Emprego da extração em fase sólida magnética dispersiva na pré-concentração e especiação de íons Cr(VI) utilizando nanotubos de carbono amino-funcionalizados como adsorvente

Abstract

In the present study, magnetic nanotubes impregnated with 3-aminopropyltrimethoxysilane (m-MWCNT-Amino) were synthesized and used as adsorbent material in the dispersive magnetic solid phase extraction (DMSPE) for the speciation / preconcentration of Cr(VI) ions in water samples. The morphology and surface properties of the adsorbent (m-MWCNT-Amino) were characterized by infrared vibration spectroscopy with Fourier Transform (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffraction (XRD), while textural parameters were studied by the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods using adsorption isotherms in nitrogen. From the kinetic studies of adsorption, it was possible to verify that the adsorption process follows the kinetic model of pseudo-second order with excellent coefficient of determination (R2 = 0.9992). As for the adsorption isotherms, the Langmuir-Freundlich model for two sites presented the best fit to the experimental data (R2 = 0.999) and the maximum adsorptive capacity of 13.27 mg g -1. All parameters affecting Cr(VI) extraction/preconcentration efficiency, such as pH, preconcentration and elution time, amount of adsorbent and type of eluent were investigated univariate and optimized conditions were established accordingly . Under optimized conditions, the preconcentration factor, limit of detection and quantification and linear range of the proposed DMSPE-FAAS method for Cr(VI) were 11.93, 2.72 ng L-1, 9.06 ng L- 1 and 0.02-0.20 mg L-1, respectively. The precision of the proposed method, defined by the relative standard deviation (RSD) (n = 10), was 0.18% and 0.28% for Cr(VI) using solutions at 0.08 mg L-1 and 0.18 mg L-1, respectively. High recovery of Cr(VI) ions in the presence of potentially interfering cations and anions (91% - 111%) were observed for the proposed method. The method was applied satisfactorily in samples of natural and mineral waters with high recovery percentage (90.19% -101.78%) and validated in GF AAS.