Effect of LbL surface modification on characteristics and performances of cellulose acetate nanofiltration membranes

Homemade Cellulose Acetate nanofiltration membranes elaborated by phase inversion were surface modified by adsorption of alternated layers of sodium alginate (ALG) and chitosan (CHI). The membranes were characterised by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive X-ray analysis (EDX) and by contact angle measurements. Separation performances of the prepared membranes are studied with 2 g/L synthetic aqueous solutions in frontal mode, under 15 bar pressure. Morphological characterization showed a formation of a lamellar structure till 15 bilayers followed by a transition to a granular structure. We observed an increase in water and salt fluxes till 20 bilayers. More adsorbed bilayers decrease fluxes. Retention rates of monovalent salts decrease and remain constant by reaching 15 bilayers. However, we observed a constant increase in the retention rate for salts containing divalent ions. Contact angle values showed a decrease till 15 bilayers followed by an increase till 30 bilayers. The correlation of the morphological characterization, contact angle measurements and the separation performances allowed as a better understanding of all the results. The layer-by-layer surface treatment makes CA membranes less sensitive to protein fouling with 15 adsorbed bilayers. (C) 2010 Elsevier B.V. All rights reserved.