This study describes the development of carbon nanofibers (CNF) for the vapor phase adsorptive removal of organic gaseous pollutants such as benzene and toluene and catalytic removal of inorganic pollutants such as sulfur dioxide and NOx. A web of micro/nano fibers was developed using activated carbon fibers (ACF) as substrate by the catalytic chemical vapor deposition (CVD) technique. The preparation steps consisted of flow-impregnation of ACF with nickel nitrate dissolved in acetone, followed by calcination at 573K and then reduction at 773K in a hydrogen atmosphere to convert oxide of nickel to metallic nickel. CNF was grown on the nickel supported ACF using a perforated disc reactor by decomposition of benzene at 1098K. The prepared CNF samples were further processed using heat and acid treatments. The resulting CNF samples were characterized by BET surface area, pore volume, pore size distribution, Boehm titrations, Fourier-Transform infrared spectroscopy (FT-IR) for acidic and basic surface functional groups, X-ray diffraction (XRD) spectroscopy for structural phases, scanning electron microscopy (SEM) for surface morphology and the state-of-art CHNSO analyzer for elemental analysis. The vapor phase removals of pollutants were carried out in a perforated tubular reactor. The exit gas concentrations were measured by gas chromatography with FID and TCD detectors for organic pollutants and sulfur dioxide respectively, whereas exit NOx concentration was measured by NOx analyzer. The effects of various operating conditions such as nickel concentration, adsorption temperature and pollutants concentration on removal efficiencies were studied. The breakthrough data for benzene and toluene revealed that removal efficiencies were maximum for the CNF samples post treated with 0.2M HCl. The maximum adsorption efficiencies for organic pollutants were attributed due to the combined effects of BET surface area, surface oxygen containing groups (O/C ratio), and total acidic surface functional groups. The study of catalytic removal of sulfur dioxide and NOx using CNF is under progress.
Keywords: Activated carbon fibers, adsorption, breakthrough analysis, surface functional groups
