A transition metal selenide catalyst based on cobalt squarate-based MOF and a preparation method thereof

Abstract

The application discloses a preparation method of a transition metal selenide catalyst based on a Co-based MOF of a square acid. The Co-based MOF of the square acid is a dice-shaped square Co nanocage, and the Co-based MOF of the square acid is stable in thermodynamic properties and chemical properties. Then, the transition metal selenide catalyst is prepared by using selenium (Se) powder as a Se source and through an anion exchange method. The prepared transition metal selenide (CoSe2) has a large interface contact area, which is beneficial to exposing more surface active sites and improving catalytic activity.

Description

Technical Field

[0001] This invention patent belongs to the field of electrocatalysis, specifically relating to a transition metal selenide catalyst based on cobalt squaric acid MOF and its preparation method. Background Technology

[0002] Metal-organic frameworks (MOFs), as inorganic-organic hybrid materials, have attracted considerable interest over the past three decades due to their potential applications in gas storage / separation, catalysis, sensing, and drug delivery. Furthermore, their high porosity and unique hybrid properties make them ideal precursors for constructing functional carbon materials and nanocomposites, further expanding the applications of MOFs. By controlling the reaction process, various morphologies of MOFs can be obtained, including nanocages, core-shell or multi-shell structures, nanotubes, and nanosheets. Among these, nanocages are gaining increasing attention due to their high surface area, low density, and high load-bearing capacity. Typically, the most direct method for synthesizing nanocages is the template method, which requires careful selection of a suitable template, and the products are usually polycrystalline structures that may collapse during template removal. In contrast, the "self-templating" method appears to be more convenient and efficient for creating nanocage structures, especially those with complex morphologies. In this invention, a uniform and monodisperse dice-shaped cobalt cage synthesized by a one-pot method is used. Through precise control of crystallization kinetics, a thermodynamically unstable phase is initially formed, which then undergoes a dissolution-regeneration process and is eventually transformed into a hollow nanocage.

[0003] Over the past few decades, transition metal chalcogenides (TMCs) have garnered increasing attention across various fields due to their abundant reserves and diverse structures and compositions. These materials represent an important branch of two-dimensional materials, exhibiting excellent electrical and optoelectronic properties. Materials composed of TMCs only a few atoms thick, such as atomically thin MoS2, demonstrate spin polarization. Recent studies have revealed that in acidic solutions, the large lattice anions in TMCs enable the effective separation of active metal sites, which is beneficial for controlling electrocatalytic reactions.

[0004] Currently, commonly used selenization methods include pyrolysis and acid etching. Although these methods are relatively mature, the active sites of the catalysts prepared so far cannot be fully exposed, which greatly affects the catalytic activity of the catalysts. Summary of the Invention

[0005] To address the problem of active sites not being exposed due to the easy collapse of hollow frames, this invention provides a transition metal selenide catalyst prepared from hollow dice-shaped cobalt cages. The selenization method is anion exchange, and the prepared transition metal selenides exhibit a hierarchical nanosheet state, which increases the interfacial contact area, facilitates the exposure of active sites, and improves electrochemical activity.

[0006] This invention discloses a method for preparing transition metal selenide catalysts based on cobalt square oxide-based MOFs, and their application in the field of electrochemical catalysis. Based on dice-shaped hollow cobalt cages and using selenium powder as the selenium source, this invention allows for the preparation of well-structured, hollow transition metal selenide catalysts at room temperature via anion exchange. The surface structure consists of stacked nanosheets, thus exposing more surface active sites. The resulting catalyst exhibits a stable structure, and the hierarchical structure with increased interfacial contact, prepared via anion exchange, is beneficial for improving electrochemical activity.

[0007] To achieve the above objectives, the present invention adopts the following solution.

[0008] A method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOF, wherein the cobalt squaric acid-based MOF is a dice-shaped cobalt cage; the selenization is carried out by anion exchange to form a nanocage structure with a hollow interior and an alternating stacked shell of CoSe2 nanosheets on the surface.

[0009] This invention provides a method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOF, comprising the following steps:

[0010] Step 1: Obtain Co-based MOFs of squaric acid;

[0011] Step 2: Dissolve NaOH, NaBH4, and Se powder in deionized water and mix thoroughly to obtain Se. 2- The source mixed solution, wherein the squaric acid Co-based MOF obtained in step 1 is dispersed in Se as a precursor 2- In the source mixed solution, the mixture is stirred until fully reacted to form a transition metal selenide with cobalt squaric acid-based MOF as the framework;

[0012] Step 3: Anneal the transition metal selenide with cobalt squaric acid-based MOF framework obtained in Step 1.

[0013] Preferably, the squaric acid Co-based MOF in step 1 is prepared by ultrasonic static settling method, including the following steps:

[0014] Squamous acid and organic ligands were dissolved in water to obtain solution A, and Co metal salt was dissolved in methanol to obtain solution B. Solution A and solution B were mixed evenly and then sonicated, then allowed to grow statically, then washed with deionized water, centrifuged and freeze-dried to obtain dice-shaped cobalt square cage structure.

[0015] Preferably, the ultrasound duration is 5 minutes.

[0016] Preferably, the annealing process includes: placing a transition metal selenide with a cobalt squartz-based MOF as the framework in a quartz boat, placing the quartz boat in the middle of a tube furnace for annealing, and removing excess Se powder.

[0017] Preferably, in step 1:

[0018] The Co metal salt is Co(CH3COO)2·4H2O; the organic ligands are: dimethylimidazolium and polyvinylpyrrolidone;

[0019] The molar ratio of Co metal salt, dimethylimidazolium and polyvinylpyrrolidone is 2:1:2;

[0020] The mass ratio of Co metal salt to squaric acid is 4:1;

[0021] The obtained squaric acid Co-based MOF has a size of 1–2 μm.

[0022] Preferably, in step 2, the Se 2- In the source mixed solution, the molar ratio of NaOH, NaBH4, and Se powder is 1:10.2:5.

[0023] Preferably, in step 3, the annealing temperature is set at 500℃, the holding time is 4 hours, and the heating rate is 10℃ / min.

[0024] This invention provides a transition metal selenide catalyst based on cobalt squaric acid-based MOF.

[0025] The catalyst uses a dice-shaped hollow cobalt cage as a framework, and CoSe2 nanosheets are stacked on the surface of the hollow cobalt cage; the surface of the dice-shaped hollow cobalt cage has through holes that communicate with the internal hollow region; the size of the catalyst is between 1 and 2 μm.

[0026] The dice-shaped hollow cobalt cage is based on a sodium salt-type cage structure; the coordination structure composed of cobalt ions, water molecules, square acid ligands and PVP organic ligands constitutes the sodium salt-type cage structure, and each sodium salt-type cage structure includes 12 cobalt ions and 6 square acid ligands.

[0027] The transition metal selenide catalyst based on cobalt squaric acid MOF exhibits a cubic shape with truncated edges. The crystal contains hollow cavities, with a uniformly distributed porosity structure on each exposed facet, which is beneficial for improving electrochemical activity.

[0028] Over the past three decades, metal-organic frameworks (MOFs) have attracted considerable interest. Furthermore, their high porosity and unique hybrid properties make them ideal precursors for constructing functional carbon materials and nanocomposites, which could further expand the applications of MOFs. MOFs are assembled from metal ions and organic linkers via coordination bonds. The reversibility of these coordination bonds allows for control over bond breaking and formation. For example, adding a capping agent with the same chemical function as the linker can inhibit the reaction between metal ions and the organic linker, which will facilitate the synthesis of nanoscale MOFs. In the preparation of a squaric acid Co-based MOF, Co ions and squaric ligands were synthesized in CH3COO during sonication. - Under the promotion of rapid assembly, a defect-rich structure was formed. During the static process, it underwent a spontaneous dissolution-regeneration process, and finally formed a nanocage structure with stable thermodynamic and chemical properties.

[0029] This invention employs anion exchange to selenize the precursor. The selenization process is carried out entirely at room temperature. The resulting squaric acid Co-based MOF is used as a precursor to prepare CoSe2, which retains its original morphology. The surface is covered by uneven CoSe2 nanosheets. The catalyst prepared in this way has a hierarchical structure with sufficient interfacial contact. The sheet-like structure is conducive to the exposure of active sites and enhances the reaction activity. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Some specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings indicate the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0031] Figure 1 Scanning electron microscope (SEM) image of the squaric acid Co-based MOF prepared in this invention.

[0032] Figure 2 This is a scanning electron microscope image of CoSe2 after annealing prepared according to the present invention.

[0033] Figure 3 Scanning electron microscope image of MOF-CoSe2 prepared for Comparative Example 1

[0034] Figure 4 Scanning electron microscope image of CoSe2 / NC-NF prepared for Comparative Example 2 Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0036] A method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOFs employs anion exchange, and the detailed preparation process is as follows:

[0037] 1) Synthesis of Co-based Squamous Acid MOF: Co(CH3COO)2·4H2O was dispersed in methanol, and dimethylimidazolium, polyvinylpyrrolidone (PVP) and squamous acid were dissolved in water. The two solutions were mixed and sonicated, and then allowed to grow statically to obtain dice-shaped cobalt cages.

[0038] 2) Synthesis of CoSe2: NaOH, NaBH4, and Se powder are mixed evenly to prepare Se2. 2- The prepared squaric acid Co-based MOF precursor was dispersed in Se... 2- In the source mixed solution, the mixture is stirred and reacted thoroughly to form a transition metal selenide with a dice-shaped cobalt cage as the basic framework.

[0039] 3) Anneal the CoSe2 synthesized in step 2 in a tube furnace to remove excess selenium powder.

[0040] The mass ratio of Co metal salt, dimethylimidazole, PVP, and squaric acid in the Co-based MOF is 4:2:4:1.

[0041] The mass ratio of NaOH, NaBH4, and selenium powder is 1:10.2:5.

[0042] When removing excess Se powder, the annealing temperature is set at 500℃, the heating rate is 10℃ / min, and the holding time is 4h.

[0043] Example 1:

[0044] Preparation of dice-shaped CoSe2 nanocage catalysts:

[0045] 1) Synthesis of Co-based Squaric Acid MOFs: Co metal salt Co(CH3COO)2·4H2O was dispersed in methanol, while dimethylimidazolium organic ligand, polyvinylpyrrolidone (PVP), and squaric acid were dissolved in water. The mass ratio of Co metal salt, dimethylimidazolium, PVP, and squaric acid was 4:2:4:1. The two solutions were mixed, sonicated, and allowed to stand. Then, the mixture was washed with deionized water, centrifuged, and freeze-dried to obtain a loose, dice-shaped cobalt square cage MOF precursor, such as... Figure 1 As shown.

[0046] 2) Synthesis of dice-shaped CoSe2 nanocages: NaOH, NaBH4, and Se powder were dissolved in 1L of deionized water at a mass ratio of 1:10.2:5 and mixed thoroughly to prepare Se nanocages. 2- The source solution, in which an appropriate amount of the prepared dice-shaped cobalt cage precursor is dispersed in Se during stirring. 2- The mixture was allowed to react fully in the source solution for 3 hours to form a transition metal selenide with a dice-shaped cobalt cage as the framework. It was then washed with deionized water, centrifuged, and dried in an oven at 60°C.

[0047] The reaction involves a continuous process of dissolution-reduction-precipitation. During the dissolution process, Co-based MOFs release a large amount of Co. 2+ Ions, Co 2+ Reduced to Co 4+ The process involves the formation of CoSe2. Since CoSe2 has low solubility in alkaline aqueous solutions, it precipitates, resulting in a rapid conversion rate. Furthermore, due to the restricted growth direction of the crystal structure, the generated cobalt diselenide further grows into a nanosheet structure. This produces a catalyst with a sufficiently hierarchical structure for interfacial contact, enhancing its electrochemical activity. Excess selenium powder can be removed by annealing in a tube furnace. Ultimately, a transition metal selenide catalyst with a dice-shaped cobalt cage as the basic framework and an outer shell of CoSe2 nanosheets is prepared.

[0048] 3) The CoSe2 synthesized in step 3 was placed in a quartz boat, which was then positioned in the center of a tube furnace. Annealing was performed in the tube furnace to remove excess selenium powder at 500℃ for 4 hours, with a heating rate of 10℃ / min. The final sample is shown below. Figure 2 As shown.

[0049] Comparative Example 1:

[0050] In-situ synthesis of cobalt selenide - refer to the following literature DOI: 10.1016 / j.electacta

[0051] 1) Synthesis of ZIF-67: 5.238 g of Co(NO3)2·6H2O and 3.955 g of C4H6N2 were dissolved in 200 ml of CH4O. Then, the latter solution was slowly added to the former solution under continuous stirring. The mixed solution was aged at room temperature for 24 h to obtain ZIF-67.

[0052] 2) Synthesis of MOF-CoSe2: Subsequently, the prepared purple ZIF-67 powder was transferred to an Ar-filled furnace tube and incubated at 900℃ for 10 min. -1The MOF-Co powder was obtained by annealing at a heating rate of 5 h. Finally, MOF-CoSe2 powder was prepared by in-situ selenization. A quartz boat loaded with MOF-Co powder and another loaded with excess Se powder were placed in a furnace under Ar2 flow and heated to 600℃, held for 3 h. When the furnace cooled to room temperature, a MOF-CoSe2 sample was obtained, as shown in the attached figure. Figure 3 As shown.

[0053] The MOF-CoSe2 prepared by this invention has a size of 1-2 μm, similar to the dice-shaped cobalt cage of this invention. It is a non-hollow structure with a relatively dense surface distribution, which is not conducive to mass transfer and exposure of active sites. The CoSe2 prepared by this invention uses a dice-shaped cobalt cage as the basic framework. The generated CoSe2 is stacked on the outside of the dice-shaped cobalt cage in a nanosheet structure, presenting a loose state, which fully exposes the active sites and is more conducive to improving electrochemical activity.

[0054] Comparative Example 2:

[0055] Synthesis of CoSe2 nanoparticles derived from metal-organic frameworks embedded with N-doped carbon nanosheets - Reference: DOI: 10.1021 / acsami.9b22606

[0056] 1) Preparation of Co-MOF precursor: Co-MOF nanosheets were synthesized on a conductive substrate using a simple precipitation method. Solution A was prepared by dissolving 0.02 mol of 2-methylimidazole in 50 mL of deionized water (DI). Simultaneously, solution B was prepared by adding 2.5 mmol of cobalt nitrate hexahydrate to 50 mL of DI. The two solutions were mixed and stirred continuously. Pretreated Ni foam (2 × 3 cm) was immersed in the mixed solution for 2 h and then washed with deionized water and ethanol. Finally, the sample (labeled Co-MOF-NF) was vacuum dried at 60 °C.

[0057] 2) Synthesis of binder-free CoSe2 / NC-NF electrode: A Co-MOF-NF electrode was placed downstream of a tube furnace, and a ceramic crucible containing 0.1 g of Se powder was placed upstream. The sample was then sintered at 400 °C under an argon atmosphere for 4 hours. After cooling to ambient temperature, a CoSe2 / NC-NF electrode with a mass loading of approximately 3.1 mg cm⁻¹ was obtained. –2 As attached Figure 4 As shown.

[0058] The original metal-organic framework structure of the metal-organic framework-derived CoSe2 nanoparticles with embedded N-doped carbon nanosheets prepared in this invention collapses, leaving only CoSe2 nanosheets. The original metal-organic framework prepared in this invention, with dice-shaped cobalt cages as the basic framework, is preserved after selenization by anion exchange, which is beneficial to the mass transfer effect.

[0059] The above description is only a part of the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOF, characterized in that, Includes the following steps: Step 1: Prepare dice-shaped hollow square acid Co-based MOFs using the ultrasonic static settling method; Step 2: Dissolve NaOH, NaBH4, and Se powder in deionized water and mix thoroughly to obtain Se. 2- The source mixed solution uses the dice-shaped hollow squaric acid Co-based MOF obtained in step 1 as a precursor dispersed in Se. 2- In the source mixed solution, the reaction is stirred at room temperature to form a transition metal selenide with a dice-shaped hollow cobalt cage as the framework by anion exchange method. Step 3: Anneal the product obtained in Step 2 to obtain a catalyst with a dice-shaped hollow cage structure whose surface is composed of stacked CoSe2 nanosheets. In step 2, Se 2- In the source mixed solution, the molar ratio of NaOH, NaBH4, and Se powder is 1:10.2:5; In step 3, the annealing temperature is 500℃, the holding time is 4h, and the heating rate is 10℃ / min.

2. The method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOF according to claim 1, characterized in that, In step 1, the ultrasonic static method includes the following steps: dissolving squaric acid and organic ligands in water to obtain solution A, dissolving Co metal salt in methanol to obtain solution B, mixing solution A and solution B evenly and then sonicating for 5 minutes, allowing static growth, then washing with deionized water, centrifuging and freeze-drying to obtain the dice-shaped hollow squaric acid Co-based MOF.

3. The method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOF according to claim 2, characterized in that, In step 1: the Co metal salt is Co(CH3COO)2·4H2O; the organic ligands are dimethylimidazolium and polyvinylpyrrolidone; the molar ratio of Co metal salt, dimethylimidazolium and polyvinylpyrrolidone is 2:1:2; and the mass ratio of Co metal salt to squaric acid is 4:

1.

4. The method for preparing a transition metal selenide catalyst based on cobalt squaric acid-based MOF according to claim 1, characterized in that, The obtained squaric acid Co-based MOFs have a size of 1~2 μm.

5. The transition metal selenide catalyst based on cobalt squaric acid-based MOF prepared by the preparation method according to any one of claims 1 to 4, characterized in that, The catalyst uses a dice-shaped hollow cobalt cage as a framework, with CoSe2 nanosheets stacked on the surface of the framework; the size of the dice-shaped hollow cobalt cage is 1-2 μm, and the surface has through holes that communicate with the internal hollow region.

6. The transition metal selenide catalyst based on cobalt squaric acid-based MOF according to claim 5, characterized in that, The dice-shaped hollow cobalt cage is based on a sodium salt cage structure. Each sodium salt cage structure includes 12 cobalt ions and 6 squaric acid ligands. The coordination structure composed of cobalt ions, water molecules, squaric acid ligands and PVP organic ligands constitutes the sodium salt cage structure.

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