Construction and Testing of Solid State Oxygen Sensor - Lab Report Example

Construction and Testing of Solid State Oxygen Sensor ABSTRACT This paper provides a detailed report of three experiments, namely; the synthesis and characterization of ruthenium complex, the luminescence quenching of Tri (2,2′-bipyridine) ruthenium (II) hexafluorophosphate and the construction and testing of a solid state oxygen sensor experiment. This experiments are essential in the understanding the various principles behind their usage and applications. Ruthenium complexes are making progress in the area of medicinal chemistry. Ruthenium complexes have been extensively used as photosensitizers in solar conservation systems. Luminescence quenching is the process that decreases the fluorescence intensity of a given substance. It has been used in many applications in industries. The construction of an oxygen gas sensor that works on the principles of fluorescence and phosphorescence and dependent on the energy absorption and dissipation is one of the new technologies. INTRODUCTION The three experiments carried out are of significant importance in chemistry, especially the application of new technologies incorporated within them. In this first experiment, the synthesis and characterization of ruthenium complex, the Ruthenium compound will be characterized by UV-Vis, fluorescence spectroscopy, and cyclic voltammetry. Figure 1. Structure of [Ru (bpy)3]2+ 1 In the second experiment, the quenching of luminescence is tested. Experimentally, luminescence is developed and quenched. This process is usually undesirable and very high requirement are therefore imposed on the purity of luminescent. Quenching may occur without any permanent change in the molecules, for example with no photochemical reactions. In static quenching, a complex is formed between the fluorophore and the quencher and the complex is nonfloures-cent. Numerous application for quenching is as a result of the requirements of molecular contact, for example quenching measurements can reveal the accessibility of fluorophores to the quencher. Both static and dynamic quenching requires molecular contact between the fluorophore and the quencher. For collisional quenching, the quencher must diffuse to the fluorophore during lifetime of the excited state. When in contact, the fluorophore returns to the ground state without emitting photons. For a static and dynamic quenching to occur, the fluorophore and the quencher must be in contact. In this experiment, tri (2,2′-bipyridine) ruthenium (II) hexafluorophosphate (C30H24F12N6P2Ru) is used with two quenchers namely phenothiazine (PTZ) and N, N, N’, N’-tetramethyl-p phenylenediamine (TMPD). Figure 2. Structure of C30H24F12N6P2Ru In the third experiment, chemical electronic transitions that are usually induced through the absorption of visible light spectrum result in excited state molecules. In the process, energy is absorbed, dissipated or both. The absorbed energy must be released to return the excited species back to the original ground state. Typically, on absorption of light at their absorption maxima, dye molecules exhibit long excited state lifetimes and emit radiation at longer wavelengths. The excited state of the luminescent dye can be quenched by an energy transfer mechanism upon collision with oxygen molecules. The intensity of luminescence is reduced along with the lifetime and the degree of quenching is proportional to the oxygen concentration. Fig. 3 shows a schematic diagram of an optical oxygen sensor. The active components of the sensor are the luminescent dye encapsulated in a polymer medium, a light source (commonly a LED or laser) for exciting the dye at a particular wavelength, (550–800 nm)1, a photodiode to detect the fluorescent radiation and an optical fiber for the transmission of light. The quenching of the luminescence can be characterized by the Stern-Volmer equation.2 I0/I = 1 + ksv [O2] Where I0 and I are the luminescent intensities in the absence and presence of oxygen, [O2] is the concentration of the oxygen as quencher and ksv is the quenching constant which determines the sensitivity of the optical oxygen sensor. Figure 3. Schematics of an optical oxygen sensor. (1) gas or liquid path, (2) lumophore dispersed on oxygen permeable membrane, (3) lens and filter, (4) exciting radiation, (5) fluorescent radiation, (6) optical fiber, (7) LED/Laser, (8) photodiode, and (9) display The main objective of the first experiment, was to synthesize and characterize ruthenium complex. The main objective the second experiment was to understand the concept of luminescence quenching and appreciate its role in oxidization of compounds. The main objective of the third experiment was to construct, test and calibrate a solid state oxygen sensor using available materials and to understand the working mechanism of the constructed sensor. EXPERIMENTAL METHODS For the first experiment The reagents used were: Acetonitrile (Fischer/BDH); Ru (III) chloride (Pressure Chemical Company); Ethylene glycol and diethyl ether (Fischer); [NH4] [PF6] and TBAH (Acros). Procedure The synthesis of [Ru (bpy)3 ]Cl2 was accomplished by a modification of the procedure by Jones et al3 The following reaction took place Ruthenium chloride of 0.1035g was used, water was excluded and 2mL of ethylene glycol was used instead of 3 mL. 0.2047g of 2, 2’-bypyridine was used as a ligand. A partially oily, red-orange substance was obtained. Following TA’s instruction, this mixture was dissolved with 50 mL of ethanol. Then it was poured into a large beaker containing 250 mL of cold ether. Precipitate was formed immediately and collected by vacuum filtration. 0.2123g of solid was collected. The solid has fine orange color. 0.0212g of the product was put aside for later characterization. The following reaction was performed: Five-fold molar excess (0.2701g) of [NH4] [PF6] was used to perform the reaction. The final crystal was collected by suction filtration. Characterization will be accomplished with the following techniques: UV-visible spectrum was obtained by UV/Vis spectrophotometer (Jasco, V-530); Luminescence spectrum were obtained by spectrofluorometer (Jasco, FP-6300); and Cyclic voltammetry and differential pulse polarography was obtained by a potentiostat (Princeton Applied Research). For the second experiment Reagents used were acetonitrile (Fischer/BDH), tri (2,2′-bipyridine) ruthenium (II) hexafluorophosphate from the previous part of the lab, phenothiazine (PTZ), and N, N, N’, N’-tetramethyl-p-phenylenediamine (TMPD). Procedure Stock solution of ruthenium complex (450mL of 2.4 x 10-3 mM) was prepared. Specific mass of PTZ was added to a 50ml volumetric flasks and was diluted with the stock solution to the line. The quencher concentration was made to be ranged from 0.00- 0.01mM after dilution. Four samples were prepared. The concentration was 0.02mM, 0.04mM, 0.06mM, 0.08mM. The samples were sparged by inserting a needle into the septa of the cell and slowly bubbling Ar through the samples. Then the samples were analyzed by fluorometer and laser. Luminescence spectrum was obtained by spectrofluorometer (Jas.co, FP-6300) and the time resolved luminescence was obtained by a pulsed N2 laser (emitting pulses 1.4688 = 1 + kq (929.2 x 10-9)(0.02 x 10-3) => kq=2.52 x 1010 τ0/τ = 1 + Ksv [Q] = 1 + τ0 kq [Q] => 1.9707 = 1 + kq (929.2 x 10-9)(0.02 x 10-3) => kq=5.22 x 1010 For experiment three: construction and calibration of an oxygen sensor Table 9: Data for Sensor Testing Nitrogen Oxygen Oxygen Ratio Signal (intensity) S0/S 101.7 0 0 0.0218 1 101.7 6.5 0.060073937 0.0212 1.02830189 101.6 12.5 0.109553024 0.0211 1.03317536 101.6 18.5 0.154038301 0.0204 1.06862745 101.6 24.9 0.196837945 0.0199 1.09547739 101.7 31.3 0.235338346 0.0194 1.12371134 Figure 16. Stern-Volmer Plot for a thin film oxygen sensor DISCUSSION From the first experiment, it is evident that the ruthenium complex was well synthesized. In the synthesis process, water was excluded because it would cause the product to be too oily and hard to crystalize. During the second reaction, due to miscalculation, ten-fold of [NH4] [PF6] was used. The absorption at λmax falls between 0.1 and 0.3 for both Ruthenium complexes. [Ru (bpy) 3]2+ absorbs UV light and visible light. In aqueous medium the molecule strongly absorbs at 452 ± 3 nm corresponding to MLCT transition (extinction coefficient of 14,600 M−1cm−1)1 . By comparing the experimental value of 13995.8 M−1cm−1 to the literature value, the compound is shown to be rather pure. The absorption for [Ru (L)3][PF6]2 at 456nm is 13,400 M−1cm−1i.. The reason might be the excess molar of [NH4][PF6] used. Luminescence spectra appeared normal. The graph was set to start the reading at 450 nm, which is obtained by the UV-Vis. In the second experiment, oxygen was eliminated by use of argon because it could lead to errors due to its oxidizing and quenching properties. Ruthenium II hexafluorophosphate complex is relatively highly luminescent. At room temperature, an aqueous solution of the compound shows strong luminescence at about 450nm. For successful quenching process to occur, electron transfer occurs. This also occurs in order for efficient luminescence between the luminescence spectrum of the donor and absorption spectrum of the acceptor. The luminescence spectrum of the samples with PTZ as the quencher were not clear enough. The curves for 0.06 mM and 0.08 mM were almost stacked up, possibly resulting from not measuring the mass of the quencher precisely. On the other hand, the combined curve for samples that used TMPD as the quencher is clearer. The separation of the curves are more even compare to the one for PTZ. The combined graphs of samples that used PTZ as the quencher was very messy. One of the reasons would be not cutting the graphs from the monitor properly. Also, the layering of the curves are not proportional to the concentration. This may results from settling the sample for too long until the laser analysis. On the other hand, the combined laser graph for TMPD looks much more organized. Although the differences is subtle, the trend line of the graphs of TMPD are better fit comparing to the trend line for the graphs of PTZ. In the third experiment, the sensor is typically characterized by three parameters: sensitivity, selectivity and response time. Sensitivity is the ability of the sensor to quantitatively measure the required parameter under given conditions. The sensitivity of a luminescence based oxygen sensor is influenced by the properties of both the luminescent material and the oxygen permeable encapsulating medium. The real-time graph of the response of the sensor on the LabView program was a little bumpy. The noise may cause by not facing the film to the detector completely. The detector might have detected the clamp that holds the glass tube. However, the Stern-Volmer plot turns out to be satisfactory. The R2 value was 0.96, which means the data is fairly fitted on the trend line. It is important to note that the calibration curve would be downward curving in the Stern-Volmer (sensitivity) plot. This shows problems in calibrating these optical sensors. Though there are models based on theoretical fitting procedures, e.g., power law model, two site model, and Gaussian distribution of τ0 and kQ1, 4 the physical understanding of the nonlinearity is still not adequate. REFERENCES [1]. Kostova, I. Ruthenium Complexes as Anticancer Agents. Current Medicinal Chemistry, 2006, 13, 1085–1107 [2]. Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106 [3]. Kalyanasundaram, K. photo physics, photochemistry and solar energy conversion with ruthenium and its analogues, 1982. [4]. Schwenz R.W and Moore, R.J Physical Chemistry: Developing a Dynamic Curriculum, 1993, American Chemical Society, Washington, DC [5]. B. R. Eggins, In “Chemical Sensors and Biosensors” (John Wiley & Sons, England, 2002) [6]. D. G. Fresnadillo, M. D. Marazuela, M. C. M. Bondi and G. Orellana, Langmuir 15 (1999) [7]. A. Mills, Sensors and Actuators B 51 (1998) Read More