Synthesis Of LaVO₄/BiOBr Composite Photocatalyst And Their Photocatalytic Performance

As a visible light catalyst,bismuth bromide possesses a layered structure and a suitable band gap.Lanthanum vanadate is a fluorescent material,which is also a photocatalyst.In this paper,LaVO4/BiOBr composite photocatalysts were synthesized by a hydrothermal process and ultrasonic hydrothermal process.The morphology of products varied with the incorporation ratio of two kinds of materials,and the visible light photocatalytic activity of composite photocatalyst was improved.The products were characterized by using XRD,XPS,SEM,PL,UV-vis DRS and other physical or chemical testing method.It revealed the heterogeneous nucleation-growth mechanism on synthesizing of LaVO4/BiOBr was proposed,and the degradation ability of the samples for the organic pollutant also studied.m-LaVO4/BiOBr photocatalyst was prepared by a two-step hydrothermal method.It was found that the crystalline morphology and photocatalytic properties of BiOBr composite photocatalysts varied with the quantity of dropped m-LaVO4.The test results of XRD and SEM showed that the sample containing 1.0 wt%m-LaVO4 exhibited the best photocatalytic performance for degrading organic pollutant(RhB),the degradation rate reached 83.37%within 60min.PL and UV-vis results showed the heterojunction was formed in the as-prepared samples,it might inhibit electron-hole recombination.When m-LaVO4 was excessively added,sample's diameter remarkably increased upto 500nm.The excessive addition of m-LaVO4 also caused particle aggregation,which reduced the sample's photocatalytic performance.t-LaVO4/BiOBr photocatalyst was prepared by a two-step hydrothermal method.It was found that the crystalline morphology and photocatalytic properties of BiOBr composite photocatalysts varied with the quantity of dropped t-LaVO4.In the preparation process of t-LaVO4,the accession to the EDTA controlled at EDTA:La3+=1:12,by which nanoparticles of t-LaVO4 could be prepared.Crystallization of BiOBr was effectively inhibited by adding t-LaVO4.Without t-LaVO4,their diameter was between 1200-1500nm,while the addition of 1.0 wt%t-LaVO4 could greatly reduce particle sizes,their diameters are appropriately 50nm.With the increasing of t-LaVO4 dropping amount,single lamellar BiOBr gradually formed into multi-lamellar structure,whose surface adhered a large number of tiny dimensional nano?sheet.Photocatalysis test showed that 1 wt%t-LaVO4 content of the hybrid photocatalyst catalytic exhibited highest photocatalytic performance.Degradation rate reached 89%within 60 min under visible light.m-LaVO4/BiOBr photocatalyst was prepared by an ultrasonic treatment-hydrothermal method.The precursor can be uniformly dispersed in the solution by ultrasonic technique.The experimental results showed that ultrasound was helpful to reduce the crystal size.Samples contained large quantities of smaller size nano-sheet in 20min ultrasonic progress and 40 min.The ultrasonic sample of 0.5wt%m-LaVO4 dropped is similar to non-ultrasonic in morphology,but when m-LaVO4 increased to 1 wt%differenced nano-sheets ratio of two orders of magnitude.Ultrasound can improve the photocatalyst dispersion and restrict generation of large size nanosheet.It has a synergistic effect on improving the photocatalytic performance.Ultrasonic progress reduced the demand for composite's dropping amount.Long time ultrasonic treatment may cause premature crystallization and adversely affect the photocatalytic performance.However,compared with non-ultrasonic photocatalytic performance of photocatalysts could be remarkably improved by ultrasonic treatment.It reduced half of time to degrade RhB to 80%than non-ultrasonic photocatalysts.