Cu(2-x)S (x = 1, 0.2, 0.03) nanocrystals were synthesized with three different chemical methods: sonoelectrochemical, hydrothermal, and solventless thermolysis methods in order to compare their common optical and structural properties. The compositions of the Cu(2-x)S nanocrystals were varied from CuS (covellite) to Cu(1.97)S (djurleite) through adjusting the reduction potential in the sonoelectrochemical method, adjusting the pH value in the hydrothermal method and by choosing different precursor pretreatments in the solventless thermolysis approach, respectively. The crystallinity and morphology of the products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which shows that most of them might be of pure stoichiometries but some of them are mixtures. The obtained XRDs were studied in comparison to the XRD patterns of previously reported Cu(2-x)S. We found consistently that under ambient conditions the copper deficient Cu(1.97)S (djurleite) is more stable than Cu(2)S (chalcocite). Corroborated by recent computational studies by Lambrecht et al. and experimental work by Alivisatos et al. This may be the reason behind the traditionally known instability of the bulk Cu(2)S/CdS interface. Both Cu(2)S and the copper-deficient Cu(1.97)S have very similar but distinguishable electronic and crystal structure. The optical properties of these Cu(2-x)S NCs were characterized by UV-vis spectroscopy and NIR. All presented Cu(2-x)S NCs show a blue shift in the band gap absorption compared to bulk Cu(2-x)S. Moreover the spectra of these Cu(2-x)S NCs indicate direct band gap character based on their oscillator strengths, different from previously reported experimental results. The NIR spectra of these Cu(2-x)S NCs show a carrier concentration dependent plasmonic absorption.

TiO 2 -x N x nanoparticles were prepared by employing the direct amination of 6−10-nm-sized titania particles. Doping on the nanometer scale led to an enhanced nitrogen concentration of up to 8%, compared to e2% in thin films and micrometer-scale TiO 2 powders. The synthesized TiO 2 -x N x nanocrystals are catalytically active and absorb well into the visible region up to 600 nm, thus exemplifying the use of a nanostructurebased synthesis as a means of producing novel photocatalytic materials.

It is well-known that inorganic nanocrystals are a benchmark model for nanotechnology, given that the tunability of optical properties and the stabilization of specific phases are uniquely possible at the nanoscale. Copper (I) oxide (Cu(2)O) is a metal oxide semiconductor with promising applications in solar energy conversion and catalysis. To understand the Cu/Cu(2)O/CuO system at the nanoscale, we have developed a method for preparing highly uniform monodisperse nanocrystals of Cu(2)O. The procedure also serves to demonstrate our development of a generalized method for the synthesis of transition metal oxide nanocrystals. Cu nanocrystals are initially formed and subsequently oxidized to form highly crystalline Cu(2)O. The volume change during phase transformation can induce crystal twinning. Absorption in the visible region of the spectrum gave evidence for the presence of a thin, epitaxial layer of CuO, which is blue-shifted, and appears to increase in energy as a function of decreasing particle size. XPS confirmed the thin layer of CuO, calculated to have a thickness of approximately 5 A. We note that the copper (I) oxide phase is surprisingly well-stabilized at this length scale.

Using a simple nanoscale exclusive synthesis route, TiO 2-x N x photocatalysts that can be tuned to absorb across the visible region are produced in seconds at room temperature. The photocatalysts are formed by employing the direct nitridation of anatase TiO 2 nanostructures with alkylammonium salts. Depending on the degree of TiO 2 nanoparticle agglomeration, catalytically active TiO 2-x N x anatase structured particles are obtained whose absorption onset extends well into the visible region at λ ∼ 550 nm. The introduction of a small quantity of palladium in the form of the chloride or nitrate facilitates further nitrogen uptake, appears to lead to a partial phase transformation, displays a counterion effect when compared also to the acetate, and produces a material absorbing well into the near-infrared. The introduction of palladium via the chloride also facilitates the formation of small tetrahedral and octahedral palladium-based crystallites throughout the TiO 2-x N x lattice. Surprisingly, no organics appear to be incorporated into the final TiO 2-x N x products. The resulting photocatalysts readily photodegrade methylene blue and lead to the catalytic oxidation of ethylene as they are placed as gels on surfaces. In contrast to the current nitridation process, which is quite facile at the nanoscale, we observe a much slower nitration of Degussa P25 nanopowders and little or no direct nitridation of micrometer-sized anatase or rutile TiO 2 powders at room temperature. We thus demonstrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron materials.

A nitrogen‐doped TiO2 nanocolloid has been successfully prepared and its properties compared with the commercially available TiO2 nanomaterial, Degussa P25. Several characterization techniques, X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM), Fourier transform infrared (FT‐IR) spectroscopy, Raman scattering, and UV‐visible reflectance spectra, are combined in order to determine the crystal phase and grain size, shape, degree of nitrogen incorporation, and nature of the resultant oxynitride chemical bonding on the surface and in the bulk. The high relative photocatalytic activity of the nitrogen doped‐TiO2 nanocolloid is evaluated through a study of the decomposition of methylene blue under visible light excitation. The ease and degree of substitutional‐insertional nitrogen doping is held accountable for the significant increase in photocatalytic activity in the porous nanocolloid versus the nitrided commercial nanopowder. It is suggested that the nitrogen incorporation produces an NO bonding region as evidenced by the resulting XPS spectrum.

Core/shell-structured CdSe/CdS nanoparticles were prepared by a one-pot procedure. The interface effect was studied by steady-state and time-resolved photoluminescence spectroscopy. Coherency strain across the CdSe/CdS interface is addressed to rationalize the measured optical response. The optical properties of the different core/shell systems agree with Matthews−Blakeslee theory, which predicts a critical thickness for a defect-free shell of less than two monolayers of capping material for the CdSe/CdS system.

This paper reports findings of an investigation of the electrocatalytic oxidation of carbon monoxide (CO) that occurs at nanocrystal gold cores with thiolate monolayer encapsulation and within a core−shell network assembly. The core−shell and network combinations allow the manipulation of core size properties and enhance the stability of nanosized catalysts against the propensity of aggregation while being catalytically active. Using alkanedithiolate-linked thin films assembled from two different gold core sizes (2 and 5 nm), we have demonstrated that the capped nanosites are both electrochemically accessible and catalytically active to CO oxidation upon electrochemical activation. Cyclic voltammetric data are presented for assessing the electrocatalytic properties. The results have important implications for the design and tailoring of nanosized gold catalysts via manipulating core−shell chemistry.

Femtosecond transient absorption and fluorescence upconversion experiments have been performed to investigate the photoinduced dynamics of the meta isomer of the green fluorescent protein chromophore, m-HBDI, and its O-methylated derivative, m-MeOBDI, in various solvent mixtures at neutral, acidic, and basic pH. The para isomer, p-HBDI, and its O- and N-methylated derivatives, p-MeOBDI and p-HBDIMe(+), were also studied for comparison. In all cases, fast quenching of the excited S1 state by internal conversion (IC) to the ground state was observed. In the para compounds, IC, presumably promoted by the internal twisting, arises in <1 ps. A similar process takes place in the meta compounds in nonaqueous solvents but with notably slower kinetics. In aqueous solutions, the meta compounds undergo ultrafast intermolecular excited-state proton transfer that competes with isomerization.