8/2/2019 Detection of Co2 and Nh3 Using Ph Sensitive Fluorescent Nano Spheres Immobilized in Different Matrices

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DETECTION OF CO2 AND NH3 USING pH SENSITIVE FLUORESCENTNANOSPHERES IMMOBILIZED IN DIFFERENT MATRICES

Aleksandar SZCHENYI a, Barna KOVCS aa University of Pcs, Faculty of Natural Sciences, Institute of Chemistry, Department of General

and Physical Chemistry, PCS, Hungary

szealex@gamma.ttk.pte.hu

The optical detection of gaseous CO2 and NH3 is often based on a pH sensitive, colorimetric orluminescent indicator. Usually different indicators are selected for the measurement of the two differentgases. In case of CO2, indicators having a pKa value greater than 7-8 are commonly used, whilemolecules with a pKa lower than 6 are proper for sensing ammonia. Having a broad range pH indicator, itis possible to construct sensors for the two gases by using the proper (and different) additives andmatrices for CO2 and NH3, respectively. The use of the same indicator in two sensors for the two gasesmeans, that we are working close to the two ends on the optical property vs. pH curve: reduced opticalsignal change, and, hence, a reduced dynamic range should be paid for that. The benefit could be,however, that the same optical design, filter setup, detector and electronics could be used for sensing.

In the present work the use of fluorescent, broad range pH sensitive nanospheres immobilized in differentmatrices for indirect sensing of gaseous CO2 and NH3 are investigated and tested. To eliminate thefluorescence intensity measurement interferences, we have used a dual lifetime referencing (DLR)method. The DLR method uses two fluorescent dyes with overlapping spectroscopic properties, one pH-sensitive, short-lived indicator and a pH-insensitive reference dye with a decay time in the s or msrange. N-allyl-4-piperazinyl-1,8-naphthalimide (APN) have been used as fluorescent pH indicator.Ruthenium(II) tris(diphenylphenanthroline) (Ru(dpp)3) complex has been used as a referencefluorophore. The fluorescence enhancement of the APN in the presence of hydrogen ions, is based onthe photon-induced electron transfer mechanism (PET).

The core of the silica sphere was prepared by dissolving an appropriate amount of Ru(dpp)3 in the

tetraethoxysilane (TEOS), after the addition of acid catalyst, ethanol and deionized water, the mixture wasstirred to form sol. The sol formation was allowed to proceed for one hour, then the mixture was cooled to4C and the process was changed from acid catalyzed to base catalyzed by addition of excess ofNH4OH. The sol was then added drop wise to mineral oil and stirred vigorously at 200C until silicaspheres appeared. The spheres were filtered, washed with ethanol and deionized water. Cocktail for theshell of the sensor was prepared in two steps. For preventing the leaching of pH sensing dye, APN wascovalently bond the to sol-gel precursor vinyltriethoxysilane (VTES) by irradiating their mixture (molarratio 1:3) with UV lamp (366nm) for 30 minutes. TEOS, ethanol, water and HCl were added, sonicated for5 minutes and left to form gel for 1 hour. The shell was formed by adding the Ru(dpp) containing spheresto shell forming gel and stirred for one hour at room temperature. The silica spheres was filtered in thecentrifuge with 0,22 mm pore diameter filter and washed with ethanol to remove the unreactedcomponents. The resulted particles were dispersed and stored in the ethanol until use. Phase shiftmeasurements were performed with dual-phase lock-in amplifier (DSP830, Stanford Research inc.) in a

home made flow through cell. Optical system consisted of a blue led (430 nm) a band pass filter,bifurcated fiber bundle, and Hamamatsu (H5783-01) PMT with long pass filter (550 nm).

For CO2 sensing the pH sensitive nanoparticles were co-immobilized in D4 hydrogel with large alkyl chainquaternary ammonium hydroxide. The pH in the sensing membrane is depending on the pCO 2 which isindicated by the increasing fluorescence. The influence of the nanospheres: quaternary ammoniumhydroxide ratio were tested.For the sensing of gaseous NH3 the APN containing nanospheres were protonated and co-immobilizedwith different polymer soluble protonic acids (acetic acid, dodecylbenzene sulfonic acid) in differentmatrices. The ammonia concentration is related to the negative response of the fluorescence. The effectof the acidic additive, its concentration, the influence of the matrices on the sensitivity, and performanceof the sensors were tested and compared.

Acknowledgment: Developing competitiveness of Universities in the South Transdanubian Region (SROP-4.2.1.B-10/2/KONV-2010-0002).