Nickel oxide/nickel ferrite/layered double hydroxide nanocomposite as a novel magnetic adsorbent for chromium speciation

Abstract

A facile hydrothermal method was used to prepare a magnetic nanocomposite (MNC) based on nickel oxide/nickel ferrite/Ni-Al layered double hydroxide (NiO/NiFe2O4/LDH). The synthesized NiO/NiFe2O4/LDH MNC was characterized using various techniques, including X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and vibrating sample magnetometry. After evaluation of its capability to selective extraction of Cr(VI) ions, an efficient magnetic solid-phase extraction method was developed for the pre-concentration and speciation of chromium species (Cr(III) and Cr(VI)) using the as-prepared NiO/NiFe2O4/LDH MNC as an adsorbent and flame atomic absorption spectrometry. Due to owning positively charged surface, the LDH can establish selective electrostatic interaction with Cr(VI) species in the form of CrO42- or HCrO4-. Numerous important parameters influencing the extraction efficiency were studied and optimized. Based on the method validation applying the optimized extraction conditions, the calibration curve was linear in the range of 0.5 to 120 ng mL−1 with a correlation coefficient of 0.9983. The limit of detection was estimated to be 0.14 ng mL−1, and the method intera- and inter-day precisions were 1.47% and 3.19%, respectively. The presented method was validated by the analysis of the certified reference material NIST SRM 1643e, and applied for the speciation of Cr(VI) and Cr(III) species in various water and industrial wastewater samples.