The ZrP, ZrHEDP, and ZrATMP membranes were synthesized by the following procedure. Firstly, phosphonic acid was added to water and methanol to prepare a solution so that i) the amount of phosphorus (P) substance per 1 g of the solution became 5.0×10 -4 mol/g, and ii) the weight ratio of water to methanol in the solution became 5 : 90. Furthermore, 1 molar nitric acid was added so that the weight ratio of the prepared solution to 1 molar nitric acid became 95 : 5. Sufficient amounts of the phosphonic acid solution were dropped onto the AcAc-Zr membrane and dried at 80℃ on a hot stirrer for about 10 minutes. The membrane was turned upside down, the solution was dropped, and then it was dried again. It was washed twice in ultrapure water and dried in a vacuum at 80°C overnight.