Semiconducting 2D Copper(I) Framework for Sub-ppb-Level Ammonia Sensing

The development of efficient materials for selective and efficient sensing of toxic gases and volatile organic compounds is highly desired, especially for environmental monitoring, industrial safety, and medical diagnosis. Herein, we report two distinct coordination polymers, 2D CuTz1 and 1D CuTz2, synthesized from the same reactant under similar conditions but in varying ratios. Remarkably, 2D CuTz1 features a unique Cu4I4 secondary building unit (SBU), while CuTz2 has a rhomboid Cu2I2 SBU. The 2D CuTz1 was found to be green emissive and semiconducting in nature and exhibits a 2D nanoflake-like morphology. Further, CuTz1 not only shows the change in emission color from green to yellow-orange in the presence of aqueous ammonia vapor, but also, the chemiresistive sensor derived from CuTz1 shows exceptional ammonia sensing capabilities. Excellent sensitivity and selectivity, accompanied by fast dynamic response/recovery time, positions CuTz1 as the most promising material among the reported MOF/CP-based ammonia sensors.