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.