Transition metal coordination polymer as well as preparation method and application thereof

Abstract

The invention belongs to the field of coordination polymers, and particularly relates to a novel transition metal coordination polymer, preparation thereof and application of the transition metal coordination polymer in electro-catalysis nitrate reduction. The invention provides a transition metal coordination polymer. The transition metal coordination polymer is prepared from the following raw materials: a multi-nitrogen-atom amino monomer, an anhydride-containing organic monomer and transition metal salt, wherein the multi-nitrogen atom amino monomer is 1H, 1 'H-[3, 3'-bi (1, 2, 4-triazole)]-5, 5 '-diamine. The coordination material obtained in the invention has a high metal load rate (close to full load), and shows excellent performance of electro-catalysis of nitrate reduction; under the conditions of 0.1 M of KNO3 and 0.5 M of K2SO4, the maximum reduction rate of NO3 <-> to produce NH3 is 37407.2, the maximum reduction rate of NO3 <-> to produce NH3 is 37885.7 [mu] g h-mgcat <->, and the maximum Faraday efficiencies are 97.6% and 97.2% respectively.

Description

Technical Field

[0001] The present invention belongs to the field of coordination polymers, and in particular relates to a novel transition metal coordination polymer and its preparation, as well as its application in electrocatalytic nitrate reduction. Background Art

[0002] As an important chemical raw material, NH3 is widely used in medicine, fertilizer, dye, plastic and other industries. Using green energy as the power, electrocatalytic reduction of NO3 - The reduction of NO3 to NH3 has attracted increasing attention as a sustainable complementary process for Haber-Bosch. Therefore, the rational design of new electrocatalysts with both high activity and high selectivity is crucial for the reduction of NO3 - (NO3RR), achieving large-scale applications and meeting high industrial demands are crucial.

[0003] In recent years, metal-based NO3RR electrocatalysts such as single-atom catalysts (SACs) and conjugated coordination polymers (CCPs) have attracted a lot of attention and research due to their advantages such as high energy conversion efficiency, mild operation, and good economic benefits. Generally, in order to achieve efficient catalysis, researchers design the catalytic center environment of SACs and CCPs to be a metal with four N atoms in the form of C 4v A symmetrical coordination pattern, known as the "MN4" structure, is proposed. Due to the coordination field formed by the metal center and nitrogen atoms, this arrangement can modulate the delocalized electronic environment of the metal center by optimizing the d-band center, potentially enhancing substrate activation and accelerating catalytic kinetics. However, studies have shown that this symmetrical structure reduces polarity and severely restricts the electronic configuration of the active metal site, resulting in suboptimal adsorption affinity for reaction substrates and intermediates. Therefore, exploring a method that can overcome the limitations of the MN4 structure and enhance the ability to fine-tune and adapt the catalytic environment is of great research significance for nitrate reduction electrocatalysis.

[0004] To achieve this goal, a range of coordination engineering approaches, including adjusting the type and quantity of coordination elements at the active center, doping, modulating neighboring metal interactions, and symmetry breaking, have garnered significant attention and research. Among these strategies, asymmetric coordination (symmetry breaking) is the only one that involves altering the MN4 structure itself. In principle, constructing an asymmetric coordination environment can reestablish the symmetrical electron distribution within the MN4 molecular structure and introduce a polar and variable coordination environment to the metal center, thereby promoting efficient charge carrier delocalization and enhancing the adsorption affinity for reaction substrates and intermediates, thereby improving reaction kinetics and performance.

[0005] Common approaches to achieving symmetry breaking include heteroatom substitution, axial doping with halogen atoms, and defect / disorder control. While these methods have proven effective in modulating the metal coordination environment and activating catalytic sites, they are typically performed top-down from the MN4 structure, lacking molecular design strategies. This makes it difficult to achieve the accuracy and uniformity required to construct high-performance and reproducible catalytic materials, ultimately leading to low metal loadings and random distribution of asymmetric sites.

[0006] Therefore, developing design methods to precisely construct asymmetric metal sites at the molecular level could make a significant contribution to this field but remains a challenge. Summary of the Invention

[0007] The purpose of the present invention is to propose a new type of coordination polymer prepared by a one-pot method and a molecular design strategy to construct a transition metal coordination polymer. The obtained coordination polymer has a high metal loading rate (close to full loading) and exhibits excellent electrocatalytic nitrate reduction performance.

[0008] The technical solution of the present invention:

[0009] The first technical problem to be solved by the present invention is to provide a transition metal coordination polymer, the raw materials of which include a polynitrogen atom amino monomer, an acid anhydride-containing organic monomer and a transition metal salt; wherein the polynitrogen atom amino monomer is 1H,1'H-[3,3'-bi(1,2,4-triazole)]-5,5'-diamine (BTDA).

[0010] Furthermore, the anhydride-containing organic monomer is selected from at least one of the following substances: (PMDA), (NTCDA) or perylenetetracarboxylic dianhydride (PTCDA).

[0011] Furthermore, the molar ratio of the anhydride-containing organic monomer to the polynitrogen atom amino monomer is 1:1, and the molar ratio of the polynitrogen atom amino monomer to the transition metal salt is 1:2-4.

[0012] Furthermore, the transition metal salt is selected from nitrates, sulfates or chlorides of transition metals.

[0013] Preferably, the transition metal in the transition metal salt is selected from one of cobalt, iron or copper; more preferably cobalt.

[0014] More preferably, the transition metal salt is selected from one of cobalt nitrate, iron nitrate or copper nitrate.

[0015] The second technical problem to be solved by the present invention is to provide a method for preparing the above transition metal coordination polymer, wherein the preparation method comprises: preparing the coordination polymer by reacting a polynitrogen atom amino monomer, an acid anhydride-containing organic monomer and a transition metal salt in the presence of a catalyst.

[0016] Furthermore, the catalyst is selected from at least one of pyridine and isoquinoline; more preferably pyridine.

[0017] Specifically, the transition metal coordination polymer can be prepared by the following method: a polynitrogen atom amino monomer, an acid anhydride-containing organic monomer, and a transition metal salt are dispersed in a solvent and ultrasonically treated for 5 to 120 seconds (preferably 60 seconds); a catalyst is then added, and the air in the reaction apparatus is exhausted through at least three cycles of freezing-vacuuming-thawing; the tube is then sealed with a flame gun at 600 to 1200°C; and finally, the reaction is carried out in a sealed container at 140 to 160°C (preferably 160°C) for at least 3 days, cooled to room temperature, and washed to obtain the coordination polymer.

[0018] Furthermore, the amount of the catalyst added is 1.5 ~ 3 mL / mmol BTDA .

[0019] Furthermore, the amount of the solvent added is 15 ~ 30 mL / mmol BTDA .

[0020] Furthermore, the solvent is selected from at least one of N-methylpyrrolidone (NMP) and mesitylene.

[0021] The third technical problem to be solved by the present invention is to point out the use of the above transition metal coordination polymer in electrocatalysis.

[0022] The fourth technical problem to be solved by the present invention is to provide a catalyst for electrocatalytic nitrate reduction reaction, wherein the catalyst is a transition metal coordination polymer, which is prepared by a multi-nitrogen atom amino monomer, an acid anhydride-containing organic monomer and a transition metal salt under the action of a catalyst; wherein the acid anhydride-containing organic monomer is selected from (PMDA), or: (NTCDA), the transition metal salt is selected from cobalt nitrate hexahydrate, and the polynitrogen atom amino monomer is 1H,1'H-[3,3'-bi(1,2,4-triazole)]-5,5'-diamine (BTDA).

[0023] Beneficial effects of the present invention:

[0024] The present invention provides a transition metal coordination polymer with high metal loading rate, single atomic dispersion of metal in the structure, a MN2O2 asymmetric structure of metal ion coordination environment and catalytic activity, which can be used as a catalyst for electrocatalysis, such as high-efficiency electrocatalytic nitrate reduction, which can reduce NO3 to the maximum under 0.1 M KNO3 and 0.5 M K2SO4 conditions. - The NH3 production rates were 37407.2 and 37885.7 μg h - ¹ mg cat - ¹, with maximum Faradaic efficiencies of 97.6% and 97.2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 . Schematic diagram of the reaction of the cobalt coordination polymer obtained in Example 1-2 of the present invention.

[0026] Figure 2 . Actual sample photos of the products obtained in Example 1 and Example 2 of the present invention; it can be seen from the figure that both samples are dark brown powders.

[0027] Figure 3 Infrared images of the coordination polymer samples obtained in Examples 1 and 2 of the present invention; As can be seen from the figure: in all products, the vibration peaks of the amino and anhydride COC groups disappear, and at the same time, the peaks at 1300~1400 cm -1 The vibration peaks characteristic of CNC bond formation are displayed, indicating that an imide bond is formed in the reaction. Therefore, the formation of an imide skeleton can be known from the infrared spectrum.

[0028] Figure 4 . XANES and EXAFS spectra of the coordination polymer samples obtained in Examples 1 and 2 of the present invention; the left figure shows the XANES spectrum. Compared with the spectra of the comparative examples and three standard reference materials (Co foil, Co2O3, and CoPc), the XANES curves of the two coordination polymers show similar profiles, indicating their similar local coordination geometric structures; the EXAFS spectrum of the right figure shows that both coordination polymers show a similar main peak at 1.59 Å, close to the Co-N / O peak in Co2O3 and CoPc; at the same time, both coordination polymers are free of Co-Co, showing their single-atom dispersion characteristics.

[0029] Figure 5 XPS spectra of the coordination polymer samples obtained in Examples 1 and 2 of the present invention; As can be seen from the figure: Co2p spectrum shows that Co exists in a divalent form in the embodiment, and the N1s spectrum analyzes the coordination environment of Co and N, combined with its NO3 - As a counter ion, the coordination structure of CoN2O2 was verified.

[0030] Figure 6 . EDS diagrams of the elemental distribution of the coordination polymers obtained in Examples 1 and 2 of the present invention. It can be seen from the figure that the C, N, O, and Co elements are uniformly distributed in Co-BT-BDI and Co-BT-NDI (the left figure is Example 1: Co-BT-BDI, and the right figure is Example 2: Co-BT-NDI).

[0031] Figure 7 SEM images of the morphology of the coordination polymers obtained in Examples 1 and 2 of the present invention; it can be seen from the figure that Co-BT-BDI and Co-BT-NDI exhibit a granular morphology.

[0032] Figure 8 Faradaic efficiency-potential diagrams of the coordination polymer samples obtained in Examples 1 and 2 of the present invention under 0.1 M KNO3 and 0.5 M K2SO4 conditions. The figure shows that both Co-BT-BDI and Co-BT-NDI can achieve Faradaic efficiency rates exceeding 90% at potentials between -0.6 and -0.65 V.

[0033] Figure 9 Ammonia generation rate-potential diagram of the coordination polymer samples obtained in Examples 1 and 2 of the present invention under 0.1 M KNO3 and 0.5 M K2SO4 conditions. The figure shows that both Co-BT-BDI and Co-BT-NDI can reach 37000 μg h at a potential of -0.8 V. - ¹ mg cat - Ammonia production rate above ¹. DETAILED DESCRIPTION

[0034] The present invention provides a series of transition metal coordination polymers, wherein the raw materials of the transition metal coordination polymers include: polynitrogen atom amino monomers, anhydride-containing organic monomers and transition metal salts; polynitrogen atom amino monomers BTDA ( ) itself can form coordination with transition metals such as Co(II) ions, and then undergo an imide reaction with the provided anhydride monomer, ultimately obtaining a transition metal coordination polymer generated under the synergistic action of coordination bonds and covalent bonds.

[0035] The embodiments of the present invention will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If the specific conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be purchased commercially. In the examples of the present invention, 1H, 1'H-[3,3'-bi(1,2,4-triazole)]-5,5'-diamine, acetone, mesitylene, pyridine, cobalt nitrate hexahydrate, etc. were purchased from Adamas-beta, PMDA and NTCDA, etc. were purchased from Anaiji Chemical, and DMF and NMP were purchased from General Reagent.

[0036] Example 1

[0037] In a 10 mL ampoule, BTDA (0.10 mmol), (PMDA) (0.10mmol) and CoNO3 . 6H2O (0.4 mmol) was dissolved in a NMP / mesitylene mixed solvent (2 mL, wherein the volume ratio of NMP to mesitylene was 1:1) and ultrasonicated for 3 min to fully disperse the monomer in the mixed solvent. 0.2 mL of pyridine was then added, and the ampoule, connected to a double-row tube, was immediately frozen in liquid nitrogen. After three cycles of freezing, vacuuming, and thawing, the air in the ampoule was expelled. The ampoule was then sealed with a high-temperature flame gun and placed in a 160°C oven for 3 days. After cooling to room temperature, the ampoule was removed and conventionally washed (three times each with N,N-dimethylformamide, tetrahydrofuran, and acetone), further purified by Soxhlet extraction, and dried in vacuo at 60°C to obtain the target product. This example was named Co-BT-BDI.

[0038] Example 2

[0039] The preparation process is the same as in Example 1, except that the anhydride organic monomer is changed to (NTCDA). This embodiment is named: Co-BT-NDI.

[0040] Example 1~2 Structural Characterization

[0041] 1) IR images of coordination polymer samples obtained using different anhydride monomers.

[0042] The coordination polymer samples obtained from different anhydride monomers were first placed in a vacuum oven and dried at 60 °C before infrared testing.

[0043] 2) XANES / EXAFS patterns of coordination polymer samples obtained by XAFS testing and software fitting.

[0044] XAFS measurements of the transition metal cobalt were performed at station BL17B at the Shanghai Synchrotron Radiation Facility (SSRF). The SSRF's electron storage ring operates at 3.5 GeV with a maximum current of 200 mA. Metal K-edge XAFS data were collected using a fixed-exit Si(111) double-crystal monochromator. Fluorescence signals were collected using a Wright detector, and the energy was calibrated using metal foil.

[0045] The acquired EXAFS data were analyzed using the ATHENA module of the IFEFFIT software package according to standard procedures. The EXAFS contributions from different coordination shells were separated using a Hanning window. Subsequently, quantitative curve fitting was performed in both R-space and Fourier-transformed k-space using the ARTEMIS module of IFEFFIT.

[0046] 3) SEM image of the coordination polymer sample obtained using field emission scanning electron microscopy.

[0047] Field emission scanning electron microscopy (FE-SEM) images were obtained using a thermo scientific Apreo 2C scanning electron microscope.

[0048] Application Example 1 Experiment on electrocatalytic nitrate reduction of the product obtained in Examples 1 and 2

[0049] Determination of NH3 products:

[0050] A three-electrode system was constructed at room temperature using a saturated calomel electrode (SCE) as the reference electrode, a platinum wire as the counter electrode, and 0.1 M KNO₃ and 0.5 M K₂SO₄ as the electrolyte. A working electrode was prepared by dispersing 5 mg of the catalyst powder obtained in Example 1 or Example 2 in a mixture of 0.8 mL of ethanol, 0.15 mL of deionized water, and 50 μL of Nafion solution (5 wt%). The suspension was sonicated for 30 minutes to obtain a uniform dispersion, which was then dropped onto carbon paper at a catalyst loading of 0.2 mg cm⁻¹. - Before the electrochemical measurement, the electrolyte was purged with high-purity argon for 10 minutes. The linear sweep voltammetry test was performed at 10 mV s - The scan rate was 100 nm. Electrolysis was performed at a constant potential for 30 minutes with 80% iR compensation. After electrolysis, the electrolyte was analyzed by UV-visible spectrophotometry.

[0051] Calculation of Faraday efficiency:

[0052] Electrocatalytic nitrate reduction to produce NH3 and NO2 - The Faradaic efficiency (FE) is calculated using the following formula: FE = (8 × F × C NH3 × V) / (17×Q), FE NO2- = (2 × F × C NO2- ×V) / (46×Q). The calculation formula of NH3 yield is as follows: NH3 =(C NH3 × V) / (t × mg cat ). Where F is the Faraday constant (96,485 C mol -1 ), C NH3 is the concentration of NH3, V is the volume of the cathode electrolyte, Q is the total charge, t is the reaction time, mg cat is the loading mass of the catalyst.

[0053] Table 1 is the ICP-AES table of the coordination polymer samples obtained in Examples 1 and 2 of the present invention. It can be seen from Table 1 that the Co element loading rates of Co-BT-BDI and Co-BT-NDI are close to the theoretical loading rates, showing a fully coordinated state.

[0054] Table 1

[0055] Sample number Sample mass (g) Constant volume V0 (mL) Test Elements <![CDATA[Test element concentration C0 (mg / L)]]> Dilution factor f <![CDATA[Element concentration C1 (mg / L) of digestion solution / original sample solution]]> Sample element content Cx (mg / kg) Sample element content W (%) 1 0.0727 25.00 Co 8.41 50 420.691 144666.849 14.467% 2 0.0725 25.00 Co 7.38 50 368.801 127172.809 12.717%

Claims

1. A transition metal coordination polymer, characterized in that The raw materials of the transition metal coordination polymer include a polynitrogen atom amino monomer, an acid anhydride-containing organic monomer and a transition metal salt; wherein the polynitrogen atom amino monomer is 1H,1'H-[3,3'-bi(1,2,4-triazole)]-5,5'-diamine.

2. A transition metal coordination polymer according to claim 1, characterized in that The anhydride-containing organic monomer is selected from 、 Or at least one of perylenetetracarboxylic dianhydride.

3. A transition metal coordination polymer according to claim 1 or 2, characterized in that: The molar ratio of the anhydride-containing organic monomer to the multi-nitrogen atom amino monomer is 1:

1.

4. A transition metal coordination polymer according to any one of claims 1 to 3, characterized in that: The molar ratio of the polynitrogen atom amino monomer to the transition metal salt is 1:2-4.

5. A transition metal coordination polymer according to any one of claims 1 to 4, characterized in that: The transition metal salt is selected from nitrates, sulfates or chlorides of transition metals; Furthermore, the transition metal in the transition metal salt is selected from one of cobalt, iron or copper; Furthermore, the transition metal salt is selected from one of cobalt nitrate, iron nitrate or copper nitrate.

6. The method for preparing the transition metal coordination polymer according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: preparing the coordination polymer by reacting a multi-nitrogen atom amino monomer, an acid anhydride-containing organic monomer and a transition metal salt under the action of a catalyst.

7. The method for preparing a transition metal coordination polymer according to claim 6, wherein: The catalyst is at least one of pyridine and isoquinoline.

8. The method for preparing a transition metal coordination polymer according to claim 6 or 7, characterized in that: The transition metal coordination polymer can be prepared by the following method: a polynitrogen atom amino monomer, an acid anhydride-containing organic monomer, and a transition metal salt are dispersed in a solvent and ultrasonically treated for 5 to 120 seconds; a catalyst is then added, and the air in the reaction apparatus is exhausted by a freeze-vacuum-thaw cycle at least three times; the reaction apparatus is then sealed with a flame gun at 600 to 1200°C; and the reaction is carried out in a sealed container at 140 to 160°C for at least 3 days, cooled to room temperature, and washed to obtain the coordination polymer. Furthermore, the solvent is selected from at least one of N-methylpyrrolidone and mesitylene.

9. Use of the transition metal coordination polymer according to any one of claims 1 to 5 in an electrocatalytic catalyst.

10. A catalyst for electrocatalytic nitrate reduction reaction, characterized in that: The catalyst is a transition metal coordination polymer, wherein the transition metal coordination polymer is prepared by a multi-nitrogen atom amino monomer, an acid anhydride-containing organic monomer and a transition metal salt under the action of a catalyst; wherein the acid anhydride-containing organic monomer is selected from or , the transition metal salt is selected from cobalt nitrate hexahydrate, and the polynitrogen atom amino monomer is 1H,1'H-[3,3'-bi(1,2,4-triazole)]-5,5'-diamine; Furthermore, the molar ratio of the anhydride-containing organic monomer to the polynitrogen atom amino monomer is 1:1; and the molar ratio of the polynitrogen atom amino monomer to the transition metal salt is 1:2-4.

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