapid synthesis approach was applied to crystallization of CHA zeolites, with a 4∼6-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Chabazite-type zeolite membranes were synthesized via the secondary growth method using a templatefree solution. The variables affecting the quality of the resulting chabazite zeolite membranes including starting materials and synthesis time were investigated to determine the optimum conditions for chabazite membrane synthesis.