Nanofiltration membranes fabricated through ultra-thin α-Co(OH)2 nanosheets with high chlorine resistance and long-term stability for efficient dye removal

At present, freshwater resources are scarce, and printing and dyeing wastewater are the main freshwater pollution sources. To purify dye wastewater, nanofiltration membrane technology was developed. This study developed a new nanofiltration membrane by mixing an ultra-thin α-Co(OH)2 nanosheets with sodium alginate (SA) and papermaking by-products calcium lignosulfonate (CaLS). X-ray diffraction (XRD), Fourier Infrared Spectroscopy (FITR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Contact angle (CA) were used to analyze ultra-thin α-Co(OH)2 nanosheets and α-Co(OH)2@CaLS/SA membrane, confirming the successful synthesis and sheet morphology of the α-Co(OH)2 nanosheets, and finding the hydrophilicity increases of the α-Co(OH)2@CaLS/SA membrane and its morphology change. Dye separation experiments showed that the α-Co(OH)2@CaLS/SA membrane has a good separation effect on Rose Bengal sodium salt, Coomassie brilliant blue and Congo red dyes, with a retention rate is above 99%. Moreover, the membrane showed high flux for Rose Bengal sodium salt 48.5 L m−2 h−1, Coomassie Brilliant Blue 60.4 L m−2 h−1, Congo Red 74.8 L m−2 h−1. In addition, the α-Co(OH)2@CaLS/SA membrane has superior chlorine resistance and long-term operation stability, which provides advantages in industrial applications.