Preparation, Characterization Of Heterojunction Photocatalyst With High Activity Under Visible Light Irradiation

With the industrial development of human society, environmental problemsbecome more and more serious. Since Fujishima and Honda reported the evolutionof oxygen and hydrogen from a TiO₂electrode under the irradiation of light in1972,photocatalysis was regarded as one of the most effective and economical ways tosolve the environmental problems. However, the most of the available light sourcesfor photocatalytic purification are UV lamps with major emission at253.7nmwavelength, providing photon energy greater than the band gap of semiconductorslike TiO₂（corresponding to388nm）. Recently, heterojunction semiconductors aretaken into consideration to improve the photocatalytic activity. Generally, severaladvantages can be obtained from the heterojunction structures:（1） improved chargeseparation properties;（2） an increase in the lifetime of the charge carriers; and （3） anenhancement of the interfacial charge-transfer efficiency to adsorbent substratematerial.In this thesis, we prepared several heterojunction photocatalysts by a simplegrinding–annealing method. The photocatalysts were characterized by X-raydiffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive X-rayspectrometer （EDS） and UV–vis diffuse refection spectroscopy （DRS）. The mainresults are as follows:（1） The p–n heterojunction photocatalysts p-CuBi₂O₄/n-ZnO were prepared bya simple grinding-anealling method. The photocatalytic activity of the photocatalystwas evaluated by photocatalytic degradation of Rh-B. The results showed that thephotocatalytic activity of the p–n heterojunction photocatalyst CuBi₂O₄/ZnO was much higher than single phase CuBi₂O₄or ZnO and the mixture of CuBi₂O₄andZnO without ball milling under visible light irradiation. The optimal percentage ofloaded CuBi₂O₄is5wt.%. The mechanisms of infuence of CuBi₂O₄on thephotocatalytic activity of CuBi₂O₄/ZnO were also discussed by the p–n junctionprinciple and the valance band theory.（2） A series of CuBi₂O₄/NaTaO₃heteronanostructures were synthesized withthe simple grinding–annealing method. The photocatalysts were characterized byX-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy-dispersivespectroscopy （EDS） and UV–vis diffuse reflectance spectroscopy （DRS）. Thephotocatalysts exhibit enhanced photocatalytic activity for methyl blue dyedegradation under visible-light irradiation. The highest photocatalytic degradationefficiency was observed when the sample calcined at500oC with50wt.%CuBi₂O₄content. As the formation of p-n junction, the photogenerated electron–hole pairs areseparated by the inner electric field, and the photocatalytic activity is enhancedgreatly.（3） Aseries of CuBi₂O₄/BaTiO₃heteronanostructures were synthesized with thesimple grinding–annealing method. The photocatalysts were characterized by X-raydiffraction （XRD）, scanning electron microscopy （SEM）, energy-dispersivespectroscopy （EDS） and UV–vis diffuse reflectance spectroscopy （DRS）. The resultsshowed that the photocatalytic activity of the p–n heterojunction photocatalystCuBi₂O₄/BaTiO₃was much higher than single phase CuBi₂O₄or BaTiO₃and themixture of CuBi₂O₄and BaTiO₃without ball milling under visible light irradiation.The best photocatalytic activity occurs when the sample calcined at600oC with30wt.%CuBi₂O₄content. As the formation of p-n junction, the photogeneratedelectron–hole pairs are separated by the inner electric field, and the photocatalyticactivity is enhanced greatly.