Design And Photocatalytic Properties Of Bi-based Composite Semiconductor Materials

As an important visible-light response photocatalyst,the Bi-based photocatalysts have received increasing attention.Most of the Bi³⁺-containing compounds are stable,and have a special layered structure of[Bi₂O₂]²⁺with the Aurivillius type.However,the low utilization rate of visible light,the slow photogenerated electron-hole migration rate and the high recombination efficiency limit the photocatalytic activity of single Bi-based materials.Researchers have solved these problems by constructing composite catalysts,metal deposition,non-metal doping and so on.In this paper,in order to improve the photocatalytic properties of single Bi-based materials,the methods of constructing ZnO/Bi₄V₂O₁₁ binary composite oxides,depositing metal Bi on the surface of defect state BiO_2-x and introducing non-metallic C and metal Bi into Bi₂WO₆ were designed.Firstly,ZnO/Bi₄V₂O₁₁ composite photocatalysts with different mass ratios were synthesized by solvothermal method.Due to the oxidative photodegradation of dye molecules,the removal rate of RhB over P25 was 48.9%under visible light irradiation for 30 min,the degradation efficiency of pure Bi₄V₂O₁₁ was 69.3%.However,after introducing ZnO,the photocatalytic activity of ZnO/Bi₄V₂O₁₁composite was significantly improved.When the mass ratio of ZnO and Bi₄V₂O₁₁ is1:1,the photocatalytic activity of the composite catalyst is the highest,and the removal rate of RhB reaches 98.4%.The enhanced photocatalytic activity of the composites may be attributed to the low photogenerated helectron-hole recombination rate at the interface between the semiconductors and the increased specific surface area.The degradation process of RhB was studied in this chapter.The results showed that RhB was completely degraded after 30 min of visible light irradiation,and TOC was also verified.Additionally,combined with capture experiments,DRS and VB XPS,a possible photocatalytic mechanism was proposed.Secondly,Bi/BiO_2-x composite photocatalyst was firstly synthesized by solvothermal and liquid exfoliation methods to form the concave tetrahedral defect state BiO_2-x,and then ethylene glycol was used as reducing agent to deposit metal Bi with different loading on BiO_2-x.Since BiO_2-x is a defective semiconductor,it can be used as electron capture center to reduce the recombination efficiency of photogenerated carriers.The intrinsic defect structure of BiO_2-x and the SPR effect of the metal Bi can effectively improve the photocatalytic activity.The experimental results showed that the Bi/BiO_2-x composite catalysts have enhanced effects on the degradation of RhB,MO,BPA and CIP,and the reduction of Cr?VI?and PNA compared with BiO_2-x.XRD,SEM,TEM and XPS further indicate the successful deposition of the metal Bi on the surface of BiO_2-x,EPR and XPS characterizations also prove the existence of oxygen vacancies.EPR results show that·O₂^-are important active species,which is in good agreement with the free radical capture experiment.On this basis,combined with the DFT,VB XPS and DRS,a possible photocatalytic mechanism was proposed.Finally,using EDTA-Bi as the precursor,the metal Bi and nonmetallic C were introduced into Bi₂WO₆ in one step by a simple solvothermal method to synthesize C/Bi/Bi₂WO₆ composites.The photocatalytic degradation activity of C/Bi/Bi₂WO₆was higher than that of pure Bi₂WO₆,P25,Bi/Bi₂WO₆ and C/Bi₂WO₆.In addition,the photocatalytic activity of C/Bi/Bi₂WO₆ composite catalyst was more higher than Bi₂WO₆ in degrading other pollutants,such as MO,BPA,CIP and phenol and the rate constants are 1.4,3.4,6.2 and 2.3 times higher than that of Bi₂WO₆.The reason for the increase of photocatalytic activity of C/Bi/Bi₂WO₆ may be ascribed to the synergistic effect of the hybrid orbital constructed by C doping and the SPR effect of Bi.SEM,TEM,XRD,XPS,EDS mapping and other characterizations proved the formation of C/Bi/Bi₂WO₆ composite catalyst,EPR and capture experiments proved that h⁺are the main active species,·OH and·O₂^-have some role in the process of photocatalytic degradation.Combined with DRS characterization and Mott-Schottky plots curve,the possible photocatalytic mechanism of photocatalytic degradation of RhB with C/Bi/Bi₂WO₆ composite was proposed.