Construction And Performance Study Of Composite Photocatalyst Based On G-C₃N₄ Traditional ? Heterojunction And Z-scheme Heterojunction

Photocatalytic technology can effectively degrade organic pollutants into inorganic molecules such as CO₂,H₂O and has become one of the most promising green technologies in the field of dye wastewater treatment.In this paper,the preparation,characterization and performance research of g-C₃N₄ based composite photocatalyst have been carried out,in order to solve low photocatalytic activity,high photogenerated electron-hole recombination rate and low solar energy utilization rate of g-C₃N_4.?1?Hollow microsphere CdS and bulk g-C₃N₄ were prepared by solvothermal method and high temperature calcination method,respectively.The traditional?CdS/g-C₃N₄heterojunction photocatalyst was successfully prepared by a facile calcination method.The structures,morphologies,optical and electrical properties of CdS/g-C₃N₄ photocatalyst were studied systematically,The CdS/g-C₃N₄ photocatalyst exhibited excellent photocatalytic activity and stability for the photodegradation of RhB,and the degradation rate constant of CdS/g-C₃N₄ with optimum mass ratio of 0.25%was about 2.1 times higher than that of pure g-C₃N₄ under the visible light irradiation for 20 min.After 4 cycles,the CdS/g-C₃N₄photocatalyst still maintained the high photocatalytic activity with the RhB degradation efficiency of 95%.Surprisingly,the photocorrosion of CdS caused by the photogenerated holes was inhibited.Based on the characterization analysis and active species capture experient,from the point of view of electron-hole generation,separation and migration,the possible mechanism of the enhancement of CdS/g-C₃N₄ photocatalytic activity was proposed.?2?Z-scheme CdS/CQDs/g-C₃N₄ heterojunction photocatalysts was successfully constructed by introducing the CQDs as the electron mediators.More interestingly,CQDs captured near infrared light and converted to visible light by its up-converting PL property,realized wide-spectrum response,improved the efficiency of solar energy utilization.Monodisperse CQDs particles were prepared by alkali-liquid ultrasonic method.The Z-scheme CdS/CQDs/g-C₃N₄ composite photocatalysts were successfully prepared by a calcination process,and the optimal binary?CdS/g-C₃N₄ and CQDs/g-C₃N₄?photocatalysts were prepared by the same method for comparison.The structures,morphologies,optical and electrical properties of Z-scheme CdS/CQDs/g-C₃N₄ composite photocatalysts were systematically studied by various characterization methods,and the Z-scheme electron transfer pathway were verified.The photodegradation of RhB by Z-scheme CdS/CQDs/g-C₃N₄ composite photocatalyst was studied,and the degradation rate of CdS/CQDs/g-C₃N₄ with optimum mass ratio of 0.25 wt%CdS and 0.5 wt%CQDs was100%under the visible light irradiation for 20 min.The photodegradation Kobs of 10 min was about 3.5 times higher than that of g-C₃N₄,2 times higher than that of CdS?0.25%?/g-C₃N₄ and 2.6 times higher than that of CQDs?0.5%?/g-C₃N₄.After four cycles,the degradation rate of RhB can still reach 93%,Z-scheme CdS/CQDs/g-C₃N₄composite photocatalyst have high stability.Surprisingly,the degradation rate of RhB by Z-scheme CdS/CQDs/g-C₃N₄ was up to 62%under the irradiation of 120 min infrared light,achieving the near-infrared light response,improving utilization of solar energy.Based on the above-mentioned characterization results and active species capture experient,the role of CQDs in the construction of Z-scheme CdS/CQDs/g-C₃N₄ heterojunction photocatalyst was revealed,and the photocatalytic degradation mechanism of dye organic pollutants by Z-scheme composite photocatalyst was proposed.Importantly,it provides a theoretical value for the degradation of organic dye pollutants by g-C₃N₄-based composite photocatalyst in wastewater.Compared with Z-scheme CdS/CQDs/g-C₃N₄ heterojunction photocatalyst,the above-mentioned traditional?CdS/g-C₃N₄ heterojunction photocatalyst can effectively reduce the photoelectron-hole recombination of g-C₃N₄ and improve its photocatalytic activity.However,based on the photogenerated electron-hole transfer pathway of the traditional?heterojunction,CdS/g-C₃N₄ has lower valence band potential and higher conduction band potential,resulting in weak redox ability.However,the Z-scheme CdS/CQDs/g-C₃N₄ heterojunction photocatalyst,the photogenerated electron-hole was transferred according to the Z-scheme pathway,so that the conduction band potential was more negative and the valence band potential was corrected,which can enhance the redox capability of the composite photocatalyst.