The transmission wavelengths were measured using FT-IR (Spectrum 100, PerkinElmer, Inc.). In addition, XRD measurements (RINT2100CMJ, Rigaku, Inc.) were performed to identify the crystal structure in the membranes. The acceleration voltage and current were 40 kV and 30 mA, respectively, and the step width and measurement time were 0.050 degrees and 1.0 s/step, respectively. The measurements were performed by the diffractometer method using Cu-Kα radiation (λ = 1.54056 Å).