Preparation, Thermal Stability And Photocatalytic Properties Of Bismuth Oxyhalide Composite Photocatalysts

In Bi-based semiconductors,BiOX?X=Cl,Br,I?is a novel kind of photocatalytic material with special layered structure and high photocatalytic performance.The strong internal electric field between the bismuth oxide layer and the halogen atom layer could effectively promote the separation of photo-generated e-/h+ pairs and exhibit good photocatalytic activity which can degrade various organics for non-toxic CO₂,H₂ O and other small molecules.The photocatalytic activity of BiOX is closed related to its composition.BiOX_xY_1-x,which contains two halogen atoms,could exhibits significantly higher photocatalytic activity than the pure BiOX.In this paper,the photocatalytic performance of BiOX_xY_1-x before and after calcination with different temperatures was investigated through degradation of rhodamine B or acid Orange II as probe reaction.Some physicochemical characterizations include X-ray diffraction?XRD?,scanning electron microscopy?SEM?,thermal gravity?TG?analysis,N2-physical adsorption,UV-Vis diffuse reflectance spectroscopy?DRS?,and Fourier translation infrared spectroscopy?FT-IR?were applied to study the thermostability of BiOX_xY_1-x catalysts and the effects of heat treatment on their crystalline phase,composition,morphology and light absorption and photocatalytic performance.The major research contents are followings:First,BiOCl_0.5Br_0.5 composite photocatalyst or precursor was prepared by co-precipitation method.The thermostability and effects of calcination on their photocatalytic performance were investigated.Results showed that when the temperature is below 500?,BiOCl_0.5Br_0.5 has good stability and no change in phase composition took place.Over 600?,Br element was gradually lost and produced Bi₂₄O₃₁Br₁₀ and the Cl element was relatively stabile.However,photocatalyst could maintain the microsphere morphology.The photocatalytic activity was improved owing to the increasing of crystalline which can accelerate the separation of photo-generated e-/h+ and produce more active radical.The activity reached the best at 450?.At even high temperature,the photocatalytic activity gradually declined because of the destruction of catalyst composition,the loss of specific surface area and surface hydroxyl group.Second,a series of BiOBr_xI_1-x photocatalysts were prepared by solvothermal method.The thermostability and effects of calcination on their photocatalytic performance were also investigated through heat treatment.Results show that,in terms of thermal stability,BiOBr_0.25I_0.75<BiOBr_0.75I_0.25<BiOBr_0.5I_0.5.I element was gradually lost and produced Bi₅O₇ I after different temperature calcination.Study on the catalytic performance of sample shows that calcination leads to the decrese in light absorption,special surface area diminution and the loss of surface hydroxyl group reduce.All these negative factors give rise to the decrease of photocatalytic activity.Third,a series of BiOCl_xI_1-x photocatalysts were prepared by solvothermal method.The result of the thermal stability and the changement of photocatalytic performance before and after calcination indicate that the stability of BiOCl_0.25I_0.75 is poor.I element was released and finally produced Bi₅O₇ I when it was calcined at 400?,while phase transition of BiOCl_0.5I_0.5 and BiOCl_0.75I_0.25 occurred at a higher temperature.The photocatalytic performance of composite materials declined in different degrees which was caused by decrease of light absorption ability,special surface area and surface hydroxyl group.The above research results indicated that the investigation in the relationship between the thermal stability and photocatalytic performance of BiOX_xY_1-x catalysts,the discussion in the displacement and release of two halogen elements could help to find the heating phase transformation of compound sample,which is important to give an insight into the property and the application on bismuth oxide halide materials.