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This work is devoted to the study of the adsorption efficiency of methylene blue and methyl orange dyes by polyaniline base (PANI), halloysite nanotubes (HNTs), and their nanocomposite (HNTs/PANI). PANI and the nanocomposite were prepared by the chemical oxidative polymerization of aniline in the absence and presence of HNTs followed by subsequent dedoping by ammonia solution. The morphology and thermal stability of the adsorbents were explored. In particular, the TEM method showed that the nanocomposite consisted of practically non-agglomerated nanoparticles with a "core-shell" morphology. Particles of pure polymer are quite agglomerated and form massive aggregates. The kinetics of decreasing the concentration of dyes in solutions upon their contact with adsorbent powders was studied by the method of electron spectroscopy. The HNTs/PANI nanocomposite was found to absorb both dyes with slightly higher efficiency than the PANI base probably due to more developed surface of the former. Processing of the obtained results of adsorption of both dyes on the studied adsorbents according to different kinetic models (pseudo-first and pseudo-second order and intraparticle diffusion) showed that in all cases this process is best described by the pseudo-second order model, which indicates the chemical nature of adsorption. The calculated adsorption capacity of the adsorbents under study appeared be quite close to the experimental one. These materials can be used as effective adsorbents for cleaning wastewaters from organic dyes. [ABSTRACT FROM AUTHOR]

microcomposite catalyst based on zinc oxide microstructures and silicon was synthesized for heterogeneous catalysis. ZnO microstructures with elements 6 μm in diameter, 15 μm long, were grown on conductive silicon (001) substrates by the vapor phase method. Methyl orange (C14H14N3NaO3S) was selected as an organic dye for testing the photocatalytic and photoelectrocatalytic properties of ZnO microstructures. The sample was placed in an aqueous solution of methyl orange in order to perform a photocatalytic decomposition of the dye. DRT-125 quartz lamp with a radiation power of no more than 26 W was used as the radiation source in the wavelength range from 315 to 400 nm. The sample with the aqueous solution of dye in a standard 3.5 ml quartz quvet was irradiated with the lamp at a distance of 10 cm from it. In order to perform the photoelectrocatalytic decomposition of the dye in the aqueous solution, an electric field of 1.5 V was applied between ZnO/Si and Al electrodes, that were simultaneously irradiated with UV for 5 cycles lasting 20 minutes (100 minutes). The degradation kinetics of the dye was determined by changing its concentration, on the basis of the optical density measurement at the absorption maximum of the dye (465 nm) using a Specord M 40 spectrometer. During the photocatalysis, the concentration of the dye decreased by 41 % in 100 min, and during the photoelectrocatalysis, by 59 % in 100 min. First-order kinetics was used for the kinetic analysis of the catalytic reactions. The reactions rate constants were found to be k = 5.1·10-3 min-1 in the case of the photocatalysis, and k = 8.8 ·10-3 min-1 in the case of the photoelectrocatalysis. The increase in the efficiency of the dye decomposition in the latter case was associated with a more efficient redistribution of charge when voltage (1.5 V) was applied and with a higher amount of hydroxyl radicals on the surface of the catalyst. [ABSTRACT FROM AUTHOR]