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The spectroscopic and electrochemical study of amino acid biological molecular corrosion inhibition of copper

Author: SongPing
Tutor: YangHaiFeng
School: Shanghai Normal University
Course: Analytical Chemistry
Keywords: cysteamine (CA) cysteine 5-hydroxytryptamine (5-HT) copper silver self-assembled monolayers surface enhanced Raman scattering (SERS) electrochemical impedance spectroscopy (EIS) electrochemistry polarizationmeasurement cyclic voltammetry (CV) density function theory (DFT)
CLC: O657.37
Type: Master's thesis
Year: 2013
Downloads: 46
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Copper is a metal that has a wide range of applications due to its goodproperties. It is used in electronics, for production of wires, sheets, tubes, and also toform alloys. Copper is resistant toward the influence of atmosphere and manychemicals. However, it is known that in aggressive media it is susceptible tocorrosion,such as Cl–, nitric acid. We used the amino acid as an inhibitor to protectcopper electrode from corrosion, amino acids form a class of“green”corrosioninhibitors which are completely soluble in aqueous media and produced with highpurity at low cost. The high sensitivity and structure-specific information availablefrom SERS technique, combined with its nondestructive feature and the ability todetect several chromophores in a sample without pre-separation, make it well-suitedfor different biological molecules detection. In this work, we used electrochemicalimpedance spectroscopy (EIS) and electrochemical polarization to investigate thecorrosion inhibition behavior of amino acids SAMs for copper in3%NaCl solution.SERS technique was used to provide insight into the interaction manner of the CAmolecules and the copper surface. In order to support experimental data, theoreticalcalculations were conducted in order to provide molecular-level understanding of theobserved experimental behavior. Among quantum chemical methods for evaluationof corrosion inhibitors, density function theory (DFT). DFT can give some informationof highest occupied molecular orbital energy level (HOMO), the lowest unoccupiedmolecular orbital energy level (LUMO), and appears to be adequate for pointing outthe changes in electronic structure responsible for inhibitory action.1. Cysteamine (CA) is a biomolecule, which has heteroatoms such asnitrogen, sulphur. These heteroatoms improve the molecule action as coppercorrosion inhibitor. The investigation of relationship between the adsorptionstructure and anticorrosion for CA monolayers at the copper surfaces formed underdifferent pH value and different immersion time had been performed by using EIS,electrochemical polarization measurement, and SERS technique. EIS andelectrochemical polarization measurements demonstrated that CA offered high protection efficiency from corrosion. CA film formed at pH2.85for5hours on thecopper surface reached the highest inhibition efficiency of90.00%. SERS spectraexplored the effect of adsorption structure on the electrochemical mechanism ofinhibition of corrosion. CA molecules adsorbed on the copper surface by twoconformers (trans-conformer and gauche-conformer). The lower gauche-/trans-ratio was, the better inhibition was. The lowest gauche-/trans-ratio was observed inSERS spectrum recorded from CA film formed at pH2.85for5hours.2. Improved anticorrosion of copper surface in3%NaCl solution after modifiedwith cysteine and cysteamine monolayers was studied by EIS, electrochemicalpolarization measurement and cyclic voltammetry. In the cysteine/cysteamine SAMssystem, the inhabition effience of the cysteine5h was not better than the cysteaminemonolayers. However, when the immersion time of cysteamine was1h, and cysteinewas3h, the EIS mechanism of the copper surface with the cysteine/cysteamine SAMssystem was in agreement with the mode of R(Q(RW)) and polarization experimentsexhibited the anticorrosive effect of the SAMs system on copper surface with a highefficiency of91.42%. The cyclic voltammetry also gave the identical results. In situelectrochemical SERS measurement suggested that the molecules of cysteine andcysteamine experienced a state of appearance and disappearance. These resultssuggested that the cysteine/cysteamine SAMs system was also formed.3.5-Hydroxytryptamine (5-HT) known as serotonin, an electroactive indolegroup within this molecule acts as an important neuro-transmitter in the brain. Inthis experiment, the SERS technique by aided with DFT calculation was employed toelucidate the adsorption behavior of5–HT at the silver surface. Under pH=11, stable5–HT monolayers could be formed at the silver surface through O11and N6atoms astwo direct adsorption sites in a tilted orientation of molecular plane. In situobservation of electrochemical desorption process of5–HT from the silver surfacewith the applied potential ranging from0.0to–0.4V, indicated that adsorption behavior of5–HT experienced several intermediate states via molecular overturningbefore its complete detachment from the silver surface.

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CLC: > Mathematical sciences and chemical > Chemistry > Analytical Chemistry > Instrument analysis ( physics and physical chemistry ) > Photochemical analysis ( spectral analysis method) > Raman spectrometry
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