Conductive Metallophthalocyanine Covalent Organic Frameworks Enable Humidity-Tolerant NO₂ Sensing

Conductive metallophthalocyanine (MPc)-based covalent organic frameworks (COFs) synthesized via solid-state reactions provide a novel platform for high-performance gas sensing under real-world conditions. Among the series developed, PdPc exhibits exceptional chemiresistive properties for room-temperature NO₂ detection, achieving a low experimental detection limit of 70 ppb, with long-term stability and outstanding selectivity. Notably, the PdPc sensor demonstrates higher response levels and prominent reversibility in high-humidity environments (≥54% RH), surpassing conventional metal oxide sensors. This enhanced performance is attributed to the material's intrinsic hydrophilicity and well-defined metal active sites, which promote proton conduction via hydrogen-bond networks under humidity conditions. Density functional theory calculations reveal strong binding affinity and significant charge transfer between PdPc and NO₂, underpinning its high sensitivity and selectivity. This work introduces a generalizable strategy for designing humidity-tolerant, conductive COF sensors, establishing a new benchmark for reliable NO₂ detection in challenging environments.