Preparation method and application of amino group modified Ti-based MOFs

Abstract

The invention provides a preparation method and application of amino group modified Ti-based MOFs (Metal-Organic Frameworks), which comprises the following steps: adding tetrabutyl titanate into a mixed organic solvent, stirring and carrying out ultrasonic treatment to obtain a mixed solvent; placing an organic ligand NH2-BDC in a mixed solvent to obtain a ligand I, and placing an organic ligand BDC in the mixed solvent to obtain a ligand II; the ligand I and the ligand II are subjected to stirring and ultrasonic treatment respectively till the organic ligands are fully dissolved in the mixed solution, and pretreatment is completed; the ligand I and the ligand II are mixed according to n (NH2-BDC) / n (BDC), the ratio of n (NH2-BDC) / n (BDC) is (2-9): (1-8), and the NM (x) photocatalyst is prepared. The problems that the titanium-based MOFs prepared by the existing method are uneven in ligand distribution, low in synthesis efficiency and insufficient in visible light utilization rate are solved.

Description

Technical Field

[0001] This invention belongs to the fields of nanotechnology and electrocatalysis technology, specifically relating to a method for preparing and applying amino-modified Ti-based MOFs. Background Technology

[0002] Against the backdrop of global energy structure transformation and the achievement of "dual carbon" goals, developing innovative technologies for the efficient conversion of solar energy has become crucial for solving energy and environmental problems. Photocatalysis can convert solar energy into chemical energy, enabling the high-efficiency application of solar energy. MOF materials, with their unique framework structure, provide a novel molecular platform for the design of photocatalytic materials. Among them, titanium-based MOFs have attracted widespread attention from researchers due to their excellent structural stability and tunable band structure; however, their insufficient visible light utilization hinders their application in practical production. Furthermore, current research largely focuses on constructing MOF materials with single ligands, neglecting the intrinsic structure and unique properties of organic ligands.

[0003] In the field of photocatalysis, MOF materials have demonstrated great potential due to their unique advantages. Organic ligands play a crucial role in the construction of MOF materials and are one of the key factors determining their performance. During the construction of MOF materials, organic ligands not only generate photogenerated carriers under the excitation of incident light, providing coordination sites for the metal center, but also the ligand length, the functional groups they carry, and the coordination mode are all closely related to the physicochemical properties of MOF materials.

[0004] The synthesis efficiency, morphological characteristics, and catalytic performance of MOF materials vary depending on the synthesis strategy employed. The solvothermal method is one of the most commonly used methods for preparing MOF materials. In a closed system (such as a high-pressure hydrothermal reactor), organic or non-aqueous solvents are used as solvents, and the reaction temperature and pressure are set to allow the original mixture to crystallize. Previous studies have mostly reported post-synthesis modification strategies: first, different MOF materials are prepared using the solvothermal method, and then ligands are re-modified through methods such as etching and heat treatment. However, this strategy results in MOF materials with low synthesis efficiency and uneven ligand distribution.

[0005] In summary, existing methods for preparing titanium-based MOFs suffer from problems such as uneven ligand distribution, low synthesis efficiency, and insufficient visible light utilization. Summary of the Invention

[0006] Purpose of the invention: This invention proposes a method for preparing and applying amino-modified Ti-based MOFs, aiming to solve the problems of uneven ligand distribution, low synthesis efficiency, and insufficient visible light utilization in titanium-based MOFs prepared by existing methods.

[0007] Technical means: The first aspect of this invention provides a method for preparing Ti-based MOFs modified with functional groups, comprising the following steps: S1. Pretreatment: Tetrabutyl titanate is added to a mixed organic solvent and stirred and sonicated to obtain a mixed solvent; organic ligand NH2-BDC is placed in the mixed solvent to obtain ligand I, and organic ligand BDC is placed in the mixed solvent to obtain ligand II; ligand I and ligand II are stirred and sonicated separately until the organic ligands are fully dissolved in the mixed solution to complete the pretreatment. S2. Preparation of MOFs materials: Ligand I and ligand II are mixed with n(NH2-BDC) / n(BDC) as n(NH2-BDC) / n(BDC) = 2-9:1-8, and reacted in a high-pressure reactor to prepare NM(x) photocatalyst. The NM(x) photocatalyst has a disc-shaped three-dimensional morphology with a smooth surface. The characteristic XRD diffraction peaks are 2θ = 6.9°, 9.8°, 11.5°, 13.3°, 14.9°, 16.5°, 18° and 19.8°.

[0008] Furthermore, the NM(x) photocatalyst has light absorption capability in the wavelength range of 200–600 nm.

[0009] Furthermore, in step S2, ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC) of 5 to 9: 1 to 5.

[0010] Preferably, in step S2, the ratio of ligand I to ligand II is 9:1, calculated as n(NH2-BDC) / n(BDC).

[0011] Furthermore, the NM(x) photocatalyst has a minimum band gap of 2.73 eV and a minimum flat band gap of -0.78 eV.

[0012] Furthermore, the preparation method of the NM(x) photocatalyst derivative is as follows: the NM(x) photocatalyst in step S2 is calcined in an air atmosphere, and after calcination, it is naturally cooled to room temperature and taken out to obtain a white powder solid, which is ground into powder in a mortar and reserved for use, and is denoted as NM(x)-TiO2.

[0013] Preferably, the calcination parameters are: temperature 430℃~480℃, heating rate 4~6℃min. -1 Time: 3.5 to 4.5 hours.

[0014] The present invention also proposes the application of NM(x)-TiO2 or its derivative NM(x)-TiO2 prepared by the method of preparing Ti-based MOFs modified with the functional group described above in the field of photocatalytic hydrogen evolution.

[0015] Furthermore, the NM(x) photocatalyst achieves a photocatalytic hydrogen evolution rate as high as 543.46 μmol·h⁻¹. -1 ·g -1 The photocatalytic hydrogen evolution rate of NM(x)-TiO2 is as high as 943.53 μmol·h⁻¹. -1 ·g -1 .

[0016] Beneficial effects: This invention addresses the problem of uneven ligand distribution in traditional synthesis strategies by optimizing the synthesis strategy of MOFs materials. A one-step ligand co-intercalation strategy is employed to precisely control different ligand ratios for the synthesis of NM(x) series MOF photocatalysts. The influence of the functional ligand ratio on the photocatalytic performance of MOF materials is investigated, as well as whether the performance of derivatized products changes under these conditions.

[0017] First, the feasibility of the one-step ligand co-intercalation strategy was confirmed by morphological characterization using XRD, FTIR, and SEM. This strategy can embed functional ligands while maintaining the complete structure of MOFs materials, and can precisely control the ligand ratio, solving the problem of uneven ligand distribution in existing methods. Morphological characterization analysis showed that the crystal structure and morphology of NM(x) photocatalysts prepared with different NH2-BDC ratios did not change significantly.

[0018] Secondly, photoelectrochemical characterization confirmed that compared with single-ligand MOFs, NM(x) with embedded functional ligands has an extended light absorption range and significantly improved photogenerated electron-hole pair separation efficiency, which is crucial for enhancing its photocatalytic performance. Photoluminescence (PL) spectroscopy revealed that the embedding of NH2-BDC ligands enables synergistic effects between the two ligands, strengthens intermolecular conjugation, promotes charge transfer, and reduces the recombination rate of photogenerated carriers. Transient photocurrent response confirmed that NM(x) has more efficient photogenerated carrier transfer performance. The photocatalytic performance was evaluated by hydrogen evolution tests on the obtained samples. Under visible light conditions, the MIL-125 catalyst synthesized with a single ligand did not exhibit hydrogen evolution performance, and the hydrogen evolution performance of MIL-125-NH2 was poor, while the sample NM(x) all showed good hydrogen evolution performance, with the hydrogen evolution rate of sample NM(90) being 543.46 μmol·h⁻¹. -1 ·g -1 It is 7.7 times that of MIL-125-NH2, which is the best value reported so far.

[0019] Finally, the sample NM(x) was used as a precursor to prepare the derivatized product TiO2. As is well known, conventional TiO2 does not have hydrogen evolution ability under visible light conditions, but TiO2 prepared by MOF derivatization does have hydrogen evolution ability under visible light conditions, and the hydrogen evolution ability is significantly improved under ultraviolet light conditions.

[0020] Meanwhile, both the NM(x) photocatalyst and its derivative TiO2 exhibit excellent photocatalytic stability. Attached Figure Description

[0021] Figure 1 For the structural characterization of the embodiments and comparative examples, (a) is the XRD pattern and (b) is the FT-IR pattern; Figure 2 The XPS spectra of Examples 1, 5 and Comparative Example 5 are shown below. (a) is the full XPS spectrum, (b) is the Ti 2p fine spectrum, (c) is the N 1s fine spectrum, and (d) is the C 1s fine spectrum. Figure 3 SEM images for examples and comparative examples; Figure 4 TEM images for examples and comparative examples; Figure 5 The following are BET test data graphs for Examples 1, 5 and Comparative Example 5: (a) is the N2 adsorption-desorption isotherm, (b) is the pore size distribution curve (0-20 nm); inset (0-70 nm). Figure 6 The graphs show the light absorption performance test and band gap calculation of Examples 1, 5 and Comparative Example 5. (a) is the UC-vis graph, (b) is the Tauc spectrum, (c) is the MS curve, and (d) is the schematic diagram of the band structure. Figure 7 Photoluminescence spectra of the embodiments and comparative examples; Figure 8 The following are the photoelectric performance test graphs for the examples and comparative examples: (a) is the transient photocurrent curve, and (b) is the electrochemical impedance spectroscopy. Figure 9 The following are the photocatalytic performance evaluation graphs for the examples and comparative examples: (a) is the hydrogen evolution performance graph, and (b) is the cycle performance graph. Figure 10 Thermogravimetric analysis diagrams for the examples and comparative examples; Figure 11 The following are structural analysis diagrams of the derivatized TiO2 in the examples and comparative examples: (a) is the XRD pattern, and (b) is the FT-IR pattern. Figure 12 SEM images of the derivatized TiO2 of Examples 1, 5 and Comparative Example 5; Figure 13The following are the photocatalytic performance evaluation diagrams of derivatized TiO2 in Examples 1, 5 and Comparative Example 5: (a) is the hydrogen evolution performance diagram for λ<365nm, (b) is the cycle performance diagram, (c) is the hydrogen evolution performance diagram for λ>420nm, and (d) is the long cycle performance diagram. Detailed Implementation

[0022] The following examples further illustrate the specific implementation of the present invention, but the implementation and protection of the invention are not limited thereto. It should be noted that any details not specifically described below are implementations or understandings by those skilled in the art based on existing technology. Reagents or instruments whose manufacturers are not specified are considered to be commercially available products.

[0023] Because the one-step ligand co-intercalation strategy proposed in this invention enables precise control of different ligand ratios in step S2 for the synthesis of NM(x) series MOF photocatalysts, the molar ratio of ligand I to ligand II in step S2 needs to be clearly defined. The concentrations of ligand I obtained from NH2-BDC and ligand II obtained from BDC in the pretreatment step are not further limited; they can be ligand I with an NH2-BDC concentration of 0.1–2 mmol / mL and ligand II with a BDC concentration of 0.01–0.2 mmol / mL. In practice, those skilled in the art can make any adjustments based on the actual situation. In this invention, the ligand I contains 1.086 g of NH2-BDC, the ligand II contains 299 mg of BDC, and the tetrabutyl titanate is added at 0.6 mL (approximately 0.034 mol / L). The solvents are 45 mL of DMF and 5 mL of CH3OH. The amount of tetrabutyl titanate added can be any concentration capable of forming MOF structures; in this application, it is preferably 0.01–0.05 mol / L.

[0024] The NM(x) photocatalysts prepared in this invention include: NM(90), NM(80), NM(70), NM(60), NM(50), NM(40), NM(30), NM(20), and NM(10); NM(x)-TiO2 includes: NM(90)-TiO2, NM(80)-TiO2, NM(70)-TiO2, NM(60)-TiO2, NM(50)-TiO2, NM(40)-TiO2, NM(30)-TiO2, NM(20)-TiO2, and NM(10)-TiO2.

[0025] Example 1 NM (90) S1. Pretreatment: 45 mL LDMF, 5 mL CH3OH, and 0.6 mL tetrabutyl titanate were placed in a beaker and stirred and sonicated for 1 hour, followed by sonication for 30 minutes (40 kHz) until fully mixed to prepare a mixed solvent. Two portions of the mixed solvent were prepared, 30 mL of each, for preparing ligand I and ligand II. 1.086 g of organic ligand NH2-BDC was weighed and placed in the mixed solvent to obtain ligand I, and 299 mg of organic ligand BDC was placed in the mixed solvent to obtain ligand II. Ligand I and ligand II were each stirred and sonicated for 1 hour, followed by sonication for 30 minutes (40 kHz) until the organic ligands were fully dissolved in the mixed solution, completing the pretreatment. Preparation of S2 and MOF materials: Ligand I and ligand II were mixed with n(NH2-BDC) / n(BDC) as n(NH2-BDC) / n(BDC) = 9:1. That is, 13.5 mL of ligand I and 5 mL of ligand II were mixed (NH2-BDC was 2.7 mmol and BDC was 0.3 mmol), and placed in a high-pressure reactor for reaction at 150 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, washed 3-5 times with DMF, and then washed 3-5 times with anhydrous methanol. NM(90) photocatalyst was prepared.

[0026] Further, the preparation of MOF-derived TiO2: The NM(90) photocatalyst from step S2 was placed in a quartz ceramic crucible, covered, and then placed in a muffle furnace with pre-set parameters for calcination in air atmosphere. The parameters were: temperature 450 ℃, heating rate 5 ℃·min. -1 After 4 hours of natural cooling to room temperature (25°C), the solid was removed and ground into a white powder. It was then ground into powder using a mortar and pestle and designated as NM(90)-TiO2.

[0027] Example 2 NM (80) The difference between Example 2 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC), which is 8:2. That is, 12 mL of ligand I and 10 mL of ligand II are mixed (where NH2-BDC is 2.4 mmol and BDC is 0.6 mmol) to prepare NM(80) photocatalyst; MOFs material-derived TiO2 is denoted as NM(80)-TiO2.

[0028] Example 3 NM (70) The difference between Example 3 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC) of 7:3. That is, 10.5 mL of ligand I and 15 mL of ligand II are mixed (where NH2-BDC is 2.1 mmol and BDC is 0.9 mmol) to prepare NM(70) photocatalyst; MOFs material-derived TiO2 is denoted as NM(70)-TiO2.

[0029] Example 4 NM (60) The difference between Example 4 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC), which is 6:4. That is, 9 mL of ligand I and 20 mL of ligand II are mixed (where NH2-BDC is 1.8 mmol and BDC is 1.2 mmol) to prepare NM(60) photocatalyst; MOFs material-derived TiO2 is denoted as NM(60)-TiO2.

[0030] Example 5 NM (50) The difference between Example 5 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC) of 5:5, that is, 7.5 mL of ligand I and 25 mL of ligand II are mixed (where NH2-BDC is 1.5 mmol and BDC is 1.5 mmol) to prepare NM(50) photocatalyst; MOFs material-derived TiO2 is denoted as NM(50)-TiO2.

[0031] Comparative Example 1: Single-ligand MIL-125 The difference between Comparative Example 1 and Example 1 is that only ligand II (3 mmol BDC) was used, and ligand I was not added to prepare a single ligand MIL-125; the MOFs material-derived TiO2 is referred to as MIL-125-TiO2.

[0032] Comparative Example 2: Single ligand MIL-125-NH2 The difference between Comparative Example 2 and Example 1 is that only ligand I (NH2-BDC is 3 mmol) was used, and no ligand I was added to prepare a single ligand MIL-125-NH2; the MOFs material-derived TiO2 is denoted as MIL-125-NH2-TiO2.

[0033] Comparative Example 3 NM (40) The difference between Comparative Example 3 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC), which is 4:6. That is, 6 mL of ligand I and 30 mL of ligand II are mixed (where NH2-BDC is 1.2 mmol and BDC is 1.8 mmol) to prepare NM(40) photocatalyst; MOFs material-derived TiO2 is denoted as NM(40)-TiO2.

[0034] Comparative Example 4 NM (30) The difference between Comparative Example 4 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC) of 3:7, that is, 4.5 mL of ligand I and 35 mL of ligand II are mixed (where NH2-BDC is 0.9 mmol and BDC is 2.1 mmol) to prepare NM(30) photocatalyst; MOFs material-derived TiO2 is denoted as NM(30)-TiO2.

[0035] Comparative Example 5 NM (20) The difference between Comparative Example 5 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC) of 2:8, that is, 3 mL of ligand I and 40 mL of ligand II are mixed (where NH2-BDC is 0.6 mmol and BDC is 2.4 mmol) to prepare NM(20) photocatalyst; MOFs material-derived TiO2 is denoted as NM(20)-TiO2.

[0036] Comparative Example 6 NM (10) The difference between Comparative Example 6 and Example 1 is that ligand I and ligand II are mixed in a ratio of n(NH2-BDC) / n(BDC) of 1:9, that is, 1.5 mL of ligand I and 45 mL of ligand II are mixed (where NH2-BDC is 0.3 mmol and BDC is 2.7 mmol) to prepare NM(10) photocatalyst; MOFs material-derived TiO2 is denoted as NM(10)-TiO2.

[0037] The following structural and morphological characterization experiments demonstrate that the NM(x) photocatalyst prepared by the one-step ligand co-intercalation method proposed in this invention can introduce functional ligands while maintaining the complete structure of MOFs materials, and can achieve precise control of the ligand ratio.

[0038] I. Structural and Morphological Characterization

[0039] X-ray diffraction (XRD) was used to investigate the MOF crystals of Examples 1-5 and Comparative Examples 1-6, which contained embedded functional ligands. Figure 1 As shown in (a), the samples of Examples 1-5 and Comparative Examples 1-6 all exhibited characteristic diffraction peaks at 2θ = 6.9°, 9.8°, 11.5°, 13.3°, 14.9°, 16.5°, 18°, and 19.8°, matching the reported literature. This confirms that the one-step ligand co-intercalation synthesis strategy can completely maintain the topological structure of MOF materials, and the introduction of the functional ligand (NH2-BDC) did not cause changes in the crystal structure of MOF materials. It is worth noting that although the diffraction peak positions of samples with different ligand ratios are consistent, their peak intensities vary. Starting from NM(50), the diffraction peak intensity decreases as the NH2-BDC intercalation ratio decreases. This phenomenon reflects that the materials with low NH2-BDC ligand content, i.e., NM(40) to NM(10), have relatively poor crystallinity.

[0040] To further determine the chemical structure of the samples, Fourier transform infrared (FTIR) spectroscopy was performed on Comparative Example 1 (MIL-125), Comparative Example 2 (MIL-125-NH2), and NM(x), and the obtained data were analyzed. Figure 1 In (b), it can be observed that at 400–800 cm -1 A distinct peak appears in this region, caused by the O-Ti-O stretching vibration, confirming the complete presence of titanium oxide clusters in MOFs materials with different ligand ratios. (1540 cm⁻¹) -1 The sharp peak appearing at 1340 cm⁻¹ is attributed to the C=C skeletal vibration of the benzene ring in the ligand. The vibrational intensity of this peak reflects the degree of ligand conjugation, confirming that the material retains its high-strength conjugation properties even with synergistic effects from different ligand ratios. Notably, at 1340 cm⁻¹... -1 Both MIL-125-NH2 and NM(x) in the sample showed obvious peaks, while MIL-125 remained unchanged. The appearance of this peak is attributed to the stretching vibration of the CN bond, confirming the successful insertion of the NH2-BDC ligand into the MOF backbone. Furthermore, compared to the single-ligand MIL-125 in Comparative Example 1, the peaks of MIL-125-NH2 and the inserted functional ligand NM(x) in Comparative Example 2 were significantly higher at 3320 cm⁻¹. -1 and 3450 cm -1 The presence of two peaks at this point indicates that these two characteristic peaks are attributed to the v of -NH2. a (NH) and v s The (NH) vibration shows that the intensity of the bimodal peaks gradually decreases as the NH2-BDC ratio decreases. This further confirms the feasibility of precisely controlling the ligand ratio using the one-step ligand co-intercalation method, providing a good foundation for the preparation of MOF catalysts with different ligand ratios and offering favorable conditions for further exploration of the optimal ligand ratio for photocatalytic performance.

[0041] like Figure 2 In (a) and (b), the presence forms and chemical bonding states of NM(90), NM(50), MIL-125 of Comparative Example 1, MIL-125-NH2 of Comparative Example 2, and NM(20) were determined by X-ray photoelectron spectroscopy (XPS) to explain the relationship between the properties and structure of MOFs materials. Measurements of the full XPS spectrum revealed that the obtained materials contained Ti, C, N, and O elements. The binding energies of Ti 2p, C 1s, N 1s, and O 1s were 459 eV, 285 eV, 401 eV, and 531 eV, respectively. Two elements belonging to Ti 2p were clearly observed in the fine spectrum of Ti 2p. 3 / 2 With Ti 2p 1 / 2 Characteristic peaks, with two peaks located near 457.7 eV and 463.3 eV respectively, indicate that Ti is present in the form of Ti... 3+ and Ti 4+ Forms coexist. Partial reduction of the valence state of titanium ions (Ti 4+ +e - =Ti 3+ This affects its photocatalytic performance.

[0042] like Figure 2 (c) Four distinct peaks were observed in the C 1s fine spectrum, located near 287.6 eV, 286.4 eV, 285.2 eV, and 283.7 eV, corresponding to C=O, CO, CN&C-H, and C=C in the aromatic ring structure, confirming that the MOF catalyst can stably maintain its characteristic framework structure under different ligand ratios. In summary, these different elemental characteristics and chemical bonding states reflect the chemical composition and structure of MIL-125 (Comparative Example 1), MIL-125-NH2 (Comparative Example 2), and NM(x) materials, confirming the successful preparation of NM(x) materials with stable framework structures and complex functions.

[0043] like Figure 2 (d) In the fine spectrum of N1s, we can see three distinct peaks located near 401.8 eV, 400.1 eV, and 398.1 eV, respectively. These peaks represent NH4+, NH4+, and NH4+, respectively. + CN&-NH2 and Ti-N&C=N. Each peak represents a different chemical state of the N atom and its role in the metal-organic framework. The energy level peak at 401.8 eV is attributed to the adsorption of H2O or CO2 in the system by the -NH2 group in the MOF catalyst to form NH4. +The energy level peak at 400.1 eV corresponds to CN and -NH2. During sample preparation, a nitrogen-containing ligand was embedded, containing CN and NH, and the catalyst contains uncoordinated -NH2, which can provide electrons beneficial for charge separation transitions in the photocatalytic reaction. The peak near 398.1 eV corresponds to a metal-nitrogen bond (such as Ti-N) and C=N (pyrrole nitrogen), indicating successful coordination between the metal cluster and the organic ligand. The presence of pyrrole nitrogen suggests that the lone pair electrons in the amino group participate in the conjugation of the aromatic ring, which is conducive to the catalytic reaction.

[0044] It is noteworthy that no characteristic peaks were observed in the XPS spectrum of the single ligand MIL-125 in Comparative Example 1 at N1s, and MIL-125-NH2, NM(90), and NM(50) in Comparative Example 2 showed a strong peak near 398 eV compared to NM(20). This is because the -NH2 group in sample NM(20) only acts on H2O or CO2 in the adsorption system to form NH2. 4+ No other chemical states were observed, therefore no obvious peak was formed. The different valence states of N confirmed the uneven electron distribution, which can enhance the charge transfer capability of the material, improve the electron-hole separation efficiency, and promote the occurrence of catalytic reactions.

[0045] To observe the surface morphology of the obtained samples, scanning electron microscopy (SEM) images were used to characterize MIL-125, MIL-125-NH2, and NM(x). Figure 3 SEM characterization of the samples clearly shows that the single-ligand MOF materials MIL-125 and MIL-125-NH2 exhibit a disc-like morphology, while the dual-ligand MOF materials NM(90), NM(80), and NM(70) also exhibit a disc-like three-dimensional morphology with relatively smooth surfaces and good crystallinity. The embedding of different proportions of NH2-BDC ligands did not significantly affect the morphology and growth of the MOFs. Notably, samples NM(50), NM(40), and NM(30) are relatively rougher than other NM(x) materials, exhibiting blocky particle aggregation and poor crystallinity, which is consistent with the XRD analysis results. This may be because the competitive growth of the organic ligands prevented complete growth within the solvothermal time. From the obtained SEM images of the samples ( Figure 3The annotations in the figure provide the following information: the diameter of the MIL-125 photocatalyst is approximately 1.6 μm, and its thickness is approximately 270 nm. The diameter of the MIL-125-NH2 material is approximately 800 nm, and its thickness is approximately 180 nm. The NM(90) constructed by embedding the functional ligand NH2-BDC has a diameter of approximately 900 nm and a thickness of 200 nm. Different proportions of NH2-BDC ligands result in different diameters and thicknesses of the obtained MOFs. This phenomenon is attributed to the use of two different ligands in this work to construct MOFs materials; the different ligands have different lengths, indicating a positional competition problem between ligands.

[0046] When the proportion of longer ligands is larger, the size of the constructed MOF material is correspondingly larger, while when the proportion of shorter ligands is larger, the size of the constructed MOF material is correspondingly smaller. To verify the morphology and structure of the obtained samples, this study further determined the particle characteristics of the MOF catalyst using transmission electron microscopy (TEM). Figure 4 The TEM images of the obtained NM(x) series samples are shown in the figure. The morphology of the catalyst is consistent with the SEM characterization. Further observation revealed that NM(40) and NM(30) have a pie-like morphology, and a bunch of irregular particles are also accumulated on the surface of the material, which is consistent with the above analysis. This indicates that in the process of constructing MOFs by controlling the ligand ratio, there may be incomplete growth or competitive growth of organic ligands leading to morphological defects, and the crystallinity of the material is poor. NM(50) to NM(90) have better crystallinity.

[0047] The porosity, specific surface area, and pore size distribution of MOF materials were studied using N2 adsorption-desorption isotherms and BET model calculations. The degassing temperature was 150℃. NM(90) was selected as a representative for comparison in the following experiments. As summarized in Table 1, the specific surface areas of samples MIL-125, MIL-125-NH2, NM(90), NM(50), and NM(20) were 1025.9455 m², respectively. 2 ·g -1 737.1188m 2 ·g -1 762.3421m 2 ·g -1 816.5160m 2 ·g -1 and 934.3527m 2 ·g -1 .

[0048] Table 1 Specific surface area of ​​sample NM(x)

[0049] During the synthesis of MOF materials, functional groups on organic ligands occupy the skeletal voids in the MOF material, resulting in changes in specific surface area. For example... Figure 5 (a) Due to the larger proportion of NH2-BDC ligands, sample NM(90) occupies more space in the MOF material, resulting in a significant decrease in its specific surface area compared to MIL-125. In contrast, sample NM(20) has a smaller proportion of NH2-BDC ligands, causing its specific surface area to recover to 934.35 m². 2 ·g -1 This phenomenon indicates that NH2-BDC ligands are not merely adsorbed onto the material surface, but rather are actually embedded within the framework during the material synthesis process, forming stable coordination with the metal clusters.

[0050] From the aperture distribution diagram ( Figure 5 b) It can be seen that the pore distribution of MIL-125 is mainly micropores (<2nm), while the pore distribution of MIL-125-NH2 is mainly mesopores (2-50 nm). Figure 5 As shown in the inset of b, the NM(x) material with embedded functional ligands has a relatively large pore size. The proportion of mesopores in the NM(x) sample gradually increases with the increase of NH2-BDC embedding amount. This is attributed to the strong polarity of the amino groups of NH2-BDC, which easily forms intermolecular hydrogen bonds in the pores, leading to micropore blockage.

[0051] In summary, the feasibility of the one-step ligand co-intercalation method was confirmed through morphological characterization using XRD, FTIR, and SEM. This method can introduce functional ligands while maintaining the complete structure of MOFs materials and can achieve precise control of the ligand ratio. Morphological characterization analysis showed that the crystal structure and morphology of NM(x) photocatalysts prepared with different NH2-BDC ratios did not change significantly.

[0052] The following photoelectric performance characterization experiments demonstrate that the NM(x) catalyst prepared in this invention still exhibits strong hydrogen evolution performance under visible light.

[0053] II. Photoelectric Performance Characterization like Figure 6As shown in (a), light absorption performance is one of the important factors determining the activity of photocatalysts. Based on the unique structure of MOF materials, functional ligands are introduced to modify MOF materials and broaden the light absorption range. The light absorption performance of MOF materials was measured by UV-Vis solid diffuse reflectance spectroscopy. Compared with MIL-125, the light absorption edges of samples MIL-125-NH2 and NM(x) both showed a red shift. Sample MIL-125 only has a high light absorption capacity in the 200-350 nm UV region, while MIL-125-NH2 and NM(x) materials have high light absorption capacity in the 200-600 nm range, and NM(90) material has the strongest visible light absorption capacity and the largest range. A wider range of light absorption (especially visible light absorption) means that the photocatalyst can utilize more light energy, thereby promoting the occurrence of photocatalytic reactions.

[0054] Based on the UV-Vis solid diffuse reflectance spectrum, it is inferred that sample NM(90) may have higher efficiency in actual photocatalytic reactions. This characterization result also indirectly proves that embedding the NH2-BDC ligand can broaden the visible light absorption range of the material, making it more suitable for photocatalytic reactions under visible light conditions. The band gap value of the NM(x) material was calculated according to the Kubelka-Munk formula (1), as follows: Figure 6 As shown in (b), the band gap of the MIL-125 material is located at 3.72 eV, while that of the MIL-125-NH2 material is located at 2.8 eV. The band gap values ​​of NM(x) materials prepared with different proportions of NH2-BDC also vary, with NM(90), NM(50), and NM(20) materials having band gap values ​​of 2.73, 2.76, and 2.83 eV, respectively. The electron-donating groups on the ligands have an impact on the band gap of MOF catalysts. The reason for choosing NH2-BDC as the functional ligand is the special nature of its -NH2 group, which can act as a strong electron-donating group to narrow the band gap of the NM(x) material.

[0055] To further investigate the band positions of the obtained material, this study calculated the flat band potential (EFB) of the prepared NM(x) using the Mott-Schottky curve (MS), and then calculated the relative potentials of CB and VB using the formula. Figure 6 (c) indicates that the flat band potentials of MIL-125, MIL-125-NH2, NM(90), NM(50), and NM(20) are -0.58, -0.74, -0.78, -0.66, and -0.63 eV, respectively. The relationship between the flat band potential and the conduction band potential (E) is known. CB =E FB -0.1), the conduction band potentials of samples MIL-125, MIL-125-NH2, and NM (90) were calculated and a schematic diagram of the band structure was drawn, as shown. Figure 6(d) From the band structure diagram, we can see that the conduction band position of NM(x) is more negative, which is more conducive to the occurrence of photocatalytic reaction.

[0056] (1) In the formula, α represents absorbance (%). h — Planck's constant (J·s) -1 ); v — Frequency of light (m·s) -1 ); B — Physical quantities related to materials; Eg — Bandgap energy (eV).

[0057] In summary, compared to the single-ligand MIL-125 and MIL-125-NH2, the band gaps of NM(90) and NM(50) materials with embedded functional ligands are reduced, with sample NM(90) exhibiting the smallest band gap at 2.73 eV, indicating that sample NM(90) possesses sufficient driving force to perform H2O. + Reduction reactions are better suited for absorbing lower-energy photons in photocatalysis. This characterization confirms that the introduction of functional ligands has a positive effect on improving the light absorption capacity of MOF materials. The reason for the narrowing band gap is that the band structure of MOF materials uses organic ligands as the VB and titanium oxide clusters as the CB. When electron-donating groups replace hydrogen on the benzene ring, the electrons carried by the functional ligands participate in the charge transfer transition process of MOF materials, increasing the charge transfer rate and thus changing the band structure.

[0058] like Figure 7 As shown, photoluminescence (PL) spectroscopy revealed the charge separation efficiency of MOFs materials with different ligand ratios. At an excitation wavelength of 275 nm, compared to the single-ligand-constructed MIL-125 material and the MIL-125-NH2 catalyst, the PL intensity of sample NM(x) was significantly reduced. With increasing NH2-BDC ligand ratio, its intensity gradually decreased, with NM(90) exhibiting the weakest PL intensity, indicating the lowest recombination degree of photogenerated electron-hole pairs in this material. Furthermore, compared to MIL-125, the photoluminescence peaks of other samples showed a redshift. This phenomenon can be attributed to the intercalation of the NH2-BDC ligand, which enables synergistic effects between the two ligands, enhancing intermolecular conjugation and promoting charge transfer while reducing the recombination rate of photogenerated carriers. It is worth noting that the PL intensity of NM(x) materials containing different NH2-BDC ligand ratios was significantly reduced, confirming that the recombination of photogenerated electron-hole pairs can be effectively suppressed under the synergistic effect of NH2-BDC and BDC ligands. The luminescence properties of the material can be modulated by adjusting the ligand ratio, which provides a good direction for improving photocatalytic performance.

[0059] like Figure 8 As shown, the photoelectric performance of the obtained sample was evaluated using transient photocurrent response, and the photoresponse capability of sample NM(x) was measured. Sample NM(x) was tested in an environment with alternating light and darkness. Figure 8 In (a), we can clearly observe that sample NM(90) exhibits a higher and more stable transient photocurrent response. As the proportion of NH2-BDC ligand decreases, its photoresponse capability also decreases. This is because the introduction of the functional group (-NH2) reduces the distance from the top of the valence band to the bottom of the conduction band, and the reduction in the band gap results in a stronger photocurrent response, confirming that the material has more efficient photogenerated carrier transfer performance. Figure 8 (b) Electrochemical impedance spectroscopy (EIS) analysis of the charge transfer capacity of sample NM(x) showed that sample NM(90) exhibited the smallest arc, indicating its low charge transfer resistance. This further confirms that the introduction of functional ligands can improve the photogenerated charge transfer rate. In contrast, MIL-125 and MIL-125-NH2 materials showed larger impedances, indicating that their charge transfer capacity was weaker than that of NM(90). Although the impedance of MOF materials is relatively large, their charges can be effectively separated, which still has a positive impact on photocatalytic reactions.

[0060] Hydrogen evolution tests on NM(x) materials further confirmed that the introduction of functional ligands can effectively improve the photocatalytic performance of the materials. Figure 9 As shown in (a), the MIL-125 and MIL-125-NH2 materials prepared by single ligands BDC and NH2-BDC do not exhibit hydrogen evolution ability or have weak hydrogen evolution ability under visible light irradiation. This is attributed to the poor light absorption ability of MOFs materials prepared by single ligands. For example, the light absorption performance of MIL-125 material is limited to ultraviolet light, thus affecting its photocatalytic hydrogen evolution performance. It is worth noting that the hydrogen evolution efficiency of NM(x) catalysts prepared by different ratios of ligands BDC and NH2-BDC is significantly improved. Among them, the hydrogen evolution performance of NM(90) photocatalyst is as high as 543.46 μmol·g. -1 ·h -1 Compared to the MIL-125-NH2 material prepared with a single ligand, the hydrogen evolution rate was increased by 7.7 times, which is the highest value reported to date for this research. Furthermore, we observed that the hydrogen evolution rate decreased with decreasing NH2-BDC ligand ratio, consistent with previous characterization results. The stability of the photocatalyst is also crucial for its practical applications. For example... Figure 9As shown in (b), the stability experiment of the photocatalytic reaction was conducted in 4-hour cycles. After 4 cycles, NM(90) consistently exhibited good stability with negligible performance degradation. In summary, partial substitution of BDC with NH2-BDC can better achieve effective separation of photogenerated electrons and holes and interfacial charge transfer. However, it should be noted that the ratio of ligands should be carefully controlled during the modification of MOFs materials. The ratio of NH2-BDC:BDC = 9:1 is currently the optimal ligand ratio for photocatalytic performance. Too much or too little functional ligand insertion will affect the relevant performance of MOFs materials and hinder the reaction.

[0061] In summary, photoelectrochemical characterization confirmed that the light absorption range of NM(x) with embedded functional ligands is extended compared to single-ligand MOFs materials, and the separation efficiency of photogenerated electron-hole pairs is significantly improved. This invention evaluates the photocatalytic performance by performing hydrogen evolution tests on the obtained samples. Under visible light conditions, the MIL-125 catalyst synthesized with a single ligand does not exhibit hydrogen evolution performance, and MIL-125-NH2 shows poor hydrogen evolution performance. In contrast, samples NM(x) all exhibit good hydrogen evolution performance, with the hydrogen evolution rate of NM(90) in Example 1 reaching 543.46 μmol·h⁻¹. -1 ·g -1 This is 7.7 times that of the control 2MIL-125-NH2, which is the best value reported so far.

[0062] III. Thermal Stability Characterization The thermal stability of the MOF framework was investigated in depth using thermogravimetric analysis (TGA). Figure 10 As shown, MIL-125 in Comparative Example 1, MIL-125-NH2 in Comparative Example 2, and NM(x) all exhibit significant weight loss, which is attributed to the thermal decomposition of organic ligands in the MOF materials under high-temperature conditions. It is noteworthy that the pyrolysis temperatures vary depending on the organic ligand. We can divide the mass loss process into three stages: For the MIL-125 sample in Comparative Example 1: In the first stage, at temperatures between 50 and 250 °C, water and the solvent DMF are removed; in the second stage, at temperatures between 350 and 450 °C, the organic ligand BDC decomposes thermally, and significant weight loss occurs at 450 °C; in the third stage, when the temperature exceeds 450 °C, the organic ligand BDC completely decomposes, generating gaseous CO2, with the remaining solid product being a metal compound.

[0063] For the MIL-125-NH2 sample of Comparative Example 2: In the first stage, at a temperature of 50–250 °C, water and solvent DMF were removed; in the second stage, at a temperature of 350–550 °C, the organic ligand NH2-BDC began to decompose upon heating. Within this temperature range, the mass continued to decrease, but no sudden weight loss trend similar to that of the MIL-125 material was observed; in the third stage, at a temperature above 550 °C, the organic ligand NH2-BDC completely decomposed, generating gaseous CO2, with the remaining solid product being a metal compound. Compared to the single-ligand MIL-125 and MIL-125-NH2 materials, the weight loss curve of the mixed-ligand NM(x) material combines the thermal decomposition trends of both. In the first stage, water and solvent DMF were removed at 50–250 °C. In the second stage, the organic ligands began to decompose upon heating at 350–550 °C. The weight loss trends of NM(90) and NM(80) materials were very similar to those of MIL-125-NH2 material, confirming the presence of NH2-BDC ligands, which accounted for a large proportion.

[0064] IV. Characterization of MOF derivatives Based on the thermogravimetric analysis (TGA) chart above, it can be determined that sample NM(x) exhibits an inflection point at 450℃, and the sample no longer shows mass decrease at 550℃. Therefore, we selected 450℃ and 550℃ as the pyrolysis temperatures for the samples. MIL-125 from Comparative Example 1, MIL-125-NH2 from Comparative Example 2, and NM(x) were calcined at 450℃ and 550℃ respectively to prepare derivative TiO2, and the structure and properties of these products were determined and characterized. Characterization of the MOF derivative prepared at 550℃ revealed complete structural collapse, rendering it unsuitable for further study. Therefore, the product prepared at 450℃ was further tested.

[0065] The derivative NM(x)-TiO2 was prepared by placing MIL-125 of Comparative Example 1, MIL-125-NH2 of Comparative Example 2 and NM(x) in an air atmosphere and calcining at 450℃ for 4 h. Figure 11 (a) shows the XRD pattern of the derivative NM(x)-TiO2. All the obtained derivatives exhibit characteristic peaks of the mixed crystal form of TiO2, consistent with anatase titanium dioxide (standard card PDF#21-1272) and rutile titanium dioxide (standard card PDF#21-1276). The characteristic diffraction angles of the anatase TiO2 peaks are mainly 2θ=25.4° (101), 38° (004), 38.6°, 48.0° (200), 55.2°, and 55.1°; the characteristic diffraction angles of the rutile titanium dioxide peaks are mainly 2θ=27.5°, 36.2°, 41.4°, and 54.3°. To further determine the structure of the samples, FT-IR spectral characterization was performed. The characterization results are as follows: Figure 11 As shown in (b). At 400–700 cm-1 The characteristic absorption peak at this location is related to the Ti-O stretching vibration. This confirms the feasibility of preparing TiO2 under these conditions.

[0066] SEM analysis was performed on the derivatized NM(x)-TiO2 to observe its surface morphology. The results are as follows: Figure 12 As shown, the derivatized product retains the original disc-shaped morphology of MOFs, but after high-temperature calcination, its surface is slightly rougher than the original MOF material, and the center collapses slightly compared to the edges. This indicates that at 450 ℃, the organic ligands decompose under heat, causing the MOF material framework structure to collapse. Compared to the original MOF material, the size of the derivatized product is significantly smaller. From the SEM image of MIL-125-NH2-TiO2 in Comparative Example 2, it can be observed that the derivatized TiO2 retains the original disc-shaped morphology while also having a large number of small particles aggregated. The essence of its disc-shaped morphology is also composed of small particle aggregation. When the calcination temperature is further increased, the disc-shaped structure will completely collapse, presenting as a large number of particle agglomerates. In summary, the MOF material derivatization product NM(x)-TiO2 retains the large specific surface area and tunable pore structure characteristics of MOFs very well, which provides an excellent research platform for the photocatalytic performance regulation of TiO2 materials.

[0067] As is well known, TiO2 does not exhibit photoresponsiveness in the visible light range. Therefore, the photocatalytic hydrogen evolution performance of MOF-derived TiO2 was first tested under ultraviolet light to evaluate whether its photocatalytic performance differed from that of commercial P25. A hydrogen evolution performance testing system was constructed. 10 mg of sample, 90 mL of deionized water, and 10 mL of TEOA (as a sacrificial agent) were sequentially placed in a reactor for pretreatment. The pretreated reactor was then transferred to a 300 W xenon lamp with a 365 nm cutoff filter for top-light irradiation. The results are as follows: Figure 13 As shown in (a), compared with commercially available P25, the photocatalytic hydrogen evolution rate of MOF-derived TiO2 is generally increased, with NM(90)-TiO2 reaching a photocatalytic rate as high as 943.53 μmol·h⁻¹. -1 ·g -1 The photocatalytic rate of ordinary commercial P25 is 582.31 μmol·h⁻¹. -1 ·g -1 NM(90)-TiO2 is 1.62 times that of TiO2.

[0068] like Figure 13 As shown in (c), TiO2 prepared by conventional methods and commercial P25 do not exhibit hydrogen evolution ability under visible light conditions, while the hydrogen evolution rate of MOF-derived TiO2 under visible light conditions is 53.3 μmol·h. -1 ·g -1This indicates that the metal compounds derived from MOFs extend their photoabsorption response from only ultraviolet light to the visible light range, which has a positive effect on improving the photocatalytic activity of the materials. The cycling stability of the constructed MOFs photocatalyst is also one of the key criteria for evaluating its photocatalytic performance. In this work, the hydrogen evolution cycle performance of MOF-derived TiO2 was tested under both ultraviolet and visible light conditions. Similar to the determination of the photocatalytic stability of MOFs materials, stability experiments were conducted with a cycle of 4 hours. After two cycles, it was found that... Figure 13 Regardless of whether under ultraviolet or visible light conditions, the MOFs-derived TiO2 samples exhibited good stability, and the photocatalytic hydrogen evolution performance of NM(90)-TiO2 remained the highest. No significant performance degradation was observed during the cyclic experiment, indicating that the sample has excellent photocatalytic stability.

[0069] In summary, this invention successfully prepared functional ligand MOF photocatalysts using a one-step ligand co-intercalation method, confirming the feasibility of this synthesis strategy. By controlling the ratio of functional ligands, the optimal photocatalytic performance was obtained at a ratio of NH2-BDC to BDC of 9:1. By intercalating functional ligands and introducing electron-donating groups, the photogenerated charge separation efficiency was improved, thereby significantly enhancing the photocatalytic reaction activity. At the same time, the performance of the derivatized products under this condition was also improved.

[0070] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing amino-modified Ti-based MOFs, characterized in that, The steps are as follows: S1. Pretreatment: Tetrabutyl titanate is added to a mixed organic solvent and stirred and sonicated to obtain a mixed solvent; organic ligand NH2-BDC is placed in the mixed solvent to obtain ligand I, and organic ligand BDC is placed in the mixed solvent to obtain ligand II; ligand I and ligand II are stirred and sonicated separately until the organic ligands are fully dissolved in the mixed solution to complete the pretreatment. S2. Preparation of MOFs materials: Ligand I and ligand II are mixed with n(NH2-BDC) / n(BDC) as n(NH2-BDC) / n(BDC) = 2-9:1-8, and reacted in a high-pressure reactor to prepare NM(x) photocatalyst. The NM(x) photocatalyst has a disc-shaped three-dimensional morphology with a smooth surface. The characteristic XRD diffraction peaks are 2θ = 6.9°, 9.8°, 11.5°, 13.3°, 14.9°, 16.5°, 18° and 19.8°.

2. The method for preparing Ti-based MOFs modified with functional groups according to claim 1, characterized in that, The NM(x) photocatalyst has light absorption capability in the wavelength range of 200–600 nm.

3. The method for preparing amino-modified Ti-based MOFs according to claim 1, characterized in that, In step S2, ligand I and ligand II are mixed, with n(NH2-BDC) / n(BDC) being 5-9:1-5.

4. The method for preparing amino-modified Ti-based MOFs according to claim 3, characterized in that, In step S2, ligand I and ligand II are mixed, with n(NH2-BDC) / n(BDC) being 9:

1.

5. The method for preparing amino-modified Ti-based MOFs according to claim 1, characterized in that, In step S2, the reaction temperature in the high-pressure reactor is 140–160°C, and the reaction time is 23–25 h; after the reaction, the reactor is washed 3–5 times each with DMF and anhydrous methanol.

6. The method for preparing amino-modified Ti-based MOFs according to claim 1, characterized in that, The NM(x) photocatalyst has a minimum band gap of 2.73 eV and a minimum flat band gap of -0.78 eV.

7. The method for preparing amino-modified Ti-based MOFs according to claim 1, characterized in that, The preparation method of the derivative of NM(x) photocatalyst is as follows: calcining the NM(x) photocatalyst in step S2 in an air atmosphere, and then naturally cooling it to room temperature to obtain a white powder solid. Grinding it into powder in a mortar and pestle for later use is denoted as NM(x)-TiO2.

8. The method for preparing amino-modified Ti-based MOFs according to claim 7, characterized in that, The calcination parameters are: temperature 430℃~480℃, heating rate 4~6℃min. -1 Time: 3.5 to 4.5 hours.

9. The application of NM(x) or its derivative NM(x)-TiO2 prepared by the method for preparing amino-modified Ti-based MOFs as described in any one of claims 1-8 in the field of photocatalytic hydrogen evolution.

10. The application according to claim 9, characterized in that, The NM(x) photocatalyst achieves a photocatalytic hydrogen evolution rate as high as 543.46 μmol·h⁻¹. -1 ·g -1 The photocatalytic hydrogen evolution rate of NM(x)-TiO2 is as high as 943.53 μmol·h⁻¹. -1 ·g -1 .

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