Study On Preparation And Properties Of Z-type G-C₃N₄/m-BiVO₄ Composite Photocatalytic Materials

Organic pollutants stably present in the water body can be completely degraded under the drive of semiconductor photocatalysis technology.The process is green and efficient,which can effectively deal with the problem of energy depletion and environmental.Monoclinic bismuth vanadate（m-BiVO₄）and graphite-like carbon nitride（g-C₃N₄）are novel catalytic materials that have highly valued in the field of photocatalysis,but have their own shortcomings and limit practical applications.The problems of monomer can be improved through modification treatment or by combining the two materials.The suitable energy band positions of g-C₃N₄and m-BiVO₄can construct an effective Z-type composite g-C₃N₄/m-BiVO₄photocatalytic material.In this paper,biomimetic template-assisted hydrothermal methods was used to synthesis m-BiVO₄catalysts with various shapes;bulk g-C₃N₄photocatalytic materials were modified by acid etching,hydrothermal and secondary calcination;Z-type g-C₃N₄/m-BiVO₄composite photocatalytic material was prepared in situ by a biomimetic template-assisted hydrothermal method.The samples were used to characterize by X-ray diffraction（XRD）,field emission scanning electron microscope（FESEM）,transmission electron microscope（TEM）and ultraviolet-visible diffuse reflection spectroscopy（UV-Vis DRS）.Rhodamine B（Rh B）dye,methyl orange（MO）dye and tetracycline hydrochloride（TC-HCl）were used as the target degradation product and a 500 W xenon lamp was used as the light source to evaluate the photocatalytic activity,stability and application range of the samples.Capture test to verify the role of the active group in the reaction.The following conclusions are drawn from the above studies:（1）Biomimetic template-assisted hydrothermal methods were successfully used to prepare m-BiVO₄photocatalytic materials with different morphologies such as flakes,worms,irregular polyhedrons,leaves and dendrites.When the amount of L-glutamic acid added is 0.5,the p H of the precursor solution is 3,and the hydrothermal reaction temperature is 180℃,the photocatalytic degradation rate of rhodamine（Rh B）dye by the irregular polyhedron m-BiVO₄reached 100%in 2 h.The degradation rate constant of Bi-0.5-3-180 sample is 5.1 times that of m-BiVO₄sample prepared without template.At the same time,the photocatalytic efficiency of Bi-0.5-3-180 sample for MO dye and TC-HCl is 61.19%/2 h and 85.19%/2 h,respectively.The maximum absorption wavelength of Bi-0.5-3-180 sample is 530 nm,and the band gap value is 2.38 e V.（2）The bulk g-C₃N₄was modified by acid etching,hydrothermal and secondary calcination.When the hydrothermal temperature of acid etching is 140℃and the secondary calcination temperature is 550℃,the photocatalytic activity of the prepared porous flake g-C₃N₄is as high as 98.76%/2 h for Rh B dye,which is 3.08 times for the photocatalytic activity of the bulk g-C₃N₄.The photocatalytic efficiency of porous flake g-C₃N₄is 53.97%/2 h for TC-HCl.Compared with the bulk g-C₃N₄,the maximum absorption wavelength of the porous flake g-C₃N₄was reduced from 470 nm to 460 nm,and the band gap increases from 2.70 e V to 2.78 e V.This is due to the increase in the specific surface area of the catalytic material,which improves the survival time of photogenerated carriers.（3）Z-type g-C₃N₄/m-BiVO₄composite photocatalytic material prepared by in-situ method is composed of porous sheet-shaped g-C₃N₄wrapped around dendritic m-BiVO₄.When the amount of porous sheet-like g-C₃N₄is 15 wt%,the photocatalytic activity of the g-C₃N₄/m-BiVO₄catalytic material reaches 98.82%/2 h for Rh B dyes,which is 2.45 times the photocatalytic activity of a single m-BiVO₄.The photocatalytic efficiency of g-C₃N₄/m-BiVO₄for MO dye and TC-HCl is 78.32%/2 h,91.87%/2 h,respectively,and the band gap is 2.37 e V.（4）After four photocatalytic cycle experiments,the degradation efficiency of m-BiVO₄,g-C₃N₄and g-C₃N₄/m-BiVO₄photocatalytic materials to Rh B is 94.87%/2 h,92.12%/2 h,92.05%/2 h,respectively.The results show that three photocatalytic materials have excellent stability.The active group capture experiments confirmed that m-BiVO₄,g-C₃N₄and g-C₃N₄/m-BiVO₄three catalytic materials play a key role is·O₂^-,the secondary role is h⁺and·OH in the reaction.