Ultraviolet-sensitized room temperature fiber optic evanescent field ammonia sensor with polyacrylamide/metal organic framework-carbon quantum dots(–COOH) gas-sensitive film

This study presents a room temperature optical fiber ammonia (NH 3 ) sensor based on a polyacrylamide/metal organic framework-carbon quantum dots(–COOH) (PAM/MOF-CQDs(–COOH)) gas-sensitive film, whose performance was further enhanced with ultraviolet (UV) light. The gas-sensitive film is elaborated by the dipping-pulling method, applying PAM/MOF-CQDs(–COOH) to the surface of a cascade-spliced fiber structure based on single mode fiber (SMF), multimode fiber (MMF), hollow core fiber (HCF), MMF and SMF (S-MHM-S). Experimental results show that the sensor achieves a sensitivity of 17 pm/ppm at room temperature, representing a 3.4-fold increase compared to the scenario without UV light enhancement. The sensor has a limit of detection (LOD) of 1 ppm, with response and recovery times of 3.97 s and 3.52 s, respectively. The response mechanism of MOF-CQDs(–COOH) to NH 3 is described in detail with the results of density functional theory (DFT) calculation. The proposed fiber NH 3 sensor operates at room temperature and has great potential in practical application.