Functional Porous Transition Metal Oxide Powders Via Solution Combustion Synthesis

Mass transport and charge transfer (especially at the interface) are two key factors in various applications of energy storage, gas sensor, and catalysis. Porous materials are the right choice for the applications above-mentioned, because they are able to provide large surface area and abundant channels. Up to now, most approaches to porous materials focus on template-assisted methods, including hard templates and soft templates. The template-assisted routes are complex and high cost. It is therefore of general interest to produce porous materials with simple and economical synthesis strategies.Solution combustion synthesis (SCS), which is self-sustained by its own exothermic reaction, is an effective, rapid, and energy-efficient method for mass productions of various metal oxides. Unfortunately, it is difficult to control the combustion process and morphology of product in SCS. In the current investigation, the two major shortcomings inherent of the SCS were focused on, through careful modifications of the combustion procedure. Several porous metal oxides with special nanofeatures via SCS were achieved for high performance functional applications. Several novel, simple, template-free, low-cost, and universal synthesis routes based on SCS were developed for mass fabrications of porous metal oxides, which possessed excellent properties arising from the unique structures when utilized for surface-relative applications of Li-ion batteries and gas sensors.It is difficult to achieve phase-pure La4Ni3010by existing synthesis methods because of the easy coexistence of several other phases encountered in the La-Ni-O system. Phase-pure layered perovskite La4Ni3010powders were synthesized by a solution combustion approach combined with a subsequent heat treatment at1000℃for3h, which demonstrated the superiority of SCS in synthesis of complex oxides. It is found that, in the presence of the LaNia3O10powders, aqueous dyes can be degraded catalytically and efficiently under ambient conditions. Neither light nor additional reagents are needed in the current reaction. A series of chemical and electrochemical experiments suggested that the dye degradation proceeds through electron transfers from the dye molecules to the catalyst and then to electron acceptors such as dissolved oxygen.In nature, volcano eruptions create large amounts of porous volcano ashes within a short duration. Inspired by such phenomena, we reported our first attempt to achieve an artificial volcano for mass productions of various oxide nanoparticles with enhanced properties for energy and environmental applications. The introduction of NaF into the SCS resulted in the formation of porous structures. The novel eruption combustion pattern observed in SCS provides a versatile alternative for SCS to control combustion behavior, microstructure, and property of the products. NiO/Ni nanocomposite yielded by the new approach exhibited a good dye-absorption ability. When utilized as anode materials for lithium-ion batteries, excellent electrochemical performances were also achieved. The new SCS pattern is versatile, emerging in various systems of Ni-Co-O, Co-O, La-O, Ni-Co-O, Zn-Co-O, and La-Ni-O.Macroporous metal oxides were achieved in a flash by the direct decomposition/combustion of a metal complex, through mainly the additive of acetate salts as gasfication agents. The fabrication route is template-free, surfactant-free, and highly effective. Taking NiO/Ni as an example, the metal complex was achieved by simply mixing nickel acetate, nickel nitrate, hydrazine hydrate, and glycine in water. The pore size, porosity, and even morphology of the porous NiO/Ni network (three-or two-dimensional architectures) can be conveniently tuned by adjusting the composition of the complex. This synthesis route can be extended to prepare other macroporous metal oxides, such as ZnO. The achieved macroporous NiO/Ni possessed excellent electrochemical performance and the coral-like hierarchical macro/meso-porous ZnO also exhibited excellent gas-sensing performance.Amorphous metal complexes were prepared by SCS applying a high fuel/oxidizer ratio, which greatly reduced the violent combustion, improving the safety of SCS. Thermal treatments of the complex in air or reactions of the complex with H2O2resulted in the formation of porous metal oxides with high specific surface area. Both the achieved porous Co3O4and the TiO2nanobelts exhibited excellent performance in anodes of lithium ion batteries. The achieved macroporous ZnO possessed ideal gas sensing properties.