A Bioinspired Capillary Force-Induced Driving Strategy for Constructing Ultra-Low-Pressure Separation Membranes

The development of low-pressure or pressureless self-driven membranes is important for saving energy and overcoming the critical trade-off effect in membrane separation processes. However, conventional self-driven membranes rely on gravity, which is effective in the separation of large-sized materials but is still ineffective in the fine separation of small molecules. Herein, inspired by the capillary effect that exists in nature, a capillary force-induced membrane-driving strategy for fine separation at ultra-low pressures is demonstrated. Hydrophilic nanoparticles are prepared by a cross-linking reaction between tannic acid and 3-aminopropyltriethoxysilane and then introduce them into membrane pores to simulate sand accumulation with an aim to generate the capillary force. The membrane is then used in ultra-low pressure membrane separation. Interestingly, it is found that the membrane has excellent performance in the separation of dye/salt mixtures (dye rejection > 99%, salt rejection < 10%) and a high permeate flux (160 L m(-2) h(-1)) under near "zero pressure" conditions. Moreover, the structural stability of the membrane is verified. Introducing capillary forces into membranes as an autonomous driving force can be a promising universal approach that can be added up to the toolbox for the efficient preparation of separation membranes.