Anomalous reactivity of ceric nitrate in ruthenium "blue dimer"-catalyzed water oxidation.

At high concentrations, nitrate ion alters the dynamics of ruthenium "blue dimer"-catalyzed water oxidation by Ce(IV) such that the oxidation rate is enhanced and a unique reaction intermediate accumulates. This intermediate is characterized by distinct EPR, optical, and resonance Raman (RR) spectra, with the appearance in the latter of a new oxygen isotope-sensitive band. Both Ce(IV) and nitrate are required to generate this intermediate, which suggests ceric-nitrate complexes as the causative agents.

Observation of charge transport in single titanium dioxide nanotubes by micro-photoluminescence imaging and spectroscopy.

We present the first report of photoluminescence spectra and images of single TiO(2) (anatase) nanotubes. In previous work using ensembles of conventional TiO(2) nanoparticles, we interpreted the broad photoluminescence (PL) spectrum to be a superposition of hole trap emission, peaking in the green, and broad red PL arising from electron traps. PL spectra of individual nanotubes in inert environment show a similar broad emission, with peaks at around 560-610 nm.

Aromatic electron acceptors change the chirality dependence of single-walled carbon nanotube oxidation.

Single-walled carbon nanotubes (SWNTs) dispersed in sodium dodecyl sulfate (SDS) suspensions exhibit diameter-dependent protonation and oxidative quenching of their E11 fluorescence. This nanotube-diameter-based difference in solution chemistry is substantially changed when complexed with aromatic electron-accepting compounds such as nitrobenzene, o-nitrotoluene, 2,4-dinitrotoluene, and 9-nitroanthracene. SWNTs were suspended in aqueous SDS, and their emission spectra were measured as a function of pH and concentration of oxidizing agent (hypochlorite or hydrogen peroxide) to observe their protonation and oxidation behavior.

Influence of TiCl4 treatment on surface defect photoluminescence in pure and mixed-phase nanocrystalline TiO2.

Room-temperature UV-excited photoluminescence spectra are reported for nanocrystalline films of anatase, rutile, and mixed-phase TiO2 (Degussa P25) before and after treatment with TiCl4 solution. The surface defect luminescence of anatase in the visible region is suppressed by TiCl4 treatment, indicating a decrease in surface traps. A similar anatase surface-defect emission is observed in the mixed-phase nanoparticles but is completely quenched following TiCl4 treatment and replaced by emission characteristic of rutile.

Room-temperature preparation of nanocrystalline TiO2 films and the influence of surface properties on dye-sensitized solar energy conversion.

An extremely easy method is presented for producing surfactant-free films of nanocrystalline TiO2 at room temperature with excellent mechanical stability when deposited on glass or plastic electrodes for dye-sensitized solar energy conversion. Prolonged magnetic stirring of commercial TiO2 nanoparticles (Degussa P25) in either ethanol or water results in highly homogeneous dispersions which are used to prepare TiO2 films with surface properties which depend on the solvent used for dispersing the particles, even after sintering. The optical and mechanical properties of films cast from ethanol and water dispersions are compared, and differences in the extent of surface defects and dye binding are observed.

Solvent effects on interfacial electron transfer from Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 to nanoparticulate TiO2: spectroscopy and solar photoconversion.

Resonance Raman spectra are reported for Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 (commonly called "N3") in ethanol solution and adsorbed on nanoparticulate colloidal TiO2 in ethanol (EtOH) and in acetonitrile (ACN), at wavelengths within the visible absorption band of the dye. Raman cross sections of free N3 in EtOH are found to be similar to those of N3 adsorbed on colloidal TiO2 in EtOH, and are generally lower than those of N3 on TiO2 in ACN. Strong electronic coupling mediated by surface states results in red-shifted absorption spectra and enhanced Raman signals for N3 adsorbed on nanocolloidal TiO2 in ACN compared to EtOH.