Ag nanoparticles decorated Ag@ZrO2 composite nanospheres as highly active SERS substrates for quantitative detection of hexavalent chromium in waste water

Abstract

A novel highly active surface enhanced Raman scattering (SERS) substrate of Ag nanoparticles decorated Ag@ZrO2 composite nanosphere was prepared and characterized. A uniform ZrO2 shell was firstly coated over Ag cores by sol-gel process using zirconium butoxide as Zr precursor to achieve Ag@ZrO2 nanospheres and then Ag nanoparticles were in situ deposited on the Ag@ZrO2 through the reduction of AgNO3 to produce Ag@ZrO2@Ag composite nanospheres. The cover density of Ag nanoparticles on Ag@ZrO2@Ag nanospheres could be controlled by changing the concentration of AgNO3. TEM, FE-SEM, EDX, UV–vis and XRD analyses were used to characterize their morphology, structure and composition. The SERS property of Ag@ZrO2@Ag was evaluated using 4-mercaptobenzoic acid (4-MBA) as Raman probe molecules. The experimental results showed Ag@ZrO2@Ag nanospheres presented remarkably SERS activity, high signal reproducibility (RSD = 6.39%) and exceptional storing stability. Subsequently, the Ag@ZrO2@Ag nanospheres acted as SERS substrates to sense Cr (VI) in water at various concentrations, and the SERS results showed great linear correlation between SERS intensities and the concentration of Cr (VI) (R2 = 0.97) with the detection limit of 0.5 μM, which is below the safety level (1 μM) in drinking water of United States Environmental Protection Agency. The Ag@ZrO2@Ag nanospheres were also successfully used to confirm the concentration of Cr (VI) in real industrial wastewater. These results demonstrated the extraordinary potential of Ag@ZrO2@Ag composite nanospheres serving as SERS substrates for trace and quantitative determination of Cr (VI) in environmental field.