Formation And Electrochemical Real-time In-situ Characterization Of Self-assembled Monolayers Of Mercaptan On Gold Electrodes In Nonaqueous Solution

Over the past three decades, self-assembled monolayers (SAMs) has been a new type of organic ultra-thin film with high-density accumulation, the rules of an orderly, uniform, excellent performance, which has been used for many different areas, such as electroanalytical chemistry, chemical and biological sensors, adhesion, lubrication, corrosion on surfaces and interfaces, electronic devices, optical element etc.,showing a broad application prospect. Real-time in-situ characterization of SAMs which can be used to prepare and regulate SAMs is one of the key technology.However, there is lacking an effective method of real-time in-situ characterization.In nonaqueous solvent, electrochemical impedance spectroscopy(EIS) was used to track the film-forming process of the 4-hydroxy thiophenol on gold electrodes.A new mothod of real-time in-situ characterization was built, then the fixed assembly time and the rules of film-forming of 4-hydroxy thiophenol self-assembled monolayers (4-HTP SAMs) was inverstigated. The major contents in this thesis are described as follows:1,Real-time in-situ characterization of the modified electrodes by 4-HTP SAMs in mixed solution of aetonitrile and waterFirstly, the test experimental conditions of EIS in mixed solution of aetonitrile and water have been optimized. The molar ratio of acetonitrile and water is 1:0.6.The polarization potential is-0.5 V.The concentration of NaClO4 and ferrocene is respectively 600mmol·L-1 and 15 mmol·L-1. In the best condition of experiment, the modified electrodes by 4-HTP SAMs are real-time in-situ characterized in mixed solution of aetonitrile and water by EIS. The results shows that the film-forming process is related to the concentration of mercaptan. Real-time in-situ characterization of EIS can be carried out, when the concentration of 4-HTP is more than lmmol·-L-1.However, when the concentration of 4-HTP is less than 1 mmol·L-1, experimental method of EIS can be not feasible.2,Real-time in-situ characterization of the modified electrodes by 4-HTP SAMs in propylene carbonate solutionPropylene carbonate(PC) is a common nonaqueous electrolyte solution which do not volatilize easily.4-HTP can dissolve in PC more easily.In this paper, PC solution has been chosen as solvent.At an open circuit potential, the modified electrodes by 4-HTP SAMs are real-time in-situ characterized in PC solution. The concentration of NaClO4 and ferrocene was respectively 500 mmol·L-1 and 15 mmol-L"1.The results show that the film-forming process is related to the concentration of mercaptan. The compact fixed assembly time is shorter and the Ret gradually is increased when the concentration of 4-hydroxy thiophenol is increased. When the concentration of 4-HTP is more than 3mmol·L-1, the film-forming process on longer changes.3,Real-time in-situ characterization of the modified electrodes by 4-HTP SAMs in ethanol solutionEthanol is a common reagent that prepares for mercaptan SAMs .The tested experimental conditions of EIS in ethanol solution has been optimized. At an open circuit potential, the modified electrodes by 4-HTP SAMs were real-time in-situ characterized in ethanol solution.The concentration of NaC104 and ferrocene was respectively 200mmol·L-and 15mmol·L-1. The surface coverage of 4-HTP SAMs/Au has got from Rct, which changes with assembled time regularly. The results show that the film-forming process is related to the concentration of mercaptan. The compact fixed assembly time is shorter and the Rct gradually is increased when the concentration of 4-HTP is increased. When the concentration of 4-HTP is more than 3mmol·L-1, the film-forming process no longer changes.The result shows that the mixed solution of aetonitrile and water is not the best choice for establishing a method of real-time in-situ characterization, because this method depends on the concentration of 4-HTP.Ethanol is a good kind of solvent,and can not only dissolve many inorganic compound,but also dissolve organic compound.Due to the volatility of ethanol, the reactor must have good leakproofness.If test time is to be longer,ethanol is not a good choice. Propylene carbonate is a kind of solvent,which has excellent properties,hgher dielectric constant,so PC is a good kind of solvent for real-time in-situ characterization.