Removal of Methylene Blue by Hydrogels based on N, N-Dimethylacrylamide and 2-Oxazoline macromonomer
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ORIGINAL PAPER
Removal of Methylene Blue by Hydrogels based on N, N-Dimethylacrylamide and 2-Oxazoline macromonomer Fátima Santillán 1 & Juan Carlos Rueda 1 Received: 4 March 2020 / Accepted: 1 August 2020 # The Polymer Society, Taipei 2020
Abstract New hydrogels (HG) were synthesized in aqueous medium by free radical polymerization of N,N-dimethylacrylamide (DMAA) and 2-oxazoline macromonomer (MM) initiated by potassium persulfate (KPS) and catalyzed by N,N,N,N′tetramethylethylenediamine (TEMED). In this polymerization, the monomer DMAA was also used as a crosslinker because it has the ability of self-crosslinking in the presence of peroxodisulfate initiator type. The macromonomer (DP = 24) was a gradient copolymer of 2-methyl-2-oxazoline and methyl-3-(oxazol-2-yl)-propionate with a styryl end group. 1H high-resolution (HR)MAS NMR spectroscopy allowed to confirm the structure of hydrogels and to determine the molar content of DMAA and MM in each of them. Hydrogels (HG-H) containing carboxylic groups were obtained by basic hydrolysis of HG. Hydrolyzed hydrogels (HG-H) were used for the adsorption of methylene blue (MB) in aqueous medium. It was found that the MB adsorption increased as the initial MB concentration increased, and maximum adsorption capacities were found. The influence of pH value on MB adsorption was evaluated, showing that the MB adsorption capacity of the hydrogels was higher at pH value ≥ 5.7. Adsorption isotherms were studied using Langmuir and Freundlich models. The latter model describes best the process suggesting a possible adsorption mechanism through electrostatic interactions between MB and HG-H hydrogels. The MB adsorbed inside the hydrogels, could be removed with an acidic solution and therefore the hydrogel could be applied to adsorb MB again. Keywords Hydrogels . DMAA self-crosslinking . Methylene blue . Polyoxazoline
Introduction The use and application of organic dyes in different industries generally produce polluted and colored wastewater that can affect aquatic flora and fauna. Treatment and removal of pollutants from wastewater can be carried out using physical, chemical, and biological techniques [1, 2]. Among these, adsorption techniques stand out due, in general, to their high colorant adsorption values, a relatively low-cost process, low complexity, and no release of toxic products [2–4]. In recent years, there has been a great interest in the investigation of Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10965-020-02239-6) contains supplementary material, which is available to authorized users. * Juan Carlos Rueda [email protected] 1
Polymer Laboratory, Physics Section, Research Department (DGI), Pontifical Catholic University of Peru (PUCP), Lima 32, Av. Universitaria 1801, Box 1761, San Miguel, Peru
hydrogels that can generate high adsorption capacity and that may have different functional groups in their structure that would allow modifications and, therefore, could make them selective for certain contaminants [2, 5–
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