Synthesis And Catalytic Properties Of Nitrogen, Phosphorus Doped Graphene

Graphene is newly emerging nonmetallic materials and has attracted great attention due to its advantages of extremely large surface area, high stability and fast charged carrier mobility. Nonmetallic element doping and modification is an effective strategy to tailor the properties of graphene and render its potential use. Doped and modified graphene materials have been widely used in fuel cell, lithium ion batteries, and catalysis etc. In this thesis, a series of doped or modified graphene materials were fabricated and applied as catalysts in cyclohexane oxidation, Knoevenagel condensation, Michael addition, transesterification, and:1. N-doped graphene was synthesized by treating graphene oxide in NH3atmosphere at different temperatures. AFM, TEM, XRD spectrum, element analysis, FT-IR, and XPS were used to study the morphology, structure and composition of as-obtained products. Three kinds of N species exist in the samples, i.e. pyridinic N, amine N, and graphitic N. The amount of total nitrogen atoms increased with increasing treating temperature and reached a maximum of10.1%(atomic ratio) at500℃and then decreased. The structure of graphene was greatly damaged at800℃.2. The N-doped graphene was used as catalyst in cyclohexane oxidation reaction. The effect of nitridation temperature and solvent employed were studied. The N-doped graphene nitridized at700℃shows the highest catalytic activity with cyclohexane conversion of9.6%. The catalytic role of organic solvent, with might be closely related with the polarity, the a-H activity, the strength of hydrogen bond formed with cyclohexane and the radical scavenging capability, must be considered. The π conjugation system and the defects of N-doped graphene are harmful for radical reaction.3. Series of N-doped and amine-grafted grapheme were obtained via hydrothermal treatment of graphene oxide in the aqueous solution of amines. AFM, TEM, XRD spectrum, Raman spectrum, element analysis, FT-IR, and XPS spectrum were used to study the morphology, structure and composition. The amount of total nitrogen atoms and the distribution of nitrogen components can be well adjusted by controlling the synthesis parameters like the type of amines and hydrothermal temperature. The maximum N content is18.0%of MAGO. There are three kinds of N species, including pyridinic N, amine N, and ammonium. The thermal stability increased distinctly after functionalization according to the results of TG and MS.4. Benzoic acid, cyclohexane oxide, phenol were used as model molecules to react with propylamine for a better understanding on the formation N-doped and amine-grafted graphene oxide. Mass spectroscopy and the XPS analysis were employed to reveal the detailed mechanism.5. The basicity of the samples was roughly analyzed by using different Hammett indicators. The results showed that all these samples are super bases by processing basic sites with pKa value of37-39. The basic strength can be well adjusted by changing the type of amine during the hydrothermal treatment. These samples are active basic catalysts for Knoevenagel condensation, Michael addition, and transesterification. Amine N species coordinated the transesterification reaction between methyl benzoate and ethylene glycol, while pyridinic N ones were responsible to the Michael addition between nitromethane and methylacrylate. The GC-MS analysis and recycle experiment results reveal that all these samples are stable heterogeneous catalysts.6. P-doped graphene were obtained via hydrothermal treatment of graphene oxide and white phosphorus in the aqueous solution of KOH. The P content is4.6%. The catalytic activity of P-doped in hydrogen generation, which is nearly the same as that of P25, is much higher than that of grapnene and N-doped graphene.