Selective and Sensitive Detection of Ammonia at Room Temperature by the WS₂-PANI Nanocomposite on a Flexible Paper-Based Sensor with Cost-Effective Chemically Expanded Graphite Ink Electrodes

A facile way of synthesizing WS2 nanosheets in an aqueous solvent and fabrication of interdigitated electrodes (IDEs) on a flexible substrate using chemically expanded graphite (CEG) conductive ink has been reported in this study. The synthesized WS2 nanosheets have been utilized for highly sensitive and selective flexible ammonia (NH3) sensors at room temperature by incorporating polyaniline (PANI) with the nanosheets, following a cost-effective route. The IDEs have been fabricated on a flexible photopaper substrate using a cost-effective spray coating method. The resistance of the fabricated IDEs is comparable to standard gold and copper electrodes. The flexible sensor shows enhanced sensing performance, with higher response, high selectivity, prolonged stability, and a low detection limit of 3 ppm experimentally (≈9 ppb, theoretically). The effect of the relative humidity level has also been investigated. The response and recovery times for 5 ppm of NH3 vapor are found to be 38 and 58 s, respectively. The sensor shows remarkable recovery after returning from the bending condition to the relaxed (normal) position. The experimental results agree with the density functional theory (DFT) analysis that has been performed to support the experimental results. The electronic charge density differences of the WS2-PANI nanocomposite in the proximity of NH3 show significant variation compared to other interfering volatile organic compounds (VOCs). In addition, the sensing mechanism of the WS2-PANI nanocomposite toward NH3 has also been discussed.