CN109332681B - Preparation method of carbon-coated iron-ferroferric carbide magnetic nanoparticles - Google Patents

Preparation method of carbon-coated iron-ferroferric carbide magnetic nanoparticles Download PDF

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CN109332681B
CN109332681B CN201811486242.0A CN201811486242A CN109332681B CN 109332681 B CN109332681 B CN 109332681B CN 201811486242 A CN201811486242 A CN 201811486242A CN 109332681 B CN109332681 B CN 109332681B
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ferroferric
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potassium bromide
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李海鹏
赵利新
戴西斌
孙雪宇
李超杰
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Hebei University of Technology
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Abstract

The invention relates to a preparation method of a carbon-coated iron-iron carbide magnetic nanoparticle, which relates to a catalyst containing iron, and is characterized in that a mixed solution of ferric citrate and potassium bromide is subjected to freeze drying to obtain ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and serve as a ferrous metal source, an iron oxide-potassium bromide catalyst precursor is obtained through calcination, then a chemical vapor deposition method is adopted to prepare a carbon-coated iron-iron carbide magnetic nanoparticle product with a carbon layer as an outer layer and an iron and iron carbide as a core, so that the defects of low purity of the prepared carbon-coated iron nanoparticle, poor dispersibility of the particle, poor controllability of the particle size, low crystallization degree of the particle, poor stability and poor comprehensive performance in the prior art are overcome.

Description

Preparation method of carbon-coated iron-ferroferric carbide magnetic nanoparticles
Technical Field
The technical scheme of the invention relates to a catalyst containing iron, in particular to a preparation method of carbon-coated iron-iron carbide magnetic nanoparticles.
Background
Carbon-coated magnetic nanoparticles (CEMNPs for short) have good electrochemical performance, optical performance, magnetic performance, adsorption performance and biocompatibility, and have great application prospects in the fields of electricity, magnetism, photocatalysis and biomedicine. Thus, in recent years, this new type of nanocomposite has attracted extensive interest and has developed a series of research works. The carbon-coated magnetic nanoparticles are of various types, wherein the carbon-coated iron-iron carbide magnetic nanoparticles are composed of an iron-iron carbide nano core obtained by dissolving and separating out nano iron particles through carbon and a carbon layer tightly surrounding the core. The unique core-shell structure provides significant performance advantages. Firstly, due to the protection effect of the inert carbon shell, the influence of the environment on the core ferromagnetic nano material, such as the oxidation of the core ferromagnetic nano material, is avoided, so that the problem that the iron-ferroferric carbide nano particles cannot be stably arranged in the air is solved; secondly, the magnetic iron-ferroferric carbide nanoparticles are coated in the carbon layer, so that strong van der Waals force among the magnetic nanoparticles can be effectively reduced, the phenomenon of agglomeration is reduced, the mutual influence of adjacent magnetic units is weakened, and the magnetic performance is greatly improved; and thirdly, the iron-ferroferric carbide magnetic nano particles coated with the carbon have the characteristics of high specific surface area, high temperature resistance and corrosion resistance of the carbon material and the magnetic property and catalytic property of the iron-ferroferric carbide nano particles. Therefore, the novel carbon-coated magnetic nanoparticles realize the multifunctionality and separability of materials, and have high application values in many fields, particularly including the fields of catalysts, magnetic recording, magnetic separation, biomedicine, targeted drug delivery, electromagnetic wave absorption, magnetic resonance imaging and nuclear waste treatment. However, in the prior art for preparing the iron-ferroferric carbide magnetic nanoparticles, the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles still have poor structures, and the stable performance of the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles is difficult to ensure; low purity, limiting its performance and application; low synthesis yield and difficult mass production. Therefore, there is still a need to further innovate the synthesis process of the carbon-coated iron-iron carbide magnetic nanoparticles, improve the purity and performance of the nanoparticles, and solve a plurality of problems in the preparation and application processes of the nanoparticles.
In the preparation of the carbon-coated iron-ferroferric carbide nano-particles, the main process methods include a carbothermic method, a pyrolysis method, a hydrothermal method, a pulse laser method, an arc discharge method and the like. For example, CN107127335A reports a method for preparing a carbon-coated iron nanocomposite, in which a short nickel rod is added to toluene, xylene or cyclohexane organic solution dissolved with ferrocene, and microwave heating is performed under the protection of nitrogen gas, so as to prepare the carbon-coated iron nanocomposite; CN106732598A discloses a preparation method of a carbon-coated iron nano catalyst, which is to drop a ferric nitrate solution into a mixed solution of sucrose and hydrazine hydrate and use a precursor prepared after dryingCarbonizing in nitrogen atmosphere, and annealing to obtain the carbon-coated iron nano catalyst; CN104785777A discloses a method for preparing a carbon nanotube/graphite-coated iron nanoparticle composite, which comprises depositing Co (Fe, Ni) on single-crystal silicon to synthesize carbon nanotubes, using carbon nanotubes and ferrocene as carriers and metal sources, respectively, and using a plasma-enhanced chemical vapor deposition method to prepare a carbon nanotube/graphite-coated iron nanoparticle composite; CN102990075A reports a method for preparing carbon-coated iron nanoparticles, and nano Fe is prepared by using ferrous sulfate and sodium hydroxidexOyHydrate and then obtaining Fe coated with organic carbon through liquid alkane refluxxOyFinally, preparing carbon-coated iron nanoparticles through heat treatment; CN102784913A reports a hydrothermal preparation method of carbon-coated iron nanoparticles, in which a powder collected after hydrothermal reaction of a mixed solution of glucose and ferric nitrate is calcined in an inert/reducing atmosphere to obtain carbon-coated iron nanoparticles; CN1935415A reports a carbon-coated magnetic ultrafine iron particle and a manufacturing method thereof, in which nano ferroferric oxide and a separant are mixed by ball milling, and then the carbon-coated magnetic ultrafine iron particle is prepared by a chemical vapor deposition method under a mixed atmosphere of hydrogen, carbon source gas and inert gas; CN104117339A reports a preparation method of an adsorbent for adsorbing dyes, which is to prepare a sodium chloride-loaded iron catalyst by using ferric trichloride and sodium hydroxide, add glucose according to a certain proportion and prepare a carbon-coated ferromagnetic nanoparticle adsorbent by a hydrothermal method; CN101710512A reports a preparation method of a graphene and carbon-coated ferromagnetic nano metal composite material, in which a precipitant is added into a mixed solution of ferromagnetic metal salt and graphene oxide, and then the collected composite powder is subjected to chemical vapor deposition under hydrogen and a carbon source gas to obtain the graphene/carbon-coated ferromagnetic nano metal composite material. The above prior art generally has the following disadvantages: the prepared carbon-coated iron nano-particles have low purity, serious agglomeration, poor controllability of particle size, low crystallization degree of the particles, poor stability and poor comprehensive performance, thereby limiting the wide application of the carbon-coated iron nano-particles in the fields of electricity, magnetism, photocatalysis, biomedicine and the like.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the preparation method of the carbon-coated iron-iron carbide magnetic nano-particles is provided, and the method comprises the steps of obtaining iron citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and serve as iron metal sources from a mixed solution of iron citrate and potassium bromide through a freeze drying technology, obtaining an iron oxide-potassium bromide catalyst precursor through calcination, preparing a carbon-coated iron-iron carbide magnetic nano-particle product with a carbon layer as the outer layer of the magnetic nano-particles and an iron and iron carbide as the core part by adopting a chemical vapor deposition method, and overcoming the defects that the prepared carbon-coated iron nano-particles are low in purity, poor in particle dispersibility and particle size controllability, low in particle crystallization degree, poor in stability and poor in comprehensive performance in the prior art.
The technical scheme adopted by the invention for solving the technical problem is as follows: a preparation method of carbon-coated iron-ferroferric carbide magnetic nanoparticles comprises the following steps of obtaining iron citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and serve as an iron metal source from a mixed solution of iron citrate and potassium bromide through a freeze drying technology, obtaining an iron oxide-potassium bromide catalyst precursor through calcination, preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a carbon layer as an outer layer and an iron and ferroferric carbide as a core by adopting a chemical vapor deposition method, and specifically comprising the following steps:
firstly, preparing an iron oxide-potassium bromide catalyst precursor:
firstly, mixing a ferric citrate pentahydrate aqueous solution with the mass percentage concentration of 1-3% and a potassium bromide aqueous solution with the mass percentage concentration of 10.03-16.7% to form a mixed solution, ensuring that the mass ratio of iron to potassium bromide is 0.01-0.05: 1, heating and stirring the mixed solution at 50-70 ℃ and the rotating speed of 300-500 rpm by using a magnetic heating stirrer for 2-4 hours, then transferring the mixed solution to a plastic test tube and placing the plastic test tube in a freeze drying box, cooling the plastic test tube to-10-50 ℃ at the cooling speed of 5-20 ℃/min, freezing the mixed solution into a solid state, then continuously drying the solid state in the freeze drying box under the vacuum of 1.3-13.0 Pa for 24-48 hours, then taking out the ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and serve as a ferrous metal source from the freeze drying process from the plastic test tube, grinding the ferric citrate particles at the rotating speed of 600-800 rpm for 10-30 minutes by using a planetary ball, putting ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as an iron metal source and obtained after ball milling into a constant-temperature box type resistance furnace, calcining for 30-90 min at 400-700 ℃ in an air atmosphere, and cooling to room temperature to obtain an iron oxide-potassium bromide catalyst precursor;
step two, preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product:
the method adopts a chemical vapor deposition method to prepare a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a carbon layer as the outer layer and a core consisting of iron and ferroferric carbide as the core, and comprises the following specific processes:
spreading the iron oxide-potassium bromide catalyst precursor prepared in the first step in a quartz square boat, placing the quartz square boat in a constant temperature area of a horizontal tube furnace, closing the tube furnace, pumping air in the tube furnace through a mechanical pump to enable the vacuum degree in the tube furnace to reach-0.05 to-0.1 MPa, then slowly introducing argon into the tube furnace at the flow rate of 5-30 mL/min, adjusting the flow rate of the argon to be 100-300 mL/min and heating the tube furnace to the reduction temperature of the iron oxide at the heating rate of 2-10 ℃/min after the vacuum degree in the tube furnace is zero, closing the argon and immediately introducing hydrogen at the flow rate of 100-200 mL/min after the reduction temperature is reached, reducing the iron oxide into iron catalyst particles by keeping for 0.5-2 h, then adjusting the furnace temperature to 300-450 ℃ of the growth temperature of the carbon-coated iron-iron carbide magnetic nano particles, closing hydrogen, immediately introducing acetylene gas with the flow rate of 10-30 mL/min and argon with a certain flow rate, ensuring that the flow rate ratio of the acetylene gas to the argon in the mixed gas of the acetylene gas and the argon is 1: 5-15, preserving heat for 10-60 min to grow the carbon-coated iron-ferroferric carbide magnetic nanoparticles, finally closing the acetylene gas, adjusting the flow rate of the argon to 100-200 mL/min, stopping heating of the tubular furnace, and cooling a reaction product to room temperature under the protection of argon atmosphere, thereby preparing the carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of the potassium bromide carrier;
adding the prepared carbon-coated iron-iron carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier into distilled water to form suspension with the concentration of 1-3 mg/mL, performing ultrasonic cleaning on the suspension for 20-40 min by using an ultrasonic disperser at the frequency of 20-50 kHz, transferring the suspension into a centrifuge tube, performing centrifugal separation on the suspension for 10-20 min at the rotating speed of 8000-10000 rpm on a high-speed centrifuge, removing supernatant in the centrifuge tube by using a rubber-head dropper, drying the centrifuge tube in an electrothermal blowing drying oven at the temperature of 50-70 ℃ for 6-8 h, thus preparing the iron-ferroferric carbide magnetic nano-particle product with the outer layer of the magnetic nano-particle being a carbon layer and the core part being a carbon-coated iron-ferroferric carbide magnetic nano-particle product with iron and ferroferric constituting the core, the purity of the alloy reaches 97-99.5%, the saturation magnetization reaches 30.53-94.8 Oemu/g, and the coercive force reaches 458.83-821.33 Oe.
In the preparation method of the carbon-coated iron-ferroferric carbide magnetic nano-particles, the related raw materials are all obtained by commercial purchase, and the used equipment and process can be mastered by those skilled in the art.
The invention has the beneficial effects that: compared with the prior art, the invention has the prominent substantive characteristics and remarkable progress as follows:
(1) compared with the preparation method of the core-shell carbon-coated iron nano composite material CN107127335A, the preparation method has the prominent substantive characteristics and remarkable progress that:
when the carbon-coated iron or iron-based magnetic nanoparticles are used in the fields of drug carriers, adsorption materials of heavy metals or organic dyes, magnetic recording materials and the like, strict requirements are provided for the particle size and the particle dispersibility of the materials. CN107127335A adopts microwave metal discharge method to prepare carbon-coated iron nano composite material, dissolving ferrocene into toluene, xylene or cyclohexane organic solvent, ultrasonically mixing uniformly, adding short nickel rod as discharge medium, then placing into industrial microwave oven, and carrying out microwave heating under the protection of argon. And after the reaction is finished, screening out the discharge medium and uniformly grinding to obtain the carbon-coated iron nano composite material. In the prior art, because the reaction environment is a liquid state or a semi-liquid state environment in the organic solvent carbonization process, the internal energy of the iron catalyst decomposed from ferrocene is increased in a high-temperature state, and thermal motion occurs in a liquid solvent, and a large amount of iron catalyst nano particles are agglomerated and bonded together to increase the particle size due to van der waals force action. According to the existing research results, the particle size of the catalyst seriously influences the catalytic performance: the catalyst particle size is increased and the catalytic performance is obviously reduced. Therefore, the agglomerated iron nanoparticles have severely reduced catalytic performance, and result in large particle size, poor dispersibility, non-uniform particle size distribution, and poor performance of the synthesized carbon-coated iron nanocomposite.
In the design process, the invention fully considers the problem of how to improve the dispersibility and uniformity of the carbon-coated iron-iron carbide magnetic nanoparticles and further improve the use performance of the carbon-coated iron-iron carbide magnetic nanoparticles, and in order to solve the problem that the carbon-coated iron-iron carbide magnetic nanoparticles prepared in the prior invention have poor dispersibility and uneven particle size distribution and cause poor use performance, innovatively proposes that ferric citrate is loaded on the surface of potassium bromide by a freeze-drying method to obtain ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as an iron metal source, in particular, potassium bromide and a ferric citrate solution which are uniformly mixed are dried and compounded in a frozen state, and the ferric citrate particles which are uniformly dispersed on the surface of the potassium bromide carrier and are used as the iron metal source are obtained by subsequent ball milling, calcining and reducing processes, wherein the ferric citrate particles are iron catalyst particles, and the particle size of the iron catalyst particles is accurately regulated and controlled by adjusting the concentration ratio of the potassium bromide solution and the ferric citrate solution and subsequent ball milling, calcining and reducing processes. In addition, in order to avoid the agglomeration of iron catalyst particles and fully exert the catalytic performance of the iron catalyst particles, the carbon-coated iron-iron carbide magnetic nano particles are synthesized by catalytically cracking acetylene by adopting a chemical vapor deposition method. In addition, the particle size and the dispersion effect of the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles are accurately regulated and controlled by controlling the growth temperature, the growth time and the gas ratio, so that the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles have small particle size, uniform dispersion and good comprehensive performance.
(2) Compared with the preparation method of the CN106732598A carbon-coated iron nano-catalyst, the preparation method has the prominent substantive characteristics and remarkable progress that:
for carbon-coated iron or iron-based magnetic nanoparticles, good stability is a precondition for ensuring full exertion of catalytic, adsorption and magnetic properties, so that improvement of graphitization degree and thermal stability of the carbon-coated layer is one of the targets of synthesis research of the carbon-coated iron or iron-based magnetic nanoparticles. CN106732598A under the ultrasonic and stirring state, the ferric nitrate solution is added into the mixed solution of sucrose and hydrazine hydrate drop by drop, dried and carbonized under the protection of nitrogen to prepare the amorphous carbon coated iron catalyst nano-particles. Because a pyrolysis method is adopted, the solid carbon source forms the carbon coating layer through an adsorption-diffusion-precipitation growth mechanism, and a very high energy barrier needs to be overcome, so that the catalytic activity of the iron catalyst particles is difficult to be fully exerted, the synthesized carbon coating layer is in an amorphous state, the poor compactness and the thermal oxidation stability of the carbon coating layer are difficult to form a good protection effect on the iron nanoparticles in the core part, and the service performance of the carbon coating layer is reduced.
In the design process, how to avoid the adverse effect of the amorphous carbon coating on the performance of the carbon-coated iron or iron-based magnetic nano-particles is fully considered, in order to achieve the purpose of enabling the catalyst to exert good catalytic activity and enabling the carbon coating to have higher graphitization degree, ferric citrate is used as an iron source, potassium bromide is used as a carrier, and iron catalyst particles with good dispersity and uniformity are obtained through the process steps of freeze drying, ball milling, calcining and reducing in sequence, so that the full exertion of the catalytic activity is ensured. And then, obtaining a carbon coating layer by adopting chemical vapor deposition of acetylene, wherein the synthesis mechanism is that a gaseous carbon source decomposes carbon atoms under the action of a catalyst and enters the catalyst, the carbon atoms reaching a saturated state are separated out along a specific crystal face of the catalyst to form the carbon coating layer, a gas-liquid-solid growth mechanism is followed, and the energy barrier to be overcome is low, so that the catalytic activity of the catalyst is fully exerted, and the formed carbon coating layer has higher crystallization degree, so that the carbon-coated iron-ferroferric carbide magnetic nanoparticles have better stability and can meet the use stability requirements of different application fields on the material.
(3) Compared with a method for preparing the carbon nano tube/graphite coated iron nano particle compound by CN104785777A, the invention has the prominent substantive features and remarkable progress that:
the carbon-coated iron or iron-based magnetic nanoparticles have wide application prospects in the fields of electricity, magnetism, optics, thermology and the like, and the fields have harsh requirements on the quality of materials, one of the requirements is high purity and low impurity content of the carbon-coated iron nanoparticles. CN104785777A synthesizes carbon nanotubes by first using Co (Fe, Ni) particles deposited on a silicon wafer, as the reaction proceeds, ferrocene is released as an iron source and decomposes iron nanoparticles and aggregates on the carbon nanotubes, and carbon nanotube/graphite coated iron nanoparticles are synthesized by a plasma enhanced chemical vapor deposition method. For the use of carbon-coated iron nanoparticles, the invention has a problem that the carbon nanotubes synthesized first cannot be removed as an impurity phase. The carbon nano tube has good structural stability, can not completely disappear along with the synthesis of the carbon-coated iron nano particles, and can continuously grow along with the reaction, so that the carbon nano tube synthesized product has carbon nano tube impurities which have high content and are difficult to remove, the purity of the carbon-coated iron nano particles is seriously influenced, and the service performance of the carbon-coated iron nano particles is reduced.
In the design process of the method, the preparation of the high-purity carbon-coated iron-iron carbide magnetic nano particles is taken as one of the targets, the purification problem of the synthesized product is fully considered, and the potassium bromide is innovatively proposed to be used as a carrier material. The melting point of the potassium bromide is 734 ℃, and the potassium bromide has good stability in a lower synthesis temperature range of the carbon-coated iron-iron carbide magnetic nano particles; potassium bromide is readily soluble in water and can be easily removed by simple water washing and centrifugation. Therefore, the method can prepare the high-purity carbon-coated iron-ferroferric carbide magnetic nanoparticles and meet the use performance requirements of different fields on the product.
(4) Compared with CN102990075A a method for preparing carbon-coated iron nano particles, the invention has the following outstanding substantive features and remarkable progress:
for carbon-coated iron or iron-based magnetic nanoparticles, good stability is a precondition for ensuring full exertion of catalytic, adsorption and magnetic properties, so that improvement of graphitization degree and thermal stability of the carbon-coated layer is one of the targets of synthesis research of the carbon-coated iron or iron-based magnetic nanoparticles. CN102990075A method for obtaining organic carbon coated Fe by liquid alkane reflux methodxOyIn the process, the organic solid carbon source forms the carbon coating layer through a growth mechanism of decomposition-adsorption-diffusion-precipitation, and a very high energy barrier needs to be overcome, so that the catalytic activity of the iron catalyst particles is difficult to be fully exerted, the synthesized carbon coating layer is in an amorphous state, the poor compactness and the thermal oxidation stability of the carbon coating layer are difficult to form a good protection effect on the iron nanoparticles in the core part, and the service performance of the carbon coating layer is reduced.
In the design process, how to avoid the adverse effect of the amorphous carbon coating on the performance of the carbon-coated iron or iron-based magnetic nano-particles is fully considered, in order to achieve the purpose of enabling the catalyst to exert good catalytic activity and enabling the carbon coating to have higher graphitization degree, ferric citrate is used as an iron source, potassium bromide is used as a carrier, and iron catalyst particles with good dispersity and uniformity are obtained through the process steps of freeze drying, ball milling, calcining and reducing in sequence, so that the full exertion of the catalytic activity is ensured. And then, obtaining a carbon coating layer by adopting chemical vapor deposition of acetylene, wherein the synthesis mechanism is that a gaseous carbon source decomposes carbon atoms under the action of a catalyst and enters the catalyst, the carbon atoms reaching a saturated state are separated out along a specific crystal face of the catalyst to form the carbon coating layer, a gas-liquid-solid growth mechanism is followed, and the energy barrier to be overcome is low, so that the catalytic activity of the catalyst is fully exerted, and the formed carbon coating layer has higher crystallization degree, so that the carbon-coated iron-ferroferric carbide magnetic nanoparticles have better stability and can meet the use stability requirements of different application fields on the material.
(5) Compared with a hydrothermal preparation method of CN102784913A carbon-coated iron nanoparticles, the method has the prominent substantive characteristics and remarkable progress that:
when the carbon-coated iron or iron-based magnetic nanoparticles are used in the fields of drug carriers, adsorption materials of heavy metals or organic dyes, magnetic recording materials and the like, strict requirements are provided for the particle size and the particle dispersibility of the materials. CN102784913A adopts a hydrothermal method to prepare carbon-coated iron nanoparticles, iron nitrate and glucose aqueous solution are mixed uniformly according to a proportion, then the mixture is transferred to a reaction kettle to react for 1 to 24 hours at the temperature of 160-220 ℃, and the carbon-coated iron nanoparticles are obtained after centrifugation and drying and calcination under the protection of inert gas. In the patent, since the hydrothermal reaction environment is a solution, the internal energy of the iron catalyst decomposed from the ferric nitrate is increased in a high-temperature state, and thermal motion occurs in a liquid solvent, so that van der waals force action inevitably causes a large amount of iron catalyst nanoparticles to be agglomerated and bonded together, thereby increasing the particle size. According to the existing research results, the particle size of the catalyst seriously influences the catalytic performance: the catalyst particle size is increased and the catalytic performance is obviously reduced. Therefore, the agglomerated iron nanoparticles have severely reduced catalytic performance, and result in large particle size, poor dispersibility, non-uniform particle size distribution, and poor performance of the synthesized carbon-coated iron nanocomposite.
In the design process, the invention fully considers the problem of how to improve the dispersibility and uniformity of the carbon-coated iron-iron carbide magnetic nanoparticles and further improve the use performance of the carbon-coated iron-iron carbide magnetic nanoparticles, and in order to solve the problem that the carbon-coated iron-iron carbide magnetic nanoparticles prepared in the prior invention have poor dispersibility and uneven particle size distribution and cause poor use performance, innovatively proposes that ferric citrate is loaded on the surface of potassium bromide by a freeze-drying method to obtain ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as an iron metal source, in particular, potassium bromide and a ferric citrate solution which are uniformly mixed are dried and compounded in a frozen state, and the ferric citrate particles which are uniformly dispersed on the surface of the potassium bromide carrier and are used as the iron metal source are obtained by subsequent ball milling, calcining and reducing processes, wherein the ferric citrate particles are iron catalyst particles, and the particle size of the iron catalyst particles is accurately regulated and controlled by adjusting the concentration ratio of the potassium bromide solution and the ferric citrate solution and subsequent ball milling, calcining and reducing processes. In addition, in order to avoid the agglomeration of iron catalyst particles and fully exert the catalytic performance of the iron catalyst particles, the carbon-coated iron-iron carbide magnetic nano particles are synthesized by catalytically cracking acetylene by adopting a chemical vapor deposition method. In addition, the particle size and the dispersion effect of the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles are accurately regulated and controlled by controlling the growth temperature, the growth time and the gas ratio, so that the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles have small particle size, uniform dispersion and good comprehensive performance.
(6) Compared with CN1935415A a carbon coated magnetic superfine iron particle and its manufacturing method, the invention has the prominent substantive features and remarkable progress that:
CN1935415A adopts a ball milling method to mix nano ferroferric oxide with separants (sodium chloride, potassium chloride and calcium chloride) and utilizes a chemical vapor deposition method to prepare the magnetic ultrafine iron particles coated with carbon. The process has obvious irrationality: because strong van der waals force exists among the nano ferroferric oxide, the agglomeration phenomenon of the nano particles is difficult to avoid and the uniform distribution of the nano particles on the surface of the isolating agent is difficult to realize only by a simple ball milling process, so that the dispersibility of the iron catalyst is poor, the particle size distribution interval is large, the particle size of the synthesized carbon-coated magnetic superfine iron particles is in a larger particle size distribution interval within the range of 50-400 nm and the phenomenon of mutual agglomeration is presented, and the service performance of the magnetic superfine iron particles is seriously reduced.
In the design process, the invention fully considers the problem of how to improve the dispersibility and uniformity of the carbon-coated iron-iron carbide magnetic nanoparticles and further improve the use performance of the carbon-coated iron-iron carbide magnetic nanoparticles, and in order to solve the problem that the carbon-coated iron-iron carbide magnetic nanoparticles prepared in the prior invention have poor dispersibility and uneven particle size distribution and cause poor use performance, innovatively proposes that ferric citrate is loaded on the surface of potassium bromide by a freeze-drying method to obtain ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as an iron metal source, in particular, potassium bromide and a ferric citrate solution which are uniformly mixed are dried and compounded in a frozen state, and the ferric citrate particles which are uniformly dispersed on the surface of the potassium bromide carrier and are used as the iron metal source are obtained by subsequent ball milling, calcining and reducing processes, wherein the ferric citrate particles are iron catalyst particles, and the particle size of the iron catalyst particles is accurately regulated and controlled by adjusting the concentration ratio of the potassium bromide solution and the ferric citrate solution and subsequent ball milling, calcining and reducing processes. In addition, in order to avoid the agglomeration of iron catalyst particles and fully exert the catalytic performance of the iron catalyst particles, the carbon-coated iron-iron carbide magnetic nano particles are synthesized by catalytically cracking acetylene by adopting a chemical vapor deposition method. In addition, the particle size and the dispersion effect of the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles are accurately regulated and controlled by controlling the growth temperature, the growth time and the gas ratio, so that the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles have small particle size, uniform dispersion and good comprehensive performance.
(7) Compared with the preparation method and the application method of the adsorbent for adsorbing the dye by CN104117339A, the invention has the prominent substantive characteristics and remarkable progress that:
(a) the preparation process and the synthesis mechanism of the two are substantially different.
CN104117339A discloses a preparation method for synthesizing a carbon-coated ferromagnetic nanoparticle adsorbent by decomposing glucose with an iron catalyst through a hydrothermal method, aiming at solving the problems that the magnetic adsorbent in the prior art is poor in physical and chemical properties, weak in magnetic property, narrow in application range, not easy to recover in the use process of the magnetic adsorbent and easy to cause secondary pollution. CN104117339A loading an iron catalyst on the surface of sodium chloride, adding glucose in proportion to prepare a suspension containing the iron catalyst, the sodium chloride and the glucose, transferring the suspension into a reaction kettle with polytetrafluoroethylene as a substrate, and keeping the suspension at a constant temperature for 9-12 h in a muffle furnace at 180-220 ℃ to obtain the carbon-coated iron nanoparticles. The technological mechanism is that in the closed space of the reaction kettle, the suspension is heated to create a high-temperature and high-pressure reaction environment, and glucose is dehydrated, carbonized and coated on the surface of the iron catalyst through adsorption. The process defect is that the method cannot accurately regulate and control the particle size and the dispersity of the carbon-coated iron nanoparticles due to the dissolution of the carrier sodium chloride and the thermal motion and mutual agglomeration of the iron nanoparticles.
The invention relates to a method for obtaining carbon-coated iron-ferroferric carbide magnetic nanoparticles by cracking gaseous carbon source acetylene by using iron catalyst particles uniformly loaded on the surface of potassium bromide by adopting a chemical vapor deposition method, which solves the problems of low purity, dispersibility of the particles, controllability of the particle size and low stability of the carbon-coated iron-ferroferric carbide magnetic nanoparticles in the prior art. The invention adopts a chemical vapor deposition method, iron oxide-potassium bromide catalyst precursor is paved in a quartz boat, and mixed gas of hydrogen, acetylene and argon is sequentially introduced, so that acetylene is subjected to catalytic cracking reaction on iron catalyst particles obtained by reducing iron oxide by hydrogen to synthesize carbon-coated iron-iron carbide magnetic nanoparticles. The mechanism of action is that the gaseous carbon source decomposes carbon atoms under the action of the catalyst and enters the catalyst, and the carbon atoms reaching the saturated state are separated out along the specific crystal face of the catalyst to form a carbon coating layer, which follows the gas-liquid-solid growth mechanism. According to the invention, the carbon coating layer is formed by in-situ carbon deposition of the iron catalyst particles loaded on the surface of the potassium bromide, and the purity, crystallization degree, particle size and dispersity of the iron-ferroferric carbide magnetic nanoparticles coated with the carbon are accurately regulated and controlled by controlling the synthesis temperature and time, the acetylene-argon ratio and other process parameters, so that the synthesis effect is better.
(b) The preparation process causes the magnetic performance of the two to have significant difference.
To prepare the iron catalyst particles, CN104117339A adopts a deposition-precipitation method, in which sodium hydroxide is added dropwise into an aqueous solution of iron chloride, and after reaction, iron hydroxide colloid and an aqueous solution of sodium chloride are obtained, and then directly dried in a drying oven and manually ground by using a mortar. In the drying process, due to the difference between the colloid state of the ferric hydroxide and the dissolution state of the sodium chloride, the drying of the ferric hydroxide and the sodium chloride has a sequence, so that a layering phenomenon is caused, further, the phenomenon of ferric hydroxide agglomeration can occur, and then, the uniform distribution of the ferric hydroxide on the surface of the sodium chloride is difficult to realize by simple grinding with an agate mortar, so that the particle size of the subsequently obtained iron catalyst particles is large and uneven in distribution, the catalytic performance is poor, the synthesized carbon-coated ferromagnetic nanoparticles are large in particle size, low in graphitization degree and poor in dispersibility, further, the magnetic performance of the synthesized carbon-coated ferromagnetic nanoparticles is poor, and the use requirements of the carbon-coated metal nanoparticles are difficult to meet.
In order to obtain iron catalyst particles with uniform particle size and good dispersion, the invention innovatively provides that ferric citrate is loaded on the surface of potassium bromide by a freeze-drying method, potassium bromide and a ferric citrate solution which are uniformly mixed are dried and compounded in a frozen state, then ball milling and uniform mixing are adopted, and the iron catalyst particles uniformly dispersed on the surface of the potassium bromide can be obtained by subsequent calcining and reducing processes, so that the full play of the catalytic activity of the iron catalyst is facilitated, the synthesized carbon-coated iron-ferroferric carbide magnetic nanoparticles have small particle size, high graphitization degree and good dispersibility, the magnetic performance is effectively improved, and the use requirements of the carbon-coated iron-ferroferric carbide magnetic nanoparticles in various fields such as adsorption materials, magnetic drug carrier materials and the like can be met.
Therefore, compared with the CN104117339A in the prior art, the method of the invention has substantial differences in design thought, process mechanism, synthesis effect and innovation, and has obvious progress.
(8) Compared with CN101710512A graphene and carbon-coated ferromagnetic nano-metal composite material and the preparation method thereof, the invention has the prominent substantive characteristics and remarkable progress that:
CN101710512A uses graphene oxide as a carrier, and obtains a graphene and carbon-coated ferromagnetic nano metal composite material by chemical vapor deposition. Because the used graphene has a nano scale and good stability, the graphene does not disappear by itself along with the reaction, and strong van der waals force exists between the graphene and the carbon-coated ferromagnetic nanoparticles, so that the graphene and the carbon-coated ferromagnetic nanoparticles are mixed together and are difficult to remove by a purification method. Thus, for carbon-coated ferromagnetic nanoparticles, graphene is an impurity and is present in high amounts. Meanwhile, as a non-ferromagnetic substance, the existence of a large amount of graphene inevitably leads to the reduction of the magnetic property of the synthesized product, and the service performance of the carbon-coated ferromagnetic nanoparticles is seriously reduced.
In the design process of the method, the preparation of the high-purity carbon-coated iron-iron carbide magnetic nano particles is taken as one of the targets, the purification problem of the synthesized product is fully considered, and the potassium bromide is innovatively proposed to be used as a carrier material. The melting point of the potassium bromide is 734 ℃, and the potassium bromide has good stability in a lower synthesis temperature range of the carbon-coated iron-iron carbide magnetic nano particles; potassium bromide is readily soluble in water and can be easily removed by simple water washing and centrifugation. Therefore, the method can prepare the high-purity carbon-coated iron-ferroferric carbide magnetic nanoparticles and meet the use performance requirements of different fields on the product.
Compared with the prior art, the method provided by the invention has the following remarkable improvements:
(1) the invention takes ferric citrate and potassium bromide as raw materials, ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as an iron metal source are obtained through a freeze drying process, ferric citrate is decomposed through ball milling to obtain an iron oxide-potassium bromide catalyst precursor, and carbon-coated iron-ferroferric carbide magnetic nanoparticles are prepared through chemical vapor deposition of hydrogen reduction ferric oxide and acetylene-argon mixed gas, and the innovation is that: (a) firstly, the uniform and controllable distribution of ferric citrate particles as an iron metal source on the surface of potassium bromide is realized by adopting a freeze drying process; secondly, the concentration ratio of the solution and the adjustment of the subsequent ball milling, calcining and reducing processes realize the accurate regulation and control of the particle size of the iron catalyst; thirdly, in the chemical vapor deposition process, the precise regulation and control of the particle size, the dispersity and the crystallization degree of the carbon-coated iron-ferroferric carbide magnetic nanoparticles are realized by adjusting the synthesis time, the synthesis temperature and the acetylene-argon ratio and integrating the effects, and the carbon-coated iron-ferroferric carbide magnetic nanoparticles with small and uniform particle size, good dispersity and high crystallization degree are obtained; (b) potassium bromide is used as a carrier material and can be easily removed through simple water washing and centrifugal separation, so that the high-purity carbon-coated iron-ferroferric carbide magnetic nanoparticles are prepared, and the comprehensive performance is excellent.
(2) The method has the advantages of simple equipment, easily obtained raw materials, simple process flow, low production cost and easy realization of batch production, and can meet the use requirements of the fields of electricity, magnetism, optics, biomedicine and the like on the carbon-coated metal magnetic nanoparticles.
(3) The invention can obtain the carbon-coated iron-ferroferric carbide magnetic nano-particle product with purity of 97-99.5%, saturation magnetization of 30.53-94.80 emu/g, coercive force of 458.83-821.33 Oe, uniform particle size, good dispersibility and high crystallization degree.
Drawings
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is an X-ray diffraction pattern of carbon-coated iron-iron carbide magnetic nanoparticles prepared in example 2 of the present invention.
Fig. 2 is a scanning electron microscope photograph of the carbon-coated iron-iron carbide magnetic nanoparticles prepared in example 2 of the present invention.
FIG. 3 is a low resolution TEM image of the carbon-coated Fe-C magnetic nanoparticles prepared in example 2 of the present invention.
Fig. 4 is a high-resolution tem photograph of the carbon-coated fe-c magnetic nanoparticles prepared in example 2 of the present invention.
Fig. 5 is a hysteresis loop of the carbon-coated iron-iron carbide magnetic nanoparticles prepared in example 2 of the present invention.
Detailed Description
Example 1
Firstly, preparing an iron oxide-potassium bromide catalyst precursor:
firstly, mixing a ferric citrate pentahydrate aqueous solution with the mass percentage concentration of 3% and a potassium bromide aqueous solution with the mass percentage concentration of 10.03% to form a mixed solution, ensuring that the mass ratio of iron to potassium bromide is 0.05: 1, heating and stirring the mixed solution for 4 hours at the temperature of 70 ℃ and the rotating speed of 500rpm by using a magnetic heating stirrer, then transferring the mixed solution to a plastic test tube, placing the plastic test tube into a freeze drying box, cooling to-50 ℃ at the cooling speed of 20 ℃/min, freezing the mixed solution into a solid state, then continuously drying the solid solution in the freeze drying box under the vacuum of 1.3Pa for 48 hours, then taking ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are obtained after freeze drying out from the plastic test tube, grinding the ferric citrate particles which are uniformly distributed on the surface of the potassium bromide carrier and are used as a ferrous metal source by using a planetary box type ball mill for 30 minutes at the speed of 800rpm, placing the ferric citrate particles which are uniformly distributed on the, calcining at 700 ℃ for 90min under air atmosphere, and cooling to room temperature to obtain an iron oxide-potassium bromide catalyst precursor;
step two, preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product:
the method adopts a chemical vapor deposition method to prepare a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a carbon layer as the outer layer and a core consisting of iron and ferroferric carbide as the core, and comprises the following specific processes:
spreading the iron oxide-potassium bromide catalyst precursor prepared in the first step in a quartz square boat, placing the quartz square boat in a constant temperature area of a horizontal tube furnace and closing the tube furnace, pumping air in the tube furnace by a mechanical pump to enable the vacuum degree in the tube furnace to reach-0.1 MPa, then slowly introducing argon into the tube furnace at the flow rate of 30mL/min, adjusting the flow rate of the argon to 300mL/min and heating the tube furnace to the reduction temperature of the iron oxide at the heating rate of 10 ℃/min when the vacuum degree in the tube furnace is zero, closing the argon, immediately introducing hydrogen with the flow rate of 200mL/min after the reduction temperature is reached, keeping for 2 hours to reduce the iron oxide into iron catalyst particles, then adjusting the furnace temperature to the growth temperature of 300 ℃ of the carbon-coated iron-iron carbide magnetic nano particles, closing the hydrogen, immediately introducing acetylene gas with the flow rate of 10mL/min and argon with a certain flow rate, ensuring that the flow ratio of acetylene gas to argon gas in the mixed gas of acetylene gas and argon gas is 1:15, carrying out heat preservation for 10min to carry out growth of the carbon-coated iron-ferroferric carbide magnetic nanoparticles, wherein in the heat preservation process of 10min, carbon atoms obtained by decomposing acetylene and iron catalyst particles interact to obtain carbon-coated iron-ferroferric carbide magnetic nanoparticles, finally closing the acetylene gas and adjusting the flow of the argon gas to 200mL/min, stopping heating of the tubular furnace to cool a reaction product to room temperature under the protection of argon gas atmosphere, thus preparing the carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of the potassium bromide carrier;
adding the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier into distilled water to form suspension with the concentration of 1mg/mL, ultrasonically cleaning the suspension by using an ultrasonic disperser at the frequency of 50kHz for 40min, transferring the suspension into a centrifuge tube, centrifugally separating the suspension on a high-speed centrifuge at the rotating speed of 10000rpm for 20min, removing supernatant in the centrifuge tube by using a rubber head dropper, and placing the centrifuge tube into an electric heating air blowing drying box to dry for 8h at 70 ℃ to obtain a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a magnetic nanoparticle outer layer and a core part comprising iron and ferroferric carbide, wherein the purity of the carbon-coated iron-ferroferric carbide magnetic nanoparticle product reaches 99.5%, the saturation magnetization reaches 94.8Oemu/g, and the coercive force reaches 458.83 Oe.
Example 2
Firstly, preparing an iron oxide-potassium bromide catalyst precursor:
firstly, mixing a ferric citrate pentahydrate aqueous solution with the mass percentage concentration of 2% and a potassium bromide aqueous solution with the mass percentage concentration of 11.14% to form a mixed solution, ensuring that the mass ratio of iron to potassium bromide is 0.03: 1, heating and stirring the mixed solution for 3 hours at the rotating speed of 400rpm at the temperature of 60 ℃ by using a magnetic heating stirrer, then transferring the mixed solution to a plastic test tube, placing the plastic test tube in a freeze drying box, cooling to-30 ℃ at the cooling speed of 15 ℃/min, freezing the mixed solution into a solid state, continuously drying for 36 hours in the vacuum of 8Pa in the freeze drying box, then taking ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as a ferric metal source, obtained after freeze drying, grinding for 20 minutes at the speed of 700rpm by using a planetary ball mill, placing the ferric citrate particles which are uniformly distributed on the surface of the potassium bromide carrier and are used as the ferric metal source in a constant temperature resistance furnace, calcining at 550 ℃ for 60min in air atmosphere, and cooling to room temperature to obtain an iron oxide-potassium bromide catalyst precursor;
step two, preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product:
the method adopts a chemical vapor deposition method to prepare a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a carbon layer as the outer layer and a core consisting of iron and ferroferric carbide as the core, and comprises the following specific processes:
spreading the iron oxide-potassium bromide catalyst precursor prepared in the first step in a quartz square boat, placing the quartz square boat in a constant temperature area of a horizontal tube furnace and closing the tube furnace, pumping air in the tube furnace through a mechanical pump to enable the vacuum degree in the tube furnace to reach-0.08 MPa, then slowly introducing argon into the tube furnace at the flow rate of 20mL/min, adjusting the flow rate of the argon to 200mL/min and heating the tube furnace to the reduction temperature of the iron oxide at the heating rate of 6 ℃/min after the vacuum degree in the tube furnace is zero, closing the argon, immediately introducing hydrogen with the flow rate of 150mL/min after the temperature of the tube furnace reaches the reduction temperature, keeping the temperature for 1h to reduce the iron oxide into iron catalyst particles, then adjusting the furnace temperature to 400 ℃ of the growth temperature of the carbon-coated iron-iron carbide magnetic nanoparticles, closing the hydrogen, immediately introducing acetylene gas with the flow rate of 20mL/min and argon with a certain flow rate, ensuring that the flow ratio of acetylene gas to argon gas in the mixed gas of acetylene gas and argon gas is 1:10, carrying out heat preservation for 30min to carry out growth of carbon-coated iron-ferroferric carbide magnetic nanoparticles, wherein in the heat preservation process of 30min, carbon atoms obtained by decomposing acetylene and iron catalyst particles interact to obtain carbon-coated iron-ferroferric carbide magnetic nanoparticles, finally closing the acetylene gas and adjusting the flow of argon gas to 150mL/min, stopping heating of the tubular furnace to cool a reaction product to room temperature under the protection of argon gas atmosphere, thus preparing the carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier;
adding the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier into distilled water to form suspension with the concentration of 2mg/mL, ultrasonically cleaning the suspension for 30min by using an ultrasonic disperser at the frequency of 30kHz, transferring the suspension into a centrifuge tube, centrifugally separating for 15min on a high-speed centrifuge at the rotating speed of 9000rpm, removing supernatant in the centrifuge tube by using a rubber-headed dropper, and drying the centrifuge tube in an electric heating blowing drying oven at the temperature of 60 ℃ for 7h to obtain a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a magnetic nanoparticle outer layer and a core part comprising iron and ferroferric carbide, wherein the purity of the carbon-coated iron-ferroferric carbide magnetic nanoparticle product reaches 98.2%, the saturation magnetization reaches 49.53emu/g, and the coercive force reaches 579.63 Oe.
Fig. 1 is an X-ray diffraction pattern of the carbon-coated iron-iron carbide magnetic nanoparticles prepared in this example. In the figure, a characteristic peak at a diffraction angle of 26.2 degrees corresponds to a (002) crystal face of carbon, a characteristic peak at a diffraction angle of 44.7 degrees corresponds to a (110) crystal face of iron, and characteristic peaks at 37.8 degrees, 39.8 degrees, 40.7 degrees, 43.8 degrees, 45.1 degrees, 45.9 degrees, 49.2 degrees and 58.1 degrees respectively correspond to (021), (200), (120), (210), (103), (211), (122) and (130) crystal faces of ferroferric carbide, which shows that a synthesized product only consists of three phases of carbon, iron and the ferroferric carbide, and potassium bromide used as a carrier can be completely removed, so that the high-purity carbon-coated iron-ferroferric carbide magnetic nano-particle is synthesized.
Fig. 2 is a scanning electron microscope photograph of the carbon-coated iron-iron carbide magnetic nanoparticles prepared in this example. The figure shows that the surface of the iron-iron carbide magnetic nano particle is successfully coated with a carbon layer, and the phenomenon of iron-iron carbide particle exposure does not occur; the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles have uniform particle size, good dispersibility and no obvious agglomeration phenomenon, thereby being beneficial to the full play of the performance of the carbon-coated iron-ferroferric carbide magnetic nanoparticles.
Fig. 3 is a low resolution tem photograph of the carbon-coated fe-c magnetic nanoparticles prepared in this example. As can be seen from the figure, the synthesized carbon-coated iron-iron carbide magnetic nanoparticles have an obvious core-shell structure, the core part of the synthesized carbon-coated iron-iron carbide magnetic nanoparticles is quasi-spherical iron-iron carbide magnetic nanoparticles, and the carbon coating layer with the thickness of 20-40nm is arranged on the outer part of the synthesized carbon-coated iron-iron carbide magnetic nanoparticles, so that the carbon coating layer can effectively prevent the iron-iron carbide magnetic nanoparticles from agglomerating and can form a good protection effect on the iron-iron carbide magnetic nanoparticles, and the iron-iron carbide magnetic nanoparticles are prevented from being corroded and oxidized by.
Fig. 4 is a high-resolution tem photograph of the carbon-coated fe-c magnetic nanoparticles prepared in this example. As can be seen from the figure, a tight interface combination is formed between the carbon coating layer and the iron-iron carbide magnetic nanoparticles, and the carbon layer has good crystallization degree, so that the synthesized carbon-coated iron-iron carbide magnetic nanoparticles have good thermal oxidation stability.
Fig. 5 is a hysteresis loop of the carbon-coated iron-iron carbide magnetic nanoparticles prepared in this example. It can be seen from the figure that the magnetization intensity of the synthesized carbon-coated iron-iron carbide magnetic nanoparticles presents a complete square ring shape and shows obvious hysteresis phenomenon along with the periodic change of the magnetic field intensity; the saturation magnetization of the alloy is 49.53emu/g, the coercive force is 579.63Oe, and the alloy shows good magnetic performance.
Example 3
Firstly, preparing an iron oxide-potassium bromide catalyst precursor:
firstly, mixing a ferric citrate pentahydrate aqueous solution with the mass percentage concentration of 1% and a potassium bromide aqueous solution with the mass percentage concentration of 16.7% to form a mixed solution, ensuring that the mass ratio of iron to potassium bromide is 0.01: 1, heating and stirring the mixed solution for 2 hours at 50 ℃ and the rotating speed of 300rpm by using a magnetic heating stirrer, then transferring the mixed solution to a plastic test tube, placing the plastic test tube in a freeze drying box, cooling to-10 ℃ at the cooling speed of 5 ℃/min, freezing the mixed solution into a solid state, then continuously drying the solid solution in the freeze drying box for 24 hours under the vacuum of 13.0Pa, then taking ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are obtained after freeze drying out from the plastic test tube, grinding the ferric citrate particles which are uniformly distributed on the surface of the potassium bromide carrier and are used as a ferrous metal source by using a planetary box type ball mill for 10 minutes at the rotating speed of 600rpm, placing the ferric citrate particles which are uniformly distributed on the surface of, calcining at 400 ℃ for 30min in air atmosphere, and cooling to room temperature to obtain an iron oxide-potassium bromide catalyst precursor;
step two, preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product:
the method adopts a chemical vapor deposition method to prepare a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a carbon layer as the outer layer and a core consisting of iron and ferroferric carbide as the core, and comprises the following specific processes:
spreading the iron oxide-potassium bromide catalyst precursor prepared in the first step in a quartz square boat, placing the quartz square boat in a constant temperature area of a horizontal tube furnace and closing the tube furnace, pumping air in the tube furnace by a mechanical pump to enable the vacuum degree in the tube furnace to reach-0.05 MPa, then slowly introducing argon into the tube furnace at the flow rate of 5mL/min, adjusting the flow rate of the argon to be 100mL/min and heating the tube furnace to the reduction temperature of the iron oxide to be 600 ℃ at the heating rate of 2 ℃/min when the vacuum degree in the tube furnace is zero, closing the argon, immediately introducing hydrogen with the flow rate of 100mL/min after the reduction temperature is reached, keeping the temperature for 0.5h to reduce the iron oxide into iron catalyst particles, then adjusting the furnace temperature to the growth temperature of the carbon-coated iron-ferroferric oxide magnetic nanoparticles to be 450 ℃, closing the hydrogen and immediately introducing acetylene gas with the flow rate of 30mL/min and argon with a certain flow rate, ensuring that the flow ratio of acetylene gas to argon gas in the mixed gas of acetylene gas and argon gas is 1:5, preserving heat for 60min to carry out growth of carbon-coated iron-ferroferric carbide magnetic nanoparticles, in the 60min heat preservation process, enabling carbon atoms obtained by acetylene decomposition to interact with iron catalyst particles to obtain carbon-coated iron-ferroferric carbide magnetic nanoparticles, finally closing the acetylene gas and adjusting the flow of the argon gas to 100mL/min, stopping heating of the tubular furnace to enable reaction products to be cooled to room temperature under the protection of argon gas atmosphere, and thus preparing the carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier;
adding the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier into distilled water to form suspension with the concentration of 3mg/mL, ultrasonically cleaning the suspension for 20min by using an ultrasonic disperser at the frequency of 20kHz, transferring the suspension into a centrifuge tube, centrifugally separating for 10min on a high-speed centrifuge at the rotating speed of 8000rpm, removing supernatant in the centrifuge tube by using a rubber head dropper, placing the centrifuge tube into an electrothermal blowing drying box, and drying for 6h at the temperature of 50 ℃ to obtain a carbon-coated iron-ferroferric carbide magnetic nanoparticle product with a magnetic nanoparticle outer layer and a core part comprising iron and ferroferric carbide, wherein the purity of the carbon-coated iron-ferroferric carbide magnetic nanoparticle product reaches 97%, the saturation magnetization reaches 30.53emu/g, and the coercive force reaches 821.33 Oe.
The raw materials referred to in the above examples are commercially available and the equipment and processes used are well known to those skilled in the art.

Claims (1)

1. The preparation method of the carbon-coated iron-ferroferric carbide magnetic nano-particles is characterized by comprising the following steps: the method comprises the following steps of obtaining ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and serve as an iron metal source by a freeze-drying technology, obtaining an iron oxide-potassium bromide catalyst precursor by calcining, and preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product by a chemical vapor deposition method, wherein the outer layer of the magnetic nanoparticle is a carbon layer, and the core of the magnetic nanoparticle is iron and ferroferric carbide to form a core, and the method comprises the following specific steps:
firstly, preparing an iron oxide-potassium bromide catalyst precursor:
firstly, mixing a ferric citrate pentahydrate aqueous solution with the mass percentage concentration of 1-3% and a potassium bromide aqueous solution with the mass percentage concentration of 10.03-16.7% to form a mixed solution, ensuring that the mass ratio of iron to potassium bromide is 0.01-0.05: 1, heating and stirring the mixed solution at 50-70 ℃ and the rotating speed of 300-500 rpm by using a magnetic heating stirrer for 2-4 hours, then transferring the mixed solution to a plastic test tube and placing the plastic test tube in a freeze drying box, cooling the plastic test tube to-10-50 ℃ at the cooling speed of 5-20 ℃/min, freezing the mixed solution into a solid state, then continuously drying the solid state in the freeze drying box under the vacuum of 1.3-13.0 Pa for 24-48 hours, then taking out the ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and serve as a ferrous metal source from the freeze drying process from the plastic test tube, grinding the ferric citrate particles at the rotating speed of 600-800 rpm for 10-30 minutes by using a planetary ball, putting ferric citrate particles which are uniformly distributed on the surface of a potassium bromide carrier and are used as an iron metal source and obtained after ball milling into a constant-temperature box type resistance furnace, calcining for 30-90 min at 400-700 ℃ in an air atmosphere, and cooling to room temperature to obtain an iron oxide-potassium bromide catalyst precursor;
step two, preparing a carbon-coated iron-ferroferric carbide magnetic nanoparticle product:
the carbon-coated iron-ferroferric carbide magnetic nanoparticle product is prepared by adopting a chemical vapor deposition method, the outer layer of the magnetic nanoparticle is a carbon layer, and the core part of the magnetic nanoparticle is a core consisting of iron and ferroferric carbide, and the specific process comprises the following steps:
spreading the iron oxide-potassium bromide catalyst precursor prepared in the first step in a quartz square boat, placing the quartz square boat in a constant temperature area of a horizontal tube furnace, closing the tube furnace, pumping air in the tube furnace through a mechanical pump to enable the vacuum degree in the tube furnace to reach-0.05 to-0.1 MPa, then slowly introducing argon into the tube furnace at the flow rate of 5-30 mL/min, adjusting the flow rate of the argon to be 100-300 mL/min and heating the tube furnace to the reduction temperature of the iron oxide at the heating rate of 2-10 ℃/min after the vacuum degree in the tube furnace is zero, closing the argon and immediately introducing hydrogen at the flow rate of 100-200 mL/min after the reduction temperature is reached, reducing the iron oxide into iron catalyst particles by keeping for 0.5-2 h, then adjusting the furnace temperature to 300-450 ℃ of the growth temperature of the carbon-coated iron-iron carbide magnetic nano particles, closing hydrogen, immediately introducing acetylene gas with the flow rate of 10-30 mL/min and argon with a certain flow rate, ensuring that the flow rate ratio of the acetylene gas to the argon in the mixed gas of the acetylene gas and the argon is 1: 5-15, preserving heat for 10-60 min to grow the carbon-coated iron-ferroferric carbide magnetic nanoparticles, finally closing the acetylene gas, adjusting the flow rate of the argon to 100-200 mL/min, stopping heating of the tubular furnace, and cooling a reaction product to room temperature under the protection of argon atmosphere, thereby preparing the carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of the potassium bromide carrier;
adding the prepared carbon-coated iron-ferroferric carbide magnetic nanoparticles uniformly distributed on the surface of a potassium bromide carrier into distilled water to form suspension with the concentration of 1-3 mg/mL, performing ultrasonic cleaning on the suspension for 20-40 min by using an ultrasonic disperser at the frequency of 20-50 kHz, transferring the suspension into a centrifuge tube, performing centrifugal separation on the suspension for 10-20 min at the rotating speed of 8000-10000 rpm on a high-speed centrifuge, removing supernatant in the centrifuge tube by using a rubber-head dropper, placing the centrifuge tube into an electric heating blast drying oven, and drying for 6-8 h at the temperature of 50-70 ℃ to prepare a carbon-coated iron-ferroferric carbide magnetic nanoparticle product, the outer layer of the magnetic nano-particles is a carbon layer, the core part is a core formed by iron and ferroferric carbide, the purity of the magnetic nano-particles reaches 97-99.5%, the saturation magnetization reaches 30.53-94.8 Oemu/g, and the coercive force reaches 458.83-821.33 Oe.
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