Modification And Visible-light Photocatalytic Properties Of Bismuth-based Photocatalysts

Semiconductor photocatalysts have broad application prospects in the environmentpurification and the development of efficient visible-light photocatalytic materials is animportant research field. BiOX（X=Cl,Br and I）photocatalysts have attracted great interestdue to the appropriate band gap and special layered structure. Especially, BiOI can beirradiated by the visible-light, so the modification of BiOI catalyst is very meaningful. Inthis paper, modifications of BiOI were carried out in four aspects. First, BiOCl_0.2Br_0.1I_0.7solid solution was synthesized to increase the specific surface area and regulate the bandstructures. Second, low-crystallinity Bi₂O₃/BiOI composite were synthesized to enhancethe electron-hole separation efficiency. Third, BiOCl/BiOI composite were synthesizedthrough thermal impregnation method. Fourth, Pd doped on BiOI were synthesizedthrough the thermal impregnation method.（1） BiOX（X=Cl, Br and I） and the solid solution BiOCl_0.2Br_0.1I_0.7were prepared bythe wet-chemical method. All the catalysts showed nanoplate morphology. The particlesize of BiOCl_0.2Br_0.1I_0.7was much smaller than that of pure BiOX（X=Cl, Br and I）. ItsBET specific surface area is13.34m2/g. The bandgap of BiOCl_0.2Br_0.1I_0.7is1.82eV. Thevalence band potential of BiOCl_0.2Br_0.1I_0.7is2.50eV, deeper than that of BiOI, whichmeans stronger oxidation ability. Formation of the solid solution can effectively changethe band structures of the materials. The visible-light photocatalytic efficiency ofBiOCl_0.2Br_0.1I_0.7was much higher than that of BiOX（X=Cl, Br and I） in thephotodegradation of methyl orange, the degradation rate was98％after the reaction for2h. The intense visible-light absorption, large specific surface area and the deep valanceband edge position gave BiOCl_0.2Br_0.1I_0.7the best visible-light photocatalytic properties.（2） The low-crystallinity composite Bi₂O₃/BiOI were synthesized using a wetchemical method. The visible-light photocatalytic efficiency of Bi₂O₃/BiOI was much higher than that of the pure BiOI and Bi₂O₃in the photodegradation of methyl orange. Thedegradation rate was97％after the reaction for1h. The bandgap of Bi₂O₃/BiOI is2.16eV. The BET specific surface area of Bi₂O₃/BiOI is29m2/g. Electron-hole pairseparation model was proposed. The intense visible-light absorption, large specific surfacearea and the separation of the photoinduced electron-hole pairs are three main factorsresponsible for the enhanced visible-light photcatalytic properties of the compositeBi₂O₃/BiOI. And it showed good stability in the cycle experiments.（3）4wt.％,15wt.％,26wt.％and42wt.％BiOCl/BiOI were synthesized using athermal impregnation method. With BiOCl content increases in the composite, theabsorption of400⁵00nm visible-light was significantly enhanced, and the specificsurface area increased. The intense visible-light absorption and large specific surface areagave4wt.％BiOCl/BiOI composite the best visible-light photocatalytic properties amongall the catalysts for the photodegradation of methyl orange, about78％after2h. Butdecreased activities were obtained with the increase of BiOCl content. The highrecombination of the photoinduced electron-hole pairs of the catalysts that lowed thequantum efficiency was believed to be the critical factor for their decreased photocatalyticactivi（t4y）.0.005wt.％,0.01wt.％,0.05wt.％,0.1wt.％Pd/BiOI were synthesized using athermal impregnation method.Pd had no obvious effect on the morphology of BiOI. Thevisible-light absorption ability was enhanced. After the reaction for2h, the degradationrate was74％,55％,41％and16％for BiOI,0.005wt.％Pd/BiOI,0.01wt.％Pd/BiOIand0.05wt.％Pd/BiOI. Especially,0.1wt.％Pd/BiOI had no photocatalytic efficiency inthe reaction. The PL spectra showed that low concentration Pd decreased recombinationrate and high concentration Pd increased the recombination rate. And different reactionsurface of BiOI particles may form and lowed the photocatalytic efficiency.