Stability and Kinetics of Silica-Protected Plasmonic Photocatalysts for Gas-Phase Degradation of Total Volatile Organic Compounds

Stability and kinetics of plasmonic photocatalysts for gas-phase toluene degradation were assessed by monitoring total volatile organic compound (TVOC) concentration versus UV-A illumination time in a recirculating batch reactor (plate-type flow-through). Plasmonic samples were produced by either coating silver on, or layering silica-protected or unprotected silver beneath, the photocatalyst. Samples were modeled using Finite difference time domain simulations, and characterized. Experimental results show that silver-coated photocatalysts, and photocatalysts layered over unprotected silver, exhibit initially high TVOC degradation rates compared to TiO, but suffer from relatively rapid deactivation attributed to silver oxidation. Photocatalysts layered over silica-protected (i.e., silica-coated) silver exhibited improved stability versus photocatalysts layered over unprotected (i.e., uncoated) silver, and demonstrated more than 50% increase in reaction rate constant and more than a threefold increase in apparent quantum yield over the non-plasmonic control sample (TiO over SiO). The results of this study demonstrate that a silica layer can help slow down fouling of silica nanoparticles, and that silica-coated silver nanoparticles not only help speed up reaction rate overall but also appear to speed up release of adventitious carbon from the photocatalyst surface during the initial phase of a reaction. Graphic Abstract: [Figure not available: see fulltext.].