Fabrication And Characterazation Of Porous Metal Oxides With Coordination Polymer As Precursors

Nano-materials are gaining growing interests because of their grain size as small as the light wave length. Compared with the bulk materials, nano-materials show much more advantageous properties. In recent years, as the development of material science, the control over the structure, morphology, and chemical composition of materials in nanoscale have raised considerable concern.Coordination polymer (CP) is a rapidly growing class of materials due to their ability to give a broad range of functional applications in gas storage, catalysis, recognition, and separation. If the size of the coordination polymer particles reduced to nanoscale, it will not only show the characteristic properties of CPs, but also gain some new characters as a nanomaterial. Currently, research on the intrinsic morphology/size-property relationship has engendered an urgent need for adjustable synthetic strategies, where the particle size and morphology of materials can be precisely controlled with designed functionalities. Within this context, chemical transformation has emerged as a useful method for tuning the composition of nanomaterials. Similar to other solid-phase fabrication approaches, CPs can be easily transformed into metal oxides via simple calcination at high temperature in air, which is an effective method to synthesize metal oxide with controlled size, morphology, structures, and properties. However, in the synthesis procedure of coordination polymers, kinds of un-environmental friendly and toxic ligand and solvent were used, or high energy cost and boring post processing will occur. These problems undoubtedly imped their further development.In this dissertation, we used biological amino acids as a green organic ligand, pure water a simple solvent, after a environmental benign procedure, kinds of novel nanostructured metal-amino acids coordination polymers were successfully fabricated. And with these coordination polymers as precursor, after a direct calcination in air, metal oxide with the morphology inherited from the precursor can be obtained. The main content of the thesis is composed of the following three parts:1. Facile synthesis of bismuth-amino acid coordination polymersDespite being a heavy metal, bismuth has been regarded as relatively nontoxic and several bismuth derivatives have been recommended as a standard treatment for gastric and duodenal ulcers, diarrhoea and SARS. We report for the first time bismuth-asparagine coordination polymers (BACP) nanostructures with diverse morphologies (one-dimensional nanowires, hierarchically microspheres and monolith multi-cellular foams), which were fabricated by a facile aqueous bottom-up coordination-based self-assembly approach. Furthermore, the BACPs exhibit unique properties in catalysis and biological aspects.The synthesis method is very simple. Typically bismuth nitrate (Bi(NO3)3·5H2O) was added into L-asparagine solution under stirring to obtain a transparent solution. When the transparent solution was left at10℃for12days, bundles of nanowires could be obtained (denoted as BACP1). If the solution of Bi(NO3)3·5H2O) and L-asparagine was reacted at80℃for24h, well-dispersed sub-micron spheres named as BACP2with an average diameter of500nm were obtained. If the transparent solution was hydrothermally treated at160℃for24h, the obtained product (denoted BACP3) was macroscopic monoliths, bismuth-asparagine CPs exhibit unique properties in catalysis and biological aspects. As the synthesis method is simple and completely green, nanostructured BACPs can be produced in large scale. It is expected that the BACPs would be potentially applicable in different fields, such as catalysis and bio-medicine.2. Controllable synthesis of porous Y2O3nanostructures by a coordination based self-assemble processIt is well know that amino acids have both acidic functional groups (-COOH) and basic functional groups (-NH2), which can not only effectively change the acid-base properties of system, but also exhibit adsorption or coordination properties. We present a facile, economical route to fabricate aesthetic self-assembled nanostructures based on coordination between metal ions and amino acids in water under mild conditions, which requires neither sophisticated techniques nor surfactants or modulators. By directly mixing the aqueous solution of asparagine (Asn) and metal ions (Y3+), self-organized nanostructures with diverse morphologies (hierarchical nanoporous foams and one-dimensional nanowires) can be conveniently obtained. Using L-lysine as an additive, under the same hydrothermal condition and post treatments, hierarchical flower-like microsphere was obtained. If we only use L-lysine as a ligand, beautiful dispersed nanocubes and microflowers assembled by nanoflakes can be obtained. Furthermore, after a simple calcination of these different shaped Y-amino acids coordination polymers, yttrium oxide nanostructures with the unique shape of precursor can be obtained. These porous Y2O3materials with relatively high specifiv surface areas may have great potential to be applied in catalysis, separation and sensors.3. Fractal porous M-Y2O3foam catalyst in low Ni content showed high Ethanol Steam Reforming activityWe present a facile one-step coordination based self-assemble way to produce a novel three dimensional (3D) fractal porous structured Y-asn coordination polymer monolith with interconnected network architecture. After a simple thermal transformation, fractal porous Y2O3inherited from the coordination polymer precursor can be successfully obtained. Furthermore, metal doped F-Y2O3can be easily obtained by directly mixing metal nitrate with Y(NO3)3during the hydrothermal treatments. To be specified compared to the nickel oxide impregnated on a commercial Y2O3nanoparticles (Ni@CYO), the embedded metallic Ni particles in the fractal porous Y2O3foam display high catalytic activity toward steam reforming of ethanol at low temperature. The carbon deposition of the fractal porous F-Ni-Y2O3is extremely low. The high catalytic activity and low carbon deposition are attributed to the high stable metallic Ni encapsulated in the porous structure. Our results demonstrate that fractal porous structures could provide an excellent catalytic activity.