Controllable synthesis of novel porous graphene-based sheets and design of ultrathin composite films by in-situ sealing technology

In this study, we proposed a novel interfacial polymerization (IP) method for porous graphene-based sheets (PGS) with 2D structure by recombining of amino graphene quantum dots (AGQDs) at the two phases interface, and then a large-area ultrathin composite films with excellent permeability and high selectivity were prepared by in-situ sealing technology with polyamide (PA) for the first time. Adjusting the pH of AGQDs solution could promote and regulate the formation of PGS with a lamella diameter of 2 μm, an ultrathin thickness of 3.2 nm and pore size of 2.71 nm, which showed a willow-leaf-like shape with a typical 2D porous structure. Then, the PGS at the interface was sealed in-situ by PA layer generated by injecting piperazine (PIP) in the IP process to form PGS/PA composite membrane. When the PGS synthesis time and PIP concentration were reached to 60 s and 0.02 w/v% respectively, the prepared PGS/PA composite membrane exhibited the best comprehensive properties, with an ultrathin thickness of 18.6 nm, super hydrophilic surface, excellent stability and strong alkali resistance. At this condition, the permeation flux of PGS/PA composite membrane could reach 28.4 L·m−2·h−1·bar−1, which was over 300% of the original PA composite membrane (9.1 L·m−2·h−1·bar−1), while the rejection of Congo red was maintained more than 99.4%, which successfully overcame the “trade-off” effect.