NH2-MIL-125 (Ti) nanocrystal adsorbent as well as preparation method and application thereof

Abstract

The invention discloses an NH2-MIL-125 (Ti) nanocrystal adsorbent as well as a preparation method and application thereof, and belongs to the technical field of adsorption materials. The preparation method comprises the following steps: (1) mixing a hydrogen bond donor and a hydrogen bond acceptor to obtain a eutectic solvent; (2) adding the eutectic solvent into N, N-dimethylformamide to obtain a mixed solution; (3) adding an organic ligand into the mixed solution, stirring, and adding a metal titanium source to obtain a mixture; and (4) transferring the mixture into a reaction kettle, and carrying out solvothermal reaction to obtain the NH2-MIL-125 (Ti) nanocrystal adsorbent. The average particle size of the NH2-MIL-125 (Ti) nanocrystal adsorbent prepared by the invention is 50-175 nm, the shape of the NH2-MIL-125 (Ti) nanocrystal adsorbent is an irregular disc shape, and the specific surface area of the NH2-MIL-125 (Ti) nanocrystal The adsorbent can efficiently, rapidly and selectively adsorb cationic dyes in dye wastewater, the adsorption rates of rhodamine B and malachite green in an aqueous solution can reach 99.7% and 98.3% respectively, and the adsorbent has a wide pH application range and good cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials and particularly relates to an NH 2 -MIL-125 (Ti) nanocrystal adsorbent and its preparation method and application. Background Art

[0002] NH 2 -MIL-125(Ti), as a titanium-based metal-organic framework material, has the advantages of unique pore structure and high specific surface area, and can be applied to a variety of wastewater treatment processes, such as dye adsorption, heavy metal removal, gas capture and organic pollutant degradation. 2 -MIL-125(Ti) has relatively limited pore size distribution, adsorption capacity and regeneration ability, which limits its adsorption efficiency in practical applications. 2 -MIL-125(Ti) can improve its performance by compounding with other materials such as semiconductors and metal oxides, but this compounding process is often complicated and requires careful control of the synthesis conditions to ensure the uniformity and stability of the material. 2 -MIL-125(Ti) nanocrystals have obvious advantages for rapid dye adsorption, which can simplify the synthesis process, reduce costs, and improve environmental friendliness and material recyclability. Therefore, it is necessary to develop a mild, simple, and environmentally friendly method for the synthesis of NH 2 -A new method for the adsorbent of MIL-125(Ti) nanocrystals is of great significance for improving its dye adsorption performance and its potential application in environmental remediation.

[0003] The traditional solvothermal method uses N,N-dimethylformamide and methanol as a mixed solvent to carry out NH 2 -MIL-125(Ti) synthesis, in which N,N-dimethylformamide plays a deprotonating role, and methanol acts as a strong hydrogen bond donor to make the titanium oxide cluster (Ti 8 O 8 (OH) 4 ) metal nodes and organic ligand 2-aminoterephthalic acid form porous organic-inorganic complexes through coordination bonding. However, the NH 2 -MIL-125(Ti) is usually a disc-shaped, decahedral or octahedral micron crystal, and its adsorption performance for dyes is poor, which is specifically manifested in slow adsorption rate, low adsorption amount, and narrow pH application range.

[0004] A low eutectic solvent is a liquid mixture formed by mixing a hydrogen bond donor and a hydrogen bond acceptor in an appropriate molar ratio, and its melting point is significantly lower than the melting point of any single component. Compared with traditional solvents such as water or organic solvents, low eutectic solvents have the following advantages: simple preparation, low cost, environmental friendliness, biodegradability, non-flammability, structural adjustability, etc. CN117843985A discloses a green synthesis method for Co-based MOF materials, which adds ligands and metal salts to a low eutectic solvent, and hydrothermally reacts the resulting mixed solution to obtain a Co-based MOF material; the low eutectic solvent can participate in the assembly of the MOF material skeleton. And CN111690148A discloses a green preparation method for a two-dimensional metal-organic framework material, which uses a low eutectic solvent and water as a reaction solvent, and prepares a two-dimensional metal-organic framework material with good crystallinity and ultra-thin thickness through a solvent thermal reaction; the low eutectic solvent used can not only replace traditional organic solvents to solve environmental pollution problems, but also can be used as a regulator to inhibit the growth of two-dimensional materials in the vertical direction.

[0005] Based on the above, the present invention provides a NH 2 -MIL-125(Ti) nanocrystal adsorbent preparation method, by using a low eutectic solvent as an additive in the solvothermal method, changing the deprotonation ability of N,N-dimethylformamide, affecting the nucleation process of the crystal, thereby achieving NH 2 -Precise control of the morphology, size and structure of MIL-125(Ti) crystals and improvement of their dye adsorption performance Summary of the invention

[0006] In view of the above problems, the present invention provides a NH 2 -MIL-125(Ti) nanocrystal adsorbent and its preparation method and application, using low eutectic solvent as additive for solvothermal method to prepare NH 2 -MIL-125(Ti) nanocrystal adsorbent, prepared NH 2 -MIL-125 (Ti) nanocrystal adsorbent is irregular disc-shaped, has more ligand defects and oxygen vacancies, and has high efficiency and selective adsorption for cationic dyes. The preparation method of the invention is simple, low-cost and environmentally friendly.

[0007] The present invention is achieved through the following technical solutions:

[0008] ANH 2 - A method for preparing a MIL-125 (Ti) nanocrystal adsorbent, comprising the following steps:

[0009] (1) mixing a hydrogen bond donor and a hydrogen bond acceptor, stirring and mixing evenly to obtain a deep eutectic solvent;

[0010] (2) adding a low eutectic solvent to N,N-dimethylformamide and stirring to uniformly mix the mixture to obtain a mixed solution;

[0011] (3) adding the organic ligand to the mixed solution, stirring, adding the metal titanium source, and continuing to stir to obtain a mixture;

[0012] (4) The mixture was transferred into a reactor for solvothermal reaction. After the reaction was completed, it was naturally cooled to room temperature. After washing, centrifugation and drying, NH 2 -MIL-125(Ti) nanocrystal adsorbent.

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

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

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

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

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

[0018] Furthermore, in step (4), the temperature of the solvent thermal reaction is 120 to 150° C., and the time is 24 to 72 hours.

[0019] A NH prepared by the preparation method as described above 2 -MIL-125(Ti) nanocrystal adsorbent.

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

[0021] A NH as described above 2 -Application of MIL-125(Ti) nanocrystal adsorbent in the adsorption of rhodamine B and malachite green.

[0022] NH of the present invention 2-Preparation principle of MIL-125(Ti) nanocrystal adsorbent:

[0023] The present invention uses a low eutectic solvent as an additive for the solvothermal method, and the titanium source and the organic ligand are dissolved in a mixed solvent consisting of the low eutectic solvent and N,N-dimethylformamide. Under heating conditions, the titanium oxide clusters (Ti 8 O 8 (OH) 4 ) metal nodes and organic ligands such as 2-aminoterephthalic acid form porous organic-inorganic complexes through coordination bonding, changing the deprotonation ability of N,N-dimethylformamide, thereby affecting the nucleation process of the crystal, making the obtained NH 2 -MIL-125(Ti) has more ligand defects and oxygen vacancies. It is a nano-scale crystal with an irregular disc shape. It has good adsorption performance for cationic dyes in dye wastewater, with fast adsorption rate, high adsorption rate, high adsorption amount and wide pH application range.

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

[0025] 1. The present invention uses a low eutectic solvent as an additive for the solvothermal method to prepare NH 2 -MIL-125(Ti) nanocrystal adsorbent, prepared NH 2 -MIL-125(Ti) nanocrystal adsorbent has more ligand defects and oxygen vacancies, with an average particle size of 50-175nm, an irregular disc shape, and a specific surface area of ​​885-900m 2 / g, and has good adsorption performance for cationic dyes in dye wastewater. The preparation method of the invention is simple, low-cost and environmentally friendly.

[0026] 2. NH prepared by the present invention 2 -MIL-125(Ti) nanocrystal adsorbent can efficiently and rapidly selectively adsorb cationic dyes in dye wastewater. The adsorption capacity of rhodamine B and malachite green can reach 79.1 mg / g and 804.1 mg / g respectively, and the adsorption rate can reach 99.7% and 98.3% respectively. The adsorption of rhodamine B has a wide pH range and good cyclic stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 These are the XRD diagrams of 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.

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

[0029] Figure 3 These are the SEM and TEM images of n-NMT-53 prepared in Example 1, and the SEM images of n-NMT-64, n-NMT-74, and n-NMT-175 prepared in Examples 2-4, respectively.

[0030] Figure 4 This is the EDX image of n-NMT-53 prepared in Example 1.

[0031] Figure 5 FT-IR images of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively.

[0032] Figure 6 N is the N of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1 respectively. 2 Adsorption-desorption isotherms.

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

[0034] Figure 8 These are the XPS graphs of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, respectively.

[0035] Fig. 9 The adsorption rate-time relationship diagram of 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 for rhodamine B and malachite green.

[0036] Fig.10 The graph is a relationship between the adsorption rate of n-NMT-53 prepared in Example 1 and time for rhodamine B and malachite green at different initial dye concentrations.

[0037] Fig.11 This is a UV-visible spectrum-time relationship diagram of n-NMT-53 prepared in Example 1 adsorbing mixed dyes.

[0038] Fig.12 This is a graph showing the adsorption rate of rhodamine B by n-NMT-53 prepared in Example 1 under different initial pH environments.

[0039] Fig.13 This is a graph showing the cyclic adsorption rate of rhodamine B by n-NMT-53 prepared in Example 1.

[0040] Fig.14 This is the XRD pattern of n-NMT-53 prepared in Example 1 before and after cyclic adsorption of Rhodamine B. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below by way of examples. These examples are only used to illustrate the present invention and do not limit the protection scope of the present invention.

[0042] Example 1

[0043] NH 2 -Preparation of MIL-125(Ti) nanocrystal adsorbent:

[0044] 20.94g (0.15mol) of choline chloride and 24.30mL (0.6mol) of methanol were stirred at room temperature for 5min to form a uniform and transparent liquid to obtain a low eutectic solvent. Take 9g of the low eutectic solvent, add it to 21mL of N,N-dimethylformamide, stir at room temperature for 5min, mix it evenly, and obtain a mixed solution. 1.5g of 2-aminoterephthalic acid was added to the mixed solution, stirred at room temperature for 5min, and then 0.85mL of tetrabutyl titanate was added. After stirring at room temperature for 30min, a mixture was obtained. The mixture was transferred into a 50mL reactor and placed in an oven at 150°C for 72h. After the reaction was completed, it was naturally cooled to room temperature. The solid obtained by centrifugation was washed three times with N,N-dimethylformamide and methanol respectively, and then dried in an oven at 60°C for 10h to obtain NH 2 -MIL-125(Ti) nanocrystal adsorbent (denoted as n-NMT-53).

[0045] Example 2

[0046] The difference between Example 2 and Example 1 is that the mass of the low eutectic solvent in Example 2 is 3 g, the volume of N,N-dimethylformamide is 27 mL, and the rest of the preparation process and conditions are the same as those in Example 1. NH 2 -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 low eutectic solvent in Example 3 is 21 g, the volume of N,N-dimethylformamide is 9 mL, and the rest of the preparation process and conditions are the same as those in Example 1, and NH 2 -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 low eutectic solvent in Example 4 is 27 g, the volume of N,N-dimethylformamide is 3 mL, and the rest of the preparation process and conditions are the same as those in Example 1, and NH 2-MIL-125(Ti) nanocrystal adsorbent (denoted as n-NMT-175).

[0051] Example 5

[0052] NH 2 -Preparation of MIL-125(Ti) nanocrystal adsorbent:

[0053] 20.94g (0.15mol) of choline chloride and 22.50mL (0.5mol) of urea were stirred at room temperature for 5min to form a uniform and transparent liquid to obtain a low eutectic solvent. Take 3g of the low eutectic solvent, add it to 12mL of N,N-dimethylformamide, stir at room temperature for 5min, mix it evenly, and obtain a mixed solution. 1.5g of terephthalic acid was added to the mixed solution, stirred at room temperature for 5min, and then 0.8mL of titanium tetrachloride was added. After stirring at room temperature for 30min, a mixture was obtained. The mixture was transferred into a 50mL reactor and placed in an oven at 150℃ for 24h. After the reaction was completed, it was naturally cooled to room temperature. The solid obtained by centrifugation was washed three times with N,N-dimethylformamide and methanol respectively, and then dried in an oven at 60℃ for 10h to obtain NH 2 -MIL-125(Ti) nanocrystal adsorbent.

[0054] Example 6

[0055] NH 2 -Preparation of MIL-125(Ti) nanocrystal adsorbent:

[0056] 20.94g (0.15mol) of choline chloride and 22.30mL (0.4mol) of ethylene glycol were stirred at room temperature for 5min to form a uniform and transparent liquid to obtain a low eutectic solvent. Take 3g of the low eutectic solvent, add it to 15mL of N,N-dimethylformamide, stir at room temperature for 5min, mix it evenly, and obtain a mixed solution. Add 2.0g of 2-aminoterephthalic acid to the mixed solution, stir at room temperature for 5min, then add 1.05mL of titanium isopropoxide, continue stirring at room temperature for 30min, and obtain a mixture. Transfer the mixture into a 50mL reactor, place it in an oven at 120℃ for 72h, and naturally cool it to room temperature after the reaction is completed. Wash the centrifuged solid three times with N,N-dimethylformamide and methanol respectively, and then dry it in an oven at 60℃ for 10h to obtain NH 2 -MIL-125(Ti) nanocrystal adsorbent.

[0057] Example 7

[0058] NH 2 -Preparation of MIL-125(Ti) nanocrystal adsorbent:

[0059] 20.94g (0.15mol) of choline chloride and 31.20mL (0.3mol) of benzyl alcohol were stirred at room temperature for 5min to form a homogeneous and transparent liquid to obtain a low eutectic solvent. Take 3g of the low eutectic solvent, add it to 20mL of N,N-dimethylformamide, stir at room temperature for 5min, mix it evenly, and obtain a mixed solution. 3.0g of terephthalic acid was added to the mixed solution, stirred at room temperature for 5min, and then 1.50mL of tetrabutyl titanate was added. After stirring at room temperature for 30min, a mixture was obtained. The mixture was transferred into a 50mL reactor and placed in an oven at 140°C for 48h. After the reaction was completed, it was naturally cooled to room temperature. The solid obtained by centrifugation was washed three times with N,N-dimethylformamide and methanol respectively, and then dried in an oven at 60°C for 10h to obtain NH 2 -MIL-125(Ti) nanocrystal adsorbent.

[0060] Comparative Example 1

[0061] NH 2 -Preparation of MIL-125(Ti) micron crystal 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 of methanol and 27 mL of N, N-dimethylformamide), stirred at room temperature for 5 min, and then 0.85 mL of tetrabutyl titanate was added. After stirring at room temperature for 30 min, a mixture was obtained. The mixture was transferred into a 50 mL reactor and placed in an oven at 150 ° C for 72 h. After the reaction was completed, it was naturally cooled to room temperature, and the solid obtained by centrifugation was washed three times with N, N-dimethylformamide and methanol, respectively, and then dried in an oven at 60 ° C for 10 h to obtain NH 2 -MIL-125(Ti) micron crystal 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 prepared in Examples 1-4 and Comparative Example 1 were characterized and analyzed by X-ray diffractometer (XRD). The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the XRD patterns of the products obtained in Examples 1-4 and Comparative Example 1 are similar to those of NH 2 -MIL-125(Ti) standard XRD pattern is consistent, indicating that when the low eutectic solvent is used as the additive of the solvothermal method in Examples 1-4, crystalline NH 2 -MIL-125(Ti).

[0066] (ii) SEM and TEM analysis

[0067] The n-NMT-53, n-NMT-64, n-NMT-74, n-NMT-175, and m-NMT prepared in Examples 1-4 and Comparative Example 1 were characterized and analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results are as follows: Figure 2 and Figure 3 shown. Figure 2 In the figure, a and b are SEM and TEM images of m-NMT prepared in Comparative Example 1, respectively. Figure 3 In the figure, a, bc are SEM and TEM images of n-NMT-53 prepared in Example 1, respectively, and d, e, and f are SEM images of n-NMT-64, n-NMT-74, and n-NMT-175 prepared 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 micron crystal with a regular morphology in the range of 0.3-1.5 μm. When a low eutectic solvent is used as an additive in the solvothermal method, NH 2 -MIL-125(Ti) nanocrystals. The product obtained in Example 1 is an irregular disk-shaped NH with an average size of 53 nm. 2 -MIL-125(Ti) nanocrystals. The products obtained in Examples 2-4 were irregular disc-shaped NH with average particle sizes of 64, 74 and 175 nm, respectively. 2 -MIL-125(Ti) nanocrystals.

[0069] (III) EDX analysis

[0070] The element distribution of n-NMT-53 prepared in Example 1 was analyzed by energy dispersive X-ray spectrometry (EDX). Figure 4 As shown. Figure 4 It can be seen that C, N, O and Ti elements are evenly distributed in the n-NMT-53 sample.

[0071] (IV) FT-IR analysis

[0072] The compositions of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1 were analyzed by Fourier transform infrared spectrometer (FT-IR). Figure 5 As shown. Figure 5 It can be seen that for m-NMT, 3439cm -1 The peak at 1626 cm is the stretching vibration of -OH. -1 The peak at -NH 2NH bending vibration, 1572cm -1 and 1531cm -1 The peak at 1427 cm is the antisymmetric stretching vibration of -C=O-. -1 and 1389cm -1 The peak at is the symmetric stretching vibration of -C=O-. Compared with m-NMT, the -OH stretching vibration peak of n-NMT-53 is red-shifted to 3429 cm -1 , indicating that there is a stronger hydrogen bond interaction in n-NMT-53. In n-NMT-53, the antisymmetric stretching vibration peak of -C=O- is located at 1574cm -1 and 1537cm -1 The symmetrical stretching vibration peak of -C=O- is located at 1435cm -1 and 1385cm -1 Compared with m-NMT, the distance between the antisymmetric stretching vibration peak and the symmetric stretching vibration peak of -C=O- in n-NMT-53 is increased, indicating that the interaction between the ligand and the titanium-oxygen cluster is weakened. This may be due to the low eutectic solvent regulation of the preparation of NH 2 -MIL-125(Ti) has ligand defects.

[0073] (V) Specific surface area and pore structure analysis

[0074] Using N 2 Physical adsorption The pore properties of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1 were analyzed, and the results showed that N 2 Adsorption-desorption isotherms Figure 6 As shown. Figure 6 It can be seen that n-NMT-53 exhibits a type IV adsorption isotherm and an H1 type hysteresis loop, which is usually a mesoporous material with a narrow pore size distribution or a spherical particle aggregate with uniform size. However, the TEM image of n-NMT-53 ( Figure 2 b) shows that there is no mesopore, indicating that N 2 The mesopores obtained by adsorption-desorption test are the accumulation pores formed by the accumulation of uniformly sized n-NMT-53 nanoparticles. The BET specific surface area of ​​n-NMT-53 is 891 m 2 / g, which is lower than the BET specific surface area of ​​m-NMT 1437m 2 / g, which may be caused by the partial blockage of the pores by the uncoordinated ligands in n-NMT-53.

[0075] (VI) Thermal stability analysis

[0076] Using N 2 Thermogravimetric analysis under atmosphere was performed to analyze the thermal stability of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1, and the obtained thermogravimetric curves are shown as follows: Figure 7 As shown. Figure 7 It 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% in the range of 110 to 303℃, and n-NMT-53 loses 19.00% in the range of 112 to 343℃, indicating that there are more ligand defects in n-NMT-53. The mass loss in the temperature range of 350 to 500℃ corresponds to the desorption of NH 2 -MIL-125(Ti) framework collapses and generates TiO 2。

[0077] (VII) XPS analysis

[0078] The surface compositions of n-NMT-53 and m-NMT prepared in Example 1 and Comparative Example 1 were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 8 As shown. Figure 8 a) It shows that C, N, O and Ti elements exist in n-NMT-53 and m-NMT, but no other elements. Figure 8 In b), the peaks of n-NMT-53 sample at 284.88eV, 286.68eV, and 288.78eV correspond to CC, CN, and CO bonds, respectively. 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 spectrum ( Figure 8 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 peaks of Ti-O and C=O in n-NMT-53 move to 530.18 eV and 531.88 eV respectively towards the low binding energy direction, which indicates that there are 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, which are attributed to the Ti in the Ti-O cluster. 4+ Compared with m-NMT, the peaks of Ti 2p3 / 2 and Ti 2p1 / 2 in n-NMT-53 shifted to 458.88eV and 464.68eV respectively towards the low binding energy direction, indicating that there may be ligand defects or oxygen vacancies in n-NMT-53. The XPS analysis results are consistent with the FT-IR analysis results, both indicating that there are more ligand defects and oxygen vacancies in n-NMT-53.

[0079] Application Example 1

[0080] Take 25 mg of n-NMT-53 prepared in Example 1 and place it in a beaker, add 25 mL of 20 mg / L rhodamine B aqueous solution, and perform adsorption experiment at a temperature of 25 ° C and a stirring speed of 300 rpm for 3 hours. The above dye is replaced with a 300 mg / L malachite green aqueous solution, and the other experimental conditions are the same. It is calculated that the adsorption rates of n-NMT-53 for rhodamine B and malachite green are 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, and the other experimental conditions are the same as those in Application Example 1. According to calculation, the adsorption rates of n-NMT-64 for rhodamine B and malachite green are 99.6% and 97.7%, respectively.

[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, and the other experimental conditions are the same as those in Application Example 1. According to calculation, the adsorption rates of n-NMT-74 for rhodamine B and malachite green are 98.2% and 93.3%, respectively.

[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, and the other experimental conditions are the same as those in Application Example 1. According to calculation, the adsorption rates of n-NMT-175 for rhodamine B and malachite green are 97.4% and 57.8%, respectively.

[0087] Application Comparative Example 1

[0088] The difference between Application Comparative Example 1 and Application Example 1 is that the adsorbent in Application Comparative Example 1 is m-NMT prepared in Comparative Example 1, and the other experimental conditions are the same as those of Application Example 1. According to calculation, the adsorption rates of m-NMT for rhodamine B and malachite green are 94.7% and 34.3%, respectively.

[0089] Material adsorption performance analysis

[0090] (I) Analysis of the adsorption performance of dyes by adsorbents at different adsorption times

[0091] The adsorption rates of rhodamine B and malachite green by the adsorbents m-NMT, n-NMT-53, n-NMT-64, n-NMT-74 and n-NMT-175 in Comparative Example 1 and Examples 1-4 vary with time. Fig. 9 (ab) shown. Fig. 9 In the figure, a and b are the adsorption rates of n-NMT-175 for rhodamine B and malachite green changing with time, respectively.

[0092] Depend on Fig. 9 It can be seen that when the adsorption time is 5 minutes, the adsorption rates of n-NMT-53 on rhodamine B and malachite green quickly reach 92.4% and 90.2%, respectively, which are much higher than the adsorption rates of m-NMT on rhodamine B (54.9%) and malachite green (22.7%) at 5 minutes. With the extension of adsorption time, the adsorption active sites gradually tend to saturation, and the adsorption gradually tends to equilibrium. When the adsorption time is 3 hours, the equilibrium adsorption rates of n-NMT-53 on rhodamine B and malachite green are 99.7% and 98.3%, respectively, which are higher than the adsorption rates of m-NMT on rhodamine B (94.7%) and malachite green (34.3%) at 3 hours, and the adsorption of m-NMT on rhodamine B and malachite green has not reached equilibrium at 3 hours.

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

[0094] The concentration of the rhodamine B aqueous solution in Application Example 1 was replaced with 20, 40, 60, 80 and 100 mg / L, and the concentration of the malachite green aqueous solution was replaced with 200, 300, 500, 800 and 1000 mg / L, and the other experimental conditions were the same as those in Application Example 1. The changes in the adsorption rates of rhodamine B and malachite green by n-NMT-53 with time at different initial dye concentrations are shown in Figure 2. Fig.10 (ab) shown. Fig.10 In the figure, a and b are the adsorption rates of n-NMT-53 to rhodamine B and malachite green changing with time, respectively.

[0095] Depend on Fig.10 It can be seen that the amount of rhodamine B and malachite green adsorbed on n-NMT-53 increases with the increase of the initial concentration of the dye, which is due to the increase in the concentration gradient that enhances the driving force for adsorption. At 25°C, the equilibrium adsorption amount of malachite green on n-NMT-53 is as high as 804.1 mg / g, and the equilibrium adsorption amount of rhodamine B is as high as 79.1 mg / g.

[0096] (III) Analysis of adsorption performance of adsorbents on mixed dyes under different mixed dyes

[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, and the mixed dye was replaced with a mixed dye aqueous solution consisting of 30 mg / L rhodamine B and 300 mg / L malachite green. The remaining experimental conditions were the same as those in Application Example 1. The changes in the UV-visible spectra of n-NMT-53 adsorbing mixed dyes with different mixed dyes over time are shown in Figure 1. Fig.11 (ab) shown. Fig.11 In the figure, a and b are the changes of the UV-visible 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 over time, respectively.

[0098] Depend on Fig.11 It can be seen that in the mixed dye composed of the cationic dye Rhodamine B and malachite green, n-NMT-53 has a good adsorption effect, and the adsorption rate of 1h can reach more than 92.9%. In the mixed dye composed of the cationic dye Rhodamine B and the anionic dye methyl orange, n-NMT-53 has a good adsorption effect on Rhodamine B, and the adsorption rate of 1h reaches 94.0%, but the adsorption effect on methyl orange is poor, and the adsorption rate of 3h can only reach 39.6%. The n-NMT-53 adsorbent shows a high adsorption efficiency for the cationic dye Rhodamine B and malachite green in the mixed dye, but the adsorption effect on the anionic dye methyl orange is relatively poor, indicating that n-NMT-53 has a high efficiency and selective adsorption for cationic dyes.

[0099] (IV) Analysis of the adsorption performance of dyes by adsorbents at different initial pH values ​​of aqueous solutions

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

[0101] Depend on Fig.12 It can be seen that the adsorption rate of n-NMT-53 for RhB in the range of pH = 2 to 9 is maintained above 96.6%, indicating that the efficient adsorption of rhodamine B by n-NMT-53 adsorbent has a wide pH applicable range.

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

[0103] After the n-NMT-53 in Application Example 1 was adsorbed for 3 hours, a sample was taken for centrifugal separation. The n-NMT-53 after centrifugal separation was immersed in methanol and stirred for 8 hours to desorb rhodamine B. After desorption, the n-NMT-53 sample was dried in an oven at 60°C for 10 hours for subsequent cyclic adsorption experiments. The adsorption cycle rate of n-NMT-53 for rhodamine B is shown in Fig.13 shown.

[0104] Depend on Fig.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 cyclic stability for the adsorption of cationic dye rhodamine B in water.

[0105] The crystal structure of n-NMT-53 before and after cyclic adsorption of Rhodamine B was characterized. Fig.14 As shown. Fig.14 It can be seen that although the crystallinity of n-NMT-53 is slightly reduced after cyclic adsorption, the original crystal framework structure can still be basically maintained.

[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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing NH2-MIL-125 (Ti) nanocrystal adsorbent, characterized in that: The following steps are involved: (1) mixing a hydrogen bond donor and a hydrogen bond acceptor, stirring and mixing evenly to obtain a deep eutectic solvent; (2) adding a low eutectic solvent to N,N-dimethylformamide and stirring to uniformly mix the mixture to obtain a mixed solution; (3) adding the organic ligand to the mixed solution, stirring, adding the metal titanium source, and continuing to stir to obtain a mixture; (4) The mixture is transferred into a reactor for a solvothermal reaction. After the reaction is completed, the mixture is naturally cooled to room temperature. After washing, centrifugation and drying, an NH2-MIL-125 (Ti) nanocrystal adsorbent is obtained.

2. The method for preparing the NH2-MIL-125 (Ti) nanocrystal adsorbent according to claim 1, characterized in that: In step (1), the hydrogen bond donor is urea, ethylene glycol, benzyl alcohol or methanol; and the hydrogen bond acceptor is choline chloride.

3. The method for preparing the NH2-MIL-125 (Ti) nanocrystal adsorbent according to claim 2, characterized in that: In step (1), the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 2 to 4:

1.

4. The method for preparing the NH2-MIL-125 (Ti) nanocrystal adsorbent according to claim 1, characterized in that: In step (2), the mass volume ratio of the low eutectic solvent to N,N-dimethylformamide is 1 g:0.1-9 mL.

5. The method for preparing the NH2-MIL-125 (Ti) nanocrystal adsorbent according to claim 1, characterized in that: In step (3), the organic ligand is terephthalic acid or 2-aminoterephthalic acid; the metal titanium source is tetrabutyl titanate, titanium tetrachloride or titanium isopropoxide.

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

7. The method for preparing the NH2-MIL-125 (Ti) nanocrystal adsorbent according to claim 1, characterized in that: In step (4), the temperature of the solvent thermal reaction is 120 to 150° C. and the time is 24 to 72 hours.

8. An NH2-MIL-125 (Ti) nanocrystal adsorbent prepared by the preparation method according to any one of claims 1 to 7.

9. The NH2-MIL-125(Ti) nanocrystal adsorbent according to claim 8, characterized in that: The NH2-MIL-125 (Ti) nanocrystal adsorbent has an average particle size of 50 to 175 nm, an irregular disc shape, and a specific surface area of ​​885 to 900 m 2 / g.

10. Use of the NH2-MIL-125 (Ti) nanocrystal adsorbent as claimed in claim 8 in the adsorption of rhodamine B and malachite green.

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