Simple and efficient method for the determination of Cr(VI) ions in water samples using m-MWCNT@APTMS through dispersive magnetic solid phase extraction

Abstract

ABSTRACT This work describes the synthesis and characterisation of a promising adsorbent nanocomposite based on magnetic multiwalled carbon nanotubes (m-MWCNTs) functionalised with 3-aminopropyltrimethoxysilane (APTMS). Was developed a method based on dispersive magnetic solid phase extraction (DMSPE). It also details its use in the development of a rapid and simple preconcentration method for Cr(VI) ions in water samples with FAAS detection. The nanocomposite was characterised using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM); the textural data measurements were obtained using the Brunauer-Emmett-Teller (BET) and Barret-Joyner-Halenda (BJH) analyses. The maximum adsorption capacity of the m-MWCNT@APTMS nanocomposite for Cr(VI) ions was 13.37 mg g-1 at an equilibrium time of 20 min. The adsorption process followed the dual-site Langmuir-Freundlich model, while the kinetic data were well fitted by the pseudo-second-order model. The important variables that affect the performance of the MSPE method, such as the pH of the sample, adsorbent mass, preconcentration and elution time, and type of eluent were univariately optimised. Under the optimised condition, an aliquot of 20 mL of sample was preconcentrated using 40 mg of m-MWCNT@APTMS for 4 min under vortex agitation. After this, the nanoparticles were separated from the solution with a magnet, then, the adsorbed Cr(VI) ions in the adsorbent were eluted with 1.0 mL of 2.0 mol L-1 HNO3 for 1.0 min and submitted to FAAS detection. The linear range studied was of 0.02 -0.2 mg L-1. When the enrichment factor was 20, the LOD and LOQ to Cr(VI) ions were 3.18 and 10.7 µg L-1, respectively, presenting RSD of 0.18% and 0.28% for solutions of Cr(VI) at 0.08 mg L-1 and 0.18 mg L-1. Finally, the proposed method was applied for the speciation of Cr(VI) in water samples and the results were compared with reference technique (GF AAS).