Magnetic metal nanochain, preparation method and application thereof

Abstract

The application discloses a kind of magnetic metal nanochain, preparation method and application, comprising the following steps: iron salt is dissolved in deionized water, and iron salt solution is obtained;Sodium borohydride is added to the iron salt solution, and the black product is obtained by magnetic stirring and incubation;The black product obtained is washed, centrifuged and dried to obtain magnetic metal nanochain, the raw material used in the application has abundant reserves and low price, and the synthesis method is simple;The metal nanochain prepared can be intertwined to form a porous structure, is not easy to aggregate, and can expose more active sites;When used, electrons can be transferred along the nanochain after applying an electric field, and the reaction kinetics is accelerated.

Description

Technical Field

[0001] This invention relates to the fields of green ammonia industry and nanomaterial preparation, specifically to a magnetic metal nanochain, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3), due to its high hydrogen content, is easy to store and transport, and is considered a highly efficient clean energy carrier. It is also a major raw material for fertilizer production, making it indispensable in agriculture; ammonia feeds more than one-third of the world's population. Currently, industrial production of NH3 mainly utilizes the high-temperature (350-550℃) and high-pressure (150-350 atm) Haber-Bosch process. However, this consumes a large amount of energy resources (1% globally) and emits significant amounts of carbon dioxide, which is detrimental to sustainable ammonia production. Furthermore, with the goals of carbon neutrality and carbon peaking, the high-temperature, high-pressure Haber-Bosch process can no longer meet the growing demand for ammonia. Therefore, developing sustainable ammonia production methods is urgently needed.

[0003] Electrocatalytic nitrogen fixation for ammonia synthesis, using nitrogen from the air and water as raw materials and renewable solar energy as a clean energy source, is considered a sustainable ammonia production technology. Recently, electrocatalytic ammonia synthesis has been widely reported and has achieved some progress. However, due to the low solubility of nitrogen and the high dissociation energy of N≡N, the efficiency and yield of electrocatalytic ammonia synthesis remain very low to date, far from meeting the requirements for industrialization. Therefore, there is an urgent need to develop novel, efficient, low-cost, and stable electrocatalysts to advance the industrialization of electrocatalytic nitrogen fixation.

[0004] Magnetic metals, including iron, cobalt, and nickel, are abundant and inexpensive on Earth, making them suitable for widespread development and large-scale use. Recently, iron-based electrocatalytic ammonia synthesis catalysts have been widely reported, exhibiting promising performance among numerous catalysts. However, these catalysts are primarily iron-based compounds and doped, making them difficult to recover and reuse. Using elemental iron directly as a catalyst facilitates recovery and reuse; however, currently synthesized iron is mainly in the form of nanoparticles, which are prone to agglomeration, hindering the exposure of active sites and thus inhibiting catalytic activity. Therefore, designing and developing iron-based catalysts with highly exposed active sites to improve catalytic performance holds great promise but remains a challenge. Summary of the Invention

[0005] In view of this, the present invention provides a magnetic metal nanochain, its preparation method and its application.

[0006] One of the objectives of this invention is achieved as follows:

[0007] A method for preparing magnetic metal nanochains, the key of which includes the following steps:

[0008] Step 1: Dissolve the iron salt in deionized water to obtain an iron salt solution;

[0009] Step 2: Add sodium borohydride to the iron salt solution and stir under heat with a magnetic stirrer to obtain a black product;

[0010] Step 3: Wash, centrifuge and dry the obtained black product to obtain magnetic metal nanochains.

[0011] As a preferred option:

[0012] The iron salts mentioned above are ferric nitrate, ferrous sulfate, ferric chloride, or ferrous chloride.

[0013] The concentration of the above iron salt solution is 1 mg·mL. -1 -10 mg·mL -1 .

[0014] The mass ratio of sodium borohydride to iron salt added is 5:1 to 50:1.

[0015] The above-mentioned heat preservation and stirring time is 1-5 hours.

[0016] The above-mentioned insulation temperature is 0-80℃.

[0017] The rotational speed of the magnetic stirrer is 600-3600 r·min. -1 .

[0018] The second objective of this invention is achieved as follows:

[0019] A magnetic metal nanochain is prepared using the method described above.

[0020] The third objective of this invention is achieved as follows:

[0021] The key to the application of a magnetic metal nanochain lies in its application in the field of electrocatalytic ammonia synthesis.

[0022] Preferably, the electrolytic cell used is an H-cell, and the nitrogen flow rate is 10-100 mL·min. -1 .

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the raw materials are abundant and inexpensive, and the synthesis method is simple; the prepared metal nanochains can intertwine to form a porous structure, which is not easy to agglomerate and can expose more active sites; when used, after applying an electric field, electrons can transfer along the nanochains, which accelerates the reaction kinetics. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation and synthesis route of the present invention;

[0025] Figure 2 X-ray diffraction pattern of the magnetic metal nanochains prepared in Example 1;

[0026] Figure 3 Field emission scanning electron microscope (FESEM) images of the magnetic metal nanochains prepared in Example 1 at different magnifications;

[0027] Figure 4 Transmission electron microscopy images of the magnetic metal nanochains prepared in Example 1 at different magnifications;

[0028] Figure 5 Strain diagram of the magnetic metal nanochains prepared in Example 1;

[0029] Figure 6 Field emission scanning electron microscope (FESEM) images of the metal nanoparticles prepared in Example 2 at different magnifications;

[0030] Figure 7 Linear sweep voltammetry curves of the electrocatalytic synthesis of ammonia from the magnetic metal nanochains prepared in Example 1;

[0031] Figure 8 The chronoamperometry curve of the electrocatalytic synthesis of ammonia from the magnetic metal nanochains prepared in Example 1;

[0032] Figure 9 The graph shows the ammonia yield and Faraday efficiency of the electrocatalytic synthesis of ammonia using magnetic metal nanochains prepared in Example 1.

[0033] Figure 10 Stability curves of the magnetic metal nanochains prepared in Example 1 for electrocatalytic ammonia synthesis;

[0034] Figure 11 The graph shows the ammonia yield and Faraday efficiency of the electrocatalytic synthesis of ammonia from the magnetic metal nanoparticles prepared in Example 2. Implementation

[0035] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0036] Example 1: A magnetic metal nanochain, the synthesis route of which is as follows Figure 1 As shown, the specific preparation steps are as follows:

[0037] Step 1: Dissolve 50 mg of ferrous chloride in 30 mL of deionized water and sonicate to obtain an iron salt solution;

[0038] Step 2: Add 500 mg of sodium borohydride to the above solution and incubate at 1600 r·min at room temperature. -1Stirred under magnetic stirring for 2 hours;

[0039] Step 3: Wash the obtained black product three times with deionized water, centrifuge, and dry to obtain magnetic metal nanochains.

[0040] The X-ray diffraction pattern of the obtained magnetic metal nanochains is as follows: Figure 2 As shown, a comparison with the standard card for iron reveals almost no obvious diffraction peaks, indicating that the obtained material is an amorphous magnetic iron. Field emission scanning electron microscopy (FEM) image, as shown... Figure 3 As shown, the magnetic iron is formed by nanoparticles linked together to form nanochains, with the length of a single nanochain ranging from 3.1 to 3.5 μm. The nanochains can intertwine to form nanopore structures, which facilitate the diffusion of electrolyte and the transfer of gas. Furthermore, it can be observed that the nanoparticles that make up the nanochains are tightly connected.

[0041] Transmission electron microscope images at different magnifications are shown below. Figure 4 As shown in the figure, 4a and 4b indicate that the individual nanochains extend laterally, and there are no obvious gaps between the nanoparticles of the nanochains, indicating that the nanochains are tightly bound in the early stage of formation. Furthermore, a thin layer was found around the nanochains. Figure 4 b), further observation shows that the thickness of the thin layer is approximately 4 nm. This thin layer is likely a protective iron oxide layer formed by oxidation of oxygen in the air. Figure 4 c), therefore, the obtained magnetic iron nanochains can be regarded as a core-shell structure with iron as the core and iron oxide as the shell. Furthermore, high-magnification transmission observation of the core and shell positions shows that both regions exhibit an amorphous structure. Figure 4 d, 4e), the corresponding diffraction results also show no diffraction spots or diffraction rings ( Figure 4 f), further proving the amorphous result. Figure 5 For the corresponding Figure 4 The strain diagram of the region shows obvious strain generation, which is due to amorphous properties.

[0042] The magnetic metal nanochains prepared by the method in Example 1 were used as a catalyst in the electrocatalytic synthesis of ammonia. H-cells were used as the electrolytic cell, and the nitrogen flow rate was 10-100 mL / min. -1 .like Figure 7 The linear sweep voltammetry curves comparing nitrogen and argon conditions are shown. It is clearly observed that the current density is higher under nitrogen conditions than under argon conditions. Therefore, magnetic iron nanochains can electrocatalyze the synthesis of ammonia. Further quantitative analysis was performed using chronoamperometry. Figure 8 ). Figure 9The ammonia yield (9a) and Faraday efficiency (9b) of the prepared magnetic metal nanochains for electrocatalytic ammonia synthesis are shown in the figure. It can be clearly seen that as the potential shifts negatively from -0.2 to -0.6 V (vs. RHE), the ammonia yield and Faraday efficiency first increase, reaching a maximum of 92.42 ug·h at -0.4 V (vs. RHE). -1 ·mg -1 At 20.02%, further increasing the potential resulted in a decrease in ammonia yield and Faraday efficiency, mainly because hydrogen evolution became severe at high overpotentials, inhibiting ammonia formation. Figure 10 The results show that the catalyst prepared by the method in Example 1 has excellent stability in electrocatalytic ammonia synthesis. After continuous operation at -0.4 V (vs. RHE) for 60 h, the current density did not change significantly, and the linear sweep voltammetric curves before and after the operation basically overlapped.

[0043] Comparative Example 1: A magnetic metal nanoparticle, prepared by the following steps:

[0044] Step 1: Dissolve 50 mg of ferrous chloride in 30 mL of deionized water and stir ultrasonically to obtain an iron salt solution;

[0045] Step 2: Add 500 mg of sodium borohydride to the above solution and let it stand at room temperature for 2 hours;

[0046] Step 3: Wash the obtained black product three times with deionized water, centrifuge, and dry to obtain magnetic metal nanoparticles.

[0047] The difference between this comparative example and Example 1 is that no stirring was performed; the mixture was simply allowed to stand, resulting in magnetic iron nanoparticles. The X-ray diffraction pattern of the obtained magnetic iron nanoparticles is basically consistent with that of Example 1. Comparison with the iron standard card shows almost no obvious diffraction peaks, indicating that an amorphous magnetic iron material was obtained. Field emission scanning electron microscopy (FEM) images are shown below. Figure 6 As shown, the magnetic iron nanoparticles exhibit irregular cross-linking and aggregation. The catalyst prepared by the method in Example 2 was applied to the electrocatalytic synthesis of ammonia, using an H-cell as the electrolytic cell and a nitrogen flow rate of 10-100 mL / min. -1 .like Figure 11 As shown, as the potential shifts negatively from -0.2 to -0.6 V (vs. RHE), the ammonia yield (11a) and Faraday efficiency (11b) also initially increase, reaching a maximum of 32.82 ug·h at -0.4 V (vs. RHE). -1 ·mg -1 The yield was 6.01%, and further increases in potential resulted in a decrease in ammonia yield and Faraday efficiency. This was mainly due to the severe hydrogen evolution at high overpotentials, which inhibited ammonia formation.

[0048] contrast Figure 9 and Figure 11 It can be seen that applying magnetic iron nanochains to the electrocatalytic synthesis of ammonia results in higher ammonia yield and Faraday efficiency. This indicates that the magnetic iron nanochains, due to their intertwining to form nanoporous structures, facilitate electrolyte diffusion and gas transfer, thereby improving catalytic efficiency.

[0049] Example 2, a magnetic metal nanochain, prepared by the following steps:

[0050] Step 1: Dissolve 50 mg of ferrous chloride in 30 mL of deionized water and stir ultrasonically to obtain an iron salt solution;

[0051] Step 2: Add 500 mg of sodium borohydride to the above solution and heat at 600 r·min -1 Stirred at 20°C for 2 hours under magnetic stirring;

[0052] Step 3: Wash the obtained black product three times with deionized water, centrifuge, and dry to obtain magnetic metal nanochains.

[0053] Example 3, a magnetic metal nanochain, prepared by the following steps:

[0054] Step 1: Dissolve 30 mg of ferric nitrate in 30 mL of deionized water and sonicate to obtain an iron salt solution;

[0055] Step 2: Add 1000 mg of sodium borohydride to the above solution and heat at 3600 r·min -1 Stirred at 0°C for 1 h under magnetic stirring;

[0056] Step 3: Wash the obtained black product three times with deionized water, centrifuge, and dry to obtain magnetic metal nanochains.

[0057] Example 4, a magnetic metal nanochain, prepared by the following steps:

[0058] Step 1: Dissolve 300 mg of ferric chloride in 30 mL of deionized water and sonicate to obtain an iron salt solution;

[0059] Step 2: Add 3000 mg of sodium borohydride to the above solution and stir at 2000 r·min -1 Stirred at 40°C for 5 h under magnetic stirring;

[0060] Step 3: Wash the obtained black product three times with deionized water, centrifuge, and dry the magnetic metal nanochains.

[0061] Example 5, a magnetic metal nanochain, prepared by the following steps:

[0062] Step 1: Dissolve 50 mg of ferrous sulfate in 30 mL of deionized water and sonicate to obtain an iron salt solution;

[0063] Step 2: Add 2500 mg of sodium borohydride to the above solution and heat at 800 r·min -1 Stirred at 80°C for 2 hours under magnetic stirring;

[0064] Step 3: Wash the obtained product three times with deionized water, centrifuge, and dry the magnetic metal nanochains.

[0065] Example 6, a magnetic metal nanochain, prepared by the following steps:

[0066] Step 1: Dissolve 150 mg of ferric chloride in 30 mL of deionized water and stir ultrasonically to obtain an iron salt solution;

[0067] Step 2: Add 750 mg of sodium borohydride to the above solution and stir at 3000 r·min -1 Stirred at 60°C for 3 hours under magnetic stirring;

[0068] Step 3: The obtained product is washed three times with deionized water, centrifuged, and dried to remove the magnetic metal nanochains.

[0069] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing magnetic metal nanochains, characterized in that... Includes the following steps: Step 1: Dissolve the iron salt in deionized water to obtain an iron salt solution with a concentration of 1 mg / mL. -1 -10 mg·mL -1 ; Step 2: Add sodium borohydride to the iron salt solution and stir under heat on a magnetic stirrer to obtain a black product. The magnetic stirrer rotates at a speed of 600-3600 r / min. -1 The time is 1-5 hours, and the mass ratio of sodium borohydride to iron salt is 5:1-50:

1. Step 3: Wash, centrifuge and dry the obtained black product to obtain magnetic metal nanochains. The magnetic metal nanochains are amorphous magnetic iron materials with a core-shell structure. The core is iron and the shell is iron oxide. The length of a single magnetic metal nanochain is 3.1-3.5 μm. The magnetic metal nanochains are intertwined to form a structure with nanopores. The obtained magnetic metal nanochains are applied in the field of electrocatalytic ammonia synthesis.

2. The method for preparing magnetic metal nanochains according to claim 1, characterized in that: The iron salt is ferric nitrate, ferrous sulfate, ferric chloride, or ferrous chloride.

3. The method for preparing magnetic metal nanochains according to claim 1 or 2, characterized in that: The insulation temperature is 0-80℃.

4. A magnetic metal nanochain, characterized in that: Prepared using the method described in any one of claims 1-3.

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