Optical recognition of CO and H2 by use of gas-sensitive Au–Co3O4 composite films

Gold–cobalt oxide (Au–Co 3 O 4 ) composite films have been prepared by the sputter-deposition of gold onto a glass plate substrate followed by pyrolysis of spin-coated cobalt 2-ethylhexanoate. The films comprise small Au particles and Co 3 O 4 nanocrystals, and exhibit different and independent optical responses to CO and H 2 in air. Carbon monoxide caused only a decrease in absorbance, while H 2 caused both a decrease and an increase in absorbance at different wavelengths. Among solid-state gas sensor materials, this Au–Co 3 O 4 composite film is probably the first example of an inorganic material which can be used for the recognition of CO and H 2 molecules through optical absorbance changes.