Macroporous titania materials functionalized with monovacant Keggin-type polyoxometalates (POMs) [Xn1W11O39](122n)2 (XW11; Xn+= P51, Si41, Ge41) were prepared by the sol-gel as well as the template technique. Lacunary XW11 clusters were incorporated into wall structures of macroporous titania, resulting in the formation of hybrid titania materials. The structural integrity of the XW11 clusters in the composites was characterized by UV diffuse reflectance spectra (UV/DRS), infrared spectra (IR), inductively coupled plasma atomic emission spectrometry (ICP-AES), 31P MAS NMR spectroscopy and thermogravimetric analysis (TGA). These investigations indicated that the primary lacunary Keggin structures remained intact in the hybrid composites. The porous structure of the composites was demonstrated via scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms, with the pore diameters in the range of 300 to 450 nm. The photocatalytic performances of the as-synthesized composites were evaluated by the degradation of aqueous textile dyes such as Rhodamine B, methyl orange and erythrosine B. S., and the intermediates and the final products of the degradation of Rhodamine B were detected by electrospray mass spectrometer (ES-MS) and ion chromatography (IC). The as-synthesized composites showed much higher photocatalytic activity than pure TiO2 and pure POMs, which has been attributed to the synergistic effect resulting from the combination of POMs and TiO2.

The composite films [Xn+W11O39](12−n)−/SiO2 (X = Si, Ge, P) (abbreviatedXW11/SiO2) were prepared by tetraethoxysilane (TEOS) hydrolysis sol-gel method via a spin-coating technique. Mono-vacant Keggin-type polyoxometalates (POMs) [Xn+W11O39](12-n)- were the inorganic precursors used in this method. Formation of the composite films is due to chemical grafting of organic silanol groups to the surface oxygen atoms at the vacant sites of [Xn+W11O39](12-n)-, resulting in the saturation of the surface of the lacunary POM. Therefore, a coordination structural model of the films was proposed. As for the films, retention of the primary Keggin structure was confirmed by UV-VIS, FT-IR, and MAS NMR spectra. The surface morphology of the films was characterized by scanning electron microscopy (SEM): the film surface is highly uniform, and the layer thickness is in the range of 250-350 nm. Aqueous formic acid (FA) (0-20 mmol/l) was degraded and mineralized into CO2 and H2O by irradiating the films in the near-UV area. The disappearance of FA follows Langmuir-Hinshelwood first-order kinetics.

Anewtype of heterogeneous photocatalytic materials, microporous polyoxotungstates such asH3PW12O40/SiO2, H4SiW12 O40/SiO2 and Na4W10O32/SiO2, were synthesized by incorporating the polyoxotungstates into the silica matrix via a sol-gel technique, and some physico-chemical properties of as-synthesized composites were measured. The photocatalytic activity of the composites was tested via degradation of the model molecule, hydroxy-butanedioic acid (malic acid, (MA)). After 90 or 180 min irradiation in the presence of Na4W10O32/SiO2 or H3PW12O40/SiO2 (H4SiW12O40/SiO2), an aqueous MA (100 mg/l) was totally degraded into the intermediates such as oxalic acid, glyceric acid, tartaric acid, butenedioic acid, acetic acid, formic acid and so on. After subsequent 90 or 60 min irradiation under the same conditions, these intermediates were totally mineralized into CO2 and H2O. Disappearance of MA (in the range of 0-200 mg/l) followed Langmuir-Hinshelwood first-order kinetics, and the reaction rate constant and adsorption equilibrium constant were measured. Most of the intermediates, identified during the process of H4SiW12O40/SiO2-photocatalyzed MA degradation, are the same with those detected during the process of TiO2-photocatalyzed MA degradation. The mechanism studies showed that the desolubilized polyoxotungstates appears to photo-oxidative degradation ofMAby both OH• radical attack and excited state polyoxotungstate direct oxidation.

Amine-functionalized mesoporous and macroporous silica materials impregnated with transition-metal-monosubstituted polyoxometalate K6[Ni(H2O)SiW11O39] (SiW11Ni) clusters were prepared by coordination of nickel centers in the cluster with the amine surface groups in silica supports. The structures and compositions of the materials were characterized by UV-vis diffuse reflectance spectra (DR-UV-vis), infrared (IR) spectra, and 29Si MAS NMR, indicating that the SiW11Ni clusters were chemically attached to the silica supports, and the primary Keggin structure remained intact in the as-synthesized composites. The topologies and porosities of the materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption determination. The heterogeneous photocatalytic behaviors of the materials were tested via degradation of dye rhodamine B (RB), and a RB degradation mechanism was proposed based on the detected intermediates and final products. That is, photocatalytic degradation of RB on the supported SiW11Ni underwent the successive steps of deethylation, deamination, decarboxylation, and cleavage of the chromophore ring structure, resulting in the final products of CO2, NO3−, and Cl− ions. A Drop of SiW11Ni clusters from the amine-modified silica matrix into the reaction system was hardly observed during the photocatalytic tests, attributed to the strong coordination interaction between the SiW11Ni molecule and the amine-modified silica support.