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A silicalite-1 nanophase material with an elementary particle size of 18-100 nm is synthesized from clear solution and isolated and purified using supercentrifugation. The nanopowder is characterized in detail using scanning electron microscopy, high-resolution transmission electron microscopy, attenuated force microscopy, 29 Si magic angle spinning NMR, 13 C cross polarization magic angle spinning NMR, X-ray diffraction, dinitrogen physisorption, and thermogravimetric analysis and compared with micrometer-sized silicalite-1. The nanosized and micrometer-sized materials have many common properties including the refined structure and the nature and concentrations of tetrapropylammonium species incorporated during the synthesis. Unique properties of the nanophase are a splitting of the characteristic framework vibration at 550 cm -1 into a doublet at 555 and 570 cm -1 , a high concentration of defect sites, and a strain in the crystallites along the "a" crystallographic direction. The nanophase exhibits a two-stage dinitrogen physisorption in the low-pressure region, ascribed to adsorptions in micropores created by the stacking of the nanoparticles in addition to adsorptions in the intracrystalline micropores.

Amorphous microporous metal oxides of titanium (AMM-Ti) modified with a few percent of a platinum(IV) halide have been prepared by a sol-gel procedure and characterized by various surface analytical methods. By these methods the metal salt is homogeneously distributed in an almost exclusively amorphous powder of high specific surface area (160-200 m 2 /g) and a pore size of 0.8 nm. From the coordination number of 4.3 and a Pt-Cl distance of 2.28 Å, as calculated from extended X-ray absorption fine structure results, we conclude that the platinum salt is present as PtCl 4 . The hybrid sample (Pt(IV)/AMM-Ti) catalyzes the photodegradation of 4-chlorophenol with visible light. Apparent disappearance quantum yields decrease from 8.6 × 10 -3 at 335 nm to 4.5 × 10 -3 at 366 nm and 2.8 × 10 -3 at 400 nm; lower values of 1.6 × 10 -3 and 1.3 × 10 -3 are found at 436 and 546 nm, respectively. The quantum yield at both 366 and 436 nm decreases linearly with the square root of the incident photon flux, suggesting increasing recombination of the photogenerated charge carriers. We postulate that the photocatalytic activity of Pt(IV)/AMM-Ti originates from local excitation of the platinum(IV) chloride chromophore, affording a halogen atom and Pt(III) as intermediate species. Charge-trapping by the titania matrix generates reducing and oxidizing surface sites from which subsequent photodegradation proceeds. Good photostability of Pt(IV)/AMM-Ti is demonstrated by repeated use of the photocatalyst.