Study Of Preparation, Modification And Photocatalytic Property Of Bismuth Oxide Based Photocatalysts

In recent years, water pollution has seriously threatened the human health andlife. Compared with the traditional water pollution treatment technology, photocatalysishas attracted wordwide attention due to its high photocatalytic efficiency, economical, nosecondary pollution and so on. Recently, many efforts of photocatalystic were mainlyconcentrated in two aspects: modification of the traditional represented by TiO2photocatalyst and development of novel semiconductor photocatalyst. As a novelsemiconductor photocatalyst, bismuth oxide based photocatalyst showing goodphotocatalytic activity has become the hot topic in the semiconductor photocatalyst field.This thesis mainly to discuss the preparation, modification and their photocatalyticperformance about several common bismuth oxide based photocatlysts. At the same time,on the basis of the band gap structure, reasonable mechanism of photocatalytic was alsoproposed.The main research contents of this thesis are presented as follows:1. Novel p-n junction photocatalysts BiOI/(BiO)2CO3with different contents of BiOIwere in situ synthesized by etching (BiO)2CO3precursor with hydroiodic acid (HI)solution. XRD, FE-SEM, FT-IR, EDS and DRS were employed to study the structures,morphologies and optical properties of the as-prepared samples. Under visible light (λ>420nm), BiOI/(BiO)2CO3hybrid displayed much higher photocatalytic activity than pure(BiO)2CO3and BiOI for the degradation of methyl orange (MO). The increasedphotocatalytic activity of BiOI/(BiO)2CO3could be attributed to the formation of the p-njunction between p-BiOI and n-(BiO)2CO3, which effectively suppresses the recombinationof photoinduced electron-hole pairs. Moreover, the tests of radical scavengers confirm that O2-and h+were the main reactive species for the degradation of MO.2. A series of (BiO)2CO3/BiOX (X=Cl, Br, I) heterostructured photocatalysts weresynthesized through acid etching method and characterized by XRD, DRS, SEM andHRTEM, respectively. Under visible light (λ>400nm),(BiO)2CO3/BiOX displayed muchhigher photocatalytic activity than pure (BiO)2CO3and corresponding BiOX for the degradation of MO. Among them,(BiO)2CO3/BiOI displayed the best photocatalyticactivities. The enhanced photocatalytic activities could be attributed to the function ofheterojunction interface between (BiO)2CO3and BiOX. Moreover, except for the role ofheterostructure, the good visible light absorption is also beneficial to the photocatalyticperformance of (BiO)2CO3/BiOX.3. Novel I--doped bismuth oxybromide (I-BiOBr) microflowers were prepared by asimple chemical precipitation method. The doped I-significantly changed the morphologyand light absorption of the samples. Under visible light (λ>400nm), I-BiOBr compositesdisplayed much higher photocatalytic activities than pure BiOBr for the degradation ofmethyl orange (MO). The improved photocatalytic activities of I-BiOBr could be mainlyattributed to the newly formed I-impurity levels on the top of valence band of BiOBr,which is beneficial to the generation of more electron-hole pairs and further improved thephotocatalytic activities of I-BiOBr samples.4. Novel rodlike Bi5O7I was successfully synthesized via precipitation transformationmethod using plate-like BiOI as a precursor at70℃. SEM and XRD results show thatBi5O7I had rodlike structure with good crystallinity and purity. DRS displays that theabsorption band edge of Bi5O7I was422nm, which ensures the good visible lightabsorption of Bi5O7I. The application of photocatalytic degrading rhodamine B (RhB)under visible light (λ>400nm) presents that the as-prepared rodlike Bi5O7I had excellentphotocatalytic activity compared to single BiOI and TiO2(P25). The more negativeconduction band potential of Bi5O7I makes it has greater reduction abilityAs stated previously, the photocatalytic activity of bismuth oxide based photocatalystcan be effectively improved by building heterojunction, doping ion and so on. This thesiscan provide a very promising method for water pollution treatment.