Dual-layered covalent organic framework/MXene membranes with short paths for fast water treatment

MXenes are receiving growing attention in wastewater treatment , but the preparation of ultrathin MXene membranes with short water pathways on macroporous substrates for improving flux is challenging due to the deformation of the flexible MXene nanosheets . Herein, we demonstrate the fabrication of ultrathin MXene membranes by constructing an intermediate porous covalent organic framework (COF) layer. COF nanosheets are first vacuum filtrated on macroporous substrates to form a porous COF layer, followed by the vacuum deposition of MXene nanosheets to produce the dual-layered COF/MXene composite membranes . The COF layer provides a smooth surface with rich pores and good hydrophilicity for depositing MXene nanosheets, leading to the well-assembled MXene layer as thin as 8 nm. The ultrathin MXene layer and the porous COF layer enable the short water transport pathways, and the well-assembled MXene nanosheets guarantee the narrow interlayer nanochannels. Membranes thereby are endowed with high permeance of 563 L/(m 2 ·h·bar) and high rejection to congo red of 99.6%, outperforming other reported COF- or MXene-based membranes. This work suggests a facile construction strategy of ultrathin MXene-based composite membranes with high separation performances, which are highly desired in water treatment.