Highly Size-Selective Water-Insoluble Cross-Linked Carboxymethyl Cellulose Membranes

Carboxymethyl cellulose (CMC) membranes have strong potential for application as molecular-scale separators. For this study, stable CMC membranes were fabricated with aluminum chloride (AlCl3) and iron(III) chloride (FeCl3) serving as cross-linkers. The resulting CMC-Al and CMC-Fe membranes were optically transparent and water-insoluble with sufficient mechanical strength for practical applications. The water permeation flux through the membranes was directly proportional to the operating pressure. With just a 10-fold increase in the molecular weight from 60 Da (urea) to 604 Da (bordeaux S), the effective diffusion coefficient (Deff) of the CMC-Al membrane increased 56-fold, and that of the CMC-Fe membrane increased 3500-fold. This significant correlation between Deff on molecular size indicated that the sizes of the mass transfer channels through the membrane were strictly monodisperse, in the range of molecular sizes that were tested.