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We have characterized and evaluated changes in graphene oxide (GO) induced by means of freeze-drying. In order to evaluate these changes, we investigated the effects of freeze-drying and chemical reduction processes on the structure, morphology, chemical composition, and Raman properties of GO and reduced GO. The freeze-dried GO had a pore structure, maintaining a pored morphology even after thermal annealing. The freeze-dried samples were composed of a single folded nanosheet or a few nanosheets stacked and folded. The oxygen-containing functional groups were removed not only during the freeze-drying but also during the reduction processes, with an accompanying decrease in the average size of the sp(2) carbon domain (i.e. an increase in the ID/IG value).

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The sensing properties of Sb2O5 nanowires are reported for the first time. By varying the heating temperature of a mixture of Sb and Bi powders, we have successfully prepared Sb2O5 nanowires. For nanowires grown at 600°C, the stem is mainly comprised of a monoclinic Sb2O5 phase, with a trace amount of a monoclinic Bi2O3 phase. The existence of Au nanoparticles at the tips suggests that the 600°C-synthesized nanowires are mainly grown via a vapor-liquid-solid process. The 500°C-grown products comprise a small amount of 1D nanostructures, whereas the 700°C-grown product does not exhibit sufficiently thin 1D nanostructures. A representative A survey XPS spectrum exhibits several peaks, including Sb 3p, Sb 3d, O 1s, C 1s, Bi 4f, and Sb 4d. At room temeperature, the sensor response, response time, and recovery time of the nanowires were measured to be 1.20, 2104 s, and 6579 s, respectively. Sensor measurements employing NO2 gas indicate that the Sb2O5 nanowires synthesized in this work have potential for use as a room-temperature NO2 chemical gas sensors.