Monolithic Nanoporous Gold Foams with Catalytic Activity for Chemical Vapor Deposition Growth of Carbon Nanostructures

While
bulk gold is generally considered to be a catalytically inactive
material, nanostructured forms of gold can in fact be highly catalytically
active. However, few methods exist for preparing high-purity macroscopic
forms of catalytically active gold. In this work, we describe the
synthesis of catalytically active macroscopic nanoporous gold foams
via combustion synthesis of gold bis­(tetrazolato)­amine complexes.
The resulting metallically pure porous gold nanoarchitectures exhibit
bulk densities of <0.1 g/cm3 and Brunauer–Emmett–Teller
(BET) surface areas as high as 10.9 m2/g, making them among
the lowest-density and highest-surface-area monolithic forms of gold
produced to date. Thanks to the presence of a highly nanostructured
gold surface, such gold nanofoams have also been found to be highly
catalytically active toward thermal chemical vapor deposition (CVD)
growth of carbon nanotubes, providing a novel method for direct synthesis
of carbon nanostructures on macroscopic gold substrates. In contrast,
analogous copper nanofoams were found to be catalytically inactive
toward the growth of graphitic nanostructures under the same synthesis
conditions, highlighting the unusually high catalytic propensity of
this form factor of gold. The combustion synthesis process described
herein represents a never-wet approach for directly synthesizing macroscopic
catalytically active gold. Unlike sol–gel and dealloying approaches,
combustion synthesis eliminates the time-consuming diffusion-mediated
steps associated with previous methods and offers multiple degrees
of freedom for tuning morphology, electrical conductivity, and mechanical
properties.