Preparation Of Rectorite-based Photocatalytic Nanocomposite Materials And Studies On Properties And Mechanisms For Removing Methylene Blue In Water

The pigment is one of the most common pollutants in aqueous solutions.Rapid decolorization and deep oxidation of pigment is one primary concern of environmental scientist.Synthesis of composite materials that have high adsorption capacity and efficient catalytic performance would be a practical way to achieve these goals.In this thesis,by taking the advantage of rectorite(has high adsorption capacity for pigment and is a suitable carrier for photocatalyst),a series of rectorite based metal oxide composite catalysts were synthesized.Further,natural rectorite was modified into mesoporous rectorite(MES-REC)that was used to synthesize MES-REC based metal oxide or organic composite catalysts.The properties of these composite catalysts were characterized by different methods.Their adsorption capacity and catalytic performance were assessed by the removal efficiency of methyl blue(MB)from aqueous solution.The main conclusions are:(1)Rectorite based TiO2 and ZnO composite(REC/TiO2/ZnO)is first synthesized,in which TiO2 and ZnO were found in the surface and interlayer of REC.The adsorption and degradation of MB over REC/TiO2/ZnO follow the Langmuir adsorption isotherm and Langmuir-Hinshelwood kinetic model,from which the obtained adsorption capacity and reaction rate constant is 34.8 mg/g and 0.17 mg/(L·min),respectively.Hydroxyl radical(·OH)is the predominant reactive oxygen species that caused the degradation of MB.(2)Magnetic rectorite based ZnO composite(REC/ZnO/Fe3O4)is synthesized and characterized to achieve the fast separation of catalyst from water.The adsorption of MB on REC/ZnO/Fe3O4 followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm model.Langmuir-Hinshelwood kinetic model fits the degradation process well,and the reaction rate constant is 0.122 mg/(L·min).Four intermediates that produced during the degradation of MB are detected by LC/MS.(3)Compared with natural REC,MES-REC has much higher BET surface area and wider pore size range.Two magnetic MES-REC based ZnO composites(Mes-REC/ZnO/Fe3O4 and Mes-Si-REC/ZnO/Fe3O4)are synthesized.The adsorption capacity of Mes-REC/ZnO/Fe3O4 and Mes-Si-REC/ZnO/Fe3O4 to MB are 107 and 128 mg/g,respectively.Further,Mes-Si-REC/ZnO/Fe3O4 possesses more efficient catalytic performance than REC/ZnO/Fe3O4.The reaction rate constant is 0.713 mg/(L·min)based on the Langmuir-Hinshelwood kinetic model calculation.(4)Four REC or Mes-REC based organic composites(REC/C3N4,Mes-REC/C3N4,REC/C3N4/C,and Mes-REC/C3N4/C)are further obtained by a multi-step fabrication process,in which Mes-REC/C3N4 is the most efficient catalyst for MB removal.Reactive oxygen species competition results demonstrate that photo-generated hole is the predominant species that induce the decolorizati on of MB.Moreover,the results demonstrate that these composites are stable during the reuse process,which shows they are practical and functional materials for the removal of MB or other pigments from aqueous solutions.