| In this dissertation, we explored and study new methods and routes to synthesize manganese oxides micro and nano-scale materials with controlled structures and attracting morphologies. Based on the room-temperature reaction and thermal decomposition technique, a manganese carbonate template based reaction system has been developed in our work. Selecting Mn2O3 hollow structures as example, by carefully adjusting the experimental conditions, such as the proper precursor, calcinations temperature, the amount of the reactant and so on, the mophpology, the thicknesses of the hollow structure and sizes of the building units of the final samples can be tuned. The main contents of the dissertation involve several parts as follows:1. Various Mn2O3 hollow structures, such as spheres, cubes, ellipsoids and dumbbells have been synthesized through the following process:The surfaces of the prepared MnCO3 microspheres, microcubes, and microellipsoids were oxidized by KMnO4 to form a core/shell structure. Similarly, the surface of dumbbell-like MnC03 intermediate can also be oxidized by KMnO4. As the MnCO3 or MnCO3 intermediate cores were dissolved by acid, the MnO2 shells were formed. Calcining these MnO2 shells at 500℃, polycrystalline Mn2O3 hollow structures were obtained. The morphologies of these hollow structures were similar to their precursors. The as-prepared hollow Mn2O3 materials were used as adsorbents in water treatment, and the hollow Mn2O3 spheres, cubes, ellipsoids and dumbbells could respectively remove about 77%,83%,81%and 78%of phenol. These results were published in The Journal of Physical Chemistry C (2009,113,17755).2. Double-shelled Mn2O3 hollow spheres have been successfully prepared on a large scale by using core-shell-structured MnCO3 microspheres as sacrificial templates. This new method is based on an inward oxidation/etching treatment and sequential heat treatment in air. The as-prepared double-shelled Mn2O3 hollow spheres consist of small nanoparticles with a size of ca.50 nm and there are many nanopores among the particles. This study was published in European Journal of Inorganic Chemistry (2010,1172).3. Although heterogeneous core/shell structures (two different kinds of material for the core and the shell) and the homogeneous core/shell structures (the same material for both the core and the shell) have been widely reported, the synthesis of core/shell structure with one material in different phase are quite novel and may bring new opportunity for materials applications. We present a novel concept of structural design for the synthesis of a new type of core/shell structure comprisingγ-MnO2 cores inside hollowα-MnO2 shells. The approach involves two main steps. First, MnCO3 microellipsoids were mixed directly with KMnO4 solution, which lead to a manganese oxide shell on the surface of the MnCO3. Then, thermal annealing of this type of core/shell structure resulted in the formation ofγ-MnO2/α-MnO2 ellipsoids, accompanying with the phase transformation in both the core and shell. As theγ-MnO2/α-MnO2 ellipsoids were employed in water treatment, they could remove about 90%of MB without any other additives.4. We further developed the MnCO3 template-assisted method. In the reaction system, the mesporous lead tungstate has been prepared by using the MnCO3 precursor. The possible growth mechanisms for the obtained porous product are discussed on the basis of experiment results. We also report the first synthesis of homogeneous core-shell Mn2O3 microcubes and microdumbbells on a large scale by using the corresponding MnCO3 precursor, and there is some hollow interior apace between the shell and the core. The mechanism is the poorly-crystallized MnCO2 and partially dissolved MnCO3 core can simultaneously transformed to crystlline Mn2O3 at 500℃.
|
PDF Full Text Request