Messages from Sub Research Leaders

Takuya Hayashi
Institute of Engineering,
Shinshu University (Atomic structure analysis)

Designing more efficient membranes through elucidating mechanisms

I have made it my mission to contribute to the development of carbon membranes with high separation and purification capabilities through advancing our theoretical understanding of the interactions occurring at the atomic or molecular level in carbon membranes developed for water purification, and elucidating the mechanisms behind the transport of water molecules. Specifically, we develop models of the structure of water separation membranes based on estimates of pore shape, membrane thickness, density and other data obtained from electron microscopy and other methods. We then get the Research Organization for Information Science and Technology or RIKEN to run simulations of atom/molecule transport, and compare the detailed data generated from these simulations with that from experiments using prototype carbon separation membranes. I feel that we will have achieved something if these efforts deliver information regarding pore size or functional group presence and type that proves useful to the design of more efficient membranes. There is still much that we do not know about the mechanisms whereby water molecules, which may be larger than some pores when hydrated, permeate water separation membranes. I have high hopes that we will also make some interesting discoveries from the perspective of water science.

Mutsumi Kimura
Professor, Division of Chemistry and Materials Course,
Institute of Textile Science and Technology,
Shinshu University (Sub-nano porous membranes)

Mimicking the cellulose membranes of mangrove roots

My mission is to precisely control membrane pore diameter to create a separation membrane that allows water to permeate while blocking salt. Salt-tolerant plants such as mangroves use cellulose membranes in their roots to desalinate seawater and also remove viruses, with the purified water then being transported upwards through vascular cells known as tracheids. I am looking at ways of mimicking this mechanism. Cellulose is easily manufactured through photosynthesis, but is difficult to break down. However, we have found ways of dissolving cellulose in ionic liquids and then molding it into various forms. We have also succeeded in making water-permeable, size-selective parylene membranes through forming films from organic compounds designed on a substrate. Reducing porosity by reducing particle size enables the creation of sub-nano porous membranes that do not allow the passage of nano-sized sodium ions, and are thus capable of desalinating water. Looking ahead, I would also like to tackle the hurdle of osmotic pressure and create a membrane capable of desalinating seawater at about half the conventional pressure. This would considerably reduce desalination-related electricity costs.

Katsuya Teshima
Director, Center for Energy and Environmental Science,
Professor, Institute of Engineering,
Shinshu University (Adsorption & ion exchange membranes)

Enabling resource recovery using high efficiency, high-precision crystalline materials and membranes

My mission in this project is to lay the path to lithium recovery through the use of an ion exchange material made from inorganic ceramic material. Conventional ion exchange resins are too expensive to become widely used in developing countries. For this reason, we have worked with manufacturers to develop water purifiers made of ceramic and other cheap inorganic crystalline materials that can remove heavy metals from water. The development of high efficiency, high-precision material separation membranes would also enable the separation at low cost of lithium and other elements, such as sodium, magnesium, potassium, and calcium. Lithium is present in high concentrations in brine, and is conventionally recovered by evaporation or precipitation using additives, but with the declining number of water sources suited to drying, the cost of such methods is expected to rise. I hope to contribute to Japan's mineral strategy as an island nation by developing devices for incorporating into large-scale seawater desalination plants to recover lithium and other useful metals contained in trace quantities in seawater.