Polydopamine-modified carboxylated cellulose nanocrystrals as functional fillers for polyethersulfone (PES) membranes to achieve superior dye/salt separation.

This study presents the development of advanced tight polyethersulfone (PES) ultrafiltration membranes enhanced with polydopamine-coated carboxylated cellulose nanocrystrals (PDA@C-CNC) as functional fillers. The PDA@C-CNC fillers were synthesized via an in situ self-polymerization approach and employed as surface segregation agents during membrane preparation. Utilizing the non-solvent-induced phase separation (NIPS) technique, the highly hydrophilic PDA@C-CNC particles migrated to the interface between the polymer solution and the coagulation bath and tightly adhered to the polyethersulfone (PES) matrix through strong hydrogen bonding and π-π interactions, forming a dense, hydrophilic selective surface layer rich in polar functional groups (amino group (-NH) and hydroxyl group(-OH)). Concurrently, the support layer developed a porous structure characterized by extended and widened cavities, facilitating enhanced mass transfer. The synergistic combination of a selective dense surface layer and an optimally structured support layer endowed the modified membranes with remarkable permeability and selectivity. Surprisingly, the water flux of the modified membrane with 0.2 % PDA@C-CNC (MPC0.2) achieved a remarkable 332 L·m·h·bar, which is 2.29 times higher than that of the unmodified membrane (M0). Additionally, MPC0.2 demonstrated exceptional dyes rejection rates (Congo red (CR) > 99.7 %, Eriochrome Black T (EBT) > 97.7 %) alongside minimal salt rejection (sodium chloride (NaCl): 0.2 %, sodium sulfate (NaSO): 1.7 %). These findings highlight the potential of PDA@C-CNC/PES composite membranes for efficient and selective removal of dyes and salts from textile wastewater.