Studies On Preparation Of One Dimensional Nano-TiO₂/Flyash Microsphere Composite Material And Its Photocatalytic Property

Nano-TiO₂shows a strong adsorption of Ultraviolet （UV） light among theoxide semiconductor materials. When irradiatedwith UV, TiO₂nanomaterialsproduce large amounts of electron-hole pairs which enable the material havingagood oxidation and reduction property. Due to its excellent chemical stability,good oxidizing ability, nontoxicity and low cost, TiO₂nanomaterials have awide range of applications at many fields such as wastewater treatment, airpurification and self-cleaning paint surface, and also have good applicationprospects as photocatalytic materials. Meanwhile, nano-TiO₂particlesaggregate easily and show poor dispersionduring preparation and applicationprocesses, so they aredifficult to be separated with aqueous media afterdegradation which limits its application in the field of photocatalysis. TiO₂isan n-type semiconductor with a wide bandgap, so that it canonly be excited bythe UV light with a wavelength less than387nm. Theenergy at UV-light onlyaccounts for3%～5%of thesunlight energy, so that the practical applicationof TiO₂photocatalyst is restricted. In this research, in order to facilitate itsrecycling and reuse, nano-TiO₂was supported on the surface of flyashmicrospheres. Surface modificationwas used to make the materials showingvisible light response.Using TiCl4as titanium source,flyash microsphereas the carrier, the flyashmicrospheresupported nano-TiO₂film composite photocatalytic materialswere prepared with hydrolysis-precipitation method. The influence of surfacepretreatment andTiCl4hydrolysis rate on the coating efficiency were studiedand discussed. The TiO₂crystalstructuresand photocatalytic propertiesof thematerials treated at different calcining temperatures were also studied. Inorder to expand the light response range of the composite materials, ionexchange method was used to treat the flyash microspheres. TheAg@AgCl/FMS/TiO₂composite material was produced with the deposition ofnano Ag@AgCl composite nanoparticles on its surface, which showed visiblelight response based on precious metals plasma resonance principle.The hydrothermal method was also used to prepare one-dimensionnano-TiO₂/flyash microsphere composite materials with improvedspecificsurface areas and the efficiency of photocatalysis.During the experiments, phases of the materials were characterized byXRD, the surface morphology was observed using FESEM, EDS and XPSwere also used to analyse the existence status and the elements of the samples.UV-Vis Diffuse Reflection Spectrometer was used to determinate the light absorbing boundary of the materials. Photo catalytic experimentswereconducted with XPA-7photochemical reaction instrument. Methyl orange wasusedto simulate the organic pollutants, mercury lampsand metal halide lampswere used as the UV light source andsunlight source respectively.The results showed that: during the hydrolysis-precipitation process,TiO₂nanoparticles formed a uniform coatingon the surface of fly ash.With theincrease of calcining temperature, anatase phase changed into rutile phasegradually, and the grain size also increased. The material calcined at500°Cshowed the best photo catalytic activity which has mixed anatase and rutilephases. The modification of Ag@AgCl composite nanoparticles made thecomposite materialsshowing visible light response.The photo catalyticexperiment showed that after radiation for80min with metal halide lamb, themethyl orange degradation rate reached95%.Meanwhile the repetitiveexperiments showed that the degradation rate of the samples could still reach85%after being used for5times, which confirms the electronic-cavitationcycle theory.By controlling the alkali concentrationand pickling of the productsin thehydrothermal process, one-dimensional nanoTiO₂/flyash microspherestructure wes obtained.The photo catalytic experiment showed that, theone-dimensionalnano TiO₂/flyash composites have a better photo catalyticefficiency than the nanoparticle TiO₂/flyash microsphere composites.Afterradiatedwith UV light for40min, the degradation rate of methyl orangeimproved from80%to99%due to its bigger specific surface area.