Porous organic polymer nanosheets doped multistage water channel ultrafiltration membrane: Accelerated phase inversion process and in-situ covalent crosslinking strategy

Mixed matrix membranes (MMMs) have attracted significant interest in the field of water treatment owing to their capability to integrate the scalability and processability of polymers with the selectivity of fillers. Despite the numerous advantages demonstrated by emerging nanofillers, currently developed MMMs are still limited by such as insufficient hydrophilicity, susceptibility to additive loss, and poor filler compatibility. To address these challenges, we developed a series of polyethersulfone (PES)-based MMMs featuring a hydrophilic surface and multistage water transport channels, thereby minimizing additive loss, and enhancing efficiency in water treatment processes. Through interfacial azo-coupling polymerization, we synthesized a series of hydrophilic and porous two-dimensional sulfonic acid-functionalized porous organic polymer nanosheets (NSsPOPs) to be used as additives in the MMMs. Owing to the exceptional hydrophilicity and favorable dispersibility of NS-sPOPs in water, the nanosheets influenced phase inversion through an accelerated phase separation process, resulting in the formation of multistage channels. Polyphosphoric acid (PPA) was used for the postcrosslinking treatment of the PES/NS-sPOP membrane. Consequently, the NS-sPOPs were immobilized within the polymer matrix to ensure stable performance in subsequent use. The prepared PES/NS-sPOP membrane exhibited outstanding water permeability (pure water flux) of 493 L.m(-2).h(-1).bar(-1), and a high bovine serum albumin rejection rate of 99.3 %. Furthermore, it exhibits consistent performance throughout a 48 h long-term stability test. Overall, the blending and crosslinking strategy of hydrophilic nanofillers enables the realization of superhydrophilic 2D nanosheet-doped multistage-water-channel MMMs with exceptional permeability and high selectivity for water purification and organic pollutant removal.