Membrane separation technology is effective for energy saving, space saving, and consecutiveness, and meets the demand of the times. The ion-exchange membrane is a functional membrane and the separation with the membrane has been used for many applications. In this review, established applications of ion-exchange membranes are described first for electrodialysis, sodium chloride electrolysis, electrodeionization, and so on. Further applications of this membrane have been investigated and some of them, mostly for the work of my group, will be noted subsequently. The selective permeation across the membrane is achieved via the specific reaction of the solute
with the ion fixed on the membrane. Amphoteric electrolytes, amino acids, can be also transported selectively by adjusting the pH of the source phase or the receiving phase solution. Some chambers separated with ion-exchange membranes can be used for desalination, electrokinetic remediation, and other novel applications. Ion-exchange membranes have established characteristics and will have further applications.
Relative stability of oxygen and hydrogen atoms of water molecules in aqueous ion-bearing solutions is presented by evaluating their reduced partition function ratios based on the theory of equilibrium isotope effects. The evaluation relied on an ab initio molecular orbital computation. The presence of an aqueous ion basically influences only the stability of oxygen / hydrogen in direct contact. The decreasing order in stability of the oxygen atom of a water molecule in the primary hydration sphere of aqueous Group 1 and Group 2 metal ions and Cl- and SO42- anions is: Mg2+> Ca2+ > Li+ > bulk water ≥ SO42- ≈ Na+ ≈ （Cl-） ≥ K+. Similarly, the decreasing order in stability of the hydrogen atom of a water molecule is: bulk water ≈ Li+ ≈ Na+ ≈ K+ ≈ Mg2+ ≥ Ca2+ ≈ SO42- > Cl-. The influence of those ions on stability of oxygen and hydrogen atoms of water molecules in the secondary and outer hydration spheres is minimal. Those computational results are consistent with experiments on isotope salt effects.
Adsorption methods using specified adsorbents are economically feasible and environmentally friendly for capturing useful and harmful ions and molecules. Our group has thus far prepared various qualities and forms of polymeric adsorbents by radiation-induced graft polymerization. Here, the preparation schemes for novel adsorbents capable of collecting catechin and palladium ions, and of removing cesium ions and urea are described along with their performance.
In cooking, salt works as a seasoning, modifying the texture and improving the storage stability of foods. Recently, inorganic components in commercially available salts vary according the production method, which can result in differences in taste. When those salts were used in cooking, the taste changed depending on content of bittern components, but it was recognized that cooking methods can affect enhancement of and imparting taste, too. Salt can interact with other taste components, which leads to enhancing or suppressing the taste. Cooperative interaction between sourness and saltiness has the effect of increasing the intensity of saltiness. When we make seasoning salt using plum, which is ume in Japanese and contains abundant organic acids, it has an effect of strengthening salty taste.
This result can be emphasized as a salt-reducing effect.
This review describes the application of flow systems for analyzing various components in seawater. Determination of trace components is essential for understanding the mass circulation and evaluating the degree of pollution in seawater. However, trace analysis is not an easy task because seawater has high ion strength. The flow system can resolve complex problems because of its easy operation, for example, automatic preconcentration of analyte and the separation of matrices. Various applications of flow analytical systems for the analysis of seawater are classified with their analytes.
Salinity gradient energy （SGE） refers to the source of renewable energy generated by mixing two solutions with different salinities. Among several technologies for extracting SGE, reverse electrodialysis （RED） has attracted both research and industrial interest as a promising membrane-based technology to directly convert SGE to electricity. Since the concept of RED was first proposed in the 1950s, many researchers have worked on the development of RED-related technologies, and tremendous advancements have been achieved. However, although several pilot-scale experiments have been recently conducted and promising outcomes have been obtained, to the
authors’ knowledge, RED has not yet reached the commercialization stage. To fill the gap between the current technical level and the required level for commercialization, the objective of this review is to present the i） principle of RED, ii） process parameters/factors controlling the performance of RED, iii） current status of performance obtained from pilot-scale RED systems, and iv） main technical barriers that remain and inhibit the commercialization of RED. In addition, the combination of RED with other desalination processes to overcome the limitations of each individual process and/or to enhance the power generation capability of RED is briefly explained.
The development of micro/nanofabrication techniques for organic polymers is essential to facilitate their potential future applications. This paper is devoted to the following two topics, i.e.,ion-track-etched porous membranes and ion-track-grafted electrolyte membranes for fuel cells and other electrochemical applications. Both membranes involve the creation of nanostructured functional membranes with swift heavy ions. Latent tracks of the MeV-GeV heavy ions in polymer films can be chemically etched to produce membranes with micro- and nano-sized through-pores, termed ion-track-etched membranes. Our focus was on track-etched membranes of poly（vinylidene fluoride）（ PVDF）, which was also considered as a matrix of polymer electrolyte membranes. Although the PVDF-based racketched membranes have already been investigated, their preparation methods have never been optimized. The etching behavior mainly depended on the energy deposition of the ion beams, and thus its depth distribution, which was estimated with theoretical simulations, was successfully applied to control the shapes and diameters of the etched pores. The cation and anion exchange membranes （CEMs and AEMs） for fuel-cell devices and separation processes were prepared by ion-track grafting, which involves direct graft polymerization into latent tracks in pol（y ethylene-co-tetrafluoroethylene）（ ETFE）. Interestingly, the resulting membranes exhibited an anisotropic ion transport, i.e., higher conductivity leading to lower resistance in the thickness direction. As determined from icroscopic observations, this is probably because the nearly columnar electrolyte phase with width ranging from tens to hundreds of nanometers extended through the membrane. This controlled structure also exhibited excellent membrane properties, e.g., high dimensional stability and low water permeability, which promoted investigations into novel electrochemical separation processes using ion-track-grafted CEMs and AEMs. Finally, worldwide recent advancements in irradiation technologies are presented to explore the potential industrial applications of our new functional membranes.
The objective of this study was to investigate the influence of the ions contained in seawater on the desorption of manganese (II) (Mn (II)) from artificially-contaminated montmorillonite. Prior to the desorption experiments, batch Mn (II) sorption experiments were performed to evaluate if ion exchange reactions played an important role in Mn(II) sorption onto montmorillonite. The results showed that the sorption of Mn(II) was not significantly influenced by pH when pHɟ.0. However, the presence of NaCl strongly hindered the sorption of Mn(II), demonstrating that ion exchange reaction does play an important role in this pH range. The results of desorption experiments showed that, as expected, the ions contained in seawater significantly enhanced the desorption of Mn(II). This suggests that Mn(II) in montmorillonite in river-suspended sediments may be desorbed at the estuaries.
The objective of this study was to synthesize layered titanate to efficiently and irreversibly adsorb strontium(II) (Sr(II)) from brackish water. At a NaCl background ion concentration of 0.01 mol/L, synthesized layered titanate demonstrated an approximately thirty-fold higher maximum Sr(II) adsorption capability than an anatase precursor. The increase in NaCl concentration to 0.1 mol/L decreased the Sr (II) adsorption capability by ～ 20 ％ , but still showed a high Sr(II) adsorption capability. It was also demonstrated that the adsorption of Sr(II) induces a structural deformation of the layered structure and that the adsorbed Sr(II) was trapped in the interlayer, resulting in an irreversible Sr(II) adsorption.
The objective of this study was to investigate the influence of 1） cation exchange capacity （CEC） of clays and 2） the percentage of seawater in leaching solutions on the immobilization efficiency of F－ with the addition of MgO. It was found that the immobilization efficiency of F－ was higher for kaolinite（ relatively lower CEC） than for montmorillonite （higher CEC） when distilled deionized water was used as a leaching solution. On the other hand, when diluted seawater was used, the difference was unremarkable. These results showed that the CEC of soils influences the formation of Mg（OH）2 and consequently F－ immobilization efficiency with MgO when the concentration of Mg2＋ in leaching solution is low.