A method for preparing metal nanoclusters

Abstract

The present invention relates to the field of chemical technology and discloses a method for preparing metal nanoclusters, comprising the following steps: synthesizing Au nanoclusters, synthesizing AuAg nanoclusters, synthesizing Au-Zn nanoclusters, synthesizing Au-Zn / Ag nanoclusters, synthesizing Au-Zn / Ag / R nanoclusters, and synthesizing Au-Zn / Cu / R nanoclusters. The gradual introduction of cations in the present invention 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 stepped energy level structure provides a jumping platform for excited electrons, it can significantly improve the PLQY from 51.2%, 83.4%, to 99.5%.

Description

Technical Field

[0001] The present 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), composed of a few to hundreds of metal atoms, possess discrete electronic energy levels, resulting in captivating molecular-like photoluminescence. Metal-core-dominated fluorescence, characterized by a small Stokes shift, narrow emission band, and short decay lifetime, is gaining increasing acceptance in applications such as lighting, sensing, and imaging. However, achieving high photoluminescence quantum yield (PLQY) remains a significant challenge. On the one hand, in addition to intrinsic metal core vibrations, vibrations of interfacial short motifs and terminal ligand groups can induce overall structural vibrations in metal NCs. This can induce low- and high-frequency vibrations in the metal core and short motifs, respectively. The coupling of multiple vibrations and excited-state electrons can generate additional nonradiative channels, ultimately quenching the fluorescence of metal NCs. On the other hand, manipulating the electron transfer process from highly light-absorbing surface motifs to the emitting centers of the metal core is a recognized potential strategy, but tuning the electron transfer dynamics (e.g., the pathway and rate of radiative relaxation) remains challenging due to poor functionalization. Given these limitations, the PLQY level of core-controlled photoluminescence in metal NCs is low (typically <10%). To date, modulating the overall structural motion and electron transfer dynamics of metal NCs remains an important task 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 modulate the structural properties (e.g., frequency, anisotropy, polarity, and size) of various chromophores (ranging from inorganic ions, organic molecules, metal-organic complexes, nano- / microcrystals, to macroscopic solids), thereby adjusting their electronic structure and excited-state electron dynamics, ultimately influencing their luminescence properties. In particular, metal NCs have been described as "superatomic complexes" with closed valence electron shells (i.e., 2, 8, 18, 20, etc.). Their electron-rich nature makes them highly susceptible to electronic / electrostatic attack. Furthermore, the dynamic adsorption-desorption equilibrium of surface ligands, in a "divide and conquer" mode, further influences their charge-dependent luminescence properties. Despite continued progress in the development of cationic additive-mediated photoluminescent metal NCs, the influence of cationic species on the PLQY remains unclear, particularly with limited enhancement. Therefore, research on cationic additive engineering of luminescent metal nanomaterials warrants significant attention to maximize and even customize their optical properties.

[0004] Given the low PLQY of metal NCs and the unclear effects of metal cations 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-mentioned shortcomings in the existing technology. 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:

[0007] A method for preparing metal nanoclusters comprises the following steps:

[0008] Step 1: Synthesis of Au nanoclusters: HAuCl4 aqueous solution was added to ultrapure water and stirred at room temperature to obtain aqueous solution 1. MPA was added to aqueous solution 1 and stirred until a precipitate formed. NaOH was then added to aqueous solution 1 until the precipitate dissolved. After incubation for 24 hours, a non-photoluminescent Au NCs solution was obtained.

[0009] Step 2: Synthesis of AuAg nanoclusters: HAuCl4 aqueous solution and AgNO3 aqueous solution were added to ultrapure water and stirred at room temperature to obtain aqueous solution II. MPA was added to aqueous solution II and stirred until a precipitate appeared. NaOH was then added to aqueous solution II until the precipitate dissolved. After incubation for 24 hours, a non-photoluminescent AuAg NCs solution was obtained.

[0010] 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.

[0011] 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.

[0012] Step 5: Synthesis of Au-Zn / Ag / R nanoclusters: To further assemble AuAg NCs, a rare earth salt solution was added to the AuAg NCs solution prepared in step 2 in addition to the Zn(OAc)2 aqueous solution. After incubation for 24 h, a bright blue emitting Au-Zn / Ag / R NCs solution was obtained.

[0013] Step 6: Synthesis of Au-Zn / Cu / R nanoclusters: Replace AgNO3 in step 2 with CuCl2 to prepare an AuCu NCs solution without photoluminescence properties. 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.

[0014] Preferably, the molar mass ratio of MPA to HAuCl4 in step 1 is 4:1.

[0015] Preferably, the molar mass ratio of HAuCl4 to AgNO3 in step 2 is 4:1.

[0016] Preferably, the stirring speed in step 1 and step 2 is 600-1000 r / min.

[0017] 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.

[0018] 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.

[0019] Preferably, the rare earth ions in steps 5 and 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.

[0020] Preferably, the concentration of rare earth ions in the rare earth salt solution added in step 5 and step 6 is 0.1M.

[0021] The beneficial effects of the present invention are:

[0022] 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 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.

[0023] The invention provides a method for preparing metal nanoclusters. The method has the advantages of simple operation, low time consumption, high photoluminescence quantum yield, high color purity and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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;

[0025] Figure 2 Calculation of PLQY of selected Au-Zn, Au-Zn / Ag and Au-Zn / Ag / Tb metal nanoclusters aqueous solutions;

[0026] Figure 3 X-ray photoelectron spectroscopy (XPS) of the selected Au-Zn, Au-Zn / Ag and Au-Zn / Ag / Tb metal nanoclusters;

[0027] Figure 4 is the emission spectra of Au-Zn / Ag clusters with different Au:Ag ratios;

[0028] Figure 5 For different contents of rare earth ions Tb 3+ Emission spectra of doped Au-Zn / Ag / Tb clusters;

[0029] Figure 6 Transmission electron microscopy (TEM) images of the selected Au-Zn, Au-Zn / Ag, and Au-Zn / Ag / Tb metal nanoclusters;

[0030] Figure 7 To add Zn 2+ 、Ag + and Tb 3+ Dynamic light scattering (DLS) measurements of a series of NCs before and after;

[0031] Figure 8 Temperature-dependent PL spectra of selected Au-Zn, Au-Zn / Ag, and Au-Zn / Ag / Tb metal nanoclusters;

[0032] Figure 9 Femtosecond transient absorption spectroscopy (fs-TA) of selected Au-Zn, Au-Zn / Ag, and Au-Zn / Ag / Tb metal nanoclusters;

[0033] Figure 10 The universality of Au-Zn / Ag / R metal nanoclusters with different rare earth ions;

[0034] Figure 11 The universality of Au-Zn / Cu / R metal nanoclusters with different rare earth ions. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described 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.

[0036] In one embodiment, a method for preparing metal nanoclusters comprises the following steps:

[0037] 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 pale yellow solution quickly turned white, and a precipitate appeared, indicating the formation of an 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, a non-photoluminescent Au NCs solution was obtained.

[0038] 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.

[0039] 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 from step 1. After incubation for 24 h, a bright blue emitting Au-Zn NCs solution was obtained.

[0040] 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 from step 2. After incubation for 24 h, a bright blue emitting Au-Zn / Ag NCs solution was obtained.

[0041] 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+ ).

[0042] 6) Synthesis of Au-Zn / Cu / R nanoclusters: Replace the AgNO3 in step 2 with CuCl2 to prepare a AuCu NCs solution without photoluminescence. 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+ ).

[0043] like Figure 1As 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 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 the figure, the surface and metal core composition of metal nanoclusters changed significantly after cation doping. + It is doped into both the metal core and the metal surface, and Zn 2+ and Tb 3+ are doped to 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 ligand) is suppressed after cation doping. Figure 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 the metal NCs and the rich energy levels of the rare earth ions. Figure 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). Figure 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.

[0044] This invention proposes a method for preparing metal nanoclusters. On the one hand, the gradual addition of metal cations reduces the phonon vibration frequency of the metal core and the coupling strength of phonons associated with surface motifs / ligands to optical ions. These effects further suppress non-radiative emission. Furthermore, the gradual addition of metal cations facilitates electron transfer from the motif to the metal core, significantly enhancing metal core-related emission. The PLQY in aqueous solution reaches nearly 100% at room temperature.

[0045] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing metal nanoclusters, characterized in that: The following steps are involved: Step 1: Synthesis of AuAg nanoclusters: HAuCl4 aqueous solution and AgNO3 aqueous solution were added to ultrapure water and stirred at room temperature to obtain aqueous solution II. MPA was added to aqueous solution II and stirred until a precipitate appeared. NaOH was then added to aqueous solution II until the precipitate dissolved. After incubation for 24 hours, a non-photoluminescent AuAg NCs solution was obtained. Step 2: 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 1. After incubation for 24 h, a bright blue emitting Au-Zn / Ag NCs solution was obtained. Step 3: Synthesis of Au-Zn / Ag / R nanoclusters: To further assemble AuAg NCs, a rare earth salt solution was added to the AuAgNCs solution prepared in step 1 in addition to the Zn(OAc)2 aqueous solution. After incubation for 24 h, a bright blue emitting Au-Zn / Ag / R NCs solution was obtained. Step 4: Synthesis of Au-Zn / Cu / R nanoclusters: Replace AgNO3 in step 1 with CuCl2 to prepare an AuCu NCs solution without photoluminescence properties. 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, wherein: The molar mass ratio of HAuCl4 to AgNO3 in step 1 is 4:

1.

3. The method for preparing metal nanoclusters according to claim 1, wherein: The stirring speed in step 1 is 600~1000r / min.

4. The method for preparing metal nanoclusters according to claim 1, wherein: In step 1, NaOH is added to the second aqueous solution to adjust the pH of the second aqueous solution to 7.90-8.

0.

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

1.

6. The method for preparing metal nanoclusters according to claim 1, wherein: The rare earth ions in steps 3 and 4 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.

7. The method for preparing metal nanoclusters according to claim 1, wherein: In the rare earth salt solutions added in step 3 and step 4, the concentration of rare earth ions is 0.1M.

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