Novel method of preparing Ag–Hg alloy on polyacrylamide films and their structure

A novel method is proposed of preparing thin Ag–Hg alloy on PAAm film surface at room temperature: The film of interest is formed by holding PAAm aqueous solution with AgNO₃ in Hg-saturated atmosphere. Two kinds of films, one of which is a conductor and the other an insulator, can be selectively formed with pH-controlled PAAm solution by ammonia. The conducting surface is assigned to the α phase of Ag–Hg alloy by means of X-ray analysis. Potentiometric titration and IR spectral studies suggest the existence of PAAm–Ag⁺ complexes. On the basis of their structure and the oxidation and reduction potential of Ag⁺ and Hg²⁺, the mechanism of film formation is also discussed.     

Enhancement of uranyl ion uptake by prestructuring of acrylamide–maleic acid hydrogels

Acrylamide–maleic acid (AAm–MA) hydrogels were prepared by gamma‐irradiation of their aqueous solutions. UO₂⁺² ion uptake on P(AAm–MA) hydrogels was investigated using two types of gel systems prepared by a simple irradiation method and a prestructured reaction. It has been observed that gels prestructured with UO₂⁺² ions adsorbed approximately 15–20% more UO₂⁺² ions than gels prepared in pure water (the usual method). It was also found that the uranyl ion adsorption capacity of hydrogels increased with an increasing amount of maleic acid in the gel system and an increasing concentration of uranyl ion in the solution. A possible interaction mechanism between the groups in the copolymeric gels and UO₂⁺² ion has been proposed based on the stoichiometry and the spectroscopic evidence. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 284–289, 2000     

Preparation and properties of macromolecular complexes consisting of [2-(diethylamino)ethyl]dextran hydrochloride and potassium metaphosphate

In aqueous solution [2-(diethylamino)ethyl]dextran hydrochloride (EA) was reacted with potassium metaphosphate (MPK) to form a series of water-insoluble macromolecular complexes (MC) at different hydrogen-ion concentrations (EA–MPK system). EA was also reacted with MPK in the presence of CaCl₂ (EA–MPK–CaCl₂ system). The structure and properties of MC obtained were compared with each other; elemental analysis, IR spectroscopy, solubilities, thermogravimetric analysis, and scanning electron microscopy were used to characterize these complexes. The molecular structure and properties of each MC were dependent on the hydrogen-ion concentration and whether the Ca²⁺ ion coexisted. It was suggested that MC prepared at acidic pH were composed of a relatively loose network including a small quantity of MPK, whereas those prepared at neutral and alkaline pH were composed of a relatively tight network including a large quantity of MPK. This seemed to be due to changes in the degree of dissociation and the conformation of EA and MPK with the hydrogen-ion concentration. MC in the EA–MPK–CaCl₂ system were supposed to have a rather tightly bound network structure due to the Ca²⁺ ion as compared with those in the EA–MPK system. © 1993 John Wiley & Sons, Inc.     

Ligating behavior and metal uptake of N‐sulphonylpolyamine chelating resins anchored on polystyrene‐divinylbenzene beads

Amberlite XAD‐2 has been functionalized by coupling through –SO₂‐with ethylenediamine, propylenediamine, and diethylenetriamine to give the corresponding polyamine chelating resins I–III. The solid metallopolymer complexes of the synthesized chelating resins with Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ were synthesized. The polyamine derivatives and their metal complexes were characterized by elemental analysis, spectral (IR, UV/V, and ESR), and magnetic studies. The batch equilibrium method was utilized for using the chelating polyamines for the removal of Cu⁺², Zn⁺², Cd⁺², and Pb⁺² ions from aqueous solutions at different pH values and different shaking times at room temperature. The selective extraction of Cu⁺² from a mixture of the four metal ions and the metal capacities of the chelating resins were evaluated using atomic absorption spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1839–1846, 2005     

Ejection of Clusters from Liquid Beam Surface by IR Laser Irradiation

A continuous liquid flow of an aqueous solution of phenol (Phe) in a vacuum (a liquid beam) was irradiated with an IR laser at 2.85 μm, which is resonant to the vibrational absorption band of the liquid water. The Phe (H₂O)_N, ejected from the liquid beam surface into the gas phase, was ionized by a UV laser at 270 nm into hydrated phenol cluster ions, Phe⁺ (H₂O)_n (n = 0 − 30), and analyzed by a time-of-flight mass spectrometer. The velocity distributions of the product cluster ions were derived from the spatial distributions measured at different elapsed times after the IR laser irradiation. The results and the analysis show that dense neutral clusters are ejected from surface regions locally heated by the intense IR laser.     

Thioether‐Functionalized Corn Oil Biosorbents for the Removal of Mercury and Silver Ions from Aqueous Solutions

Heavy‐metal contamination is one of the most important environmental problems faced in the world, particularly in developing countries. Metals such as silver and mercury from drinking water, food, and air sources can accumulate in living organisms and present significant health concerns. Meanwhile, the demand for these metals in many industries continues to increase. In the present study, thioether‐functionalized corn oil (TFCO) from a photoinitiated thiol‐ene synthesis was utilized to remove Ag⁺ and Hg²⁺ ions from an aqueous solution. An aqueous solution containing AgNO₃ and Hg[NO₃]₂ was prepared and contacted directly with TFCO. After vortex mixing for 60 s, the experiment ran for 351 min with the aqueous phase being periodically sampled for the analysis of metal ions (M ⁿ⁺). Results showed that 88.9% of Ag⁺ and 99.6% of Hg²⁺ ions were removed from the aqueous phase by the TFCO. Mass balances indicated that the total M ⁿ⁺ concentration in the oil phase was 13.890 g kg^?1 under the conditions studied. TFCO exhibited higher selectivity for removing Hg²⁺ than for Ag⁺ ions. Analysis of the adsorption kinetics showed that a pseudosecond‐order model may be used to determine the rate of Ag⁺ ion sorption by the oil phase. The presence of the Hg²⁺ ions interfered with the adsorption of Ag⁺ ions from the aqueous solution.     

IR spectroscopic investigation of interaction between sodium aluminosilicate electrode glasses and aqueous solutions

The effect of introduction of aluminum oxide into the composition of sodium silicate glasses has been studied by IR absorption and reflection spectroscopy. The change in the spectroscopic characteristics of glasses after their treatment with HNO₃ and AgNO₃ aqueous solutions is analyzed. The concentration profiles of Na₊ and Ag₊ ions in the surface layers of these glasses are determined by the HF-sectioning technique. It is found that silver ions predominantly interact with the [AlO_4/2]^- groups in the glass. The leaching of sodium ions, formation of amorphous silica in the surface layers of the treated glass samples, and exchange of sodium ions by hydrogen ions are revealed from changes in the spectra.     

Evaluation of solvated radii of ions in non-aqueous solvents

In addition to the solvents reported in the previous paper, the empirically modified form of the Stokes' law as proposed from this laboratory has been found to be applicable for Et₄N⁺ ion in some more non-aqueous solvents. By the use of such a modified equation the ionic radii for Me₄N⁺, Pr₄N⁺ and Bu₄N⁺ ions in solution of various non-aqueous solvents have been calculated. These values of ionic radii in solution show that Me₄N⁺ ion is solvated by most of the non-aqueous solvents while Pr₄N⁺ and Bu₄N⁺ ions possess ionic radii in solution, which in most of the solvents agree well with the corresponding crystallographic radii estimated by Coetzee and Cunningham from Fisher—Taylor—Hirschfelder models.     

IR spectroscopic investigation of interaction between sodium aluminosilicate electrode glasses and aqueous solutions

The effect of introduction of aluminum oxide into the composition of sodium silicate glasses has been studied by IR absorption and reflection spectroscopy. The change in the spectroscopic characteristics of glasses after their treatment with HNO₃ and AgNO₃ aqueous solutions is analyzed. The concentration profiles of Na₊ and Ag₊ ions in the surface layers of these glasses are determined by the HF-sectioning technique. It is found that silver ions predominantly interact with the [AlO_4/2]^- groups in the glass. The leaching of sodium ions, formation of amorphous silica in the surface layers of the treated glass samples, and exchange of sodium ions by hydrogen ions are revealed from changes in the spectra.     

Production of macroporous resins for heavy‐metal removal. I. Nonfunctionalized polymers

The aim of this work was the synthesis of macroporous resins with large specific surface areas through the use of organic solvents (known as porogens or pore‐forming agents) for applications in hexavalent chromium (Cr⁺⁶) removal operations. The synthesis of these materials by suspension polymerization allowed the generation of macroporous structures. The comonomers 4‐vinylpyridine and divinylbenzene were considered in different ratios. Poly(vinyl alcohol) was used as a suspension agent in a mixture of toluene and hexane. The materials produced were characterized with Fourier transform infrared spectroscopy, elemental analysis, thermogravimetry, nitrogen adsorption, and scanning electron microscopy. The macroporous resin with the largest surface area (130 m²/g) was thermally stable up to 300°C and had a structure that included spherical domains with a mean diameter of 68 μm, uniform porosity, and expected high sorption capability. The sorption properties of the resins were evaluated for applications in water‐treatment operations to eliminate Cr⁺⁶ ions at a pH near 7. The advantages of these materials were their high removal capability, high selectivity, and fast adsorption kinetics at a pH 6.5. An aqueous solution of 4 ppm K₂Cr₂O₇ was used to quantify the Cr⁺⁶ content by ultraviolet–visible spectroscopy. A remarkable sorption level (94%) of chromate ions (Cr⁺⁶) was obtained during a 15‐h period for the resin with the highest pyridine group content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Ammonia Removal from Aqueous Solutions by Iranian Natural Zeolite

Abstract

The capability of Iranian natural clinoptilolite for ammonia removal from aqueous solutions has been thoroughly studied. Both batch and continuous (column) experiments were carried out. The viability of this natural zeolite in reducing the leakage of ammonia to the environment through waste water streams was a main focus of this research. Through the batch experiments, the effect of process variables such as the size of zeolite particles, pH, and ammonia concentration of the feed solution on the kinetics of ammonia uptake were investigated. Ammonia removal occurred rapidly and within the first 15 minutes of contact time, a major part of ammonia was removed from the solution. An adsorption capacity about 17.8 mg NH₄ ⁺/g zeolite at feed ammonia concentration of 50 mg/L was obtained and the optimum range for pH was achieved about 5.5–7.6. The adsorption capacity of clinoptilolite in the continuous mode was about 15.16 and 15.36 mg NH₄ ⁺/g zeolite for the original and regenerated types of clinoptilolite, respectively, where feed ammonium concentration was 50 mg/L. Increasing the feed ammonium concentration to 100 mg/L did not reduce the capability of the column for its ammonium removal and up to a bed volume (BV) of 85, there was only less than 1 mg/L ammonium in the column outlet. Presence of cations such as Ca²⁺, Mg²⁺ and Na⁺ in the feed solution reduced the clinoptilolite adsorption capacity to about 11.68 mg NH₄ ⁺/g zeolite. Regeneration experiments were carried out using concentrated sodium chloride solutions, as well as tap water. Where tap water was used as the regenerant, gradual release of ammonium from exhausted clinoptilolite was observed.     

Dipolar polymeric compounds and their properties in the aqueous medium

Reactions between poly(4-vinylpyridine) and acrylic acid as well as poly(vinylimidazole) and the same acid led to polymers containing carboxybetaine repeating units with a percentage higher than 90%. Chemical structures and compositions of chemically modified polymers were established from their ¹H NMR and IR spectra. The solution properties of the two poly(carboxybetaines) were analyzed by potentiometric titrations and viscometric measurements. Deionized water as well as CaCl₂ and NaCl aqueous solutions of different concentrations were used as solvents. From potentiometric titrations with 0.5 M HCl, the apparent pK_a values were determined using Henderson–Hasselbach equation. These values are strongly depended of the solvent nature. Thus, both poly(carboxybetaines) have the lowest pK_a values when deionized water was used as solvent. Therefore, the lowest binding ability of the H⁺ by COO⁻ groups occurs in this solvent.The viscometric measurements revealed that reduced viscosity values are non-responsive towards the polymer solution concentrations irrespective of the used solvent (i.e., deionized water or NaCl and CaCl₂ aqueous solutions). Therefore, the behaviour of these carboxybetaine macromolecules in the above-mentioned solvents is that of hung up hard spheres. Consequently, the intrinsic viscosity values were calculated according to the Einstein–Simha equation applicable for such systems. The [η] versus salt solution concentration plots show a decreasing part in the concentration range from 0 to 0.05 M that is followed by a slow [η] increasing.In 0.5 M HCl both poly(carboxybetaines) exhibit the viscometric polyelectrolyte behaviours because of their shift to the corresponding cationic polyelectrolytes.     

Synthesis and Mechanism of Spherical Ag-doped Polypyrrole Assisted by Complexing Agents

Highly dispersed Ag-doped Polypyrrole (PPy) spherical composites can be efficiently synthesized via oxidative polymerization of pyrrole with FeCl₃ in an aqueous Ag⁺-containing solution in the presence of trisodium citrate, followed by concentrated ammonia treatment. However, the formation mechanisms involved in how to control the shape and how to get the metallic Ag⁰ need further investigation. In order to elucidate the formation mechanisms, the intermediates in different reaction stage were collected and investigated. Combining the experimental phenomenon and the structure characterization of the samples, it was found that citrate ions make a role of complexing Ag⁺ to produce [Ag₃(C₆H₅O₇)_n+1]^3n? complexes in the early reaction stage, then mainly play a role of steric stabilizer of AgCl micelles and are responsible for the shape tailoring of PPy composite as well as the reduction of Ag⁺ in the process of ammonia treatment. Evidently, negative-charged AgCl micelles become the main nucleation sites of pyrrole polymerization through the electrostatic attraction between the negative and positive ions. Concentrated ammonia is adopted to eliminate AgCl cores from the precursor of Ag-doped PPy composites obtained by chemical redox reaction and provides an accelerated reaction condition for reduction of Ag⁺ by reductants (citrate ion or pyrrole monomer). Ag-containing micelles induction method is a facial chemical method to obtain uniform Ag-doped composites and can be broadened to design other Ag-containing functional materials.

     

Synthesis of Eu-doped gahnite in water and water–ammoniac fluids

The effect of ammonia contained in water fluid on the synthesis and properties of gahnite (ZnAl₂O₄) doped with (0.4–4 mol%) europium was investigated. Gahnite synthesized in water–ammoniac fluid has a smaller crystal size than does the one synthesized in water fluid, and bound nitrogen is detected in its structure. However, europium ions more effectively incorporate into the structure of nascent gahnite during synthesis in water fluid and generate formation there of complexes with oxygen vacancies. The excitation efficiency of luminescence of Eu³⁺ ions in the absorption band of oxygen vacancies in gahnite increases with the concentration of Eu³⁺. After annealing in air of gahnite samples synthesized in fluids of various compositions, the changes of Eu³⁺ ions luminescence differ. We conclude that ammonia not only participates in the processes of gahnite formation, causing an increased nucleation rate but it also remains in the gahnite structure.     

Thermodynamics of transfer of p-nitroaniline from water to aqueous 2-methoxyethanol mixtures and the solvent effect on the dissociation of the protonated base

Free energies (ΔG⁰_t), entropies (ΔS⁰_t), and enthalpies of transfer of the nonelectrolyte p-nitroaniline from water to aqueous mixtures of 2-methoxyethanol have been determined from solubility measurements at different temperatures. The results for ΔG⁰_t have been ascribed chiefly to dispersion interactions between the aromatic nucleus and the hydrocarbon moieties of the solvent mixtures. The observed pronounced maxima in ΔS⁰_t-composition profiles have been attributed to the promotion of the water structure brought about by these solvents. Furthermore, the solvent effects have been discussed in terms of the free energies of transfer (ΔG⁰_t) from water to the aqueous 2-methoxyethanol solvents, of the three species B, BH⁺, and H⁺ participating in the equilibrium. Finally, the chemical free energies of transfer, ΔG⁰_t,ch of BH⁺ and H⁺ were evaluated using Hepler's method, and the results have been interpreted in terms of specific ion—solvent interactions.     

Redox chemistry of highly dispersed rhodium in zeolite NaY

NaY zeolite exchanged with [Rh(NH₃)₅Cl]²⁺ ions have been studied using temperature programmed oxidation (TPO), temperature programmed reduction (TPR), and Fourier transformed infrared spectroscopy. The TPO profiles show that ammine ligands in NaY encaged [Rh(NH₃)₅Cl]²⁺ are destroyed above 300 °C, whereas the Rh precursor ion remains intact after calcination at 200 °C. TPR profiles in conjunction with the CO_ads IR spectra show that the reducibility of Rh by H₂ is largely controlled by the concentration of the surface protons, i.e. Rh³⁺+H₂Rh⁺+2H⁺ Rh⁺ + 1/2H₂Rh⁰+H⁺ In the presence of ammonia, the protons are neutralized and Rh³⁺ is reduced to Rh⁰. However, reduction remains incomplete when the concentration of protons is high. The ammonia was provided either by NH₃ admission or by conservation of ammine ligands by controlled calcination. CO adsorption does not lead to reoxidation of Rh⁰ particles to Rh⁺ ions.     

High Diffusion Permeability of Anion-Exchange Membranes for Ammonium Chloride: Experiment and Modeling

It is known that ammonium has a higher permeability through anion exchange and bipolar membranes compared to K⁺ cation that has the same mobility in water. However, the mechanism of this high permeability is not clear enough. In this study, we develop a mathematical model based on the Nernst–Planck and Poisson’s equations for the diffusion of ammonium chloride through an anion-exchange membrane; proton-exchange reactions between ammonium, water and ammonia are taken into account. It is assumed that ammonium, chloride and OH⁻ ions can only pass through membrane hydrophilic pores, while ammonia can also dissolve in membrane matrix fragments not containing water and diffuse through these fragments. It is found that due to the Donnan exclusion of H⁺ ions as coions, the pH in the membrane internal solution increases when approaching the membrane side facing distilled water. Consequently, there is a change in the principal nitrogen-atom carrier in the membrane: in the part close to the side facing the feed NH₄Cl solution (pH < 8.8), it is the NH₄⁺ cation, and in the part close to distilled water, NH₃ molecules. The concentration of NH₄⁺ reaches almost zero at a point close to the middle of the membrane cross-section, which approximately halves the effective thickness of the diffusion layer for the transport of this ion. When NH₃ takes over the nitrogen transport, it only needs to pass through the other half of the membrane. Leaving the membrane, it captures an H+ ion from water, and the released OH⁻ moves towards the membrane side facing the feed solution to meet the NH₄⁺ ions. The comparison of the simulation with experiment shows a satisfactory agreement.     

Solvent-dependent selective fluorescence sensing of Al3 + and Zn2 + using a single Schiff base

The selective assay of Al^3 + and Zn^2 + ions is reported using fluorescence enhancement of a simple Schiff base receptor 1 (1 = 1-((E)-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)naphthalen-2-ol) in aqueous solvents. The Schiff base receptor 1 showed a turn-on fluorescence in the presence of Al^3 + in a mixture of methanol–water, as a result of a restricted CN isomerization mechanism. The ion selectivity of 1 could be switched for Zn^2 + by swapping the solvent from methanol–water to DMF–water mixture. In particular, this chemosensor could clearly distinguish Zn^2 + from Cd^2 +. The binding properties of 1 with the metal ions were investigated by UV–vis, fluorescence, electrospray ionization mass spectroscopy and ¹H NMR titration.     

用Cluster-Continuum模型计算水溶液中VO2+/VO2+电对溶剂化自由能

利用Cluster-Continuum模型,通过B3LYP方法计算出VO₂⁺/VO²⁺电对的第一溶剂化层的水分子数分别为3和5个,并得到了水溶液中VO₂⁺、VO²⁺离子的溶剂化自由能。利用此计算数值并通过热力学计算推算出VO₂⁺/VO²⁺电对的标准反应电势为1.29 V,与理论值相差不大。这表明利用Cluster-Continuum模型可以较为准确地描述VO₂⁺、VO²⁺离子的溶剂化作用。     

‘Optical and FT Infrared Absorption Spectra of Soda Lime Silicate Glasses Containing nano Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Effects of Gamma Irradiation

The optical absorption spectra of undoped soda lime silicate glass together with two glasses doped with either (1 % nano Fe₂O₃ ) or with both (1 % Nano Fe₂O₃ + 5 % cement dust) have been measured from 200 to 2400 nm before and after gamma irradiation with a dose of 8 Mrad. The undoped glass reveals strong UV absorption with two distinct peaks which are attributed trace ferric iron ions present as impurity. Upon gamma irradiation , this base glass exhibits three peaks at 240,310 and 340 nm and the resolution of an induced broad visible band centered at 530 nm. The two doped glasses show an additional small visible band at about 440 nm and followed by a very broad band centered at 1050 nm. Upon gamma irradiation, the two doped samples reveal the decrease of the intensities of the spectrum. The two additional bands are related to ferric (Fe⁺³) ions to the band at (440 nm) while and the broad band at 1050 nm is due to ferrous iron (Fe⁺²) ions. The decrease of the intensities of the UV-visible spectrum upon irradiation can be related to of capturing freed electrons during irradiation . Infrared spectra of the glasses reveal repetitive characteristic absorption bands of silicate groups including bending modes of Si–O–Si or O–Si–O, symmetric stretching , antisymmetric stretching and some other peaks due to carbonate , molecular water , SiOH vibrations . Upon gamma irradiation, the IR spectra reveal a small change in the base spectrum while the IR spectra of the two doped glasses remain unchanged. The change of the IR spectrum of the base glass is related to suggested changes in the bond angles or bond lengths of the mid band structural units. The doped glasses show resistance to gamma irradiation because the nano Fe₂O₃ can capture released electrons and positive holes.