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.