Cellulose acetate membranes functionalized with complex polyelectrolytes via layer-by-layer assembly for improved low-pressure desalination.

The development of energy-efficient desalination membranes capable of operating under low pressure remains challenging due to the trade-off between permeate flux and salt rejection in conventional membranes. In this study, a cellulose acetate (CA)-based multilayer membrane was developed using poly (allylamine hydrochloride) (PAH) and poly (acrylic acid) (PAA) through a layer-by-layer (LbL) dip-coating approach. The pristine CA-PEG membrane prepared via phase inversion exhibited a microfiltration structure with a maximum pore size of 296.88 nm and a high permeate flux of 190.61 L·m-2·h-1 at 1.5 bar, but limited salt rejection (~50%). After PAH-PAA multilayer deposition (5-20 bilayers), the membrane pore size decreased to 39-100 nm, forming an ultrafiltration structure with smoother surface morphology (Ra ≈ 4-5 nm). The optimized multilayer membrane (MM15) demonstrated significantly improved desalination performance, achieving salt rejection of ~97% while maintaining high permeate flux (≈178-230 L·m-2·h-1) at low operating pressures (1.5-3 bar). In addition, the multilayer membrane exhibited improved short-term antifouling behavior and better reusability during repeated filtration. Application to real seawater samples resulted in salt rejection up to 98% with permeate flux ranging from 13 to 15 L·m-2·h-1. These findings demonstrate that CA-PEG/PAH-PAA multilayer membranes are promising candidates for energy-efficient low-pressure desalination with improved permeability, selectivity, antifouling, and reusability.