Composite membranes with cellulose acetate surface layer for water treatment

Microporous composite membranes containing from one to three ultrathin layers are obtained by a multistage immersion of a paper base in a solution of cellulose acetate in acetone. The physicochemical properties of the membranes are studied and the parameters of the membrane separation of heavy metal ions from tap water are determined. An increase in the particle size and a decrease in the absolute value of the ζ potential with the increase in the concentration of cellulose acetate in acetone are revealed. It is found that the membrane porosity increases from 47 to 51% depending on the number of ultrathin cellulose acetate layers on the substrate surface. A decrease in the moisture absorption of the composite membranes and an increase in the contact angle of wetting with distilled water from 30.0 to 68.8°, depending on the number of ultrathin layers, are observed. The scanning electron microscopy investigation of the membrane surface shows that the ultrathin layer consists of many pores with sizes less than 1 μm. The absorption bands in the IR spectra of the cellulose acetate and the surface of the composite microporous cellulose acetate (MCA) membrane are identical. The retention capacity of the composite MCA membranes is found by separation of iron ions from an iron(III) chloride solution and ranges from 47.5 to 97.4% depending on the number of cellulose acetate layers on the substrate surface for the specific performance ranging from 27.9 to 7399 dm3/(m2 h) and pressure 0.35 MPa. A high selectivity of a microporous membrane with three cellulose acetate layers (MCA-3) for heavy metal ions contained in tap water is found: Cr3+ (96%) > Cu2+ (92%) > Fe3+ (90%) > Mn2+ (45%).