Structure Tuning And Performance Study Of Graphitic Carbon Nitride Photocatalyst

In recent years,with the increasing number of the population,the situation of energy shortage has become critical.At the same time,environmental problems such as air pollution and greenhouse effect caused by fossil fuel combustion have also plagued people.Therefore,people have been trying to find the energy-rich renewable clean energy as an alternative to fossil fuels.Hydrogen releases a lot of energy during combustion and produces only water,which is a clean energy.Nano-sized photocatalysis material can utilize solar energy to drive photocatalytic decomposition of water to produce hydrogen,converting solar energy into chemical energy,which has been studied intensively and extensively.Among them,the organic semiconductor graphite carbon nitride（g-C₃N₄）has an appropriate band gap and band position for the preparation of hydrogen by water decomposition,which is considered to be one of the photocatalytic materials with broad prospects.However,the shortcomings of g-C₃N₄ are also exposed:low specific surface area,less active sites,weak absorption in the visible-light region,serious charge recombination,and short lifetime of photogenerated carriers,which limits the development of g-C₃N₄.In this dissertation,g-C₃N₄ photocatalyst is chosen as the subject of our study.By means of element doping and structural regulation of g-C₃N₄,its photocatalytic hydrogen production performance could be optimized.The specific research contents are as follows:（1）S-doped g-C₃N₄（SCNB-5）was obtained by one-step high-temperature calcination of melamine with a simple sulfur-containing amino acid taurine as the sulfur source.The X-ray photoelectron spectroscopy（XPS）and energy dispersive X-ray spectrometer（EDX）results confirm that S atoms have been successfully introduced into the triazine ring structure of g-C₃N₄.The doping of S makes the conduction band（CB）of g-C₃N₄ shift down;the band gap（BG）narrow and the visible light absorption range expand.In addition,the photoelectric properties and photocatalytic hydrogen production performance of SCNB-5 are further studied.The results show that,comparing with the bulk g-C₃N₄（CNB）,SCNB-5 possesses smaller resistance and higher photogenerated carrier separation efficiency,so it shows a better photocatalytic hydrogen production performance.（2）C-doped g-C₃N₄ was obtained through 6-methyl-2-thiouracil mechanically mixing with melamine in a certain proportion,followed by the thermal-induced copolymerization.Various characterizations have been used to systematically study the phase structure,optical and electrical properties of the C-doped g-C₃N₄photocatalyst.And the activity of water photocatalytic decomposition for hydrogen production has also been investigated.The results show that 6-methyl-2-thiouracil can induce extra C atoms into the triazine ring of g-C₃N₄.Comparing with the undoped g-C₃N₄,the photoelectric properties of C-doped g-C₃N₄ are optimized,thus showing a higher photocatalytic rate of water decomposition for hydrogen production.（3）Methyl-modified g-C₃N₄（DCN）has been successfully prepared by copolymerization of thiourea and acetamide.Through systematic characterizations and experiments,it is proved that-CH₃ modified g-C₃N₄ and pure g-C₃N₄ have the same morphology.The addition of acetamide can successfully introduce-CH₃ into the structure of g-C₃N₄.The introduction of methyl can improve the photoelectric properties of g-C₃N₄,such as the decrease of optical energy band,the increase of visible light absorption edge wavelength and the effective separation of carriers,which is benefit to the photocatalytic hydrogen production.Finally,it shows a better photocatalytic hydrogen production performance than that of the pure g-C₃N₄,its hydrogen production rate is about 2.35 times higher than that of pure g-C₃N₄.