Directed Synthesis of Asymmetric Au/ZnS Photocatalytic Nanomaterials by M13 Bacteriophage Spheroids
- Author(s): Plank, Joshua
- Advisor(s): Haberer, Elaine D
- et al.
Recently, the M13 bacteriophage has been developed as a versatile material template, where it has been shown to bind and grow a wide range of materials both organic and inorganic. Also, despite the discovery over 30 years ago of its ability to transform into a range of structures, far removed from its native filament, its other forms have been barely researched for their capabilities in nanostructure assembly. The M13, in all of its forms, is an asymmetric, bifunctional template, meaning it can grow two materials together, in a non-centrosymmetric fashion. Not only is this fairly unique among virus templates, but is also extremely useful in the creation of catalytic materials. A material’s catalytic properties can be augmented or enhanced when combined with other materials.
Semiconductor photocatalysts tend to be enhanced when combined with other semiconductors or metals, which help with light absorption and the charge separation necessary for catalytic reactions. The orientation and assembly of the combined materials can have significant impacts on their functionalities, where growing the materials over the surface of one another can limit their catalytic activity. For these types of particles, reactive surface area is a major contributing factor in performance. Therefore, with Janus-like, asymmetric particles, which expose equal amounts of each material, photocatalytic properties can be expected to be greatly enhanced.
In this study, we investigated the M13’s spheroid form in its controlled synthesis of ZnS and then Au, and the photocatalytic activity of these materials. We showed that the spheroid transformation process required modification with the ZnS and Au binding peptides both displayed on the virus. We then demonstrated that the growth of each material was limited to their respective protein group, and could be controlled for its size. When both Au and ZnS were present on the template, the combined particle could be used in the photocatalytic degradation of multiple dyes, and the activity of which was greater than either of materials alone. Further, the addition of Au to ZnS allowed photocatalytic activity under visible light excitation, which is normally impossible for the wide bandgap semiconductor. In the development towards a more efficient photocatalyst nanostructure, hierarchical structures were then assembled, in an effort to create so-called
core satellite structures of varying complexity. These structures made use of a Au nanoparticle as the core, with M13 filaments or spheroid decorating its surface, which could be used to synthesize ZnS. This research laid the groundwork for a much more efficient photocatalytic nanostructure.