Selective solid-phase extraction using 1,5-diphenylcarbazide-modified magnetic nanoparticles for speciation of Cr(VI) and Cr(III) in aqueous solutions

In the present work, selective magnetic solid-phase extraction speciation of Cr(VI) and Cr(III) from aqueous solution with synthesized magnetic nanoparticles modified with 1,5-diphenylcarbazide (DPC). Cr(VI) could be separated from Cr(III) due to its complexation with 1,5-diphenylcarbazide. Fe3O4@SiO2@DPC with an average size of 22nm has been characterized by X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The optimized conditions for adsorption were established by adjusting the parameters affecting speciation of Cr(VI) and Cr(III), such as pH, sample volume, metal ion concentration, adsorbent dosage, and time. The modified magnetic nanoparticles preferably adsorbed Cr(VI) at pH=2.5 and made it possible to speciate it from Cr(III). Four times recovery of magnetic solid phase was investigated by eluting Fe3O4@SiO2@DPC with different concentrations of HCl, HNO3 and H2SO4 and it was found that 10mL of 1M HNO3 was the best eluent. The obtained data fitted with Langmuir isotherm of adsorption which indicates that the adsorption of Cr(VI) onto Fe3O4@SiO2@DPC is a type of monolayer sorption. Finally, magnetic nanoparticles were evaluated for chromium electroplating wastewater where it showed a sufficient ability to work in a real media.