The Research Of Bismuth Vanadate Modified By Silver Nanoparticles And Reduction Of Graphene Oxide And Their Photocatalytic Performance

With the global energy crisis and environmental pollution becoming serious,it has become a research topic to find visible light responding photocatalysts which can use solar energy effectively to degrade pollutants in the environmental sicence and technology.Bismuth vanadate which is a new kind of environmental photocatalyt has attracted much attention due to its narrow bandgap and high visible photocatalytic activity.However,it is difficult to separate the electron and hole pairs from the photoelectron-hole pair of pure bismuth vanadate because the pairs are easily recombined on the catalyst body and surface.As a result,the quantum efficiency of bismuth vanadate and the photocatalytic activity of degradating pollutants both are much low.In this paper,silver nanoparticles and reductive graphene oxide were used as modifying agents on the basis of comprehensive analysis of the existing photocatalyst modification technology.Reduced graphene oxide has many merits,such as high carrier mobility,maximal surface area and so on,while silver nanoparticles can show the local surface plasmon resonance phenomenon which can enhance the absorption of visible light.The new photocatalyst was prepared by using silver nanoparticles and reductive graphene oxide and this material is called BiVO4-Ag-reductive graphene oxide(AgGB).The physical and chemical properties of AgGB were characterized and its degradation performance was tested by a series of methods.The main contents and conclusions of this paper are following:(1)The photocatalystic composites of AgGB were prepared by one step hydrothermal method and then charactered.Ultraviolet-visible diffuse-reflection spectroscopy UV vis DRS,X ray diffraction XRD,X ray photoelectron spe--c troscopy,Raman scattering spectroscopy,scanning electron microscopy SEM and energy dispersive X-ray(EDX)were used to characterize the prepared composites.The results showed that bulk monoclinic needle-like BiVO4 and Ag nanoparticles with a diameter of approximately 40 nm formed microspheres(diameter,4–7 ?m)with a uniform size which distributed on the rGO sheets.This can facilitate the transport of electrons photogenerated in BiVO4,thereby reducing the rate of recombination of photogenerated charge carriers in the coupled AgGB composites system.Other Ag nanoparticles were dispersed on the surface of the rGO sheets,which can exhibite a localized surface plasmon resonance phenomenon and could enhance visible light absorption.The forbidden band width of the systhetic photocatalyst sample is 2.42 eV,while the monoclinic BiVO4 has a band gap of 2.4 eV.The experimental result is in agreement with the theoretical value.(2)The formation of hydroxyl radical and superoxide radicals in BiVO4 and composites were analyzed by electron paramagnetic resonance method.The results showed that hydroxyl radical and superoxide radical were hardly produced in dark condition.The hydroxyl radical and superoxide radicals produced by the composites with time during the lamp-on reaction.(3)The photocatalytic degradation of AgGB composites was carried out by adding 0.1 mmol silver nitrate(electron trapping agent)and 0.1 mmol potassium sodium tartrate(hole-trapping agent)respectively to discuss the effects of electrons and holes during the photocatalytic activity.The results showed that the photocatalytic reaction rate was obviously inhibited by the addition of the hole-trapping agent in the degradation process.The degradation rate of the photocatalyst was much faster after adding the electron capture reagents.In the catalytic reaction system,the holes played a major role in degradation process.(4)The photocatalytic degradation of rhodamine B was investigated by adding benzoquinone to caputure hydroxyl trapping agents and isopropanol to capture superoxide radicals scavenger.The results showed that superoxide radicals play important roles in the degradation of rhodamine B during the degradation.