A continuous preparation method for Pd-based bimetallic nanoflowers

Abstract

This invention relates to a continuous preparation method of Pd-based bimetallic nanoflowers, comprising the following steps: a. mixing raw material A and raw material B in a first micromixer to obtain a first mixture, wherein raw material A is an aqueous solution of palladium salt, and raw material B is an aqueous solution of a transition metal salt other than palladium salt, and both raw material A and raw material B contain cationic surfactants; b. mixing the first mixture with raw material C in a second micromixer to obtain a second mixture, wherein raw material C is an aqueous solution of a reducing agent; c. passing the second mixture into a microreactor for a redox reaction to obtain Pd-based bimetallic nanoflowers. This invention achieves rapid and uniform mixing of reaction raw materials through microfluidic technology, and the prepared Pd-based bimetallic nanoflowers possess a unique hierarchical structure and high specific surface area, with uniform particle size and morphology distribution.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and relates to a continuous preparation method of Pd-based bimetallic nanoflowers, specifically a continuous preparation method of Pd-based bimetallic nanoflowers based on microfluidic technology. Background Technology

[0002] Bimetallic nanomaterials have attracted widespread attention in recent years due to their unique physicochemical properties, surface catalytic activity, and excellent electrochemical performance. In particular, Pd (palladium)-based bimetallic nanomaterials have been extensively studied due to their superior performance in catalysis, energy conversion, and energy storage.

[0003] Reference 1 discloses a method for preparing controllable bimetallic alloy nanoparticles. This method uses n-butyllithium as a strong reducing agent and oleylamine and tri-n-octylphosphine as protective agents to simultaneously reduce the acetylacetone salt, chloride salt or acetate salt of Pt / Pd-M (where M is Ni, Fe, Co, Mn, Pd, Zn, Cu, Mo, etc.) to form uniform Pt / Pd-M alloy nanoparticles with controllable size.

[0004] Reference 2 discloses a method for preparing Bi-Pd bimetallic nanocrystals. The method includes dissolving Bi salt and Pd salt in oleylamine, heating and reducing the reaction, and then centrifuging, drying and other steps to prepare Bi-Pd bimetallic nanocrystals with specific morphology and size.

[0005] Nanoflower structures are unique nanostructures whose layered or petal-like morphology endows them with abundant pores and a high specific surface area, significantly enhancing the catalytic performance of materials. Nanoflower-like alloys not only provide more active sites but also optimize reactant transport pathways, thereby increasing catalytic reaction rates. Nanoflower structures have demonstrated superior performance in fields such as energy catalysis, sensors, and electrochemistry.

[0006] Reference 3 discloses a method for preparing a three-dimensional flower-like supported bimetallic copper-nickel nanocatalyst. This method involves growing layered copper-nickel-aluminum bimetallic hydroxides in situ on the surface of amorphous alumina microspheres, followed by calcination and reduction at high temperature to finally obtain a highly dispersed flower-like bimetallic CuNi nanocatalyst.

[0007] Reference 4 discloses a method for preparing palladium-copper bimetallic nanoflower peroxides. The method involves mixing sodium tetrachloropalladium, tungsten hexacarbonyl, copper chloride dihydrate, dimethylformamide, and glacial acetic acid, followed by ultrasonication, oil bath heating, centrifugal washing, and other steps to prepare palladium-copper bimetallic nanoflowers.

[0008] Microfluidics, as an emerging synthetic approach, provides an innovative technical means for the preparation of nanomaterials by achieving precise fluid control and enhanced mass transfer mixing within microreactors. Compared with traditional batch synthesis, microreactors, with their unique flow characteristics and high surface area-to-volume ratio, can significantly improve mixing efficiency, shorten reaction time, and reduce energy consumption. In the preparation of nanomaterials, microfluidics offers advantages such as efficient mixing and heat / mass transfer, precise control of reaction parameters, scalability and reproducibility, and environmental friendliness.

[0009] Reference 5 discloses a microfluidic preparation technique for size-controllable monodisperse gold nanoparticles, including a microreaction system constructed based on the gold nanoparticle preparation method, the acquisition and transfer of the gold nanoparticle reaction precursor solution, the continuous and controllable preparation of gold nanoparticles, and the obtaining of a uniform monodisperse gold nanoparticle toluene solution.

[0010] References:

[0011] Reference 1: CN103192086A

[0012] Reference 2: CN113664215B

[0013] Reference 3: CN106955709A

[0014] Reference 4: CN111992732A

[0015] Reference 5: CN108555309A Summary of the Invention

[0016] The problem the invention aims to solve

[0017] Existing research, such as the bimetallic nanoflowers prepared in the above-mentioned literature (cited literature 3 and cited literature 4), usually adopts the traditional batch synthesis process. This synthesis process has problems such as difficulty in accurately controlling reaction conditions, uneven product particle size and morphology, poor batch-to-batch reproducibility, and low synthesis efficiency, which cannot meet the requirements of efficient, large-scale continuous preparation.

[0018] Microfluidic technology, as an advanced synthetic method, has been initially applied in the preparation of metal nanomaterials, particularly demonstrating certain advantages in the synthesis of single-metal nanoparticles (e.g., reference 5). However, due to the complex hierarchical structure and compositional distribution of bimetallic nanoflowers, their morphology and the formation process of their alloying or core-shell structures place higher demands on the selection of the reaction system, and also impose more stringent requirements on the control of reaction conditions (e.g., rapid mixing and uniform concentration / temperature field). Currently, there are no reports on the preparation of such complex structures via microreactors. Furthermore, traditional methods often use toxic reducing agents (e.g., oleylamine) or energy-intensive synthetic processes, which not only increase the environmental burden but also raise production costs. Therefore, developing an efficient, green, and controllable method for preparing Pd-based bimetallic nanoflowers based on microfluidic technology has significant scientific and practical value.

[0019] Solution for solving the problem

[0020] Through research, the inventors have proposed a continuous preparation method for Pd-based bimetallic nanoflowers based on microfluidic technology. This method utilizes a microfluidic synthesis platform to achieve efficient control of reaction conditions by selecting metal precursors and rationally adjusting process parameters, thereby ensuring that the products have uniform size and morphology.

[0021] Specifically, the present invention solves the technical problem by means of the following solution.

[0022] [1]. A continuous preparation method for Pd-based bimetallic nanoflowers, comprising the following steps:

[0023] a. Raw material A and raw material B are passed into a first micro mixer to mix and obtain a first mixture. Raw material A is an aqueous solution of palladium salt, and raw material B is an aqueous solution of other transition metal salts besides palladium salt. Both raw material A and raw material B contain cationic surfactants.

[0024] b. The first mixture and raw material C are passed into a second micro mixer to mix and obtain a second mixture, wherein the raw material C is an aqueous solution of a reducing agent;

[0025] c. Pass the second mixture into a microreactor to carry out a redox reaction to obtain Pd-based bimetallic nanoflowers.

[0026] [2]. According to the preparation method described in [1], wherein,

[0027] The second mixture is essentially a homogeneous dispersion system, and the mixing time in step b is 0.1 to 10 s.

[0028] [3]. According to the preparation method described in [1] or [2], wherein,

[0029] The palladium salt is selected from one or more of sodium tetrachloropalladium and potassium tetrachloropalladium.

[0030] The other transition metal salts besides palladium salts are selected from one or more of copper chloride, silver nitrate, chloroauric acid, and potassium chloroplatinate.

[0031] The cationic surfactants include quaternary ammonium salt cationic surfactants.

[0032] [4]. The preparation method according to any one of [1]-[3], wherein,

[0033] The concentration of palladium salt in raw material A is 0.001–0.01 mol / L;

[0034] The concentration of transition metal salts other than palladium salt in raw material B is 0.001–0.01 mol / L;

[0035] The concentrations of cationic surfactants in raw material A and raw material B are each independently 0.001–0.05 mol / L.

[0036] [5]. The preparation method according to any one of [1]-[4], wherein,

[0037] The molar ratio of palladium salt in raw material A to other transition metal salts (excluding palladium salt) in raw material B is (1-10):1.

[0038] [6]. The preparation method according to any one of [1]-[5], wherein,

[0039] The reducing agent is selected from one or more of ascorbic acid and citric acid.

[0040] [7]. The preparation method according to any one of [1]-[6], wherein,

[0041] The concentration of the reducing agent in raw material C is 0.1–0.5 mol / L.

[0042] [8]. The preparation method according to any one of [1]-[7], wherein,

[0043] The first micromixer and the second micromixer are each independently a microchannel mixer, a membrane dispersion mixer, or a microsieve mixer;

[0044] The microreactor is a microchannel reactor or a coil-type microreactor.

[0045] [9]. The preparation method according to any one of [1]-[8], wherein,

[0046] The temperature in the first micro-mixer is 10–50°C, and the mixing time is 0.1–10 s;

[0047] The temperature in the second micro-mixer is 10–50°C;

[0048] The temperature in the microreactor is 10–60°C, and the residence time is 0.1–20 min.

[0049]

[10] . Pd-based bimetallic nanoflowers prepared according to any one of [1]-[9], wherein the particle size of the Pd-based bimetallic nanoflowers is less than 500 nm.

[0050] The effects of the invention

[0051] This invention provides a continuous preparation method for Pd-based bimetallic nanoflowers based on microfluidic technology, which not only significantly improves the morphology and size uniformity of the product but also enhances reaction efficiency and batch-to-batch reproducibility. This method utilizes environmentally friendly raw materials and processes, demonstrating excellent potential for industrial application. Furthermore, the method of this invention has strong versatility and can be extended to the continuous and controllable synthesis of other bimetallic and even multimetallic nanomaterials, possessing broad reference value and application potential.

[0052] Specifically, the present invention achieves the following beneficial technical effects:

[0053] 1. This invention achieves rapid and uniform mixing of reaction raw materials through microfluidic technology. The prepared Pd-based bimetallic nanoflowers have a unique hierarchical structure and high specific surface area, and the particle size and morphology distribution are uniform. Compared with the traditional batch synthesis method, the preparation method of this invention effectively avoids the problem of product dispersion caused by insufficient mixing.

[0054] 2. Based on the enhanced mass and heat transfer performance of microreactors, this invention significantly improves reaction efficiency, shortens reaction time, and provides a practical solution for industrial-scale nanomaterial synthesis through continuous production.

[0055] 3. This invention uses green reducing agents such as ascorbic acid to replace traditional toxic chemicals, and at the same time utilizes the efficient mass transfer characteristics of microreactors to reduce energy consumption, embodying the concept of green chemistry and providing a new approach for the preparation of environmentally friendly nanomaterials.

[0056] 4. Based on the high-precision control characteristics of microfluidic technology, this invention is not only applicable to the preparation of Pd-based bimetallic nanoflowers, but can also be extended to the continuous and controllable synthesis of other bimetallic or even multimetallic nanomaterials by adjusting the type of metal precursor and process parameters, further enhancing the applicability and practical application value of this method. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the process flow of a specific embodiment of the preparation method of the present invention;

[0058] Figure 2 TEM images of the PdCu bimetallic nanoflowers prepared in Examples 1-3;

[0059] Figure 3 The image shows a TEM image of the flowerless PdCu bimetallic nanoparticles prepared in Comparative Example 4.

[0060] Figure 4 HRTEM and EDS images of the PdCu bimetallic nanoflowers prepared in Example 3;

[0061] Figure 5 The XRD patterns of the PdCu bimetallic nanoflowers prepared in Examples 1-3 are shown below.

[0062] Figure 6 XPS images of the PdCu bimetallic nanoflowers prepared in Examples 1-3;

[0063] Figure 7 HAADF-STEM and EDS images of the Pd-based bimetallic nanoflowers prepared in Examples 4-6;

[0064] Figure 8 The images show the XRD patterns of the Pd-based bimetallic nanoflowers prepared in Examples 4-6. Detailed Implementation

[0065] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0066] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0067] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0068] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0069] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0070] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0071] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0072] In this specification, the terms "optional" or "optional / optionally" are used to indicate the use or non-use of certain substances, components, procedures, application conditions, etc.

[0073] Unless otherwise specified, “room temperature” or “room temperature” as used in this instruction manual usually refers to a temperature of 23±2℃.

[0074] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" used refers to weight or mass percentage content.

[0075] In this specification, the terms "comprising," "having," "including," or "containing" can mean included or open-ended, and do not exclude additional, uncited elements or method steps. At the same time, "comprising," "having," "including," or "containing" can also mean closed-ended, excluding additional, uncited elements or method steps.

[0076] In this specification, the terms "substantially" or "truly" mean that the error compared to the relevant perfect or theoretical standard is less than 1%, or less than 0.8%, or less than 0.6%. Furthermore, when "all" or "entire" is used in this specification, it also means "all" or "entire" in the sense of "substantially" or "truly".

[0077] Unless otherwise stated, in this instruction manual, "more" in "multiple", "multi-variety", "multiple", etc., means a value of 2 or more.

[0078] In this specification, transition metals include five elements: palladium (Pd), copper (Cu), gold (Au), silver (Ag), and platinum (Pt).

[0079] In this specification, transition metal salts include their various hydrates, such as copper chloride, which includes anhydrous copper chloride, copper chloride dihydrate, etc.

[0080] The purpose of this invention is to provide a continuous preparation method for Pd-based bimetallic nanoflowers, which includes the following steps:

[0081] a. Raw material A and raw material B are passed into a first micro mixer to mix and obtain a first mixture. Raw material A is an aqueous solution of palladium salt, and raw material B is an aqueous solution of other transition metal salts besides palladium salt. Both raw material A and raw material B contain cationic surfactants.

[0082] b. The first mixture and raw material C are passed into a second micro mixer to mix and obtain a second mixture, wherein the raw material C is an aqueous solution of a reducing agent;

[0083] c. Pass the second mixture into a microreactor to carry out a redox reaction to obtain Pd-based bimetallic nanoflowers.

[0084] The following describes each step in the preparation method of the present invention in detail.

[0085] Step a

[0086] In this invention, raw material A and raw material B are fed into a first micro-mixer for mixing. This allows the reaction raw materials for producing Pd-based bimetallic nanoflowers to undergo liquid-liquid mixing and / or liquid-liquid dispersion in the micro-mixer. Because the micro-mixer can increase the contact surface area between raw material A, which contains an aqueous solution of palladium salt, and raw material B, which contains an aqueous solution of other transition metal salts besides palladium salt, the mixing and / or dispersion of the raw materials before the reaction is more uniform, which is beneficial to the subsequent reaction.

[0087] In this invention, raw material A is an aqueous solution of a palladium salt and contains a cationic surfactant. This invention does not particularly limit the palladium salt used, as long as it is water-soluble. In some specific embodiments, the palladium salt is selected from one or more of sodium tetrachloropalladium, potassium tetrachloropalladium, or their hydrates.

[0088] In this invention, raw material B is an aqueous solution of a transition metal salt other than palladium and contains a cationic surfactant. In some specific embodiments, the other transition metal salt is selected from one or more of copper chloride, silver nitrate, chloroauric acid, potassium chloroplatinate, or their hydrates.

[0089] In this invention, the palladium salt and other transition metal salts are selected appropriately so that the first mixture formed after mixing raw material A and raw material B is essentially in a solution state, thereby facilitating the thorough mixing of the palladium salt and other transition metal salts. In some specific embodiments, the first mixture is essentially a homogeneous dispersion system.

[0090] In some specific embodiments, the concentration of palladium salt in raw material A is 0.001–0.01 mol / L, preferably 0.001–0.005 mol / L, more preferably 0.002–0.005 mol / L, for example, it can be 0.001 mol / L, 0.002 mol / L, 0.0025 mol / L, 0.003 mol / L, 0.004 mol / L, 0.005 mol / L, 0.006 mol / L, 0.007 mol / L, 0.008 mol / L, 0.009 mol / L, 0.01 mol / L, etc.

[0091] In some specific embodiments, the concentration of transition metal salts other than palladium salt in raw material B is 0.001–0.01 mol / L, preferably 0.001–0.005 mol / L, more preferably 0.002–0.005 mol / L, for example, it can be 0.001 mol / L, 0.002 mol / L, 0.0025 mol / L, 0.003 mol / L, 0.004 mol / L, 0.005 mol / L, 0.006 mol / L, 0.007 mol / L, 0.008 mol / L, 0.009 mol / L, 0.01 mol / L, etc.

[0092] It should be noted that the upper limit of the above concentration range is general. For specific palladium salts and other transition metal salts, the upper limit of the above concentration should also be below their solubility.

[0093] In some specific embodiments, the molar ratio of palladium salt in raw material A to other transition metal salts (excluding palladium salt) in raw material B is (1-10):1, preferably (1-5):1, more preferably (1-3):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. By adjusting the ratio of palladium salt to other transition metal salts (excluding palladium salt) within the above range, it can be ensured that the generated Pd-based bimetallic nanoparticles do not agglomerate and self-assemble into a flower-like structure.

[0094] In this invention, the cationic surfactants in raw materials A and B are adsorbed onto the surface of metal ions via electrostatic interactions, preventing premature reduction or aggregation of the metal ions. This serves both as a stabilizer in the metal precursor preparation process and as a structure-directing agent for the formation of Pd-based bimetallic nanoflowers. Specifically, the cationic surfactants first react with palladium ions (in the form of negatively charged PdCl4) in raw material A via electrostatic interactions. 2- The palladium ions are combined in the form of Pd, and then the palladium ions are reduced to Pd clusters under the action of a reducing agent. The Pd clusters can catalyze the reduction of other transition metal ions in raw material B, except for palladium ions, and thus obtain Pd-based bimetallic nanoflowers. In this process, the cationic surfactant prevents the agglomeration of nanoparticles through the steric hindrance effect of its long carbon chain, and also acts as a structure guiding agent for the formation of Pd-based bimetallic nanoflowers.

[0095] In some specific embodiments, the cationic surfactant includes quaternary ammonium salt cationic surfactants, such as one or more of hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), octadecyltrimethylammonium bromide (OTAB), and octadecyltrimethylammonium chloride (OTAC).

[0096] In some specific implementations, the concentrations of the cationic surfactants in raw material A and raw material B are each independently 0.001–0.05 mol / L, preferably 0.001–0.02 mol / L, more preferably 0.002–0.01 mol / L, for example, 0.001 mol / L, 0.003 mol / L, 0.005 mol / L, 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, etc.

[0097] In some specific implementations, a pump (e.g., a horizontal flow pump, a syringe pump, a diaphragm pump, etc.) is used to feed raw material A and raw material B into the first micro mixer.

[0098] In some specific implementations, raw material A and raw material B are introduced into the first micro mixer at a flow rate of 0.01 to 1 mL / min, preferably 0.1 to 0.5 mL / min.

[0099] In some specific implementations, the flow ratio of the two feed liquids in the first micro-mixer, i.e., the flow ratio of raw material A to raw material B, is adjusted so that the molar ratio of palladium salt contained in raw material A to other transition metal salts contained in raw material B, excluding palladium salt, is (1-10):1.

[0100] Furthermore, the flow ratio of raw material A to raw material B can be adjusted by regulating the flow rates of raw material A and raw material B into the first micro-mixer. In some specific embodiments, the volumetric flow ratio of raw material A to raw material B can be (0.5~5):1.

[0101] The present invention does not particularly limit the first micromixer used in step a, and it can be any micromixer known in the art suitable for liquid-liquid mixing, such as microchannel mixers, membrane dispersion mixers, or microsieve mixers. In a preferred embodiment, the first micromixer is a microchannel mixer.

[0102] In some specific implementations, the channel diameter of the first micro mixer is 0.1 to 2 mm, preferably 0.2 to 0.8 mm, for example, it can be 0.2 mm, 0.25 mm, 0.5 mm, etc.

[0103] In some specific implementations, the temperature in the first micro mixer is 10-50°C, preferably 20-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, etc.; by controlling the temperature in the micro mixer within the above range, blockage of the reaction pipeline can be prevented and mixing efficiency can be improved.

[0104] In some specific implementations, the mixing time of raw material A and raw material B in the first micro mixer is 0.1–10 s, preferably 0.2–5 s, for example, 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, etc.; by controlling the mixing time within the range of 0.1–10 s, sufficient mixing can be ensured while also maintaining production efficiency. Here, "mixing time" refers to the average residence time of the materials in the micro mixer.

[0105] Step b

[0106] In this invention, the first mixture and raw material C are mixed in a second micromixer to obtain a second mixture. The first mixture and raw material C are dispersed in the second micromixer to ensure thorough mixing. In this invention, the first mixture containing the metal precursor solution is pre-mixed with the raw material C containing the reducing agent solution before the redox reaction. Due to the small internal size of the second micromixer, the surface area at contact between the two is large, resulting in strong shear force. This allows for immediate and effective dispersion of the metal precursor solution and the reducing agent solution after mixing in the second micromixer. In other words, the uniform dispersion of the reaction precursor provides uniform reaction conditions for the subsequent reduction of metal ions and the nucleation and growth of metal nanoparticles.

[0107] Specifically, a pump (e.g., a horizontal flow pump, a syringe pump, a diaphragm pump, etc.) can be used to introduce raw material C into the second micromixer. Additionally, the flow ratio of the first mixture to raw material C can be adjusted by regulating the flow rates of the first mixture and raw material C into the second micromixer. In some specific embodiments, the volumetric flow ratio of the first mixture to raw material C is (0.5–5):1, for example, 0.8:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, etc.

[0108] The present invention does not particularly limit the second micromixer used in step b; it can be any micromixer known in the art suitable for liquid-liquid mixing, such as microchannel mixers, membrane dispersion mixers, or microsieve mixers. In a preferred embodiment, the second micromixer is a microchannel mixer.

[0109] In some specific implementations, the channel diameter of the second micromixer is 0.1 to 2 mm, preferably 0.2 to 0.8 mm, for example, 0.2 mm, 0.25 mm, 0.5 mm, etc.

[0110] In some specific embodiments, the temperature in the second micro-mixer is 10–50°C, preferably 20–40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, etc.; by controlling the temperature in the second micro-mixer to 10–50°C, uniform mixing of the metal precursor solution and the reducing agent solution can be achieved. The mixing time in the second micro-mixer is 0.1–10 s, preferably 0.2–5 s, for example, 0.5 s, 1 s, 3 s, 5 s, 7 s, 9 s, etc.; by controlling the mixing time to 0.1–10 s, production efficiency can be considered while ensuring good dispersion.

[0111] It should be noted that the second micro-mixer mainly disperses the metal precursor solution and the reducing agent solution, but at the same time, a certain amount of metal precursor and reducing agent will also undergo redox reactions. Therefore, a certain amount of metal atoms or nanoclusters will also be generated after mixing in the second micro-mixer.

[0112] In some specific implementations, the reducing agent is selected from one or more of ascorbic acid and citric acid.

[0113] In some specific implementations, the concentration of the reducing agent in the raw material C is 0.1 to 0.5 mol / L, preferably 0.2 to 0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc.

[0114] In some specific embodiments, the raw material C is introduced into the second micromixer at a flow rate of 0.01 to 1 mL / min, preferably 0.1 to 0.5 mL / min.

[0115] In some specific implementations, the second mixture is substantially a homogeneous dispersion system.

[0116] Step c

[0117] In this invention, the second mixture is passed into a microreactor to carry out a redox reaction to obtain Pd-based bimetallic nanoflowers.

[0118] In some specific implementations, the metal precursor solution in the second mixture undergoes a redox reaction with a reducing agent in a microchannel reactor to nucleate and grow Pd-based bimetallic nanoflowers, and the formed nanoflowers are dispersed in water in colloidal form under the stabilizing effect of cationic surfactants.

[0119] In this invention, the reducing agent reduces metal ions in the metal precursor solution to metal atoms, for example, reducing palladium ions (in the form of PdCl4) to metal atoms. 2- (Existing in its original form) and other transition metal ions (such as Cu2+) are reduced to metal atoms (Pd, Cu, etc.).

[0120] In this invention, the cationic surfactant regulates the reduction of metal ions and the growth of nanoparticles through electrostatic interaction and steric hindrance effect, and guides the self-assembly of nanoparticles to form layered or petal-shaped nanoflower structures.

[0121] The present invention does not impose any particular limitation on the microreactor used in step c; it can be any microreactor known in the art suitable for liquid-liquid mixing, such as microchannel reactors or coil microreactors. In a preferred embodiment, the microreactor is a microchannel reactor. The channel diameter of the microreactor is 0.8–5 mm, preferably 0.8–2 mm, for example, 0.8 mm, 1 mm, 1.5 mm, etc.; the length is 1–20 m, preferably 3–10 m.

[0122] In this invention, there are no particular restrictions on the material of the microreactor; for example, it can be selected from one or more of polytetrafluoroethylene, perfluoroethylene propylene, and soluble polytetrafluoroethylene.

[0123] In some specific implementations, the reaction temperature in the microreactor is 10–60°C, preferably 20–50°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc. By controlling the reaction temperature within the above range, it is possible to ensure sufficient reaction between the metal precursor solution and the reducing agent, while maintaining a stable nucleation environment. Too low a reaction temperature will result in a slow reaction rate, which is not conducive to initial nucleation; while too high a reaction temperature will cause the reaction to be too fast, making it difficult to form the desired pore structure, thus leading to the aggregation of nanoflowers. Therefore, selecting an appropriate reaction temperature range is crucial for obtaining the ideal nanoflower structure.

[0124] In some specific implementations, the residence time in the microreactor is 0.1–20 min, preferably 3–10 min, for example, 0.5 min, 1 min, 3 min, 5 min, 7 min, 9 min, 10 min, 13 min, 15 min, 17 min, 19 min, etc. By controlling the residence time within the above range, uniform nucleation and growth of metal atoms can be ensured, forming a stable nanoflower structure, and avoiding adverse phenomena such as incomplete reaction or insufficient nucleation caused by too short a residence time.

[0125] Other steps

[0126] The preparation method of the present invention may optionally include one or more steps selected from the steps of setting up a reaction apparatus, post-processing of the product, and purification.

[0127] In some specific embodiments, the preparation method of the present invention further includes a step of assembling a reaction apparatus before step a. Specifically, in this step, the various components of the reaction apparatus are connected to allow the reactants to flow within the reaction apparatus. The various components of the reaction apparatus include, but are not limited to, the pump, micromixer, microreactor, etc., described above.

[0128] In some specific embodiments, the preparation method of the present invention further includes a post-processing purification step after step c, which involves purifying the obtained Pd-based bimetallic nanoflowers. The post-processing purification step includes one or more steps selected from centrifugation, water washing, alcohol washing, etc.

[0129] In some specific implementations, after step c, the resulting reaction solution containing Pd-based bimetallic nanoflowers is centrifuged at a speed of 5000–10000 r / min for 5–10 min. The centrifuged Pd-based bimetallic nanoflowers are then washed multiple times with one or more of deionized water, ethanol, or isopropanol. Water washing and / or alcohol washing can be performed once or multiple times. After each water or alcohol wash, centrifugation and / or filtration are used to remove unreacted substances and surfactants, ultimately obtaining high-purity Pd-based bimetallic nanoflowers.

[0130] This invention also relates to a Pd-based bimetallic nanoflower prepared according to the method of this invention. Through the implementation of the above preparation method, the Pd-based bimetallic nanoflower prepared by this invention possesses a high specific surface area and abundant active sites.

[0131] The Pd-based bimetallic nanoflowers prepared by this invention have a particle size of less than 500 nm, preferably less than 400 nm, more preferably less than 300 nm, and even more preferably 10–200 nm. The particle size is obtained by statistical analysis of the nanoflower particle size in the TEM image using Nano Measurer software.

[0132] The Pd-based bimetallic nanoflowers prepared by the method of this invention exhibit high dispersion of nanoflower particles. In this invention, high dispersion means that the Pd-based bimetallic nanoflowers are dispersed as individual particles, and the dispersion is relatively uniform, without large-area aggregation or agglomeration between particles. The highly uniform dispersion of the nanoflower particles can be fully demonstrated by the morphological structure characterized by high-resolution transmission electron microscopy (HRTEM) and transmission electron microscopy (TEM) images.

[0133] Example

[0134] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0135] The parameters of the microreactor used in the following examples are as follows:

[0136] The first micro mixer is a T-type microchannel mixer with a channel diameter of 0.5 mm.

[0137] The second micromixer is a T-type microchannel mixer with a channel diameter of 0.5 mm.

[0138] The microreactor is a microchannel reactor made of polytetrafluoroethylene, with a channel diameter of 0.8 mm and a length of 5 m.

[0139] Example 1:

[0140] A continuous preparation method for PdCu bimetallic nanoflowers, such as Figure 1 The specific steps are as follows:

[0141] Sodium tetrachloropalladium aqueous solution (concentration 0.0025 mol / L) was used as raw material A, anhydrous copper chloride aqueous solution (concentration 0.0025 mol / L) was used as raw material B, and ascorbic acid aqueous solution (concentration 0.3 mol / L) was used as raw material C. Hexadecyltrimethylammonium chloride (CTAC, concentration 0.005 mol / L) was added as a surfactant to both raw material A and raw material B. Raw material A was pumped to a first micromixer (mixing temperature 30℃, mixing time 1 s) using a horizontal flow pump (flow rate 0.3 mL / min), and raw material B was pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) using a syringe pump (flow rate 0.1 mL / min) to obtain a first mixture. Raw material C and the first mixture were then pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) using a syringe pump (flow rate 0.1 mL / min) to obtain a second mixture. The second mixture enters a microchannel reactor connected to the outlet of the second micromixer (reaction temperature 30℃, residence time 5min) for redox reaction, followed by centrifugation (centrifugation speed 10000rpm, centrifugation time 10min), and is washed with water about three times and with alcohol about three times to obtain PdCu bimetallic nanomaterials (denoted as Pd3Cu1), which are then dispersed in ethanol or water for storage.

[0142] Example 2:

[0143] Compared with Example 1, the difference is that the total flow rate of raw material A and raw material B is 0.4 mL / min, and the flow rate ratio of raw material A and raw material B is 2:1.

[0144] The PdCu bimetallic nanomaterial prepared in this embodiment is designated as Pd2Cu1 and stored by dispersing it in ethanol or water.

[0145] Example 3:

[0146] Compared with Example 1, the difference is that the total flow rate of raw material A and raw material B is 0.4 mL / min, and the flow rate ratio of raw material A and raw material B is 1:1.

[0147] The PdCu bimetallic nanomaterial prepared in this embodiment is denoted as Pd1Cu1 and is stored by dispersing it in ethanol or water.

[0148] Example 4:

[0149] A continuous preparation method for PdAu bimetallic nanoflowers, such as Figure 1 The specific steps are as follows:

[0150] Sodium tetrachloropalladate aqueous solution (concentration 0.0025 mol / L) was used as raw material A, chloroauric acid aqueous solution (concentration 0.0025 mol / L) was used as raw material B, and ascorbic acid aqueous solution (concentration 0.3 mol / L) was used as raw material C. Hexadecyltrimethylammonium chloride (CTAC, concentration 0.005 mol / L) was added as a surfactant to both raw material A and raw material B. Raw material A was pumped to a first micromixer (mixing temperature 30℃, mixing time 1 s) using a horizontal flow pump (flow rate 0.2 mL / min), and raw material B was pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) for mixing. The total flow rate of raw material A and raw material B was 0.4 mL / min, with a flow rate ratio of 1:1, to obtain a first mixture. Raw material C and the first mixture were then pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) using a second micromixer for mixing to obtain a second mixture. The second mixture enters a microchannel reactor connected to the outlet of the second micromixer (reaction temperature 30℃, residence time 5min) for redox reaction, followed by centrifugation (centrifugation speed 10000rpm, centrifugation time 10min), and is washed with water about three times and with alcohol about three times to obtain PdAu bimetallic nanomaterials (denoted as PdAu), which are then dispersed in ethanol or water for storage.

[0151] Example 5:

[0152] A continuous preparation method for PdAg bimetallic nanoflowers, such as Figure 1 The specific steps are as follows:

[0153] Sodium tetrachloropalladium aqueous solution (concentration 0.0025 mol / L) was used as raw material A, silver nitrate aqueous solution (concentration 0.0025 mol / L) as raw material B, and ascorbic acid aqueous solution (concentration 0.3 mol / L) as raw material C. Hexadecyltrimethylammonium chloride (CTAC, concentration 0.005 mol / L) was added as a surfactant to both raw material A and raw material B. Raw material A was pumped to a first micromixer (mixing temperature 30℃, mixing time 1 s) using a horizontal flow pump (flow rate 0.2 mL / min), and raw material B was pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) for mixing. The total flow rate of raw material A and raw material B was 0.4 mL / min, with a flow rate ratio of 1:1, to obtain a first mixture. Raw material C and the first mixture were then pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) using a second pump (flow rate 0.1 mL / min) for mixing to obtain a second mixture. The second mixture enters a microchannel reactor connected to the outlet of the second micromixer (reaction temperature 30℃, residence time 5min) for redox reaction, followed by centrifugation (centrifugation speed 10000rpm, centrifugation time 10min), and is washed with water about three times and with alcohol about three times to obtain PdAg bimetallic nanomaterials (denoted as PdAg), which are then dispersed in ethanol or water for storage.

[0154] Example 6:

[0155] A continuous preparation method for PdPt bimetallic nanoflowers, such as Figure 1 The specific steps are as follows:

[0156] Sodium tetrachloropalladate aqueous solution (concentration 0.0025 mol / L) was used as raw material A, potassium chloroplatinate aqueous solution (concentration 0.0025 mol / L) was used as raw material B, and ascorbic acid aqueous solution (concentration 0.3 mol / L) was used as raw material C. Hexadecyltrimethylammonium chloride (CTAC, concentration 0.005 mol / L) was added as a surfactant to both raw material A and raw material B. Raw material A was pumped to a first micromixer (mixing temperature 30℃, mixing time 1 s) using a horizontal flow pump (flow rate 0.2 mL / min), and raw material B was pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) for mixing. The total flow rate of raw material A and raw material B was 0.4 mL / min, with a flow rate ratio of 1:1, to obtain a first mixture. Raw material C and the first mixture were then pumped to a second micromixer (mixing temperature 30℃, mixing time 1 s) using a second micromixer for mixing to obtain a second mixture. The second mixture enters a microchannel reactor connected to the outlet of the second micromixer (reaction temperature 30℃, residence time 5min) for redox reaction, followed by centrifugation (centrifugation speed 10000rpm, centrifugation time 10min), and is washed with water about three times and with alcohol about three times to obtain PdPt bimetallic nanomaterials (denoted as PdPt), which are then dispersed in ethanol or water for storage.

[0157] Comparative Example 1:

[0158] Compared with Example 1, the difference is that the flow rate of raw material A is 0.4 mL / min and the flow rate of raw material B is 0 mL / min.

[0159] The nanomaterials prepared in this comparative example are Pd nanoparticles.

[0160] Comparative Example 2:

[0161] Compared with Example 1, the difference is that the flow rate of raw material A is 0 mL / min and the flow rate of raw material B is 0.4 mL / min.

[0162] Nanoparticles were not prepared in this comparative example.

[0163] Comparative Example 3:

[0164] Using the same flow rate as in Example 1, raw materials A, B, and C were simultaneously injected into a microchannel reactor (reaction temperature 30°C, residence time 5 min) for oxidation-reduction reaction. Afterward, the mixture was centrifuged (centrifugation speed 10000 rpm, centrifugation time 10 min) and subjected to approximately three water washes and three alcohol washes (ethanol).

[0165] The PdCu bimetallic nanomaterials prepared in this comparative example have extremely uneven particle size distribution and exhibit self-nucleated Pd nanoparticles.

[0166] Comparative Example 4:

[0167] Compared with Example 3, the difference is that neither raw material A nor raw material B contains cationic surfactants.

[0168] Characterization and Analysis

[0169] The obtained nanomaterials were characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) to determine their composition, structure, morphology, etc.

[0170] The preparation process of TEM and HRTEM characterization samples is as follows: the bimetallic nanomaterials prepared in each example and comparative example are dispersed in ethanol, 1 to 3 drops of dispersion are dropped onto an ultrathin carbon film, and then dried appropriately.

[0171] 1. Characterization using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDS).

[0172] The PdCu bimetallic nanomaterials prepared in Examples 1-3 and Comparative Example 4 were characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and energy dispersive spectroscopy (EDS).

[0173] Transmission electron microscopy (TEM) images were taken using a Japanese high-performance HT7700 transmission electron microscope (TEM), with image acquisition achieved using an accelerating voltage of 120 kV.

[0174] High-resolution transmission electron microscopy (HRTEM) images and energy dispersive spectroscopy (EDS) images were captured using a JEM high-resolution field emission transmission electron microscope from NEC. Ultra-high resolution image acquisition was achieved using a 200 kV field emission transmission electron microscope. At the same time, nanoscale components were acquired using a STEM attachment combined with energy dispersive spectroscopy.

[0175] from Figure 2The transmission electron microscope (TEM) images shown reveal that PdCu bimetallic nanomaterials with different proportions all exhibit a flower-like hierarchical structure, while the nanomaterials obtained without Cu (Comparative Example 1) are non-uniform Pd nanoparticles. Furthermore, as the proportion of Cu precursor increases, the nanoparticles become more uniform in size and exhibit narrower branches. It is noteworthy that when the proportion of Cu precursor exceeds that of Pd precursor, the Cu content in the final nanomaterial no longer increases, and the morphology no longer changes. Additionally, nanoparticles cannot be prepared with only Cu precursor present (Comparative Example 2).

[0176] Figure 3 This is a transmission electron microscope (TEM) image of the PdCu bimetallic nanomaterial (Pd1Cu1) prepared in Comparative Example 4. From... Figure 3 As can be seen, the nanomaterials obtained without the addition of cationic surfactants are unbranched PdCu bimetallic nanoparticles.

[0177] Figure 4 A, Figure 4 B represents the high-resolution transmission electron microscope (HRTEM) image and energy dispersive spectroscopy (EDS) image of the PdCu bimetallic nanomaterial (Pd1Cu1) prepared in Example 3, respectively. Figure 4 A clear hierarchical flower-like structure was observed in A. Figure 4 B shows that Pd and Cu elements are uniformly distributed on the nanoflowers, proving the uniformity of the composition.

[0178] 2. Inductively Coupled Plasma Optical Spectroscopy (ICP-OES) Analysis

[0179] Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis was performed using an Agilent 5800 ICP-OES analyzer to determine the actual metal ratio. The ICP-OES detection results of the PdCu bimetallic nanomaterials prepared in Examples 1-3 are shown in Table 1.

[0180] Table 1. ICP-OES test results

[0181] Example Pd (molar percentage) Cu (molar percentage %) Example 1 76.92 23.08 Example 2 69.00 31.00 Example 3 55.23 44.77

[0182] As shown in Table 1, the proportion of PdCu and the feed ratio of metal precursors in the PdCu bimetallic nanomaterials prepared in Examples 1-3 are basically the same.

[0183] 3. X-ray diffraction (XRD) characterization

[0184] X-ray diffraction (XRD) was performed using a Rigaku D / max-2550 X-ray diffractometer from Japan. The test conditions were continuous scanning with an angle range of 35-75°.

[0185] The X-ray diffraction (XRD) patterns of the PdCu bimetallic nanomaterials prepared in Examples 1-3 are shown below. Figure 5 As shown. By Figure 5 It can be seen that, except for Pd3Cu1, Pd2Cu1 and Pd1Cu1 both formed a uniform alloy structure without phase separation. As the Cu content increases, the diffraction peaks gradually redshift, and Pd3Cu1 shows diffraction peak splitting, indicating that some Pd self-nucleated to form Pd nanoparticles.

[0186] 4. X-ray photoelectron spectroscopy (XPS) characterization

[0187] X-ray photoelectron spectroscopy (XPS) was performed using an Axis Supra X-ray photoelectron spectrometer from Shimadzu Corporation of Japan. The system was equipped with an Al Kα X-ray source (1486.6 eV), a measurement scan power of 200 W, and a core-level spectral power of 300 W.

[0188] The X-ray photoelectron spectroscopy (XPS) spectra of the 3d orbitals of palladium and the 2p orbitals of copper in the PdCu bimetallic nanomaterials prepared in Examples 1-3 are shown below. Figure 6 As shown. By Figure 6 It can be seen that as the copper content in PdCu bimetallic nanomaterials increases, the 3d peak of palladium shifts to a lower binding energy, while the 2p peak of copper shifts to a higher binding energy. This proves that there is an electronic interaction between copper and palladium during the PdCu bimetallic alloying process.

[0189] 5. Characterization using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with energy dispersive spectroscopy (EDS)

[0190] The morphology and composition of the Pd-based bimetallic nanomaterials obtained in Examples 4-6 were characterized using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with energy dispersive spectroscopy (EDS).

[0191] The HAADF-STEM and EDS images of the Pd-based bimetallic nanomaterials prepared in Examples 4-6 are shown below. Figure 7 As shown. By Figure 7 It can be seen that, except for PdAu bimetallic nanomaterials, PdAg bimetallic nanomaterials and PdPt bimetallic nanomaterials are all homogeneous alloy structures, while the reason why PdAu bimetallic nanomaterials form a gold core-palladium shell structure is that AuCl4 - The standard electrode potential is much higher than that of PdCl4 2- .

[0192] Furthermore, the XRD patterns of the Pd-based bimetallic nanomaterials prepared in Examples 4-6 are shown below. Figure 8As shown. By Figure 8 Further evidence shows that PdAu bimetallic nanomaterials have a unique core-shell structure, while PdAg and PdPt bimetallic nanomaterials are both homogeneous alloy structures.

[0193] 6. Particle size analysis

[0194] The particle size was obtained by statistical analysis of the nanoparticle size in the TEM image using Nano Measurer software, and the results are shown in Table 2.

[0195] Table 2. Particle size analysis results

[0196] Example Nanomaterials Particle size (nm) Example 1 Pd3Cu1 14 Example 2 Pd2Cu1 26 Example 3 Pd1Cu1 24 Example 4 PdAu 200 Example 5 PdAg 60 Example 6 PdPt 200 Comparative Example 1 Pd 36 Comparative Example 4 Pd1Cu1 30

[0197] Industrial availability

[0198] The preparation method of this invention is simple, efficient, and has good versatility. It can be widely used in the large-scale preparation of bimetallic nanoflowers in industry, and has important application prospects, especially in the field of catalysts.

Claims

1. A continuous preparation method for Pd-based bimetallic nanoflowers, characterized in that, Includes the following steps: a. Raw material A and raw material B are passed into a first micro mixer to mix and obtain a first mixture. Raw material A is an aqueous solution of palladium salt, and raw material B is an aqueous solution of a transition metal salt other than palladium salt. Both raw material A and raw material B contain cationic surfactants. The transition metal salt other than palladium salt is selected from one or more of copper chloride, silver nitrate, chloroauric acid, and potassium chloroplatinate. b. The first mixture and raw material C are passed into a second micro mixer to mix and obtain a second mixture, wherein the raw material C is an aqueous solution of a reducing agent; the second mixture is essentially a homogeneous dispersion system, and the mixing time in step b is 0.1 to 10 s; c. The second mixture is passed into a microreactor to carry out a redox reaction to obtain Pd-based bimetallic nanoflowers; the temperature in the microreactor is 10-60℃ and the residence time is 0.1-20 min. The concentration of palladium salt in raw material A is 0.001–0.01 mol / L; The concentration of transition metal salts other than palladium salt in raw material B is 0.001–0.01 mol / L; The concentrations of cationic surfactants in raw material A and raw material B are each independently 0.001–0.05 mol / L; The molar ratio of palladium salt in raw material A to other transition metal salts (excluding palladium salt) in raw material B is (1-10):

1.

2. The preparation method according to claim 1, characterized in that, The palladium salt is selected from one or more of sodium tetrachloropalladium and potassium tetrachloropalladium. The cationic surfactants include quaternary ammonium salt cationic surfactants.

3. The preparation method according to claim 1 or 2, characterized in that, The reducing agent is selected from one or more of ascorbic acid and citric acid.

4. The preparation method according to claim 1 or 2, characterized in that, The concentration of the reducing agent in raw material C is 0.1–0.5 mol / L.

5. The preparation method according to claim 1 or 2, characterized in that, The first micromixer and the second micromixer are each independently a microchannel mixer, a membrane dispersion mixer, or a microsieve mixer; The microreactor is a microchannel reactor or a coil-type microreactor.

6. The preparation method according to claim 1 or 2, characterized in that, The temperature in the first micro-mixer is 10–50°C, and the mixing time is 0.1–10 s; The temperature in the second micro-mixer is 10–50°C.

7. The Pd-based bimetallic nanoflowers prepared by the method according to any one of claims 1-6, characterized in that, The particle size of the Pd-based bimetallic nanoflowers is below 500 nm.

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