Synthesis Of Porous Carbon Based On Graphene/Polyacrylonitrile Composites And Its Applications

Porous carbon materials have been widely applied in catalyst supports, gas storage and electrode materials due to their developed specific surface area, excellent chemical stability and superior conductive properties. It has significant research value to design carbon materials based on the practical application. But, it is still a great challenge to control the structure and surface chemistry of carbons to meet the application requirements. So, a new synthesis method of porous carbon were developed based on the graphene/polyacrylonitrile nanocomposites and expored their application properties.(1) Acrylonitrile (AN) and ammonium persulfate (APS) were selected to conduct experiments according to the method of water phase precipitation which was like the synthesis of polyacrylonitrile. Then, the two reactants were mixed with the aqueous solution of graphene oxide which was acted as the substrate. The monomer would in situ polymerized around the graphene oxide at elevating temperature and then the graphene/polyacrylonitile nanocoposites were obtained. Nitrogen-doped carbon materials can be generated after the oxidative stabilization, carbonization and activation. The design synthesis of nitrogen-doped macro-microporous carbon can be realized by changing the dosage of graphene. The obtained carbon has a developed specific surface area of 787 m2 g-1 and pore volume of 1.98 cm3 g-1. The nitrogen content is as high as 6.2 wt% and the graphitic-N was the dominant configuration which accounted for 40%. Using this carbon as the support for loading Cu nanoparticles for the dehydrogenation of ethanol to acetaldehyde, the catalyst showed an excellent catalytic performance with 83% ethanol conversion and superior stability (ethanol conversion remain 80% after 500 min). Further comparison revealed that the catalyst with 94% acetaldehyde selectivity also surpassed the conventional SiO2 and Al2O3 supported copper catalysts (70% acetaldehyde selectivity). By assuming the Cu particles being spherical, the dispersion of Cu on the catalyst is 18.3%. In comparison of the fresh and spent catalysts, the copper particles retained almost constant size distribution (from 6.3 nm to 6.7 nm) before and after reactions. A considerable acetaldehyde yield was obtained at ultrahigh space velocities, revealing the advantages of such pumice-like structure with thin skeleton and open macropores allowing quick kinetic transfer. Theoretical calculations reveal that the nitrogen dopants (graphitic-N, pyridinic-N and pyrrolic-N sites) show enhanced adsorption energy for copper nanoparticles, among which the graphitic-N sites are the most significant accounting 40% in total nitrogen content as determined from XPS analysis(2) The above carbon material with macroporous and nitrogen heteroatoms was promising absorbent for CO2 adsorption and separation after potassium carbonate activation. The optimal activation conditions were concluded by investigating the activation temperature, carbonization temperature and post-treatment. Polymer, preoxide and carbide were selected to activate respectively. The specific surface area and pore volume were enhanced obviously. The content of N was still abundant and the macroporous structure of carbon was maintained. This series of carbons show outstanding CO2 sorption and separation capacities, high selectivity. At 1 atm, the highest equilibrium capacities of the carbon are 6.5 mmol g-1 at 0 ?, and 4.0 mmol g-1 at 25 ?; while the dynamic capacity was 1.03 mmol g-1 at 25 ? using a mixture of CO2:N2=1:5 (mol) indicating that the dynamic capacity was equal to the static adsorption capacity under the corresponding pressure. The carbon also exhibited excellent cycle performance, and they undergo a facile CO2 release in Ar purge at 25 ?.