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

Photoinduced blue shifts in CdS colloids have been time resolved by picosecond pump-probe measurements. The blue shift appears within the time domain of the pump pulse (18 ps) and is found to increase with increased pump light intensity. Calculations of the predicted blue shift from a dynamic Burstein-Moss shift agree with the experimental results at the lower laser intensities, but the predicted shifts are greater than observed values at the higher light intensities.

Dynamic Burstein-Moss shift in semiconductor colloids

Electrophoretically deposited single-wall carbon nanotube (SWCNT) films on optically transparent electrodes are photoelctrochemically active and generate photocurrent upon visible excitation A low photon-to-current conversion efficiency of 015% suggests that most of the photogenerated charge carriers are lost in the recombination process Time-resolved transient absorption experiments confirm the charge separation following the laser-pulse excitation of SWCNTs Relaxation of photogenerated charge carriers in the SWCNT to the lowest energy gap occurs in ∼1 ps

Single-Wall Carbon Nanotube Films for Photocurrent Generation. A Prompt Response to Visible-Light Irradiation

Single-wall and multiwall carbon nanotubes are employed as carbon supports in direct methanol fuel cells (DMFC). The morphology and electrochemical activity of single-wall and multiwall carbon nanotubes obtained from different sources have been examined to probe the influence of carbon support on the overall performance of DMFC. The improved activity of the Pt-Ru catalyst dispersed on carbon nanotubes toward methanol oxidation is reflected as a shift in the onset potential and a lower charge transfer resistance at the electrode/electrolyte interface. The evaluation of carbon supports in a passive air breathing DMFC indicates that the observed power density depends on the nature and source of carbon nanostructures. The intrinsic property of the nanotubes, dispersion of the electrocatalyst and the electrochemically active surface area collectively influence the performance of the membrane electrode assembly (MEA). As compared to the commercial carbon black support, single wall carbon nanotubes when employed as the support for anchoring the electrocatalyst particles in the anode and cathode sides of MEA exhibited a approximately 30% enhancement in the power density of a single stack DMFC operating at 70 degrees C.

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Single wall carbon nanotube supports for portable direct methanol fuel cells.

Both pulse radiolysis and laser flash photolysis techniques have been employed to characterize the triplet excited state behavior of C 60 and C 70 in benzene at 296 K. Apart from the previously reported absorption in the visible, we were able to characterize its absorption in the UV region and determine the extinction coefficients in the visible region. Pulse radiolysis experiments give indirect confirmation for the spectral features of the triplet excited states

Prashant V. Kamat

Papers

Dynamic Burstein-Moss shift in semiconductor colloids

Single-Wall Carbon Nanotube Films for Photocurrent Generation. A Prompt Response to Visible-Light Irradiation

Single wall carbon nanotube supports for portable direct methanol fuel cells.

Triplet excited state behavior of fullerenes: pulse radiolysis and laser flash photolysis of fullerenes (C60 and C70) in benzene

Ligand Assisted Transformation of Cubic CsPbBr3 Nanocrystals into Two-Dimensional CsPb2Br5 Nanosheets