A method for ultrasonic-assisted continuous controllable synthesis of one-dimensional core-shell structure nanomaterials

Abstract

The application discloses a kind of ultrasonic-assisted continuous controllable synthesis one-dimensional core-shell structure nanomaterials method.The method is through online dispersion device, maintains silver nanowire feed stable, adopts acoustic transparent coil type micro-flow reactor, and realizes the heterogeneous growth of ZIF67 on the surface of silver nanowire under the action of ultrasonic field.By synergic control of ultrasonic power, flow rate ratio, reaction temperature and residence time, one-dimensional core-shell structure nanomaterials with complete, uniform coating layer can be stably and repeatedly prepared in specific parameter window.The method overcomes the problems of low efficiency, poor controllability and easy settlement and agglomeration of one-dimensional materials in micro-fluidic system, realizes continuous synthesis with precise and controllable structure and high space-time yield, and the obtained fully-coated materials exhibit high faradaic efficiency and selectivity in the field of electrocatalytic nitrate reduction to ammonia due to their complete and uniform core-shell structure, which verifies the advantages of the method in preparing high-performance catalytic materials.

Description

Technical Field

[0001] This invention relates to the field of nanocomposite material preparation technology, specifically to a method for ultrasonic-assisted continuous and controllable synthesis of one-dimensional core-shell structured nanomaterials. Background Technology

[0002] Silver nanowires@zeolite imidazole ester (ZIF) core-shell materials, by combining the excellent electrical and mechanical properties of silver nanowires with the structural tunability and high stability of ZIFs, have shown significant application potential in many fields such as surface-enhanced Raman scattering (SERS) detection, electrocatalysis, photocatalysis, adsorption, antibacterial, and sensing. However, the potential of this material in practical applications is limited by its synthesis process; efficient, uniform, and controllable continuous preparation remains a core technological bottleneck.

[0003] Traditional batch reactor processes typically involve mixing silver nanowire dispersions with ZIF precursor solutions (such as alcoholic solutions of 2-methylimidazole, cobalt salts, or zinc salts) in a single reaction vessel, achieving material contact through mechanical stirring, and then allowing the reaction to proceed statically at room temperature or under heating. This process suffers from inherent drawbacks such as long reaction cycles (1-24 hours) and poor batch-to-batch uniformity, making it difficult to precisely control the morphology and thickness of the ZIF coating layer, thus failing to meet the demands for high-quality, high-throughput synthesis. In contrast, ultrasonic cavitation significantly enhances micro-mixing and mass transfer processes, theoretically reducing key reaction steps to minutes (3-12 minutes), providing a new technical approach for achieving rapid and controllable coating.

[0004] Microfluidic technology, with its efficient mass and heat transfer and precise fluid control capabilities, provides an ideal platform for the continuous and controllable preparation of nanocomposite materials. Currently, some domestic patents involve the continuous preparation of core-shell materials. For example, patent publication number CN202011215238.8 discloses a method for rapidly synthesizing MOF nanoparticles, and patent publication number CN202510615184.0 discloses a paper-based composite film, which involves a method for preparing microfluidic chips for the controllable synthesis of Ag@ZIF-8 nanocomposite materials. However, these existing technologies are mainly geared towards spherical particle systems, and their reactor designs and process parameters are difficult to adapt to one-dimensional silver nanowires with high aspect ratios, easy entanglement, agglomeration, and sedimentation. For such one-dimensional materials, sedimentation in microfluidic systems leads to uneven feed concentration, agglomeration causes microchannel blockage, and homogeneous nucleation is difficult to suppress. These problems severely restrict the feasibility and stability of continuous production of high-quality core-shell structures. Therefore, although microfluidic technology itself is relatively mature, there is still a significant technological gap in the continuous synthesis method for uniform coating of one-dimensional nanomaterial shells.

[0005] To achieve continuous synthesis of one-dimensional nanomaterial core-shell structures, two key challenges must be systematically overcome: Firstly, at the feed end, there is an urgent need to develop online dispersion technology suitable for confined spaces such as syringes, fundamentally solving the sedimentation and aggregation problems of one-dimensional nanomaterials and ensuring a consistently stable feed concentration. Existing solutions, such as the magnetic stirrer for an injection pump invented in patent publication number CN201720057367.6, require the stirring component to be placed inside the syringe and connected to an internal support, thus encroaching on the reaction space; and the solution stirring device for a clamp-on microfluidic syringe invented in patent publication number CN202420277850.5, require an external mechanical clamping structure to fix the device to a specific position on the syringe. The former poses a risk of contamination, is inconvenient to clean, and has a limited stirring range; the latter is cumbersome to operate, has poor adaptability, and a fixed stirring area. Neither of these solutions can meet the stringent requirements of continuous synthesis for ease of operation, wide stirring range, and high equipment compatibility. Secondly, within the reactor, a specialized microreactor needs to be designed to efficiently couple with the ultrasonic field, suppressing homogeneous nucleation of ZIFs in the bulk solution and guiding their heterogeneous growth on the surface of silver nanowires. This places extremely high demands on the acoustic transparency of the reactor material to ensure that ultrasonic energy can be efficiently transferred to the reaction system.

[0006] Furthermore, from the perspective of materials design and performance, an ideal silver nanowire@ZIF67 core-shell catalyst needs to form a complete and uniform fully coated structure. This is because: when silver nanowires are used as nitrate reduction catalysts, their product selectivity is often poor; while pure ZIF67 material has poor conductivity, limiting charge transport efficiency. Theoretically, constructing a tight core-shell structure can achieve complementary advantages, with silver nanowires serving as the conductive framework and ZIF67 as the active shell. However, if the ZIF67 shell coating is incomplete (such as semi-coating or necklace-like), not only will the synergistic interface not be fully exposed, but the exposed part of the silver core may also trigger side reactions, resulting in the overall catalytic performance (such as Faraday efficiency and selectivity) falling far short of expectations. Therefore, how to stably and repeatedly prepare silver nanowire@ZIF67 materials with a complete fully coated structure through a controllable synthesis method has become a key prerequisite for improving its electrocatalytic performance and promoting practical applications. Summary of the Invention

[0007] To overcome the shortcomings of the aforementioned background technology, this invention aims to provide a method for the continuous and controllable synthesis of one-dimensional core-shell structured nanomaterials assisted by ultrasound. This invention overcomes the problems of low efficiency, poor reproducibility, and inability to achieve continuous production in traditional batch processes by integrating in-situ online dispersion at the feed end, an acoustically transparent reactor, and multi-parameter synergistic control of a microfluidic system. It also addresses the issues of unstable feed, uneven reaction, and channel blockage in existing microfluidic technologies when processing one-dimensional materials. This allows for the controllable preparation of a complete and uniform fully encapsulated structure of ZIF67 on the surface of silver nanowires, thereby obtaining a continuous synthesis of electrocatalytic materials with both high conductivity and high selectivity, exhibiting high performance.

[0008] This invention provides a method for the continuous and controllable synthesis of one-dimensional core-shell structured nanomaterials with ultrasound assistance, comprising the following steps:

[0009] 1) Construct a system for synthesizing one-dimensional core-shell nanomaterials, the system comprising a feed pump for pumping precursor solutions, a micromixer, a coiled microfluidic reactor, an ultrasonic generator for generating an ultrasonic field, and a product collection device for collecting products; the coiled microfluidic reactor is made of an acoustically transparent polymer material and is positioned within the area of ​​the ultrasonic field generated by the ultrasonic generator; the ultrasonic generator includes an ultrasonic generator and a temperature controller connected thereto, for simultaneously providing an ultrasonic field and maintaining a low-temperature reaction environment during the reaction; the product collection device is a collection bottle placed in an ice-water bath;

[0010] 2) In a syringe equipped with an online dispersion device, silver nanowires are dispersed in an organic solvent to obtain silver nanowire suspension A. The online dispersion device is used to maintain the dynamic and stable suspension of silver nanowires in silver nanowire suspension A.

[0011] Organic ligands are dissolved in organic solvents to obtain ligand solution B; metal salts are dissolved in organic solvents to obtain metal salt solution C.

[0012] 3) Pump the three solutions from step 2) into the micro mixer separately using a raw material pump for thorough mixing;

[0013] 4) The mixed solution is passed into a coil-type microfluidic reactor and reacted under the action of an ultrasonic field to achieve complete and uniform full coating of ZIF67 on the surface of silver nanowires;

[0014] 5) The reaction products are collected and post-processed to obtain the one-dimensional core-shell structured nanomaterial.

[0015] According to some specific embodiments of the present invention, in step 4), by synergistically controlling the ultrasonic power, precursor flow rate ratio, reaction temperature and residence time, ZIF67 is completely and uniformly coated on the surface of silver nanowires.

[0016] Preferably, the ultrasonic power is 90-130 W; the flow rate ratio of silver nanowire suspension A, ligand solution B and metal salt solution C is 1 : (0.5-1.5) : (0.1-0.6); the reaction temperature is 8-12℃; and the residence time is 4-8 minutes.

[0017] According to some specific embodiments of the present invention, the raw material pump in step 1) is an injection pump used to pump silver nanowire suspension A, ligand solution B and metal salt solution C respectively; the microfluidic mixer is a cross-shaped, T-shaped or Y-shaped structure; the coil-type microfluidic reactor is made of an acoustically transparent polymer material with an acoustic impedance of (1.1-1.5) MRayl.

[0018] As a preferred embodiment of the present invention, the acoustically transparent polymer material is PFA or PTFE; the coiled microfluidic reactor is wound around a hollow support tube.

[0019] As a preferred embodiment of the present invention, the micro mixer in step (1) is made of polymer material and has an internal channel size of 0.5-2.5 mm, preferably 1.5-2.5 mm; the inner diameter of the coiled microfluidic reactor is 1.0-2.0 mm and the length is 3.0-6.0 m, preferably 4.0-5.0 m.

[0020] As a preferred embodiment of the present invention, the organic solvent in step (2) is ethanol or methanol, preferably ethanol; the organic ligand is 2-methylimidazole; the metal salt is a cobalt salt, which is cobalt acetate, cobalt chloride or cobalt nitrate, preferably cobalt acetate.

[0021] As a preferred embodiment of the present invention, in step (2), the mass concentration of silver nanowires in the silver nanowire suspension A is 0.2-1.0 mg / mL, preferably 0.3-0.6 mg / mL; the mass concentration of 2-methylimidazole in the ligand solution B is 60-120 mg / mL, preferably 70-90 mg / mL; and the mass concentration of metal salt in the metal salt solution C is 5-30 mg / mL, preferably 5-15 mg / mL.

[0022] As a preferred embodiment of the present invention, the flow rate ratio of silver nanowire suspension A, ligand solution B and metal salt solution C in step (3) is 1 : (1.0-1.4) : (0.2-0.5).

[0023] As a preferred embodiment of the present invention, in step (4), the ultrasonic power is 100-120 W, the reaction temperature is 8-12℃, and the reaction dwell time is 5-7 min.

[0024] As a preferred embodiment of the present invention, the online dispersion device is a magnetic stirring device sleeved outside the syringe, which drives the magnetic stir bar set inside the syringe to rotate through a rotating magnetic field, so as to maintain the dynamic and stable suspension of the silver nanowires.

[0025] The present invention also provides a system for implementing the aforementioned method, comprising:

[0026] A syringe for storing silver nanowire suspension A is equipped with a magnetic stir bar inside.

[0027] An online dispersion device is installed at the syringe storing silver nanowire suspension A. It is used to drive a magnetic stir bar installed inside the syringe to rotate by a rotating magnetic field, thereby maintaining the dynamic and stable suspension of silver nanowires.

[0028] Several raw material pumps are configured to pump silver nanowire suspension A, ligand solution B and metal salt solution C respectively;

[0029] A micro mixer receives the solution pumped by the feed pump and mixes the feed materials;

[0030] The coil-type microfluidic reactor, which serves as the main site for the reaction, is made of an acoustically transparent polymer material and is used to achieve controllable heterogeneous growth of the shell on the surface of silver nanowires under the action of an ultrasonic field.

[0031] An ultrasonic generating device includes an ultrasonic generator for generating an ultrasonic field and a temperature controller for monitoring the reaction temperature inside a coil-type microfluidic reactor.

[0032] Product collection device, used to collect reaction products flowing out of the coiled microfluidic reactor.

[0033] The present invention also provides a one-dimensional core-shell structured nanomaterial obtained by the aforementioned preparation method, wherein the one-dimensional core-shell structured nanomaterial is a silver nanowire@ZIF67 core-shell material.

[0034] This invention also provides an application of the aforementioned silver nanowire@ZIF67 core-shell material in the field of electrocatalytic nitrate reduction to ammonia production.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention adopts a collaborative system design of an integrated online magnetic stirring and dispersing device and a coil-type ultrasonic microreactor made of acoustic transparent polymer material, and constructs an integrated platform of "stable feeding-efficient mixing-precise reaction", which solves the problem of sedimentation and agglomeration of one-dimensional silver nanowires in continuous pumping and reaction process from the source, and ensures the long-term continuous stability of material transportation and reaction process.

[0037] (2) This invention achieves stable and repeatable preparation of silver nanowires@ZIF67 core-shell materials with complete and uniform fully encapsulated structures by precisely coupling ultrasonic fields and microfluidic fields and synergistically controlling process parameters, including ultrasonic power, precursor flow rate ratio, reaction temperature, and residence time. This structure is the key foundation for the material to obtain excellent performance and fills the technological gap in the continuous synthesis of high-quality core-shell structures of one-dimensional nanomaterials.

[0038] (3) The present invention introduces an ultrasonic-assisted continuous flow process, which overcomes the inherent defects of low reaction efficiency and poor batch uniformity of traditional batch reactor process. The reaction time is reduced by more than 95%, the time-space yield is increased by tens of times, and the production efficiency is significantly improved.

[0039] (4) The online dispersion device of the present invention adopts a plug-and-play magnetic stirring device with a non-clamping design that allows for free axial movement. While achieving convenient "plug-and-play" operation, it ensures that the stir bar can cover the entire propulsion stroke of the syringe, realizing "stroke-adaptive stirring". This fundamentally eliminates the uneven concentration or sedimentation of silver nanowires caused by stirring dead zones, providing a source guarantee for the uniformity of the fully encapsulated structure. This modular design can be adapted to various syringes by replacing the hollow gears, significantly improving the versatility and scalability of the system.

[0040] (5) This invention explores and optimizes the parameters of the core material of the ultrasonic microreactor. It uses an acoustically transparent polymer material with a specific acoustic impedance to manufacture a coil reactor, which ensures that the ultrasonic energy is efficiently and uniformly transmitted to the reaction system. This provides key equipment support for the controllable growth of the fully encapsulated structure and fills the gap in the design of ultrasonic coil microfluidic reactors.

[0041] (6) The method of the present invention has mild overall reaction conditions, is carried out at low temperatures close to room temperature (5-20℃), has low energy consumption, and uses ethanol as a green solvent, making it environmentally friendly. This synthesis strategy and system can be easily extended to the controllable coating process of other one-dimensional nanomaterials and different metal-organic framework materials, showing good universality and application prospects. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the entire process device for preparing AgNWs@ZIF67 core-shell material using ultrasound-assisted microfluidic control according to the present invention.

[0043] Figure 2 This is a schematic diagram of the plug-and-play magnetic stirring device of the present invention;

[0044] Figure 3 These are scanning electron microscope images of the AgNWs@ZIF67 composite material prepared in Example 1;

[0045] Figure 4 This is the XRD characterization diagram of the AgNWs@ZIF67 composite material prepared in Example 1;

[0046] Figure 5 These are transmission electron microscope images of the AgNWs@ZIF67 composite material prepared in Example 1;

[0047] Figure 6 These are scanning electron microscope images of the AgNWs@ZIF67 composite material prepared in Example 2;

[0048] Figure 7 These are scanning electron microscope images of the AgNWs@ZIF67 composite material prepared in Example 3;

[0049] Figure 8 These are scanning electron microscope images of the AgNWs@ZIF67 composite material prepared in Example 4;

[0050] Figure 9 These are scanning electron microscope images of the AgNWs@ZIF67 composite material prepared in Example 5;

[0051] Figure 10 The voltage-current graph of AgNWs@ZIF67 obtained by linear sweep voltammetry in Example 1 with and without nitrate in the electrolyte;

[0052] Figure 11 The graph shows the total Faradaic efficiency and ammonia production of AgNWs@ZIF67 in Example 1 with and without nitrate in the electrolyte;

[0053] Figure 12 A comparison of the Faraday efficiency of the main product and byproduct of different samples at the same potential of -0.5V;

[0054] Figure 13 Ammonia yield graphs for different samples;

[0055] Figure 14 The graph shows the Faraday efficiency and ammonia yield of AgNWs@ZIF67 at different potentials in Example 1.

[0056] In the diagram: 1-Injection pump, 2-Injector, 3-Plug and play magnetic stirrer, 4-Microfluidic cross mixer, 5-Microfluidic tubular reactor, 6-Ultrasonic bath, 7-Collection bottle, 3-1 Hollow gear, 3-2 Modular gear, 3-3 Magnetic ring, 3-4 Chain track, 3-5 Cross shaft, 3-6 Modular motor, 3-7 Modular battery box, 3-8 Magnetic stir bar. Detailed Implementation

[0057] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0058] This invention uses the synthesis of silver nanowires@ZIF67 in an ultrasonic microreactor as a model system. By controlling the reactor structure, materials and ultrasonic conditions, the continuous synthesis of composite core-shell materials is achieved.

[0059] like Figure 1 As shown, this invention provides a system for the continuous synthesis of silver nanowires@ZIF67 within an ultrasonic microreactor, comprising:

[0060] 1) Feeding and micro-mixing unit

[0061] The system is equipped with three syringe pumps1, used to deliver silver nanowire ethanol suspension (central stream), 2-methylimidazole ethanol solution, and metal salt ethanol solution, respectively. The flow rates of the three pumps are related to the residence time of the reaction solution in the microreactor.

[0062] The three fluid streams are rapidly and uniformly mixed using a microfluidic cross mixer made of PTFE material. The mixer channel size is on the millimeter scale, which helps to improve mass transfer efficiency.

[0063] A plug-and-play magnetic stirrer 3 is installed outside the syringe 2 that delivers the silver nanowire suspension. Figure 2 As shown, the device consists of a hollow gear 3-1, a modular gear 3-2, a magnetic ring 3-3, a chain track 3-4, a cross shaft 3-5, a modular motor 3-6, a modular battery box 3-7, and a magnetic stirrer 3-8. The modular battery box 3-7 supplies power to the modular motor 3-6. The modular motor 3-6 drives the modular gear 3-2 to rotate via the cross shaft 3-5. The modular gear 3-2 drives the hollow gear 3-1 and the magnetic ring 3-3 to rotate via the chain track 3-4. The magnetic ring 3-3 generates an external rotating magnetic field that drives the magnetic stirrer 3-8 inside the syringe to rotate continuously. This fundamentally solves the problem of sedimentation and aggregation of silver nanowires inside the syringe, ensuring the stability of the injection concentration and providing a uniform raw material input for subsequent continuous reactions.

[0064] 2) Microreactor Unit

[0065] The cavitation and acoustic flow effects of ultrasound in liquid phases are highly dependent on the acoustic properties of the reactor tube wall in terms of intensity and distribution. The acoustic impedance (Z) and ultrasonic attenuation coefficient (α) of a material are two core parameters for evaluating its interaction with the ultrasonic field. The acoustic impedance (Z=ρc, where ρ is density and c is sound velocity) determines the energy transmission efficiency of ultrasound at the interface; the ultrasonic attenuation coefficient characterizes the energy loss of sound waves propagating within the material, with lower values ​​indicating better sound transmission. Based on the interaction mechanism with the ultrasonic field, tube materials suitable for microreactors can be mainly divided into three categories: (i) Reflective: high acoustic impedance, with most incident ultrasonic energy reflected at the interface, such as metals and glass; (ii) High-loss: high ultrasonic attenuation coefficient, with ultrasonic energy rapidly absorbed and attenuated within the tube wall, such as silicone rubber; (iii) Transmissive: possessing low acoustic impedance similar to that of the solvent and a relatively low ultrasonic attenuation coefficient, allowing for efficient ultrasonic penetration.

[0066] For the application scenario of this invention, the microfluidic tubular reactor 5 is immersed in the acoustic coupling medium within the ultrasonic bath 6. The core principle is that ultrasonic energy can be efficiently transferred to the reaction solution, rather than being excessively absorbed or reflected by the tube wall material. The acoustically transparent material must possess low acoustic impedance (Z < 5 MRayl) and a low acoustic attenuation coefficient (α < 10 dB / cm) that matches the coupling medium and reaction solvent. Furthermore, these acoustic parameters should exhibit good temperature and frequency stability (e.g., change < 1% over a 100°C temperature rise). This invention selects an acoustically transparent material with an acoustic impedance of 1-2 MRayl and an ultrasonic attenuation coefficient less than 2.5 dB / cm to ensure that ultrasonic waves can efficiently penetrate the tube wall and enter the reaction system.

[0067] Furthermore, this invention selects transmissive fluoroplastics as the material for the coil-type microfluidic reactor. Typical, but not limited, materials include polytetrafluoroethylene (PTFE) and perfluoroalkoxyalkanes, which have low acoustic impedance (approximately 1.1-1.5 MRayl) and extremely low ultrasonic attenuation coefficients at 20 kHz (0.08-0.3 dB / cm). In addition, perfluoroalkoxyalkanes exhibit excellent resistance to solvents commonly used in ZIF synthesis, such as methanol, ethanol, and N,N-dimethylformamide (DMF), showing no swelling or contaminant precipitation even after long-term contact, ensuring the purity and stability of the reaction system, making them preferred materials for this invention. Traditional materials, such as reflective metals like stainless steel, have extremely high acoustic impedance (38-48 MRayl), and ordinary glass has relatively high acoustic impedance (12-15 MRayl), both exhibiting low ultrasonic attenuation coefficients at 20 kHz (0.008-0.05 dB / cm and 0.01-0.03 dB / cm, respectively). High-loss materials such as silicone rubber have low acoustic impedance (approximately 1.0-1.2 MRayl), but extremely high ultrasonic attenuation coefficient at 20 kHz (15-30 dB / cm).

[0068] The microfluidic tubular reactor finally designed in this invention is an ultrasonic coil-type microfluidic reactor, made of polytetrafluoroethylene or perfluoroalkoxyalkane, with an inner diameter of 1.0-2.0 mm and a length of 3.0-6.0 m.

[0069] 3) Ultrasonic and temperature control unit

[0070] The coil-type microreactor is entirely immersed in an ultrasonic bath 6, with the ultrasonic power adjustable from 50-180W. The ultrasonic field, utilizing cavitation and acoustic flow effects, directionally promotes the heterogeneous nucleation and controlled growth of ZIF67 precursors on the surface of silver nanowires, while continuously suppressing secondary aggregation of silver nanowires and deposition on the reactor inner wall during the flow process. This effect, combined with the stirring and dispersion at the feed end, forms a spatiotemporal synergy, ensuring the overall dispersion stability of the material from feed to the reaction endpoint, thus guaranteeing long-term continuous and stable system operation. Furthermore, an external circulating cooling system precisely maintains the reaction temperature between 5-20℃ to suppress the ultrasonic thermal effect and ensure a stable and controllable reaction process.

[0071] 4) Product collection unit

[0072] The reaction products flow continuously into the collection bottle 7, which is placed in an ice-water bath, through the outlet pipeline to achieve rapid quenching and collection, which facilitates subsequent centrifugation, washing and drying.

[0073] Example 1: Preparation of AgNWs@ZIF67 fully coated core-shell material

[0074] Silver nanowires with a diameter of approximately 55 nm and a length of approximately 10 mm were dispersed in anhydrous ethanol and sonicated to obtain a homogeneous suspension with a mass concentration of 0.484 mg / mL, which was designated as solution A. 1.2 g of 2-methylimidazole was weighed and dissolved in 15 mL of anhydrous ethanol to prepare a clear solution with a mass concentration of 80 mg / mL, which was designated as solution B. 75 mg of cobalt acetate tetrahydrate was weighed and dissolved in 7.5 mL of anhydrous ethanol to prepare a clear solution with a mass concentration of 10 mg / mL, which was designated as solution C.

[0075] Solutions A, B, and C were injected into three separate syringes and attached to a syringe pump. A plug-and-play magnetic stirrer was fitted to the outside of the syringe containing solution A to ensure continuous and uniform dispersion of the silver nanowires. The flow rates of solutions A, B, and C were set to 0.6 mL / min, 0.72 mL / min, and 0.18 mL / min, respectively (flow rate ratio of 1:1.2:0.3). The three solutions were thoroughly mixed using a microfluidic cross mixer before entering a coil-type microfluidic reactor. The reactor used PFA tubing (1.59 mm inner diameter), 4.5 m in length, wound around a 20 mm outer diameter hollow polypropylene support tube. The entire reactor was immersed in an ultrasonic water bath with an ultrasonic power of 120 W. The reaction temperature was controlled at 10 °C using a circulating water bath, and the average residence time was 6 min. The product was collected in an ice-water bath.

[0076] The collected liquid was centrifuged (7000 rpm, 2 min), washed twice with anhydrous ethanol, and vacuum dried at 50 °C for 6 h to obtain AgNWs@ZIF67 core-shell material.

[0077] Figure 3 The image shows a scanning electron microscope (SEM) image of the obtained product. It can be seen that ZIF67 forms a continuous, complete and dense full-coverage layer on the surface of silver nanowires. There are no obvious exposed segments of silver nanowires, and the shell thickness is uniform, about 59.21 nm. Figure 4 The X-ray diffraction (XRD) pattern of the product shows clear ZIF67 characteristic diffraction peaks, indicating good crystallinity. Figure 5 Image (a) shows a transmission electron microscope (TEM) image of the product, clearly revealing the core-shell structure of silver nanowires uniformly coated with ZIF67; its high-resolution image... Figure 5 As shown in (b), the interplanar spacing measured in the core region is approximately 0.24 nm, corresponding to the (111) plane of face-centered cubic silver (Ag) (JCPDS No. 04-0783). Figure 5 Image (c) shows that the interplanar spacings measured in the outer shell region are approximately 0.215 nm and 0.179 nm, consistent with the (111) and (200) interplanar spacings of ZIF67. This result directly confirms at the atomic scale that the product consists of a silver (Ag) core and a cobalt (Co)-containing ZIF67 shell. Under these conditions, the space-time yield of the reactor can reach 21.56 g·L⁻¹. -1 ·h -1 It is a traditional batch reactor (1.35 g·L). -1 ·h -1 The efficiency of spatiotemporal efficiency is nearly 16 times that of other methods, resulting in a significant improvement.

[0078] Example 2: Preparation of AgNWs@ZIF67 fully coated core-shell material

[0079] This embodiment further demonstrates the stability and repeatability of the method in preparing fully encapsulated structures within the optimization window by adjusting key parameters.

[0080] Solutions A, B, and C were prepared with concentrations of 0.5 mg / mL, 80 mg / mL, and 10 mg / mL, respectively. The flow rates for solutions A, B, and C were set to 0.6 mL / min, 0.6 mL / min, and 0.3 mL / min, respectively (flow rate ratio of 1:1:0.5). The reaction conditions were set as follows: ultrasonic power 110 W, temperature 15 ℃, and residence time 6 min.

[0081] Figure 6 The SEM images of the product show that the morphology is uniform and fully coated, with a shell thickness of approximately 104.82 nm, which confirms the effectiveness of the process window.

[0082] Example 3: Preparation of AgNWs@ZIF67 fully coated core-shell material

[0083] This embodiment aims to verify that, within the optimization window, a specific combination of parameters can stably prepare high-quality fully coated materials.

[0084] Following the method in Example 1, silver nanowire ethanol suspension A with a concentration of 0.5 mg / mL; 2-methylimidazole ethanol solution B with a concentration of 80 mg / mL; and cobalt acetate ethanol solution C with a concentration of 10 mg / mL were prepared.

[0085] System assembly and reaction: The system assembly was the same as in Example 1. The flow rates of solutions A, B, and C were set to 0.6 mL / min, 0.675 mL / min, and 0.225 mL / min, respectively (flow rate ratio of 1:1.125:0.375), the ultrasonic power was 100 W, the reaction temperature was 10 °C, and the residence time was 6 min.

[0086] The obtained product is then post-processed. Figure 7 SEM images showed that ZIF67 formed a complete and continuous fully coated layer with uniform thickness of approximately 40.95 nm, further verifying the reliability of the method.

[0087] Example 4: Preparation of AgNWs@ZIF67 semi-coated core-shell material

[0088] This embodiment aims to verify that when relevant parameters deviate from the optimization window, high-quality fully encapsulated materials cannot be obtained.

[0089] Following the method in Example 1, silver nanowire ethanol suspension A with a concentration of 0.5 mg / mL; 2-methylimidazole ethanol solution B with a concentration of 80 mg / mL; and cobalt acetate ethanol solution C with a concentration of 10 mg / mL were prepared.

[0090] System assembly and reaction: The system assembly was the same as in Example 1. The flow rates of solutions A, B, and C were set to 0.6 mL / min, 0.72 mL / min, and 0.18 mL / min, respectively (flow rate ratio of 1:1.2:0.3), the ultrasonic power was 30 W, the reaction temperature was 10 °C, and the residence time was 5 min.

[0091] Figure 8 SEM characterization showed that ZIF-67 crystals formed a necklace-like semi-encapsulated structure on the surface of silver nanowires, with some of the silver nanowires exposed. The encapsulation coverage was about 50%, and the average shell thickness was about 49.15 nm.

[0092] Example 5: Synthesis of AgNWs@ZIF67 under no-feed stirring and ultrasonic field

[0093] This comparative example illustrates the results of synthesis relying solely on the microfluidic confinement effect under conditions of no feed stirring and no ultrasonic external field assistance. Except for not turning on the stirring device and the ultrasonic generator (i.e., ultrasonic power of 0 W), the solution preparation, feed flow rate (0.6 mL / min A, 0.72 mL / min B, 0.18 mL / min C), reaction temperature (10 ℃), and residence time (6 min) are completely consistent with Example 1.

[0094] During the reaction, the silver nanowire suspension inside the syringe and in the tubing was observed to settle slowly. The inner wall of the coiled microfluidic reactor gradually showed obvious white and purple deposits. After about 30 minutes of reaction, obvious color deposition appeared at the bottom of the coil.

[0095] Figure 9 SEM characterization of the collected products revealed that the material mainly consisted of a large number of free ZIF67 particles (homogeneous nucleation products) and severely aggregated silver nanowire bundles. Only a very small number of discontinuous crystals adhered to the surface of the silver nanowires, failing to form a complete core-shell structure. Experimental results demonstrate that, in the absence of synchronous ultrasonic field assistance, the microfluidic system alone cannot suppress homogeneous nucleation in the bulk solution, nor can it solve the sedimentation and aggregation problems of one-dimensional materials within the channel. This proves the crucial synergistic effect of the ultrasonic field on heterogeneous nucleation and stable dispersion.

[0096] Example 6: Electrocatalytic nitrate reduction (NO3RR) performance test of AgNWs@ZIF67 core-shell material

[0097] 5 mg of the AgNWs@ZIF67 material prepared in Example 1 was mixed with 970 μL of anhydrous ethanol and 30 μL of 5% perfluorosulfonic acid (Nafion) solution in a certain proportion, and then ultrasonically treated to prepare a homogeneous catalyst slurry. This slurry was quantitatively coated onto pretreated carbon paper (coating area 1 cm²). 2 The surface was used as the working electrode and dried at room temperature. Unless otherwise specified, other comparative catalysts were prepared using the same procedure.

[0098] Electrochemical tests were conducted in a standard H-type electrolytic cell, with the anode and cathode compartments separated by a Nafion 117 proton exchange membrane. The cathode electrolyte was 0.1 M KOH + 0.1 M KNO3, and the anolyte was 0.1 M KOH. A Hg / HgO electrode was used as the reference electrode, and a carbon rod was used as the counter electrode. All tests were performed using a KOSTER CS2350M electrochemical workstation.

[0099] The testing methods included: (i) linear sweep voltammetry (LSV): recording current-potential curves at a scan rate of 10 mV / s to evaluate the macroscopic electrocatalytic activity of the catalyst; and (ii) chronoamperometry (it): conducting electrochemical reactions for 1 hour at different constant cathode potentials (-0.3 V to -0.7 V vs. RHE). After the reaction, the NH4+ in the cathode electrolyte was accurately determined using the indophenol blue standard colorimetric method. + The concentration was determined, and the Faraday efficiency (FE) and ammonia yield at the corresponding potential were calculated.

[0100] Example 7: Comparative Analysis of Electrocatalytic Performance of Materials with Different Structures

[0101] To investigate the influence of material structure on performance, this embodiment systematically compared the following five groups of samples: (a) pure AgNWs; (b) pure ZIF67; (c) the semi-coated sample with a large area of ​​exposed silver nanowires prepared in Example 4 (denoted as AgNWs@ZIF-67-1); (d) the fully coated AgNWs@ZIF-67 sample prepared under optimal conditions in Example 1 (denoted as AgNWs@ZIF-67-2); and (e) the sample with an excessively thick shell prepared in Example 2 (denoted as AgNWs@ZIF-67-3).

[0102] (1) The effect of the presence of nitrate ions: Figure 10 and Figure 11 Comparisons were made between those containing and without NO3. -The LSV curves and corresponding Faradaic efficiency and ammonia yield of the AgNWs@ZIF-67-2 sample in the cathode electrolyte were analyzed. The results show that the introduction of nitrate ions significantly increased the cathode current density and greatly improved the selectivity of ammonia synthesis, demonstrating that the catalytic system possesses intrinsically high activity and high specificity for NO3RR.

[0103] (2) Comparison of performance of different samples: Figure 12 and Figure 13 The electrocatalytic performance of the five groups of samples at -0.5 V vs. RHE is compared, including the main product (NH3) and key byproducts (such as NO2). - The results showed that only the AgNWs@ZIF-67-2 sample with a complete and uniform fully encapsulated structure achieved the highest ammonia yield and a total Faradaic efficiency of nearly 100%, while effectively suppressing the formation of byproducts. Samples with pure components or other structural defects exhibited varying degrees of performance degradation, directly confirming that the close synergy between the silver nanowire core and the complete ZIF67 shell is a necessary condition for obtaining superior performance.

[0104] (3) Optimal performance data: such as Figure 14 As shown, at the optimized potential of -0.6 V (vs. RHE), the AgNWs@ZIF-67-2 catalyst achieves an NH3 yield of 0.32 mmol h⁻¹. -1 cm -2 The overall Faraday efficiency is approximately 100%, with NO2 as a byproduct. - The Faraday efficiency was significantly suppressed to below 3%.

[0105] (4) Mechanism analysis: The excellent NO3RR performance of this system is directly attributed to the complete fully encapsulated core-shell structure prepared in Example 1: 1) Continuous conductive network: The silver nanowire core constructs a through-through electron "highway", ensuring efficient charge transport; 2) Sufficient and stable active interface: The dense, uniform and moderately thick ZIF67 shell provides a large number of uniform active sites, while generating an electronic synergistic effect through the tight core-shell interface, optimizing the reaction path; 3) Structural stability: The complete encapsulation effectively prevents the aggregation, corrosion or shedding of silver nanowires during the catalytic process.

[0106] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for the continuous and controllable synthesis of one-dimensional core-shell structured nanomaterials with ultrasound assistance, characterized in that, Includes the following steps: 1) Construct a system for synthesizing one-dimensional core-shell nanomaterials, the system comprising a feed pump for pumping precursor solutions, a micromixer, a coiled microfluidic reactor, an ultrasonic generator for generating an ultrasonic field, and a product collection device for collecting products; the coiled microfluidic reactor is made of an acoustically transparent polymer material and is positioned within the area of ​​the ultrasonic field generated by the ultrasonic generator; the ultrasonic generator includes an ultrasonic generator and a temperature controller connected thereto, for simultaneously providing an ultrasonic field and maintaining a low-temperature reaction environment during the reaction; the product collection device is a collection bottle placed in an ice-water bath; 2) In a syringe equipped with an online dispersion device, silver nanowires are dispersed in an organic solvent to obtain silver nanowire suspension A. The online dispersion device is used to maintain the dynamic and stable suspension of silver nanowires in silver nanowire suspension A. Organic ligands are dissolved in organic solvents to obtain ligand solution B; metal salts are dissolved in organic solvents to obtain metal salt solution C. 3) Pump the three solutions from step 2) into the micro mixer separately using a raw material pump for thorough mixing; 4) The mixed solution is passed into a coil-type microfluidic reactor and reacted under the action of an ultrasonic field to achieve complete and uniform full coating of the shell on the surface of the silver nanowires; 5) The reaction products are collected and post-processed to obtain the one-dimensional core-shell structured nanomaterials.

2. The method according to claim 1, characterized in that, In step 4), by synergistically controlling the ultrasonic power, precursor flow rate ratio, reaction temperature and residence time, a complete and uniform full coating of the shell on the surface of the silver nanowire is achieved. The ultrasonic power is 90-130 W; The flow rate ratio of silver nanowire suspension A, ligand solution B, and metal salt solution C was 1:(0.5-1.5):(0.1-0.6); the reaction temperature was 8-12℃; and the residence time was 4-8 minutes.

3. The method according to claim 1, characterized in that, The micromixer mentioned in step 1) has a cross-shaped, T-shaped, or Y-shaped structure; the coil-type microfluidic reactor is made of an acoustically transparent polymer material with an acoustic impedance of (1.1-1.5) MRayl.

4. The method according to claim 3, characterized in that, The acoustically transparent polymer material is a perfluoroalkoxyalkane or polytetrafluoroethylene; the coiled microfluidic reactor in step 1) is wound around a hollow support tube.

5. The method according to claim 1, characterized in that, The internal channel size of the micromixer mentioned in step 1) is 0.5-2.5 mm; the inner diameter of the pipe of the coil-type microfluidic reactor is 1.0-2.0 mm and the length is 3.0-6.0 m.

6. The method according to claim 1, characterized in that, In step 2), the organic solvent is ethanol or methanol; the organic ligand is 2-methylimidazole; the metal salt is cobalt salt; the mass concentration of silver nanowires in silver nanowire suspension A is 0.2-1.0 mg / mL; the mass concentration of organic ligands in ligand solution B is 60-120 mg / mL; and the mass concentration of metal salt in metal salt solution C is 5-30 mg / mL.

7. The method according to claim 1, characterized in that, The online dispersion device is a magnetic stirring device fitted outside the syringe. It drives a magnetic stir bar inside the syringe to rotate through a rotating magnetic field, thereby maintaining the dynamic and stable suspension of the silver nanowires.

8. A system for implementing the method according to any one of claims 1-7, characterized in that, include: A syringe for storing silver nanowire suspension A is equipped with a magnetic stir bar inside. An online dispersion device is installed at the syringe storing silver nanowire suspension A. It is used to drive a magnetic stir bar installed inside the syringe to rotate by a rotating magnetic field, thereby maintaining the dynamic and stable suspension of silver nanowires. Several raw material pumps are configured to pump silver nanowire suspension A, ligand solution B and metal salt solution C respectively; A micro mixer receives the solution pumped by the feed pump and mixes the feed materials; The coil-type microfluidic reactor, which serves as the main site for the reaction, is made of an acoustically transparent polymer material and is used to achieve controllable heterogeneous growth of the shell on the surface of silver nanowires under the action of an ultrasonic field. An ultrasonic generating device includes an ultrasonic generator for generating an ultrasonic field and a temperature controller for monitoring the reaction temperature inside a coil-type microfluidic reactor. Product collection device, used to collect reaction products flowing out of the coiled microfluidic reactor.

9. A one-dimensional core-shell structured nanomaterial obtained by the method according to any one of claims 1-7, wherein the one-dimensional core-shell structured nanomaterial is a silver nanowire@ZIF67 core-shell material.

10. The application of the silver nanowire@ZIF67 core-shell material according to claim 9 in the field of electrocatalytic nitrate reduction to ammonia production.

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