Fabrication of organic solvent nanofiltration membrane using commercial PVDF substrate via interfacial polymerization on top of metal-organic frameworks interlayer

Interfacial polymerization (IP) is a rapid and convenient approach to fabricating thin-film composite (TFC) membranes with high permeance and satisfactory rejection for organic solvent nanofiltration (OSN). However, it is normally difficult to directly conduct the IP approach on the commercial membrane substrate (particularly, in the microfiltration range) because the monomers on the substrate are unevenly distributed during the IP reaction. In the current work, Cu-TCPP nanosheets were in-situ grown on commercial PVDF microfiltration substrate (pore size of 0.45 μm) by using preinstalled Cu2O nanoparticles as a copper ion source. The Cu-TCPP nanosheets covered the large pores and penetrated the surface layer of the PVDF substrate. The obtained PVDF/i-Cu-TCPP was then used as a substrate to conduct the IP and to fabricate the PVDF/i-Cu-TCPP/PA membrane. It was found that i-Cu-TCPP which serves as an interlayer could store the aqueous solution of the amine and was critical to the formation of a thin and defect-free polyamide separation layer. In comparison, loading of the Cu-TCPP on the PVDF substrate by filtration led to the formation of PVDF/e-Cu-TCPP/PA, which however exhibited inferior separation performance as compared to the PVDF/i-Cu-TCPP/PA membrane. More importantly, the PVDF/i-Cu-TCPP/PA membrane exhibited higher tensile strength (6.0 vs. 2.8 MPa) compared to the PVDF/e-Cu-TCPP/PA membrane, due to the enhanced interaction (adhesion) between the PVDF substrate and the i-Cu-TCPP interlayer. Under optimal synthetic conditions, the permeance of the PVDF/i-Cu-TCPP/PA membrane was almost 4 times that of the PVDF/PA membrane (1.93 vs. 0.49 L m-2 h-1 bar-1) without compromising rejection (>96%). The optimal TFC membrane also showed excellent OSN performance towards various organic solvents and good long-term stability to VB12/ethanol mixtures (50 h). Furthermore, the concentration test of erythromycin in methanol solution indicated that the PVDF/i-Cu-TCPP/PA membrane has great potential in the pharmaceutical industry for drug concentration and organic solvent recovery.