Tailorable regulation of mass transfer channel in environmentally friendly calcium alginate membrane for dye removal

Abstract Environmentally friendly polymer membranes for dye contamination removal were prepared from edible calcium alginate. The stable gel structure was formed by molecular chains of sodium alginate cross-linked by chelate-formation with calcium ions. To improve the water permeability of the membranes and make them suitable for membrane separation processes, their mass transfer channels were precisely regulated to form fine voids via the addition of oligoethylene glycol (OEG) or polyethylene glycol (PEG) to a casting polymer solution and subsequent removal of the OEG or PEG from the membranes by a washing process after cross-linking. Fourier transform infrared spectroscopy confirmed that the chemical properties of the membranes with voids formed by OEG or PEG were the same as the properties of the original calcium alginate membrane without void forming. Despite their same chemical properties, the performance of the membranes clearly differed. The effect of the different void structures on the mass transfer channels was investigated using pure water permeation, Methyl Orange dye rejection, and volumetric void fraction measurements, as well as morphological observations by field-emission scanning electron microscopy. The membrane with voids formed by OEG exhibited to an increase in water permeability compared with the original membrane, whereas the molecular separation performance was maintained within the nanofiltration region. Meanwhile, the membrane with voids formed by PEG was suitable for use in high-flux ultrafiltration processes for pretreating wastewater. The biocompatible membranes with tailorable separation ability presented herein are candidates for use in purification processes for recovering dye-polluted water resources.