Facet-controlled Synthesis Of Bi₂₄Ga₂O₃₉ And Its Visible Light Photocatalytic Activity For Reduction Of Cr???

In today's society,environmental pollution is an important factor that hinders sustainable development.Among these environmental pollution,heavy metal ions pollution in water that brought by the rapid development of industrialization is also becoming increasingly serious.Photocatalysis technology has gained much attention since being found because of its many advantages,such as unique redox properties,non-secondary-pollution,cleanliness and economizing energy.Among various photocatalytic materials,sillenite,as a new type of photocatalyst with the visible light response,has unique electronic structure and has been studied intensively.In the present study,sillenite-type Bi₂₄Ga₂O₃₉ photocatalysts and Bi₂₄Ga₂O₃₉/graphene composites were prepared by a simple and controlled hydrothermal method,Cr???aqueous solution was chosen as model heavy metal pollutant to evaluate the photocatalytic activity of the as-prepared catalysts under visible light irradiation??>400 nm?.The main research work is as follows:The as-prepared Bi₂₄Ga₂O₃₉ samples were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,ultraviolet visible diffuse reflectance spectrum?UV-vis DRS?.XRD and SEM analyses revealed that Bi₂₄Ga₂O₃₉micro-tetrahedrons enclosed by{111}facets and micro-cubes enclosed by{100}facets were obtained successfully.UV-vis DRS analysis showed that the onset absorption wavelength of the as-prepared samples through the hydrothermal route was shifted toward visible region as compared to the sample prepared by a solid state reaction.Hydrothermal time and temperature showed little influence on the phase and morphology of the sample enclosed by{100}facets?BGO-C?,but the composition of mineralizer greatly affected the phase and morphology of BGO-C.Photocatalytic removal of Cr???showed that BGO-C exhibited enhanced photocatalytic activity as compared to other samples.The decrease of initial pH values and initial concentration of Cr???,and the increase of photocatalyst dosage were beneficial to photocatalytic removal of Cr???.The removal mechanism of Cr???demonstrated that the reduction of Cr???to Cr?III?occurred in the presence of Bi24Ga2O39 photocatalyst under visible light irradiation.The theoretical calculations were carried out based on density functional theory.The calculated surface energy showed that the cleavage energy of?100?surface was lower than that of?111?surface,which was consistent with our experimental results.The surface electronic structures analysis showed that the metal-like electronic properties of{100}surface are confirmed,promoting separation of the photo-generated electrons and holes,which might result in the higher photocatalytic property.What's more,photoluminescence spectra?PL?also confirmed this conclusion.XRD,transmission electron microscopy?TEM?and laser Raman spectroscopy?Raman?analyses revealed that Bi24Ga2O39/graphene composites were prepared successfully.UV-vis DRS analysis showed that an obvious red shift occurred and the absorption intensity was increased for the composite photocatalyst.PL analysis revealed that Bi₂₄Ga₂O₃₉/graphene composites had higher separation efficiency of photogenerated electron-hole pairs,and with the increase of the content of graphene,the separation efficiency became higher.Photocatalytic reduction of Cr???showed that the efficiency of Cr???reduction was enhanced with the increase of the content of graphene.