Preparation And Study On The Enhanced Photocatalytic Activity Of Modified BiVO₄ Photocatalyst

As one of n-type semiconductors,BiVO₄ displays good photocatalytic performance under visible-light irradiation and attracts much attention in photocatalysis field in recent years.However,low separation efficiency of photogenerated hole-electron as well as poor adsorption capacity of visible light of BiVO₄ largely limits its practical application.Thus taking reasonable measures to enhance the absorption of sunlight,improve the photogenerated carrier migration velocity and separation efficiency has important scientific significance and social value.In this paper,pure BiVO₄,Cu-doped BiVO₄,Yb-doped BiVO₄,Ag/BiVO₄ and BiVO₄/BiOCl composites were synthesized by a low temperature hydrothermal process.The main work is as followed:1.Taking Bi（NO₃）₃.5H2 O and NH₄VO₃ as precursors,urea as precipitating agent,metal-doped BiVO₄ with different molar ratios were successfully synthesized via low-temperature hydrothermal method by adjusting the amount of CuSO4.5H2 O and YbCl3·6H2O.X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,UV-Vis diffuse reflectance spectroscopy（DRS）,X-ray photoelectron spectroscopy（XPS）were employed to characterize the composition and structure of the as-synthesized products.The effects of different metal amount on the Rhodamine B（RhB）degradation efficiency of the doped BiVO₄ composites were also discussed.Experimental results showed that Cu-BiVO₄ and Yb-BiVO₄ composites had better photocatalytic performance of RhB under visible light irradiation compared with pure BiVO₄.In the Cu-BiVO₄ composties,the doping Cu substituted the place of Bi ions in the crystal lattice of BiVO₄ and acted as electron capture centers to accelerate the separation of photogenerated electrons and holes and finally result in a superior photocatalytic property.In the Yb-BiVO₄ composties,the doped Yb element contributed to the formation to tetragonal phase and affected the bandgap value of BiVO₄.The states calculations demonstrated that the formation of tetragonal BiVO₄ played an important role in the improvement of photocatalytic activity.2.Ag/BiVO₄ composites with different Ag/Bi（molar ratio）were synthesized through a photo-reduction method.Due to the low recombination rate of photoelectron-hole,the as-synthesized Ag/BiVO₄ photocatalysts displayed enhanced photocatalytic activity of RhB.Moreover,the 10 at% Ag/BiVO₄ composite displayed the highest photocatalytic activity and exhibited favorable recycling characteristics.The mechanism of enhanced photocatalytic activity of Ag/BiVO₄ was also discussed.The decrease of photogenerated electron-hole recombination rate by suitable loading amount of Ag nanoparticles and the surface plasmon effect of the Ag nanoparticles were the main reason for the enhancing catalytic performance of Ag/BiVO₄ composites.3.BiOCl/BiVO₄ composites were successfully prepared through a simple two-step hydrothermal method.BiVO₄,KCl were used as bismuth source and chlorine source during the reaction.Besides,the best hydrothermal reaction time was found according to the photocatalytic activity.The photoelectric properties and catalytic properties of BiOCl/BiVO₄ composites were measured and the reason of enhanced photocatalytic performace was also studied by trapping experiment and other related tests.Compared with pure BiVO₄ and BiOCl,BiOCl/BiVO₄ composites own good photocatalytic activity,light stability and recyclability.Photocurrent response,electrochemical impedance spectroscopy,fluorescence spectra results shown that the formation of BiOCl/BiVO₄ composite has a benefit to the separation of the photogenerated electron-hole pairs and result in a better photocatalytic performace than pure BiOCl and BiVO₄ in the degradation of RhB under visible light.And the trapping experimental result demonstrated that the photogenerated holes were the main active species in the Rhodamine B degradation process.