Preparation And Photocatalytic Performance Of Defective GC₃N₄ Nanotubes And Their Composite

Graphite phase carbon nitride(g-C3N4)materials have become a new type of organic semiconductor photocatalyst materials that attract much attention and have great development prospects because of its electronic structure suitable for absorbing visible light.However,the rapid recombination of charge carriers during migration greatly limits the light conversion efficiency of g-C3N4.Therefore,it is of great research significance to promote the efficient separation of charge carriers in g-C3N4 and improve its photocatalytic performance.In this paper,a kind of porous carbon nitride nanotube(TCN)photocatalyst was successfully prepared by a simple and pollution-free high-temperature calcination method.By using a tubular structure,the specific surface area of the material is increased,the charge transfer speed is accelerated,and the visible light hydrogen production efficiency is improved.In order to further improve the photocatalytic performance,defect construction and composite preparation were carried out on the basis of TCN to improve the separation efficiency of photo generated electrons holes and further enhance its photocatalytic activity.This thesis consists of three parts:1.This paper deals with the preparation of a porous g-C3N4 nanotube(TCN)photocatalyst by means of simple high temperature calcination.It has a specific surface area of 34 m2·g-1.Compared with the bulk phase g-C3N4(BCN),the tubularity of porous nanotubes is advantageous for electron transmission.At the same time,surface active substances are more easily obtained inside and outside the tube,and exhibit low resistance to transfer photo generated carriers,thereby further improving its photocatalytic performance.In visible light(λ≥420 nm),the photocatalytic water hydrogen evolution rate of this catalyst is 266 μmol·g-1·h-1,which is 7.5 times higher than that of BCN.2.On the basis of TCN,the defects of the porous g-C3N4 nanotubes(DTCN)were fabricated by one pot thermal polymerization method.It is possible to control defects by varying the calcination temperature.The results showed that the light absorption ability of the sample(DTCN)obtained after calcination at 450℃ was significantly improved,and its band gap decreased from 2.72 eV to 2.59 eV,significantly improving the separation efficiency of photo generated charges.The hydrogen production rate of this catalyst has reached 1078 μmol·g-1·h-1,4.7 times that of TCN.3.On the basis of DTCN,an amorphous nickel oxide/defect type porous g-C3N4 nanotube composite(a-NiO/DTCN)photocatalyst was constructed.By adjusting the loading capacity of a-NiO,the optimal NiO loading capacity was selected to be 20%(denoted as a-NiO/DTCN-20).The results showed that the band gap of the composite material was further reduced from 2.59 eV to 2.40 eV,and the Ni-O-C bond formed in the heterojunction served as a transport channel for rapid charge transfer,further promoting charge separation and migration.In addition,due to the amorphous nature of a-NiO,it shows a strong Urbach band tail absorption,and provides more abundant active site for reaction.The photocatalytic activity has been further improved,and the photocatalytic hydrogen production rate under visible light can reach 1779 μmol·g-1·h-1.