Characterization of activated carbon, graphitized carbon fibers and synthetic diamond powder using TPD and DRIFTS Original Research Article

A high surface area activated carbon, graphitized carbon fibers and synthetic diamond powder were characterized by X-ray diffraction, temperature-programmed desorption and diffuse reflectance infrared (IR) spectroscopy (DRIFTS). The activated carbon was analyzed as received as well as after either a nitric acid treatment to introduce oxygen functional groups on its surface or a high temperature treatment (HTT) in H2 at 1223 K to remove surface groups. TPD evolution profiles of CO and CO2 were combined with DRIFTS spectra of these carbon surfaces before and after pretreatments in H2 at 723 and 1223 K to provide complementary information regarding the nature of these surface groups. Significant amounts of both low- and high-temperature CO2 desorption occurred from the HNO3-treated carbon, indicating that both strongly and weakly acidic groups were introduced on this surface and, in addition, comparable amounts of CO and CO2 were desorbed. With the graphitized carbon fibers and diamond powder, larger amounts of CO were desorbed compared to CO2, indicating the presence of predominantly weakly acidic or non-acidic groups on these surfaces. For the HNO3-treated carbon, IR peaks associated with surface carboxylic acid groups initially present disappeared after treatment at 723 K, while bands attributable to anhydride, quinone, ester and phenol species remained. Small amounts of ether, furan and phenol groups were detected on the graphitized fiber surface, while ketonic carbonyl groups were dominant on diamond. Significant amounts of chemisorbed hydrogen were also detected, presumably occurring on edge atoms made available by the decomposition of CO-yielding complexes at temperatures >873 K.