The Size Effect Of Surface Plasmons On Gold And Silver And Their Role In The Catalytic Oxidation Of PATP

Surface plasmon resonance(SPR)is the free electrons’ collective oscillations that are confined evanescently on a metal surface.It’s excited by incident light at a specific wavelength and has some unique optical properties.Because of the radiative damping of surface plasmons result in a significant enhancement of the localized electromagnetic field,surface plasmons have been widely used in surface enhanced spectroscopies.On the other hand,the hot electrons(holes)that nonradioactively decay from surface plasmons can trigger chemical reactions.Size of metals nanostructure has a significant effect on the surface plasmon intensity and the corrosion resistance of metals is closely related to their surface microstructure.This work focused on the surfaces of gold plates which were prepared through a polishing process with different sizes of α-Al2O3.By means of SEM and AFM characterizations,the surface microstructures of the gold plates were distinct,indicating that the polished gold plates had surface microstructures similar to those of real work-pieces.The effects of the gold surface scratches on surface plasmon and corrosion resistance were investigated.Surface plasmons have recently been discovered that have catalytic activity and can catalyze p-Aminothiophenol(PATP)coupling to p,p’-dimercaptoazobenzene(DMAB).However,the mechanism of this plasmon catalytic reaction is not clear yet.In this work,we prepared substrates with strong surface plasmon and tested them by home-made in situ Raman electrochemical system.The effects of hot electrons(holes),oxygen and substrate on surface catalysis of PATP were investigated.The mechanical polishing that using different sizes of α-Al2O3 was conducted to prepare gold plates and ensured that the gold plates surface had different-sized scratches.By means of SEM and AFM characterizations,the sizes of the gold plates surface scratches were distinct.The effects of the gold surface scratches on surface enhanced Raman spectroscopy(SERS)were investigated.SERS on the gold surface scratches with different average feature sizes were tested using Rhodamine B(RhB)as a probe molecule.When the average feature sizes increasing,the surface plasmon intensity was first increasing and then decreasing and reached maxima when the average feature size of the surface scratches is close to 50 nm.Then,the effects of the gold surface scratches on corrosion resistance were tested by electrochemical polarization measurements.The result showed that,when the average feature size of the surface scratch is bigger than 50 nm,a good coherence exists between the surface plasmon intensity and the free corrosion potential of the gold plates.Through Raman signal can evaluate the corrosion resistance of the gold plates.These results indicate that SERS technique could be applied for the corrosion resistance analysis of the work-pieces.By the means of smearing probe molecules and using a handheld Raman spectrometer,quick analysis of the work-pieces corrosion resistance is very promising.The gold and silver nanoparticles which have uniform size and strong surface plasmon were prepared on graphite substrate by electrochemical deposition.By means of electrochemical surface-enhanced Raman spectroscopy,the influence of the atmosphere on the reaction rate of P ATP adsorbed on Ag NPs/C was investigated.The result showed that the oxygen up the coupling reaction of PATP.By adding ethanol as hole capturer to study the effects of hot holes on surface plasmon catalytic coupling reaction of PATP,it was found that hot holes were the oxidant of the coupling reaction of PATP under Ar atmosphere and that oxygen molecules which were activated by hot electrons accelerated the coupling reaction of PATP under O2 atmosphere.The influence of the pH on the coupling reaction was investigated.The result showed that the silver oxide on the Ag NPs played an important role in the coupling reaction under O2 atmosphere,and proved that hot holes were the oxidant of the coupling reaction of PATP under Ar atmosphere again.In addition,the influence of the atmosphere on the coupling reaction rate of PATP adsorbed on Au NPs/C was investigated.The result was similar to the reaction of PATP adsorbed on Ag NPs/C.