Modification Of Ultra-thin Bi₄O₅Br₂ Nanosheets Photocatalyst And Its Photocatalytic Mechanism

BiOX(X = Cl,Br,I)as a Ⅴ-Ⅵ-Ⅶ ternary oxide,is an important semiconductor material with layer structure.BiOX shows marked activity for the photocatalytic degradation of organic pollutants in wastewater because of its excellent chemical stability,nontoxicity,outstanding recyclability,the appropriate band gap,etc.Ultrathin Bi4O5Br2 nanosheets,as a new semiconductor materials,which was widely used in the preparation of high performance catalysts.In this work,ultra-thin Bi4O5Br2 nanosheets are successfully synthesized via a hydrothermal method.And Bi4O5Br2 was modified by depositing noble metals,constructing composite structures,and doping with metal ions.The phase structure,microstructure,and photochemical properties of Bi4O5Br2 and its composites were conducted.The mechanism of photocatalytic degradation of pollutants was also elucidated.First of all,the pure phase ultrathin Bi4O5Br2 nanosheets were synthesized by hydrothermal method.XRD analysis showed that the prepared samples were monoclinic Bi4O5Br2.The SEM results show that the Bi4O5Br2 has a nanosheet structure with the thickness of 9 nm.The noble metal Pd particles with diameter of 3-6 nm are successfully dispersed on Bi4O5Br2 nanosheets in Pd/Bi4O5Br2.The photodegradation rate of bisphenol A was used to evaluate the catalytic performance of Pd/Bi4O5Br2.The results showed that the photodegradation activities of 1.0 wt%Pd/Bi4O5Br2 is superior to pure phase ultrathin Bi4O5Br2,which was attributed to the fact that Pd could trap the electrons from the conduction band of Bi4O5Br2,which promoted the separation of electrons and holes on the surface of Bi4O5Br2.The scavengers experiments show that superoxide radical(·O2-)are the main active species responsible for the oxidization of BPA under visible light irradiation,and the role of hydroxyl radicals(·OH),electron,and holes have a negligible effect on BPA degradation.Second,AgNO3 was precipitated onto Bi4O5Br2 nanosheets via chemical precipitation method.The as-prepared samples were characterized by the phase structure,microstructure and optical properties.It was found that the monoclinic Bi4O5Br2 and cubic AgBr are coexisted in the sample.XPS results confirmed that the Ag element is presented in the as-prepared sample.According to the absorption spectra,the absorption edge of pure phase of Bi4OsBr2 is around 460 nm,and that of Ag/AgBr/Bi4O5Br2 composite is around 490 nm.The absorption edge of Ag/AgBr/Bi4O5Br2 composite catalyst display continuous red shift,as compared with pure Bi4O5Br2,which extends the light absorption from UV to visible region.The Ag/AgBr/Bi4O5Br2 exhibits a significantly enhanced absorption spectra in wavelength of 600 nm due to the surface plasma effect of Ag nanoparticles.The photocatalytic experimental results show that the photodegradation rate of Bi4O5Br2 nanosheets with loading 20%Ag/AgBr is about 2.6 times higher than that of pure Bi4O5Br2.PL spectra and photocurrent results indicated that the Ag/AgBr may inhibit the recombination of photogenerated electrons and holes on the surface of Bi4O5Br2,and result in a higher photocatalytic activity of Ag/AgBr/Bi4OsBr2.The scavengers experiments show that ·O2-and h+ play a major role in the catalysis process.Finally,the Fe-doped Ag-Fe/Bi4O5Br2 samples were successfully prepared by hydrothermal method.The XRD results showed that the diffraction peak of Ag-Fe/Bi4O5Br2 was similar to the pure phase Bi4O5Br2,and no impurity phase has been detected.From the TEM image,it can be seen that the Ag nanoparticles were successfully loaded on the Bi4O5Br2 nanosheets.XPS results indicated that Fe3+ is present in the Ag-Fe/Bi4O5Br2 sample.The photocatalytic performance of Fe/Bi4O5Br2 with different amount of Ag was evaluated by degradation of bisphenol A.The photocatalytic results showed that 0.5%Ag-Fe/Bi4O5Br2 can reach the highest degradation rate of bisphenol A.The significant enhancement in photoactivity can be attributed to Fe3+ will be oxidized by the hole to generate the Fe4+,whereas the holes would be consumed so that photogenerated electrons and holes recombination rate are reduced on the surface of Ag-Fe/Bi4OsBr2.Furthermore,the photogenerated electrons on the surface of Ag-Fe/Bi4OsBr2 could be captured by the Ag nanoparticles,which further promote the efficient separation of photogenerated carriers in the nanohybrid photocatalyst.Under light irradiation,·02-plays a major role in the catalytic degradation of bisphenol A,the h+ make a very small contribution to the photocatalytic reaction.