Rapid and ultrasensitive surface enhanced Raman scattering detection of hexavalent chromium using magnetic Fe3O4/ZrO2/Ag composite microsphere substrates

It is greatly significant to sense hexavalent chromium (Cr (VI)) in water because Cr (VI) is one of the most toxic heavy metals and is extremely harmful for human health and environment. In this study, we explored sensitive surface-enhanced Raman scattering (SERS) substrates for rapid detection of Cr (VI) using magnetic Fe 3 O 4 /ZrO 2 /Ag composite microspheres. We firstly coated uniform zirconium dioxide layer around Fe 3 O 4 cores to achieve Fe 3 O 4 /ZrO 2 microspheres and then deposited silver nanoparticles onto their surface via controlled reduction of AgNO 3 by n-butylamine. The SERS sensitivity of Fe 3 O 4 /ZrO 2 /Ag composite microspheres were easily tailored via facilely changing the concentration of AgNO 3 to tune the coverage of silver nanoparticles on the Fe 3 O 4 /ZrO 2 /Ag. We used 4-mercaptobenzoic acid (4-MBA) as a Raman molecule to evaluate the SERS activity of Fe 3 O 4 /ZrO 2 /Ag. They illustrated excellent SERS property as well as magnetic responsibility. The optimized Fe 3 O 4 /ZrO 2 /Ag were employed to quantitatively detect Cr (VI) in aqueous solution. The results showed good linear relationship between SERS intensities and logarithm concentrations of Cr (VI) (R 2 = 0.98) with a detection limit of low down to 10 −7 M, which is much lower than the safety value (1 μM) in drinking water of United States Environmental Protection Agency. Moreover, the highly uniform and robust Fe 3 O 4 /ZrO 2 /Ag composite microspheres display outstanding signal reproducibility (RSD = 8.34 %) and good storage stability. These results indicate that the prepared Fe 3 O 4 /ZrO 2 /Ag composite microspheres have promising application prospect for SERS analysis of environmental pollutants.