Semi-conducting metal oxide (SMO) based sensors for the detection of chemical warfare agents (CWA) and toxic industrial materials (TIM) exhibit sensitivities on the order of parts per billion. SMO based sensors have potential advantages over other methods of chemical agent detection in terms of size, weight and cost. One limiting factor in the use of SMO based sensors for CWA/TIM detection is that these materials are non-selective. That is, there are many molecules, in addition to the agent of interest, which will yield positive detection results. The proposed work is focused on improving the selectivity of semi-conducting metal oxide sensors and the reduction of false positive responses.
Controlling the adsorption of CWA/IM onto the surfaces and their subsequent diffusion through the pores and key factors in the design of such devices. This can be done via a pre-filtering scheme, where a mixed gas stream in passed through a ceramic membrane or activated carbon. Pore size, shape and chemical composition can be tailored to selectively adsorb the molecule of interest. After being concentrated in the pre-filter, the CWA/TIM is released by a chemical displacer or a thermal pulse and sent to the SMO for detection. An alternative approach to pre-filtering is to use templating to form porous semi-conducting metal oxides with high selectivity to the target molecule. In the proposed work, molecular simulation is used to determine the absorption behavior of CWA and their simulants in the molecular sieve MCM-41.
The difficult nature of performing experiments on CWA/TIM motivates the proposed use of computational methods. Molecular simulations is well suited to the study to the toxic material and can be used to extract information on the roles specific intermolecular interactions play in the adsorption process. Because appropriate models (force fields) so not exist for the molecules of interest, significant effort is proposed on the development of transferable united-atom force fields for organophosphates, including the chemical warfare agents sarin and VX. The development of molecular models is a required first step in use of simulation for the design of SMO based sensors. These molecular models will allow for the use of simulation to investigate the effects of pore size, shape and composition on the selectivity of porous materials with respect to specific CWA/TIM. Atomistic simulations and ab initio methods are used to identify specific porous structures (shape/size) with the high selectivity necessary for the sensing of CWA/TIM with low false positives.
Broader Impacts
Recent world events, such as the release of sarin gas into the Tokyo subway system and the current concern over potential adversaries suspected development and use of chemical and biological warfare agents underscore the importance of developing highly mobile, accurate sensors and decontamination equipment for these materials. As an outcome of the proposed research, the PI expects to overcome the current limitations of the field by developing the necessary computational infrastructure for the use of simulation in the design of novel templated molecular recognition materials. These templated molecular recognition materials hold the promise of high selectivity and sensitivity to chemical warfare agents compared to other porous materials. Development of adsorbents with high affinity to a specific target molecule is expected to result I improved sensors, filters and catalytic materials. Such developments are expected to reduce the threat of the use of chemical warfare agents by terrorist organizations, improving national security and public health. Furthermore, accurate force fields describing the interactions between quest molecules and metal oxide surfaces will allow other research groups to use molecular simulation as a too to design novel adsorbent and catalytic materials for other purposes.
This research is integrated with education. Undergraduates, particularly underrepresented minorities and women, are encouraged to participate in undergraduate research projects. The undergraduate research experience is used as a mentoring tool to improve the recruitment and retention of students in minority groups with historically low retention rates.
