Preparation Of Ag-based Composite SERS Substrates For Detecting Organic Dye Pollutants In Water

Organic dye pollutants in water environment is threatening the safety of drinking water of human beings. High sensitive detection of organic dye pollutants from water has become a crucial problem in our society. Applying surface enhanced Raman scattering technique to analyze organic dye pollutants in water environment to ensure the safety of drinking water has great significance. In this work, we have synthesized four "core-shell" SERS substrates based on chemical reduction, solvent hot, chemical coupling and situ polymerization methods. We have exploited X-ray diffractometer, scanning electron microscope, projection electron microscope, infrared spectrum and ultraviolet spectrometer instruments to characterize and analyze the SERS(Surface enhanced Raman scattering) active substrate which can detect organic dye pollutants in water environment.We have prepared different shapes of Ag nanoparticles to select the most excellent Ag nuclear. First, Ag spheres with the size of 1 μm and 300 nm were selected as nucleus, and GO was prepared by improving Hummer’s method. Based on GO with larger specific surface area and the fluorescent quenching effect, green synthesis method was adopted to prepare GO/Ag and core-shell Ag@GO substrates. The Ag particles were easily oxidized in the prepared GO/Ag substrate, while the prepared Ag@GO basement had oxidation resistance. Even after 12 months, it still had the SERS enhancement effect. Ag@GO has stronger SERS signal than Ag when they were used to test the 10-3 mol/L rhodamine 6G, rhodamine B and crystal violet solutions. The SERS spectrum can appear GO interference peak when Ag@GO was used to detect the 10-5 mol/L rhodamine 6G solution. The experimental results also demonstrated that the prepared Ag@GO was reusable for detecting 10-4 mol/L rhodamine B.Ag flowers with better morphology were prepared by chemical reduction method and Ag@MIP active SERS substrates were produced by coating molecularly imprinted film on the Ag flowers. As the reaction time was prolonged, the films become thicker. The SERS substrate which exhibited flower morphology still showed Raman characteristic peak even when the intensity of the laser was used as low as 0.14 μW. The detection limit of MIP for template molecule rhodamine B was 10-10 mol/L, which showed weak interference phenomenon in the background peak, and the enhancement factor of the EF was estimated as 1.6x105.By solvothermal method, nanoplate of Ag was prepared in this work, and the results show that Ag nanoplate has uniform size, neat appearance, and sharp edges and corners. In addition, this work also prepared Ag@MIPs substrate by using the Ag nanoplate as the kernel, and its detection limit was 10-12 mol/L for the rhodamine B solution. By comparison, the detection limit of the flower Ag@MIPs was increased by two orders of magnitude. Besides, experimental results show that the Ag@MIPs have reusability and competitive selectivity for target molecules.In addition, in this work, Ag spheres were firstly prepared by chemical reduction method, then by using virtual template technology to replace Ag molecules with virtual template, Ag@DMIPs SERS substrate was synthesized by coating virtual molecularly imprinted film on the surface of the Ag spheres. Through TEM characterization, the thickness of the synthesized DMIPs was 4.7 nm. And the enhancement effect of Ag@DMIPs for crystal violet was higher than Ag ball, with the detection limit up to 10-9 mol/L. Ag@DMIPs substrate itself did not have background interference peaks. For comparison purposes, this work also prepared molecularly imprinted polymer-SERS substrate(Ag@MIPs) which used crystal violet as molecule template, and its detection limit was 10-10 mol/L. But since the prepared Ag@MIPs basement had Raman background peaks, its detection accuracy was degraded. In addition, the Ag@DMIPs had the competitive ability of identifying molecules and the enhancement factor was estimated as 6.55x106.The prepared four kinds of "core-shell" active SERS substrates have oxidation resistance, reusability and competitive identification capabilities. They can detect organic dye pollutants in water environment, and show high detection sensitivity to trace of organic dyes in water.