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.

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.

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.

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.

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.