Temperature-Dependent Photoluminescence of Silver-Indium-Sulfide Nanocrystals in Aqueous Colloidal Solutions

The temperature dependence of the photoluminescence (PL) intensity of colloidal semiconductor nanocrystals (NCs) makes them an appealing option in bio-sensing applications. Here, we probed the temperature-dependent PL behavior of aqueous glutathione (GSH)-capped Ag−In−S (AIS) NCs and their core/shell AIS/ZnS heterostructures. We show that both core and core-shell materials reveal strong PL quenching upon heating from 10 to 80 °C, which is completely reversible upon cooling. The PL quenching is assigned to the thermally activated dissociation of complexes formed by ligands with the metal cations on the NC surface and the introduction of water into the NC coordination sphere. This unique mechanism of the thermal PL quenching results in a much higher temperature sensitivity of the aqueous colloidal AIS (AIS/ZnS) NCs as compared with previously reported analogs capped by covalently bound ligands. Our results are expected to stimulate further studies on aqueous ternary NCs as colloidal luminescent nano-thermometers applicable for ratiometric temperature sensing.     

Effects of metal ions on the ethylene/ethane ratio in the oxidative conversion of methane

Modified forms of natural mordenites containing transition-metal ions catalyze the oxidative conversion of methane. The ethane-ethylene ratio in the C₂ hydrocarbon fraction is correlated with the metal ion hydrogenating and dehydrogenating capacity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 4, pp. 368–371, July–August, 1992.     

Effect of a bias field on the dielectric properties of NaNbO3 solid solutions in the range of the giant temperature hysteresis of a phase transition

The effect of a bias field E on the value and temperature dependence of permittivity ɛ of ceramic samples of solid solutions 0.6NaNbO₃-0.4 NaTaO₃ (I), and 0.97[0.9NaNbO₃-0.1Na_0.5Bi_0.5TiO₃]-0.03LiNbO₃ (II) possessing an anomalously large temperature hysteresis of ɛ(T) dependence is studied. The character of the dependences of both the height and the temperature of the ɛ(T) maximum on the field show that composition (I) has antiferroelectric properties, while composition (II) has ferroelectric properties. It is found that up to 8 kV/cm, the strength of the bias field has actually no effect on the width of the ɛ(T) temperature hysteresis of the compositions under study.     

Photocatalytic Reduction of Zn(II) with Participation of ZnS Nanoparticles

We have studied the photochemical processes occurring in colloidal ZnS solutions containing zinc chloride and sodium sulfite as additives. Irradiation of such systems leads to reduction of Zn(II), the rate of which increases as the size of the ZnS nanoparticles decreases. Based on analysis of the kinetic curves for the reaction, we hypothesize that photoreduction of Zn(II) is a two-electron process. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 4, pp. 231–235, July–August, 2005.     

Photoinduced variations in the size of nanoparticles of CdS in colloidal solutions

The possibility of decreasing the size of colloidal nanoparticles of CdS in the oxidative photocorrosion reaction in the presence of methylviologen and of increasing their size during photocatalytic reduction of sulfur in ethanol in the presence of cadmium acetate. A dependence of the quantum yield of the latter reaction on the initial size of CdS nanoparticles was observed, which was interpreted as a result of quantum size effects. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 170–175, May–June, 2007.     

Photopolymerization of water-soluble acrylic monomers induced by colloidal CdS and Cd x Zn1 − x S nanoparticles

Photocatalytic activity of CdS and Cd _x Zn_1−x S nanoparticles in the polymerization of acrylamide and acrylic acid in aqueous solutions has been found. It has been shown that the most probable way of the photogeneration of primary radicals is the reduction of an adsorbed monomer by the conduction band electrons of the semiconductor nanoparticles, a monomer oxidation by the valence band holes and atomic hydrogen addition to a monomer being complementary photoinitiation routes. A correlation between the composition of Cd_xZn_1-xS nanoparticles and their photocatalytic activity in the acrylamide polymerization has been established. It has been shown that an increase in the quantum yield of the photopolymerization in a sequence СdS < Cd_0.75Zn_0.25S < CdS_0.5Zn_0.5S < Cd_0.3Zn_0.7S originates from a concurrent increase of the conduction band potential of the semiconductor nanoparticles. A kinetic equation of the photocatalytic acrylamide polymerization has been derived. Quantum yields of the photoinitiation have been found to be as small as 10⁻⁴ to 10⁻³.     

Photocatalytic hydrogen evolution over mesoporous TiO2/metal nanocomposites

Na⁺ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m²/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO₂ samples prepared were found to have photocatalytic activity in Cu^II, Ni^II and Ag^I reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO₂ Degussa P25.The effects of the thermal treatment of mesoporous TiO₂ upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO₂/Ag⁰ to TiO₂/Ni⁰ to TiO₂/Cu⁰ was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites.     

Synthesis,characterization, and antileukemic activity of new water-soluble analogs of prodimin

Russian Chemical Bulletin - Two new compounds from the class of bis(3-halopropionyl)amides were synthesized by the reaction of 3-halopropionyl chloride with N,N′-dimethylethylenediamine....     

Optical Characteristics of Colloidal Nanoparticles of CdS Stabilized with Sodium Polyphosphate and Their Behavior during Pulse Photoexcitation

The optical and photophysical characteristics of quantum-dimensional particles of CdS stabilized in water (the oscillator force of the first exciton transition, the forbidden band width, the conduction and valence band potentials) were determined. It was established that pulse excitation of CdS nanoparticles gives rise to nonstationary bleaching of the colloid, due to the accumulation of excess electrons in the conduction band. Their amount and their consumption rate are determined by the nature and concentration of the electron donors and acceptors present in the system.     

Optical and dielectric studies of phase transitions in single crystals of NaNbO<Subscript>3</Subscript>-Gd<Subscript>1/3</Subscript>NbO<Subscript>3</Subscript> solid solutions

The temperature dependences of the permittivity ? and the false-color image patterns obtained by the rotating polarizer method for single crystals of (1 ? x)NaNbO_3?x Gd_1/3NbO₃ (x = 0.003, 0.090) solid solutions with different degrees of diffuseness of the phase transition are investigated. A multifractal analysis of the false-color images has revealed anomalies in the temperature dependences of the parameter ?_∞ of the multifractal spectrum. For a sample with a sharp phase transition (x ≈ 0.003), the temperature of this anomaly is in good agreement with the temperature of the jumps in the permittivity ?(T) and birefringence. For an NNG crystal with x ≈ 0.09, which exhibits a diffuse maximum of ?(T), the temperatures of the anomalies of ?_∞(T) differ in the central and peripheral regions, which correlates with the distribution of Gd over the crystal.