Positively Charged Polysulfonamide Nanocomposite Membranes Incorporating Hydrophilic Triazine-Structured COFs for Highly Efficient Nanofiltration

Although covalent organic frameworks (COFs) have attracted extensive attention in recent years due to their unique advantages, the use of triazine-structured COFs in the nanofiltration (NF) membrane separation processes for acid wastewater containing heavy metal ions has not been explored. We selected hydrophilic triazine-structured COF nanosheets (NENP-1) that were added to a polysulfonamide (PSA) layer via interfacial polymerization to fabricate nanocomposite membranes (NENP-1-PSA/PES). The NENP-1 brings about the synergy of improved hydrophilicity and positive charge ability with suitable pore sizes that facilitate high permeation for water molecules and high rejection for inorganic salts. Meanwhile, the NENP-1 was covalently linked to PSA matrix with better interface compatibility and membrane stability. The water flux and MgCl2 rejection of the membrane increased up to 15.1 L/m2·h·bar and 93.3%, respectively, after adding only 0.1 w/v% NENP-1, which corresponded to increases of 149.6% and 4.6% compared to the pristine PSA membrane. In addition, the membrane also exhibited good stability in acid condition. This study paves the way for the development of membrane materials with the excellent separation performances in desalination and acidic environments.