Research On Modification Of Bi-based Semiconductor Photocatalysts

In this paper,two typical bismuth-based semiconductor materials,bismuth oxide and bismuth ferrite,are selected to be modified by element doping,heterojunction construction,and the coupling synergy between element doping and heterojunction construction,aiming to obtain photogenerated electrons.Heterojunction photocatalysts with high separation efficiency of/hole pairs and good catalytic performance,explore new ways for the controllable construction of visible light catalysts,and clarify the effects of different methods on the photocatalytic performance of bismuth-based semiconductor materials.The photocatalytic performance of the synthesized materials was evaluated by the degradation of organic compounds（methyl orange,MO）.The active species in the photocatalytic oxidation process were detected by the radical trapping experiment.The energy band of prepared semiconductors were carried out,and the possible photocatalytic mechanism of MO was proposed.It is expected to provide a new strategy for the development of bismuth-based heterojunction photocatalytic materials with high visible light catalytic activity.Its main research contents are as follows:（1）Based on the element doping strategy,5%Y³⁺-doped bismuth ferrite and 15%Y³⁺-doped bismuth oxide were synthesized by low-temperature thermal decomposition of coordination precursors.Compared with the undoped samples,5%Y³⁺doping did not significantly affect the crystal phase of bismuth ferrite,but 15%Y³⁺doped bismuth oxide changed the crystal phase from monoclinic to tetragonal.At the same time,doping can reduce the particle size of the samples,Y³⁺doping significantly improves the catalytic properties of bismuth ferrite and bismuth oxide.（2）Based on the strategy of constructing heterojunctions,Bi₂O₃/BiFeO₃heterojunctions with different bismuth oxide loadings（5%-25%）were synthesized by a simple hydrothermal method.It is found that there is an optimal ratio for constructing a heterojunction.When the loading of bismuth oxide is 20at.%,the separation and transmission efficiency of photogenerated carriers reaches the highest.The photocatalytic performance of the sample was tested with 20 mg/L MO solution as the simulated dye,and it was found that the degradation rate of 0.2BO was 28%and 17%higher than that of P-BO and P-BFO,respectively.The degradation mechanism of 0.2BO was analyzed by band structure and radical trapping experiments,indicating that the heterojunction belongs to type II heterojunction,which can effectively separate photogenerated electrons and holes in space.（3）Based on the strategy of coupling synergy between element doping and heterojunction construction,a simple hydrothermal method was used to synthesize 15Y-BO/5Y-BFO heterojunctions with 5%～25%.20%BO showed the highest photocatalytic activity in the degradation of 20mg/LMO solution,and the degradation rate could reach 98%when illuminated for 100 min,which was 38%and 27%higher than that of 15Y-BO and 5Y-BFO,respectively.The doping of elements changes the energy band structure,reduces the forbidden band width,widens the valence band,and forms a special direct Z-type heterojunction structure,which utilizes the redox ability of photogenerated electrons and holes to a greater extent.After five recycling cycles,the degradation rate of 20%BO remained at 95%.It provides a new strategy for constructing catalysts with excellent visible light catalytic performance.