Rare earth-tungsten cluster bridged polyoxometallate, preparation method thereof and application of polyoxometallate as fluorescence sensor

Abstract

The invention discloses a rare earth-tungsten cluster bridged polyoxometallate and a preparation method thereof. The chemical formula of the rare earth-tungsten cluster bridged polyoxometallate is [N (CH3) 4] 10.334 H0. 66Na2 [Ln4 (H2O) 10W6O13 (H2MA) 2Ac] [SeW9O33] 4. 86H2O (Ln4Se4W42; ln = Eu < 3 + > and Tb < 3 + >; hAc = acetic acid, and H3MA = D, L-malic acid). The compound is prepared by reacting sodium tungstate dihydrate, sodium selenite and rare earth nitrate in the presence of organic ligand tetramethylammonium chloride, acetic acid and D, L-malic acid. The polyoxometallate material [N (CH3) 4] 10.334 H0. 666Na2 {Eu0. 2Tb3. 8 (H2O) 10W6O13 (H2MA) 2Ac] [SeW9O33] 4}. 86H2O (Eu0. 2Tb3. 8Se4W42) containing double luminescence centers of Tb < 3 + > and Eu < 3 + > is successfully prepared through a rare earth doping method, Tb < 3 + > and Eu < 3 + > respectively provide a strongly changing fluorescence signal and a stable internal reference fluorescence signal, so that a ratio type fluorescence sensor is constructed, and the anthrax bun marker (2, 6-pyridinedicarboxylic acid) in water is detected through the luminous intensity ratio of Tb < 3 + > to Eu < 3 + >. The ratio type sensor has excellent selectivity, sensitivity and anti-interference capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of new chemical materials, and in particular relates to rare earth-tungsten cluster bridged polyoxometalates and a preparation method thereof and an application thereof as a fluorescence sensor. Background Art

[0002] Anthrax is a type of infection caused by inhalation of concentrations exceeding 10 4 An acute disease caused by Bacillus anthracis spores that infects humans and animals (W. Beyer, PC Turnbull, Mol. Aspects Med ., 2009, 30, 481). In addition, these spores have been mistakenly used as biological weapons in bioterrorism attacks, posing a significant threat to humanity. 2,6-Pyridinedicarboxylic acid (DPA) is one of the main components of anthrax, accounting for 5–15% of the total weight of dry anthrax, and is commonly used as a biomarker for anthrax detection. Therefore, the detection of DPA is crucial for the effective prevention of anthrax infection and terrorist attacks. Fluorescence sensing technology has become the preferred technology for analytical detection in environmental and biological systems due to its inherent advantages such as simplicity of operation, low cost, real-time monitoring, rapid analysis, high sensitivity and high selectivity. Currently, single-emission fluorescence sensing methods have been widely used for the detection of DPA. However, this method's sensitivity to external conditions such as instrument type and parameters, background interference, and environmental factors limits its widespread application. Ratiometric fluorescence sensors have a unique self-calibration function that can minimize external fluctuations caused by instrumentation or environmental factors, thereby obtaining more reliable and accurate results (SY Wu, H.Min, W. Shi, et al., Adv. Mater. , 2020, 32, 1805871; Y.-S. Liu, R. Xue, B.Yan, Coord. Chem. Rev. , 2025, 523, 216280). Therefore, it is of great significance to develop a suitable ratiometric fluorescence sensor for sensitive and accurate detection of DPA.

[0003] Polyoxometalates are a class of atomically precise metal oxygen clusters. The highly ordered arrangement of their internal atoms not only deepens our understanding of structural information and structure-activity relationships, but also provides the conditions for the purposeful design and construction of polyoxometalate materials with specific functions. Rare earth cations as luminescent and connecting units can not only induce the assembly of polyoxometalate fragments to prepare new rare earth-substituted polyoxometalate structures, but also facilitate the functional transfer of metal cations, endowing them with excellent luminescent properties (C. Boskovic, Acc. Chem. Res., 2017, 50, 2205). In recent years, a variety of smart sensing materials based on rare earth substituted polyoxometalates have been successfully prepared (SY Zhang, TTGong, CY Liu, et al., Inorg. Chem. Front. , 2024, 11, 5004; PP Sun, SSZhang, ZY Xiang, et al., J. Colloid Interface Sci. , 2019, 547, 60; J. Lua,Q. Kang, JH Xiao, et al., Carbohydr. Polym., 2018, 200, 560). These materials exhibit excellent performance in identifying metal ions, biomolecules, and environmental pollutants. Their fluorescence sensing response modes include unidirectional "on-off" or "off-on" modes, as well as bidirectional "on-off-on" modes. However, current research in this field mainly focuses on constructing single-emission polyoxometalate fluorescence sensors. In contrast, research on ratiometric polyoxometalate fluorescence sensors is still in its early stages. Therefore, the development of polyoxometalates with dual rare earth emission centers and the further construction of ratiometric fluorescence sensors for the quantitative and sensitive detection of DPA is a challenging but significant research task.

[0004] Based on this, this application was developed. Summary of the Invention

[0005] The present invention aims to overcome the defects of the prior art and provides a rare earth-tungsten cluster-bridged polyoxometalate material, which exhibits characteristic emission of rare earth ions.

[0006] The present invention also provides a preparation method of the rare earth-tungsten cluster bridged polyoxometalate material and its application as a fluorescence sensor.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A rare earth-tungsten cluster-bridged polyoxometalate, wherein the chemical formula of the polyoxometalate is: [N(CH3)4] 10.334 H 0.666 Na2[Ln4(H2O) 10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O, where Ln = Eu 3+ and Tb 3+ ; HAc = acetic acid, H3MA = D,L-malic acid.

[0008] The present invention provides a method for preparing the above-mentioned rare earth-tungsten cluster bridged polyoxometalate, which is prepared by reacting sodium tungstate dihydrate, sodium selenite and rare earth nitrate in the presence of organic ligands tetramethylammonium chloride, acetic acid and D,L-malic acid; specifically comprising the following steps: Under stirring conditions, sodium tungstate dihydrate, sodium selenite, tetramethylammonium chloride and D, L-malic acid were dissolved in distilled water to obtain a clear reaction solution; then glacial acetic acid was added and stirred for 15-30 minutes, and rare earth nitrate was added. The pH of the reaction system was adjusted to 4.5-5.0 with acid, and after continuous stirring for 15-30 minutes, the reaction solution was placed at 80-95°C. o Heat in a water bath at 5–7°C for 1.5–2.5 h, cool, filter, and place the filtrate at 5–7°C. o C, which is a rare earth-tungsten cluster-bridged polyoxometalate (Eu 0.2 Tb 3.8 4W 42 ); The rare earth nitrate is composed of a mixture of europium nitrate hexahydrate and terbium nitrate hexahydrate.

[0009] Specifically, in the above preparation method, the molar ratio of the sodium tungstate dihydrate, sodium selenite, tetramethylammonium chloride, D,L-malic acid, glacial acetic acid, rare earth nitrate and distilled water can be 7.6–12.2: 0.46–0.59: 9.1–10.9: 1.8–2.6: 8.1–9.1: 0.65–0.85: 1500–1800.

[0010] Further preferably, the rare earth nitrate is composed of a mixture of europium nitrate hexahydrate and terbium nitrate hexahydrate in a molar ratio of 0.05:0.95.

[0011] The present invention also provides the use of the rare earth-tungsten cluster bridged polyoxometalate as a ratiometric fluorescence sensor. Further, it can be used to detect the concentration of DPA in water, and it exhibits good recognition and detection effect on DPA. The polyoxometalate contains Tb 3+ and Eu 3+ Double luminous center.

[0012] Furthermore, the above application is specifically as follows: under 378 nm excitation, the emission spectrum of rare earth-tungsten cluster bridged polyoxometalates shows Tb 3+ and Eu 3+ The characteristic emission peaks of Tb ions; with the increase of DPA concentration, 3+ The fluorescence intensity of Eu 3+ The fluorescence intensity of Tb 3+ and Eu 3+ The ratio change of fluorescence intensity was used to achieve sensitive detection and concentration determination of DPA.

[0013] The present invention also provides a Tb 3+ and Eu 3+ Application of polyoxometalates with dual luminescent centers as ratiometric fluorescence sensors in biological detection.

[0014] The present invention provides a method comprising Tb 3+ and Eu 3+ This invention uses a polyoxometalate material with dual luminescent centers as a ratiometric fluorescence sensor for the quantitative detection of DPA in water. This innovative use of polyoxometalates as a self-calibrating fluorescence sensing platform expands their potential applications in biological detection, environmental monitoring, and other fields. Compared to existing technologies, this invention has the following advantages: 1) The rare earth-tungsten cluster-bridged polyoxometalates provided by the present invention have a clear crystal structure that can be accurately determined by X-ray single crystal diffractometry; 2) The rare earth-tungsten cluster-bridged polyoxometalates provided by the present invention can be synthesized by a one-step in-situ assembly method using simple raw materials. The operation is simple and easy, and the crystal growth cycle is short, and the target product can be obtained in a few hours. 3) The present invention provides a Tb 3+ and Eu 3+ Polyoxometalates with dual luminescent centers can be 3+ / Eu 3+ The doping method embeds the two into the same crystal lattice, and the preparation process is simple, and high-quality crystal products can be obtained; 4) The present invention provides a method comprising Tb 3+ and Eu 3+ Polyoxometalates with dual luminescent centers are used as ratiometric fluorescence sensors to achieve quantitative detection of DPA with good sensitivity, selectivity and anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The polyoxometalate Eu4Se4W of the present invention 42 Molecular structure assembly diagram; where (a) is Eu4Se4W 42 Structural diagram of the anion skeleton; (b) is the structure of Eu4Se4W 42 In the two dimers {[Eu2(H2O)5W3O6][SeW9O 33 ]2} 4– The unit is connected by ligand and [W2O 11 ] 10– The oxygen atoms in the fragment are connected; (c) is the relative position of the four selenium atoms; (d) is Eu4Se4W 42 Simplified model diagram; (e) is [Eu4(H2O) 10 W6O13 (H2MA)2Ac] 19+ Multimetallic clusters and two [B- α -SeW9O 33 ] 8– Relative arrangement of fragments; (f) is [Eu4(H2O) 10 W6O 13 (H2MA)2Ac] 19+ Ball-and-stick diagram of polymetallic clusters; (g) is Ac – and H2MA – Coordination mode of the ligand and the metal; (h) is a trigonal bipyramid formed by two europium and three tungsten atoms; Figure 2 The polyoxometalate Ln4Se4W of the present invention 42 Infrared spectrum of Ln = Eu 3+ (a) or Tb 3+ (b); Figure 3 The polyoxometalate Ln4Se4W of the present invention 42 Thermogravimetric analysis of Ln = Eu 3+ (a) or Tb 3+ (b); Figure 4 The polyoxometalate Ln4Se4W of the present invention 42 X-ray powder diffraction pattern of; Ln = Eu 3+ (a) or Tb 3+ (b); Figure 5 The present invention contains Tb 3+ and Eu 3+ Polyoxometalates with dual luminescent centers (abbreviated as Eu 0.2 Tb 3.8 4W 42 ) and X-ray powder diffraction patterns of polyoxometalates (abbreviated as Tb4Se4W 42 )Comparison Figure (b); Figure 6 The present invention contains Tb 3+ and Eu 3+ Polyoxometalates with dual luminescent centers (abbreviated as Eu 0.2 Tb 3.8 4W 42 ) fluorescence spectrum; Figure 7 (a) is the present invention contains Tb 3+ and Eu 3+Fluorescence spectra of polyoxometalates with dual luminescent centers (5 mg / mL) with different concentrations of DPA added; (b) shows the change in fluorescence intensity of the characteristic peaks at 545 nm and 616 nm with DPA concentration; (c) shows the ratio of fluorescence intensity of the characteristic peaks at 545 nm and 616 nm. I 545 / I 616 Linear relationship graph with DPA concentration; Figure 8 (a) is the present invention contains Tb 3+ and Eu 3+ Selective test of polyoxometalates with dual luminescent centers for DPA; (b) the present invention contains Tb 3+ and Eu 3+ Anti-interference ability test of polyoxometalates with dual luminescence centers; Figure 9 The present invention contains Tb 3+ and Eu 3+ Fluorescence lifetime decay curves of polyoxometalates with dual luminescent centers when different concentrations of DPA are added; Figure 10 The present invention contains Tb 3+ and Eu 3+ Energy level diagram of the energy transfer pathway between polyoxometalates with dual luminescent centers and DPA molecules.

[0016] Specific implementation methods The present invention is further described in detail below through examples, but this does not mean that the scope of the present invention is limited to the following examples.

[0017] In the following examples, unless otherwise specified, all raw materials used are common commercial products available in the art.

[0018] Room temperature refers to 25±5°C.

[0019] In order to study the crystal structure of polyoxometalates, the present invention first synthesized a rare earth-tungsten cluster-bridged polyoxometalates (Ln4Se4W) with a single luminescent center using Examples 1 to 3. 42 ; Ln = Eu 3+ or Tb 3+ ), and then prepare a Tb doped with a small amount of europium 3+ and Eu 3+ Polyoxometalate materials with dual luminescent centers (Eu 0.2 Tb 3.8 4W 42 , see Example 4), and further explored its application as a ratiometric fluorescence sensor.

[0020] Example 1: Rare earth-tungsten cluster-bridged polyoxometalates, with the chemical formula: [N(CH3)4] 10.334 H 0.666 Na2[Ln4(H2O) 10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O; abbreviated as Ln4Se4W 42 ; Ln = Eu 3+ or Tb 3+ ;HAc = acetic acid, H3MA = D, L-malic acid, colorless block crystals, four [B- α -SeW9O 33 ] 8– The fragment is bridged by a double flexible ligand to a rare earth-tungsten cluster stabilized by [Ln4(H2O) 10 W6O 13 (H2MA)2Ac] 19+ Multi-metal clusters assembled.

[0021] The rare earth-tungsten cluster-bridged polyoxometalate material is obtained by a one-step in-situ assembly method using simple raw materials. The specific preparation method involves the following steps: Under stirring conditions, sodium tungstate dihydrate (4.003 g, 12.136 mmol), sodium selenite (0.102 g, 0.590 mmol), tetramethylammonium chloride (1.006 g, 9.179 mmol), and D,L-malic acid (0.307 g, 2.290 mmol) were dissolved in 30 mL of distilled water. 500 μL of glacial acetic acid was added under continuous stirring. After stirring for 15 min, europium nitrate hexahydrate (0.304 g, 0.683 mmol) or terbium nitrate hexahydrate (0.302 g, 0.667 mmol) was added to the above solution. 6 mol·L –1 The pH of the reaction system was adjusted to 4.8 with HCl, and the mixture was stirred for 15 min. The mixture was heated in a 90 °C water bath for 2 h, taken out, cooled at room temperature and allowed to stand for 24 h, filtered, and the filtrate was heated at 5–7 o C and allowed to stand for several hours to evaporate, and colorless block crystals were precipitated to obtain the target product polyoxometalate material (Eu4Se4W 42 or Tb4Se4W 42 ).

[0022] Example 2: Rare earth-tungsten cluster-bridged polyoxometalates, with the chemical formula: [N(CH3)4] 10.334 H 0.666 Na2[Ln4(H2O)10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O; abbreviated as Ln4Se4W 42 ; Ln = Eu 3+ or Tb 3+ ; HAc = acetic acid, H3MA = D,L-malic acid.

[0023] The rare earth-tungsten cluster-bridged polyoxometalate material is obtained by a one-step in-situ assembly method using simple raw materials. The specific preparation method involves the following steps: Under stirring conditions, sodium tungstate dihydrate (3.015 g, 9.141 mmol), sodium selenite (0.102 g, 0.590 mmol), tetramethylammonium chloride (1.006 g, 9.179 mmol), and D,L-malic acid (0.307 g, 2.290 mmol) were dissolved in 30 mL of distilled water. 500 μL of glacial acetic acid was added under continuous stirring. After stirring for 15 min, europium nitrate hexahydrate (0.304 g, 0.683 mmol) or terbium nitrate hexahydrate (0.302 g, 0.667 mmol) was added to the above solution. 6 mol·L –1 The pH of the reaction system was adjusted to 5.0 with HCl, and the mixture was stirred for 15 min. The mixture was heated in a 90 °C water bath for 2 h, cooled and allowed to stand for 24 h, filtered, and the filtrate was heated at 5–7 o C and allowed to stand for several hours to evaporate, colorless block crystals were precipitated, which was the target product polyoxometalate material (Eu4Se4W 42 or Tb4Se4W 42 ).

[0024] Example 3: Rare earth-tungsten cluster-bridged polyoxometalates, with the chemical formula: [N(CH3)4] 10.334 H 0.666 Na2[Ln4(H2O) 10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O; abbreviated as Ln4Se4W 42 ; Ln = Eu 3+ or Tb 3+ ; HAc = acetic acid, H3MA = D,L-malic acid.

[0025] The rare earth-tungsten cluster-bridged polyoxometalate material is obtained by a one-step in-situ assembly method using simple raw materials. The specific preparation method involves the following steps: Under stirring conditions, sodium tungstate dihydrate (4.003 g, 12.136 mmol), sodium selenite (0.102 g, 0.590 mmol), tetramethylammonium chloride (1.006 g, 9.179 mmol), and D,L-malic acid (0.255 g, 1.902 mmol) were dissolved in 30 mL of distilled water. 500 μL of glacial acetic acid was added under continuous stirring. After stirring for 15 min, europium nitrate hexahydrate (0.304 g, 0.683 mmol) or terbium nitrate hexahydrate (0.302 g, 0.667 mmol) was added to the above solution. 6 mol·L –1 The pH of the reaction system was adjusted to 5.0 with HCl, and the mixture was stirred for 15 min. The mixture was heated in a 90 °C water bath for 2 h, cooled and allowed to stand for 24 h, filtered, and the filtrate was heated at 5–7 o C and allowed to stand for several hours to evaporate, colorless block crystals were precipitated, which was the target product polyoxometalate material (Eu4Se4W 42 or Tb4Se4W 42 ).

[0026] Example 4: Contains Tb 3+ and Eu 3+ The polyoxometalate with dual luminescent center has the chemical formula: [N(CH3)4] 10.334 H 0.666 Na2[Eu 0.2 Tb 3.8 (H2O) 10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O; abbreviated as Eu 0.2 Tb 3.8 4W 42 , where HAc = acetic acid and H3MA = D,L-malic acid.

[0027] The above contains Tb 3+ and Eu 3+ The preparation process of the polyoxometalate with dual luminescent centers is similar to the above method, and the specific preparation method involves the following steps: Under stirring conditions, sodium tungstate dihydrate (4.003 g, 12.136 mmol), sodium selenite (0.102 g, 0.590 mmol), tetramethylammonium chloride (1.006 g, 9.179 mmol), and D,L-malic acid (0.307 g, 2.290 mmol) were dissolved in 30 mL of distilled water. 500 μL of glacial acetic acid was added under continuous stirring. After stirring for 15 min, terbium nitrate hexahydrate (0.28522 g, 0.6296 mmol) and europium nitrate hexahydrate (0.01478 g, 0.0332 mmol) were added to the above solution in sequence. 6 mol·L –1 The pH of the reaction system was adjusted to 4.8 with HCl, and the mixture was stirred for 15 min. The mixture was heated in a 90 °C water bath for 2 h, cooled and allowed to stand for 24 h, filtered, and the filtrate was heated at 5–7 o C and allowed to stand for several hours to evaporate, colorless block crystals were precipitated, which was the target product polyoxometalate material (Eu 0.2 Tb 3.8 4W 42 ).

[0028] The present invention measured and characterized the crystal structure of the polyoxometalate prepared in Example 1 above, as follows: The two rare earth-tungsten cluster-bridged polyoxometalates are isostructural compounds, colorless blocky crystals, and belong to the trigonal system. R -3c space group, so [N(CH3)4] 10.334 H 0.666 Na2[Eu4(H2O) 10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O (Eu4Se4W 42 ) is used as a representative to describe the structure of this type of compound. The unit cell parameters of the compound are a = 34.037(7) Å, b = 34.037(7) Å, c = 136.36(3) Å, α = 90º, β= 90º, γ = 120º, V = 136812(48) Å 3 .like Figure 1 As shown in a–b, the anion skeleton contains two identical dimers {[Eu2(H2O)5W3O6][SeW9O 33 ]2} 4–unit, in a twisted manner through the ligand and [W2O 11 ] 10– The oxygen bridges of the fragments are connected. α -SeW9O 33 ] 8– If the fragment is simplified into a sphere, then "Se1, Se2, Se1A" and "Se1, Se1A, Se2A" respectively form two planes with an included angle of 72.935° ( Figure 1 c). The compound can also be viewed as consisting of four staggered [B- α -SeW9O 33 ] 8– The fragment is stabilized by a double ligand bridged rare earth-tungsten cluster [Eu4(H2O) 10 W6O 13 (H2MA)2Ac] 19+ Multi-metal clusters connected ( Figure 1 d–e). Two adjacent [B- α -SeW9O 33 ] 8– The fragments share {WO6} units, forming an open " C -type" sandwich dimer fragment, providing ample space for the embedding of multi-metal clusters. [Eu4(H2O) 10 W6O 13 (H2MA)2Ac] 19+ The multimetallic cluster contains four Eu 3+ ion, a common vertex [W2O 11 ] 10– fragment, four additional {WO6} octahedra and two flexible organic ligands (one Ac – and two H2MAs – ), whose skeleton exhibits an airplane-like configuration ( Figure 1 f). It is worth noting that the two carboxyl oxygen atoms of the acetate ligand simultaneously bind to [W2O 11 ] 10– Fragment coordination, forming a stable "C1–O76–W1–O4–W1A–O76A" six-membered ring ( Figure 1 g). The long-chain malic acid ligand contains one hydroxyl (–OH) and two carboxyl (–COOH) coordination sites. The carboxyl group at one end provides an oxygen atom to bind to Eu 3+ ion coordination, while the hydroxyl and carboxyl groups at the other end jointly provide two oxygen atoms to coordinate with one W atom ( Figure 1 g). Thus, it can be seen that flexible organic ligands, with their abundant binding sites and the ability to twist and rotate, can flexibly chelate with metal centers and play a key bridge role in the assembly process of polyoxometalates.– and H2MA – After the ligand is removed, two [Eu2(H2O)5W3O6] bridged by O4 atoms are obtained. 12+ Fragment. In [Eu2(H2O)5W3O6] 12+ In the fragment, three tungsten atoms are located in the middle, and two europium ions are located at the upper and lower ends, forming a trigonal bipyramid configuration ( Figure 1 h).

[0029] The present invention is to polyoxometalate Eu4Se4W 42 or Tb4Se4W 42 The infrared spectrum ( Figure 2 ), thermogravimetric curve ( Figure 3 ) and X-ray powder diffraction ( Figure 4 ), and including Tb 3+ and Eu 3+ Infrared spectrum and X-ray powder diffraction pattern of polyoxometalates with dual luminescence centers ( Figure 5 ) were analyzed.

[0030] Figure 2 Four groups of characteristic vibration peaks appear at 969 and 970 cm –1 , 890 and 861–860 cm –1 , 782 and 787 cm –1 , 740 and 742 cm –1 , corresponding to Ln4Se4W 42 (Ln = Eu 3+ or Tb 3+ ) skeleton W−O t , W−O b , Se−O and W−O c Asymmetric stretching vibration of the bond. Located at 3470–3430 cm –1 and 1631–1635 cm –1 The absorption vibration peaks in the range can be attributed to the stretching and bending vibrations of water molecules. – The asymmetric stretching vibration of the group appears at 1635–1631 cm –1 However, it is covered by the strong absorption band of water molecules; while 1450–1371 cm –1 The peak at represents CO2 – The symmetrical stretching vibration of the group corresponds to the acetate and malate ligands present in the molecule. In addition, the 3037 and 3039 cm –1 and 1485 and 1486 cm –1 The vibration peak at 453 cm corresponds to the stretching and bending vibration of the –CH3 group, while the –1The vibration peaks correspond to the bending vibrations of the C–N bonds, indicating the presence of tetramethylammonium cations in the structure.

[0031] Figure 3 The target material is Ln4Se4W 42 (Ln = Eu 3+ or Tb 3+ ) are 25–290 o C. 290–650 o C. 650–1000 o C undergoes a three-step weight loss process. The first step weight loss is 12.74% (theoretical value is 12.51%) and 12.29% (theoretical value is 12.49%), corresponding to the loss of 86 crystal water molecules and 10 coordinated water molecules. The second step weight loss is 9.88% (theoretical value is 9.62%) and 9.56% (theoretical value is 9.60%), corresponding to the loss of 10.33 tetramethylammonium cations, 0.33 protons, 1 Ac – Ligand and 2 H2MA – Loss of ligands. As the temperature continues to rise, the target material framework collapses.

[0032] Figure 4 The polyoxometalate Ln4Se4W of the present invention is given in 42 X-ray powder diffraction pattern of; Ln = Eu 3+ (a) or Tb 3+ (b) As can be seen in the figure, the experimental diffraction data of the target material is in good agreement with the simulated diffraction pattern of its single crystal structure, indicating that the target material has a high purity.

[0033] Figure 5 In, Eu 0.2 Tb 3.8 4W 42 The infrared vibration peaks and powder diffraction patterns of the target materials are basically consistent with those of the target materials, indicating that their structures are the same.

[0034] Figure 6 In this study, the steady-state transient fluorescence spectrometer was used to test the Eu 0.2 Tb 3.8 4W 42 Fluorescence behavior of the material (5 mg / mL) in water. Under 378 nm excitation, the emission spectrum of the material produced Eu at 593, 614, 651, and 702 nm. 3+ The characteristic emission peak of the ion is attributed to 5 D0→ 7 F J (J = 1–4) transitions, generating Tb at 489 and 544 nm.3+ The characteristic emission peak of the ion is attributed to 5 D4→ 7 F J (J = 6–5) transition, indicating that Eu 3+ and Tb 3+ ions are embedded in the same lattice at the same time, and we have successfully constructed a structure containing Tb 3+ and Eu 3+ Polyoxometalates with dual luminescent centers.

[0035] Application test: The present invention obtains Tb 3+ and Eu 3+ Eu polyoxometalate with dual luminescence centers 0.2 Tb 3.8 4W 42 Research on the use of ratiometric fluorescence sensor for DPA detection.

[0036] We recorded the fluorescence response of the material when different concentrations of DPA were added. Figure 7 As shown in a and 7b, as the DPA concentration gradually increased from 0 to 120 μM, Tb 3+ The emission peak intensity of Eu 3+ The emission peak intensity of the ions remains relatively unchanged, which makes the material a ratiometric fluorescence sensor (based on the ratio of the fluorescence emission intensity at 545 nm and 616 nm). I 545 / I 616 is the signal) for quantitative detection of DPA. In the entire concentration range, I 545 / I 616 The ratio has a good linear relationship with the DPA concentration, which is consistent with the equation I 545 / I 616 = 0.0086 C + 0.2763 ( Figure 7 c), the detection limit was 1.58 μM, which was significantly lower than the infectious dose of spores (60 μM), which means that Eu 0.2 Tb 3.8 4W 42 The material can be used as a ratiometric sensor to detect DPA reliably and sensitively.

[0037] To evaluate its selectivity and anti-interference performance, we screened a series of analytes, such as 2-pyridinecarboxylic acid (2-PA), 2,3-pyridinedicarboxylic acid (2,3-PDCA), 2,4-pyridinedicarboxylic acid (2,4-PDCA), 2,5-pyridinedicarboxylic acid (2,5-PDCA), terephthalic acid ( p -PA), benzoic acid (BA), cysteine ​​(Cys), benzoic acid (TMA), 2,3-quinolinedicarboxylic acid (2,3-QDC) and D-alanine (D-Ala) were tested under the same experimental conditions for their effects on Eu 0.2 Tb 3.8 4W 42 The effect of luminescence, see the results Figure 8 .like Figure 8 As shown, after adding equal amounts of interfering substances (120 μM), I 545 / I 616 The ratio remains basically unchanged ( Figure 8 a), the ratio increased significantly only after the addition of DPA and was not affected by interferences ( Figure 8 b), indicating that the ratiometric sensor has excellent selectivity and anti-interference ability.

[0038] In addition, the fluorescence lifetime of the material showed a sharp upward trend with the increase of DPA concentration, reaching a maximum value of 1262.35 μs ( Figure 9 ). Compared with Eu 3+ ions, Tb 3+ The energy levels of ions and DPA are more closely matched ( Figure 10 ), so when DPA and Eu 0.2 Tb 3.8 4W 42 Interacts and preferentially replaces Tb 3+ Water molecules in the ion coordination environment, and Tb 3+ The ion chelation reduces the quenching caused by water molecules, resulting in a significant enhancement of fluorescence emission and lifetime.

[0039] In summary, the present invention prepares and reports rare earth-tungsten cluster-bridged polyoxometalates by a one-step in situ assembly method from simple raw materials, and uses a chemical doping strategy to regulate the Tb 3+ / Eu 3+ A polyoxometalate with dual luminescent centers was synthesized in a ratiometric manner and can be used as a ratiometric fluorescence sensor for sensitive and rapid detection of trace amounts of DPA. This invention not only provides a facile route for synthesizing novel rare-earth-substituted polyoxometalates, but also pioneers the application of polyoxometalates as self-calibrating fluorescence sensors in fields such as biological detection and environmental monitoring.

Claims

1. Rare earth-tungsten cluster-bridged polyoxometalates, characterized in that: The chemical formula of the polyoxometalate is [N(CH3)4] 10.334 H 0.666 Na2[Ln4(H2O) 10 W6O 13 (H2MA)2Ac][SeW9O 33 ]4·86H2O, where Ln = Eu 3+ and Tb 3+ ; HAc = acetic acid, H3MA = D,L-malic acid.

2. The method for preparing the rare earth-tungsten cluster bridged polyoxometalate according to claim 1, characterized in that: The steps include: Under stirring conditions, sodium tungstate dihydrate, sodium selenite, tetramethylammonium chloride and D, L-malic acid were dissolved in distilled water, and then glacial acetic acid was added. After stirring for 15-30 minutes, rare earth nitrate was added, and the pH of the reaction system was adjusted to 4.5-5.

0. After stirring for 15-30 minutes, the reaction mixture was placed at 80-95°C. o Heat in a water bath at 5–7°C for 1.5–2.5 h, cool, filter, and place the filtrate at 5–7°C. o The crystals precipitated under C are rare earth-tungsten cluster-bridged polyoxometalates; The rare earth nitrate is composed of a mixture of europium nitrate hexahydrate and terbium nitrate hexahydrate.

3. The method for preparing the rare earth-tungsten cluster bridged polyoxometalate according to claim 2, characterized in that: The molar ratio of the sodium tungstate dihydrate, sodium selenite, tetramethylammonium chloride, D,L-malic acid, glacial acetic acid, and rare earth nitrate is 7.6–12.2: 0.46–0.59: 9.1–10.9: 1.8–2.6: 8.1–9.1: 0.65–0.

85.

4. The method for preparing the rare earth-tungsten cluster bridged polyoxometalate according to claim 2, wherein: The rare earth nitrate is composed of a mixture of europium nitrate hexahydrate and terbium nitrate hexahydrate in a molar ratio of 0.05:0.

95.

5. Use of the rare earth-tungsten cluster bridged polyoxometalate according to claim 1 as a ratiometric fluorescence sensor.

6. The use according to claim 5, characterized in that Used for detection of DPA concentration in water.

7. The use according to claim 6, characterized in that Under 378 nm excitation, the emission spectrum of rare earth-tungsten cluster-bridged polyoxometalates shows Tb 3+ and Eu 3+ Characteristic emission peaks of ions; With the increase of DPA concentration, Tb 3+ The fluorescence intensity of Eu 3+ The fluorescence intensity of Tb 3+ and Eu 3+ The ratio change of fluorescence intensity was used to achieve sensitive detection and concentration determination of DPA.

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