Study On Preparation Of Z-scheme α-Bi₂O₃/g-C₃N₄ Composite Photocatalysts And Their Photocatalytic Properties

At present,the problem of environmental pollution is getting worse.In order to solve environmental problems,semiconductor-based photocatalytic technology has been discovered.Conventional semiconductor photocatalysts(such as Ti O_2,Zn O)have narrow visible light response range and poor stability.It leads to low photocatalytic efficiency and is difficult to be widely used.Therefore,finding a new and efficient semiconductor photocatalyst has become a research hotspot in this field.α-Bi₂O₃has a band gap of 2.6 eV-2.8 eV,which can be excited by visible light and has high utilization of visible light.g-C₃N₄has a band gap of about 2.7 eV,which has good visible light absorption efficiency,non-toxicity,low cost,high stability and easy preparation.The two semiconductor composites can produce a Z-scheme system,which significantly increases the stability and quantum efficiency of the photocatalyst.L-arginine is used as a bionic template because it is cheap and easy to obtain.The L-arginine can be decomposed and removed by heating after synthesized the samples.In this paper,the biomimetic synthesis technology（using L-arginine as a biomimetic template）was firstly prepared with a hierarchical structure ofα-Bi₂O₃photocatalysts,and then defective g-C₃N₄nanosheets were prepared.Finally,g-C₃N₄andα-Bi₂O₃were compounded to prepare Z-scheme composite photocatalyst.Synthesized samples were characterized by XRD,FESEM,TEM,XPS and UV-Vis DRS.The specific research results are as follows:（1）Theα-Bi₂O₃photocatalysts were successfully synthesized by the biomimetic synthesis-assisted hydrothermal method(the calcination temperature is 500℃,and the molar ratio of n[L-arginine]:n[Bi³⁺]is 0.5:1).At present,α-Bi₂O₃with porous block structure is prepared,when the p H value of precursor solution was 3;α-Bi₂O₃with nanosheet structure is prepared,when the p H value of precursor solution was 12.The degradation efficiency of B-3 and B-12 for Rh B dye is 75.3%/4 h and 64.5%/4 h,which is 24.6%and 13.8%higher than that of template-free B-0.The photocatalytic performance of B-3 with porous structure is better than that of B-12 nanosheet structure.h⁺and·OH^-are the main active groups in the photocatalytic process,and B-3 has good cycle stability.（2）With defective g-C₃N₄photocatalyst was prepared by thermal exfoliation method(the thermal exfoliation temperature is 550℃,the heating rate is 2.5℃·min^-1and the holding time is 4 h).Due to the etching of oxygen,the van der Waals force between the layers of bulk g-C₃N₄was destroyed.Then the nanosheet structure with the thickness of 9.346 nm was obtained.The absorption band edge of CN4 shifted from 478nm blue of CNB to 454 nm,and the band gap widened from 2.68 eV to 2.88 eV.The degradation efficiencies of TC-HCl and Rh B by CN4 are 82.9%/4 h and 97.0%/2 h,which are 46.9%and 64.9%higher than that of CNB;the degradation rates of TC-HCl and Rh B by CN4 are 0.0074(min^-1)and 0.0267(min^-1),which are 4.6 and 8.3 times higher than that of CNB.Among them,h⁺is the main active group,·O₂^-is the secondary active group.（3）The Z-schemeα-Bi₂O₃/g-C₃N₄composite photocatalysts were prepared by mechanical mixing withα-Bi₂O₃as matrix and g-C₃N₄as reinforcement.The optimum mass percentage of g-C₃N₄is 20 wt%.Due to the incorporation of g-C₃N₄,the absorption band edge of BG-20 photocatalyst was widened from 464 nm to 477 nm,which promoted the response efficiency in the visible region.The degradation efficiency of Rh B dye by BG-20 is 99.5%/4 h,which is 24.2%higher than that of pureα-Bi₂O₃.The degradation rate of Rh B dye by BG-20 is 0.0179(min^-1),which is 3.4 times higher than that of pureα-Bi₂O₃.The main active group in the photocatalytic reaction is h⁺and·O₂^-,and BG-20 has good cycle stability.