(498d) Building a 3D Graphene/Graphene Oxide Matrix for Cooperative Catalysis

Reduced graphene oxide and
graphene oxide (GO) based materials have many unique properties that make them
intriguing candidates for catalyst supports. These materials have high surface
areas, high adsorption capacities, can transfer π-electron density to
supported catalytic metal particles, can have high electron mobility which can
facilitate electron transfer during catalytic reactions, and also can be
chemically transformed through the large number of oxygenate groups on the
surfaces. One of the challenges encountered when utilizing graphene oxide materials
for catalyst supports is the regraphitization and reduction in surface area
when the catalyst is dried to a powder. The reduced graphene oxide layers
restack via the strong π-π interactions between layers. This leads to
a reduction in access to active sites on the interior basal planes of the
catalyst. A number of methods have been explored to reduce this restacking
interaction, for example, by creating 3D structures such as
graphene-organic-frameworks (GOFs), graphene aerogels, and graphene hydrogels.

We have explored using 3-D graphene/graphene
oxide based framework to create catalytic ?pockets? in which we can engineer a
micro- or nano- environment that can influence catalytic performance. These
?pockets' are designed to create a partially nanoconfined or sterically
hindered environment in which functional groups are placed near each other to
work cooperatively and influence the catalytic active site or the reaction
mechanism pathways. We made use of graphene oxides synthesized with nanosized in-plane
defects or ?holes' that also have a high density of carboxylic acid groups and that
allows for quicker diffusion of reactants and products to the interior areas of
the 3-D structure. By reacting the GO support with compounds such as the
diamine compound, 4-aminobenzylamine, the reaction of the two primary amine
groups with the carboxylic acid or epoxy groups on the surface of the graphene oxide support would form a bridge between two separate
graphene oxide sheets. The phenyl ring of this compound provides enough
rigidity to increase the d-spacing of the material, forming pockets, and thus
preventing re-graphitization. The introduction of catalytically relevant amine
functional groups is accomplished by the utilization of another diamine complex,
N-Boc-p-phenylenediamine or N-Boc-ethylenediamine, in which one of the amine
functional groups is temporarily protected to prevent it from also becoming a
bridging species. The protecting N-Boc group is then chemically or thermally
removed which then result in a catalyst with a free primary amine can be
located near residual surface carboxylic acid groups. The synthesis and
characterization of 3-D structures prepared by this and similar methods will be
described, including their structural, chemical and catalytic properties.