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 (D_eff) of the CMC-Al membrane increased 56-fold, and that of the CMC-Fe membrane increased 3500-fold. This significant correlation between D_eff 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.