| Althought nanometer TiO2 shows excellent performances in many fields, high energy gap lead to that only UV-light could excite nanometer TiO2 with highe photocatalytic activity. On the other hand, it’s difficult for powder catalysts to suspend fully in large-scale reactor. Nevertheless, high energy consumption in reclamation or aftertreatment and secondary pollution are open question for catalysts applied in the form of powder. In this article, we composited upconversion fluorescence materials with nanometer TiO2 by using a Sol-Gel method, and prepared composite film materials by dip-coating the substrate, glass slide and fiberglass, into the mixed Sols. Consequently, the photocatalytic activities of the said materials have been investigated on organic pollutants in visible light environment.Titanium dioxide (TiO2) powder, Pr3+:Y2SiO5 powder and Pr3+:Y2SiOs/TiO2 powders are prepared by using a Sol-Gel method. The investigation results of XRD, SEM, size distribution test and fluorescence spectrophotometerindicated that TiO2 belongs to anatase, Pr3+:Y2SiO5 belongs to low-temperature phase X1. The mean grain diameter of TiO2 powder, up-conversion fluorescence material and composite material powder are 1.66μm,3.42μm and 1.46μm, respectively. The specific surface areas of the three kinds of materials are 231.6 m2/g,12.34m2/g and 127.9m2/g, respectively. The fluorescent range of Pr3+:Y2SiO5 powder is 279-350 nm in the excitation of 488nm light.Glass slide and fiberglass were employed as the substrate to prepare composite film and TiO2 film by dip-coating. The XRD and SEM study finds that, two kinds of film are both anatase with a thickness of about 25μm. The photocatalytic degradation test under visible light of the two films on methylene blue and p-nitrophenol shows that five-layers composite film with a substrate of glass slide cost 0.443 g catalyst,need a 100 w light intensity environment, and when the initial concentration of pollutants is 5 mg/L, the removal of methylene blue in 12 h could reach 95.7%,which would still reach 67.8% after four times reuse; with the same situation, the removal of nitrobenzene in 12 h may reach 80.1%, and 57.6% after four times reuse. The composite film with a substrate of fiberglass perform better, when the initial concentration of methylene blue is 5 mg/L,catalyst consumption is 0.45 and in 100 W visible light, removal of methylene blue could get 98.1%,82.2% after four times reuse. Same initial concentration of nitrobenzene with 140 W light intensity,0.4 g catalyst consumption, initial PH=3.5, the removal of nitrobenzene would be 87.2% in 12 h,69.7% after four times reuse.The dynamics of degradation of two pollutions conform to Langmuir-Hinshelwood (L-H) model. During 12h of photocatalysis, dynamic characteristics appear with four stages, every stage coincides the pseudo-first order reaction dynamic model and reaction rate constant trend to decrease and then increase. Finally, comparison among the visible light degradation properties of different forms of catalytic material shows that composite film with fiberglass substrate performs best; composite film with glass slide substrate comes second. Up-conversion composite materials have higher specific surface area, but it’s difficult to keep suspending completely, which results in that partial catalyst couldn’t contact illumination effectively and appear no activity. With regard to the low performance of TiO2 film with a substrate of fiberglass or glass slide, it’s because that visible light perform not very well in motivating TiO2 to process degradation. |
