Modification And Photocatalytic Effect Of Two-dimensional Black Phosphorus

The two-dimensional black phosphorus has the property of a direct band gap,with a band gap width of 0.3-2 eV,which can widely absorb ultraviolet light,visible light and near-infrared light.Due to its unique physical,chemical,optical and electrical properties,two-dimensional black phosphorus has been widely used in transistors;,battery materials and photocatalysis.At present,the biggest limitation of the application of black phosphorus is the rapid recombination of photogenerated electrons and holes,and the construction of composite materials is conducive to the separation of photogenerated charge carriers.The types of composite materials usually involve oxides,precious metals,sulfides or carbon-related materials.In order to construct a high-efficiency photocatalytic material,this study first analyzed the efficiency of the two-dimensional black phosphorescent catalyst to degrade methyl orange and proposed a material loading scheme.Secondly,from the perspective of improving the black phosphorescent catalytic activity,Ag/BP composite materials were prepared,and the photocatalytic degradation effects of composite materials were analyzed.Finally,photocatalytic-related mechanisms such as band gap structure and electron transfer were discussed.Deionized water was used as the solvent,and black phosphorous nanosheets(LBP)with different layers were prepared by the two-step method of liquid phase stripping method and differential centrifugation method.Scanning electron microscope(SEM),transmission electron microscope(TEM),atomic force microscope(AFM),raman spectroscopy(Raman),X-ray diffraction(XRD),ultraviolet visible spectroscopy(UVVis)and X-ray photoelectron spectroscopy(XPS)were used to analyze the morphology,structure and optical properties of black phosphorus.The results showed that the black phosphorous nanosheets with different layers were successfully prepared by the twostep method,and the light absorption range was wide.Driven by visible light,with methyl orange(MO)as the target pollutant,the photocatalytic degradation efficiency of MO was explored under different conditions of LBP layer number,LBP concentration,environmental atmosphere and pH value.The results showed that the low-layer black phosphorus(LBP-1,1-5 nm)exhibited strong photocatalytic performance,and the photocatalytic degradation rate constant was 6.45×10-3 min-1.The degradation efficiency of MO was positively related to the concentration of black phosphorus.The photocatalytic degradation rate of MO was the highest under acidic conditions and in the oxygen environment.Singlet oxygen(1O2)was the main active substance in the photocatalytic degradation of LBP.It is preliminarily confirmed that the yield of 1O2 is negatively correlated with the number of layers of LBP.The chemical deposition method was used to load nano-silver on the black phosphorus,and the morphology,structure and optical properties of the material were analyzed by TEM,Raman,XRD and other characterization methods.The results showed that the nano-silver was tightly adsorbed on the black phosphorous nanosheets through electrostatic interaction,and the particle size of the nano-silver with different loadings was different.The average particle sizes were 27 nm,32 nm,34 nm and 35 nm,and the phenomenon of Ag dimers and Ag agglomeration were observed.Under the irradiation of visible light,different loadings of Ag/BP were used for photocatalytic degradation of MO.The results showed that the agglomeration of nano-silver was not conducive to the progress of the photocatalytic reaction.The 7.5 wt%Ag/BP exhibited the strongest photocatalytic activity,and the degradation rate constant of MO was 9.38×10-3 min-1.The photocurrent density-time curve showed that compared with pure black phosphorus,the enhanced activity of the composite material was due to the improved separation efficiency of photogenerated electrons and holes.Finally,considering the differences in the Fermi levels of different layers of black phosphorus,a transfer mechanism that depends on the thickness of the black phosphorus was proposed.There may be a unidirectional transfer of electrons between the thin layer of black phosphorous and nano-silver,while the electron transfer mode of the thicker black phosphorus may be bidirectional.