Preparation And Surface Characterization Of The Carbon Nitride Materials

Nitrogen-containing carbon materials,including nitrogen-doped graphene(NG),covalent triazine framework(CTF),and carbon nitride(CN)etc.,are receiving more and more attention nowadays.Owing to their specific atomic and electronic struc-ture,as well as chemical stability,the nitrogen-containing carbon materials have found wide applications in photocatalysis,degradation of organic pollutes,capture and trans-formation of CO2,fuel cell,and support of monoatomic catalyst and so on.Particu-larly,the graphitic carbon nitride(g-C3N4)holds a layered structure which thus attracts peoples’s large efforts for exfoliation into two-dimensional nanosheets in order for im-proved properties in various applications.However,the syntheses of g-C3N4 materials from the general thermal polymerization of various N-containing precursors all result in melon,i.e.[C6N7(NH2)(NH)]n,which is far from the crystallized structure of g-C3N4.Therefore,it remains a large challenge to prepare the defect-free g-C3N4 crystals es-pecially the two-dimensional g-C3N4(2D-CN)crystallized films.Moreover,the lack of the surface investigations of the 2D-CN also hinders the understanding of the phys-ical mechanisms of the CN materials in corresponding applications.With this respect,this thesis looks at the nitrogen-containing carbon materials from a surface chemistry point of view,and focuses on the preparation and the surface characterizations of the two-dimensional carbon nitride material.The obtained main results are as following:1.Using melamine as the precursor,we successfully synthesized the g-C3N4 pow-der via the general thermal polymerization method.We then conducted the exfoliation treatments in two different solvents and characterized the dispersed g-C3N4 fragments on various substrates with atomic force microscopy(AFM).With the detailed analy-ses,and compared with various control experiments,we found that the small particles which appeared on all kinds of substrates may be the real fragments of g-C3N4 after ex-foliation.However,the ultrathin nanosheets that appeared only on mica substrate holds an unreasonably large lateral size and uniform thickness,and displays no overlapping or wrinkle structures.Such film-like features can hardly be assigned as the exfoliated g-C3N4.2.Through chemical vapor deposition(CVD),we successfully grew nitrogen-doped graphene film with the nitrogen content about 11.8%on Cu foils from dicyan-diamide molecule for the first time.We also tried to use the same method but milder conditions to grow CN films on Cu foils,but always result in the formation of N-doped graphene film.3.By pre-crystallizing the melamine precursors with hydrogen chloride,we have prepared the CN powder with improved crystalline quality.However,due to the loss of the nitrogen atoms during the condensation with HCl,the synthesized CN showed higher C/N ratio compared to the ideal g-C3N4,reflecting the unavoidable defective structure.Nevertheless,this method showed great potential which may finally lead to the perfect g-C3N4 crystals.