Ru/CdS Quantum Dots Templated on Clay Nanotubes as Visible-Light-Active Photocatalysts: Optimization of S/Cd Ratio and Ru Content.

A nanoarchitectural approach based on in situ formation of quantum dots (QDs) within/outside clay nanotubes was developed. Efficient and stable photocatalysts active under visible light were achieved with ruthenium-doped cadmium sulfide QDs templated on the surface of azine-modified halloysite nanotubes. The catalytic activity was tested in the hydrogen evolution reaction in aqueous electrolyte solutions under visible light. Ru doping enhanced the photocatalytic activity of CdS QDs thanks to better light absorption and electron-hole pair separation due to formation of a metal/semiconductor heterojunction. The S/Cd ratio was the major factor for the formation of stable nanoparticles on the surface of the azine-modified clay. A quantum yield of 9.3 % was reached by using Ru/CdS/halloysite containing 5.2 wt % of Cd doped with 0.1 wt % of Ru and an S/Cd ratio of unity. In vivo and in vitro studies on the CdS/halloysite hybrid demonstrated the absence of toxic effects in eukaryotic cells and nematodes in short-term tests, and thus they are promising photosensitive materials for multiple applications.

Study of Nanostructured TiO2 Rutile with Hierarchical 3D-Architecture. Effect of the Synthesis and Calcinations Temperature.

The effect of TiCl4 hydrolysis temperature on the structural, textural and morphological properties of the resulting rutile and on the changes of these properties upon calcination was studied. The XRD, Raman spectroscopy, mercury porosimetry, BET, SEM and TEM studies have revealed that TiO2 rutile has a hierarchical 3D-architecture. The obtained nanostructured rutile had a cauliflowerlike/ spherical morphology composed of fan-shaped nanofibers. Rutile samples were shown to have a heterogeneous pore structure including micro-, meso- and macropores with a BET surface area of 110-140 m2/g. According to the mercury porosimetry, among mesopores and macropores the latter dominate in the samples. Elevation of the synthesis temperature from 50-70 to 80-90 °C decreased the fraction of macropores from 95 to 70%. The BET method showed that the samples synthesized at low temperatures (50-70 °C) contain 30-44% of micropores in the total amount of mesopores and micropores. The fraction of micropores decreases to 25-18% with a subsequent increase in the fraction of mesopores as the synthesis temperature is raised to 80-90 °C. As shown by a study of the samples upon calcination in the temperature range of 100-1000 °C, temperature is the key factor that produces changes in the crystallites size, nanofiber length and packing density, and 3D particle shape at different levels of the hierarchical system and determines features of the porous structure and morphological properties of nanostructured rutile. The assessment of photocatalytic activity in the oxidation of acetone vapor demonstrated that, regardless of the hydrolysis temperature, the synthesized samples of nanostructured rutile are able to oxidize acetone vapor to carbon dioxide and water. In the process, activity of the samples is comparable with that of commercial photocatalysts under UV light and is superior to the activity of commercial photocatalysts P25 (2-4 times) and TiO2 KRONOS vlp 7000 (1.2-2 times) under visible light in dependence on the synthesis temperature.

Synthesis of Cd1-xZnxS photocatalysts for gas-phase CO2 reduction under visible light.

Novel photocatalysts for CO2 reduction, which consist of a cadmium and zinc sulfide solid solution (Cd1-xZnxS), were successfully prepared by a simple two-step technique. The photocatalysts were characterized by X-ray diffraction, UV-VIS diffuse reflectance spectroscopy, and low-temperature N2 adsorption techniques and were tested in the gas-phase photocatalytic reduction of CO2 under visible light (λ = 450 nm). All the synthesized Cd1-xZnxS solid solutions were capable of enabling the chemical transformations of CO2 under the conditions considered. Carbon monoxide was the major product during the CO2 reduction over Cd1-xZnxS (x = 0-0.87). Methane and hydrogen were also detected in the gas phase in low amounts. The activity of the prepared samples and the distribution of the reduction products strongly depended on the actual cadmium to zinc ratio. The Cd0.94Zn0.06S photocatalyst showed the highest activity, 2.9 µmol CO per gram per hour, and selectivity, 95%, during CO2 reduction under visible light in the presence of water vapor. The achieved values are very high for the sulfide-based photocatalysts.

Low power upconversion using MLCT sensitizers.

Selective low energy excitation of the metal-to-ligand charge transfer (MLCT) transition in [Ru(dmb)(3)](2+)(dmb = 4,4'-dimethyl-2,2'-bipyridine) in the presence of anthracene or 9,10-diphenylanthracene yields easily visualized upconverted singlet fluorescence resulting from triplet-triplet annihilation at low excitation power.

Synthesis and properties of novel fluorescent switches.

[reaction: see text] Photochromic dithienylethene moieties were covalently attached to fluorescent 4,4-difluoro-8-(4'-iodophenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (iodo-BODIPY) via a phenylacetylene linker. UV light induced isomerization of the photochrome results in significant decrease in fluorescence intensity. This fluorescence can be recovered with visible light. Steady-state fluorescence measurements demonstrate that the emission of the dye can be modulated by external light. An intramolecular energy transfer mechanism accounts for the fluorescence quenching in the UV light produced isomers.

Anti-Stokes delayed fluorescence from metal-organic bichromophores.

Long wavelength excitation of [Ru(dmb)(2)(bpy-An)](2+) (dmb is 4,4'-dimethyl-2,2'-bipyridine and bpy-An is 4-methyl-4'-(9-anthrylethyl)-2,2'-bipyridine) in CH(3)CN solution produces upconverted delayed singlet anthracene fluorescence via bimolecular triplet-triplet annihilation.

Room temperature phosphorescence from ruthenium(II) complexes bearing conjugated pyrenylethynylene subunits.

We describe the synthesis, electrochemistry, and photophysical properties of several Ru(II) complexes bearing different numbers of pyrenylethynylene substituents in either the 5- or 5,5'-positions of 2,2'-bipyridine, along with the appropriate Ru(II) model complexes bearing either bromo- or ethynyltoluene functionalities. In addition, we prepared and studied the photophysical behavior of the diimine ligands 5-pyrenylethynylene-2,2'-bipyridine and 5,5'-dipyrenylethynylene-2,2'-bipyridine. Static and dynamic absorption and luminescence measurements reveal the nature of the lowest excited states in each molecule. All model Ru(II) complexes are photoluminescent at room temperature and exhibit excited-state behavior consistent with metal-to-ligand charge transfer (MLCT) characteristics. In the three Ru(II) molecules bearing multiple pyrenylethynylene substituents, there is clear evidence that the lowest excited state is triplet intraligand (3IL)-based, yielding long-lived room temperature phosphorescence in the red and near IR. This phosphorescence emanates from either 5-pyrenylethynylene-2,2'-bipyridine or 5,5'-dipyrenylethynylene-2,2'-bipyridine, depending upon the composition of the coordination compound. In the former case, the excited-state absorption difference spectra that were measured for the free ligand are easily superimposed with those obtained for the metal complexes coordinated to either one or two of these species. The latter instance is slightly complicated since coordination of the 5,5'-ligand to the Ru(II) center planarizes the diimine structure, leading to an extended conjugation on the long axis with a concomitant red shift of the singlet pi-pi absorption transitions and the observed room temperature phosphorescence. As a result, transient absorption measurements obtained using free 5,5'-dipyrenylethynylene-2,2'-bipyridine show a marked blue shift relative to its Ru(II) complex, and this extended pi-conjugation effect was confirmed by coordinating this ligand to Zn(II) at room temperature. In essence, all three pyrenylethynylene-containing Ru(II) complexes are unique in this genre of chromophores since the lowest excited state is 3IL-based at room temperature and at 77 K, and there is no compelling evidence of interacting or equilibrated excited states.