Silver nanocluster co-protected by 2, 4-dimethylthiophenol and triphenylphosphine and preparation method thereof

Abstract

The invention discloses a 2, 4-dimethylthiophenol and triphenylphosphine co-protected silver nanocluster and a preparation method thereof.The center of the silver nanocluster is a sulfur atom, the central sulfur atom is connected with six silver atoms in the form of mu-6 to form a cube framework, and a sulfur-silver conjugated network is constructed; a sulfur atom of the triphenylphosphine ligand is located at the center of a cube surface, and ligand electron cloud is connected with an inner core through an Ag-S bond to form a cross-plane charge transmission path, so that the electron delocalization dimension is further widened; the symmetric framework of the cube and the number of fixed ligands constrain the size of the cluster. The electron-space structure of the silver nanocluster is reconstructed at the atomic scale through a sulfur centralization inner core and multistage ligand connection strategy, the inherent limitation of a metal inner core is broken through, and a new material basis is provided for high-sensitivity sensing, efficient photocatalysis and stable photoelectric devices.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic synthetic chemistry and nano material preparation, and relates to a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine and a preparation method thereof. Background Art

[0002] Silver nanoclusters (AgNanoclusters, AgNCs) are a class of nanomaterials composed of a small amount of silver atoms, usually less than 2nm in size, showing unique quantum size effects and discrete energy level structures. Compared with traditional silver nanoparticles, silver nanoclusters have excellent fluorescence, electrical and catalytic properties, and are widely used in biosensing, imaging, catalysis, optoelectronic devices, antibacterial materials and chemical detection. For example, its high fluorescence quantum yield and good biocompatibility make it useful for DNA detection and cell imaging, its high surface energy gives it catalytic potential in oxygen reduction reactions and pollutant degradation, and its surface-enhanced Raman scattering (SERS) and fluorescence quenching effect make it useful for ultra-sensitive detection of heavy metal ions and organic pollutants. In addition, silver nanoclusters can release silver ions and show excellent antibacterial activity.

[0003] However, the practical application of silver nanoclusters still faces many challenges, including poor stability, easy oxidation and aggregation, low controllability of preparation methods, difficulty in mass production, need to improve photoelectric conversion efficiency, and insufficient assessment of biosafety. To this end, researchers proposed a dual-ligand co-protection strategy, which is to modify silver nanoclusters with two different ligands (such as small molecules + polymers or two organic molecules). On the one hand, the synergistic effect of dual ligands can effectively improve the stability of clusters and prevent oxidation and fluorescence quenching; on the other hand, it can precisely control the size, morphology and optical properties of clusters, improve the repeatability and yield of synthesis, and thus provide reliable technical support for the large-scale application of silver nanoclusters. However, the cores of existing dual-ligand co-protected silver nanoclusters are mostly metal atoms. The strong metal bonds of the metal core limit the range of electron delocalization, making it difficult to achieve dynamic regulation of the electronic structure through external stimuli (light, electricity, and chemical environment), limiting its response sensitivity in optical sensing or catalysis. In addition, the atoms in the metal core are bonded to each other by metal bonds, and the electronic energy levels tend to a continuous state, weakening the quantum size effect. At the same time, the electronic interaction between the metal core and the ligand is weak, making it difficult to form a strong coordination bond or charge transfer channel. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, thereby solving the technical problems in the prior art that the metal core of the silver nanocluster co-protected by double ligands has limited electron delocalization range, weakened quantum size effect and insufficient ligand-core charge transfer channels.

[0005] The present invention is realized through the following technical solutions:

[0006] A silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, wherein the unit cell of the cluster contains two silver nanoclusters and two tetraphenylborate counterbalance ions;

[0007] The framework of the silver nanocluster is a regular cube structure, and the center of the silver nanocluster is a sulfur atom, and the central sulfur atom is connected to 6 silver atoms around it in the form of μ-6 sulfur;

[0008] One silver nanocluster contains 6 triphenylphosphine ligands and 12 2,4-dimethylbenzenethiol ligands;

[0009] The sulfur atoms in the 6 triphenylphosphine ligands are located at the six face centers of the regular cube structure framework, and each sulfur atom is connected to one silver atom;

[0010] The sulfur atoms in the 12 2,4-dimethylbenzenethiol ligands are connected to silver atoms in the form of μ-3 sulfur.

[0011] The preparation method of the above silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine includes the following steps:

[0012] Step 1: Add silver nitrate to a mixed solvent of dichloromethane and methanol, stir until the silver nitrate is completely dissolved, first add the ligand 2,4-dimethylbenzenethiol under continuous stirring, stir and react, and then add triphenylphosphine. After the reaction is completed, obtain system A;

[0013] Step 2: Add sodium borohydride solution to system A under continuous stirring. After the reaction is completed, obtain system B;

[0014] Step 3: Perform oil-water phase separation on system B, wash the oil phase, and prepare the silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0015] Preferably, in step 1, the molar ratio of silver ions in silver nitrate to 2,4-dimethylbenzenethiol is (0.5-4):1, and the molar ratio of silver ions in silver nitrate to triphenylphosphine is (2-6):1.

[0016] Preferably, in step 1, silver nitrate is added to a mixed solvent of dichloromethane and methanol and stirred until the silver nitrate is completely dissolved, wherein the stirring rate is 800 to 1600 r / min and the stirring time is 6 to 25 min.

[0017] Preferably, in step 1, the stirring rates after adding 2,4-dimethylbenzenethiol and after adding triphenylphosphine are both 400 to 900 r / min, and the stirring times are both 10 to 60 min.

[0018] Preferably, in step 1, the reaction temperatures after adding 2,4-dimethylbenzenethiol and after adding triphenylphosphine are both -5°C to 20°C.

[0019] Preferably, in step 1, the reaction temperatures after adding 2,4-dimethylbenzenethiol and after adding triphenylphosphine are both -10°C to 10°C.

[0020] Preferably, in step 2, in the sodium borohydride solution, the ratio of the solvent to sodium borohydride is 2 mL:(10 to 80) mg.

[0021] Preferably, in step 2, the molar ratio of sodium borohydride to silver ions in silver nitrate is (1 to 10):1.

[0022] Preferably, in step 2, the sodium borohydride solution is added to system A under continuous stirring, the stirring rate is 600 to 1200 r / min, and the reaction time is 8 to 24 h.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] The present invention discloses a silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine. First, at the center of the silver nanocluster is a sulfur atom. The central sulfur atom is connected to 6 silver atoms in a μ-6 form to form a regular cube skeleton. The lone pair electrons of sulfur hybridize with the d orbitals of silver, breaking the strong metallic bond rigidity of the pure metal core and constructing a sulfur-silver conjugate network, which extends the electron delocalization range from the local of the pure silver core to the sulfur-silver multi-center system, significantly enhancing the electron mobility. The sulfur atom of the triphenylphosphine ligand is located at the face center of the cube, connecting the ligand electron cloud with the core through the Ag-S bond to form a cross-plane charge transfer path, further broadening the electron delocalization dimension. The symmetry framework of the regular cube and the fixed ligand number (6 triphenylphosphines + 12 thiophenols) forcibly constrain the cluster size, causing the electron energy levels to transform from a continuous state to discrete quantum states. The strong electron donor property of the thiophenol ligand (connected through μ-3 sulfur) and the steric hindrance effect of triphenylphosphine cooperate to finely regulate the electron density distribution of the core, enhancing the exciton binding energy and reducing non-radiative recombination. In the present invention, a three-level charge transfer channel is formed by μ-6 central sulfur (core), μ-3 thiophenol sulfur (surface), and face-centered sulfur (triphenylphosphine). The tetraphenylborate stabilizes the surface charge of the cluster through electrostatic interaction, reducing ligand shedding and ensuring the long-term effectiveness of the charge transfer channel. Through the sulfur-centered core and multi-level ligand connection strategy, the present invention reconstructs the electron-space structure of the silver nanocluster at the atomic scale, breaking through the inherent limitations of the metal core and providing a new material basis for highly sensitive sensing, efficient photocatalysis, and stable optoelectronic devices.

[0025] In addition, the present invention also discloses a preparation method of the above silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine. First, 2,4-dimethylbenzenethiol (thiol ligand) is added, which preferentially forms a strong Ag-S coordination bond with Ag + to directionally construct a cube skeleton centered on the sulfur atom. Then, triphenylphosphine (phosphine ligand) is introduced to form a steric hindrance layer on the surface through the Ag-P bond. This sequence avoids the competitive coordination of the two ligands and ensures the formation of the sulfur-centered core structure in the interior, solving the problem of structural disorder caused by the synchronous addition in the traditional dual-ligand method. The μ-6 sulfur atom at the center of the cube hybridizes the lone pair electrons with the d orbitals of 6 Ag atoms to form discretized energy levels, enhancing the quantum size effect. During the preparation process, dichloromethane and methanol are used as a mixed solvent to form a dual-solvent system. The dual-solvent system realizes the uniform dispersion of Ag + and reduces the uneven cluster size caused by solvent stratification. At the same time, sodium borohydride is used as a reducing agent. The strong reducibility of NaBH4 makes Ag +It can be rapidly reduced, reducing the growth time deviation of the intermediate silver core and improving batch consistency. At the same time, in terms of the purification of the product, only oil-water separation and washing are required, avoiding complex purification steps such as gel chromatography, simplifying the experimental procedures. This method rapidly experiments on the preparation of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine through stepwise coordination, rapid reduction, and targeted purification.

[0026] Furthermore, in step 1, the molar ratio of silver ions in silver nitrate to 2,4-dimethylbenzenethiol is (0.5 - 4):1. By regulating the thiol ratio, the cluster size is restricted, the quantum confinement effect is strengthened, and the light / electric response sensitivity is improved. The molar ratio of silver ions in silver nitrate to triphenylphosphine is (2 - 6):1. The benzene ring conjugate structure of the phosphine ligand combines with the electron donor characteristics of the thiol to form a three-dimensional charge transport network (inner core sulfur → Ag → surface phosphine ligand), enhancing the carrier mobility.

[0027] Furthermore, in step 1, silver nitrate is added to a mixed solvent of dichloromethane and methanol and stirred until silver nitrate is completely dissolved. Among them, the stirring rate is 800 - 1600 r / min, and the stirring time is 6 - 25 min. First of all, methanol, as a strongly polar solvent, promotes the dissociation of silver nitrate into Ag + , providing an ionic dispersion environment. Dichloromethane, as a low-polarity solvent, effectively dissolves the hydrophobic ligand to form a homogeneous reaction medium. A stirring rate of 800 - 1600 r / min can accelerate the two-phase mixing, avoiding non-uniform nucleation caused by local supersaturation of Ag + . The shear force generated by high rotation speeds can break the silver core aggregates formed in the initial stage, forcibly restricting the cluster size.

[0028] Furthermore, in step 1, the stirring rates after adding 2,4-dimethylbenzenethiol and after adding triphenylphosphine are both 400 - 900 r / min, and the stirring times are both 10 - 60 min. The stirring rate is reduced after adding the ligand to avoid the high-speed shear force from destroying the gradual binding process of the ligand (thiol, phosphine) and Ag + . The thiol ligand (with strong coordination ability) first forms a stable Ag-S bond with Ag + , constructing a sulfur-centered cubic skeleton. The subsequently added phosphine ligand precisely occupies the face-centered position through the Ag-P bond, reducing the misalignment caused by ligand competition and avoiding structural distortion.

[0029] Furthermore, in step 1, the reaction temperatures after adding 2,4-dimethylbenzenethiol and after adding triphenylphosphine are both -5°C to 20°C. First of all, the low temperature slows down the reaction rate, ensuring that 2,4-dimethylbenzenethiol (thiol) preferentially reacts with Ag +Full coordination forms a cubic skeleton centered on sulfur atoms (Ag-S bonds). At this temperature, the coordination of thiophenol is dominant, preventing the premature participation of subsequently added triphenylphosphine (PPh3) in competition and ensuring the directional construction of the core structure. In addition, triphenylphosphine slowly covers the surface of the core through Ag-P bonds at a lower temperature, forming a uniform steric hindrance layer to prevent cluster aggregation and avoid ligand desorption or structural reorganization caused by high temperature; at the same time, low temperature reduces the thermodynamic activity of the reaction system and reduces Ag + The risk of spontaneous reduction or solvent decomposition, ensuring that the coordination process is the main reaction. Moreover, low temperature delays the growth rate of nanoclusters, making Ag + Uniformly dispersed in the mixed solvent (dichloromethane / methanol), reducing size non-uniformity caused by too high local concentration and improving the monodispersity of the product. Low temperature inhibits the dissolution-redeposition process of small particles, avoiding uneven size growth during the formation of nanoclusters and maintaining the quantum size effect of the cubic skeleton.

[0030] Furthermore, in step 2, in the sodium borohydride solution, the ratio of the solvent to sodium borohydride is 2 mL:(10 - 80) mg. This ratio can control the concentration of the sodium borohydride solution, slow down the reduction rate, and avoid instantaneous nucleation and aggregation of silver nuclei due to violent reaction, thereby generating smaller-sized and higher-monodispersity nanoclusters. On the premise of ensuring the reduction efficiency, by quickly consuming Ag + Shorten the growth time of the intermediate silver nuclei, reduce the growth deviation between different batches, and improve the product consistency.

[0031] Furthermore, in step 2, the molar ratio of sodium borohydride to silver ions in silver nitrate is (1 - 10):1. Excessive NaBH4 ensures that all Ag + Is fully reduced to Ag 0 , avoiding residual unreacted Ag + Resulting in subsequent oxidation or uneven surface charge of the clusters, thereby improving the purity and stability of the product. At a high ratio (such as 10:1), NaBH4 quickly reduces Ag + , shortening the transition time of silver nuclei from the metastable state to the stable state, reducing the uneven size distribution of clusters caused by growth time differences, and improving batch consistency. In addition, when NaBH4 is in excess, Ag + Is quickly reduced to Ag 0 , and the ligand can be quickly adsorbed on the surface of the silver nuclei to form stable Ag-S and Ag-P bonds, avoiding Ostwald ripening or aggregation of the bare silver nuclei due to high surface energy.

[0032] Further, in step 2, a sodium borohydride solution is added to system A under continuous stirring. The stirring rate is 600 - 1200 r / min, and the reaction time is 8 - 24 h. The shear force generated by high-speed stirring can quickly break the interfacial tension between the sodium borohydride solution and the oil phase (dichloromethane / methanol), promoting the uniform dispersion of the reducing agent (NaBH4) in the form of droplets into system A, ensuring the sufficient contact between Ag + and H - (from NaBH4), avoiding uneven silver nucleus sizes caused by excessive local concentration. Additionally, continuous high-speed stirring maintains the dynamic suspension state of the silver nuclei, preventing the aggregation of nanoclusters due to gravity or van der Waals forces and enhancing the monodispersity of the product. Moreover, high-speed stirring accelerates the reduction process of Ag + , promoting the rapid nucleation of silver atoms and forming a large number of initial nuclei (small-size advantage). The subsequent long reaction time (8 - 24 h) allows the nuclei to transition to the thermodynamically stable state through Ostwald ripening, ultimately forming nanoclusters with uniform sizes. The long reaction time provides sufficient adsorption time for thiophenol (Ag-S bond) and PPh3 (Ag-P bond), optimizing the surface coverage through ligand exchange and enhancing the structural stability of the clusters. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a crystal structure diagram of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0036] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0037] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0038] In this text, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0039] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered to be within the scope described in this specification.

[0040] As Figure 1 shown, the present invention provides a silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine. The unit cell of this cluster contains two silver nanoclusters and two tetraphenylborate counterbalance ions. Therefore, the charge carried by this silver nanocluster is +1 valence; the framework of the silver nanocluster is a regular cube structure, and the center of the silver nanocluster is a sulfur atom. The central sulfur atom connects 6 silver atoms around it in the form of μ-6 sulfur; one silver nanocluster contains 6 triphenylphosphine ligands and 12 2,4-dimethylbenzenethiol ligands; the sulfur atoms in the 6 triphenylphosphine ligands are located at the six face centers of the regular cube structure framework, and each sulfur atom connects one silver atom; the sulfur atoms in the 12 2,4-dimethylbenzenethiol ligands are connected to silver atoms in the form of μ-3 sulfur.

[0041] The framework structure of the silver nanocluster co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine in the present invention is highly symmetric. The phosphorus atoms of the 6 triphenylphosphine ligands are respectively located in the front, back, left, right, and up and down positions at the outermost vertices of the cluster and are connected to 1 silver atom. The 12 sulfur atoms from the 2,4-dimethylbenzenethiol ligands are connected to silver atoms in the form of μ-3 sulfur. A sulfur atom is located at the center of the entire cluster, and it connects 6 silver atoms around it in the form of μ-6 sulfur.

[0042] In coordination chemistry, the symbol μ represents a bridging ligand, where μ-3 sulfur refers to a sulfur atom (from the 2,4-dimethylbenzenethiol ligand) acting as a tridentate bridging ligand, bonding to three silver atoms simultaneously. That is, in the silver nanocluster, μ3-S connects three adjacent silver atoms through three Ag-S bonds, forming a local triangular plane or a three-dimensional cross-linked network, enhancing the rigidity and stability of the cluster framework. And μ-6 sulfur refers to the central sulfur atom acting as a hexadentate bridging ligand, bonding to six silver atoms simultaneously. The central sulfur atom is located at the core of the cubic framework and is connected to six silver atoms through six Ag-S bonds, forming a highly symmetric octahedral coordination geometry (six silver atoms are arranged in an octahedron around the sulfur atom). This ultra-high bridging mode (μ6-S) can stabilize the cubic framework through strong covalent interactions (hybridization of Ag-S bonds), and at the same time provide an electron delocalization channel for the center, enhancing the quantum size effect.

[0043] In the present invention, except for the silver atoms at the vertices, any other silver atom in the cluster is surrounded by sulfur atoms, and the sulfur atoms are surrounded by silver atoms. The average bond length between silver atoms and phosphorus atoms is The average bond length between the central sulfur atom and silver atoms is And the bond length between the remaining sulfur atoms and silver atoms varies in the range of to The average distance is

[0044] In addition, the present invention also discloses a method for preparing the above-mentioned silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, comprising the following steps:

[0045] Step 1: Add silver nitrate to a mixed solvent of dichloromethane and methanol, stir until the silver nitrate is completely dissolved and becomes transparent. Under continuous stirring, first add the ligand 2,4-dimethylbenzenethiol, stir for 5 - 10 min, and then add an appropriate amount of triphenylphosphine. After the reaction is completed, obtain system A;

[0046] Among them, the molar ratio of silver ions in silver nitrate to 2,4-dimethylbenzenethiol is (0.5 - 4):1, and the molar ratio of silver ions in silver nitrate to triphenylphosphine is (2 - 6):1. In this ratio control, if the ratio is too large, precipitation will form at the bottom of the solution during stirring; if the ratio is too small, nanoparticles will form and nanoclusters cannot be obtained.

[0047] In this step, the initial stirring rate is 800 - 1600 r / min and the stirring time is 6 - 25 min. That is, silver nitrate is added to the mixed solvent of dichloromethane and methanol, with a stirring rate of 800 - 1600 r / min and a stirring time of 6 - 25 min. After adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine, the stirring rate is 400 - 900 r / min and the stirring time is 10 - 60 min, preferably 10 - 30 min. The control of this stirring process is based on the "kinetic control" strategy. The initial stirring rate is 800 - 1600 r / min and the stirring time is 6 - 25 min. After adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine, the stirring rate is adjusted to 400 - 900 r / min and the stirring time is 10 - 60 min. At this time, the precursors of metal ions and ligands will be fully generated.

[0048] In addition, the reaction temperature after adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine is -5°C to 20°C, preferably -10°C to 10°C. Here, based on the "thermodynamic selection" strategy, the reaction temperature after adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine is -5°C to 20°C. If the temperature is too high, nanoparticles will be generated, and if the temperature is too low, the reaction will slow down and the reaction time will increase.

[0049] Step 2: Add sodium borohydride solution to system A under continuous stirring. After the reaction ends, system B is obtained.

[0050] Among them, sodium borohydride is used as a reducing agent. Sodium borohydride has strong reducibility. Before use, it is dissolved in deionized water, ethanol or a mixed solution of deionized water and ethanol according to the liquid-to-material ratio of 2 mL:(10 - 80) mg. That is, when the solvent is selected as deionized water, the ratio of deionized water to the reducing agent is 2 mL:(10 - 80) mg. That is, in the sodium borohydride solution, the ratio of the solvent to sodium borohydride is 2 mL:(10 - 80) mg, and the solvent is water, ethanol or a mixed solution of water and ethanol. Water is preferably deionized water.

[0051] Furthermore, the molar ratio of sodium borohydride to silver ions in silver nitrate is (1 - 10):1. If this ratio is too large, nanoparticles will be generated, and if it is too small, the metal ion and ligand precursors cannot be fully reduced, resulting in a decrease in the yield and even the inability to prepare the target clusters.

[0052] In this step, the stirring rate is 600 - 1200 r / min, preferably 600 - 1000 r / min. If the stirring rate is too fast here, nanoparticles will be easily generated, and if the stirring is too slow, particle precipitation will occur. In addition, the reaction time in this step is 8 - 24 h. If the reaction time is too long, nanoparticles will be generated, and if the time is too short, metastable clusters will be generated instead of the target clusters.

[0053] Step 3: Perform oil-water phase separation on system B. After washing the oil phase, silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine are obtained.

[0054] Among them, the washing in this step refers to centrifugal washing with methanol 3 to 5 times at a centrifugal speed of 8000 r / min.

[0055] A preparation method of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine disclosed in the present invention adopts a simple one-step method. Add silver nitrate into a mixed solvent of dichloromethane and methanol, stir until the silver nitrate is completely dissolved, and then successively add the ligand 2,4-dimethylbenzenethiol and triphenylphosphine under continuous stirring to obtain a precursor of metal ions and ligands. Then, reduce the precursor solution with a reducing agent, and finally prepare silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine. The prepared silver nanoclusters are monodisperse, the raw materials are easily available, the synthesis operation is simple, the separation and washing process is simple, and it has good repeatability, broadening and enriching the types of silver nanoclusters, providing a theoretical and material basis for related research and development.

[0056] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0057] Conventional instrument equipment in the art is used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0058] Example 1

[0059] A preparation method of silver nanoclusters of 2,4-dimethylbenzenethiol and triphenylphosphine includes the following steps:

[0060] (1) Add a mixed solvent of dichloromethane and methanol with a volume ratio of 1:2 into a 250 mL single-necked round-bottom flask, and then transfer 10 mg of silver nitrate into the solvent containing the above solvent. Stir at 800 r / min for 15 min to obtain a silver nitrate solution after complete dissolution;

[0061] (2) Adjust the stirring rate to 400 r / min, and successively add 2,4-dimethylbenzenethiol (Ag+ : Ligand molar ratio = 0.5:1) and triphenylphosphine (Ag + : Ligand molar ratio = 2:1), maintain the temperature of the reaction system at -10 °C, and continuously stir for 30 min;

[0062] (3) Adjust the stirring rate to 600 r / min. After mixing sodium borohydride and deionized water at 10 mg / mL (NaBH4:H2O), slowly add the solution obtained in step (2) (the molar ratio of NaBH4:Ag + is 1:1), and continuously stir for 20 h to terminate the reaction;

[0063] (4) Perform oil-water separation on the crude product after the reaction. Take the oil phase and centrifuge and wash it with methanol (8000 r / min, 5 min each time), repeat 5 times, and finally obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0064] Example 2

[0065] A preparation method of silver nanoclusters of 2,4-dimethylbenzenethiol and triphenylphosphine, comprising the following steps:

[0066] (1) Add a dichloromethane-methanol mixed solvent with a volume ratio of 1:2 to a 250 mL single-necked round-bottom flask, and then transfer 10 mg of silver nitrate to the above solvent, and stir at 800 r / min for 15 min. After complete dissolution, a silver nitrate solution is obtained;

[0067] (2) Adjust the stirring rate to 600 r / min, and sequentially add 2,4-dimethylbenzenethiol (Ag + : Ligand molar ratio = 1:1) and triphenylphosphine (Ag + : Ligand molar ratio = 3:1), maintain the temperature of the reaction system at -10 °C, and continuously stir for 30 min;

[0068] (3) Adjust the stirring rate to 800 r / min. After mixing sodium borohydride and deionized water at 10 mg / mL (NaBH4:H2O), slowly add the solution obtained in step (2) (the molar ratio of NaBH4:Ag + is 2:1), and continuously stir for 20 h to terminate the reaction;

[0069] (4) Perform oil-water separation on the crude product after the reaction. Take the oil phase and centrifuge and wash it with methanol (8000 r / min, 5 min each time), repeat 5 times, and finally obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0070] Example 3

[0071] A preparation method of silver nanoclusters of 2,4-dimethylbenzenethiol and triphenylphosphine, comprising the following steps:

[0072] (1) Add a dichloromethane-methanol mixed solvent with a volume ratio of 1:2 to a 250 mL single-necked round-bottom flask, and then transfer 10 mg of silver nitrate to the above solvent. Stir at 800 r / min for 15 min to obtain a silver nitrate solution after complete dissolution;

[0073] (2) Adjust the stirring rate to 400 r / min, and sequentially add 2,4-dimethylbenzenethiol (Ag + : ligand molar ratio = 2:1) and triphenylphosphine (Ag + : ligand molar ratio = 4:1). Maintain the temperature of the reaction system at -10 °C and continuously stir for 30 min;

[0074] (3) Adjust the stirring rate to 1000 r / min. After mixing sodium borohydride and deionized water at 10 mg / mL (NaBH4:H2O), slowly add the solution obtained in step (2) (NaBH4:Ag + molar ratio = 4:1), and continuously stir for 20 h to terminate the reaction;

[0075] (4) Perform oil-water separation on the crude product after the reaction. Take the oil phase and centrifuge and wash it with methanol (8000 r / min, 5 min each time), repeat 5 times, and finally obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0076] Example 4

[0077] A method for preparing silver nanoclusters of 2,4-dimethylbenzenethiol and triphenylphosphine, comprising the following steps:

[0078] (1) Add a dichloromethane-methanol mixed solvent with a volume ratio of 1:2 to a 250 mL single-necked round-bottom flask, and then transfer 10 mg of silver nitrate to the above solvent. Stir at 800 r / min for 15 min to obtain a silver nitrate solution after complete dissolution;

[0079] (2) Adjust the stirring rate to 400 r / min, and sequentially add 2,4-dimethylbenzenethiol (Ag + : ligand molar ratio = 3:1) and triphenylphosphine (Ag + : ligand molar ratio = 5:1). Maintain the temperature of the reaction system at -10 °C and continuously stir for 30 min;

[0080] (3) Adjust the stirring rate to 1000 r / min. After mixing sodium borohydride and deionized water at 10 mg / mL (NaBH4:H2O), slowly add the solution obtained in step (2) (NaBH4:Ag + molar ratio = 6:1), and continuously stir for 20 h to terminate the reaction;

[0081] (4) After the crude product of the reaction is subjected to oil-water separation, the oil phase is centrifugally washed with methanol (8000 r / min, 5 min each time), and the operation is repeated 5 times to finally obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0082] Example 5

[0083] A preparation method of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, comprising the following steps:

[0084] (1) Add a dichloromethane-methanol mixed solvent with a volume ratio of 1:2 to a 250 mL single-necked round-bottom flask, and then transfer 10 mg of silver nitrate to the above solvent, and stir at 800 r / min for 15 min. After complete dissolution, a silver nitrate solution is obtained;

[0085] (2) Adjust the stirring rate to 400 r / min, and sequentially add 2,4-dimethylbenzenethiol (Ag + : ligand molar ratio = 4:1) and triphenylphosphine (Ag + : ligand molar ratio = 6:1), maintain the temperature of the reaction system at -10 °C, and continuously stir for 30 min;

[0086] (3) Adjust the stirring rate to 1000 r / min. After mixing sodium borohydride and deionized water at 10 mg / mL (NaBH4:H2O), slowly add the solution obtained in step (2) (NaBH4:Ag + molar ratio = 10:1), and continuously stir for 20 h to terminate the reaction;

[0087] (4) After the crude product of the reaction is subjected to oil-water separation, the oil phase is centrifugally washed with methanol (10000 r / min, 5 min each time), and the operation is repeated 5 times to finally obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0088] Example 6

[0089] This example discloses a preparation method of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, comprising the following steps:

[0090] Step 1: Add silver nitrate to a mixed solvent of dichloromethane and methanol, stir until the silver nitrate is completely dissolved and becomes transparent. Under continuous stirring, first add the ligand 2,4-dimethylbenzenethiol, and after stirring for 5 min, then add an appropriate amount of triphenylphosphine. After the reaction, system A is obtained;

[0091] Among them, the molar ratio of silver ions in silver nitrate to 2,4-dimethylbenzenethiol is 0.5:1, and the molar ratio of silver ions in silver nitrate to triphenylphosphine is 2:1. Silver nitrate is added to the mixed solvent of dichloromethane and methanol, the stirring rate is 800 r / min, and the stirring time is 25 min; after adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine, the stirring rate is 400 r / min, and the stirring time is 60 min. The reaction temperature after adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine is -5°C.

[0092] Step 2: Add a sodium borohydride solution to system A under continuous stirring. After the reaction is completed, system B is obtained.

[0093] Among them, in the sodium borohydride solution, the ratio of the solvent to sodium borohydride is 2 mL:10 mg, the solvent is water, and the molar ratio of sodium borohydride to silver ions in silver nitrate is 1:1. The stirring rate in this step is 600 r / min, and the reaction time is 24 h.

[0094] Step 3: Perform oil-water phase separation on system B, and centrifuge and wash the oil phase with methanol 3 times to obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0095] Example 7

[0096] This example discloses a preparation method of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, including the following steps:

[0097] Step 1: Add silver nitrate to the mixed solvent of dichloromethane and methanol, stir until silver nitrate is completely dissolved and becomes transparent, first add the ligand 2,4-dimethylbenzenethiol under continuous stirring, and after stirring for 10 min, then add an appropriate amount of triphenylphosphine. After the reaction is completed, system A is obtained.

[0098] Among them, the molar ratio of silver ions in silver nitrate to 2,4-dimethylbenzenethiol is 4):1, and the molar ratio of silver ions in silver nitrate to triphenylphosphine is 6:1. Silver nitrate is added to the mixed solvent of dichloromethane and methanol, the stirring rate is 1600 r / min, and the stirring time is 6 min; after adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine, the stirring rate is 900 r / min, and the stirring time is 10 min. The reaction temperature after adding the ligands 2,4-dimethylbenzenethiol and triphenylphosphine is 20°C.

[0099] Step 2: Add a sodium borohydride solution to system A under continuous stirring. After the reaction is completed, system B is obtained.

[0100] Among them, in the sodium borohydride solution, the ratio of the solvent to sodium borohydride is 2 mL:80 mg, the solvent is ethanol, and the molar ratio of sodium borohydride to silver ions in silver nitrate is 10:1. The stirring rate in this step is 1200 r / min, and the reaction time is 8 h.

[0101] Step 3: Perform oil-water phase separation on system B, and centrifuge and wash the oil phase with methanol 5 times to obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0102] Example 8

[0103] This example discloses a preparation method of silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine, including the following steps:

[0104] Step 1: Add silver nitrate to a mixed solvent of dichloromethane and methanol, stir until silver nitrate is completely dissolved and becomes transparent, first add the ligand 2,4-dimethylbenzenethiol under continuous stirring, after stirring for 8 min, then add an appropriate amount of triphenylphosphine, and obtain system A after the reaction ends;

[0105] Among them, the molar ratio of silver ions in silver nitrate to 2,4-dimethylbenzenethiol is 2:1, the molar ratio of silver ions in silver nitrate to triphenylphosphine is 4:1. When adding silver nitrate to the mixed solvent of dichloromethane and methanol, the stirring rate is 1000 r / min, and the stirring time is 20 min; the stirring rate after adding the ligand 2,4-dimethylbenzenethiol and triphenylphosphine is 500 r / min, the stirring time is 40 min, and the reaction temperature after adding the ligand 2,4-dimethylbenzenethiol and triphenylphosphine is 10 °C.

[0106] Step 2: Add a sodium borohydride solution to system A under continuous stirring, and obtain system B after the reaction ends;

[0107] Among them, in the sodium borohydride solution, the ratio of the solvent to sodium borohydride is 2 mL:60 mg, the solvent is a mixed solution of water and ethanol, and the molar ratio of sodium borohydride to silver ions in silver nitrate is 5:1. The stirring rate in this step is 1000 r / min, and the reaction time is 20 h.

[0108] Step 3: Perform oil-water phase separation on system B, and centrifuge and wash the oil phase with methanol 3 times to obtain silver nanoclusters co-protected by 2,4-dimethylbenzenethiol and triphenylphosphine.

[0109] Use a mixed solution of dichloromethane and n-hexane with a volume ratio of 3:1 to perform crystal growth cultivation on the silver nanocluster stock solutions prepared in Example 1, Example 2, Example 3, Example 4 and Example 5, and obtain the novel Ag 14 S(DMBT) 12The crystal structures of (PPh3)6 alloy nanoclusters are as follows Figure 1 shown.

[0110] As Figure 1 can be seen, the unit cell of this cluster contains two silver nanoclusters and two counterbalance ions. Therefore, the charge carried by this silver nanocluster is +1 valence. Its framework structure is highly symmetric. The phosphorus atoms of 6 triphenylphosphine ligands are located at the front, back, left, right, top, and bottom of the outermost vertices of the cluster and are connected to 1 silver atom. 12 sulfur atoms from the 2,4-dimethylbenzenethiol ligand are connected to silver atoms in the form of μ-3 sulfur. A sulfur atom is located at the center of the entire cluster, which is connected to 6 surrounding silver atoms in the form of μ-6 sulfur. Except for the silver atoms at the vertices, any other silver atom in this cluster is surrounded by sulfur atoms, and the sulfur atoms are surrounded by silver atoms. The average bond length between silver atoms and phosphorus atoms is The average bond length between the central sulfur atom and silver atoms is while the bond length between the remaining sulfur atoms and silver atoms varies in the range of to The average bond length is

[0111] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine, characterized in that: The unit cell of the 2,4-dimethylthiophenol and triphenylphosphine co-protected silver nanoclusters contains two silver nanoclusters and two tetraphenylborate counter-balance ions; The framework of the silver nanocluster is a regular cubic structure, the center of the silver nanocluster is a sulfur atom, and the central sulfur atom is connected to 6 silver atoms around it in the form of μ-6 sulfur; The silver nanocluster contains 6 triphenylphosphine ligands and 12 2,4-dimethylthiophenol ligands; The sulfur atoms in the six triphenylphosphine ligands are located at the six face centers of the regular cubic structure framework, and each sulfur atom is connected to a silver atom; The sulfur atoms in the 12 2,4-dimethylthiophenol ligands are connected to the silver atom in the form of μ-3 sulfur.

2. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Add silver nitrate to a mixed solvent of dichloromethane and methanol, stir until the silver nitrate is completely dissolved, add the ligand 2,4-dimethylthiophenol under continuous stirring, stir for reaction, then add triphenylphosphine, and after the reaction is completed, obtain system A; Step 2: Add sodium borohydride solution to system A under continuous stirring, and obtain system B after the reaction is completed; Step 3: performing oil-water phase separation on system B, and washing the oil phase to obtain the silver nanoclusters co-protected by 2,4-dimethylthiophenol and triphenylphosphine.

3. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 1, the molar ratio of silver ions in silver nitrate to 2,4-dimethylthiophenol is (0.5-4):1, and the molar ratio of silver ions in silver nitrate to triphenylphosphine is (2-6):

1.

4. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 1, silver nitrate is added to a mixed solvent of dichloromethane and methanol, and stirred until the silver nitrate is completely dissolved, wherein the stirring rate is 800 to 1600 r / min and the stirring time is 6 to 25 min.

5. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 1, the stirring rates after adding 2,4-dimethylthiophenol and after adding triphenylphosphine are both 400-900 r / min, and the stirring time is both 10-60 min.

6. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 1, the reaction temperature after adding 2,4-dimethylthiophenol and triphenylphosphine is -5°C to 20°C.

7. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 1, the reaction temperature after adding 2,4-dimethylthiophenol and triphenylphosphine is -10°C to 10°C.

8. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 2, in the sodium borohydride solution, the ratio of solvent to sodium borohydride is 2 mL: (10-80) mg.

9. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 2, the molar ratio of the sodium borohydride to the silver ions in the silver nitrate is (1-10):

1.

10. The method for preparing a silver nanocluster co-protected by 2,4-dimethylthiophenol and triphenylphosphine according to claim 2, characterized in that: In step 2, sodium borohydride solution is added to system A under continuous stirring, the stirring rate is 600-1200 r / min, and the reaction time is 8-24 h.

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