2.5 Characterizations
X-ray diffraction (XRD) patterns were obtained using a Bruker-D8 ADVANCE under Cu Kα radiation (40 kV, 40 mA). Scanning electron microscopy (SEM) with a Hitachi SU8100 equipped with an Oxford Energy Dispersive X-ray Spectrometer was used to investigate the morphology of the materials (Oxford EDS, INCA software). Atomic force microscopy (AFM) pictures were captured on Bruker MultiMode 8. Fourier transform infrared spectroscopy (Nicolet 5700 spectrometer) was employed to determine the chemical structures of the membranes in the 400~4000 cm-1 range. X-ray photoelectron spectroscopy (XPS) measurements were carried out utilizing a conventional Al Kα source on an Escalab 250Xi spectrometer outfitted with two ultra-high vacua (UHV) chambers. The Zeta potential and lateral size of the nanosheets were tested with a Zetasizer ULTRA nanoparticle size and Zeta potential analyzer produced by Malvern Instruments, UK. The pore size distribution of the porous stainless steel substrate was measured with a PSDA-30 microfiltration membrane pore size analyzer produced by Nanjing Gaoqian Functional Materials Technology Co., Ltd., China.