Fe3O4–MWCNTPhCOOH composites for ammonia resistive sensors

Hybrid composites of Fe3O4 and multiwalled carbon nanotubes (MWCNT) chemically functionalized with the benzoic acid group (PhCOOH) are described as novel sensing materials for resistive-type ammonia gas sensors. Fe3O4/MWCNTPhCOOH composites have been synthesized by a simple procedure. The morphological and microstructural characterization has been performed by using TGA, FT-IR, XRD and TEM. TGA and FT-IR confirmed the covalent attachment of the benzoic acid groups, thus creating highly localized sites with high affinity toward ammonia molecules. Fe3O4 nanoparticles, about 7 nm in diameter, were found homogeneously distributed on the functionalized MWCNTPhCOOH surface.The ammonia sensing characteristics of samples synthesized with different Fe3O4 loading have been investigated at low temperature. Sensor devices fabricated with the hybrid Fe3O4/MWCNTPhCOOH composites have shown more higher variation of resistance upon exposure to NH3 compared to pristine MWCNT and functionalized MWCNTPhCOOH ones, indicating a combined effect between the organic group and metal oxide in improving the response toward the target gas. The reversibility of the sensor was improved operating under UV irradiation.