Light stimulated room-temperature H2S gas sensing ability of Cl-doped carbon quantum dots supported Ag nanoparticles

Light-activation of gas sensors is recognized as a potential alternative to the traditional thermal-activation that has several drawbacks such as high power consumption. However, strategies to exploit outstanding light-response characteristics of carbon quantum dots (CQDs) for light-activated gas sensing are not established effectively. In the present study, Ag nanoparticles, which have good affinity to hydrogen sulfide (H2S) gas molecules, visible-light absorption, and excellent oxygen dissociation ability, are in-situ grown on Cl-doped CQDs (Cl-CQDs) that exhibit strong UV-light absorption and prolonged charge separation. The developed hybrids with strong interfacial connection between Ag and Cl-CQDs (Ag@Cl-CQDs) exhibited exceptional selectivity and sensitivity towards the (HS)-S-2 gas under light irradiation. The sensitivity depends on the photogenerated electrons flow direction at the Ag-Cl-CQDs heterojunction; UV-light (254 nm, 12.7 mW/cm(2)) facilitated the migration of electrons from Cl-CQDs to Ag, while the visible-light (457 nm, 152 mW/cm(2)) favored the electrons flow in the opposite direction. The excellent oxygen dissociation ability of Ag nanoparticles is further fueled by the photogenerated electrons migrated from Cl-CQDs and, as a result, UV-light-activated sensor exhibited higher H2S gas response than the sensor under visible-light irradiation or dark condition. The remarkable sensing performance of UV-light-activated Ag@Cl-CQDs is exploited to detect the H2S gas at lower concentrations (2 ppm-200 ppb). The effect of humidity (20-60%) on the device performance is also investigated. Further, the mechanism behind the Ag@Cl-CQDs sensor's superior performance under UV-light irradiation compared to visible-light irradiation is discussed in detail.