Nitrogen And Phosphorus Heteroatom-Doped Carbon Materials Derived From Schiff-base Conjugated Microporous Polymers

Porous carbon materials have been widely applied in gas adsorption and separation,water purification,catalysis and electrochemistry due to their wide range of precursor sources,low cost of preparation,good biocompatibility and chemical stability.The main factors influencing the performance of porous carbon materials are heteroatom doping,porous structure and specific surface area.As a CO2 adsorbent,high specific surface area and microporous structure can increase the carbon materials CO2 uptake,and heteroatoms can increase the affinity of the material for CO2 and increase the CO2/N2 selectivity.For electrochemical applications,the doped heteroatoms can effectively modify the electronic structures and surface chemical properties of the carbon networks,facilitating the electrochemical reaction on the carbon surface;hierarchical porous architecture(including micro-,meso-and macropores)can facilitate the O2 and electrolyte ions transportation by shortening the diffusion pathways;the large surface area can increase the effective catalytically active sites of porous carbon materials.Microporous organic polymers(MOPs)as a class of polymers that consist of light elements such as C,N,O,and H,have a high specific surface area and rich microporous structures.Most MOPs have rigid aromatic structure,which can retain a microstructure under high temperature carbonization to form porous carbon material without additional cross-linking or pre-oxidation.The diversity and flexibility of polymer design and chemical synthesis of MOPs,as well as their own pore structure and morphology characteristics,provide new ideas for the design and preparation of porous carbon materials.In this thesis,Hexakis(4-formylphenoxy)cyclotriphosphazene and different amine monomers were selected.Schiff base reaction was used to synthesize porous organic polymers containing N,P heteroatoms in one step.The procedure is facile and non-metal involved.N,P-doped porous carbon material with large specific surface area was obtained after directly pyrolysis.The morphology,structure and composition of the materials were characterized by scanning electron microscopy(SEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and Specific surface area and pore size analyzer.Among them,C-POP-2-900 shows the highest CO2 adsorption capacity at pressures of 1 bar,273 K and 298 K,which were 18.6 wt% and 12.2 wt%,respectively.This N,P-doped porous carbon materials exhibits favorable activity towards ORR with better long-term durability and higher tolerance to methanol crossover than the commercial Pt/C reference electro-catalyst.Therefore,this method is promising in the preparation of multi-heteroatom doped carbon materials for electrochemical applications.In addition,the research in the electrochemical field of porous carbon materials mainly focuses on controling the pore structure and heteroatom doping,while the research on the influence of microscopic morphology on electrocatalytic activity is rarely reported.In this study,core-shell structure of Si O2@POP were prepared by Schiff base reaction with aminomodified Si O2 as a template.After carbonizing at high temperature and etching the template N,P-doped hollow carbon spheres were formed.By optimizing the experimental process,although the pre-designed hollow carbon spheres were not prepared,the optimization process still had a certain trend and still need further exploration.