Integration of P84 and porphyrin-based 2D MOFs (M-TCPP, M = Zn, Cu, Co, Ni) for mixed matrix membranes towards enhanced performance in organic solvent nanofiltration

Mixed matrix membranes (MMMs) are promising candidates for organic solvent nanofiltration (OSN), but the thick separation layer and poor compatibility between polymer and fillers are two critical challenges needed to be solved. Herein, a series of tetrakis(4-carboxyphenyl)porphyrin (abbreviation: TCPP) based metal-organic frameworks (MOFs, M-TCPP (M=Zn, Cu, Co, Ni)) have been synthesized in the form of two-dimensional nanosheets, which were then used as thin fillers in P84 matrix to fabricate M-TCPP/P84 MMMs for the OSN application. The effects of the types of M-TCPP and loading contents in the resultant MMMs on the OSN performance were systematically investigated. All the obtained MMMs exhibited higher permeance and slightly declined rejection of brilliant blue R (BBR) as compared with the pristine P84 membranes, among which ZnTCPP/P84 MMM showed the greatest permeance improvement due to its flower-like structure assembled by wrinkled nanosheets as building blocks. Moreover, the permeance of MMMs showed volcanic type curves as increasing the MOFs loading content, while the rejection did not sacrifice too much. The optimum loading contents for Cu-TCPP/P84 and Zn-TCPP/P84 MMMs were 1 wt% and 1.5 wt%, respectively. In addition, the water-stable Cu-TCPP MOF can be further disassembled by an ultrasonic probe to achieve monodispersed CuTCPP nanosheets. It is interesting to find that the permeance of the MMM incorporating 1.5 wt% of the monodispersed Cu-TCPP nanosheets was enhanced nearly 2-fold as compared with the MMM with the untreated CuTCPP MOFs and the rejection to BBR only slightly decreased (94.7 vs. 95.7%). Besides, the general applications of Cu-TCPP/P84 membranes for other organic solvents (methanol, isopropanol, acetone, acetonitrile, hexane, etc.), diverse organic dye/ethanol separation, vitamins B12/ethanol long-term separation test (36 h) indicated that the M-TCPP-based MMMs have great potentials in the field of organic solvent-related separation.

Automated summary

The study focuses on the use of TCPP-based metal-organic frameworks (MOFs) in P84 matrix to fabricate mixed matrix membranes (MMMs) for organic solvent nanofiltration, with optimal loading contents identified as 1 wt% for Cu-TCPP/P84 and 1.5 wt% for Zn-TCPP/P84 MMMs. Furthermore, ultrasonic disassembly of Cu-TCPP MOFs into monodispersed nanosheets significantly enhances the permeance of MMMs.