A fluorescent silver nanocluster material and a preparation method and application thereof

Abstract

The application discloses a fluorescent silver nanocluster material and a preparation method and application thereof, and the molecular formula of the fluorescent silver nanocluster material is L x [Ag8(Li3Nb 81 O 225 )2], wherein L is a counter cation or a cationic group, and 1 < x ≤ 78; the fluorescent silver nanocluster material is composed of [Ag8(Li3Nb 81 O 225 )2] anion clusters and corresponding counter cations or cationic groups; the fluorescent silver nanocluster material is composed of two {Li3Nb 81 O 225} units, a sandwich type cluster with an eight-core double-capped octahedral silver cluster {Ag8} and different counter cations or cationic groups; the fluorescent silver nanocluster material has very good stability in an atmospheric environment and in an aqueous solution, has a solid-state fluorescence with a temperature change response, can reversibly change between orange light and yellow light, has a liquid-state fluorescence with an acid-base change response, can reversibly change between red light, orange light, yellow light and quenching, and has the advantages of a simple synthesis process, good crystallinity and the like.

Description

Technical Field

[0001] This invention relates to the field of anti-counterfeiting materials and synthesis technology, specifically to a fluorescent silver nanocluster material and its preparation method and application. Background Technology

[0002] The application of fluorescent codes or patterns is one of the most effective methods for advanced anti-counterfeiting due to its characteristics of being difficult to replicate, easy to read, low-cost, convenient, and visually appealing. The security of anti-counterfeiting patterns and designs largely depends on the materials used. Currently, typical anti-counterfeiting patterns employ small molecules that emit a single color, and in rare cases, dual-color emission exists. Most anti-counterfeiting patterns can be correctly read by ultraviolet light excitation. These anti-counterfeiting designs are not truly secure; counterfeiters can easily find substitutes to imitate or easily crack them. Materials that can change their emission color in response to external stimuli are, on the one hand, difficult to replicate, and on the other hand, offer better design flexibility and security. Therefore, developing an anti-counterfeiting material that exhibits a fluorescent color change in response to external stimuli has significant application value.

[0003] Ligand-protected silver nanoclusters are a new class of luminescent nanomaterials. These luminescent silver nanoclusters, ranging from a few to hundreds of atoms, are a novel type of chromophore, possessing advantages such as ease of preparation, ultrafine size, low toxicity, and excellent photostability, showing broad application prospects in lighting, imaging, sensing, and anti-counterfeiting. Polyoxometalates, or polyacids for short, typically refer to inorganic oxometalates of high-valence transition metals such as vanadium, niobium, tantalum, molybdenum, and tungsten, which undergo condensation and dehydration to form polynuclear metal cluster structures. They possess unique structures (nanoscale size, oxygen-rich surfaces) and properties (including tunable acidity / basicity, delocalized electrons, photosensitive chemistry, and reversible redox properties). These unique structures and physicochemical properties make polyoxometalates an important class of ligands that can be used to protect silver nanoclusters.

[0004] Compared with various known ligand-protected silver nanoclusters luminescent materials, silver nanoclusters protected by niobium polyacids have many unique advantages: 1) Most silver nanoclusters in traditional luminescent materials are protected by flexible organic ligands, which have poor stability, making the materials difficult to resist external influences and prone to bleaching. Niobium polyacids, as a type of redox inert and highly negatively charged anionic cluster, can endow silver nanoclusters with greater stability and unique optical properties; 2) Most traditional luminescent materials are poorly soluble in water, and materials that are stably soluble in water and have good anti-counterfeiting security design are extremely rare. Therefore, designing and synthesizing silver nanocluster materials with good stability, unique optical properties, and water solubility for optical anti-counterfeiting is both challenging and of great practical significance. Summary of the Invention

[0005] To solve the above problems, the present invention provides a fluorescent silver nanocluster material, a preparation method and use thereof.

[0006] The present invention adopts the following technical solutions:

[0007] A fluorescent silver nanocluster material, the molecular formula of the fluorescent silver nanocluster material is L x [Ag8(Li3Nb 81 O 225 )2], wherein L is a counter cation or a cationic group, and 1 < x ≤ 78; the fluorescent silver nanocluster material is composed of [Ag8(Li3Nb 81 O 225 )2] anionic cluster and corresponding counter cations or cationic groups.

[0008] Preferably, the fluorescent silver nanocluster material is formed by two {Li3Nb 81 O 225} units co-sandwiching an octanuclear double-capped octahedral silver cluster {Ag8} to form a sandwich-type cluster, together with different counter cations or cationic groups.

[0009] Preferably, the counter cation or cationic group is K + , Na + , Cs + , H + , TBA + , Li + , Ba 2+ one or more of the above; guest solvents exist in cluster molecules of the fluorescent silver nanocluster material, and the guest solvents include H2O.

[0010] Preferably, the excitation spectrum of the fluorescent silver nanocluster material shows that the solid-state excitation wavelength range is stably 200-500 nm, and the maximum emission wavelengths are stably at 600±20 nm and 750±20 nm; the excitation spectrum of the fluorescent silver nanocluster material shows that the aqueous solution-state excitation wavelength range is stably 200-500 nm, and the maximum emission wavelength is stably at 750±20 nm.

[0011] Preferably, when excited by light within a certain excitation wavelength range at room temperature, the fluorescent silver nanocluster material has an orange-red fluorescence emission characteristic.

[0012] Preferably, when excited at a certain excitation wavelength, the fluorescent silver nanocluster material has a color-changing fluorescence response to different temperature conditions; when excited at a certain excitation wavelength, the fluorescent silver nanocluster material has a color-changing fluorescence response to different acid-base conditions.

[0013] A preparation method of a fluorescent silver nanocluster material, specifically comprising the following steps:

[0014] S1, Synthesis of niobate precursor K7HNb6O 19 ·13H2O;

[0015] S2, nitrate and niobate precursor K7HNb6O 19 · 13H2O, borate, first solvent, and second solvent are added to a polytetrafluoroethylene reactor and stirred at room temperature to mix them evenly. Then, bicarbonate and silver salt are added, and the mixture is stirred at room temperature and then sealed.

[0016] S3. Place the polytetrafluoroethylene kettle in an oven for heating reaction at a temperature of 100℃-200℃ to obtain fluorescent silver nanoclusters.

[0017] Preferably, the nitrate is one or more of potassium nitrate, sodium nitrate, and barium nitrate; the borate is one or more of lithium tetraborate, sodium tetraborate, and potassium tetraborate; the first solvent is deionized water; the second solvent is one or more of ammonia and acetonitrile; the bicarbonate is one or more of sodium bicarbonate and potassium bicarbonate; and the silver salt is one or more of silver trifluoroacetate and silver nitrate.

[0018] Preferably, the nitrate and niobate precursor K7HNb6O in step S2 19 The molar ratio of ·13H2O, lithium tetraborate, sodium bicarbonate, and silver salt is 650:216:160:1071:141.

[0019] An application of a fluorescent silver nanocluster material, wherein the fluorescent silver nanocluster material exhibits a reversible fluorescence response to external stimuli; the silver nanocluster material possesses fluorescence properties that respond to temperature changes and changes in solution acidity / alkalinity, and is applied in the fields of information encryption, optical anti-counterfeiting, solvent probes, and sensing.

[0020] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0021] 1. The fluorescent silver nanocluster material prepared by this invention has excellent water solubility and stability under atmospheric conditions, providing an important guarantee for exploring stable anti-counterfeiting materials.

[0022] 2. The fluorescent silver nanocluster material prepared by this invention can be used to design a highly secure anti-counterfeiting material by rapidly changing fluorescence in response to temperature and pH.

[0023] 3. This invention employs a simple solvothermal treatment process to synthesize fluorescent silver nanoclusters in a one-pot method. The synthesis process is simple, with good crystallinity and high yield. The fluorescent silver nanoclusters can be used as anti-counterfeiting materials and applied in the fields of information encryption, optical anti-counterfeiting, solvent probes, and sensing. Attached Figure Description

[0024] Figure 1 These are unit cell parameters obtained in some embodiments of the fluorescent silver nanocluster material prepared according to the present invention;

[0025] Figure 2 The image shows a physical crystal of the fluorescent silver nanocluster material prepared according to Example 1.

[0026] Figure 3 This is a crystal structure diagram of the fluorescent silver nanoclusters prepared according to Example 1;

[0027] Figure 4 The image shows the electrospray ionization mass spectrum (ESI-MS) of the fluorescent silver nanoclusters prepared according to Example 1.

[0028] Figure 5 This is a matching diagram of the experimental signal peaks and simulated peaks from the electrospray ionization mass spectrum of the fluorescent silver nanoclusters prepared according to Example 1;

[0029] Figure 6 This is a high-angle annular dark-field scanning transmission electron microscope (HADDF-STEM) image of the fluorescent silver nanoclusters prepared according to Example 1 in aqueous solution.

[0030] Figure 7 The infrared spectra of the fluorescent silver nanoclusters prepared according to Example 1 before and after storage in an atmospheric atmosphere;

[0031] Figure 8 The UV-Vis spectra of the fluorescent silver nanoclusters prepared according to Example 1 before and after storage in an atmospheric atmosphere;

[0032] Figure 9 The fluorescence emission spectrum of the fluorescent silver nanoclusters prepared according to Example 1 in the solid state is shown.

[0033] Figure 10 The fluorescence emission spectrum of the fluorescent silver nanoclusters prepared according to Example 1 in aqueous solution is shown.

[0034] Figure 11 This is a luminescence image of the fluorescent silver nanoclusters prepared according to Example 1 as a function of temperature in the solid state;

[0035] Figure 12The fluorescence emission spectrum of the fluorescent silver nanoclusters prepared according to Example 1 as a function of temperature in the solid state is shown.

[0036] Figure 13 The image shows the luminescence of the fluorescent silver nanoclusters prepared according to Example 1 in aqueous solution as pH changes.

[0037] Figure 14 The fluorescence emission spectrum of the fluorescent silver nanoclusters prepared according to Example 1 in aqueous solution as a function of pH is shown. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following examples are exemplary and should not be construed as limiting the invention.

[0039] In this invention, a fluorescent silver nanocluster material is provided, which is composed of [Ag8(Li3Nb] 81 O 225 [2] The anionic cluster is composed of a corresponding countercation or cationic group. This anionic cluster consists of two {Li3Nb} groups. 81 O 255 The unit is composed of a sandwich-type cluster consisting of an octahedral silver cluster {Ag8} with an octahedral double capped core and different counter cations or cationic groups.

[0040] In this invention, countercations refer to cations or cationic groups used to balance the negative charge of anionic clusters, including but not limited to K. + Na + Cs + H + TBA + Li + Ba 2+ One or more common equilibrium charges in the system.

[0041] In this invention, the fluorescent silver nanoclusters may contain or lack guest solvent molecules depending on their different reaction solvents and the different degrees of water loss of the crystals.

[0042] In some embodiments, the fluorescent silver nanoclusters have different cell parameters and crystallize in different space groups, but the silver nanoclusters in these embodiments are still composed of [Ag8(Li3Nb]... 81 O 225 [2] Anionic clusters are composed of corresponding countercationic cation groups. Therefore, the fluorescent silver nanoclusters described in this invention have multiple cell parameters and crystallize in multiple space groups due to different cell stacking modes. Figure 1As shown. This can be understood as the fluorescent silver nanoclusters being composed of [Ag8(Li3Nb]... 81 O 225 [2] Anionic clusters, different counter cations, and a certain amount of guest solvent may be present and crystallize through different stacking methods.

[0043] The pharmaceutical reagents used in the examples provided below are all commercially available or can be synthesized using known methods.

[0044] Example 1: H 34 Na 32 K 12 [Ag8(Li3Nb 81 O 225 Preparation of 6H2O:

[0045] 1) Synthesis of niobate precursor K7HNb6O 19 ·13H2O, synthesized according to the method provided in the literature "Inorganic Chemistry" (Vol. 18, 1979, pp. 93-103).

[0046] 2) Weigh out the K7HNb6O obtained in 1) sequentially. 19 ·13H2O (0.432 mmol, 0.590 g), KNO3 (1.306 mmol, 0.132 g), and Li2B4O7 (0.320 mmol, 0.054 g) were added to a 23 mL polytetrafluoroethylene (PTFE) reactor. 8 mL of deionized water and 0.2 mL of ammonia were added, and the mixture was stirred for 30 minutes. Then, NaHCO3 (2.142 mmol, 0.180 g) and AgNO3 (0.282 mmol, 0.048 g) were weighed out, and the mixture was stirred at room temperature for 1 hour to ensure homogeneity. The PTFE reactor was then placed in a constant temperature oven for a solvothermal reaction at 160 °C for 3 days. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The crystals were then extracted, vacuum dried, and 0.2-3.3 mm golden-yellow rhomboid crystals were obtained (see...). Figure 2 This is Example 1, whose unit cell parameters are: α=β=90°, γ=120°.

[0047] Characterization and performance testing of the crystals obtained in Example 1:

[0048] (1) Crystal structure determination: Select a single crystal of suitable size, regular shape and transparency under a microscope, and use a Rigaku HyPix-6000HE diffractometer at 100K to monochromate Ga-Kα rays using a graphite monochromator. The crystal was used as an incident light source to collect diffraction data. In the structural analysis, the Shelextl-2018 program was used to directly analyze and refine the crystal structure. Simultaneously, non-hydrogen atoms and their anisotropic treatment parameters were corrected using the full-matrix least squares method. All hydrogen atoms were obtained through theoretical hydrogenation. The resulting crystal structure is shown below. Figure 3 As shown, some crystallographic data and refinement parameters are shown in Table 1.

[0049] Table 1: Crystal Parameter Table of Example 1

[0050]

[0051]

[0052] (2) Dispersion / Stability Characterization: The stability of the fluorescent silver nanoclusters prepared in Example 1 in aqueous solution was studied by electrospray ionization mass spectrometry (ESI-MS), such as... Figure 4 and Figure 5 As shown, six groups with different negative charges (13) were observed in the ESI-MS spectrum. - 12 - 11 - 10 - 9 - 8 - The signal peak of ) is in very good agreement with the theoretical m / z value of the corresponding polyanion cluster (see Table 2). Furthermore, such as Figure 6 As shown, high-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM) images demonstrate that the fluorescent silver nanoclusters prepared in Example 1 can be uniformly dispersed in aqueous solution, with an average diameter of approximately 3.18 nm, which is close to the size determined by SCXRD analysis. Therefore, the solubility and excellent stability of the fluorescent silver nanoclusters prepared in Example 1 provide a unique opportunity for systematically studying their optical behavior in aqueous solution.

[0053] Table 2: Mass spectral peak fitting and related molecular formulas of the fluorescent silver nanoclusters prepared in Example 1 under different valence states.

[0054]

[0055]

[0056] (3) Infrared spectroscopy and ultraviolet-visible spectroscopy characterization: such as Figure 7 and Figure 8 As shown, the fluorescent silver nanoclusters prepared in Example 1 exhibit fluorescence at 3000-3500 cm⁻¹. -1 and 1645cm -1 The absorption peaks appearing at 1000-400 cm⁻¹ are attributed to the characteristic absorption of water molecules in the structure.-1 Several absorption peaks appearing within the range can be attributed to characteristic absorption peaks of Nb-O bonds. The fluorescent silver nanoclusters prepared in Example 1 were placed in an atmospheric environment for 8 months, and their infrared and ultraviolet-visible spectra did not show significant changes, indicating their good stability.

[0057] (4) Fluorescence spectroscopy characterization: such as Figure 9 and Figure 10 As shown, the solid-state and aqueous-state excitation spectra of the fluorescent silver nanoclusters prepared in Example 1 were measured at an emission wavelength of 750 nm. The excitation spectra showed that the optimal excitation wavelength for the solid state was 456 nm; the aqueous state exhibited three excitation wavelengths of 334 nm, 448 nm, and 511 nm, with the optimal excitation wavelength being 448 nm. When the fluorescent silver nanoclusters prepared in Example 1 were excited again at the optimal excitation wavelength, the solid state showed two emission peaks at 600 nm and 750 nm, exhibiting orange fluorescence; the aqueous state showed a distinct emission peak at 750 nm, also exhibiting orange fluorescence.

[0058] (5) Exploration experiment on optical properties with anti-counterfeiting performance:

[0059] 1) Reversible fluorescence experiment of the temperature response of the fluorescent silver nanoclusters prepared in solid state Example 1: The emission spectrum of the fluorescent silver nanoclusters prepared in solid state as a function of temperature was measured using an FLS980 fluorescence spectrometer. The image of this reversible emission transition was recorded using a Canon Eos 4000D. Figure 11 and Figure 12 As shown, as the temperature decreased from 298K to 83K, the emission intensity at the 750nm wavelength did not increase significantly, while the emission intensity at the 600nm wavelength continuously increased. This caused the emission color of the fluorescent silver nanoclusters prepared in Example 1 to change from orange to yellow. As shown in the figure, when the temperature returned to 298K from 83K, the emission color of the fluorescent silver nanoclusters prepared in Example 1 also returned from yellow to orange. Therefore, the fluorescent silver nanoclusters prepared in Example 1 can serve as an effective temperature-dependent anti-counterfeiting material.

[0060] 2) Reversible fluorescence test of the pH response of the fluorescent silver nanoclusters prepared in Example 1 in aqueous solution: The emission spectrum of the fluorescent silver nanoclusters prepared in Example 1 in aqueous solution as a function of pH was measured using an FLS980 fluorescence spectrometer. The pH of the solution was adjusted using NaOH and HCl. Figure 13 and Figure 14As shown, when pH increases, the emission intensity at 750 nm decreases, while the emission at 600 nm disappears completely, causing the solution's luminescence color to change to red. When pH decreases, the emission intensity at 600 nm continuously increases, while the emission intensity at 750 nm continuously decreases, causing the luminescence color to change from red to orange and then to yellow. When the pH decreases to 3.3, fluorescence quenching occurs. Luminescence is restored upon the addition of NaOH. Therefore, the fluorescent silver nanoclusters prepared in Example 1 can serve as an effective pH-dependent anti-counterfeiting material.

[0061] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fluorescent silver nanocluster material, characterized in that: The molecular formula of the fluorescent silver nanocluster material is L x [Ag8(Li3Nb 81 O 225 )2], wherein L is a counter cation or a cationic group, and 1 < x ≤ 78; the fluorescent silver nanocluster material consists of [Ag8(Li3Nb 81 O 225 )2] anionic cluster and corresponding counter cation or cationic group.

2. The fluorescent silver nanocluster material as described in claim 1, characterized in that: The fluorescent silver nanocluster material consists of two {Li3Nb} 81 O 225 The unit is composed of a sandwich-type cluster consisting of an octahedral silver cluster {Ag8} with an octahedral double capped core and different counter cations or cationic groups.

3. The fluorescent silver nanocluster material as described in claim 1, characterized in that: The counter cation or cationic group is K. + Na + Cs + H + TBA + Li + Ba 2+ One or more of the following; the fluorescent silver nanoclusters contain a guest solvent, which includes H2O.

4. The fluorescent silver nanocluster material as described in claim 1, characterized in that: The excitation spectrum of the fluorescent silver nanoclusters shows that its solid-state excitation wavelength range is stable at 200-500 nm, and its maximum emission wavelength is stable at 600 ± 20 nm and 750 ± 20 nm; the excitation spectrum of the fluorescent silver nanoclusters shows that its aqueous-state excitation wavelength range is stable at 200-500 nm, and its maximum emission wavelength is stable at 750 ± 20 nm.

5. The fluorescent silver nanocluster material as described in claim 1, characterized in that: The fluorescent silver nanoclusters exhibit orange-red fluorescence emission characteristics when excited by light within a certain wavelength range at room temperature.

6. The fluorescent silver nanocluster material as described in claim 1, characterized in that: The fluorescent silver nanoclusters exhibit color-changing fluorescence responses to different temperature conditions when excited at a certain excitation wavelength; the fluorescent silver nanoclusters also exhibit color-changing fluorescence responses to different acid and alkaline conditions when excited at a certain excitation wavelength.

7. A method for preparing fluorescent silver nanoclusters as described in any one of claims 1-6, characterized in that, Specifically, the following steps are included: S1, Synthesis of niobate precursor K7HNb6O 19 ·13H2O; S2, nitrate and niobate precursor K7HNb6O 19 · 13H2O, borate, first solvent, and second solvent are added to a polytetrafluoroethylene reactor and stirred at room temperature to mix them evenly. Then, bicarbonate and silver salt are added, and the mixture is stirred at room temperature and then sealed. S3. Place the polytetrafluoroethylene kettle in an oven for heating reaction at a temperature of 100℃-200℃ to obtain fluorescent silver nanoclusters.

8. The method for preparing a fluorescent silver nanocluster material as described in claim 7, characterized in that: The nitrate is one or more of potassium nitrate, sodium nitrate, and barium nitrate; the borate is one or more of lithium tetraborate, sodium tetraborate, and potassium tetraborate; the first solvent is deionized water; the second solvent is one or more of ammonia and acetonitrile; the bicarbonate is one or more of sodium bicarbonate and potassium bicarbonate; and the silver salt is one or more of silver trifluoroacetate and silver nitrate.

9. The method for preparing a fluorescent silver nanocluster material as described in claim 8, characterized in that: The nitrate and niobate precursor K7HNb6O mentioned in step S2 19 The molar ratio of ·13H2O, lithium tetraborate, sodium bicarbonate, and silver salt is 650:216:160:1071:

141.

10. An application of the fluorescent silver nanocluster material as described in any one of claims 1-6, characterized in that: The fluorescent silver nanoclusters exhibit reversible fluorescence response to external stimuli; the silver nanoclusters also possess fluorescence properties that respond to temperature changes and changes in solution acidity / alkalinity, and can be applied in the fields of information encryption, optical anti-counterfeiting, temperature sensing, and pH sensing.

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