Construction of anti-swelling circuit board-like activated graphene oxide lamellar nanofilms with functionalized heterostructured 2D nanosheets

The assembly of 2D nanosheets into graphene nanofilm is attracting great interests because of their distinctive properties. However, it remains a big challenge to break through the unfixed interlayer channels caused by swelling for selective separation. In this study, novel activated graphene oxide lamellar nanofilms fixed by functionalized heterostructured MEA-C3N4 nanosheets with superior anti-swelling ability were successfully synthesized via post-synthesis activation (PSA) and alignment oriented slow deposition (AOSD). Different from traditional cross-linking by random packing, the structure-directed g-C3N4 nanosheets can not only be immobilized on activated GO to eliminate unstable interlayer structures by forming strong ionic and covalent bondings, but also act as building block to organize circuit board-like structure with highly interconnected microporosity by varying the thickness of electrical layer and the deposition rate. The strong interactions generated between building blocks reinforced the stability of interlayer sub-nanochannels and greatly suppressed swelling during cross-flow filtration for at least 120 h, in which the difference of interlayer spacing in dry condition and in water was as low as 0.2 Å. The prepared nanofilms with unique structure exhibited ultrahigh rejection (≥99.5%) toward low molecular weight organic matters. Meanwhile, due to the unique circuit board-like structure, very high water permeance (25.6 L m-2h-1 bar-1) and competitive rejection (91.0 %) for Na2SO4 were achieved, surpassing most reported GO-based or commercial nanofiltration membranes. Importantly, the permselectivity of constructed nanofilms can easily be adjusted by varying the space and type of intercalated nanosheets. The results indicate that this promising route will offer more opportunities in the synthesis of various 2D membranes with oriented structure for versatile applications.