Biomimetic Janus membrane with unidirectional water transport ability for rapid oil/water separation

Abstract

• Janus membrane was prepared by electrospinning nanofibers on hydrophilic Cu mesh. • Water flux of 5305 L/m 2. h was much higher than other reported Janus membranes. • Membrane surface wettability was stable under high saline and varied pH conditions. • The optimized membrane can achieve unidirectional collection of water from oil. Janus membrane (JM) with asymmetric surface wettability on opposite two surfaces has demonstrated high application potential on the oil/water separation process due to its unique unidirectional water permeation property. In this study, a novel Janus membrane was prepared by electrospinning a thin layer of silica nanoparticle doped poly(vinylidene fluoride- co -hexafluoropropylene) nanofibers (PVDF-HFP/SiO 2 ) on the surface of superhydrophilic polyamine (PDA) coated Cu@Cu(OH) 2 mesh. The thickness and compactness of the nanofiber layer could be controlled by varying the electrospinning time, in which the water contact angle (WCA) value of the hydrophobic layer and critical water breakthrough column height of the membrane were able to be optimized. The Janus membrane (JM-5) with the electrospinning time of 5 min exhibited a large WCA difference of approximately 140°, achieving a spontaneous water permeation from the hydrophobic to hydrophilic direction but blocking the water flow in the reverse direction. The water flux of JM-5 membrane was estimated as 5305 L/m 2. h only under the Laplace pressure. There is no obvious change in the WCA value of the JM-5 membrane observed when the membrane was employed in high saline solutions with a wide pH range of 1–13. The JM-5 membrane could maintain a stable water flux during the 6-cycle oil/water separation process. Such Janus membrane with the function of water diode could be potentially applied for the treatment of oily wastewater and other application fields, e.g., the water removal from oil-type solutions in chemical industry.