Tailoring NH₃ Sensing Responsiveness through Amine Modification of Imine-Based Nanoporous Covalent Organic Polymer

Abstract

An efficient and affordable NH3 sensor is crucial for accurately monitoring atmospheric pollution and human health. Nanoporous covalent organic polymers (nCOPs) are promising candidates for detecting NH3 due to their abundant functional groups on the surface, excellent electrical properties, and nanoporous structure. This enables precise detection with exceptional selectivity and sensitivity. Herein, we have developed an imine-containing nanoporous COP (nCOPI) and further reduced the imine bonds (CN) to synthesize an amine (C–N)-containing nanoporous COP (nCOPA). We have employed these as sensing materials for detecting NH3 at 25 °C. Interestingly, the nCOPA sensor displays an impressive 18.6 times increased response of 1700% toward 500 ppm of NH3 compared to the nCOPI sensor (91%) with a response/recovery time of 60/70 s. Furthermore, the nCOPA sensor demonstrates exceptional selectivity, complete reversibility, excellent repeatability, and long-term stability, achieving limit of detection (LOD) and limit of quantification (LOQ) values of 0.25 and 0.86 ppb, respectively. The plausible sensing mechanism is attributed to the charge-transfer process and hydrogen bonding between the NH functional group present in nCOPA and NH3 gas molecules, which alters the resistance of the nCOPA sensor. Based on these findings, the nCOPA sensor holds significant potential for NH3 sensing, and its application could provide an efficient method for the real-time monitoring of NH3.