Spontaneous and rapid electrostatic solvent nanofiltration based on a conductive layered membrane†

Separating water from miscible organic solvents could significantly reduce the environmental impact of solvent waste, improve solvent purification and help recycling. Yet, it remains energy- and cost-intensive. Herein, we demonstrate an electrostatic solvent nanofiltration (ESN) method that can separate water from a variety of miscible solvents with high flux and negligible energy consumption. The method utilizes the dramatic difference in electrical response between water and organic matter. By using a conductive, non-permeable layered membrane with molecular narrow channels, we can selectively switch on the spontaneous permeation for water using a low-power (10⁻¹ W m⁻²) electrical bias. As a result, water permeated at a flux of a few L m⁻² h⁻¹ under the pressure of its own gravity. The flux is comparable to the state-of-art pervaporation membranes while the specific energy consumption is negligible. Thanks to the poor electrical response of organics, during the ESN of a miscible mixture containing water, acetone, n-butanol, and iso-butanol, the rejection rate reached 99.64% for acetone, 96.38% for n-butanol, and 98.33% for iso-butanol. We expect our work to advance the separation and recycling of solvents by exploiting their different physical properties on the molecular scale.