Oxalic acid cross-linked sodium alginate and carboxymethyl chitosan hydrogel membrane for separation of dye/NaCl at high NaCl concentration

Dye desalination is a challenge in the treatment of textile wastewater with high salt concentration. It is imperative to develop salt resistance membrane that is from sustainable materials to effectively treat dye/salt mixtures. And most polymer membrane materials are non-renewable petrochemical resources. In this paper, a green hydrogel membrane (CMCS-OA-NaAlg) was prepared by non-metallic ions of oxalic acid (OA) cross-linking of two natural macromolecules of sodium alginate (NaAlg) and carboxymethyl chitosan (CMCS). The membrane showed excellent anti-swelling at high salt concentration (swelling rate less than 8.0% in 10.0 wt% NaCl solution) and good anti-fouling performance. The membrane exhibited a rejection higher than 95.0% for dyes (bright blue, direct black, direct red, and Congo red) and lower than 7.0% for NaCl, which can achieve better dye/NaCl separation performance. This study provides a promising membrane material for high salt textile wastewater treatment only using water and carbohydrates as raw materials without any organic solvents.