Recycling Of Nanowire Templates And Fabrication Of Nanowire Assembly

The template-directed synthesis has attracted wide attention as one of the most straightforward methods for the synthesis of nanostructures, due to its simple, high-throughput procedure and variability in controlling structure and chemical composition of the products. Recently, tellurium and silver nanostructures with high chemical reactivity have been widely used for the template synthesis of porous, hollow and core-shell nanostructures or carbon nanomaterials, showing great application potential in various fields, such as photodetectors, catalysts, biological medicine, sensors, energy storage, and so on. Although great progress has been made in the synthesis of tellurium/silver nanostructures for their template synthesis, the waste of highly cost tellurium and silver in ionic species were always ignored after the template reactions. From the economic and environmental viewpoints, it is highly important to develop a green process for the recycling of templates, especially for large-scale templating synthesis.This dissertation will focus on the template synthesis of functional nanomaterials and the recycling of tellurium/silver nanotemplates after the template reactions for further applications. Through the simple chemical conversion process, the wasted tellurium and silver ions were successfully transferred to sodium tellurite and silver nitrate for the synthesis of tellurium and silver nanowires by modified hydrothermal method and polyol process respectively. Furthermore, we have manipulated the assembly of silver and tellurium nanowires by Langmuir-Blodgett and spin-coating techniques and investigated their applications in the fields of flexible transparent electrodes, electrochromic devices, and photodetectors. The main results can be concluded as follows:1. Tellurium nanowires were synthesized by recycling the wasted nanotemplates after template reactions. Ultrathin tellurium nanowires used as physical and chemical templates for the synthesis of carbon nanofibers (CNFs), Pt/Pd@CNFs, Pt nanotubes/nanoparticles composites and Pd nanowires were etched out from the products or consumed during the template synthesis. By using modified hydrothermal process, we have resynthesized tellurium nanowires after transforming the wasted tellurium element to sodium tellurite. We further studied the recycle ratio of different reaction systems and the physical and chemical properties of the recycled tellurium nanowires. Using Langmuir-Blodgett technique, we have manipulated the assembly of silver and tellurium nanowires and fabricated the silver nanowire flexible transparent electrodes with tunable pitch (distance between two adjacent nanowires) by etching out the highly reactive tellurium nanowires. We also studied the influence of the different ratios of silver and tellurium nanowires in the assembly process and the mechanical stability of the transparent electrodes. Moreover, the tellurium nanowires used here as templates could be recycled, making the fabrication of electrodes at much lower cost.2. Silver nanowires were synthesized by recycling the wasted nanotemplates after template reactions and used for the fabrication flexible transparent electrochromic devices. The shape-controlled silver nanostructures were used as templates for the synthesis of hollow or porous Au and Pt nanostructures and transformed to silver chloride. By reaction with ammonium hydroxide, hydrazine hydrate, and nitric acid respectively, we separated the silver chloride from the valuable products and obtained silver nitrate. By using modified polyol process, we have synthesized silver nanowires from the recycled silver nitrate. We further studied the recycle ratio of different reaction systems and the physical and chemical properties of the recycled silver nanowires. Using the silver nanowires as conductors, we manipulated the assembly of silver and W19O48 nanowires for the fabrication of flexible transparent electrochromic devices. We have studied the influence of the different ratios of silver and W19O48 nanowires in the assembly process and the mechanical stability of the devices. Besides, we have also fabricated the electrochromic films with display pixels and characters of "USTC", indicating the easy-operation of this method.3. Ordered silver and tellurium nanowires were obtained by using spin-coating method for the fabrication of transparent electrodes and photodetectors. A series of experiments have been carried out to understand the factors in controlling the alignment of the nanowires, such as the rotation speed, flow distance, concentration and volume of nanowire suspension and wettability of substrate. The alignment of nanowires was demonstrated by polarized transmission spectra. Using this method, we have assembled the silver nanowires into mesh-like structures for the fabrication of transparent electrodes. The transparency and conductivity of the electrodes can be controlled by adjusting the volume of the silver nanowire suspensions. Combined with nano fabrication technology, we have fabricated tellurium nanowire photodetectors with radial structure and studied the photoelectric properties of the tellurium nanowires/nanotubes with different diameters.