Synthesis Of Porous Nanomaterials By A Precursor-Calcination Strategy And Their Property Investigation

With the porous characteristic, porous nanomaterials are more than just the size extension to nm scale of macromaterials, which endows them with great potential in the fields of, e.g., catalysis, sensing and energy storage. In this thesis, we have synthesized porous Ni、NiO、NiO/Ni、ZnO and carbon nano structures conveniently by calcining corresponding labile precursors which are preformed by a solution co-precipitation method. Our study was concentrated on the synthesis, morphology and formation mechanism of this kind of porous nanomaterials, and their properties and related applications had also been researched. The main contents of this thesis are summarized as follows:1. As one of important transition metals, Ni is featured by its magnetic properties and wide applications in catalysis and alloy materials. Various Ni nano structures have been obtained to date. However, the synthesis of porous Ni nanostructures, which should be quite unique in catalysis due to the much increased surface area combined with the strong magnetism, is still a challenge and rarely reported. Herein we firstly synthesized the microfolwer-like Ni-based precursor by a solution co-precipitation method using hexamethylenetetramine and oxalic acid as co-precipitators without templates or surfactants. By directly calcining the precursor in Ar, porous hierarchical Ni nanostructures have been prepared without any additional reducer. The formation process of Ni has been in situ examined by thermogravimetry-differential scanning calorimetry-mass spectroscopy. The as-prepared Ni-335℃showed high BET specific surface area up to24.5m2g-1and good soft ferromagnetism. With such unique features, its application as magnetically separable catalyst was explored. The catalyst demonstrated excellent performance with high conversion and selectivity, stable recycling and good anti-oxidation for the selective hydrogenation of ACT to PE, showing great potential in substituting for the noble catalysts and Raney Nickel.2. NiO shows well-defined pseudo-capacitive behavior and has been extensively studied as electrodes for supercapacitors due to its high theoretical specific capacitance, low cost and environmental friendliness. Various NiO nanostructures have been synthesized and their electrochemical performance has been explored as electrode materials for capacitors. However, the poor conductivity and low surface area limited further improvement in its specific capacitance. Here, NiO/Ni composite nanostructures have been prepared by calcining the Ni-based precursor. The Ni content was regulated by changing the relative amount of hexamethylenetetramine and oxalic acid in the precursor synthesis. The results indicated that the NiO/Ni composite nanostructures roughly retained the spherical flower like morphology of the precursor and presented high specific capacitance as electrode materials for supercapacitors. The improvement in its electrochemical performance is possibly associated with the increased conductivity originating from Ni species and rapid diffussion of electrolytes within the porous structure.3. As one of the important n-type semiconductors, ZnO shows great potential in many fields. The conductivity of ZnO depends on the concentrationon of adsorped species on the surface when exposed to the testing gas, hence ZnO could be used as gas-sensing material. Herein, three-dimensional ZnO porous microflowers with large surface area have been obtained by calcining the microflower-like Zn-baesd precursor, which was preformed by co-precipitation method. The gas sensor fabricated by the as-prepared ZnO porous microflowers shows strong response to ethanol even at low temperature and low gas consentration. The ZnO microflowers were also used as templates to synthesize porous N-and B-doped carbon nanosheets, which show more positive reduction potential and higher electrocatalytic activity then undoped sample in the ORR. These results had important implications in revealing the catalytic mechanism of metal-free doped carbon electrocatalysts in the ORR.