Controlled Synthesis, Characterization And Properties Of Carbon And Carbonaceous Composite Materials

In this dissertation, controlled synthesis and properties were developed to prepare carbon and carbonaceous composite materials with novel structures. Carbon/carbon core/shell nanofibers and flower-like N-doped carbon nanosheets have been prepared by co-pyrolysis at high temperature. Worm-like palladium/carbon (Pd/C) core-shell nanocomposites have been hydrothermally prepared at low temperature. We also study their electrocatalytic activity toward biomolecules through cyclic voltammetry (CV). The main points are summarized as follows:1. Carbon/carbon core/shell nanofibers with diameters of ⁵0 nm and lengths up to several micrometres have been prepared by co-pyrolysis of tetrahydrofuran and ferrocene in a stainless steel autoclave at 600°C. The diameter of carbon core is ¹0 nm, and the thickness of carbon shell is ²0 nm. It is found that the graphene layers of carbon core are perpendicular to the ones of carbon shell in stacking orientation. When hollow hexapod-like carbon materials can be obtained with water introduced into reaction system. Moreover, the ferrocene is absence, only solid carbon spheres are observed. Comparative experiments confirm that the metallic iron catalysts, originating from the decomposition of ferrocene, are responsible for the formation of nanofibers. And a possible growth process for the three shaped carbon materials is proposed.2. Worm-like palladium/carbon (Pd/C) core-shell nanocomposites have been hydrothermally prepared starting from PdCl₂ andα-lactose monohydrate (α-LM) in the presence of polyacrylamide (PAM) at 200°C. The thickness of carbonaceous shells varied from 5 to 45 nm with increasing temperature from 140 to 200°C. When the dose of PAM or PdCl₂ was increased, spherical Pd/C core-shell nanocomposites were obtained. Time-dependent experiments confirmed that formation of Pd/C core-shell nanocomposites underwent an entrapment-reduction-carbonization process. Cross-linked PAM clusters with rich -CONH₂ entrap the Pd²⁺ ions in solution by a coordination effect. Then the chelated Pd²⁺ ions are gradually reduced to metallic Pd byα-LM. Finally, carbonization coating occurs on the surfaces of Pd nanoparticles fixed by PAM clusters. Such a route has also been extended to synthesize spherical Ag/C core-shell composites. A cyclic voltammetry (CV) study reveals that the as-prepared Pd/C core-shell nanocomposites exhibit electrocatalytic activity toward oxidation of ascorbic acid (AA).3. Flower-like N-doped carbon nanosheets with the thickness of 2-3 nm and the sizes up to several microns have been prepared by co-pyrolysis of pyrrole and 3MgCO₃·Mg(OH)₂·3H₂O in a stainless steel autoclave at 700°C. We also obtain N-doped carbon nanotubes and nanobelts when varying the reaction temperature. The influence of reaction temperature on the nitrogen contents and chemical states are also studied. It is found that the graphitic N is dominant at high temperature, while the pyrrolic N is dominant at low temperature. The order of thermal stability follows graphitic N > pyridinic N > pyrrolic N. A cyclic voltammetry (CV) study reveals that the N-doped carbon nanosheets exhibit good electrocatalytic activity toward the oxidation of H₂O₂. A linear relationship between the amperometric responses and the scan rates square-root is observed, indicating that the electrode process is spread control.