UC Riverside

The overall objective of this work is the development of a high density sensor array using singe wall carbon nanotube (SWNT) hybrid structures as the platform material for the realization of highly sensitive, selective and discriminative gas sensors for monitoring of industrial and automotive emissions in the environment. To conceive such desired sensor characteristics SWNTs were surface functionalized with metal and metal oxide active materials [i.e. ZnO, Ag, Pt, Pd, Au] to target specific analytes. Detailed analysis of ZnO electrodeposition on to SWNTs was performed to investigate structure property relations between ZnO particle size, density, material quality, catalyst type, and combination thereof, towards the sensing performance and analyte specificity.

Room temperature gas sensing performance of environmentally significant gases such NH3, SO2, H2S, NO2, CO, CO2, benzene derivatives, alkanes, and alcohols was evaluated using the metal and metal oxide hybrid structures. The ZnO-SWNT hybrid structures exhibited characteristic selectivity towards H2S, with enhanced sensitivity, response and recovery time contingent of crystal orientation; additionally as synthesized ZnO-SWNT hybrid structures displayed conductance response cognizance of xylene isomers (ortho, para, meta). Furthermore, at the hand of sequential incorporation of a metal catalysts (Au, Ag, Pt, and Pd), the ZnO-SWNT system showed distinct charge dependant pattern recognition towards less detectable analytes such as SO2 and NO2; metal-SWNT hybrid structures with Pd as the second deposited metal demonstrated enhanced sensitivity towards NO2 and NH3 due to the enhanced dissociation of the molecular adsorbate on the catalytically active Pd nanoparticle surface.

Understanding of the deposition process was then extended to the deposition of binary metals Au, Pd, Pt, followed by sequential deposition of a combination of metals. Emphases was placed on both the gas sensing aspect of the resultant hybrid structures, and also on the ability to site specifically control the deposition of the second metal. A detailed examination of these hybrid nanostructures and the nature of their responses towards different gaseous environments was studied and compared with the performance of unfunctionalized carbon nanotubes.