CN111185211B - Carbon-coated nickel nanocomposite and preparation method thereof - Google Patents

Carbon-coated nickel nanocomposite and preparation method thereof Download PDF

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CN111185211B
CN111185211B CN201811358334.0A CN201811358334A CN111185211B CN 111185211 B CN111185211 B CN 111185211B CN 201811358334 A CN201811358334 A CN 201811358334A CN 111185211 B CN111185211 B CN 111185211B
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water
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吴耿煌
荣峻峰
达志坚
宗明生
于鹏
谢婧新
林伟国
纪洪波
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Sinopec Research Institute of Petroleum Processing
China Petroleum and Chemical Corp
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Abstract

There is provided a method of preparing a carbon-coated nickel nanocomposite comprising the steps of: s1, mixing water-soluble fatty acid containing amino group with Ni (NO) 3 ) 2 Mixing the materials in water, heating and stirring to form a homogeneous solution, removing water, and grinding the obtained solid to form a precursor; s2, pyrolyzing the precursor at a high temperature in an inert protective atmosphere or a reducing atmosphere. The invention also provides a carbon-coated nickel nanocomposite prepared by the method. The high-temperature pyrolysis precursor of the invention is directly prepared from Ni (NO) 3 ) 2 The precursor Ni is obtained by heating and stirring the precursor Ni and the water-soluble fatty acid containing amino under the conditions of normal pressure and pure water phase, and the atomic utilization rate of the precursor Ni can reach 100%. In addition, nitrate is decomposed in the pyrolysis process to form a unique multistage pore structure in the material, so that the effective regulation and control of the pore structure of the carbon-coated nickel core-shell structure nanoparticle is realized.

Description

Carbon-coated nickel nanocomposite and preparation method thereof
Technical Field
The invention belongs to the field of preparation and application of carbon-coated metal composite materials, and particularly relates to a nitrogen-oxygen doped carbon-coated nickel nanocomposite material, and a preparation method and application thereof.
Background
Nanomaterials have some special physicochemical characteristics that differ from conventional size materials, including surface effects, dielectric confinement, quantum size, small size effects, macroscopic quantum tunneling, and the like. Among them, metal nanoparticles are receiving a great deal of attention due to their excellent optical, electrical, and magnetic properties. However, the metal nano particles have high activity, are easy to agglomerate or oxidize and even burn in the air, and greatly influence the performance and application of the materials. The nano carbon material has the advantages of acid and alkali corrosion resistance, stable chemical property and the like. In addition, the nanocarbon material with defects and heteroatoms also exhibits excellent catalytic properties in characteristic reactions. Recent studies have shown that coating metal nanoparticles with single or multiple layers of graphite can effectively combine the advantages of both materials and exhibit new properties, and have attracted considerable attention from researchers.
Currently, methods for coating metal nanoparticles with carbon mainly include an arc method, a Chemical Vapor Deposition (CVD) method, a pyrolysis method, and the like. The arc method has the advantages of complex equipment, poor operability, high energy consumption and difficult realization of large-scale preparation. Compared with the arc method, the CVD method has lower cost and higher yield and productivity, but the metal nano-particles or the compound particles thereof are required to be prepared in advance. In general, such deposition precursors have the disadvantages of nonuniform particle size, difficult effective dispersion, complex preparation and the like, thereby influencing the properties of the final product. Similar to CVD methods, the structure and properties of the products of pyrolysis methods are greatly affected by the precursor materials. But the pyrolysis method has the advantages of simple process, low cost, high yield, controllable metal content and the like, and is one of the methods with the largest preparation prospect at present.
The pyrolysis method can be mainly divided into two main types, and the first method is to directly mix a carbon source (typically dicyandiamide, melamine, etc.) and a metal source and then subject the mixture to high-temperature pyrolysis in an inert or reducing atmosphere. The dicyandiamide, melamine and other carbon sources are easy to decompose at high temperature, and the direct mixing interaction of the dicyandiamide, melamine and other carbon sources and metal particles is weak, so that the ligand utilization rate is low, and the carbonization yield is low. In addition, the cyanamide substance is carbon and nitrogen sources, so that a carbon nano tube coating material is easy to generate, and the product is impure. Another class of methods involves first forming a metal-organic framework (MOF) compound as a precursor by self-assembling and linking metal ions to organic ligands under a characteristic reaction. The preparation of such precursors generally requires the use of organic solvents and high temperature, high pressure reactions in a reaction vessel. Unlike the pyrolysis of cyanamides, the metal in MOF forms an atomic level uniform dispersion and is therefore considered as a more ideal pyrolysis precursor, which has become a research hot spot in recent years in this field. Such as Deng (DOI: 10.1002/anie.201409524Angewandte Chemie International Edition,2015, 54.7:2100-2104.) and the like in Co (NO 3 ) 2 、Ni(NO 3 ) 2 As a metal source, tetrasodium ethylenediamine tetraacetate is used as a carbon source, a self-assembled precursor is prepared under the conditions of high temperature and high pressure, and nitrogen and oxygen doped carbon cladding is prepared by pyrolysis under Ar atmosphereCobalt nickel alloy nanoparticles. An (DOI: 10.1039/c6ta 0239 h, mesoporous Ni@C hybrids for a high energy aqueous asymmetric supercapacitor device, electronic Supplementary Material (ESI) for Journal of Materials Chemistry A) and the like use iminodiacetic acid as a carbon source, ni (NO) 3 ) 2 Self-assembled precursors are also prepared as a metal source under high temperature and high pressure conditions and further thermally pyrolyzed in Ar atmosphere to prepare carbon-coated nickel nanoparticles, and by N 2 And the aperture corresponding to the aperture distribution peak is 17.8nm according to the adsorption and desorption isothermal curve. In summary, the existing preparation of the carbon-coated nickel core-shell structure nanomaterial still has the problems of low preparation efficiency, complicated steps, single pore structure of the product and the like. How to efficiently prepare the carbon-coated nickel core-shell structure nano particles and regulate and control the pore structure of the carbon-coated nickel core-shell structure nano particles, in particular to prepare a material with rich hierarchical pore structure, which has important significance for promoting the application of the carbon-coated nickel core-shell structure nano particles.
Disclosure of Invention
In order to overcome the defects, the invention provides a carbon-coated nickel nanocomposite and a preparation method thereof.
The invention provides a carbon-coated nickel nanocomposite, which comprises carbon-coated nickel nanoparticles, wherein the carbon-coated nickel nanoparticles consist of a nickel nanoparticle inner core and a nitrogen-and oxygen-doped graphitized carbon layer outer shell coated on the surface of the nickel nanoparticles; and the composite material has two distribution peaks with the pore diameter of 30-50 and 50-300 nm.
According to an embodiment of the present invention, the composite material comprises Ni 5-80%, C20-93%, O0.5-6%, N0.5-6% and H0.1-2.5% based on the total mass of the composite material.
According to another embodiment of the invention, wherein the nickel nanoparticle core comprises a face-centered cubic lattice structure and a hexagonal compact lattice structure.
According to another embodiment of the invention, wherein the composite material has a pickling loss of less than 60%, preferably less than 20%, more preferably less than 10%, most preferably less than 2%.
In another aspect, the present invention provides a method for preparing the carbon-coated nickel nanocomposite, comprising the steps of: s1, mixing water-soluble fatty acid containing amino group with Ni (NO) 3 ) 2 Mixing the materials in water, heating and stirring to form a homogeneous solution, removing water, and grinding the obtained solid to form a precursor; s2, pyrolyzing the precursor at a high temperature in an inert protective atmosphere or a reducing atmosphere.
According to an embodiment of the invention, wherein the amine group containing water-soluble fatty acid is one or more of ethylenediamine tetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, diethylenetriamine pentaacetic acid and 1, 3-propylenediamine tetraacetic acid.
According to another embodiment of the present invention, wherein the Ni (NO 3 ) 2 The molar ratio of the amino-containing water-soluble fatty acid to the amino-containing water-soluble fatty acid is 1:0.5-10.
According to another embodiment of the present invention, wherein the heating and stirring temperature is 30 to 150 ℃.
According to another embodiment of the present invention, in the step S2, the inert atmosphere is nitrogen or argon, the pyrolysis is heated to a constant temperature section at a rate of 0.5-30 ℃/min, the constant temperature section is maintained for a constant temperature time of 20-600min, and the temperature of the constant temperature section is 400-800 ℃; preferably, the heating rate is 1-10 ℃/min, the constant temperature is kept at 450-800 ℃ in a constant temperature section, and the temperature of the constant temperature section is 20-480 min.
According to another embodiment of the present invention, further comprising: and S3, purifying the product obtained in the step S2 in an acid solution to remove the incompletely coated Ni inner core.
According to another embodiment of the invention, wherein the acidic solution of the purification step is an aqueous solution of one or more of hydrochloric acid or sulfuric acid or hydrofluoric acid, at a concentration of 0.1 to 3mol/L.
The high-temperature pyrolysis precursor of the invention is directly prepared from Ni (NO) 3 ) 2 The precursor Ni is obtained by heating and stirring the precursor Ni and the water-soluble fatty acid containing amino under the conditions of normal pressure and pure water phase, and the atomic utilization rate of the precursor Ni can reach 100%. The preparation process does not need to use dicyandiamide and melamine which are commonly used in the traditional methodAmine and the like are easy to sublimate or decompose, and the ligand of the carbon nano tube is easy to generate; and overcomes the defects of the prior art that a high-temperature high-pressure reaction kettle is required to be used for self-assembly for preparing the precursor of the metal-organic framework structure, a large amount of organic solvents are wasted, the purification steps are complicated and the like. In addition, nitrate is decomposed in the pyrolysis process to form a unique multistage pore structure in the material, so that the effective regulation and control of the pore structure of the carbon-coated nickel core-shell structure nanoparticle is realized. Further, the preparation method uses inexpensive Ni (NO) 3 ) 2 The precursor is obtained by directly stirring and evaporating the precursor with the water-soluble fatty acid containing the amino in the water phase as a metal source, is simple and convenient to operate, and is easy to realize industrialized mass production.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate the invention and together with the description serve to explain, without limitation, the invention. In the drawings:
fig. 1 is an XRD pattern of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 1.
Fig. 2 is a TEM photograph of the nitrogen-doped carbon-coated nickel nanocomposite material prepared in example 1.
FIG. 3A is N of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 1 2 Adsorption and desorption isotherm curves.
FIG. 3B is a graph showing pore size distribution of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 1.
Fig. 4 is an XRD pattern of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2.
Fig. 5 is an SEM photograph of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2.
FIG. 6 is an XPS spectrum of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2.
FIG. 7 is a pore size distribution diagram of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2.
FIG. 8 is a pore size distribution plot of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 3.
FIG. 9 is a pore size distribution curve of the nitrogen-doped carbon-coated nickel nanocomposite prepared in comparative example 1.
Detailed Description
The invention will now be described in further detail by way of specific examples with reference to the accompanying drawings, it being understood that the specific embodiments described herein are for illustration and explanation only, and are not intended to limit the invention in any way.
The term "core-shell structure" in the invention means that the inner core is cobalt nano particles, and the shell is an oxygen doped graphitized carbon layer or a nitrogen and oxygen doped graphitized carbon layer. The "graphitized carbon layer" refers to a carbon structure which is "layered" rather than amorphous and has an interlayer spacing of about 0.34nm, which is clearly observed under high resolution transmission electron microscopy.
The term "oxygen" in the "oxygen doped graphitized carbon layer" refers to oxygen element, wherein the "oxygen content" of the nanocomposite refers to the content of oxygen element, and specifically, the graphitized carbon layer is formed to contain oxygen element in various forms during the preparation process of the carbon coated nanocomposite, and the "oxygen content" is the total content of all forms of oxygen element.
The term "mesoporous distribution peak" refers to a mesoporous distribution peak on a pore distribution curve calculated according to the Barrett-Joyner-Halenda (BJH) method on a desorption curve.
The term "pickling loss rate" refers to the loss ratio of transition metal after pickling of the finished carbon-coated transition metal nanocomposite product. Reflecting how tightly the graphitized carbon layer coats the transition metal. If the graphitized carbon layer does not cover the transition metal tightly, the transition metal of the inner core is dissolved by the acid after the acid treatment and is lost. The higher the acid washing loss rate, the lower the tightness degree of the graphitized carbon layer on the transition metal coating is, and the lower the acid washing loss rate is, the higher the tightness degree of the graphitized carbon layer on the transition metal coating is.
The "acid wash loss rate" was measured and calculated as follows:
1g of the sample was added in a proportion of 20mL of an aqueous sulfuric acid solution (1 mol/L), the sample was treated at 90℃for 8 hours, then washed with deionized water to neutrality, dried, weighed, analyzed, and the acid washing loss rate was calculated as follows.
The pickling loss rate= [1- (mass fraction of transition metal in the composite after pickling x mass of the composite after pickling)/(mass fraction of transition metal in the composite to be pickled x mass of the composite to be pickled) ] ×100%.
The carbon-coated nickel nanocomposite comprises carbon-coated nickel nanoparticles, wherein the carbon-coated nickel nanoparticles consist of a nickel nanoparticle inner core and a nitrogen-and oxygen-doped graphitized carbon layer outer shell coated on the surface of the nickel nanoparticles; and the composite material has two distribution peaks with mesoporous pore diameters of 30-50 and 50-300 nm.
Preferably, based on the total mass of the composite material, the Ni content is 5-80%, the C content is 20-93%, the O content is 0.5-6%, the N content is 0.5-6%, and the H content is 0.1-2.5%
Preferably, the nickel nanoparticle core comprises a face-centered cubic lattice structure and a hexagonal close lattice structure.
Preferably, the composite has a pickling loss of less than 60%, preferably less than 20%, more preferably less than 10%, most preferably less than 2%.
The carbon-coated nickel nanocomposite of the present invention is prepared by a method comprising the steps of: s1, mixing water-soluble fatty acid containing amino group with Ni (NO) 3 ) 2 Mixing the materials in water, heating and stirring to form a homogeneous solution, removing water, and grinding the obtained solid to form a precursor; s2, pyrolyzing the precursor at high temperature under an inert protective atmosphere or a reducing atmosphere.
Preferably, the amine group-containing water-soluble fatty acid is one or more of ethylenediamine tetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, diethylenetriamine pentaacetic acid and 1, 3-propylenediamine tetraacetic acid.
Ni(NO 3 ) 2 The molar ratio of the amino-containing water-soluble fatty acid to the amino-containing water-soluble fatty acid is 1:0.5-10.
The temperature of heating and stirring is 30-150 ℃.
In the step S2, the inert atmosphere is nitrogen or argon, the high-temperature pyrolysis is carried out at the speed of 0.5-30 ℃/min to a constant temperature section, the constant temperature time is kept at the constant temperature section for 20-600min, and the temperature of the constant temperature section is 400-800 ℃; preferably, the temperature rising rate is 1-10 ℃/min, the constant temperature time is 450-800 ℃ in the constant temperature section, and the temperature in the constant temperature section is 20-480 min.
Preferably, the method further comprises: s3, purifying the product obtained in the step S2 in an acid solution to remove the incompletely coated Ni inner core.
Wherein the acidic solution in the purification step is one or more aqueous solutions of hydrochloric acid, sulfuric acid or hydrofluoric acid, and the concentration is 0.1-3 mol/L.
Preparation of carbon-coated nickel nanocomposite
Example 1
30mmol Ni (NO) was weighed out 3 ) 2 ·6H 2 O and 15mmol EDTA are added into 100mL deionized water, the mixture is stirred at 85 ℃ to obtain a homogeneous solution, the homogeneous solution is continuously heated and evaporated to dryness, and the solid is ground to obtain a precursor.
And placing the precursor in a porcelain boat, placing the porcelain boat in a constant temperature area of a tube furnace, introducing nitrogen, heating to 625 ℃ at a speed of 2.5 ℃/min, keeping the temperature for 120min, stopping heating, and cooling to room temperature in a nitrogen atmosphere to obtain the carbon-coated nickel nanomaterial.
The obtained composite material is added into 50mL of 1mol/L HCl solution, the solution is filtered by suction after being stirred and refluxed for 4 hours at 90 ℃, and the powder is dried for 2 hours in a baking oven at 100 ℃ after being washed to be neutral by deionized water, so as to obtain the purified carbon-coated nano material.
Example 2
Weigh 20mmol Ni (NO) 3 ) 2 ·6H 2 O and 10mmol EDTA were added to 100mL deionized water, stirred at 85deg.C to give a homogeneous solution, and the solution was heated to dryness and the solid was ground to give the precursor.
Placing the obtained precursor into a porcelain boat, placing the porcelain boat in a constant temperature area of a tube furnace, introducing nitrogen into the porcelain boat, heating to 700 ℃ at a speed of 2.5 ℃/min, keeping the temperature for 120min, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain the carbon-coated nickel nanomaterial.
The obtained composite material is added into 50mL of 1mol/L HCl solution, the solution is filtered by suction after being stirred and refluxed for 4 hours at 90 ℃, and the powder is dried for 2 hours in a baking oven at 100 ℃ after being washed to be neutral by deionized water, so as to obtain the purified carbon-coated nano material.
Example 3
Weigh 20mmol Ni (NO) 3 ) 2 ·6H 2 O and 20mmol iminodiacetic acid are added into 100mL deionized water, the mixture is stirred at 80 ℃ to obtain a homogeneous solution, the homogeneous solution is continuously heated and evaporated to dryness, and the solid is ground to obtain a precursor.
Placing the obtained precursor into a porcelain boat, placing the porcelain boat in a constant temperature area of a tube furnace, introducing nitrogen into the porcelain boat, heating to 550 ℃ at the speed of 2.5 ℃/min, keeping the temperature for 180min, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain the carbon-coated nickel nanomaterial.
40mL of 1mol/L H was added to the resulting composite 2 SO 4 And (3) in the solution, stirring and refluxing at 85 ℃ for 6 hours, carrying out suction filtration on the solution, washing with deionized water to be neutral, and then placing the powder in a 100 ℃ oven for drying for 2 hours to obtain the purified carbon-coated nano material.
Comparative example 1
60mmol Ni (OH) was weighed out 2 And 30mmol of EDTA is added into 100mL of deionized water, the mixture is stirred at 85 ℃ to obtain a homogeneous solution, the homogeneous solution is continuously heated and evaporated to dryness, and the solid is ground to obtain a precursor.
Placing the obtained precursor into a porcelain boat, placing the porcelain boat in a constant temperature area of a tube furnace, introducing nitrogen into the porcelain boat, heating to 625 ℃ at a speed of 2.5 ℃/min, keeping the temperature for 120min, stopping heating, and cooling to room temperature under the nitrogen atmosphere to obtain the carbon-coated nickel nanomaterial.
The obtained composite material is added into 50mL of 1mol/L HCl solution, the solution is filtered by suction after being stirred and refluxed for 4 hours at 90 ℃, and the powder is dried for 2 hours in a baking oven at 100 ℃ after being washed to be neutral by deionized water, so as to obtain the purified carbon-coated nano material.
Characterization of results
Information such as the composition of the material, the structure or morphology of atoms or molecules within the material, and the like is obtained by XRD. The XRD diffractometer is XRD-6000 type X-ray powder diffractometer (Shimadzu Japan), and the XRD test conditions are as follows: cu target, ka radiation (wavelength λ=0.154 nm), tube voltage 40kV, tube current 200mA, scan speed 10 ° (2θ)/min.
The surface morphology of the material was observed by Scanning Electron Microscopy (SEM). The Scanning Electron Microscope (SEM) is a Supar55 field emission scanning electron microscope (Chuiss, germany), and the scanning electron microscope test conditions are as follows: the thermal field emission type has the working voltage of 20kV and the amplification factor range of 12-900 k.
The elements of the material surface were detected by X-ray photoelectron spectroscopy (XPS). The X-ray photoelectron spectroscopy analyzer used was an ESCALab220i-XL type radiation electron spectroscopy manufactured by VG scientific company and equipped with Avantage V5.926 software, and the X-ray photoelectron spectroscopy analysis test conditions were: the excitation source was monochromatized A1K alpha X-rays with a power of 330W and a base vacuum of 3X 10-9mbar at the analytical test.
The pore structure properties of the materials were examined by the BET test method. Specifically, the specific surface area of the catalyst is measured by a Quantachrome AS-6B type analyzer, the specific surface area of the catalyst is obtained by a Brunauer-Emmett-Taller (BET) method, and a pore distribution curve is obtained by calculating a desorption curve according to a Barrett-Joyner-Halenda (BJH) method.
Analysis of four elements of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) was performed on a Elementar Micro Cube elemental analyzer. The specific operation method and conditions are as follows: 1-2mg of sample is weighed in a tin cup, put in an automatic sample feeding disc, enter a combustion tube through a ball valve for combustion, the combustion temperature is 1000 ℃ (in order to remove atmospheric interference during sample feeding, helium purging is adopted), and then reduction copper is used for reducing the burnt gas to form nitrogen, carbon dioxide and water. The mixed gas is separated by three desorption columns and sequentially enters a TCD detector for detection. The analysis of oxygen element is to convert oxygen in the sample into CO by pyrolysis under the action of a carbon catalyst, and then detect the CO by TCD.
The content of the metal element is normalized after the content of carbon, hydrogen, oxygen and nitrogen is removed by the material.
Fig. 1 is an XRD pattern of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 1. In the figure, curve (a) represents an unpurified carbon-coated nickel nanocomposite, and curve (b) represents a purified carbon-coated nickel nanocomposite. As can be seen from the figure, both the material before and after pickling had a distinct phase corresponding to face-centered cubic packed Ni (fcc-Ni) and hexagonal close packed Ni (hcp-Ni), indicating that a large amount of carbon-coated nickel nanoparticles remained after pickling. Fig. 2 is a TEM photograph of the nitrogen-doped carbon-coated nickel nanocomposite material prepared in example 1. It can be clearly seen that the nickel nanoparticles are densely distributed on the carbon support, and the outer layer of the nickel nanoparticles is coated with a plurality of graphitized carbon layers. FIG. 3A is N of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 1 2 Adsorption and desorption isotherm curves. FIG. 3B is a graph showing pore size distribution of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 1. The isothermal adsorption and desorption curve of nitrogen is a typical isothermal line of IV, and the pore size distribution curve has a distribution peak at 40.5nm and 246nm respectively, which proves that the nitrate-containing precursor is utilized to effectively generate a multi-stage pore structure containing abundant macropores on a carbon matrix in the pyrolysis process. The content of the nano material C is 26.56%, the content of H is 2.09%, the content of N is 1.44%, the content of O is 5.32%, and the content of Ni is 64.59% after normalization. The acid washing loss rate of the composite material before purification prepared in the embodiment is 30 percent, and the acid washing loss rate of the composite material after purification is less than 1 percent, which is measured and calculated according to the method of the terminology part. The pickling time is continuously increased on the basis of the method described in the term part, and the pickling loss rate is basically kept unchanged.
Fig. 4 is an XRD pattern of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2. As can be seen from the figure, the acid washed material still had a distinct phase corresponding to face-centered cubic packed Ni (fcc-Ni) and hexagonal close packed Ni (hcp-Ni), indicating that a large amount of carbon-coated nickel nanoparticles were still present after acid washing. Fig. 5 is an SEM photograph of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2. It can be clearly seen that a plurality of obvious holes exist on the integral material frame, which proves that the material has a rich hierarchical pore structure. FIG. 6 is an XPS spectrum of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2. The spectral peak corresponding to C, N, O, ni was clearly seen to have a surface composition of 78.32% C, 3.07% N, 8.24% O and 10.38% Ni calculated on an atomic scale. FIG. 7 is a pore size distribution diagram of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 2. The pore size distribution curve has a distribution peak at 39.2nm and 109nm, respectively, which demonstrates that the nitrate-containing precursor is effective in producing a multi-stage pore structure with abundant macropores on the carbon matrix during pyrolysis. The content of the nano material C is 37.14%, the content of H is 1.65%, the content of N is 1.67%, the content of O is 5.12%, and the content of Ni after normalization is 54.42% as measured by an elemental analyzer. The acid washing loss rate of the composite material before purification prepared in the embodiment is 56% and the acid washing loss rate of the composite material after purification is less than 1% measured and calculated according to the method of the terminology part. The pickling time is continuously increased on the basis of the method described in the term part, and the pickling loss rate is basically kept unchanged.
FIG. 8 is a pore size distribution plot of the nitrogen-doped carbon-coated nickel nanocomposite prepared in example 3. The pore size distribution curve has one distribution peak at 38.1nm and 74.1nm each, and also demonstrates that the use of nitrate-containing precursors effectively creates a multi-stage pore structure with abundant macropores on the carbon matrix during pyrolysis. The content of C in the nano material is 34.01 percent, the content of H is 2.43 percent, the content of N is 2.81 percent, the content of O is 7.14 percent, and the content of Ni after normalization is 53.61 percent. The acid washing loss rate of the composite material before purification prepared in the embodiment is 51% and the acid washing loss rate of the composite material after purification is less than 1% measured and calculated according to the method of the term part. The pickling time is continuously increased on the basis of the method described in the term part, and the pickling loss rate is basically kept unchanged.
FIG. 9 is a pore size distribution curve of the nitrogen-doped carbon-coated nickel nanocomposite prepared in comparative example 1. It can be seen that the pores of the material are mainly mesoporous with the pore diameter smaller than 15nm, and the precursor does not contain nitrate radical, so that the pore structure is obviously different from that of the embodiment.
The high-temperature pyrolysis precursor of the invention is directly prepared from Ni (NO) 3 ) 2 The precursor Ni is obtained by heating and stirring the precursor Ni and the water-soluble fatty acid containing amino under the conditions of normal pressure and pure water phase, and the atomic utilization rate of the precursor Ni can reach 100%. The preparation process does not need to use dicyandiamide, melamine and other ligands which are commonly used in the traditional method and are easy to sublimate or decompose, and carbon nano-tubes are easy to generate; and overcomes the defects of the prior art that a high-temperature high-pressure reaction kettle is required to be used for self-assembly for preparing the precursor of the metal-organic framework structure, a large amount of organic solvents are wasted, the purification steps are complicated and the like. In addition, nitrate is decomposed in the pyrolysis process to form a unique multistage pore structure in the material, so that the effective regulation and control of the pore structure of the carbon-coated nickel core-shell structure nanoparticle is realized. Further, the preparation method uses inexpensive Ni (NO) 3 ) 2 Is a metal source, is directly stirred with water-soluble fatty acid containing amino in a water phase and evaporated to dryness to obtain a precursor, is simple and convenient to operate, and is easy to realize industrialized mass production.
Of course, the present invention is capable of other various embodiments and its several details are capable of modification and variation in light of the present invention, as will be apparent to those skilled in the art, without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (7)

1. The carbon-coated nickel nanocomposite comprises carbon-coated nickel nanoparticles, wherein the carbon-coated nickel nanoparticles consist of a nickel nanoparticle inner core and a nitrogen-and oxygen-doped graphitized carbon layer outer shell coated on the surface of the nickel nanoparticles; the composite material has two distribution peaks with the aperture of 25-50 nm and 50-300 nm, and the pickling loss rate of the composite material is less than 2%;
the method for coating the nickel nanocomposite by carbon comprises the following steps:
s1, mixing water-soluble fatty acid containing amino group with Ni (NO) 3 ) 2 Mixing the materials in water, heating and stirring to form a homogeneous solution, removing water, and grinding the obtained solid to form a precursor;
s2, pyrolyzing the precursor at a high temperature in an inert protective atmosphere or a reducing atmosphere;
s3, purifying the product obtained in the step S2 in an acid solution to remove the incompletely coated Ni inner core;
wherein the water-soluble fatty acid containing amino groups is one or more of ethylenediamine tetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, diethylenetriamine pentaacetic acid and 1, 3-propylenediamine tetraacetic acid;
wherein the Ni (NO) 3 ) 2 The molar ratio of the amino-containing water-soluble fatty acid to the amino-containing water-soluble fatty acid is 1:0.5-10; the inert atmosphere is nitrogen or argon, the high-temperature pyrolysis is heated to a constant temperature section at the speed of 0.5-30 ℃/min, the constant temperature time is kept at the constant temperature section for 20-600min, and the temperature of the constant temperature section is 400-800 ℃.
2. The carbon-coated nickel nanocomposite according to claim 1, wherein the content of Ni is 5 to 80%, the content of C is 20 to 93%, the content of O is 0.5 to 6%, the content of N is 0.5 to 6%, the content of H is 0.1 to 2.5%, and the sum of the contents of the components in the composite is 100%, based on the total mass of the composite.
3. The carbon-coated nickel nanocomposite of claim 1, wherein the nickel nanoparticle core comprises a face-centered cubic lattice structure and a hexagonal compact lattice structure.
4. A method of preparing the carbon-coated nickel nanocomposite of any of claims 1-3, comprising the steps of:
s1, mixing water-soluble fatty acid containing amino group with Ni (NO) 3 ) 2 Mixing the materials in water, heating and stirring to form a homogeneous solution, removing water, and grinding the obtained solid to form a precursor;
s2, pyrolyzing the precursor at a high temperature in an inert protective atmosphere or a reducing atmosphere;
s3, purifying the product obtained in the step S2 in an acid solution to remove the incompletely coated Ni inner core;
wherein the water-soluble fatty acid containing amino groups is one or more of ethylenediamine tetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, diethylenetriamine pentaacetic acid and 1, 3-propylenediamine tetraacetic acid;
wherein the Ni (NO) 3 ) 2 The molar ratio of the amino-containing water-soluble fatty acid to the amino-containing water-soluble fatty acid is 1:0.5-10; the inert atmosphere is nitrogen or argon, the high-temperature pyrolysis is heated to a constant temperature section at the speed of 0.5-30 ℃/min, the constant temperature time is kept at the constant temperature section for 20-600min, and the temperature of the constant temperature section is 400-800 ℃.
5. The method of claim 4, wherein the heating and stirring temperature is 30-150 ℃.
6. The method according to claim 4, wherein in the step S2, the temperature rising rate is 1 to 10 ℃/min, the constant temperature is kept at 450 to 800 ℃ in a constant temperature period, and the constant temperature period is 20 to 480min.
7. The method according to claim 4, wherein the acidic solution in the purifying step is an aqueous solution of one or more of hydrochloric acid, sulfuric acid or hydrofluoric acid, and the concentration is 0.1-3 mol/L.
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