Synthesis Of Bismuth Oxide-based Photocatalysts And Study On The Photodegradation Of Organic Pollutants

The organic pollutants in wastewater could be mineralized completely by semiconductor photocatalytic technology under mild and controllable conditions,which has potential prospects in wastewater treatment.Bismuth oxide（Bi₂O₃）,an important semiconductor material with unique photoelectric properties,has been widely used in superconductor,capacitance,catalysis and other fields.Because of the suitable band structure（2.4-2.9 e V）,α-Bi₂O₃ andβ-Bi₂O₃ have better photocatalytic performance than other phases of bismuth oxide.However,the low photocatalytic efficiency and high recombination rate of photo-induced charge carriers,which greatly limit the photocatalytic performance in practical applications.As one of the most effective methods,construction of composite could improve the separation and transfer of photo-induced charge carriers and make up for the defects of single components.In this work,we prepared different bismuth oxide-based composites by simple synthesis methods.On the one hand,the effect of temperature on the crystal structure of bismuth oxide was used to synthesize the bismuth oxide hetero-phase junction.On the other hand,by using the crystal growth ofβ-Bi₂O₃ in the solvo-thermal process and by changing the growth substrate ofβ-Bi₂O₃,two completely different systems ofα/β-Bi₂O₃hetero-phase junction and g-C₃N₄/β-Bi₂O₃ heterojunction were constructed.（1）Bi（NO₃）₃·5H₂O was used as Bi source to synthesizeβ-Bi₂O₃ by solvothermal method.After calcination at different temperatures,it was found that the crystal phase of bismuth oxide gradually transformed fromβ-phase toα-phase,and theα/β-Bi₂O₃ hetero-phase junction was obtained at the intermediate temperature.The physical and chemical properties and photoelectrical properties of the materials were characterized by X-ray diffraction,fourier transform infrared spectroscopy,electron microscopy,UV-vis diffuse reflectance spectroscopy,X-ray photoelectron spectroscopy and fluorescence spectroscopy.The photocatalytic degradation of tetracycline hydrochloride（TC-HCl）by this series of bismuth oxide materials was investigated;（2）Bi（NO₃）₃·5H₂O was directly calcined at high temperature to produceα-Bi₂O₃,which was added into the solvothermal system for the synthesis ofβ-Bi₂O₃.A series ofα/β-Bi₂O₃ hetero-phase junction materials were obtained by adjusting the mass ratios of two kinds of bismuth oxides with different crystal phases.Different from the previous part,the hetero-phase junction obtained here has controllable composition and regular morphology,and the electron transfer direction at the hetero-phase junction interface in the photocatalytic process was determined by X-ray photoelectron spectroscopy and reactive species analysis.The photocatalytic degradation activities of rhodamine B（Rh B）and TC-HCl were investigated.（3）Melamine（C₃H₆N₆）was used as the precursor to synthesize graphitic carbon nitride（g-C₃N₄）,which was added into the solvothermal system for the synthesis ofβ-Bi₂O₃.A series ofβ-Bi₂O₃/g-C₃N₄heterojunction materials were successfully obtained.The growth process ofβ-Bi₂O₃on the surface of g-C₃N₄was observed by scanning electron microscopy（SEM）,and the chemical reaction was analyzed.The mechanism of the heterojunction in photocatalytic degradation of Rh B and p-nitrophenol（PNP）was investigated by X-ray photoelectron spectroscopy,fluorescence spectroscopy and free radical capture experiments.A novel Z-scheme charge transfer path way was proposed.