Spectroelectrochemical synthesis of gold nanoparticles using cyclic voltammetry in the presence of a protective agent

Abstract

Modification of electrodes with metal nanoparticles (NPs) is attracting intense interest because the widespread applications of these electrodes as sensors in electroanalysis. In the present study, we have analysed the electrodeposition of gold nanoparticles (Au NPs) on a platinum electrode in presence of polyvinylpyrrolidone using UV/Vis spectroelectrochemistry, which allows us to obtain in-situ evidences on the kind of nanoparticles deposited on the electrode. Under the selected experimental conditions, it has been possible to understand the reaction pathway for the synthesis of Au NPs in a voltammetry experiment. We establish that generation of NPs of a specific size is dramatically favoured during the different oxidation and reduction processes. Experiments with and without protective agent revealed that NPs generation is favoured since the first cycle when a protective agent is present in solution. IntroductionSynthesis of noble-metal nanoparticles (NPs) has received significant attention in recent years. [1][2][3][4] The ability to generate NPs with controlled size and shape is very important to advance in many areas of science and technology. In fact, scientists are beginning to understand the complex physics that leads to the generation of NPs with controlled size and shape. [5][6][7] In general, the chemical synthesis route is more developed than the electrochemical one, as it allows better control of the final type of NPs. 5,8,9 However, a number of studies have shown that it is also possible to control Au NPs morphology using electrochemistry, 10-16 although a lot of them use a gold sacrificial anode like source of gold ions.13-15 Electrochemical synthesis offers important advantages such as the production of NPs with high purity. 3 With chemical synthesis is possible to obtain well-defined NPs controlling the ratio between the reductive agent, gold precursor and protective agent. 5,8,9 On the other hand, electrochemical synthesis is very interesting to understand the mechanism of NPs generation because it is possible to control easily the potential at which the reaction takes place.In the case of the electrochemical synthesis, the reaction mechanism can be better understood when in-situ characterization techniques are coupled to electrochemistry to provide more information about the process that is taking place. [17][18][19][20][21] Here electrochemistry is combined with UV/Vis absorption spectroscopy to follow the formation of Au NPs. UV/Vis spectroelectrochemistry provides mechanistic information on Au NPs synthesis because the electrochemical process can be easily followed by observing gold characteristic plasmon band. 2,22 Recently, we have demonstrated that a multipulse technique yields monodisperse spherical Au NPs. 19This method was based on the application of several consecutive oxidation/reduction steps. In order to understand better the electrochemical process, here we have developed a new synthesis route based on cyclic voltammetry, where reduction and oxidation potentials are alternated d...

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