Hydrogen sulfide monitoring has become essential in the natural gas industry, biogas production, wastewater treatment plants, paper mills, sewers, and landfills of waste due to its toxic, irritating, extremely flammable, and corrosive features. However, each of the current monitoring technologies (gas chromatography, lead acetate tape, electrochemical, UV and NIR absorption) has its own limitations. Furthermore, the existing luminescent molecular probes for H 2 S cannot monitor it continuously due to the irreversibility of their reaction with the analyte. Herein, we report the development and application of the first reversible H 2 S luminescent sensor. The sensing layer capitalizes on the highly photooxidizing phosphorescent [bis(1,10-phenanthroline)-(1,4,5,8-tetraazaphenanthrene)]ruthenium(II) dication immobilized on alkali-treated silica microspheres, interrogated with a dedicated fiberoptic phase-sensitive luminometer. The chemosensing mechanism is a fully reversible electron transfer from the analyte to the photoexcited dye. The H 2 S optosensor exhibits a 0.34−50 ppmv dynamic range, a limit of detection equal to 0.025 ppmv, repeatability, and reproducibility better than 3.2%, plus response and recovery times (t 90 and t −90 ) shorter than 240 s. The H 2 S luminescent sensor performance has been verified for more than six months in a biomethane production plant, showing an excellent stability with automatic daily maintenance.

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