Sergey K. Poznyak

Enhancement of active corrosion protection via combination of inhibitor-loaded nanocontainers.

The present work reports the synthesis of layered double hydroxides (LDHs) nanocontainers loaded with different corrosion inhibitors (vanadate, phosphate, and 2-mercaptobenzothiazolate) and the characterization of the resulting pigments by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The anticorrosion activity of these nanocontainers with respect to aluminum alloy AA2024 was investigated by electrochemical impedance spectroscopy (EIS). The bare metallic substrates were immersed in dispersions of nanocontainers in sodium chloride solution and tested to understand the inhibition mechanisms and efficiency. The nanocontainers were also incorporated into commercial coatings used for aeronautical applications to study the active corrosion protection properties in systems of industrial relevance. The results show that an enhancement of the active protection effect can be reached when nanocontainers loaded with different inhibitors are combined in the same protective coating system.

Novel Inorganic Host Layered Double Hydroxides Intercalated with Guest Organic Inhibitors for Anticorrosion Applications

Zn-Al and Mg-Al layered double hydroxides (LDHs) loaded with quinaldate and 2-mercaptobenzothiazolate anions were synthesized via anion-exchange reaction. The resulting compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. Spectrophotometric measurements demonstrated that the release of organic anions from these LDHs into the bulk solution is triggered by the presence of chloride anions, evidencing the anion-exchange nature of this process. The anticorrosion capabilities of LDHs loaded with organic inhibitors toward the AA2024 aluminum alloy were analyzed by electrochemical impedance spectroscopy. A significant reduction of the corrosion rate is observed when the LDH nanopigments are present in the corrosive media. The mechanism by which the inhibiting anions can be released from the LDHs underlines the versatility of these environmentally friendly structures and their potential application as nanocontainers in self-healing coatings.

Synthesis of surface-modified colloidal semiconductor nanocrystals and study of photoinduced charge separation and transport in nanocrystal-polymer composites

Abstract This paper provides an overview of semiconductor nanocrystals, which were synthesized either by an aqueous technique in the presence of different thiols as stabilizing agents (CdS, CdSe, CdTe, Cd x Hg 1− x Te and HgTe) or via organometallic reactions (CdSe, CdTe, InP and InAs). In all cases, successful wide-range tuning of the semiconductor band-gap energies was achieved by the control of the nanocrystal size. In addition, the surface properties of the nanocrystals can be controlled by the exchange of the capping ligand. Blends of nanocrystals and conducting polymers, were prepared using CdTe nanocrystals and polyaniline, polypyrrole or poly(3,4-ethylenedioxythiophene) (PEDT), and considered with respect to possible optoelectronic applications. The photoinduced charge separation and transport in the CdTe–PEDT composites was investigated by photoelectrochemical methods.

Effect of electron and hole acceptors on the photoelectrochemical behaviour of nanocrystalline microporous TiO2 electrodes

Abstract A comparative study of the photoelectrochemical properties of nanocrystalline microporous, compact polycrystalline and single-crystal TiO 2 electrodes has been performed with an emphasis on the analysis of the short-wavelength region of the action spectra. Adding to the solution or immobilizing on the electrode surface some electron or hole scavengers has been shown to exert significantly more appreciable influence on the short-wavelength edge of photocurrent spectra of nanostructured electrodes as compared with those of polycrystalline compact or single-crystal electrodes. This influence is markedly stronger in basic solutions in comparison with acidic ones. The effects observed are explained by the change of limiting steps of the overall photoelectrochemical process in going from the conventional macroscopic to nanostructured electrodes.

Photoinduced and dark underpotential deposition of lead on selenium

Abstract The processes of the dark and photoinduced underpotential deposition (upd) of Pb ad-atoms on p-type Se electrodes have been studied. Under illumination with light absorbed by Se, the photoinduced upd of Pb ad-atoms (approximately a monolayer) onto the Se electrode occurs. The upd shift is about 800 mV. The Pb ad-atoms modify the Se surface and form electronic surface states in the Se bandgap, which promotes an efficient electron exchange between the valence band and redox species in solution. The surface states act as effective recombination centers for the photogenerated charge carriers and give rise to the subbandgap photocurrent enhancement. In the dark, the Pb upd occurs only on the electrode surface on which PbSe clusters were deposited. These clusters are formed both as a result of the chemical interaction of surface Se atoms with Pb bulk particles deposited at the cathodic polarization and due to the interaction of electrochemically generated H 2 Se with Pb 2+ cations. The Pb ad-atoms deposited on the Se surface are electrochemically oxidized at more positive potentials (by ca. 150 mV) than those deposited on the surface of PbSe clusters.

Correlation between surface properties and photocatalytic and photoelectrochemical activity of In2O3 nanocrystalline films and powders

Nanocrystalline In2O3 thin films and powders have been prepared by sol–gel procedure and characterized by various bulk and surface techniques (X-ray diffraction, X-ray photoelectron spectroscopy and photoelectrochemical spectroscopy). Photocatalytic reactivity for rhodamine 6G photodestruction and photoelectrochemical (PEC) properties have been studied for the In2O3 samples heated at different temperatures. The photocatalytic activity of the powder grows initially with increasing annealing temperature from 200 to 300°C and then drops sharply with further increase in temperature. A strikingly large difference in photocurrent onset potentials and photocurrent quantum yields has been revealed for the films heated at 200 and 400°C. The susceptibility of the oxide surface to hydroxylation appears to be a key factor responsible for the sharp change in photoreactivity and PEC properties.

Characterization and photoelectrochemical properties of nanocrystalline In2O3 film electrodes

Abstract The photoelectrochemical properties of nanocrystalline In 2 O 3 film electrodes prepared by sol-gel method have been studied. The surface and bulk characterization of sol-gel-derived In 2 O 3 films and powders heated at different temperatures has been performed using X-ray diffraction analysis, X-ray photoelectron, IR-absorption and photoelectrochemical spectroscopies. A significant shift of the photocurrent onset potential in the positive direction and a rise in the photocurrent quantum yield are observed as the temperature of the electrode heat treatment increases from 200 to 400°C. A tentative explanation for this effect has been provided, taking into account the formation of the finest hydroxide layer at the nanocrystallite surface of slightly heated In 2 O 3 films.

Optical properties and charge transport in nanocrystalline TiO2–In2O3 composite films

This work involves a comparative study of nanocrystalline titanium and indium oxides as well as TiO2–In2O3 composites prepared by a sol–gel method from concentrated hydrous titanium dioxide and indium hydroxide sols. Highly transparent uniform films were fabricated from the sols by a spin-coating technique. TiO2–In2O3 nanocomposites possess pronounced extreme dependencies of both the apparent bandgap and the refractive index on the film composition. No chemical interaction between the oxides was observed during annealing to temperatures between 200 and 700 °C. This behavior was attributed to the effect of surface states formed at the nanocrystallite interfaces. Other possible causes of the pronounced dependence of the optical and electronic properties on the TiO2-to-In2O3 ratio are also discussed. Abrupt changes in resistivity, photoresistivity and photocurrent decay time of the composite films were observed for composites where the TiO2 content ranged from 25 to 50 wt.% and are associated with the formation of a three-dimensional infinite cluster of interconnected In2O3 nanoparticles.

Light-Induced Water Splitting Causes High-Amplitude Oscillation of pH-Sensitive Layer-by-Layer Assemblies on TiO2.

We introduce a simple concept of a light induced pH change, followed by high amplitude manipulation of the mechanical properties of an adjacent polymer film. Irradiation of a titania surface is known to cause water splitting, and this can be used to reduce the environmental pH to pH 4. The mechanical modulus of an adjacent pH sensitive polymer film can thus be changed by more than an order of magnitude. The changes can be localized, maintained for hours and repeated without material destruction.

Electrochemical preparation of lead-doped amorphous Se films and underpotential deposition of lead onto these films

Abstract The process of the underpotential deposition (UPD) of Pb adatoms (Pb ad ) onto Se was used to produce nanocomposite films consisting of amorphous Se and nanosized PbSe clusters distributed throughout the film bulk. It was found that doping lead into Se films modifies their optical and photoelectrochemical properties and increases the efficiency of the charge transfer both in the film bulk and through the semiconductor | electrolyte interface. Introducing lead into the bulk of Se films significantly promotes the process of Pb ad UPD onto Se surface. The underpotentially deposited Pb ad interact chemically with Se surface atoms, resulting in the formation of a PbSe monolayer. The PbSe formed can be identified by the anodic peak corresponding to its electrochemical oxidation.