Influência dos parâmetros reacionais na síntese de Carboximetilquitosana e estudo cinético e termodinâmico de sua Interação com íons de cobre (II) em soluções aquosas

Abstract

Toxic metals are naturally found in mineral deposits, but arise in natural waters due to discharge of industrial effluents. The removal of these metals is indispensable, however, conventional methods become inefficient when these metals are present in trace levels, with the adsorption appears as an interesting alternative. Chitosan and derivatives can be used in the adsorption process. Chitosan derivatives synthesized via chemical reactions have been obtained to improve its solubility in water, in which one can mention the CMC. The CMC is used for the removal of metal ions, however, in order to improve its selectivity for adsorption, chemical modifications have been applied, such as crosslinking with glutaraldehyde, which is used to enhance the selectivity of adsorption, and allow regeneration and reuse. In the present study was optimized using a central composite design 23, the process of carboxymethylation of chitosan, in which the mass of the solutions ranged from monochloroacetic acid and sodium hydroxide, addition of reaction time. The samples were characterized as to degree of substitution, and infrared solubility in water, in which the best result was obtained using 23 g of 40% NaOH solution, 17.5 g of monochloroacetic acid solution: isopropanol 1/1 (g / g ) and reaction time of 10.6 h, yielding degree of substitution of 1.85 and solubility of 99.70%. After optimization, three samples with different values of degree of substitution between them (0.82, 1.61 and 1.09) were selected, which were characterized for solubility in different ranges of pH and molar mass viscosimetric, and as GS higher, the higher the solubility at different pH ranges and lower viscosimetric molecular weight. They were then crosslinked with glutaraldehyde, which had its degree of crosslinking determined to be soon after you incorporate adsorptive on a study, which noted that the adsorption follows pseudo-secondorder mechanism, the Langmuir isotherm, with a value of Qmax that ranging from 49 to 59.524 mg-1 g, and the exothermic process was obtained. Finally, the samples were characterized by vibrational spectroscopy in the infrared, X-ray diffraction and thermogravimetric analysis, which confirmed the carboxymethylation and complexation with copper (II) ions.