Preparation of Fe3O4@Ag SERS substrate and its application in environmental Cr(VI) analysis

A novel sensitive and recyclable SERS substrate which can actively concentrate chromate (Cr(VI)) in water and substantially enhance Raman signal was synthesized as uniform Fe3O4@Ag nanoparticles. The surface morphology, structure, and magnetic properties were characterized using transmission electron microscopy, atomic force microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and vibrating sample magnetometry analysis. The closely spaced Fe3O4@Ag substrate with a core–shell structure exhibited a 25 nm surface roughness. The high saturation magnetization at 48.35 emu g−1 enabled the complete and rapid separation of the substrate from the solution. The sensitivity and reproducibility of the substrate were confirmed using a common SERS probe molecule, rhodamine 6G. SERS spectra of Cr(VI) in simulated and real contaminated water showed that the symmetric stretching vibrations of Cr–O occurred at 796 cm−1. This SERS peak area exhibited a linear dependence (R2 = 0.9992) on the Cr(VI) concentration between 5 and 100 μg L−1. Coexisting anions such as sulfate, nitrate, chloride, carbonate, and humic acid could decrease the sensitivity of the SERS analysis. However, the adverse effect of the competing ions may be eliminated by proper dilution of the raw sample. This study provides a reliable method for qualitative and quantitative analysis of Cr(VI).

Graphical abstractThe synthesized Fe3O4@Ag nanoparticles with an average of 27 nm particle size and 25 nm surface roughness could be used as active SERS substrates for Cr(VI) determination.Figure optionsDownload full-size imageDownload high-quality image (74 K)Download as PowerPoint slideHighlights► A simple process was introduced to synthesize Fe3O4@Ag magnetic nanostructures. ► The SERS substrate can adsorb Cr(VI) and substantially enhance Raman signal. ► Determination of Cr(VI) was achieved using a portable Raman spectrometer.