Synthesis Of Graphitic Phase Carbon Nitride Composite Catalysts With Enhanced Photocatalytic Performance

With the environmental problems becoming increasingly serious,people's awareness of environmental protection has gradually increased.Due to its environmental friendliness,high stability and strong activity,photocatalytic technology has received more attentions in energy and environmental protection,especially in photocatalytic degradation of water.Graphite phase g-C₃N₄ is a typical non-metal semiconductor.Due to its unique chemical stability,good thermal stability,special photoelectrochemical structure,easy preparation,wide range of raw materials and low cost,the fields of photocatalytic degradation of pollutants,photocatalytic hydrogen production and carbon dioxide reduction have been deeply studied.However,the simple specific surface area and high electron-hole recombination rate of g-C₃N₄ prepared by simple calcination method weaken its photocatalytic activity and limit its applications.In order to improve the photocatalytic performance of g-C₃N₄ and inhibit the recombination of photogenerated electrons and holes,the band structure can be adjusted by changing the microstructure of g-C₃N₄,compositing with other semiconductors,noble metals and metals.In this paper,the basic principles of semiconductor photocatalysis and the current research progress of g-C₃N₄ photocatalyst are summarized and reviewed.The common methods for improving the photocatalytic performance of g-C3N4 are summarized.And by using the common printing and dyeing wastewater as the target pollutant,the commonly used printing and dyeing wastewater treatment methods are summed up.This topic uses two common methods to modify g-C₃N₄ in order to improve the photocatalytic performance of g-C₃N₄.Firstly,MoO₃/g-C₃N₄ composites were prepared by doping MoO₃ and its photocatalytic properties were investigated.Secondly,the morphology of g-C₃N₄ was modified by laser treatment.Finally,RhB was used as the target pollutant to determine the photocatalytic degradation efficiency,repeat utilization rate and catalytic performance difference of different mass ratios.At the same time,the catalytic performance of the catalyst for different dyes was studied,and the catalytic degradation mechanism of the materials was discussed as well.The research results are summarized as follows:A series of MoO₃/g-C₃N₄ heterostructure photocatalysts with different mass ratios were prepared by mixed calcination method.The characterization and photocatalytic degradation of RhB can be used to obtain the doping of MoO₃,which effectively improves bulk g-C₃N₄ Photocatalytic performance of g-C₃N₄.When the doping ratio of MoO₃ is 7.5%,the photocatalytic effect of MoO₃/g-C₃N₄ composite is the best,and 98%of RhB solution can be degraded in about 20 min.The experimental results show that the MoO₃/g-C₃N₄ composite material is stable and has obvious degradation advantages for various dyes.The analysis of the photocatalytic degradation mechanism of MoO₃/g-C₃N₄ composites mainly reveals the following reasons:1)The heterojunction structure reduces the recombination between photocarriers and holes,enhances the utilization rate of photogenerated carriers and holes;2)The active·O₂^-free radical and hole play a major role in the photocatalytic degradation reaction.The effect of OH in the degradation of RhB is small;the charge transfer mode between the particles is the Z-scheme type.A series of g-C₃N₄ photocatalysts with different laser irradiation time were prepared by laser irradiation modification.We analyzed the material and found that the g-C₃N₄ layer was peeled off and showed a porous structure.The results of photocatalytic degradation experiments show that after laser treatment,the photocatalytic performance of g-C₃N₄ has been greatly improved and it has good stability.The results of electrochemical experiments show that the laser treatment reduces the recombination of photocarriers and holes in g-C₃N₄,improves the utilization of photogenerated carriers and holes,so that improves the catalytic effect of photocatalytic materials.Through ESR electron paramagnetic resonance spectroscopy,free radical scavenging experiments and photoelectrochemical analysis,it is concluded that·OH plays a minor role in the degradation of RhB,and the main role is active·O₂^-free radicals and holes.The enhancement of photocatalytic performance may caused by the structure changes of g-C₃N_4.The purpose of this paper is to improve the photocatalytic activity of g-C₃N₄.By combining g-C₃N₄ with MoO₃ to change the photo-electron and hole transport modes,the photocatalytic activity of g-C₃N₄ was improved.In addition,laser technology was used to treat g-C₃N₄,and a thin layer of porous g-C₃N₄ was peeled off to promote separation of photogenerated electrons from holes.The photocatalytic degradation experiments,material characterization and free radical trap experiments were used to investigate the reasons for the increase of photocatalytic activity after g-C3N4 and MoO₃ recombination and laser treatment.The mechanism of photocatalytic degradation of dyes and its influence on photocatalytic performance were analyzed.The research results of this subject can provide some investigations for the application of g-C₃N₄ semiconductor in the field of photocatalysis.