Abstract:
This research focuses on synthesizing silver (Ag)/titanium dioxide (TiO2) photocatalysts by either
chemical reduction or photodeposition. Ag particles act as cocatalysts by trapping photoexcited electrons
and suppressing electron-hole recombination in TiO2. The hypothesis was that the shape and surface
morphology of Ag cocatalyst could affect the activity and selectivity of a photocatalytic process.
Truncated Ag nanoprisms on TiO2 were synthesized by either chemical reduction or
photodeposition. Only chemical reduction produced truncated Ag nanoprisms of consistent shape and
attachment to TiO2. This is a seed-mediated synthesis, where Ag seeds were deposited on TiO2 first to
provide strong anchoring, then Ag was additionally deposited to form truncated nanoprims.
In a different approach, Ag was deposited on TiO2 through photodeposition using the same
corresponding chemicals except reducing agent. While photodeposited Ag nanoparticles appear to
strongly adhere to TiO2, they grow big and multifaceted or rounded. The shape-guiding and size limiting
effects of the capping ligands are virtually absent in photodeposition.
The performance of the synthesized Ag/TiO2 nanocomposites was tested in the photocatalytic
reduction of m-dinitrobenzene in non-aqueous solution under visible light of 400-405nm wavelength.
When prepared with the same amount of Ag by weight of TiO2, the two types of catalysts behave
differently. Truncated triangular Ag nanoprisms deposited by chemical reduction, where the majority of
the exposed surfaces on cocatalyst are of {111} close-packed type, exhibit 100% conversion and 100%
selectivity for the reduction of m-dinitrobenzene to m-nitroaniline. Photodeposited irregular Ag
nanoparticles on TiO2, where multiple facets are exposed on cocatalyst, exhibit 100% conversion of mdinitrobenzene into two products: m-nitroaniline (selectivity 15%) and m-phenylenediamine (85%). This
demonstrates that more uniform surfaces of the metal cocatalyst lead to more selective conversion.
