Student: Jose Edgardo Lopez Cazares
Committee: Dr. Jerry Y. S. Lin
Abstract:
P-xylene is a volatile organic compound with relevant industrial applications mainly used as raw material in the polyesters industry. It is also known that safety precautions should be taken due to its inherent fire and toxicity hazards [1]. Effective safety management requires on-site accurate detection for this low reactivity compound. From the available analysis methods, chemo-resistive sensor technology has demonstrated to detect and monitor reliably in real-time the presence of hazardous reducing gases. Its relevance has not only a positive impact on the industrial workplace sector but also on the daily-life quality of indoor spaces. Their working principle and performance rely on the extent of change of the electrical properties of semiconductor metal oxides (e.g., ZnO) when are exposed to reducing analytes that carry out surface redox reactions, charge transfer, and adsorption-desorption processes. However, most of the ZnO sensor research works are commonly devoted to assessing its operation under steady-state conditions. This work evaluated the kinetics of the response and the recovery stages of ZnO sensor devices under a constant p-xylene concentration in air at different temperatures. This work revealed a good correlation with a Langmuir first-order kinetics model. Additionally, the analysis of the dependence of the kinetic time constants of the response and recovery shown a larger energy barrier for the sensor recovery stage than that exhibited during the response stage (20 KJ/mol vs 88.05 KJ/mol). Such experimentally obtained parameters for the ZnO sensor are in good agreement with the reported range (77-106KJ/mol) in several reports [2][3][4][5] that only address O2 chemisorption on pure ZnO films (recovery process). On the contrary, this work is the first experimental effort to determine the adsorption barrier, 20 KJ/mol, for p-xylene on a composite Au-ZnO sensor. Recent molecular simulation work provides insights into the activation energy of p-xylene adsorption on a pure ZnO surface (130 KJ/mol) [6]. This discrepancy is explained by the fact that Au doping promotes a catalytic effect decreasing the activation energies and improving the sensor response.
Zoom Room: https://asu.zoom.us/j/2462257468
Presentation Time: 12:00-1:00 PM (Arizona Time)
