MXene-intercalated covalent organic framework membranes for high-flux nanofiltration

Covalent organic framework (COF) membranes are envisioned as promising materials for precise molecular separations. The manipulation of interlayer spacing to offer additional mass transfer channels in COF membranes may be an effective way towards high-flux separation processes but still challenging. Herein, the COF membranes with 1D/2D mixed-dimensional channels are explored by the intercalation of MXene for high-flux dye separations. Thereinto, porous TpPa-SO3H nanosheets offer the 1D in-plane channels, and smaller-sized Ti3C2Tx-NH2 nanosheets serve as the intercalators to generate 2D interlayer channels. By tuning the content of Ti3C2Tx-NH2, the interlayer spacing is enlarged from 0.32 nm to 0.46 nm, affording low diffusion energy barrier and ultrafast diffusion kinetics. Compared to the pristine TpPa-SO3H membrane, the COF/Mx-8 membrane exhibits an 90% increase in water flux to 375.8 L m-2 h-1 bar-1, while maintaining high rejections toward various dye molecules. The strategy of MXene-intercalated mixed-dimensional channels is suitable for diverse types of 2D COF membranes.