Polymeric Materials for Detection of Chemical Warfare Agents
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Chemical Warfare Agents (CWAs) are toxic synthetic chemicals that can have incapacitating or lethal effects. The 1997 Chemical Weapons Convention (1997 CWC) restricted production, stockpiling and use of CWAs, including their precursors/munitions, and classified them under specific categories. However, it is difficult to completely eliminate and prohibit production of CWAs, as many related chemicals find applications in manufacturing industries. Therefore, it is important to rapidly detect and identify CWAs present in our surroundings. Phosgene is a relatively simple molecule, easy to synthesize and more accessible among all commonly known CWAs. Therefore, it is of interest to devise gas sensing polymeric materials for its detection. However, due to the highly toxic nature and restricted use of phosgene or other CWAs, “simulants” or “surrogate” molecules (similar physical and chemical properties but less toxic than CWAs) are used in research and development of sensors for detection of CWAs. Formaldehyde being chemically and physically ‘similar’ to phosgene was selected as a surrogate gas while evaluating sensing materials. Polyaniline (PANI) and poly (2,5-dimethyl aniline) (doped and undoped with metal oxides) were tested for their ability to detect formaldehyde. PANI was doped with different loadings of In2O3 and P25DMA was doped with 20 wt.% of TiO2 and 10% NiO. Sensing materials were tested for their sensitivity and selectivity towards formaldehyde. Sensing materials were finally tested for their stability to evaluate effects of environmental factors on their sensing performance. Sensing materials were also characterized using techniques such as scanning electron microscope (SEM), energy dispersive x-rays (EDX), and X-ray diffraction (XRD), in order to explain and obtain extra corroboration of sorption trends. PANI doped with 1.25% In2O3 and P25DMA with 10% NiO were found to be most suitable for sensing formaldehyde with respect to sensitivity (low detection limit). With respect to selectivity, PANI doped with 5% In2O3 was most selective towards formaldehyde over benzene, whereas PANI with 10% In2O3 was most selective towards formaldehyde over acetaldehyde. Pristine PANI was equally selective towards formaldehyde and acetaldehyde. PANI and P25DMA sensing materials were found to be very stable with respect to other environmental factors (temperature and ageing). The final selection of an appropriate sensing material becomes an interesting trade-off between sensitivity and selectivity, if the objective is the identification of an ‘optimal’ sensing material. An optimal sensing material can be specific to the application and its targets. On considering all the results and observations, it was concluded that PANI with 5% In2O3 was optimal in that trade off sense.
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Bhoomi Het Mavani (2021). Polymeric Materials for Detection of Chemical Warfare Agents. UWSpace. http://hdl.handle.net/10012/17744