One-step exfoliation and etching of layered double hydroxide nanosheets to construct nanofiltration membranes with high water permeance

Two-dimensional nanosheets are considered promising materials for membranes. However, the excessively long interlayer channels parallel to the membrane surface are not conducive to molecular transport. Creating defects on the nanosheets is an effective method to shorten the transport distance in the membrane. This study involved exfoliating and etching several commonly used layered double hydroxide (LDH) nanosheets using an alkali solution in a single step. This process resulted in porous oligolayered nanosheets modified layered double hydroxide (MgAl-MLDH) with an average pore size of approximately 18 ± 2 nm and a thickness of around 8 nm. These ultrathin porous MgAl-MLDH nanosheets were used to create a composite membrane using a vacuum-assisted filtration method. The structure of the MgAl-MLDH membrane was optimized by adjusting the etching conditions. The water flux of MgAl-MLDH membrane in Eriochrome black T aqueous solution was 530 L/m2 h MPa. Compared with the non-etched LDH membrane (179 L/m2 h MPa), the permeance of MLDH membrane was increased by 2 to 3 times, while the rejection rate remained at approximately 99 %. Furthermore, due to the excellent strength of LDH, the membrane exhibited good stability in both structure and separation performance.