Designed Synthesis And Formation Mechanism Of Metal Phosphide Nanostructures

The aim of this dissertation is to explore, design and build new chemical methods and systems for the preparation of metal phosphide nanomaterials. Based on the design and performance of new Ullmann-type reactions between elemental metals (or metalorganic compounds) and organic arylphosphines such as triphenylphosphine (PPh3), we have successfully built a new and general route to synthesize metal phosphide nanomaterials by creactively using the technique of vacuum-sealed tube (ampoule). In the dissertation, a series of phosphide nanocrystals have been systematically and controllably synthesized, including III-V semiconductor phosphide nanowires/nanofibers,3d transition metal phosphide nanowries, phosphide/carbon core/shell nanocables, and phosphorus-rich (P-rich) transition metal phosphide nanocrystals. Meanwhile, reaction mechanisms, structure and phase evolution, growth mechanisms of products and significant factors to the synthesis have been studied carefully, and further structure or phase-related physical properties of the as-prepared phosphide nanomaterials investigated properly.The main contents are summarized as follows:1. Creating a novel method for the preparation of III-V semiconductor phosphide nanomaterials by new Ullmann-type reaction strategy, in which InP and GaP nanowires/nanofibers were successfully obtained from the reactions of IIIA metals (In/Ga) with PPh3 in vacuum-sealed tubes. We investigated the influences of different triarylphosphine and temperature on the shape and structure of phosphide products, extended the Ullmann strategy to prepare III-V arsenide (InAs/GaAs) nanocrystals, and comparably studied the difference and relationship between the synthesis of phosphide and arsenide nanocrystals. Meanwhile, the structure and growth charateritics of zinc-blende or wurzite phosphide and arsenide nanocrystals were carefully analyzed, and the reasons for the formation of wurzite III-V semiconductor structures and the growth mechanism of nanowires/nanofibers were discussed. From the aspect of steric effect and bond energy, the order of difficulty in the synthesis of III-V semicondutor nanocrystals from triphenyl compounds of VA elements (N, P, As and Sb) is as follows:â…¢N>â…¢P>â…¢s>â…¢Sb. 2. Successfully realizing the phase-controlled synthesis of transition metal phosphide nanostructures based on new Ullmann-type reactions between transition metals and PPh3 in vacuum-sealed tubes. A number of 3d transition metal phosphide nanowires (Fe2P and FeP, Co2P and CoP, Ni2P and NiP2) were selectively prepared and the phase control in nanosized transition metal phosphides was accessed by tuning preparation parameters including metal/PPh3 molar ratio and concertration, reaction temperature and time, heating rate as well as the addition of inert agent. By carefully studying the effects of various preparation parameters on nanowire morpology and phase, the mechanism of phase control in transition metal phosphide nanowires was reasonably verified. A phenyl radical reaction mechanism was proposed at the molecular level for the Ullmann-type reaction by analyzing the components of organic sideproducts from reaction using GC-MS technique, Moreover, the comparable magnetic studies of Co2P and CoP nanowires exemplify the phase-dependent magnetic properties of phosphide nanowires.3. Using metalorganic molecular precursor ferrocene (Fe(C5H5)2) and PPh3 as reactants, a new type of composite core/shell nanocables of amorphous carbon coated transition metal phosphide nanowires were first synthesized:Fe2P/C and FeP/C, and the two phases were controllable. Experiments established that the pyrolysis of (Fe(C5H5)2) yielded uniform Fe nanoparticles and provided Fe and C sources for the nanocable formation. The homogeneous solution formed from the melting metalorganic molecular precursor and PPh3 is favorable for the burst nucleation of phosphide nanocrystals at the molecular or nanocluster level and the final production of uniform products. The two type of nanocables with different phosphide phases exhibit different magnetic properties.4. Establishing a new, facile and general chemical route for the preparation of P-rich transition metal phosphide nanomaterials. A array of P-rich phosphide nanocrystals including CuP2,NiP2,PdP2,PtP2 and AgP2 were successfully synthesized through reactions of excess PPh3 with corresponding metal powder or nanocrystals in vacuum-sealed tubes. The effects of reaction conditions on the formation of P-rich phase products were investigated, and it is found that the size and shape of metal particles have templated effects on phospide nanocrystals. In short, the new Ullmann reaction strategy proposed in the dissertation is a completely new synthetic idea for the metal phosphide nanomaterials, and it can be extended to prepare a number of other inorganic nanomaterials such as arsenides. The contents of this dissertation will enrich and develop the synthetic chemistry of inorganic materials, and also extend the application range of traditional organic reactions.