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Unprecedented reversible real-time luminescent sensing of HS in the gas phase 2
Idoia Urriza-Arsuaga, Maximino Bedoya, and Guillermo Orellana Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b04811 • Publication Date (Web): 26 Dec 2018 Downloaded from http://pubs.acs.org on December 26, 2018
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Unprecedented reversible real-time luminescent sensing of H2S in the gas phase Idoia Urriza-Arsuaga, Maximino Bedoya*, Guillermo Orellana* Optical Chemosensors & Applied Photochemistry Group (GSOLFA), Department of Organic Chemistry, Faculty of Chemistry, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
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ABSTRACT: Hydrogen sulfide monitoring has become essential in – the natural gas industry, biogas production, waste water treatment plants, paper mills, sewers and landfills of waste due to its toxic, 54 irritating, extremely flammable and corrosive features. However, 53 each of the current monitoring technologies (gas chromatography, 52 lead acetate tape, electrochemical, UV and NIR absorption) has its 51 own limitations. Furthermore, the existing luminescent molecular 50 probes for H2S cannot monitor it continuously due to the 49 0 2 irreversibility of their reaction with the analyte. Herein, we report the 48 4 development and application of the first reversible H2S luminescent 47 6 20 8 sensor. The sensing layer capitalizes on the highly photooxidizing 25 30 10 35 phosphorescent [bis(1,10-phenanthroline) (1,4,5,8T (ºC ) tetraazaphenanthrene)] ruthenium(II) dication immobilized on alkalitreated 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 H2S optosensor exhibits a 0.34 to 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 (t90 and t-90) shorter than 240 s. The H2S luminescent sensor performance has been verified for more than 6 months in a biomethane production plant, showing an excellent stability with automatic daily maintenance.
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H2S [H
2S
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m v)
(º)
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Analytical Chemistry
Hydrogen sulfide (H2S) is a colourless reducing gas with a distinct smell of rotten eggs that is commonly formed as a result of the organic matter decomposition in anaerobic atmospheres.1 It is toxic and risky to humans, as it causes olfactory fatigue above 100 ppmv, eye and respiratory tract irritation, respiratory failure, and is lethal over 1000 ppmv.2 It is also an extremely flammable gas, and has corrosive effects on engines, pipelines and fittings. Due to the aforementioned features, in situ real-time H2S monitoring has become essential in those areas where this gas is typically encountered (natural gas extraction and refining, biogas production, waste water treatment plants, paper mills, sewers or landfills of waste), and is getting even more critical as new regulations for this poisonous gas are being released by regulatory bodies. For instance, as a result of the anaerobic fermentation of organic feedstock, H2S is formed during the biogas generation process leading to biomethane, a sustainable energy source that is becoming an interesting alternative to non-renewable fuels. The subsequent upgrading process, in which biogas is cleaned of most impurities including H2S, generates the biomethane mentioned above. The required composition of this gas depends on its final use; the European Organization for Standardization has recently released the European Norm EN 16723-1,3 that details the biomethane specifications for injection in natural gas pipelines, being 5 mg m3 the
maximum H2S limit. Thus, quantification of H2S in biomethane has now become mandatory to preserve the energetic quality and the consumers’ safety, protect the infrastructures involved, and meet the legal limits.4 Several analytical methods for H2S measurements in the gas phase can be found in the literature,5 and a variety of commercial sensing technologies are currently available. The most widespread include gas chromatography coupled to sulfur chemiluminescence or flame photometric detectors,6-7 the “lead acetate tape” optical dosimeter,8 solid-state electrochemical devices,9,10 tunable laser diodes with mid-IR (700 – 2000 nm) detection,11 and the direct UV (200 – 400 nm) absorption of the analyte. Although these techniques have already demonstrated their suitability for H2S quantification, some of them are costly, require qualified personnel due to the operational complexity, necessitate sample pre-conditioning, demand time-consuming maintenance, or show poor sensitivity and selectivity, displaying interferences from other gases such as CO, SO2, NO, NO2, BTX and/or NH3. Luminescent sensors are particularly attractive because they display high sensitivity and selectivity, allow long-distance monitoring, can operate in explosive or flammable areas, are easy to operate, require low maintenance and, nowadays, are affordable enough.12,13 So far, many luminescent dosimeters (i.e. non-reversible probes)14 have been designed and
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successfully used for H2S recognition and quantification. Among them, fluorescein mercury acetate (FMA) and its derivatives have been used in solution,15 and immobilized on different solid supports (ethyl cellulose,16 filter paper17). Although improvements have led to shorter response times (from 60 min to 1 min), reduced FMA consumption, lower waste generation (from mL to L), enhanced sensitivity (down to a few ppbv) and stability upon irradiation,17 these H2S sensors are irreversible due to the direct reaction between the gas and reagent. Thionine has also been investigated for H2S detection. Although the sensing mechanism was described as a “reversible photoreduction”,18 further research revealed a nonreversible response with incomplete recovery of the signal, probably due to dye bleaching or leaching and slow response times (> 30 min).19 Furthermore, many other irreversible, i.e. “reaction-based”, fluorescent probes have been developed for selective detection of H2S,20,21 being the most commonly strategies those based on reduction, nucleophilic, or metal sulfide precipitation mechanisms. Although such probes have been mostly applied to biological samples, some additional examples of gaseous H2S detection can be found in the literature encompassing metallo-fluorescent probes,22-24 dinuclear transition metal complexes,25 or fluorescence transition metal-based metal-organic frameworks (MOFs).26,27 Unfortunately, the known luminescence-based probes cannot monitor continuously the levels of such gas due to the irreversibility of the reaction by which the H2S recognition occurs. Table S1 provides an account of the best H2S sensors reported so far. However, it should be noted that not all the sensors may be used for the sought application. In this paper, we report the development of a reversible H2S gas sensor based on the phosphorescent bis(1,10phenanthroline)(1,4,5,8-tetraazaphenanthrene)ruthenium(II) dihexafluorophosphate dye or RP2T, capable of measuring in situ, continuously and in real-time. The novel luminescent optode is interrogated by modulated LED excitation, and the luminescence phase-shift is detected with a ruggedized portable instrument specifically designed for environmental and industrial monitoring. Finally, its application to real biomethane production plant measurements is also described.
MATERIALS AND METHODS Chemicals. 1,10-Phenanthroline (99.0+%) and lithium chloride (99%) were from Acros (Geel, Belgium). 1,4,5,8Tetraazaphenanthrene was from Janssen (Beerse, Belgium); RuCl3 hydrate (99%) and ammonium hexafluorophosphate from Fluorochem (Derbyshire, UK). Tetrakis(dimethylsulfoxide)dichlororuthenium(II) (96%), 2,2’bipyrazine (97%), SP Sephadex C-25, lithium hydroxide (98%), sodium sulfide nonahydrate (99.99+%) and potassium tert-butoxide (98%) were from Sigma-Aldrich Química (Madrid, Spain). Di-Sodium hydrogen phosphate anhydrous (98.0 – 100.5%), sodium phosphate (pure), calcium hydroxide, barium hydroxide and sodium carbonate were from Panreac (Barcelona, Spain). N,N-Dimethylformamide (99.8%, over molecular sieves), acetonitrile (HPLC), ethylamine (70% in water), cesium hydroxide monohydrate (99.95%) and 1,4diazabicyclo[2.2.2]octane (DABCO, 97%) were from Acros. Acetone, methanol and ethanol (all HPLC) were from VWR International Eurolab (Barcelona, Spain). Sodium hydroxide, potassium hydroxide, sodium phosphate and triethylamine (synthesis grade) were from Scharlau Chemie (Sentmenat,
Spain). Purified water was produced by a Direct-Q 3 UV purification system from Merck Millipore (Bedford, MA). Benzenesulfonic acid-functionalized glass beads (Isolute SCX, 50 m particle size) were from Biotage (Uppsala, Sweden) (SCX), hydrophilic fumed silica S-5130 (0.007 m particle size) was from Sigma-Aldrich (S-5130), hydrophobic fumed silica Aerosil R812 (40 m particle size) from Evonik (Hanau, Germany) (R812), spherical amino-functionalized silica beads (40–75 m diameter) (NH2-silica) from Supelco, silica microspheres SiliaSphereTM PC (40–75 m diameter) were from SiliCycle (Quebec, Canada)(SiO2 microspheres), neutral (N) and basic (B) aluminium oxide (alumina) were from Scharlau Chemie, and titanium(IV) oxide (anatase form, 99%) from Alfa Aesar (Haverhill, MA) (TiO2). N2 (99.9999%) and CH4 (99.9995%) gases from cylinders (Contse, San Sebastián de los Reyes, Spain) were passed through an Agilent (Santa Clara, CA) OT3-2-SS oxygen/water trap to decrease their O2 and moisture content (
