Porous regenerated cellulose nanofiltration membrane enabled by nano calcium carbonate modulation for high-efficiency ionic liquid recovery

Objective As an effective solvent for cellulose, ionic liquids (ILs) play a crucial role in green recycling through efficient recovery. However, current nanofiltration recovery technologies face challenges such as low ILs retention rates, poor membrane strength, and non-biodegradability. This study focuses on pore formation based on high-strength regenerated cellulose membranes to optimize pore structure and develop green, biodegradable nanofiltration membranes, aiming to achieve efficient ILs recovery.

Method This study utilized cellulose as the raw material and ILs as the solvent, incorporating nano-calcium carbonate (NCC) as a porogen to prepare porous regenerated cellulose substrate membranes (PRCMs) through dissolution-regeneration coupled with gas in-situ foaming technology. By regulating the interface polymerization conditions, a polyamide separation layer was constructed on the surface of PRCMs to prepare porous regenerated cellulose-based nanofiltration membranes (PRC-NFs). The pore size, specific surface area, chemical composition, surface morphology, mechanical properties, surface charge characteristics and ILs recovery performance of the membrane materials were analyzed.

Result (1) The addition amount of NCC can effectively regulate the pore structure, mechanical properties, and water flux of PRCMs. When the addition amount is 0.30%, the porous basement membrane PRCM2 exhibits optimal comprehensive performance (tensile strength of 52.5 MPa, water flux of 5.41 L/(m²·h)). (2) Interface polymerization was conducted on the surface of PRCM2 to construct PRC-NFs. Under conditions of 0.5% anhydrous piperazine (PIP) by mass fraction, 0.30% 1,3,5-trimethylcarboxylic chloride (TMC) by mass fraction, and a polymerization time of 3 minutes, the PRC-NF6 surface exhibited a dense and uniform wrinkled network structure with the smallest pore size (1.65 nm) and the strongest surface electronegativity. (3) The retention rate of PRC-NF6 for ILs was 49.22%, with a water flux of 4.25 L/(m²·h), demonstrating superior performance compared to previously reported non-porous high-strength regenerated cellulose nanofiltration membranes (with a rejection rate increase of 1.88-fold).

Conclusion In this study, a porous regenerated cellulose-based nanofiltration membrane with controllable pore structure and high ILs rejection rate was successfully prepared by dissolution regeneration-gas foaming-interfacial polymerization method, and the green and efficient recovery of ILs was realized.