Synthesis of core / shell nanoparticles

Abstract

The present invention belongs to the field of nanoparticles and nanoparticle synthesis. In particular, the present invention relates to a method and system for producing core / shell nanoparticles, as well as core / shell nanoparticles. A method for producing core / shell nanoparticles is provided, comprising: - producing nanoparticles; - transporting the nanoparticles by a gas stream; - forming one or more shells around the nanoparticles while the nanoparticles are transported by the gas stream.

Description

Background Technology

[0001] This invention belongs to the field of nanoparticles and nanoparticle synthesis. Specifically, this invention relates to a method and system for producing core / shell nanoparticles, and core / shell nanoparticles themselves.

[0002] Nanoparticles have attracted considerable attention over the past few decades. Due to their small size, nanoparticles possess unique properties compared to larger-scale materials, such as micrometer-sized particles or bulk materials. These properties include a large surface area to volume ratio, as well as unique mechanical, optical, and electronic properties. Because of these properties, the use of nanoparticles is growing in various fields such as molecular biology, physics, organic and inorganic chemistry, and materials science, for example, in applications in (e)catalysis, sensors, and energy storage / conversion. Due to their small size, nanoparticles can, for example, enter human cells, thus also holding interest for (bio)medical applications.

[0003] Recently, there has been increased attention on core / shell nanoparticles. Core / shell nanoparticles typically comprise a core at the center of the particle, surrounded by one or more shells. Core / shell nanoparticles can possess properties and functionalities derived from their core or one or more shells, or a combination of both. In principle, core / shell nanoparticles can be made from a wide range of materials, including inorganic / inorganic (i.e., an inorganic core with an inorganic shell), inorganic / organic (i.e., an inorganic core with an organic shell), organic / inorganic, and organic / organic materials. Core / shell nanoparticles containing at least one inorganic core and at least one organic core and / or shell are often referred to as hybrid core / shell nanoparticles.

[0004] Typically, the core and one or more shells are made of different materials with different properties. In this way, core / shell nanoparticles can have different functionalities within a single particle. For example, the shell can act as a protective layer or barrier, enhancing the chemical and / or mechanical stability of the core / shell nanoparticles. Alternatively or additionally, one or more shells may also have properties that enhance the solubility or dispersibility of the core / shell nanoparticles in certain media.

[0005] However, while many types of core / shell nanoparticles can theoretically be conceived, they are not always achievable. Furthermore, even if the production of a particular type of particle is possible, synthesis often involves complex chemical methods that are cumbersome and / or expensive. Additionally, using methods known in the art, it may be difficult to obtain particles of sufficient quality, such as in terms of purity or particle size distribution. Scale-up synthesis methods are also typically challenging, making it difficult to prepare core / shell nanoparticles on an industrial scale.

[0006] Techniques for the industrial-scale production of conventional nanoparticles (i.e., as opposed to core / shell nanoparticles) include mechanical / mechanical chemical milling, chemical precipitation, and sol-gel condensation. Adapting these methods to synthesize a shell around the nanoparticle is not straightforward. Some of these methods can be adapted or extended (by adding additional processing steps) to enable the production of core / shell nanoparticles if they are compatible with the more complex structures of core / shell nanoparticles. However, adapting synthetic methods is often limited by chemical compatibility between precursors and requires the use of schemes that are difficult to scale up. Therefore, it is difficult to produce core / shell nanoparticles on a sufficiently large scale for practical applications, and most core / shell nanoparticle synthesis methods remain confined to basic research.

[0007] Other drawbacks of these known methods are that additional steps (such as functionalization, purification, oxidation, or steps that allow other chemical reactions to occur) need to be added to the procedure. Especially when some steps are performed in solution, extensive purification may be required between different steps.

[0008] One object of the present invention is to solve at least one of the aforementioned difficulties in the synthesis of core / shell nanoparticles.

[0009] Another object of the present invention is to enable the production of a variety of core / shell nanoparticles with well-defined morphology and / or high purity, preferably having a narrow particle size distribution.

[0010] Another objective is to provide a system that can be used to conveniently synthesize core / shell nanoparticles. Summary of the Invention

[0011] According to the present invention, a method for producing core / shell nanoparticles is provided, comprising the following steps: - producing nanoparticles; - conveying nanoparticles by airflow; - forming one or more shells around the nanoparticles while they are being conveyed by airflow.

[0012] The inventors have discovered that by forming one or more shells around nanoparticles while they are being transported by an airflow, it is possible to produce a variety of core / shell nanoparticles with high purity, and to achieve a uniform distribution of one or more shells around the core. Furthermore, core / shell nanoparticles with narrow size distributions can be formed. Another advantage is that this method is environmentally friendly in that it does not require the use of harmful solvents, meaning reduced waste. Moreover, the method can be well tuned to change morphology and composition. In addition, compared to existing multi-step methods, this method is less complex and can be scaled up without generating a large amount of additional waste.

[0013] Furthermore, the core / shell nanoparticles produced using this technology can be directly incorporated into subsequent processing steps, such as by depositing them on electrode surfaces through methods like impaction, electrostatic deposition, or diffusion. In this way, the core / shell nanoparticles can be directly applied to the final product.

[0014] A core / shell nanoparticle is also provided, comprising a core surrounded by one or more shells, which can be obtained by means of the methods described herein.

[0015] In addition, a system for producing core / shell nanoparticles as described herein is provided, comprising a nanoparticle production unit, a collection chamber, and a conduit through which nanoparticles can be transported from the nanoparticle production unit to the collection chamber by an airflow. The system also includes one or more inlets for introducing reactive reagents and / or vapors into the conduit. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating examples of different core / shell nanoparticles that can be produced.

[0017] Figure 2-9 Experimental results for different core / shell nanoparticles are shown. Detailed Implementation

[0018] According to the present invention, a method for producing core / shell nanoparticles is provided, comprising the following steps: - producing nanoparticles; - conveying nanoparticles by airflow; - forming one or more shells around the nanoparticles while they are being conveyed by airflow.

[0019] As used herein, nanoparticles refer to solid particles having a diameter of less than 500 nm, for example, 1-100 nm. Nanoparticles can be discrete or aggregated into clusters. Depending on the size of the clusters, the clusters themselves can also be considered nanoparticles. Preferably, nanoparticles are spherical or near-spherical.

[0020] The term core / shell nanoparticles refer to nanoparticles in which the core of the particle has a different chemical composition and / or different properties than the one or more shells surrounding the core. Preferably, the one or more shells are continuous, meaning that they cover the entire core or inner shell they enclose, and the surface of the core or inner shell is not directly exposed to the surrounding atmosphere.

[0021] The term hybrid core / shell nanoparticles refers to nanoparticles that have both inorganic and organic components. For example, nanoparticles having an inorganic core and at least one organic shell, or vice versa, are called hybrid core / shell nanoparticles.

[0022] In the methods described herein, the formation of one or more shells around a core can be achieved by chemically reacting the core or a previously formed shell, i.e., by altering the composition of the outer layer of the core or a previously formed shell through a chemical reaction, thereby forming a shell with a different chemical composition. This chemical reaction may, for example, include oxidation, reduction, or nitriding. For instance, a metal oxide shell can be formed by subjecting nanoparticles with a metallic surface to an oxidizing agent. Therefore, in embodiments, forming one or more shells involves introducing a substance reactive to the nanoparticles, i.e., a substance capable of altering the chemical composition of the nanoparticles (outer layer), into an airflow. In embodiments, the substance reactive to the nanoparticles is selected from oxidizing agents, reducing agents, free radicals, and combinations thereof.

[0023] Alternatively or additionally, the shell can be formed by depositing a layer on the nanoparticles. This can be achieved, for example, by introducing one or more vapors into a gas stream. Depending on the chemical composition of the gas stream and the vapors, and depending on the conditions in the gas stream (e.g., temperature and pressure), these vapors can be deposited on the nanoparticles by physical and / or chemical vapor deposition. Preferably, chemical vapor deposition is used to deposit one or more vapors, meaning that the vapors react to form chemical bonds with the nanoparticles.

[0024] Many different vapors can be used to deposit one or more shells. Vapors can be generated, for example, using a vaporizer and introduced into the gas stream through an inlet. In principle, the vaporizer can be loaded with any solid and / or liquid reagent or solvent that can be vaporized, which provides high flexibility and a wide range of possibilities for the optimization and fine-tuning of one or more shells.

[0025] For example, when an organic shell is to be deposited on a metal core or shell or a metal oxide core or shell, one or more vapors of compounds having functional groups known to coordinate with the metal or metal oxide, such as carboxylic acids, sulfonic acids, silanes, imidazole salts, thiols, and / or amines, including biomolecules such as amino acids or proteins, can be used. Deposition of such compounds can result in hybrid core / shell nanoparticles with an organic layer (e.g., an organic monolayer) deposited on their outer surface.

[0026] Preferably, the metal core is subjected to an oxidizing agent (e.g., oxygen) using the method described herein, thereby transforming the outer layer of the metal core into a metal oxide shell. An organic shell is preferably deposited on this metal oxide shell. By providing the oxide shell, the organic shell can be more strongly bonded to the nanoparticle. A variety of organic shells can be provided in an efficient manner, and the properties of the organic shells can be easily tuned by introducing different vapors. Therefore, the organic shell can be designed to be tailored for a specific application. For example, it has been found that nanoparticles having an iron core surrounded by an iron oxide shell and an organic shell prevent the oxidation of the iron core, which allows the inherent magnetic properties of the metal core to be retained and also avoids the formation of hollow nanoparticles.

[0027] Other vapors that can be introduced to form a shell around the nanoparticles are linkers for metal-organic frameworks (MOFs). In this case, an MOF shell can be formed around the nanoparticles. Preferably, the reaction conditions are optimized for MOF synthesis. The production of such nanoscale hybrid materials can bring many applications and development opportunities in a wide range of fields.

[0028] The nanoparticle core is preferably spherical or near-spherical and may have a diameter of 1.0-500 nm, preferably 1.0-100 nm, for example 5-75 nm, 5-25 nm, or 2-20 nm. Each of one or more shells may have a thickness ranging from less than 1.0 nm (which may be, for example, the thickness of an organic monolayer) to 100 nm. Preferably, each shell has a thickness of less than 1.0 nm to 50 nm.

[0029] After one or more shells are formed around the nanoparticles, the core / shell nanoparticles can be collected from the gas stream. Preferred options for collecting the core / shell nanoparticles include filtration and / or deposition of the core / shell nanoparticles onto a substrate. Alternatively or additionally, the core / shell nanoparticles can be collected from the gas stream by bubbling the gas stream in a solvent to form a dispersion of the core / shell nanoparticles.

[0030] Nanoparticles can be advantageously produced via spark ablation. Spark ablation is a physical phenomenon that generates a spark between two electrodes, resulting in localized ablation of the electrodes. This ablation produces a vapor of the material contained within the electrodes, which is then rapidly cooled. This vapor initially consists primarily of single atoms, which collide and grow over time into larger particles containing multiple atoms—a process described as coagulation. The size of the particles achieved through this mechanism depends primarily on the initial vapor concentration and the allowed growth time. Approximately, the average particle mass *m* at a given time can be calculated by dividing the initial vapor mass concentration *C* by the particle number concentration *N* at time *t*. According to coagulation theory (which is assumed to apply to this invention), the particle number concentration decreases substantially in a proportion to 1 / t, therefore *m* = *C* / N, which is proportional to *C*×t. By operating with short process times, small particle masses and thus small particle sizes can be obtained while maintaining high concentrations. High particle concentrations lead to higher productivity and faster, more efficient nanoparticle production. The production of nanomaterials via spark ablation is described, for example, in WO2016080837, the contents of which are incorporated herein by reference. One advantage of producing nanoparticles via spark ablation is that the nanoparticles are formed in an airflow during the process, making this method particularly suitable for steps involving the formation of one or more shells around the nanoparticles while they are being transported by the airflow. Therefore, there is less chance of nanoparticle agglomeration before the formation of one or more shells, resulting in a more uniform distribution of the one or more shells around the core and a narrower particle size distribution.

[0031] During spark ablation, a short-lived plasma is formed by a discharge between two electrodes containing conductive (or semi-conductive) materials. This plasma reaches temperatures well above the material's boiling point and generates a cloud of metal vapor. Upon cooling, the metal condenses to form a nanoparticle aerosol, which is subsequently carried away by a gas flow. Preferably, the carrier gas flow is inert to the nanoparticles formed from the vapor cloud. Once the nanoparticles have formed, a shell can be formed around them to produce core / shell nanoparticles.

[0032] When using spark ablation to produce nanoparticles (the core), the nanoparticles transported in the gas stream and generated by the spark may be charged, which increases the likelihood of surface reactions and / or the deposition of a shell around the nanoparticles.

[0033] In spark ablation, the size of the resulting nanoparticles depends on the initial concentration of the evaporated material, which is directly proportional to the energy of the spark (i.e., the breakdown voltage of the discharge) and inversely proportional to the flow rate of the carrier gas. Therefore, the size of the nanoparticles can be easily adjusted.

[0034] However, the process can also be performed using nanoparticles produced in ways different from those produced by spark ablation (e.g., mechanical / mechanical chemical milling, chemical precipitation, and sol-gel condensation), and these nanoparticles can be introduced into the carrier gas flow.

[0035] Advantageously, the methods described herein can be carried out at atmospheric pressure and generally do not require operation under vacuum conditions. The pressure during shell formation around the nanoparticles can vary depending on the process type (e.g., chemical reaction with the nanoparticles, physical vapor deposition, or chemical vapor deposition). Preferably, the absolute pressure during the formation of one or more shells is 0.25-2.5 bar, more preferably 0.5-2 bar, and even more preferably 0.8-1.7 bar, for example 0.9-1.4 bar.

[0036] Using the methods described herein, core / shell nanoparticles can be produced in a time-efficient manner. Preferably, the steps include: producing nanoparticles; - conveying nanoparticles via an airflow; and - forming one or more shells around the nanoparticles for 30 seconds or less, more preferably 20 seconds or less, such as 10 seconds or less.

[0037] Preferably, the nanoparticles are metallic nanoparticles before forming one or more shells. Metallic nanoparticles can have advantageous properties in terms of electrical conductivity and mechanical strength, and in some cases, also advantageous optical and magnetic properties. Furthermore, metallic nanoparticles can be readily made from a wide variety of metals, for example, using spark ablation. Alternatively, the nanoparticles can also be carbon nanoparticles before forming one or more shells, which can also be produced, for example, using spark ablation. When the nanoparticles are metallic before forming one or more shells, the metal is preferably selected from zinc, iron, nickel, gold, aluminum, silver, platinum, and iridium.

[0038] According to a second aspect, a core / shell nanoparticle is provided, comprising a core surrounded by one or more shells, which can be obtained by the methods described herein.

[0039] In this embodiment, the core of the core / shell nanoparticle is metallic, and at least one of the one or more shells, preferably the shell directly adjacent to the core, is a metal oxide. In this case, preferably, the metal of the core is selected from zinc, iron, nickel, aluminum, titanium, silicon, and manganese. Preferably, the metal oxide of the shell adjacent to the core is a metal oxide corresponding to the metal of the metal core. Such a metal oxide shell can be formed, for example, by subjecting the metal core to an oxidizing agent, resulting in the oxidation of the outer layer of the metal core.

[0040] In this implementation, one of the core and / or shell comprises an organic material. For example, the shell may comprise one or more polymers. Examples of suitable polymers include biopolymers, cellulose polymers, and polymer systems for drug delivery (e.g., arginine, chitosan, dextran, poly(ethyleneimine), polysaccharides, or polyols). By adding the polymer precursor as a vapor, the resulting polymer can be directly attached to the underlying inorganic core or shell (e.g., a metal oxide layer), meaning that another organic layer is not required.

[0041] In one embodiment, at least one of the shells comprises a metal-organic framework.

[0042] Many variations of the above-described embodiments are possible, such as a metal core surrounded by a metal oxide shell or a metal core surrounded by an organic shell. One advantage of surrounding the metal core with a metal oxide shell is that, relative to the metal core, the metal oxide shell can improve the reactivity of the nanoparticles to the grafting reaction with organic vapors, thereby leading to a stronger bond between the organic shell and the nanoparticles. For example, hydroxyl groups present in the metal oxide shell can enable acid-base reactions leading to silane functionalization and / or dehydration reactions leading to carboxylate coordination.

[0043] In this embodiment, the core / shell nanoparticles are hybrid core / shell nanoparticles.

[0044] In one embodiment, the core / shell nanoparticle comprises a metal core surrounded by a metal oxide shell.

[0045] In one embodiment, the core / shell nanoparticle comprises a metal core surrounded by a first metal oxide shell and a second organic shell.

[0046] The second organic shell may, for example, contain one or more selected from carboxylate, silane, and metal-organic frameworks.

[0047] In the case of core / shell nanoparticles containing a metal core, a metal oxide shell, and / or a shell containing a metal-organic framework, the metals in the core and the corresponding shell can be the same and / or different metals.

[0048] In one embodiment, the core / shell nanoparticle comprises a metal core surrounded by a metal oxide shell and a shell containing a metal-organic framework, wherein the metal in the core and the shell are the same.

[0049] In one embodiment, the core / shell nanoparticle has a zinc core surrounded by a first shell containing zinc oxide, which is then surrounded by a second shell containing a zinc-containing metal-organic framework (e.g., ZIF-8).

[0050] In cases where one of the one or more shells contains a metal-organic framework, the metal-organic framework can be crystalline and / or amorphous. In a preferred embodiment, the metal-organic framework is amorphous.

[0051] As explained above, the method of the present invention can result in core / shell nanoparticles with well-defined morphologies, such as well-controlled shape, shell thickness, and / or particle size. Therefore, a plurality of core / shell nanoparticles as described above are provided, wherein the core / shell nanoparticles are spherical or near-spherical.

[0052] Preferably, the core / shell nanoparticles have an average particle diameter of 1-100 nm, more preferably 5-100 nm, and a standard deviation of 20% or less, more preferably 10% or less, more preferably 8% or less, for example 5% or less.

[0053] The core / shell nanoparticles according to the present invention can be used in a wide variety of applications. For example, zinc-based materials for biomedical applications can be produced, but it will be understood that many different materials and core / shell combinations are possible. Zinc oxide is considered low in toxicity and has been approved by the FDA for use in cosmetic formulations. However, for applications in drug delivery, there are concerns due to the metallic nature of ZnO nanoparticles and their potential harmful effects on body cells. This risk can be mitigated by functionalizing their surface with organic groups (i.e., providing an organic shell around the nanoparticles). Currently, the synthesis of such core / shell nanoparticles for biomedical applications is limited to bottom-up methods that rely on the assembly of nanoscale building blocks through chemical synthesis. These methods are liquid-phase methods in aqueous or non-aqueous media, requiring multi-step synthetic procedures where various physical and chemical parameters must be finely tuned. The fact that such zinc-based hybrid core / shell nanoparticles are currently synthesized in the liquid phase introduces uncertainty regarding the influence of contaminant species such as surfactants or solvents. In contrast, when using the method of the present invention, core / shell nanoparticles are produced in a highly controlled manner and in the absence of solvents and contaminants. In this way, core / shell nanoparticles that meet strict medical regulations can be produced.

[0054] The core / shell nanoparticles according to the present invention, such as metal particles with an organic shell, can be used for medical imaging and / or therapy. The organic phase of the hybrid core / shell nanoparticles can improve in vivo stability and enable cell or tissue targeting.

[0055] The core / shell nanoparticles according to the present invention can also be used in other technologies, such as chemical sensing, as well as energy storage and / or conversion.

[0056] A system for producing core / shell nanoparticles is also provided, preferably using the method described above. The system includes a nanoparticle production unit, a collection chamber, and a conduit through which nanoparticles can be transported from the nanoparticle production unit to the collection chamber by an airflow. To form one or more shells around the nanoparticles, the system may further include one or more inlets for introducing reactive reagents and / or vapors into the conduit.

[0057] Because the system includes one or more inlets for introducing reactive reagents and / or vapors into the conduit, the amount of reactive reagents and / or vapors that the nanoparticles experience during gas flow transport can be conveniently adjusted and controlled, even during the production of core / shell nanoparticles. One or more inlets can be used to introduce reactive reagents and / or vapors individually and / or as a mixture of one or more reactive reagents and / or vapors into the conduit.

[0058] One or more inlets can be configured to regulate the rate of introduction of reactive reagents and / or vapors. This can be used, for example, to control the thickness of one or more shells. For this purpose, at least one of the one or more inlets may include a flow controller, such as a mass flow controller or a needle valve. In embodiments, different inlets are placed at different locations along the length of the conduit, thereby enabling the nanoparticle core to be coated sequentially, for example, with shells of different chemical properties.

[0059] Preferably, the nanoparticle production unit is a spark ablation generator.

[0060] The conduit may be, for example, a tube in which reactive reagents and / or vapors are introduced. The conduit may also include a mixing chamber in which conditions for shell formation, such as temperature and pressure, can be controlled.

[0061] In one embodiment, the system includes one or more vaporizers connected to one or more inlets. Preferably, the one or more vaporizers are configured to heat a quantity of liquid or solid material, such as an organic material, to generate vapor that can be introduced into a conduit. Vaporizers may also be absent if the system will be used with (organic) vapor that is already in the vapor phase at room temperature (e.g., at ambient temperature and pressure (NTP)).

[0062] The length of the catheter can be in the range of 10-100 cm, preferably 20-50 cm.

[0063] Unless otherwise specified herein or in obvious contradiction in the context, the terms “a / an”, “the”, and similar pronouns used in the context of describing the invention (especially in the context of the following claims) should be interpreted as covering both the singular and plural. Unless otherwise stated, the terms “comprising,” “having,” “including,” and “containing” should be interpreted as open-ended terms (i.e., meaning “including but not limited to”). Unless otherwise specified herein, the description of numerical ranges herein is intended only as a convenient way of referring individually to each individual value falling within that range, and each individual value is incorporated into this specification as if it were described separately herein. Unless otherwise specified herein or in obvious contradiction in the context, all methods described herein may be performed in any suitable order. Unless otherwise stated, the use of any and all instances or exemplary language (e.g., “such as”) provided herein is intended only to better illustrate the invention and does not constitute a limitation on the scope of the invention. No language in this specification should be construed as indicating that any unclaimed element is necessary for the implementation of the invention.

[0064] This document describes preferred embodiments of the invention, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors intend that those skilled in the art will suitably employ such variations, and the inventors intend that the invention be practiced in ways other than those specifically described herein. Therefore, the invention includes all modifications and equivalents of the subject matter set forth in the appended claims as permitted by applicable law. Furthermore, unless otherwise specified herein or otherwise obviously contradicted by the context, any combination of the foregoing elements in all possible variations is covered by the invention.

[0065] Although the invention has been described with respect to specific examples including preferred embodiments of the present invention, those skilled in the art will understand that many variations and arrangements of the above-described systems and techniques fall within the spirit and scope of the invention as set forth in the appended claims.

[0066] Figure 1 This is a schematic diagram of possible core / shell nanoparticles.

[0067] The core / shell nanoparticle (1) comprises a core (10) and one or more shells (11, 13, 14). The core (10) may be, for example, a metallic core or a carbon core, but other core materials are also possible. The first shell (11) may, for example, comprise a metal oxide. In embodiments where the core (10) is metallic, the first shell (11) may, for example, be a metal oxide corresponding to the metal of the core (10). The additional shells (13, 14) may be, for example, organic. The thickness of such shells may depend on the chemical properties and / or the manner in which the shells are applied. For example, the MOF layer may be a relatively thick layer (13) compared to a thinner monolayer (14) (e.g., a carboxylate or silane monolayer).

[0068] Example

[0069] Different core / shell nanoparticles were synthesized and analyzed. In the examples below, the nanoparticles were generated using a VSP-G1 spark ablation generator from VSPARTICLE and a zinc electrode. Different types of shells were formed around the nanoparticles. The resulting core / shell nanoparticles were characterized using PXRD, ATR, SEM / STEM, and TGA / DSC.

[0070] Unless otherwise stated, all chemicals were purchased from commercial suppliers and used without further purification. The Zn electrode, along with VSP-G1, was obtained from VSPARTICLE.

[0071] Powder X-ray diffraction (PXRD) patterns were measured using a Rigaku MiniFlex II diffractometer at a scan rate of 2.5° / min using Cu K-α radiation (λ = 1.5406 Å).

[0072] Fourier transform infrared spectroscopy (FTIR) was performed on a Thermo Fisher Scientific Nicolet iS50 FTIR spectrometer equipped with a Specac Quest ATR accessory.

[0073] Thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) were performed using a NETZSCH Jupiter STA 449F3 instrument under an argon atmosphere at a heating rate of 5 K / min.

[0074] Scanning electron microscopy (SEM) was performed using a FEI Verios 460 with a typical electron energy of 5 keV and a current of 100 nA.

[0075] Scanning transmission electron microscopy (STEM) images were acquired using a HAADF (high-angle annular dark field) detector, and energy-dispersive spectroscopy (EDS) data were obtained using an Oxford Xmax 80 mm microscope. 2Silicon drift detectors were obtained. Both detectors were mounted on the aforementioned FEI Verios 460.

[0076] TEM images were obtained using a FEI TecnaiG2 20 X-Twin. Samples were either deposited directly or drop-cast from an ethanol dispersion onto a TEM grid (Formvar / carbon, 300 mesh, from Ted Pella Inc.).

[0077] Example 1 - Zn / ZnO nanoparticles.

[0078] Core / shell nanoparticles (Zn / ZnO nanoparticles) with a zinc core surrounded by a zinc oxide shell were synthesized. The core was prepared by spark ablation using VSP-G1 (VSPARTICLE) under a nitrogen flow (2 L / min) as the carrier gas. Typically, 1.2 kV and 8 mA were used to generate the spark. A small amount of air and / or water in the system was used as the oxygen source downstream of the spark ablation.

[0079] After the zinc oxide shell is formed, the nanoparticles are collected either on filter paper (ø 47 mm) or on a 1 cm x 1 cm silicon substrate placed in a VSP-G1 filter unit. The product is collected 10 to 24 hours after synthesis.

[0080] ATR-IR spectrum, PXRD pattern, TGA / DSC curve, and SEM / STEM images are shown in Figure 2 In the middle. ATR-IR shows the characteristic OH stretching vibrations of hydroxyl groups on its surface at 3400 cm⁻¹. -1 It has a broad spectral band in the vicinity, and at 1250 cm⁻¹ -1 and 1500 cm -1 It exhibits a bimodal distribution. Typical Zn-O stretching vibrations can occur at 600-400 cm⁻¹. -1 Within the range observed. PXRD indicates that the nanoparticles are mainly composed of ZnO with a small amount of metallic Zn. The peaks at 31.8°, 34.5°, 36.2°, 47.6°, 56.6°, 62.9°, and 68.0° correspond to the (100), (002), (101), (102), (110), (103), and (112) crystal planes of wurtzite, respectively. The metallic phase is confirmed by the weaker peaks at 35.4°, 43.3°, and 53.0°, which correspond to the (002), (101), and (102) crystal planes, respectively.

[0081] TGA-DSC indicates that core / shell nanoparticles lose 8.7% of their mass in the low-temperature range, which may be caused by the desorption of water or solvent molecules, and then remain stable up to 700°C.

[0082] Example 2 - Hybrid Zn / ZnO nanoparticles having a molecular shell coordinated by a carboxylic acid group.

[0083] Carboxylate groups can coordinate with metal oxides (e.g., zinc oxide, nickel oxide). Although the bonding is usually weak, carboxylate groups can form a monolayer (i.e., a 2D shell) on the surface of metal oxides, significantly altering the properties of the functionalized material.

[0084] Nanoparticles with molecular shells having two different types of carboxylic acid (CA) bonds, namely citric acid (CA) and 2-naphthoic acid (NA), were also synthesized. The synthesis was the same as in Example 1, except that vapors of either of the aforementioned two molecules were introduced instead.

[0085] Carboxylic acid molecules were placed in a vaporizer and heated to 125°C under a nitrogen flow (0.5 L / min), while Zn / ZnO nanoparticles were produced from VSP-G1 using the conditions described above.

[0086] Figure 3 The PXRD pattern, ATR-IR spectrum, and SEM image of nanoparticles with a citric acid shell are shown.

[0087] As expected, because citric acid exists only in a monolayer, the PXRD pattern and SEM images are similar to those of Zn / ZnO nanoparticles.

[0088] Infrared spectroscopy confirmed the presence of citrate ions coordinated at the NP. Vibrational bands attributable to the asymmetric stretching, symmetric stretching, and bending vibrations of COO- were observed at 1565, 1410, and 1270 cm⁻¹, respectively. -1 At 1700 cm. Furthermore, at 1700 cm -1 The absence of a C=O stretching band indicates that the three carboxylic acid groups of the linker are deprotonated and therefore coordinated.

[0089] Figure 4 The PXRD pattern, ATR-IR spectrum, TGA / DSC curve, and schematic diagram of nanoparticles with a naphtholic acid shell are shown.

[0090] Similar to citric acid, the PXRD pattern is not significantly different from that of Zn / ZnO nanoparticles.

[0091] IR analysis revealed that all OH-related bands (1300 cm⁻¹) -1 1159 cm -1 The bands at NA disappear, while those attributable to carboxyl groups and C / C or CH bonds shift. Furthermore, nanoparticles with NA shells show a shift at 1700 cm⁻¹. -1No free carboxylate bands were observed nearby, confirming that the organic phase consists of a unique molecular layer coordinated through its carboxylate groups. Asymmetric and symmetric stretching vibrations of COO- were observed at ~1550 cm⁻¹. -1 and ~1400 cm -1 Vibrations associated with CC and CH were observed at [location].

[0092] The concave shape of the TG curve during water and other solvent loss at low temperatures (<250 °C) suggests a hydrophobic surface, as expected for aromatic monolayers. This first desorption event accounts for 3.4% of the total sample mass. Desorption of naphthoic acid molecules occurs between 250 °C and 550 °C. A sharp weight loss of 9.1% at approximately 425 °C corresponds to the major desorption event of coordinating molecule loss. Thereafter, increasing temperatures up to 700 °C do not trigger any further mass loss. The strong endothermic peak in the DSC signal at 430 °C corresponds to the evaporation of naphthoic acid, which occurs at a temperature higher than the boiling point of the non-coordinating linker (300 °C).

[0093] Example 3 - Hybrid Zn / ZnO nanoparticles with APTES shell.

[0094] Nanoparticles with an organo(3-aminopropyl)triethoxysilane (APTES) shell were also synthesized. The synthesis was the same as in Example 2, except that APTES vapor was introduced instead.

[0095] APTES was placed in a vaporizer and heated to 80°C under a nitrogen flow (0.5 L / min) while Zn / ZnO nanoparticles were produced from VSP-G1 using the conditions described above.

[0096] Figure 5 The ATR-IR spectrum, schematic diagram, TGA / DSC curve, and TEM image of nanoparticles with APTES shells are shown.

[0097] ATR-IR confirmed the successful anchoring of the silane on the surface. The spectrum showed a band (1165 cm⁻¹) associated with the CH₃CH₂O functional group. -1 1100 cm -1 953 cm -1 The graft disappeared as expected. Furthermore, multiple vibrational bands (1645 cm⁻¹) attributable to the NH and CH bonds of the molecule were observed. -1 1390 cm -1 762 cm -1 Two strong spectral bands (1100 cm⁻¹) -1 and 880cm -1 The vibrational modes belong to the Si-O-Si groups. Additionally, the CH stretching vibration of the APTES backbone occurs at 2975 cm⁻¹.-1 2930 cm -1 and 2887 cm -1 It can be seen at various locations. Finally, at 1050 cm... -1 The clear Si-O-Si vibrational bands observed at the surface indicate that at least some APTES on the surface have undergone cross-linking polymerization with their neighboring molecules.

[0098] TGA data indicate that nanoparticles lose 6.3% of their mass due to desorption from water and / or solvents in the low-temperature range (35–250 °C), and 7.1% of their mass from 250 °C onwards. The major desorption event (i.e., loss of the organic phase) occurs at approximately 350 °C. Considering the boiling point of the original APTES is 217 °C, these observations further confirm our conclusions drawn from IR analysis.

[0099] The multiple endothermic peaks (335 °C, 368 °C, and 428 °C) observed on the DSC curves during organic phase desorption indicate a multi-step process. This multi-step desorption may originate from the heterogeneity in the APTES-substrate binding and / or from crosslinking polymerization, which further supports the aforementioned interpretation of the IR data.

[0100] Example 4 - Hybrid ZnO nanoparticles with MOF shell.

[0101] Nanoparticles with a zeolite imidazole ester framework (ZIF-8) shell were also synthesized. The synthesis was the same as in Examples 2 and 3, except that 2-methylimidazole vapor was introduced instead.

[0102] 2-Methylimidazole was placed in a vaporizer and heated to 100°C under a nitrogen flow (0.5 L / min) while Zn / ZnO nanoparticles were produced from VSP-G1 under the conditions described above. The product was collected 10 to 24 hours after synthesis.

[0103] Figure 6 The PXRD pattern, ATR-IR spectrum, TGA / DSC curve, and schematic diagram of nanoparticles with ZIF-8 shells are shown.

[0104] In the PXRD pattern, the nanoparticles synthesized via ZIF-8 linker (2-methylimidazole) vapor did not show any clear peaks associated with one of the ZIF-8 crystalline phases (e.g., sodalite, katsenite, or diamonite). Nevertheless, the baseline of the diffraction pattern was not flat in the region of interest for ZIF-8 (6° to 28°), and some bulges were visible in the noise at the relevant angles.

[0105] Although amorphous, the formation of ZIF-8 nanoparticles synthesized in the presence of 2-methylimidazole vapor in the system was confirmed by infrared analysis. CN and CH vibrations indicate the presence of 2-methylimidazole molecules in the sample, while the NH vibrational band (bending at 620 cm⁻¹) shows a similar pattern. -1 and 1595 cm -1 ; Stretchable between 2200-3100 cm -1 The disappearance of the Zn-N stretching vibration and the frequency shift of the CN vibration support the hypothesis of cohesive basis coordination. Strong Zn-N stretching vibration (420 cm⁻¹) -1 Although it overlaps with the broad Zn-O stretching band, it is still clearly visible, which is another argument supporting the existence of an amorphous ZIF-8 layer encapsulating Zn / ZnO nanoparticles.

[0106] TGA data indicate that nanoparticles lose 9.7% of their mass due to desorption of moisture and / or solvent in the lower temperature range (35–250 °C), similar to the situation with Zn / ZnO nanoparticles. In the second temperature range (250 °C to 550 °C), nanoparticles lose 20.0% of their weight due to the collapse of the ZIF-8 framework structure. At 700 °C, most of the organic phase has been lost, leaving 69.4% of the initial mass.

[0107] DSC analysis showed a sharp exothermic peak at 450℃, which is associated with the initial collapse of the ZIF-8 frame.

[0108] Example 5 - Fe / Fe x O y Nanoparticles.

[0109] Core / shell nanoparticles (Fe / Fe) with an iron core surrounded by an iron oxide shell were synthesized. x O y (Nanoparticles). The synthesis was the same as in Example 1, except that an iron electrode was used instead.

[0110] Figure 7 Fe / Fe x O y ATR-IR spectrum, PXRD spectrum and SEM / STEM images of nanoparticles.

[0111] ATR-IR revealed the characteristic OH stretching vibrations of hydroxyl groups on its surface at 3370 cm⁻¹. -1 Nearby (between 3000 and 3600 cm) -1 (between) and at 1631 cm -1 It exhibits a broad spectral band. Typical Fe-O stretching vibrations can be observed in the 600-400 cm⁻¹ region. -1 Seen within the range.

[0112] PXRD indicates that the nanoparticles consist of Fe(0) and Fe2+. x O y Composition. The metallic phase is evidenced by a sharper peak at 44.7° corresponding to the (110) crystal plane. The peaks at 36.0° and 61.0° are close to the theoretical positions of the characteristic peaks of maghemite (γ-Fe2O3) and magnetite (Fe3O4). The broadening of the sample peaks may be due to the presence of both phases and the overlap of their peaks (maghemite: 57.5° and 63.2°; magnetite: 62.4°).

[0113] Example 6 - Hybrid Fe / Fe with APTES shell x O y Nanoparticles.

[0114] Nanoparticles with an organo(3-aminopropyl)triethoxysilane (APTES) shell were also synthesized. The synthesis was the same as in Example 3, except that an iron electrode was used instead.

[0115] APTES was placed in a vaporizer and heated to 80°C under a nitrogen flow (0.5 L / min), while Fe / Fe was produced from VSP-G1 using the conditions described in Example 5 above. x O y Nanoparticles.

[0116] Figure 8 Fe / Fe with APTES shell is shown x O y ATR-IR spectrum, PXRD spectrum and SEM / STEM images of nanoparticles.

[0117] As expected, because APTES exists only as a monolayer, the PXRD pattern is consistent with Fe / Fe x O y The similarities of nanoparticles.

[0118] ATR-IR confirmed the successful anchoring of the silane on the surface. The spectrum showed, as expected after grafting, the band associated with the CH3CH2O functional group (1165 cm⁻¹). -1 1100 cm -1 953 cm -1 The vibrational intensity was noticeably weak. Furthermore, multiple vibrational bands (1645 cm⁻¹) attributable to the NH and CH bonds of the molecule were observed. -1 1390 cm -1 Strong spectral bands (~900 cm⁻¹) belonging to the vibrational modes of Si-O-Si and Si-O-Fe groups. -1 This indicates that at least some APTES on the surface have undergone cross-linking polymerization with adjacent molecules. Additionally, the CH stretching vibration of the APTES backbone at 2975 cm⁻¹...-1 2930 cm -1 and 2887 cm -1 It can be seen everywhere.

[0119] Figure 9 The magnetization versus magnetic field curves of iron nanoparticles with and without an APTES shell are shown, verifying the superparamagnetic properties of the nanoparticles. The average barrier temperature is approximately 220 K.

Claims

1. A method for producing core / shell nanoparticles, comprising the following steps: - Production of nanoparticles; - The nanoparticles are transported via airflow; - While the nanoparticles are being transported by the airflow, one or more shells are formed around the nanoparticles, wherein the step of forming one or more shells includes: - Introducing a substance reactive to the nanoparticles into the airflow, and - Introducing one or more vapors into the airflow, wherein the one or more vapors contain at least one organic vapor.

2. The method according to claim 1, wherein the substance reactive to the nanoparticles is an oxidizing agent.

3. The method according to claim 1 or 2, wherein an organic layer is deposited on the nanoparticles by introducing one or more vapors into the gas flow.

4. The method according to any one of the preceding claims is followed by collecting the core / shell nanoparticles, preferably by filtering an airflow containing the core / shell nanoparticles.

5. The method according to any one of the preceding claims, wherein the nanoparticles are produced by spark ablation.

6. The method according to any one of the preceding claims, wherein the steps are performed at atmospheric pressure.

7. The method according to any one of the preceding claims, wherein the at least one organic vapor is selected from carboxylic acids, silanes, thiols, amines, peptides / proteins, and combinations thereof.

8. The method according to any one of the preceding claims, wherein the nanoparticles are metal nanoparticles prior to the formation of the one or more shells.

9. Core / shell nanoparticles comprising a core surrounded by one or more shells, said core / shell nanoparticles being obtainable by a method according to any one of the preceding claims, wherein at least one of said one or more shells comprises an organic material.

10. The core / shell nanoparticle of claim 9, comprising a metal core surrounded by a first shell comprising a metal oxide adjacent to the metal core, and the first shell being surrounded by a second shell, wherein the second shell preferably comprises an organic material.

11. The core / shell nanoparticle of claim 10, wherein the metal oxide of the first shell is an oxide of the metal of the metal core.

12. The core / shell nanoparticles according to any one of claims 9 to 11, wherein the organic material is a metal-organic framework.

13. The core / shell nanoparticles according to any one of claims 9 to 12, comprising a zinc core surrounded by a first shell comprising zinc oxide and a second shell comprising ZIF-8.

14. The core / shell nanoparticles according to any one of claims 9 to 12, comprising a metallic iron core surrounded by a first shell comprising iron oxide and an organic shell.

15. A plurality of core / shell nanoparticles according to any one of claims 9 to 14, wherein the core / shell nanoparticles are spherical or near-spherical, preferably having an average particle diameter of 5-100 nm and a standard deviation of 10% or less.

16. A system for producing core / shell nanoparticles, preferably produced using the method according to any one of claims 1 to 8, the system comprising a nanoparticle production unit, a collection chamber, and a conduit through which nanoparticles can be conveyed from the nanoparticle production unit to the collection chamber by an airflow, the system further comprising one or more inlets for introducing reactive reagents and / or organic vapors into the conduit.

17. The system of claim 16, wherein the nanoparticle production unit is a spark ablation generator.

18. The system of claim 16 or 17, wherein at least one of the one or more inlets includes a flow controller.

19. The system according to any one of claims 16 to 18, further comprising a vaporizer connected to one or more of the inlet.

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