Electrochemical Reductive Desorption Voltammetry Studies On The Surface Coverage Kinetics Of Dodecanethiol And Ter-butanethiol Self-assembly Monolayers On Polycrystalline Gold With Five Different Pretreatments

Surface coverage Γm is one of the important interface characterizing parameters of CnSH-S AMs-Au, and it can intuitively represent the macroscopic properties of SAMs-Au. We can obtain the kinetic information of SAMs by inspecting the surface coverage Γm of alkanethiol on different modified time. In all the methods of determining coverage Fm, the electrochemical reductive desorption shows unique advantages due to its simple operation and accurate measurement. In this dissertation, we use long-chain and short-chain alkanethiol as the typical research systems and explore the coverage kinetics of two kinds of alkanethiol SAMs on polycrystalline gold electrode (C12SH-SAMs-Au and C4SH-SAMs-Au). In addition, the influence factors of pretreatment time and electrochemical polishing on the preparation of C12SH-SAMs-Au are investigated. The main research works are categorized as followings:1. Self-assembled monolayers (SAMs) of alkanethiols on gold surfaces possess considerable potential for the development of biosensing interfaces due to their ability to mimic biological menbranes and their good stability. There are mainly three methods for investigating the monolayer’s properties:electrochemical methods, spectroscopic characterization and imaging techniques. The alkanethiol monolayers are assembled on gold to form CnSH-SAMs-Au and the coverage Γm is determined by the electrochemical reductive voltammetry. Therefore the microscopic property of the compactness for SAMs can be intuitively presented. However, it is difficult to prepare absolute close-packed SAMs-Au with defect free. In order to discuss how to make highly ordered and compacted monolayer on An, we should grasp the research progress of alkanethiol self-assembled monolayers and the influence factors for SAM’s preparation. In this chapter, we make a summary from the three aspects, including research progresses for the forming of alkanethiol self-assembled monolayers, the influence factors for SAM’s preparation, and the methods for the determining of surface coverage Γm.2. The coverage self-assembly kinetics of long-chain and short-chain alkanethiol monolayers on five different pretreatments polycrystalline are investigated systemically by electrochemical reductive desorption voltammetry. The five different pretreatment methods are:(Ⅰ) aqua regia pretreatment,(Ⅱ) reductive annealed pretreatment,(Ⅲ) UV/O3pretreatment,(Ⅳ) piranha reagents pretreatment and (Ⅴ) simple polishing pretreatment. The following three sections are obtained from the experimental results:The surface coverage Fm can be recorded as a function of assembly time for two kinds of alkanethiol (dodecanethiol and ter-butanethiol). The film coverage Fm increases as the assembly time become longer. The differences are observed on the equilibrium adsorption time, for C12SH the coverage Γm can reach a stable value after24h, while for C4SH requires90h; The electrode pretreatments have great influence on the self-assembly of alkanethiol on gold, the "Γm-t" kinetic curves indicate that the coverage Γm of alkanethiol acquiring from the same assembly time on the gold surface pretreated by aqua regia and reductive annealing are greater than other three pretreatments; The kinetic parameters (adsorption rate k and the saturated coverage Γms) for the C12SH-SAMS-AU and C4SH-SAMS-AU by different pretreatments can be obtained by Langmuir fitting, further providing the evidence that Langmuir adsorption model could be used to describe the adsorption kinetic process of alkyl thiols on gold.3. An investigation of the effect of pretreatment time and electrochemical polishing on the surface coverage Γm of dodecanethiol self-assembled monolayer on polycrystalline gold electrode (C12SH-SAMs-Au) is carried out by electrochemical reductive desorption voltammetry. The following two aspects are included in this work:(1) Investigating the influence of different pretreatment time on the coverage of C12SH-SAMs-Au. The experimental results demonstrate that the best pretreatment time for five different pretreatment methods are as follows:Aqua regia pretreatment t=5min, Reductive pretreatment time t=1min, UV/O3pretreatment t=20min, Piranha reagent pretreatment t=2min and Polished sonicated pretreatment t=15min;(2) Inspecting the influence of electrochemical polishing cycles on the coverage of C12SH-SAMS-Au. The experimental results show that the coverage values of C12SH-SAMs-Au on Au increase and gradually stabilize as the m increases, indicating that the electrochemical polished electrode surface is more beneficial to forming a closed-packed and well-ordered monolayer.