Preparation And Electrocatalytic Characterization Of Graphene - Based Metal Nano - Modified Electrode

Nano materials have become the forward area of many scientific researches due to their quantum effect, large specific area, high conductivity, surface effect and other particular physical and chemical properties. Noble metal nanoparticles are important part compositions of nano particles and have become one of the most active branches in nanomaterial area, which have distinct electronic, magnetic and phototic properties as well as catalytic ability different from their bulk metals. The combination of both specific physico-chemical properties of the noble bulk metals and particular properties of noble metal nanoparticles provided wide applicable perspectives in chemical, electrochemical catalysis, energy, electronic and biological fields. Carbon materials contain a wealth of carbon area because the element of carbon have particular sp/sp2/sp3 hybrid orbital to form different chemical bonds. In the past two decades, the carbon materials quickly developed from zero dimension:fullerene, one-dimension:carbon nanotube, to two-dimension:graphene, which have been used as ideal carrier materials due to their good conductivity, large specific area and wide applicable potential window. Graphene is a carbon atom crystal with tightly piled two-dimension honeycomb structure. Comparing with other carbon materials such as fullerene and carbon nanotube, graphene possesses even larger specific area and higher conductivity, is considered as one of the best catalyst carriers. In this dissertation, we studied the catalytic ability of the combined modified electrodes with noble metal nanoparticles and graphene, the applications of electrocatalytic reduction of nitrophenol and oxidation of glucose, and the catalytic mechanism of these reactions. The obtained results in this work will expand the potential applications of the noble metal nanoparticles-modified graphene in the electrochemistry and water treatment.The main research works in this dissertation are divided into the following four parts:1. The electrocatalytical reduction of m-nitrophenol on palladium nanoparticles modified glassy carbon electrodesPalladium nanoparticles modified glassy carbon electrodes (Pd/GCE) were prepared via the electrodeposition of palladium on a glassy carbon electrode (GCE) using cyclic voltammetry (CV) in different sweeping potential ranges. The scanning electron microscope images of palladium particles on the GCE electrodes indicate that palladium particles with diameters of 20 to 50 nm were homogeneously dispersed on the GCE electrode at the optimal deposition conditions, which can effectively catalyze the reduction of m-nitrophenol (m-NP) in aqueous solutions, but their catalytic activities are strongly related to the deposition conditions of Pd. The X-ray photoelectron spectroscopy (XPS) spectra of the Pd/GCE electrode confirmed that 37.1% Pd was contained in the surface composition (Pd, C, O) of the Pd/GCE electrode. The CVs of the Pd/GCE electrode in the solution of m-NP show that the reduction peak of m-NP shifts towards the more positive potentials, accompanied with an increase in the peak current compared to the bare GCE electrode. The electrocatalytic activity of the Pd/GCE electrode is affected by pH values of the solution. In addition, the electrolysis of m-NP under a constant potential indicates that the reduction current of m-NP on the Pd/GCE electrode is approximately 20 times larger than that on the bare GCE electrode.2. Electrocatalytical reduction of m-nitrophenol on reduced graphene oxide modified glassy carbon electrodeReduced graphene oxide (RGO) modified glassy carbon electrode (GCE), RGO/GCE, was used to investigate electrocatalytic reduction of m-NP. This reduction behavior was explored by cyclic voltammetry and linear sweep voltammetry. The reduction potential of m-NP on the RGO/GCE shifts toward the positive potential relative to the GCE or GO/GCE. The reduction peak current on the RGO/GCE was much greater than that on the GCE or GO/GCE. The reduction peak current on RGO/GCE is 12 times of that on bare GCE, and 8 times of that on GO/GCE. The results show much better catalytic ability than ever reported works. The influence of pH and m-NP concentration on the electrocatalytic ability of the RGO/GCE was also studied. The optimal pH is found to be 5.50. The reduction mechanism of m-NP on the RGO/GCE is presented.3. Electrochemical oxidation of glucose on gold nanoparticle-modified reduced graphene oxide electrodes in alkaline solutionsA given amount of gold is electrodeposited on the reduced graphene oxide (RGO)/glassy carbon (GCE) electrodes to form Au/RGO/GCE electrodes, which are carried out at different potentials. Among them, the Au/RGO/GCE electrode with Au loading of 250μg cm-2 prepared at a constant potential of -0.30 V (vs. SCE) exhibits the best electrochemical activity to glucose oxidation in alkaline solutions because of homogeneous dispersion of gold nanoparticles with smaller sizes on the RGO surface. Cyclic voltammograms of glucose on the Au/RGO/GCE electrodes, obtained under different experimental conditions, show a wealth of information on glucose oxidation, which is favorable for the explanation of the mechanism of glucose oxidation in alkaline solution. The Au/RGO/GCE electrode shows long-term stability, rapid charge transfer ability, and higher current density compared to other gold electrodes reported previously. X-ray photoelectron spectroscopy (XPS) spectra demonstrate that no gold oxide is detected on the Au/RGO/GCE electrode surface in our experimental conditions.4. The electrocatalytic oxidation of glucose on the bimetallic Au-Ag particles-modified reduced graphene oxide electrodes in alkaline solutionsA given amount of Au and Ag is electrodeposited on the reduced graphene oxide (RGO)/ glassy carbon electrodes to form the Au/Ag/RGO/GCE and Ag/Au/RGO/GCE electrodes. The electrodeposition potential of Au and Ag is set at-0.30 V (vs. SCE). The electrochemical oxidation of glucose is carried out in NaOH solutions. The experimental results indicate that Ag in the bimetallic Au-Ag electrodes plays an important role in the electrocatalytic oxidation of glucose; the electrochemical behavior of glucose oxidation is very sensitive to the ratio of Ag to Au loading density in the bimetallic composition. The electrocatalytic activity and stability of the bimetallic Au-Ag electrodes are assessed by cyclic voltammetry. The peak current density of the bimetallic Au-Ag electrodes at about 0.24 V is about 4.5 times as large as the gold nanoparticles deposited on the GCE electrode reported previously. Enhancing current density is due to the synergetic catalytic effect of Au and Ag. The Ag/Au/RGO/GCE electrode lost only 26.2% of its original activity after 500 cycles in a solution consisting of 10.0 mM glucose and 0.10 M NaOH, which is better than that of the Au/Ag/RGO/GCE electrode, Ag/Au/GCE and Au/Ag/GCE electrodes. The reason for this is caused by the electrode structure and RGO used in this work.