(2ey) Low Temperature Selective Detection of Ammonia Gas with Cu-En Functionalized Polyaniline

Ammonia is 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 work place. 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-en) composite by chelation of copper chloride with ethylenediamine. The gas sensitive thin films of Cu-en functionalized PANI-CSA mixture were fabricated by spin coating on ITO-PET electrodes. The Cu-en nanocomposite was decorated at protonated sites in PANI as confirmed by XPS, TEM, and SAED characterizations. The ethylenediamine in Cu-en deprotonated PANI which result 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 temperature (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 in nanocomposite improved selectivity for NH₃ sensing over H₂S, CH₄, C₂H₅OH, and NO.