Synergetic Removal Of Heavy Metals And Organic Compounds On Visible Light Responsive Bi₂O₃-TiO₂ Catalyst

Combined pollutions of heavy metals and organic compounds have widely existed in water,which are more complex and difficult to be controlled than a single pollution.However,at present,the compound pollutions are mainly concentrated in a respective and alone way,lacking of the effective control method.The narrow band semiconductor Bi₂O₃ was used to combine with TiO₂ catalyst,which could be achieved in visible light to deal with heavy metals and orgnic compounds combined pollutions.Here,heavy metals can trap photo-generated electronics,and organic matters can trap photo-generated holes,which can effectively inhibit the recombination of holes-electronic pairs,improving the photocatalytic processing efficiency of compound pollutions.Photocatalytic technology can cut down the toxicity of heavy metals and organic matters,realizing the coordination treatment of the reduction of heavy metals and the mineralization of organic matters.The Bi₂O₃-TiO₂ composite catalyst was prepared by hydrothermal process,with Bi（NO3）3 and butyl titanate as precursors.The structures of samples were characterized by X-ray diffraction（XRD）,X photoelectron spectroscopy（XPS）,Ultraviolet-visible spectroscopy（UV-Vis）,energy spectrum analysis（EDS）.The effect of amounts of Bi₂O₃ on the removal of heavy metal Cr（Ⅵ）and refractory organic DBP compound pollutions in water was investigated,as well as pH.What’s more,the mechanism of coordination processing of compound pollutions was discussed.The result showed that the best removal effect with the mass fraction of Bi₂O₃ was 4%.The optimal pH value for the removal of Cr（Ⅵ）or DBP pollution by Bi₂O₃-TiO₂ composite catalyst was 3.The conduction band of Bi₂O₃ is 0.36 eV,determining that the reduction of Pb（Ⅱ）can not happen(the reduction potential of Pb²⁺ turning to Pb⁰ is 0.1262 eV).However,it was found that Pb（Ⅱ）could be reduced,over Bi₂O₃-TiO₂ composite catalyst dealing with the compound pollutions of Pb（Ⅱ）and DBP in visible light.Moreover,the reaction could not happen over pure Bi₂O₃ or TiO₂.After illumination for 8 h,Pb²⁺ turned into PbO,Pb⁰ and PbO₂.After the light on for 18 h,there was no Pb ion residual in the solution,and Pb²⁺ turned into PbO and Pb⁰,deposited on the catalyst.In addition,the possible formation mechanism of Bi₂O₃-TiO₂ composite was proposed..Cu-EDTA complexometric compound wastewater was processed,using Bi₂O₃-TiO₂ semiconductor as catalyst in visible light.The reduction rate of Cu²⁺ in Cu-EDTA wastewater was much higher than that in the single Cu²⁺ wastewater,as well as the oxidation rate of EDTA.Cu²⁺could act as the electron capture agent,thus the oxidation rate of EDTA was accelerated,leading to the increasing of COD removal efficiency.In addition,EDTA could serve for the sacrifice of the cavitation agent,accelerating the separation of e--h+.The complexed Cu²⁺ was released into the solution again,and Cu²⁺ trapped e-to be reduced.After the treatment of Cu-EDTA on Bi₂O₃-TiO₂,Cu particles were deposited on the surface of Bi₂O₃-TiO₂.After calcination,the gemerated catalyst CuO/Bi₂O₃-TiO₂ could be used in the photo-catalytic reaction,and the photocatalytic efficiency increased.This provides a possible way to purify water,recycle Cu at the same time,solving the urgent environmental problems.