Abstract
In this study we present an NIR carbon dioxide gas sensor based on an inner filter process that includes an ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4), to improve its stability, dynamic behavior and lifetime, which are usually the main drawbacks with these sensors. The presence of CO2 causes a displacement of a simple boron-dipyrromethene-type fluorophore, azaBODIPY, as the pH indicator towards its acid form. This increases the emission intensity of Cr(III)-doped gadolinium aluminium borate (GAB) as the luminophore. The characterization of the prepared sensor was carried out and a discussion of the results is presented. The response and recovery times improved considerably, 23 and 49 s, respectively, with respect to the sensor without IL, at 60 and 120 s, respectively,. Additionally, the measurement range is extended when using IL, able in this case to measure in the complete range up to 100% CO2; without IL the measurement range is limited to 60% CO2. The detection limit ranges from 0.57% CO2 without IL to 0.26% CO2 when IL is added. The useful lifetime of the sensing membrane was 20 days for membranes with IL and only 6 days for membranes without IL, with the sensor always kept in the dark and without the need to maintain a special atmosphere.
Highlights
-called green solvent ionic liquids are salts that remain as a liquid at temperatures below 100 ◦C, composed of a combination of organic cations and organic/inorganic anions
Carbon dioxide occurs in the combustion of fossil fuels and is considered one of the gases that contributes to the global warming of the planet
The sensing membrane for CO2 contains 0.5 mg azaBODIPY dissolved in 0.5 mL of ethanol, 1 mL of HPMC 1% in water, 5 μl of Tween 20, 5 μL of a tetramethylammonium hydroxide pentahydrate (TMAOH) solution containing 14 mg TMAOH in 1 mL 1:1 ethanol:water, 6 μL ionic liquid (IL), and 1.5 mg gadolinium aluminium borate (GAB)
Summary
-called green solvent ionic liquids are salts that remain as a liquid at temperatures below 100 ◦C, composed of a combination of organic cations and organic/inorganic anions. Carbon dioxide occurs in the combustion of fossil fuels and is considered one of the gases that contributes to the global warming of the planet This makes the accurate, continuous monitoring of CO2 levels a matter of necessity [16]. Our research group found an improvement that involves including ionic liquids in sensing membranes for the determination of gaseous carbon dioxide in fluorescent optical sensors [30]. Including an ionic liquid improves the useful life of the sensor and the response and recovery time In this way, sensors are obtained that increased the sensitivity of CO2 monitoring, using lower amounts of reagents. The system worked at a total pressure of 760 Torr and a flow rate of 500 cm3·min−1
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