Robust, versatile, and hemicellulose-derived biocomposite Janus membrane for saline wastewater desalination

Our society faces substantial challenges related to water scarcity and the treatment of saline wastewater. Hydrophobic polymers, such as polyvinylidene fluoride (PVDF), have gained widespread recognition for their application in membrane distillation (MD) to desalinate water. This technique is favored for its simplicity and impressive salt removal capabilities. However, when treating saline industrial wastewater, the use of hydrophobic membranes in MD is greatly limited due to issues of wetting and fouling caused by low surface tension substances. In this study, we present a facile approach to fabricating commercial PVDF-based biocomposite Janus membranes that effectively treat saline wastewater and simultaneously repel salt and low surface tension substances. The approach involves the creation of a positively charged hydrophilic layer using quaternized hemicellulose (QHC), derived from a biorefinery waste stream, which covalently bonds with PVDF to form a PVDF-QHC biocomposite Janus membrane with asymmetric wettability. The modified surface exhibits hydrophilicity when in contact with air (29.1°) and oleophobicity when submerged in emulsion (146.8°). Using saline oil emulsion feed in direct contact membrane distillation (DCMD), this Janus membrane demonstrated an excellent salt rejection rate of 99.99 %. Additionally, the amount of oil adhering to the membrane was reduced by 97% compared to that on a pristine PVDF membrane after 50 h of continuous operation. Our method offers a straightforward means to extend a cost-effective and environmentally friendly hemicellulose-derived hydration layer to commercially available PVDF membranes, resulting in a robust and versatile biocomposite Janus membrane. It has the potential to effectively treat challenging industrial wastewater with contaminants and salinity.