Síntese de hidrogéis de poliacrilamida e quitosana por rota tradicional e assistida por micro-ondas para remoção do corante aniônico Acid Blue 113

Abstract

The removal of synthetic dyes from industrial effluents is of crucial importance to the environment. The adsorption process for dye removal is practical, low cost and very efficient. In this work, hydrogels of chitosan (Ch) with polyacrylamide and the cross-linker N,N'-methylenebisacrylamide (MBA) were synthesized by conventional and microwave-assisted (MW) methods for the adsorption of Acid Blue 113 dye (AB 113). It was analyzed the effect of concentration of chitosan, MBA crosslinker, N,N,N’,N'-tetramethylethylenediamine reagent (TEMED) and the time of microwave synthesis, in the removal efficiency of AB 113 and the capacity of swelling in water. The hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), elemental analysis, scanning electron microscopy (SEM) and Fluorescence confocal microscopy. The effects of the initial solution pH, adsorbent dosage, temperature, contact time, SDS surfactant concentration, dye concentration and ionic strength were explored in dye removal. The reaction time via MW is much lower and the reaction yield is greater than via conventional method synthesis. The degree of swelling in water is influenced by the presence of chitosan, synthetic route and MW time. The removal efficiency of AB 113 was shown to be dependent on chitosan content, crosslinker and time of synthesis in MW. For the continuity of the experiments, the hydrogels PAMCh2.5M6x (conventional method) and the hydrogels synthesized via MW: PAMCh2.5M6xT-120 (with TEMED) and PAMCh2.5M6xST-120 (without TEMED) were chosen. The FTIR spectra did not show differences between the hydrogels, but the SEM images showed differences in the surfaces of the materials. Analysis by confocal microscopy showed that chitosan is well distributed in the hydrogel structure. Hydrogels adsorbed about 98% of the dye from aqueous solutions, but hydrogels via MW showed greater adsorption capacity and less sensitivity to pH than via conventional method. The adsorption follows the kinetic model of pseudo-second order, the adsorption behavior of PAMCh2.5M6x hydrogel was according to the Langmuir isotherm model, and the PAMCh2.5M6xT-120 and PAMCh2.5M6xST-120 hydrogels followed the Freundlich model. For PAMCh2.5M6x the removal efficiency increased with the ionic strength, the thermodynamic parameters show a spontaneous and endothermic process, and the hydrogel proved to be promising for use in the adsorption column. The results show that the hydrogels are promising for adsorption of the dye AB 113 from aqueous solutions.