Production of a porous carbon material and a carbon-iron oxide hybrid using tubular iron oxide of bacterial origin

An amorphous Fe(III) oxide material, which is naturally produced by an aquatic bacterium, Leptothrix ochracea, has a tubular morphology with a diameter of ca. 1 µm. We used thesee iron oxide tubes as a template to produce a novel porous carbon and a humidity sensor. Furfuryl alcohol or resorcinol-formaldehyde resin mixed with iron oxide was polymerized and carbonized. After treatment with hydrochloric acid followed by hydrofluoric acid, the samples retained the tubular shape and showed high BET surface areas in the range 220∼1260 m2 g−1. The surface of the iron oxide tubes can be coated by carbon layer using CVD with a 20 vol% C2H2/Ar gas at 400 °C. The electrical resistance of the carbon-coated iron oxide tube (C/BIOX) was measured. Since the resistance depended on the humidity of the atmosphere at room temperature, C/BIOX may be used as an extremely small humidity sensor.