Nanofibrous Polyacrylonitrile Membranes Coated with Nanosheets of Zn-Tetrakis(4-Carboxyphenyl) Porphyrin for Enhanced Pressure Resistance and Dye/Salt Separation

Two-dimensional metal–organic framework (MOF) nanosheets have been utilized to fabricate loose nanofiltration membranes, capitalizing on their unique lamellar structure and regular nanopores, which facilitate ultrafast and efficient separations. However, the structural stability of current MOF nanosheet membranes remains suboptimal due to the weak interlayer bonding between nanosheets when a single vacuum-assisted deposition method is employed. To overcome this challenge, poly(vinyl alcohol) (PVA) and glutaraldehyde (GA) were introduced as cross-linking agents in the vacuum-assisted deposition of zinc(II)-tetrakis(4-carboxy-phenyl) porphyrin) (ZnTCPP) nanosheets onto electrospun polyacrylonitrile (PAN) nanofibrous supports. The chemical bonding between nanosheets, PVA and GA, contributed to the superior mechanical performance of the ZnTCPP-PVA-GA/PAN thin-film nanofibrous composite (TFNC) membrane, exhibiting an elongation at break of 62.4%, surpassing that of commercial nanofiltration counterparts by 2.6 times while maintaining a comparable tensile strength of 21.3 MPa. Furthermore, the optimized TFNC demonstrated a high permeance of 49.5 L m –2 h –1 bar –1 and a retention rate of 99.0% for Congo Red (CR) when separating CR from a mixture with NaCl, achieving a CR/NaCl separation factor of 92.9. Simultaneously, this membrane presented excellent compression resistance and was capable of withstanding pressure up to 8 bar without compromising separation performance.