Synthesis And Photocatalytic Performance Of BiVO₄/RGO Composites For Degradation Of Orange ?

Dye wastewater is recognized as one of the refractory wastewater.It will cause serious water pollution if discharged into the water.Nowadays,it has become one of the factors threatening the safety of water environment.However,traditional water treatment technologies have less degradation efficiency.It is urgent to find an effective way to treat dye wastewater.As a kind of advanced oxidation process,photocatalytic technology has the advantages of rapid reaction,good treatment effect and no secondary pollution.Compared with other advanced oxidation processes,photocatalytic technology has mild reaction conditions and high stability,thus is considered to be the most promising water treatment technology.Bismuth vanadate?BiVO₄?is a common photocatalyst.It has attracted wide attention because of its narrow band gap.However,its defects in practical applications,such as insufficient adsorption properties and easy combination of photogenerated e^--h⁺pairs,which seriously restrict the photocatalytic activity of BiVO₄ and its application in the field of photocatalysis.Graphene has excellent photoelectric properties and large specific surface area.The modification of BiVO₄ with graphene is considered to be an effective method for solving BiVO₄ defects.Based on the above,BiVO₄/Reduced Graphene Oxide?BiVO₄/RGO?composites were prepared by hydrothermal synthesis method in this study.The process of preparation,the method of characterization,the experiment of photocatalytic performance and recyclability of the composites were also studied and the photocatalytic mechanism was explored.The specific research results are as follows:1.In this study,a simple hydrothermal method was employed to synthesize BiVO₄/RGO composites by using Bi?NO₃?₃·5H₂O,NH₄VO₃ and Graphite powder as precursors.The morphology character,crystalline information and structural property of the photocatalyst were characterized by SEM,TEM,XRD,FTIR,UV-Vis DRS and XPS.It is confirmed that the prepared BiVO₄ is monoclinic BiVO₄.The introduction of RGO can change the electronic structure of BiVO₄ in BiVO_4/RGO composites,thereby reducing the band gap of BiVO₄/RGO,broadening the optical response range,improving photocatalytic performance.2.The photocatalytic activity of BiVO₄/RGO composite was evaluated by degradation of orange II?AO7?as the target pollutant.To evaluate the effect of different preparation conditions and reaction conditions on the degradation efficiency of the AO7,a series of experiments were carried out under various conditions.Results show that the prepared BiVO₄/RGO composite exhibited much higher photocatalytic activity than pure BiVO₄.The prepared BiVO₄/RGO composites have the highest photocatalytic properties under the preparation conditions of hydrothermal temperature?180?C?,hydrothermal time?6 h?,the doping amount of GO?16.7%?and pH of precursor fluid?pH=9?.The dosage of catalyst affects the photocatalytic effect,the removal rate increases first and then decreases.In addition,the initial concentration of the solution also affects the photocatalytic effect.At lower concentration,the composite exhibited better photocatalytic activity.Finally,the BiVO₄/RGO composite with the best photocatalytic activity was selected for three reuse experiments.It can be found that the recyclability of the material still has great room for improvement.3.Through the analysis of three-dimensional fluorescence spectrum,ultraviolet-visible spectroscopy?UV-Vis?and chemical oxygen demand?COD?,it is concluded that the photocatalytic mechanism of BiVO₄/RGO is as follows:Firstly,electron-hole pairs are excited within BiVO₄ upon irradiation.Then,the electrons are transferred quickly from the conduction band?CB?of BiVO₄ to the surfaces of the RGO and consumed by dissolved oxygen to yield·O₂^-,which can react with H₂O/H⁺to form·OH.Meanwhile,the holes on the valence band?VB?of BiVO₄ can oxidize H₂O/OH^-to also form·OH.·O₂^-and holes equipped with strong oxidizability also can oxidize AO7 molecules.In order to testify the existence of different radicals and compare the roles in the degradation of AO7,a set of radical trapping experiments were carried out.Results showed that·O₂^-is the primary radical for the degradation of AO7.It can be known that AO7 dye molecules cannot be directly mineralized into CO₂ and H₂O during photocatalytic degradation,but a series of intermediate organics are formed by the destruction of chromophore and benzene-like structures,and then degraded into CO₂ and H₂O.In conclusion,BiVO₄/RGO composites with excellent photocatalytic activity were prepared by hydrothermal synthesis method.The characterization and photocatalytic activity experiments showed that BiVO₄/RGO composites had good removal effect on AO7 solution.In addition,the effects of preparation conditions and reaction conditions on photocatalytic activity were discussed.And the photocatalytic degradation mechanism of AO7 dye wastewater by BiVO₄/RGO composite was explored by a series of testing methods.