Synergistic Effects of ZIF-8 and ZIF-67 in Bilayer Membranes on Separation Tuning of pH- Sensitive Antitumor Drug

In this research, pH sensitive bilayer membranes including ZIF-8 containing polyamide top-layer (ZnZIF) and ZIF-67 containing polyacrylonitrile sub-layer (CoZIF) named iZnZIF/jCoZIF were used for separating DOX1 pH-sensitive drug. Presence of CoZIF in the membrane sub-layer was associated with 26% increase in porosity and 9 nm RMS roughness reduction. It, in turn, caused elevation of flux from 3.7 to 9 LMH and flux recovery from 55 to 89% for the 0ZnZIF/1CoZIF membrane compared to the virgin membrane (0ZnZIF/0CoZIF). Presence of ZnZIF in the top-layer resulted in enhanced cross-linking (as confirmed by ATR2 test), boosted hydrophilicity, elevated surface charge density, increased surface layer thickness (as confirmed by SEM3 test), and reduced size of pores (as verified by MWCO4 test). Thus, the extent of flux recovery of DOX grew from about 55% for 0ZnZIF/0CoZIF to 90% for 1ZnZIF/0CoZIF membrane. Due to the synergistic effect of presence of pH-sensitive agents in both layers of the membrane, the flux, separation, and flux recovery of the 1ZnZIF/1CoZIF membrane reached 9.2 LMH, 92%, and 97%, respectively, showing 110%, 3%, and 7% enhancement compared to the 1ZnZIF/0CoZIF,2%, 10%, and 8% increase compared to the 0ZnZIF/1CoZIF membrane as well as 150%, 10%, and 42% growth compared to the 0ZnZIF/0CoZIF membrane. BET test measured the membrane pore size at pH=3, 7, and 9 as 41, 32, and 35 nm, respectively. The sensitivity of the membrane pore size to pH, on the one hand, and sensitivity of surface charge of DOX to pH, on the other, were associated with enhanced separation by pH variations of the environment for the membrane. Specifically, the flux, rejection, and cake resistance for the 1ZnZIF/1CoZIF membrane at pH=5 were 21.8 LMH, 99%, and 17.4%, respectively, while these values at pH=7 were 9.27 LMH, 92%, and 43.24%, respectively.