Ag/Ag-NiO Derived From Ag Modified MOF-74 (Ni) for High Selectivity Anti Humidity Sensor of Formaldehyde at Low Temperature: Mechanism and Humidity-Tolerant Role of Ag0 and Ag.

Ag modified MOF-74 (Ni) are prepared by a simple oil bath method, and Ag loaded and doped NiO (x at% Ag/Ag-NiO, x is the atomic ratio of Ag to Ni) derived by Ag modified MOF-74 (Ni), resulting in Ag0 and Ag+ species modified NiO. The Ag modified NiO nanosheets exhibit excellent sensing performance (11.6 at% Ag/Ag-NiO response value of 284 ± 5) for 10 ppm formaldehyde gas at low temperatures of 100°C and can detect low concentrations of 50 ppb formaldehyde gas. Under high humidity conditions (80% RH), 11.6 at% Ag/Ag-NiO maintains a response value of 80%, with a resistance increase of only 20%. The excellent gas sensing performance is attributed to the fact that a portion of Ag0 is loaded on the surface of NiO and a portion of Ag+ is doping into NiO, resulting in more oxygen defects. The synergistic improvement of Ag0 sensitization and defect density enhances the excellent gas sensing performance toward formaldehyde at low temperatures. Through in situ DRIFTS, it is demonstrated that Ag modified NiO interface preferentially absorbs reactive oxygen species, which are supplemented by electron transfer between Ag0/Ag+ and Ni2+ and Ni3+ to achieve high-performance sensors under humidity.