Nanotubular SnO2 Templated by Cellulose Fibers: Synthesis and Gas Sensing

SnO2 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 SnO2 gel layers by the surface sol−gel process using Sn(O i Pr)4 as precursor, followed by calcination in air to give SnO2 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 SnO2 nanocages (outer diameter 100−200 nm), which were composed of rutile-phase SnO2 nanocrystallites with sizes of 10−20 nm. The thermal behavior and the crystalline property of the powder obtained from calcination of the as-prepared SnO2 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 SnO2. A sensor setup was fabricated from the SnO2 nanotube sheet, and the sensor performance was measured for H2, CO, and ethylene oxide. The sensor signal, S, was 16.5 at 450 °C to 100 ppm H2, and was comparable to that of the conventional SnO2 sensor. Finally, the sensor characteristics were discussed in relation to the morphology of the nanotube sheet.