Metal nanoparticles with adjustable size, structure and performance, and preparation method and application thereof

Abstract

The invention belongs to the technical field of metal nano material preparation, and discloses metal nano particles with adjustable size, structure and performance as well as a preparation method and application thereof. According to the method, a primary product containing specific ligands is firstly prepared through a co-reduction reaction and then subjected to post-synthesis heat treatment without additional addition of metal salts. According to the method, internal reconstruction and curing of a primary product are driven through additive-free heat treatment, and the limitation that a metal source needs to be additionally arranged in a traditional seed growth method is broken through. By regulating and controlling heat treatment conditions, the size of the product can be continuously controlled, and the evolution of an electronic structure of the product from a non-metal characteristic to a strong metalloid plasma resonance absorption characteristic is realized. The obtained nanoparticles have high structural integrity and strong metalloid performance especially in a critical size range of 2-3 nanometers, show a synergistic enhancement effect in the aspects of photothermal conversion efficiency and SERS sensitivity, and are suitable for the fields of photothermal therapy, sensing detection, catalysis and the like.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of nanomaterials and coordination chemistry, specifically relating to a metal nanoparticle with tunable size, structure and properties, a method for its preparation, and the application of the metal nanoparticle in biomedicine and sensing detection. Background Technology

[0002] Metallic nanoparticles serve as a crucial bridge connecting discrete atoms with macroscopic bulk materials. Their atomically precise structure provides an ideal model for understanding the "size effect" and "structure-property relationship" of nanomaterials at the molecular / atomic level. When the particle size increases to a certain critical value (typically 2-3 nanometers), its electronic structure undergoes a transition from nonmetallic (with discrete electronic energy levels) to metallic / metallic (with quasi-continuous electronic bands), potentially exhibiting properties such as localized surface plasmon resonance (LSPR). The properties of metallic nanomaterials are strongly dependent on their size and structure. In-depth exploration of this size evolution is crucial for understanding the fundamental physicochemical principles of the nanoscale and developing high-performance functional materials.

[0003] However, the development of this field has long been limited by a "gap" in synthetic methodology. On the one hand, methods for synthesizing atomically precise metal clusters (typically <2 nm) (such as ligand-protected single-phase reduction methods) can obtain structurally well-defined model materials, but it is difficult to achieve continuous and controllable "growth" to larger sizes, and large-scale preparation is challenging. On the other hand, traditional techniques for preparing larger nanocrystals (>3 nm) (such as the classic seed growth method) can control the size, but their growth process usually requires the continuous addition of metal precursors, resulting in non-uniform structures at the atomic scale and making it impossible to internally "refine" and optimize the formed primary nanostructures. Taking the closest prior art (for example, Chinese patent publication number CN113118432B) as an example, it explicitly discloses the preparation of the "seed solution" and the subsequent "growth" steps, which require the addition of a new metal source and a second reducing agent. This "must-addition-to-grow" technical approach is the mainstream understanding in the current field, which brings problems including: 1) It is difficult to obtain a series of model materials that change continuously from clusters to nanoparticles, which hinders the systematic study of the "size-structure-performance" relationship; 2) It is difficult to achieve the synergistic integration of the special properties of small-sized clusters (such as high SERS activity) and the advantageous properties of large-sized particles (such as strong photothermal effect) in the same material system.

[0004] Therefore, developing a universal method that can overcome the aforementioned biases of "additive growth" technology and achieve intrinsic "refinement" and performance leap of primary nanostructures without introducing exogenous metals has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for preparing metal nanoparticles with tunable size, structure, and properties. This method overcomes the limitations of existing technologies that rely on external additions and achieves continuous and precise control over the size, structure, and properties of metal-like nanoparticles from atomically precise clusters through a strategy of "additive-free" post-synthesis heat treatment.

[0006] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing metal nanoparticles with tunable size, structure, and properties, comprising the following steps: S1. Dissolve the metal salt, auxiliary metal salt, and first organic ligand in a first mixed organic solvent and stir to obtain a homogeneous solution A; under an inert atmosphere, add the second organic ligand and reducing agent to the solution A and carry out a co-reduction reaction at room temperature for 10-30 minutes; the mass ratio of the metal salt, auxiliary metal salt, first organic ligand, first mixed organic solvent, reducing agent, and second mixed organic ligand satisfies 1 : (2~5) : (0.5~1) : (100~300) : (2~8) : (1~3); S2. After the reaction is complete, a precipitant is added to precipitate the product. After centrifugation and washing, a solid crude product is obtained. The solid crude product is dissolved in an organic solvent and purified by chromatographic separation technology to obtain atomic-level clusters, which are denoted as solid metal nanoparticles 1.

[0007] Further improvements to the preparation method of metal nanoparticles with tunable size, structure, and properties: Preferably, solid metal nanoparticles 1, a reducing agent, and a structure-directed ligand are added to a second mixed organic solvent and subjected to a first-stage heat treatment reaction at 40-120°C for 3-6 hours to induce ligand exchange and obtain a first reaction solution. After cooling the first reaction solution, a precipitant is added to precipitate the product. After centrifugation, washing, and redissolving, the product is then placed in a third mixed organic solvent and subjected to a second-stage heat treatment reaction at 40-120°C for 6-12 hours to obtain a second reaction solution. After cooling the second reaction solution, a precipitant is added to precipitate the product. After centrifugation, washing, and crystallization purification, solid metal nanoparticles 2 are obtained. The mass ratio of the solid metal nanoparticles 1, the reducing agent, the structure-directed ligand, the second mixed organic solvent, and the third mixed organic solvent satisfies a mass ratio of 1 : (0~0.2) : (1~20) : (100~300) : (100~300).

[0008] Preferably, solid metal nanoparticles 1, a reducing agent, and a structure-directed ligand are added to a second mixed organic solvent and subjected to a first-stage heat treatment reaction at 40-120°C for 3-6 hours to induce ligand exchange, yielding a first reaction solution. After cooling the first reaction solution, a precipitant is added to precipitate the precipitate. Following centrifugation and washing, the precipitate is redissolved in a third mixed organic solvent and subjected to a second-stage heat treatment reaction at 40-120°C for 6-12 hours, yielding a second reaction solution. After cooling the second reaction solution, a precipitant is added to precipitate the precipitate. Following centrifugation and washing, the precipitate is redissolved in a fourth mixed organic solvent containing an excess of the structure-directed ligand and subjected to a third-stage heat treatment reaction at 40-120°C for 6-12 hours, yielding a third reaction solution. After cooling the third reaction solution, a precipitant is added to precipitate the product. Following centrifugation, washing, and crystallization purification, metal nanoparticles 3 are obtained. The mass ratio of the solid metal nanoparticles 1, reducing agent, structure-directed ligand, second mixed organic solvent, third mixed organic solvent, and fourth mixed organic solvent satisfies 1 : (0~0.2): (0.5~5) : (100~300) : (100~300): (100~300); Alternatively, solid metal nanoparticles 2 are dissolved in a fourth mixed organic solvent containing structure-directing ligands, and subjected to a first-stage heat treatment reaction at 40-120°C for 6-12 hours to obtain a reaction solution; after cooling the obtained reaction solution, a precipitant is added to precipitate the product, which is then purified by centrifugation, washing, and crystallization to obtain metal nanoparticles 3; the mass ratio of the solid metal nanoparticles 2 to the fourth mixed organic solvent satisfies 1:(100~300).

[0009] Preferably, solid metal nanoparticles 1, 2, or 3, and a reducing agent are added to a second mixed organic solvent, and a first-stage heat treatment reaction is carried out at 40-120°C for 5-30 minutes to obtain a first reaction solution. After cooling the first reaction solution, a precipitant is added for precipitation, and after centrifugation, washing, and redissolved in a third mixed organic solvent containing a small amount of structure-directed ligands, a second-stage heat treatment reaction is carried out at 40-120°C for 10-60 minutes to obtain a second reaction solution. After cooling the second reaction solution, a precipitant is added for precipitation, and after centrifugation, washing, and purification, metal nanoparticles 4 are obtained. The mass ratio of solid metal nanoparticles 1, 2, or 3, reducing agent, second mixed organic solvent, structure-directed ligands, and third mixed organic solvent satisfies 1 : (0.1~0.5) : (100~300) : (0.1~0.5) : (100~300).

[0010] Preferably, the metal salt includes at least one of the nitrates, acetates, or chlorides of silver, gold, copper, platinum, and palladium; the auxiliary metal salt includes at least one of the nitrates, acetates, or chlorides of zinc, cobalt, nickel, manganese, iron, aluminum, and magnesium.

[0011] Preferably, the reducing agent includes at least one selected from metal hydrides, elemental metals, non-metal hydrides, triethylsilane, sodium sulfite, and potassium formate.

[0012] Preferably, the metal hydride is sodium borohydride or lithium aluminum hydride; the non-metal hydride is hydrogen sulfide.

[0013] Preferably, the first mixed organic solvent is a mixture of tetrahydrofuran and methanol in a volume ratio of 2:1; the second mixed organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 10:3; the third mixed organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 1:1; the fourth mixed organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 5:1; and the precipitant is methanol and / or dichloromethane.

[0014] Preferably, the first organic ligand, the second organic ligand, and the structure-directing ligand are at least one of thiols, triphenylphosphine and their derivatives having 4-20 carbon atoms, or primary amines and secondary amines having 2-12 carbon atoms.

[0015] The second objective of this invention is to provide a method for preparing metal nanoparticles with adjustable size, structure and properties as described in any one of the above-mentioned methods.

[0016] A second objective of this invention is to provide an application of the aforementioned metal nanoparticles in the preparation of photothermal conversion materials, surface-enhanced Raman scattering sensing substrates, catalytic materials, or biomedical materials.

[0017] The advantages of this invention compared to the prior art are as follows: This invention provides a method for preparing metal nanoparticles with tunable size, structure, and properties: Step S1: Multi-component co-reduction to construct a specific precursor with "refinement" potential. Metal salts, auxiliary metal salts, and organic ligands undergo a co-reduction reaction under the action of a reducing agent to generate a primary product with a well-defined structure (such as metal nanoclusters with specific compositions). This step is not a simple nucleation growth, but rather a directional synthesis of an initial compound with high atomic precision and a specific structure through the synergistic reduction and assembly of multiple metals and ligands. This is a fundamental material with a defined, homogeneous structure and rich intrinsic reconstruction potential. The specific stoichiometry and structure of this primary product form the chemical and structural basis for subsequent steps to achieve directional and controllable "refinement," ensuring a highly accurate and reproducible starting point for the entire technical path. The principle lies in utilizing the differences in electronegativity and coordination preference of different metals, as well as the spatial and electronic effects of ligands, to construct a thermodynamically metastable "precursor" with specific internal bonding and stress states. This differs from the ordinary, surface-dynamic nanocrystals used as "seeds" in existing technologies.

[0018] Step S2: Post-synthesis heat treatment without additives, driving internal reconstruction to achieve a performance leap. The primary product obtained in S1 is heat-treated in the range of 40-120°C in the presence of structure-directing ligands without adding any additional metal salts or new reactants. This step is the core of the invention. It completely abandons the traditional principle of achieving size / structure changes by adding external metal sources and undergoing "epitaxy deposition" or "Ostwald ripening". The technical principle of this step is "thermally driven internal atomic / cluster rearrangement, structural relaxation and directional ripening". Thermal energy activates atomic migration within the primary product, promoting the transformation of the metastable structure into a more stable and ordered morphology, while the structure-directing ligands mainly play a role in surface stabilization and guiding the reconstruction direction. This is an inside-out "refinement" process without introducing external assistance.

[0019] Direct and significant intrinsic property optimization: Due to the optimization and densification of the internal structure, this step directly improves the electronic structure quality of the product. The most intuitive and verifiable effect is that the final particles treated in this step exhibit a significant enhancement in the metalloplasmoresonance absorption in their UV-Vis absorption spectrum compared to the primary product of S1. This conclusively proves the intrinsic improvement in its metallic / plasmoresonance properties, an effect that cannot be directly achieved by the "addition-growth" method.

[0020] Achieving continuous and precise control over size and electronic states: By precisely controlling the temperature, time, and stage of this step, it is like operating a "precision knob" to guide the depth and path of internal reconstruction, thereby achieving continuous control over the final particle size within the range of 1-20 nanometers. Furthermore, by precisely controlling the temperature, time, and stage of the heat treatment, it is like operating a "precision knob" to continuously control the size of the final product and realize its electronic structure from discrete molecular states (such as (AgZn)).44 From the metallic state (e.g., Ag) to the metallic state (e.g., Ag) 252 Ag 252 The continuous evolution of Zn2).

[0021] Breaking through the performance bottleneck at ultra-small sizes: At the critical size of 2-3 nanometers, traditional methods often face the contradiction between structural disorder and weak metallicity. This invention, through this internal "refinement" step, successfully prepares nanoparticles (such as Ag) that possess both atomically precise structures (resolvable single crystals) and strong metal-like optical responses. 252 This breaks through the limitations of traditional cognition.

[0022] This method imparts superior and synergistic application performance to products: the high crystallinity and enhanced electronic states derived from optimized internal structure directly translate into top-tier and multifunctional application characteristics. For example, Ag atoms with a size of approximately 2.3 nanometers prepared using this method... 252 Zn2 particles can simultaneously achieve a photothermal conversion efficiency of over 50% and up to 1 The M-scale SERS detection limit synergistically enhances photothermal therapy and biochemical sensing performance at ultra-small scales, breaking through the technical barrier that it is difficult for such critical-size particles to achieve both high performance. Attached Figure Description

[0023] Figure 1 The (AgZn) prepared in Examples 1, 2, 3, and 5 of this invention. 44 Ag 252 Zn2 and Ag 252 The atomic structure diagram illustrates the structural evolution from clusters to nanoparticles; Figure 2 Transmission electron microscopy (TEM) images and corresponding size distribution statistics of silver nanoparticles of approximately 3.2 nanometers prepared in Examples 4, 6, and 7; Figure 3 This is a comparison of the UV-Vis absorption spectra of the samples prepared in Examples 1, 2, 3, and 5. (AgZn) 44 (Example 1) shows discrete absorption peaks in the molecular state; while Ag 252 Zn2 (Example 2) and Ag 252 (Examples 3 and 5) all exhibited significantly enhanced and broad metalloid plasmon resonance absorption bands in the 400-500 nm range, which directly demonstrates the effect of "additive-free heat treatment" on improving optical performance. Figure 4 The figures show the solution temperature change over time of the products from Examples 1, 2, 3, 4, 5, 6, and 7 under 450 nm near-infrared laser irradiation, and a comparison of the photothermal conversion efficiency calculated based on this data, illustrating the effect of Ag. 252 Zn2 and Ag 252 Excellent photothermal properties; Figure 5 The Raman spectra of the products from Examples 1, 2, 3, 4, 5, 6, and 7, used as surface-enhanced Raman scattering (SERS) substrates, obtained under 633 nm laser excitation, show their high detection sensitivity for surface ligand molecules.

[0024] Figure 6 Transmission electron microscopy (TEM) image of silver nanoparticles prepared for Comparative Example 1. Detailed Implementation

[0025] 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 embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] Example 1

[0027] This embodiment provides an atomic-level cluster (AgZn) The preparation method of [the substance] specifically includes the following steps: S1. Silver nitrate (AgNO3, 50 mg) and zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 150 mg) were dissolved in a mixed solvent of 10 mL tetrahydrofuran and 5 mL methanol. Triphenylphosphine (TPP, 20 mg), the first organic ligand, was added and stirred until dissolved. This solution was labeled as solution A. Under nitrogen protection, 3,5-dimethylthiophenol (3,5-DMBT, 100 μL), the second organic ligand, was added to solution A, and the solution turned pale yellow. Subsequently, sodium borohydride (NaBH4, 200 mg) aqueous solution was added all at once with vigorous stirring, and the solution color rapidly turned dark brown. The reaction was allowed to proceed at room temperature for 30 minutes. S2. After the reaction is complete, add excess methanol (50 mL) to precipitate the product. Centrifuge at 8000 rpm for 5 minutes to collect the solid and wash it three times with methanol to obtain crude product B. The crude product B was dissolved in dichloromethane and separated by preparative thin-layer chromatography (PTLC) (PTLC, silica gel plate, developing solvent: V(dichloromethane) / V(petroleum ether) = 6:1). After elution and concentration, high-purity atomic-level clusters (AgZn) were obtained. , denoted as metal nanoparticle 1.

[0028] The above-prepared (AgZn) UV-Vis absorption spectra of clusters (with appendix) Figure 3 It exhibits multiple sharp, discrete absorption peaks, corresponding to electronic transitions within the molecule, and lacks continuous plasmon resonance absorption characteristics, indicating its typical non-metallic / molecular properties.

[0029] Example 2

[0030] This embodiment provides a metal nanoparticle A Z The preparation method of [the substance] specifically includes the following steps: Take the (AgZn) prepared in Example 1 50 mg of toluene and 10 mg of sodium borohydride (reducing agent) were dissolved in a mixed solvent of toluene (10 mL) and dichloromethane (3 mL) containing the structure-directed ligand 3,5-DMBT (60 μL). The mixture was heated in an oil bath at 60 °C for 6 hours to obtain the first reaction solution. The first reaction solution was cooled to room temperature, and 30 mL of methanol was added to precipitate the product. The product was centrifuged and the supernatant was discarded. The solid product was washed twice with methanol and then redissolved in 10 mL of toluene / dichloromethane (1:1, v / v) mixed solvent. The mixture was heated in an oil bath at 60 °C with stirring for 3 hours to obtain the second reaction solution. The second reaction solution was cooled to room temperature, and methanol and dichloromethane were added to precipitate the product. The product was centrifuged and washed to obtain Ag. 252 Crude product of Zn2.

[0031] Take Ag 252 The crude Zn2 product was dissolved in 2 mL of toluene and filtered. The filtrate was placed in a 20 mL glass sample vial, and approximately 15 mL of acetonitrile was slowly added as a poor solvent. The sample vial was sealed and left to stand at room temperature. After several days, black blocky single crystals precipitated, thus yielding atomic-level Ag clusters. 252 Zn2, with the precise structure Ag 252 Zn2(3,5-DMBT) 85 (MeCN)2, denoted as metal nanoparticle 2.

[0032] By scaling up the amounts of metal salt and ligand, and collecting the crystals through filtration, metal nanoparticles Ag weighing up to 2.04 g can be prepared. 252 Zn2.

[0033] As attached Figure 3 The image shows (AgZn) prepared in Example 1. 44 Compared with Ag prepared in Example 2 252 The UV-Vis absorption spectrum of Zn2 presents a stark contrast: it exhibits a significantly enhanced, broad, and strong absorption band at approximately 450 nm, which is a typical localized surface plasmon resonance (LSPR) absorption characteristic of metal-like nanoparticles. This definitively demonstrates the decisive role of the "additive-free heat treatment" step in enhancing the metallicity of the particles.

[0034] Example 3

[0035] This embodiment provides a metal nanoparticle Ag. 252 The method for preparing clusters specifically includes the following steps: Take Ag obtained in Example 2 252 Zn2 clusters (15 mg) were dissolved in 5 mL of toluene, and excess 4-tert-butylthiophenol (TBBT, 1 mL) was added. The mixture was stirred at 80 °C for 12 hours. After the reaction was complete, methanol was added to precipitate the product, which was then centrifuged and washed three times with methanol to obtain Ag. 252 Crude products of clusters.

[0036] For Ag 252 The crude product was dissolved in 2 mL of toluene and filtered. The filtrate was placed in a 20 mL glass sample vial, and approximately 15 mL of acetonitrile was slowly added as a poor solvent. The sample vial was sealed and left to stand at room temperature. After several days, black blocky single crystals precipitated, thus obtaining high-quality single-crystal Ag. 252 The precise structure is Ag. 252 Cl2(3,5-DMBT)4(TBBT) 81 , denoted as metal nanoparticles 3.

[0037] The single-crystal Ag obtained above 252 UV-Vis absorption spectrum (with appendix) Figure 3 ) and Ag 252 Similar to Zn2, it retains strong and broad plasmonic resonance absorption, indicating that its core metalloid properties are preserved during ligand exchange and possible fine-tuning of the intranuclear component (Zn).

[0038] Example 4

[0039] This embodiment provides a metal nanoparticle Ag. 252 The method for preparing clusters specifically includes the following steps: Take the (AgZn) prepared in Example 1 50 mg of methyl methacrylate (MDA) and sodium borohydride (10 mg) as a reducing agent were dissolved in a mixed solvent of toluene (10 mL) and dichloromethane (3 mL) containing the structure-directed ligand 3,5-DMBT (60 μL). The mixture was heated in an oil bath at 60 °C for 6 hours to obtain the first reaction solution. The first reaction solution was cooled to room temperature, and 30 mL of methanol was added to precipitate the product. The product was centrifuged and the supernatant was discarded. The solid product was washed twice with methanol and then redissolved in 10 mL of a toluene / dichloromethane (1:1, v / v) mixed solvent. The mixture was heated in an oil bath at 60 °C with stirring for 3 hours to obtain the second reaction solution. The second reaction solution was cooled to room temperature, and methanol and dichloromethane were added to precipitate the product. The product was centrifuged and washed. The washed product was dissolved in 5 mL of toluene, and excess 4-tert-butylthiophenol (TBBT, 1 mL) was added. The mixture was stirred at 80 °C for 12 hours. After the reaction was completed, methanol was added to precipitate the product, and the product was centrifuged and washed three times with methanol to obtain Ag. 252 Crude product of the cluster. Ag 252 The crude product was dissolved in 2 mL of toluene and filtered. The filtrate was placed in a 20 mL glass sample vial, and about 15 mL of acetonitrile was slowly added as a poor solvent. The sample vial was sealed and left to stand at room temperature. After several days, black blocky single crystals precipitated, thus obtaining high-quality single-crystal Ag. 252 , denoted as metal nanoparticles 3.

[0040] Example 5

[0041] This embodiment provides a method for preparing (~3.2 nm) silver nanoparticles, specifically including the following steps: Metal nanoparticle 1 (30 mg) obtained in Example 1 was dissolved in a mixed solvent of toluene (5 mL) and dichloromethane (1.5 mL), and an excess of sodium borohydride (approximately 20 mg) as a reducing agent was added to the solution. The mixture was stirred at 40 °C for 15 minutes to obtain the first reaction solution. After the reaction was completed, methanol was added to precipitate the solid, which was collected by centrifugation and washed with methanol. The product was dissolved in 5 mL of a toluene / dichloromethane (5:1, v / v) mixed solvent containing 3,5-DMBT (60 μL), and stirred and heated in an oil bath at 40 °C for 10 minutes. Methanol was added to precipitate the solid, which was then centrifuged, washed, and finally dried at room temperature in a vacuum drying oven to obtain a dark gray solid powder, denoted as metal nanoparticle 4.

[0042] Characterization by scanning electron microscopy (SEM) (with appendix) Figure 2 Its particles are approximately spherical with a narrow size distribution and an average particle size of about 3.2 nm.

[0043] Example 6

[0044] This embodiment provides a method for preparing (~3.2 nm) silver nanoparticles, specifically including the following steps: Take the Ag obtained in Example 2 252 Zn2 cluster crystals (30 mg) were dissolved in a mixed solvent of toluene (5 mL) and dichloromethane (1.5 mL). Sodium borohydride (approximately 20 mg) as a reducing agent was added to this solution. The mixture was stirred at 40 °C for 15 minutes to obtain the first reaction solution. After the reaction was complete, methanol was added to precipitate the solid, which was collected by centrifugation and washed with methanol. The product was dissolved in 5 mL of a toluene / dichloromethane (5:1, v / v) mixed solvent containing 3,5-DMBT (60 μL), and heated in an oil bath at 40 °C with stirring for 10 minutes. Methanol was added to precipitate the solid, which was then centrifuged, washed, and finally dried at room temperature in a vacuum drying oven to obtain a dark brown solid powder, denoted as metal nanoparticle 4.

[0045] Example 7

[0046] This embodiment provides a method for preparing (~3.2 nm) metal nanoparticle clusters, specifically including the following steps: Take the Ag obtained in Example 3 252 Cluster crystals (30 mg) were dissolved in a mixed solvent of toluene (5 mL) and dichloromethane (1.5 mL). Sodium borohydride (approximately 20 mg) as a reducing agent was added to this solution. The mixture was stirred at 40 °C for 15 minutes to obtain the first reaction solution. After the reaction was complete, methanol was added to precipitate the solid, which was collected by centrifugation and washed with methanol. The product was dissolved in 5 mL of a toluene / dichloromethane (5:1, v / v) mixed solvent containing 3,5-DMBT (60 μL), and the mixture was heated and stirred in an oil bath at 40 °C for 10 minutes. Methanol was added to precipitate the solid, which was then centrifuged, washed, and finally dried at room temperature in a vacuum drying oven to obtain a dark brown solid powder, designated as metal nanoparticle 4.

[0047] Comparative Example 1

[0048] Take the (AgZn) prepared in Example 1. 44Clusters (30 mg) were dissolved in a mixed solvent of toluene (5 mL) and dichloromethane (1.5 mL). Silver nitrate (AgNO3, 10 mg) and sodium borohydride (approximately 20 mg) as a reducing agent were added to this solution. The mixture was stirred at 40 °C for 15 minutes to obtain the first reaction solution. After the reaction was completed, methanol was added to precipitate the product, the solid was collected by centrifugation and washed with methanol. The product was dissolved in 5 mL of a toluene / dichloromethane (5:1, v / v) mixed solvent containing 3,5-DMBT (60 μL), and the mixture was heated and stirred in an oil bath at 40 °C for 10 minutes. Methanol was added to precipitate the product, the mixture was centrifuged, washed, and finally dried at room temperature in a vacuum drying oven. Characterization of the obtained product revealed that transmission electron microscopy (TEM) showed a wide particle size distribution (1.5-8 nm); the particle size was non-uniform, indicating that the size uniformity and structural integrity of the product were not as good as those of the product obtained by the "additive-free heat treatment" method of this invention.

[0049] Performance testing: 1. Photothermal conversion performance test To verify the photothermal properties of the material, (AgZn) was used. 44 (Example 1), Ag 252 Zn2 (Example 2), Ag 252 (Example 3) and 3.2 nm Ag NPs (Example 4) were precisely prepared into toluene solutions with the same silver atom concentration (e.g., [Ag] = 0.1 mg / mL). Two mL of each solution was placed in identical quartz cuvettes. A continuous laser with an output wavelength of 450 nm was used as the light source, with the power density adjusted to 0.6 W / cm², and the solution was vertically irradiated to its center. The temperature change in the central region of the solution was recorded and monitored in real time using an infrared thermal imager, with irradiation time ranging from 1 to 15 minutes. Experimental results are attached. Figure 4 As shown: Ag 252 Zn2 and Ag 252 After 5 minutes of laser irradiation, the temperature of the solution increased by more than 35°C, while (AgZn) 44 The solution temperature rise was less than 8°C, while the temperature rise of 3.2 nm Ag NPs was approximately 10°C. The photothermal conversion efficiency (η) was calculated using standard methods for Ag. 252 Zn2 and Ag 252 The η values ​​of all samples were higher than 50%, significantly better than those of other samples. This test result directly proves that the 2-3 nanoparticles with strong plasma absorption obtained by the "additive-free heat treatment" of this invention have extremely excellent photothermal conversion capabilities, and their performance is even better than that of larger nanoparticles.

[0050] 2. Surface-enhanced Raman scattering (SERS) performance testing

[0051] To evaluate the SERS activity of the material, (AgZn) was used. 44 Ag 252 Zn2, Ag 252 Prepared separately at concentrations as low as 1 A toluene solution of M was prepared. A small amount (e.g., 2 µL) of the above solution was dropped onto a clean silicon wafer surface. After the toluene evaporated naturally, a thin film of nanoparticles was formed. The film was tested using a confocal Raman spectrometer equipped with a 633 nm He-Ne laser. The laser power was set to 1 mW. The experimental results are attached. Figure 5 As shown: In Ag 252 Zn2 and Ag 252 The Raman spectrum of the sample clearly distinguishes the characteristic Raman vibration peaks originating from its surface ligands TPP, TBBT, and 3,5-DMBT, exhibiting a high signal-to-noise ratio. Even at such low concentrations, (AgZn) 44 It also showed some SERS signal, but Ag 252 Zn2 and Ag 252 The signal enhancement effect is even more significant. This experiment shows that even after heat treatment to achieve strong metallicity, these atomically precise nanoparticles still retain extremely high surface enhancement capabilities. More importantly, Ag... 252 Zn2 and Ag 252 It possesses both excellent photothermal performance (Example 5) and ultra-high SERS sensitivity, achieving a synergistic effect of two high-performance properties on a single material, which is an unexpected advantage brought about by the method of this invention.

[0052] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing metal nanoparticles with tunable size, structure, and properties, characterized in that, Includes the following steps: S1. Dissolve the metal salt, auxiliary metal salt, and first organic ligand in a first mixed organic solvent and stir to obtain a homogeneous solution A; under an inert atmosphere, add the second organic ligand and reducing agent to the solution A and carry out a co-reduction reaction at room temperature for 10-30 minutes; the mass ratio of the metal salt, auxiliary metal salt, first organic ligand, first mixed organic solvent, reducing agent, and second mixed organic ligand satisfies 1 : (2~5) : (0.5~1) : (100~300) : (2~8) : (1~3); S2. After the reaction is complete, a precipitant is added to precipitate the product. After centrifugation and washing, a solid crude product is obtained. The solid crude product is dissolved in an organic solvent and purified by chromatographic separation technology to obtain atomic-level clusters, which are denoted as solid metal nanoparticles 1.

2. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 1, characterized in that, Solid metal nanoparticles 1, a reducing agent, and a structure-directed ligand are added to a second mixed organic solvent and subjected to a first-stage heat treatment reaction at 40-120℃ for 3-6 hours to induce ligand exchange, yielding a first reaction solution. After cooling the first reaction solution, a precipitant is added to precipitate the product. After centrifugation, washing, and redissolving in a third mixed organic solvent, a second-stage heat treatment reaction is carried out at 40-120℃ for 6-12 hours to obtain a second reaction solution. After cooling the second reaction solution, a precipitant is added to precipitate the product. After centrifugation, washing, and crystallization purification, solid metal nanoparticles 2 are obtained. The mass ratio of the solid metal nanoparticles 1, the reducing agent, the structure-directed ligand, the second mixed organic solvent, and the third mixed organic solvent satisfies the mass ratio 1 : (0~0.2) : (1~20) : (100~300) : (100~300).

3. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 2, characterized in that, Solid metal nanoparticles 1, a reducing agent, and a structure-directed ligand are added to a second mixed organic solvent and subjected to a first-stage heat treatment reaction at 40-120°C for 3-6 hours, resulting in ligand exchange and yielding a first reaction solution. After cooling the first reaction solution, a precipitant is added to precipitate the ligand. Following centrifugation and washing, the precipitant is redissolved in a third mixed organic solvent and subjected to a second-stage heat treatment reaction at 40-120°C for 6-12 hours, yielding a second reaction solution. After cooling the second reaction solution, a precipitant is added to precipitate the ligand. Following centrifugation and washing, the precipitant is redissolved in a fourth mixed organic solvent containing an excess of the structure-directed ligand and subjected to a third-stage heat treatment reaction at 40-120°C for 6-12 hours, yielding a third reaction solution. After cooling the third reaction solution, a precipitant is added to precipitate the product. Following centrifugation, washing, and crystallization purification, metal nanoparticles 3 are obtained. The mass ratio of the solid metal nanoparticles 1, reducing agent, structure-directed ligand, second mixed organic solvent, third mixed organic solvent, and fourth mixed organic solvent satisfies 1 : (0~0.2): (0.5~5) : (100~300) : (100~300):(100~300); Alternatively, solid metal nanoparticles 2 are dissolved in a fourth mixed organic solvent containing structure-directing ligands, and subjected to a first-stage heat treatment reaction at 40-120°C for 6-12 hours to obtain a reaction solution; after cooling the obtained reaction solution, a precipitant is added to precipitate the product, which is then purified by centrifugation, washing, and crystallization to obtain metal nanoparticles 3; the mass ratio of the solid metal nanoparticles 2 to the fourth mixed organic solvent satisfies 1:(100~300).

4. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 3, characterized in that, Solid metal nanoparticles 1, 2, or 3, and a reducing agent are added to a second mixed organic solvent. A first-stage heat treatment reaction is carried out at 40-120°C for 5-30 minutes to obtain a first reaction solution. After cooling the first reaction solution, a precipitant is added for precipitation. After centrifugation, washing, and redissolved in a third mixed organic solvent containing a small amount of structure-directed ligands, a second-stage heat treatment reaction is carried out at 40-120°C for 10-60 minutes to obtain a second reaction solution. After cooling the second reaction solution, a precipitant is added for precipitation. After centrifugation, washing, and purification, metal nanoparticles 4 are obtained. The mass ratio of solid metal nanoparticles 1, 2, or 3, the reducing agent, the second mixed organic solvent, the structure-directed ligand, and the third mixed organic solvent satisfies 1:(0.1~0.5):(100~300):(0.1~0.5):(100~300).

5. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 1, characterized in that, The metal salt includes at least one of the nitrates, acetates, or chlorides of silver, gold, copper, platinum, and palladium; the auxiliary metal salt includes at least one of the nitrates, acetates, or chlorides of zinc, cobalt, nickel, manganese, iron, aluminum, and magnesium.

6. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 1, characterized in that, The reducing agent includes at least one of the following: metal hydride, elemental metal, non-metal hydride, triethylsilane, sodium sulfite, and potassium formate.

7. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 3, characterized in that, The first mixed organic solvent is a mixture of tetrahydrofuran and methanol in a volume ratio of 2:1; the second mixed organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 10:3; the third mixed organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 1:1; the fourth mixed organic solvent is a mixture of toluene and dichloromethane in a volume ratio of 5:1; and the precipitant is methanol and / or dichloromethane.

8. The method for preparing size-, structure-, and performance-tunable metal nanoparticles according to claim 1, characterized in that, The first organic ligand, the second organic ligand, and the structure-directing ligand are at least one of thiols, triphenylphosphine and their derivatives having 4-20 carbon atoms, or primary amines and secondary amines having 2-12 carbon atoms.

9. Metal nanoparticles prepared by the method for preparing metal nanoparticles with adjustable size, structure and properties as described in any one of claims 1-8.

10. The application of the metal nanoparticles of claim 9 in the preparation of photothermal conversion materials, surface-enhanced Raman scattering sensing substrates, catalytic materials or biomedical materials.

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