CN114516886B - Europium metal organic complex, preparation method thereof and application of europium metal organic complex as pH fluorescent probe - Google Patents
Europium metal organic complex, preparation method thereof and application of europium metal organic complex as pH fluorescent probe Download PDFInfo
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- 229910052693 Europium Inorganic materials 0.000 title claims abstract description 79
- OGPBJKLSAFTDLK-UHFFFAOYSA-N europium atom Chemical compound [Eu] OGPBJKLSAFTDLK-UHFFFAOYSA-N 0.000 title claims abstract description 78
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 67
- 239000002184 metal Substances 0.000 title claims abstract description 65
- 239000007850 fluorescent dye Substances 0.000 title claims abstract description 12
- 238000002360 preparation method Methods 0.000 title abstract description 16
- OYFRNYNHAZOYNF-UHFFFAOYSA-N 2,5-dihydroxyterephthalic acid Chemical compound OC(=O)C1=CC(O)=C(C(O)=O)C=C1O OYFRNYNHAZOYNF-UHFFFAOYSA-N 0.000 claims abstract description 26
- 239000003446 ligand Substances 0.000 claims abstract description 25
- 238000006243 chemical reaction Methods 0.000 claims abstract description 20
- NBPGPQJFYXNFKN-UHFFFAOYSA-N 4-methyl-2-(4-methylpyridin-2-yl)pyridine Chemical compound CC1=CC=NC(C=2N=CC=C(C)C=2)=C1 NBPGPQJFYXNFKN-UHFFFAOYSA-N 0.000 claims abstract description 9
- 238000000034 method Methods 0.000 claims abstract description 8
- 150000004687 hexahydrates Chemical class 0.000 claims abstract description 4
- 150000001450 anions Chemical class 0.000 claims abstract description 3
- 150000001768 cations Chemical class 0.000 claims abstract description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 19
- 239000000243 solution Substances 0.000 claims description 16
- -1 salt hexahydrate Chemical class 0.000 claims description 12
- 239000007864 aqueous solution Substances 0.000 claims description 8
- 239000008367 deionised water Substances 0.000 claims description 8
- 229910021641 deionized water Inorganic materials 0.000 claims description 8
- 238000003756 stirring Methods 0.000 claims description 6
- JVYYYCWKSSSCEI-UHFFFAOYSA-N europium(3+);trinitrate;hexahydrate Chemical group O.O.O.O.O.O.[Eu+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O JVYYYCWKSSSCEI-UHFFFAOYSA-N 0.000 claims description 5
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- 239000001257 hydrogen Substances 0.000 claims description 5
- 238000002156 mixing Methods 0.000 claims description 4
- AWDWVTKHJOZOBQ-UHFFFAOYSA-K europium(3+);trichloride;hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].[Cl-].[Cl-].[Eu+3] AWDWVTKHJOZOBQ-UHFFFAOYSA-K 0.000 claims description 3
- ZHUXMBYIONRQQX-UHFFFAOYSA-N hydroxidodioxidocarbon(.) Chemical group [O]C(O)=O ZHUXMBYIONRQQX-UHFFFAOYSA-N 0.000 claims description 3
- 229910021645 metal ion Inorganic materials 0.000 claims description 3
- 239000013354 porous framework Substances 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 230000009471 action Effects 0.000 claims description 2
- 238000001816 cooling Methods 0.000 claims description 2
- 101100153586 Caenorhabditis elegans top-1 gene Proteins 0.000 claims 1
- 101100370075 Mus musculus Top1 gene Proteins 0.000 claims 1
- 239000002253 acid Substances 0.000 abstract description 7
- 239000003513 alkali Substances 0.000 abstract description 5
- 238000004064 recycling Methods 0.000 abstract description 4
- 239000002994 raw material Substances 0.000 abstract description 3
- 239000003086 colorant Substances 0.000 abstract description 2
- 238000001027 hydrothermal synthesis Methods 0.000 abstract 1
- 150000003839 salts Chemical class 0.000 abstract 1
- 239000012621 metal-organic framework Substances 0.000 description 26
- 239000013078 crystal Substances 0.000 description 23
- 230000008859 change Effects 0.000 description 8
- 238000001514 detection method Methods 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical group CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 4
- 238000002189 fluorescence spectrum Methods 0.000 description 4
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 4
- 239000004810 polytetrafluoroethylene Substances 0.000 description 4
- 239000002585 base Substances 0.000 description 3
- 238000002050 diffraction method Methods 0.000 description 3
- 230000035484 reaction time Effects 0.000 description 3
- 230000004044 response Effects 0.000 description 3
- 238000002791 soaking Methods 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 230000002378 acidificating effect Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000004020 luminiscence type Methods 0.000 description 2
- 230000005588 protonation Effects 0.000 description 2
- 230000035440 response to pH Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000009210 therapy by ultrasound Methods 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000005595 deprotonation Effects 0.000 description 1
- 238000010537 deprotonation reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 238000002329 infrared spectrum Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000012046 mixed solvent Chemical group 0.000 description 1
- WHQSYGRFZMUQGQ-UHFFFAOYSA-N n,n-dimethylformamide;hydrate Chemical compound O.CN(C)C=O WHQSYGRFZMUQGQ-UHFFFAOYSA-N 0.000 description 1
- 238000005580 one pot reaction Methods 0.000 description 1
- 239000013110 organic ligand Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 125000004076 pyridyl group Chemical group 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
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Abstract
The invention discloses a europium metal organic complex, a preparation method thereof and application thereof as a pH fluorescent probe. The structural formula of the europium metal organic complex is as follows: [ Eu (H) 2 dobdc) 2 (H 2 O)][Hdmbpy]·3H 2 O, wherein: h 2 The dobdc ligand expresses a divalent anion of 2, 5-dihydroxyterephthalic acid losing two protons; hdmbpy ligand means that 4,4 '-dimethyl-2, 2' -bipyridine gives a monovalent cation of one proton. The europium metal organic complex is formed by H 4 The dobdc, dmbpy and the hexahydrate metal salt are obtained through a hydrothermal reaction one-step method, the reaction raw materials are easy to obtain, the preparation method is simple, and the yield is high. The europium metal organic complex can keep stable structure in strong acid and alkali environments, presents different luminescent colors in different pH solutions, can be used as a pH fluorescent probe for recycling, and has higher application value.
Description
Technical Field
The invention belongs to the field of metal complexes, and particularly relates to a europium metal organic complex, a preparation method thereof and application thereof as a pH fluorescent probe.
Background
The concentration of hydrogen ions or the pH value is an important parameter affecting the normal morphology and function of organisms, and plays a key role in crop growth and environmental protection. Therefore, rapid, sensitive identification of aqueous pH is of great significance to curr.opin.cell biol.2007,19,483-492; nat.Rev.Microbiol.2011,9, 330-343.). Luminescent metal organic complexes (MOFs) formed by the coordination bond connection of inorganic metals and organic ligands can be used as a high-efficiency pH detection sensor (Adv. Mater.2020,32, e 1805871). By basicity on MOFs ligands,The protonation/deprotonation of acidic or hydrogen bonding sites directly affects the emission or energy transfer process of the ligand center, thus making a rapid visual reaction of pH changes (inorg. Chem.2020,59,15421-15429; chem. Eur. J.2016,22,13023-13027; j. Am. Chem. Soc.2013,135, 13934-13938). However, studies on luminescent MOFs in terms of pH response are still rare at present, mainly because most MOFs are poor in water stability and acid-base stability, severely limiting their use in aqueous solutions (J. Am. Chem. Soc.2021,143,8838-8848; adv. Mater.2020,32, e 1907090). Thus, the H-bridge is created without damaging the frame structure + Or OH (OH) - The functional site of interaction and converting this interaction into a luminescent reaction for a specific response of pH is an important and challenging task.
Disclosure of Invention
In view of the above problems in the prior art, a first object of the present invention is to provide a europium metal-organic complex having a good luminescence response to pH, exhibiting good water stability and acid-base stability.
The second aim of the invention is to provide a preparation method of the europium metal organic complex, which uses simple and easily available raw materials to synthesize the europium metal organic complex in one step, and has simple operation and low cost.
The third object of the present invention is to provide an application of europium metal organic complex as fluorescent probe for detecting the pH change of solution, and the change can be distinguished by visual color change, and the europium metal organic complex has high sensitivity and can be recycled.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the europium metal organic complex is prepared from 2, 5-dihydroxyterephthalic acid (H) 4 dobdc) and 4,4 '-dimethyl-2, 2' -bipyridine (dmbpy), the structural formula is: [ Eu (H) 2 dobdc) 2 (H 2 O)][Hdmbpy]·3H 2 O, wherein: h 2 The dobdc ligand expresses a divalent anion of 2, 5-dihydroxyterephthalic acid losing two protons; hdmbpy ligand represents a monovalent cation of 4,4 '-dimethyl-2, 2' -bipyridine to give one proton; eu represents a positive trivalent europium ion.
The invention selects H 4 The dobdc and dmbpy are used as ligands, the structure of the ligand contains carboxyl, hydroxyl and pyridyl, on one hand, the ligand shows various coordination modes, on the other hand, the ligand is used as a pH recognition site, a hydrophilic environment is provided, and the formed europium metal organic complex has good water stability and acid-base stability.
Further, the europium metal organic complex is crystallized in a triclinic system, belongs to the P-1 space group, and one asymmetric unit comprises a mononuclear europium metal center and four half-occupied H 2 A dobdc ligand, a Hdmbpy ligand and a number of water molecules. H 2 The dobdc ligand adopts four different coordination modes to connect europium metal ions to form a three-dimensional porous framework, wherein part H 2 The carboxyl oxygen atoms on the dobdc ligand do not participate in coordination reaction, face the inside of the porous tunnel, form hydrogen bond action with the protonated Hdmbpy ligand, provide functional sites for pH detection, and can be used as potential pH probes.
The preparation method of the europium metal organic complex comprises the following specific steps:
stirring and mixing 2, 5-dihydroxyterephthalic acid, 4 '-dimethyl-2, 2' -bipyridine, europium metal hexahydrate and deionized water to obtain an aqueous solution; uniformly mixing, reacting for 60-84 hours at a constant temperature of 135-145 ℃, and cooling to 25-35 ℃ after 12-20 hours to obtain the europium metal organic complex.
The solution is kept at the temperature of 140 ℃ for more than 60 hours to provide proper energy, so that ligand and rare earth ions are easier to form coordination bonds; the solution is slowly cooled to about 30 ℃ over 12 hours to better produce single crystals.
Preferably, the concentration of the 2, 5-dihydroxyterephthalic acid in the aqueous solution is 0.009-0.011 mmol/mL, the concentration of the 4,4 '-dimethyl-2, 2' -bipyridine is 0.01-0.011 mmol/mL, and the concentration of the europium metal salt hexahydrate is 0.007-0.011 mmol/mL.
Preferably, the ratio of the amounts of the substances added to the reaction 2, 5-dihydroxyterephthalic acid and 4,4 '-dimethyl-2, 2' -bipyridine is 1 to 1.2:1.
preferably, the ratio of the amounts of the substances of 2, 5-dihydroxyterephthalic acid and europium metal salt hexahydrate that are put into the reaction is 1:0.76 to 1.2. The crystals precipitated at this ratio are purer.
Preferably, the europium metal hexahydrate is europium nitrate hexahydrate or europium chloride hexahydrate.
The invention also provides application of the europium metal organic complex as a pH fluorescent probe.
The europium metal organic complex can keep stable structure in strong acid or alkali environment, and the fluorescent signal of the complex is changed regularly along with the change of the pH value of the solution.
Preferably, the europium metal-organic complex exhibits a yellow fluorescence at 550nm with a maximum emission peak at pH 8.5. When the pH of the solution was gradually reduced to 2.0, the maximum emission peak was gradually blue shifted to 513nm, and green fluorescence was exhibited. Ratio F of fluorescence intensities at 550nm and 513nm 550 /F 513 The change of the pH is particularly obvious, and the europium metal organic complex is in an S-shaped rule, so that the europium metal organic complex can be applied as a ratio metering type fluorescent probe of the pH.
Preferably, after the europium metal organic complex undergoes a change from yellow to green, the alkalinity of the solution is continuously increased, fluorescence is restored to yellow, and the change of pH can be accurately and sensitively detected and can be recycled.
Compared with the prior art, the invention has the beneficial effects that: the europium metal organic complex provided by the invention has the advantages of simple preparation method, easily obtained reaction raw materials, high yield and low cost, and can be obtained through one-step reaction, thereby being beneficial to industrial production; the europium metal organic complex prepared by the invention has good stability and luminous performance in a wider pH range; the europium metal organic complex provided by the invention has the advantages that the protonation reaction is carried out in a solution with the pH value of 2-6, the fluorescence intensity and the maximum emission wavelength are correspondingly changed, the color change which can be distinguished by naked eyes is presented, the operation is simple, the sensitivity is high, the europium metal organic complex can be recycled, and the europium metal organic complex can be used as a pH ratio metering type fluorescent probe to be applied to an acidic environment.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are required in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that it is within the scope of the invention to one skilled in the art to obtain other drawings from these drawings without inventive faculty.
FIG. 1 is a crystal structure diagram of europium metal-organic complex in example 1 of the present invention;
FIG. 2 is a schematic view showing the three-dimensional porous structure of the europium metal-organic complex in example 1 of the present invention;
FIG. 3 is an infrared spectrum of the europium metal organic complex in example 1 of the present invention;
FIG. 4 is a powder diffraction pattern of the europium metal organic complex in example 1 of the present invention;
FIG. 5 is a powder diffraction pattern of the europium metal organic complex in example 1 of the present invention after soaking in solutions of different pH;
FIG. 6 is a graph showing fluorescence spectra of europium metal-organic complexes in solutions of different pH in example 1 of the present invention;
FIG. 7 is a CIE color chart of the europium metal organic complexes in example 1 of the present invention;
FIG. 8 is a graph showing the luminescence intensity F of the europium metal-organic complex in example 1 of the present invention 550 /F 513 A pH-dependent curve of the values of (2);
FIG. 9 is a graph showing F of the europium metal organic complex in five cycles in example 1 of the present invention 550 /F 513 The upper point pH was about 8.5 and the lower point pH was about 2.
Detailed Description
The present invention will be further described in detail with reference to specific examples for the purpose of making the objects, technical solutions and advantages of the present invention more clear, but the purpose of these exemplary embodiments is to be construed as merely illustrative and not limitative of the actual scope of the present invention in any way.
Example 1: europium metal organic complex [ Eu (H) 2 dobdc) 2 (H 2 O)][Hdmbpy]·3H 2 Preparation of O (also abbreviated as Eu-MOF in the present application)
0.1mmol of europium nitrate hexahydrate (0.0446 g), 0.099mmol of 2, 5-dihydroxyterephthalic acid (0.0196 g, abbreviated as H in the present application) 4 dobdc) and 0.1mmol of 4,4 '-dimethyl-2, 2' -bipyridine (0.0184 g, abbreviated as dmbpy in this application) were added to 10mL of deionized water, mixed uniformly under stirring, then placed in a polytetrafluoroethylene reaction vessel and sealed, reacted at a constant temperature in an oven at 140℃for 72 hours, and cooled slowly to 30℃over 15 hours to give pale yellow bulk crystals with a yield of 71.6% (based on H) 4 dobdc)。
The crystals obtained in this example were selected and tested using a Bruker Smart-APEXII CCD X-ray single crystal diffractometer. The resulting crystallographic structure refinement data are shown in table 1 below and the partial bond lengths are shown in table 2.
Table 1: structural refinement data of Eu-MOF
Table 2: partial bond length of Eu-MOF
The asymmetric unit of the europium metal organic complex comprises a mononuclear europium metal center and four half-occupied H 2 A dobdc ligand, a Hdmbpy ligand and several water molecules (fig. 1). H 2 The dobdc ligand adopts four different coordination modes to connect europium metal ions to form a three-dimensional porous framework, whereinPart H 2 The carboxyl oxygen atoms on the dobdc ligand do not participate in coordination reaction, face the inside of the porous tunnel (figure 2), and form hydrogen bonding with the protonated Hdmbpy ligand, so that a functional site is provided for pH detection.
The Eu-MOF of this example was characterized using an IRAfforescence-1S infrared spectrometer, with the following results: 3521.11 (m), 1631.81(s), 1605.77(s), 1494.86 (m), 1441.81(s), 1355.98 (m), 1240.25(s), 1112.95 (m), 1031.93 (vw), 990.46 (vw), 921.99 (w), 910.42 (w), 872.80 (m), 814.94(s), 795.65 (m), 750.32 (w), 609.52 (m), 550.69(s), 509.22 (w), 466.78 (vw), 416.63 (w) (fig. 3).
The Eu-MOF prepared in example 1 of the present invention was characterized for phase purity and stability using a Bruker D8 ADVANCE powder diffractometer. As shown in FIG. 4, it can be seen from the comparison of the curve obtained by the experiment with the curve obtained by the simulated crystal data that the Eu-MOF prepared by the above method is a pure phase.
Comparative examples 1 to 1
The water added in example 1 was replaced with N, N-dimethylformamide or a mixed solvent of water and N, N-dimethylformamide, and the remaining conditions were unchanged; as a result, no crystals or powder products were produced.
Comparative examples 1 to 2
The reaction temperature in example 1 was changed to 125℃or less, and the remaining conditions were unchanged; as a result, no crystals or powder products were produced.
Comparative examples 1 to 3
The reaction time in example 1 was changed to 60 hours or less, and the remaining conditions were unchanged; as a result, no crystals or powder products were produced.
As is clear from comparison of examples 1 to comparative examples 1 to 3, the objective europium metal-organic complex cannot be obtained in the present invention if water is exchanged for other solvents, which is caused by the solvent effect. If the reaction temperature is lowered or the reaction time is shortened, the target europium metal-organic complex cannot be obtained. The present invention therefore uses water as a solvent and requires sufficient reaction temperature and reaction time to provide the energy required for the reaction.
Example 2: eu-MOF preparation
0.1mmol of europium chloride hexahydrate (0.0366 g), 0.099mmol of H 4 dobdc (0.0196 g) and 0.1mmol dmbpy (0.0184 g) were added to 10mL deionized water, mixed uniformly under stirring, then placed in a polytetrafluoroethylene reaction vessel, sealed, reacted at constant temperature in an oven at 140℃for 72 hours, cooled slowly to 30℃over 15 hours to give pale yellow bulk crystals with a yield of 65.7% (based on H) 4 dobdc)。
The crystals obtained in this example were subjected to single crystal diffraction analysis, and the pale yellow bulk crystals were determined to be Eu-MOF, which was the same as that obtained by the preparation method of example 1.
Example 3: eu-MOF preparation
0.076mmol of europium nitrate hexahydrate (0.0339 g), 0.1mmol of H 4 dobdc (0.0198 g) and 0.1mmol dmbpy (0.0184 g) were added to 10mL deionized water, mixed well under stirring, then placed in a polytetrafluoroethylene reaction vessel, sealed, reacted at constant temperature in an oven at 135℃for 84 hours, cooled slowly to 30℃over 12 hours to give pale yellow bulk crystals with a yield of 63.1% (based on H) 4 dobdc)。
The crystals obtained in this example were subjected to single crystal diffraction analysis, and the pale yellow bulk crystals were determined to be Eu-MOF, which was the same as that obtained by the preparation method of example 1.
Example 4: eu-MOF preparation
0.11mmol of europium nitrate hexahydrate (0.0491 g) and 0.092mmol of H were mixed 4 dobdc (0.0182 g) and 0.11mmol dmbpy (0.0203 g) were added to 10mL deionized water, mixed well with stirring, then placed in a polytetrafluoroethylene reaction vessel, sealed, reacted at constant temperature in an oven at 145℃for 60 hours, cooled slowly to 35℃over 20 hours to give pale yellow bulk crystals with a yield of 65.5% (based on H) 4 dobdc)。
The crystals obtained in this example were subjected to single crystal diffraction analysis, and the pale yellow bulk crystals were determined to be Eu-MOF, which was the same as that obtained by the preparation method of example 1.
Example 5: stability detection of Eu-MOF in strong acid and strong alkali environments
To verify the stability of the europium metal organic complex in strong acid and strong alkaline environments, 20mg of Eu-MOF prepared in example 1 of the present invention was immersed in aqueous solutions having pH values in the range of 2 to 12 for 24 hours, respectively, and after taking out, dried in air and tested using a Bruker D8 ADVANCE powder diffractometer. As shown in fig. 5, the curve obtained after soaking is still consistent with the original curve of the complex before soaking, which indicates that the europium metal organic complex has good stability, can resist the damage of external strong acid and strong alkali to the crystal structure, and provides a guarantee for the application of the europium metal organic complex as a pH fluorescent probe.
Example 6: europium metal organic complex applied to detection of aqueous solutions with different pH values
In order to verify the response capability of the europium metal-organic complex to pH, the Eu-MOF prepared in example 1 of the present invention was accurately weighed and put into 100mL of deionized water, and the Eu-MOF was uniformly dispersed in water by ultrasonic treatment for 10min to prepare a suspension having a concentration of 0.05mg/mL, and fluorescence spectrum titration was performed on the Eu-MOF in the aqueous solution. As can be seen from FIG. 6, in an alkaline environment (pH greater than 7), the maximum emission wavelength of Eu-MOF is 550nm, at which time the solution appears yellow. As the pH of the solution was reduced, the emission intensity at 550nm was gradually reduced while the maximum emission wavelength was blue shifted, and at pH 2 the maximum emission wavelength was 513nm, at which point the solution appeared green (fig. 7). Using Eu-MOF ratio F of fluorescence intensities at 550nm and 513nm 550 /F 513 And pH as shown in fig. 8, the ratio varies significantly over a range of pH from 2 to 6. Fitting the obtained curve by using Boltzmann equation can obtain Eu-MOF with pKa of 3.1, which shows that the europium metal-organic complex can be suitable for detecting pH in polar acid environment.
Example 7: recycling of europium metal organic complex applied to pH detection
In order to verify the recycling property of the europium metal organic complex applied to pH detection, the Eu-MOF prepared in the embodiment 1 of the invention is accurately weighed and put into 100mL of deionized water, and the Eu-MOF is uniformly dispersed in the water by ultrasonic treatment for 10min to prepare a suspension with the concentration of 0.05 mg/mL. Will beThe pH of the suspension is adjusted between 8 and 2 for 5 cycles, and corresponding fluorescence spectra are collected to obtain 10 fluorescence spectrum curves, F is obtained from each curve 550 /F 512 And drawing figure 9. It can be seen that this ratio remains almost unchanged over 5 cycles, indicating that the europium metal-organic complex can achieve a reversible fluorescence response to pH.
The europium metal organic complex can keep stable structure in strong acid and alkali environments, presents different luminescent colors in different pH solutions, can be used as a pH fluorescent probe for recycling, and has higher application value. The preparation method is simple, high in yield and low in cost, and is suitable for large-scale popularization and application.
Claims (8)
1. An europium metal organic complex which is characterized in that: the structure is as follows: [ Eu (H) 2 dobdc) 2 (H 2 O)][Hdmbpy]·3H 2 O, where H 2 The dobdc ligand expresses a divalent anion of 2, 5-dihydroxyterephthalic acid losing two protons; the Hdmbpy ligand represents a monovalent cation of 4,4 '-dimethyl-2, 2' -bipyridine to a proton;
the europium metal organic complex is crystallized in a triclinic system and belongs toP-1 space group; h 2 The dobdc ligand adopts four different coordination modes to connect europium metal ions to form a three-dimensional porous framework, wherein part H 2 The carboxyl oxygen atoms on the dobdc ligand do not participate in coordination reaction, face the inside of the porous tunnel, and form hydrogen bond action with the protonated Hdmbpy ligand.
2. The method for preparing the europium metal organic complex according to claim 1, wherein: stirring and mixing 2, 5-dihydroxyterephthalic acid, 4 '-dimethyl-2, 2' -bipyridine, europium metal hexahydrate and deionized water to obtain an aqueous solution; uniformly mixing, reacting for 60-84 hours at a constant temperature of 135-145 ℃, and cooling to 25-35 ℃ after 12-20 hours to obtain the europium metal organic complex.
3. The method for preparing the europium metal organic complex according to claim 2, wherein: the concentration of the 2, 5-dihydroxyterephthalic acid in the aqueous solution is 0.009-0.011 mmol/mL, the concentration of the 4,4 '-dimethyl-2, 2' -bipyridine is 0.01-0.011 mmol/mL, and the concentration of the europium metal salt hexahydrate is 0.007-0.011 mmol/mL.
4. The method for preparing the europium metal organic complex according to claim 2, wherein: the ratio of the amounts of the 2, 5-dihydroxyterephthalic acid and 4,4 '-dimethyl-2, 2' -bipyridine added to the reaction is 1 to 1.2:1.
5. the method for preparing the europium metal organic complex according to claim 2, wherein: the ratio of the amounts of the substances of 2, 5-dihydroxyterephthalic acid and europium metal salt hexahydrate put into the reaction was 1:0.76 to 1.2.
6. The method for preparing the europium metal organic complex according to claim 2, wherein: the europium metal salt hexahydrate is europium nitrate hexahydrate or europium chloride hexahydrate.
7. The use of a europium metal organic complex according to claim 1, wherein: as a pH fluorescent probe; as the solution pH changed from 8.5 to 2, the fluorescence of the europium metal-organic complex changed from yellow to green.
8. The use of a europium metal organic complex according to claim 7, characterized in that: the europium metal organic complex can be reused in five cycles.
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