Design & Synthesis Of Phosphorus-doped Carbon-based Materials And Their Application In Catalysis

To meet the increasing industrial production demands, the research and development of green and efficient catalysts have aroused wide concern. Carbon namomaterials have tremendous potential in the areas of catalysis, biology, photoelectricity and sensing due to their low cost, low toxicity, excellent biocompatibility and long-term stability. In recent years, the study discovered that doping non-metal heteroatoms into the carbon framework can enhance the catalytic performance of primary materials. In our study, we have synthesized phosphorus-doped macroporous carbon spheres(PMCS), phosphorus-doped carbon nanodots(PCDs) and phosphorus-doped activated carbon(PAC) and composite catalysts based on PCDs. We further explore the change on the property of carbon materials by phosphorus doping and their applications in catalysis. The main contents include the following parts:(1) We have synthesized the phosphorus-doped macroporous carbon spheres(PMCS) by using phytic acid as the precursors of carbon and phosphorus. The specific surface area of PMCS was 574.68 m2 g-1 and the highest phosphorus content was 6%. We confirmed the macroporous structure of PMCS by SEM, TEM and XRD, and the XPS, EDS and FT-IR characterizations certified the successful doping of phosphorus. The PMCS were used for catalyzing the selective oxidation of cyclooctene. A series of experiments proved that the PMCS had excellent capability for the catalysis of selective oxidation of cyclooctene under mild condition(conversion based on cyclooctene was 50.69% and the selectivity to epoxycyclooctane was 88.47%) due to the distinct porous structure, high specific surface area and numerous active sites in PMCS generated from phosphorus doping.(2) We have prepared phosphorus-doped carbon nanodots(PCDs) by a facile electrochemical etching method. The TEM image showed the PCDs were 3 to 5 nm in diameter. EDS, XPS and FT-IR characterizations proved the successful doping of phosphorus and the PCDs had unique ultraviolet and fluorescence properties. The PCDs were used to catalyze oxygen reduction reaction(ORR) with positive onset potential, high current density, long-term stability and improved tolerance to methanol oxidation. We optimized the proportions of ultrapure water and phosphoric acid to obtain PCDs with tunable phosphorus dopant content and elucidated the influence of the phosphorus content on electrocatalytic performance.(3) We have synthesized the Au nanoparticle/phosphorus-doped carbon nanodots composites(Au/PCDs) by a stirring method. The as-prepared Au/PCDs were characterized by TEM, XRD, Raman and PL for the structure and morphology and used to catalyze ORR. The research found that the Au nanoparticles further enhanced the optical response of PCDs and the synergistic interaction between them improved the catalytic performance of individual component vastly. The composites showed outstanding electrocatalytic activity toward ORR with similar onset potential, improved current density, long-term stability and high tolerance to methanol oxidation compared with commercial Pt/C under visible light. With the phosphorus contents increasing in the composites, the ORR activity had an increasing trend.(4) We have prepared the cobalt phosphate/phosphorus-doped carbon nanodots composites(Co Pi/PCDs) via a photochemical method. The CoPi/PCDs were characterized by SEM, TEM, XRD, FT-IR, Raman and PL for the structure and morphology and used for catalyzing OER. The experimental result showed that the composites could be used as a high-efficiency catalyst for water oxidation both under neutral and alkaline conditions with a lower overvoltage, a substantial enhancement of the current density and a smaller Tafel slope. Moreover, the protection of the covering layer of PCDs on the surface of CoPi led to the high durability of the composites.(5) We have demonstrated the synthesis of phosphorus-doped activated carbon(PAC) through an effective heating approach with triphenylphosphine(TPP) as the phosphorus precursor source. The SEM, TEM, XRD, FT-IR and Raman characterizations showed the morphology and structure and the PAC were used as the ORR catalyst. We found that the PAC exhibited excellent ORR activity with positive onset potential, high current density, long-term stability and good tolerance to methanol oxidation under alkaline conditions.