Preparation Of Ag@PDA@Au Nanocomposites For Surface Plasmon Induced Nitration Reaction

Surface-enhanced Raman scattering(SERS) is widely used to detect low concentration of chemical and biological molecules. In recent years, based on SERS technology, surface plasmon catalytic reaction(SPAC) is found.It can realize some catalytic reactions which conventional catalysts can not realize. Surface plasmon(SP) can be described as the resonant photon-induced collective oscillation of valence electrons. Hot electrons and thermal effect induced by laser are helpful for the study of catalytic reaction.In this paper, study the surface plasmon inducing nitration reaction based on in situ SERS technique on single particles. The nitration reaction requires nitric acid,while silver is easy to be corroded, so the SERS substrate needs to be modified. Prepare Ag@PDA@Au composite particles based on the strong adhesion and weak reducing ability of Polydopamine(PDA).Study the effects of polymerization time of PDA and the concentration of chlorine acid solution to the composite particles by SEM, XRD, TEM, EDS, SERS. The results prove that the composite particles perform best when the period of dopamine polymerization time is 45 minutes and the concentration of chlorine acid solution is 10 mmol/L.Study the nitration reaction between thiophenol and nitric acid on the Ag@PDA@Au composite particles based on the in situ SERS technique.The study finds that a new Raman peak appears at 1330 cm-1 as the laser irradiation.The density functional theory(DFT) calculations indicate that the production is nitrothiophenol(NTP). Further studies show that the rate of the nitration reaction is proportional to the laser intensity and the SERS substrate is a necessary condition for the nitration reaction occurs. The reaction system including Ag@PDA@Au composite particles, nitric acid and thiophenol is heated to different temperatures, finding that the speed of the nitration reaction will accelerate as the temperature increasing, proving that SP plays a role of plasmon hot source in the reaction.Study the same nitration reaction on gold nanoparticles and silver nanoparticles as comparison, finding that the reaction is first to stabilize on the gold nanoparticles, while the nitration reaction needs more time to stabilize on silver nanoparticles. It proves that gold can reduce the energy barrier of the nitration reaction. Study the effect of hydrogenion to the nitration reaction,and the study proves that hydrogenion acts as a catalyst to the reaction, so the mechanism of the nitration reaction is obtained. Study the nitrition reaction of thionaphthol, cysteine, p-aminophenol and p-toluenethiol, finding the group type and molecular structure of the reactant molecules can affect the occurrence of SP induced nitrition reaction.