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Synthesis And Characterization Of Novel Photocatalytic Composite Oxides

Posted on:2008-02-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:X M LvFull Text:PDF
GTID:1101360272985355Subject:Environmental Engineering
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With the grave pollution of environment,the treatment of mankind living environment especially the treatment of organic pollution has become hot topic.As one of the novel technology,photocatalysis gains more and more attention in the field of environmental treatment field.It is important to develop new photocatalysts to extend the absorbed wavelength range into the visible region,where less expensive light sources exist.In recent years,many research groups devoted to the exploration of more effective photocatalysts by increasing the efficency of charge separation and extending the photo-harvesting range.In the present dissertation,we prepared several novel photocatalysts by new synthesis method.Their physical property and chemical property have been systemic investigated as well as their photocatalytic activity and photocatalytic mechanism.Some significant results are as follows:1) Take d zone oxide-TiO2 as an example,titania particles doped with nitrogen and Fe3+,Cu2+,V5+,Pd2+(x(M)=0.005) as dopants were synthesized by sol-gel and hydrothermal method.Influence of dopants to the structure,light absorption,crystal size of TiO2 has been discussed.Also, influence of single dopant and composite dopants to photocatalytic property and photocatalytic mechanism has been studied.The result indicated that dopant had not only widened the light absorption but improved the photocatalytic efficiency.The photocatalytic activity was investigated and formaldehyde was taken as test gas.The photodegradation rate is in the following order:Cu-TiO2/N>Fe-TiO2/N>V-TiO2/N>Pd-TiO2/N>TiO2/N.Good dispersion of Cu2+ dopant onto the surface of titania,adequate surface area and decrease of recombination center on the surface of Cu-TiO2/N photocatalyst may contribute to its comparatively higher photocatalytic activity.Take p zone oxide-Bi2O3 as example,Bi2O3 samples doped with transition metal ions,M-Bi2O3(M=VⅤ,PbⅡ,AgⅠand CoⅡ) were synthesized by wet chemical precipitation method in the presence of sodium dodecyl benzene sulphonate(SDBS).The obtained monoclinic microcrystal samples not only have different morphology but also visible light harvesting.The photo-catalytic activity of M-Bi2O3 was evaluated by decolorization of Rhodamine B under visible light illumination.The photodecolorization efficiency varied with the type of the transition metal ions and followed the order:Bi2O3(V5+)>Bi2O3(Pb2+)>Bi2O3(Ag+)>Bi2O3(Co2+)>Bi2O3.The ionic radii,surface morphology and photo absorption property may attribute to the difference of photodegradation activity.The above results indicated that semiconductor could develop into another novel photocatalyst afer being appropriately doped.On the one hand,visible-light-driven photocatalysts have been synthesized and on the other hand,photodegradation of room pollution gas and low concentration ozodye have been achieved,which have provided demonstrating study for the treatment of environmental pollution.2) Since the structure of polyoxometallate is similar with TiO2 and its changeable absorption spectra,tetrabutylammonium salt of SiW10Fe2 and CoⅡW12/SiO2 composite catalyst were synthesized and oze dye(methyl orange and orangeⅡ) were taken as test pollutant.The result indicated that the above composites got wider pH application range and via the change of polyoxometallate composite,the spectra property of polyoxometallate has changed and visible-light driven photocatalyst has been obtained.3) Composite oxides may possess visible-light excited band structure and high mobility of carrier,which had been widely studied as effectively potential photocatalyst.Photocatalytic performance of BiFeO3 has been studied.The morphology,photo absorption and its influence to the photocatalytic activity have also been discussed.The result indicated that BiFeO3 nanoplates have a potential application for photodegradation of orangeⅡunder the condition of H2O2.A novel microwave-assisted progress for the preparation of nanocrystalline pure YFeO3 phase has been developed.Synthesis of perovskite YFeO3 has been achieved with carbon to enhance microwave absorption,polyvinyl alcohol as inhibitor and urea as homogeneous precipitator.Photocatalytic activity for the degradation of orangeⅡin water under visible light irradiation shows that perovskite YFeO3 is superior to TiO2(P-25).Oxygen vacancies of the perovskite sample may explain its high activity.Effects of microwave irradiation time and calcination temperature on the phase structure of the product were also studied.Considersing the band structure of YFeO3,YFeO3-TiO2 composite photocatalysts with p-n heterojunction have been prepared by physical amalgamation.Effects of calcination temperature and constitute content on structure and surface characterizations have also been investigated.Results show that the presence of p-n junction not only has visible light harvesting but potential force for hole-electron pair separation.A preliminary investigation of photocatalytic activity on orangeⅡshowed that YFeO3-TiO2 heterojunctions can be activated under visible light irradiation. The optimum junction is sample ofω(TiO2)=0.90 after calcining at 600℃.The improved photocatalytic activity,comparing with that of pure TiO2 and pure YFeO3,might attribute to the p-n heterojunction composed of p-type YFeO3 and n-type TiO2.Study of the process of electron and hole migratation will facilitate the exploitation of novel,highly efficient, visible-light-driven photocatalyst.
Keywords/Search Tags:photocatalytic, titanium oxide, Bi2O3, SiW10Fe2-H2O2, CoIIW12/SiO2, BiFeO3, YFeO3-TiO2
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