Study On The High-efficiency Bismuth-containing Composite Photocatalysts: Design, Synthesis And Applications

Photocatalysis, one important potential method for environmental remediation andclean energy production by using solar energy, has been developing quickly in the pastdecades. Photocatalyst is the core part of photocatalysis. Development of highly efficientand visible light driven photocatalysts is still a big challenge and has being a hot topic inthe field of photocatalysis. Many photocatalysts have been developed in the past decadesand can be divided into two categories: TiO2or TiO2-containing photocatalysts,non-TiO2-containing photocatalysts. However, the reported photocatalysts have one ormore disadvantages below:(1) only be excited by ultraviolet light which takes only4%of the solar energy;(2) low light absorption efficiency;(3) low efficiency in chargecarriers separation;(4) unstable and serious photocorrosion;(5) complicated preparationmethods, requirement of toxic solvent and/or structure-directing agent;(6) difficulty inlarge-scale synthesis;(7) low photocatalytic activity under the irradiation of solar light.So developing of green and facile methods for scale-up synthesis of high-efficiency,stable and visible-light-driven photocatalysts is a great issue in photocatalysis technique.What’s more, the study on the relationship between photocatalytic performances andstructures of catalysts is another great issue.Considering that most of the bismuth-containing photocatalysts can be excited undervisible light and construction of heterojunctions can enhance photocatalytic activities. Aseries of bismuth-containing composite photocatalysts with heterojunctions weresynthesized by facile methods in this thesis. The physical and chemical properties of theas-prepared samples were characterized by various techniques. The photocatalyticactivities were evaluated by degradation of organic dyes under visible light irradiationand the relationship between strucutures and catalytic performances was invesitigated.Listed below are the results:1) By a simple solvothermal method using ethylene glycol and water as solutionand L-lysine as surfactant, peanut-like BiVO4and hollow, porous Bi2O3-BiVO4composite were successfully synthesized. The Bi2O3-BiVO4composite showed highactivity towards methylene blue (MB，2×10-5mol/L) degradation under a Xe lamp (350W), much higher than BiVO4and Bi2O3. This could be ascribed to the porous andunsmooth surface of the Bi2O3-BiVO4composite, which is favorable for light absorptionand thus enhance the amount of photogenerated charges. Then the charge carriers could be efficiently separated on the p-n junctions between Bi2O3and BiVO4.2) Ag-doped BiVO4composites with hollow and porous structures were preparedby keeping the Ag amount at6.5wt%. The hollow and porous Ag/BiVO4showed highervisible-light-driven catalytic activity than BiVO4towards degradation of dyes(rhodamine B and methylene blue,2×10-5mol/L, respectively). The results could beowing to the enhancement of visible light absorption ability by multiple scattering oflight and plasma resonance of Ag on the surface. What’s more, the schottky junctionbetween Ag metal and BiVO4can promote charges separation. It also showed muchhigher activity than Ag/BiVO4composite prepared by traditional method (namely aphotoreduction method for Ag doping).3) The hollow and branched Bi2O3-Bi2S3composite was synthesized from Bi2O3microtubes by a so-called corrosion-regrowth method. The preparation process is simpleand environmental-friendly, without using any organic solvent or toxic surfactants. Thecomposite showed higher activity than Bi2O3and Bi2S3towards Rh-B degradation undervisible light irradiation. It was deduced that the good photocatalytic activity is closelyrelated to high visible light absorption ability of the composite and the presence ofheterojunctions between Bi2O3and Bi2S3.4) Porous spongy-like and urchin-like CuS-Bi2S3composites were successfullysynthesized using Bi(NO3)3·5H2O as Bi source, potassium thiocyanate (PT) and thiourea(TU) as sulfur sources, respectively. The porous spongy-like composites were composedfrom ultrathin nanoplates (about20nm) which intercrossed with each other, and theurchin-like ones composed from nanoneedles radially grown from a center. Thevisible-light-driven photocatalytic activity of Bi2S3towards dyes decomposition (Rh-B,crystal violet and a mixture of them) was greatly improved by coupling with CuS.Because the ultrathin nanoplates as well as the nanoneedles are favorable for chargestransfer; the recombination of photogenerated electrons and holes on Bi2S3can be greatlyprevented due to the presence of heterojunctions between CuS and Bi2S3.5) For the first time, flower-like BiOX (X=Cl, Br, I), Bi2O2CO3andBiOI-Bi2O2CO3composites were fast synthesized at room temperature using water assolvent, L-lysine and cetyltrimethyl ammonium bromide (CTAB) as surfactant,respectively. It provides a green, fast, energy-saving and universal way for thepreparation of BiOX photocatalyst or other bismuth-containing oxides. TheBiOI-Bi2O2CO3composite showed much higher activity for dyes degradation undervisible light than BiOI and Bi2O2CO3, since the p-n junctions were formed, and thevisible light absorption and charges separation abilities of the compoiste were enhanced. It also showed good reusability and stability, there is no apparent loss of activity after10cycles. The composite photocatalyst will find wide applications in wastewater treatmentdue to its high activity, stability and simple for scale-up preparation prodedure.