Carbon dioxide (CO2) has been shown to contribute to poor indoor air quality and associated human health consequences, such as shortness of breath, nasal and optic irritation, dizziness, and nausea. Nondispersive infrared (NDIR) sensors can probe low CO2 concentrations (< 400 ppm) but these devices are characteristically expensive and difficult to miniaturize. In this work, we address these shortcomings by using metal-organic frameworks (MOFs) as highly-porous, crystalline, chemically-stable sorbents for strong adsorption of CO2. Our first-generation colorimetric CO2 gas sensor consisted of a post-synthetic mixture of three components: (i) the MOF sorbent, ZIF-8; (ii) the CO2 capturing group, ethylenediamine (ED); and (iii) the pH indicator, phenolsulfonpthalein (PSP). However, in mixing PSP in the ZIF-8 precursor reaction broth and adding ED post-synthetically, we have achieved a second-generation sensor whose CO2 response is greatly enhanced in dry atmosphere. More recently, the inclusion of mixed, highly-conjugated dyes has resulted in a multi-color response to ambient CO2. UV-vis ratiometric analysis and RGB colorimetric profiles quantitatively demonstrate an improvement in CO2 detection in environments typical of indoor air.
Updated: Aug 11, 2021