日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Separation membranes are attracting increasing attention because they can contribute to realizing a carbon neutral and sustainable society through energy reduction of energy-consuming separation processes and through recycling of resources. Among numerous research elements on this topic, research on membrane materials is one topic of importance because it determines their separation characteristics. A group of inorganic crystals with molecular-sized micropores (microporous inorganic crystals), also called molecular sieves, are promising separation membrane material candidates. Among them, the authors have proposed hexagonal tungsten oxide as a potential molecular sieve-type membrane material. Because this material possesses uniaxial pores parallel to its crystallographic c-axis, c-plane oriented hexagonal tungsten oxide membrane is expected to function as a molecular sieve type-separation membrane; however, its application as a separation membrane material has not been considered. Here, we introduce our recent attempts on challenging to synthesize dense c-plane oriented hexagonal tungsten oxide film, and the experimental results seeking its possibility to apply as liquid/liquid and/or gas/gas separation membranes. The obtained membrane was confirmed to selectively separate water from a water/acetic acid mixture. Furthermore, results on the permeability of various liquids and gas molecules implied that the membrane functions as a molecular sieve-type separation membrane for small molecules through utilization of its micropores. This discovery is expected to contribute to expanding options for membrane materials.