Construction And Photocatalytic Properties Of Bismuth Based Oxide Semiconductor Heterojunction

Semiconductor photocatalytic technology has great prospects in the fields of new energy,organic synthesis and environment purification due to its green environment protection,will not cause secondary pollution and other advantages.However,the performance of the traditional photocatalyst TiO₂ in the utilization of visible light and the migration and separation of photogenerated carries is not satisfactory,which severely limits the expression of its photocatalytic activity.Bismuth-based semiconductor photocatalytic materials exhibit potential photocatalytic activity due to their unique electronic and crystal structure,and therefore have received extensive attention.Bi₂WO₆ is a multi-element layered oxide with a perovskite layered structure.The valence band of Bi₂WO₆ is formed by hybridization of O 2p and Bi 6s orbitals,while the conduction band is dominated by W 5d orbitals.The special crystal and energy band structure are conductive to the separation of photogenerated electron-hole pairs and the absorption of visible light,thus giving Bi₂WO₆ potential photocatalytic activity.NaBiO₃ has high photogenerated carrier separation efficiency and visible light response capability attributed to its unique layered structure and suitable band gap value.However,the recombination rate of photogenerated carriers in the pure phase material is much greater than the separation rate,which causes up to about 95%of the photogenerated carriers to be consumed in the recombination process.Therefore,how to weaken the recombination process of carriers is extremely important and sometimes even decisive for improving the photocatalytic activity of materials.As visible light photocatalyst,the main merit of bismuth oxides（Bi _XO_Y）are their suitable bandgap energy between 1.5～3.0 e V,which can largely expand the light absorption range.Based on this,this project uses Bi₂WO₆ and NaBiO₃ as raw materials to construct heterojunction to solve the above problems and the following conclusions are obtained:1.The Bi₂O₄/Bi₂WO₆ heterojunction microspheres are prepared by hydrothermal method successfully.Rod-shaped Bi₂O₄ grows in situ on the surface of Bi₂WO₆ microspheres.The photocatalytic test results show that the degradation rate of Bi₂O₄/Bi₂WO₆-3 composite material to degrade Rhodamine B（Rh B）and Methyl Orange（MO）under visible light irradiation is 5 and 90 folds than that of pure phase Bi₂WO₆,respectively.The results of the active radical capture experiment show that superoxide radicals（·O₂^-）and holes（h⁺）are the main active species in the photocatalytic reaction process.2.The NaBiO₃/BiO_2-x heterojunction is constructed in situ by the electrochemical method with NaBiO₃ as the only raw material,which reduces the carrier recombination rate effectively.Studies have shown that the degradation rate of NaBiO₃/BiO_2-x composite to degrade Rhodamine B under visible light is 1.69 folds than that of pure NaBiO₃.NaBiO₃/BiO_2-x exhibits universal photocatalytic degradation activity for other pollutants（Methyl Orange（MO）,Bisphenol A（BPA）and Ciprofloxacin（CIP））.3.By adjusting the PH value of the electrolyte to alkaline in the preparation system of the second work mentioned above,the NaBiO₃/Bi₂O₃/Bi₂O_2.75 three-phase heterojunction was successfully prepared.Both NaBiO₃ and Bi₂O₃,NaBiO₃ and Bi₂O_2.75 form a type II heterojunction,which reduces the recombination of carriers.The photocatalytic degradation rate of NaBiO₃/Bi₂O₃/Bi₂O_2.75 composite to degrade Rhodamine B is 1.45 folds than that of pure phase NaBiO₃ under visible light.In addition,the synthesized NaBiO₃/Bi₂O₃/Bi₂O_2.75 exhibits excellent photocatalytic activity against a variety of pollutants（Congo Red,Methyl Orange,Methylene Blue and Bisphenol A）.4.In addition,we have conducted preliminary explorations on the formation mechanism,charge transfer mechanism and performance improvement mechanism of Bi₂O₄/Bi₂WO₆,NaBiO₃/BiO_2-x and NaBiO₃/Bi₂O₃/Bi₂O_2.75 composite materials.