Investigated Of Sulfur-containing Compounds On Nano-active Substrate By Surface-enhanced Raman Scattering And Its Application In Determination

Surface-enhanced Raman scattering?SERS?,a rapid and sensitive technique for surface analysis,has been applied in multiple areas,especially in life chemistry,medicinal chemistry and analytical testing.Nowadays,it focuses on developing nano-active substrates.Compared with the conventional electrode substrate,the detection sensitivity of nano-active substrate has been greatly enhanced because of the controllable particle size and morphology,which makes it to be an effective method and characterization techniques for molecular structure,interfacial chemistry and adsorption behavior of surface.Fe₃O₄/Ag nanoparticles,nano-Ag particles,nano-Au particles and nano-Au@Ag core-shell particles with high SERS activity were prepared by co-precipitation and chemical reduction.The structure and morphology were characterized by Ultra-visible absorption spectrometer,energy spectrometer and transmission electron microscopy.2-thiophene-carboxylic acid?2-TCA?,oxamyl,phosmet molecules were calculated and optimized by density functional theory?DFT?and their normal Raman scattering?NRS?and SERS spectra were obtained.Moreover,the Raman spectral characteristics and the adsorption mechanism of the sulfur-containing compound?2-TCA,oxamyl,phosmet?on the nano-active substrate were studied from the point view of theory and practice.Firstly,the prepared Fe₃O₄/Ag nanoparticles with regularand nearly spherical morphology and a diameter of 30-60 nm were characterized and they show strong SERS effect for oxamyl and 2-TCA.Enhancement factor of oxamyl on Fe₃O₄/Ag surface was determined and calculated as 2.08×10⁵,which indicated that Fe₃O₄/Ag have significant absorption enrichment and Raman enhancement effect.Furthermore,the theroy spectra of oxamyl,2-TCA and complexes of Ag-oxamyl,Ag-2-TCA were calculated by DFT,which were similar with the results coming from experiment.At the same time,the DFT caculation was closer to the measured value when more molecules were bonded on Ag atoms.Secondly,SERS of oxamyl and 2-TCA molecule on the Fe₃O₄/Ag surface were studied and it shows that the SERS effect was related to solution concentration and pH.The Raman signal response had excellent performance in the concentration of1×10^-4 mol·L^-1 at pH 3.It was infered that oxamyl was adsorbed on Fe₃O₄/Ag by double bond side N atom and S atom.N atom closer to double bond was adsorbed on the Ag surface preferentially,and then the whole molecule was gradually closed to the Ag surface.Finally,the N atom and S atom were both adsorbed on the Ag surface.On the other hand,the neutral molecules of 2-TCA was vertically adsorbed on the Ag surface with S atom by the formation of S-Ag coordination bond to produce SERS spectra.And 2-TCA^–was adsorbed on Ag surface with S-Ag coordinate bond and O-Ag covalent bond by the?double-bonged?side pattern to produce SERS spectra.The nano-Ag particles,nano-Au particles and nano-Au@Ag core-shell particles were characterized with regular and nearly spherical morphology and a diameter of50-60 nm?20-25 nm and about 30 nm respectively.The SERS effect of phosmet molecules on different active substrates of nano-Ag particles,nano-Au particles and nano-Au@Ag core-shell particles were further studied and the results showed that it was related to the kind of active substrate.It was further infered that phosmet was adsorbed on nano-Ag particles surface by S atom with single bond to produce SERS spectra.When phosmet was adsorbed on nano-Au particles surface,it mainly depended on S atom with single bond and O atom on N heterocyclic as the active sites to produce SERS.phosmet was adsorbed on nano-Au@Ag core-shell particles surface by O atom on N heterocyclic,which makes that the whole molecule was vertically adsorbed on the nano-Au@Ag surface to produce strong SERS.Finally,the concentration of phosmet adsorbed on nano-Ag particles was determined via interpreting the corresponding SERS spectra.Potassium thiocyanate?KSCN?was selected as the internal standard and the relative intensity was formed by Raman characteristic peak(S-P stretching vibration of 503 cm^-1)of phosmet with different concentrations and characteristic peak(2120 cm^-1)of SCN^-.The results showed that a good linear relationship was obtained between the relative intensity of SERS and the concentration of phosmet in range of 5×10^-71.2×10^-5 mol·L^-1 and the linear correlation coefficient was 0.9978.The detection limit was caculated as2.82×10^-7 mol·L^-1.The relative standard deviation?RSD?of simulated sample was less than 5.47%and the recoveries were in the range of 88.7%¹10.2%.The proposed method could be further extended to the determination of similar compound molecules and has a certain practical application value.