BF ₂ -Postmodified Cobalt–Porphyrin Covalent Organic Framework for High-Performance Specific Detection of NH ₃

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.