| Dissolved oxygen sensor based on fluorescence quenching has many advantages over others, such as fast responding speed, high measuring precision, no oxygen consumption, high anti-interference, operation convenience and ability to monitor dissolved oxygen on line. It has been used widely in environmental monitoring, sewage treatment, aquaculture, biochemical reaction and so on. The key component of the sensor is its oxygen sensitive fluorescent membrane, which determines the performance and lifetime of the sensor. Currently, most oxygen-sensitive fluorescent membranes are made of physically immobilized phosphor through adsorption or embedding and have problems of phosphor leaching or lowing responding speed.In this thesis, to solve the problem in immobilizing phosphor, reactive Ru(Ⅱ)-diimine phosphors were synthesized and chemically bonded to optic fiber materials; the stability and responding time of the resultant oxygen sensitive fluorescent membrane were investigated. With 4,7-diphenyl-1,10-phenanthroline(dpp), 5-amino-phenanthroline(phen-NH2) and ruthenium trichloride, an amine-containing Ru(Ⅱ)-diimine phosphor [Ru(dpp)2(phen-NH2)]Cl2 was synthesized by a two-step process; then, the phosphor reacted with γ-isocyanate triethoxysilane to synthesize a siloxane containing Ru(Ⅱ)-diimine phosphor [Ru(dpp)2(phen-Si)]Cl2. The phosphor [Ru(dpp)2(phen-NH2)]Cl2 was chemically bonded to hydrolyzed PMMA plate through amine group to form oxygen sensitive fluorescent membrane; also, a silica sol with unsaturated carbon chain was synthesized and coated on glass slides, the phosphor [Ru(dpp)2(phen-Si)]Cl2 was chemically bonded to porous silica gel. The synthesized phosphors and their chemical bonding to substrates were verified with FT-IR, 1H, 13 CNMR spectroscopy, ES-MS. The fluorescent features of the phosphors and oxygen-sensitive fluorescent membranes were measured with UV-visible absorption spectroscopy and fluorescence spectrometry. The effects of reaction conditions on the structure and fluorescent intensity of oxygen-sensitive fluorescent membranes were investigated and the variation of the fluorescence intensity with immersed time of oxygen-sensitive fluorescent membranes in water at 50℃ was monitored.With 5-amino-phenanthroline and di(4,7-diphenyl-phenanthroline) ruthenium(Ⅱ) dichloride, the phosphor [Ru(dpp)2(phen-NH2)]Cl2 could be synthesized conveniently. It exhibited absorption around 460 nm and fluorescent emission around 570 nm. In solution, the phosphor [Ru(dpp)2(phen-NH2)]Cl2 could chemically bonded to hydrolyzed PMMA through amine group and generated oxygen sensitive fluorescent membrane with fluorescent emission peaking at 590 nm; whereas PMMA matrix would not change significantly at immobilizing temperature 60℃. With increasing immobilizing time and phosphor concentration, the fluorescent intensity of obtained oxygen sensitive fluorescent membranes increased. At 0.5 % of phosphor, 60℃ immobilizing temperature and 1.5 hr immobilizing time, the obtained oxygen-sensitive fluorescent membrane exhibited strongest fluorescent emission. The phosphor [Ru(dpp)2(phen-NH2)]Cl2 chemically bonded to PMMA exhibited fast response speed; the responding time from the nitrogen saturated water to the oxygen saturated water was less than 10 seconds and the oxygen quenching ratio I0/I100 was 4. After the PMMA with [Ru(dpp)2(phen-NH2)]Cl2 was immersed in water at 50℃ for 8 months, the fluorescence intensity decreased less than 1%.In anhydrous methylene dichloride, phosphor [Ru(dpp)2(phen-NH2)]Cl2 could react with γ-isocyanate propyl triethoxysilane and generated a phosphor [Ru(dpp)2(phen-Si)]Cl2. The transformation of reactive functional group didn’t affect the fluorescent features of the phosphor significantly. Ordinary glass is smooth and has low content of silicon hydroxyl; they are not sufficient to chemically immobilize phosphor [Ru(dpp)2(phen-Si)]Cl2 to form fluorescent membrane. Porous silica gel coatings from modified silica sol have sufficient silicon hydroxyl for chemical immobilization of [Ru(dpp)2(phen-Si)]Cl2 and formation of good oxygen sensitive fluorescent membrane.As organic unsaturated carbon chains were introduced to inorganic silica sol, the sol could be UV cured at room temperature before the formation of inorganic network. This would reduce the contracting stress and increase the gel strength during the condensation of silicon hydroxyl groups; thus, improve the film-formability of the sol significantly. The pore size of the gel coating could be 30-300 nm, varying with sol compositions and curing temperature. As the R/Si ratio of precursors increased, the pore size and porosity of the gel coating decreased. At R/Si ratio was 1.0, a membrane with separated pores generated. When R/Si changed from 0.6 to 1.0, the pendulum hardness decreased from 0.69 s to 0.57 s. With prolonged aging time, the sol viscosity and coating thickness increased whereas the p orosity and pendulum hardness increased at beginning and then decreased. Within aging time 12 hrs, the fluorescence intensity of the gel coating bonded with [Ru(dpp)2(phen-Si)]Cl2 increased slowly. As the baking temperature increased, the pore size of resultant gel coatings increased, whereas the porosity increased at beginning and then decreased, in contrary, the pendulum hardness decreased and then increased; both got extremes at 70℃. The fluorescence intensity of the coating with chemically immobilized [Ru(phen-Si)2](dpp)Cl2 had positive correlation with the porosity. At R/Si ratio of 0.69, aging time 10 hours, baking temperature 70℃, the resultant membrane had good toughness, a wealth of pores and high fluorescence emission after bonded with [Ru(phen-Si)2](dpp)Cl2.The response time of oxygen sensitive fluorescent gel membranes was less than 30 sec from air to oxygen free oxygen water. After the membrane was immersed in water at 50℃ for two months, the fluorescence emission decreased less than 9.0 %. In contrast, oxygen sensitive fluorescent gel membrane with embedded phosphor Ru(dpp)3Cl2, the response time was 3 min and the fluorescence emission decayed more than 50%. Chemical immobilization of phosphor can improve the stability of oxygen sensitive fluorescent membrane and the responding speed to dissolved oxygen as well. |
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