A hydrophobic-hydrophilic MXene/PVDF composite hollow fiber membrane with enhanced antifouling properties for seawater desalination

Abstract

Hollow fiber membrane-based humidification-dehumidification desalination of seawater is a low-carbon freshwater-harvesting technology that can be powered by low-grade solar energy. Polyvinylidene fluoride (PVDF) can be easily fabricated into membranes and is considered the most promising material for industrial seawater desalination. However, membrane fouling and wetting have always been major obstacles with this technology. In this study, a hydrophobic-hydrophilic MXene/PVDF composite hollow fiber membrane (PVDF-MP) with remarkable antiwetting and antifouling properties was successfully prepared using a chemical grafting method. The interfacial dehydration reaction between the hydrophilic substrate layer (PVDF-OH) and the hydrophobic skin layer (MXene-P [MP]) was verified by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy, and a detailed reaction mechanism was provided. The hydrophilic substrate layer decreased moisture transfer resistance, while the hydrophobic skin layer reduced the membrane surface energy and increased the surface roughness. This resulted in a contact angle of 156.2°, which was measured using a new method that accounted for the curvature of the membrane. The superhydrophobic surface possessed a strong repulsive force toward water, and the air gap between the water and membrane impeded pollutant deposition on the inner surface of the membrane. Moreover, the rough surface created high entry pressure and prevented water from entering the membrane pores. Thus, the permeate flux of the PVDF-MP membrane persisted over 120 h during desalination tests, surpassing the performance of traditional materials.