Preparation of highly smooth nanofiltration membranes based on lignin nanoparticle hydrogels and study of interfacial mechanism

• The polycondensation reaction rate regulation and interfacial stabilization improvement were achieved simultaneously. • A novel lignin nanoparticle hydrogel for replacing conventional aqueous phase interfacial materials was synthesized. • A novel highly smooth and anti-fouling nanofiltration membrane was prepared. Limited by the synthetic materials, traditional nanofiltration membranes have always suffered from high surface roughness due to the fast interfacial polymerization rate and the interfacial perturbation during the preparation process. Herein, a method for developing lignin nanoparticle hydrogels to replace traditional aqueous phase materials is proposed, synchronizing interfacial polymerization rate modulation and interfacial stabilization enhancement for the preparation of smooth and anti-fouling nanofiltration membranes. The surface, structural and performance of the fabricated membrane were evaluated comprehensively and compared. The atomic force microscope analysis revealed that the surface roughness of prepared membrane decreased by 63 % (Ra = 34.3 nm), while SEM analysis confirmed its thinner filtering interface (46 nm) when lignin nanoparticle-based hydrogel was incorporated into NF membrane. The surface of the fabricated membrane presented –23.67 mV zeta potential and 36.85° contact angle, also implying better anti-fouling property. Thanks to these characteristics, the developed membranes exhibited a higher fouling resistance and flux recovery ratio (FRR, 95.4 %). In addition, the mechanical strength of the prepared membranes was improved by 45 %. The density functional theory (DFT) further confirmed that the binding energy of lignin and 1,3,5-benzenetricarbonyl trichloride (TMC) was −8.92 kcal · mol −1 , which was lower than that of conventional nanofiltration membranes, facilitating the mild and controllable reaction that benefited the thin and smooth surface on the NF membrane. This study provided a new technique for fabricating a more sustainable NF membrane with improved mechanical strength, surface smoothness.