Construction Of Composite Metal Oxide Nanoarrays And Applications Study

Nanoarray materials have received worldwide concern with the development of nanotechnology. Having many structure advantages (exposed active crystal face, adjustable size, and good adhesion to the substrate, etc.), nanoarrays have widely been used as emission materials, interface materials, electrochemical electrodes, heterogeneous catalysts, and sensors, etc. Among those nanoarray materials, transition metal oxides nanoarrays, because of their low price, high stability, and favorable structural characteristics, have important prospects in electrochemical energy storage and catalysis. In addition, due to the synergistic effect, composite metal oxide nanoarrays usually exhibit more favorable physical and chemical properties than corresponding single metal oxide nanoarrays.In this paper, a series of composite metal oxide nanoarrays were prepared by liquid-phase chemical deposition method, and their growth process and applications in the field of heterogeneous catalysis and electrochemical energy storage were studied. This study is helpful for people to understand the relationship between the composition, morphology and their properties. The main contents of this paper are as follows:1. NiCoFe spinel-type oxide nanosheet arrays were fabricated by using layered double hydroxides (LDH) as precursors and investigated as structural catalysts for alkenes oxidation. The NiCoFe spinel-type oxide nanosheet arrays exhibited high catalytic activity (72% conversion) and selectivity (64% for benzaldehyde) towards the oxidation of styrene by tert-butyl hydroperoxide (TBHP). These good catalytic performances were mainly attributed to the unique porous nanosheet arrays providing large surface area and structural stability and the substitution of cobalt leading to the appearance of new active Co3+ sites at the surface of the samples.2. We developed a one-step hydrothermal method for synthesizing a series of hierarchical nanoarrays. Based on the related experiments, we put forward a method of synthesizing transition metal oxide hierarchical nanoarrays utilizing the co-deposition of transition metal ions under alkaline hydrothermal condition, which included the following three points of view:(1) When two kinds of transition metal ions deposit in alkaline hydrothermal condition to generate hierarchical nanoarray structure, the one with a smaller metal hydroxide solubility deposit and hydroxide grow prior to the one with a bigger metal hydroxide solubility. (2) Transition metal ions which deposit and hydroxide grow under the specific alkaline hydrothermal condition will form metal hydroxides or subcarbonate with certain crystal type and morphology characteristics. (3) The lattice-matching sediment can secondarily grow on the previous deposits. As a result, we can synthesize a specific transition metal oxide hierarchical nanoarrays based on the corresponding properties of the metal iron and hydroxide. Under the guidance of this method, we successfully synthesized a variety of transition metal ions doped hierarchical nanoarrays (Zn2+/Ni2+, Co2+/Ni2+, Mn2+/Ni2+, Mn2+/Zn2+, etc.), proving the effectiveness of the proposed method.3. We used a one-step hydrothermal method to construct the hierarchical ZnO/NiO composite nanoarrays on copper foam substrate. The hierarchical structure of primary rhombus-shaped nanorod arrays (Zn2+ deposition) with secondary nanoflakes (Ni2+ deposition) grown on them was obtained by utilizing the different solubility of Zn(OH)2 and Ni(OH)2 which led to Zn2+ depositing and hydroxide growth prior to Ni2+. Moreover, by simply adjusting the ratio of Zn2+ to Ni2+, nanoarrays with different morphology could be obtained, including nanorod and nanosheet arrays. As a supercapacitor, the hierarchical nanoarrays exhibited much higher capacitive performance than the other two nanoarray materials:6.2 F·cm-2 and 1512.1 F·g-1 at the current density of 5 mA·cm-2. In addition, a remarkable rate capability (maintain 69.3% of the initial capacitance at the current density of 30 mA·cm-2) is observed. This substantially enhanced performance was attributed to the unique hierarchical nanostructures that provided larger specific area, higher porosity and higher active-site density on the surface.