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Study on Synthesis and Mechanism of Micro-/Nano-Materials Binary Manganese Compounds

Author: GuiYiCai
Tutor: QianXueFeng
School: Shanghai Jiaotong University
Course: Inorganic Chemistry
Keywords: micro- /nano-materials hydrothermal complex reagent salt phase transformation six-rod structur
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 40
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Abstract


Manganese is one of the most abundant element in the earth’s crust and occurs in nature in the +2, +3 and +4 oxidation states. there have abundant resource of manganese and wide distribution in our country. Manganese oxides/sulfides are commonly used in a wide range of applications including batteries, pigments, catalysts, semiconductors and solar energy conversion, they have aroused more and more attention in recent years. Nanomaterals have many special properties and the chemical/physical properties are related fundamentally to their morphology. So it is a important research direction to synthesize nanomaterals with different morphologies by simple method. In this thesis, we have successfully prepared several micro-/nano-materials of binary manganese compounds, which basied on hydrothermal method. We changed the reaction condition and studied the reaction progress and mechanism. The concrete research contents are summarized as following:1. Different phases/morphologies of MnS nanocrstals have been successfully synthesized via a simple hydrothermal route. The MnS nanocrystals can transform from metastable phase (γ-MnS) to stable phase (α-MnS) by being added complex reagent. At the same time, the morphologies of nanocrystals changed. Further studies showed that the suitable complex reagents were key factors to induce this transformation by changing the coordination number of Mn. The result of other complex reagents further approved this theory.2. In recent years, there are many reports about synthesis different phases of MnO2 by adding inorgnical salt, but it is the first time to modify the morphologies of MnO2 nanocrystals by salt. In this paper, we used salt as phase modifier and morphology modifier. The study result suggested that cation can change the phase of MnO2 nanocrystals and anion can modify the morphology. We successfully synthesizedα-MnO2 nanowires,β-MnO2 nanotubes andβ-MnO2 nanorods.3. We prepared six-rod Mn3O4 nanocrystals via hydroyhermal route by carefully controlling the fundamental experimental parameters, including the temperature, the modifers, and the reaction time. It was found that anion can induce to six-rod Mn3O4 nanocrytals, because it can reduce reactants diffusion rate and form a concentric grads around the crystals. This makes the apexes of a polyhedral crystal, which protrude further into the region of higher concentration, grow faster than the central parts of facets, thus forming six-rod structure.

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