Formation of graphitic structures in cobalt- and nickel-doped carbon aerogels.
ABSTRACT We have prepared carbon aerogels (CAs) doped with cobalt or nickel through sol-gel polymerization of formaldehyde with the potassium salt of 2,4-dihydroxybenzoic acid, followed by ion exchange with M(NO3)2 (where M = Co2+ or Ni2+), supercritical drying with liquid CO2, and carbonization at temperatures between 400 and 1050 degrees C under a N2 atmosphere. The nanostructures of these metal-doped carbon aerogels were characterized by elemental analysis, nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Metallic nickel and cobalt nanoparticles are generated during the carbonization process at about 400 and 450 degrees C, respectively, forming nanoparticles that are approximately 4 nm in diameter. The sizes and size dispersion of the metal particles increase with increasing carbonization temperatures for both materials. The carbon frameworks of the Ni- and Co-doped aerogels carbonized below 600 degrees C mainly consist of interconnected carbon particles with a size of 15-30 nm. When the samples are pyrolyzed at 1050 degrees C, the growth of graphitic nanoribbons with different curvatures is observed in the Ni- and Co-doped carbon aerogel materials. The distance of graphite layers in the nanoribbons is approximately 0.38 nm. These metal-doped CAs retain the overall open cell structure of metal-free CAs, exhibiting high surface areas and pore diameters in the micro- and mesoporic region.
- European Urology Supplements - EUR UROL SUPPL. 01/2010; 9(6):590-590.
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ABSTRACT: CNTs were grown on iron-modified mesoporous graphitized carbon aerogel (GCA) at 700 °C, 800 °C and 900 °C using catalytic CVD method. Resultant CNT/GCA materials composition, morphology and structure were studied to understand their electrochemical stability and performance for oxygen reduction reaction (ORR) in acidic medium. CNT growth was increased from 700 °C to 800 °C, dominated by MWCNTs formation. In the temperature range from 800 °C to 900 °C, the growth was reduced by forming nanofiber/nanoribbon structures accompanied by MWCNTs. Mesoporosity of CNT/GCA composites declined at 700 °C and 800 °C due to MWCNT formation. However, CNT/GCA growth at 900 °C improved mesoporosity with substantial increase in pore volume (∼3 times of GCA) due to formation of nanofibers and nanoribbons. The structure of CNT/GCA materials revealed nitrogen doping and dispersion of FeNx phase. A synergistic contribution of CNT/GCA material structure and morphology to ORR activity was noticed. Among CNT/GCA materials, CNT-800 °C/GCA material showed ORR activity at lowest onset potential of 0.5 V. However, CNT-900 °C/GCA exhibits the highest ORR mass activity, with a half-wave onset potential difference of 120 mV with Pt (40 wt.%)/C. Moreover, CNT-900 °C/GCA demonstrates high selectivity (>3.97) to 4 electron ORR path, excellent methanol tolerance and electrochemical durability which makes it a potential DMFC cathode candidate.Carbon 09/2014; 79:518-528. · 6.16 Impact Factor
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ABSTRACT: Nanoporous carbon particles with magnetic Co nanoparticles (Co/NPC particles) are synthesized by one-step carbonization of zeolitic imidazolate framework-67 (ZIF-67) crystals. After the carbonization, the original ZIF-67 shapes are preserved well. Fine magnetic Co nanoparticles are well dispersed in the nanoporous carbon matrix, with the result that the Co/NPC particles show a strong magnetic response. The obtained nanoporous carbons show a high surface area and well-developed graphitized wall, thereby realizing fast molecular diffusion of methylene blue (MB) molecules with excellent adsorption performance. The Co/NPC possesses an impressive saturation capacity for MB dye compared with the commercial activated carbon. Also, the dispersed magnetic Co nanoparticles facilitate easy magnetic separation.Small 03/2014; · 7.82 Impact Factor