Comparison of polyamide, polyesteramide and polyester nanofiltration membranes: properties and separation performance

In this study, three different kinds of nanofiltration membranes with polyamide (PA), polyesteramide (PEA), and polyester (PE) active layers were respectively synthesized by using piperazine, serinol and meso-erythritol as the aqueous monomers for interfacial polymerization. The three types of membranes achieved comparable rejections for the reference organic solute (i.e., xylose) via optimization of preparation conditions, based on which the characteristics of different active layers were comprehensively investigated. Results showed that the PA, PEA and PE membranes exhibited distinct surface morphologies. The special surface structures of PEA membranes and the larger active layer thickness of PE membranes resulted in their lower water permeance compared to PA membranes. Different from PA active layers, the absence of positively charged regions in the PEA and PA active layers was beneficial for the passage of divalent cations and the rejection of NaCl. Moreover, despite the comparable mean pore size, PA membranes exhibited a more uniform membrane pore size resulting in a higher rejection of organic matters in natural water than PEA and PE membranes. This study presented the differences in physicochemical properties and separation performance among the different membrane active layers, which could provide references for the rational selection of nanofiltration membrane types during application.