Voltage-controlled organic solvent nanofiltration using conjugated microporous polymer membranes.

Voltage-controlled nanofiltration offers a promising approach for precise, on-demand molecular separation. However, its application in organic solvent nanofiltration (OSN) remains underexplored, given the poor solute dissociation in organic solvents. Here, we fabricate conductive and robust conjugated microporous polymer (CMP) membranes to investigate voltage-controlled OSN. Our results show that while solvent permeance slightly decreases with the applied voltage, due to the uneven electron density distribution of solvent molecules, solute rejection is significantly enhanced. This enhancement arises from a dual-barrier mechanism comprising ion migration in the bulk solution and a Donnan-like equilibrium at the feed-membrane interface under an applied voltage. Specifically, in methanol, applying a positive voltage increases the rejection of positively charged methylene blue (MB) from 8.3 % at 0 V to 91.3 % at 5 V. Our study also reveals that the degree of solute dissociation contributes significantly to the effectiveness of voltage-controlled rejection. Lastly, the successful separation of mixed dyes of similar size, together with the enhanced rejection of real pharmaceutical and agrochemical compounds under applied voltage, highlights the potential of in-situ voltage application in OSN for addressing challenging separations.