P22 virus templated synthesis of plasmonic photocatalytic nanostructures
The objective of the work presented in this dissertation is to examine the fabrication of novel viral-templated gold-cadmium sulfide (Au-CdS) plasmonic photocatalytic nanostructures and to investigate their photocatalytic behavior via photodegradation of methylene blue. Bacteriophage P22 shells, assembled from 420 copies of coat protein, have been demonstrated to act as selective biotemplates for the growth of ordered gold nanostructures in two different routes: 1) the incubation of gold precursor with P22 biotemplates before the addition of reducing agent; 2) and the direct reduction of gold precursor in the solution of P22 biotemplates with a pre-existing reducing agent. In both routes, gold nanocrystals could find their selective binding sites to form an ordered nanostructure over P22 shells. However, in our current study, the incubation of inorganic precursor with biotemplates, which is a common practice in the biotemplated synthesis of inorganic nanoparticles, did not produce better outcome compared to direct reduction without protein/gold precursor interaction. Genetically engineered scaffolding proteins evenly positioned inside P22 virus-like particles (VLP) can act as selective biotemplates for the constrained growth of CdS nanocrystals. The formation of CdS confined inside the VLP involves initial uniform nucleation and growth at the genetically engineered sites of the scaffolding proteins, followed by a more stochastic growth for longer reaction periods. The presence of the biotemplates does not affect the reaction order for the formation of CdS, but significantly influences the rate constant for the hydrolysis of thioacetamide (TA) and subsequent reaction of released S ions with Cd2+. Combining the coat protein templated synthesis of gold and the scaffolding protein templated synthesis of CdS, we have been able to utilize genetically engineered P22 VLP as a robust nanoplatform for fabricating gold/CdS plasmonic photocatalytic nanostructures. The controlled formation of gold nanoparticles on the outer shell of VLP-CdS dramatically enhances the photoactivity of CdS confined inside the VLP. However, the gold nanoparticles by themselves exhibit no significant effect on the photodegradation of MB. These findings are relevant for the synthesis of a wide range of alternative plasmonic photocatalytic materials with desired components, architectures, and performance.