Preparation Of G-C₃N₄ Based Nanocomposites And Study On Photocatalytic Degradation Of Dyes

With the rapid development of science and technology,industrial and human activities will discharge a large number of refractory organic pollutants,heavy metal ions and radionuclides into the natural environment,causing serious pollution to the environment.Photocatalysis is an environmentally friendly technology and a green and efficient method to degrade many organic pollutants.Graphitic carbonitrides（g-C₃N₄）have attracted extensive attention due to their excellent performance in the purification of environmental pollutants.However,g-C₃N₄ has some defects,such as low specific surface area,limited light absorption,quantum confinement effect,etc.,which inhibit its photocatalytic activity.The construction of heterojunctions for g-C₃N₄ is an efficient method to enhance their photocatalytic degradation performance.In this paper,the g-C₃N₄-based materials are modified by morphology modification and construction of heterojunction to improve the separation and mobility of photogenerated carriers.The main research contents of this paper are as follows:（1）Zn₃V₂O₈ was prepared by co-precipitation method and calcination method,then Zn₃V₂O₈ and g-C₃N₄ were composited by hydrothermal method,and finally Z-scheme heterojunction Zn₃V₂O₈/g-C₃N₄（x=40,60,80 wt%,x:Zn₃V₂O₈ and g-C₃N₄ mass percentage）was constructed.The samples were characterized by a series of characterization methods such as XRD,SEM,TEM,BET,FT-IR,UV-Vis DRS,PL and photoelectrochemical tests.The analysis proved that the heterojunction was successfully constructed and effectively promoted the separation and migration of photogenerated electron-hole pairs,and the composite sample had excellent photocatalytic performance and optical stability.Among them,when the mass fraction of Zn₃V₂O₈ was 60 wt%,the photocatalytic performance of Zn₃V₂O₈（60）/g-C₃N₄ was the best.Under the condition of simulated sunlight,the degradation rate of the dye Rhodamine B（Rh B）reached 91%by Zn₃V₂O₈（60）/g-C₃N₄ for 120 min,while that of pure g-C₃N₄ could only reached 57%.（2）Convert g-C₃N₄ into nanosheet g CNNS and hydrothermally obtained Co WO₄ by thermal polymerization method,and finally prepared Co WO₄（x）/g CNNS in different proportions（x=20,30,40,50 wt%,x:mass percentage content of Co WO₄）composite material,the samples were analyzed by XRD,SEM,TEM,BET,UV-Vis DRS,PL,photoelectrochemical tests and other characterization methods.The results showed that the morphology of g-C₃N₄was modified to g CNNS caused its specific surface area of the nanosheets was greatly improved,providing more active sites for photocatalytic reactions.The formation of heterojunctions reduced the recombination rate of electron-hole pairs,broadened the response area of visible light,and increased the photocatalytic performance of g-C₃N₄,when the percentage of Co WO₄was 40 wt%,the photocatalytic performance of Co WO₄（40）/g CNNS was the best.Under the condition of simulated sunlight,the degradation rate of the Rh B reached 100%by Co WO₄（40）/g CNNS for 40 min,and the quenching experiments revealed that the active components involved in the photocatalytic degradation of Co WO₄（x）/g CNNS were mainly·OH and·O₂^-.（3）The semiconductor MoO₃,Bi OI and g-C₃N₄ were compounded by a simple hydrothermal method,and finally the double Z-scheme heterojunction Bi OI（x）/MoO₃/g-C₃N₄（x=6.25,12.50,18.75,25.00 wt%,x:mass percentage of Bi OI）was constructed.The characterization resulted from HRTEM and XRD indicated that Bi OI/MoO₃/g-C₃N₄ composites were successfully compounded.The band gap of the composite sample was narrowed on the surface of UV-Vis DRS,and the optical response range was enhanced.The PL and photoelectrochemical test characterizations showed that the existence of the heterojunction effectively delayed the recombination of electrons and holes.The dye Methyl Orange（MO）was degraded under simulated sunlight conditions and its photocatalytic activity was studied.Bi OI（18.75）/MoO₃/g-C₃N₄ had the most excellent photocatalytic performance and optical stability,and the degradation rate of 30 mg/L MO was 53%for 40 min,which is 4 times that of pure g-C₃N₄.The ESR characterization indicated that the main active material components for the photocatalytic degradation of Bi OI/MoO₃/g-C₃N₄ were·OH and·O₂^-,and by calculating the positions of the valence and conduction bands of Bi OI,MoO₃ and g-C₃N₄,it is indicated that the three substances are band staggered structures.