V. M. Granchak

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.

Photocatalytic Reduction of CO2 on Mesoporous TiO2 Modified with Ag/Cu Bimetallic Nanostructures

A study was carried out on the photocatalytic behavior of mesoporous TiO2 modified with Ag/Cu bimetallic nanostructures in the gas-phase reduction of carbon dioxide. The TiO2/Ag/Cu nanoheterostructure was found to have much higher activity than TiO2/Ag and TiO2/Cu nanocomposites. The highest rate of the photocatalytic reduction of carbon dioxide to give methane is found for the optimal 1 : 6 Ag/Cu mole ratio. The activity of the nanoheterostructures was found to depend on the sequence of deposition of the metals onto the TiO2 surface. The greatest rate of methane accumulation was found in the case of deposition of Ag0 particles with subsequent deposition of copper onto this layer.

Photocatalytic Reduction of Carbon Dioxide by Water Vapor on Mesoporous Titania Modified by Bimetallic Au/Cu Nanostructures

A study was carried on the photochemical reduction of CO2 using mesoporous TiO2 modified with bimetallic Au/Cu nanostructures. The bimetallic nanocomposites display greater activity than monometallic TiO2/Au and TiO2/Cu nanocomposites. An optimal gold/copper ratio exists, at which the rate of photocatalytic methane formation is greatest. The activity of the nanoheterostructures depends on the sequence of deposition of the metals and increases in the series TiO2/Cu@Au < TiO2/Au/Cu < TiO2/Au@Cu.

Light-Emitting Materials – Active Components of Luminescent Solar Concentrators

Recent advances in the investigation of various types of fluorescent materials (organic dyes, coordination compounds of metals, semiconductor quantum dots) used in the development of luminescent solar concentrators are discussed. The advantages and disadvantages of various types of phosphors and also the influence of plasmon effects in the nanoparticles of metals, the nature of the matrix, etc. on the luminescence efficiency of the concentrators are analyzed.

Photocatalytic Reduction of CO2 Using Titanium Dioxide and Metal–Semiconductor Nanostructures Made from Titanium Dioxide

A study was carried out on the photochemical reduction of CO2 involving titanium dioxide and metal–semiconductor nanostructures made using titanium dioxide. These metal–semiconductor nanocomposites display much higher activity than pure TiO2 particles. The activity of the composites studied in the photocatalytic reduction of CO2 increases in the series: TiO2/Ag < TiO2/Au < TiO2/Cu.

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.

Photocatalytic Activity of Layered KNb3O8 and K3H3Nb10.8O30 in Gas-Phase Decomposition of Methanol

It was established that treatment of layered KNb3O8 with nitric acid leads to the formation of K3H3Nb10.8O30. The obtained material has a layered structure and consists of crystals with lengths of 5-20 μm and widths in the order of 200-500 nm similar to the initial KNb3O8. Potassium niobate KNb3O8 and its transformation product K3H3Nb10.8O30 can act as photocatalysts in the decomposition of methanol. They have practically the same activity in this process.

Influence of Nanosized Silicon Oxide on the Luminescent Properties of ZnO Nanoparticles

For practical use of nanosized zinc oxide as the phosphor its luminescence quantum yields should be maximized. The aim of this work was to enhance luminescent properties of ZnO nanoparticles and obtain high-luminescent ZnO/SiO2 composites using simpler approaches to colloidal synthesis. The luminescence intensity of zinc oxide nanoparticles was increased about 3 times by addition of silica nanocrystals to the source solutions during the synthesis of ZnO nanoparticles. Then the quantum yield of luminescence of the obtained ZnO/SiO2 composites is more than 30%. Such an impact of silica is suggested to be caused by the distribution of ZnO nanocrystals on the surface of silica, which reduces the probability of separation of photogenerated charges between the zinc oxide nanoparticles of different sizes, and as a consequence, there is a significant increase of the luminescence intensity of ZnO nanoparticles. This way of increasing nano-ZnO luminescence intensity facilitates its use in a variety of devices, including optical ultraviolet and visible screens, luminescent markers, antibacterial coatings, luminescent solar concentrators, luminescent inks for security printing, and food packaging with abilities of informing consumers about the quality and safety of the packaged product.

Photopolymerization of Butyl Methacrylate in the Presence of Nanoparticles of ZnO, Sensitized to Visible Light with Xanthene Dyes

The photopolymerization of butyl methacrylate in isopropanol with participation of nanoparticles of wide-gap semiconductor ZnO has been studied. The possibility of sensitizing ZnO nanoparticles to visible light with a series of halogenated fluoresceins has been established. The rate of photoinitiation of polymerization in the systems studied is principally determined by the rate of electron transfer from the photoexcited molecule of the sensitizer into the conduction zone of the semiconductor nanoparticles.

Polymerization of Butylmethacrylate in Isopropanol, Photoinduced by Quantum-Sized CdS Particles

We have established that polymerization of butylmethacrylate photoinduced by cadmium sulfide nanoparticles in isopropanol solutions is of the free-radical type. We give an interpretation of the characteristic features we see in the polymerization kinetics. We have observed and explained quantum-size effects that appear in the dependence of the efficiency of the process on the photocatalyst particle size.