Dual-polymers inserted graphene oxide membranes with enhanced anti-wetting and anti-scaling performance for membrane distillation

Graphene oxide (GO) based membranes with exquisite sieving nanochannels are promising for advanced separation process. The goal-directed GO nanochannels can be skillfully regulated by inserting various molecules. Although GO has been employed to enhance the permeation of hydrophobic membrane during the membrane distillation (MD), the effectiveness of GO layer and decorated 2D nanochannel with molecules on the wetting and scaling of MD have not been systematically investigated yet. Herein, a novel GO Janus membrane inserted by polyethyleneimine (PEI) and poly (acrylic acid) (PAA) was developed. According to our results, the intercalation of PEI or PEI-PAA sustained the constructure stability of GO layer via multiple binding forces, which also created a defect-free and dense membrane surface. Moreover, the synergism of stabile 2D nanochannels and phase change in the PEI-PAA-GO membrane generated a continuous capillary force, which protected the substance polyvinylidene fluoride (PVDF) membrane from wetting. The fabricated PEI-PAA-GO membrane resisted the 0.4 mM sodium dodecyl sulfate (SDS) and prolonged the MD test for 17 h compared with GO membrane. Molecular dynamics simulation verified that polymer insertion increased the energy barrier of transport and desorption of SDS molecules from the 2D nanochannels. In addition, the rationally inserted PAA decorated GO nanochannels with more carboxyl groups, which stabilized the scale precursor and nascent CaSO4 nuclei, postponing the growth of crystalline gypsum. The MD operation of scaling test was prolonged for 42 h in the optimal PEI-PAA-GO membrane, which was 10 times higher than that of GO membrane. This work synchronously promoted the anti-wetting and anti-scaling of GO based Janus membrane during the distillation process of hypersaline wastewater.