The Study On Preparation, Characterization And Photocatalytic Degradation Typical Organic Pollutants Of Nanometer H₃PW₁₂O₄₀/TiO₂Composite Films

Nanometer H₃PW₁₂O₄₀/TiO₂composite films were prepared by the sol-gel combinedtemperature programmed hydrothemal method and spin coating technique. The novelcomposite films had abtained excellent physical and chemical properties through adjusting themolar ratio of saturation Keggin-type H₃PW₁₂O₄₀, titanium tetraisopropoxide, isopropylalcohol and water. The surface morphology of the as-prepared composite films wascharacterized by various analysis tests to reveal the quantity-effect relation between materialstructure and photocatalytic activity. Under simulated sunlight （wavelength extent:320nm-780nm） irradiation, the photocatalytic activities of the composite films were studied viathe degradation of many typical organic compounds （dyes, endocrine disrupters and antibioticdrugs）. The various influences on degradation were investigated systematically, includingH₃PW₁₂O₄₀loadings, initial concentration and solution pH and so on. Photocatalytic oxidationmechanism and recycling performance of composite film, corresponding dynamic models,degradation pathway and mineralization degree of organic pollutant were also discussed indepth.The main results was concluded as follows:1.Composition, crystal structure, optical absorption, pore structure characteristic, surfacemorphology of the as-prepared composite film was characterized by various analysis tests,including ICP-AES, EDS, FTIR, Ramman, XRD, UV-Vis DRS, Nitrogenadsorption-desorption, SEM and TEM. The results indicated that H₃PW₁₂O₄₀could dopedprimely in TiO₂lattice structure and the Keggin-type unit retained intact in H₃PW₁₂O₄₀/TiO₂composite films, the doping amount was from3.2%to16.7%; TiO₂showed pure anatasecrystal in all as-prepared composite films, grain diameter was8.48-12.32nm; The sphericalcatalysts particles well-dispersed in H₃PW₁₂O₄₀/TiO₂composite films could not be foundobvious agglomeration phenomenon, specific surface area of the catalyst was137.8-171.6m2/g, the interior possessed microporous structure and the catalyst particles stacked eachother to form mesoporous and spongeous structure; The absorption wavelength of compositefilm happened redshift and enhanced the utiization ratio of the sunlight after dopingH₃PW₁₂O₄₀.2. Through the study and observation on photocatalytic activities of H₃PW₁₂O₄₀/TiO₂composite films and influencing factors for the degradation of RhB, BPA and SMZ, theoptimum reaction condition is comfirmed. The optimum condition of RhB: the H₃PW₁₂O₄₀ loading is14.7%, initial concentration is25mg/L, solution pH is4.4; The optimum conditionof BPA: the H₃PW₁₂O₄₀loading is6.3%, initial concentration is5mg/L, solution pH is8.2;the optimum condition of SMZ: the H₃PW₁₂O₄₀loading is7.7%, initial concentration is50mg/L, solution pH is5.5. All photocatalytic reactions followed apparent first orderLangmuir-Hinshelwood kinetic model, the reaction rate constant of RhB, BPA and SMZrespectively is0.018,0.023and0.008min-1under the optimum condition; after240minirradiation, the efficiency of photocatalytic degradation is98.5%,100.0%and87.0%,respectively.3. BPA as target pollutant, photocatalytic oxidation mechanism of composite film wasstudied through free radicals capture experiment. The result indicated that synergistic actionbetween H₃PW₁₂O₄₀and TiO₂inhibited effectively the recombination of e--h+pairs,H₃PW₁₂O₄₀possessed strong electron-accept capacity, and prompted h+reacting with H2Oadequately to generate more active hydroxyl radicals. Hydroxy free radicals are highlyoxidizing and no selectivtiy group can have degradation organic pollutants effectively.4. The degradation pathway of BPA was presumed according to intermediate productsduring degradation process identified. It was that hydroxy radical attacked benzene rings ofBPA molecules at first, two groups of benzene happened breakage to produce p-hydroxybenzene propanol, phenol and p-hydroxybenzaldehyde, then further oxidized translated intohydroquinone and p-hydroxybenzoic acid, and finally opened aromatic ring to form formic,acetic acids, CO2and H2O.5. Mineralization ability to H₃PW₁₂O₄₀/TiO₂composite films for RhB, BPA and SMZwas observed through TOC analysis. After simulated sunlight irradiation for12h,mineralization degree respectively was77.7%,76.7%and66.6%, higher than TiO₂film（63.3%,69.9%and53.2%）.6. Recycle and reuse of the H₃PW₁₂O₄₀/TiO₂composite films was studied throughdegradation RhB and BPA. The research found that above95.0%of RhB and BPA could stillbeen degraded after three times cycle by the composite film, and BPA photocatalyticdegradation efficiency still can achieve70%above after ten times cycle.