Scalable\nMelt Polymerization Synthesis of Covalent\nOrganic Framework Films for Room Temperature Low-Concentration SO<sub>2</sub> Detection

The\ndevelopment of highly efficient sensors for low-concentration\nSO<sub>2</sub> at room temperature is important for human health and\nfine chemistry, but it still faces critical challenges. Herein, a\nscalable olefin-linked covalent organic framework (COF) with an ultramicroporous\nstructure and abundant binding sites is first developed as the SO<sub>2</sub> sensing material. The COF can adsorb SO<sub>2</sub> of 220\ncm<sup>3</sup>/g at 1 bar and 40 cm<sup>3</sup>/g at 0.01 bar and\n298 K, surpassing all reported COFs. The computational and kinetic\nadsorption studies deeply unveil the selective adsorption mechanism\nfor low-concentration SO<sub>2</sub>. Furthermore, the multicomponent\ngas mixture breakthrough experiments confirm that the COF can specifically\ncapture low-concentration (2000 ppm) SO<sub>2</sub>. We innovated\na melt polymerization technology to fabricate COF films with adjustable\nsubstrates and film thicknesses. COF films are directly grown on the\ninterdigital electrodes to prepare the SO<sub>2</sub> sensor device,\nwhich possesses a low detection limit (86 ppb) and excellent selectivity\nfor SO<sub>2</sub> in the presence of 10 other potentially interfering\ngases. Compared to other reported SO<sub>2</sub> sensors, its overall\nperformance is among the top. Prominently, the sensor maintains a\nstable output signal for more than two months, and recovery can be\neasily achieved by simply purifying nitrogen at room temperature without\nheating. This study marks the first use of COFs for SO<sub>2</sub> sensing, opening new possibilities for COFs in the detection of\nlow-concentration toxic gases and manufacturing gas sensor devices.