Cellulose Nanofiber Modified Poly (Acrylic Acid-Co-N-Vinyl Pyrrolidone) Hydrogel as Forward Osmosis Draw Agent

Cellulose nanofibers (CNFs) as a hydrophilic natural nanomaterial with high surface area, high strength, and tunable surface chemistry are widely used to improve the characteristics of hydrogels. So, in this study, we proposed to improve the performance of poly (acrylic acid-co-N-vinyl pyrrolidone) hydrogel as forward osmosis (FO) draw agent with CNFs. The successful incorporation of CNFs was confirmed by using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X-Ray diffraction (XRD) analysis. Then, the CNF-modified hydrogels' physicochemical characteristics such as swelling ratio, regeneration, and water recovery were thoroughly studied. Additionally, the FO performance of all hydrogels was carefully measured. The results showed that by the incorporation of CNFs, the swelling ratio and the water flux of hydrogel increased. This is due to the combined effects of the surface porosity and provided osmotic pressure. However, by increasing CNF concentration up to 2 wt%, FO water flux slightly decreased due to the rigid and compact structure of the hydrogel. Moreover, CNF-based hydrogel indicated an acceptable recycling capability with a slight flux decline in five frequent FO process cycles. To treat Direct Red-80 dye by FO process, the PH-CNF1.0 hydrogel (modified with 1 wt% CNFs) was used as a draw agent. The result revealed PH-CNF1.0 capable of generating a proper FO water flux of 3.6 LMH from an aqueous solution containing 200 ppm Direct Red-80. Our finding offers a simple and efficient method to enhance the hydrogel-based draw agent's FO performance by incorporation of CNFs.