Selection of crosslinkers and control of microstructure of vapor-phase crosslinked composite membranes for organic solvent nanofiltration

A fast and green chemical modification method has been developed by using amine vapor to fabricate hybrid composite membranes consisting of crosslinked polyimides and nano-size UiO-66-NH2 metal-organic frameworks (MOFs) with higher selectivity for organic solvent nanofiltration (OSN). Three amine vapor-phase crosslinking (VPC) reagents; namely, N,N'-Bis(3-aminopropyl)-1,3-propanediamine (APPD), 1,4-Bis(3-aminopropyl) piperazine (BAPP) and polyethylenimine (PEI) were employed. It was found that APPD and PEI vapor are more effective to generate smaller pores in the dense-selective layer than the BAPP vapor. In addition, the PEI modified membranes are more suitable for polar and aprotic solvents nanofiltration applications, while the APPD and BAPP modified membranes are for applications involving wider solvents. The selected hybrid membranes cast on polyester (PET) non-woven fabrics have rejections of tetracycline (MW = 444 gmol(-1)) more than 90% in four organic solvents under continuous cross-flow filtration tests for over 120 h. All fluxes and selectivities remain stable without showing significant fluctuations, evidencing great potentials of designed membranes for industrial applications. Besides, the VPC modification process is environmental-friendly because it uses a tiny amount of amine vapors without extra chemical waste production. Therefore, this study offers a promising sustainable, greener and scalable strategy to produce high performance OSN membranes.