Rapid Cation Exchange Research Articles

Highly sensitive and selective ratiometric fluorescent and visual detection of Cu2+ based on the hydroxytyrosol–naphthoresorcin–quantum dots sensing platform

Fluorescence-based visual analysis has attracted considerable attention in on-site detection owing to their distinct color gradient changes, easy operation and high sensitivity. In this work, we construct an exceptionally simple dual-emission ratio fluorescence sensor through the synergy of hydroxytyrosol (HYT), naphthoresorcin (NR) and ZnCdSe/ZnS quantum dots (QDs), namely HYT–NR–QD, for the fluorescent and visual detection of Cu2+. The design of ratiometric nanosensor is based on our new finding that Cu2+ can catalyze the reaction between HYT and NR to produce a cyan-emitting fluorophore (emission: 480 nm), and the copper species existed in the form of Cu+ and Cu2+ in reaction system. After adding QDs (emission: 605 nm), the free Cu+, Cu2+ and the resulting fluorophore in this system caused a great reduction in the FL intensity of QDs, due to the rapid cation exchange reaction between QDs and Cu2+/Cu+ as well as the inner filter effect between QDs and the resulting fluorophore. Overall, Cu2+ induced emission intensity changes at 480 and 605 nm leads to a distinct color change from red to cyan. A ratiometric fluorescence Cu2+ sensor with a lowest concentration of 3.42 nM was developed. Furthermore, the concentration of Cu2+ can be conveniently reflected with a smartphone application by identifying the RGB value. Moreover, the method proposed by us can be explored for Cu2+ determination in environmental water samples with a satisfying result, providing a novel, simple-operating and on-site detection of Cu2+ in water samples.

CdTe magic-size cluster synthesis via a cation exchange method and conversion mechanism.

The quasi-metallic nature of Te is not conducive to telluride formation and crystallization, which makes the synthesis of CdTe magic-size clusters (MSCs) in a single-ensemble form still challenging. CdTe MSCs are usually synthesized by direct synthesis, a method that must avoid the formation of quantum dots by selecting suitable active precursors and precisely controlling the reaction temperature. In addition, the organic Cd compounds and superhydrogenated precursors used are air-sensitive. Herein, CdTe MSC-448 in a single-ensemble form was synthesized for the first time via a cation exchange method using ZnTe MSC-389 as a template and Cd2+ as an exchange ion. In situ absorption spectroscopy characterization combined with the two-pathway model proposed by Yu's group reveals that the conversion of ZnTe MSC-389 into CdTe MSC-448 is assisted by their corresponding precursor compounds (PCs). After the addition of Cd precursors to ZnTe MSC-389 solution, ZnTe MSC-389 is transformed into ZnTe PC-389, which then undergoes a rapid cation exchange reaction with Cd2+ to yield CdTe PC-448, and CdTe PC-448 is finally converted into CdTe MSC-448. CdTe MSCs in single-ensemble form were obtained by cation exchange in air at room temperature, avoiding the formation of quantum dots (QDs) at high temperatures in the direct synthesis method conducted without the use of toxic and expensive active precursors, which provides a new route to the synthesis of CdTe MSCs.

Highly Controllable Hierarchically Porous Ag/Ag2S Heterostructure by Cation Exchange for Efficient Hydrogen Evolution

AbstractEstablishing the hierarchical porous architectures has been considered to be the most efficient approach to realize the efficient mass diffusion and large exposed active sites of designed micro/nanomaterial catalysts for hydrogen evolution reactions (HER). In this work, the nonequivalent cation exchange strategy is developed to fabricate the hierarchically porous Ag/Ag2S heterostructure based on the rapid cation exchange by the metal‐organic framework (MOF)‐derived CoS. The as‐prepared Ag/Ag2S inherits the original 3D hollow morphology of CoS with porous nature, possessing abundant S‐vacancies and lattice strain simultaneously due to the coordination loss and in‐situ epitaxial growth of metallic Ag on the surface. Owing to the optimizations of lattice and electronic structures, the unique hierarchically porous Ag/Ag2S heterostructure exhibits superior catalytic performance than previously reported catalysts derived from MOF. Theoretical calculations have confirmed that the co‐existence of Ag cluster and sulfur vacancies activates the electroactivity of the interfacial defective region to boost the HER process. The binding strength of the proton and energetic trend of HER has been optimized with the formation of Ag/Ag2S heterostructure, which guarantees the efficient generation of H2. This study opens a new strategy for the utilization of the nonequivalent cation exchange strategy to efficiently synthesize advanced electrocatalysts with high performances.

Ionic Liquid-Driven Formation of and Cation Exchange in Layered Sulfido Stannates - a CH2 Group Makes the Difference.

Two types of layered sulfido stannates or a molecular cluster compound are obtained upon ionothermal treatment of the simple sulfido stannate salt K4[SnS4] · 4H2O that is based on binary tetrahedral [SnS4]4− anions. The formation of the respective products, novel compounds (C4C1C1Im)2[Sn3S7] (1 a), (C4C1C2Im)2[Sn3S7] (1 b), and (C4C1C2Im)2[Sn4S9] (2) with layered anionic substructures, or the recently reported compound (C4C1C1Im)4+x[Sn10O4S16(SMe)4][An]x (A) comprising a molecular cluster anion, is controlled by both the choice of the ionic liquid cation and the reaction temperature. We report the scale‐up of the syntheses by a factor of 100 with regard to other reported ionothermal syntheses of related compounds, and a procedure of how to isolate them in phase‐pure form – both being rare observations in chalcogenido stannate chemistry in ionic liquids. Moreover, the synthesis of compound 1 a can be achieved by rapid cation exchange starting out from 1 b, which has not been reported for organic cations in any chalcogenido stannate salt to date.

Dispersion and Stabilization of Alkylated 2D MXene in Nonpolar Solvents and Their Pseudocapacitive Behavior

Summary To date, MXene dispersions have been mostly limited to polar solvents. Here, we show that when the lithium cations present between MXene multilayers after etching are exchanged with di(hydrogenated tallow)benzyl methyl ammonium chloride (DHT), they become organophilic and form highly stable colloidal suspensions in nonpolar solvents. The rapid cation exchange occurs under ambient conditions and the resulting two-dimensional flakes are well dispersed and remain oxide free. A 142 ± 0.7-μm thick film (≈10 mg ⋅ cm−2) made from a DHT-Ti3C2Tz suspension in toluene exhibits pseudocapacitive behavior, with a capacitance of 305 F ⋅ g−1 at a scan rate 2 mV ⋅ s−1. The moduli and tensile strengths of solution-processed polyethylene nanocomposites are increased by ≈11% and 32% with a loading of ≈1 vol% DHT-Ti3C2Tz. Our approach may enable the use of MXenes in multiple research and industrial fields.

Aqueously synthesized color-tunable quaternary Cu-In-Zn-S quantum dots for Cu(II) detection via mild and rapid cation exchange

Non-cadimum photoluminescent I−III−VI semiconductor nanocrystals have attracted increasing attention due to their low toxicity, extraordinary optical and electronic properties. Herein, water-soluble quaternary Cu-In-Zn-S quantum dots (CIZS QDs) with tunable emission from 535 nm to 645 nm were successfully synthesized via ecofriendly one-pot aqueous method. The full width at half-maximum (FWHM) of the emissions are about 68 nm–88 nm, which are rather narrow among Cu-based semiconductors and preferred to facilitate improving color purity. The photoluminescence of water-soluble QDs was enhanced by ZnS coating with the absolute quantum yield (QY) up to 30.8%. Further, a novel fluorescent sensor for Cu2+ detection was developed based on the alteration of intrinsic optical properties of the CIZS/ZnS QDs after cation exchange at room temperature within 10 min, presenting a linear range of 0.020–20 μM and a detection limit down to 6.7 nM. Mechanism studies revealed that the QDs served as the template for cation exchange, through UV–vis absorption and fluorescence spectra in combination with the chemical composition and time-resolved photoluminescence decay analysis. Ions interference experiments demonstrated the good selectivity of the QDs towards Cu2+ and the sensor showed comparable accuracy to ICP-AES method as well as good performance in real sample detection, manifesting the reliability of the current strategy for sensing Cu2+ mildly and rapidly.

Direct cation exchange of surface ligand capped upconversion nanocrystals to produce strong luminescence.

We develop a facile and rapid cation exchange method for upconversion nanocrystals (UCNCs) without removing surface ligands. It avoids the tedious pretreatment of as-synthesized UCNCs, and the luminescent intensities of nanocrystals after Tb3+ exchange using the new method are much stronger than those of the nanocrystals obtained using conventional cation exchange in water.

Mn-Doped ZnSe quantum dots initiated mild and rapid cation exchange for tailoring the composition and optical properties of colloid nanocrystals: novel template, new applications.

Although cation exchange (CE) has been studied for many years and some mechanisms were proposed, there is still a knowledge gap in CE and problems such as the need for high temperature and it being time-consuming are still unaddressed. We developed a new mild strategy for CE by introducing a new ideal template and first applied this doping strategy to detect Cd2+ and Hg2+. This strategy adopted Mn-doped ZnSe quantum dots (QDs) as the template and the introduction occurs via a two-step CE reaction: first Zn2+ was partially substituted by X (X = Cd2+, Hg2+, Cu2+, Ag+ or Pb2+), later Mn2+ (in the deep structure of QDs) was substituted by X. Remarkably, Mn2+ in the lattice can be easily substituted by a dopant and its replacement by a dopant helps to bury the metal ions. The ultra-fast introduction of Cd2+ and Hg2+ (70 minutes for Cd2+ and 19 minutes for Hg2+) was realized at room temperature; other metal ions such as Ag+, Cu2+ and Pb2+ can be buried at 50 °C. This mild reaction temperature offers a solution for introducing impurities without sacrificing the interfacial structure of nanocrystals. HRTEM, XPS and ICP measurements were applied to analyze the introduction process. Furthermore, the spectroscopic method was employed to analyze the introduction, migration and distribution of metal ions. Then, we proposed a mechanism for the chemical conversion of nanocrystals by CE. Through this strategy, full-color light-emitting doped QDs were fabricated. Strikingly, a new turn-on probe for the detection of Cd2+ and Hg2+ with improved selectivity was developed by adopting this doping strategy. The detection limit is 36 nM for Cd2+ and 20 nM for Hg2+, which is competitive with the limit of detection reported by other groups using QDs as sensors.

Permeability and frictional strength of cation‐exchanged montmorillonite

Smectites, such as montmorillonite, are abundant throughout the upper crust and are commonly found in fault gouge. They are known for their weak frictional strength and low permeability. Smectites are swellable clays in which the interlayer cation can easily be exchanged. In this study, we measure permeability and frictional strength of montmorillonite exchanged with Na+, K+, Ca2+, and Mg2+ using a triaxial shear apparatus. We find that the interlayer cation influences both permeability and the friction coefficient. K‐montmorillonite is significantly stronger (μ=0.26) than Na‐montmorillonite (μ=0.15) and Ca‐ or Mg‐montmorillonite (μ=0.11). Permeability for all four clays is between 10−21 and 10−23 m2 in the pressure range between 10 MPa and 100 MPa, with K‐montmorillonite the most permeable clay gouge. Mg‐, Ca‐, and Na‐montmorillonite show relative similar permeabilities of which Na‐montmorillonite is least permeable. We relate the higher frictional strength and permeability of K‐montmorillonite to reduce interlayer water content caused by differences in cation hydration and adsorption. The results show that the rapid cation exchange process in montmorillonite can influence macroscale parameters, such as permeability and strength, which can contribute to changes in local pressure conditions and frictional strength of shallow fault zones.

Rapid method for determination of 228Ra in water samples

A new rapid method for the determination of 228Ra in natural water samples has been developed at the SRNL/EBL (Savannah River National Lab/Environmental Bioassay Laboratory) that can be used for emergency response or routine samples. While gamma spectrometry can be employed with sufficient detection limits to determine 228Ra in solid samples (via 228Ac), radiochemical methods that employ gas flow proportional counting techniques typically provide lower minimal detectable activity levels for the determination of 228Ra in water samples. Most radiochemical methods for 228Ra collect and purify 228Ra and allow for 228Ac daughter ingrowth for ~36 h. In this new SRNL/EBL approach, 228Ac is collected and purified from the water sample without waiting to eliminate this delay. The sample preparation requires only about 4 h so that 228Ra assay results on water samples can be achieved in 90 %), followed by rapid cation exchange removal of calcium. Lead, bismuth, uranium, thorium and protactinium isotopes are also removed by the cation exchange separation. 228Ac is eluted from the cation resin directly onto a DGA Resin cartridge attached to the bottom of the cation column to purify 228Ac. DGA Resin also removes lead and bismuth isotopes, along with Sr isotopes and 90Y. La is used to determine 228Ac chemical yield via ICP-MS, but 133Ba can also be used instead if ICP-MS assay is not available. Unlike some older methods, no lead or strontium holdback carriers or continual readjustment of sample pH is required.

Sources and controls of calcium and magnesium in storm runoff: the role of groundwater and ion exchange reactions along water flowpaths

Abstract. A combined hydrological and chemical investigation was undertaken in a small moorland catchment at Plynlimon to determine the processes controlling storm runoff chemistry. Flow from natural soil pipes, overland flow from peat soils, throughflow from a mineral horizon and streamflow were gauged and sampled intensively during seven storms. Stormflow Ca and Mg concentrations in stream water consistently exceeded those observed in overland flow, pipeflow and throughflow. The response of Ca and Mg to increases in streamflow varied between the storms and could not be explained readily by the mixing of the dominant source waters monitored within the catchment. Intensive sampling of pipe water along a major stormflow pathway revealed a large and consistent increase in the concentration of dissolved Ca and Mg accompanied by a corresponding decrease in acidity, the magnitude of which was strongly influenced by antecedent conditions. Analyses of soil exchangeable cations along the stormflow pathway revealed soils enriched in divalent cations probably derived from a groundwater source. Laboratory leaching experiments confirmed that rapid cation exchange reactions could explain the changes in pipe water chemistry along the stormflow pathway. The relative contribution of flow from pathways where these ion exchange reactions occur strongly influences the stormflow response of Ca and Mg in the stream. The results also highlight a potentially important, indirect role for base-rich groundwater in modifying storm runoff chemistry along water flowpaths.

Copper Chelation Assay For Histamine in Tuna

ABSTRACTA reported copper chelation method for histamine determination was modified for use in decomposing yellowfin tuna steaks. The assay consisted of histamine extraction with hot methanol, purification by rapid cation exchange chromatography, and addition of copper and a dye to the purified sample to form an easily visualized red complex with the histamine. This method detected histamine in the low mg% range in yellowfin tuna steaks with an accuracy comparable to the standard fluorometric histamine assay. It is an alternative to the standard assay when a visual test is desirable or a fluorometer is not available.

Fractionation of gliadins from common wheat by cation exchange FPLC

Crude gliadin from common wheat was fractionated by rapid cation exchange chromatography (FPLC) on a mono-S column. Buffers used previously for gliadin fractionation on SP-trisacryl M (a soft cation exchange gel) were used first. It was thus possible to compare gliadin fractionations carried out under very similar conditions by cation exchange FPLC and low pressure chromatography. In both cases the elution times of the components were related to their charges at acid pH. Fractionation can be achieved more rapidly on a mono-S column than on SP-trisacryl M, and the resolution is greater. Mono-S FPLC did not yield pure gliadin components, but each gliadin group was separated into several fractions. The elution times and the resolution are slightly modified by the quantity of protein loaded onto the column, but such variations should not be critical in routine analysis of flour samples extracted under standard conditions. A well-controlled column washing procedure is necessary to ensure reproducible chromatographic profiles that can be used routinely to discriminate between common wheat cultivars. The patterns of 18 genotypes were compared. All were distinguishable from each other. This preliminary investigation showed that cation exchange FPLC may provide an alternative method for wheat cultivar identification.

Soil-water interactions

The composition of water flowing through and out of soils and rocks reflects the composition of the material that it has passed through. The chemical processes involved are mainly relatively rapid cation exchange reactions with soil colloidal materials, and slow acid hydrolysis reactions which decompose primary minerals. Examples are given of the results of these processes during flow through acid podzolic soils into surface waters. This pattern is modified during periods of high water discharge. The proportion of flow that takes different routes through the land surface, and the contact time with soil or rock, are then important for water composition. Sources of acidity can be generated within soil, when chemically reduced material in anaerobic environments is exposed to air by changes in the soil water regime. It is suggested that only detailed soil-water investigations in the field can satisfactorily explain lake and stream water composition at any specific site.

Reduction of higher polymethylbenzenes by the rapid cation exchange of H-mordenite in the conversion of methanol to hydrocarbons

The product distribution in methanol conversion on mordenite is changed by potassium ion exchange depending on the method of ion exchange. The rapid exchange method was the most effective to suppress the formation of higher polymethylbenzenes.

Shape-selective disproportionation of xylene over partially cation-exchanged H-mordenite

The shape-selective disproportionation of xylene to form 1,2,4-trimethylbenzene over the partially exchanged H-mordenite catalysts by various cations has been studied. The catalysts were prepared by a conventional or rapid cation-exchange method. The shape selectivity depends on the ionic radius of exchanged cation. The most suitable ionic radius is nearly 0.096 nm. The most suitable catalyst is the H-mordenite exchanged by Cu cation. This catalyst has a high selectivity, not only because there is not enough space to form the transition state leading to 1,3,5-trimethylbenzene, but also because the diffusion of 1,3,5-trimethylbenzene is inhibited. The rapid cation exchange is more effective than the conventional one, because a smaller amount of cation controls the pore dimension and provides a high selectivity without a drop in activity.

Relation of shape and metabolism in human erythrocytes: I. Volume, ATP, and monovalent cation interdependence of cells incubated at 37°C

Erythrocytes of whole blood incubated at 37°C underwent large increases in average density and cellular hemoglobin (indicative of volume decrease) soon after depletion of ATP. Coincident were rapid exchanges of cell potassium with plasma sodium ions. The incubation time corresponding to loss of 90% or more of ATP correlated with the onset of cell contraction and rapid cation exchange. This time (approximately 45 hr) in whole blood preserved in ACD was diminished in heparinized blood or ACD blood containing fluoride, approximately the same in four units of previously frozen red cells, and extended by 15 or more hr in whole blood containing adenine, adenine + inosine, or adenine + inosine + guanosine.

Spectrophotometric Determination of Tungsten in Nuclear Materials and Steels by Extraction with 8-Quinolinol.

A spectrophotometric method for the determination of W in Zr, zircaloy, U, Be, and steels by extraction with 8quinolinol-- chloroform is described. The procedure involves the preliminary extraction of interfering Mo from hydrofluoric acid solution, addition of boric acid, and extraction of the W from the solution adjusted to pH 2.0. Interferences in the final chloroform extract are removed with ammonium sulfate-sulfuric acid washings. Large amounts of Co and V, as found in certain types of stainless steels, interfere, but these elements are removed by a rapid cation exchange separation prior to the extraction of Mo and W. Slight modifications in the procedure are necessary for the analysis of Be. Nb and Ta are among the many elements that do not interfere. The results are reproducible and the agreement with standard samples tested is good. The method is more rapid and precise than existing methods. (auth)