Preparation And Photocatalytic Properties Of Bismuth Based Semiconductor Composites

In recent years,the problems of environment have become a growing concern of all over the world.This leads to the technological development of the research activities and the pollution control.Titanium dioxide?TiO₂?has been extensively used and investigated as an excellent photocatalyst because of its exceptional properties such as nontoxicity,low cost,and long-termstability.However,TiO₂ has a wide band gap energy,which results in the fact that TiO₂ is only responsive to the UV region of the solar spectrum.In order to make full use of the richness of solar light,the development of efficient optical photocatalysts is imperative.Bismuth iodide?Bi OI?has the maximum absorption ability in visible-light region due to its smallest band gap,which can make up for the shortcomings that TiO₂ can only respond to ultraviolet light.Therefore,by preparing BiOI-TiO₂ heterojunction will greatly improve the photocatalytic activity of the photocatalyst.Moreover,BiOI has a unique layered structure characterized by[Bi₂O₂]²⁺slabs interleaved by double slabs of halogen ions,and its layered structure can induce an static electric field between the[Bi₂O₂]²⁺slab and double[I]^-slabs,which can effectively separated the electron-hole pairs in the BiOI samples.The double iodine atomic layers are bound by the non-bonding force between iodine atoms,which easily leads to the dissociation of the[Bi₂O₂]²⁺layer along the[001]crystal plane.Furthermore,the exposed oxygen atoms on the surface of[001]crystal plane can easily escape from a lattice to form vacancies,which should affect the physical and chemical properties to a large extent.As a result,facet engineering exposed with[001]crystal plane is an exciting direction for developing highly active new photocatalysts.In this paper,pure anatase TiO₂ was prepared by solvothermal method at low temperature using Ti?OCH₄?₄ as titanium source.BiOI-TiO₂ heterojunction samples were prepared by chemical precipitation method and ultrasonic method.The graphene oxide was prepared by Hummers method,GO-BiOI complex was prepared by the combination of GO and BiOI,and r GO-BiOI complex was prepared by reducing the composite by thermal reduction.The crystal structure,morphology and elemental distribution of the samples were investigated by XRD,SEM,TEM and EDS.The factors that may affect the photocatalytic activity and the microstructure of the samples were investigated by BET,UV-vis DRS and XPS.Methyl orange,a labile and degradable azo dye,was used as a simulated pollutant to test the photocatalytic activity of the samples.The mechanism of action of different reactive groups was studied by adding active group scavenger to the system.The main conclusions are as follows:1.The formation of heterojunction is beneficial to the dispersion of nanoscale titanium dioxide,with the increase of bismuth iodide content,the proportion of titanium dioxide agglomeration decreases.Moreover,because of the addition of titanium dioxide,it affects the unique layered microsphere structure of bismuth iodide and forms the heterojunction microsphere.The interaction between the TiO₂ and BiOI,not only reflected in the topography,but also further improve the visible light catalytic activity of the sample,the degradation rate of 80%BiOI-Ti O₂ samples to methyl orange?MO?is97.2%in two hours,and the degradation is almost complete.2.The 80%BiOI-TiO₂ sample prepared under ultrasonic 3h conditions is a nanosheet with side lengths of 100-500nm.TiO₂ was distributed on BiOI nanosheet and the 80%BiOI-TiO₂ sample have the largest specific surface area of 47.28 m²/g.Moreover,The 80%BiOI-TiO₂ prepared by ultrasonic irradiation showed the higher adsorption performance compared with the 80%BiOI-TiO₂ sample prepared by chemical precipitation,which degradation rate to MO has reached 93%within 1 h.3.The diameter of rGO-BiOI complex is greatly increased compared with the pure BiOI.Based on the unique structural rigidity of rGO,BiOI nanosheets can grow to larger sizes up to 15?m.At the same time,the photoresponse of the rGO-BiOI composite increases with the increase of graphene content.Due to the addition of graphene oxide in the system,the?001?crystal plane of BiOI is exposed,and the oxygen atoms exposed on the?001?crystal plane can easily escape from the crystal lattice to form oxygen vacancies.When the molar ratio of rGO/BiOI was 1:400,the composite exhibited the best photocatalytic performance.The degradation efficiency of methyl orange with GO_1/400-BiOI reached almost 96.2%within 2 h,which was 4.1 times that of pure BiOI.