The Preparation And Research On Heterojunction Of Bi-based Photocatalysts

In recent decades,with the increasingly serious environmental pollution,the photocatalytic technology for pollution treatment has attracted lots of attention.The preparation and application of photocatalysts with high photocatalytic activity,chemical stability,and non-toxicity have become hot topics for researchers in the areas.In the field of photocatalysis,Bi-based photocatalysts were regarded as a promising material for photocatalytic application,because of their low valence bands,high chemical stability and excellent photocatalytic activity even under sunlight.In this paper,the photocatalysts of Bi2O2CO3/?-Bi2O3 and MnOx/BiPO4 were synthetized to obtain higher photocatalytic activity.The main findings of this paper were exhibited as follows.(1)Using Bi(NO3)3·5H2O as raw materials,with the mixture of ethylenediamine and deionized water as dissolvent,the n-p Bi2O2CO3/?-Bi2O3 heterojunction microtubes were prepared via a one-step solvothermal process for the first time.The effects of ethylenediamine-water ratio(Ven:Vwater)on the structure and morphology for the ?-Bi2O3 microtubes and Bi2O2CO3/?-Bi2O3 heterostructure were characterized by XRD,SEM,TEM,HRTEM and IR.The photocatalytic activities of Bi2O2CO3/?-Bi2O3 heterojunction microtubes were evaluated on the degradation of MB under visible-light irradiation(?>410 nm).The mechanisms of Bi2O2CO3/?-Bi2O3 heterojunction microtubule formation,microtubes growth and photocatalytic activity enhancement were discussed,respectively.The results indicated that the composition and morphology of the samples have been effects on the ratio of Ven:Vwater.Bi2O2CO3/a-Bi2O3 heterojunction microns with Bi2O2CO3 molar percentage 6.1%were obtained with Ven:Vwater= 2:6 and 140 ?solvothermal reaction temperature.The excellent Bi2O2CO3/?-Bi2o3 heterojunction had been formed via Bi2O2CO3 nanopar-ticles stomgly attached on the surface of ?-Bi2O3 microtubes.The results of XRD,SEM,TEM,and IR confimed that the tubular structure was formed via self-assembly of ?-Bi2O3 nanoplates,and the Bi2O2CO3/?-Bi2O3 heterostucture was created by situ carbonatization on the surface of ?-Bi2O3 microtubes.Compairing with ?-Bi2O3 microtubes,the Bi2O2CO3/?-Bi2O3 heterojunction shows higher photocatalytic activity when the molar percentage of Bi2O2CO3 is 6.1%,cause the matching band structure between Bi2O2CO3 and ?-Bi2O3,the photoelectron-hole pair would be migrated effectively via heterojunction interface to the two semiconductor surface,then reacted oxidation-reduction reaction,respectively,so as to improve the quantum efficiency.But excessive Bi2O2CO3 would covergare the surface of ?-Bi2O3 lead to reduce the absorption of visible light by a-Bi2O3,and reducing reactivity sites of the MB degradation.Furtherly,the structure and heterojunction interface of microtubes was destroyed,which resulted in the photocatalytic activity of composite materials would be reduced.(2)Using Na3PO4·12H20?Bi(NO3)3·5H2O as raw materials,CTAB as structure-directed agent,the rod-like monoclinic BiPO4 was prepared via hydrothermal route.Then using MnSO4·H2O as raw materials,MnOx/BiPO4 heterojunctions were formed by loading MnOx nanoparticles on the surfaces of BiPO4 rods via photo-deposition process.The as-prepared samples were characterized by XRD,SEM,TEM,XPS,FL,and UV-vis.The photocatalytic activities of MnOx/BiPO4 heterojunctions were evaluated on the degradation of MB under UV-light irradiation.And the mechanisms of MnOx/BiPO4 heterojunction materials photocatalytic activity enhancement were discussed.The results showed that MnOx nanoparticles were strongly anchored to the surfaces of BiPO4 rods when the atomic ratio of Mn/Bi was controlled at 0.08,forming MnO./BiPO4 heterojunctions with effective and sound interfaces.The MnOx/BiPO4 heterojunctions of the atomic ratio of Mn/Bi = 0.05 and 0.08 exhibited higher photoactivity than pristine BiPO4 for photodegradation of MB under UV irradiation,especially the sample of the atomic ratio of Mn/Bi = 0.08 had the highest photoactivity.Which could be attributed that MnOx was a deriving-hole-type cocatalyst,MnOx/BiPO4 heterojunction effectively promotes the separation of photo generated carriers and improves their photocatalytic activity.In addition,the combination of MnOx and BiPO4 can improve the absorption of light at the wavelength of 300-420 nm and the photocatalytic efficiency.