BF2-Postmodified Cobalt-Porphyrin Covalent Organic Framework for High-Performance Specific Detection of NH3.

The development of high-performance ammonia (NH3) sensors is critical for environmental and industrial safety; however, conventional chemiresistive materials face challenges in sensitivity and humidity interference. This work presents a covalent organic framework synthesized by Co-5,10,15, 20-tetrakis (4-aminophenyl) (CoTAPP) and 2,5-dihydroxy terephthalaldehyde (DTA) postmodified with electron-deficient BF2 groups (COF-CoDT-BF2) to address these limitations. First, the construction of donor-acceptor interfaces between cobalt porphyrin and BF2 groups enhances charge transport while modulating Co-site electron density for optimized NH3 adsorption. Moreover, BF2 groups serve as secondary active sites, synergistically strengthening the NH3 adsorption anchoring. Hydrophobic transformation via BF2 incorporation enables stable operation across 0-98% relative humidity, overcoming water competition effects that plague conventional chemiresistive gas sensors (CGSs). The optimized COF-CoDT-BF2-based CGSs achieve record sensitivity (722.3% ppm-1), sub-ppb detection limit (0.9 ppb), excellent environmental tolerance, and stability. Density functional theory calculations corroborate the dual adsorption charge-transfer mechanism, while in situ spectroscopic analyses reveal reversible NH3 adsorption dynamics. This molecular engineering strategy establishes a paradigm for designing multifunctional sensing materials, paving the way for intelligent gas monitoring systems in precision agriculture and food safety detection.