Preparation And Photocatalytic Activity Of Graphene-BiOX Based Composites

Energy shortages and environmental degradation are the most important issues of concern in the world today.China is not only a big energy shortage country,but also a big energy consuming country.With the rapid development of economy,fossil energy consumption and pollution emissions are becoming more and more serious.Photocatalysis has opened up a feasible way to achieve this energy cycle process because it can utilize directly sunlight to drive a series of chemical processes that are difficult to perform under mild conditions.Semiconductor TiO₂ has attracted much attention due to its high stability,low cost and non-toxicity.It is widely used in the field of photocatalysis.However,TiO₂could only respond to the UV region of the solar specturm,which lead to low utilization rate of sunlight,high recombination of carries and lower quantum efficiency.Therefore,searching for a new photocatalysts driven by visible light has become a topic of increasing concern.BiOX?X=F,Cl,Br,I?as a ternary compound is considered to be one of the high-activity photocatalysts due to its particular layered structure.The unique layered structure not only exhibits many excellent properties,for example,optical properties,electrical properties,and structural anisotropy,but also facilitates the formation of an internal electric field.In this way,the photogenerated carriers of BiOX could be separated and transferred efficiently through the formation of an internal electric field.Nonetheless,BiOX has low photocatalytic activity and limited response to visible light,so it is complexed with narrow band gap BiVO₄.BiVO₄ is able to respond well to visible light and is harmless and high stability.The graphene,as a novel two-dimensional material,has a large specific surface area and high-efficiency carrier mobility.Besides,the graphene has good electrical and thermal conductivity.The photocatalytic performance of the semiconductor can be greatly improved through compounding with graphene.In this paper,the Graphene-BiOX based composites with different proportions were prepared by hydrothermal method.XRD,SEM,TEM,UV-Vis DRS and XPS were employed to characterize the crystal structure,morphology,optical properties and chemical state of the prepared samples.The main conclusions are as follows:1.The rGO/TiO₂/BiOI ternary complexes of different Bi/Ti ratios were synthesized by hydrothermal method.The photodegradation of methyl orange under visible light was measured.The degradation rate of methyl orange by GTB photocatalyst with 80%Bi/Ti was almost 100%within one hour.Compared with the pure samples,the photocatalytic activity of the prepared photocatalyst was greatly improved.By measuring the band structure of the composite materials,the possible photocatalytic mechanism is proposed.The improvement of photocatalytic performance is attributed to the formation of p-n heterostructure by interface contact between TiO₂ and BiOI.In addition,graphene as the carrier,which is conducive to the transfer of electrons and promotes the separation efficiency of carriers,thereby the photocatalytic activity of GTB compounds could be improved.2.The rGO/BiOI/BiOCl composites were prepared through ultrasonic coupled with a hydrothermal process.The results of XRD,UV-Vis DRS show that the prepared samples have good crystallinity and optical properties.The photodegradation of methyl orange under visible light was measured and the degradation rate of GBB 200 sample to methyl orange is almost98%within 1 h.The degradation efficiency of methyl orange with GBB 200 photocatalyst was about 3.3 times that of pure BiOI,which was twice that of BiOCl.Compared with the pure samples,the photocatalytic activity of synthesized samples has been greatly improved.3.The rGO/BiVO₄/BiOCl composite materials were synthesized by hydrothermal method.The synthesized photocatalysts were characteristiced by XRD,UV-Vis DRS,XPS and the results showed that the samples had good crystallinity,purity and optical properties,and had a good response to visible light.XPS results showed that Bi⁵⁺was present in the sample and Bi⁵⁺was favorable to the generation of oxygen vacancy.The photodegradation of methylene blue in visible light was also measured.Compared with two pure samples,it shows that the methylene blue was completely degraded in 2 hours by GVB1000 photocatalyst and the photocatalytic performance was greatly improved.Meanwhile,the band structure of composites was plotted by the measurement of MS and VBXPS.Besides,the possible photocatalytic mechanism of prepared photocatalysts was suggested.Graphene as a substrate is beneficial to transfer electron between BiVO₄ and BiOCl,and promotes the separation efficiency of photogenerated carriers,so photocatalytic activity of GVB samples could be enhanced.