Preparation, Characterization And Photocatalytic Behaviors Of Polyoxometalates-Titania Hybid Porous Materials

Three types of polyoxometalates(POMs)-containing titania porous composites such asPW₁₁-TiO₂, SiW11₁₁-TiO₂, GeW₁₁-TiO₂, PW₁₁Ni-APS-TiO₂, PW₁₁Co-APS-TiO₂ andPW₁₂-TiO2 were prepared by the method of sol-gel via templating and programmedtemperature solvothermal technique. The structure integrity of the starting POMs inas-synthesized composites were confirmed by UV/DRS, FT-IR,XRD, solid state NMR andICP-AES. The results showed that the strong chemical interactions between POM moleculesand titania network existed. The surface morphology of composites were confirmed by SEM,TEM and nitrogen adsorption-desorption isotherm, indicating PW₁₁-TiO₂, SiW₁₁-TiO₂ andGeW₁₁-TiO₂ are macroporous materials, PW₁₁Ni-APS-TiO₂ and PW₁₁Co-APS-TiO₂ aremesoporous materials, and PW₁₂-TiO₂ is a novel bimodal pore material withmicro/mesoporosities. The photocatalytic activities of XW₁₁-TiO₂ (X = P, Si and Ge) were tested via thedegradation of aqueous dye, Rhodamine B (RhB) under UV irradiation. It was observed thatthe photocatalytic activities of as-prepared composites are much higher than that of TiO₂,attributed to the synergistic effect resulting from the combination of POM and titania. In thisPOMs-containing TiO₂ system, the recombination of hole (h⁺) and electron (e^-) was inhibiteddue to interfacial electron transfer from photoexcited TiO₂ to the POMs. Therefore, thephotocatalytic activities of POMs-containing TiO₂ are improved greatly. The pathway andthe mechanism were inferred according to the nature of the intermediates and the finalproducts of degradation of Rhodamine B. The leakage of the active component fromcomposites was hardly observed during the degradation reaction,indicating that theseas-prepared composites were stable. These mesoporous PW₁₁Ni-APS-TiO₂ and PW₁₁Co-APS-TiO₂ composites were used tophotodegrade an organochlorine pesticide, hexachlorobenzene (HCB), and three kinds ofdifferent dyes under UV irradiation. The conversions of organochlorine pesticide (HCB) anddyes remarkably increased on UV-irradiating these as-prepared catalysts compared with theresults over traditional anatase TiO₂. With good photocatalytic activity under UV irradiationand the ability to be readily separated from the reaction system, this novel kind of catalystexhibited the potential to be effective in the treatment of organic pollutants in aqueoussystems. Anatase TiO₂ crystalline particles coupled by homogeneously dispersedpolyoxotungstate at a lower temperature via combination of the sol–gel technique with theprogrammed temperature solvothermal method. This new photocatalyst exhibitedvisible-light catalytic activity to decompose ten various organic dyes in aqueous system. Weinvestigated the kinetics of dye degradation in aqueous solution. It follows an apparentfirst-order in agreement with a generally observed Langmuir–Hinshelwood kinetics model.The photocatalytic activity of PW₁₂-TiO₂ can be enhanced by: (1) the synergistic effectresulting from the combination of the starting polyoxotungstate and anatase TiO2 support; (2)the bimodal porous structure (micro/mesoporosities).