Ammonia is a highly reactive gas, and it is considered as an air pollutant. The OSHA upper limit for NH3 exposure has been set to 25 ppm for 8 hours at the workplace. Therefore, ammonia detection is needed for industrial safety, and environmental considerations. Conducting polymers, such as polyaniline (PANI), and their composites with metal nanoparticles have been studied extensively to develop an NH3 sensor operating at room temperature. The metal-organic nanocomposites have played significant role in enhancement of sensitivity as well as selectivity for gas sensing. In this work, we have synthesized bis-ethylenediamine Cu(II) chloride (Cu-EDTA) composite by chelation of copper chloride with ethylenediamine. The gas sensitive thin films of Cu-EDTA functionalized PANI-CSA mixture were fabricated by spin coating on ITO-PET electrodes. The Cu-EDTA nanocomposite was decorated at protonated sites in PANI as confirmed by XPS, TEM, and SAED characterizations. The ethylenediamine in Cu-EDTA deprotonated PANI which results in increased resistance of the nanocomposite compared to pristine PANI. The Cu2+ ions have shown strong affinity for lone pair of NH3, due to which the resistance was increased 3.8 times upon exposure to 100 ppm of NH3 at 20 °C in air. The response was decreased slightly for sensing at high temperatures (28 °C, and 35 °C) due to increased charge conduction in sensing film, and high rate of desorption for NH3. The modified Randles circuit with two semicircle characteristics in Nyquist plot using impedance spectroscopy confirmed contribution of Cu2+ ions in gas sensing mechanism. The nanocomposite sensor can be regenerated by application of moderate heat (75 °C), and it is capable of detecting NH3 concentrations as low as 2 ppm. The response time (63.2% of saturation value) has been calculated as 50 seconds. The Cu2+ ions at protonated sites in nanocomposite improved selectivity for NH3 sensing over H2S, CH4, C2H5OH, and NO.

Highly sensitive Cu-ethylenediamine/PANI composite sensor for NH3 detection at room temperature

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