Síntese e aplicação de nanocompósitos magnéticos revestidos por sílica e nanotubos de carbono como adsorventes para pré-concentração de íons de Cd(II) e determinação por TS-FF-AAS

Abstract

In the present study, magnetite nanoparticles coated with silica (Fe3O4@SiO2) and magnetic carbon nanotubes (MWCNT-Fe3O4) both functionalized with 3-[(2- aminoethylamino)propyl]trimethoxysilane (3-APTS) and 2-aminobenzothiazole (2-ABT) were synthesized and used as promising adsorbents for extraction and preconcentration of cadmium ions using the magnetic solid phase extraction method (MSPE) and TS-FF-AAS detection. The characterization of the nanocomposites was performed by FT-IR, SEM, TEM, XRD, TG/DTG and textural analysis using the BET method. The mechanism of adsorption of Cd(II) ions in nanocomposites follows the pseudo-second order kinetic model and the Freundlich-Langmuir adsorption model for two active sites, with an equilibrium time of 15 minutes and maximum adsorptive capacities of 99.94 and 45.52 µg g-1 for Fe3O4@SiO2-ABT and MWCNT-Fe3O4@-ABT, respectively. The parameters that influenced the MSPE, such as adsorbent mass, eluent type, preconcentration and elution time were multivariately optimized through a full factorial design 2 4 , while the pH parameter was univariately optimized in the range of 2.0 to 9.0. Under optimized conditions, the proposed method achieved preconcentration factors of 19.36 and 10.10 times, detection limits of 0.02 and 0.11 µg L-1 and quantification limits of 0.064 and 0.38 µg L-1 for Fe3O4@SiO2-ABT and MWCNT-Fe3O4@-ABT adsorbents, respectively. Furthermore, the preconcentration of Cd(II) ions in the nanocomposites was not affected in the presence of potentially interfering ions, studied in different proportions. After 10 consecutive adsorption/desorption cycles, the adsorbents proved to be stable and with high reuse potential, attested by recovery values between 93.04% and 103.19%. To evaluate the applicability of the proposed method, samples of of tap water, mineral water, rice, tea and tobacco were analyzed using addition and recovery tests to determine the cadmium concentration, in which high percentages of recovery were observed (90.74% - 107.20%). The accuracy of the method was verified using GFAAS as a reference technique, which showed no statistical difference evaluated by the paired t test.