Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials Photocatalytic water splitting and H2 evolution using abundant compounds as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen production, and a solution of global energy and environmental issues in the future (361 references)

Heterogeneous photocatalyst materials for water splitting

The surface science of titanium dioxide

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

The homogeneous gas-phase reaction of propane and propene with molecular oxygen was investigated at 360-520°C under atmospheric pressure using a quartz reactor in a continuous-flow system. At a high concentration (65 vol%) and low conversions of hydrocarbons, the overall oxidation rate and the selectivity to propylene oxide were markedly enhanced by mixing propane and propene. At a specific propane/propene ratio, for example 10:3, the net conversion of propene was found to become zero at around 450°C, indicating that the consumption of propene was compensated by the formation from propane and only propane substantially reacted to form propylene oxide and the others. The major product was propylene oxide, and its selectivity exceeded 30%. Other products were ethylene, CO, acetaldehyde, methane, CO 2 , acrolein, propanal, methanol, and so forth

Formation of Propylene Oxide by the Gas-Phase Reaction of Propane and Propene Mixture with Oxygen

The methanol decomposition to carbon monoxide and hydrogen is catalyzed at 250°C over nickel-silica composites prepared by the sol-gel method while the activity is increased with increase in the content of nickel up to 40 wt%. The activity of nickel supported on silica prepared by the conventional impregnation technique is also increased with the nickel content but almost reaches a plateau at the nickel content of 10 wt%. The maximum activity found with the former is significantly higher than that with the latter.

Catalytic methanol decomposition to carbon monoxide and hydrogen over NiSiO2 of high nickel content

Gold-nickel oxide (AuNiO) composite films were prepared by sputter-deposition of fine Au particles on a glass plate substrate followed by pyrolysis of spin-coated nickel 2-ethylhexanoate. They showed reversible changes in visible-near IR light absorption due to CO in air. The pretreatment of the AuNiO composite films with NO2 appreciably enhanced the CO-sensitive absorbance change, allowing optical CO detection over a wide concentration range of 50-10 000 ppm.

Large optical CO sensitivity of NO2-pretreated AuNiO composite films

Three-dimensional (3-D) nanostructures of gold catalysts supported on TiO2 were analysed by electron holography and high-resolution electron microscopy. The contact angle of the gold particle on TiO2 tended to be >90 degrees in the case of gold particles with a size (height) of >4 nm and it tended to be <90 degrees for gold particles with a height of <2 nm. The change in morphology increases the perimeter at the Au/TiO2 interface as the particle size decreases. This change in 3-D structure should be attributed to a change in electronic structure at the interface. It was found that electron holography enabled 3-D analysis at the atomic level and was effective for analysing nanostructured particles.

Masatake Haruta

Papers

Formation of Propylene Oxide by the Gas-Phase Reaction of Propane and Propene Mixture with Oxygen

Catalytic methanol decomposition to carbon monoxide and hydrogen over NiSiO2 of high nickel content

Large optical CO sensitivity of NO2-pretreated AuNiO composite films

Electron holographic 3-D nano-analysis of Au/TiO2 catalyst at interface.

Enhancing effect of gold deposition in the optical detection of reducing gases in air by metal oxide thin films