(174ci) Plasmonic Photocatalysis for Gas-Phase Toluene Degradation: Effect of Illumination Time on Catalyst Stability

Plasmonic Photocatalysis for degradation of gas-phase toluene in a recirculating batch reactor was investigated by examining catalyst activity versus illumination time, particle size (and associated inter-particle distances). Each plasmonic photocatalyst sample was prepared by depositing a silver thin film, via electron beam evaporation, onto a layer of zinc oxide nanoparticles on a ribbed aluminum substrate. Hemispherical silver nanoparticles (Ag NP) were then formed by rapid thermal annealing of each sample in a nitrogen atmosphere at 500 C for 1 minute, followed by rapid cooling. Prepared samples were then tested for their photocatalytic activity in a plate-type flow-through reactor placed in an air-tight steel chamber, into which toluene was then injected via a septum. For each run, once toluene concentration was stable, the run was initiated by switching on the ultraviolet A (UVA) lamps (peak at 365 nm, FWHM ~20 nm). Experimental runs were repeated numerous times for each sample to determine how photocatalytic activity varied as a function of Ag NP size (and associated inter-particle distances), and catalyst deactivation over illumination time. Apparent quantum yields and reaction rate constants (pseudo first-order kinetics) over the course of each experimental run were compared to observed experimental degradation rates of toluene, showing that apparent quantum yield alone may not always provide sufficient information on catalyst performance. The results demonstrate that the plasmonic photocatalysts showed significant improvement over pure zinc oxide and, in some cases, over titanium dioxide (P25), but that the catalyst activity is consistently diminished as the plasmonic photocatalyst samples are illuminated with UVA light. The results of this study support the findings that plasmonic photocatalysts show significant improvement over baseline materials (zinc oxide, titanium dioxide), but that deactivation of plasmonic photocatalysts, which is a phenomenon not thoroughly investigated nor often cited in the literature of plasmonic photocatalysts, is an important challenge that must be overcome prior to commercialization of plasmonic photocatalytic materials.