Preparation Of TiO₂ Based Photocatalyst By Bio-template Method And Degradation Of Dye Wastewater

The study aims to design a novel magnetic composite nanomaterials with large surface area and high photocatalytic activity in the visible light.The refractory organic wastewater would be degradated highly in photocatalytic process.The details are as follows:1)The porous Ti O₂ was synthesized using yeast cells as biotemplate.The structure of porous Ti O₂ belongs to anatase phase.The results revealed that the pore diameter of Ti O₂is 2～3μm and a pore wall thickness is in the range of 1～1.5μm.The value of surface area was as high as 207.9 m²·g^-1,which was about 5 folds compared to the common Ti O₂without biotemplate addition.In the process of synthesis,the yeast cells template was removed by calcination to obtain porous Ti O₂.The absorption edge was slightly red shifted for the porous Ti O₂.Its photocatalytic activity was investigated under simulated sunlight through degradation of Acid Red 3R（AR3R）.Illumination for 120 min,the degradation efficiency of AR3R can achieve 99.8%,comparing the porous Ti O₂ with that without adding yeast templates,the photocatalytic activity increased 23.3%.In the photocatalytic process,the porous Ti O₂ can product large amount of·OH and H⁺,due to the photoexcited electron transition.In the first,the-N=N-double bond of AR3R was attacked by·OH,which was gradually decomposed into small molecules organic compounds,CO₂ and H₂O.And the degradation process of AR3R accords with the first order kinetics.2)The novel polyoxometalate of（NH₄）₃PW₁₁O₃₉Sn was prepared.In the molecule,the tungsten atom was replaced by the tin atom in the form of Sn⁴⁺and the Sn-O bond was formed.It maintained the Keggin type structure.The band gap of（NH₄）₃PW₁₁O₃₉Sn was2.55 e V and the absorption wavelengths was 486 nm.Illumination 30 min,the degradation efficiency of AR3R can achieve 95%.The photocatalytic mechanism of（NH₄）₃PW₁₁O₃₉Sn was similar with semiconductor Ti O₂.The electrons were excited by the light,which can product amount of·OH and H⁺.3)（NH₄）₃PW₁₁O₃₉Sn/Ti O₂ composite photocatalyst was prepared by using Ti O₂ and（NH₄）₃PW₁₁O₃₉Sn as raw materials.The active fraction of（NH₄）₃PW₁₁O₃₉Sn remained Keggin type structure.The microstructure of Ti O₂ was not destroyed in（NH₄）₃PW₁₁O₃₉Sn/Ti O₂ composite.And the pore size has an average diameter of 3.0～4.0μm and a pore wall thickness is in the range of 2～3μm.The band gap of（NH₄）₃PW₁₁O₃₉Sn/Ti O₂ decreased to 2.45 e V and the absorption wavelength was 506 nm.Illumination 30 min,the degradation efficiency of AR3R can achieve 99%.In the catalytic system,PW₁₂O₄₀^3-can provide trap sites for Ti O₂ to reduce the recombination of electrons and holes.The AR3R was oxidized to small molecules,and further mineralized to CO₂and H₂O.4)The（NH₄）₃PW₁₁O₃₉Sn/Ti O₂/Fe₃O₄ was prepared by Fe₃O₄ as magnetic core.The results showed that（NH₄）₃PW₁₁O₃₉Sn/Ti O₂ was successfully loaded to the surface of Fe₃O₄,and the saturation magnetic strength was 7.15 emu·g^-1.The band gap of catalyst decreased to 2.15 e V,and the absorption wavelength increased to 577 nm.Illumination 15min,the degradation efficiency of AR3R can achieve 99%.In the system,the amount of free·OH and H⁺were increased,due to the presence of Fe₃O₄.The molecular structure of AR3R was destroyed by·OH.Then the AR3R gradually decompose to CO₂ and H₂O.In summary,the study found that the porous Ti O₂ was synthesized using yeast cells as biotemplate,which had a high surface area and had high photocatalytic activity under simulated sun light.The novel polyxometalate（NH₄）₃PW₁₁O₃₉Sn,composite photocatalyst（NH₄）₃PW₁₁O₃₉Sn/Ti O₂andmagneticcompositenanomaterials（NH₄）₃PW₁₁O₃₉Sn/Ti O₂/Fe₃O₄ all had high degradation efficiencyunder visible light.The study expanded the application of Ti O₂,polyoxometalate and Fe₃O₄ in the field of photocatalysis.