Tuning the pore size of graphene quantum dots composite nanofiltration membranes by P-aminobenzoic acid for enhanced dye/salt separation

Nanofiltration (NF) is a promising technology for fast molecular and ionic separation. Pore engineering is a critical but challenging strategy to fabricate NF membranes with high permeability and precise sieving ability. Herein, we proposed a post-modification approach to regulate the pore size of graphene quantum dots (GQDs) composite NF membranes by using a small molecule p-aminobenzoic acid (PABA) as a modifier. First, GQDs were used as the aqueous phase monomer of interfacial polymerization to react with trimesoyl chloride within the pores of the porous substrate, thereby fabricating large-pore-size GQDs composite NF membranes. After that, the self-polymerization of PABA within the pores of GQDs NF membranes would form nanoaggregates with different sizes, thus finely tuning the pore size of the as-prepared membrane. The PABA-modified membranes exhibited a range of pore sizes from 2.18 to 1.50 nm with the increased concentration of PABA. Specifically, the optimal PABA-modified membrane showed high water permeance of 128.1 L m −2  h −1  bar −1 and complete interception of 1000 Da-higher dye molecules, with desirable dye/salt selectivity factors of 877.0 and 175.4 for Alcian Blue/Na 2 SO 4 and Evans Blue/Na 2 SO 4 separation systems, respectively. Moreover, the membranes exhibited outstanding physicochemical stability. This study provides a facile method for pore size regulation of NF membranes.