Remazol red dye removal using poly(acrylamide-co-acrylic acid) hydrogels and water absorbency studies

Acrylamide (AAm) and acrylic acid (AAc) were copolymerized in aqueous solution using 2,2-azobis(2-amidinopropane) hydrochloride (V-50) as initiator and N,N′-methylenebisacrylamide (NMBAM) as cross-linking agent to obtain high swelling hydrogels. The effects of AAm/AAc ratio and the amount of cross-linking agent on the swelling properties were studied. It was observed that swelling characteristics of hydrogels are highly affected by the presence of carboxylic groups of AAc units in the hydrogels and by the cross-linking amount in the polymer chains. Hydrogel with 70/30 ratio of AAm/AAc showed the highest swelling degree, until 69.2 g of water/g of dried hydrogel, which represents approximately 7000%25 of swelling. Swelling kinetic was well represented by a second-order kinetic model for all the AAm/AAc compositions with maximum weight swelling ratio between 20.4 and 82.6 g/g for the hydrogels synthesized using 1%25 of NMBAM. Diffusion behavior analyses determined that water diffusion into hydrogels followed the anomalous Fickian behavior. The as synthesized hydrogels were used in the removal of Remazol Red 3BS (RR3BS) dye from aqueous solutions, finding that the maximum dye adsorption capacity for an equilibrium aqueous concentration of 130 mg/L of RR3BS was 44.19 mg of RR3BS/g of dried hydrogel with 1%25 of NMBAM, with an adsorption mechanism well represented by the Langmuir model. © 2016, Springer-Verlag Berlin Heidelberg.

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