Preparation And Photocatalytic Properties Of Graphite Phase Carbonitride-based Composites

Semiconductor photocatalysis is one of the most promising methods to solve environmental pollution issues.Among many photocatalysts,graphitic carbon nitride?g-C₃N₄?has attracted considerable scientific interest owing to its high light conversion efficiency,high chemical stability,high thermal stability,non-toxic and easy access to obtain raw materials.However,the fast recombination of charge carriers generated from photocatalytic reactions would weaken the photocatalytic activity of g-C₃N₄.In addition,the small specific surface area of g-C3N4 also affects its photocatalytic degradation process.In order to overcome the above-mentioned shortcomings,this article did some researches on the modification of g-C3N4,mainly including the preparation,characterization and analysis of g-C3N4-based composites.The photocatalytic degradation properties of the composites were evaluated by measuring the photodegradation of organic pollutants under simulated sunlight irradiation.The specific research topics are as follows:1.Preparation of Zeolitic imidazolate framework-8/g-C₃N₄?ZIF-8/g-C₃N₄?composites and study on photocatalytic degradation towards rhodamine B.Firstly,g-C₃N₄ was prepared by high-temperature calcination treatment of melamine.Then,ZIF-8/g-C3N4 composites were successfully synthesized through a facile solvothermal method,in which zinc nitrate hexahydrate and 2-methyl imidazole were used as the sources.The prepared samples were characterized by various analytical techniques,including X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,UV-vis diffuse reflectance spectroscopy?UV–vis DRS?,specific surface areas?BET?,PL spectroscopy and transient photocurrent density.The specific surface area of ZIF-8/g-C3N4 composites was about 1.4 times than that of pure g-C3N4,which provides more active sites for photocatalytic reaction.The transient photocurrent density of ZIF-8/g-C3N4 composites was about 1.7 times than that of pure g-C3N4,which indicates that the charge transfer ability of the composites was enhanced and the recombination rate of photoelectron-hole was decreased.The photocatalytic properties of prepared samples were evaluated by the photodegradation towards rhodamine B?RhB?as a model pollutant under simulated sunlight irradiation.The results confirmed that the ZIF-8/g-C3N4 composites exhibited a much higher photocatalytic activity than pure g-C3N4 and the degradation rate of the ZIF-8/g-C3N4 composites toward RhB could reach up to 99.8%in 60 min.In addition,the photocatalytic mechanism of ZIF-8/g-C₃N₄ was discussed in details in this section.2.Preparation of Sb₂WO₆/g-C₃N₄ composites and study on photocatalytic degradation towards RhB.Firstly,g-C3N4 was prepared by high-temperature calcination treatment of melamine.Then,Sb2WO6/g-C3N4 composites were successfully synthesized through a facile solvothermal method,in which ammonium tungstate and antimonous chloride were used as the sources.The prepared samples were characterized by various analytical techniques,including XRD,FTIR,SEM,XPS,UV–vis DRS,BET,PL.The absorption wavelength range of Sb₂WO₆/g-C₃N₄ is larger than that of g-C₃N₄.The specific surface area of Sb₂WO₆/g-C₃N₄composites was about 2.15 times than that of pure g-C₃N₄.The photocatalytic properties of prepared samples were evaluated by the photodegradation towards rhodamine B?RhB?as a model pollutant under simulated sunlight irradiation.The results confirmed that the Sb2WO6/g-C3N4 composites showed a much higher photocatalytic activity than g-C3N4 and the degradation rate of the Sb₂WO₆/g-C₃N₄ could reach up to 99.3%in 60 min,which was about 5.43 times than that of pure g-C3N4.In addition,the photocatalytic mechanism of Sb₂WO₆/g-C₃N₄ was discussed in details in this section.3.Study on influencing factors of the photocatalytic degradation of organic dyes by catalysts.The effect of dye type,pH value,sodium chloride and initial dye concentration on the photocatalytic properties of ZIF-8/g-C3N4 and Sb2WO6/g-C3N4 composites were investigated.The results showed that the above four factors had similar effect on ZIF-8/g-C₃N₄ and Sb₂WO₆/g-C₃N₄.The photocatalytic activity of the composites photocatalyst decreased with the increase of the molecular structure stability of the target dye.Furthermore,the acidic condition can promote the photocatalytic activity of the composite photocatalyst,while the alkaline condition can inhibit its photocatalytic effect.In addition,the photocatalytic activity of the catalyst decreased with the increase of sodium chloride concentration in the solution.Moreover,when the initial concentration of the pollutant solution increases,the degradation rate of the pollutant decreases,but the degradation amount of the pollutant did not decrease.When the initial concentration of the contaminant solution increased,the degradation rate of the contaminant reduced,while the degradation amount did not decrease.