Preparation method and application of a cerium-based metal-organic framework photocatalyst

Abstract

The present invention relates to the technical field of catalysts, and discloses a preparation method and application of a cerium-based metal-organic framework photocatalyst, which comprises the following steps: (1) dispersing a tetravalent cerium salt and an organic ligand in an organic solvent, adding a crystallization regulator and carrying out a heating reaction; after the reaction, washing and drying to obtain a Ce(IV)-MOF material; (2) dispersing the Ce(IV)-MOF material after vacuum activation in an exchange solvent, adding a nickel salt and carrying out a Ni functionalization reaction, and the nickel salt is nickel acetate, nickel nitrate, nickel sulfate, nickel chloride or nickel bromide; after the reaction, washing and drying to obtain a Ce(IV)-MOF-Ni material. The present invention successfully prepares a Ce(IV)-MOF material with a good crystal structure, and at the same time, the prepared Ni-functionalized Ce(IV)-MOF-Ni material has excellent photocatalytic water splitting hydrogen production efficiency and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a preparation method and application of a cerium-based metal organic framework photoelectric catalyst. Background Art

[0002] In recent years, photoelectrocatalytic water splitting to produce hydrogen has attracted more and more attention as a clean and sustainable energy conversion technology. Among the many hydrogen production catalysts, metal organic framework materials (MOFs) are considered to be highly promising photoelectrocatalytic materials due to their high specific surface area, adjustable pore size and diverse chemical functionality. UiO-67-bpydc is a Zr-based metal organic framework material with zirconium (Zr) as the central metal and 2,2'-bipyridine-5,5'-dicarboxylic acid (bpydc) as the organic ligand. Due to its highly ordered crystal structure, excellent chemical stability and functionalization potential of bipyridine sites, it has certain research value in the field of photoelectrocatalytic hydrogen production. For example, the invention patent with publication number CN109912809A discloses non-precious metal-metal organic framework composite materials, their preparation methods and applications. The composite material is represented by the chemical formula M-MOFs; M represents the non-precious metal ion Zn(II), and MOFs represents the Zr(IV) metal organic framework carrier material modified with 2,2'-bipyridine-5,5'-dicarboxylic acid as an organic ligand. However, since the d electron orbit of Zr itself is empty, its electronic structure lacks catalytic activity, resulting in weak visible light absorption ability of UiO-67-bpydc in photocatalytic water splitting, low photogenerated electron-hole separation efficiency, and thus limiting its catalytic activity and hydrogen production efficiency.

[0003] Cerium-based MOFs (Ce-MOFs) have shown great potential in photocatalysis and electrocatalysis due to their excellent chemical and thermal stability, tunable electronic structure, and abundant oxygen vacancies. Ce-UiO-67-bpydc (Ce(IV)-MOF) is a Zr-based MOF analogue that has good structural stability and is considered to be an excellent modified material for Zr-based MOFs due to the unique electronic properties of Ce.

[0004] In addition, introducing nickel (Ni) as an active site in MOFs is a key means to improve the photoelectrocatalytic hydrogen production performance of materials. First, the d-orbital electron structure of Ni has good coordination ability with the π system of bipyridine ligands, which can effectively promote the separation and transport of photogenerated charges. Second, as an efficient catalytic site for the hydrogen evolution reaction (HER), Ni can significantly reduce the overpotential of the hydrogen evolution reaction and improve the activity of the catalyst. More importantly, Ni functionalization can also enhance the light absorption ability and surface reaction activity of the material by regulating the electron distribution of Ce-MOF. In addition, the coordination of Ni ions with ligands can stabilize the active sites and extend the lifespan of the catalyst. Therefore, Ni functionalization not only has the potential to optimize the photoelectrochemical properties of Ce-MOF, but also provides more active sites, enabling it to exhibit excellent performance in photoelectrocatalytic water splitting for hydrogen production, which provides an important idea for the development of efficient and stable photoelectrocatalysts. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a preparation method and application of a cerium-based metal-organic framework photoelectrocatalyst. By using the solvothermal stirring method, Ce(IV)-MOF analogs are rapidly synthesized, effectively maintaining the porous ordered framework structure of the UiO-67-bpydc material and avoiding the generation of by-products such as Ce(III) formate complexes during the synthesis of Ce(IV)-MOF. Further, by complexing Ni catalytic active sites at the organic ligand sites of Ce(IV)-MOF, the Ni-functionalized Ce-UiO-67-bpydc-Ni material is obtained, improving the dispersion of the active sites. The prepared Ce-UiO-67-bpydc-Ni material has excellent photoelectrocatalytic water splitting hydrogen production efficiency and stability.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a cerium-based metal-organic framework photoelectrocatalyst, including the following steps:

[0008] (1) Dispersing a tetravalent cerium salt and an organic ligand in an organic solvent, adding a crystallization regulator and carrying out a heating reaction. The crystallization regulator is water, formic acid, acetic acid or benzoic acid; after the reaction, washing and drying are carried out to obtain a Ce(IV)-MOF material;

[0009] (2) After vacuum activating the Ce(IV)-MOF material, dispersing it in an exchange solvent, adding a nickel salt and carrying out a Ni-functionalization reaction. The nickel salt is nickel acetate, nickel nitrate, nickel sulfate, nickel chloride or nickel bromide, and the molar ratio of nickel ions in the Ce(IV)-MOF material to the nickel salt is 1:0.1 - 2; after the reaction, washing and drying are carried out to obtain a Ce(IV)-MOF-Ni material.

[0010] Preferably, in step (1), the molar ratio of the tetravalent cerium salt, the organic ligand, and the organic solvent is 1: 0.8-1.5: 50-300.

[0011] Preferably, in step (1), the molar ratio of cerium ions to the crystallization regulator in the tetravalent cerium salt is 1: 1-50; more preferably, the molar ratio of cerium ions to the crystallization regulator in the tetravalent cerium salt is 1: 5-20.

[0012] Preferably, in step (1), the conditions for the heating reaction are stirring and reacting at 80-140 °C for 10-100 min; more preferably, the heating conditions are 100-120 °C, and the stirring reaction time is 10-60 min.

[0013] Preferably, in step (1), the tetravalent cerium salt is ammonium cerium nitrate, cerium tetrachloride, cerium nitrate, or cerium acetate.

[0014] Preferably, in step (1), the organic ligand is 2,2'-bipyridine-5,5'-dicarboxylic acid, biphenyl dicarboxylic acid, 2,5-thiophene dicarboxylic acid, or 2,5-pyrazole dicarboxylic acid.

[0015] Preferably, in step (1), the organic solvent is one or more of DMF, methanol, ethanol, dichloromethane, dimethyl sulfoxide, ethylene glycol, ether, acetone, and tetrahydrofuran.

[0016] Preferably, in step (1), the post-reaction washing and drying treatment is as follows: after the reaction is completed, the solid is separated by centrifugation, and then washed statically with DMSO, DMF, and methanol washing solutions for 1-12 hours in sequence, followed by centrifugation and drying to obtain the Ce(IV)-MOF material to be functionalized, denoted as Ce-UiO-67-bpydc. More preferably, the static washing time of the washing solution is 2-4 h.

[0017] Preferably, in step (2), the conditions for the vacuum activation are activation at 40-120 °C under vacuum for 1-24 h.

[0018] Preferably, in step (2), the exchange solvent is one or more of ethanol, water, ethylene glycol dimethyl ether, and acetonitrile; more preferably, it is ethanol and / or water, and most preferably, it is a mixed solution of ethanol and water with a volume ratio of 2-4: 1.

[0019] Preferably, in step (2), when the Ce(IV)-MOF material is dispersed in the exchange solvent, the ratio of the Ce(IV)-MOF material to the exchange solvent is 1 g: 10-15 mL.

[0020] Preferably, in step (2), the Ce(IV)-MOF material is dispersed in an exchange solvent and stirred for 10 - 30 min, and then a nickel salt is added and stirred for 10 - 30 min.

[0021] Preferably, in step (2), the molar ratio of the Ce(IV)-MOF material to nickel ions in the nickel salt is 1:1 - 2.

[0022] Preferably, in step (2), the Ni functionalization reaction is carried out by stirring at 40 - 100 °C for 2 - 24 h; more preferably, it is stirred at 60 - 80 °C for 10 - 14 h.

[0023] Preferably, in step (2), the post-reaction washing and drying treatment is as follows: after the reaction is completed, the solid is separated by centrifugation, washed with deionized water and allowed to stand for 1 - 6 h, and then centrifuged and dried to obtain the Ce(IV)-MOF-Ni material, denoted as Ce-UiO-67-bpydc-Ni.

[0024] In a second aspect, the present invention provides an application of the cerium-based metal-organic framework photocatalyst prepared by the above preparation method in photocatalytic hydrogen production.

[0025] Compared with unfunctionalized UiO-67-bpydc, the catalytic hydrogen production efficiency of the Ce-UiO-67-bpydc-Ni material is significantly improved, and the reaction stability is good, showing good application prospects.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) It is difficult to synthesize modified Ce(IV)-MOF by the traditional hydrothermal method because Ce(IV) is easily reduced to Ce(III) by interacting with ligands or solvents in many reaction environments, generating Ce(III) complexes, resulting in the failure to successfully form the Ce(IV)-MOF framework structure. The present invention synthesizes by the solvothermal stirring method. Through the optimization of process parameters and the screening of suitable crystallization regulators, Ce(IV)-UiO-67-bpydc with a good crystal structure is successfully prepared. Compared with the hydrothermal synthesis method, this synthesis method is fast and convenient and can well maintain the porous ordered framework structure of Ce(IV)-MOF.

[0028] (2) Regarding the difficulty of 2+ directionally introducing Ni 2+Regarding the problems of low binding ability and introduction efficiency, and the difficulty in maintaining the stability of the MOF framework structure under high-temperature reactions, the present invention uses the solvent-assisted exchange method to complex Ni catalytic active sites at the organic ligand sites. By optimizing the nickel salt and the exchange reaction conditions, Ni catalytic reaction active sites are successfully introduced onto the MOF organic ligand with high introduction efficiency. Moreover, the functionalized Ce(IV)-MOF-Ni has a high specific surface area and pore structure, and its crystal structure remains stable.

[0029] (3) The traditional UiO-67x material has extremely low efficiency in the photoelectrocatalytic water splitting reaction. The functionalized Ce-UiO-67-bpydc-Ni prepared by the present invention has excellent photoelectrocatalytic water splitting hydrogen production efficiency and stability. Compared with the non-functionalized UiO-67-bpydc material, the hydrogen production efficiency is increased by about 15 times, the reaction overpotential is significantly reduced, and the activity remains stable during 6 consecutive hydrogen production cycle tests with a total of 12 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the X-ray diffraction pattern (XRD) of the products of Examples 1-3.

[0031] Figure 2 It is the nitrogen adsorption and desorption isotherm (BET) of the products of Examples 1-3.

[0032] Figure 3 It is the 1H nuclear magnetic resonance spectrum (1HNMR) of the product of Example 1.

[0033] Figure 4 It is the scanning electron microscope image of the products of Examples 2 and 3.

[0034] Figure 5 It is the elemental scanning distribution map of the product of Example 2.

[0035] Figure 6 It is the X-ray diffraction pattern (XRD) of the product of Example 4.

[0036] Figure 7 It is the X-ray diffraction pattern (XRD) of the products of Examples 5-9.

[0037] Figure 8 It is the X-ray diffraction pattern (XRD) of the products of Examples 24-28.

[0038] Figure 9 It is the visible light catalytic hydrogen production time-hydrogen production amount curve of the products of Examples 1-3.

[0039] Figure 10 It is the photoelectrocatalytic hydrogen production volt-ampere characteristic curve of the products of Examples 1-3.

[0040] Figure 11It is the cyclic catalytic hydrogen production stability diagram of the product in Example 2. Detailed implementation manners

[0041] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0042] The preparation of the cerium-based metal-organic framework photocatalyst in the present invention includes the following steps:

[0043] (1) Dispersing a tetravalent cerium salt and an organic ligand in an organic solvent, with the molar ratio of the tetravalent cerium salt, the organic ligand, and the organic solvent being 1:0.8 - 1.5:50 - 300. Adding a crystallization regulator, with the molar ratio of cerium ions in the tetravalent cerium salt to the crystallization regulator being 1:1 - 50, and carrying out a heating reaction, stirring and reacting at 80 - 140 °C for 10 - 100 min; after the reaction is completed, centrifuging to separate the solid, and successively statically washing with DMSO, DMF, and methanol washing solutions for 1 - 12 h, centrifuging and drying to obtain the Ce(IV)-MOF material to be functionalized, denoted as Ce-UiO-67-bpydc.

[0044] (2) Activating the Ce(IV)-MOF material at 40 - 120 °C under vacuum for 1 - 24 h. Vacuum activation is used to remove the solvent and guest molecules in the pores, exposing unsaturated coordination sites; then dispersing the vacuum-activated Ce(IV)-MOF material in an exchange solvent, with the dispersion ratio of the Ce(IV)-MOF material to the exchange solvent being 1 g:10 - 15 mL, stirring for 10 - 30 min; adding a nickel salt and stirring for 10 - 30 min, with the molar ratio of the Ce(IV)-MOF material to nickel ions in the nickel salt being 1:0.1 - 2, carrying out a Ni functionalization reaction, stirring and reacting at 40 - 100 °C for 2 - 24 h; after the reaction is completed, centrifuging to separate the solid, statically washing with deionized water washing solution for 1 - 6 h, centrifuging and drying to obtain the Ce(IV)-MOF-Ni material, denoted as Ce-UiO-67-bpydc-Ni.

[0045] In the specific embodiments of the present invention, the tetravalent cerium salt is ammonium cerium nitrate, cerium tetrachloride, cerium nitrate, or cerium acetate.

[0046] In the specific embodiments of the present invention, the organic ligand is 2,2'-bipyridine-5,5'-dicarboxylic acid, biphenyl dicarboxylic acid, 2,5-thiophene dicarboxylic acid, or 2,5-pyrazole dicarboxylic acid.

[0047] In the specific embodiments of the present invention, the organic solvent is one or more of DMF, methanol, ethanol, dichloromethane, dimethyl sulfoxide, ethylene glycol, ether, acetone, and tetrahydrofuran.

[0048] In a specific embodiment of the present invention, the crystallization regulator is water, formic acid, acetic acid or benzoic acid.

[0049] In a specific embodiment of the present invention, the exchange solvent is one or more of ethanol, water, ethylene glycol dimethyl ether and acetonitrile; further preferably ethanol and / or water, and most preferably a mixed solution of ethanol and water with a volume ratio of 2-4:1.

[0050] In a specific embodiment of the present invention, the nickel salt is nickel acetate, nickel nitrate, nickel sulfate, nickel chloride or nickel bromide.

[0051] Example 1 (Preparation of Ce(IV)-MOF material (Ce-UiO-67-bpydc))

[0052] At room temperature, 271.2 mg of tetravalent cerium salt (ammonium cerium nitrate) and 156.3 mg of organic ligand (2,2'-bipyridine-5,5'-dicarboxylic acid) were weighed and ultrasonically dissolved in 10.0 mL of organic solvent (N,N-dimethylformamide). At room temperature, 200 μL of crystallization regulator (formic acid) was added, and ultrasonic treatment was carried out for 3 min to dissolve it uniformly. The mixed solution was transferred to an oil bath at 110 °C and magnetically stirred for 15 min. After the reaction solution was cooled to room temperature, it was centrifuged at 10000 rpm for 4 min to separate and collect the precipitate, which was washed three times with 5.0 mL of DMSO, 5.0 mL of N,N-dimethylformamide, and 15.0 mL of methanol respectively, and each time was allowed to stand for 2 h for washing. It was centrifuged at 10000 rpm for 4 min to separate the milky white solid, and dried overnight at 80 °C to obtain the Ce(IV)-MOF material, denoted as Ce-UiO-67-bpydc.

[0053] Example 2 (Preparation of Ce(IV)-MOF-Ni material (Ce-UiO-67-bpydc-Ni))

[0054] At room temperature, 0.6 mmol of the Ce-UiO-67-bpydc material prepared in Example 1 was vacuum-activated at 80 °C for 12 h, and was ultrasonically dispersed together with 0.6 mmol of nickel salt (nickel acetate) in 20 mL of exchange solvent (a mixed solution of 15 mL of ethanol and 5 mL of deionized water), and stirred at 70 °C for 12 h for Ni functionalization reaction. After the reaction solution was cooled to room temperature, it was centrifuged at 10000 rpm for 4 min to separate and collect the precipitate, which was washed three times with 10.0 mL of deionized water and 15.0 mL of acetone respectively, and each time was allowed to stand for 2 h for washing. It was centrifuged at 10000 rpm for 4 min to separate the milky white solid, and dried overnight at 80 °C to obtain the Ce(IV)-MOF-Ni material, denoted as Ce-UiO-67-bpydc.

[0055] Example 3 (Preparation of Zr-MOF material (UiO-67-bpydc), traditional hydrothermal method)

[0056] At room temperature, 135.0 mg of zirconium tetrachloride was weighed and ultrasonically dissolved in a mixed solution of 50.0 mL of N,N-dimethylformamide and 2.5 mL of deionized water. Then, 212.0 mg of benzoic acid regulator was added and ultrasonically dissolved to make it homogeneous. 141.5 mg of 2,2'-bipyridine-5,5'-dicarboxylic acid ligand was weighed and ultrasonically dispersed in the solution. Then, the mixed solution was transferred to a reaction kettle and subjected to a solvothermal reaction at 120 °C for 24 h. After the reaction solution was cooled to room temperature, it was centrifuged at 10000 rpm for 4 min to separate and collect the precipitate, which was washed three times with 5.0 mL of DMSO, 5.0 mL of N,N-dimethylformamide, and 15.0 mL of methanol respectively, and each time it was allowed to stand for 2 h for washing. It was centrifuged at 10000 rpm for 4 min to separate the milky white solid, and dried overnight at 80 °C to obtain the Zr-MOF material, denoted as UiO-67-bpydc.

[0057] Example 4 (Preparation of Ce(IV)-MOF material (Ce-UiO-67-bpydc - without regulator))

[0058] The difference from Example 1 is that no crystallization regulator was added in Example 4. The specific steps are as follows:

[0059] At room temperature, 271.2 mg of tetravalent cerium salt (ammonium cerium nitrate) and 156.3 mg of organic ligand (2,2'-bipyridine-5,5'-dicarboxylic acid) were weighed and ultrasonically dissolved in 10.0 mL of organic solvent (N,N-dimethylformamide), and ultrasonically dissolved for 3 min to make it homogeneous. The mixed solution was transferred to an oil bath at 110 °C and magnetically stirred for 15 min. After the reaction solution was cooled to room temperature, it was centrifuged at 10000 rpm for 4 min to separate and collect the precipitate, which was washed three times with 5.0 mL of DMSO, 5.0 mL of N,N-dimethylformamide, and 15.0 mL of methanol respectively, and each time it was allowed to stand for 2 h for washing. It was centrifuged at 10000 rpm for 4 min to separate the milky white solid, and dried overnight at 80 °C to obtain the Ce(IV)-MOF material, denoted as Ce-UiO-67-bpydc - without regulator.

[0060] Examples 5 - 8

[0061] The difference from Example 1 is that the oil bath reaction time was different when preparing the Ce(IV)-MOF material (Ce-UiO-67-bpydc) in Examples 5 - 8, as shown in Table 1 specifically.

[0062] Table 1 Ce-UiO-67-bpydc materials with different reaction times

[0063]

[0064] Examples 9 - 16

[0065] The difference from Example 2 is that when preparing the Ce(IV)-MOF-Ni material (Ce-UiO-67-bpydc-Ni) in Examples 9 - 16, the exchange solvent is different, as shown in Table 2 specifically, where Ni 2+ The binding rate is calculated from the ICP test results of the product after washing, for Ni 2+ Binding rate = Content of Ni ions actually measured in the solution / Content of Ni ions theoretically calculated based on the mass of the added sample 2+ * 100%. 2+

[0066] Table 2 Influence of exchange solvent on Ni 2+ binding rate

[0067]

[0068] As can be seen from Table 2, when using a single solvent, deionized water as the solvent has the best binding effect on Ni 2+ Since nickel acetate has low solubility in ethanol, in a single ethanol solvent, the binding efficiency of Ni 2+ with the coordination sites in MOF is not high. Further, by adjusting the ratio of the ethanol / water mixed solvent, the Ni 2+ binding rate will be affected. Water helps the dissolution of nickel salt, and ethanol as a low-polarity solvent helps Ni 2+ bind with the coordination sites in MOF. The Ni 2+ binding rate is the highest when the volume ratio of ethanol / water is 3:1. Increasing the volume ratio of ethanol / water further will instead reduce the Ni 2+ binding rate.

[0069] Examples 17 - 22

[0070] The difference from Example 2 is that when preparing the Ce(IV)-MOF-Ni material (Ce-UiO-67-bpydc-Ni) in Examples 17 - 22, the Ni functionalization reaction time is different, as shown in Table 3 specifically, where Ni 2+ The binding rate is calculated from the ICP test results of the product after washing.

[0071] Table 3 Influence of Ni functionalization reaction time on Ni 2+ binding rate

[0072]

[0073] ​As can be seen from Table 3, during the Ni-functionalization reaction of the Ce(IV)-MOF-Ni material, when the reaction time was 1 - 8 h, the Ni 2+ binding efficiency increased rapidly with the increase of the reaction time. Subsequently, as the reaction time continued to increase, when the reaction time was 8 - 10 h, the Ni 2+ binding efficiency increased slowly. When the reaction time exceeded 10 h, the Ni 2+ binding efficiency was basically stable, and the maximum binding rate was about 80%.

[0074] Examples 23 - 27

[0075] The difference from Example 2 is that when preparing the Ce(IV)-MOF-Ni material (Ce-UiO-67-bpydc-Ni) in Examples 23 - 27, different nickel salts were used, as shown in Table 4 specifically. Among them, the Ni 2+ binding rate was calculated from the ICP test results of the product after washing. The crystallization situation of Ce-UiO-67-bpydc-Ni is as Figure 8 shown.

[0076] Table 4 Influence of nickel salts on the Ni 2+ binding rate

[0077]

[0078] From Table 4 and Figure 8 it can be seen that the nickel salts used in the Ni-functionalization reaction have a certain influence on the Ni 2+ binding efficiency and the crystal form of the material in Ce-UiO-67-bpydc-Ni. When nickel acetate was used as the nickel salt for exchange, the crystal form of the Ce-UiO-67-bpydc material was well maintained, and the Ni 2+ binding efficiency was the highest, reaching 80%. When nickel tetrafluoroborate was used as the nickel salt for exchange, nickel tetrafluoroborate seriously damaged the crystal structure of Ce-UiO-67-bpydc. In addition, when nickel nitrate, nickel sulfate, nickel chloride, and nickel bromide were used as the nickel salts for exchange, the original crystal structure of the material could be basically maintained. However, the Ni 2+ binding rate was slightly lower, but still higher than the Ni 2+ binding rate when nickel tetrafluoroborate was used as the nickel salt.

[0079] Performance test:

[0080] Test the material properties of each example and comparative example:

[0081] (1) As Figure 1The X-ray diffraction patterns of the materials in Examples 1-3 are shown. The results show that the X-ray diffraction pattern of the cerium-based analogue Ce-UiO-67-bpydc obtained in Example 1 is similar to that of the zirconium-based UiO-67-bpydc obtained in Example 3, indicating that the cerium-based analogue Ce-UiO-67-bpydc synthesized by the crystallization regulator-assisted solvothermal stirring method has no effect on the MOF structure, and the cerium-based analogue Ce-UiO-67-bpydc synthesized in the present invention has the same crystal structure as the original parent MOF. Further comparison of the Ni-functionalized Ce-UiO-67-bpydc-Ni material prepared in Example 2 shows that its diffraction pattern is similar to that of the non-functionalized materials in Examples 1 and 3, indicating that the preparation method of Ce-UiO-67-bpydc-Ni by solvent-assisted complexation of Ni at the organic ligand sites of MOF has no effect on the MOF structure and the crystal form remains stable.

[0082] (2) As Figure 2 shown are the results of nitrogen adsorption and desorption experiments on the materials in Examples 1-3. The results show that the three MOFs prepared in Examples 1-3 are all type I adsorption-desorption isotherms, indicating that they are all microporous materials. The BET specific surface area of the unmodified UiO-67-bpydc material prepared in Example 3 is 2301.2 m 2 / g, and the BET specific surface area of the cerium-based analogue Ce-UiO-67-bpydc material prepared in Example 1 is 2287.4 m 2 / g, which indicates that the pore structure of the cerium-based analogue prepared in the present invention is similar to that of the original MOF. The BET specific surface area of the Ni-functionalized Ce-UiO-67-bpydc-Ni material prepared in Example 2 is 2192.7 m 2 / g, indicating that with the introduction of Ni into the Ce-UiO-67-bpydc material, the specific surface area decreases slightly, which may be due to the coordination grafting of Ni ions with organic ligands resulting in the blocking of nitrogen, but the overall specific surface area is still large, indicating that the Ni treatment does not damage the MOF framework structure and generate mesopores.

[0083] (3) Dissolve the Ce-UiO-67-bpydc obtained in Example 1 in a mixed solution of deuterated hydrochloric acid (DCl) and deuterated dimethyl sulfoxide (d6-DMSO) with a molar ratio of 1:0.07, and perform nuclear magnetic resonance hydrogen spectrum analysis. The results are as Figure 3 shown. The nuclear magnetic resonance hydrogen spectrum confirms the presence of the 2,2'-bipyridine-5,5'-dicarboxylic acid ligand in the Ce-UiO-67-bpydc material, and the chemical formula is determined by calculation to be the Ce-UiO-67-bpydc material.

[0084] (4) As Figure 4Shown are the scanning electron microscope images of the materials in Example 2 and Example 3, as Figure 5 Shown is the elemental scanning analysis image of the Ni-functionalized Ce-UiO-67-bpydc-Ni material prepared in Example 2. The results show that both the UiO-67-bpydc material and the Ce-UiO-67-bpydc-Ni material exhibit a uniform octahedral structure with a smooth surface and a particle size of approximately 400 nm. It also shows that the Ni-functionalization of the cerium-based MOF-like material in the present invention has no obvious effect on the morphology and size of the material, and the MOF structure remains stable. The elemental scanning analysis image shows that nickel has been successfully introduced into the Ni-functionalized Ce-UiO-67-bpydc-Ni material prepared in Example 2, and all elements (cerium, nickel, carbon, oxygen, and nitrogen) are evenly distributed.

[0085] (5) As Figure 6 Shown is the X-ray diffraction pattern of the material in Example 4. The results show that during the preparation of the Ce-UiO-67-bpydc material in Example 4, due to the absence of a crystallization regulator, the peak of the diffraction pattern is significantly reduced and the baseline fluctuates, indicating that the Ce-UiO-67-bpydc crystal structure is difficult to form. This shows that the addition of the crystallization regulator plays an important role in helping the formation of the Ce-UiO-67-bpydc crystal.

[0086] (6) As Figure 7 Shown are the X-ray diffraction patterns of the Ce-UiO-67-bpydc materials in Examples 5-9. The results show that in Examples 5-9, the Ce-UiO-67-bpydc materials were prepared with different oil bath reaction times. The material obtained with a reaction time of 15 min shows a diffraction pattern consistent with that of Ce-UiO-67-bpydc, indicating the successful synthesis of the MOF. For reaction times from 30 min to 1 h, the diffraction patterns of the obtained materials are all consistent with the diffraction pattern of Ce-UiO-67-bpydc. However, when the oil bath reaction time is too long, at 2 h, an additional diffraction peak appears in the diffraction pattern of Ce-UiO-67-bpydc at 16.6°. This may be due to the reduction of tetravalent cerium under a long-term heating environment, resulting in the formation of [Ce(O2CH)3] of Ce(iii). When the oil bath reaction time is continuously extended to 5 h, the peak intensity of the by-product [Ce(O2CH)3] of Ce(iii) further increases, indicating that a too long oil bath reaction will produce by-products, which has an adverse effect on the formation of the Ce-UiO-67-bpydc crystal structure.

[0087] (7) Weigh 20.0 mg of the materials in Examples 1 - 3 respectively, and ultrasonically disperse them in 50 mL of an aqueous solution of methanol (10 vol%). Under dark conditions, introduce nitrogen into the reaction solution system for 30 min to evacuate the air. Under a nitrogen atmosphere, irradiate the reaction suspension system with four 1W 420 nm monochromatic LED lights to conduct a catalytic hydrogen production test in water, and investigate the effect of MOF functionalization on the catalytic hydrogen production activity. The results are as Figure 9 shown. For the Zr - based UiO - 67 - bpydc material in Example 3, the catalytic hydrogen production activity of the cerium - based analogue Ce - UiO - 67 - bpydc in Example 1 is improved under 420 nm light. Further, the catalytic hydrogen production activity of Ce - UiO - 67 - bpydc - Ni after Ni functionalization in Example 2 is significantly improved.

[0088] (8) Weigh 5 mg of the materials in Examples 1 - 3 respectively and disperse them in a mixed solution of 500 μL of ethanol and 30 μL of Nafion perfluorinated resin, and ultrasonically disperse for 10 min to make it uniformly dispersed. Then take 50 μL of the suspension and evenly coat it on an FTO conductive glass (1×2 cm) to prepare a working electrode. Use a platinum mesh as the counter electrode and a saturated Ag / AgCl electrode as the reference electrode. Using an FX - 300HU xenon lamp with a 420 nm filter as the light source, measure the photoelectrocatalytic hydrogen evolution reaction of the catalyst in a 0.5 M sodium perchlorate electrolyte. The results are as Figure 10 shown. At a given potential, the current density of proton reduction is Ce - UiO - 67 - bpydc - Ni > Ce - UiO - 67 - bpydc > UiO - 67 - bpydc, and the proton reduction potential is Ce - UiO - 67 - bpydc - Ni < Ce - UiO - 67 - bpydc < UiO - 67 - bpydc, indicating that the Ni - functionalized Ce - UiO - 67 - bpydc - Ni material in Example 2 is beneficial to reducing the hydrogen evolution reaction potential and improving the catalytic hydrogen production efficiency.

[0089] (9) Weigh 20.0 mg of the material in Example 2 and ultrasonically disperse it in 50 mL of an aqueous solution of methanol (10 vol%). A cyclic experiment of catalytic hydrogen production in a nitrogen atmosphere for a total of 12 hours in 6 cycles is carried out to investigate the stability of the Ce - UiO - 67 - bpydc - Ni catalyst during the hydrogen production process. For the cyclic test, take the upper - layer gas every 30 min to test the hydrogen content. Each cycle is 2 h. After each cycle, purge the system with N2 for 30 min again, without replacing the solvent or other conditions, and conduct the next cycle. As Figure 11As shown, after 6 cycles, the hydrogen production activity of Ce-UiO-67-bpydc-Ni did not decrease significantly, and the hydrogen production activity only decreased by 1.7% in 12 hours, indicating that the prepared Ni-functionalized Ce-UiO-67-bpydc-Ni catalyst maintained good cycle stability during the catalytic hydrogen production process.

[0090] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A preparation method of a cerium-based metal-organic framework photocatalyst, characterized in that, It includes the following steps: (1) Disperse a tetravalent cerium salt and an organic ligand in an organic solvent. The organic ligand is 2,2'-bipyridine-5,5'-dicarboxylic acid. Add a crystallization regulator and carry out a heating reaction. The crystallization regulator is water, formic acid, acetic acid or benzoic acid. After the reaction, wash and dry to obtain a Ce(IV)-MOF material; (2) Vacuum activate the Ce(IV)-MOF material and disperse it in an exchange solvent. Add a nickel salt and carry out a Ni functionalization reaction. The nickel salt is nickel acetate, nickel nitrate, nickel sulfate, nickel chloride or nickel bromide. The molar ratio of nickel ions in the Ce(IV)-MOF material to the nickel salt is 1:0.1-2. After the reaction, wash and dry to obtain a Ce(IV)-MOF-Ni material.

2. The preparation method of the cerium-based metal-organic framework photocatalyst according to claim 1, characterized in that, In step (1), the molar ratio of the tetravalent cerium salt, the organic ligand, and the organic solvent is 1:0.8-1.5:50-300; the molar ratio of cerium ions in the tetravalent cerium salt to the crystallization regulator is 1:1-50.

3. The preparation method of the cerium-based metal-organic framework photocatalyst according to claim 1, characterized in that, In step (1), the conditions for the heating reaction are stirring reaction at 80-140 °C for 10-100 min.

4. The preparation method of the cerium-based metal-organic framework photocatalyst according to any one of claims 1-3, characterized in that, In step (1), the tetravalent cerium salt is ammonium cerium nitrate, cerium tetrachloride, cerium nitrate or cerium acetate.

5. The preparation method of the cerium-based metal-organic framework photocatalyst according to any one of claims 1-3, characterized in that, In step (1), the organic solvent is one or more of DMF, methanol, ethanol, dichloromethane, dimethyl sulfoxide, ethylene glycol, ether, acetone and tetrahydrofuran.

6. The preparation method of the cerium-based metal-organic framework photocatalyst according to claim 1, characterized in that, In step (2), the exchange solvent is one or more of ethanol, water, ethylene glycol dimethyl ether and acetonitrile.

7. The preparation method of the cerium-based metal-organic framework photocatalyst according to claim 1, characterized in that, In step (2), the Ni functionalization reaction is stirring reaction at 40-100 °C for 2-24 h.

8. The preparation method of the cerium-based metal-organic framework photocatalyst according to claim 1 or 6 or 7, characterized in that, In step (2), the conditions for the vacuum activation are activation at 40-120 °C under vacuum conditions for 1-24 h.

9. Application of a cerium-based metal-organic framework photocatalyst prepared by the preparation method according to any one of claims 1-8 in photocatalytic hydrogen production.

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