Design, Fabrication And Property Of Hierarchical Nanostructures Of Titanium/Iron-based Compounds

Recently, transition metal compounds with hierarchical nanostructures have attracted considerable attentions in basic scientific research and potential technological applications, owing to their integration of the size effect of nanometer materials and the structural stability of micrometer materials. Based on that, to construct different functional materials together with purposeful design is highly required to achieve the multi-functional integration and new functional introduction. It is an appealing and challenging branch in the field of nanotechnology. In this dissertation, our research persist in taking the functional customization as our orientation, and mainly concentrates on the composite design, formation mechanism and functional assembly of hierarchical titanium-and iron-based compounds, and the novel electrochemical/catalytical properties of the as-obtained new-type nanostructures are also investigation. The detailed work and the main innovation are divided into the four parts addressed as follows.1. Two hierarchical hybrid nanostructures consisting of TiO2 nanowires /nanoparticles that interact with carbon nanotubes (CNT) have been designed and synthesized via an in situ solvothermal method, combined with a simple thermal treatment. With the fine control of the the ratio between the precursor (TiO2 or TiCl4) and CNT, the former developed an interpenetrating networks, and the latter formed a "coating" CNT network. Upon testing in a Li electrochemical half-cell, the TiO2 nanowires/CNT composite electrodes (with 25 wt% content of CNT) demonstrated higher capacities (over 150 mA h g-1 at a current density of 0.2 C) and better rate capabilities (over 80 mA h g-1 at 10 C).2. One-pot template-free solvothermal route were first proposed for the synthesis of a novel type of porous TiO2 hollow spheres with nanosheet-based shells and precisely carbon incorporation. The synthesis involves titanium source and additives of 2,2’-bipyridine-5,5’-dicarboxylic acid and trifluoroacetic acid. The trifluoroacetic acid etching strategy is critical to construct the nanosheet-assembled shell and hollow structures by one step. This unique hierarchical strcture with high surface area and appropriate carbon doping endows the anatase TiO2 with superior capacity and rate performance (204 mA h g-1 at 1 C and retained at 105 mA h g-1 at a high rate of 20 C) as an anode for lithium-ion batteries.3. A series of porous TiO2 nanodisc and TiO2/C composites has been obtained by annealing the precursor of Ti-MIL-125/NH2-MIL-125 under different atmosphere. The microstructure and composition of TiO2 can be fine controlled by the regulation of the type of Ti-MOF, calcination atmosphere and temperature. The morphologies, phase and doping of TiO2 on their photocatalytic properties have also investigated through the degradation experiment of rhodamine B under simulated solar light. The results show that TN-1000 has best photocatalytic property for the degradation of RhB under sunlight with the rate of 0.00473 min-1, which is 1.8 times of P25 under the same conditions.4. The layer-by-layer assembly and encapsulation routes have been employed to prepare yolk-Fe3O4@shell-Cu3(BTC)2 composite and Fe3O4/Fe-MOF composite, respectively. The strategies were successful for imparting magnetic functionality to the catalytic MOFs. The encapsulation method is much easier for practical larger-scale preparation, and the layer-by-layer assembly method is time-consuming and obtained a fragile shell structure during the construction of hollow structure. In particular, the experiment results of the embedded Fe3O4/Fe-Mil-101 composite in aerobic oxidation of alcohols not only display that the magnetic NP/MOF catalysts could be easily recovered and recycled, but also demonstrate that the Fe-MIL-101 with large specific surface area and high density of active site impart high yield and selectivity in the oxidation of alcohols using molecular oxygen as the oxidant. The functional integration of inexpensive magnetic nanoparticles with ferric nanocomposite materials makes the great advantage of Fe3O4-NP/Fe-MOF as a sustainable, environmentally friendly and economic catalyst for oxidation processes.