Synthesis And Property Studies Of Mixed Metal Oxide Ultrathin Nanosheets Or Hollow Structures

It is well known that the features of functional materials,such as composition,structural and morphology characteristics,would greatly influence the performances of nanomaterials.The diversified composition and novel structure of nanomaterials bring significant advances and great potential in physical-chemical properties,such as enhanced catalytic performance,specific surface activity,remarkable magnetism and high electrical conductivity,etc.For mixed metal oxides,multiple valences of different metal cations,diversified chemical compositions,increased donor-acceptor chemisorption sites and their synergetic effects leads to the exceptionally high specific capacitance.Large contacting areas and tremendous exposed surface atoms brought by atomic-thick nature of the ultrathin inorganic nanosheets,would open up a new door for significantly promoting the reaction activity of active materials during reaction processes.Moreover,two-dimensional nanocrystals with horizontal constraint will bring synergic advantages of modulated electrical properties and superior electrochemical activities.Therefore,the strategy for controlled synthesis of 2D nanostructures with high crystallinity is extremely significant to meet the booming demand for practical applications.The intriguing structural features of the hollow micro-/nanostructures,including large surface area,high surface permeability,a kinetically favorable open structure and low density,contribute to great technological capacity in many applications,such as electrochemical energy storage systems,catalysis,drug delivery.Therefore,the rational design of ultrathin nanosheets and hollow structures of the mixed metal oxide with multiple valences of different metal cations becomes more and more vital and fascinating for both scientific researches and practical applications.In this thesis,we have developed a series of facile and efficient strategies to fabricate ultrathin nanosheets and hollow structures of the mixed metal oxide with multiple valences of different metal cations.The reaction conditions have adjusted to regulate their compositions,structural and morphology characteristics.The composition features,morphology characteristics and the properties in the energy storage system were systematically investigated.1.Generalized low-temperature fabrication of scalable multi-type two-dimensional nanosheets with a green soft-templateWe successfully developed a generalized low-temperature synthetic method for polytype ultrathin two-dimensional nanosheets,including hydroxides(such as Ni(OIH)2,Co(OIH)2,Cd(OH)2,and Mg(OH)2),metal oxide(such as ZnO and Mn3O4)and layered mixed transition-metal hydroxides(CoNi-LDH,FeNi-LDH,FeCo-LDH.Ni-Co-Fe layerd ternary hydroxides)with a green soft-template.When evaluated as electrode materials for pseudocapacitors,the Co-Ni LDH exhibits a high specific capacitance of 1087 F·g-1 at a current density 1 A·g-1 and excellent stability with 103%retention after 500 cycles superior to that of Ni(OH)2 with simple configuration.2.Generalized synthesis and energy storage performance of the double shelled dumbbel-like binary metal oxidesThe unique double-shelled dumbbel-like binary metal oxides ZnFe2O4 were synthesized through a precursors calcinalion.By a typical hydrothermal process,the double-headed carbonaceous precursors with metal ions dispersed inside can be obtained.Under a rapid annealing process in air,the double shelled dumbbel-like binary metal oxides can be easily generated owing to the deformation stress during the process of crystallization.To verify the generality of this strategy,we explored the experiment condition to other metal ions and the double shelled dumbbel-like structures of ZnMn2O4/ZnO materials are first synthesized.The electrochemical energy storage performance of ZnFe2O4 are then evaluated.3.Formation of hollow structures with PB analogue nanocubes as the precursors of mixed metal oxidesIn order to realize the controlled synthesis of the Prussian Blue Analogue nanocubes,PVP was used to adjust the viscosity of reaction solution.Moreover the unbalanced competition between citrate and Fe(CN)63+ will further slow the release of metal ions into the reaction solution.Different PBA naoncubes with different metal ions distributions and different structures details have been obtained.Under a rapid annealing process in air,the corresponding mixed metal oxides can be easily obtained.Due to the different metal ions in the precursors,the morphology characteristics of the products are discriminating.Three-dimensional structure of cubic consist of hierarchical nanosheets can be obtained by the annealing Zn-Co PBA.The hollow nanocages with sunk facets can be obtained by annealing of the Ni-Co PBA.After a annealing process of the Zn-Mn PBA and Co-Mn PBA,the hollow nanocages with a thick shell and thin shell can be obtained respectively.