New Methods On The Assembly Of Nanoparticulate Gold And Palladium At The Water-air Interface And Their Applications

Nanopartices (NPs) and their assembly films of noble metals like gold and palladium have attracted a great deal of attention due to their broad application in such areas as optics, nanoelectronics, sensing, catalysis, and so forth. In recent years lots of efforts have being made to the preparation of noble metal NPs and their assembly at the interfaces of gas-liquid, liquid-liquid. Therefore it is of great significance to develop new interfacial assembly methods on fabricating two-and three-dimensional functional films of noble metal NPs. In this thesis, we prepared colloidal gold and palladium with excessive divalent tin Sn(â…¡) as both reductant and capping agent, made assembly films of the two kinds of NPs at the air-water interface, studied the assembly mechanisms, and showed the applications of the assembled films in surface-enhanced Raman scattering (SERS) and/or electrocatalysis. The main contents are summarized as follows:1. A gold colloid was synthesized by the reduction of AuCl4- with excessive divalent tin Sn(â…¡) in an acid medium, which was stable for months under airproof condition by the protection of Sn(â…¡)Cl3-. However, ultrathin nanoporous gold films were formed at the air-water interface by aging the colloid for some time under air contact. Experiments including Raman spectroscopy proved that the interfacial assembly process involves the ligand exchange induced by the O2 from the air, namely, the protective Sn(â…¡) species (mostly SnCl3-) of the gold colloid could be gradually replaced by Cl-in the solution while the strongly chemically adsorbed Sn(â…¡) species on the Au NPs at the superficial layer of the colloid was oxidized by the O2 from the air contact. The Au NPs become unstable and form assembly films at the air-water interface. In addition, density functional theory (DFT) calculations were used to explain the ligand exchange mechanism.2. The ultrathin nanoporous films of Au NPs display excellent SERS effect and good electrocatalytic activity. The SERS spectra of pyridine,1, 10-phenanthroline, nicotinamide etc. can be got easily by using the ultrathin nanoporous films of Au NPs as SERS substrates. And the modified glass carbon electrode by the assembled film of Au NPs shows better electrocatalytic activity toward the electrooxidation of ethanol, glucose, and ascorbic acid in alkaline solution.3. Stable Pd colloids were synthesized by the reduction of PdCl2 using excessive divalent tin Sn(â…¡) under heating in an acid medium. The assembled films of Pd NPs at the air-water interface could be obtained by aging the colloid for a while with continuous heating, involving diffusion of Pd NPs from the bulk colloid to the air-water interface with the help of heating. The modified smooth Pd or glassy carbon electrode by the assembled film of Pd NPs display good electrocatalytic activity toward the electrooxidation of ethanol and formic acid in alkaline solution.