Chemiresistive Sensing of Ambient CO2 by an Autogenously Hydrated Cu3(hexaiminobenzene)2 Framework

A growing demand for indoor atmosphere monitoring relies critically on the ability to reliably and quantitatively detect carbon dioxide. Widespread adoption of CO 2 sensors requires vastly improved materials and approaches because selective sensing of CO 2 under ambient conditions, where relative humidity (RH) and other atmosphere contaminants provide a complex scenario, is particularly challenging. This report describes an ambient CO 2 chemiresistor platform based on nanoporous, electrically conducting two-dimensional metal-organic frameworks (2D MOFs). The CO 2 chemiresistive sensitivity of 2D MOFs is attained through the incorporation of imino-semiquinonate moieties, i.e., well-defined N-heteroatom functionalization. The best performance is obtained with Cu 3 (hexaiminobenzene) 2 , Cu 3 HIB 2 , which shows selective and robust ambient CO 2 sensing properties at practically relevant levels (400-2500 ppm). The observed ambient CO 2 sensitivity is nearly RH-independent in the range 10-80% RH. Cu 3 HIB 2 shows higher sensitivity over a broader RH range than any other known chemiresistor. Characterization of the CO 2 -MOF interaction through a combination of in situ optical spectroscopy and density functional theory calculations evidence autogenously generated hydrated adsorption sites and a charge trapping mechanism as responsible for the intriguing CO 2 sensing properties of Cu 3 HIB 2 .