From asymmetry to symmetry: Biomimetic multi-channel structures for enhanced desalination using co-dissolving porogens

Abstract

The asymmetric structures constructed via traditional methods fundamentally determine the “trade-off” bottleneck of cellulose triacetate reverse osmosis (RO) membrane in desalination. So, based on the structure-determined performance, inspired by the pore mechanism of frozen tofu through “water-ice-water” phase transition, the biomimetic RO membrane with high symmetry and homogeneity was successfully utilized in desalination. The co-solubilized N-methyl-2-pyrrolidone (NMP) narrowed the structural differentiation between Top and Bottom, increasing the number of through-water channels, surface hydrophilicity, and flatness of RO membrane. Typically, the prepared membrane with 0.125% NMP concentration has a salt rejection rate of 98.9% for NaCl, and excellent retention rate for other inorganic salts (MgCl2, LiCl). Notably, the NMP-modified membrane has a water flux of up to 17.2 L m−2 h−1, which is nearly 660% higher than that of No porogen-RO membrane (2.6 L m−2 h−1). Further, the membrane retained its separation capacity even after continued operation for 700 min, owing to the enhanced compression of the ductile pores by NMP. Overall, this novel cellulose-based RO membrane represents a structural mechanism for the design of innovative biomimetic multi-channel structures for long-term and efficient desalination.