Photocatalysis of the Release of Molecular Hydrogen from Aqueous Solutions of Sodium Sulfite by Composite CdS/Ni Nanoparticles

The photocatalytic reduction of Ni²⁺ cations at the surface of CdS nanoparticles was investigated. It was found that the CdS/Ni nanocomposite formed as a result of the reaction exhibits photocatalytic activity in the release of molecular hydrogen from aqueous solutions of sodium sulfite. The kinetic relationships of the process are studied, and a mechanism for the studied reactions is proposed.     

Optical and electroluminescent characteristics of CdS nanoparticles stabilized by guanidine-containing dendrimers

Colloidal CdS nanoparticles measuring 1.9-2.3 nm and stabilized by guanidine-containing dendrimers were produced. It was established that such nanoparticles are characterized by photoluminescence in a wide spectral range (2.1-3.2 eV) with an average radiative lifetime of 55-85 ns depending on the energy of the emitted quanta and also by electroluminescence in the visible region of the spectrum (1.8-2.8 eV).     

Photocatalytic conversions of ethanol,initiated by processes of electron phototransfer,in alkoxide-chloride complexes of titanium

A study has been made of the composition of reaction mixtures obtained in the process of photocatalytic formation of molecular hydrogen in ethanol solutions of titanium tetrachloride. It has been established that this process is accompanied by reactions of oxidation and decomposition of the ethanol molecules. Methane, ethane, acetaldehyde, and ethyl chloride have been identified. Kinetic relationships have been found for the formation of these compounds, and the quantum yields have been determined. In the initial stage of irradiation, CH₄, C₂H₆,and CH₃CHO are obtained. In the second stage, when most of the titanium ions are already in the +3 state of oxidation, the formation of methane and acetaldehyde ends, and H₂ and C₂H₆ become the main products. Possible reasons for the change in composition of the photolysis products are examined, and the basic features of the mechanism of this photocatalytic process are discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 44–51, January–February, 1986.     

Photocatalysis by titanium complexes of the reaction of ClO4 −, ions with alcohol molecules

In the photolysis of perchloric acid solutions of titanium(IV) with additions of ethanol, the formation of titanium(III) compounds was detected. Irradiated solutions ([HClO₄]=0.8 M) at 77K are characterized by an anisotropic ESR signal with parameters g ₁=1.994, g ₁=1.904, which correspond to pseudo-octahedral aqua-complexes of titanium(III). With the passage of time, the signal intensity of the titanium(III) compounds decreases, which is explained by their oxidation by ClO₄ ions. During prolonged photolysis of titanium(IV) compounds in 7 M HClO₄ with an addition of ethanol, a multicomponent signal of the paramagnetic chlorine oxide ClO₂ with parameters g _xx=2,004, a _xx(³⁷Cl)=6.0. mTl a _xx(³⁵Cl)=7,30 mTl, is recorded instead of the signal of titanium(III) compounds. Evidently ClO₂ is formed as a result of a rapid dark reaction between compounds of trivalent titanium (products of the photochemical step) and chlorate ions, which are accumulated in the solution as a result of successive photochemical and dark redox conversions of the titanium compounds, perchlorate ions, arid free radicals from the alcohol molecules. The formation of free radicals in the system was established by the ESR method after irradiation of frozen solutions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 679–686, November–December, 1986.     

Radical pairs generated by electron phototransfer in peroxide complexes of titanium(IV)

During irradiation of frozen alcohol solutions of the peroxide complexes of titanium(VI) in the near UV region corresponding to the peroxide ligand-central ion charge-transfer band a series of paramagnetic products, identified by the ESR spectra as radical pairs (RP), are formed. They represent associated or dimeric complexes of titanium(IV), containing not less than two radical particles (HO ₂ ^. or O ₂ ^. ) at strictly specified distances from each other, as ligands. The spectroscopic parameters D, D and E characterizing each of the radical pairs in a zero field were determined, and the distances between the paramagnetic centers in the pairs were calculated. Geometric models of the possible initial dimeric peroxide complexes of titanium(IV), the photolysis of which leads to the formation of the radical pairs, were analyzed. It was shown that all the discovered radical pairs can be obtained from one type of structure, i.e., dimeric peroxide complexes of titanium(IV) containing double bridges from the peroxide ligand and also O^2– or OH^–.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 568–576, September–October, 1988.     

Interrelationship of Structural-Adsorption Characteristics of Titanium Dioxide and Its Photocatalytic Activity in the Gas-Phase Oxidation of Acetone and Ethanol

X-ray phase analysis and adsorption techniques were used to study the effect of heat treatment of starting amorphous titanium dioxide on its structural-adsorption characteristics, which determine the photocatalytic activity in the gas-phase oxidation of acetone and ethanol. In addition to the specific photocatalytic activity of the samples due to the amount of the active anatase TiO₂ modification, the adsorption capacity of the photocatalysts, which is a function of the specific surface and pore adsorption volume, affects the rate of the reactions studied.     

The Effect of the Conditions of Catalytic Synthesis of Nanoparticles of Metallic Silver on Their Plasmon Resonance

The formation of nanoparticles of metallic silver in the reduction of Ag⁺ ions catalyzed by colloidal Ag₂S was investigated. It was established that the position of the surface plasmon resonance bands of the Ag nanoparticles is affected by the concentration of the catalyst, its particle size and the amount of particles with the same size, the stabilization conditions, the concentration of Ag⁺ ions, and the temperature at which the process is conducted. An explanation for the spectral changes that occur is proposed.     

Influence of ZnO Nanoparticles on the Behavior of the Short-Lived Products of the Pulse Photolysis of Fluorescein and Its Halogen Derivatives in Isopropanol

Rapid processes, which occur on photoexcitation of fluorescein and a series of its halogen derivatives in the presence of ZnO nanoparticles in isopropanol, have been studied by pulse photolysis. The short-lived intermediates have been identified and the kinetics of their destruction have been studied. It is shown that photoinduced transfer of an electron from the singlet and triplet excited molecules of the dyestuffs into the conduction zone of the semiconductor occurs in the presence of ZnO nanoparticles.     

Quantum Size Effects and Nature of Photoprocesses in Nanoparticles of Ag2S

Nanoparticles of silver sulfide with quantum size effects have been prepared. Photoexcitation of the nanoparticles causes direct or indirect interband electron transitions depending on the wavelength of the exciting light. The energies of these transitions have been determined for nanoparticles prepared in different ways and stabilized under various conditions.