Preparation method of metal nanocluster

Abstract

The invention relates to the technical field of chemistry, and discloses a preparation method of a metal nanocluster, which comprises the following steps: synthesis of an Au nanocluster, synthesis of an AuAg nanocluster, synthesis of an Au-Zn nanocluster, synthesis of an Au-Zn / Ag nanocluster, synthesis of an Au-Zn / Ag / R nanocluster, and synthesis of an Au-Zn / Cu / R nanocluster. The gradual cation introduction not only leads to the shrinkage of the vibration of the overall structure, but also accelerates the transition of shell-core electrons, and particularly, Tb < 3 + > as an inherent stepped energy level structure provides a jumping platform for excited electrons. Therefore, the PLQY can be remarkably improved from 51.2%, 83.4% to 99.5%, and the PLQY can be remarkably improved from 51.2% to 83.4%.

Description

Technical Field

[0001] The invention relates to the field of chemical technology, and in particular to a method for preparing metal nanoclusters. Background Art

[0002] Monolayer protected metal nanoclusters (NCs) consist of a few to hundreds of metal atoms with discrete electronic energy levels, thus exhibiting fascinating molecular-like photoluminescence. In general, metal core-dominated fluorescence with small Stokes shift, narrow emission band and short decay lifetime is increasingly accepted in lighting, sensing, imaging and other fields. However, achieving high photoluminescence quantum yield (PLQY) is still a great challenge at this stage. On the one hand, in addition to the intrinsic metal core vibration, the vibration of the interfacial short motifs and terminal ligand groups can lead to the overall structural vibration of metal NCs. On this basis, low-frequency and high-frequency vibrations can be induced in the metal core and short motifs, respectively. The coupling of multiple vibrations and excited-state electrons can generate additional non-radiative channels, which ultimately quench the fluorescence of metal NCs. On the other hand, manipulating the electron transfer process from the surface motifs with high light absorption ability to the emission center of the metal core is a recognized potential strategy, but it is still challenging to adjust the electron transfer dynamics (e.g., the pathway and rate of radiative relaxation) due to its poor functionalization. Considering these limitations, the PLQY level of core-controlled photoluminescence in metal NCs is low (generally <10%). To date, it remains an important task to modulate the overall structural motion and electron transfer dynamics of metal NCs to meet the growing demand for emission intensity enhancement in the colloidal state.

[0003] Cationic additive engineering has been recognized as an effective strategy to tune the structural properties (e.g., frequency, anisotropy, polarity, and size of structural motions) of various chromophores (from inorganic ions, organic molecules, metal-organic complexes, nano / microcrystals to macroscopic solids), thereby adjusting their electronic structures and excited-state electronic dynamics, ultimately affecting their luminescence properties. In particular, metal NCs are described as a “superatomic complex” model with closed valence electron shells (i.e., 2, 8, 18, 20, etc.). The electron-rich nature makes them highly susceptible to electronic / electrostatic attacks. In addition, the dynamic adsorption-desorption equilibrium of surface ligands, in a “divide and conquer” mode, further deepens the influence on their charge-dependent luminescence properties. Despite the continuous progress in cationic additive-mediated photoluminescent metal NCs, they still have unclear rules in terms of the effect of cationic species on PLQY, especially limited enhancement. Therefore, the research on cationic additive engineering of luminescent metal nanomaterials deserves attention to maximize or even customize their optical properties.

[0004] The PLQY of metal NCs is low, and the metal cations have unclear effects on the electronic structure and excited state electron dynamics of metal NCs. It is indeed necessary to provide a universal method to achieve efficient and stable blue-emitting metal NCs to overcome the above defects in the prior art. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preparing metal nanoclusters.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing metal nanoclusters comprises the following steps: Step 1: Synthesis of Au nanoclusters: Add HAuCl4 aqueous solution into ultrapure water and stir at room temperature to obtain aqueous solution 1, add MPA into aqueous solution 1 and stir until a precipitate appears, then add NaOH into aqueous solution 1 until the precipitate dissolves, and after incubation for 24 hours, obtain an Au NCs solution without photoluminescence characteristics; Step 2: Synthesis of AuAg nanoclusters: HAuCl4 aqueous solution and AgNO3 aqueous solution were added to ultrapure water, stirred at room temperature to obtain aqueous solution 2, MPA was added to aqueous solution 2 and stirred to produce a precipitate, and NaOH was added to aqueous solution 2 until the precipitate was dissolved. After incubation for 24 hours, an AuAg NCs solution without photoluminescence properties was obtained; Step 3: Synthesis of Au-Zn nanoclusters: To trigger the assembly of Au NCs, aqueous Zn(OAc)2 solution was added to the Au NCs solution prepared in step 1. After incubation for 24 h, a bright blue emitting Au-Zn NCs solution was obtained. Step 4: Synthesis of Au-Zn / Ag nanoclusters: To trigger the assembly of AuAg NCs, aqueous Zn(OAc)2 solution was added to the AuAg NCs solution prepared in step 2. After incubation for 24 h, a bright blue emitting Au-Zn / Ag NCs solution was obtained. Step 5: Synthesis of Au-Zn / Ag / R nanoclusters: In order to further assemble AuAg NCs, in addition to the Zn(OAc)2 aqueous solution, a rare earth salt solution was added to the AuAg NCs solution prepared in step 2. After incubation for 24 h, a bright blue emitting Au-Zn / Ag / R NCs solution was obtained; Step 6: Synthesis of Au-Zn / Cu / R nanoclusters: Replace the AgNO3 in step 2 with CuCl2 to prepare an AuCu NCs solution without photoluminescence properties, and add Zn(OAc)2 aqueous solution and rare earth salt solution to the AuCu NCs solution to prepare Au-Zn / Cu / R NCs with bright blue emission.

[0007] Preferably, the molar mass ratio of MPA to HAuCl4 in step 1 is 4:1.

[0008] Preferably, the molar mass ratio of HAuCl4 to AgNO3 in step 2 is 4:1.

[0009] Preferably, the stirring speed in step 1 and step 2 is 600-1000 r / min.

[0010] Preferably, in step 1, NaOH is added to aqueous solution 1 to adjust the pH of aqueous solution 1 to 7.90-8.0; in step 2, NaOH is added to aqueous solution 2 to adjust the pH of aqueous solution 2 to 7.90-8.0.

[0011] Preferably, the molar mass ratio of HAuCl4 to AgNO3 in step 1 and step 2 is one of 2:1, 3:1, 4:1 and 5:1.

[0012] Preferably, the rare earth ions in step 5 and step 6 include Tb 3+ 、Ce 3+ , Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Dy 3+ 、Ho 3+ , Er 3+ 、Tm 3+ , Yb 3+ One of them.

[0013] Preferably, the concentration of rare earth ions in the rare earth salt solution added in step 5 and step 6 is 0.1M.

[0014] The beneficial effects of the present invention are: The present invention proposes a method for preparing metal nanoclusters. The gradual introduction of cations not only leads to the contraction of the overall structural vibration, but also accelerates the transition of shell-core electrons, especially Tb 3+ As its inherent step-like energy level structure provides a jumping platform for excited electrons, it can significantly improve the PLQY from 51.2%, 83.4%, to 99.5%. Moreover, the proposed step-by-step cation addition strategy is universal, and can be used to improve the PLQY by using different coin metal cations (Cu) and other rare earth ions (Ce 3+ , Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Dy 3 +、Ho 3+ , Er 3+、Tm 3+ , Yb 3+ ) can be verified.

[0015] The invention provides a method for preparing metal nanoclusters. The method is simple to operate, less time consuming, and has high photoluminescence quantum yield, high color purity and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The synthesis process and absorption, excitation and emission spectra of the selected Au-Zn, Au-Zn / Ag and Au-Zn / Ag / Tb metal nanoclusters; Figure 2 The calculation of PLQY of the selected Au-Zn, Au-Zn / Ag and Au-Zn / Ag / Tb metal nanoclusters aqueous solutions; Figure 3 X-ray photoelectron spectroscopy (XPS) of the selected Au-Zn, Au-Zn / Ag and Au-Zn / Ag / Tb metal nanoclusters; Figure 4 is the emission spectra of Au-Zn / Ag clusters with different Au:Ag ratios; Figure 5 For different contents of rare earth ions Tb 3+ Emission spectra of doped Au-Zn / Ag / Tb clusters; Figure 6 Transmission electron microscopy images (TEM) of the selected Au-Zn, Au-Zn / Ag and Au-Zn / Ag / Tb metal nanoclusters; Figure 7 To add Zn 2+ 、Ag + and Tb 3+ Dynamic light scattering (DLS) measurements of a series of NCs before and after; Figure 8 Variable temperature PL spectra of selected Au-Zn, Au-Zn / Ag, and Au-Zn / Ag / Tb metal nanoclusters; Fig. 9 Femtosecond transient absorption spectroscopy (fs-TA) of selected Au-Zn, Au-Zn / Ag, and Au-Zn / Ag / Tb metal nanoclusters; Fig.10 The universality of Au-Zn / Ag / R metal nanoclusters with different rare earth ions; Fig.11 The universality of Au-Zn / Cu / R metal nanoclusters with different rare earth ions. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0018] In one embodiment, a method for preparing metal nanoclusters comprises the following steps: 1) Synthesis of Au nanoclusters: 400 μL (50 mM) of HAuCl4 aqueous solution was added to 4.6 mL of ultrapure water and stirred at 600 rpm for 1 min at room temperature. Then, 69 μL of MPA was added to the aqueous solution. The light yellow solution quickly turned white and precipitated, indicating the formation of Au(I)-(MPA) complex. After stirring for 15 min, a certain amount of NaOH (1 M) was added to the reaction solution, and the pH of the aqueous solution was adjusted to 7.90 to dissolve the white precipitate. After incubation for 24 hours, an Au NCs solution without photoluminescence properties was obtained.

[0019] 2) Synthesis of AuAg nanoclusters: 320 μL of HAuCl4 aqueous solution (50 mM) and 80 μL of AgNO3 aqueous solution (50 mM) were added to 4.6 mL of ultrapure water and stirred at 600 rpm for 1 min at room temperature. Then, 69 μL of MPA was added to the above aqueous solution, which quickly turned white and precipitated, indicating the formation of Au(I)@Ag(I)-(MPA) complex. After stirring for 15 min, a certain amount of NaOH (1 M) was added to the reaction solution, and the pH of the aqueous solution was adjusted to 7.90 to dissolve the white precipitate. After incubation for 24 h, an AuAg NCs solution without photoluminescence properties was obtained.

[0020] 3) Synthesis of Au-Zn nanoclusters: To trigger the assembly of Au NCs, 1 mL of Zn(OAc)2 (0.1 M) aqueous solution was added to the Au NCs solution in step 1. After incubation for 24 h, a bright blue emitting Au-Zn NCs solution was obtained.

[0021] 4) Synthesis of Au-Zn / Ag nanoclusters: To trigger the assembly of AuAg NCs, 1 mL of Zn(OAc)2 (0.1 M) aqueous solution was added to the AuAg NCs solution in step 2. After incubation for 24 h, a bright blue emitting Au-Zn / Ag NCs solution was obtained.

[0022] 5) Synthesis of Au-Zn / Ag / R nanoclusters: In order to further assemble AuAg NCs, 100 μL (50 mM) rare earth salt solution was added to the AuAgNCs solution prepared in step 2 in addition to 1 ml (0.1 M) Zn(OAc)2 aqueous solution. After incubation for 24 h, a bright blue emitting Au-Zn / Ag / R NCs solution was obtained (R represents the rare earth ion Ce). 3+ , Pr 3+ 、Nd 3 + 、Sm 3+ 、Eu 3+ 、Dy 3+ 、Ho 3+ , Er 3+ 、Tm 3+ , Yb 3+ ).

[0023] 6) Synthesis of Au-Zn / Cu / R nanoclusters: Replace the AgNO3 in step 2 with CuCl2 to obtain a AuCu NCs solution without photoluminescence properties. Add Zn(OAc)2 aqueous solution and rare earth salt solution to the AuCu NCs solution to prepare a bright blue emitting Au-Zn / Cu / R NCs solution (R represents the rare earth ion Ce 3+ , Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Dy 3+ 、Ho 3+ , Er 3+ 、Tm 3 + , Yb 3+ ).

[0024] like Figure 1 As shown in the figure, the characteristic absorption, excitation and emission peaks of the synthesized metal nanoclusters indicate that with the addition of metal cations, the contribution of the photoinduced electron transfer (PET) band and the excitation of the motif unit gradually increase. The PLQY of the metal nanoclusters is significantly improved after metal cation doping, and the full width at half maximum (FWHM) of these NCs is narrow (86~108 meV) and the Stokes shift is small (61~85 meV). Figure 2 As shown in Figure 2, PLQY increased significantly from 51.2%, 83.4%, to 99.5%. Figure 3 As shown in Figure 2, the surface and metal core compositions of metal nanoclusters undergo significant changes after cation doping. + It is doped into both the metal core and the metal surface, and Zn 2+ and Tb3+ are doped onto the surface. Figure 4 and 5 As shown, the molar ratio of Au:Ag and the rare earth ion Tb are optimized. 3+ The content of Figure 6 and 7 As shown in Figure 2, a series of cation-doped metal nanoclusters synthesized are assembled structures. Figure 8 As shown in Figure 2, the overall structural vibration of metal nanoclusters (metal core, interface motif, and surface ligands) is suppressed after cation doping. Fig. 9 As shown in Figure 2, the time component of tens of picoseconds gradually decreases. This can be explained by the faster transfer of the excited state electrons of the motif to the metal core. The relaxation process of the excited electrons mentioned above is mainly related to the composition and density of metal NCs and the rich energy levels of rare earth ions. Fig.10 As shown in Figure 2, it is proved that the energy level of rare earth ions plays a key role in PET, and the ideal energy level of rare earth ions as PET bridges should be between the S1 energy level of the motif and the S1 energy level of the metal core (light purple area). Fig.11 As shown in the figure, replacing Ag with Cu and adding different rare earth ions have the same luminescence properties as Au-Zn / Ag / R, which proves the universality of this synthesis method.

[0025] The present invention provides a method for preparing metal nanoclusters. On the one hand, the step-by-step addition of metal cations can reduce the phonon vibration frequency of the metal core and the coupling strength of phonons and optics related to the surface motif / ligand. These effects further suppress non-radiation. On the other hand, the step-by-step addition of metal cations is more conducive to the transfer of electrons from the motif primitive to the metal core, significantly improving the emission related to the metal core, and the aqueous solution reaches a PLQY close to 100% at room temperature.

[0026] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing metal nanoclusters, characterized in that: The following steps are involved: Step 1: Synthesis of Au nanoclusters: Add HAuCl4 aqueous solution into ultrapure water and stir at room temperature to obtain aqueous solution 1, add MPA into aqueous solution 1 and stir until a precipitate appears, then add NaOH into aqueous solution 1 until the precipitate dissolves, and after incubation for 24 hours, obtain an Au NCs solution without photoluminescence characteristics; Step 2: Synthesis of AuAg nanoclusters: HAuCl4 aqueous solution and AgNO3 aqueous solution were added to ultrapure water, stirred at room temperature to obtain aqueous solution 2, MPA was added to aqueous solution 2 and stirred to produce a precipitate, and NaOH was added to aqueous solution 2 until the precipitate was dissolved. After incubation for 24 hours, an AuAg NCs solution without photoluminescence properties was obtained; Step 3: Synthesis of Au-Zn nanoclusters: To trigger the assembly of Au NCs, aqueous Zn(OAc)2 solution was added to the Au NCs solution prepared in step 1. After incubation for 24 h, a bright blue emitting Au-Zn NCs solution was obtained. Step 4: Synthesis of Au-Zn / Ag nanoclusters: To trigger the assembly of AuAg NCs, aqueous Zn(OAc)2 solution was added to the AuAg NCs solution prepared in step 2. After incubation for 24 h, a bright blue emitting Au-Zn / Ag NCs solution was obtained. Step 5: Synthesis of Au-Zn / Ag / R nanoclusters: In order to further assemble AuAg NCs, in addition to the Zn(OAc)2 aqueous solution, a rare earth salt solution was added to the AuAgNCs solution prepared in step 2. After incubation for 24 h, a bright blue emitting Au-Zn / Ag / R NCs solution was obtained; Step 6: Synthesis of Au-Zn / Cu / R nanoclusters: Replace the AgNO3 in step 2 with CuCl2 to prepare an AuCu NCs solution without photoluminescence properties, and add Zn(OAc)2 aqueous solution and rare earth salt solution to the AuCu NCs solution to prepare Au-Zn / Cu / R NCs with bright blue emission.

2. The method for preparing metal nanoclusters according to claim 1, characterized in that: The molar mass ratio of MPA to HAuCl4 in step 1 is 4:

1.

3. The method for preparing a metal nanocluster according to claim 1, characterized in that: The molar mass ratio of HAuCl4 to AgNO3 in step 2 is 4:

1.

4. The method for preparing a metal nanocluster according to claim 1, characterized in that: The stirring speed in step 1 and step 2 is 600~1000r / min.

5. The method for preparing metal nanoclusters according to claim 1, characterized in that: In step 1, NaOH is added to aqueous solution 1 to adjust the pH of aqueous solution 1 to 7.90-8.0; In step 2, NaOH is added to the aqueous solution 2 to adjust the pH of the aqueous solution 2 to 7.90-8.

0.

6. The method for preparing metal nanoclusters according to claim 1, characterized in that: The molar mass ratio of HAuCl4 to AgNO3 in step 1 and step 2 is one of 2:1, 3:1, 4:1 and 5:

1.

7. The method for preparing metal nanoclusters according to claim 1, characterized in that: The rare earth ions in step 5 and step 6 include Tb 3+ 、Ce 3+ , Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Dy 3+ 、Ho 3+ , Er 3+ 、Tm 3+ , Yb 3+ One of them.

8. The method for preparing metal nanoclusters according to claim 1, characterized in that: In the rare earth salt solution added in step 5 and step 6, the concentration of rare earth ions is 0.1M.

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