Synthesis, Characterization And Application Of Inorganic Layered Materials （BN, MoS₂）

Inorganic layer hollow materials have many promising applications based on their unique structure and special properties. They are the front and hot research fields of chemistry and materials currently. The goal of this dissertation is to explore the facile chemistry principle and synthesis approach to obtain inorganic hollow nano/micro materials and further study their application. The innovative achievements of this dissertation include:propose the reaction mechanism of synthesis of novel boron nitride submicro-boxes in solid-phase system under high-temperature and high-pressure environments. SnO2photocatalyst was deposited on BNMB by a simple wet chemistry method and the photocatalytic performance of SnO2/BNMB has been investigated. This dissertation also prepare the MoS2hierarchical hollow structures, hollow spheres and tubes, which assembled by nanosheets synthesized by the liquid-phase solvothermal technique. We explore the possible formation mechanisms, structural features and their lithium storage performance of the MoS2hierarchical hollow structures. Thesis is summarized as follows:1In this study, hexagonal boron nitride submicro-boxes (BNMB)(0.50～1.4μm) have been synthesized by using KBH4, NH4F and Zn in a stainless steel autoclave at450℃. The formation process was studied by XRD, TEM and EDS, and it is considered that the in situ formed KZnF3intermediate cubes serve as templates for the formation of BNMB. The as-formed BNMB, with unique structural features, high specific surface area and good chemical properties, can be applied as a catalyst support for SnO2. The UV-Vis diffuse reflectance spectrum of SnO2/BNMB shows the absorption edge in the visible region (-470run), making it suitable for photocatalytic application. The experimental result indicates that the SnO2/BNMB exhibited excellent photocatalytic activity on the degradation of methyl orange (MO), which was up to92%after30min of visible-light irradiation. The good photocatalytic activity was attributed mainly to its suitable band gap energy, strong adsorption ability for MO, and effective charge separation at the SnO2/BNMB photocatalyst interface. 2MoS2, due to its layered structure and high theoretical capacity, has been regarded as a potential candidate for electrode materials in lithium secondary batteries. But it suffers from the poor cycling stability and low rate capability. Here, hierarchical hollow nanoparticles of MoS2, with the diameter of400～800μm, assembled by increased interlayer-distance nanosheets are synthesized by a simple solvothermal reaction at a low temperature. The formation of hierarchical hollow nanoparticles is based on the intermediate, K2NaMoO3F3, as a self-sacrificed template. These hollow nanoparticles exhibit a reversible capacity of902mAh g-1at100mA g-1after80cycles, much higher than the solid counterparts. At a current density of1000mA g-1, the reversible capacity of the hierarchical hollow nanoparticles could be still maintained at780mAh g-1. The enhanced lithium storage performances of the hierarchical hollow nanoparticles in reversible capacities, cycling stability and rate performances can be attributed to their hierarchical surface, hollow structure feature and increased layer distance of S-Mo-S. Hierarchical hollow nanoparticles as an ensemble of these features, could be applied to other electrode materials for the superior electrochemical performance.3Hierarchical hollow nanotubes assembled by nanosheets have been fabricated in high yield by a mild solvothermal route at low temperature. A possible formation mechanism of the samples was also proposed. During the reaction process, the MnMo04nanorods were firstly formed at a lower temperature, in which the intermediate crystals resulted from the reaction between MoO42-and Mn2+and formed in-situ and then served as the self-sacrificed template. The highly wrinkled surface combined with the hollow structure would offer a huge specific surface area for electrochemical reactions, which benefits the electrode material to interact effectively with the Li+in the electrolyte and shorten the diffusion length of the charge carriers. Meanwhile, there are much empty space in this electrode material, which can effectively tolerate the volume change during the discharge/charge processes. Furthermore, the introduction of hollow channel inside the1D nanostructures can enhance the effective interaction and reduce the diffusion distance of lithium ions between the electrolyte and the electrode. The hierarchical hollow nanotubes show the better electrochemical performance.