Ultrathin bimodal porous membranes with uniform small pores separated by laminated large pores for efficient water separation
Yuhang Guo, Hong Wu, Shaoyun Guo, Jianhui Qiu
Abstract
Bimodal pore structure design of separation membranes is a promising way to simultaneously improve permeability and selectivity. However, the thickness limitation of bimodal porous membranes is an obstacle to further improving the separation efficiency. In this study, a novel bimodal porous structure with uniform small pores on the surface and a unique laminated large pore structure in the thickness direction was successfully constructed through biaxial stretching of gel films in ultra-high molecular weight polyethylene membranes. With an increase in the draw ratio to 12 × 12, the uniformly refined small pores increased the rejection rate of the carbon nanoparticle solution (particle size distribution of 60–400 nm) to 99.4%, and the unique laminated large pore structure enabled the permeance to reach 1141.8 L m-2h−1 bar−1. By further increasing the draw ratio to 16 × 16, the membrane thickness decreased to 0.91 μm and the permeance was further increased to 2008.2 L m-2h−1 bar−1 while the selectivity slightly decreased to 98.9%. Furthermore, a bimodal porous membrane with sufficient strength (237 MPa of 16 × 16) was efficient for long-term water separation. This study proposes a new design idea for ultrathin porous membranes, which can be further expanded to prepare various antifouling, self-cleaning, and multifunctional separation membranes.