Magnesium Carbonates Templates To Synthesize Complex Micro/nanostructures And Characterization

Complex micro/nanostructures have received considerable attention due to their unique physical and chemical properties and promising applications, such as energy storage, drug delivery, catalysis, sensor and water treatment. Up to now, templating method has been proved to the most straight-forward, versatile and effective approach for fabricating complex micro-/nanostructures, but some difficulties, such as high cost and hard removal condition of template are still hardly overcome. Recently, our group has paid much attention on the development and utilization of magnesium resources. During this time, the magnesium carbonate (MC) have interested us because of its list features:tunable particle size and morphology, controllable phase transformation process (MC+CO2←→Mg(HCO3)2), higher solubility product—better chemical activity. Base on these, a new synthetic concept—MC templated method was proposed to prepare complex micro/nanostructures for avoiding high cost and hard removal condition in the traditional template method. To test this idea, we have systemically investigated the tunable influence and mechanism of reaction condition on the morphologies of MC template firstly in this doctoral dissertation. Then, employed MC as recyclable and sacrificial template for fabricating complex micro/nanostructures and relative adsorption performance (such as specific surface area, pore structure and organic dye adsorption, etc.) of the products were discussed. The main points and contents are summarized as follows:Synthesis of the magnesium carbonates templates. MgCO3·3H2O microrods were synthesized via a thermal-decomposition process in the presence of ethanol with Mg(HCCO3)2as the reactant. Meanwhile, microscale hierarchical4MgCO3·Mg(OH)2·4H2O and cubelike MgCO3were prepared by phase transformation method using MgCO3·3H2O as precursor. And the influence rule and mechanism of reaction condition on MC were systemically investigated. The results show that the crystallization rate plays key role in the size control of product. The size of MgCO3·3H2O was determined by stirring speed, while the4MgCO3·Mg(OH)2·4H2O and MgCO3can be controlled by size of MgCO3·3H2O precursor.Use of magnesium carbonates as recycle template for fabricating hollow structures. The SiO2, TiO2, Al2O3microtubes and SiO2, TiO2-SiO2hierarchical structures were successfully synthesized via sol-gel and phase transformation process with the MC as template and alkoxide as raw materials. The Mg(HCO3)2filtrate was used for recycling MC template, in which the reborn templates have similar morphology and size with the initial one. The as-prepared SiO2, TiO2-SiO2hierarchical structures exhibit high adsorption capacity and rate, which can be candidate for potential functional absorption materials.Use of magnesium carbonates as sacrificial template for fabricating complex structures. NiO microtube and hierarchical structure as a representative was synthesized by using MC as template and Ni(NO3)2as raw materials. The formation mechanism of hollow and hierarchical structure is based on kirkendall effect and replacement reaction. Besides, Fe2O3, CO3O4, Gd2O3microtubes and Fe2O3, Gd2O3hierarchical structures were also synthesized via this similar route. Hierarchical Fe2O3and NiO show high adsorption capacity and rate when applied as adsorption materials.Use of magnesium carbonates precursors as templates for preparing MgO. The influence of reaction conditions on the morphologies of MgO and adsorption performance were systemically investigated. The result shows that the MgO micro/nanostructures can be obtained through calcining MC and keep the template morphology, what’s more, the calcination temperature, heating rate, size and morphology of MC have no evident effect on the morphology of MgO but its adsorption properties. Tubular hierarchical MgO shows superior adsorption capacity of Congo red (up to4400mg/g), which is much higher than the reported adsorbents. After adsorption, the material was dissolved by CO2-H2O acid into Mg(HCO3)2for achieving recycling MgO nanoadsorbent while the Congo red was treated through H2O2photocatalytic oxidation.