Aqueous Sodium Sulfate Solutions Research Articles

The Anodic Behavior of Manganese Silicide-Germanides in Aqueous Sodium Sulfate Solutions: The Effect of the Germanium Content

The Anodic Behavior of Manganese Silicide-Germanides in Aqueous Sodium Sulfate Solutions: The Effect of the Germanium Content

Supercapacitor Performance of MXene-Coated Carbon Nanofiber Electrodes

MXenes consisting of thin layers of transition metal carbides or nitrides are good candidates for electrode materials due to their excellent electrical conductivity and fast ion transfer. Electrospun carbon nanofibers are highly porous and electrically conductive, making them attractive for electrode materials. In this study, free-standing electrodes were prepared by the dip-coating of carbon nanofibers (CNFs) in the MXene (Ti3C2) colloidal solution, which was synthesized via the wet-etching of MAX (Ti3AlC2) phase, and their chemical structures were investigated by X-ray diffraction and Fourier transform infrared spectroscopy. In addition, scanning and transmission electron microscopy were used to investigate the morphological and crystallographic features of MXene-coated CNFs. Surface area and pore volumes were investigated by nitrogen adsorption/desorption measurements. Supercapacitor performance was studied by assembling a 3-electrode system with 1M aqueous sodium sulfate solution as an electrolyte. MXene-coated CNFs exhibited a maximum specific capacitance of 514 F/g at 0.5 A/g, with energy and power densities of 71.4 Wh/kg at 0.5 A/g and 2.3 kW/kg at 5 A/g, respectively, which are relevantly higher compared to the pristine CNFs due to the pseudocapacitive behavior of MXenes. They also showed comparable cyclic stability during 5000 cycles with the CNFs. This result indicates that MXene-coated carbon nanofibers can be effective electrode materials for electrochemical energy storage.

Thermodynamic analysis for the dissolution of two similar amino acids in sodium sulfate aqueous solution

In the current work, the analyti cal static gravimetric technique was used to assess the solubilities of DL-α-amino butyric acid and DL-valine in an aqueous binary solvent mixture of sodium sulfate (Na2SO4) under equilibrium saturation conditions in between temperature range 288.15 and 308.15 K. Different thermodynamic factors along with transfer Gibbs energetics and entropies under standard conditions were estimated by using computational as well as theoretical method by using the experimental solubilities. Several modes of interactions that occur during solvation were also explained. The manner that solvent molecules of solute amino acids are surrounded in the aforementioned medium employed during the process is taken into consideration. Amino acids become more soluble as the temperature rises. The study also helps us to reach the conclusion that physical properties of electrolyte (Na2SO4), mixed solvent, and the size of the amino acids’ molecules are the main governing factors for the chemical stability as well as other thermodynamic and physical property like solubility of solute amino acids.

Микроэкстракционное концентрирование неионными ПАВ и цветометрическое определение фенола

The extraction of the tungsten blue complex formed by the reaction of phenol with Folin-Ciocalteu reagent (FCR) in the presence of a nonionic surfactant Triton X-100 in alkaline medium using the methodology of micellar extraction based on «clouding point» has been studied for the first time. Aqueous solutions of sodium carbonate and sodium sulfate were used to create pH and as a desalting agent. The latter, having a desalting effect, promotes phase separation in the system under study into a micellar phase saturated with surfactant (Triton X-100) and an aqueous phase depleted in surfactant without additional heating at room temperature. Optimal conditions for micellar phenol extraction were determined: FCR (0,2 n.) – Na2CO3 (6%) – Triton X-100 (2%) – Na2SO4 (3,2%). It is shown that micellar-saturated phases of Triton X-100 effectively extract the analytical form (tungsten blue complex), can be proposed for extraction-spectrophotometric and colorimetric determination of phenol. So, for the spectrophotometric determination of phenol (λmax= 760 nm), the Beer-Bouguer-Lambert law obeys an equation of the form: y = 0,0007x – 0,0079, R2 = 0,997. The range of defined contents is in the interval 7·10-7 – 6·10-5 M. A technique for the colorimetric determination of phenol in aqueous media (channel R) has been developed. The intensity of the chromaticity channel R (IR) linearly depends on pc(phenol) in accordance with the equation: y = 95,0x – 455; R2 = 0,997. The range of defined contents is in the interval 7·10-7 – 1·10-5 M. The profiles of the petal diagrams in the RGB CMYK color coordinates are constructed, the dependences of their area are obtained (S) and perimeter (P) from -lgc : (perimeter (P) y = 150x – 284; R2 = 0,994; area (S) y = 17710x – 66930; R2 = 0,994).

ИССЛЕДОВАНИЕ СТОЙКОСТИ ХЛОРМАГНЕЗИАЛЬНЫХ КОМПОЗИТОВ К НАСЫЩЕННЫМ СУЛЬФАТАМИ СРЕДАМ

This article studies the resistance of composites based on dolomitic magnesian binders mixed with an aqueous solution of magnesium chloride to long-term exposure to liquid media saturated with sulfate ions. We evaluated the effect of the long-term saturation of samples in an aqueous solution of sodium sulfate on the change in their mass, linear dimensions, strength characteristics, and phase composition. Since magnesia binders belong to the group of air-hardening binders, two series of control samples were kept in air-dry conditions and in a state saturated with water. The duration of the experiment was six months. During this period, the change in the physical and mechanical characteristics and phase composition of the samples stored in water and an aqueous solution of sulfates are similar in nature and are caused by a low coefficient of water resistance of magnesia binders. No traces of chemical interaction of magnesium stone minerals with sulfate ions were found. Thus, chloromagnesium composites, provided that they have a high water-resistance coefficient, can be used in aggressive sulfate environments.

Efficient frequency conversion and the crossing-pump effect of stimulated Raman scattering in an aqueous sodium sulfate solution.

The cascaded stimulated Raman scattering (SRS) of an aqueous sodium sulfate solution was investigated as well as the generation of the crossing-pump effect. With the introduction of dual sample cells, the first-order Stokes of the O-H stretching vibrational mode was able to act as the pump light to excite the Stokes of the S-O stretching vibrational mode, and a new Raman peak was obtained at 4423 cm-1. The dual sample cell device not only lowered the SRS threshold, but also enhanced the four-wave mixing (FWM) process. Compared to the input laser of 7 ns/pulse, the first-order Stokes of O-H was compressed to a pulse width of 413 ps after passing through the dual sample cells. The SRS of aqueous sodium sulfate solution covered an ultrabroad wavelength ranging from 441 nm to 720 nm (a Raman shift ranging from -3859 cm-1 to 4923 cm-1). The cone-shaped launch ring of the FWM process was also recorded. This work provides a reference for the establishment of laser frequency conversion devices using an aqueous sodium sulfate solution as the Raman medium.

Symmetric supercapacitors with cellulose-derived carbons and Na2SO4 electrolytes operating in a wide temperature range

The performance of symmetric supercapacitors with activated carbon electrodes, obtained from cellulose acetate microspheres as a precursor, has been studied using neutral aqueous sodium sulphate solutions as electrolytes. Although water-based electrolytes can safely operate in a broad temperature range, studies of supercapacitors beyond conventional room temperature conditions are rather limited, while most of investigations are focused on ionic liquids as electrolytes. However, since water represents a cheap, easy to handle and environmentally friendly solvent, detailed temperature investigations of supercapacitors with aqueous electrolytes are of importance. In the present work, we evaluated the behaviour of supercapacitors with electrolytes having various Na2SO4 concentrations, in a temperature range between 0 °C and 60 °C. Since stable and safe operation of supercapacitors with carbon electrodes exclusively depends on the electrolyte properties at these non-ambient conditions, the electrolytes were characterized with regard to their conductivity and viscosity at various temperatures. Activated carbon materials were produced by a one-step carbonization procedure of home-made cellulose acetate microspheres (CAM) using KOH as an activator, which was added to cellulose acetate microspheres in form of a solution for better homogenization. Supercapacitors with a neutral 1 M Na2SO4 solution as the best electrolyte composition were tested between 0 °C and 60 °C and provided specific capacitances between 91 F g−1 and 117 F g−1, demonstrating a good cycling stability with a retention of at least 95 % of the initial capacitance over 2000 cycles. Energy densities of 16.6 Wh kg−1 at a power density of 16 kW kg−1 are provided at 25 °C, whereas the energy density is improved at 60 °C to 21.5 Wh kg−1 at a slightly lower power density of 13.7 kW kg−1. No sign of electrochemical corrosion of battery housings was observed after cycling, in contrast to acid-based electrolytes with H2SO4 tested for comparison.

Electrochemical and Catalytic Properties of Carbon Dioxide-Activated Graphite Felt.

The commercial graphite felt GFA 10 was subjected to an activation process with the use of CO2 at 900 °C for 35 and 70 min. Pristine and heat-treated materials were characterized using various methods: low-temperature N2 adsorption, SEM, and EDS. Voltammetric measurements of GFA samples (before and after activation) as the working electrode were carried out. Voltammograms were recorded in aqueous solutions of 4-chlorophenol and sodium sulfate as supporting electrolyte. The catalytic activity of GFA samples in the process of 4-chlorophenol oxidation with the use of H2O2 was also investigated. The influence of graphite felt thermal activation in the CO2 atmosphere on its electrochemical and catalytic behavior was analyzed and discussed. Results of the investigation indicate that GFA activated in CO2 can be applied as an electrode material or catalytic material in the removal of organic compounds from industrial wastewater. However, the corrosion resistance of GFA, which is decreasing during the activation, needs to be refined.

Sterilizer of Knives in the Meat Industry, Working by Activating Aqueous Solutions with Glow Discharge Plasma

The development of approaches for the non-thermal sterilization of instruments is an urgent task to ensure the safety of meat industry products, where the use of hot water leads to the formation of condensates and a deterioration in the hygienic condition of the premises. In this study, an installation for sterilizing knives was created, which works by activating aqueous salt solutions with a glow discharge. The power consumption of the installation reactor is only 125–150 Wh. The temperature rise of the sterilizing agent used is about 1.1 ± 0.2 °C/min/L. The effectiveness of the installation for plasma-activation of aqueous solutions of chloride and sodium sulfate by glow discharge (PAW) in relation to the inactivation of microorganisms, including Staphylococcus aureus, Salmonella typhimurium, Pseudomonas gessardii and L. monocytogenes, on steel surfaces was evaluated. Samples of stainless steel (parts of knives) were used in two versions (new and artificially aged). Mono- and polyspecies bacterial biofilms were grown on the surface of the samples. The treatment was carried out by immersing samples of steel plates in plasma-activated aqueous solutions. It was found that the treatment of plates in a knife sterilizer for 1 min had an effective effect on the inhibition of all types of studied bacteria.

Effect of Nanopatterning on Concentration Polarization during Nanofiltration.

Membranes used for desalination still face challenges during operation. One of these challenges is the buildup of salt ions at the membrane surface. This is known as concentration polarization, and it has a negative effect on membrane water permeance and salt rejection. In an attempt to decrease concentration polarization, a line-and-groove nanopattern was applied to a nanofiltration (NF) membrane. Aqueous sodium sulfate (Na2SO4) solutions were used to test the rejection and permeance of both pristine and patterned membranes. It was found that the nanopatterns did not reduce but increased the concentration polarization at the membrane surface. Based on these studies, different pattern shapes and sizes should be investigated to gain a fundamental understanding of the influence of pattern size and shape on concentration polarization.

Thin Al2O3 Coatings Produced by Electrochemical Method, Subjected to Thermo-Chemical Treatment

The article presents the effect of the anodizing parameters, as well as the thermo-chemical treatment, of Al2O3 layers produced on an aluminum alloy on the characterization of structure, geometrical structure of the surface (SGS), the thickness of the oxide layers, the phase composition, and their microhardness. The oxide layers were produced by the method of direct current anodizing in a three-component electrolyte. Then, thermo-chemical treatment was carried out in distilled water and aqueous solutions of sodium dichromate and sodium sulphate. The anodizing parameters and compounds for the thermo-chemical treatment were selected on the basis of Hartley’s plans. The research showed the effect of anodizing parameters on the thickness of the Al2O3 layers and the increase in the thickness of the layers as a result of the thermo-chemical treatment. The research showed a significant increase in the microhardness of the layers as a result of thermo-chemical treatment and its influence on the phase composition of Al2O3 layers. A significant influence of the thermo-chemical treatment on the geometrical structure of the surface was also found.

Manganese oxide nanoflakes grown around cobalt oxide nanobundles with improved charge-storage performance for supercapacitors

Cobalt oxide nanobundle arrays (denoted as CoO) consisting of nanorods were homogeneously grown around the stainless steel wire mesh (SSWM) through a simple hydrothermal synthesis and subsequent heat treatment. The highly dispersed CoO can act as a supporting platform for the deposition of manganese oxide (MnO2) nanoflakes to engineer a CoO@MnO2 core-shell array structure. Without the CoO supports, the MnO2 was found to be prone to form aggregated nanoflakes on the SSWM substrate. CoO arrays with a one-dimensional nanorod skeleton can mitigate the aggregation of two-dimensional MnO2 nanoflakes. The CoO@MnO2 core-shell arrays integrate the advantages of abundant active edge sites, conductive networks for charge transfer, and pore channels for easy transport of electrolyte. The CoO@MnO2 electrode realizes a larger charge-storage capacity than the pristine MnO2 electrode in an aqueous sodium sulfate solution (1 M). The specific capacitances of CoO@MnO2 under 0.15 mA cm-2 and 7.50 mA cm-2 reach 79 mF cm-2 and 53 mF cm-2, respectively, much more than that of MnO2 (31 mF cm-2 and 20 mF cm-2). The CoO@MnO2 core-shell electrode shows a definite improvement in supercapacitive behavior compared to the pristine MnO2 electrode, resulting from reduced charge- and mass-transfer resistance during charge-storage process.

Modeling of the Refractive Index for the Systems MX+H2O, M2X+H2O, H3BO3+MX+H2O, and H3BO3+M2X+H2O. M = K+, Na+, or Li+ and X = Cl− or SO42−

The modeling of the refractive index for binary aqueous solutions of boric acid, sodium chloride, potassium chloride, sodium sulfate, lithium sulfate, and potassium sulfate, as well as ternary aqueous solutions of boric acid in the presence of sodium sulfate, lithium sulfate, or potassium chloride, is reported. The refraction index was represented by molar refraction. It was described as the sum of solutes’ partial molar refraction and solvent molar refraction. The solutes’ partial molar refraction was estimated from the molar refraction of the binary solutions. The excess molar refraction for these systems was described with the equation of Wang et al. The polarizability of the solutes present in the studied systems was estimated using the Lorenz–Lorenz relation. The results showed the model is appropriate for describing the systems studied; the interactions of boric acid, sodium, potassium, lithium, chloride, and sulfate ions with water molecules are relevant to explain the molar refraction and refractive index, and those for the binary systems of lithium chloride and sodium chloride are also relevant the ion–ion interactions. The model is robust and presents estimation capabilities within and beyond the concentrations and temperature range studied. Therefore, the outcomes represent valuable information to understand and follow the industrial processing of natural brines.

Optimal Performance of Thin-Film Composite Nanofiltration-Like Forward Osmosis Membranes Set Off by Changing the Chemical Structure of Diamine Reacted with Trimesoyl Chloride through Interfacial Polymerization.

Thin-film composite (TFC) polyamide membranes formed through interfacial polymerization can function more efficiently by tuning the chemical structure of participating monomers. Accordingly, three kinds of diamine monomers were considered to take part in interfacial polymerization. Each diamine was reacted with trimesoyl chloride (TMC) to manufacture TFC polyamide nanofiltration (NF)-like forward osmosis (FO) membranes. The diamines differed in chemical structure; the functional group present between the terminal amines was classified as follows: aliphatic group of 1,3-diaminopropane (DAPE); cyclohexane in 1,3-cyclohexanediamine (CHDA); and aromatic or benzene ring in m-phenylenediamine (MPD). For FO tests, deionized water and 1 M aqueous sodium sulfate solution were used as feed and draw solution, respectively. Interfacial polymerization conditions were also varied: concentrations of water and oil phases, time of contact between the water-phase solution and the membrane substrate, and polymerization reaction time. The resultant membranes were characterized using attenuated total reflectance-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, atomic force microscopy, and surface contact angle measurement to identify the chemical structure, morphology, roughness, and hydrophilicity of the polyamide layer, respectively. The results of FO experiments revealed that among the three diamine monomers, CHDA turned out to be the most effective, as it led to the production of TFC NF-like FO membrane with optimal performance. Then, the following optimum conditions were established for the CHDA-based membrane: contact between 2.5 wt.% aqueous CHDA solution and polysulfone (PSf) substrate for 2 min, and polymerization reaction between 1 wt.% TMC solution and 2.5 wt.% CHDA solution for 30 s. The composite CHDA-TMC/PSf membrane delivered a water flux (Jw) of 18.24 ± 1.33 LMH and a reverse salt flux (Js) of 5.75 ± 1.12 gMH; therefore, Js/Jw was evaluated to be 0.32 ± 0.07 (g/L).

Electrochemical preparation of Cu/Cu2O-Cu(BDC) metal-organic framework electrodes for photoelectrocatalytic reduction of CO2

Abstract Thin films of the metal-organic framework (MOF) Cu(BDC) were electrochemically grown by anodic deposition of the ligand 1,4-benzenedicarboxylate (1,4-BDC) on metallic copper to form Cu/Cu2O-Cu(BDC) electrode. The construction of the electrode was optimized by investigating parameters such as current density, time of anodization, and temperature that directly affect its stability and photoactivity. The best performing electrode was prepared when a current density of 2.5 mA cm−2 was applied for 6.5 min at 110 °C. A methanol concentration of 234 μmol L-1 was produced from the photoelectron reduction of CO2 under UV–vis irradiation for 3 h, an applied potential of +0.10 V, and 0.1 mol L-1 aqueous sodium sulfate solution saturated with CO2 as supporting electrolyte. The rate of CO2 reduction to methanol was found to be ∼20 times that obtained using Cu/Cu2O electrode alone presumably due to preconcentration of dissolved CO2 in the MOF. The capture of CO2 in the MOF surface and/or cavities was confirmed by ATR and DRIFT spectroscopy.

Wet corrosion of Al 1050 alloy in ethyl bromide-containing environment

The natural passivity, or induced by anodizing process, does not always result in an effective corrosion barrier for aluminium when exposed to environments containing specific chemicals that can cause material degradation phenomena with localized corrosion morphology. The present work investigates the effects of ethyl bromide (EtBr), a neutral organic molecule, sometimes used as a fumigant in packaging containers, that has been recently indicated as a possible cause of corrosion in aluminium alloy components. The study was conducted on Al 1050 alloy samples in aqueous solutions of sodium sulphate at increasing EtBr concentrations, ranging from 500 to 8600 ppm. Long-term exposure tests (936 h) and electrochemical experiments (potentiodynamic and potentiostatic polarizations, as well as time-dependent corrosion potential monitoring) were carried out, together with SEM and EDS examinations of the morphology and nature of the corrosion products. The results showed that the alloy undergoes different corrosion behaviours depending on the concentration of EtBr, spanning from passivity at the lowest concentrations to pitting at the highest, passing through the initiation and propagation of crevice at intermediate EtBr contents. A crucial role of the exposure time was detected, tentatively attributed to ethyl bromide hydrolysis in aqueous solution that liberates the bromide anion that is aggressive towards the passive state of aluminium alloys.

ИСПЫТАНИЯ ОГНЕТУШАЩЕЙ СПОСОБНОСТИ ГИДРОГЕЛЯ АЛЮМИНИЯ ПРИ ТУШЕНИИ МОДЕЛЬНЫХ ПРИРОДНЫХ НИЗОВЫХ ПОЖАРОВ

Extinguishing natural fires largely depends on the effective use of fire extinguishers by firefighters. Nevertheless, there are objective limits to the fire extinguishing ability of known substances and materials, which cannot be overcome by either tactical or technological methods. In the work, a method for extinguishing ground fires using aluminum hydrogels with different concentrations as fire extinguishing compositions is proposed, which makes it possible to simultaneously realize three extinguishing methods: cooling, insulation, and combustion inhibition. Investigation of fire extinguishing ability of the selected fire extinguishing compositions has been carried out according to a specially developed technique that simulates formation and development of ground natural fire in experimental plots. Extinguishing efficiency was assessed by comparing the results of the total cost of extinguishing agents to a unit of length of the edge of the fire and a unit of area of the fire. It was shown that the best fire extinguishing ability has an aqueous solution of aluminum hydrogel with a concentration of 3.5-7 g/l. Fire extinguishing ability of aluminum hydrogels was investigated. The obtained results were compared with the fire extinguishing ability of water and aqueous solutions of sodium carbonate (soda) and sodium sulfate. The use of other aqueous solutions (soda and sodium sulfate) has not shown significant contribution to fire extinguishing. Therefore, fire extinguishing effect is completely due to the chemical composition and physical and chemical properties of aluminum hydrogel. Based on the data obtained, aluminum hydrogel costs per unit length and area of the fire, its lowest concentration, which retains the fire extinguishing effect and the technological conditions for its preparation and use, have been determined

Tunable electrochemical activity of polyaniline salt by doping anion exchange

The exchange of mobile anion of chemically synthesized polyaniline with counter anions of electrolyte solutions is studied by using cyclic voltammetry (CV). The synthesized polyaniline (PANI) doped with sulfuric acid (H2SO4) and dodecyl benzenesulfonic acid (DBSA) is soluble in a wide range of organic solvents which makes it appealing for further processability. The exchange of dopant anions (of H2SO4 and DBSA) with a variety of counter anion has been inspected by electrochemical cycling in aqueous sodium sulfate (Na2SO4), sodium perchlorate (NaClO4), and sodium hydroxide (NaOH) solution. The CV measurements have revealed that PANI remains redox active at higher scan rate and there is exchange of dopant anion with SO42- and ClO41- of electrolytes. In NaOH solution, the emeraldine salt form of PANI is transformed into emeraldine base due to deintercalation of the anion form polymer matrix. The results indicate a significant change in electrochemical conductance and behavior of PANI in each electrolyte. Furthermore, the polymer film displayed a high specific capacitance value of 588 F/g in 1.0 M NaClO4 solution in the optimized potential window of -0.2 V to 0.9 V at 20 mV/s.

In situ electrodeposition of conducting polymer/metal oxide composites on iron electrode for energy storage applications

Conducting polymers and their metals or metal oxides-based composites are promising for applications in aerospace engineering, construction, computer chips, electronic circuits, energy storage systems, catalysis of reaction and so on. Supercapacitor electrodes and devices comprising polymers/metal oxides composites are envisaged to bridge the gap between existing carbon-based supercapacitors and batteries to form units of intermediate specific energy. In this work, polyaniline (PAni) and its composite with MnO2 were successfully deposited by electrochemical method. Simultaneous polymerization of aniline to PAni, and in situ formation and incorporation of MnO2 into the PAni matrix, and their deposition on Fe substrate took place during the cycling of potential in oxalic acid solution containing aniline and a salt of manganese. Elemental characterization and investigation of morphology and microstructure of the deposits were performed by infra-red, UV–visible reflectance and energy dispersive X-ray spectroscopy and scanning electron microscopy. The band gap energy of PAni was substantially higher compared to PAni/MnO2 composite. The specific capacitance of the electrodes prepared was investigated using cyclic voltammetry and charge–discharge test by chronopotentiometry. Fe-PAni and Fe-PAni/MnO2 composite modified electrodes exhibited excellent supercapacitive property, energy density and power density compared to their bulk Fe electrodes in aqueous sodium sulfate solution.

Nanofiltration of Succinic Acid in Strong Alkaline Conditions.

Nanofiltration is considered to be an appropriate separation technique in the production of bio-based materials. For the utilization of process streams from the viscose-fiber production, understanding the separation behavior of organic compounds in highly alkaline solutions is necessary. Experiments with succinic acid in sodium hydroxide (NaOH) solutions with varying concentrations up to 5 mol L−1 were performed with the NP030 membrane from Microdyn Nadir. Furthermore, experiments with aqueous disodium succinate and solutions of sodium sulfate in sodium hydroxide were carried out. The influence of concentration ratios and temperature was studied. The Spiegler and Kedem model as well as the Pusch model were applied to fit the experimental data. Additionally, scanning electron microscopy (SEM) and infrared (ATR–IR) measurements were performed to validate the chemical and thermomechanical stability of the membrane. The succinic acid retention varies with its degree of dissociation. In a fully dissociated form, the NaOH concentration shows no impact on the retention. In contrast, the retention of sulfate decreases with increasing NaOH concentration.