Surface sol-gel process was used to replicate the hierarchical morphology of natural cellulosic substances with nanometer precision. The resultant artificial fossils are ceramic nanomaterials composed of metal oxide nanotubes.

SnO 2 nanotubular materials were prepared by using a natural cellulosic substance (filter paper) as template, and their morphologies were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cellulose fibers were first coated with SnO 2 gel layers by the surface sol-gel process using Sn(O i Pr) 4 as precursor, followed by calcination in air to give SnO 2 nanotubular materials as hollow replicas of natural cellulose fibers. The nanotubes obtained by calcination at 450 °C were amorphous-like and composed of fine particles with sizes smaller than ca. 5 nm. The outer diameters are tens to two hundred nanometers, and wall thicknesses are 10-15 nm. Calcination at 1100 °C yielded tubelike polycrystalline SnO 2 nanocages (outer diameter 100-200 nm), which were composed of rutile-phase SnO 2 nanocrystallites with sizes of 10-20 nm. The thermal behavior and the crystalline property of the powder obtained from calcination of the as-prepared SnO 2 sheet were examined in the temperature range of 300-900 °C. The sizes of the nanoparticle obtained by calcination at 300 and 900 °C were 2.0 and 9.2 nm, respectively, in fair agreement with TEM observation. Calcination temperatures above 500 °C are needed to obtain pure SnO 2 . A sensor setup was fabricated from the SnO 2 nanotube sheet, and the sensor performance was measured for H 2 , CO, and ethylene oxide. The sensor signal, S, was 16.5 at 450 °C to 100 ppm H 2 , and was comparable to that of the conventional SnO 2 sensor. Finally, the sensor characteristics were discussed in relation to the morphology of the nanotube sheet.

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