Fiber-optic carbon dioxide sensor based on fluorinated xerogels doped with HPTS

Abstract

Abstract This paper presents a high-performance fiber-optic carbon dioxide (CO 2 ) sensor based on hybrid xerogels composed of alkyl and perfluoroalkyl ORMOSILs (organically modified silicates) doped with pH-sensitive fluorescent dye. The sensor film consists of 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt (HPTS, PTS − ), tetraoctylammonium cation (TOA + ), and a tetraoctylammonium hydroxide (TOAOH) phase transfer agent (i.e. the base) immobilized within the hybrid xerogels. The experimental results indicate that the fluorescence intensity of the HPTS dye decreases as the CO 2 gas phase concentration increases. The sensor has a response level of ( I 0 − I )/ I ≈ 18, where I 0 and I are the fluorescence intensities in 100% N 2 and in 100% CO 2 , respectively, and exhibits a linear response to CO 2 concentrations in the range 0–30%. The resolution is ±2.5% in this level and the limit of detection (LOD) is 0.03% CO 2 , calculated as three times the standard deviation (3 σ ). The response time of the sensor is 1.7 s when switching from a pure nitrogen atmosphere to a pure CO 2 atmosphere and 38.5 s when switching from CO 2 to nitrogen. The signal changes are fully reversible as the atmosphere is switched repeatedly between nitrogen and CO 2 . Overall, the experimental results demonstrate that the use of hybrid xerogels doped with HPTS enhances both the response level and the response speed of the proposed optic-fiber CO 2 sensor.