2.4. Membrane characterizations
The morphological structure of as-prepared membranes was observed by scanning electron microscope (SEM, S-4800, Hitachi, Japan). The samples were prepared for cross-sectional observation by freeze-fracturing the membranes in liquid nitrogen. About 2.5 nm-thick platinum layer was coated on the surface of samples before observation using a coater (JFC-1600, JEOL, Japan). The elemental composition of the samples was determined by the energy dispersion spectrum (EDS) of SEM. X-ray diffraction (XRD) spectra was acquired by XRD meter (Ultima IV, Rigaku, Japan) with a Cu-Kα source at 40 kV and 30 mA. The d -spacing of the membranes could be calculated from XRD spectra by
\(d=\lambda/(2sin\theta)\) (1)
where d is d -spacing (nm), λ is wavelength (λ = 0.15 nm), θ is incidence angle (degree). Moreover, surface hydrophilicity was determined by contact angle meter (DSA30, Kruss, Germany).