Controlled Synthesis And Properties Characterization Of Ag And Ag₂S Nanomaterials

This dissertation is focused on the solution-based synthesis of Ag and Ag2S nanomaterials, including nano/submicron Ag particles, hollow cubic Ag microboxes, and monodisperse Ag/Ag2S core/shell nanocrystals. Investigations are based on several aspects including synthetic procedure, formation mechanism, properties, and applications. The contents are comprised of size-controlled and size-designed synthesis of nano/submicron Ag particles using ascorbic acid to reduce AgCl in aqueous solution at ambient conditions, synthesis of hollow cubic Ag microboxes with netlike nanofiber structure in an ethanol system under ambient conditions via a cubic NaCl crystal templating route, facile synthesis of monodisperse Ag/Ag2S core/shell nanocrystals and fabrication of Ag2S resistive switching device. The formation mechanism and properties of the products were investigated in detail, revealing the intriguing potential of these nanomaterials in practical applications. This work is not only enriching the investigations of Ag and Ag2S nanomaterials, but also beneficial to the fundamental research of the formation and growth of nanomaterials.1. Size-controlled and Size-designed Synthesis of Nano/Submicron Ag ParticlesA series of nano/submicron Ag particles with uniform size-distribution are prepared using ascorbic acid to reduce AgCl in aqueous solution and at ambient conditions. NaOH is used to adjust the redox potential of ascorbic acid and polyvinylpyrrolidone (PVP) is used to balance the relative rates at which various crystallographic planes of Ag grow. Under the reaction conditions, the nucleation and growth steps are separated, thus controlling the anisotropic growth of the Ag crystals. The products are studied using TEM (transmission electron microscope), HR-TEM (high-resolution TEM), FE-SEM (field emission-scanning electron microscope), XRD (X-ray diffraction), and UV-vis spectrophotometer. On this basis, an equation for the relationship between the synthesis conditions and the size of the product was established, which can be applied to produce quantitatively size-controlled and size-designed Ag particles. Scale-up of the synthetic procedure is also conducted to test the prospect of large-scale synthesis of Ag particles for practical industrial applications.2. Fabrication of Hollow Cubic Ag Microboxes with Netlike Nanofiber Structure and Their Surface Plasmon ResonanceWe designed a new templating synthesis to produce hollow cubic Ag microboxes with netlike nanofiber structure in an ethanol system under ambient conditions. Our synthesis strategy was firstly to prepare NaCl/AgCl core/shell structures in ethanol, and then fabricate hollow Ag microboxes by chemically reducing these core/shell structures with ascorbic acid, finally removing the sodium chloride cores by simple water washing. The fabrication mechanism for the hollow cubic Ag boxes was illustrated on the basis of investigating the problem of how to promote the heterogeneous nucleation of AgCl particles at the NaCl crystal surfaces, and how to obtain the morphology-preserved product when the cubic NaCl/AgCl core-shell structures participate in the redox reaction. The Ag boxes are characterized by TEM (transmission electron microscope), HR-TEM (high-resolution TEM), FE-SEM (field emission-scanning electron microscope), and XRD (X-ray diffraction), which illustrates their novel hierarchical structure-the boxes are composed of metallic Ag crystallites which connect together into a netlike structure to form the walls of the boxes, and the six walls close to form the final hollow cubic Ag microbox. Structural analysis and comparative tests are employed to shed light on the formation mechanism of the netlike nanofiber structure, which was considered as an attachment of Ag nanocrystals based on preferential crystal orientation. The structure-dependent surface plasma resonance (SPR) properties of the as-prepared Ag microboxes and nanofibers are described based on the UV/Vis/NIR absorption spectra.3. Monodisperse Ag@Ag2S Nanocrystals:Synthesis and Resistive Switching ApplicationWe designed a novel resistive switching nanomaterials, the monodisperse Ag/Ag2S core/shell (Ag@Ag2S) nanocrystals, which have been successfully synthesized in situ by a redox reaction between S and Ag on a well-defined Ag nanoparticle template. The as-obtained nanocrystals with well-defined spherical morphology allow us to assemble a compact film by dispersing the nanocrystals in ethanol and coating them on the surface of an aluminum foil. On this basis, a resistive switching device was built composed of Ag@Ag2S film and aluminum electrodes. Such a switching device, with the characteristics of simple structure, ease of operation, scalable synthesis, and low-cost, as well as exhibiting an excellent switching effect with strong electronic signals and electrically stable and reliable, revealing the intriguing potential of these nanocrystals in building nanoscale devices for application in present-day electronics.