Negatively Charged Nanofiltration Membranes Containing In-Situ Grown ZIF-L from Cross-Substrate Counter Diffusion Involving Zn(II)/Cyclen Complexes

Cross-substrate counter diffusion (CSCD) between imidazole and Zn(II)-loaded polyamide (PA) layers is carried out to in-situ grow zeolitic imidazole framework-leaf (ZIF-L) particles and improve the nanofiltration (NF) performances of negatively charged NF membranes. To achieve uniform distribution of Zn(II) in the formed PA layer, Cyclen was used to complex Zn(II) precursors during the interface polymerization (IP) between piperazine (PIP) and trimesoyl chloride (TMC) to dissolve the Zn(II)/PIP precipitation in the aqueous phase. Results showed that the addition of Cyclen improved the uniform dispersion and firm combination of ZIF-L particles (PTs) in the PA layers, improving both the water permeance and salt rejection of the formed TFN NF membranes. Under optimal conditions, TFN-PC 0.10-0.15 /ZIF membrane achieves a Na 2 SO 4 rejection of 90.2-96.8%, a pure water permeance of 25.8-32.8 L·m -2 ·h -1 ·bar -1 , a NaCl/Na 2 SO 4 mixed salt separation factor of 9.0-29.8, and good anti-fouling and operational stability.