A kind of novel and efficient catalyst, mesoporous TiO2 (anatase) modified by two transition metal-monosubstituted polyoxometalates (POMs), i.e., K5[Ni(H2O)PW11O39] (PW11Ni) and K5[Co(H2O)PW11O39] (PW11Co), was used to photodegrade an organochlorine pesticide, hexachlorobenzene (HCB), and three kinds of different dyes under UV irradiation. These dyes have various chemical structures, either azoic (Congo red (CR), methyl orange (MO)), or anthraquinonic (Alizarin S (AS)) or fluorescent (neutral red (NR)). TiO2 (anatase) was prepared by combined sol-gel and programmed temperature hydrothermal methods at a lower temperature (200℃), and these as-synthesized TiO2 particles were further functionalized by 3-aminopropyltriethoxysilane (APS). Amine-functionalized TiO2 materials impregnated with monosubstituted polyoxometalates were prepared by coordination of Ni or Co in the units of polyoxometalates with surface amine groups in TiO2. The resulting materials have been characterized by several methods, including UV diffuse reflectance spectroscopy (UV/DRS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), 31P magic-angle spinning nuclear magnetic resonance (MAS NMR), transmission electron microscopy (TEM), and nitrogen adsorption. The conversions of organochlorine pesticide (HCB) and dyes (CR, MO, AS and NR) remarkably increased on UV-irradiating these as-prepared catalysts compared with the results over traditional anatase TiO2; in particular, HCB conversion reached above 98% after UV-irradiating the catalysts for 60 min. With good photocatalytic activity under UV irradiation and the ability to be readily separated from the reaction system, this novel kind of catalyst exhibited the potential to be effective in the treatment of organic pollutants in aqueous systems.

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.

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.

High loading, three-dimensionally ordered macroporous (3DOM) hybrid silica materials based on monovacant Keggin-type polyoxometalates (POMs) [Xn1W11O39](12-n)- (XW11; Xn1+= P51, Si41, Ge41, B31) were prepared via sol-gel as well as templating techniques. XW11 clusters were incorporated into the wall structures of macroporous silica, resulting in hybrid XW11-SiO2 composites. Formation of the hybrid materials was due to the chemical grafting of organosilanol groups from the silica network onto the surface oxygen atoms at vacant sites on the XW11 clusters. The products were characterized by UV diffuse reflectance spectra (UV/DRS), infrared (IR) spectra, 29Si and 31P MAS NMR, inductively coupled plasma atomic emission spectrometry (ICP-AES), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption isotherms. The study indicates that the primary Keggin structures remain intact in the hybrid materials, and that the products demonstrate three-dimensionally ordered macropores with pore diameters in the range of 285 to 385 nm. The composites exhibited photocatalytic activity to degrade aqueous malic acid (MA) under irradiation in the near-UV region; leakage of XW11 from the hybrid materials was hardly observed during catalytic tests.

Photoluminescent organic-inorganic composite films incorporating the rare-earth-containing polyoxometalate Na9 [EuW10O36] (EW) and poly (allylamine hydrochloride) (PAH) have been prepared by the layer-by-layer self-assembly method. UV-vis spectroscopy and ellipsometry were used to follow the fabrication process of the EW/PAH composite films. The experimental results show that the deposition process is linear and highly reproducible from layer to layer. An average EW/PAH bilayer thickness of ca. 2.1nm was determined by ellipsometry. In addition, scanning electron microscopy and atomic force microscopy images of the EW/PAH composite films indicate that the film surface is relatively uniform and smooth. The photoluminescent properties of these films were investigated by fluorescence spectroscopy.

Zn/Al/W(Mn) mixed oxides were prepared via calcination of the precursors of monovacant and monosubstituted Keggin type polyoxometalate (POM) intercalated layered double hydroxides (LDHs) such as Zn2Al(OH)6-[SiW11O39]0.12 • 0.2H2O and Zn2Al(OH)6[SiW11O39Mn(H2O)]0.16 • 0.3H2O at 600-700℃. The physicochemical properties of the products were characterized by the methods of powder X-ray diffraction, elemental analysis, scanning electron microscopy, UV diffusion reflectance spectroscopy, infrared spectroscopy, thermogravimetric analysis, electron spin resonance and N2 adsorption-desorption measurements. Phase changes during the process of calcination of the POM containing LDH precursors were studied, indicating that the precursors decomposed at 400℃ and formed ZnO and Al2O3-like phases together with an X-ray amorphous phase, and then yielded a mixture of well-crystallized phase of ZnAl2O4 formal spinel and ZnWO4 inverse spinel at 600-700℃. As for the thermally decomposed products, the changes of BET surface areas and pore sizes are related to their crystallinity and structures. Compared with the POMLDH precursors, the mixed oxides thus obtained exhibited higher photocatalytic activity to degrade aqueous organochlorine pesticides hexachlorocyclohexane.

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.

Layered double hydroxide pillared by Paratungstate A ion, Mg12Al6(OH)36(W7O24)•4H2O, was prepared via anion exchange reaction of the synthetic precursor, Mg4Al2(OH)12TA•xH2O (TA2−=D terephthalate), and [W7O24]6− ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized intoCO2 and HCl by irradiating aMg12Al6(OH)36-(W7O24) 4H2O suspension in the near UV area. Disappearance of trace HCH follows Langmuir-Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg12Al6(OH)36(W7O24)•4H2O were proposed, indicating that the interlayer space is the reaction field, and that photogeneration of OH• radicals are responsible for the degradation pathway.

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.