A. V. Korzhak

Photoinitiation of buthylmethacrylate polymerization by colloidal semiconductor nanoparticles

Abstract Nanoparticles of zinc and iron oxides as well as cadmium sulfide of different size were synthesized in 2-propanol, their band gaps and allowed bands positions were determined. The foregoing nanoparticles turned out to be efficient photoinitiators of butylmethacrylate polymerization. On the basis of the kinetic parameters of the process a free radical mechanism of the butylmethacrylate photopolymerization induced by investigated nanosized semiconductors was inferred. An increase in the specific rate of the butylmethacrylate photopolymerization with the decrease in the average CdS nanoparticles diameter was explained in terms of the theory of quantum confinement effects in semiconductors and was attributed to an increase in the probability of monomer reduction by photogenerated electrons of CdS nanocrystals conduction band with the diminishing of crystals size. It was shown that a number of xanthene dyes—fluorescein and its halogenated derivatives are efficient sensitizers of ZnO nanoparticles to the visible light. Butylmethacrylate photopolymerization rates grow at the presence of ZnO nanoparticles and sensitizers symbately with an increase in singlet and triplet-excited states energy of dyes studied. Such relation indicates the determining role of the process of electron transfer from photoexcited sensitizers to the ZnO nanoparticles conduction band in the initiation stage of polymerization. Flash photolysis was used for the investigation of the nature and decay characteristics of short-lived intermediates generated in systems consisting of ZnO nanoparticles, sensitizers and monomer. Schemes of the mechanism of the butylmethacrylate photopolymerization induced by investigated nanosized semiconductors were proposed.

Catalysis of the Sodium Sulfide Reduction of Methylviologene by CuS Nanoparticles

Feasibility was demonstrated for the catalysis of the sodium sulfide reduction of methylviologene (MV2+) in aqueous solution using cupric sulfide nanoparticles. The catalytic activity of the nanoparticles depends on their size. The basic features were found for the formation of the MV+· radical–cation in the reduction of MV2+ by HS− anions in the presence of CuS nanoparticles as the catalyst. This is an equilibrium reaction.

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.

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.

Homogeneous photocatalysis of ethanol reduction of nitrobenzene by titanium complexes

It was shown that when ethanol solutions of nitrobenzene are irradiated with near-UV light, which is absorbed by labile complexes of titanium(IV) present in the system, aniline is accumulated. The quantum yield of C6H5NH2 formation if weakly dependent on the C6H5N02 concentration and increases with increasing titanium(lV) content in solution.

Effect of Metal Inclusions on the Porous Structure and Photocatalytic Activity of Titanium Dioxide

A study was carried out on the effect of the inclusion of a series of transition metals (V, Cr, Mn, Fe, Ni, Cu, Zr, Mo) and also Al, Si, Zn, and Sn into titanium dioxide on its porous structure, anatase formation, and photocatalytic activity in the generation of molecular hydrogen from aqueous ethanol. An increase in the content of these metals leads to a decrease in photocatalytic activity, while an increase in the anatase content in titanium dioxide leads to an increase in such activity.

Catalysis of the Reduction of Silver Ions by Ag2S Nanoparticles

Silver sulfide nanoparticles were found to catalyze the reduction of Ag+ ions by sodium sulfite and hydroquinone. The change in the absorption spectrum of the reaction mixtures was studied. New bands were found to arise at 403, 415, and 426 nm depending on the reaction conditions. These bands were identified as plasmon bands of metallic silver nanoparticles. The kinetics of this process was determined under various conditions and Ag2S nanoparticles were found to be a highly active catalyst.

Sensitization of cadmium sulfide by cyanine dyes in the photocatalytic production of hydrogen

The possibility of photocatalysis of hydrogen production from aqueous alcohol mixtures by heterostructures of cadmium sulfide with dyes under the action of light with λ >600 nm was shown. A probable mechanism of the sensitization is proposed on the basis of an examination of the spectral, photochemical, and electrochemical data obtained.

Photochemical behavior of nanoparticles of cadmium sulfide in the presence of a reducing agent

Irradiation of colloidal solutions of cadmium sulfide nanoparticles stabilized with polyvinyl alcohol or gelatine in the presence of strong reducing agents (sulfite, hydrazine) causes reduction of part of the Cd2+ ions in the CdS lattice to Cd0 with a quantum efficiency of about 10−4.

Quantum-sized effects and the nature of the primary photoprocesses in copper(I) and copper(II) sulfide nanoparticles

The spectral and semiconductor properties of copper(I) and copper(II) sulfides in aqueous solution were studied. The colloids studied display quantum-sized effects. Two types of optical transitions, namely, indirect band-band and intraband transitions, are responsible for light absorption by the nanoparticles in the visible range.