Silver-Functionalized Metal Oxide Nanofibers for High Precision Chlorine Sensing at the Parts-Per-Billion Scale with Tunable Selectivity.

Chlorine (Cl2) is a hazardous industrial gas and a choking agent, making highly sensitive ppb-level detection with tunable selectivity toward chemical warfare agent-related (CWA-related) analytes important. Here, we synthesized Ag-functionalized SnO2 and WO3 nanofibers by electrospinning and investigated how the host oxide governs Cl2 sensing and selectivity toward CWA-related analytes. The optimized Ag-functionalized SnO2 sensor (AgS5) showed a response of 6.89 to 500 ppb Cl2, an experimentally validated detection limit of 10 ppb, and a calculated lower limit of detection of 0.12 ppb. The host oxide also strongly altered selectivity: SnO2-based sensors showed higher responses to Cl2 and hydrogen cyanide, whereas WO3-based sensors were more sensitive to 2-chloroethyl ethyl sulfide and methyl salicylate. X-ray photoelectron spectroscopy revealed host-dependent Ag speciation, with Ag+ favored on SnO2 and Ag0 on WO3. Temperature-modulated measurements and density functional theory calculations further showed that this difference changes interfacial charge-transport barriers and adsorption energetics, thereby governing both sensitivity and selectivity. These results suggest a trace-level Cl2 sensor and demonstrate that the sensing characteristics of noble metal-decorated chemiresistors can be rationally tuned through host-oxide selection, providing a general design strategy for selective, ppb-level Cl2 detection.