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Novel Chemical Strategies for Gas Sensing and Separations Novel Chemical Strategies for Gas Sensing and Separations DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Chenhu Sun Graduate Program in Chemistry The Ohio State University 2015 Dissertation Committee: Professor Prabir K. Dutta, Advisor Professor Heather Allen Professor James Coe Copyright by Chenhu Sun 2015 Abstract 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 WO3 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℃ were carried out. Using the sensor design with the adjacent alignment of n-type WO3 and p-type Cr2O3 resulted in optimal performance. This sensor design exploits the different majority carriers in these two semiconducting oxides for selective NO gas sensing. The advantage of such a sensor system is that the device can be sensitive to NO at low ppb level (18 ppb detection limit) and discriminate against CO at concentrations a thousand-fold higher (20 ppm). The sensing mechanism was investigated by in situ diffuse reflectance infrared studies. Characterization of the adjacent p-n interface was done by scanning electron microscopy (SEM) and Raman imaging study. Practical application of this device is demonstrated by measuring NO in human breath samples. 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 NH3 (< 100 ppb), the change in resistance with NiO was anomalous at 300 ℃, the ii 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 -1 - band at 1267 cm , which was assigned to O2 and the change in intensity of this band with o time mirrored the transient change in resistance with 1 ppm NH3 at 300 C, indicating that - NH3 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 iii 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 SO2, 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 template- free 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. iv This dissertation is dedicated to my family. v Acknowledgments First and foremost I would like to express my greatest gratitude to my advisor, Professor Prabir Dutta, for providing me the opportunity to experiment in his lab and develop as a scientist. It was my honor to work with Dr. Dutta and pursue my PhD under his guidance. He has lead me to a new level of understanding science and it is undoubtedly worth spending five years on what I have gained from my interactions with him. Moreover, He went above and beyond the basics of being an advisor. He not only helped me with academics, but also acted as a confidant and mentor. I will remember most his kindness, his diligence, his enthusiasm in chemistry, his thirst for innovation, and his relentless scientific ethics. I am deeply indebted to the previous and current members of Dutta group, including Dr. Suvra Mondal, Dr. Maduraiveeran Govindhan, Dr. Michael Severance, Dr. Andrew Zane, Dr. Joselyn Del Pilar, Dr. Max Mullen, Subhrakanti Chakraborty, Bo Wang, Sweta Shrestha and Adam Fulmer. I thank them for their invaluable assistance on my research and willingness to share their insight and wisdom. I also thank the visiting scholars Dr. Jiawen Jian, Dr. Xiaogan Li and Dr. Yangong Zheng for their collaboration and friendship. My research involved contributions from many facilities and their respective scientists at OSU. I would like to thank the staff of the Center for Electron Microscopy and Analysis (CEMAS) and Campus Microscopy & Imaging Facility (CMIF), particularly Hendrik vi Colijn, Cameron Begg, Brian Kemmenoe and Richard Montione for their help acquiring the electron micrographs that constitute part of this work. I would also like to thank Gordon Renkes and Lisa Hommel in CBC for their fruitful discussion and instrumental support. As an international student, being at the United States for the last five years has been the most amazing experience of my life. I would like to thank all my American friends who have helped me enjoy the land of the free and the home of the brave, particularly my host family Vicky and Chip Shillington who treat me like a real family member and take care of my life in Columbus. I would like to thank my Chinese friends who enrolled in the class of 2015 with me, including Xijun Piao, Wenlong Lian, Lin Chen, Mingzhe Yu, Xin Fang, Fang Liu, Yu Lu, Zhongjie Huang, Mengqi Zhou, Zhaomin Chen and Ran Li for the wonderful memories they gave me in the past five years. Finally, I would like to thank my parents and grandparents, without their love, encouragement and support I would not be here and become the person I am today. vii Vita 2008................................................................B.S. Chemistry, Hunan University 2010................................................................M.S. Analytical Chemistry, Hunan University 2010 to present ..............................................Graduate Research/Teaching Associate, Department of Chemistry and Biochemistry, The Ohio State University Publications [1] C Sun, P K Dutta. Selective detection of part per billion concentrations of ammonia using a p-n semiconducting oxide heterostructure. Sensors and Actuators B: Chemical, 2015, in press. [2] L Zhao, Y Chen, B Wang, C Sun, S Chakraborty, K Ramasubramanian, P K Dutta, W S Ho. Multilayer zeolite Y/polymer composite membrane structure for CO2/N2 separation. Journal of Membrane Science, 2016, 498, 1-13. [3] B Wang, C Sun, Y Li, L Zhao, W S Ho, P K Dutta. Rapid synthesis of faujasite/polyethersulfone composite membrane and application for CO2/N2 separation. Microporous and Mesoporous Materials, 2015, 208, 72-82 [4] A Fulmer, M Mullen, C Sun, P K Dutta. Novel strategies for development of gas viii sensors for combustion and medical applications. Proc. Of SPIE, 2014, Vol 9083, 90830W-1 [5] C Sun, G Maduraiveeran, P K Dutta. Nitric oxide sensors using combination of p- and n-type semiconducting oxides and its application for detecting NO in human breath. Sensors and Actuators B: Chemical, 2013, 186, 117-125 Fields of Study Major Field: Chemistry ix Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. vi Vita
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