Gas sensors based on alpha-Fe2O3 nanorods, nanotubes and nanocubes

Nanorods, nanotubes, and nanocubes of alpha-Fe2O3 were synthesized via a hydrothermal process and subsequent calcination treatment. The typical nanorod has about 71 nm in width, 7 nm in thickness, and 314 nm in length. The nanotube has outer diameter of 90-110 nm, inner diameter of 40-80 nm, and lengths of 250-400 nm. The nanocubes are rhombus cubes with an edge length of about 680 nm. The nanorods, nanotubes and nanocubes were fabricated into chemiresistive sensors. The responses (R(a)/R(g)) of the nanotube sensor to ethanol, acetone, formaldehyde, and ammonia are greatly higher than those of the nanorod/the nanocube sensors. The nanotubes showed enhancing gas-sensitive properties. The responses of the nanotube sensor reached 75, 26, 6.8, 1.7 to 200 ppm acetone, ethanol, formaldehyde, and ammonia at 270 degrees C and a 30-45% relative humidity, respectively, which shows high selectivity. So the nanotubes are gas-sensing materials more excellent than nanorods and nanocubes.