Construction And Photocatalytic Mechanism Of SnO₂/g-C₃N₄ Heterostructure Photocatalysts

As an important semiconductor material,tin dioxide（SnO₂）shows great application potential in the field of photocatalysis,due to high chemical stability,non-toxicity,and harmlessness,etc.However,the wide band gap can only absorb ultraviolet light,and the probability of photo-generated electron-hole recombination is high,which severely restricts its application in photocatalysis.In this thesis,SnO₂ is used as the material basis to construct a heterojunction with graphite-like carbon nitride（g-C₃N₄）to improve its photocatalytic performanc.The light absorption capacity,carrier separation efficiency and enhanced photocatalytic mechanism of the heterojunction have been studied.The main contents are as follows:1.The 0D SnO₂/2D CNNSs heterojunction photocatalyst with excellent photocatalytic performance have been synthesized by the electrostatic self-assembly method.The degradation efficiency of SnO₂/CNNSs on RhB reaches 96.9%in 50 minutes under visible light.The reaction rate k is 0.0909 min^-1,which is 32.3 times and 1.5 times that of SnO₂ and CNNSs,respectively,and SnO₂/CNNSs heterojunction possesses good cycle stability.2.The enhanced photocatalytic mechanism of SnO₂/CNNSs has been revealed through experiments and theoretical calculations.A built-in electric field exists at the contact interface of SnO₂/CNNSs type II heterojunction.The existence of the built-in electric field and more negative conduction band potential of CNNSs provide greater driving force to promote the separation and transfer of charges.In addition,after the recombination of SnO₂and CNNSs,the readjustment of the energy band improves the redox capacity of SnO₂/CNNSs.3.SnO_2-xNPs with narrower band gap have been prepared by self-doping.SnO_2-x NPs with different mass ratios have been anchored on bulk g-C₃N₄（BCN）by ultrasonic-assisted deposition method to prepared SnO_2-x/BCN composites.The results show that 50wt.%SnO_2-x/BCN exhibits the optimal photocatalytic activity,and the degradation efficiency on RhB is 96.5%in 60 minutes under visible light.The reaction rate k is 0.061 min^-1,which are 21.3 times and 9.3 times that of SnO_2-x and BCN,respectively.4.The SnO_2-x/BCN composites follow the direct Z-scheme charge transfer mechanism.First,the electrons in conduction band of SnO_2-x recombine with holes in the valence band of BCN.Subsequently,the electrons in the conduction band of the BCN can reduce the chemically adsorbed oxygen on the photocatalyst surface to·O₂-.The holes in the valence band of SnO_2-x can oxidize OH^-to·OH,and then participate in the degradation of organic pollutants.The excellent photocatalytic performance can be attributed to the boosted visible light absorption,improved photogenerated electron-hole separation efficiency and enhanced redox capability.