Co (II)-based coordination polymer photoelectrode crystalline material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photoelectrocatalysis, in particular to a Co (II) coordination polymer photoelectrode crystalline material and a preparation method and application thereof. The Co (II) coordination polymer {[Co (H2O) (Br-BDC) (BMIP)]. H2O} n is obtained from organic ligands BMIP, H2 (Br-BDC) and cobalt salt through a solvothermal method, cobalt (II) ions serve as three connection nodes, BMIP and H2 (Br-BDC) ligands serve as bridging ligands to be in mutual bridging, a two-dimensional honeycomb structure is formed, and a three-dimensional supramolecular structure is formed between layers through intermolecular hydrogen-bond interaction and pi-pi stacking. Wherein H2 (Br-BDC) is 2, 5-dibromoterephthalic acid, BMIP is 1, 3-bis (dimethylimidazolyl) propane, and n is a positive integer. The Co (II) coordination polymer shows relatively good photoelectric property, has the potential of serving as a photoelectrode material, has good optical and electrical characteristics, can be used for constructing an efficient photoelectrocatalysis water decomposition system, and has an application prospect in the aspects of photoelectric hydrolysis water oxidation and the like.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalysis technology, and particularly relates to a Co(II) coordination polymer photoelectrode crystalline material, its preparation method, and its application. Background Technology

[0002] The continued growth in global energy demand and the environmental problems caused by fossil fuel consumption have prompted humanity to urgently seek clean and sustainable alternative energy sources. Solar energy, as a widely distributed and massive renewable energy source, is a key pathway to solving future energy problems through efficient capture and conversion. Among numerous solar energy conversion technologies, photoelectrochemical (PEC) water splitting technology, which can directly convert solar energy into hydrogen energy, is considered one of the most promising solutions. The core of this technology lies in developing efficient, stable, and low-cost photoelectrode materials to drive photogenerated charges to participate in the redox reaction of water.

[0003] Traditional photoelectrode materials (such as metal oxides like TiO2, WO3, and BiVO4) have been extensively studied, but they still face inherent bottlenecks such as narrow light absorption range, low charge separation efficiency, and slow carrier mobility. In recent years, crystalline coordination polymers (CPs), including metal-organic frameworks (MOFs) and coordination polymer networks, have provided revolutionary new ideas for the design of photoelectrode materials due to their tunable composition, high specific surface area, well-defined and ordered pore structure, and designable active sites. Compared with disordered or amorphous materials, the long-range ordered structure of crystalline CPs facilitates the directional migration of photogenerated carriers and reduces recombination losses, thus potentially significantly improving photoelectric conversion efficiency.

[0004] Among many metallic centers, cobalt (Co) ions have attracted much attention due to their unique electronic structure. 2+ / Co 3+ Redox couples possess excellent electrochemical activity and relatively suitable energy level positions, making them highly efficient catalytic centers for the water oxidation reaction (OER). Introducing Co ions into a coordination polymer framework to construct Co-based crystalline photoelectrode materials cleverly integrates three major functions: light absorption, charge separation, and catalytic conversion. The organic ligands act as photosensitive antennas, effectively capturing visible light; the highly ordered crystalline framework provides a "highway" for rapid charge transport; and the Co sites serve as catalytic reaction sites, efficiently driving the water oxidation reaction. This "multi-site synergy" design concept provides an effective strategy to overcome the mismatch between light absorption and catalytic activity in traditional materials.

[0005] Despite the promising applications of Co-based coordination polymer (CP) crystalline photoelectrode materials, their research still faces numerous challenges. For example, most CP materials exhibit low intrinsic conductivity; their long-term chemical stability in strong acid / base electrolytes is insufficient; furthermore, precisely controlling their band structure to perfectly match the thermodynamic barrier of photoelectrochemical water splitting remains a key research challenge. Therefore, developing novel, high-performance, and highly stable Co-based crystalline photoelectrode materials through rational ligand design, structural engineering (such as constructing π-conjugated systems and introducing donor-acceptor units), and interface modification, and deeply exploring their structure-property relationships and charge dynamics, is of significant scientific importance and research value for promoting the practical application of photoelectrochemical water splitting technology. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a Co(II) coordination polymer photoelectrode crystalline material, its preparation method, and its application. This invention aims to overcome the problems of low yield, low reproducibility, and excessive influence of reaction conditions in existing Co(II) coordination polymer preparation methods. The material is prepared by solvothermal methods and exhibits good photoelectric properties. It can be used to construct efficient photoelectrocatalysis and water oxidation, and has application prospects in photocatalytic hydrogen production and solar energy conversion.

[0007] This invention provides a Co(II) coordination polymer photoelectrode crystalline material, wherein the single-crystal molecular formula of the Co(II) coordination polymer photoelectrode crystalline material is C2. 38 H 40 Br4Co2N8O 12 The chemical formula of the Co(II) coordination polymer photoelectrode crystalline material is {[Co(H2O)(Br-BDC)(BMIP)]·H2O}. n .

[0008] According to the Co(II) coordination polymer photoelectrode crystalline material provided by the present invention, the ligand (Br-BDC) in the chemical formula of the Co(II) coordination polymer photoelectrode crystalline material is deprotonated H2 (Br-BDC), and the ligand BMIP in the chemical formula of the Co(II) coordination polymer photoelectrode crystalline material is 1,3-bis(dimethylimidazolylpropane).

[0009] The H2(Br-BDC) is 2,5-dibromo-terephthalic acid, and its structural formula is: ;

[0010] The structural formula of the BMIP is: .

[0011] According to the Co(II) coordination polymer photoelectrode crystalline material provided by the present invention, the Co(II) coordination polymer photoelectrode crystalline material is triclinic with space group P-1 and cell parameters including a=10.1808(8) Å, b=11.2016(10) Å, c=11.4165(10) Å, α= 66.195(3)°, β= 72.244(3)° and γ= 89.057(3)°.

[0012] This invention provides a method for preparing the above-mentioned Co(II) coordination polymer photoelectrode crystalline material, comprising the following steps:

[0013] S1. Cobalt salt, H2 (Br-BDC) and BMIP are added to DMF to obtain a mixed solution. After reacting at a constant temperature, the solution is allowed to stand to obtain the reaction product.

[0014] S2. The reaction product obtained in S1 is cooled and crystallized. The crystallized product is then washed, filtered and dried in sequence to obtain the Co(II) coordination polymer photoelectrode crystalline material.

[0015] According to the preparation method provided by the present invention, the cobalt salt in S1 is cobalt nitrate hexahydrate, and the mass-volume ratio of the cobalt salt, H2 (Br-BDC), BMIP and DMF is 0.1-0.5 mmol: 0.1-0.5 mmol: 0.05-0.2 mmol: 4-10 mL.

[0016] According to the preparation method provided by the present invention, the temperature of the constant temperature reaction in S1 is 90-110 °C, the time of the constant temperature reaction is 48 h, and the standing time is 12 h.

[0017] According to the preparation method provided by the present invention, the rinsing agent used for rinsing in S2 is deionized water, the filtration is vacuum filtration, the drying temperature is 60 °C, and the drying time is 2 to 4 h.

[0018] The present invention also provides an application of the above-mentioned Co(II) coordination polymer photoelectrode crystalline material, wherein the Co(II) coordination polymer photoelectrode crystalline material is used as a semiconductor photocatalyst.

[0019] This invention uses an organic ligand H2 (Br-BDC), BMIP, and a cobalt salt to obtain a Co(II) coordination polymer via a solvothermal method. In this cobalt(II)-based metal-organic framework crystalline material, its asymmetric unit comprises one Co(II) ion, one BMIP ligand, and one Br-BDC. 2- The ligand is a monodentate water molecule. The Co(II) ion is six-coordinated, with the six atoms originating from two Br-BDC ions. 2-The ligand has three O atoms (O4, O5, O7) and a monodentate water molecule oxygen (O6).

[0020] The two N atoms (N9, N) coordinated with the Co(II) center 11 The two BMIP ligands originate from two different BMIP ligands, which connect two adjacent Co(II) ions to form an elliptical [Co2(BMIP)2]. 4+ Secondary structural unit, Br-BDC 2- The ligands bridge the Co(II) ions in the secondary structural unit to form a two-dimensional honeycomb structure. The layers are connected by intermolecular hydrogen bonding and π-π stacking to form a three-dimensional supramolecular configuration.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention provides a Co(II) coordination polymer photoelectrode crystalline material, its preparation method, and its application. The {[Co(H2O)(Br-BDC)(BMIP)]·H2O} material is prepared via solvothermal methods. n Its asymmetric unit contains one Co(II) ion, one BMIP ligand, and one Br-BDC. 2- The ligand is a monodentate water molecule. The Co(II) ion is six-coordinated, with the six atoms originating from two Br-BDC ions. 2- The ligand contains three O atoms (O4, O5, O7) and one monodentate oxygen molecule (O6) coordinated to the Co(II) center. Two N atoms (N9, N2) are also coordinated to the Co(II) center. 11 The two BMIP ligands originate from two different BMIP ligands. These two BMIP ligands connect two adjacent Co(II) ions to form an elliptical [Co2(BMIP)2] ion. 4+ Secondary structural unit, Br-BDC 2- The ligands bridge the Co(II) ions in the secondary structural unit to form a two-dimensional honeycomb structure. Layers are then connected by intermolecular hydrogen bonds and π-π stacking to form a three-dimensional supramolecular configuration. This exhibits good photoelectric properties and can be used to construct efficient photoelectrocatalytic water splitting systems, showing promising applications in photoelectrocatalytic water oxidation. Attached Figure Description

[0023] Figure 1 Asymmetric unit diagram of Co(II) coordination polymers;

[0024] Figure 2 A two-dimensional layered structure diagram of a Co(II) coordination polymer;

[0025] Figure 3The three-dimensional supramolecular structure of the Co(II) coordination polymer;

[0026] Figure 4 IR spectrum of Co(II) coordination polymer;

[0027] Figure 5 XRD pattern of Co(II) coordination polymerization;

[0028] Figure 6 Cyclic voltammetry curves for Co(II) coordination polymers;

[0029] Figure 7 Mott-Schottky curves for Co(II) coordination polymers;

[0030] Figure 8 Electrochemical impedance Nyquist plot for Co(II) coordinated polymers;

[0031] Figure 9 Photocurrent response curves of Co(II) coordination polymers after 50 seconds of xenon lamp on / off irradiation;

[0032] Figure 10 Linear scan voltammetry for Co(II) coordination polymers;

[0033] Figure 11 The UV-Vis diffuse reflectance spectrum of the Co(II) coordination polymer;

[0034] Figure 12 Tafel slope diagram for Co(II) coordination polymers;

[0035] Figure 13 The double-layer capacitance diagram for Co(II) coordinated polymers. Detailed Implementation

[0036] Example 1

[0037] This embodiment provides a method for preparing a Co(II) coordination polymer photoelectrode crystalline material, including the following steps:

[0038] S1. Mix 0.1 mmol of cobalt nitrate hexahydrate, 0.1 mmol of 2,5-dibromoterephthalic acid (H2(Br-BDC)), 0.05 mmol of 1,3-bis(dimethylimidazolylpropane) (BMIP) and 4 mL of N,N-dimethylformamide (DMF) to obtain a mixture. The mixture in a glass scintillation bottle is subjected to a solvothermal reaction at 90 °C for 48 h, followed by standing for 12 h to obtain the reaction product.

[0039] S2. The reaction product was allowed to cool naturally and crystallize. After washing with deionized water and filtering under reduced pressure, purple needle-like crystals were obtained. After being placed in an oven at 60 °C for 3 h, Co(II) coordination polymer photoelectrode crystalline material was obtained, denoted as Co(II) coordination polymer 1, with a yield of approximately 69.1%.

[0040] Example 2

[0041] This embodiment provides a method for preparing a Co(II) coordination polymer photoelectrode crystalline material, including the following steps:

[0042] S1. Mix 0.5 mmol of cobalt nitrate hexahydrate, 0.5 mmol of 2,5-dibromoterephthalic acid, 0.2 mmol of BMIP and 10 mL of DMF to obtain a mixture. The mixture in a glass scintillation bottle is subjected to a solvothermal reaction at 110 °C for 48 h, and then allowed to stand for 12 h to obtain the reaction product.

[0043] S2. The reaction product was allowed to cool naturally and crystallize. After washing with deionized water and filtering under reduced pressure, purple needle-like crystals were obtained. After being placed in an oven at 60 °C for 2 h, Co(II) coordination polymer photoelectrode crystalline material was obtained, denoted as Co(II) coordination polymer 2, with a yield of approximately 64.9%.

[0044] Example 3

[0045] This embodiment provides a method for preparing a Co(II) coordination polymer photoelectrode crystalline material, including the following steps:

[0046] S1. Mix 0.2 mmol of cobalt nitrate hexahydrate, 0.2 mmol of 2,5-dibromoterephthalic acid, 0.1 mmol of BMIP and 6 mL of DMF to obtain a mixture. The mixture in a glass scintillation bottle is subjected to a solvothermal reaction at 95 °C for 50 h, and then allowed to stand for 12 h to obtain the reaction product.

[0047] S2. The reaction product was allowed to cool naturally and crystallize. After washing with deionized water and filtering under reduced pressure, purple needle-like crystals were obtained. After being placed in an oven at 60 °C for 4 h, Co(II) coordination polymer photoelectrode crystalline material was obtained, denoted as Co(II) coordination polymer 3, with a yield of approximately 70.5%.

[0048] Example 4

[0049] The Co(II) coordination polymer 1 prepared in Example 1 was characterized as follows:

[0050] (1) Determination of the crystal structure of Co(II) coordination polymers

[0051] X-ray diffraction experiments were conducted on single crystals of appropriate size at room temperature under a microscope. Diffraction data were collected using a Bruker-Apex П X-ray single crystal diffractometer, with Mo-Kα rays (λ = 0.71073 Å) monochromated using a graphite monochromator, and diffraction points were collected using ω-2θ scanning. All data were corrected for factors and empirical absorption. The crystal structure was solved directly using a program, and hydrogen atoms were determined by difference Fourier synthesis and fixation at their calculated optimal positions. Using the SHELX-97 program, all non-hydrogen atoms and their anisotropic thermal parameters were corrected using a full-matrix least squares method. Detailed crystal measurement data are shown in Table 1, and bond length and bond angle data are shown in Table 2.

[0052] Table 1. Key crystallographic data of Co(II) coordination polymer 1

[0053] Table 2. Important bond lengths (Å) and bond angles (°) of Co(II) coordination polymer 1

[0054] In Table 1, a, b, and c represent the edge lengths of the crystal along the three crystal axes, α, β, and γ represent the angles between axes a and b, a and c, and b and c, respectively; Z is the number of molecules in a unit cell; the diffraction index range of the restriction factor is (h, k, l); F(000) is the number of electrons in a unit cell; Final R indices [I>2σ(I)] is the residual factor R value for observable diffraction points; R is the unweighted consistency factor; R1 and wR2 are both weighted consistency factors; symmetry code: 1 -X,1-Y,1-Z ;

[0055] In Table 2, Co(1) in the first row refers to Co atom 1 in Co(II) coordination polymer 1, O(4) refers to O atom 4 in Co(II) coordination polymer 1, Co(1)-O(4) represents the bond length between Co atom 1 and O atom 4, which is 2.184±8Å, where 8 is the standard deviation; O(4)-Co(1)-O(5) represents the bond angle between O atom 4, Co atom 1 and O atom 5, which is 59.4±3.

[0056] In cobalt(II)-based metal-organic framework crystalline materials, the asymmetric unit contains one Co(II) ion, one BMIP ligand, and one Br-BDC ion. 2- The ligand is a monodentate water molecule. The Co(II) ion is six-coordinated, with the six atoms originating from two Br-BDC ions. 2-The ligand contains three O atoms (O4, O5, O7) and one monodentate oxygen molecule (O6) coordinated to the Co(II) center. Two N atoms (N9, N2) are also coordinated to the Co(II) center. 11 They come from two different BMIP ligands.

[0057] Two BMIP ligands connect two adjacent Co(II) ions to form an elliptical [Co2(BMIP)2] ion. 4+ Secondary structural unit, Br-BDC 2- Ligands bridge the Co(II) ions in this secondary structural unit to form a two-dimensional honeycomb structure. Layers are connected by intermolecular hydrogen bonds and π-π stacking interactions to form a three-dimensional supramolecular configuration, such as... Figure 3 As shown, Figure 3 Different colors are used to distinguish the four different layers for easy observation.

[0058] (1) IR spectral characterization

[0059] Figure 4 The IR spectrum of Co(II) coordination polymer 1 was obtained from samples with infrared spectra collected from 500 to 4000 cm⁻¹. -1 KBr tablets were used.

[0060] Depend on Figure 4 It can be seen that 1492–1521 cm -1 The three peaks between are benzene ring stretching vibration peaks, 3135 cm⁻¹. -1 The peak at this point corresponds to the stretching vibration of the OH bond in a water molecule. Therefore, the molecular formula of this Co(II) coordination polymer 1 is {[Co(H2O)(Br-BDC)(BMIP)]·H2O}. n .

[0061] (2) Characterization of the phase purity of Co(II) coordination polymer 1

[0062] Powder XRD characterization of Co(II) coordination polymer 1 was performed using a Bruker / D8 Advance X-ray diffractometer. The simulated conditions for the Co(II) coordination polymer involved mixing cobalt nitrate hexahydrate, carboxylic acid ligands, imidazole ligands, and an organic solvent to obtain a mixture, which was then reacted at 105 °C for 72 h. Actual results showed that its characteristic peaks corresponded to the standard card, and the characterization results demonstrated reliable phase purity, ensuring its application as a catalyst. Figure 5 As shown.

[0063] (3) Photoelectrocatalytic characterization of Co(II) coordination polymer 1

[0064] To evaluate the photoelectrochemical capabilities of the Co(II) coordination polymer 1, a three-electrode environment consisting of ITO conductive glass, carbon rod, and saturated calomel electrode was used.

[0065] Co(II) coordination polymer 1 powder was coated on an area of ​​1.0 cm². 2 On the surface of ITO conductive glass, using 0.5 mol / L Na₂SO₄ as the electrolyte, cyclic voltammetry (CV) was performed on Co(II) coordination polymer 1 before and after irradiation with a photocatalytic xenon lamp at a scan rate of 50 mV / s. Figure 6 As shown, the cyclic voltammetry curves of Co(II) coordination polymer 1 under darkness and xenon lamp irradiation at 50 mV / s exhibit obvious redox peaks. The semiconductor type of Co(II) coordination polymer 1 was determined by using Mott-Schottky (MS) curves.

[0066] like Figure 7 As shown, the slope of the MS curve of Co(II) coordination polymer 1 is positive when the frequency is 500 Hz, 1000 Hz and 1500 Hz, indicating that Co(II) coordination polymer 1 is an n-type semiconductor.

[0067] By performing linear fitting on the MS curves at three frequencies, the minimum conduction band energy (CBM) is found to be -1.62. This value can be determined using the band gap obtained from the solid-state ultraviolet diffuse reflectance, such as... Figure 11 As shown, the calculated valence band maximum (VBM) is 1.59. Since the VBM of this Co(II) coordination polymer 1 is greater than the standard potential of the OER reaction of 1.23 V, it is favorable for the OER reaction and also confirms its activity as an OER photocatalyst.

[0068] Figure 8 The impedance (Z') changes of the Co(II) coordination polymer 1 under dark and light conditions are shown. Electrochemical impedance spectroscopy (EIS) shows that the Co(II) coordination polymer 1 has the smallest arc radius under light conditions, indicating that the electron conduction within the composite material is rapid and the charge separation efficiency is high.

[0069] like Figure 9 As shown, the experiment was conducted alternately under dark and light conditions with a 50-second interval. Co(II) coordination polymer 1 exhibited a stable photocurrent during irradiation.

[0070] Figure 10The current-potential curves of Co(II) coordination polymer 1 under dark and light conditions were compared, indicating that Co(II) coordination polymer 1 can generate photogenerated charge carriers to participate in electrochemical reactions under light, which helps to evaluate its separation and transport efficiency of photogenerated charge in photoelectrocatalysis.

[0071] The Tafel slope is used to describe the kinetic properties of electrocatalysts in electrocatalytic processes, depicting the relationship between potential cross-sites and current density, such as... Figure 12 As shown. A series of cyclic voltammetry (CV) tests were performed at 10 mV / s intervals within a scan rate range of 40-80 mV / s, as follows... Figure 13 As shown.

[0072] Co(II) coordination polymer 1 exhibits high photoelectrocatalytic performance, making it a highly efficient catalytic semiconductor material. This provides new progress for the construction of novel Co(II) coordination polymer 1 and its performance in photoelectrocatalysis.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A Co(II) coordination polymer photoelectrode crystalline material, characterized in that, The single-crystal molecular formula of the Co(II) coordination polymer photoelectrode crystalline material is C1. 38 H 40 Br4Co2N8O 12 The chemical formula of the Co(II) coordination polymer photoelectrode crystalline material is {[Co(H2O)(Br-BDC)(BMIP)]·H2O}. n .

2. The Co(II) coordination polymer photoelectrode crystalline material according to claim 1, characterized in that, In the chemical formula of the Co(II) coordination polymer photoelectrode crystalline material, the ligand (Br-BDC) is deprotonated H2 (Br-BDC), and the ligand BMIP in the chemical formula of the Co(II) coordination polymer photoelectrode crystalline material is 1,3-bis(dimethylimidazolylpropane). The H2(Br-BDC) is 2,5-dibromo-terephthalic acid, and its structural formula is: ； The structural formula of the BMIP is: 。 3. The Co(II) coordination polymer photoelectrode crystalline material according to claim 1, characterized in that, The Co(II) coordination polymer photoelectrode crystalline material is triclinic with space group P-1 and cell parameters including a=10.1808(8) Å, b=11.2016(10) Å, c=11.4165(10) Å, α= 66.195(3)°, β= 72.244(3)° and γ= 89.057(3)°.

4. A method for preparing a Co(II) coordination polymer photoelectrode crystalline material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Cobalt salt, H2 (Br-BDC) and BMIP are added to DMF to obtain a mixed solution. After reacting at a constant temperature, the solution is allowed to stand to obtain the reaction product. S2. The reaction product obtained in S1 is cooled and crystallized. The crystallized product is then washed, filtered and dried in sequence to obtain the Co(II) coordination polymer photoelectrode crystalline material.

5. The preparation method according to claim 4, characterized in that, The cobalt salt mentioned in S1 is cobalt nitrate hexahydrate, and the mass-to-volume ratio of the cobalt salt, H2 (Br-BDC), BMIP and DMF is 0.1–0.5 mmol: 0.1–0.5 mmol: 0.05–0.2 mmol: 4–10 mL.

6. The preparation method according to claim 4, characterized in that, The constant temperature reaction time in S1 is 90–110 °C, the constant temperature reaction time is 48 h, and the settling time is 12 h.

7. The preparation method according to claim 4, characterized in that, The rinsing agent used in S2 is deionized water, the filtration is vacuum filtration, the drying temperature is 60 ℃, and the drying time is 2 to 4 h.

8. An application of the Co(II) coordination polymer photoelectrode crystalline material as described in any one of claims 1-3, characterized in that, The Co(II) coordination polymer photoelectrode crystalline material is used as a semiconductor photocatalyst.

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