Redox Synergy: Enhancing Gas Sensing Stability in 2D Conjugated Metal-Organic Frameworks via Balancing Metal Node and Ligand Reactivity.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as promising candidates in gas sensing, owing to their tunable porous structure and conductivity. Nevertheless, the reported gas sensing mechanisms heavily relied on electron transfer between metal nodes and gas molecules. Normally, the strong interaction between the metal sites and target gas molecule would result poor recovery and thus bad recycling property. Herein, we propose a redox synergy strategy to overcome this issue by balancing the reactivity of metal sites and ligands. A 2D c-MOF, Zn 3 (HHTQ) 2 , was prepared for nitrogen dioxide (NO 2 ) sensing, which was constructed from active ligands (hexahydroxyltricycloquinazoline, HHTQ) and inactive transition-metal ions (Zn 2+ ). Substantial characterizations and theoretical calculations demonstrated that by utilizing only the redox interactions between ligands and NO 2 , not only high sensitivity and selectivity, but also excellent cycling stability in NO 2 sensing could be achieved. In contrast, control experiments employing isostructural 2D c-MOFs with Cu/Ni metal nodes exhibited irreversible NO 2 sensing. Our current work provides a new design strategy for gas sensing materials, emphasizing harnessing the redox activity of only ligands to enhance the stability of MOF sensing materials.