Promoted deposition of polydopamine by carbon quantum dots to construct loose nanofiltration membranes

Polydopamine (PDA) coating offers an environmentally friendly and facile method to modulate membrane surface properties. However, the oxidation of dopamine process by air normally needs a long time and forms uneven PDA coatings, which limit the applications of PDA. Herein, we proposed a strategy to promote the fast deposition of PDA triggered by carbon quantum dots (CQDs) under visible light irradiation. The reactive oxygen species generated by CQDs enhance the covalent polymerization and deposition rate of dopamine, thus, forming a uniform and smooth nanofiltration membrane surface. Under the optimized conditions, the PDA coating triggered by CQDs endows the membrane with superior dye rejection of methyl blue (99.7%) and water flux of 24.4 L m-2 h-1 at 0.6 MPa. Moreover, the membrane exhibits great potential in selective separation between dye and salt, the separation factor of methyl blue /NaCl can be 199.8. This work provides an efficient strategy to construct smooth PDA coatings with a fast deposition rate, which is beneficial to tailor loose nanofiltration membrane surfaces for wide applications.