4 - Aminoantipyrine Forest (4-aap) And 2 - Amino-5 - (4 - Pyridyl) -1,3,4 Thiadiazole (4-aptd) Molecules On The Silver Electrode Surface Raman Spectroscopy And Electrical Chemical Research

Surface-enhanced Raman Scattering has been developed in the mid 1970s. It exhibits high sensitivity and at some specific conditions even can reach the single molecule level. Currently, Surface-enhanced Raman scattering has been widely used in the study of surface adsorption, biological macromolecules adsorption orientation and configuration and structure analysis etc. In-situ Surface-enhanced Raman Scattering (in-situ SERS) technology is considered as one kind of on-line, real-time research techniques which can study surface adsorption and interface reaction with the dependence of different conditions. Self-assembled monolayers (SAMs), is an orderly arranged and thermodynamics stable single-layer film, which can be formed by inter-molecular forces. The monolayer holds the properties of good uniformity, high-density accumulation and less defects etc. Self-assembled technology was widely used in surface analysis and can provide molecular template for surface research. The Electrochemical Impedance Spectroscopy (EIS) is a transient, in-situ electrochemical technology, which has been widely used in electrochemical process, anticorrosion mechanism of inhibitors, and evaluation of corrosion inhibitor performance. EIS can evaluate the performance of corrosion inhibitors membrane and monitor its integrity. Corrosion inhibitors have got more and more attention because of its low consumption and convenient operation characteristic. Anticorrosion mechanism of different inhibitor is not very clearly, and anticorrosion mechanism even changed at different environment for the same inhibitors and metals. Research of anticorrosion mechanism for inhibitors is so important that it can guide the application of the inhibitor.Surface-enhanced Raman Spectroscopy (SERS) technology combine with the electrochemical method can monitor the adsorption behavior and performance of the corrosion inhibition at the molecular level, which helps understand the anticorrosion mechanism of inhibitor molecule. According to this basic concept, the present thesis mainly includes the following aspects of content.1. 4-aminoantipyrine (4-AAP) molecular was self-assembled on silver surface to form a monolayer. Surface-enhanced Raman Spectroscopy (SERS) was used to investigate the adsorption mechanism of the 4-aminoantipyrine (4-AAP) on silver surface at different potentials and the solution pH. Based on density functional theory (DFT) calculation results, the approximate assignment of 4-AAP Raman and SERS spectrum was conducted. In situ SERS results indicated that the adsorption behavious of 4-AAP monolayer on the electrode surface changed with the applied potentials, the benzene ring changes to a more vertical mode and pyrine ring exhibits a more parallel fashion with the potential shifting to the more negative voltage. When the applied potential reached -0.8V, the 4-AAP monolayers desorped completely from the silver surface. The 4-AAP SAMs formed in acid medium chose to perpendicularly interact with silver surface through the N15 and O3 atoms from the benzene ring and the pyrine ring, resepctively. In the case of the alkaline solution, pyrine ring chose to be parallel to the silver surface and the benzene ring tended to being more perpendicular.2. SERS spectra of the 2-amino-5-(4-pyridinyl)-1, 3, 4-thiadiazole (4-APTD) on the silver surface was recorded and assigned by its theoretical vibrational modes calculated using B3LYP/6-311G**. With the help of B3LYP/6-311G**Density functional theory (DFT) method, SERS results indicated that 4-APTD molecule was adsorbed on electrode surface through the tilted orientation via the adsorption of N12, S1 and C2 atoms. Potential-dependent SERS results further indicated that 4-APTD molecule was adsorbed onto the electrode surface through the vertical orientation with its thiadiazole ring. The 4-APTD molecule detached completely from the surface as the potential applied at -1.3 V vs. SCE. Electrochemical impedance spectroscopy (EIS) and polarization experiments confirmed the sound anticorrosive effect of the 4-APTD film on silver surface with an efficiency of 89.5%.3. 2-amino-5-(4-pyridiyl)-1, 3, 4-thiadiazole (4-APTD) molecule that containing an amino group can be easily protonated, which leading to the change of its adsorption behavior on the silver surface. It is necessary to examine the adsorption behavior of the 4-APTD molecules on the silver electrode at different pH environment, and then investigate the different performance of the 4-APTD thin film to protect the silver electrode. SERS spectroscopy can provide information at the molecular level to thus illustrate the adsorption configuration and molecular orientation at electrode surface. By integrating the results of the electrochemical impedance spectroscopy and polarization curve, we have investigated the anticorrosion mechanism of the 4-APTD at different pH. The results suggested that at pH = 1, 4 - APTD molecular mainly adsorbed on silver surface through S1 atoms with C6 and C7 atoms of pyridine approach to the electrode surface and the whole molecular plane vertical with the electrode surface. When pH is equal to 7, 4 - APTD molecules will interact with the silver surface via N12, S1 and C2 atomics, with C6 and C7 atoms close to and the whole molecular tilt to the electrode. When the pH changes to 13, 4 - APTD molecule will react with the silver through the N12, S1 and C2 atoms and the whole molecular plane tends to be parallel with the electrode surface as compared with that of pH = 7. Polarization curves and impedance spectra showed that 4 - APTD molecular thin film exhibits the best anticorrosion efficiency at pH = 13.