This Perspective is focused on the photocatalytic activity of gold nanoparticles supported on titania (Au/TiO2). Titania is the most widely used photocatalyst, but its limited activity under visible light irradiation has motivated the quest for modified titania materials absorbing visible light. The review starts by justifying how doping with metallic elements is a related strategy, but different, to that leading to the use of Au/TiO2 in photocatalysis. Data supporting and confirming the photoactivity of gold nanoparticles in colloidal solutions are briefly presented to justify the possibility of gold photosensitization of titania by electron injection into the conduction band. After describing the most common procedures used to prepare Au/TiO2, the central part of this article is focused on the photocatalytic activity reported for Au/TiO2 for hydrogen generation, dye decoloration, phenol decomposition and carboxylic acid degradation, among other processes. Emphasis is given to the role that parameters like Au loading, particle size, surface area, spatial structuring and others play on the photocatalytic activity. One important issue has been to distinguish those reports using visible light from those other in which direct titania excitation by UV light has been used. These Au/TiO2 photocatalysts can find real applications in the near future for environmental remediation and for hydrogen generation.

Titania supported gold nanoparticles as photocatalyst

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 m2/g) and a pore size of 0.8 nm. From the coordination number of 4.3 and a Pt−Cl distance of 2.28 A, as calculated from extended X-ray absorption fine structure results, we conclude that the platinum salt is present as PtCl4. 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 r...

Amorphous microporous titania modified with platinum(iv) chloride-a new type of hybrid photocatalyst for visible light detoxification

Anatase, rutile, and amorphous titania powders were surface-modified by grinding with PtCl4 and H2[PtCl6]. Only the anatase modification afforded hybrid photocatalysts capable of degradation of 4-chlorophenol (4-CP) with visible light, with sufficient stability towards decomplexation. Grinding with K2[PtCl4] produced materials of only low photocatalytic activity. Most efficient photocatalysts contained up to 2 wt% of PtIV. At higher surface loading the excess fraction of the complex is desorbed into the aqueous solution. Scavenging experiments with benzoic acid and tetranitromethane revealed that hydroxyl radicals are produced by the primary reduction of oxygen by conduction band electrons generated through electron injection from a postulated surface platinum(III) complex. It is proposed that the latter is formed from a charge-transfer ligand-to-metal (CTLM) excited state through homolysis of the Pt-Cl bond. Accordingly. the primary oxidation of 4-CP may occur by adsorbed chlorine atoms, the intermediary existence of which was demonstrated by scavenging experiments with phenol.

Photosensitization of crystalline and amorphous titanium dioxide by platinum(IV) chloride surface complexes.

Solid-supported metal catalysts have been widely used in industrial processes. The morphology of coated metal on the support is usually an important factor affecting the efficiency of the catalyst....

E.L. Wehry

Papers

Photoaquation of hexachloroplatinate(IV)

Photoreduction of the mono(2,9-dimethyl-1,10-phenanthroline) copper(II) cation in methanolic media