A zif-8 derived metal monatomic solvent and a preparation method thereof
The method of preparing single-atom metal solvents derived from ZIF-8 has solved the problems of dispersion and stability of single-atom catalysts in liquid-phase reaction systems, achieving high catalytic activity and colloidal stability, which is suitable for energy, catalysis and sensing fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XI AN JIAOTONG UNIV
- Filing Date
- 2026-02-10
- Publication Date
- 2026-06-02
AI Technical Summary
In existing technologies, single-atom catalysts are unevenly dispersed in liquid-phase reaction systems, have limited mass transfer, and are cumbersome to separate and recover. Furthermore, solid powdered single-atom catalysts are prone to agglomeration in batch or continuous flow reactions, have uneven accessibility of active sites, and are inconvenient to operate and measure.
M-ZIF-8 was synthesized using a ZIF-8-derived metal single-atom solvent preparation method via co-precipitation of zinc nitrate and target metal salt. Subsequently, it was carbonized under an inert atmosphere to form a nitrogen-doped carbon material with a hierarchical porous structure. The material was then dispersed in a solvent using a periodic thermal stress pulverization method to form a highly stable and homogeneous liquid product.
It achieves high dispersion and stability of metal single atoms in liquid catalysts, solves the problems of uneven dispersion and cumbersome operation, and provides high efficiency of catalytic activity and colloidal stability, which is suitable for energy, catalysis and sensing fields.
Smart Images
Figure CN122124834A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of advanced nanocatalytic materials and their formulations, specifically a ZIF-8 derived metal single-atom solvent and its preparation method. Background Technology
[0002] Single-atom catalysts have attracted widespread attention due to their extreme atomic utilization and unique catalytic performance. However, their industrial application faces two major challenges: first, how to achieve universal and highly stable preparation of single-atom catalysts from different metals; and second, how to solve engineering problems such as uneven dispersion, limited mass transfer, and cumbersome separation and recovery of solid powder catalysts in actual liquid-phase reaction systems.
[0003] Metal-organic frameworks (MOFs) are excellent precursors for constructing single-atom catalysts. Among them, ZIF-8, a zeolite imidazole ester framework formed by the coordination of zinc ions and 2-methylimidazolium, has become a star template for preparing single-atom catalysts because the zinc component can volatilize during pyrolysis, leaving a porous carbon framework rich in nitrogen defects. Existing technologies mostly focus on preparing solid powdered single-atom catalysts using ZIF-8, but this form still suffers from inherent drawbacks when applied to batch or continuous flow reactions, such as easy catalyst agglomeration, uneven accessibility of active sites, and inconvenient metering. Pre-preparing high-performance single-atom catalysts into a homogeneous, stable, and directly meterable liquid form—i.e., a "single-atom solvent"—is an ideal solution to overcome the above-mentioned engineering application bottlenecks. Currently, no method has been reported for systematically preparing such single-atom solvent products based on the ZIF-8 template. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing ZIF-8 derived metal single-atom solvents, which solves the problems of poor uniformity and stability of single-atom solvent products prepared in the prior art.
[0005] The present invention also provides a ZIF-8 derived metal single-atom solvent to solve the problems of poor uniformity and stability of single-atom solvent products in the prior art.
[0006] To address the aforementioned problems, this invention proposes a method for preparing a ZIF-8 derived metal single-atom solvent. The technical solution employed is as follows: A method for preparing a ZIF-8 derived metal single-atom solvent includes the following steps: Step 1: Dissolve zinc nitrate and the target metal salt M together in the first solvent to form a precursor solution; Step 2: After adding 2-methylimidazole solution to the precursor solution to carry out the precipitation reaction, the M-ZIF-8 precursor is obtained by solid-liquid separation and drying. Step 3: The M-ZIF-8 precursor is carbonized in an inert atmosphere to obtain a nitrogen-doped carbon solid material with a porous structure supported by a single metal atom. Step 4: Disperse the nitrogen-doped carbon solid material with porous structure supported by metal single atoms in a second solvent by periodic thermal stress crushing dispersion method to obtain ZIF-8 derived metal single atom solvent.
[0007] The beneficial effects of this invention are as follows: This invention uses zinc nitrate and the target metal salt as a bimetallic source, and 2-methylimidazole in a 2-methylimidazole solution as an organic ligand and nitrogen source to synthesize a metal-doped zeolite imidazole ester framework material (M-ZIF-8) in one step via precipitation, allowing the target metal ions to be introduced in situ during the nucleation and growth of ZIF-8 crystals. Subsequently, carbonization is carried out under an inert atmosphere to transform the ZIF-8 framework in the M-ZIF-8 precursor into nitrogen-doped carbon with a hierarchical porous structure. By utilizing the selective volatilization of zinc nitrate during carbonization and the in-situ coordination between the target metal and the nitrogen-rich carbon framework, a solid catalytic material in which the target metal is highly dispersed in the form of single atoms in a high specific surface area, nitrogen-rich carbon matrix is obtained, which is beneficial to the full contact between the reactants and the single-atom active sites. Finally, the obtained nitrogen-doped carbon solid material loaded with metal single atoms is dispersed in a second solvent by a periodic thermal stress pulverization dispersion method to form a highly stable and homogeneous metal single-atom solvent. This invention transforms high-performance single-atom catalysts into liquid products, solving problems such as uneven dispersion and cumbersome processing associated with solid catalysts. This invention provides a general and controllable preparation method for single-atom catalysts derived from zeolite imidazole ester framework materials and their liquid formulations. Specifically, it describes a method for preparing nitrogen-doped carbon-supported metal single-atom solid materials using ZIF-8 as a template through co-precipitation doping and controllable carbonization, and further converting these materials into stable single-atom solvents. The ZIF-8-derived metal single-atom solvents prepared by this invention possess excellent colloidal stability and catalytic activity, and can be used directly as reaction media or catalyst additives, showing broad application prospects in energy, catalysis, and sensing fields.
[0008] To obtain stable and diverse single-atom metal solvents, preferably, the target metal salt is a compound containing at least one metal element selected from platinum, palladium, ruthenium, nickel, copper, cobalt, zirconium, or cerium.
[0009] Preferably, the target metal salt includes at least one of cobalt nitrate hexahydrate, chloroplatinic acid, copper nitrate trihydrate, and cerium nitrate hexahydrate.
[0010] In order to precisely control the metal loading in the final metal single-atom solvent and improve the stability of the metal single-atom solvent, preferably, the mass ratio of zinc nitrate to the target metal salt is 1:(0.01-0.04); and the mass ratio of zinc nitrate to 2-methylimidazole in the 2-methylimidazole solution is 1:(1-1.1).
[0011] In order to obtain a carbon support while maintaining the stability of the metal single atoms to the greatest extent, preferably, the heating rate of the carbonization treatment is 3-5℃ / min, the temperature is 800-900℃, and the time is 2-3h.
[0012] To obtain a homogeneous precursor solution, preferably, the first solvent is selected from methanol, ethanol, or N,N-dimethylformamide, and the volume of the first solvent is 30-40 mL.
[0013] In order to ensure sufficient dispersion of the nitrogen-doped carbon solid material supported by metal single atoms, preferably, the second solvent includes at least one of methanol, ethanol, isopropanol, water, N-methylpyrrolidone, N,N-dimethylformamide or dimethyl sulfoxide, and the volume of the second solvent is 5-10 ml.
[0014] Preferably, the dispersion method of periodic thermal stress pulverization includes the following steps: A porous, single-atom-loaded nitrogen-doped carbon solid material is added to a second solvent and then subjected to a cyclic process of rapid heating and low-temperature cooling. This disperses the porous, single-atom-loaded nitrogen-doped carbon solid material in the second solvent, with a dispersion concentration of 0.5-50 mg / mL. The core of this cyclic thermal stress pulverization dispersion method is to utilize the internal stress caused by the difference in thermal expansion coefficients between the material and the solvent to break up hard agglomerates. Specifically, when the agglomerates of porous, single-atom-loaded nitrogen-doped carbon solid material are rapidly heated with the second solvent, the components undergo differential volume expansion due to their different thermal expansion coefficients, generating shear stress at the contact interfaces of the particles within the agglomerates. Subsequently, when the above system is rapidly cooled (thermal shock), the sharp contraction of each component will again generate reverse tensile stress at the interface; through periodic and intense thermal expansion and contraction cycles, the stress continuously concentrates and releases at the weak parts of the agglomerates (such as particle junctions), ultimately leading to fatigue fracture and breakage of the agglomerates from the inside. This results in highly dispersed nitrogen-doped carbon solid materials supported by metal single atoms, and allows the obtained ZIF-8-derived metal single-atom solvent to be stored for a long time without sedimentation. This process relies entirely on the physical stress induced by heat transfer, without introducing any chemical impurities or mechanical wear. By designing controllable thermal shock cycles, the ubiquitous thermal expansion phenomenon is transformed into a highly efficient and clean "physical pulverizer," solving the key dispersion problem in the post-processing of ZIF-8-derived carbon materials. It is applicable to all solvents from water to DMSO, demonstrating extremely high versatility.
[0015] More preferably, the dispersion concentration of the nitrogen-doped carbon solid material supported by a metal single atom with a porous structure in the second solvent is 1-20 mg / mL.
[0016] To improve the efficiency of highly dispersed nitrogen-doped carbon solid materials supported by metal single atoms, preferably, the rapid heating temperature is 80-100°C and the time is 3-10 min; the low-temperature cooling temperature is -10 to -15°C and the time is 3-10 min.
[0017] Preferably, the method for preparing the 2-methylimidazole solution includes the following steps: dissolving 2-methylimidazole in a first solvent to obtain a 2-methylimidazole solution; The mass ratio of 2-methylimidazole to the volume of the first solvent is 1.232 g: 30 ml.
[0018] This invention also proposes a ZIF-8 derived metal single-atom solvent, the technical solution of which is as follows: A ZIF-8 derived metal single-atom solvent is prepared by the above-mentioned method for preparing ZIF-8 derived metal single-atom solvents.
[0019] The beneficial effects of the present invention are as follows: The ZIF-8 derived metal single-atom solvent of the present invention comprises a second solvent and nitrogen-doped carbon solid material particles uniformly dispersed therein, supported by metal single atoms; wherein, the metal active centers in the nitrogen-doped carbon solid material particles supported by metal single atoms are dispersed in the nitrogen-doped carbon substrate in the form of single atoms, and the metal active centers and the carrier nitrogen atoms mainly form an M-N4 coordination structure, the metal is atomically dispersed, and the entire liquid system has excellent colloidal stability. Attached Figure Description
[0020] Figure 1 This is the XRD pattern of the crystal structure of Co-SAS / ZIF-8 prepared in Example 1 of this invention.
[0021] Figure 2 This is a SEM image of Co-SAS / ZIF-8 prepared in Example 1 of this invention.
[0022] Figure 3 The Co K-edge XANES spectra of Co-SAS / ZIF-8 prepared in Example 1 of this invention with Co foil, CoO and Co3O4 are shown.
[0023] Figure 4 The Fourier transform spectrum of the k³ weighted EXAFS signal of Co-SAS / ZIF-8 prepared in Example 1 of this invention with Co foil, CoO and Co3O4 is shown.
[0024] Figure 5 The results are the weak external absorption spectrum fitting results of Co-SAS / ZIF-8 prepared in Example 1 of this invention; where (a) is k-space and (b) is R-space.
[0025] Figure 6 These are contour plots of the weak cobalt K-edge external absorption spectra of Co-SAS / ZIF-8, Co foil, CoO, and Co3O4 prepared in Example 1 of this invention; wherein, (a) Co foil, (b) CoO, (c) Co3O4, and (d) Co-SAS / ZIF-8.
[0026] Figure 7 This is a sample image of the Co-SAS / ZIF-8 / EtOH single-atom solvent prepared in Example 1 of this invention. Detailed Implementation
[0027] Existing technologies produce single-atom solvent products with poor uniformity and stability. This invention proposes a method for preparing a ZIF-8 derived metal single-atom solvent, comprising the following steps: Step 1: Dissolve zinc nitrate and the target metal salt M together in the first solvent to form a precursor solution; Step 2: After adding 2-methylimidazole solution to the precursor solution, the mixture is precipitated and dried to obtain the M-ZIF-8 precursor. Step 3: The M-ZIF-8 precursor is carbonized in an inert atmosphere to obtain a nitrogen-doped carbon solid material with a porous structure supported by a single metal atom. Step 4: Disperse the nitrogen-doped carbon solid material with porous structure supported by metal single atoms in a second solvent by periodic thermal stress crushing dispersion method to obtain ZIF-8 derived metal single atom solvent.
[0028] The technical concept of this invention is as follows: First, zinc nitrate is blended with a target metal salt to form a precursor solution; wherein, zinc nitrate and the target metal salt serve as bimetallic sources; then, a 2-methylimidazole solution is added to the precursor solution, and a metal-doped zeolite imidazole ester framework material (M-ZIF-8) is synthesized in one step via precipitation, allowing the target metal ions to be introduced in situ during the nucleation and growth of ZIF-8 crystals; wherein, 2-methylimidazole in the 2-methylimidazole solution serves as both an organic ligand and a nitrogen source; subsequently, the M-ZIF-8 precursor is carbonized under an inert atmosphere, transforming the organic ligands in the ZIF-8 framework into a nitrogen-doped carbon network, causing zinc nitrate to volatilize and creating abundant nitrogen anchoring sites; simultaneously, the pre-doped... In this dynamic process, target metal ions are effectively captured, reduced, and anchored into stable single-atom states, resulting in nitrogen-doped carbon solid materials supported by metal single atoms with porous structures. Finally, the nitrogen-doped carbon solid materials supported by metal single atoms with porous structures are dispersed in a second solvent through a periodic thermal stress pulverization dispersion method, transforming the solid catalyst into an easy-to-use liquid product form, forming a highly stable and homogeneous ZIF-8-derived metal single-atom solvent. Among these methods, the periodic thermal stress pulverization dispersion method creatively uses the development and application of thermal stress as the core mechanism for dispersing hard agglomerates. By designing controllable thermal shock cycles, the ubiquitous thermal expansion phenomenon is transformed into a highly efficient and clean "physical pulverizer." The ZIF-8 derived metal single-atom solvent of this invention comprises a second solvent and nitrogen-doped carbon solid material particles with porous structures supported by metal single atoms, uniformly dispersed therein. The metal active centers in the nitrogen-doped carbon solid material particles with porous structures are dispersed in the nitrogen-doped carbon substrate in single-atom form, and the metal active centers and the carrier nitrogen atoms mainly form an M-N4 coordination structure. The metal is atomically dispersed, and the entire liquid system exhibits excellent colloidal stability. The preparation method of the ZIF-8 derived metal single-atom solvent of this invention is mild, simple, and highly versatile, providing a general solution for the large-scale and controllable preparation of various metal single-atom solvents such as platinum, palladium, ruthenium, nickel, copper, cobalt, zirconium, and cerium. Specifically, such as Figure 1 As shown, the preparation method of ZIF-8 derived metal single-atom solvent includes the following steps: First, the synthesis of the M-ZIF-8 precursor: zinc nitrate hexahydrate and the target metal salt are dissolved together in a first solvent and magnetically stirred for 30 min to form a homogeneous solution (solution A); wherein the mass ratio of zinc nitrate to the target metal salt is 1:(0.01-0.04); wherein the target metal salt is a compound containing at least one metal element selected from platinum, palladium, ruthenium, nickel, copper, cobalt, zirconium or cerium; Then, 2-methylimidazole was dissolved in 30-40 ml of the first solvent to form a homogeneous solution (solution B). At the same time, solution B was quickly poured into solution A under vigorous stirring. The reaction was continued at room temperature for 2-12 h. After the reaction was completed, the precipitate was collected by centrifugation, washed three times with methanol, and dried under vacuum to obtain the metal-doped zeolite imidazole ester framework material, denoted as M-ZIF-8 precursor. Next, solid materials were prepared by carbonization: the M-ZIF-8 precursor was placed in a tube furnace and heated to 800-900℃ at 3-5℃ / min under a nitrogen atmosphere. The temperature was maintained for carbonization for 2-3 hours. After natural cooling, solid powder was obtained. After grinding, nitrogen-doped carbon solid material with porous structure and supported by metal single atoms was obtained. Finally, the preparation of the single-atom solvent: The nitrogen-doped carbon solid material supported by the metal single atom with the above porous structure was added to 5-10 mL of the second solvent, and a uniform ZIF-8-derived metal single-atom solvent was obtained by cyclically performing rapid heating and low-temperature cooling 3-5 times in sequence; wherein, the rapid heating temperature was 80-100°C and the time was 3-10 min; the low-temperature cooling temperature was -10 to -15°C and the time was 3-10 min.
[0029] Specifically, the first solvent is selected from methanol, ethanol, or N,N-dimethylformamide.
[0030] Specifically, the second solvent includes at least one of methanol, ethanol, isopropanol, water, N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide.
[0031] The implementation process of the present invention will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments. It should be noted that the endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0032] In the following examples, all raw materials used are common commercially available products that can be purchased directly or can be prepared using conventional techniques in the art.
[0033] I. Examples of the preparation method of the ZIF-8 derived metal single-atom solvent of the present invention Example 1 The preparation method of the cobalt single-atom solvent (Co-SAS / ZIF-8 / EtOH) provided in this embodiment includes the following steps: First, the synthesis of the M-ZIF-8 precursor: Weigh 1.16 g of zinc nitrate hexahydrate and 0.029 g of cobalt nitrate hexahydrate, dissolve them together in 30 mL of methanol, and stir magnetically for 30 min to form a homogeneous solution (solution A). Then, 1.232 g of 2-methylimidazole was weighed and dissolved in 30 mL of methanol to form a homogeneous solution (solution B). At the same time, solution B was quickly poured into solution A under vigorous stirring. The reaction was continued to be stirred at room temperature for 6 hours. After the reaction was completed, the precipitate was collected by centrifugation, washed three times with methanol, and dried under vacuum at 70 °C for 12 hours to obtain a light purple powdery Co-ZIF-8 precursor. Next, solid materials were prepared by carbonization: 0.5 g of Co-ZIF-8 precursor was weighed and placed in a tube furnace. The temperature was raised to 800°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours. After natural cooling, black solid powder was obtained. After grinding, nitrogen-doped carbon solid material with porous structure and supported by metal single atoms was obtained, which was denoted as Co-SAS / ZIF-8 (solid). Finally, the preparation of the single-atom solvent: Weigh 100.0 mg of the above Co-SAS / ZIF-8 solid powder, place it in a sample bottle, add 10.00 mL of anhydrous ethanol, first rapidly heat at 80℃ for 10 min, then cool at -10℃ for 10 min, repeat the rapid heating and low-temperature cooling 3 times, so that the nitrogen-doped carbon solid material with porous structure supported by metal single atoms is dispersed in anhydrous ethanol, and a uniform ZIF-8 derived cobalt single-atom solvent is obtained.
[0034] Example 2 The preparation method of platinum single-atom solvent (Pt-SAS / ZIF-8 / NMP) provided in this embodiment includes the following steps: First, the synthesis of the M-ZIF-8 precursor: 1.16 g of zinc nitrate hexahydrate and 0.018 g of chloroplatinic acid were weighed and dissolved together in 30 mL of methanol. The mixture was magnetically stirred for 30 min to form a homogeneous solution (solution A). Then, 1.232 g of 2-methylimidazole was weighed and dissolved in 30 mL of methanol to form a homogeneous solution (solution B). At the same time, solution B was quickly poured into solution A under vigorous stirring. The reaction was continued to be stirred at room temperature for 6 hours. After the reaction was completed, the precipitate was collected by centrifugation, washed three times with methanol, and dried under vacuum at 70 °C for 12 hours to obtain a white powdery Pt-ZIF-8 precursor. Next, solid materials were prepared by carbonization: 0.5 g of Pt-ZIF-8 precursor was weighed and placed in a tube furnace. The temperature was increased to 900°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours. After natural cooling, solid powder was obtained. After grinding, nitrogen-doped carbon solid material with porous structure and supported by metal single atoms was obtained, denoted as Pt-SAS / ZIF-8 (solid).
[0035] Finally, the preparation of the single-atom solvent: 60.0 mg of the above Pt-SAS / ZIF-8 solid powder was weighed and dispersed in 8.00 mL of N-methylpyrrolidone. The mixture was first rapidly heated at 100 °C for 3 min, and then cooled at -15 °C for 3 min. The rapid heating and low-temperature cooling were repeated 5 times to disperse the nitrogen-doped carbon solid material with porous metal single atoms in N-methylpyrrolidone, resulting in a uniform black dispersion, which is the ZIF-8 derived platinum single-atom solvent.
[0036] Example 3 The preparation method of the copper single-atom solvent (Cu-SAS / ZIF-8 / DMF) provided in this embodiment includes the following steps: First, the synthesis of the M-ZIF-8 precursor: Weigh 1.16 g of zinc nitrate hexahydrate and 0.024 g of copper nitrate trihydrate, dissolve them together in 30 mL of methanol, and stir magnetically for 30 min to form a homogeneous solution (solution A). Then, 1.232 g of 2-methylimidazole was weighed and dissolved in 30 mL of methanol to form a homogeneous solution (solution B). At the same time, solution B was quickly poured into solution A under vigorous stirring. The reaction was continued to be stirred at room temperature for 6 hours. After the reaction was completed, the precipitate was collected by centrifugation, washed three times with methanol, and dried under vacuum at 70 °C for 12 hours to obtain a blue powder Cu-ZIF-8 precursor. Next, solid materials were prepared by carbonization: 0.5 g of Cu-ZIF-8 precursor was weighed and placed in a tube furnace. The temperature was increased to 900°C at 5°C / min under a nitrogen atmosphere and carbonized for 2 hours. After natural cooling, solid powder was obtained. After grinding, nitrogen-doped carbon solid material with porous structure and supported by metal single atoms was obtained, denoted as Cu-SAS / ZIF-8 (solid).
[0037] Finally, the preparation of the single-atom solvent: 40.0 mg of the above Cu-SAS / ZIF-8 solid powder was weighed and dispersed in 5.00 mL of N-methylpyrrolidone. The mixture was first rapidly heated at 60 °C for 8 min, and then cooled at -12 °C for 8 min. The rapid heating and low-temperature cooling were repeated 4 times to disperse the nitrogen-doped carbon solid material with porous metal single atoms in N-methylpyrrolidone, thus obtaining a uniform ZIF-8-derived copper single-atom solvent.
[0038] Example 4 The preparation method of the cerium single-atom solvent (Ce-SAS / ZIF-8 / DMSO) provided in this embodiment includes the following steps: First, the synthesis of the M-ZIF-8 precursor: 1.16 g of zinc nitrate hexahydrate and 0.043 g of cerium nitrate hexahydrate were weighed and dissolved together in 30 mL of methanol. The mixture was magnetically stirred for 30 min to form a homogeneous solution (solution A). Then, 1.232 g of 2-methylimidazole was weighed and dissolved in 30 mL of methanol to form a homogeneous solution (solution B). At the same time, under vigorous stirring, solution B was quickly poured into solution A. The reaction was continued to be stirred at room temperature for 6 hours. After the reaction was completed, the precipitate was collected by centrifugation, washed three times with methanol, and dried under vacuum at 70 °C for 12 hours to obtain a white and slightly yellow powder Ce-ZIF-8 precursor. Next, solid materials were prepared by carbonization: 0.5 g of Ce-ZIF-8 precursor was weighed and placed in a tube furnace. The temperature was increased to 850°C at 3°C / min under a nitrogen atmosphere and carbonized for 3 hours. After natural cooling, solid powder was obtained. After grinding, nitrogen-doped carbon solid material with porous structure and supported by metal single atoms was obtained, denoted as Ce-SAS / ZIF-8 (solid).
[0039] Finally, the preparation of the single-atom solvent: 80.0 mg of the above Ce-SAS / ZIF-8 solid powder was weighed and dispersed in 10.00 mL of dimethyl sulfoxide. The mixture was first rapidly heated at 60 °C for 8 min, and then cooled at -12 °C for 8 min. The rapid heating and low-temperature cooling were repeated 4 times to disperse the nitrogen-doped carbon solid material with porous metal single atoms in dimethyl sulfoxide, thus obtaining a uniform ZIF-8-derived cerium single-atom solvent.
[0040] II. Experimental Examples Experimental Example 1: XRD Characterization The crystal structure of Co-SAS / ZIF-8 prepared in Example 1 was characterized by XRD, and the obtained spectrum is shown below. Figure 1 As shown, three broadened diffraction peaks were observed at approximately 13°, 26°, and 43°, corresponding to the (100), (002), and (101) planes of graphitized carbon, respectively. No diffraction signals of any elemental or compound cobalt phase were found. This diffraction characteristic is consistent with the typical structure of a single-atom catalyst, indicating that metallic cobalt was highly dispersed during the carbonization process.
[0041] Experimental Example 2: Microscopic Morphology The microstructure of Co-SAS / ZIF-8 obtained in Example 1 was characterized. Specifically, scanning electron microscopy (SEM) images were used to characterize the microstructure of Co-SAS / ZIF-8, such as... Figure 2 As shown, the Co-SAS / ZIF-8 sample is composed of a large number of polyhedral particles, and its overall morphology still partially retains the rhombic dodecahedral characteristics of the ZIF-8 precursor. The particle surfaces are rough, with obvious mesopores and microcracks. This hierarchical porous structure is beneficial for increasing the specific surface area of the material and promoting full contact between the reactants and the dispersed single-atom active sites.
[0042] Experimental Example 3: Electronic Structure and Coordination Environment of the Cobalt Active Center in Co-SAS / ZIF-8 The electronic structure and coordination environment of the cobalt active centers in the Co-SAS / ZIF-8 sample obtained in Example 1 were analyzed compared with those in the reference samples (Co foil, CoO, and Co3O4). The analysis method was as follows: Co K-edge X-ray absorption spectra of the samples were acquired in fluorescence mode under synchrotron radiation, and real-time energy calibration was performed using metallic cobalt foil to obtain the Co K-edge XANES spectra of Co-SAS / ZIF-8, Co foil, CoO, and Co3O4, as shown in the figure. Figure 3 As shown, the absorption edge position of Co-SAS / ZIF-8 is close to that of CoO and Co3O4, indicating that the average oxidation state of cobalt is between +2 and +3, closer to +2. This confirms that cobalt species exist mainly in the higher oxidation state in the support and there is obvious charge transfer between them and nitrogen ligands.
[0043] Further analysis of its local structure was performed using EXAFS. Specifically, the k³-weighted EXAFS oscillation signal was subjected to Fourier transform to obtain the Fourier transform spectra of the k³-weighted EXAFS signals of Co-SAS / ZIF-8, Co foil, CoO, and Co3O4. For example... Figure 4As shown, it can be concluded that in the Fourier transform spectrum of the k³-weighted EXAFS signal of Co-SAS / ZIF-8, a dominant peak appears at about 1.62 Å, which can be attributed to the Co–N coordination shell. However, no scattering peak corresponding to the Co–Co metallic bond is observed near about 2.17 Å, indicating that cobalt exists in the form of atomically dispersed single atoms and has not formed metal particles or clusters.
[0044] The weak external absorption spectrum of Co-SAS / ZIF-8 was fitted based on EXAFS data. Specifically, least-squares curve fitting was performed based on the FEFF theoretical model to obtain the precise coordination parameters of the cobalt center in Co-SAS / ZIF-8, such as... Figure 5 As shown, each cobalt atom is coordinated to approximately four nitrogen atoms on average (CN ≈ 4), and the average Co–N bond length is 1.93 Å. This configuration is consistent with the typical planar tetragonal M–N4 structure. This well-defined structural model provides a crucial structural basis for the high activity and selectivity exhibited by the Co-SAS / ZIF-8 catalyst in the reaction.
[0045] To further verify the above conclusions, wavelet transform analysis was performed on the cobalt K-edge of Co-SAS / ZIF-8 and reference samples Co foil, CoO, and Co3O4. Specifically, a continuous wavelet transform was performed on the k³-weighted EXAFS signal, as shown below. Figure 6 As shown, it can be concluded that the signal distribution of Co-SAS / ZIF-8 in K space and R space is significantly different from that of Co foil, CoO and Co3O4, reflecting characteristics related to the nitrogen-coordinated single-atom structure.
[0046] Experimental Example 4: Dispersibility of Co-SAS / ZIF-8 / EtOH Single-Atom Solvent The Co-SAS / ZIF-8 / EtOH single-atom solvent sample was left to stand at 25℃ for 72 hours. Figure 7 As shown, the Co-SAS / ZIF-8 / EtOH single-atom solvent still exhibits good dispersion stability, with no sedimentation or aggregation.
[0047] This demonstrates that the preparation method of the ZIF-8 derived metal single-atom solvent of the present invention is mild, simple, and highly universal, providing a general solution for the large-scale and controllable preparation of various metal single-atom solvents such as platinum, palladium, ruthenium, nickel, copper, cobalt, zirconium, and cerium. The ZIF-8 derived metal single-atom solvent prepared by the method provided in this application comprises a second solvent and uniformly dispersed nitrogen-doped carbon solid material particles supported by metal single atoms. The metal active centers in the nitrogen-doped carbon solid material particles are dispersed in the nitrogen-doped carbon substrate in single-atom form, and the metal active centers and the carrier nitrogen atoms mainly form an M-N4 coordination structure. The metal is atomically dispersed, and the entire liquid system exhibits excellent colloidal stability.
[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.
Claims
1. A method for preparing a ZIF-8 derived metal single-atom solvent, characterized in that, Includes the following steps: Step 1: Dissolve zinc nitrate and the target metal salt M together in the first solvent to form a precursor solution; Step 2: After adding 2-methylimidazole solution to the precursor solution to carry out the precipitation reaction, the M-ZIF-8 precursor is obtained by solid-liquid separation and drying. Step 3: The M-ZIF-8 precursor is carbonized in an inert atmosphere to obtain a nitrogen-doped carbon solid material with a porous structure supported by a single metal atom. Step 4: Disperse the nitrogen-doped carbon solid material with porous structure supported by metal single atoms in a second solvent by periodic thermal stress crushing dispersion method to obtain ZIF-8 derived metal single atom solvent.
2. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 1, characterized in that, The target metal salt is a compound containing at least one metallic element selected from platinum, palladium, ruthenium, nickel, copper, cobalt, zirconium, or cerium.
3. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 2, characterized in that, The target metal salt includes at least one of cobalt nitrate hexahydrate, chloroplatinic acid, copper nitrate trihydrate, and cerium nitrate hexahydrate.
4. The method for preparing the ZIF-8 derived metal single-atom solvent according to any one of claims 1-3, characterized in that, The mass ratio of zinc nitrate to the target metal salt is 1:(0.01-0.04); the mass ratio of zinc nitrate to 2-methylimidazole in the 2-methylimidazole solution is 1:(1-1.1).
5. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 1, characterized in that, The heating rate of the carbonization process is 3-5℃ / min, the temperature is 800-900℃, and the time is 2-3h.
6. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 1, characterized in that, The first solvent is selected from methanol, ethanol or N,N-dimethylformamide, and the volume of the first solvent is 30-40 mL.
7. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 1, characterized in that, The second solvent includes at least one of methanol, ethanol, isopropanol, water, N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide, and the volume of the second solvent is 5-10 mL.
8. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 1, characterized in that, The dispersion method of periodic thermal stress pulverization includes the following steps: A nitrogen-doped carbon solid material supported by a metal single atom with a porous structure is added to a second solvent and then subjected to a periodic cycle of rapid heating and low-temperature cooling, so that the nitrogen-doped carbon solid material supported by a metal single atom with a porous structure is dispersed in the second solvent; wherein, the dispersion concentration of the nitrogen-doped carbon solid material supported by a metal single atom with a porous structure in the second solvent is 0.5-50 mg / mL.
9. The method for preparing the ZIF-8 derived metal single-atom solvent according to claim 8, characterized in that, The rapid heating temperature is 80–100°C, and the time is 3–10 min; the low-temperature cooling temperature is -10–-15°C, and the time is 3–10 min.
10. A ZIF-8 derived metal single-atom solvent, characterized in that, It is prepared by the method for preparing ZIF-8 derived metal single-atom solvent as described in any one of claims 1 to 9.