Metal Cations In Water Research Articles

Sensory layers of poly(methyl metacrylate) for capacitive sensors for analysis of the content of heavy metal cations in water

The results of using poly(methyl methacrylate) coatings for the development of the capacitive sensors for analyzing the content of heavy metals in water (using Ni2+ ions as example) are presented. Structural and morphological characteristics of the formed conductive nickel layer and nanostructured poly(methyl methacrylate) films were studied by atomic force microscopy. Based on the analysis of the dependence of the capacitive characteristics of the original sensor on the frequency at different concentrations of Ni2+ ions, the following operating characteristics of the sensor were established: response time – 5 min; operating range of Ni2+ ion concentrations: 1 ‧ 10–3–50 mM; lower detection limit ≈ 0,06 mg/l. It is shown that the formation of a poly(methyl methacrylate) coating on a conductive nickel layer by the spin coating method increases the service life of the sensor to eight cycles while maintaining the level of sensor sensitivity.

‘Turn-on’ fluorescence sensing of Al(III) ions in water using a simple N-hydroxy-4-amino-1,8-naphthalimide chemosensor

A simple fluorophore, N-hydroxy-4-amino-1,8-naphthalimide (Nap-OH), has been designed and used as a fluorescent “turn-on” chemosensor for sensing metal cations in water. Nap-OH exhibited solvent-dependent photophysics in different solvents and displayed high selectivity and reversible sensing ability for Al(III) ions with femtomolar (10−15 M) sensitivity. The initial emission intensity of Nap-OH was drastically enhanced upon the addition of Al(III) ions and the calculated Stern-Volmer binding constant (KSV) is 4.70 × 104 M−1. The selective sensing of Al(III) was also reflected by sharp visual color changes and further demonstrated the use of Nap-OH for sensing Al(III) in real-water samples.

Quenching of Photoluminescence of Carbon Dots by Metal Cations in Water: Estimation of Contributions of Different Mechanisms

Quenching of Photoluminescence of Carbon Dots by Metal Cations in Water: Estimation of Contributions of Different Mechanisms

A Water-Stable 3D Eu(III)-Organic Framework as a Bi-Functional Ratiometric Luminescent Sensor for Fast, Sensitive and Selective Detection of ODZ and Hg2+ in Aqueous Media

The fast, sensitive and selective detection of some antibiotics and heavy metal cations in water is highly desirable for environmental protection and human health, but it is still currently challenging. In this work, a new luminescent Eu(III)-based metal-organic framework (MOF), {[(CH3)2NH2][Eu(L)2(H2O)2]·xDMF}n (1) [H2L = 4,4’-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid], was solvothermally synthesized. Complex 1 exhibits good water stability and luminescent property and could serve as a bifunctional ratiometric luminescent sensor for fast, sensitive and selective detection of ornidazole (ODZ) and Hg2+ in aqueous solution. The corresponding luminescent mechanism has also been discussed. This work indicates that 1 as a promising luminescent material exhibits luminescent quenching behavior for ODZ and luminescent enhancement behavior for Hg2+ in H2O, which will promote the practical application of Ln-MOF-based ratiometric luminescent sensors in monitoring antibiotics and metal ions pollutants in the environmental water matrices.

Caracterización de algas recolectadas en la Baixada Santista litoral y sus posibles usos como biosorbentes de cationes de metales pesados

This work aims to characterize biosorbent materials based on seaweed present on the littoral of Baixada Santista (São Paulo state, Brazil), and test their adsorption properties to remove heavy metal cations (Co+2, Pb+2, and Cd+2) in water, aiming its future application in situ remediations degraded ecosystems. Three types of natural seaweed were studied: Sargassum sp, Ulva lactuca, and Padina sp. These biosorbents were collected, pretreated, and modified by two chemical treatments: 1) Protonation with HCl, and, 2) Oxidation with KMnO4. The preliminary results showed that the Ulva lactuca is promising for the adsorption of heavy metal cations in water, which is also very attractive due to its great availability in the ecosystem, and it is renewable. The biosorbents (natural and modified by chemical treatments) were characterized by Fourier Transform Infrared Spectroscopy (FTIR), and by Scanning Electron Microscopy (SEM). The best heavy metal removal values for the best biosorbent Ulva lactuca (after chemical treatment) were:  65 mg.g-1  for Co (II), 71 mg.g-1 for Cd(II), and 78 mg.g-1 for Pb(II).

Structure of the Nearest Environment of Na+, K+, Rb+, and Cs+ Ions in Oxygen-Containing Solvents

The review generalizes and analyzes published data on different methods of studying structural characteristics of the solvation environment of alkali metal ions (except for Li+) in various electron-donor oxygen-containing solvents. Coordination numbers of alkali metal ions, interspecies distances, and types of ion association are discussed. The solvation structures of alkali metal cations in water and some nonaqueous systems are compared. The number of solvent molecules and the distance between the cation and oxygen atom of solvent molecule in the first coordination sphere are independent of physicochemical properties of the solvent.

Classification of Metal Binders by Naïve Bayes Classifier on the Base of Molecular Fragment Descriptors and Ensemble Modeling.

Here, we report two-class classification models for organic molecules ("ligands") able to bind various metal cations in water. The modeling was performed on 30 data sets, each corresponding to a particular metal, using the Naïve Bayes method and the ISIDA fragment descriptors. The ligands were classified on weak and strong binders according to threshold of the logarithm of the stability constant of the 1 : 1 (metal : ligand) complexes. The "consensus models" consisted each of 50 best individual models demonstrated a good predictive performance in 5-fold cross validation: the balanced accuracy (BA) varies from 0.965 (Yb3+ ) to 0.767 (Mg2+ ). The best predictions (BA>0.90) were obtained for the binders of rare-earth metals (Yb3+ , Tm3+ , Er3+ , Lu3+ , Ho3+ , Gd3+ and Dy3+ ) and Pb2+ . For 17 small external test sets of new ligands, BA varies from 0.800 to 1. The impact of variables selection on the predictive performance of the models is discussed.

Ion association with tetra-n-alkylammonium cations stabilizes higher-oxidation-state neptunium dioxocations

Extended-coordination sphere interactions between dissolved metals and other ions, including electrolyte cations, are not known to perturb the electrochemical behavior of metal cations in water. Herein, we report the stabilization of higher-oxidation-state Np dioxocations in aqueous chloride solutions by hydrophobic tetra-n-alkylammonium (TAA+) cations—an effect not exerted by fully hydrated Li+ cations under similar conditions. Experimental and molecular dynamics simulation results indicate that TAA+ cations not only drive enhanced coordination of anionic Cl– ligands to NpV/VI but also associate with the resulting Np complexes via non-covalent interactions, which together decrease the electrode potential of the NpVI/NpV couple by up to 220 mV (ΔΔG = −22.2 kJ mol−1). Understanding the solvation-dependent interplay between electrolyte cations and metal–oxo species opens an avenue for controlling the formation and redox properties of metal complexes in solution. It also provides valuable mechanistic insights into actinide separation processes that widely use quaternary ammonium cations as extractants or in room temperature ionic liquids.

Extraction of chloride acido complexes of triply charged metal cations in water–oxyethylated nonylphenol–salting-out agent systems

The characteristic features of extraction of chloride acido complexes of iron(III), thallium(III), indium, and gallium in water–oxyethylated nonylphenol (neonol AF-9-12)–salting-out agent systems are studied. The role of temperature, nature of the salting-out agent, and its salting-out ability is shown.

Neutral glycoconjugated amide-based calix[4]arenes: complexation of alkali metal cations in water.

Cation complexation in water presents a unique challenge in calixarene chemistry, mostly due to the fact that a vast majority of calixarene-based cation receptors is not soluble in water or their solubility has been achieved by introducing functionalities capable of (de)protonation. Such an approach inevitably involves the presence of counterions which compete with target cations for the calixarene binding site, and also rather often requires the use of ion-containing buffer solutions in order to control the pH. Herein we devised a new strategy towards the solution of this problem, based on introducing carbohydrate units at the lower or upper rim of calix[4]arenes which comprise efficient cation binding sites. In this context, we prepared neutral, water-soluble receptors with secondary or tertiary amide coordinating groups, and studied their complexation with alkali metal cations in aqueous and methanol (for the comparison purpose) solutions. Complexation thermodynamics was quantitatively characterized by UV spectrometry and isothermal titration calorimetry, revealing that one of the prepared tertiary amide derivatives is capable of remarkably efficient (log K ≈ 5) and selective binding of sodium cations among alkali metal cations in water. Given the ease of the synthetic procedure used, and thus the variety of accessible analogues, this study can serve as a platform for the development of reagents for diverse purposes in aqueous media.

Metal-organic framework as an efficient filter for the removal of heavy metal cations in water.

Heavy metal ions from water and wastewater are non-biodegradable and tend to accumulate in the soil and living organisms, polluting the environment and causing serious health hazards in humans. Therefore, effective treatment of heavy metal ions in aqueous media is critical for public health and environmental sustainability. In this paper, we employ molecular dynamics simulations to investigate the removal efficiency of heavy metal cations (Cd2+, Hg2+, and Pb2+) by a zirconium phosphonate based metal-organic framework (MOF) filter and also to explore its underlying molecular mechanism. Our results show that the inherently porous MOF filter shows a superior efficiency (>95%) in the removal of heavy metal cations under a wide range of pressures (50 to 350 MPa). This superior efficiency is achieved by absorption and blockage of these cations within MOF filters via two distinct binding patterns, "loose mode" with water molecules as a mediator, and ''tight mode'' without any mediating molecules. These findings provide new insight for applying the MOF nanopores as potential filters in the removal of hazardous heavy metal cations in the environment.

Selective and Sensitive Chromogenic Detection of Trivalent Metal Cations in Water

Abstract An azopyridine derivative for the selective and sensitive chromogenic detection of trivalent metal cations in water is described.

Separation and quantification of quantum dots and dissolved metal cations by size exclusion chromatography–ICP-MS

ABSTRACTThe prevalence of engineered metallic nanoparticles within electronic products has evoked a need to assess their occurrence and fate within environmental systems upon potential release of these nanoparticles. Quantum dots (QDs) are mixed-metal nanocrystals with the smallest of particle sizes (2–10 nm) that readily leach heavy metal cations in water, potentially creating a co-occurrence of nanoparticulate and dissolved metal pollutants. In this report, we develop a size exclusion chromatography–inductively coupled plasma–mass spectrometry method (SEC-ICP-MS) for the rapid separation and quantification of ~5-nm-sized CdSe/ZnS QDs and dissolved Cd2+ and Zn2+ cations in water. The SEC-ICP-MS method provided a wide chromatographic separation of CdSe/ZnS QDs and dissolved Cd2+ and Zn2+ cations only when using the smallest SEC column pore size available and an eluent composition that prevented loss of metals to column polymer surfaces by using a surfactant to ensure elution of QDs (ammonium lauryl sulfate) and a complexing ligand to ensure elution of metal cations (ethylenediaminetetraacetate). Detection limits were between 0.2 and 2 µg L–1 for Cd2+ and Zn2+ among dissolved cation and QD phases, and ranges of linearity covered two to three orders of magnitude. Gold nanoparticles of sizes 5, 10, 20 and 50 nm were also effectively separated from dissolved Au3+ cations, illustrating the method applicability to a wide range of nanoparticle sizes and compositions. QD and dissolved metal concentrations measured by SEC-ICP-MS were comparable to those measured using the more conventional method of centrifuge ultrafiltration on split samples for dissolved and total metals. The applicability of the SEC-ICP-MS method to environmental systems was verified by measuring QDs and dissolved metals added to samples of natural waters. The method was also applied to monitoring CdSe/ZnS dissolution kinetics in an urban river water. The SEC-ICP-MS developed here may offer improved automation for characterising heterogeneous suspensions containing >1 µg L–1 heavy metals.

Elucidating the mechanism behind the stabilization of multi-charged metal cations in water: a case study of the electronic states of microhydrated Mg2+, Ca2+ and Al3+

Metal atoms typically have second and higher ionization potentials (IPs) that are larger than the IP of water, resulting in the Coulombic explosion of the first few [M(H2O)n](+q) (q≥ 2) gas phase clusters as the M(+(q-1)) + (H2O)n(+) or MOH(+(q-1)) + H3O(+)(H2O)n-2 energy levels are energetically more stable than the M(q+) + (H2O)n ones for small n. We present a theoretical analysis of the various electronic states arising from the sequential hydration of the Ca(2+), Mg(2+) and Al(3+) cations with up to six water molecules. Our results quantify the relative shift of those electronic states with the degree of solvation, identify their complex interaction with other states arising from different dissociation channels and shed light on the mechanism behind the energetic stabilization of the multi-charged hydrated M(+q)(H2O)n complexes observed in aqueous solution with respect to the water ionization products.

Molecular dynamics simulation study for ion mobility of alkali earth metal cations in water at 25°C

We present the results of molecular dynamics simulations for alkali earth metal cations (Mg2+, Ca2+, Sr2+ and Ba2+) in an aqueous solution at 25°C using the extended simple point charge water potential with Ewald summation. The ion mobilities (defined by ui = DiziF/RT) obtained from the simulations are in good accord with the experimental measures. The strong divalent cation–water interactions explain well the static and dynamic properties of the alkali earth metal cations. The classical solvent-berg picture describes the ion mobilities of these cations in water adequately.

Mechanism for Different Fluorescence Response of a Coumarin–Amide–Dipicolylamine Linkage to Zn(II) and Cd(II) in Water

A coumarin-amide-dipicolylamine linkage (L) was synthesized and used as a fluorescent receptor for metal cations in water. The receptor dissolved in water with neutral pH shows almost no fluorescence due to the photoinduced electron transfer (PET) from the amide and amine nitrogens to the excited state coumarin moiety. Coordination of Zn(2+) or Cd(2+) with L creates strong fluorescence at 437 or 386 nm, respectively, due to the suppression of PET. In contrast, other metal cations scarcely show fluorescence enhancement. IR, NMR, and potentiometric analysis revealed that both Zn(2+) and Cd(2+) are coordinated with two pyridine N, amine N, and amide O; however, the Zn(2+) center is also coordinated with a hydroxide anion (OH(-)). The structure difference for Zn and Cd complexes results in longer- and shorter-wavelength fluorescence. Ab initio calculations revealed that π electrons on the excited state Cd complex are delocalized over the molecules and the Cd complex shows shorter-wavelength emission. In contrast, π electrons of OH(-)-coordinated Zn complex are localized on the coumarin moiety. This increases the electron density of coumarin moiety and shows longer-wavelength fluorescence.

Rhodamine‐labeled Sensor Bead as a Colorimetric and Fluorometric Dual Assay for Hg2+Ions in Water

AbstractRhodamine‐based receptor1recognizes Hg2+and Cu2+ions in aqueous CH3CN, but when immobilized onto Merrifield resin to give bead2, this sensor system selectively detects Hg2+ions over a series of other metal cations in water. The detection can be performed colorimetrically and fluorimetrically. The ensemble of2–Hg2+can also distinguishdl‐homocysteine fromL‐cysteine in water by both analytical methods.

Molecular Simulations of Carbon Dioxide and Water: Cation Solvation

Proposed carbon dioxide sequestration scenarios in sedimentary reservoirs require investigation into the interactions between supercritical carbon dioxide, brines, and the mineral phases found in the basin and overlying caprock. Molecular simulations can help to understand the partitioning of metal cations between aqueous solutions and supercritical carbon dioxide where limited experimental data exist. In this effort, we used classical molecular dynamics simulations to compare the solvation of alkali and alkaline-earth metal cations in water and liquid CO(2) at 300 K by combining a flexible simple point charge model for water and an accurate flexible force field for CO(2). Solvation energies for these cations are larger in water than in carbon dioxide, suggesting that they will partition preferentially into water. In both aqueous and CO(2) solutions, the solvation energies decrease with cation size and increase with cation charge. However, changes in solvation energy with ionic radii are smaller in CO(2) than in water suggesting that the partitioning of cations into CO(2) will increase with ion size. Simulations of the interface between aqueous solution and supercritical CO(2) support this suggestion in that some large cations (e.g., Cs(+) and K(+)) partition into the CO(2) phase, often with a partial solvation sphere of water molecules.

Novel Analysis of Cation Solvation Using a Graph Theoretic Approach

A new method for analyzing molecular dynamics simulation data is employed to study the solvent shell structure and exchange processes of mono-, di-, and trivalent metal cations in water. The instantaneous coordination environment is characterized in terms of the coordinating waters' H-bonding network, orientations, mean residence times, and the polyhedral configuration. The graph-theory-based algorithm provides a rapid frame-by-frame identification of polyhedra and reveals fluctuations in the solvation shell shape--previously unexplored dynamic behavior that in many cases can be associated with the exchange reactions of water between the first and second solvation shells. Extended solvation structure is also analyzed graphically, revealing details of the hydrogen bonding network that have practical implications for connecting molecular dynamics data to ab initio cluster calculations. Although the individual analyses of water orientation, residence time, etc., are commonplace in the literature, their combination with graphical algorithms is new and provides added chemical insight.

What first principles molecular dynamics can tell us about EXAFS spectroscopy of radioactive heavy metal cations in water

Abstract In this paper we show how molecular dynamics simulation can improve comprehension of structure and dynamics of water solvent around heavy cations. In particular, metal-water radial distribution function obtained from molecular dynamics can be used into EXAFS equation to improve the experimental signal fitting. Here we show results on structure and dynamics of Co2+, that is a radiocontaminant cation in its isotopic form 60Co, and lanthanoids(III) that are the chemical analogues of actinides(III) in aqueous solution.