Molecular shape recognition by a tin oxide chemical sensor coated with a silica overlayer precisely designed using an organic molecule as the template

A tin oxide gas sensor was modified by chemical vapor deposition (CVD) of silicon alkoxide using various preadsorbed aldehydes as the template. The deposition of silica without the template suppressed the sensitivities for all of the used alkanes, but the deposition under the presence of the preadsorbed template did not affect the sensitivities to n-hexane and octane, linear C-6 and C-8 alkanes. The use of benzaldehyde as the template suppressed the sensitivities to 2,2-dimethylbutane and -hexane, namely, the isomers with two methyl branches, and cyclohexane and cyclooctane. A n-butyraldehyde template suppressed the sensitivities to these isomers and, in addition, the sensitivities to 2-methylpentane and -heptane, which are the isomers with one methyl branch. The microstructure of the silica surface layer is considered to be precisely controlled by the template molecule to possess the pores whose size and shape were the same as those of the template molecule. Catalytic activity for complete oxidation of the alkanes was also shown to be controlled by the shape and size of pores in the silica layer.