Concentration Of Alkali Ions Research Articles

Steering the Selectivity of CORR from Acetate to Ethanol via Tailoring the Thermodynamic Activity of Water

AbstractThe electrochemical conversion of carbon monoxide (CO) into oxygenated C2+ products at high rates and selectivity offers a promising approach for the two‐step conversion of carbon dioxide (CO2). However, a major drawback of the CO electrochemical reduction in alkaline electrolyte is the preference for the acetate pathway over the more valuable ethanol pathway. Recent research has shed light on the significant impact of thermodynamic water activity on the electrochemical CO2 reduction reaction pathways, but less is understood for the electrochemical reduction of CO. In this study, we investigated how the water activity at the electrified interface can be enhanced to adjust the selectivity between acetate and ethanol. We employed an ionomer modifier to lower the local concentration of alkali ions (via Donnan exclusion), successfully enhancing ethanol production while suppressing acetate formation. We observed a remarkable improvement in the Faradaic efficiency of ethanol and alcohol (i. e. ethanol, propanol etc), which reached 42.5 % and 55.1 %, respectively, at a current density of 700 mA cm−2. The partial current densities of ethanol and alcohol reached 698 and 942 mA cm−2 at 2000 mA cm−2. Furthermore, we achieved a 3.7‐fold increase in the ethanol/acetate ratio, providing clear evidence of our successful modulation of product selectivity.

Steering the Selectivity of CORR from Acetate to Ethanol via Tailoring the Thermodynamic Activity of Water.

The electrochemical conversion of carbon monoxide (CO) into oxygenated C2+ products at high rates and selectivity offers a promising approach for the two-step conversion of carbon dioxide (CO2). However, a major drawback of the CO electrochemical reduction in alkaline electrolyte is the preference for the acetate pathway over the more valuable ethanol pathway. Recent research has shed light on the significant impact of thermodynamic water activity on the electrochemical CO2 reduction reaction pathways, but less is understood for the electrochemical reduction of CO. In this study, we investigated how the water activity at the electrified interface can be enhanced to adjust the selectivity between acetate and ethanol. We employed an ionomer modifier to lower the local concentration of alkali ions (via Donnan exclusion), successfully enhancing ethanol production while suppressing acetate formation. We observed a remarkable improvement in the Faradaic efficiency of ethanol and alcohol (i.e. ethanol, propanol etc), which reached 42.5% and 55.1%, respectively, at a current density of 700 mA cm-2. The partial current densities of ethanol and alcohol reached 698 and 942 mA cm-2 at 2000 mA cm-2. Furthermore, we achieved a 3.7-fold increase in the ethanol/acetate ratio, providing clear evidence of our successful modulation of product selectivity.

Effect of silica fume on the efflorescence, strength, and micro-properties of one-part geopolymer incorporating sewage sludge ash

The application of sewage sludge ash (SSA) in alkali activated cementitious material, i.e., geopolymer, was one of the effective measures to dispose of and recycle the sewage sludge. However, the geopolymer efflorescence could be aggravated due to elevated alkali content, especially for one-part geopolymer, where the dissolution reaction of solid alkali activator was less sufficient. This study focused on the efflorescence of GGBS-SSA based one-part geopolymer, as compared to two-part geopolymer, and the effect of silica fume on the efflorescence, strength and micro-properties of the one-part geopolymer. The results showed that the extent of efflorescence crystallization and the concentration of leached Na+ ions in the one-part geopolymer were more severe than the two-part geopolymer, due to the lower degree of geopolymerization reaction and the heterogeneous dense microstructure of the one-part geopolymer. After adding silica fume to the one-part geopolymer, the extent of efflorescence crystallization and the concentration of leached Na+ ions reduced significantly, and the compressive strength increased from 41.6 MPa to 57 MPa when the silica fume content was 10 %, but then decreased slightly. Adding the silica fume reduced the release rate of reaction heat, which helped to increase the solubility of solid alkali activator and improve the geopolymerization reaction, thus significantly reducing the content of mobile alkali ions and enhancing the compressive strength. Moreover, the silica fume with tiny spherical particle had better ball effect and micro-aggregate filling effect, which refined the pore size and reduced the connectivity of pore network, significantly reducing the diffusion rate and leaching of mobile alkali ions.

Enhanced CO2 reduction with hydrophobic cationic-ionomer layer-modified zero-gap MEA in acidic electrolyte.

A hydrophobic cationic-ionomer layer of quaternary ammonium poly(N-methyl-piperidine-co-p-terphenyl) and PTFE is presented to enhance the CO2 electroreduction in a zero-gap membrane electrode assembly (MEA) electrolyzer under acidic and low alkali ion concentration conditions. The modified MEA achieved a maximum CO faradaic efficiency of 95.6% at 100 mA cm-2.

Mechanisms on the inhibition of alkali-silica reaction in supersulfated cement

The supersulfated cementitious system gains increasing popularity for lowering carbon emissions of the construction industry. However, the alkali-silica reaction (ASR) behavior of this sulfate-rich cement is still unclear. This study first reports the characteristics and suppressing mechanisms of ASR in supersulfated cement (SSC). The results show that nearly no ASR-induced expansion is found in the SSC even if 100% glass aggregates are used, while the expansion ratio of the traditional OPC is twenty times higher than the SSC. In the SSC, the further hydration of unreacted slag during the ASR test refines the pore size and enhances the compressive strength of the matrix. Meanwhile, the consumption of the alkali ions in the pore solution during the formation of N-A-S-H gel reduces the concentration of the alkali ions and the contact possibility with the aggregates. The high bulk electrical resistance of the SSC can mitigate the diffusion of alkali ions from the external solution to the mortar. Moreover, the higher Al/Si ratio of C-A-S-H in the SSC than C–S–H in the OPC system results in a higher adsorption capacity of Na+ due to the more negatively charged surface, reducing the concentration of alkali ions in the pore solution. Furthermore, the high concentration of SO42− in the pore solution of SSC can inhibit the diffusion of OH−. As a result, the low-carbon SSC system would be a promising cementitious material to mitigate the ASR risk.

INVESTIGATION OF THE STRUCTURE AND INFLUENCE OF ION EXCHANGE ON THE MICROHARDNESS OF LOW-ALKALI TRANSPARENT GANITE GLASS-CERAMICS

Transparent glass-ceramics are attracting more and more attention as a material for protecting the screens of electronic devices. The paper considers the possibility of carrying out ion-exchange of transparent gahnite glass-ceramics containing a small Na2O content. The structure and properties of glass-ceramics before and after ion-exchange were studied by x-ray diffraction analysis, transmission electron microscopy, Raman spectroscopy, laser-induced breakdown spectroscopy, and Vickers hardness determination. It is shown that, under certain conditions, ion-strengthening of glass ceramics with a low content of alkali ions can lead to an increase in microhardness values.

Non-Destructive Study of Egyptian Emeralds Preserved in the Collection of the Museum of the Ecole des Mines

In the present study, rough emerald single crystals and rough emeralds in the host rock from the ruins of Alexandria and from the Mount Zabargad in Egypt, preserved in the collection of the museum of the Ecole des Mines (Mines Paris—PSL) since the late 19th or early 20th century, are investigated. All samples were characterized by non-destructive spectroscopic and chemical methods during a week-long loan to the LFG. Raman, FTIR and UV-Vis-NIR spectroscopy revealed that Egyptian emeralds contain H2O molecules accompanied by relatively high concentrations of alkali ions and are colored by chromium and iron. Additionally, EDXRF showed that the emeralds from Egypt contain up to 84 ppm Rb and low amounts (below 200 ppm) of Cs. Inclusions and parts of the host rock were also observed under optical microscope and analyzed with Raman spectroscopy. Tube-like structures, quartz, calcite, dolomite, albite and phlogopite are associated minerals, and inclusions are identified in these historic emeralds from Egypt. This work will hopefully further contribute to the characterization of emeralds of archaeological significance.

Role of the alkalis of supplementary cementing materials in controlling pore solution chemistry and alkali-silica reaction

Declining supplies of quality fly ash in many parts of the world necessitates a search for new sources of supplementary cementing materials (SCMs) to meet the growing demand for sustainable materials to partially substitute for portland cement in concrete. In recent years finely-ground waste glass, landfilled/ponded coal ashes and natural pozzolans have (re)drawn the attention of researchers and the industry to fill this gap. In this study a wide range of SCMs were characterized for water-soluble and available alkalis using, respectively, ASTM C114 and ASTM C311. Pastes containing portland cement and SCM were prepared at a 25 % replacement level and cured in airtight containers at 23 °C. The pore solution of these pastes at 28 and 91 days was analyzed for the concentration of alkali (Na+ and K+) and hydroxyl (OH−) ions. The efficiency of SCMs in mitigating alkali-silica reaction (ASR) was determined using the Pyrex mortar bar test, ASTM C441. The results indicate that all alkali oxides of SCMs are neither water-soluble nor “available.” Many natural pozzolans contain a large portion of insoluble alkalis. Except for high-alkali (Type GS) ground glass and Class C fly ash, the use of all other reactive SCMs considerably decreases the presence of alkali ions in the pore solution at 91 days. Compared to available alkalis in C311, pore solution concentration provides a better indication of the efficacy of SCMs in mitigating ASR.

Cellulose nanofibrils with and without nanosilica for the performance enhancement of Portland cement systems

This article presents a comprehensive investigation on the effects of pure cellulose nanofibrils (CNF) and nanosilica containing CNF on the performance of ordinary portland cement (OPC) paste. The effects of CNFs on cement paste rheology, hydration, microscopic phase formation, compressive strength, and fracture parameters were monitored. Sol-gel method was used to synthesis nanosilica particles within CNF slurry. The effects of CNF on cement hydration was found to be dependent on the water to cement ratio (w/c). Specifically, CNFs accelerated the early age cement hydration at 0.35 w/c, but this acceleration effect was not prominent for 0.45 w/c. Such w/c dependent effect was attributed to the negatively charged hydroxyl and carboxyl surface sites of CNFs which can bind alkali ions or cement particles. The concentration of alkali ions in cement pore solution depends on the w/c and hence, resulting the w/c dependent effects of CNF. The colloidal stability of CNF was found to improve due to the addition of nanosilica particles. Addition of CNF was found to increase the flexural strength of cement paste up to 75%. The effects of CNF addition on the compressive strength of cement paste matrix was negligible.

Metal doping of dielectric thin layers by electric field assisted film dissolution

The incorporation of metal ions in dielectric layers by means of electric field assisted film dissolution is investigated. The samples consist of alkali-containing glass substrates coated first with SiO2 and then Ag thin films. The application of moderately elevated temperatures and DC voltages induces thermal poling in the glass matrix and metal film dissolution, resulting in the incorporation of metal ions in both dielectric layer and glass matrix. First, the process dynamics are simulated by modelling the migration of metal film ions and alkali species under an applied electric field. Numerical solution of the model indicates that metal ions progressively dope the dielectric layer until they reach the glass matrix. Then the dopant distribution in the layer becomes steady-state and further injection of ions contributes to increase the dopant concentration in glass. The influence on the process of alkali and dopant ion mobilities and alkali ion concentration is analysed. Additionally, Ag doping of SiO2 layers deposited on soda-lime and borosilicate glasses is experimentally carried out and characterized using spectroscopic ellipsometry. The evolution of refractive index profiles through both, SiO2 layer and glass substrate, is correlated with ion migration and confirms the model trends. Overall, this study shows that glass poling and film dissolution can be used to control metal doping of dielectric layers, with potential application in optical and photonic devices.

Thermodiffusion of alkali ions in alkali niobophosphate glasses

AbstractA method is proposed for determination of the thermal diffusion coefficients of mobile ions through the study of ionic thermoelectric power. Ionic Seebeck coefficients and the heats of ion transport have been measured in [Li(Na,K)]2O‐Nb2O5‐P2O5 glasses. The mixed alkali effect influence on the thermoelectric power has been reported for the first time in glasses. Soret coefficients have been calculated for all monoalkali glass samples synthesized in this work. Type of the alkali ion and Nb2O5 content dependence of the heat of transfer and thermal diffusion coefficient have been analyzed and discussed.

First-principles calculations of structural and electronic properties of layered AxRhO2 (A = Li, Na, K, Rb, Cs)

Layered transition metal oxides, such as NaxCoO2, are known for their various interesting physical phenomena, which are mainly due to the strong correlation of the transition elements and tunable concentration of alkali metals. Here, we have systematically investigated the structural and electronic properties of 4d layered transition metal oxides AxRhO2 (A = Li, Na, K, Rb, Cs) by first-principles calculations. It is found that when the concentration (x) of alkali ions in AxRhO2 increases, the in-plane lattice constant (a) increases while the out-of-plane one (c) decreases. In the case of stoichiometric ARhO2 (i.e., x = 1), both lattice constants (a and c) increase when the alkali ions changes from Li to Cs. The calculated electronic band structures and density of states indicate that all the stoichiometric ARhO2 compounds are indirect band-gap semiconductors with band gaps ranging from 3 eV to 3.6 eV. Finally, we calculate the Fermi surfaces of KxRhO2 and demonstrate the Lifshitz transition, which could be triggered by potassiation/depotassiation in experiments. Despite the structural similarity between these materials, we have observed the difference in their band structures at the valence band maximum, which will possibly result in a different behavior of the Lifshitz transition. Our calculations point out the similarities and the subtle differences between different alkali rhodates, which give some useful information for future experimental works on these materials.

Alkali-exchanged Y zeolites as superior deacidifying protective materials for paper relics: Effects of accessibility and strength of basic sites

Abstract Paper is the most important writing carrier and its degradation (acidification, aging, and ink removal) is a major issue in the protection of cultural heritage. In this work, we first propose alkali ion-exchanged Y zeolites (Ae-Y) as superior deacidification agents for paper. Their features such as the high surface area, adjustable alkali ion content, strength, good structural stability, and safety/non-toxicity or biocompatibility are very promising for preserving paper-based materials, as demonstrated by aging experiments carried out on both historical wood-pulp paper and modern hand-made bamboo paper samples. Through H2O-mediated dispersion of Ae-Y in target paper samples, the pH of the paper can be modified to a neutral or weakly basic state, and can be maintained for a long time even under harsh accelerated aging conditions. Meanwhile, the Ae-Y coating hardly alters the chromatic aberration and water wettability of papers. This new deacidifying agent does not trigger color changes in alkali-sensitive pigments (i.e., does not cause fading or blanching of pigments). Moreover, a systematic evaluation of the structure-performance relationship indicates the important roles of adequate accessible basic sites and controllable and mild basicity of Ae-Y in the long-term deacidification, anti-aging, and anti-fading effects exerted on paper relics. These findings not only shed light on the design of protective materials for paper-based cultural relics but also expand our knowledge on the deacidification and protection mechanisms of zeolites.

Effects of OH− anion additive concentration in nitrate salt baths on chemical strengthening of Li2O–Al2O3–SiO2 (LAS) glass

Two ion-exchange processes of K+-Na+ and Na+-Li+ were used to strengthen LAS glass materials, and the effects of OH− anion additive (introduced by hydroxide additive) in molten salt baths were investigated. The K+-Na+ ion-exchange was superior than Na+-Li+ ion-exchange in the strength enhancement, and with the hydroxide additive, the thickness of ion-exchange layer, the ion-exchange rate and the flexural strength of LAS glass specimens were enhanced remarkably. In detail, for two ion-exchange processes, the optimized ion-exchange time decreased from 24 h to 2 h and from 6 h to 1 h, and the thickness of ion-exchange layer increased from 16 μm to 22 μm and from 23 μm to 34 μm, respectively. Consequently, the corresponding optimized flexural strength increased from 360 MPa to 520 MPa and from 270 MPa to 460 MPa, attributing to the increased thickness of ion-exchange layer and the increased concentration of alkali ions. It is believed that the broken chemical bonds along with the depolymerized glass network induced by OH− anion decreased the diffusion activation energy Ea and increased the diffusion coefficient D of alkali ions for ion-exchange, and thereby the chemical strengthening process of LAS glass materials was improved.

Effect of Temperature, Pressure, and Chemical Composition on the Electrical Conductivity of Schist: Implications for Electrical Structures under the Tibetan Plateau.

The experimental study on the electrical conductivities of schists with various contents of alkali ions (CA = K2O + Na2O = 3.94, 5.17, and 5.78 wt.%) were performed at high temperatures (623–1073 K) and high pressures (0.5–2.5 GPa). Experimental results indicated that the conductivities of schist markedly increased with the rise of temperature. Pressure influence on the conductivities of schist was extremely weak at the entire range of experimental temperatures. Alkali ion content has a significant influence on the conductivities of the schist samples in a lower temperature range (623–773 K), and the influence gradually decreases with increasing temperature in a higher temperature range (823–1073 K). In addition, the activation enthalpies for the conductivities of three schist samples were fitted as being 44.16–61.44 kJ/mol. Based on the activation enthalpies and previous studies, impurity alkaline ions (K+ and Na+) were proposed as the charge carriers of schist. Furthermore, electrical conductivities of schist (10−3.5–10−1.5 S/m) were lower than those of high-conductivity layers under the Tibetan Plateau (10−1–100 S/m). It was implied that the presence of schist cannot cause the high-conductivity anomalies in the middle to lower crust beneath the Tibetan Plateau.

Onsite paper-type colorimetric detector with enhanced sensitivity for alkali ion via polydiacetylene-nanoporous rice husk silica composites

A paper-type colorimetric detector for identifying the degree of alkali ion concentration with the naked eye was fabricated using polydiacetylene/nanoporous rice husk silica (PDA/NP-SiO2) nanocomposites as a potentially effective, rapid, and facile approach to detect alkali ion in aqueous solution. This study is worth investigating because it has the advantage of visually confirming the alkaline ion in aqueous solution without the aid of other analytical instruments directly at on-site as if pH indicator analysis. The concept of this study is the facile synthetic route of PDA and NP-SiO2. Nanoporous rice husk silica (NP-SiO2) with a high specific surface area 450 m2/g was extracted from leached rice husk ash via a sol-gel process and utilized for efficient absorption of alkali ion. PDA was used as a material to differentiate the degree of alkali ion drawing using only the change of color. By compositing these two materials on the surface of filter paper using the spray drying method, the resulting PDA/NP-SiO2 composites with NP-SiO2 of the different specific surface areas showed a different change of color indicated by the degree of alkali ions even at a low concentration of less than 122 μm. The composite was further analyzed by UV spectroscopy for a change of color and images for screening depending on the alkali ion concentrations. The color response percentage of the PDA/NP-SiO2 composites (PDA/449S; SBET 449.9213 m2/g) was 23.39% at 0.122 mM of NH4OH. Consequently, the result from this study showed the possibility of sensitively distinguishing the alkali ions ranging from pH 9.86 to pH 11.38 using only the naked eye, brought potential features that can be used as a convenient and facile primary water testing kit in practical applications.

Peranan Stemflow dan Throughfall Vegetasi Hutan Kota dalam Menurunkan Kandungan Unsur Kimia Hujan Asam

Impact of acid rain on people's lives were studied but study of the vegetation role in reducing chemical elements of rainwater that reach the soil surface were limited. The purpose of this study was to analyze the role of urban forest vegetation around the Medan Industrial Zone to reducing acid rain that reached the soil surface through the mechanism of stemflow and throughfall. This research was conducted by analyzing the chemical content of stemflow and througfall water from Pterocarpus indica Will., Mangifera indica, and Gnetum gnemon plants. Parameters analyzed were water acidity (pH), electrical conductivity (EC), SO42-, NO3-, NH4 +, Ca 2+, Mg 2+ and Na +. Water analysis carried out in the Laboratory of the Environmental Agency of North Sumatra Province. The results indicate that the water that has been through the process of stemflow and throughfall consistently raises the pH, electrical conductivity, NH4 +, Ca 2+, Mg 2+ and Na + and reduce the content of anion SO42- and NO3 compared with water from open area. Stemflow and throughfall were able to reduce the content of acidic ions and increasing the content of alkali ions and reduced rain water acidity.

Electrodiffusion of alkali ions in alkali niobophosphate glasses and glass‐forming melts

AbstractElectrical conductivity of Li(Na,K)2O‐Nb2O5‐P2O5 glasses and glass‐forming melts has been measured in a wide temperature range (298‐1173 K). Logarithm of the preexponential factor and activation energy of migration have been determined. Mixed alkali effect has been observed in niobophosphate glass‐forming melts. Diffusion coefficients for Li+, Na+, and K+ ions have been calculated. The influence of the type of alkali ion and Nb2O5 content on the diffusion coefficients has been determined.

Calorimetric Study of Alkali Metal Ion (K+, Na+, Li+) Exchange in a Clay-Like MXene

Intercalation of ions in layered materials has been explored to improve the rate capability in Li-ion batteries and supercapacitors. This work investigates the energetics of alkali ion exchange in a clay-like MXene, Ti3C2Tx, where Tx stands for anionic surface moieties, by immersion calorimetry in aqueous solutions. The measured immersion enthalpies of clay-like Ti3C2Tx, ΔHimm, at 25 °C in 1 M KCl, 1 M NaCl, 1 M LiCl, and nanopure water are −9.19 (±0.56), −5.90 (±0.31), −1.31 (±0.20), and −1.29 (±0.13) kJ/mol of MXene, respectively. Inductively coupled plasma mass spectrometry is used to obtain the concentrations of alkali ions in the solid and aqueous phases. Using these concentrations, the enthalpies of exchange of alkali metal ions (Li+, Na+, and K+) are calculated; ΔHex in 1 M KCl, 1 M NaCl, 1 M LiCl, and nanopure water are −9.3 (±2.2), 21.0 (±0.9), −1.3 (±0.2), and 302.4 (±0.6) kJ/mol of MXene, respectively. Both immersion and exchange enthalpies are most exothermic for potassium. This suggests that ...

Inorganic-Organic Ionic Liquid Electrolytes Enabling High Energy-Density Metal Electrodes for Energy Storage

It has recently been shown, in the case of the bis(fluorosulfonyl)amide (FSI) based ionic liquids, that as the concentration of the alkali metal salt (LiFSI or NaFSI) is increased, the alkali metal cation transference number increases, despite an increase in viscosity and decrease in conductivity. At the same time significant enhancements in electrochemical stability and rate performance of devices are also observed. Here we overview some of the recent findings already in the literature and in addition demonstrate the feasibility of stable, high rate room temperature lithium battery cycling in an electrolyte comprised of 60 mol% LiFSI in a trimethyl, isobutyl phosphonium FSI ionic liquid using a high voltage NMC cathode. We also demonstrate that the high rate cycling of lithium and sodium metal in these phosphonium FSI electrolytes leads to a nanostructured anode deposit and a lowering of the interfacial impedance, suggesting a stable SEI layer formation. Finally, we propose a hypothesis that may explain some of the observations thus made, by which the high alkali ion concentration in these mixed electrolyte systems leads to the effective elimination of the mass transport limitations that are chiefly responsible for the formation of dendrites in traditional electrolytes. This work suggests that a new type of ionic liquid consisting of a mixture of metal cations with organic cations can provide a solution to the instability of the reactive alkali metal anodes and hence enable higher energy density technologies.