Abstract
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).