Study on Fabrication,Catalytic and Separation Performances of Graphitic Carbon Nitride

Author:Wang Yang

Supervisor:liu bo

Database:Doctor

Degree Year:2019

Download:57

Pages:125

Size:12566K

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Graphitic carbon nitride(GCN)is an emerging two-dimensional laminated material that shows favorable application prospects in catalysis and separation fields in recent years.With advantages in feasible synthesis,visible-light absorption,excellent thermal and chemical stability,GCN can realize facile conversion of sustainable solar energy into clean chemical fuels,thus providing solutions to well address the energy crisis caused by the booming modern industry.Also,GCN-based separation membranes are anticipated to be potentially applied in seawater desalination,sewage purification and biological medicine,by virtue of the rich and tailorable two-dimensional nanopores within the GCN network.In this dissertation,controllable synthesis of GCN,photocatalytic hydrogen evolution and separation performance and mechanism of GCN are explored,aiming at in-depth understanding of the relationship among synthetic strategy,microstructure and photocatalytic activity in GCN system,as well as optimizing the photocatalytic performance of GCN.Meanwhile,the interlayer distance and environment of GCN are tailored using(chiral)anion-type supporters with diverse sizes and functions that intercalate in-between the protonated interlayer of GCN,upon which GCN-based membrane can realize precise sieving of molecules and ions at sub-nanometer scale,as well as enantioselective permeation of varied chiral enantiomers.The main respects included in this dissertation are as follows:1.Limited by the low polymerization degree,weak crystallinity,low specific surface area,narrow visible-light absorption range,rapid recombination of photo-excited electron-hole pairs,conventional GCN is generally featured with poor activity in photocatalytic reactions for hydrogen evolution.We managed to synthesize highly crystalline GCN in closed system,further liquid exfoliation of the bulk material into ultrathin nanosheets using mixed solvents was also realized.The overall results indicate that bulk GCN with high crystallinity extends the visible-light absorption range,facilitates electron delocalization and charge transfer,suppresses the recombination of photo-excited carriers and decreases the defects of the system.These beneficial attributes effectively improve the photocatalytic activity for hydrogen evolution.The exfoliated GCN nanosheets with high crystallinity provide additionally high specific surface area for the reaction and further boosts the performance.This work offers new idea for rational design and preparation of crystalline GCN,as well as optimization of catalytic performance at micro-level.2.The anion of strong acid(H2SO4,SA)was utilized to tailor the interlayer distance of GCN.Specifically,we found that uniformly and certainly distributed sp2 N atoms on the conjugated plane of GCN can be protonated,and the electrostatic repulsion between protonated GCN and anion(SO42-)that intercalated in-between GCN layers enables stable structure of the composite system,accompanied with enlarged interlayer distance by 10.8 A Vacuum filtration was further used to prepare amphipathic GCN-SA membrane,upon which the species with diverse sizes and charges can selectively pass through,while the molecules with hydrated radii larger than 5.4 A are blocked.In this regard,GCN-based membrane is capable of realizing precise sieving at sub-nanometer scale.This woik lays solid foundation for reasonable tailoring of GCN interlayer distance and realizing highly efficient separation at nanoscale,which also provides reference for exploring other two-dimensional materials that role as separation membranes.3.Anions of organic strong acids can simultaneously tailor the interlayer distance and introducing chiral group to change interlayer environment of GCN.We used(lR)-(-)-10-camphorsulfonic acid(CSA)to functionalize GCN and tailor the interlayer distance and environment,creating chiral sites in-between GCN layers.The nano-composites was further assembled into GCN-CSA membrane.The results show that a diverse class of chiral enantiomers with varied molecular weights can selectively permeate through chiral guiion supported GCN-CSA membrane,among which the enantiomeric excess(ee)value of limonene racemate can reach high up to 89%,thereby demonstrating the superior enantioselective ability of GCN-CSA membrane.This work is of great importance in interlayer tailoring of two-dimensional materials using chiral group,which extends the idea and strategy for the separation of chiral drugs with added value.