Evaluating the Catalytic Activity of Iron and Nickel Impurities in Bare High-Pressure High-Temperature Nanodiamond

Many metal nanoparticles are used as catalysts for various reactions and are held on supports. High-Pressure High-Temperature nanodiamonds (HPHT ND) are able to support metal nanoparticles even under strenuous chemical environments due to their robust nature. The production of HPHT ND includes the use of transition metals like iron and nickel which are left behind after synthesis. These metals have been shown to exhibit catalytic activity on their own so the iron and nickel impurities may give HPHT ND catalytic function. Here the catalytic ability of unmodified HPHT nanodiamond is studied using the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. Five samples from four different manufacturers are tested for their catalytic capabilities. The samples are also characterized to find their surface area and concentrations of Fe and Ni. There is no correlation between the concentrations of Ni and Fe and the apparent rate constant (Kapp), but the nanodiamond does exhibit catalytic activity from the various metals distributed through the lattice including iron and nickel. The apparent rate constant does correlate with the surface area of the sample with the exception of one sample from Eastwind Diamond classified as being 125 nm. This understanding of HPHT ND's catalytic activity allows for a better understanding of its use as catalytic supports and as catalysts for chemically harsh environments.