Co ₃ [Co(CN) ₆ ] ₂ -Mediated Olfactory and Visual Dual-Modality Ammonia Sensing

In the emerging ammonia (NH₃) economy, both olfactory and visual sensing are desired for leakage detection, in which olfactory sensing enables a fast response and wide detection range, while visual sensing ensures high selectivity. However, little is reported on the sensing material as a mediator to synergistically combine the dual-modality NH₃ sensing. Here, Co₃[Co(CN)₆]₂ microcubes (Co-CN MCBs) mediators have been developed for olfactory and visual dual-modality NH₃ sensing. In olfactory sensing, porous chitosan-decorated Co₃O₄/Co₃[Co(CN)₆]₂ microcages (CS@Co-O/Co-CN MCGs) have been obtained via [Co(CN)₆]^3--governed self-assembly, glycerol-assisted reduction, and Kirkendall effect-driven hollowing. Beneficially, MCGs exhibit a 1 s fast response (500 ppm) and a 0.5-10,000 ppm wide detection range at room temperature. In visual sensing, colorimetric sensing paper (CSP) incorporated with anthocyanin, Co-CN, and poly(vinyl alcohol) has been achieved, which presents 10-320 ppm visual NH₃ detection through a pink-to-brown transition. Further, highly selective NH₃ sensing has been acquired through machine learning-powered classification of MCGs' response and CSP's specific NH₃ chromogenic behavior. Notably, combining dual-modality sensing has achieved desired NH₃ detection due to the boosted NH₃ adsorption on Co-CN MCBs' active sites and the synergistic effect of their-mediated heterostructures. Practically, our dual-modality sensing device has been integrated to detect NH₃ with reliable responses.