Nano-carboxymethylcellulose, polyacrylamide, and γ-Fe2O3-SO3H cross-linked to a hydrophobic linker: An organic-inorganic hydrogel for adsorptive removal of dyes

Abstract

Dye removal by magnetic hydrogel adsorbents has the potential to compliment water treatment. Here, a new pH-responsive and magnetic hydrogel implanted with the hydrophobic chlorophenyl groups was prepared by cross-linking the cotton-derived nanocarboxymethylcellulose crystals (NCMCC), γ-Fe2O3-SO3H, and polyacrylamide (PAAmide) to the N,N'-((4-chlorophenyl)methylene) diacrylamide (NNCMDA). Besides to the hydrogel's magnetizing agent, γ-Fe2O3-SO3H was the catalyst in synthesis of bis-acrylamide NNCMDA that cross-linked the components in hydrogel NCMCC/PAAmide/γ-Fe2O3-SO3H/NNCMDA characterized by FT-IR, FESEM, TGA, BET, VSM, and XRD analyses. While implantation of hydrogel by hydrophobic cross-linker NNCMDA caused ∼1.5 times drop in swelling capacity, a general adsorptive removal plus to selectivity were observed for cationic dyes of Methylene blue (MB) and Rhodamine B (RB) with adsorption capacities of 717.0 mg/g and 61.0 mg/g, respectively. Adsorption mechanism for MB was in agreement with the Langmuir model (R2 = 0.99) and a monolayer adsorption of dye on the hydrogel surface, whereas adsorption kinetics was compatible by the pseudo-second-order model (R2 = 0.99). The advantages of the present hydrogel are simultaneous entering of the nano-CMC, hydrophobic implant NNCMDA, and the pH-responsive magnetizing agent γ-Fe2O3-SO3H into the hydrogel matrix and upgrading the removal performance of hydrogel to 74.68% for MB and 50.85% for RB without change after the fifth recycling run. All results confirmed the more adsorptive effectiveness of the NCMCC/PAAmide/γ-Fe2O3-SO3H/NNCMDA in dye removal versus the reported cellulose-based hydrogels.