| Since the semiconductor photocatalyst has the abilities for environmental restoration and the potential applications of producing clean energy,it has aroused the interest and attention of the whole word's scientists.As one of them,TiO2 semiconductor has been widely researched and applied due to its non-toxic,remarkable stability and low cost.But,the band gap of TiO2(approximate 3.2 eV)is too wide to use in the visible region,and can only absorb the ultraviolet light accounted less than 7%of the whole solar spectrum,and other 50%is visible light,in order to utilize it,photocatalyst that can efficiently separate and transport the photogenerated carriers by visible light needs to be investigated and developed.While multiferroic BiFeO3 materials has become a hotspot due to its narrow bandgap structure of about 2.2 eV,which can respond to visible light.However,there still exists some challenges for the BiFeO3 photocatalyst,such as low separation efficiency of electron-hole pair and incapable degradability of some more stable pollutants.And some strategies have been proposed to elevate the transfer and separation efficiency of photo-generated carriers.One of them is to perform complex modification with another semiconductor,which means constructing a heterojunction interface between two types of semiconductor materials with matching lever,which can promote the transfer of interface charge and enhance the separation of photoinduced charge.Based on the idea of compound modification between the semiconductors,the thesis will be summarized as follow:(1)Pure BiFeO3,Bi2Fe4O9 and Bi2Fe4O9/BiFeO3 heterostructure nanofibers were successfully synthesized by a simple wet chemical process followed by electrospinning technique.And compared to pure BiFeO3 nanofibers,Bi2Fe4O9/BiFeO3 can make its absorption edges occurred redshift,promote the absorption of visible light and enhance the segregation efficiency of photogenerated carriers.In addition,the prepared Bi2Fe4O9/BiFeO3 nanofibers demonstrate higher photocatalytic activity in the degradation rhodamine B and H2 evolution from water,and the hydrogen production of Bi2Fe4O9/BiFeO3 heterojunction nanofibers is about 2.0 times of pure Bi2Fe4O9 nanofibers under 8h of visible light irradiation.Based on the results of photocatalysis and photoelectric properties,we make an investigation of the photoreaction mechanism of Bi2Fe4O9/BiFeO3 nanofibers.(2)We prepared a novelty visible-light-induced g-C3N4/BiFeO3 composites with various contents of g-C3N4 by using PEG2000.By HRTEM analysis,we find that pure BiFeO3 is microspherical with a diameter of about 0.6?m after calcination treatment.While for the g-C3N4/BiFeO3 composite system,the BiFeO3 microsphere were maintained and the g-C3N4 sheets were uniformly decorated on the surface of microspheres.Next,we evaluate the abilities of g-C3N4/BiFeO3 composites to degrade methylene blue and H2 production from water under visible light irradiation.Due to the synergistic effect between g-C3N4 and BiFeO3 in promoting the separation of photogenerated electron-hole pairs,the g-C3N4/BiFeO3 composites show higher photocatalytic activity than pure g-C3N4 and BiFeO3.And we hypothesise the possible photocatalytic mechanism of g-C3N4/BiFeO3 composites.(3)The new types of visible-light-driven photocatalysts of WO3/BiFeO3 composites with BiFeO3 as matrix and BiFeO3/WO3 composites with WO3 as matrix were successfully constructed.And we characterize the as-prepared samples by XRD,HRTEM,XPS,UV-Vis DRS,transient photocurrent response(I-t)and photoluminescence spectrum(PL).The results indicate that the photocatalytic oxygen production activity of BiFeO3/WO3 composites is stronger than that of WO3/BiFeO3 composites or pure WO3 nanorods and BiFeO3 microspheres,and the oxygen production yield is about 3.3 times,2.2 times and 11.2 times of them,respectively.We also analyze the reason of excellent photocatalytic oxygen production activity of BiFeO3/WO3 composites. |
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