Dissolved oxygen sensor based on sol-gel matrix doped with tris(2,2 - bipyridine)ruthenium dichloride

Transcription

1 Journal of Chongqing University (English Edition) [ISSN ] Vol. 12 No. 1 March 2013 Article ID: (2013) To cite this article: XIONG Xiao-li, TANG Yan, ZHENG Bao-zhan. based on sol-gel matrix doped with tris(2,2 -bipyridine)ruthenium dichloride [J]. J Chongqing Univ: Eng Ed [ISSN ], 2013, 12(1): based on sol-gel matrix doped with tris(2,2 - bipyridine)ruthenium dichloride XIONG Xiao-li 1,, TANG Yan 1, ZHENG Bao-zhan 2 1 College of Chemistry and Materials Science, Sichuan Normal University, Chengdu , P. R. China 2 Institute of Chemical Engineering, Sichuan University, Chengdu , P. R. China Received 15 November 2012; received in revised form 5 January 2013 Abstract: To establish a immobilization method of oxygen sensitive dye, a dissolved oxygen sensor based on a sol-gel matrix doped with ruthenium complex ([Ru(bpy) 3 ] 2 ) as the oxygen-sensitive material is reported. The results indicate that the I 0 /I 100 value of the [Ru(bpy) 3 ] 2 -doped in tetraethylorthosilane (TEOS) composite films are estimated to be 10.6, where I 0 and I 100 correspond to the detected fluorescence intensities in pure nitrogen saturated water and pure oxygen saturated water, respectively. Also, the Stern-Volmer plot shows a very good linearity at low dissolved oxygen concentrations. The response time of the composite films is 5 s upon switching from nitrogen saturated water to oxygen saturated water and 10 s from oxygen saturated water to nitrogen saturated water. The dissolved oxygen sensors based on the ruthenium complex/teos composite films exhibit greater sensitivity, stability and faster response time as compared to the existing ones. Furthermore, the thin films possess greatly minimized dye leaching effect. Keywords: dissolved oxygen sensor; ruthenium complex; sol-gel CLC number: O Document code: A 1 Introduction a The measurement of dissolved oxygen concentration is important in various areas of chemical, physical and environmental monitoring. Many techniques have been developed over the pass years to detect oxygen in both gas and liquid phase. In recent years, optical oxygen sensors are more attractive than conventional methods due to the following advantages: faster response time, high sensitivity and selectivity, no O 2 consumption, no poison and no requirement for a reference electrode, inertness against sample flow rate or stirring speed, and Corresponding author, XIONG Xiao-li ( 熊小莉 ): @qq.com. Funded by the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials of Sichuan Province (No.10zxfk23) and Scientific Research Project of Sichuan Normal University (No.11KYL06). immunity to exterior electromagnetic field interference [1-7]. Usually, these optical oxygen sensors are based on the dye embedded in a support matrix. The support matrix acts as a medium for supporting the dye and for oxygen transport from the surroundings. The creation of novel doped materials via the sol-gel process has evolved into an expanding area of research with promising useful materials for the design of optical sensors, photochromic and luminescent materials [6-13]. Organic luminescent molecules and dyes can be easily incorporated in sol-gel matrices by reaction with silicon alkoxydes in mild conditions. The resulting materials show promising performances for optical sensing applications as the sol-gel matrix exhibits good optical transparency in the spectral region of the dopant dye, chemical and photochemical stability, high porosity, rigidity, chemical nertness, negligible swelling in the liquids, low temperature processing, possibility of different configurations (films, blocks, powder, micro- and nanospheres) and, usually, 11

2 the entrapped molecules retain much of their chemical and physical characteristics [13] [10]. Ding et al. immobilized [Ru(dpp) 3 ] 2 in a TEOS sol-gel matrix. The sensitivity and response times were better than that immobilized in a polymer matrix. On the other hand, Chae et al. [6] also immobilized [Ru(dpp) 3 ] 2 in an Octyl-triEOS/TEOS sol-gel matrix, and the sensitivity was higher than the oxygen-sensitive dyes immobilized in polymer matrices, but authors did not report the response times. The aim of our work is to immobilize [Ru(bpy) 3 ] 2 into a sol-gel monolith which is considerably more stable to light than a polymer matrix thus providing stable luminescence and hence better sensitivity and stability. In this study, [Ru(bpy) 3 ] 2 -doped inorganic glasses were prepared using the sol-gel process under acidic condition and application to optical sensing of dissolved oxygen was studied. Oxygen sensors were prepared by sol-gel process, which hydrolyzed the mixture of tetraethoxylsilane (TEOS) under the acidcatalyzing conditions. The results show that fluorescence intensity ratio in the absence to presence of oxygen were plotted against the oxygen concentration and so formed the Stern-Volmer plot. 2 Experimental details 2.1 Chemicals and reagents Tris(2,2 -bipyridine)ruthenium dichloride(ru(bpy) 3 Cl 2 ) was obtained from Fluka Chemicals (Buchs, Switzerland). Tetraethoxysilane (TEOS) and the other chemicals were purchased from Kelong Chemicals (Chengdu, China). All chemicals were of analytical reagent grade. Water was doubly deionized and distilled. Glass microscope slides were obtained from Huashun special glass Co. Inc., Jiangyin, China (cut to dimensions: 12 mm 25 mm), which were used as substrates for the sensor films. All other chemicals were analytical grade and used without further purification. 2.2 Instrumentation All fluorescence spectra were recorded by using a fluescence spectrometer F-4500 (Hitachi, Tokyo, Japan) at ambient temperatures (26 C±1 C). The excitation wavelength was 470 nm and the emission wavelength was 608 nm. The excitation and emission bandpass were 10 nm. 2.3 Preparation of sample The sol-gel derived thin films for an oxygen sensor were prepared using Ru(bpy) 3 Cl 2 as one of the precursor, which reacted with TEOS by hydrolysis and condensation. The following particular procedure was chosen because it is representative of TEOS-based xerogels reported in Refs. [6] and [15] to [19]. A starting solution was prepared by 8 ml TEOS which was mixed with 2.5 ml EtOH, 1.5 ml 0.1 mol/l HCl and 1 ml deionized water. The mixture was then capped and stirred at room temperature for 6 h when a clear homogeneous solution of TEOS sol was formed. Meanwhile, the oxygen-insensitive dye solution was prepared by dissolving 2 mg [Ru(bpy)]C1 2 6H 2 O into 10 ml THF and then added to the sol solution. The resulting solution was then capped and stirred magnetically for 30 min at room temperature. The coated slides were cured at room temperature in the dark for 2 weeks, when transparent, optically clear films were obtained which were not affected by prolonged immersion in water. The films appeared to be unchanged after standing in the dark, at room temperature, for more than 16 weeks. Before the dip-coating process, the glass substrates were cleaned by soaking in NaOH for 24 h, rinsed with copious amounts of deionized water and EtOH, and then dried at 110 C for 2 h. Finally, xerogel films were formed by dip-coating on the glass substrates, and the withdrawing rate was set as 5 cm/min. The assynthesized thin films was dried under ambient conditions in the dark for at least 1 week before any measurement. Finally, optically transparent crack-free thin films were obtained and the adhesion of the sol to the substrate was found to be excellent. 2.4 Oxygen sensing system The sol-gel derived films with doped Ru(bpy) 3 Cl 2 were mounted at 45 in a quartz cell to minimize scattering light from the sample and substrate. Two gas flow systems were used to introduce O 2 standards into the flow-through cell. Fig. 1 illustrates a schematic diagram of the continuous injection mode of O 2 standards to the experimental setup. A stream of N 2 /O 2 mixtures of various specified compositions, spanning the range from 0 to 100 (v/v) O 2, was generated with two mass flow controllers (Brooks Instrument BV, Veenendaal, The Netherlands). These N 2 -O 2 gas mixtures were employed to prepare various 12 J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(1): 11-15

3 concentrations of oxygenated-water solutions. The total gas flow rate was kept at 100 ml min 1. The dissolved O 2 concentrations in water were calculated from the O 2 solubility data of the Yellow Springs oxygen electrode manual (Yellow Springs Instruments Co. Inc., Yellow Springs, OH). shows considerable positive deviation from linearity (downward curvature) at higher oxygen concentrations. The Stern-Volmer constant K sv obtained from the linear part of the graph is ml/m 3. Compared with the results that we reported before [1], the ratio of I0 / I 100 increased, indicating that the fluorescence quenching of [Ru(bpy) 3 ] 2 in the sol-gel by dissolved oxygen is efficient. Fig. 1 Schematic diagram of the continuous injection mode gas mixing system for generation of oxygen standards 3 Results and discussions 3.1 Spectroscopic behavior of the oxygen-sensitive films The luminescence of most Ru(II)-bipyridine complexes could be quenched effectively by molecular oxygen. Fig. 2 shows the fluorescence spectra [Ru(bpy) 3 ] 2 -doped sensor subjected to several concentrations of dissolved oxygen. We can see that the relative intensity decreases markedly with increasing the oxygen concentration. The relative luminescent intensities of the [Ru(bpy) 3 ] 2 -doped thin film oxygen sensor decrease by 90.6 upon changing from pure nitrogen to pure oxygen. The O 2 quenching process can be described by the well-known Stern- Volmer equation [20] : Fig. 2 Fluorescence emission spectra of the oxygen-sensitive composite film when subjected to various concentrations of oxygenated water of 1) 0 ml/m 3 O 2 ; 2) 2.17 ml/m 3 O 2 ; 3) 4.33 ml/m 3 O 2 ; 4) 6.5 ml/m 3 O 2 ; 5) 8.67 ml/m 3 O 2 ; 6) 17.3 ml/m 3 O 2 ; 7) 26 ml/m 3 O 2 ; 8) ml/m 3 O 2 ; and 9) ml/m 3 O 2 where the excitation wavelength is 470 nm I / I 1 K [O ] 0 sv 2 where I 0 and I are the detected fluorescence signals under N 2 -saturated and volumetrically 100 oxygenated water, respectively, [O 2 ] is the dissolved O 2 concentration, and K sv is the Stern-Volmer quenching constant. The relative emission intensity rations can be used as an approximate measure of the sensitivity. Fig. 3 shows plots of I / 0 I 1 against the dissolved O 2 concentration in water. In this case, I0 / I , where I 0 and I 100 are the detected fluorescence signals under N 2 -saturated and volumetrically 100 oxygenated water, respectively, which can be used as an approximate measure of the sensitivity. The plot is linear at low dissolved oxygen concentrations, up to about 20 ml/m 3, but unusually Fig. 3 Stern-Volmer plot of the oxygen-sensitive composite film at room temperature 3.2 Response time of oxygen-sensitive composite film Fig. 4 shows the typical response curves of the oxygen-sensitive composite film when switching the N 2 -saturated and O 2 -saturated water repeatedly. The response times of the film were 5 s upon switching from nitrogen to oxygen and 10 s from oxygen to nitrogen. The signal changes were fully reversible. The J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(1):

4 response times are very short and the fast response time obviously comes from the microporous structure of the sol-gel matrix. from oxygen saturated water to nitrogen saturated water. The results indicate that [Ru(bpy) 3 ] 2 immobilized in a sol-gel matrix are photostable and highly sensitive to oxygen. The method can be further improved via changing the sol-gel reaction conditions and further work is in progress. Fig. 4 Response time and fluorescence intensity change of the oxygen-sensitive composite film on switching between the water saturated with nitrogen and the water saturated with oxygen at room temperature 3.3 Photostability of oxygen-sensitive composite film A major consideration for a real application of an optical oxygen sensor is the photostability of the sensing material. Fig. 5 shows that the proposed sensor using the oxygen-sensitive composite film is very stable by continuously irradiating at 470 nm for 1 h with a xenon lamp of 70 W. Thus, the photostability of our oxygen-sensitive composite film is very good. The long-term stability of the oxygen-sensitive composite film is also good since its analytical performance did not show any change over 3 months storage in a dry box. 4 Conclusions Preparation of optical sol-gel derived composite film for oxygen sensor method with high photochemical stability and good linearity Stern-Volmer plot was presented in this article. No leaching effect can be observed since these luminescence molecules were doped to the matrix. The I 0 / I 100 as the sensitivities of oxygen-sensitive composite films was estimated to be 10.6, and the typical Stern-Volmer plot showed a very good linearity at low dissolved oxygen concentrations. The response time of [Ru(bpy) 3 ] 2 doped in TEOS composite films were 5 s upon switching from nitrogen saturated water to oxygen saturated water and 10 s Fig. 5 Photostability of the oxygen-sensitive composite film Acknowledgements We appreciate the financial support from the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials of Sichuan Province (10zxfk23) and Scientific Research Project of Sichuan Normal University (11KYL06). References [1] Xiong XL, Xiao D, Martin MFC. Dissolved oxygen sensor based on fluorescence quenching of oxygensensitive ruthenium complex immobilized on silica-ni- P composite coating [J]. Sensors and Actuators B, 2006, 117(1): [2] Han BH, Manners I, Winnik MA. Oxygen sensors based onmesoporous silica particles on layer-by-layer self-assembled films [J]. Chemistry of Materials, 2005,17(12): [3] Tripathi VS, Lakshminarayana G, Masayuki N. Optical oxygen sensors based on platinum porphyrin dyes encapsulated in ORMOSILS [J]. Sensors and Actuators B, 2010, 147(2): [4] Anastasova S, Milanova M, Kashchieva E, et al. Morphology of sol-gel produced composite films for optical oxygen sensors [J]. Applied Surface Science, 2008, 254(6): [5] Chu CS, Lo YL. Optical fiber dissolved oxygen sensor based on Pt(II) complex and core-shell silica nanoparticles incorporated with sol-gel matrix [J]. 14 J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(1): 11-15

5 Sensors and Actuators B, 2010, 151(1): [6] Chae KH, Hong DW, Lee MK, et al. Anti-fouling solgel-derived sensing membrane entrapped with polymer containing phosphorylcholine groups for an optical O 2 sensor application [J]. Sensors and Actuators B, 2012,173: [7] Duong HD, Rhee J. Enhancement of the sensitivity of a quantum dot-based fiber optic temperature sensor using the sol-gel technique [J]. Sensors and Actuators B, 2008, 134(2): [8] Estella J, WencelJohn D, Moore P, et al. Fabrication and performance evaluation of highly sensitive hybrid sol-gel-derived oxygen sensor films based on a fluorinated precursor [J]. Analytica Chimica Acta, 2010, 666(1-2): [9] Zhang HR, Li B, Lei BF, et al. Preparation and oxygen sensing properties of a sol-gel derived thin film based on a covalently grafted ruthenium(ii) complex [J]. Sensors and Actuators B, 2007, 123(1): [10] Ding JJ, Li B, Zhang HR, et al. Oxygen-sensing properties of ormosil hybrid materials doped with ruthenium(ii) complexes via a sol-gel process [J]. Materials Letters, 2007, 61(16): [11] Chu CS, Lo YL. Highly sensitive and linear calibration optical fiber oxygen sensor based on Pt(II) complex embedded in sol-gel matrix [J]. Sensors and Actuators B, 2011, 155(1): [12] Chu CS, Lo YL. Ratiometric fiber-optic oxygen sensors based on sol-gel matrix doped with metalloporphyrin and 7-amino-4-trifluoromethyl coumarin [J]. Sensors and Actuators B, 2008, 134(2): [13] García EA, Fernández RG, Díaz-García ME. Tris(bipyridine)ruthenium(II) doped sol-gel materials for oxygen recognition in organic solvents [J]. Microporous and Mesoporous Materials, 2005, 77(2-3): [14] Watkins AN, Wenner BR, Jordan JD, et al. Portable, low-cost, solid-state luminescence-based O 2 sensor [J]. Journal of Applied Spectroscopy, 1998, 52(5): [15] Chu CS, Lo YL, Sung TW. Review on recent developments of fluorescent oxygen and carbon dioxide optical fiber sensors [J]. Photonic Sensors, 2011, 1(3): [16] Oter O, Ertekin K, Derinkuyu D. Photophysical and optical oxygen sensing properties of tris(bipyridine)ruthenium(ii) in ionic liquid modified sol gel matrix [J]. Materials Chemistry and Physics, 2009, 113(1): [17] Yeh TS, Chu CS, Lo YL. Highly sensitive optical fiber oxygen sensor using Pt(II) complex embedded in solgel matrices [J]. Sensors and Actuators B, 2006, 119(2): [18] Chu CS, Lo YL. Ratiometric fiber-optic oxygen sensors based on sol-gel matrix doped with metalloporphyrin and 7-amino-4-trifluoromethyl coumarin [J]. Sensors and Actuators B, 2008, 134(2): [19] Gillanders RN, Tedford MC, Crilly PJ, et al. A composite sol gel/fluoropolymer matrix for dissolved oxygen optical sensing [J]. Journal of Photochemistry and Photobiology A: Chemistry, 2004, 163(1-2): [20] Lakowicz JR. Principles of fluorescence spectroscopy [M]. 2nd ed. New York: Kluwer Academic/Plenum Press, J. Chongqing Univ. Eng. Ed. [ISSN ], 2013, 12(1):