A nanocrystalline adsorbent of NH2-MIL-125(Ti) and its preparation method and application

Abstract

This invention discloses an NH2-MIL-125(Ti) nanocrystalline adsorbent, its preparation method, and its application, belonging to the field of adsorption material technology. The preparation method of this invention includes the following steps: (1) mixing a hydrogen bond donor and a hydrogen bond acceptor to obtain a eutectic solvent; (2) adding the eutectic solvent to N,N-dimethylformamide to obtain a mixed solution; (3) adding an organic ligand to the mixed solution, stirring, and then adding a titanium source to obtain a mixture; (4) transferring the mixture to a reaction vessel for a solvothermal reaction to obtain the NH2-MIL-125(Ti) nanocrystalline adsorbent. The NH2-MIL-125(Ti) nanocrystalline adsorbent obtained by this invention has an average particle size of 50–175 nm, an irregular disc shape, and a specific surface area of ​​885–900 m². 2 / g. This adsorbent can efficiently and rapidly selectively adsorb cationic dyes in dye wastewater, achieving adsorption rates of 99.7% and 98.3% for Rhodamine B and malachite green in aqueous solution, respectively. It also has a wide applicable pH range and good cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of adsorption material technology, specifically relating to an NH2-MIL-125(Ti) nanocrystalline adsorbent, its preparation method, and its application. Background Technology

[0002] NH2-MIL-125(Ti), as a titanium-based metal-organic framework material, possesses unique advantages such as a unique pore structure and high specific surface area, making it applicable to various wastewater treatment processes, including dye adsorption, heavy metal removal, gas capture, and organic pollutant degradation. However, the relatively limited pore size distribution, adsorption capacity, and regeneration ability of NH2-MIL-125(Ti) restrict its adsorption efficiency in practical applications. Although the performance of NH2-MIL-125(Ti) can be improved by combining it with other materials such as semiconductors and metal oxides, such composite processes are often complex and require precise control of synthesis conditions to ensure material homogeneity and stability. In contrast, constructing single NH2-MIL-125(Ti) nanocrystals for rapid dye adsorption offers significant advantages, simplifying the synthesis process, reducing costs, and improving environmental friendliness and material recyclability. Therefore, developing a mild, simple, and environmentally friendly method for synthesizing NH2-MIL-125(Ti) nanocrystal adsorbents is of great significance for improving their dye adsorption performance and their application potential in environmental remediation.

[0003] The traditional solvothermal method uses N,N-dimethylformamide and methanol as a mixed solvent to synthesize NH2-MIL-125(Ti). N,N-dimethylformamide acts as a deprotonating agent, while methanol serves as a strong hydrogen bond donor, enabling the titanium oxide cluster (Ti8O8(OH)4) metal nodes to coordinate with the organic ligand 2-aminoterephthalic acid to form a porous organic-inorganic complex. However, NH2-MIL-125(Ti) prepared by the traditional solvothermal method is usually in the form of disc-shaped, decahedral, or octahedral micron-sized crystals, exhibiting poor adsorption performance for dyes, specifically characterized by slow adsorption rates, low adsorption capacities, and a narrow pH range.

[0004] Eutectic solvents are liquid mixtures formed by mixing hydrogen bond donors and acceptors in an appropriate molar ratio, with melting points significantly lower than those of any single component. Compared to traditional solvents such as water or organic solvents, eutectic solvents offer advantages such as simple preparation, low cost, environmental friendliness, biodegradability, non-flammability, and structural tunability. CN117843985A discloses a green synthesis method for Co-based MOF materials, which involves adding ligands and metal salts to an eutectic solvent and subjecting the resulting mixture to a hydrothermal reaction to obtain Co-based MOF materials; the eutectic solvent can participate in the assembly of the MOF material framework. CN111690148A discloses a green preparation method for two-dimensional metal-organic framework materials, which uses an eutectic solvent and water as reaction solvents to prepare two-dimensional metal-organic framework materials with good crystallinity and ultrathin thickness through a solvothermal reaction; the eutectic solvent used not only replaces traditional organic solvents to solve environmental pollution problems but also acts as a regulator to inhibit the vertical growth of two-dimensional materials.

[0005] Based on the above, this invention provides a method for preparing NH2-MIL-125(Ti) nanocrystalline adsorbent. By using a eutectic solvent as an additive in the solvothermal method, the deprotonation ability of N,N-dimethylformamide is altered, affecting the crystal nucleation process. This allows for precise control of the morphology, size, and structure of NH2-MIL-125(Ti) crystals and enhances their dye adsorption performance. Summary of the Invention

[0006] To address the above problems, this invention provides an NH2-MIL-125(Ti) nanocrystalline adsorbent, its preparation method, and its applications. The NH2-MIL-125(Ti) nanocrystalline adsorbent is prepared using a eutectic solvent as an additive in a solvothermal method. The resulting NH2-MIL-125(Ti) nanocrystalline adsorbent is irregularly disc-shaped, possessing more ligand defects and oxygen vacancies, exhibiting highly efficient and selective adsorption of cationic dyes. The preparation method of this invention is simple, low-cost, and environmentally friendly.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing an NH2-MIL-125(Ti) nanocrystalline adsorbent includes the following steps:

[0009] (1) Mix the hydrogen bond donor and the hydrogen bond acceptor, and stir until they are evenly mixed to obtain a eutectic solvent;

[0010] (2) Add the eutectic solvent to N,N-dimethylformamide and stir to mix it evenly to obtain a mixed solution;

[0011] (3) Add the organic ligand to the mixed solution, stir, add the titanium source, and continue stirring to obtain the mixture;

[0012] (4) The mixture was transferred into a reaction vessel for a solvothermal reaction. After the reaction was completed, it was naturally cooled to room temperature. After washing, centrifugation and drying, NH2-MIL-125(Ti) nanocrystal adsorbent was obtained.

[0013] Further, in step (1), the hydrogen bond donor is urea, ethylene glycol, benzyl alcohol or methanol; and the hydrogen bond acceptor is choline chloride.

[0014] Further, in step (1), the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2 to 4:1.

[0015] Further, in step (2), the mass-to-volume ratio of the eutectic solvent and N,N-dimethylformamide is 1 g: 0.1-9 mL.

[0016] Further, in step (3), the organic ligand is terephthalic acid or 2-aminoterephthalic acid; the titanium source is tetrabutyl titanate, titanium tetrachloride or titanium isopropoxide.

[0017] Further, in step (3), the ratio of the organic ligand, the titanium source and the eutectic solvent in step (2) is 0.1-1g:0.05-0.5mL:1g.

[0018] Furthermore, in step (4), the temperature of the solvothermal reaction is 120-150°C and the time is 24-72h.

[0019] An NH2-MIL-125(Ti) nanocrystal adsorbent prepared by the method described above.

[0020] Furthermore, the NH2-MIL-125(Ti) nanocrystalline adsorbent has an average particle size of 50–175 nm, an irregular disc shape, and a specific surface area of ​​885–900 m². 2 / g.

[0021] Application of the NH2-MIL-125(Ti) nanocrystal adsorbent as described above in the adsorption of Rhodamine B and Malachite Green.

[0022] The preparation principle of the NH2-MIL-125(Ti) nanocrystal adsorbent of the present invention:

[0023] This invention uses a eutectic solvent as an additive in a solvothermal process. A titanium metal source and organic ligands are dissolved in a mixed solvent composed of the eutectic solvent and N,N-dimethylformamide. Under heating conditions, the titanium oxide clusters (Ti8O8(OH)4) in the titanium metal source coordinate with organic ligands such as 2-aminoterephthalic acid to form porous organic-inorganic complexes. This alters the deprotonation ability of N,N-dimethylformamide, thereby affecting the crystal nucleation process. The resulting NH2-MIL-125(Ti) has more ligand defects and oxygen vacancies, forming nanoscale crystals with an irregular disk-like shape. It exhibits excellent adsorption performance for cationic dyes in dye wastewater, with fast adsorption rate, high adsorption capacity, and a wide applicable pH range.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0025] 1. This invention uses a eutectic solvent as an additive in a solvothermal method to prepare NH2-MIL-125(Ti) nanocrystalline adsorbents. The obtained NH2-MIL-125(Ti) nanocrystalline adsorbents have more ligand defects and oxygen vacancies, with an average particle size of 50–175 nm, an irregular disc shape, and a specific surface area of ​​885–900 m². 2 / g, exhibiting excellent adsorption performance for cationic dyes in dye wastewater. The preparation method of this invention is simple, low-cost, and environmentally friendly.

[0026] 2. The NH2-MIL-125(Ti) nanocrystalline adsorbent prepared by this invention can efficiently and rapidly selectively adsorb cationic dyes in dye wastewater. The adsorption capacities for Rhodamine B and malachite green can reach 79.1 mg / g and 804.1 mg / g, respectively, and the adsorption rates can reach 99.7% and 98.3%, respectively. The adsorption of Rhodamine B has a wide pH range and good cycle stability. Attached Figure Description

[0027] Figure 1 The XRD patterns are of n-NMT-53, n-NMT-64, n-NMT-74, n-NMT-175, and m-NMT obtained in Examples 1-4 and Comparative Example 1, respectively.

[0028] Figure 2 The images shown are SEM and TEM images of the m-NMT prepared in Comparative Example 1.

[0029] Figure 3 The images show SEM and TEM images of n-NMT-53 obtained in Example 1, and SEM images of n-NMT-64, n-NMT-74, and n-NMT-175 obtained in Examples 2-4, respectively.

[0030] Figure 4The image shows the EDX plot of n-NMT-53 obtained in Example 1.

[0031] Figure 5 The images show the FT-IR spectra of n-NMT-53 and m-NMT obtained in Example 1 and Comparative Example 1, respectively.

[0032] Figure 6 The N2 adsorption-desorption isotherms of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively, are shown.

[0033] Figure 7 Thermogravimetric curves of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively.

[0034] Figure 8 XPS images of n-NMT-53 and m-NMT obtained in Example 1 and Comparative Example 1, respectively.

[0035] Figure 9 The adsorption rate-time relationship of rhodamine B and malachite green for n-NMT-53, n-NMT-64, n-NMT-74, n-NMT-175 and m-NMT prepared in Examples 1-4 and Comparative Example 1, respectively.

[0036] Figure 10 The graph shows the adsorption rate-time relationship of n-NMT-53 prepared in Example 1 for Rhodamine B and malachite green under different initial dye concentrations.

[0037] Figure 11 The image shows the UV-Vis spectrum-time relationship of the n-NMT-53 adsorbed mixed dye prepared in Example 1.

[0038] Figure 12 The graph shows the adsorption rate of rhodamine B by n-NMT-53 prepared in Example 1 under different initial pH conditions.

[0039] Figure 13 The graph shows the cyclic adsorption rate of rhodamine B by n-NMT-53 prepared in Example 1.

[0040] Figure 14 The image shows the XRD pattern of n-NMT-53 prepared in Example 1 before and after cyclic adsorption of Rhodamine B. Detailed Implementation

[0041] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0042] Example 1

[0043] Preparation of NH2-MIL-125(Ti) nanocrystal adsorbent:

[0044] 20.94 g (0.15 mol) of choline chloride and 24.30 mL (0.6 mol) of methanol were stirred at room temperature for 5 min to form a homogeneous and transparent liquid, yielding a eutectic solvent. 9 g of the eutectic solvent was added to 21 mL of N,N-dimethylformamide and stirred at room temperature for 5 min to ensure homogeneity, resulting in a mixed solution. 1.5 g of 2-aminoterephthalic acid was added to the mixed solution, and after stirring at room temperature for 5 min, 0.85 mL of tetrabutyl titanate was added. Stirring continued at room temperature for 30 min to obtain a final mixture. The mixture was transferred to a 50 mL reactor and reacted in an oven at 150 °C for 72 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed three times by centrifugation with N,N-dimethylformamide and methanol, respectively, and then dried in an oven at 60 °C for 10 h to obtain the NH2-MIL-125(Ti) nanocrystalline adsorbent (denoted as n-NMT-53).

[0045] Example 2

[0046] The difference between Example 2 and Example 1 is that the mass of the eutectic solvent in Example 2 is 3g, the volume of N,N-dimethylformamide is 27mL, and the rest of the preparation process and conditions are the same as those in Example 1, thus obtaining NH2-MIL-125(Ti) nanocrystal adsorbent (denoted as n-NMT-64).

[0047] Example 3

[0048] The difference between Example 3 and Example 1 is that the mass of the eutectic solvent in Example 3 is 21g, the volume of N,N-dimethylformamide is 9mL, and the rest of the preparation process and conditions are the same as those in Example 1, thus obtaining NH2-MIL-125(Ti) nanocrystal adsorbent (denoted as n-NMT-74).

[0049] Example 4

[0050] The difference between Example 4 and Example 1 is that the mass of the eutectic solvent in Example 4 is 27g, the volume of N,N-dimethylformamide is 3mL, and the rest of the preparation process and conditions are the same as those in Example 1, thus obtaining NH2-MIL-125(Ti) nanocrystal adsorbent (denoted as n-NMT-175).

[0051] Example 5

[0052] Preparation of NH2-MIL-125(Ti) nanocrystal adsorbent:

[0053] 20.94 g (0.15 mol) of choline chloride and 22.50 mL (0.5 mol) of urea were stirred at room temperature for 5 min to form a homogeneous and transparent liquid, yielding a eutectic solvent. 3 g of the eutectic solvent was added to 12 mL of N,N-dimethylformamide and stirred at room temperature for 5 min to ensure homogeneity, resulting in a mixed solution. 1.5 g of terephthalic acid was added to the mixed solution, and after stirring at room temperature for 5 min, 0.8 mL of titanium tetrachloride was added. Stirring continued at room temperature for 30 min to obtain a final mixture. The mixture was transferred to a 50 mL reactor and placed in an oven at 150 °C for 24 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed three times by centrifugation with N,N-dimethylformamide and methanol, respectively, and then dried in an oven at 60 °C for 10 h to obtain the NH2-MIL-125(Ti) nanocrystalline adsorbent.

[0054] Example 6

[0055] Preparation of NH2-MIL-125(Ti) nanocrystal adsorbent:

[0056] 20.94 g (0.15 mol) of choline chloride and 22.30 mL (0.4 mol) of ethylene glycol were stirred at room temperature for 5 min to form a homogeneous and transparent liquid, yielding a eutectic solvent. 3 g of the eutectic solvent was added to 15 mL of N,N-dimethylformamide and stirred at room temperature for 5 min to ensure homogeneity, resulting in a mixed solution. 2.0 g of 2-aminoterephthalic acid was added to the mixed solution, and after stirring at room temperature for 5 min, 1.05 mL of titanium isopropoxide was added. Stirring continued at room temperature for 30 min to obtain a final mixture. The mixture was transferred to a 50 mL reactor and placed in an oven at 120 °C for 72 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed three times by centrifugation with N,N-dimethylformamide and methanol, respectively, and then dried in an oven at 60 °C for 10 h to obtain the NH2-MIL-125(Ti) nanocrystalline adsorbent.

[0057] Example 7

[0058] Preparation of NH2-MIL-125(Ti) nanocrystal adsorbent:

[0059] 20.94 g (0.15 mol) of choline chloride and 31.20 mL (0.3 mol) of benzyl alcohol were stirred at room temperature for 5 min to form a homogeneous and transparent liquid, yielding a eutectic solvent. 3 g of the eutectic solvent was added to 20 mL of N,N-dimethylformamide and stirred at room temperature for 5 min to obtain a homogeneous solution. 3.0 g of terephthalic acid was added to the solution, and after stirring at room temperature for 5 min, 1.50 mL of tetrabutyl titanate was added. Stirring continued at room temperature for 30 min to obtain a final mixture. The mixture was transferred to a 50 mL reactor and reacted in an oven at 140 °C for 48 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting solid was washed three times by centrifugation with N,N-dimethylformamide and methanol, respectively, and then dried in an oven at 60 °C for 10 h to obtain the NH2-MIL-125(Ti) nanocrystalline adsorbent.

[0060] Comparative Example 1

[0061] Preparation of NH2-MIL-125(Ti) microcrystalline adsorbent:

[0062] 1.5 g of 2-aminoterephthalic acid was added to a mixed solution of 30 mL of N,N-dimethylformamide and methanol (3 mL methanol and 27 mL N,N-dimethylformamide). After stirring at room temperature for 5 min, 0.85 mL of tetrabutyl titanate was added, and stirring was continued at room temperature for 30 min to obtain a mixture. The mixture was transferred to a 50 mL reaction vessel and placed in an oven at 150 °C for 72 h. After the reaction was completed, the mixture was naturally cooled to room temperature, and the solid obtained by centrifugation was washed three times with N,N-dimethylformamide and methanol, respectively. Then, it was dried in an oven at 60 °C for 10 h to obtain NH2-MIL-125(Ti) microcrystalline adsorbent (denoted as m-NMT).

[0063] Material characterization analysis

[0064] (I) XRD Analysis

[0065] The n-NMT-53, n-NMT-64, n-NMT-74, n-NMT-175, and m-NMT samples prepared in Examples 1-4 and Comparative Example 1, respectively, were characterized and analyzed using X-ray diffraction (XRD). The results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the XRD patterns of the products obtained in Examples 1-4 and Comparative Example 1 are consistent with the standard XRD pattern of NH2-MIL-125(Ti), indicating that crystalline NH2-MIL-125(Ti) was successfully prepared in Examples 1-4 when a eutectic solvent was used as an additive in the solvothermal method.

[0066] (II) SEM and TEM Analysis

[0067] Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize and analyze n-NMT-53, n-NMT-64, n-NMT-74, n-NMT-175, and m-NMT prepared in Examples 1-4 and Comparative Example 1, respectively. The results are as follows: Figure 2 and Figure 3 As shown. Figure 2 In the figure, a and b are SEM and TEM images of the m-NMT prepared in Comparative Example 1, respectively. Figure 3 In the figures, a and bc are SEM and TEM images of n-NMT-53 obtained in Example 1, respectively, and d, e, and f are SEM images of n-NMT-64, n-NMT-74, and n-NMT-175 obtained in Examples 2-4, respectively.

[0068] Depend on Figure 2 It can be seen that the sample prepared in Comparative Example 1 is a decahedral microcrystal with a regular morphology in the scale range of 0.3-1.5 μm. In Examples 1-4, NH2-MIL-125(Ti) nanocrystals were synthesized using a eutectic solvent as an additive in the solvothermal method. The product obtained in Example 1 was an irregularly shaped disk-like NH2-MIL-125(Ti) nanocrystal with an average size of 53 nm. The products obtained in Examples 2-4 were irregularly shaped disk-like NH2-MIL-125(Ti) nanocrystals with average particle sizes of 64, 74, and 175 nm, respectively.

[0069] (III) EDX Analysis

[0070] The elemental distribution of n-NMT-53 prepared in Example 1 was analyzed using energy-dispersive X-ray spectroscopy (EDX), and the results are as follows: Figure 4 As shown. By Figure 4 It can be seen that C, N, O and Ti elements are uniformly distributed in the n-NMT-53 sample.

[0071] (iv) FT-IR Analysis

[0072] The composition of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively, was analyzed using Fourier transform infrared spectroscopy (FT-IR). The results are as follows: Figure 5 As shown. By Figure 5 It can be seen that for m-NMT, 3439cm -1 The peak at 1626 cm⁻¹ is due to the stretching vibration of -OH. -1 The peak at 1572 cm⁻¹ represents the NH bending vibration of -NH₂. -1 and 1531cm -1 The peak at 1427 cm⁻¹ is an antisymmetric stretching vibration of -C=O⁻. -1 and 1389cm -1The peak at that point represents the symmetric stretching vibration of -C=O-. Compared to m-NMT, the -OH stretching vibration peak of n-NMT-53 is redshifted to 3429 cm⁻¹. -1 This indicates the presence of stronger hydrogen bonding interactions in n-NMT-53. In n-NMT-53, the antisymmetric stretching vibration peak of -C=O- is located at 1574 cm⁻¹. -1 and 1537cm -1 The symmetric stretching vibration peak of -C=O- is located at 1435 cm⁻¹. -1 and 1385cm -1 Compared to m-NMT, the increased spacing between the antisymmetric and symmetric stretching vibration peaks of -C=O- in n-NMT-53 indicates a weakened interaction between the ligand and the titanium-oxygen cluster. This may be due to ligand defects in NH2-MIL-125(Ti) resulting from the preparation using a eutectic solvent.

[0073] (V) Specific Surface Area and Pore Structure Analysis

[0074] The pore properties of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively, were analyzed using N2 physical adsorption, and the N2 adsorption-desorption isotherms were obtained as follows: Figure 6 As shown. By Figure 6 It can be seen that n-NMT-53 exhibits a type IV adsorption isotherm and an H1 hysteresis loop, typically a mesoporous material with a narrow pore size distribution or a uniformly sized aggregate of spherical particles. However, the TEM image of n-NMT-53 ( Figure 2 (b) The absence of mesopores indicates that the mesopores obtained from the N2 adsorption-desorption test are packing pores formed by the accumulation of uniformly sized n-NMT-53 nanoparticles. The BET specific surface area of ​​n-NMT-53 is 891 m². 2 / g, with a BET specific surface area of ​​1437m² below m-NMT. 2 / g, which may be caused by partial blockage of the pores by uncoordinated ligands in n-NMT-53.

[0075] (vi) Thermal stability analysis

[0076] The thermal stability of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively, was analyzed by thermogravimetric analysis under N2 atmosphere. The obtained thermogravimetric curves are shown below. Figure 7 As shown. By Figure 7It can be seen that the mass loss in the temperature range of 30℃ to 110℃ corresponds to the removal of residual solvent molecules in the material. The mass loss in the temperature range of 110℃ to 350℃ corresponds to the desorption of the uncoordinated organic ligand 2-aminoterephthalic acid. m-NMT loses 13.35% of its weight in the temperature range of 110~303℃, and n-NMT-53 loses 19.00% of its weight in the temperature range of 112~343℃, indicating that there are more ligand defects in n-NMT-53. The weight loss in the temperature range of 350~500℃ corresponds to the collapse of the NH2-MIL-125(Ti) framework and the formation of TiO2. 2。

[0077] (vii) XPS Analysis

[0078] The surface composition of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively, was analyzed by X-ray photoelectron spectroscopy (XPS). The results are as follows: Figure 8 As shown. Total score ( Figure 8 a) This indicates that C, N, O, and Ti elements are present in n-NMT-53 and m-NMT, and no other elements are present. (In the C1s spectrum...) Figure 8 In b), the peaks at 284.88 eV, 286.68 eV, and 288.78 eV in the n-NMT-53 sample correspond to C, CN, and CO bonds, respectively. In the N1s spectrum ( Figure 8 In c), the peak at 399.48 eV of the n-NMT-53 sample is attributed to CN, and the peak at 402.98 eV is attributed to -NH. + - In the O1s map ( Figure 8 In d), the peak at 530.48 eV is attributed to Ti-O, and the peak at 531.98 eV is attributed to C=O. Compared with m-NMT, the peak positions of Ti-O and C=O in n-NMT-53 shift towards lower binding energies to 530.18 eV and 531.88 eV, respectively, indicating the presence of abundant oxygen vacancies in n-NMT-53. (Ti 2p spectrum) Figure 8 In e), the binding energies of Ti 2p3 / 2 and Ti 2p1 / 2 in m-NMT are located at 459.08 eV and 464.88 eV, respectively, belonging to the Ti-O cluster. 4+ Compared to m-NMT, the peaks of Ti 2p3 / 2 and Ti 2p1 / 2 in n-NMT-53 shifted to lower binding energies, reaching 458.88 eV and 464.68 eV, respectively, indicating the possible presence of ligand defects or oxygen vacancies in n-NMT-53. XPS analysis results, consistent with FT-IR analysis, both indicate the presence of more ligand defects and oxygen vacancies in n-NMT-53.

[0079] Application Example 1

[0080] 25 mg of n-NMT-53 prepared in Example 1 was placed in a beaker, and 25 mL of a 20 mg / L Rhodamine B aqueous solution was added. Adsorption experiments were conducted at 25°C and a stirring speed of 300 rpm for 3 hours. The dye was then replaced with a 300 mg / L malachite green aqueous solution, with all other experimental conditions remaining the same. The calculated adsorption rates of n-NMT-53 for Rhodamine B and malachite green were 99.7% and 98.3%, respectively.

[0081] Application Example 2

[0082] The difference between Application Example 2 and Application Example 1 is that the adsorbent in Application Example 2 is n-NMT-64 prepared in Example 2, while the other experimental conditions are the same as in Application Example 1. Calculations showed that n-NMT-64 exhibited adsorption rates of 99.6% for Rhodamine B and 97.7% for malachite green.

[0083] Application Example 3

[0084] The difference between Application Example 3 and Application Example 1 is that the adsorbent in Application Example 3 is n-NMT-74 prepared in Example 3, while the other experimental conditions are the same as in Application Example 1. Calculations showed that n-NMT-74 exhibited adsorption rates of 98.2% for Rhodamine B and 93.3% for malachite green.

[0085] Application Example 4

[0086] The difference between Application Example 4 and Application Example 1 is that the adsorbent in Application Example 4 is n-NMT-175 prepared in Example 4, while the other experimental conditions are the same as in Application Example 1. Calculations showed that n-NMT-175 exhibited adsorption rates of 97.4% for Rhodamine B and 57.8% for malachite green.

[0087] Application Comparative Example 1

[0088] The difference between Comparative Example 1 and Application Example 1 is that the adsorbent in Comparative Example 1 is m-NMT prepared in Comparative Example 1, while the other experimental conditions are the same as in Application Example 1. Calculations showed that m-NMT exhibited adsorption rates of 94.7% for Rhodamine B and 34.3% for malachite green.

[0089] Material Adsorption Performance Analysis

[0090] (I) Analysis of the adsorption performance of the adsorbent for dyes at different adsorption times

[0091] The adsorption rates of Rhodamine B and malachite green by adsorbents m-NMT, n-NMT-53, n-NMT-64, n-NMT-74, and n-NMT-175 in Comparative Example 1 and Application Examples 1-4 change over time as follows: Figure 9 As shown in (ab). Figure 9 In the figure, figures a and b show the changes in the adsorption rates of n-NMT-175 for Rhodamine B and malachite green over time, respectively.

[0092] Depend on Figure 9 It can be seen that when the adsorption time is 5 min, the adsorption rates of n-NMT-53 for Rhodamine B and malachite green rapidly reach 92.4% and 90.2%, respectively, which are much higher than the adsorption rates of m-NMT for Rhodamine B (54.9%) and malachite green (22.7%) at 5 min. With the extension of adsorption time, the adsorption active sites gradually approach saturation, and the adsorption gradually approaches equilibrium. When the adsorption time is 3 h, the equilibrium adsorption rates of n-NMT-53 for Rhodamine B and malachite green are 99.7% and 98.3%, respectively, which are higher than the adsorption rates of m-NMT for Rhodamine B (94.7%) and malachite green (34.3%) at 3 h. Furthermore, the adsorption of Rhodamine B and malachite green by m-NMT has not reached equilibrium at 3 h.

[0093] (II) Analysis of the adsorption performance of the adsorbent for dyes at different initial dye concentrations

[0094] The concentrations of the rhodamine B aqueous solution in Application Example 1 were replaced with 20, 40, 60, 80, and 100 mg / L, and the concentrations of the malachite green aqueous solution were replaced with 200, 300, 500, 800, and 1000 mg / L, with all other experimental conditions remaining the same as in Application Example 1. The adsorption rates of n-NMT-53 for rhodamine B and malachite green over time at different initial dye concentrations are shown below. Figure 10 As shown in (ab). Figure 10 In the figure, figures a and b show the changes in the adsorption rates of rhodamine B and malachite green by n-NMT-53 over time.

[0095] Depend on Figure 10 It can be seen that the amounts of rhodamine B and malachite green adsorbed on n-NMT-53 increase with the increase of the initial dye concentration, which is because the increase of the concentration gradient promotes the enhancement of the adsorption driving force. At 25℃, the equilibrium adsorption capacity of n-NMT-53 for malachite green is as high as 804.1 mg / g, and the equilibrium adsorption capacity for rhodamine B is as high as 79.1 mg / g.

[0096] (III) Analysis of the adsorption performance of adsorbents for mixed dyes under different mixed dye conditions

[0097] The Rhodamine B aqueous solution in Application Example 1 was replaced with a mixed dye aqueous solution consisting of 30 mg / L Rhodamine B and 30 mg / L methyl orange. Furthermore, this mixed dye was replaced with a mixed dye aqueous solution consisting of 30 mg / L Rhodamine B and 300 mg / L malachite green. All other experimental conditions remained the same as in Application Example 1. The UV-Vis spectra of n-NMT-53 adsorbing the mixed dyes over time under different mixed dyes are shown below. Figure 11 As shown in (ab). Figure 11 In the figure, figures a and b show the changes in the UV-Vis spectra of the mixed dye aqueous solution composed of n-NMT-53 Rhodamine B and methyl orange, and the mixed dye aqueous solution composed of Rhodamine B and malachite green, respectively, over time.

[0098] Depend on Figure 11 It can be seen that n-NMT-53 exhibits good adsorption performance in mixed dyes composed of cationic dyes Rhodamine B and malachite green, with adsorption rates exceeding 92.9% after 1 hour. In mixed dyes composed of cationic dye Rhodamine B and anionic dye methyl orange, n-NMT-53 shows good adsorption performance for Rhodamine B, reaching an adsorption rate of 94.0% after 1 hour, but its adsorption performance for methyl orange is poor, with an adsorption rate of only 39.6% after 3 hours. The n-NMT-53 adsorbent demonstrates high adsorption efficiency for cationic dyes Rhodamine B and malachite green in mixed dyes, but relatively poor adsorption performance for anionic dye methyl orange, indicating that n-NMT-53 has highly selective adsorption capacity for cationic dyes.

[0099] (iv) Analysis of the adsorption performance of the adsorbent for dyes at different initial pH values ​​of aqueous solutions

[0100] The initial pH of the Rhodamine B aqueous solution in Application Example 1 was adjusted to 1, 2, 3, 5, 7, 9, and 11, respectively, using 0.1 mol / L hydrochloric acid or sodium hydroxide. All other experimental conditions remained the same as in Application Example 1. The adsorption rates of n-NMT-53 for Rhodamine B at different initial pH values ​​of the aqueous solution are shown below. Figure 12 As shown.

[0101] Depend on Figure 12 It can be seen that the adsorption rate of n-NMT-53 for RhB remains above 96.6% in the pH range of 2 to 9, indicating that the n-NMT-53 adsorbent has a wide pH range for the efficient adsorption of Rhodamine B.

[0102] (V) Analysis of the adsorption cycle stability of dyes by the adsorbent

[0103] In Application Example 1, after n-NMT-53 adsorption for 3 hours, a sample was taken for centrifugation. The centrifuged n-NMT-53 was then soaked in methanol and stirred for 8 hours to desorb Rhodamine B. After desorption, the n-NMT-53 sample was dried in a 60°C oven for 10 hours for subsequent cyclic adsorption experiments. The adsorption cycle rate of n-NMT-53 for Rhodamine B is as follows: Figure 13 As shown.

[0104] Depend on Figure 13 It can be seen that after 4 cycles, the adsorption rate of n-NMT-53 for Rhodamine B did not decrease significantly and remained above 98.7%, indicating that the n-NMT-53 adsorbent has good cycle stability for the adsorption of the cationic dye Rhodamine B in water.

[0105] The crystal structure of n-NMT-53 before and after cyclic adsorption of Rhodamine B was characterized, and the results are as follows: Figure 14 As shown. By Figure 14 It can be seen that although the crystallinity of n-NMT-53 decreases slightly after cyclic adsorption, it can still basically maintain the original crystal framework structure.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an NH2-MIL-125(Ti) nanocrystalline adsorbent, characterized in that, Includes the following steps: (1) The hydrogen bond donor and the hydrogen bond acceptor are mixed and stirred until homogeneous to obtain a eutectic solvent; the hydrogen bond donor is urea, ethylene glycol, benzyl alcohol or methanol; the hydrogen bond acceptor is choline chloride; the molar ratio of the hydrogen bond donor and the hydrogen bond acceptor is 2 to 4:

1. (2) Add the eutectic solvent to N,N-dimethylformamide and stir to mix them evenly to obtain a mixed solution; the mass-volume ratio of the eutectic solvent to N,N-dimethylformamide is 1g:0.1~9mL; (3) Add the organic ligand to the mixed solution, stir, add the titanium source, and continue stirring to obtain a mixture; the organic ligand is terephthalic acid or 2-aminoterephthalic acid; the titanium source is tetrabutyl titanate, titanium tetrachloride or titanium isopropoxide; (4) The mixture is transferred into a reaction vessel for solvothermal reaction. After the reaction is completed, it is naturally cooled to room temperature. After washing, centrifugation and drying, NH2-MIL-125(Ti) nanocrystal adsorbent is obtained. The temperature of the solvothermal reaction is 120-150℃ and the time is 24-72h.

2. The preparation method of the NH2-MIL-125(Ti) nanocrystalline adsorbent according to claim 1, characterized in that, In step (3), the ratio of the organic ligand, the titanium source and the eutectic solvent in step (2) is 0.1-1g:0.05-0.5mL:1g.

3. An NH2-MIL-125(Ti) nanocrystal adsorbent prepared by the preparation method described in claim 1 or 2.

4. The NH2-MIL-125(Ti) nanocrystalline adsorbent according to claim 3, characterized in that, The NH2-MIL-125(Ti) nanocrystalline adsorbent has an average particle size of 50–175 nm, an irregular disc shape, and a specific surface area of ​​885–900 m². 2 / g.

5. The application of the NH2-MIL-125(Ti) nanocrystalline adsorbent as described in claim 3 in the adsorption of Rhodamine B and malachite green.

Images