Covalent organic framework-immobilized wood membrane for efficient, durable, and high-flux nanofiltration

Covalent organic frameworks (COFs) are promising for the construction of nanofiltration membranes owing to their uniform, ordered channel structures and high chemical stability. However, developing a low-cost strategy for fabricating COF-based nanofiltration membranes and increasing the long-term stability of the membranes are challenging. Here, we developed a TpPa-wood membrane through the in-situ formation of massive imine COFs on the top surface of a wood block for the rapid and efficient nanofiltration-based separation of organic pollutants. The numerous hydroxyl groups of cellulose in wood provided nucleation sites for the growth of dense, defect-free COFs with a diameter of 1.8 nm. The nano porous COFs enabled efficient separation, while the long and low-tortuosity channels of wood with a diameter of 10–30 μm facilitated rapid water transport and augmented the mechanical robustness of the membrane. Therefore, the prepared TpPa-wood membrane showed an outstanding separation efficiency of ∼97.0% toward organic pollutants such as dyes and pharmaceutical molecules at a flux rate of 600 L m−2 h−1. In addition, the TpPa-wood membrane exhibited excellent stability at a wide pH range (3–11) and over continuous filtration for 48 h. The TpPa-wood membrane opens up a new avenue for rapid and efficient nanofiltration by combining the merits of nano porous COFs and biomass with numerous micro-channels and high hydrophilicity.