ZnO filled opal arrays: Photo and cathodoluminescence studies

The photo and cathodoluminescence of zinc oxide (ZnO) filled opal arrays, as well as ZnO nanocrystals prepared by a chemical deposition method were investigated. The photoluminescence (PL) from the arrays was studied using angular resolution. The PL spectra of the filled opal exhibited a dip corresponding to the array’s photonic band gap. ZnO nanocrystals embedded in the opal matrix demonstrated quenched excitonic emission while the opal matrix showed enhanced emission. This effect is explained by an energy transfer from ZnO nanocrystals to the opal matrix.     

Heterogeneous Photocatalytic Oxidation of Pollutants in Air on TiO<Subscript>2</Subscript> Particles

A semiempirical method has been developed for analyzing the mechanism of heterogeneous reactions based on the Langmuir–Hinshelwood kinetic model modified using the first- order double-exponential decay approach. The method proved useful for describing the kinetics of photocatalytic oxidation (PCO) on TiO₂ particles in air for a wide range of substances: ketones, organophosphorus compounds, alkyl sulfides, and chlorinated hydrocarbons. The range of substances can certainly be considerably expanded. An equation of implicit function was derived that describes the kinetics of heterogeneous PCO of the zeroth, first, and intermediate (between the zeroth and first) orders. Approximation of the experimental time dependence of concentration using this equation makes it possible to determine the reaction order including the intermediate one, the characteristic decay time of the substance, and the fraction of the exponential components in the kinetic equation. This semiempirical method was used for processing both the original experimental data obtained in the present study and the literature data. The time dependences of trichloroethylene (TCE) concentrations in a closed space during the heterogeneous PCO on TiO₂ aerosol catalyst particles were studied using a specially designed unit. The catalytic activity increased with the aerosol concentration C _as : at C _as = 10.23, 14.17, and 19.85 g/m³, 90% purification of air from TCE was reached in 8.5, 5.0, and 1.5 min, respectively.     

Features of Structural Phase Transitions of Aluminum Hydroxides under Laser Processing

The results of the studies of laser processing of alkoxide aluminum hydroxides with micrometer and nanometer particle sizes are presented. It is shown that the pseudo-boehmite processing process and phase composition of formed oxides are controlled by particle packing, laser radiation propagation in powder, and specific energy deposition. The main phases formed upon laser heating are γ, α-Al₂O₃; the content of δ, θ-Al₂O₃ is low. The minimum corundum crystallite size is ～50 nm.