Alkali Cation Type Research Articles

Effect of interlayer cations on the adsorption of ionic liquid on montmorillonite clays: comparative study

Industries are the most important resource of water pollution due as a result of toxic pollutants including surfactant or ionic liquids. It becomes urgent to propose low cost and environmentally friendly involving the use of local resources. Here,one of the main ionic liquids (BMImCl) were intercalated into three alkaline-earth, Mg2+, Ca2+, and Ba2+ exchanged montmorillonites. For all samples interlayer spacing after intercalation are similar about 13 Å as measured by X-ray diffraction. These findings are compared with previous results on similar montmorillonite exchanged with every type of alkali cations, i.e. Li+, Na+, K+, Rb+, and Cs+. The basal spacing of intercalated montmorillonite increased as the ionic potential (Z/R) is increased. The FTIR is another tool to confirm the differences between modified and unmodified montmorillonite samples. More specifically, the results showed that the formation of new bands of vibrations (1400–1500 cm-1) and (2850–2900 cm-1).Thermal measurements indicate that homoionic clay display two distinct regions. ‎(I) from room temperature to 160 0C corresponding to physical adsorption and removal of water of hydration, (II) dehydroxylation of the silicate structure in the temperature range of 160-700 0C.

Probing Cation Effects on *CO Intermediates from Electroreduction of CO2 through Operando Raman Spectroscopy.

Cations in an electrolyte modulate microenvironments near the catalyst surface and affect product distribution from an electrochemical CO2 reduction reaction, and thus, their interaction with intermediate states has been tried to be probed. Herein, we directly observed the cation effect on *CO intermediates on the Cu(OH)2-derived catalyst in real time through operando surface-enhanced Raman spectroscopy at high overpotentials (-1.0 VRHE). Atop *CO peaks are composed of low-frequency binding *CO (*COLFB) and high-frequency binding *CO (*COHFB) because of their adsorption sites. These two *CO intermediates are found to have different sensitivities to the cation-induced field, and each *CO is proposed to be suitably stabilized for efficient C-C coupling. The proportions between *COHFB and *COLFB are dependent on the type of alkali cations, and the increases in the *COHFB ratio have a high correlation with selective C2H4 production under K+ and Cs+, indicating that *COHFB is the dominant and fast active species. In addition, as the hydrated cation size decreases, *COLFB is more sensitively red-shifted than *COHFB, which promotes C-C coupling and suppresses C1 products. Through time-resolved operando measurements, dynamic changes between the two *CO species are observed, showing the rapid initial adsorption of *COHFB and subsequently reaching a steady ratio between *COLFB and *COHFB.

Effects of mineral wool waste in alkali activated-artificial aggregates for high-temperature applications

In this study, an alternative utilization route for Mineral Wool Waste (MWW) as a solid precursor for artificial aggregate manufacturing is proposed. The process parameters including alkali activation (Na or K) and curing regimes are investigated. Room and high-temperature (1000 °C) characterizations are performed on the plain aggregates and when incorporated in geopolymer composite. The results reveal that with an optimum pre-curing regime at room temperature for 3 days, artificial aggregates with particle density ranging from 1960 to 2090 kg/m3 and crushing strength of 7.0 to 7.9 MPa can be obtained. The behaviour of aggregates is strongly related to the alkali cation type. The Na-based activator with high viscosity resulted in a more irregular grain shape with a lower particle density and a crushing strength as compared to K-activated aggregates. High crystallinity is observed in K-activated aggregates, causing better thermal stability. The alkali-activated artificial aggregates show a geopolymer-like behaviour in geopolymer composites, which contributes to higher strength development over normal sand aggregate.

Ion-Pairs in Aluminosilicate-Alkali Synthesis Liquids Determine the Aluminum Content and Topology of Crystallizing Zeolites.

Using hydrated silicate ionic liquids, phase selection and framework silicon-to-aluminum ratio during inorganic zeolite synthesis were studied as a function of batch composition. Consisting of homogeneous single phasic liquids, this synthesis concept allows careful control of crystallization parameters and evaluation of yield and sample homogeneity. Ternary phase diagrams were constructed for syntheses at 90 °C for 1 week. The results reveal a cation-dependent continuous relation between batch stoichiometry and framework aluminum content, valid across the phase boundaries of all different zeolites formed in the system. The framework aluminum content directly correlates to the type of alkali cation and gradually changes with batch alkalinity and dilution. This suggests that the observed zeolites form through a solution-mediated mechanism involving the concerted assembly of soluble cation-oligomer ion pairs. Phase selection is a consequence of the stability for a particular framework at the given aluminum content and alkali type.

Effect of alkali cation type on the plasticizing effect of ligno-sulfonate in alkali-activated systems

The rheological properties of alkali-activated systems are significantly affected by the nature of the alkaline activator. Hydroxide-activated systems’ workability is typically lower than that of alkali-activated systems but can be improved by lignosulfonate plasticizer. However, the lignosulfonate plasticizer’s effectivity depends on the dosage of lignosulfonate, the nature of hydroxide and pH of their solutions. Therefore, in this study, the effectiveness of lignosulfonate plasticizer with respect to alkali ion type (Na+, K+, Li+) in alkali hydroxide-activated systems based on ground granulated blast furnace slag was evaluated. The concentration of the alkaline activator (NaOH, KOH and LiOH) was the same in all cases of 4M. The superplasticizer dosage was 0%, 0.5% and 1.0% of dry matter of lignosulfonate plasticizer to the slag weight. Rheological properties were determined using a rotational rheometer equipped with vane in-cup geometry working in oscillation amplitude sweep mode, from which critical strain and corresponding viscoelastic variables were obtained.

Effect of alkali cation type on compressive strength and thermal performance of the alkali-activated omphacite tailing

Storage of mine tailings in mining industry has led to a series of economic, ecological, and environmental problems. Alkali activation is an effective way to make use of tailings, but pan-alkali and environmental pollution caused by the use of strong alkali is also another knotty problem. In this work, omphacite tailing was employed as a precursor of alkali-activated material, and the relatively mild alkali (NH4OH) was adopted to investigate the effects of alkali cation type (Na+ and NH4+) on the mechanical and thermal performance of alkali-activated omphacite tailing. Results show that the alkali-activated omphacite tailing with high mechanical performance can be synthesized by both types of alkali cations via compression molding, and the highest compressive strength of NH4-sample and Na-sample can reach 119.39 MPa and 71.51 MPa, respectively. Comparing the two, Na-samples have higher compressive strength but lower heat-resistance temperatures. With the increase of Na/Na + NH4 ratio, the compressive strength exhibits a rising trend while the heat-resistance temperature is the opposite. By TG-DTA, FTIR, XRD, CT, and SEM characterization analysis, the effects of different cations on the mechanical and thermal properties were revealed. It indicates that omphacite tailing and NH4OH are feasible as a precursor and alkali activator of alkali-activated materials, and the alkali-activated omphacite tailing can be tailored, in mechanical strength and thermal performance, for structural application.

Review on the Adhesion of Geopolymer Coatings.

Geopolymers are considered to be green materials with excellent fire resistance performance and potential substitutes for ordinary Portland cement (OPC). This review article focuses on the adhesion of geopolymer coatings subjected to elevated temperature. Their high adhesion strength is the basis for geopolymers being used as coating materials to work with the substrate. The adhesion strength is related to many factors, such as chemical composition of the raw materials, the formulation of the geopolymer, substrate type, surface roughness of the substrate, etc. The Si/Al ratio has different effects on compressive strength and bonding strength. The water content affects the polymerization process—the adhesion strength decreases with increasing water content. Careful tailoring of the mix ratio design is essential to make the geopolymer coating have excellent adhesive performance. These mix design factors include Si/Al ratio, Al/Na ratio, water content, precursor type, alkali cation type, curing conditions, etc.

Alkali cation effects on chloride binding of alkali-activated fly ash and metakaolin geopolymers

In this work, the chloride binding capacity and chloride penetration resistance of alkali-activated fly ash and metakaolin geopolymers synthesized with various alkali cation types (i.e., sodium or potassium) and aluminosilicate composition (i.e., combination of metakaolin and low-calcium pulverized fly ash) are studied. The chloride binding isotherms are measured using a modified equilibrium method and the effect of chloride exposure on the mineralogical alteration of geopolymers is studied by means of X-ray diffraction. The results show that the type of alkali cation considerably affects the chloride binding behaviors of metakaolin-fly ash geopolymers, regardless of aluminosilicate composition. In comparison to the potassium-based activator, sodium activator results in higher strength development, stronger chloride binding capacity, and better resistance to chloride penetration. The metakaolin-fly ash geopolymers immobilize chloride ions through both chemisorptions via the formation of chloride-bearing zeolites (e.g., Cl-chabazite) as well as physical adsorption. The dominant role of physical adsorption in binding mechanism suggests that a high proportion of hydroxyl group in the structure of sodium (or potassium)-aluminosilicate-hydrate (i.e., (N, K)-A-S-H) is exchangeable with chloride ions.

Influence of the Nature and Rate of Alkaline Activator on the Physicochemical Properties of Fly Ash‐Based Geopolymers

The influence of alkali cations on mix design of geopolymers is essential for their mechanical, thermal, and electrical performance. This research investigated the influence of alkali cation type on microscale characteristics and mechanical, dielectric, and thermal properties of fly ash‐based geopolymer matrices. The geopolymers were elaborated via class F fly ash from the thermal plant Jorf Lasfar, El Jadida (Morocco), and several alkaline solutions. Morphological, structural, mechanical, dielectric, and thermal characteristics of materials synthesized via fly ash with different proportions of KOH and NaOH aged 28 days were evaluated. The physicochemical properties of class F fly ash‐based geopolymers were assessed using X‐ray diffraction (XRD), Fourier‐transform infrared spectrometry (FTIR), and scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy (SEM/EDX) analyses. Based on readings of the results obtained, XRD and FTIR analysis detected the creation of semicrystalline potassium/sodium aluminate‐silicate hydrate (KASH/NASH) gel in the elaborated matrices after the geopolymerization reaction. The SEM analysis proved the formation of alkali alumina‐silicate hydrate gel in the raw material particles after the polycondensation stage. Experimental compressive strength data indicated that the highest compressive strength (39 MPa) was produced by the alkaline activator (75% KOH/25% NaOH). The dielectric parameters values of the elaborated materials changed depending of the mass ratios KOH/NaOH. Dielectric findings demonstrated that geopolymers containing 100% NaOH have better dielectric performances. The fire resistance study revealed that the geopolymer binders induced by KOH are stable up to 600°C. Based on these results, it can be deduced that the formulated geopolymer concrete possesses good mechanical, dielectric, and fire resistance properties.

The role of composition in the structure and water-binding in alkali-silica reaction sol and gel

The discrepancy between alkali cation (Na+) used in accelerated assessments of potential alkali-silica reactivity (ASR) and those predominant in portland cements (larger amounts of K+ than Na+) leads to questions regarding the reliability of standardized test methods to predict concrete field performance. To better understand the role of alkali cation type in ASR, this study investigates the influence of alkali cation type on the structure and water-binding ability of ASR sols and gels of varying composition. Results obtained by small-angle neutron scattering, 1H NMR relaxometry, and rheological measurements indicate the formation of densified agglomerate structures with increasing silica-to-alkali molar mass ratios (S/A). However, Na-based sols exhibit a greater tendency to agglomerate and a higher dynamic viscosity than K-based ones. Furthermore, at high S/A, 1H NMR relaxometry shows the greater ability of K-based gels to bind water, suggesting the better dispersion of siliceous structures and the development of finer porosities.

Development of metakaolin-based geopolymer for solidification of sulfate-rich HyBRID sludge waste

Radioactive waste which contains high sulfate ion is an abiding challenge for cementitious solidification due to the formation of sulfate mineral such as ettringite. Such secondary mineral formation can cause the expansion and disintegration of cement waste form, resulting in the increase of leachability. To alleviate this problem, we proposed metakaolin-based geopolymer waste form to solidify the radioactive waste containing high sulfate content generated from the Hydrazine Based Reductive metal Ion Decontamination (HyBRID) process. Although ettringite formation was observed in the cement waste form, this mineral did not form in the geopolymer waste form. The addition of HyBRID sludge waste significantly increased the compressive strength of geopolymers at Si/Al ratio of 1.6 from 13.6 MPa to 49.6 MPa. The partial dissolution of cristobalite was confirmed during geopolymerization induced by potassium silicate solution, which increases the amount of silicon that enters geopolymerization. The maximum waste loading of 53.8% was achieved when geopolymer composition was K2O∙2.8SiO2∙Al2O3∙15.2H2O, which had compressive strength of 14.3 MPa, exceeding the repository acceptance criterion (3.44 MPa). Potassium-based geopolymer showed high compressive strength, low leachability, and high waste loading. These results increase our understanding of the solidification mechanism for HyBRID sludge waste using geopolymer waste form, and highlight the importance of considering the type of alkali cations and different Si/Al ratios when designing the chemical compositions of geopolymer waste form.

Effect of alkali cation type on strength endurance of fly ash geopolymers subject to high temperature exposure

Choice of alkali cation in mix design of geopolymers is critical for their thermal performance. However, the influence of alkali cation type on strength endurance of geopolymers subject to high temperature exposure and the underlying governing mechanisms have not been studied. This study investigated the effects of alkali cation type on high temperature response of fly ash geopolymers aiming towards structural applications. In-depth investigation was carried out to discover the underlying mechanisms governing the strength endurance of fly ash geopolymers subject to high temperature exposure and its correlation with their volume stability and chemical stability. Results showed that potassium geopolymer exhibited significant strength enhancement (30–40%) and sodium geopolymer displayed reduced strength (10%), and the strength of mixed sodium and potassium geopolymer remained unchanged after exposure to elevated temperature. While the binders were chemically stable without deterioration and formation of new crystal phases after high temperature exposure, the volume stability varied with the type of alkali cation used. Formation of cracks and gel densification due to shrinkage, and healing of micro-cracks and change of pore sizes due to sintering were identified as responsible mechanisms at different temperature ranges. While crack development and enlargement of pores lowered the strength, densification of matrix and healing of micro-cracks favored strength gain. These competing mechanisms determine the strength endurance of geopolymers depending on the type of alkali cation used. Overall, it shows that geopolymers can be tailored, such that stable (or even enhanced) strengths upon thermal exposure are realized, for structural applications.

Oxygen evolution catalysis in alkaline conditions over hard templated nickel-cobalt based spinel oxides

In this work, two series of cobalt-based spinel catalysts, Co3O4 and NiCo2O4, were synthesised by a hard template method with SBA-15 and were investigated as non-noble catalysts for the oxygen evolution reaction (OER) under basic conditions. The effect of synthesis conditions, i.e., heating rate and calcination temperature, and the addition of minor amounts of iron were evaluated with respect to the OER activity. Moreover, the influence of the alkali cation type in the electrolyte (Li, Na, K) was also evaluated. The highest activity was found for the NiCo2O4 obtained with the lowest heating rate. The increase in the heating rate and calcination temperature results in the decrease of the available surface area for the reaction, leading to the deterioration of the activity. The incorporation of 3 wt% of iron in the lattice of NiCo2O4 and Co3O4 resulted in a decrease of the OER activity, however, the deactivation was much less severe in the case of NiCo2O4 than for Co3O4. Among the alkaline electrolytes used, KOH resulted in the highest catalytic activity both for NiCo2O4 and Co3O4.

Effect of acid attack on microstructure and composition of metakaolin-based geopolymers: The role of alkaline activator

The mineral composition of raw materials and the type of alkali cation plays an important role in the acidic resistance of geopolymers. This paper focuses on the study of chemical durability in hydrochloric acid of potassium and sodium based geopolymers. The study was carried out on two Algerian kaolins and compared with a kaolin from Charente (France). The acid degradation was studied using X-ray Diffraction, Fourier-Transform Infrared and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy. The samples based on Algerian kaolins seems to have the lowest loss in mass for formulations based on potassium due to the presence of secondary minerals (quartz and muscovite). They could have occupied the pores avoiding the release of alkali cations into the acidic solution. Regarding to sodium geopolymers, the best behavior was observed with the kaolin from Charente, which can be attributed to a more stable aluminosilicate cross-linked polymer structure formed for this material, which was corroborated with the Fourier-Transform Infrared analysis.

One-Pot Conversion of Carbohydrates in Biomass to Isobutyroin-Rich Branched Oxygenates: Carbohydrate Depolymerization and Methyl Introduction in Supercritical Methanol

This study proposes a one-pot conversion of carbohydrates in biomass to branched oxygenates in methanol, employing noble metal and alkali cation as catalysts. The main product, isobutyroin, is highly concentrated when the reaction temperature and consequent pressure reach the supercritical point of methanol. The type of alkali cation and ratio of feedstock/alkali also significantly influence the production of isobutyroin. In comparison to Na+, K+ favors the production of isobutyroin from carbohydrates in biomass, especially when a low feedstock/K+ ratio is used. The formation of isobutyroin is explained by a series of reactions starting from methanol and cellulose/hemicellulose-derived acetic acid intermediate based on an isotope-labeling experiment. The isobutyroin-rich products can be used as high-quality gasoline precursors or high-value-added chemicals.

Electroosmosis through α-Hemolysin That Depends on Alkali Cation Type.

We demonstrate experimentally the existence of an electroosmotic flow (EOF) through the wild-type nanopore of α-hemolysin in a large range of applied voltages and salt concentrations for two different salts, LiCl and KCl. EOF controls the entry frequency and residence time of small neutral molecules (β-cyclodextrins, βCD) in the nanopore. The strength of EOF depends on the applied voltage, on the salt concentration, and, interestingly, on the nature of the cations in solution. In particular, EOF is stronger in the presence of LiCl than KCl. We interpret our results with a simple theoretical model that takes into account the pore selectivity and the solvation of ions. A stronger EOF in the presence of LiCl is found to originate essentially in a stronger anionic selectivity of the pore. Our work provides a new and easy way to control EOF in protein nanopores, without resorting to chemical modifications of the pore.

Structure of alkali borosilicate glasses and melts according to Raman spectroscopy data

Using the technique of high-temperature Raman scattering spectroscopy, we studied the structure of glasses and melts of the systems Na2O-B2O3-SiO2, K2O-B2O3-SiO2, and Cs2O-B2O3-SiO2 with the relations $${{X_{M_2 O} } \mathord{\left/ {\vphantom {{X_{M_2 O} } X}} \right. \kern-\nulldelimiterspace} X}_{B_2 O_3 } = 1$$ (M = Na, K, Cs) and $${{X_{SiO_2 } } \mathord{\left/ {\vphantom {{X_{SiO_2 } } X}} \right. \kern-\nulldelimiterspace} X}_{B_2 O_3 } = 3$$ and 4/3. Based on the analysis of the registered spectra, we have shown that, at a high content of SiO2, the disordered network of glasses is composed of the Q 4, Q 3, [BO4/2]− tetrahedrons and BO3/2 triangles. When the content of SiO2 reduces, asymmetric borate triangles BO2/2O− are formed in the structure in addition. A substantial part of borate tetrahedrons are included into the content of mixed borosilicate rings composed of two silicon-oxygen and two boron-oxygen tetrahedrons. The amount of borate structural units joined into purely borate superstructural groups increases with a decrease of the silicon oxide content, depends on the alkali kation type, and grows in the direction from Cs to Na. An increase in the temperature causes a decrease of various types of rings and growth of the concentration of asymmetric triangles. Both in glasses and melts, the fraction of the BO2/2O− triangles depends on the alkali cation type and increases in the succession Cs → K → Na. The results obtained present the basis to suggest that there is some differentiation in the mechanisms of structural reconstruction of the glasses under study by their heating depending on the modifying oxide.

Luminescence of modified nonbridging oxygen hole centers in silica and alkali silicate glasses

This paper reports on the results of the investigation of the cathodoluminescence spectra of silica and alkali silicate glasses upon excitation with a pulsed electron beam (energy, 180 keV; current density, 700 A/cm2; pulse duration, 2 ns). The luminescence band observed in the energy range 2.4–2.6 eV is assigned to modified structural defects of the ≡Si-O·/Me+ type. These defects are revealed under high-density electronic excitation and, unlike the known L centers in alkali silicate glasses, are interpreted as a variety of nonbridging oxygen hole centers (defects of the dangling bond type) subjected to a disturbing action of the nearest neighbor alkali metal cations. The cathodoluminescence of similar centers is observed in neutron-irradiated silica glasses with lithium impurities; alkali silicate glasses with Li, Na, and K cations; and glasses in the two-alkali Na-K systems. It is established that the energy of the radiative transition of a modified nonbridging oxygen hole center, namely, ≡Si-O·/Me+, depends on the alkali cation type.

Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures

The effects of geopolymer binder systems exposed to elevated temperatures are examined. Geopolymers investigated were synthesized from metakaolin, activated by combinations of sodium/potassium silicate and sodium/potassium hydroxide. The specimens were then exposed to temperatures of 800 °C. The factors studied were: (1) calcining temperatures of kaolin; (2) Si/Al ratio of the geopolymer; (3) activator/metakaolin ratio; (4) curing temperature; and (5) alkali cation type. Altogether 30 geopolymer formulations were studied. The samples were subjected to compressive strength, thermogravimetry, and scanning electron microscopy tests. Results showed that Si/Al ratio has a significant influence on elevated temperature exposure deterioration. Lesser strength loss due to elevated temperature exposures were observed in geopolymer with high Si/Al ratios (>1.5). The geopolymer binders activated by potassium-based activators showed an enhanced post-elevated temperature exposure performance compared to sodium-based systems. The optimum calcining temperature of kaolin and curing temperatures for improved temperature performance are also reported.

Control on arrangement of AgI clusters incorporated into zeolite LTA

AgI clusters were incorporated into Li, Na, and K-form LTA zeolites with a loading number of four AgI molecules per α-cage. The X-ray powder diffraction (XRD) patterns and optical absorption spectra of the samples were obtained. The XRD patterns indicate that the sizes of the clusters and their arrangements depend on the type of alkali-cations. AgI clusters with different sizes, i.e., (AgI)n and (AgI)8–n (5≤n≤7), are arrayed alternatively in Na-form LTA conforming to the space group of P213. AgI-loaded Li-form LTA also conformed to the space group of P213, although (AgI)n clusters seem to be distributed disorderly. On the contrary, (AgI)4 cluster is in each cage in K-form LTA conforming to the space group of \( Fm\bar 3c \) or \( F\bar 43c \). The optical spectra showed that Li and Na-form LTAs include (AgI)n (5 ≤n), and that K-form LTA includes (AgI)4 cluster in each cage.