Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H₂SO₄ (concentrations: 0·5 mol dm^?3 and 2·5 mol dm^?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (X_m) and the apparent equilibrium constants (K_a) of the samples; X_m and K_a values range respectively for 4·11 mg g^?1 and 1·90 dm³ g^?1 for the sample acid-treated with 2·5 mol dm^?3 H₂SO₄ [(B)-A(2·5)] up to 16·50 mg g^?1 and 30·67 dm³ g^?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g^?1 and 0·07 dm³ g^?1, also for B-A(2·5), up to 4·54 mg g^?1 and 0·45 dm³ g^?1 [B-N-200], for the adsorption process of zinc. X_m and K_a values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.     

The interaction of alkaline earth cations with metal-oxygen cluster compounds and the implications for their use as heterogeneous catalysts

The magnesium, calcium, strontium and barium salts of 12-tungstophosphoric and 12-molybdophosphoric acids have been prepared. Evidence of the presence of the Keggin anion (primary structure) was obtained from infrared spectroscopic measurements but powder X-ray diffraction and differential thermal analysis measurements indicated that changes to the secondary structure had occurred. BET surface areas were small for all of the materials studied and no dependence on the cation radius was observed. A crystallographic investigation demonstrated that divalent cations were not incorporated into the lattice suggesting that materials believed to be divalent 12-heteropoly salts are mixtures of the parent acid and a divalent cation salt.     

Synthesis and properties of new side-chain-type poly(arylene ether sulfone)s containing tri-imidazole cations as anion-exchange membranes

In order to enhance the properties of polymer anion-exchange membranes (AEMs), a class of side-chain-type poly (arylene ether sulfone)s containing tri-imidazole cations in pendant phenoxyphenyl spacer (i.e., Im-PES-xx) were designed and prepared by polymer grafting reaction. Based on these imidazole functionalized polymers, a series of new AEMs were successfully prepared by their solution coating and ion exchange. The obtained membranes exhibited good alkaline stability with the retention of ion-exchange capacity in the range of 78.5%–83.3% after immersion in 4 M NaOH solution at 80 °C for 336 h. The membranes also had high hydroxide conductivity with the values of 34.1–70.5 mS cm^?1 at 80 °C. Meanwhile, these membranes possessed good dimensional stability, and their swelling ratio was in the range of 2.5%–7.0% at 80 °C. The incorporation of the dense and local imidazole cations in the side chains for AEMs plays an important role for their properties.     

Gelling Properties of Gellan Solutions Containing Monovalent and Divalent Cations

Gelling temperatures of gellan solutions with the addition of Na⁺ and K⁺ ranging from 15 to 450 mM or Ca⁺⁺ and Mg⁺⁺ from 2 to 40 mM were determined by dynamic rheological testing at four polymer concentrations between 0.4 and 2.0% (w/w). Gelling temperatures were much higher for gellan solutions containing divalent cations than for those containing the same amount of monovalent cations. Solutions containing K⁺ gelled at higher temperatures than those containing Na⁺. Effects of Ca⁺⁺ and Mg⁺⁺ on gelling temperatures were not significantly different. A general model was developed to predict the gelling temperature of gellan solutions as functions of cation and polymer concentrations.     

Density functional theory study of hydroxide-ion induced degradation of imidazolium cations

The imidazolium cation degrades in accordance with a three-step degradation mechanism under alkaline conditions. This mechanism usually includes a nucleophilic reaction, a ring-opening reaction, and a rearrangement reaction. In this study, we have further ascertained the degradation mechanism of a α-C methyl substituted imidazolium cation (trimethylimidazolium, TMIM), and of three α-C unsubstituted imidazolium cations (dimethylimidazolium, DMIM, 1 – benzyl-3 – methyl imidazole, BeMIM, and 1-butyl-3 – methylimidazolium, BMIM) using density functional theory (DFT). For these four Imidazolium cations, the activation energies of the nucleophilic reaction and the ring-opening reaction were calculated, along with the lowest unoccupied molecular orbital (LUMO) energy. The results obtained revealed that under alkaline conditions, the α-C methyl substituted imidazolium cation (TMIM) was more stable than the α-C unsubstituted imidazolium cations (DMIM, BeMIM, and BMIM) due to the hyper-conjugation between the methyl group at the α-C and the imidazole ring, and due to the stearic effect of the methyl group. The activation energies for the nucleophilic reaction and the ring-opening reaction for TMIM were 57.1 and 107.6 kJ/mol respectively, and its LUMO energy was −1.013 eV.     

Fertilization of sugar maple showing dieback symptoms in the Quebec Appalachians,Canada

A research project on foliar and soil chemistry in declining sugar maple (Acer Saccharum, Marsh) stands was carried out in the Beauce-Mégantic region of southern Quebec. Foliar nutrient concentrations in declining stands were low in P, K, and in some cases, Ca and Mg. Fertilizers and liming materials containing Ca, Mg, and K were applied in 1987. Foliar and soil nutrient levels of base cations were increased as a result of treatment and visual evaluation of tree health indicated an improvement. Data are also presented on the number of samples required to obtain a statistically significant change in foliar and soil chemistry in response to fertilization.     

Synthetic ionophores for the separation of Li, Na, K, Ca, Mg metal ions using liquid membrane technology

Carrier-assisted transport through liquid membranes is one of the important applications of supramolecular chemistry. This work investigates the use of synthetic carrier (ionophore) for the separation of metal ions. We have tested the effect of structure of ionophore on the separation of metal ions. For this purpose, we have used a new series of non-cyclic ionophores having different end groups and chain length (R₁–R₅). 1,5 bis (2-naphthyloxy)-3-oxapentane (R₁), 1,8 bis (2-naphthyloxy)-3,6-di-oxaoctane (R₂), 1,11 bis (2-naphthyloxy)-3,6,9-tri-oxaundecane (R₃) 1,11-(dianthraquinonyloxy) 3,6,9-trioxaundecane (R₄), 1,8 (dianthraquinonyloxy) 3, 6-dioxaoctane (R₅) have been used in extraction, bulk liquid membrane (BLM) and supported liquid membrane (SLM) transport of alkali (Li⁺, Na⁺, K⁺) and alkaline earth metal cations (Ca²⁺, Mg²⁺). The supported liquid membrane consisted of a porous cellulose nitrate and and an onion membrane support impregnated with ionophore using chloroform as a solvent. The results reveal that ionophores R₁, R₂ and R₃ are better extractants for K⁺ while R₄ and R₅ are better extractants for Ca²⁺. Among these ionophores R₃ and R₄ are best extractants for K⁺ and Ca²⁺ ions. The results of BLM reveal that ionophores R₁, R₂ and R₃ transport Na⁺ at a greater extent, while R₄ and R₅ transport Ca²⁺ and K⁺ at a greater extent. In SLM experiments using a cellulose nitrate membrane support, it was observed that naphthyl end group bearing ionophores (R₁–R₃) transports Na⁺ > K⁺, and anthraquinone bearing ionophores (R₄ and R₅) transport K⁺ > Na⁺ > Ca²⁺ respectively. In the onion membrane support R₄ transports Ca²⁺ and Na⁺ equally and R₅ transports K⁺ selectively. On comparing the membrane support, the cellulose nitrate membrane is found better support for the transport of metal ions. The results suggest that due to the presence of different end groups and chain lengths the selectivity of non-cyclic ionophores towards metal ions is enhanced. Thus selectivity of ionophores may have fruitful application in ion selective electrodes and separation of metal ions.     

Effects of alkaline cations （M^＋ = Li^＋, Na^＋, K^＋, Cs^＋） on the electrochemical synthesis of polyaniline in nitric acid electrolyte

The effects of alkaline cations （M^＋ = Li^＋, Na^＋, K^＋, Cs^＋）on the electrochemical synthesis of polyaniline were carfled out under cyclovoltammetric conditions using nitrates of Li^＋, Na^＋, K^＋, and Cs^＋ as the supporting electrolytes. The results show that the oxidation potentials of aniline in the electrolytes decrease as the protonation extent of aniline decreases from the fast scan, which is caused by the decrease of the ionic radius of alkaline metal ions at the same concentration of alkaline cations. With the scan number increasing, the deposit charge Q as the characteristic growth function also depends on the protonation of aniline, and it increases with the ionic radius of alkaline cations increasing. SEM images show the effect of alkaline cations on the morphology of polyaniline. It is clear that the ionic mobility of alkaline cations is further lower than that of W. Alkaline cations and counter-ions were the species responsible for the enhancement of Pani electrosynthesis. Therefore, this is exactly what SEM images show： a relatively rough fibrous structure in the case of Pani-H^＋ suggesting a sponge-like structure and a highly orderly fiber-like structure in the case of Pani-M^＋.     

A mesoporous silica supported Hg2+ chemodosimeter

A chemical reaction type chemodosimeter immobilized on mesoporous silica materials ( CFMS ) was reported and showed fluorescent ratiometric, colorimetric, and even naked‐eye recognizable manner with a detection limit of ～2 μM for mercury (II). The characterization of CFMS indicated that the ordered mesoporous structure was well preserved after the immobilization. It was found that only the addition of Hg²⁺ resulted in significant color change and large fluorescence spectral shift whereas other cations didn't induce any color or emission change. In addition, CFMS was also coated as films onto glass substrates. When aqueous Hg²⁺ rapidly passed through the glass substrate, the green emission of supported CFMS became blue under a 365 nm lamp. These considerable signal changes, easy‐to‐prepare materials, and simple‐to‐operate technique suggested the potential application of CFMS for fluorescent ratiometric detection of Hg²⁺ ion in the practical environmental field. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Effect of Crown Ethers on Sr2+, Ba2+, and Ra2+ Uptake by Tunnel‐Structure Ion Exchangers

Abstract

The effect of 15‐crown‐5 and 18‐crown‐6 ethers on the uptake of alkaline earth cations by tunnel‐structure ion exchangers polyantimonic acid (PAA) and cryptomelane manganese dioxide (CMD) was examined. In the case of PAA, 15‐crown‐5 and especially 18‐crown‐6 strongly influence the uptake of Sr²⁺ vs Ba²⁺ and Ra²⁺. For separation of the Ra²⁺‐Ba²⁺ pair, the effect of the crown ethers is insignificant. In CMD a small difference in complex formation between crown ethers and Ba²⁺ and Ra²⁺ gives an increase of separation. This effect is observed especially in 15‐crown‐5 solutions.