There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Two organolead halide perovskite nanocrystals, CH3NH3PbBr3 and CH3NH3PbI3, were found to efficiently sensitize TiO2 for visible-light conversion in photoelectrochemical cells. When self-assembled on mesoporous TiO2 films, the nanocrystalline perovskites exhibit strong band-gap absorptions as semiconductors. The CH3NH3PbI3-based photocell with spectral sensitivity of up to 800 nm yielded a solar energy conversion efficiency of 3.8%. The CH3NH3PbBr3-based cell showed a high photovoltage of 0.96 V with an external quantum conversion efficiency of 65%.

Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells

Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

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.

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

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Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

The influence of solution matrix on the photocatalytic degradation of TNT in TiO2 slurries

Incorporating colloidal CdSe quantum dots (QDs) into CdSe nanowire (NW)-based photoelectrochemical solar cells increases their incident-photon-to-carrier conversion efficiencies (IPCE) from 13% to 25% at 500 nm While the effect could, in principle, stem from direct absorption and subsequent carrier generation by QDs, the overall IPCE increase occurs across the entire visible spectrum, even at wavelengths where the dots do not absorb light This beneficial effect originates from an interplay between NWs and QDs where the latter fill voids between interconnected NWs, providing electrically accessible conduits, in turn, enabling better carrier transport to electrodes The presence of QDs furthermore reduces the residual polarization anisotropy of random NW networks Introducing QDs therefore addresses an important limiting constraint of NW photoelectrochemical solar cells The effect appears to be general and may aid the future design and implementation of other NW-based photovoltaics

A CdSe Nanowire/Quantum Dot Hybrid Architecture for Improving Solar Cell Performance

Charge injection from excited CdSe quantum dots into nanostructured TiO(2) film can be modulated by varying solution pH. At increasing solution pH, the conduction band of TiO(2) shifts 59 mV/pH unit to a more negative potential, thereby decreasing the driving force and thus decreasing the rate of nonradiative electron transfer from excited CdSe. The emission yield and the average emission lifetime increase with increasing pH, thus providing a way to monitor the variation in medium pH.

Modulation of Electron Injection in CdSe―TiO2 System through Medium Alkalinity

Environmentally Benign Photocatalysts

The massive use of herbicides in the agricultural industry has led to measurable levels in natural bodies of water, many of which supply the human population with fresh drinking water. Advanced oxidation processes such as photocatalysis, sonolysis, and radiolysis show promise in eliminating the dangers of exposure to herbicides and the products of their natural breakdown. A basic understanding of the mechanistic details involved in the oxidative transformations remains the key for improving the effectiveness of the advanced oxidation processes. The role of the hydroxyl radical in the breakdown of the common herbicide 2,4-D (2,4-dichlorophenoxyacetic acid), its breakdown product 2,4-DCP (2,4-dichlorophenol), and related compounds is elucidated through the determination of degradation rates, analyses of the transformation intermediates, and studies using computational chemistry methods.

Prashant V. Kamat

Papers

The influence of solution matrix on the photocatalytic degradation of TNT in TiO2 slurries

A CdSe Nanowire/Quantum Dot Hybrid Architecture for Improving Solar Cell Performance

Modulation of Electron Injection in CdSe―TiO2 System through Medium Alkalinity

Environmentally Benign Photocatalysts

Hydroxyl radical's role in the remediation of a common herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D)