Stability And Reactivity Of Functional Inorganic Elemental Nanowires

As a bridge between microcosmic atoms and macroscopic materials, nanomaterials have received considerable attention in recent years. Unlike bulk materials, almost all nanomaterials are far away from equilibrium state. The unsaturated "dangling" bonds on the surface of nanoparticles are extremely sensitive to the external environment, which gives nanomaterials a dual nature:high reactivity and poor stability. The stability and the reactivity of nanoparticles constitute a contradictory unity, but complement and restrict mutually. This dual nature of nanomaterials is of crucial importance for their application, but the long-term effects of stability and reactivity of nanomaterials under practical conditions are still not well understood. People are generally more interested in the high reactivity of nanoparticles, but the poor stability is always ignored or considered useless. Actually, undesired processes derived from the poor stability can be an advantage in some cases, because they can act as an excellent platform for fabricating unique functional nanomaterials. We think more attention should be given to this topic, which is highly meaningful to reinforce the foundation of nanoscience, find new design and preparation platforms for nanomaterials and set the technical standards for nanomaterials in practical applications.This dissertation will focus on the concrete manifestation, quantitative characterization and rational mechanism explanation of the stability and reactivity of Te nanowires (TeNWs) and Cu nanowires (CuNWs). Choosing our laboratory synthesized ultrathin TeNWs as a model material, we have successfully studied the stability and reactivity of TeNWs in aqueous solution by a modified Beer-Lambert law. In addition, we find it is an excellent platform to help us synthesize and design one-dimensional functional nanomaterials by capturing the intermediate nanostructures during the dynamic oxidation process of TeNWs. Furthermore, we have systematically investigated the stability of CuNWs in the liquid and gas phase by monitoring the change of morphology, phase, and valence state of CuNWs during storage. Finally, we carefully investigated the synthesis mechanism of TeNWs by experimental characterizations and density functional theory (DFT). The main results of this dissertation are summarized as follows:1. An accelerated oxidation experiment for ultrathin TeNWs was performed in a self-made apparatus under different reaction conditions to study the stability and reactivity of TeNWs. Chemical kinetics information about this oxidation process was easily obtained by converting UV-Vis absorption spectroscopy data. The results indicated that the oxidation kinetics for ultrathin TeNWs was in accord with the first order reaction kinetics model, and the corresponding apparent activation energy was about 13.53 kJ·mol-1.The oxidation process of ultrathin TeNWs in aqueous solution can be divided into three stages, namely oxygen limiting, ultrathin TeNWs limiting and mass transfer resistance limiting stages. Interestingly, after incomplete oxidation, ultrathin TeNWs evolved into a chain-dotted line nanostructure, which still maintained high reactivity and could act as an excellent platform for the template synthesis of other functional nanomaterials, such as Te@C nanocable. Ag2Te nanowire, Pt nanotube, Pt nanowire, Pt nanoparticle, Te@MnOx nanotube and bimetallic oxide nanotube with double shells. In addition, we found that oxygen free conditions and adding suitable reductants are effective ways to prevent the oxidation of the freshly prepared ultrathin TeNWs and retain good stability during storage.2. Stability of CuNWs in both liquid and gas phase has been investigated systematically. CuNWs coated with ethylenediamine showed good dispersibility in polar solvents, but nonpolar solvents caused serious aggregation of CuNWs. Polar organic solvents could prevent CuNWs from oxidizing, while CuNWs stored in water or nonpolar organic solvents were heavily oxidized and evolved into a mace-like structure. In the gas phase, CuNWs were oxidized into CuO nanotubes with thin shells by heating. More importantly, the different oxidation pathways have significant effects on the final morphology, surface area, phase, optical absorption, band gap, and vibrational property of the oxidation product. We found that adding suitable reductants is an effective way to prevent the oxidation of fresh CuNWs during storage. However, slight oxidation of CuNWs on the surface is inevitable, and thus we should take this into consideration when we use CuNWs.3. A new strategy was used to modulate the lateral size of TeNWs by competitive adsorption between PVP and NVP. We found that PVP bind to TeNWs through the carbonyl group. The preferential adsorption of PVP to Te{100}/{101} planes is revealed by density functional theory (DFT), and it was about 1011/107 times to Te {001} plane when Nc=9, while that of NVP is 40/30 times, indicating PVP is beneficial to crystal anisotropic growth. This is furtherly demonstrated by the synthesis of Pd nanocrystals; the number of Pd cubes rather than Pd nanowires increased with increasing the amount of NVP.