The AcAc-Zr powder was dissolved in methanol to obtain a 3 wt.% AcAc-Zr methanol solution. The solution was dropped onto a porous substrate and dried at room temperature, and the procedure was repeated about five times until the film became transparent. After the first drop, the substrate was kept in a vacuum at room temperature for about 1 min (vacuum method ). The transparent film was washed twice with ultrapure water and dried in a vacuum environment at 80°C for more than 30 min to obtain a transparent AcAc-Zr membrane.