SnO₂ Nanorods Arrays On Graphene And Other Substrates: Synthesis, Properties And Devices

The physical and chemical properties of nanomaterials are highly depended on their structures. Therefore, the practical application of nanomaterials is fundamentally determined by their geometric morphology and physicochemical property. It is of great significance constructing functional nanostructures in the scale of atoms and molecular, by using the one-dimensional nanostructures as building blocks. The ordered arrays made up with individual nano-units not only show the individual characters, but also reflect the synergistic effect of combination, and meet the requirements of designing devices. Applied as excellent gas sensing material and electrode of lithium ion battery, SnO2 has been investigated widely. Our paper selected one-dimensional SnO2 nanomaterials as the subject and a series of two-dimensional substrates (such as graphene sheets, SnO2 polycrystal sheets, metal foils and carbon fibers), and synthesized the three-dimensional array structures with different morphologies. By varying the preparation conditions during the hydro thermal routes, characterizing the structures, measuring the properties of the products, and the forming mechanisms of the novel structures were investigated. These structures of SnO2 nanorods arrays on different substrates have been explored as gas sensors and electrodes of lithium ion battery and show excellent performances. The main research results are listing as follows:1. Highly aligned SnO2 nanorods on graphene 3-D array structures were synthesized by a straightforward nanocrystal-seeds-directing hydrothermal method. The diameter and density of the nanorods grown on the graphene can be easily tuned as required by varying the seeding concentration and temperature. The structure and morphology of the products were characterized by SEM, TEM, XRD, BET methods. The SnO2/G 3-D array structures were formed first by the hydrolytic growth of nanocrystal seeds on the graphene sheets, which strongly depended on conditions such as the hydrolysis concentration and sintering temperature, followed by a second hydrothermal growth of SnO2 nanorods on the graphene substrates. The array structures were used as gas sensors and exhibited improved sensing performances to a series of gases in comparison to that of SnO2 nanorod flowers. For nanorod arrays of optimal diameter and distribution, these structures were proved to exert an enhanced sensitivity to reductive gases (especially H2S), which was twice as high as that obtained using SnO2 nanorod flowers. The improved sensing properties are attributed to the synergism of the large surface area of SnO2 nanorod arrays and the superior electronic characteristics of graphene. Also, photoluminescence property and the lithium ion battery electrode's performance have been tested and both well behaved.2. Self-supporting SnO2 nanorods array structures were synthesized by the hydrothermal route. This novel structure is including the first formed SnO2 nanocrystal flat and then the thin SnO2 nanorods that standing on both of its sides. Via systematic experiments, the best array structure was obtained with the right conditions. According to the characteristic of chemical reaction and crystal growth, the forming mechanism of the self-supporting SnO2 nanorods array structures was proposed. With the assistance of the anionic surfactant SDS, water droplet in the oil phase forming the so-called "reverse micelle", in which the Sn4+ hydrolyze into precipitate adhering on the two-phase interface. During the subsequently hydrothermal process, SnO2 nanorods grow along the [001] direction via Ostwald repening, forming the self-supporting SnO2 nanorods array structures. The array structures were used as gas sensors and exhibit excellent sensing performances to ethanol. Also, photoluminescence property and the lithium ion battery electrode's performance were tested and compared, which performed excellently. 3. The SnO2 nanorods arrays on copper foils and nickel screen metal substrates, carbon fiber material substrates have been prepared successfully via a simple and general hydrothermal route. Large acreage of branched SnO2 nanorods arrays structures grew on copper foil via a two-step growth process. On the nickel screen with a large surface area, large scale of vertically aligned SnO2 nanorods arrays formed, which is expected to have a large surface area. The carbon fibers were also surrounded by the large area of ordered SnO2 nanorods arrays. According to the characteristic of chemical reaction and crystal growth, the mechanism of the general formation of SnO2 nanorods array structures was proposed. At last, the potential applications of SnO2 nanorods arrays structures with different substrates were indicated.