| Semiconductor photocatalytic technology has attracted much attention because it can purify toxic pollutants in the air.In recent years,many bismuth-based semiconductors have shown good application prospects due to their visible light photocatalytic activities.MgBi2O6 belongs to the n-type semiconductor and has a particular three-layer rutile structure.However,its energy band gap is rather small（about 1.8 e V）,which makes the recombination of photogenerated electrons and holes occur easily during the photocatalytic reaction and leads to the relatively poor photocatlytic activity of MgBi2O6.It is an effective way to improve the photocatalytic activity of MgBi2O6 by constructing the semiconducting heterojunction with different semiconductors with the matching energy gaps.In this paper,the preparation and photocatalytic performance of three kinds of heterostructured photocatalysts containing MgBi2O6（MgBi2O6/Cd S,MgBi2O6/Pt-Ti O2 and MgBi2O6/WO3）were studied.The specific content includes the following three aspects:（1）A series of MgBi2O6/Cd S composite photocatalysts were prepared by the chemical precipitation method.Some experimental techniques like XRD,SEM,TEM,XPS and UV-Vis DRS were used to analyze the phase structure,micromorphology and chemical valence state.The results showed that the composite catalyt has the best photocatalytic efficiency when the molar ratio of MgBi2O6 to Cd S is about 0.1%.After 5 hours of visible light irradiation,the amount of hydrogen produced from photocatalytic water splitting over0.1%MgBi2O6/Cd S composite can reach 3970μmol g-1,and photocatalytic activity is significantly better than that of pure MgBi2O6 and Cd S.The improvement in photocatalytic performance of MgBi2O6/Cd S composites is mainly attributed to the synergistic effect of Cd S and MgBi2O6 with narrow band gap,which enables the photogenerated electrons and holes to be effectively separated and transported.（2）Pt-Ti O2 was first synthesized by the photochemical deposition method and then MgBi2O6/Pt-Ti O2composite photocatalysts were successfully prepared by the one-step hydrothermal method.Pure MgBi2O6,Pt-Ti O2,and MgBi2O6/Pt-Ti O2 composite photocatalysts were characterized by XRD,SEM,XPS and UV-Vis DRS.The measured results showed that the prepared MgBi2O6/Pt-Ti O2 composite photocatalysts are composed of MgBi2O6 and Pt-Ti O2 without any impurity phase.The micromorphology of MgBi2O6in the composite photocatalyst has been not changed and MgBi2O6 particles are uniformly distributed around Pt-Ti O2 particles.When the molar ratio of MgBi2O6 to Pt-Ti O2 is 0.2%,the composite shows the best photocatalytic performance.The amount of hydrogen produced over 0.2%MgBi2O6/Pt-Ti O2 under visible light irradiation for 5h is about 23005μmol g-1.The reason for the improved photocatalytic performance is that the built-in electric field built by the MgBi2O6/Pt-Ti O2 heterostructure effectively improves the separation efficiency of the electron-hole pairs.（3）A series of MgBi2O6/WO3 heterostructured photocatalysts were synthesized by a one-step hydrothermal method and further characterized by XRD,SEM,TEM,XPS,EIS and other methods.The photocatalytic activity of the reduction of hexavalent chromium（Cr（VI））solution was studied under visible light（λ>420nm）irradiation.Compared with pure MgBi2O6 and WO3,the photocatalytic performance of MgBi2O6/WO3 composite catalyst is significantly improved.When the molar ratio of WO3 to MgBi2O6 is 1:1,the composite catalyst has the best photocatalytic activity and stability.After 35 minutes of visible light irradiation,the reduction rate of Cr（VI）solution with a concentration of 1.0mg/L reached 95%.The significant improvement of photocatalytic efficiency of the composite semiconductor is mainly ascribed to the heterojunction formed between MgBi2O6 and WO3 which can effectively limit the recombination of photogenerated carriers. |
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