Abstract
Polymeric hydrogels of acrylic acid (AA), acrylamide (AAm) and N,N-Dimethylacrylamide (DMAm) were prepared by free-radical polymerization at 70°C in methanol, using allylpentaerythritol (APE) as a multifunctional crosslinker and benzoyl peroxide (BPO) as an initiator. The effects of DMAm concentration and variation of pH solutions on the swelling behavior of polymers were investigated. Also AA/AAm/DMAm hydrogel was used in experiments on adsorption of a water soluble monovalent cationic dye such as Basic Blue 9 (BB-9; Methylene blue). FT-IR results confirmed the Structural features of the obtained hydrogels. Results from SEM observation showed a three dimensional porous structure of the hydrogels. Thermogravimetric analysis (TGA) of hydrogels was performed to investigate the thermal properties. The swelling results showed an increase of the swelling of AA/AAm/DMAm hydrogels as the content of DMAm increases in the hydrogel. The swelling percentage and swelling kinetics parameters such as initial swelling rate and swelling rate constant were determined. It was also shown that the swelling of hydrogels increased with the increase of pH and the maximum extent was reached at pH 8 in all compositions. The uptake of BB-9 to AA/AAm/DMAm hydrogel is studied by batch adsorption technique at 25°C. The hydrogel in the dye solution showed coloration. Kinetics and isotherms of dye adsorption were also studied. It was found that the adsorption kinetics of hydrogels followed a pseudo-second-order model. Equilibrium isotherms were analyzed using the Langmuir and Freundlich isotherms. It was seen that the Freundlich model fits the adsorption data better than the Langmuir model.
Highlights
The use of dyes in industries like textile, dying, printing, cosmetics, food coloring, papermaking, etc. can generate colored effluents
The water absorbed by acrylic acid (AA)/AAm/DMAm hydrogels is quantitatively represented by the equilibrium water content (EWC) [35, 36], where
The hydrogel samples were synthesized via crosslinking free radical polymerization of AA, AAm and DMAm in a methanol as polymerization medium using APE as a crosslinking agent
Summary
The use of dyes in industries like textile, dying, printing, cosmetics, food coloring, papermaking, etc. can generate colored effluents. Considerable researches have been done on the characterization and swelling behaviour of synthetic hydrogels prepared by simultaneous free radical copolymerization and crosslinking in the presence of an initiator and a crosslinking agent [27,28,29,30,31,32] They can show stimuli-responsive properties to the various external parameters such as temperature, pH, solvent composition and salt composition depending on the type of functional groups in the structure [33, 34]. The adsorption kinetics and isotherms for BB-9 dye onto the hydrogels were studied
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