The photooxidation of ethylene glycol (EG) on nanotube TiO2 electrodes synthesized by anodization of titanium foil was studied in aqueous electrolytes at different pH levels (5.9 and 13.6) and EG concentrations (0.01 to 10 M). Chronoamperometry, linear potential scanning, and electrochemical impedance spectroscopy (EIS) were shown that electrochemical reduction activation of electrodes by cyclic voltammetry (CV) leads to an increase in the surface states density. This contributes to the effective e-/h+ exciton separation, an increase in the charge transfer rate at the electrode/electrolyte interface, and, accordingly, the photocurrent density. The photocurrent was found to increase with EG addition, with this magnitude being affected by EG concentration, pH level, and the surface state of the photoanode. The EIS results aligned with transient photocurrent measurements, indicating a competition between water oxidation and EG oxidation. EG oxidation proceeded through various pathways, including both direct and indirect hole transfer to molecules adsorbed on the electrode surface.

The electrochemical reduction of levulinic acid (LA) on a gas diffusion hydrophobic electrode with a lead (Pb) catalyst has been studied using electrochemical impedance spectroscopy (EIS). The EIS spectra obtained were analyzed using the Warburg impedance model for a finite- length element, and the apparent double- layer capacitance (C-dl) was calculated. The individual contributions of the ohmic, activation, and diffusion components to the resistance of the LA reduction process in 0.5 M H2SO4 were determined. It was found that the capacity of the double layer, charge transfer resistance, and diffusion resistance decrease as the electrode potential increases. An increase in the volume concentration of LA leads to an increase in C-dl and a decrease in both diffusion and activation resistance.

TiO(2)photonic crystal nanostructure films are anodic synthesized with pulsed and stepwise voltage changes. The obtained photonic structures were activated by cyclic voltammetry in 0.5M Na2SO4. The photoelectrochemical activity of the electrodes was studied in the water splitting reaction in the wavelength range 360-700 nm. Activation leads to a change in the band gap energy, a red shift in the IPCE spectrum and an increase in its values in the studied wavelength range.

The electrochemical conversion of biobased levulinic acid (LA) into renewable chemicals and biofuel precursors represents an important and reasonable alternative to the high temperature conventional catalytic processes of great importance for the development of a sustainable and cost-effective biorefinery. The establishment of the mechanism of levulinic acid reduction is a promising strategy in choosing the optimal electrocatalyst for the redox-transformation of biobased substrates. Herein, we report a new approach to study an electrochemical reduction mechanism of levulinic acid using of proton-deficient non-aqueous reaction media. The electrochemical reduction of levulinic acid to γ-valerolactone (GVL) and valeric acid (VA) in aqueous and organic solutions on various electrodes (glassy carbon, graphite, Al, Pb) was studied. The mechanism of LA electrochemical reduction and major reaction products significantly was found to depend on the solvent, the presence of proton donors, the material of cathode, and the magnitude of the applied potential. In an aqueous solution the process proceeded with the formation of valeric acid on all the electrodes studied. In acetonitrile in the presence of protons, the electrochemical reduction of LA proceeded by various mechanisms, both with the participation of atomic hydrogen and the protonated form of LA, and led to the formation of GVL and/or VA. The difference (ΔE1/2) between the reduction half-wave potential of protons and levulinic acid was found to play an important role in the reduction pathway of LA carbonyl group. At a large ΔE1/2, as in the case of the GC electrode, the LA reduction resulted in the GVL formation. LA can be completely reduced to VA by transferring four electrons due to the close reduction potentials of protons and LA (a low ΔE1/2), as on a Pb electrode. The pathway depends on the conditions of the reduction process and can be estimated based on electrochemical data obtained in the study of reaction products in organic media.

A facile and eco-friendly method for activating anodic TiO2 nanotubes (TNTs) by cyclic voltammetry (CV) is proposed, and photoelectrochemical properties of CV-activated TNTs are compared with those of non-activated TNTs and of TNTs activated by hydrogen-thermal reduction. EPR and luminescence studies show that the pristine samples demonstrate rather large content of paramagnetic and luminescing defects, while hydrogenation and CV-activation lead to the different type of rearrangement of defects. TNTs activated by CV-Na2SO4 demonstrate significantly improved photocurrent density (2.25 mA cm(-2)) in comparison with that of the hydrogen treated and pristine ones (0.93 mA cm(-2) and 0.31 mA cm(-2)) under NUV-irradiation at 0.2 V (RHE). Enhanced photoactivity of Na2SO4-activated TNTs correlates with higher luminescence quantum yield, lowest paramagnetic defects content and larger decay time of the luminescence. Thus, a decrease in the content of defects is an important factor that reduces the non-radiative recombination of charge carriers. The activation-induced redistribution of surface and bulk defects in nanotubes explains the increased photoelectrochemical activity of TiO2-based anodes. Cyclic voltammetry has been proved to be a reliable method to increase the efficiency of TNTs in PEC water splitting.

TiO 2 films with a 1D nanotube structure were obtained by electrochemical anodic oxidation of titanium foil. Electrochemical reductive activation of the TiO 2 -nanotube-based electrodes was carried out using the method of cyclic voltammetry. The activated electrodes showed significantly higher current density and quantum efficiency of the photoelectrochemical water splitting as compared to native TiO 2 nanotubes. Electrochemical treatment of the electrodes by the cyclic voltammetry leads to increase in the photocurrent density by a factor of 4 to 14, depending both on the used wavelength and applied potential. The analysis of electrochemical impedance spectra showed that the increase in the photoelectrochemical process performance is due to increase in the charge transfer rate at the semiconductor/electrolyte interface, as well as improved electronic conductivity of the oxide layer, which contributes to better charge carrier separation and decrease in their recombination rate.

Kinetics and selectivity of indirect electrocatalytic resorcinol oxidation by active oxygen forms (AOF) in situ generated from oxygen in gas diffusion electrode (GDE) mesostructured carbon CMK‑3 and Pt, Pb/PbO2 at different pH were studied. The high resorcinol oxidation process effectivity in both Pt-GDE at pH=10 (99 %) and Pb/PbO2 + Fe2+ at рН=2 (99 %) systems was shown; the resorcinol oxidation scheme was proposed

The electrochemical hydrogenation of levulinic acid in H2SO4 solution at aluminium, lead, graphite and glassy carbon electrodes is studied. The process is identified to proceed selectively to valeric acid. The conversion, selectivity and faradaic efficiency are significantly influenced by the material electrode nature. The levulinic acid hydrogenation at glassy carbon is shown for the first time to proceed to valeric acid, and the process selectivity is affected by the concentration of surface functionalities.

Electrocatalytic oxidation of aromatic pollutants (aniline, Methyl Orange, Eriochrome blue SE) is studied on lead dioxide, boron doped diamond, and ruthenium- and titanium-oxide-based anodes (DSA, dimensionally stable anode). The catalytic properties of the tested materials are studied using cyclic voltammetry and galvanostatic electrolysis. The activity of electrodes toward the electrochemical conversion of organics is shown to increase in the sequence of DSA < lead dioxide < boron doped diamond. The oxidation rate decreases in the order of Eriochrome blue SE > Methyl Orange > aniline for all electrodes. The oxidation process of the compounds corresponds to the pseudo-first-order reaction kinetics. The apparent rate constant grows at an increase in the applied current density and decrease in the initial pollutant concentration. The formation of both •OH and $${\text{SO}}_{4}^{{2\centerdot {\kern 1pt} - }}$$ radicals is confirmed by the free radical quenching studies; their contribution to the Eriochrome blue SE dye destruction process is evaluated.

The results and prospects of the in situ (in the cell volume) and ex situ (outside the cell) use of aqueous solutions of hydrogen peroxide electrogenerated from oxygen in gas-diffusion electrodes (GDE) of carbon black are discussed. It is shown that using GDE based on technological A-437E carbon (acetylene black) and mesostructured carbon CMK-3 allows the Н2О2 solution with the concentration higher than 3 M to be obtained. It is found that electrosynthesized hydrogen peroxide may be used in situ with the high efficiency both in the indirect electrosynthesis of important organic and inorganic target products and in the destruction of organic and inorganic pollutants present in waste waters of different origin. Under the ex situ conditions, it is possible to synthesize the more concentrated solutions of Н2О2, organic peroxoacids, and inorganic peroxosolvates and also to carry out mineralization of exometabolites in autonomous life-support systems. These results may be helpful in selecting the most appropriate versions of using hydrogen peroxide solutions electrogenerated from oxygen for solving particular problems.

In this work, the electrooxidation as environmentally clean technology has been studied to the degradation of Mordant Blue 13 azo dye (MB13) using boron-doped diamond (p-Si/BDD) and oxide ruthenium titanium (Ti/Ru0.3Ti0.7O2 (DSA)) anodes in various water matrices: distilled water (DW), hot tap water (HTW), and simulated wastewaters with (SWS) and without surfactant (SW). The influence of experimental parameters, such as current density, initial dye concentration, electrolysis time/specific charge, and pH on the MB13 degradation rate, current efficiency, and energy consumption, has been determined. The enhanced rate of both color and chemical oxygen demand (COD) removal in sulfate aqueous solutions with BDD was observed, which indicates that sulfate (SO4−•) radicals along with •OH ones might be responsible for the degradation process. The MB13 decolorization process obeyed a pseudo-first-order reaction kinetics with the apparent rate constant from 7.36 × 10−2 min−1 to 4.39 × 10−1 min−1 for BDD and from 9.2 × 10−3 min−1 to 2.11 × 10−2 min−1 for DSA depending on the electrolysis conditions. The effect of water matrix on the decolorization and COD removal efficiency has been evaluated. Inorganic ions, mordant salt, and surfactant contained in simulated effluents decelerated the COD decay compared to DW and HTW for the both anodes; meanwhile, they differently affected the discoloration process. A comparison of the specific energy consumption for each electrocatalytic material under different experiment conditions has been made. The BDD electrode was more efficient than the DSA to oxidize the MB13 dye in all kinds of water.

Electrochemical oxidation for degradation of industrial dye Methyl Orange in aqueous sulfate solutions with various electrocatalytic materials: boron-doped diamond electrode and electrode based on titanium and ruthenium oxides. The influence exerted by the main working parameters of electrolysis (current density, concentration of Methyl Orange, pH) on the discoloration efficiency and on the chemical oxygen demand (COD) was examined. It was shown that an increase in the current density and a decrease in the pollutant concentration improve the process efficiency. However, this leads to an increase in the specific electric energy consumption per unit mass of COD. It was found that the boron-doped diamond electrode is a more efficient electrocatalytic material, compared with electrode based on titanium and ruthenium oxides. At low concentrations of Methyl Orange (<50 mg L–1), there exists the possibility in principle of using the electrode based on titanium and ruthenium oxides not only for discoloration, but also for making lower the COD level.

Kinetics and selectivity of oxidation of dyes (Methyl Orange and Chrome Dark Blue) on a lead dioxide (Pb/PbO2) anode at various current densities, substrate concentrations, and pH values with the use of various active oxygen species was studied. It was shown that the electrochemical oxidation of dyes on the Pb/PbO2 anode occurs rather effectively under the chosen conditions. The mineralization efficiency in 5 h was 51 to 89.5 and 93 to 100% for, respectively, Methyl Orange and Chrome Dark Blue, depending on the electrolysis conditions.

Comparison of the results obtained in integrated processing of a titanium-containing ore based on three minerals (ilmenite, sphene, and rutile) demonstrated the high efficiency of the high-temperature carbochlorination (at 800°C for 60 min). The degree of titanium extraction was 99%, and that of iron, 98%, whereas hydrometallurgical methods enable not more than a 47% extraction.

Two stage processing – acid leaching and carbochlorination – is proposed for titanium extraction from titanite (CaTiSiO5). Calcium oxide and 40–60wt.% of titanium oxide in titanite were dissolved by leaching in recyclable hydrobromic acid. Titanium dioxide of 99.5wt.% purity was obtained by thermal hydrolysis of titanium containing acid solution. On the second stage, solid leaching residue was carbochlorinated at 1100°С in a rotary tube furnace to produce titanium tetrachloride. An overall titanium extraction of 93.7% was obtained. Pyrohydrolysis of CaBr2 at 1100–1200°С was used for the hydrobromic acid recycling.

Kinetics and selectivity of the aniline oxidation on a boron-doped diamond electrode and lead dioxide anode (Pb/PbO 2 ) in an acid electrolyte were studied under various generation conditions of active oxygen species. The resulting kinetic dependences can be described by a pseudo-first-order equation. The apparent rate constants of the process were determined for two electrolysis modes: direct anodic oxidation and oxidation with addition of hydrogen peroxide. UV spectroscopy was used to determine that the aniline destruction process occurs via formation of a number of intermediate products (benzoquinone, carboxylic acids). It was shown that the aniline destruction process can occur with a rather high efficiency (~80–90%) on the electrode types under study.

A procedure for treatment of simulated wastewater solutions to remove Cu2+, Ni2+, and SCN− ions using various combinations of aluminum and iron electrodes in the electro- and peroxyelectrocoagulation processes was studied. The influence exerted by the current density, pH of solution, and concentrations of impurities and hydrogen peroxide on the efficiency of removal of these ions was analyzed. Electrocoagulation using aluminum anode does not lead to a significant decrease in the thiocyanate concentration. In the peroxyelectrocoagulation process, the efficiency of removal of SCN− ions increases with an increase in the [H2O2]: [SCN−] ratio. The electrocoagulation efficiency with the Fe/Fe electrode pair reaches 87% for SCN− and 99.5% for Cu2+ and Ni2+ at a current density of 20 mA cm–2 and electrolysis time of 20 min.