Construction of stable triazine porous organic polymer nanofiltration membrane for selective separation: The role of substrate on the membrane formation and separation performance

Porous organic polymers (POPs) have been regarded as potential candidates for high-performance membrane building blocks ascribed to their robust structure, tunable pore size, and high surface area. Normally, the POPs membrane possesses a POPs selective layer on the porous substrate for its real application. Numerous efforts have been paid to manipulate the POPs selective layer to enhance the separation performance, however, except from providing mechanical strength, the role of substrates in the formation and separation performance of POPs membrane receives less attention. In this work, we employed a systematic study to reveal the role of substrates in the governing POPs membrane formation by choosing substrates with diverse properties. The relationship between the properties of substrate (e.g., pore size, porosity, roughness, hydrophilicity, and surface functional groups) and the assembly structure of POPs membranes was in-detail analyzed. We found that the hydrolyzed polyacrylonitrile substrate induced a better assembly of POPs nanoparticles. Its rough surface and carboxylic functional groups created Van der Waals interactions and hydrogen bonding interactions to reinforce interfacial adhesion between the substrate and POPs selective layer, which facilitated the formation of intact and defect-free POPs membranes. The resulting POPs membrane displayed a high water permeance of 121.3 L m -2 h −1 bar −1 with a congo red rejection of 98.9 %. Moreover, benefiting from the robust interfacial interactions between POPs selective layer and the substrate, the POPs membrane enabled itself to maintain structure stability under harsh environments, such as acidic, alkaline, and organic solvents. This work gives new insights to producing robust and high-performance POPs membranes.