A naphthacene-based two-dimensional conductive metal-organic framework for highly efficient chemiresistive sensing of ammonia

Two-dimensional conductive metal-organic frameworks (MOFs) have emerged as a group of promising materials for chemiresistive sensing; however, they still face the challenges of balancing high sensitivity and quick response/recovery kinetics. This study demonstrates the development of a highly efficient gas sensor for ammonia (NH₃) detection using a naphthacene-based conductive MOF synthesized by interconnecting Cu ions and a specially designed organic ligand, octahydroxyl tetrabenzonaphthacene (OHTBN). The resulting MOF, Cu-OHTBN, with high crystallinity exhibits a high surface area of 307 m² g⁻¹ and unique semiconductive properties of a low bandgap of 0.064 eV and a moderately high room-temperature conductivity of 2.35 × 10⁻³ S cm⁻¹. When integrated into chemiresistive devices, Cu-OHTBN exhibits good linearity for 2-80 ppm NH₃ and remarkable sensitivity with a low experimental detection limit of 0.061 ppm, while showing excellent sensing dynamics with a short response time of 0.52 min (80 ppm NH₃) at room temperature. The sensing performance is superior to that of most other 2D conductive MOFs currently used for NH₃ sensing. A mechanistic study combining DRIFTS and DFT calculations shows that the key to high sensitivity and quick sensing kinetics is the electron perturbation of the whole plane caused by the adsorption of NH₃ on the MOF.