Influence of the Fabrication Conditions on the Physical Properties and Water Treatment Efficiency of Cellulose Acetate Porous Membranes

In membrane-based water purification technology, control of the membrane pore structure is fundamental to defining its performance. The present study investigates the effect of the preparation conditions on the final pore size distribution and on the dye removal efficiency of cellulose acetate membranes. The membranes were fabricated by means of phase inversion (using different speeds of film casting and different thicknesses of the casted solution) and introducing modifications in the preparation conditions, such as the use of a coagulation bath instead of pure water and the addition of a surfactant as a solution additive. Both isotropic and anisotropic membranes could be fabricated, and the membranes' pore size, porosity, and water permeability were found to be greatly influenced by the fabrication conditions. The removal capacity towards different types of water contaminants was investigated, considering, as model dyes, Azure A and Methyl Orange. Azure A was removed with higher efficiency due to its better chemical affinity for cellulose acetate, and for both dyes the uptake could be fitted using a pseudo-second order model, evidencing that the rate-limiting step is chemisorption involving valency forces through the sharing or exchange of electrons between the dye and the membrane.