| Summary: | Detection of carbon dioxide (CO<sub>2</sub>) is very important for environmental, health, safety and space applications. We have studied novel multiwall carbon nanotubes (MWCNTs) and an iron oxide (Fe<sub>2</sub>O<sub>3</sub>) nanocomposite based chemiresistive sensor for detection of CO<sub>2</sub> at room temperature. The sensor has been miniaturized to a chip size (1 cm × 2 cm). Good sensing performance was observed with a wide detection range of CO<sub>2</sub> concentrations (100−6000 ppm). Structural properties of the sensing materials were characterized using Field-Emission Scanning Electron Microscopy, Fourier-Transform Infrared and Raman spectroscopies. The greatly improved sensitivity of the composite materials to CO<sub>2</sub> can be attributed to the formation of a depletion layer at the p-n junction in an MWCNT/iron oxide heterostructure, and new CO<sub>2</sub> gas molecules adhere to the high surface area of MWCNTs due to the concentration gradient. The test results showed that the CO<sub>2</sub> sensor possesses fast response, compact size, ultra-low power consumption, high sensitivity and wide dynamic detection range.
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