Effect Of Exchangeable Cations Research Articles

Facile preparation and enhanced photocatalytic hydrogen evolution of cation-exchanged zeolite LTA supported TiO2 photocatalysts

Photocatalytic hydrogen evolution (PHE) is an attractive green way to produce clean energy. Zeolite-supported titanium dioxide (TiO2) offers a cost-efficient pathway to prepare an efficient and recyclable photocatalyst for PHE. As known, zeolite has an excellent cation exchange capacity, and the exchangeable cations show considerable influence on its properties. However, the effect of exchangeable cations within zeolite-supported TiO2 photocatalysts on their PHE activity remains unclear. Here, we prepared a series of zeolite LTA-supported TiO2 photocatalysts (TXA, X = Na, K, Ca) with various cations (Na+, K+, Ca2+) inside the zeolite and investigated the effect of cations on their PHE activity. The results demonstrated that all TXA photocatalysts exhibit significantly enhanced PHE activity, and TCaA shows the highest hydrogen evolution rate, which is 3.84 times higher than that of P25. According to experimental results, TCaA possesses a higher solid-acid concentration and a larger surface area, which provides more proton sources and active sites for PHE, facilitates charge separation, and reduces photogenerated electron-hole pair recombination. We believe this work will offer a new exploration strategy for regulating the PHE performance of zeolite-supported TiO2-based photocatalysts and shed new light on the rational design of cost-efficient PHE catalysts.

A theoretical study of the effect of exchange cations in surface of ZSM-5 lamellar zeolites

The electronic properties of various cationic forms of MFI type lamellar zeolites were studied using DFT calculations and compared with their bulk counterparts. In this study, Na+ and H+ cations were considered for the effect of charge deficit compensation on the surface of lamellar zeolites. The results show that lamellar zeolites in different cationic forms exhibit two distinct band gap widths, whose values are lower than those of their bulk counterparts and arise from the surface atoms. Furthermore, the results suggest that the Na+ cation behaves as a structure-directing agent on the surface, while H+ passivates the surface of the lamellar zeolites.

DIFERENCIAÇÃO CATIÔNICA DE BENTONITAS POR INFRAVERMELHO: UM ESTUDO DOS EFEITOS DA HIDRATAÇÃO DOS CÁTIONS TROCÁVEIS

CATIONIC DIFFERENTIATION OF BENTONITES BY INFRARED: A STUDY OF THE HYDRATION EFFECTS OF EXCHANGEABLE CATIONS. In the bentonite industry, the most common procedure for quality control of the ore and the sodium activation process is the swelling method. However, this tool is restricted only to the differentiation of the sodium and non-sodium types, not considering the other cationic varieties. The objective of this study was to establish parameters for cationic differentiation of bentonites based on Near Infrared (NIR) and Medium (MIR) spectroscopy, which proved to be an effective technique in the cationic differentiation of bentonites using the characteristic bands “7072 cm-1” and “3620 and 3430 cm-1” under the condition of the dry-hydrated sample and not under the anhydrous condition. NIRS can be considered a measure of great scientific and technological contribution, as it allows the cationic differentiation of bentonites in a practical way and with low analytical cost.

Effect of Exchangeable Cation in Clays on the Yield and Quality of the Bio-Oil during Microwave Pyrolysis of Cellulose

Bio-oil (pyrolysis oil) is an essential feedstock for the production of renewable fossil-free fuels and valuable chemicals. Enhancement of the pyrolysis oil yield and its quality are significant challenges for an efficient and sustainable biorefinery. Here, we report the microwave (MW)-assisted noncatalytic pyrolysis of cellulose, as a green and controllable alternative to conventional heating, in the presence of eco-friendly Li-, Na-, K-, Mg-, Ca- and Ba-bentonites. The detailed analysis of the MV heating traces demonstrates that the bentonite MW activity significantly depends on the presence of internal water. The intensity of this interaction is controlled by the cation nature reduced in the order: Li+ > Na+ > K+ and Mg2+ > Ca2+ > Ba2+. A unique experimental design for the MW-assisted pyrolysis of cellulose in the presence of Li-doped clays helps to increase the bio-oil yield to 37.8% with high selectivity towards the commercially useful levoglucosan (purity: 39.36%). The combination of an alternative green heating method and environmentally friendly bentonites can be used many times without recycling. We believe that the improved yields of bio-oil are due to: (i) high MW activity of bentonites, which conventionally increases the heating rates of cellulose; and (ii) production of water by hydrophilic clay minerals, favouring depolymerisation of cellulose.

Charge sparsity: An index to quantify cation effects on clay dispersion in soils

Few approaches have been developed to measure the isolated effect of exchangeable cations on clay dispersion in soils. In this study, the charge sparsity (CS) index was proposed using the ratio between the cations hydrated ionic radius and valence. The index capacity to measure cation effects on clay dispersion in soils was also evaluated. Three Ferralsols, sampled at different sites in Parana State, Brazil, were homoionized with Ca2+, Mg2+, K+, or Na+ prior to evaluation of the clay dispersion degree. Published independent data for two soils and clays were also used. We tested the capacity of CS and II, the latter proposed by Marchuck and Rengasamy (2011), to predict clay dispersion in soils. The CS predicted the dispersion degree more accuratelly than the ionicity index did, in soils where Ca2+ and Mg2+ behaved similarly. The response of Parana soils to CS varied with soil characteristics. Soils with a lower pH at the isoelectric point were more dispersible by cations with high CS (K+ and Na+). The CS was efficient to quantify the isolated effect of cations on the clay dispersion process in soils. Therefore, qualitative and quantitative studies can benefit from the CS as an index to understand the effect of cations on clay dispersion in soils.

Carbohydrate concentrations and enzyme activities as influenced by exchangeable cations, mineralogy and clay content

Abstract Enzymes can exist in bound or free form within the soil, but the impact of interactions between extracellular enzymes with the amount and type of clay minerals and exchangeable cations on the activities of enzymes and decomposition or retention of carbohydrates in soil is still poorly understood. Appropriate amounts of homoionic Na-, Ca- and Al-clay minerals from Georgia kaolinite, Illinois illite and Wyoming montmorillonite were mixed with pure sand to prepare artificial soils with different clay contents, exchange cations and clay types to examine the effects of exchangeable cations, mineralogy and clay content on the concentrations of hot water and dilute acid extractable carbohydrates and activities of acid and alkaline phosphatases and CM-cellulase. There was a significant effect of clay content on the concentrations of carbohydrates and activities of enzymes. The concentrations of carbohydrates increased when the clay contents of soils increased from 0 to 5 and 10%, respectively, showing that the clay contents influence the capacity of soils for stabilization of carbohydrates. But opposite trends were found in enzyme activities. The enzyme activities decreased significantly as the clay contents of the artificial soils increased. The concentrations of carbohydrates and activities of enzymes were significantly affected by exchangeable cations. In soils with 5 and 10% clay, the concentrations of carbohydrates were maximum in Al-soils and minimum in Ca-soils, in contrast, the activities of enzymes were maximum in Ca-soils and minimum in Al-soils. There was a significant effect of clay mineralogy on the concentrations of carbohydrates and activities of enzymes. The concentrations of carbohydrates were highest in soils with Wyoming montmorillonite clay mineral and lowest in soils with Georgia kaolinite clay mineral. But the activities of enzymes were lower in soils with Wyoming montmorillonite clay mineral than soils with Georgia kaolinite and Illinois illite clay minerals, indicating the influence of specific surface area (SSA) and cation exchange capacity (CEC) of clay minerals on carbohydrate retention and enzyme activities. The results of this study indicate that carbohydrates are stabilized in soils through the interaction with clay minerals and a small amount of clay (5%) significantly increases carbohydrate retention and reduces enzyme activities in soils. Exchangeable cations exert their influence on enzyme activities and hence carbohydrate dynamics by controlling the activities of enzymes through modifying the physicochemical characteristics of soils.

Effects of exchangeable cations, mineralogy and clay content on the mineralization of plant residue carbon

Interactions of clay minerals with organic materials and the consequences of these interactions on dynamics of organic carbon (OC) have been reviewed in detail. However, the effects of exchangeable cations and clay types on the turnover rate of OC have not been given much attention. Appropriate amounts of homoionic Na-, Ca- and Al-clays from Georgia kaolinite, Illinois illite and Wyoming bentonite were mixed with pure sand to prepare artificial soils with different clay contents, exchange cations and clay types. Alfalfa plant residues were incorporated into the artificial soils and the soils were inoculated with microbes from a natural soil and incubated for 184days to study the effects of clay contents, exchangeable cations and clay types on the mineralization of OC and plant residue derived microbial biomass. Mineralization of plant residue carbon was significantly (⁎⁎p<0.01) more rapid in pure sand than in soils containing 5 and 10% clay, indicating that clay contents influence the capacity of soils to protect and store OC. The amounts of biomass carbon were lowest in pure sand and highest in soils with 10% clay. There was a significant influence (⁎⁎p<0.01) of exchangeable cations on microbial biomass and hence the mineralization of OC over a period of 184days. At 5 and 10% clay contents, the amounts of microbial biomass carbon and the mineralization of plant residue carbon were highest in Ca-soils and lowest in Al-soils. Statistical analysis of data showed a significant effect (⁎⁎p<0.01) of clay type on mineralization of plant residue carbon and microbial biomass. However, the effects of clay types on the mineralization of OC were much less than those of clay contents and exchangeable cations. The mineralization of plant residue carbon was highest in soils with Georgia kaolinite clay and lowest in soils with Wyoming bentonite clay. The amounts of biomass carbon were slightly lower in soils with Wyoming bentonite clay than soils with Georgia kaolinite and Illinois illite clay minerals. The results of this study indicate that OC and microbial biomass are stabilized in soils through the interaction with clay minerals and a small amount of clay (5%) slows OC decomposition significantly and reduces carbon dioxide emission from soils. Exchangeable cations exert their influence on microbial biomass and hence carbon dynamics by controlling the size and activity of the microbial population through modifying the physicochemical characteristics of microbial habitats.

Near-Infrared Study of Water Adsorption on Homo-Ionic Forms of Montmorillonite

AbstractThe potential of near-infrared (NIR) spectroscopy to track the adsorption of water on montmorillonite saturated with different exchangeable cations is demonstrated in the present study. The Na+, K+, Ca2+, and Mg2+ forms of JP montmorillonite (Jelšový Potok, Slovakia) were first dried and then hydrated at 23, 52, 88, and 100% relative humidity (RH). The combination band of water molecules, (ν+δ)H2O$\end{document}, allowed the study of the effect of exchangeable cations on the strength of H bonds between water molecules and on the amount of adsorbed water. With increasing ionic potential (IP) of the exchangeable cation, the strength of the H bonds increased and the (ν+δ)H2O\$\end{document} band was shifted to lower wavenumbers. The area of the (ν+δ)H2O\$\end{document} band, corresponding to the amount of adsorbed water, was compared with results from gravimetry. The good correlation (R2 &gt; 0.97) between the two independent methods confirmed that the (ν+δ)H2O\$\end{document} band area reflected reasonably well the amount of H2O in montmorillonite. The peak-fitting analysis of the (ν+δ)H2O\$\end{document} band allowed differentiation of weakly and strongly H-bonded water molecules. The position of the high-frequency component at 5260–5250 cm−1, related to H2O weakly H-bonded to basal oxygens of the tetrahedral sheets, was influenced only slightly by the exchangeable cations. Two low-frequency components were assigned to the combination modes involving asymmetric (ν3) and symmetric (ν1) stretching vibrations of strongly H-bonded H2O. Only the (ν1+δ)H2O\$\end{document} component (5055–5000 cm−1) showed significant dependence on the type of exchangeable cation and hydration level. Peak-fit analysis revealed a small effect of the type of exchangeable cation on the amount of water molecules weakly H-bonded to the siloxane surface but a pronounced effect on the content of strongly hydrogen-bonded H2O. The amount of weakly H-bonded H2O remained stable after reaching a certain level of hydration, but a gradual increase in the strongly H-bonded water molecules with increasing RH was observed.

Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): Effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure.

Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): Effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure.

Influence of different exchangeable cations (Li+, Na+ and Ca2+) on the modification effects and properties of organomontmorillonites used in oil-based drilling fluids/muds

The effects of exchangeable cations on the structure, surface polarity and thixotropy of CA-OMts.

Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): Effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure

This study deals with the adsorption of PolyCarboxylate Poly(ethylene glycol) esters (PCP) superplasticizers on Na-, Mg- and Ca-saturated Montmorillonite (Mmt) clays. The interactions have been examined through different experimental methods: adsorption isotherms, zeta potential measurements and sedimentation experiments. It was found that PCP adsorption depends both on the architecture of PCP molecules and the nature of cation located on the interlayer exchange sites of the Montmorillonite. Whatever the PCP, a larger amount was adsorbed on Na-Mont than on Mg-Mont or Ca-Mont. This indicates the occurrence of two adsorption mechanisms: (i) a superficial adsorption via electrostatic interactions between the carboxylate groups of PCP and positively charged sites on clay surfaces, (ii) intercalation of ether units of the PCP grafts in the interlayer space by displacement of water molecules coordinated to the exchangeable cations.Furthermore, despite the weak negative values of the zeta potential, the addition of PCP promotes the stability of the suspensions which is attributed to steric repulsion acting between particles.

Sorption of chlorimuron-ethyl on montmorillonite clays: effects of exchangeable cations, pH, and ionic strength.

Sorption interaction of chlorimuron-ethyl with montmorillonite clays was investigated under varied types of exchangeable cation, pH, and ionic strength conditions. Chlorimuron-ethyl sorption on bentonites exhibited pronounced cation dependency, and the sorption ability increased as the sequence Ca(2+)- < Na(+)- < Al(3+)- < Fe(3+)-bentonite, due to different sorption mechanisms, whereas the cation dependency was influenced by the clay type and much weaker for montmorillonites. The decrease of pH at the range of 4.0-6.0 prominently increased sorption of chlorimuron-ethyl on all cation-exchanged montmorillonite clays, and nearly a neglected sorption (about 2 %) can be observed at pH over 7.0. In the presence of CaCl2, sorption of chlorimuron-ethyl on Fe(3+)-bentonite was promoted because of complexion of Ca(2+) and the surface of Fe(3+)-bentonite. However, as the concentration of CaCl2 increased, chlorimuron-ethyl sorption on Ca(2+)- and Fe(3+)-exchanged bentonite decreased, suggesting that Ca bridging was not the prevailing mechanism for sorption of chlorimuron-ethyl on these clays. Furthermore, chlorimuron-ethyl sorption was relatively sensitive to pH, and the change of pH may obscure effect of other factors on the sorption, so it was quite necessary to control pH at a constant value when the effect of other factor was being studied.

Adsorption of paraquat on soil organic matter: Effect of exchangeable cations and dissolved organic carbon

Herbicides that interact with soil organic matter do so with both the solid and the dissolved fractions, so that the distribution of herbicide between the soil solution and solid phases is determined by competitive effects. In the present study, adsorption experiments were carried out with the cationic herbicide paraquat and untreated and acid-washed samples of a peat soil, at different values of pH and ionic strength. Less herbicide was adsorbed onto the untreated peat than onto the acid-washed peat; the difference was due to the presence of exchangeable cations, as demonstrated in experiments carried out by adding Ca2+ to suspensions of acid-washed peat. The results were interpreted by an electrostatic model and the fitting parameters indicated that the adsorption constants were the same for both samples of peat, although the number of binding sites available was different. Simultaneous resolution of the adsorption equilibrium of paraquat for the soil organic matter (SOM) and of the binding equilibrium between paraquat and dissolved organic matter (DOM) enabled the distribution of paraquat between the solid and solution phases to be determined. The increased solubility of the SOM with increasing pH led to a decrease in the fraction of paraquat retained on the peat surface above pH 5.5, which favors the mobility of the herbicide in the soil.

Effect of Exchangeable Cation on Interlayer Water of Li+, Na+, K+, Rb+, and Cs+Modifications of Kenyaite.

Effect of Exchangeable Cation on Interlayer Water of Li+, Na+, K+, Rb+, and Cs+Modifications of Kenyaite.

A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

Hydraulic conductivities were determined for compacted Fe(III)-montmorillonite sample. The Fe(III)-montmorillonite sample used in this study, which was prepared by the ion-exchange treatment of Namontmorillonite in FeCl3 solution, contains less than 20% of Na+ ions as exchangeable cations and negligibly small amounts of iron precipitates. The measured hydraulic conductivities of compacted Fe(III)-montmorillonite were determined to be the order of 10−9, 10−11, and 10−13 ms−1 at dry densities of 0.80, 1.01, and 1.20 Mgm−3, respectively. These values were found to be kept constant during the experimental period, suggesting no significant change in the physicochemical properties of Fe(III)-montmorillonite during the experiment. When compared with Na-montmorillonite, remarkably high values of hydraulic conductivities were found for Fe(III)-montmorillonite at the dry densities of 0.8 and 1.0Mgm−3. On the other hand, almost the same value of hydraulic conductivity was obtained at the dry density around 1.2Mgm−3. This different effect of exchangeable cations on the hydraulic conductivity of montmorillonite could be attributed to the different sizes of macropores in compacted montmorillonite and/or the different thicknesses of electrical double layers formed over montmorillonite sheets.

Effect of exchangeable cations on apparent diffusion of Ca 2+ ions in Na- and Ca-montmorillonite mixtures

Compacted Na-bentonite, of which the major mineral is montmorillonite, is a candidate buffer material for the geological disposal of high-level radioactive waste. A potential alteration of the bentonite in a repository is the partial replacement of the exchangeable cations of Na + with Ca 2+. The Ca 2+ cations could be released from cementitious materials and diffuse into the buffer material in the repository. In this study, to evaluate the alteration that could reduce the performance of the bentonite buffer, the apparent diffusion coefficients of HTO and Ca 2+ ions were determined from non-steady, one-dimensional diffusion experiments using Na- and Ca-montmorillonite mixtures with different ionic equivalent fractions of Ca 2+ ions. The apparent diffusion coefficient of HTO at a dry density of 1.0 Mg m −3 slightly increased with an increase in the ionic equivalent fraction of Ca 2+ ions. However, the apparent diffusion coefficient of Ca 2+ and the activation energy for diffusion at the same dry density were independent of the ionic equivalent fraction of Ca 2+ ions. These findings suggest that unlike HTO, which can be postulated to diffuse mainly in pore water, Ca 2+ ion diffusion could occur predominantly in interlayer spaces, of which the basal spacing was determined to be constant by the XRD technique.

Adsolubilization of drugs onto natural clinoptilolite modified by adsorption of cationic surfactants

The combined adsorption onto purified natural clinoptilolite (NZ) of the cationic surfactant benzalkonium chloride (BC) and the model drugs metronidazole and sulfamethoxazole has been studied in order to design systems for the storage and release of drugs. The equilibrium adsorption of benzyldimethylalkylammonium chloride surfactants with hydrocarbon chain lengths corresponding to 12, 14 and 16 carbon atoms (BC12, BC14 and BC16) onto NZ from aqueous solutions was compared to that of BC. The effect of exchangeable cations on the NZ structure and that of acid–base pre-treatment of NZ on the adsorption capacity of BC was evaluated. It was shown that the nature of the exchangeable cations had little influence on the adsorption of BC onto NZ, and that acid–base treatments of NZ led to a decrease in the amount of surfactant adsorbed. The results indicated that the adsorption of the less polar drug, sulfamethoxazole, was enhanced by the presence of BC12 at the solid–liquid interface, whereas the uptake of metronidazole was independent of the surfactant adsorption.

Cation Exchange Reactions of Vermiculite With Cu-Triethylenetetramine as Affected by Mechanical and Chemical Pretreatment

AbstractThe cation exchange capacity (CEC) is a characteristic property of expandable clay minerals, such as smectites and vermiculites. The aim of this work was to examine the cation exchange behavior of vermiculite using the Cu-triethylenetetramine (Cu-trien) CEC method and the influence of mechanical and chemical pretreatment, with the ammonium acetate method serving as a reference. The Cu-trien method makes rapid and direct CEC measurements possible. Three different kinds of mill were used to grind a vermiculite sample from Russia, in order to reduce the particle size to &lt;10 µm. The Netzsch CGS 10 dry mill reduced the particle size more effectively than the other grinding methods. Chemical pretreatments were used to remove carbonates, organic matter, Fe oxides, and divalent exchangeable cations from vermiculite samples prior to CEC measurements. Subsamples of ground and chemically pretreated vermiculite samples were saturated with Na, Li, Mg, Ca, and Cu cations to determine the effect of exchangeable cations on measured CEC values. Chemical pretreatment, monovalent cation pretreatment, and 48 h of shaking time were needed to measure vermiculite CEC values effectively using the Cu-trien method.

Partitioning of hydrophobic pesticides within a soil–water–anionic surfactant system

Surfactants can be added to pesticide-contaminated soils to enhance the treatment efficiency of soil washing. Our results showed that pesticide (atrazine and diuron) partitioning and desorbability within a soil–water–anionic surfactant system is soil particle-size dependent and is significantly influenced by the presence of anionic surfactant. Anionic surfactant (linear alkylbenzene sulphonate, LAS) sorption was influenced by its complexation with both the soluble and exchangeable divalent cations in soils (e.g. Ca 2+, Mg 2+). In this study, we propose a new concept: soil system hardness which defines the total amount of soluble and exchangeable divalent cations associated with a soil. Our results showed that anionic surfactant works better with soils having lower soil system hardness. It was also found that the hydrophobic organic compounds (HOCs) sorbed onto the LAS-divalent cation precipitate, resulting in a significant decrease in the aqueous concentration of HOC. Our results showed that the effect of exchangeable cations and sorption of HOC onto the surfactant precipitates needs to be considered to accurately predict HOC behavior within soil–water–anionic surfactant systems.

Sorption–Desorption of Trinitrotoluene in Soils: Effect of Saturating Metal Cations

Clay minerals in soils control the sorption and mobility of nitroaromatics in munitions contaminated soils. Therefore, effect of exchangeable cations (NH4+ , K+, Ca2+, and Al3+) on sorption-desorption of trinitrotoluene (TNT) was studied in two reference soils viz sandy loam and silty clay. Compared to control soils, K+ ion saturation significantly increased TNT sorption in both the soils, while other cations decreased TNT sorption. Effect of K+ saturation on sorption of TNT was more pronounced in organic matter poor sandy loam soil (seven times) then silty clay (two times). Desorption followed the reverse trend and greater amounts of sorbed TNT were retained in the K+ saturated soils.