Fabrication and characterization of positively charged hybrid ultrafiltration and nanofiltration membranes via the in-situ exfoliation of Mg/Al hydrotalcite

Layered double hydroxides (LDHs) recently have attracted intense research for their electric property. In particular, the exfoliation of LDHs provides a new type ultimate two-dimensional nanosheet with higher positive charge density. In this work, Mg/Al hydrotalcite was prepared and exfoliated in dimethylacetamide (DMAc) and then the resulting colloidal solution was used to fabricate antisymmetric membranes using polyethersulfone as membrane material via phase inversion method. Both ultrafiltration and nanofiltration membranes were prepared to investigate the effect of exfoliated Mg/Al hydrotalcite content on the membrane properties. The morphology of membranes was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hydrophilicity, water flux, and rejections of all prepared membranes were tested and the results indicated that both ultrafiltration and nanofiltration membranes showed good separation property. Ultrafiltration membranes exhibited higher rejection (above 85%) for PEG 20000 and lower protein adsorption amount for positively charged proteins, which may be used in some separation fields of proteins. Nanofiltration membranes showed higher rejection for PEG 400 but a much lower value for MgSO₄, and therefore such membrane may have a potential application in desalination for organic matter.