Preparation method and application of a nickel-cobalt functionalized metal organic framework catalyst

Abstract

The application relates to the field of catalytic materials, and discloses a preparation method of a nickel-cobalt functionalized metal organic framework catalyst and application thereof. The preparation method comprises the following steps: 1) preparing MOF-808; 2) placing the MOF-808 in a polar solvent and heating to activate in a refluxing mode, separating, vacuum activating, and dispersing in a diffusing hydrophobic solvent; adding a hydrophilic solvent containing nickel salt and cobalt salt into the diffusing hydrophobic solvent drop by drop to diffuse and dope, centrifuging, washing and drying after an exchange reaction, and obtaining the nickel-cobalt functionalized metal organic framework catalyst. The method can avoid destroying the porous ordered framework structure of the MOF in the nickel-cobalt doping process; when the nickel-cobalt functionalized metal organic framework catalyst prepared by the method is applied to a photoelectrocatalytic water splitting reaction, the active component can be inhibited from dissolving out, so that the catalyst has excellent catalytic efficiency and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalytic materials, in particular to a preparation method of a nickel-cobalt functionalized metal organic framework catalyst and application thereof. BACKGROUND

[0002] Photoelectric-driven semiconductor catalytic water splitting for hydrogen production is widely considered as a promising green hydrogen production route due to its clean and pollution-free, simple and easy-to-operate reaction. Among numerous semiconductor catalysts, metal organic frameworks (MOFs) have attracted extensive attention in the field of photoelectric catalytic water splitting due to their adjustable composition structure, high specific surface area and rich pore structure, which exhibit excellent semiconductor-like properties. MOF-808 material constructed with zirconium as metal nodes has excellent chemical and thermal stability, and the six-nuclear metal cluster (Zr6O4(OH)4) has open coordination sites, which shows good potential in catalytic water splitting. However, MOF-808 itself has problems such as weak visible light response ability and low electron-hole separation and migration efficiency, which limits its catalytic efficiency under solar energy driving, so its photoelectric catalytic performance still needs to be further improved.

[0003] Currently, introducing functional metals is an effective strategy to improve the photocatalytic performance of MOFs. Compared with traditional noble metals, transition metal doping has become a promising optimization method due to its cost advantage and adjustable electronic structure. Theoretical calculations and experimental studies have shown that transition metal doping can effectively broaden the visible light response, introduce electron capture shallow potential well to significantly improve the carrier separation efficiency, optimize the electronic structure of active sites, and reduce the reaction overpotential. In particular, the bimetallic doping system often exhibits excellent performance beyond the single metal doping system due to the unique synergistic effect and electronic interaction between the two metals. For example, nickel-cobalt (Ni / Co) bimetallic nanoparticles have attracted much attention due to their special electronic structure and catalytic activity (Phys. Chem. Chem. Phys., 2012, 14, 11596-11599), and studies have shown that such bimetallic nanoparticles can rival noble metal platinum nanoparticles in terms of photocatalytic performance. Therefore, Ni / Co bimetallic functionalization is a promising optimization strategy to improve the catalytic performance of MOFs.

[0004] However, the development of transition metal-doped MOF catalysts still faces major technical challenges. First, the introduction process of multi-metallic components easily destroys the ordered framework structure of MOF materials, resulting in the collapse of the pore and the decrease of the specific surface area. Second, in the long-term photoelectrocatalytic process, the active components of transition metals are prone to leaching, which not only causes the attenuation of catalytic activity, but also may cause secondary pollution. These problems seriously restrict the practical application of bimetallic functionalized MOF catalysts. Therefore, under the premise of maintaining the stability of the MOF structure, realizing the efficient construction and stable fixation of Ni-Co bimetallic functionalized MOF is a key research direction for efficient photoelectrocatalytic water splitting. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a preparation method of a nickel-cobalt functionalized metal organic framework catalyst and its application. The method of the present application can avoid destroying the porous ordered framework structure of MOF during nickel-cobalt doping; when the nickel-cobalt functionalized metal organic framework catalyst prepared by the method of the present application is applied to the photoelectrocatalytic water splitting reaction, the leaching of active components can be inhibited, thereby having excellent catalytic efficiency and stability.

[0006] The specific technical solutions of the present application include:

[0007] In the first aspect, the present application discloses a preparation method of a nickel-cobalt functionalized metal organic framework catalyst, which comprises the following steps:

[0008] 1) Preparation of MOF-808.

[0009] 2) After placing MOF-808 in a polar solvent and heating to reflux activation, separation, vacuum activation of the obtained solid (the above two activation steps can activate Zr-O metal oxygen clusters in the MOF template and remove solvents and guest molecules in the pores, open the pores of MOF and expose open sites), then disperse in a diffusion hydrophobic solvent; add a hydrophilic solvent containing nickel salt and cobalt salt to the diffusion hydrophobic solvent for Ni / Co diffusion doping, centrifugal washing and drying after exchange reaction, to obtain a nickel-cobalt functionalized metal organic framework catalyst, namely Ni / Co-MOF-808.

[0010] In the above preparation method of the present application, the MOF-808 template with Zr group is first synthesized, then the metal oxide clusters in the MOF-808 template are activated by refluxing in a polar solvent, and then the nickel-cobalt bimetal is introduced into the MOF-808 template through a hydrophobic / hydrophilic double solvent system, so as to obtain the nickel-cobalt bimetal functionalized Ni / Co-MOF-808 catalyst. Compared with the traditional hydrothermal one-pot method, the method of the present application effectively maintains the porous and ordered framework structure of the MOF material, avoids the collapse of the MOF structure caused by the doping of multiple metals, and further avoids the dissolution of the active components in the process of photoelectrocatalytic reaction due to the stable fixation of Ni / Co. Therefore, the nickel-cobalt functionalized metal organic framework catalyst prepared by the method of the present application has excellent catalytic efficiency and stability when applied to the photoelectrocatalytic water splitting reaction.

[0011] As preferred, in step 2), the diffusing hydrophobic solvent is one or more of dichloromethane, n-hexane, cyclohexane and petroleum ether; the hydrophilic solvent is one or more of N,N-dimethylformamide solvent, deionized water, methanol and ethanol; most preferably, the diffusing hydrophobic solvent is n-hexane; and the hydrophilic solvent is N,N-dimethylformamide solvent (DMF).

[0012] The present application finds that, compared with the conventional metal ion doping using a single polar solvent, the hydrophilic / hydrophobic double solvent system can significantly improve the metal ion exchange rate. The polar hydrophilic solvent in the double solvent system can effectively dissolve the Ni 2+ / Co 2+ precursor, promote exchange doping; the non-polar diffusing hydrophobic solvent can form an interface to limit the rapid penetration of metal ions, promote accurate loading, and avoid framework damage. Through experiments, the above-mentioned diffusing hydrophobic solvent and hydrophilic solvent have a better compounding effect, in which n-hexane / DMF shows the best exchange doping effect. The reason is that DMF as a polar hydrophilic solvent can effectively dissolve the metal salt precursor and form a controllable complex (such as [Ni(DMF)6] 2+ , [Co(DMF)6] 2+ ) with the metal to regulate the reaction rate, and the combination of non-polar n-hexane can form a stable interface diffusion, which stabilizes the MOF framework structure while realizing the efficient and stable doping of metal ions.

[0013] As preferred, in step 2), the volume ratio of the diffusing hydrophobic solvent to the hydrophilic solvent is 1-5:1; most preferably, 3:1.

[0014] In step 2), the volume ratio of the diffusing hydrophobic solvent to the hydrophilic solvent has an important influence on the subsequent exchange reaction. Through experiments, it is found that the effect is better under the above-mentioned volume ratio. Among them, when the volume ratio of n-hexane / DMF is 3:1, the interface diffusion mechanism has the best effect, and the Ni 2+ / Co 2+The exchange rate is the highest.

[0015] As preferred, in step 2), the temperature of the exchange reaction is 60-80℃, and the time is 20-40h.

[0016] The conditions of the exchange reaction will significantly affect the performance of the product. In terms of temperature, the doping effect is good for Ni 2+ and Co 2+ at the above-mentioned temperature; if the temperature is too low, the diffusion rate of Ni 2+ / Co 2+ is low, and the solvent has weak dehydrating ability, resulting in limited replacement kinetics; on the contrary, if the temperature is too high, the MOF cluster combination is unstable, the integrity of the MOF framework is damaged, the ligand or metal is released, and the problems of structure collapse or doped metal dissolution from the site occur. In terms of time, if the reaction time is short, the ion exchange is limited by diffusion and kinetics, and the exchange rate is low; as the reaction time continues to increase, the exchange rate of Ni 2+ / Co 2+ increases with the reaction time. When the reaction time is too long, the exchange rate of Ni 2+ / Co 2+ is basically stable, and the marginal benefit decreases with the continuous extension of time, and part of the structure starts to decrease in stability.

[0017] As preferred, in step 2), the molar ratio of nickel and cobalt in the nickel salt and the cobalt salt is 4-0.5:1; most preferably 2:1.

[0018] Ni and Co can complementarily adjust the electronic structure of the active site in catalysis. Ni shows excellent oxygen evolution activity in the hydrogen evolution reaction; Co can promote the migration of oxygen ions and show good oxidation activity, which is also conducive to the stability of the electronic structure. The combination of the two produces a synergistic effect, promotes the two half-reactions, improves the kinetics of the water splitting reaction, and forms a more active center than a single metal.

[0019] If the proportion of Ni is too high, the adsorption of the reaction intermediate will be too strong, making it difficult for the reaction intermediate to desorb to form H2; in addition, too high Ni content will also lead to structural disorder, easy formation of large particles or agglomeration, and reduction of active site exposure; and increase the charge transfer resistance. On the other hand, if the proportion of Co is too high, it will lead to more oxidation states, and the hydrogen production activity of the catalyst will decrease. The present application finds that at a ratio of 2:1, the interaction between Ni and Co is best, and at this ratio, Co can effectively regulate the electronic density of the Ni site, optimize the adsorption energy of the intermediate, and optimize the material structure to expose more active sites, thereby obtaining a catalyst material with high activity, high stability, and fast charge transport capability.

[0020] As preferred, in step 2), the polar solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, methanol and ethanol; further preferably methanol.

[0021] As preferred, in step 2), the heating reflux activation is reflux activation at 60-150℃ for 4-48h, further preferably reflux activation at 60-80℃ for 8-24h.

[0022] As preferred, in step 2), the vacuum activation is activation at 60-150℃ under vacuum for 4-24h.

[0023] As preferred, in step 2), the nickel salt is one or more of nickel sulfate, nickel acetate, nickel chloride, nickel nitrate and nickel perchlorate; the cobalt salt is one or more of cobalt chloride, cobalt sulfate, cobalt acetate, cobalt bromide and cobalt nitrate.

[0024] As preferred, in step 2), the temperature of the exchange reaction is 50-80℃, and the time is 18-36h.

[0025] As preferred, in step 2), the washing and drying is sequentially dipping in N,N-dimethylformamide and acetone washing liquid for 3-5 times, each for 1-6h, and centrifugal separation.

[0026] As preferred, step 1) specifically comprises: dispersing the zirconium salt and the organic ligand in the organic solvent, adding a crystallization regulator and heating the reaction; after the reaction, washing and drying by centrifugation to obtain MOF-808.

[0027] As preferred, in step 1), the molar ratio of the zirconium salt, the organic ligand and the organic solvent is 1:0.2-2.0:100-500.

[0028] As preferred, in step 1), the volume ratio of the crystallization regulator and the organic solvent is 1:1-10.

[0029] As preferred, in step 1), the heating reaction is hydrothermal reaction at 90-150℃ for 12-72h; further preferably stirring reaction at 100-130℃ for 24-48h.

[0030] As preferred, in step 1), after the reaction, the washing and drying by centrifugation is: after the reaction is completed, centrifugal separation of the solid, sequentially dipping in DMF and acetone washing liquid for 3-5 times, each for 1-12h, centrifugal separation and drying.

[0031] As preferred, in step 1), the zirconium salt is zirconium chloride, zirconium nitrate, zirconium oxychloride, zirconium oxynitrate, zirconium sulfate or zirconium acetate; the organic ligand is trimesic acid, 2-aminobenzene-1,3,5-tricarboxylic acid, 1-hydroxybenzene-2,4,6-tricarboxylic acid, 2-bromobenzene-1,3,5-tricarboxylic acid or 2,4,6-tribromobenzene-1,3,5-tricarboxylic acid; the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, methanol, ethanol and dimethyl sulfoxide; and the crystallization regulator is one or more of water, formic acid, acetic acid and benzoic acid.

[0032] In a second aspect, the present application provides a use of the nickel-cobalt functionalized metal organic framework catalyst prepared by the above preparation method in photoelectrocatalytic water splitting.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] (1) In view of the problems of the traditional hydrothermal one-pot method for synthesizing double-metal doped MOF, such as difficulty in maintaining the stability of the framework structure, low binding ability and low introduction efficiency of the Ni / Co active metal active sites when the MOF structure is introduced with the Ni / Co active metal active sites, and dissolution of the MOF active components in the catalytic reaction, the present application uses a post-exchange method based on a MOF template to synthesize, and through optimization of the post-exchange process parameters and the combination of hydrophilic and hydrophobic solvents, a nickel-cobalt functionalized metal organic framework catalyst with a good crystal structure is successfully prepared, the introduction efficiency of the Ni / Co double metal is high, and the functionalized Ni / Co-MOF-808 has a high specific surface area and pore structure, and the active site binding remains stable and is not easy to dissolve out.

[0035] (2) The traditional zirconium-based MOF-808 material has very low photoelectrocatalytic water splitting reaction efficiency, the nickel-cobalt functionalized metal organic framework catalyst prepared by the present application has excellent photoelectrocatalytic water splitting efficiency and stability, compared with the unfunctionalized MOF-808 material and the single-metal functionalized MOF material, the water splitting hydrogen and oxygen production efficiency is significantly improved, the reaction overpotential is significantly reduced, and in the 7 times of continuous water splitting cycle test for 14 hours, the catalyst activity remains stable and there is no obvious dissolution of the active components. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The X-ray diffraction patterns of the materials obtained in Example 1 and Example 2.

[0037] Figure 2 The scanning electron microscope images of the materials obtained in Example 1-2 and Comparative Example 1.

[0038] Figure 3 The element scanning distribution map of the material obtained in Example 2.

[0039] Figure 4Nitrogen adsorption-desorption isotherms of the materials obtained in Example 1-2 and Comparative Example 1.

[0040] Figure 5 Photocatalytic hydrogen production time-hydrogen production curves of the materials obtained in Example 1, Example 2, Example 18-21, Comparative Example 12 and Comparative Example 13.

[0041] Figure 6 Cyclic catalytic hydrogen production stability curves of the material obtained in Example 2.

[0042] Figure 7 Photocatalytic total hydrolysis activity diagrams of the materials obtained in Example 2, Example 18-21, Comparative Example 12 and Comparative Example 13.

[0043] Figure 8 Photoelectrocatalytic water splitting redox voltammetry curves of Example 1, Example 2, Comparative Example 12 and Comparative Example 13. DETAILED DESCRIPTION

[0044] The application will be further described below in conjunction with examples.

[0045] In a first aspect, a method for preparing a nickel-cobalt functionalized metal organic framework catalyst, comprising the following steps:

[0046] 1) Preparation of MOF-808: disperse zirconium salt and organic ligand in organic solvent, add crystallization regulator and heat the reaction; centrifugal washing and drying after reaction to obtain MOF-808.

[0047] In some preferred embodiments, in step 1), the molar ratio of the zirconium salt, the organic ligand and the organic solvent is 1:0.2-2.0:100-500.

[0048] In some preferred embodiments, in step 1), the volume ratio of the crystallization regulator and the organic solvent is 1:1-10.

[0049] In some preferred embodiments, in step 1), the heating reaction is hydrothermal reaction at 90-150℃ for 12-72h; further preferably, stirring reaction at 100-130℃ for 24-48h.

[0050] In some preferred embodiments, in step 1), the washing and drying after reaction is: after the reaction is completed, centrifugal separation of the solid, sequentially immerse and wash with DMF, acetone washing liquid for 3-5 times, 1-12h each time, centrifugal separation and drying.

[0051] In some preferred embodiments, in step 1), the zirconium salt is zirconium chloride, zirconium nitrate, zirconyl chloride, zirconyl nitrate, zirconium sulfate or zirconium acetate; the organic ligand is trimesic acid, 2-aminobenzene-1,3,5-tricarboxylic acid, 1-hydroxybenzene-2,4,6-tricarboxylic acid, 2-bromobenzene-1,3,5-tricarboxylic acid or 2,4,6-tribromobenzene-1,3,5-tricarboxylic acid; the organic solvent is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N,N-diethylformamide, methanol, ethanol and dimethyl sulfoxide; and the crystallization regulator is one or more of water, formic acid, acetic acid and benzoic acid.

[0052] 2) After placing MOF-808 in a polar solvent, heating and refluxing to activate, separation, and after vacuum activation of the obtained solid, dispersing in a diffusion hydrophobic solvent; adding a hydrophilic solvent dissolving nickel salt and cobalt salt to the diffusion hydrophobic solvent to perform Ni / Co diffusion doping, centrifugal washing and drying after 20-40 h of exchange reaction at 60-80 °C, to obtain a nickel-cobalt functionalized metal organic framework catalyst, namely Ni / Co-MOF-808.

[0053] In some preferred embodiments, in step 2), the diffusion hydrophobic solvent is one or more of dichloromethane, n-hexane, cyclohexane and petroleum ether; the hydrophilic solvent is one or more of N,N-dimethylformamide solvent, deionized water, methanol and ethanol; most preferably, the diffusion hydrophobic solvent is n-hexane; and the hydrophilic solvent is N,N-dimethylformamide solvent.

[0054] In some preferred embodiments, in step 2), the polar solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, methanol and ethanol; and further preferably, the polar solvent is methanol.

[0055] In some preferred embodiments, in step 2), the volume ratio of the diffusion hydrophobic solvent to the hydrophilic solvent is 1-5:1; and most preferably, the volume ratio is 3:1.

[0056] In some preferred embodiments, in step 2), the molar ratio of nickel to cobalt in the nickel salt and the cobalt salt is 4-0.5:1; and most preferably, the molar ratio is 2:1.

[0057] In some preferred embodiments, in step 2), the polar solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, methanol and ethanol; and further preferably, the polar solvent is methanol.

[0058] In some preferred embodiments, in step 2), the heating reflux activation is reflux activation at 60-150°C for 4-48h, further preferably reflux activation at 60-80°C for 8-24h.

[0059] In some preferred embodiments, in step 2), the vacuum activation is activation at 60-150°C under vacuum for 4-24h.

[0060] In some preferred embodiments, in step 2), the nickel salt is one or more of nickel sulfate, nickel acetate, nickel chloride, nickel nitrate and nickel perchlorate; and the cobalt salt is one or more of cobalt chloride, cobalt sulfate, cobalt acetate, cobalt bromide and cobalt nitrate.

[0061] In some preferred embodiments, in step 2), the temperature of the exchange reaction is 50-80°C, and the time is 18-36h.

[0062] In some preferred embodiments, in step 2), the washing and drying is sequentially dipping in N,N-dimethylformamide and acetone washing liquid for 3-5 times, each for 1-6h, and centrifugal separation.

[0063] In the second aspect, the application provides a use of the nickel-cobalt functionalized metal organic framework catalyst prepared by the above method in photoelectrocatalytic water splitting.

[0064] Specific embodiments and comparative examples.

[0065] Example 1 (MOF-808 material)

[0066] At room temperature, 322.2mg of zirconium oxychloride octahydrate and 105.1mg of benzene-1,3,5-tricarboxylic acid ligand were weighed and ultrasonically dissolved in 25mL of N,N-dimethylformamide solvent for 5min, 25mL of formic acid modifier was added and ultrasonically mixed; the mixed solution was transferred to a polytetrafluoroethylene-lined reaction kettle, and solvent thermal reaction was carried out at 110°C for 48h; after cooling to room temperature, the solid was centrifugally separated, sequentially dipped in 10mL of N,N-dimethylformamide and acetone washing liquid for 3 times, and centrifugally separated at 10000rpm for 6min to obtain a white solid, which was vacuum dried at 90°C overnight to obtain the MOF-808 material to be functionalized.

[0067] Example 2 (Ni / Co-MOF-808 material)

[0068] At room temperature, 200 mg of MOF-808 material prepared in Example 1 was ultrasonically dispersed in 40 mL of polar solvent (methanol), activated by refluxing at 65 °C for 15 h, and the white solid was collected by centrifugation at 10,000 rpm for 6 min, and activated at 90 °C under vacuum for 12 h. 136 mg of the activated MOF-808 material was ultrasonically dispersed in 37.5 mL of n-hexane solvent; 99.5 mg of nickel acetate tetrahydrate and 49.8 mg of cobalt acetate tetrahydrate were ultrasonically dissolved in 12.5 mL of DMF solvent, and the metal salt solution was slowly added into the n-hexane suspension under continuous magnetic stirring, and Ni / Co doping was carried out by heating and stirring at 60 °C for 24 h; after the reaction was completed, the solid was separated by centrifugation, and the white solid was obtained by sequentially immersing and washing with 10 mL of DMF, acetone washing solution for 3 times, separated by centrifugation at 10,000 rpm for 6 min, and dried at 80 °C overnight to obtain the Ni / Co-MOF-808 material.

[0069] Comparative Example 1 (traditional hydrothermal one-pot method for preparing Ni / Co-MOF-808 material)

[0070] At room temperature, 161.1 mg of zirconium oxychloride octahydrate, 83.1 mg of nickel acetate tetrahydrate, 41.5 mg of cobalt acetate tetrahydrate, and 105.1 mg of the benzene-1,3,5-tricarboxylic acid ligand were ultrasonically dissolved in 25 mL of N,N-dimethylformamide solvent for 5 min, 25 mL of formic acid modifier was added, and the mixture was ultrasonically mixed; the mixture was transferred into a polytetrafluoroethylene-lined reaction kettle, and solvent thermal reaction was carried out at 110 °C for 48 h; after cooling to room temperature, the solid was separated by centrifugation, and the white solid was obtained by sequentially immersing and washing with 10 mL of N,N-dimethylformamide, acetone washing solution for 3 times, separated by centrifugation at 10,000 rpm for 6 min, and dried at 90 °C under vacuum overnight to obtain the Ni / Co-MOF-808 material, which was denoted as Ni / Co-MOF-808-one-pot method.

[0071] Examples 3-10 and Comparative Examples 2-4

[0072] The difference between Example 2 and Examples 3-10 is that the Ni / Co-MOF-808 material prepared in Examples 3-10 selects different hydrophilic / hydrophobic dual solvent systems, and Comparative Examples 2-4 use a single solvent system, as shown in Table 1, wherein the Ni 2+ exchange rate and Co 2+ The exchange rate was calculated from the ICP test results of the washed exchanged product, and the exchange rate = actual measured metal ion content / theoretical metal ion content of the sample added × 100%.

[0073] Table 1: Effect of exchange solvent combination on Ni 2+ / Co 2+ exchange rate

[0074]

[0075] As can be seen from Table 1, compared with single polarity solvent, the metal ion exchange rate is significantly improved by the hydrophilic / hydrophobic dual solvent system. Since the polar hydrophilic solvent in the dual solvent system can effectively dissolve the Ni 2+ / Co 2+ precursor, promote exchange doping; the non-polar hydrophobic solvent can form an interface to limit the rapid penetration of metal ions, promote accurate loading, and avoid framework damage. Among them, n-hexane / DMF shows the best exchange doping effect, because DMF as a polar hydrophilic solvent can effectively dissolve the metal salt precursor, and can form controllable complexes with metals (such as [Ni(DMF)6] 2+ , [Co(DMF)6] 2+ ) to regulate the reaction rate, combined with the non-polar n-hexane to form a stable interface diffusion, while stabilizing the MOF framework structure, realizing the efficient and stable doping of metal ions.

[0076] Examples 11-14 and Comparative Examples 5-6

[0077] The difference from Example 2 is that the volume ratio of the hydrophilic / hydrophobic dual solvent is different when preparing the Ni / Co-MOF-808 material in Examples 11-14 and Comparative Examples 5-6, as shown in Table 2. Among them, the Ni 2+ exchange rate and Co 2+ exchange rate are calculated from the ICP test results of the washed exchanged product.

[0078] Table 2: Effect of exchange solvent ratio on Ni 2+ / Co 2+ exchange rate

[0079]

[0080] As can be seen from Table 2, when the volume ratio of the exchange solvent n-hexane / DMF is 3:1, the interface diffusion mechanism works best, and the Ni 2+ / Co 2+ exchange rate is the highest.

[0081] Examples 15-17 and Comparative Examples 7-8

[0082] The difference from Example 2 is that the exchange reaction temperature is different when preparing the Ni / Co-MOF-808 material in Examples 15-17 and Comparative Examples 7-8, as shown in Table 3. Among them, the Ni 2+ exchange rate and Co 2+ exchange rate are calculated from the ICP test results of the washed exchanged product. Ni 2+ dissolution rate after reaction and Co 2+The post-reaction leaching rate was calculated by the ICP test results of the catalyst samples before and after the 14-hour catalytic cycle reaction, and the post-reaction leaching rate = the metal ion content in the post-reaction catalyst measured by ICP / the metal ion content in the pre-reaction catalyst sample measured by ICP x 100%

[0083] Table 3: Effect of exchange reaction temperature on Ni 2+ / Co 2+ incorporation rate and post-reaction leaching rate

[0084]

[0085] As can be seen from Table 3, the exchange reaction temperature of 60℃ is the best for Ni 2+ and Co 2+ doping effect. When the temperature is too low, the diffusion rate of Ni 2+ / Co 2+ is low, and the solvent dehydration ability is weak, resulting in limited replacement kinetics. When the temperature is too high, it is easy to cause the MOF cluster to be unstable, destroy the integrity of the MOF framework, release the ligand or metal, and cause problems such as structure collapse or doping metal dissolution from the site. Therefore, the reaction temperature of 60℃ is the best temperature for metal exchange and leaching.

[0086] Comparative Examples 9-11

[0087] The difference between Example 2 and Comparative Examples 9-11 is that the exchange reaction time for preparing the Ni / Co-MOF-808 material in Comparative Examples 9-11 is different, as shown in Table 4, wherein the Ni 2+ exchange rate and Co 2+ exchange rate were calculated by the ICP test results of the washed exchanged products. 2+ post-reaction leaching rate and Co 2+ post-reaction leaching rate was calculated by the ICP test results of the catalyst samples before and after the 14-hour catalytic cycle reaction.

[0088] Table 4: Effect of exchange reaction time on Ni 2+ / Co 2+ incorporation rate and post-reaction leaching rate

[0089]

[0090] As can be seen from Table 4, during the Ni / Co doping functionalization reaction of the Ni / Co-MOF-808 material, when the reaction time is short, the ion exchange is limited by diffusion and kinetics, and the exchange rate is low. As the reaction time continues to increase, the Ni 2+ / Co 2+ exchange rate increases with the increase of reaction time. When the reaction time exceeds 24h, the Ni 2+ / Co 2+The exchange rate is basically stable, and the marginal benefit decreases with the continuous extension of time, and part of the structure starts to decrease in stability, so the exchange reaction time of 24h is optimal.

[0091] Examples 18-21 and Comparative Examples 12-13

[0092] The difference from Example 2 is that the mass ratio of doped Ni / Co in the preparation of Ni / Co-MOF-808 material in Examples 18-21 is different, and Comparative Examples 12-13 use single metal doping, as shown in Table 5.

[0093] Table 5: Ni / Co-MOF-808 materials with different doping Ni / Co ratios

[0094]

[0095] Performance test

[0096] The performance of the materials of each example and comparative example is tested:

[0097] (1) As shown in Figure 1 , the X-ray diffraction patterns of the materials prepared in Example 1 and Example 2 are shown. The results show that the X-ray diffraction pattern of the zirconium-based MOF-808 material obtained in Example 1 is similar to that of the Ni / Co-MOF-808 functionalized by Ni / Co bimetallic in Example 2, and shows consistent diffraction characteristic peaks at 2θ of 4.33°, 8.32°, 8.69°, 10°, 10.9°, 13°, 14.2° and 19.32°, etc. No new impurity phase peak or significant peak shift is observed. The peak intensity of Ni / Co bimetallic functionalization is only partially weakened, indicating that the functionalized metal ions are doped into the original MOF framework structure. The X-ray diffraction pattern results prove that the introduction of bimetallic does not destroy the crystal framework of MOF-808, and the material maintains good structural crystal phase stability before and after functionalization.

[0098] (2) As shown in Figure 2 , the scanning electron microscope images of the materials prepared in Examples 1-2 and Comparative Example 1 are shown, as Figure 3Elemental scanning analysis diagram of Ni / Co bimetallic functionalized Ni / Co-MOF-808 material prepared in Example 2 is shown. The scanning electron microscopy results show that the MOF-808 material prepared in Example 1 exhibits obvious octahedral configuration, the edge corners are relatively clear, the overall morphology is regular and stable, the surface is smooth, and the particle size is about 300-400 nm, indicating that the MOF-808 is successfully synthesized. The Ni / Co-MOF-808 material prepared in Example 2 is basically consistent with the morphology of the MOF-808 material, and both present regular octahedral structure, clear geometric shape, and uniform particle size (300-400 nm), indicating that the Ni / Co doping method of the present application has no obvious effect on the morphology and size of the material, does not destroy the morphology of the material, and effectively maintains the micro-stability and overall uniformity of the material. In Comparative Example 1, Ni 2+ and Co 2+ are introduced into the MOF-808 by the traditional one-pot hydrothermal method, and the crystal morphology of the prepared Ni / Co-MOF-808 is obviously degraded. No regular octahedral or cubic crystal morphology is observed in the SEM diagram, but a significant agglomeration structure is observed, indicating that the one-pot method is easy to cause the collapse of the MOF framework when introducing multi-metal function, and the post-solvent exchange method can maintain the crystal structure and channel stability of the template MOF-808. The elemental scanning analysis diagram shows that the Ni / Co in the bimetallic functionalized Ni / Co-MOF-808 material prepared in Example 2 has been successfully introduced, and each element (zirconium, nickel, and cobalt) is uniformly distributed.

[0099] (3) As shown in Figure 4 , the results of the nitrogen adsorption and desorption experiments on the materials prepared in Examples 1-2 and Comparative Example 1 are shown. The results show that the three MOFs prepared in Examples 1-2 and Comparative Example 1 are type I adsorption and desorption isotherms, indicating that they are all microporous materials. The BET specific surface area of the MOF-808 material prepared in Example 1 is 2011.4 m 2 / g, and the BET specific surface area of the Ni / Co functionalized Ni / Co-MOF-808 material prepared in Example 2 is 1945.8 m 2 / g, which indicates that the pore structure of the Ni / Co-MOF-808 prepared by the present application is similar to that of the original MOF-808. The Ni / Co metal ion coordination causes the Ni / Co sites to be incorporated along the edges of the tetrahedral cavity in the MOF-808, resulting in the blocking of nitrogen adsorption and desorption in the pore. The slight decrease in the nitrogen adsorption and desorption capacity of the functionalized MOF. The BET specific surface area of the Ni / Co-MOF-808 prepared by the traditional one-pot hydrothermal method in Comparative Example 1 is significantly lower than that of the zirconium-based MOF-808 prepared in Example 1, indicating that compared with the post-solvent exchange method, directly synthesizing bimetallic functionalized MOF-808 by the traditional one-pot hydrothermal / solvothermal method is more likely to cause the collapse of the structure and pore, and reduce the pore integrity and topological stability of the material.

[0100] (4) Respectively, 10.0 mg of the material obtained in Example 1, Example 2, Examples 18-21 and Comparative Examples 12-13 was ultrasonically dispersed in 20 mL of an aqueous solution containing 10 vol% methanol sacrificial agent, and nitrogen was bubbled into the reaction system for 30 min under dark conditions. The reaction suspension system was irradiated with a 300 W xenon lamp equipped with an AM 1.5G filter under a nitrogen atmosphere to test the catalytic water splitting for hydrogen production, and the effect of the Ni / Co functionalized MOF on the catalytic hydrogen production activity was investigated, and the results are shown in Figure 5 Comparative Example 1. The Ni / Co-MOF-808 material in Example 2 had a significantly improved catalytic hydrogen production activity under simulated sunlight, and was higher than that of single metal functionalized Ni-MOF-808 and Co-MOF-808, and the activity of the further bimetallic functionalized material was greater than the sum of the single metal functionalized materials, indicating that the bimetallic functionalization had a synergistic effect. Further, the catalytic water splitting for hydrogen production activities of Ni / Co-MOF-808 with different doping ratios of Ni / Co were 2-Ni / Co-MOF-808 > 1-Ni / Co-MOF-808 > 3-Ni / Co-MOF-808 > 0.5-Ni / Co-MOF-808 > 4-Ni / Co-MOF-808, indicating that the Ni / Co-MOF-808 in Example 2 with a Ni / Co doping ratio of 2:1 had the optimal catalytic hydrogen production activity.

[0101] (5) 10.0 mg of the Ni / Co-MOF-808 material in Example 2 was ultrasonically dispersed in 20 mL of an aqueous solution containing 10 vol% methanol sacrificial agent under a nitrogen atmosphere, and the reaction suspension system was irradiated with a 300 W xenon lamp equipped with an AM 1.5G filter to perform 7 cycles of 14 hours of catalytic hydrogen production, and the stability of the Ni / Co functionalized MOF in the catalytic reaction process was investigated. As shown in Figure 6 , after 7 cycles of 14 hours of catalytic reaction, the catalytic activity of Ni / Co-MOF-808 did not decrease significantly, and the 14-hour hydrogen production activity only decreased by 4.5%, indicating that the prepared Ni / Co functionalized Ni / Co-MOF-808 catalyst maintained good cycle stability during the catalytic hydrogen production process.

[0102] (6) Respectively, 10.0 mg of the material obtained in Example 2, Examples 18-21 and Comparative Examples 12-13 was ultrasonically dispersed in 20 mL of deionized water, and the reaction suspension system was irradiated with a 300 W xenon lamp equipped with an AM 1.5G filter under a nitrogen atmosphere to perform a 4-hour catalytic total water splitting for hydrogen and oxygen production activity experiment, and the catalytic activity of the different Ni / Co ratio functionalized MOF-808 materials in the catalytic total water splitting was investigated. As shown in Figure 7As shown, the catalytic full-hydrolysis activities of the Ni / Co-MOF-808 materials with different Ni / Co doping ratios are 2-Ni / Co-MOF-808>1-Ni / Co-MOF-808>3-Ni / Co-MOF-808>0.5-Ni / Co-MOF-808>4-Ni / Co-MOF-808, indicating that the Ni / Co-MOF-808 material has the optimal full-hydrolysis activity when the Ni / Co doping ratio is 2:1 in Example 2.

[0103] (7) 3 mg of the materials prepared in Example 1, Example 2, Comparative Example 12 and Comparative Example 13 were weighed and dispersed in a mixed solution of 300 μL of ethanol and 20 μL of Nafion perfluorinated resin, and ultrasonically dispersed for 10 min. Then, 30 μL of the suspension was uniformly coated on FTO conductive glass (active area 10 mm x 10 mm) to prepare a working electrode. A three-electrode system was used, with a platinum mesh as a counter electrode, a saturated Ag / AgCl electrode as a reference electrode, and a 300 W xenon lamp with an AM 1.5G filter as a light source, to measure the photoelectrocatalytic water splitting reaction of the catalyst in the electrolyte, and the results are shown in Figure 8 As shown, the reduction current density and the initial potential size at a given potential are Ni / Co-MOF-808>Ni-MOF-808>Co-MOF-808>MOF-808, and the water oxidation current density and the potential size are Ni / Co-MOF-808>Co-MOF-808>Ni-MOF-808>MOF-808, indicating that the functionalized Ni / Co-MOF-808 material in Example 2 is beneficial to reduce the overpotential of the hydrogen evolution and oxygen evolution reaction, and effectively improve the photoelectrocatalytic water splitting efficiency.

[0104] The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0105] The above description is only a preferred embodiment of the present application, and does not limit the present application in any way, and any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application are still within the protection scope of the technical solution of the present application.

Claims

1. A method of preparing a nickel-cobalt functionalized metal-organic framework catalyst, characterized by: Comprise: 1) preparing MOF-808; 2) placing MOF-808 in a polar solvent and heating to activate under reflux, separating, dispersing the obtained solid in a diffusion hydrophobic solvent after vacuum activation; adding a hydrophilic solvent dissolving nickel salt and cobalt salt dropwise into the diffusion hydrophobic solvent for diffusion doping, centrifuging, washing and drying after exchange reaction at 60-80℃ for 20-40h, to obtain a nickel-cobalt functionalized metal organic framework catalyst; The diffusion hydrophobic solvent is one or more of dichloromethane, n-hexane, cyclohexane and petroleum ether; The hydrophilic solvent is one or more of N,N-dimethylformamide solvent, water, methanol and ethanol; The volume ratio of the diffusion hydrophobic solvent to the hydrophilic solvent is 1-5:1; The molar ratio of nickel to cobalt in the nickel salt and the cobalt salt is 4-0.5:

1.

2. The method of claim 1, wherein: In step 2), The polar solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, methanol and ethanol; The heating under reflux activation is reflux activation at 60-150℃ for 4-48h; The vacuum activation is activation under vacuum at 60-150℃ for 4-24h.

3. The production method according to claim 1 or 2, characterized by: In step 2), The diffusion hydrophobic solvent is n-hexane; The hydrophilic solvent is N,N-dimethylformamide solvent; The volume ratio of the diffusion hydrophobic solvent to the hydrophilic solvent is 3:

1.

4. The production method according to claim 1 or 2, characterized by: In step 2), The nickel salt is one or more of nickel sulfate, nickel acetate, nickel chloride, nickel nitrate and nickel perchlorate; The cobalt salt is one or more of cobalt chloride, cobalt sulfate, cobalt acetate, cobalt bromide and cobalt nitrate; The molar ratio of nickel to cobalt in the nickel salt and the cobalt salt is 2:

1.

5. The production method according to claim 1 or 2, characterized by: In step 2), the temperature of the exchange reaction is 50-80℃, and the time is 18-36h.

6. The production method according to claim 1 or 2, characterized by: In step 2), the washing and drying are sequentially immersing and washing with N,N-dimethylformamide, acetone washing liquid for 3-5 times, each for 1-6h, and centrifugal separation.

7. The method of claim 1, wherein: Step 1) specifically comprises: dispersing a zirconium salt and an organic ligand in an organic solvent, adding a crystallization regulator and heating to react; centrifuging, washing and drying after the reaction to obtain MOF-808.

8. The method of claim 7, wherein: In step 1), The molar ratio of the zirconium salt, the organic ligand and the organic solvent is 1:0.2-2.0:100-500; The volume ratio of the crystallization regulator to the organic solvent is 1:1-10; The heating reaction is hydrothermal reaction at 90-150℃ for 12-72h; The centrifuging, washing and drying after the reaction are: centrifuging the solid after the reaction, sequentially immersing and washing with DMF, acetone washing liquid for 3-5 times, each for 1-12h, and centrifuging and drying.

9. The method of manufacturing according to claim 7 or 8, characterized in that: In step 1), The zirconium salt is zirconium chloride, zirconium nitrate, zirconyl chloride, zirconyl nitrate, zirconium sulfate or zirconium acetate; The organic ligand is trimesic acid, 2-aminobenzene-1,3,5-tricarboxylic acid, 1-hydroxybenzene-2,4,6-tricarboxylic acid, 2-bromobenzene-1,3,5-tricarboxylic acid or 2,4,6-tribromobenzene-1,3,5-tricarboxylic acid; The organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, methanol, ethanol and dimethyl sulfoxide; The crystallization modifier is one or more of water, formic acid, acetic acid, and benzoic acid.

10. Use of the nickel-cobalt functionalized metal organic framework catalyst obtained by the preparation method according to any one of claims 1-9 in photoelectrocatalytic water splitting.

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