Characterization of activated carbon, graphitized carbon fibers and synthetic diamond powder using TPD and drifts

A high surface area activated carbon, graphitized carbon fibers and synthet ic diamond powder were characterized by X-ray diffraction, temperature-prog rammed desorption and diffuse reflectance infrared (IR) spectroscopy (DRIFT S). 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 H-2 at 1223 K to remove surface g roups. TPD evolution profiles of CO and CO2 were combined with DRIFTS spect ra of these carbon surfaces before and after pretreatments in H-2 at 723 an d 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 stro ngly and weakly acidic groups were introduced on this surface and, in addit ion, comparable amounts of CO and CO2 were desorbed. With the graphitized c arbon fibers and diamond powder, larger amounts of CO were desorbed compare d to CO2, indicating the presence of predominantly weakly acidic or non-aci dic groups on these surfaces. For the HNO3-treated carbon, IR peaks associa ted 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 group s were detected on the graphitized fiber surface, while ketonic carbonyl gr oups were dominant on diamond. Significant amounts of chemisorbed hydrogen were also detected, presumably occurring on edge atoms made available by th e decomposition of CO-yielding complexes at temperatures >873 K. (C) 1998 E lsevier Science Ltd. All rights reserved.