S. Ya. Kuchmii

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.

Energetics of electron processes in semiconductor photocatalytic systems

The energetics of electron processes in photocatalytic systems based on dispersed semiconductors, their nanocomposites and heterostructures are examined. Methods for the approximate estimation and quantitative determination of their energetic characteristics are evaluated and energy diagrams of photocatalytic systems based on semiconductor nanocomposites and their heterostructures are plotted. Analysis of the diagrams permits the elucidation of the nature of their photocatalytic effects in redox reactions.

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.

Spectral, Optical, and Photocatalytic Characteristics of Quantum-Sized Particles of CdTe

Methods were developed for the synthesis of quantum-sized particles of CdTe, stabilized in aqueous solutions of thioglycolic acid, using H2Te or NaHTe produced in situ by electrochemical reduction of tellurium. The spectral and optical characteristics of the synthesized CdTe nanoparticles were studied. It was found that they have photocatalytic activity in the reduction of methylviologen with sodium sulfite.

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.

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.

Photoinduced Electron Transfer between CdS and CdTe Nanoparticles in Colloidal Solutions

The photochemical behavior of solutions containing a mixture of CdS and CdTe nanoparticles under pulsed irradiation conditions was investigated. It was shown that electron transfer from the CdS particles to the CdTe nanoparticles occurs during the photoexcitation of such systems. The effectiveness of the process is increased with increase in the size of the CdTe nanoparticles. Such behavior is due to decrease in the potential of the CdTe conduction band with increase in the size of the nanoparticles as a result of the appearance of quantum-dimensional effects.

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.

Oxidation of Polysulfide Ions Induced by CdS Nanoparticles under Pulsed Photolysis Conditions

We have studied the photochemical behavior of colloidal solutions of cadmium sulfide containing polysulfide ions under pulsed irradiation conditions. We have established that the pulsed photolysis product responsible for absorption in the 520-650 nm region is the radical anion S3∸. We have studied the kinetic characteristics of disappearance of this intermediate under various conditions, and we propose a scheme for the mechanism of these processes.