Improving properties of thin film nanocomposite membrane through polyethyleneimine intermediate layer: a parametric study

Abstract

In this work, the polyethyleneimine (PEI)-interlayered thin film nanocomposite (iTFN) membranes were developed by establishing graphene oxide (GO)-incorporated polyamide (PA) layer atop PEI-coated polysulfone (PSf) substrate for reverse osmosis process. The effects of PEI layer sandwiched between selective layer and substrate were studied by varying several main parameters of the PEI coating process, i.e., PEI concentration (0.005–0.2 wt/v%), drying time (0–120 min), and coating layer number (1–3 layers). The positively charged PEI interlayer was found to alter not only the hydrophilicity and pore structure of the substrate but also improve the orientation and distribution of deposited GO through electrostatic interaction. Synergic effects of GO and PEI, including enhanced substrate surface hydrophilicity and increased amine content, eventually formed a rough but thin PA layer. As a result, almost all iTFN membranes exhibited higher NaCl rejection and water permeability than the control TFN membrane (without PEI intermediate layer). This experiment revealed that PSf substrate modified with a single layer of 0.05 wt/v% PEI followed by 60-min drying yielded the TFN membrane (i.e., iTFN-C0.05-T60-L1) with the best desalination performances (96.66% NaCl rejection and 2.24 L/m2·h·bar). The control TFN membrane meanwhile showed lower performance, i.e., 95.61% NaCl rejection and 1.69 L/m2·h·bar.