Understanding the Effects of Ultrasound (408 kHz) on the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER) on Raney-Ni in Alkaline Media

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) occurring at the Raney-Ni mesh electrode in 30 wt.-% aqueous KOH solution were studied in the absence (silent) and presence of ultrasound (408 kHz, ∼54 W, 100% acoustic amplitude) at different electrolyte temperatures (T = 25, 40 and 60 °C). Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) experiments were performed to analyse the electrochemical behaviour of the Raney-Ni electrode under these conditions. Under silent conditions, it was found that the electrocatalytic activity of Raney-Ni towards the HER and the OER depends upon the electrolyte temperature, and higher current densities at lower overpotentials were achieved at elevated temperatures. It was also observed that the HER activity of Raney-Ni under ultrasonic conditions increased at low temperatures (e.g., 25 °C) while the ultrasonic effect on the OER was found to be insignificant. In addition, it was observed that the ultrasonic effect on both the HER and OER decreases by elevating the temperature. In our conditions, it is suggested that ultrasound enhances the electrocatalytic performance of Raney-Ni towards the HER due to principally the efficient gas bubble removal from the electrode surface and the dispersion of gas bubbles into the electrolyte, and this effect depends upon the behaviour of the hydrogen and oxygen gas bubbles in alkaline media.     

Synthesis of a new potassium titanate,KTiO2(OH) by hydrothermal oxidation of Ti

Abstract

A new titanium hydroxide KTi₂O(OH) has been synthesized by hydrothermal oxidation of titanium powder in concentrated potassium hydroxide solution. A formation diagram of products synthesized in Ti-KOH-H₂O system at the region of KOH concentration from 0 to 90mol.kg-^?1-H₂O and the temperature from 150 to 350°C has been also constructed.     

Stable colloidal suspensions of nanostructured zirconium oxide synthesized by hydrothermal process

Nanocrystalline zirconium oxide was synthesized by hydrothermal treatment of ZrO(NO₃)₂ and ZrOCl₂ aqueous solutions at different temperatures and time in presence of hydrogen peroxide. Hydrothermal treatment of zirconium salts (0.25 and 0.50 mol L^?1) produced nanocrystalline monoclinic ZrO₂ powders with narrow size distribution, which were formed by the attachment of the smaller particles with crystallites size of 3.5 nm, estimated by means of the Scherrer’s equation and confirmed by transmission electronic microscopy. Typical monoclinic zirconium oxide X-ray powder diffraction patterns and Raman spectra were obtained for all the crystalline powders. It was observed that the crystallization depends strongly on the temperature, resulting in amorphous material when the synthesis was realized at 100 °C, and crystalline with monoclinic phase when synthesized at 110 °C, independently of the salt used. Zirconium oxide colloidal nanoparticles were formed only at hydrothermal treatments longer than 24 h. The stability of the colloids was successfully characterized of zeta potential, showing an initial value of + 59.2 mV in acid media and isoelectric point at pH = 5.2, in good agreement with previous studies.     

Increasing the ·OH radical concentration synergistically with plasma electrolysis and ultrasound in aqueous DMSO solution

In recent years, significant increases in waste processing and material engineering have been seen by using advanced oxidation processes. The treatment results and energy yields of these processes are largely determined by the generation and retention of reactive oxygen species (ROS). However, increasing the amount of ROS remains a key challenge because of the unavailability of performance- and energy-efficient techniques. In this study, plasma electrolysis, ultrasound, and plasma electrolysis combined with ultrasound were used to treat dimethyl sulfoxide (DMSO) solutions, and the results showed that the two methods can synergistically convert filament discharge into spark discharge, and the conversion of the discharge mode can significantly increase the concentration of OH radicals and effectively improve the efficiency of DMSO degradation. We verified the rationality of the results by analyzing the mass transfer path of ROS based on the reaction coefficients and found that the ·OH radicals in aqueous solution were mainly derived from the decomposition of hydrogen peroxide. These findings indicated that the synergistic action of plasma electrolysis and ultrasound can enhance the production of chemically reactive species, and provide new insights and guiding principles for the future translation of this combined strategy into real-life applications. Our results demonstrated that the synergistic strategy of ultrasound and plasma electrolysis is feasible in the switching mode and increasing the ROS, and may open new routes for materials engineering and pollutant degradation.     

Hydrogen accumulation and distribution during the saturation of a VT1-0 titanium alloy by an electrolytic method and from a gas atmosphere

The accumulation, distribution, and thermally stimulated release of hydrogen in a VT1-0 titanium alloy during electrolytic saturation and gas-phase saturation are studied. After electrolytic saturation, a 0.4-μm-thick surface layer consisting of δ hydrides with a binding energy of 108 kJ/mol forms in the alloy. The hydride dissociation after electrolytic saturation in heating occurs in the temperature range 320–370°C. After saturation from a gas atmosphere, δ hydrides with a binding energy of 102 kJ/mol form throughout the alloy volume. The dissociation of the hydrides formed during gas-phase saturation in heating occurs in the temperature range 520–530°C. A further increase in the temperature is accompanied by the transformation of titanium from the α into the β modification. At 690–720°C, the phase transformation is completed, and another hydrogen desorption peak appears in a thermally stimulated hydrogen desorption spectrum.     

氯盐溶液近红外光谱分析研究

氯盐近红外光谱分析在生物医学上有着十分重要的意义。在室温下对氯化钠,氯化钾,氯化钙水溶液的近红外光谱采集分析表明,氯盐溶液浓度的变化会影响水分子的氢键而使得水溶液的近红外光谱发生变化。通过选择合理波长区间以及温度变化影响为零的波长点(等吸光点),减小温度的干扰对溶液近红外光谱影响,采用偏最小二乘法建立了氯盐溶液的浓度模型用于预测氯盐的离子浓度。分析氯盐溶液中氯盐阳离子的离子半径大小、离子电荷数和离子在水中络合效应等因素对水的近红外光谱所造成的影响以及产生影响因素的原因。实验结果表明,温度和浓度都会影响溶液的近红外光谱,氯盐溶液浓度较低时,温度的影响占主导地位;氯盐浓度高时,浓度的影响占主导地位。氯盐在水溶液中形成络合物,并与氯盐阳离子共同作用对水的氢键产生影响,对于浓度相同种类不同的氯盐溶液, 形成的络合物和阳离子破坏效应对水的氢键的破坏作用为: CaCl₂>NaCl>KCl。最终建立的样品浓度模型校正集的决定系数(R2)=99.97%,交叉验证均方误差(RMSECV)=4.51,剩余预测偏差(RPD)=62.7,满足日常生化检测精度要求。     

In-depth study of the sulfur migration and transformation during hydrothermal carbonization of sewage sludge

This study investigated the effect of temperature on sulfur transformation behavior during the hydrothermal carbonization of raw sludge, water washed sludge and the corresponding filtrate solution at 110–235 °C. The different sulfur species in the various products were determined, primarily focusing on the sulfur species present in the aqueous product. At 110 °C, 31.9% of sulfur migrated to the aqueous product, primarily in the form of sulfone-S and sulfoxide-S. As the temperature increased to 160 °C, the hydrolysis of aliphatic-S and aromatic-S was enhanced, and the former species further transformed to other organic-S or SO₄²-S in the aqueous product. High temperature is beneficial to the formation of sulfate-S and thiophene-S/aromatic-S in the aqueous and hydrochar products, along with the release of H₂S and CH₃SH. This caused a retention of only 29.2% sulfur (i.e., sulfate-S) in the hydrochar at 235 °C, with a large amount of sulfur migrating to the aqueous product (51.1%), followed by the gas product (9.1%). Among all the sulfur species in raw sludge, aliphatic-S was the most thermally unstable. SO₄²-S and sulfur-containing gas were primarily formed from the decomposition of water-insoluble aliphatic-S, while part of thiophene-S/aromatic-S in aqueous products was generated from water-soluble sulfone-S and sulfoxide-S at high temperatures of ≥160 °C. The results indicate that 210 °C is the optimal temperature for preparing of sludge-based fuel during hydrothermal carbonization, and water washing pre-treatment is a good strategy for enhancing the removal of sulfur in hydrochar and reducing the release of sulfur-containing odorous gas.     

Enhanced photocatalytic–electrolytic degradation of Reactive Brilliant Red X-3B in the presence of water jet cavitation

Photocatalysis, electrolysis, water jet cavitation (WJC), alone and in combinations were applied to degrade an azo dye, Reactive Brilliant Red X-3B (X-3B). Experiments were conducted in a 4.0 L aqueous solution with different initial dye concentrations, TiO₂ dose, and solution pH. WJC substantially increased the photocatalytic, electrolytic and photocatalytic–electrolytic rates of the dye removal. The observed first-order rate of X-3B decolorization in the process of combined photocatalysis and electrolysis coupled with WJC was 1.6–2.9 times of that in the process of combined photocatalysis and electrolysis coupled with mechanical stirring. The rate enhancements may be attributed primarily to the reduced diffusion layer thickness on the electrodes and the deagglomeration of photocatalyst particles due to the chemical and physical effects of WJC. Under the conditions of 80 mg/L X-3B solution, 100 mg/L TiO₂ dose and solution pH 6.3, 97% and 71% of color and chemical oxygen demand (COD_Cr) were removed, respectively, within 90-min photocatalytic–electrolytic treatment coupled with WJC. During this process, azo groups and naphthalene, benzene and triazine structures of the dye can be destroyed. Industrial textile effluent was also investigated, and a positive synergistic effect between photocatalytic–electrolytic system and WJC was observed considering color removal.     

The adsorption of hydrogen and the reaction of hydrogen with oxygen on Pt (100)

The adsorption of hydrogen on Pt (100) was investigated by utilizing LEED, Auger electron spectroscopy and flash desorption mass spectrometry. No new LEED structures were found during the adsorption of hydrogen. One desorption peak was detected by flash desorption with a desorption maximum at 160 °C. Quantitative evaluation of the flash desorption spectra yields a saturation coverage of 4.6 × 10¹⁴ atoms/cm² at room temperature with an initial sticking probability of 0.17. Second order desorption kinetics was observed and a desorption energy of 15–16 kcal/mole has been deduced. The shapes of the flash desorption spectra are discussed in terms of lateral interactions in the adsorbate and of the existence of two substates at the surface. The reaction between hydrogen and oxygen on Pt (100) has been investigated by monitoring the reaction product H₂O in a mass spectrometer. The temperature dependence of the reaction proved to be complex and different reaction mechanisms might be dominant at different temperatures. Oxygen excess in the gas phase inhibits the reaction by blocking reactive surface sites. At least two adsorption states of H₂O have to be considered on Pt (100). Desorption from the prevailing low energy state occurs below room temperature. Flash desorption spectra of strongly bound H₂O coadsorbed with hydrogen and oxygen have been obtained with desorption maxima at 190 °C and 340 °C.     

Sulfur removal from bauxite water slurry (BWS) electrolysis intensified by ultrasonic

Effects of ultrasonic on desulfurization ratio from bauxite water slurry (BWS) electrolysis in NaOH solution were examined under constant current. The results indicated that ultrasonic improved the desulfurization ratio at high temperatures because of the diffusion and transfer of oxygen gas in electrolyte. However, due to the increase in oxygen gas emission, ultrasonic could not improve the desulfurization ratio obviously at low temperatures. Additionally, the particle size of bauxite became fine in the presence of ultrasonic, indicating that the mass transfer of FeS₂ phase was improved. According to the polarization curves, the current density increased in the presence of ultrasonic, indicating that the mass transfer of liquid phase was improved. The apparent activation energy (AAE) of electrode reaction revealed that ultrasonic did not change the pathway of water electrolysis. However, ultrasonic changed the pathway of BWS electrolysis, converting indirect oxidation into direct oxidation. The AAE of BWS electrolysis in the presence of ultrasonic was higher than that in the absence of ultrasonic. And the low AAEs (less than 20 kJ/mol) clearly indicated the diffusion control during BWS electrolysis reaction.     

The influence of nonpolar organics adsorption on the electrochemical behaviour of powdered activated carbon electrodes in aqueous electrolytes

Adsorption and electrochemical studies were carried out on three activated carbon samples first oxidized, then heat-treated under vacuum (at 180, 500 and 900 °C). The investigations were performed with aqueous electrolyte (Na₂HPO₄ and H₃PO₄) solutions containing selected nonpolar organics (benzene and n-hexane). Adsorption measurements were carried out on solution with a wide range of organics concentration (up to saturation point). Cyclovoltammetric curves of powdered electrodes prepared from the activated carbon samples were recorded for the organics in saturated solutions. The electric double layer capacities of the anodic and cathodic parts were estimated, and the surface anodic and cathodic charge was calculated both in absence and presence of organics in the electrochemical systems. The relative surface charge (in relation to systems without organics) was found to decrease with a reduction in the concentration of surface oxygen-containing groups. Other physicochemical parameters characterizing the degree of surface oxidation (total oxygen concentration, primary water adsorption centres) were also taken into consideration. The correlation between adsorption capacity towards the nonpolar organic compounds (obtained from adsorption isotherms) and change of surface charge was analyzed.     

An In Situ Testing Method for Analyzing the Changes of Active Groups in Coal Oxidation at Low Temperatures

This study details an in situ Fourier transform infrared spectroscopy analytical system that was employed to follow chemical variations in the functional groups on coal surface during the oxidation process at low temperatures. In the reported in situ Fourier transform infrared spectroscopy system, a special chamber was used to contain the coal powders, and a gas inlet tube and a programmable heater were used to simulate different reaction atmospheres and temperatures. The comparisons between in situ and ex situ Fourier transform infrared spectroscopy spectra indicate that the in situ Fourier transform infrared spectroscopy data offer a more accurate reflection of changes in the functional groups. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups in a lignite coal sample were analyzed from 30°C to 220°C using in situ Fourier transform infrared spectroscopy. The experimental results indicate that the chemical variations in the functional groups are affected by their relative chemical activities. The results show that the presence of aliphatic groups on the coal surface varies with temperature. Over the range of 30–70°C the presence of these groups decreases, but then their abundance increases over the range of 70–180°C and finally decreases again when the temperature is increased to between 180°C and 220°C. With respect to oxygen-containing functional groups, three various trends were observed as the test temperature was varied. Our conclusion was that these variations are a function of the reaction activities of the various oxygen-containing functional groups.     

Propylene deep oxidation on the Pt(111) surface: temperature programmed studies over extended coverage ranges

Propylene oxidation was studied on the Pt(111) surface over a wide range of reaction stoichiometries using temperature programmed methods. Reaction of propylene with excess oxygen results in complete oxidation to water and carbon dioxide, with oxydehydrogenation to form water beginning at 290 K. The initiation of skeletal oxidation occurs after water formation begins, except for the highest propylene coverages. A stable dehydrogenated intermediate with a C₃H₅ stoichiometry is formed in the 300 K temperature range during oxidation. Reaction of propylene with substoichiometric amounts of oxygen results in incomplete oxidation with hydrocarbon decomposition dominating after depletion of surface oxygen. Increasing oxygen coverage results in more complete oxidation. Oxidation processes result in water, carbon dioxide, and carbon monoxide, while decomposition results in hydrogen, propylene, and propane desorption with some surface carbon remaining. Propylene-d₆ and selectively labeled propylene-3,3,3-d₃ (CH₂CHCD₃) experiments indicated initial water formation results from oxydehydrogenation of one of the olefinic hydrogens. At the highest propylene and oxygen coverages studied, we observed small amounts of partial oxidation which indicate that the vinyl hydrogen is removed initially, resulting in the formation of an adsorbed H₂CCCH₃ intermediate. The partial oxidation products observed are acetone desorbing at 200 K and acetic acid at 320 K. Removal of the first skeletal carbon begins at 320 K, except for the highest propylene coverages. Preadsorption of molecular oxygen limits adsorption of propylene and preadsorption of propylene limits molecular oxygen adsorption at 110 K. Similar oxidation mechanisms are observed following initial adsorption of both molecular and atomic oxygen, which is expected since molecular oxygen dissociates and/or desorbs well below oxidation temperatures.     

A novel hydrothermal route to synthesize solid SnO2 nanospheres and their photoluminescence property

Solid tin oxide (SnO₂) nanospheres were fabricated via one-step hydrothermal treatment of tin foil in aqueous alkaline solutions at 180°C. Based on the time-dependent experiments, the evolution behavior of Ostwald ripening is proposed to explain the formation mechanism. Besides a broad emission band at 600 nm, the SnO₂ nanospheres, synthesized for 24 h, show an additional emission band at 490 nm that has a great sensitivity to the content of oxygen. Spectral examinations and analyses reveal that the two emission bands originate from the electronic states determined by the oxygen interstitials, intrinsic surface states, and oxygen vacancies.     

Salt deposition from hydrothermal solutions in a flow reactor

A flow hydrothermal setup with a tubular reactor equipped with a plunger pump and back pressure valves is used to study the effects of scaling in the K₂SO₄-KCl-H₂O, K₂SO₄-K₂CO₃-H₂O, and Na₂SO₄-NaCl-H₂O systems at pressures of up to 270–340 kg/cm², temperatures of 400–600°C, and flow rates of 5.0 and 2.5 ml/min in order to establish conditions for the formation of salt plugs of type 2 (K₂SO₄, Na₂SO₄) in the flow mode at supercritical (SC) state parameters and to explore ways of eliminating such salt deposits by means of hydrothermal solvents, more specifically, high-temperature aqueous solutions of salts of type 1 (KCl, K₂CO₃, and NaCl). The concentrations of hydrothermal solvents sufficient to prevent the plugging of flow systems with solutions containing 0.26–0.27 mol % K₂SO₄ or Na₂SO₄ are determined, and the effects of the flow rate and chemical composition of type 1 salts on this process are studied. The results show that the phenomenon of scaling with the formation of salt plugs, which hinders the practical use of supercritical water oxidation technology, can be eliminated by adding readily soluble electrolytes, salts of type 1, to initial aqueous solution of type 2 salts.     

Data for scaling-up hydrothermal waste water treatment process

Abstract

Hydrothermal oxidation of wastes is developed as an alternative technique in order to limit the toxic end-product formation, the waste volume and the energy supply. We are now working on the transfer of this technology, and so on the determination of data for scaling-up the hydrothermal oxidation process. The main data concern the knowledge of reactive pathway, the determination of reaction kinetic and thermal parameter. Kinetic and thermal data have been determined for the hydrothermal oxidation of acetic acid as well as the reactive pathway of hydrothermal oxidation of a C, H, O, N compound, the fenuron (C₆H₅-NH-CO-N(CH₃)₂).     

A Turbidity Study of the Rate of Dissolution of Zinc-Monoglycerolate in Aqueous Solution

Abstract

The turbidity of suspensions of polymeric zinc monoglycerolate (ZMG) has been used to determine dissolution rates in aqueous solution. The rate was found to be first order with respect to the concentration of undissolved ZMG and of order 1/2 with respect to the hydrogen ion concentration in the pH range 4.1–5.8 and a temperature range of 20°C - 45°C. The temperature dependence at constant pH obeys the Arrhenius equation and the activation energy of the dissolution process was found to be near 35 k J mol^?1.     

Enlargement of the stability range and superconducting domain of the T/O type phase of the La2)CuO4-Nd2CuO4 system after treatment under oxygen pressure

Abstract

Two main solid solutions exist in the La(2)CuO(4)-Nd(Z)CuO(4) system. The structure of the first one is related to that of tetragonal K(2)NiF(4) and is labelled as T/O; copper ions are in sixfold coordination (elongated octahedron), The second one has an original structure, called T′, in which copper ions are in square planar coordination. When synthezised in air at 800°C, the upper limit of the T/O type solid solution is 0.55. By subsequent treatment under 40 MPa oxygen pressure between 920 and 94O°C, this limit is shifted up to ? 0.80, and an ultimate oxidation by electrochemistry induces a bulk superconductivity, as in the case of normaly prepared T/O phases (x ≥ 0.55). Data are given on the change in the unit cell parameters, deviation from oxygen stoichiometry and conduction properties consecutive to the oxidizing treatments.     

Reactivation of Promoted Nickel Catalysts for Deuterium Exchange between Hydrogen and Water in the Vapour Phase

Binary promoted nickel – chromium oxide and ternary promoted nickel – chromium oxide – aluminium oxide mixed catalysts were prepared for use in the present study. The catalysts were prepared by co-precipitation of the corresponding metal nitrates as carbonates followed by calcination in nitrogen atmosphere at 350 °C and reduction in hydrogen atmosphere at 320 °C. To prevent spontaneous oxidation of the catalysts, bidistilled water was added followed by heating of the catalyst mixtures at about 110 °C in hydrogen atmosphere for few hours. Deactivation of catalysts was studied by measurements of the variation of their activities with the time of contact of the reacting gas mixtures with the catalyst surface in the reaction chamber. It was found that while the catalytic activity of ternary catalysts for the isotopic exchange of deuterium between hydrogen and water vapour was higher than that of the binary one, the loss in activity of the former teas faster than the latter. Reactivation of the catalysts were carried out at different temperatures between 110–160°C in hydrogen atmosphere. Catalytic activity measurements indicated that higher temperatures are better for the reactivation process.     

Measurement of stable isotope activities in saline aqueous solutions using optical spectroscopy methods

The requirement to measure the stable isotopic compositions of saline pore fluids by optical methods has prompted a re-evaluation of the isotopic salt effect for common salts. Hydrogen and oxygen isotopic salt effects were measured at room temperature (21°C) by optical methods. For hydrogen isotopes, our results agree well with those of previous studies and better define these effects at low temperatures. In contrast, measured oxygen isotope salt effects disagree within error for NaCl and CaCl₂ solutions from those reported previously. Subtle differences between measurement methods may account for the discrepancy. In studies that involve highly saline fluids, the isotopic salt effect must be taken into account because modern methods that measure stable isotopic compositions as activities or concentrations may be not directly comparable to historical data sets.