Cu(I) Coordination Polymer-Based NH₃ Gas Sensor with High Response at Room Temperature

High performance in NH₃ gas sensor is highly demanded because ammonia which has highly toxic and corrosive properties causes ailments in human body under the certain concentration of NH₃. Up to date, metal oxide gas sensor (MOS) is widely used for detecting NH₃ gas; however, high operating temperatures and producing costs are considered as limitation in the effective applications.<br/>Here, we report on a new type of NH₃ gas sensor with high response (&gt; 800% at 100 ppm) and low detection limit (&lt;0.25 ppm) at room temperature. The sensor is semiconducting coordination polymers (CPs) containing Cu(I) ions and thiourea derivatives, which can be produced by cost-effective solution-based method within 10 min. For improving NH₃ gas sensing performance, Ag was doped into CPs. It exhibits the excellent gas sensing capability with ~ 2000 % at 100 ppm which is the best of our knowledge. Additionally, response and recovery time decreased by 8% and 70%, respectively compared to that of parent CPs. Ag in CPs was detected by XPS measurements, which verified that Ag elements exist individually inside of CPs. To determine the origin of outstanding gas sensing properties of CPs, we performed a simulation of crystal structure based on the PXRD results. And In-situ FT-IR spectroscopy was used to identify the mechanism of NH₃ gas sensing in CPs. NH₃ gas and NH₄⁺ ions acted as Lewis, Brønsted acid site, and additionally NH₃-Cu⁺ peaks were observed at 1620 cm^-1, and it could be inferred that the high reactivity of the sensor was caused by Cu⁺ acting on NH₃ detection.