A Mn(II) coordination polymer photoelectrode crystalline material and its preparation method and application

Abstract

The present invention relates to the field of photoelectrocatalysis technology, and in particular to a Mn(II) coordination polymer photoelectrode crystalline material, its preparation method, and application. The present invention comprises a H4(DODDA) organic ligand and a manganese salt through a solvothermal method to obtain a Mn(II) coordination polymer {[Mn2(H2O)6(DODDA)]·4H2O} n The asymmetric unit contains two Mn(II) ions with different coordination modes, in which adjacent Mn2 ions are bridged by the carboxyl oxygen of the ligand to form a straight chain, and the two adjacent Mn2 straight chains are further bridged by the H4(DODDA) ligand to form a horizontal ladder-shaped one-dimensional chain. The one-dimensional chains form a three-dimensional supramolecular structure through a large number of intermolecular hydrogen bonds. This Mn(II) coordination polymer exhibits good photoelectric properties and has the potential to be used as a photoelectrode material. It has good optical and electrical properties and can be used to construct an efficient photoelectrocatalytic water splitting system. It has application prospects in photocatalytic hydrogen production and solar energy conversion.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectrocatalysis, and in particular relates to a Mn(II) coordination polymer crystalline photoelectrode crystalline material and a preparation method and application thereof. Background Art

[0002] With the growth of global energy demand and the intensification of environmental problems, the development of efficient and sustainable clean energy technologies has become a core task of scientific research. Photoelectrocatalytic water splitting, as a technology that converts solar energy into chemical energy, is considered to be one of the ideal ways to solve the energy crisis and environmental pollution problems. However, currently commercial photoelectrocatalysts such as titanium dioxide and cadmium sulfide generally have problems such as narrow light absorption range, low carrier separation efficiency, and insufficient catalytic activity, resulting in their energy conversion efficiency far below the theoretical value (about 1% to 5%). In addition, these materials usually require precious metal co-catalysts to improve activity, which significantly increases the preparation cost and limits their large-scale application.

[0003] Mn is a highly abundant, low-cost, and environmentally friendly transition metal element. Due to its unique electronic structure and diverse oxidation states, it exhibits great potential in photoelectrocatalysis. For example, MnO2, a typical Mn oxide, exhibits high activity in photoelectrocatalytic water splitting. However, conventional MnO2 materials are typically amorphous or low-surface-area nanoparticles with poor electron transport properties, limiting their practical applications.

[0004] Mn(II) coordination polymers are multidimensional crystalline materials formed by the self-assembly of metal ions and organic ligands through coordination bonds. Compared with traditional inorganic materials, Mn(II) coordination polymers offer significant advantages, including structural tunability, high surface area, good electrical conductivity, and exceptional light absorption. However, current research still faces major challenges, including insufficient surface area, poor electrical conductivity, limited light absorption, and complex preparation processes.

[0005] In response to the above problems, the present invention proposes a crystalline photoelectrode material based on a Mn(II) coordination polymer and a preparation method thereof. By rationally designing the ratio and coordination mode of metal ions and organic ligands, the material successfully constructs a three-dimensional porous crystal structure. This structure not only significantly improves the specific surface area and conductivity of the material, but also greatly broadens its light absorption range. Experimental results show that the Mn(II) coordination polymer photoelectrode material prepared by the present invention has excellent photoelectrochemical activity in the visible light region, and its photocurrent density and quantum efficiency are significantly higher than those of traditional Mn(II)-based materials. In addition, the preparation process proposed by the present invention is simple, low-cost and easy to mass produce, which provides a new idea for the industrial preparation of high-performance photoelectrocatalysts. In the future, this material is expected to play an important role in the fields of solar cells, water decomposition to produce hydrogen, and provide strong support for the efficient utilization and sustainable development of clean energy. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a Mn(II) coordination polymer photoelectrode crystalline material and its preparation method and application, aiming to overcome the problems of low yield, very low reproducibility and excessive influence of reaction conditions in the existing Mn(II) coordination polymer preparation method. The material is prepared by solvent thermal method, exhibits good photoelectric performance, can be used to construct an efficient photoelectrocatalytic water splitting system, and has application prospects in photocatalytic hydrogen production and solar energy conversion.

[0007] The present invention provides a Mn(II) coordination polymer photoelectrode crystalline material, wherein the single crystal molecular formula of the Mn(II) coordination polymer photoelectrode crystalline material is C 14 Mn2O 17 N2H 18 , the chemical formula is {[Mn2(H2O)6(DODDA)]·4H2O} n .

[0008] According to the Mn(II) coordination polymer photoelectrode crystalline material provided by the present invention, the Mn(II) coordination polymer photoelectrode crystalline material is an orthorhombic crystal system, the space group is Imma, and the unit cell parameters include a=21.802(15) Å, b=26.295(17) Å, c=7.319(6) Å, α= 90.00°, β= 90.00° and γ= 90.00°

[0009] The present invention provides a method for preparing the above-mentioned Mn(II) coordination polymer photoelectrode crystalline material, comprising the following steps:

[0010] S1. Add H4 (DODDA) and manganese salt to DEF to obtain a mixed solution, keep the solution at a constant temperature for sufficient reaction, and then allow the solution to stand to obtain a reaction product;

[0011] S2. Cooling the reaction product obtained in S1 to crystallize, and washing, filtering and drying the crystallized product in sequence to obtain a Mn(II) coordination polymer photoelectrode crystalline material.

[0012] According to the preparation method provided by the present invention, the H4 (DODDA) in S1 is 1-(3,5-dicarboxyphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylic acid, and the structural formula of the H4 (DODDA) is:

[0013] .

[0014] According to the preparation method provided by the present invention, the manganese salt in S1 is manganese nitrate tetrahydrate, and the mass volume ratio of the H4(DODDA), manganese salt and DEF is 0.1 mmol:0.1 mmol:1.8-2.2 mL.

[0015] According to the preparation method provided by the present invention, the temperature of the constant temperature full reaction in S1 is 80-95°C, the time of the constant temperature full reaction is 45-50 hours, and the standing time is 12 hours.

[0016] According to the preparation method provided by the present invention, the rinsing agent in S2 is deionized water, the filtration is reduced-pressure filtration, the drying temperature is 60° C., and the drying time is 2 to 4 h.

[0017] The present invention also provides an application of the above-mentioned Mn(II) coordination polymer photoelectrode crystalline material, wherein the Mn(II) coordination polymer photoelectrode crystalline material is used as a semiconductor photocatalyst.

[0018] The invention uses a solvent thermal method to obtain a Mn(II) coordination polymer by using H4(DODDA) organic ligand and manganese salt, and then in {[Mn2(H2O)6(DODDA)]·4H2O} n The asymmetric unit contains two Mn(II) ions with different coordination modes, a deprotonated DODDA 4- The Mn1 ion is connected to two monodentate coordinated water molecules and four oxygen atoms from the carbonyl and carboxyl groups. Both Mn1 and Mn2 ions have a hexacoordinate structure, but unlike the coordination environment of Mn1, the center of the Mn2 ion is connected to the two carboxyl oxygens of the H4 (DODDA) ligand and four monodentate coordinated water atoms. Adjacent Mn2 ions are bridged by the carboxyl oxygens of the ligand to form straight chains. Two adjacent Mn2 straight chains are further bridged by the H4 (DODDA) ligand to form horizontal ladder-shaped one-dimensional chains. The one-dimensional chains form a three-dimensional supramolecular structure through a large number of intermolecular hydrogen bonds.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The present invention provides a Mn(II) coordination polymer crystalline photoelectrode crystalline material and its preparation method and application, wherein {[Mn2(H2O)6(DODDA)]·4H2O} is prepared by solvent thermal method. n The asymmetric unit contains two Mn(II) ions with different coordination modes, a deprotonated DODDA 4- The H4 (DODDA) ligand is composed of six monodentate water molecules and four crystal waters. The Mn1 ion is connected to two monodentate coordinated water molecules and four oxygen atoms from carbonyl and carboxyl groups. Both Mn1 and Mn2 ions have a six-coordinate structure, but the coordination environment of Mn1 is different. The center of the Mn2 ion is connected to the two carboxyl oxygens of the H4 (DODDA) ligand and four monodentate coordinated waters. The adjacent Mn2 ions are bridged by the carboxyl oxygen of the ligand to form a straight chain, and the two adjacent Mn2 straight chains are further bridged by the H4 (DODDA) ligand to form a horizontal ladder-shaped one-dimensional chain. A large number of intermolecular hydrogen bonds are used between the one-dimensional chains to form a three-dimensional supramolecular structure. It exhibits good photoelectric performance and can be used to construct an efficient photoelectrocatalytic water decomposition system. It has application prospects in photocatalytic hydrogen production and solar energy conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the single molecule image of Mn(II) coordination polymer 1;

[0022] Figure 2 is the one-dimensional structure of Mn(II) coordination polymer 1;

[0023] Figure 3 The three-dimensional supramolecular structure of Mn(II) coordination polymer 1;

[0024] Figure 4 is the IR spectrum of Mn(II) coordination polymer 1;

[0025] Figure 5 is the XRD pattern of Mn(II) coordination polymer 1;

[0026] Figure 6 is the cyclic voltammogram of Mn(II) coordination polymer 1;

[0027] Figure 7 is the Mott-Schottky plot of the Mn(II) coordination polymer 1;

[0028] Figure 8 is the electrochemical impedance Nyquist plot of Mn(II) coordination polymer 1;

[0029] Figure 9The photocurrent response curve of Mn(II) coordination polymer 1 under xenon lamp on / off irradiation for 50 seconds;

[0030] Figure 10 is the linear sweep voltammogram of Mn(II) coordination polymer 1;

[0031] Figure 11 is the UV-visible diffuse reflectance spectrum of Mn(II) coordination polymer 1;

[0032] Figure 12 is the Tafel slope plot of Mn(II) coordination polymer 1;

[0033] Figure 13 The double-layer capacitance diagram of Mn(II) coordination polymer 1. DETAILED DESCRIPTION

[0034] Example 1

[0035] This embodiment provides a method for preparing H4(DODDA), and the specific steps are as follows:

[0036] S1. Dissolve 12.00 g of diethyl 5-aminoisophthalate in 110 mL of distilled water. Add 50 mL of concentrated hydrochloric acid and 20 mL of 3 mol / L NaNO2 solution dropwise at 0°C in an ice bath to obtain a clear yellow diazonium salt solution.

[0037] S2. Under an ice bath, 0.15 mol of sodium acetate was dissolved in 300 mL of distilled water and 300 mL of anhydrous ethanol and stirred for 15 min. Then, 11.30 g of diethyl 1,3-acetonedicarboxylate was added and stirring was continued for 15 min. Then, the diazonium salt solution prepared in S1 was slowly added and the reaction was continued for 2 hours. The mixture was filtered and the filter cake was washed until neutral. The filter cake was dried at room temperature to obtain diethyl 2-(2-(3,5-diethoxycarbonylphenyl)hydrazino)-3-oxoglutarate.

[0038] S3, dissolve the diethyl 2-(2-(3,5-diethoxycarbonylphenyl)hydrazine)-3-oxoglutarate obtained in S2 in toluene, and add 6.19 g DMF-DMA ( N , N -dimethylformamide dimethyl acetal), then react at 100 ° C for 12 hours, concentrate to remove toluene, and obtain a black-red viscous substance 1-(3,5-diethoxycarbonylphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylic acid diethyl ester;

[0039] S4. Dissolve the diethyl 1-(3,5-diethoxycarbonylphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylate obtained in S3 in 100 mL of distilled water, add 16.64 g of NaOH solid and stir, heat the reaction system to 60 °C and react for 3 h, cool to room temperature, add 150 mL of distilled water to the system, add HCl solution to adjust the pH to 2, filter, wash the filter cake to neutrality, and dry to obtain 1-(3,5-dicarboxyphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylic acid, i.e., H4(DODDA).

[0040] The preparation steps are specifically shown in the following formula:

[0041] .

[0042] Example 2

[0043] This embodiment provides a method for preparing a Mn(II) coordination polymer photoelectrode crystalline material, comprising the following steps:

[0044] S1, 0.1 mmol of manganese nitrate tetrahydrate, 0.1 mmol of 1-(3,5-dicarboxyphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylic acid (H4(DODDA)) and 2 mL N , N -diethylformamide (DEF) to obtain a mixture, the mixture was subjected to solvothermal reaction at 80 °C in a glass scintillation vial for 48 h, and then allowed to stand for 12 h to obtain a reaction product;

[0045] S2. The reaction product was naturally cooled and crystallized, rinsed with deionized water and filtered under reduced pressure to obtain transparent block crystals. The crystals were placed in an oven at 60 °C for 3 h to obtain Mn(II) coordination polymer 1 with a yield of about 71.2%.

[0046] Example 3

[0047] This embodiment provides a method for preparing a Mn(II) coordination polymer photoelectrode crystalline material, comprising the following steps:

[0048] S1. 0.1 mmol of manganese nitrate tetrahydrate, 0.1 mmol of H4(DODDA), and 1.8 mL of DEF were mixed to obtain a mixture. The mixture was subjected to a solvothermal reaction at 88°C in a glass scintillation vial for 50 h, and allowed to stand for 12 h to obtain a reaction product.

[0049] S2. The reaction product was naturally cooled and crystallized, rinsed with deionized water and filtered under reduced pressure to obtain transparent block crystals. The crystals were placed in an oven at 60 °C for 2 h to obtain Mn(II) coordination polymer 2 with a yield of about 65.4%.

[0050] Example 4

[0051] This embodiment provides a method for preparing a Mn(II) coordination polymer photoelectrode crystalline material, comprising the following steps:

[0052] S1. 0.1 mmol of manganese nitrate tetrahydrate, 0.1 mmol of H4(DODDA), and 2.2 mL of DEF were mixed to obtain a mixture. The mixture was subjected to a solvothermal reaction at 95°C in a glass scintillation vial for 45 h, and allowed to stand for 12 h to obtain a reaction product.

[0053] S2. The reaction product was naturally cooled and crystallized, rinsed with deionized water and filtered under reduced pressure to obtain transparent block crystals. The crystals were placed in an oven at 60 °C for 4 h to obtain Mn(II) coordination polymer 3 with a yield of about 68.5%.

[0054] Example 5

[0055] The Mn(II) coordination polymer 1 prepared in Example 2 was characterized as follows:

[0056] (1) Crystal structure determination of Mn(II) coordination polymer

[0057] Single crystals of appropriate size were selected under a microscope for X-ray diffraction experiments at room temperature. Diffraction data were collected on a Bruker-ApexП X-ray single crystal diffractometer and monochromated with a graphite monochromator. Mo-Kα ray (λ = 0.71073 Å), with ω-2θ Diffraction points were collected in a scanning mode. All data were corrected by factors and empirical absorption. The crystal structure was solved by a direct method using a program. Hydrogen atoms were determined by difference Fourier synthesis and fixed in the calculated optimal position. Using the SHELX-97 program, all non-hydrogen atoms and their anisotropic thermal parameters were corrected by the full matrix least squares method. Detailed crystal determination data are shown in Table 1, bond length and bond angle data are shown in Table 2, and the crystal structure is shown in Table 2. Figure 1 As shown, when observing the one-dimensional structure of the polymer from the c-axis direction, obvious molecular channels can be seen, such as Figure 3 shown.

[0058] Table 1

[0059]

[0060] Table 2

[0061]

[0062] Symmetric code: 1 +X,3 / 2-Y,+Z; 2 3 / 2-X,3 / 2-Y,3 / 2-Z; 3 1-X,+Y,+Z;

[0063] In Table 1, a, b, and c represent the edge lengths of the crystal in the directions of the three crystal axes, respectively; α, β, and γ represent the angles between a and b, a and c, and b and c, respectively; Z is the number of molecules contained in the unit cell; the diffraction index range of the limiting factor is (h, k, l); F(000) is the number of electrons in the unit cell; Final R indices [I>2σ(I)] is the residual factor R value for the observable diffraction point; R is the non-weighted consistency factor; R1 and wR2 are both weighted consistency factors;

[0064] In the first row of Table 2, Mn(1) refers to Mn atom 1 in the Mn(II) coordination polymer 1 single crystal, O(1) refers to O atom 1 in the Mn(II) coordination polymer 1 single crystal, Mn(1)-O(1) represents the bond length between Mn atom 1 and O atom 1, which is 2.081±3, with 3 being the standard deviation; O(5)-Mn(2)-O(9) represents the bond angle between O atom 5, Mn atom 2, and O atom 9, which is 83.14±9;

[0065] (1) IR spectrum characterization

[0066] Figure 4 This is the IR spectrum of Mn(II) coordination polymer 1. The infrared spectrum of the sample was collected from 500 to 4000 cm -1 , using KBr pellets.

[0067] Depend on Figure 4 It can be seen that 1492~1621 cm -1 The three peaks between them are benzene ring stretching vibration peaks, 3135 cm -1 The OH bond stretching vibration peak in water molecules is 1621 cm -1 The stretching vibration peak of the carbonyl group is at . Therefore, the molecular formula of the Mn(II) coordination polymer 1 is {[Mn2(H2O)6(DODDA)]·4H2O} n .

[0068] (2) Phase purity characterization of Mn(II) coordination polymer 1

[0069] The powder XRD characterization results of the Mn(II) coordination polymer 1 using a Bruker / D8Advance X-ray diffractometer showed that it had reliable phase purity, which provided a guarantee for its application as a catalyst, such as Figure 5 shown.

[0070] (3) Photoelectrocatalytic characterization of Mn(II) coordination polymer 1

[0071] In order to evaluate the photoelectrochemical ability of the Mn(II) coordination polymer 1, a three-electrode environment consisting of ITO conductive glass, carbon rod, and saturated calomel electrode was used.

[0072] The Mn(II) coordination polymer 1 powder was coated on an area of ​​1.0 cm 2 The surface of ITO conductive glass was prepared by cyclic voltammetry (CV) of Mn(II) coordination polymer 1 before and after irradiation with a photocatalytic xenon lamp at a scan rate of 50 mV / s using 0.5 mol / L Na2SO4 as the electrolyte. Figure 6 As shown, the cyclic voltammetry curves of Mn(II) coordination polymer 1 in the dark and under 50 mV / s xenon lamp irradiation exhibit obvious redox peaks, and the semiconductor type of Mn(II) coordination polymer 1 is determined by using Mott-Schottky (MS) curves.

[0073] like Figure 7 As shown in Figure 3, when the frequencies are 500 Hz, 1000 Hz and 1500 Hz, the slopes of the MS curves of the Mn(II) coordination polymer are all positive, indicating that the Mn(II) coordination polymer 1 is an n-type semiconductor.

[0074] By linearly fitting the MS curves at three frequencies, we can know that the conduction band minimum (CBM) is 0.79. At this time, the band gap width can be obtained based on the solid ultraviolet diffuse reflectance, such as Figure 11 As shown in the figure, the calculated valence band maximum (VBM) is 1.94. Since the VBM of the Mn(II) coordination polymer 1 is greater than the standard potential of the OER reaction of 1.23 V, it is beneficial to the OER reaction and proves its activity as an OER photocatalyst.

[0075] Figure 8 The impedance (Z') changes of the Mn(II) coordination polymer 1 under dark and light conditions are shown. Electrochemical impedance spectroscopy (EIS) shows that the arc radius of the Mn(II) coordination polymer 1 is smallest under light conditions, indicating rapid electron conduction and efficient charge separation within the composite material.

[0076] like Figure 9As shown, the experiment was performed alternately under dark and light conditions with an interval of 50 seconds. The Mn(II) coordination polymer 1 exhibited a stable photocurrent during the irradiation process.

[0077] Figure 10 The current-potential curves of the Mn(II) coordination polymer 1 under dark and light conditions were compared, indicating that the Mn(II) coordination polymer 1 can generate photogenerated carriers to participate in electrochemical reactions under light, which is helpful to evaluate the separation and transfer efficiency of photogenerated charges in the photoelectrocatalytic process.

[0078] The Tafel slope is used to reflect the kinetic properties of electrocatalysts in the electrocatalytic process and describes the relationship between the transition point and the current density, such as Figure 12 A series of cyclic voltammetry (CV) tests were performed in the scan rate range of 50-100 mV / s with an interval of 10 mV / s, as shown in Figure 13 shown.

[0079] The Mn(II) coordination polymer 1 exhibits high photoelectrocatalytic performance, making it a highly efficient catalytic semiconductor material, providing new progress in the construction of new Mn(II) coordination polymer 1 and its performance in photoelectrocatalysis.

[0080] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A Mn(II) coordination polymer photoelectrode crystalline material, characterized in that: The single crystal molecular formula of the Mn(II) coordination polymer photoelectrode crystalline material is C 14 Mn2O 17 N2H 18 The chemical formula of the Mn(II) coordination polymer photoelectrode crystalline material is {[Mn2(H2O)6(DODDA)]·4H2O} n The Mn(II) coordination polymer photoelectrode crystalline material is an orthorhombic crystal with a space group of Imma. The unit cell parameters include a=21.802(15) Å, b=26.295(17) Å, c=7.319(6) Å, α= 90.00°, β= 90.00° and γ= 90.00°. In the chemical formula, DODDA 4- is deprotonated H4(DODDA), wherein H4(DODDA) is 1-(3,5-dicarboxyphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylic acid, and the structural formula of H4(DODDA) is: 。 2. A method for preparing the Mn(II) coordination polymer photoelectrode crystalline material as claimed in claim 1, characterized in that: The following steps are involved: S1. Add H4 (DODDA) and manganese salt to DEF to obtain a mixed solution, keep the solution at a constant temperature for sufficient reaction, and then allow the solution to stand to obtain a reaction product; S2. Cooling the reaction product obtained in S1 to crystallize, and washing, filtering and drying the crystallized product in sequence to obtain a Mn(II) coordination polymer photoelectrode crystalline material.

3. The preparation method according to claim 2, characterized in that The manganese salt in S1 is manganese nitrate tetrahydrate, and the mass volume ratio of the H4(DODDA), manganese salt and DEF is 0.1 mmol:0.1 mmol:1.8-2.2 mL.

4. The preparation method according to claim 2, characterized in that The temperature of the constant temperature full reaction in S1 is 80-95° C., the time of the constant temperature full reaction is 45-50 h, and the standing time is 12 h.

5. The preparation method according to claim 2, characterized in that The rinsing agent in S2 is deionized water, the filtration is reduced-pressure filtration, the drying temperature is 60° C., and the drying time is 2 to 4 hours.

6. A use of the Mn(II) coordination polymer photoelectrode crystalline material as claimed in claim 1, characterized in that: The Mn(II) coordination polymer photoelectrode crystalline material is used as a semiconductor photocatalyst.

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