Preparation And Properties Of Nitrogen-doped Carbon Microspheres And Carbon Quantum Dots

Nitrogen-doped porous carbon microspheres is a significant type of carbon material possessing high specific surface area, good electric conductivity and hydrophilicity, which can be widely applied in supercapacitor electrode, heterogeneous catalysis, and catalyst in oxygen reduction reaction etc. Nitrogen doped carbon quantum dots is another type of neoteric carbon nanomaterials with strong fluorescence, low cytotoxicity and well biological compatibility, therefore owns great potential in ions and molecules probing. The synthesis of nitrogen containing carbon materials by simple and efficient methods from proper precursor and sufficiently explore of their prospective is significant for the exploiation and performance enhancement of novel carbon materials. Beer is a popular beverage possessing rice amino acids, saccharides and other nourishment components, hence beer can be employed as ideal carbon and nitrogen source for the solution processable synthesis of hetero-elementals doped carbon materials. In this thesis, beer was employed as precursor for the simultaneous synthesis of nitrogen doped carbon microspheres and carbon quantum dots by a facile hydrothermal reaction. The carbon microspheres demonstrated excellerent performances in electrodes of supercapacitors and oxygen reduction reaction and heterogeneous catalysis, whereas the carbon quantum dots exhibited excellent fluorescence with high quantum yield and superior fluorescence stability. Detailed structural characterizations and performances analyse of the two materials were carefully performed. The main content of this thesis are shown as follows:(1) Nitrogen-doped porous carbon microspheres(PCM) precipitation was hydrothermally synthesized using beer as precursor. The subsequent high temperature activation by ZnCl2 resulted in activated-nitrogen doped carbon microspheres(a-PCM) with dramatically increased specific surface area, conductivity and hydrophilicity. The structural analysis indicates that the pyridinic- and graphitic-carbon in carbon framework is beneficial for the application performances of a-PCM. The supercapacitor based on a-PCM electrode can offer a high electric double layrer(EDL) capacitance and certain pesudocapacitance, a specific capacitance of 273.2 F g-1 was achieved at 1 A/g, which is amongst the highest values in various carbon microspheres materials.(2) A-PCM could also serve as efficient non-noble metal catalyst for reduction conversion of 4-nitrophenol to 4-aminophenol by NaBH4 with high activity and well reusability. Structural analysis shows that the doping of nitrogen atoms can alter the electronegativity of the adjacent carbon atoms, rendering the metallic catalytic properties of these carbon atoms. Moreover, relative to traditional noble metal metal catalysts, a-PCM, as a heterogeneous non-metal catalysts can efficiently reduce the cost of catalyst, thus possesses huge potential in heterogeneous catalysis.(3) A-PCM can be used as catalysts of cathode for the oxygen reduction reaction(ORR) as a alternative to traditional Pt or Pd based catalysts. When a-PCM were used as catalyst in alkali oxygen reduction system could exhibit high catalytic activity in ORR. The utilization of a-PCM ORR catalysis can substantially decrease the cost while increase the catalytic activity in ORR.(4) Fluorescent nitrogen containing carbon quantum dots(NCQDs) was synthesized by a facile hydrothermal method using beer as precursor, the NCQDs is sensitive to pH of solution. Considering the well biocompatibility of carbon quantum dots, NCQDs can be used as pH sensitive fluorescent probe in biological and biomedical applications. Additionally, the addition of different cations and anions almost not cause cause decay in fluorescence emission intensity of NCQDs, evidencing the robust anti-interference ability in complicated chemical environments. Besides, NCQDs still maintains well fluorescence performance in dry state.(5) 3D-graphene/nitrogen-doped carbon quantum dots(3DG/NCQDs) composites were synthesized via a facile hydrothermal method using NCQDs and graphene oxide(GO) as reactants. The as-prepared composites exhibited three-dimensional cylindrical shape with high specific surface areas and excellent electric conductivity. When employed of the 3DG/NCQDs as electrodes of supercapacitors, a maximal specific capacitance of 287.5 F/g can be achieved at 1A/g, which is drastically higher over that of merely 3DG(127.4F/g). Simultaneously, the composites can also provide excellent rate capability and cycling stability, showing the prospective of 3DG/NCQDs in supercapacitors.the capacitive properties of the asformed 3DG/NCQDs composite was evaluated in symmetrical supercapacitors.