Electrochemical Assembly And Applications Of Gold And Platinum Nanoparticles

On account of their good stability, surface effect, unique optical properties and excellent biocompatibility, Au and Pt nanoparticles (NPs) have wide applications in catalysis, optics, electronic, fuel cells and biosensors. The assembly of NPs has attracted considerable attention and there are various kinds of methods on assembly of NPs. Among them, electrochemical method provides a promising way to prepare assembly films of NPs because the equipment is simple, the operation is convenient, and the reaction conditions are mild and controllable. In this thesis, firstly we assembled aggregated colloidal gold NPs on a gold electrode via in situ produced H+ ions by the electrochemical oxidation of QH2; and then we prepared assembled films of Pt NPs, mixed NPs of Au and Pt, and alloyed NPs of Au-Ag by using the same strategy; at last, we fabricated nanoporous gold films with an Au-Sn alloy by a potential step in 2 M HCl. The assembled films of NPs and the fabricated nanoporous Au film can be used as excellent substrates for surface-enhanced Raman scattering (SERS) and showed great applications in electrocatalysis of organic/ biomolecules. The main contents are summarized as follows:1. A novel method on the assembly of gold nanoparticles (NPs) protected by citrate at the gold electrode surface was reported here, which utilizing the in situ produced H+ ions at the electrode surface through the electrooxidation of hydroquinone (QH2). In situ Raman spectroscopy was employed to monitor the assembly by detecting the signal of adsorbed QH2. Contributions to the assembly both from the electrophoretic deposition and from the redox of gold substrate are negligible, comparing with the much stronger action of the in situ produced H+ ions. Chosen pyridine (Py), melamine, rhodamine B (Rh B) and nicotinamide (NAD) as the probe molecule, the assembled film can serve as an excellent substrate for SERS. Colloidal Au NPs with a capping reagent of polyvinylpyrrolidone (PVP) can also be assembled on the gold electrode, which could avoid aggregating of Au NPs. Electrooxidation of other molecules like ascorbic acid (VC) can also be utilized to the assembly of gold NPs at the electrode surface.2. Pt NPs was assembled on the gold electrode by in situ produced H+ ions at the surface through the electrooxidation of VC. The assembled films of Pt NPs showed great electrocatalytic activity toward the electrooxidation of ethanol in an alkaline solution and formic acid in acidic medium. Mixed Pt and Au colloidal NPs, and Au-Ag alloy colloidal NPs were also successfully assembled onto the gold electrode, forming assembly film of binary noble metal NPs.3. A very fast one-step electrochemical method on the fabrication of a nanoporous gold film (NPGF) of high surface area was reported, it can be fulfilled in 5 seconds with an Au-Sn alloy electrode in a 2 M HCl medium by applying a step potential. The surface morphology and element analysis have been characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectrometer, respectively. The formation mechanism is discussed and is compared with a pure gold electrode. The as-prepared NPGF electrode exhibits high electrocatalytic activity for the oxidation of ethanol and glucose, and can also serve as an excellent SERS substrate.