Preparation and characterization of poly(vinyl alcohol)/sodium alginate/TEMPO-oxidized cellulose nanofiber hydrogel for dye removal

The composite hydrogel of poly(vinyl alcohol) (PVA)/sodium alginate (SA)/TEMPO-oxidized cellulose nanofiber (CNF) was prepared and employed as an effective adsorbent for dye removal. The effect of the weight ratio of incorporated SA and CNF components on the mechanical and dye removal properties of the hydrogel was examined in detail. While the PVA concentration and the SA + CNF concentration were maintained as constant (7.5 and 1.0 wt%, respectively), the weight ratios of SA:CNF were changed from 10:0 to 7:3. Cross-linking of PVA, SA, and CNF were carried out by using boric acid/borax and calcium chloride. The mechanical properties of prepared hydrogels were investigated by a compressive stress test and a durability test under severe agitation in a solution. The PVA/SA hydrogel with no CNF addition (the 10:0 hydrogel) showed the highest compressive strength, and the elastic modulus is approximately 40 times greater than the highest reported value of the conventional PVA hydrogel cross-linked by glutaraldehyde (GA). The hydrogel prepared with SA:CNF ratio of 9:1 (the 9:1 hydrogel) showed the second-highest elastic modulus. In terms of durability, the 9:1 hydrogel was the highest. While the breakage ratio of the 9:1 hydrogel under very severe agitation condition of 2750 rpm was essentially negligible, it was reported that the conventional PVA hydrogel crosslinked with sodium sulfate was completely broken. Even under 3000 rpm, only 12% of the beads were broken for the 9:1 hydrogel. Dye removal experiment was carried out by using methylene blue (MB) as a model dye. The result shows that the highest MB adsorption capacity of 243.9 mg g-1 was obtained for the 9:1 hydrogel. The value was 1.4 times higher than that of the highest reported value for the conventional PVA-based adsorbent. With superior mechanical and dye adsorption properties, the developed PVA/SA/CNF hydrogel can be considered as a potential alternative for dye removal