Tannic acid/Fe3+ interlayer for preparation of high-permeability polyetherimide organic solvent nanofiltration membranes for organic solvent separation

Organic solvent nanofiltration (OSN) membranes have a great application prospect in organic solvent separation, but the development of OSN membranes is mainly restricted by trade-off between permeability and rejection rate. In this work, a TA/Fe3+ polymer was introduced into polyetherimide (PEI) ultrafiltration membranes crosslinked with hexamethylene diamine as the intermediate layer, and OSN membranes with high separation performance and solvent permeability were obtained through interfacial polymerization and solvent activation. The interlayer with high surface hydrophilicity and a fixed pore structure controlled the adsorption/diffusion of the amine monomer during interfacial polymerization, forming a smooth (average surface roughness < 5.5 nm), ultra-thin (separation layer thickness reduced from 150 to 16 nm) and dense surface structure polyamide (PA) layer. The PA-Fe33+-HDA/PEI membrane retained more than 94% of methyl blue (BS) in 0.1 g·L−1 BS ethanol solution at 0.6 MPa, and the ethanol permeation reached 28.56 L−1·m−2·h−1. The average flux recovery ratio (FRR) of PA-Fe33+-HDA/PEI membrane was found to be 84%, which has better fouling resistance than PA-HDA/PEI membrane, and it was found to have better stability performance through different solvent immersion experiments and continuous operation in 0.1 g·L−1 BS ethanol solution. Compared with thin-film composite nanofiltration membranes, the PA-Fe33+-HDA/PEI membrane can be manufactured from an economical and environment-friendly method and overcomes the trade-off between permeability and rejection rate, showing great application potential in organic solvent separation systems.