Two-dimensional Cu-porphyrin nanosheet membranes for nanofiltration

A kind of two-dimensional (2D) metal-organic framework (MOF) material, Cu-meso-tetrakis (4-carboxyphenyl) porphine (Cu-TCPP) nanosheets with wrinkled and flat morphologies are used as building blocks to assemble membranes by vacuum filtration (VF) and electrophoretic deposition (EPD) as energy-efficient nanofiltration (NF) membranes to remove dyes from water. Since the nanosheets with wrinkled structure can provide additional water transport channels, thereby increasing the water permeance, in the premise of a high rejection (> 97.0%) for the dye brilliant blue G (BBG) (1.60 nm × 1.90 nm), the water permeance of the membrane assembled by the wrinkled nanosheets (~ 1170 nm) is about 4 times that of the membrane assembled by the flat nanosheets (~ 530 nm), reaching 16.39 L·m⁻²·h⁻¹·bar⁻¹. Additionally, the use of the relatively flat nanosheets and the membrane preparation method of electrophoretic deposition is more conducive to stack nanosheets orderly and reduce defects. Therefore, the water permeance of the membrane prepared by EPD (~ 1170 nm) with flat nanosheets is about twice that of the membrane prepared by VF (~ 530 nm), achieving 9.40 L·m⁻²·h⁻¹·bar⁻¹ with similar rejection (> 97.0%) of dye evans blue (EB) (3.10 nm × 1.20 nm). Furthermore, these membranes still exhibit good separation performance at high pressure of 0.6 MPa. Nanosheets with diverse structures and various membrane fabrication processes provide new directions for the separation performance optimization of 2D MOF materials for water purification.