Abstract
Molybdenum disulfide (MoS2) was supported on graphene oxide (GO) by hydrothermal method. The resulting nanocomposite (MoS2-rGO) was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The experiments show that at pH 2, MoS2-rGO has a great affinity for adsorption of hexavalent chromium ions while Cr(III) ions remain in aqueous sample. In the adsorption process, the dominant role plays chemisorption. The determined adsorption capacity is 583.5 mg g−1. Parameters affecting the extraction process, namely sample pH, sample volume, contact time, and matrix ions, were investigated by sequential batch tests. Under optimal conditions (pH 2, sample volume 50 mL, sonication time 10 min, adsorbent mass 1 mg), the calibration curve covers the 1–200 ng mL−1 range with a correlation coefficient (R2) of 0.998. The recovery of the method is 97 ± 3%. Other data of merit include a relative standard deviation of < 3.5%, enrichment factor of 3350, and detection limit of 0.050 ng mL−1. The accuracy of the method was confirmed by analysis of the reference materials QC1453 (chromium VI in drinking water) and QC3015 (chromium VI in seawater). The method was successfully applied to chromium speciation in water samples, including high salinity ones. The concentration of Cr(III) was calculated as the difference between the total concentration of chromium (after oxidation of Cr(III) to Cr(VI) with potassium permanganate) and the initial Cr(VI) content.Graphical abstractSchematic presentation of a method for determination of chromium species by energy dispersive X-ray fluorescence spectrometry after preconcentration on molybdenum disulfide supported on reduced graphene oxide.
Highlights
Determination of chromium species in waters is of prime interest due to their contrasting bioavailability and physiologicalElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.According to the literature, there are three main procedures for chromium speciation: (i) selective preconcentration of Cr(III) or Cr(VI) and further oxidation or reduction determining its total concentration, (ii) preconcentration of both 542 Page 2 of 10Microchim Acta (2020) 187: 542 chromium states at different pH values and subsequent elution with different solvents, or (iii) preconcentration of both forms of chromium at the same sample pH and subsequent elution with different solvents
For preconcentration of chromium species from environmental samples, various types of nanomaterials including oxidized multiwalled nanotubes (MWCNTs) [10], MWCNTs and graphene oxide (GO) modified with Aliquat 336 [11, 12], MWCNTs modified with 3-(2aminoethylamino) propyltrimethoxysilane (AAPTS-MWCNTs) [13], GO decorated with triethylenetetramine-modified magnetite [14], GO functionalized with 3-(2aminoethylamino) propyltrimethoxysilane (GO-1N) [15], and molybdenum disulfide (MoS2) [16] were used
It can be seen that new peaks (C–S in carbon line and Mo-O/ S-O in oxygen line) assigned to surface groups are present in the spectra
Summary
A method for chromium speciation in waters by energy dispersive X-ray fluorescence spectrometry (EDXRF) after preconcentration on molybdenum disulfide supported on reduced graphene oxide (MoS2-rGO) is described. The method is based on a selective adsorption of hexavalent chromium on the MoS2-rGO surface. Considering that the adsorption of Cr(VI) occurs at acidic conditions, the method is resistant to high concentration of other coexisting anions, alkali, and alkaline earth cations usually present in water samples and for that reason can be used for sensitive hexavalent chromium determination and speciation in high salinity samples.
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