Gold nanoparticles (GNs) have shown tremendous catalytic activity for a variety of reactions such as, alcohol oxidation, reduction of aromatic nitro-compounds, CO oxidation, and the water gas shift (WGS) reaction. Much is known about the catalytic properties of GNs: the reaction rate and selectivity are highly dependent on the size and the nature of crystallographic orientation of the support. For example, a decrease in the size of the GNs typically results in an increase in activity, and GNs on certain crystal planes (110, and 100) of a ceria support were found to be most active for the WGS reaction. However, there is little information on the effect of the environment.
Graphene and graphene oxide (GO), a highly oxidized form of graphene, are materials with incredibly interesting chemical and mechanical properties. These materials can have high surface areas and electrical properties can be tuned by reducing the amount of oxygenates on the surface. We have begun to explore how graphene oxide can be used to modify properties of gold nanoparticles. We hypothesize that the catalytic activity of gold nanoparticles on a metal oxide support can be modified by a graphene oxide over-coat. The graphene oxide coating could help reduce metal leaching during reaction, and modify catalytic activity through electron donation/withdrawal as well as hydrogen bonding with substrates. A polymer wrapped gold colloid is deposited on nonporous silica and treated with ozone to gently remove organic moieties which results in less than 2 nanometer gold. The silanols on the silica are then converted to amines to produce a sample that is positive in charge at neutral pH. Submicron graphene oxide, which is electrostatically negatively charged, is then added and due to the favorable electrostatic interaction wrapped around the silica effectively capping the gold and silica. The catalytic activity for these gold nanoparticles versus non coated particles was tested for a variety of reactions including the catalytic reduction of p-nitrobenzaldehyde.