Preparation, Characterization And Performance Of Porous Nitrogen-Doped Carbon Materials

Porous carbon materials with well-developed pore, high specific surface area,excellent heat resistance and/or unique electronic conduction properties are of greatinterest for their important applications in many fields such as adsorption, catalysis,biology and electronics. The introduction of nitrogen into the carbon materials canfurther tune their structure, surface chemical properties and electronic conductivity,thus giving rise to a wide spectrum of potential applications. In the fields ofheterogeneous catalysis and adsorption, porous nitrogen-doped carbon materials haveshown unique advantage as new types of solid base catalysts or adsorbents. Currently,the preparation of high active porous nitrogen-doped carbon materials for theapplications in some importent basic catalytic reactions and the removal of heavymetal ions (such as mercury ion) have attention in the related fields.In this thesis, a series of porous nitrogen-doped carbon materials were prepared bysol-gel route, combining with high temperature carbonization and post-modificationmethods. The structure and surface properties of porous nitrogen-doped carbonmaterials were studied by various characterization means. The adsorption propertiesof mercury ion, as well as the catalytic properties for the transeterification of dimethyloxalate with phenol or dimethyl carbonate with diethyl carbonate were investigatedover various porous nitrogen-doped carbon materials. The main study contents andresults are summarized as follows:A series of porous carbon (NC) materials with mesoporous characteristics wereprepared by sol-gel method via high temperature carbonization using sucrose andcitric acid as the carbon and nitrogen precursors. The nitrogen amount in theethylenediamine-modified porous carbon (NC-EDA) is higher than that of NCmaterials. The materials of NC, NC-EDA and thermal-treated NC-EDA-873(NC-EDA after thermal-treatment at873K) possess high specific surface area, similarpore size distributions and various oxygen-containing and nitrogen-containing groups.The adsorption performance of NC, NC-EDA and NC-EDA-873for mercury (â…¡)ions were investigated in aqueous system. The NC material exhibited relatively high adsorption capacity for mercury (â…¡) ions, which can be improved significantly byethylenediamine modification. The adsorption capacity of the NC-EDA-873materialstill maintained at a relatively high level. Kinetic experimental results indicated thatthe adsorption isotherms can be fitted well using Langmuir model. Based on variouscharacterization results, it can be proposed that the presence of abundant N-containingfunctional groups on the surface of NC materials is beneficial for the adsorption ofmercury ions. Basic species of the materials can interact with mercury ions directly,and thus significantly improving the adsorption capacity of carbon material.A series of porous carbon materials with different thermal-treatment temperature(NC-T) were prepared, and their catalytic properties were investigated in thetransesterificatoion of dimethyl carbonate (DMC) with diethyl carbonate (DEC). Withincrease of thermal-treatment, the amount of surface O-containing functional groups(including nitrogen oxides) decreased, and the types and contents of N-containingfunctional groups also changed somewhat. All NC materials were ateive catalysts forthe transesterification of DEC with DMC. It was found that NC-473show very highactivity, stability, and can be easily recycled without any special treatment on the usedcatalyst. On the basis of XPS results, it can be concluded that the presence ofabundant amio-functional groups on the surface of porous carbon NC-T materialshould play a critical role on the activation of the reactants in the transesterificationreaction.A series of nanoporous nitrogen-doped carbon (NNC) materials were prepared bysol-gel method, with hexamethylene tetramine (HMT) and citric acid as the carbonand nitrogen precursors. The structure and surface properties of these NNC materialswere characterized by different characterization methods. The materials of NNCmaterials possess high specific surface area, similar pore size distributions. Besidespossessing various oxygen-containing groups, these NNC materials also containdifferent types of nitrogen-containing groups, including pyridinic-N, pyrrolic-N andquaternary-N groups. The resulting NNC materials are highly active and selectiveheterogeneous catalysts for the transesterification of dimethyl oxalate (DMO) withphenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO), and canbe easily recycled after simple filtrening, washing with acetone and drying. Thepresence of suitable surface basic sites should be mainly responsible for the excellentcatalytic performance of NNC materials in the transesterification reaction.