Preparation of organic solvent-resistant nanofiltration membranes through copper sulfate (CuSO4)/hydrogen peroxide (H2O2) oxidation triggered polydopamine (PDA)/polyethyleneimine (PEI) deposition interlayer

Abstract

In this study, a novel organic solvent-resistant nanofiltration membrane was prepared on a polyimide ultrafiltration base membrane using a copper sulfate (CuSO₄)/hydrogen peroxide (H₂O₂) oxidation triggered polydopamine (PDA)/polyethyleneimine (PEI) deposition interlayer. The PDA/PEI interlayer exhibits strong adhesion with base membrane, effectively connecting the ultrafiltration base membrane to the polyamide active layer, thus enhancing the solvent resistance of the nanofiltration membrane. The CuSO₄/H₂O₂ catalyst significantly reduces the deposition time of PDA/PEI on polyimide base membrane. Additionally, copper (II) ions (Cu²⁺) can form complexes with the amino groups (NH₂) of the aqueous phase monomer m-phenylenediamine (MPD), thereby slowing the diffusion rate of MPD into the organic phase. The interlayer contains a significant number of hydroxyl and amino groups, which can engage in hydrogen bonding interactions with MPD, thereby further regulating the reaction rate. The resulting nanofiltration membranes exhibit excellent hydrophilicity, as demonstrated by their minimal water contact angle, and are capable of positively influencing the permeance of polar solvents. Notably, the nanofiltration membrane prepared with a deposition time of 15 min and a CuSO₄ concentration of 45 mmol/L exhibited optimal performance, achieving a methanol permeance of 16.20 L m^-2h⁻¹ bar⁻¹ and Rhodamine B dye rejection rate of 96.9 %. The permeance of different solvents was determined to rely on the inherent characteristics of those solvents. Furthermore, the membrane maintained good separation performance after being immersed in N, N-dimethylformamide at 80 °C for 6 days. This method offers a novel perspective for the development of nanofiltration membranes that are resistant to organic solvents.