An Ag / Double-Ligand Sn-MOF Composite Material, Its Preparation Method and Application

Abstract

The present invention relates to the technical field of material preparation, and specifically discloses an Ag / bidentate ligand Sn-MOF composite material, its preparation method and application. In the present invention, Sn<supgt;2+< / supgt; is used as the metal active center, and aromatic carboxylic acid ligands and alkyl imidazole ligands are used as organic ligands. A bidentate ligand Sn-MOF material with high stability and high photocatalytic activity is prepared by a solvothermal method. Then, Ag nanoparticles are loaded onto the bidentate ligand Sn-MOF material by a photodeposition method. This not only increases the specific surface area of the material and provides more reactive sites, but also the formation of the Ag / Sn-MOF heterostructure reduces the recombination of electron-hole pairs, significantly improving the charge transfer efficiency. In addition, the heterojunction formed between Ag and the bidentate ligand Sn-MOF material can effectively enrich and store photogenerated electrons and release photogenerated electrons in the dark environment, thus facilitating the realization of continuous degradation reactions under light and dark conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of photocatalytic materials, and particularly relates to an Ag / bidentate ligand Sn-MOF composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Printing and dyeing wastewater not only has a deep color and a high chemical oxygen demand, but also contains a large amount of toxic and harmful substances, and it is difficult to achieve an ideal treatment effect through conventional treatment methods. Photocatalytic technology is a kind of advanced oxidation method. When a photocatalyst is excited by light, electron-hole pairs are generated, and then active groups such as hydroxyl radicals (·OH) and superoxide radicals (·O2 - )are generated. These active groups come into contact with organic pollutants in the water body, causing the organic pollutants to be oxidized and degraded into CO2 and H2O, thereby realizing the harmless treatment of organic wastewater. Photocatalytic technology has developed rapidly because it can convert solar energy into chemical energy and has a wide application prospect in the field of treating refractory printing and dyeing wastewater. However, once the light is stopped (such as at night), the generation of photo-generated carriers in the photocatalyst will immediately stop, and the separation of electron-hole pairs will stop, resulting in the immediate disappearance of catalytic activity, which is also a bottleneck factor restricting the development of photocatalytic technology.

[0003] Metal-Organic Frameworks (abbreviated as MOFs) are a class of porous crystalline solid materials formed by the self-assembly of metal ions or metal clusters and organic ligands. MOFs have characteristics such as a high specific surface area, multiple active sites, a structure that can be tailored, and easy functionalization, and these characteristics have attracted extensive attention in the field of photocatalysis.

[0004] However, single MOF materials have disadvantages such as low chemical stability, limited thermal stability, and catalytic activity in the aqueous phase. When used in the environmental field, their environmental sensitivity and chemical stability must be considered. At the same time, MOF materials also have the disadvantage of deactivating in the dark environment, and some MOF materials are prone to photocorrosion or structural damage during the photocatalytic process, resulting in a decline in photocatalytic performance. Therefore, it is necessary to develop a photocatalytic material with excellent catalytic activity and photocatalytic stability, and that can also effectively catalyze the degradation of organic matter in the dark, so as to provide a new solution for the efficient and environmental protection treatment of printing and dyeing wastewater. Summary of the Invention

[0005] In view of the problems existing in the photocatalysts for degrading printing and dyeing wastewater in the prior art, such as low catalytic activity, easy deactivation, and immediate disappearance of catalytic activity under dark conditions, the present invention provides an Ag / bidentate ligand Sn-MOF composite material, a preparation method thereof, and an application thereof. The present invention uses an aromatic carboxylic acid ligand and an alkylimidazole ligand as organic ligands to prepare a bidentate ligand Sn-MOF material, and deposits Ag on the bidentate ligand Sn-MOF material by photodeposition to form a photocatalytic material with a memory catalytic function, providing an excellent catalyst for industrial treatment of printing and dyeing wastewater and having high popularization and application value.

[0006] To solve the above technical problems, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a preparation method of an Ag / bidentate ligand Sn-MOF composite material, and the preparation method includes the following steps:

[0008] S1, dissolving a bidentate organic ligand in an organic solvent to obtain a ligand solution; the bidentate organic ligand includes an aromatic carboxylic acid ligand and an alkylimidazole ligand;

[0009] S2, adding a soluble tin salt to the ligand solution, mixing uniformly, performing a hydrothermal reaction at 120°C to 180°C, washing, and drying to obtain an Sn-MOF material;

[0010] S3, dispersing the Sn-MOF material in a silver salt solution, adding an alcohol solvent, and depositing silver nanoparticles on the surface of the Sn-MOF material by a photoreduction method to obtain an Ag / bidentate ligand Sn-MOF composite material.

[0011] Compared with the prior art, the preparation method of the Ag / bidentate ligand Sn-MOF composite material provided by the present invention uses Sn 2+ as a metal active center, uses an aromatic carboxylic acid ligand and an alkylimidazole ligand as organic ligands, and prepares a bidentate ligand Sn-MOF material with excellent adsorption characteristics, high stability, and high photocatalytic activity by a solvothermal method. At the same time, Ag nanoparticles are loaded onto the bidentate ligand Sn-MOF material by a photodeposition method, which not only increases the specific surface area of the material and provides more reactive sites, but also the formation of an Ag / Sn-MOF heterostructure reduces the recombination of electron-hole pairs, significantly improving the charge transfer efficiency and further enhancing the photocatalytic performance of the composite material; in addition, the heterojunction formed between Ag and the bidentate ligand Sn-MOF material can effectively enrich and store photogenerated electrons and release photogenerated electrons in a dark environment, thus facilitating the realization of continuous degradation reactions under light and dark conditions.

[0012] Sn can form strong coordination bonds with aromatic carboxylic acid ligands to form a rigid and interconnected framework structure. Using Sn as the metal active center can significantly improve the chemical stability of MOFs materials in aqueous environments. However, the degree of deprotonation of single-ligand MOFs materials with aromatic carboxylic acids is relatively low, resulting in insufficient active sites in the materials, and deficiencies in the stability, reaction selectivity, and adsorption performance of the materials. Therefore, in the present invention, alkylimidazole ligands are used as competitive ligands to bridge the deprotonated aromatic carboxylic acid ligands, regulate the structure and morphology of the materials, increase the specific surface area of the materials, provide more active sites and catalytic substrate / product transport channels; at the same time, it can also promote the nucleation and growth of crystals, form a crystalline ordered structure, thereby reducing the recombination of photo-generated electrons and holes and improving the photocatalytic efficiency. In addition, using Ag as a dopant helps to improve the separation efficiency of photo-generated carriers, and Ag itself can act as an electron trap to capture photo-generated electrons and has the ability to store electrons. Its cooperation with the dual-ligand Sn-MOF material can further enhance the enrichment and storage of photo-generated electrons. Therefore, the doping of Ag not only improves the photocatalytic activity of the dual-ligand Sn-MOF, but also achieves the purpose of releasing photo-generated electrons in the dark environment and continuously degrading organic pollutants.

[0013] Further, the aromatic carboxylic acid ligand is terephthalic acid, phthalic acid, isophthalic acid, or trimesic acid.

[0014] Preferably, the aromatic carboxylic acid ligand is terephthalic acid.

[0015] Further, the alkylimidazole ligand is 2-methylimidazole, 4-methylimidazole, 1,2-dimethylimidazole, or 2,4-dimethylimidazole.

[0016] Preferably, the alkylimidazole ligand is 2-methylimidazole.

[0017] The types of ligands play a crucial role in the structure of MOFs materials and have a significant impact on photocatalytic activity. In the present invention, using aromatic carboxylic acid ligands and alkylimidazole ligands as dual ligands for MOFs materials can effectively increase the specific surface area and porosity of MOFs materials, increase the active sites of MOFs materials. At the same time, the aromatic carboxylic acid ligands and alkylimidazole ligands can promote the transfer of electrons from the ligand to the metal center through the metal-ligand charge transfer process, improving the separation efficiency of photo-generated electrons. In addition, the preferred ligands can also improve the water stability of MOFs materials, solving the defects of high environmental sensitivity and low chemical stability of existing MOFs materials.

[0018] Further, the molar ratio of the aromatic carboxylic acid ligand to the alkylimidazole ligand is 1:0.5 to 1:3.

[0019] The preferred ligand ratio is beneficial to improving the photocatalytic activity and chemical stability of the Sn-MOF material.

[0020] Furthermore, the concentration of the aromatic carboxylic acid ligand in the ligand solution is 20 mmol / L to 60 mmol / L.

[0021] Preferably, the concentration of the aromatic carboxylic acid ligand in the ligand solution is 20 mmol / L to 40 mmol / L.

[0022] Furthermore, in S1, the organic solvent is a mixed solution of N,N-dimethylformamide and absolute ethanol with a volume ratio of 1:2 to 1:4.

[0023] Preferably, in S1, the organic solvent is a mixed solution of N,N-dimethylformamide and absolute ethanol with a volume ratio of 1:2.5 to 1:3.5.

[0024] The preferred organic solvent can fully dissolve the organic ligand and the soluble tin salt, thus facilitating the full reaction between the two during the subsequent hydrothermal reaction.

[0025] Furthermore, in S2, the soluble tin salt is stannous chloride or stannous sulfate.

[0026] Preferably, in S2, the soluble tin salt is stannous chloride.

[0027] Furthermore, the molar ratio of the soluble tin salt to the total amount of the bis-organic ligand is 1:0.5 to 1:2.

[0028] Preferably, the molar ratio of the soluble tin salt to the total amount of the bis-organic ligand is 1:0.8 to 1:1.5.

[0029] The preferred ratio of the soluble tin salt to the bis-organic ligand is beneficial to improving the photocatalytic activity of the Sn-MOF material.

[0030] Furthermore, in S2, the time of the hydrothermal reaction is 8 h to 15 h.

[0031] Preferably, in S2, the temperature of the hydrothermal reaction is 140 °C to 160 °C, and the time is 10 h to 12 h.

[0032] The preferred reaction temperature and time can improve the crystallinity of the Sn-MOF material, reduce the recombination of photogenerated electrons and holes, and improve the photocatalytic efficiency.

[0033] Furthermore, in S3, the silver salt solution is an aqueous solution of silver nitrate with a concentration of 0.20 g / L to 0.30 g / L.

[0034] Preferably, in S3, the silver salt solution is an aqueous solution of silver nitrate with a concentration of 0.25 g / L.

[0035] Further, in S3, the mass ratio of the Sn-MOF material to the silver salt in the silver salt solution is 15:1 to 25:1.

[0036] Preferably, in S3, the mass ratio of the Sn-MOF material to the silver salt in the silver salt solution is 18:1 to 22:1.

[0037] The preferred doping amount of Ag can further improve the photocatalytic activity of the Sn-MOFs material, as well as the ability of the Sn-MOFs material to enrich and store photogenerated electrons, and increase the reaction duration in the dark environment.

[0038] Further, in S3, a xenon lamp is used for photoreduction deposition of silver nanoparticles, and the power of the xenon lamp is 300W to 500W, and the illumination time is 1h to 2h.

[0039] Further, in S3, the alcohol solvent is methanol.

[0040] Further, in S3, after the photoreduction deposition of silver nanoparticles reaction is completed, solid-liquid separation is carried out, and the obtained solid is washed with deionized water, dried, and ground to obtain an Ag / double-ligand Sn-MOF composite material.

[0041] Exemplarily, in S3, an optical reactor is used for the deposition of Ag nanoparticles.

[0042] The present invention also provides an Ag / double-ligand Sn-MOF composite material, which is prepared by the preparation method of the Ag / double-ligand Sn-MOF composite material described in any one of the above.

[0043] The Ag / double-ligand Sn-MOF composite material provided by the present invention has excellent photocatalytic activity, high chemical stability, can maintain activity for a long time in the absence of light, can realize the continuous degradation of pollutants under light and dark conditions, provides a catalyst with excellent performance for the industrial treatment of organic pollutant wastewater, and has high practical value.

[0044] The present invention also provides the application of the above Ag / double-ligand Sn-MOF composite material in the degradation of organic pollutants in wastewater.

[0045] Further, the wastewater is printing and dyeing wastewater.

[0046] Further, when degrading printing and dyeing wastewater, the concentration of the Ag / double-ligand Sn-MOF composite material is 1g / L to 3g / L, and the concentration of organic pollutants in the printing and dyeing wastewater is 10mg / L to 100mg / L.

[0047] Compared with traditional MOF materials, the Ag / double-ligand Sn-MOF composite material provided by the present invention has significantly improved adsorption and degradation efficiency for organic substances. Different from ordinary doped materials, it has good structural stability and can be recycled. At the same time, it also has a high continuous catalytic degradation efficiency in the dark environment and has more advantages in degrading organic pollutants, especially printing and dyeing wastewater. Description of the Drawings

[0048] Figure 1 Scanning electron microscope (SEM) images of Sn-PTA-MI and Ag / Sn-PTA-MI composite materials prepared in Example 1; where (a) is Sn-PTA-MI and (b) is the Ag / Sn-PTA-MI composite material.

[0049] Figure 2 EDX spectrum of the Ag / Sn-PTA-MI composite material prepared in Example 1; the upper right inset shows the elemental mass percentage and atomic percentage of each element in the Ag / Sn-PTA-MI composite material.

[0050] Figure 3 Transmission electron microscope images of the Ag / Sn-PTA-MI composite material prepared in Example 1, (a) TEM, (b) HRTEM.

[0051] Figure 4 X-ray diffraction (XRD) patterns of Sn-PTA-MI and Ag / Sn-PTA-MI composite materials prepared in Example 1.

[0052] Figure 5 Fourier transform infrared (FTIR) spectra of Sn-PTA-MI and Ag / Sn-PTA-MI composite materials prepared in Example 1.

[0053] Figure 6 X-ray photoelectron spectroscopy (XPS) spectra of the Ag / Sn-PTA-MI composite material prepared in Example 1; where (a) is the full spectrum, (b) is Sn 3d, (c) is C1s, (d) is N 1s, (e) is O 1s, and (f) is Ag 3d.

[0054] Figure 7 N2 adsorption-desorption isotherms of Sn-PTA-MI and Ag / Sn-PTA-MI composite materials prepared in Example 1; the inset shows the pore size distribution diagrams of Sn-PTA-MI and Ag / Sn-PTA-MI composite materials.

[0055] Figure 8 Electrochemical impedance spectroscopy (EIS) diagrams of Sn-PTA-MI and Ag / Sn-PTA-MI composite materials prepared in Example 1.

[0056] Figure 9 To change the influence of the illumination time during the photo-deposition of Ag nanoparticles in step S3 of Example 1 on the absorbance of the Ag / Sn-PTA-MI composite material;

[0057] Figure 10 It is a comparative diagram of the catalytic effects of Sn-PTA, Sn-MI, Sn-PTA-MI, Ag / Sn-PTA, Ag / Sn-MI, and Ag / Sn-PTA-MI materials in Example 1 under photocatalysis;

[0058] Figure 11 It is a comparative diagram of the catalytic effects of Sn-PTA, Sn-MI, Sn-PTA-MI, Ag / Sn-PTA, Ag / Sn-MI, and Ag / Sn-PTA-MI materials in Example 1 in the dark environment; gray represents the dark reaction stage;

[0059] Figure 12 It is a comparative diagram of the catalytic effects of Sn-PTA, Sn-MI, Sn-PTA-MI, Ag / Sn-PTA, Ag / Sn-MI, and Ag / Sn-PTA-MI materials in Example 1 in the light-dark alternating environment;

[0060] Figure 13 It is a comparative diagram of the catalytic effects of the Ag / Sn-PTA-MI composite material prepared in Example 1 after being recycled 5 times;

[0061] Figure 14 It is the three-dimensional fluorescence spectrum of the Ag / Sn-PTA-MI composite material prepared in Example 1; among them, (a) MO solution, (b) dark reaction, (c) photocatalytic reaction, (d) light-dark alternating reaction. Detailed implementation manners

[0062] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0063] To better illustrate the present invention, further illustrative examples are given below through embodiments.

[0064] Example 1

[0065] The embodiment of the present invention provides a preparation method of an Ag / double-ligand Sn-MOF composite material, including the following steps:

[0066] Step 1: Weigh 2.5 mmol of terephthalic acid (PTA) and 2.5 mmol of 2-methylimidazole (2-MI) and dissolve them in a mixed solution of 20 mL of N,N-dimethylformamide and 60 mL of absolute ethanol. Stir for 15 min to obtain a ligand solution;

[0067] Step 2: Weigh 5 mmol of SnCl2·2H2O and pour it into the above ligand solution. Stir for 15 min, transfer it to a hydrothermal reactor, react at 150 °C for 12 h, filter, wash the precipitate alternately with ultrapure water and absolute ethanol 3 times, dry at 60 °C, and grind to obtain Sn-PTA-MI;

[0068] Step 3: Weigh 0.1 g of the prepared Sn-PTA-MI and ultrasonically disperse it in 20 mL of an aqueous AgNO3 solution with a concentration of 0.25 g / L. After stirring for 15 min, add 0.5 mL of methanol, place it in a photoreactor, turn on the xenon lamp, set the power to 400 W, irradiate for 2 h, filter, wash the solid precipitate with deionized water, dry, and grind to obtain the Ag / Sn-PTA-MI composite material.

[0069] Characterization of the catalyst:

[0070] The SEM image of the Ag / Sn-PTA-MI composite material prepared in this example is as shown in Figure 1 As can be seen from (a), the Sn-PTA-MI material has a microspherical and some blocky structures. After depositing Ag nanoparticles, the Ag / Sn-PTA-MI composite material ( Figure 1 (b)) shows a fluffy and uneven particle structure. In addition, the blocky particles on the material surface decrease. Figure 2 The EDX spectrum of the Ag / Sn-PTA-MI composite material in

[0071] The TEM image of the Ag / Sn-PTA-MI composite material prepared in this example is as shown in Figure 3 As shown in Figure 3 (a), it can be seen that dark Ag nanoparticles are sparsely distributed on the surface of the Sn-PTA-MI material, and there is almost no agglomeration phenomenon. As can be observed from Figure 3 (b), obvious lattice fringes with a lattice spacing of 0.23 nm can be observed, which correspond to the (111) crystal plane of Ag nanoparticles (JCPDS No. 01-071-3762); the lattice fringes with a lattice spacing of 0.26 nm correspond to the (101) crystal plane of SnO2 (JCPDS No. 46-1088), which is consistent with what is observed in the XRD pattern, further proving that the Ag nanoparticles are effectively dispersed on the surface of Sn-PTA-MI.

[0072] The XRD pattern of the Ag / Sn-PTA-MI composite material prepared in this example is as follows Figure 4 shown. It can be seen from the figure that the crystal structure of Ag / Sn-PTA-MI is mainly composed of the (121) and (017) crystal planes of C3H7NO6Sn (PDF#19-0074) corresponding to 2θ = 29.6° and 37.1°, and the (110), (101), and (211) crystal planes of SnO2 (JCPDS No. 46-1088) corresponding to 2θ = 26.6°, 33.8°, and 51.8°. The broadening of the diffraction peak range of the (110) crystal plane at 2θ = 26.6° is attributed to the influence of some impurity peaks. It should be noted that since the content of Ag in the catalyst is low, the characteristic diffraction peak of Ag is not shown in the XRD pattern of Ag / Sn-PTA-MI.

[0073] The FTIR pattern of the Ag / Sn-PTA-MI composite material prepared in this example is as follows Figure 5 shown. It can be seen from the figure that Sn-PTA-MI and Ag / Sn-PTA-MI show very similar characteristics in the bonding vibration. The characteristic peak of the -OH group appears at 3450 cm -1 −1, which is attributed to the bound water molecules contained in the sample. The C≡N band signal at 2340 cm -1 −1 is masked with the loading of Ag. Bands around 1600 cm -1 −1 and 1340 cm -1 −1 appear in both Sn-PTA-MI and Ag / Sn-PTA-MI, corresponding to the symmetric stretching vibration characteristic peak and asymmetric stretching characteristic peak of COO - −. The stretching vibration characteristic peak of Sn-O appears around 545 cm -1 −1 in both Sn-PTA-MI and Ag / Sn-PTA-MI. It should be noted that Ag is a material susceptible to oxygen, yet no characteristic peak of the Ag-O bond appears in the FT-IR pattern, indicating that Ag remains stable after being loaded on Sn-PTA-MI and will not be oxidized due to environmental conditions. Similar to the above XRD results, no abnormal crystal phase structure related to Ag is found.

[0074] The XPS pattern of the Ag / Sn-PTA-MI composite material prepared in this example is as follows Figure 6 shown. As shown in Figure 6 (a), the elements Sn, C, N, O, and Ag appear in the full element spectrum of the sample, proving the existence of these elements in the sample and revealing the formation of the heterostructure of Ag nanoparticles and Sn-PTA-MI. As shown in Figure 6As shown in (b), the characteristic peaks of Sn at the binding energies of 487.1 eV and 495.5 eV are attributed to the Sn 3d5 / 2 and Sn 3d3 / 2 orbitals, indicating the presence of Sn 4+ in Ag / Sn-PTA-MI. In the C 1s spectrum ( Figure 6 (c)), the characteristic peaks at the binding energies of 284.8 eV, 286.0 eV, and 288.9 eV correspond to C-C, C-O, and O-C=O bonds. In the N 1s spectrum ( Figure 6 (d)), the peak at 400.7 eV can be attributed to the N-C bond brought by the imidazole ring in the 2-MI ligand. In the O 1s spectrum ( Figure 6 (e)), the characteristic peaks appearing at 530.9 eV and 531.6 eV correspond to -OH and C=O bonds, respectively. In the Ag 3d spectrum ( Figure 6 (f)), the peaks at 367.9 eV and 374.0 eV correspond to metallic Ag, demonstrating that AgNO3 reduces metallic Ag by storing photogenerated electrons and deposits it on the catalyst, which is beneficial for the subsequent release of electrons during the dark reaction to continuously carry out the catalytic reaction.

[0075] The BET specific surface area, pore size, and pore volume of the Sn-PTA-MI and Ag / Sn-PTA-MI samples prepared in this example were tested using nitrogen adsorption-desorption isotherms. As Figure 7 shown, both Sn-PTA-MI and Ag / Sn-PTA-MI exhibit type IV isotherms with H4 hysteresis loops, indicating the presence of narrow pores in the materials, which is beneficial for the exposure of active sites. It can be seen from the inset that the pore size distributions of both mainly concentrate in the range of 1 nm to 5 nm, and the pore structure is mainly composed of micropores and mesopores.

[0076] The specific surface area, pore volume, and pore size results of the samples are shown in Table 1. After introducing Ag, the specific surface area and pore volume of Ag / Sn-PTA-MI are significantly improved compared to Sn-PTA-MI. This indicates that Ag / Sn-PTA-MI can provide more reaction sites for the contact between the catalyst and pollutants, which is beneficial for improving the catalytic activity. However, the pore size of Ag / Sn-PTA-MI is smaller than that of Sn-PTA-MI because Ag nanoparticles fill some of the larger pores, resulting in a reduction in the pore size of Ag / Sn-PTA-MI. The shift of the peak of the pore size distribution of Ag / Sn-PTA-MI towards smaller nanometers in the inset is also caused by this reason.

[0077] Table 1 Specific surface area, pore volume, and pore size of the samples

[0078]

[0079] The EIS diagrams of Sn-PTA-MI and Ag / Sn-PTA-MI prepared in this example are as follows Figure 8 As shown, it can be seen from the figure that the radius of the semicircular EIS Nyquist diagram of Ag / Sn-PTA-MI is smaller than that of Sn-PTA-MI. Therefore, it shows that the charge transfer resistance at the interface of the Ag / Sn-PTA-MI sample electrode is smaller than that of Sn-PTA-MI, which also reflects that Ag / Sn-PTA-MI has a high charge transfer rate, a more excellent separation effect of photo-generated electron-hole pairs, and better catalytic activity.

[0080] AgNO3, as an electron capturer, can capture photoelectrons for the reduction of Ag, and capture and store more photoelectrons with the increase of photoexcitation time. Figure 9 The effect of illumination time on the photo-deposition of Ag on Sn-PTA-MI was studied. The specific experimental process is as follows:

[0081] Take 0.1 g of the Sn-PTA-MI material prepared in Example 1 and ultrasonically disperse it in 20 mL of 0.25 g / L AgNO3 solution. After stirring the mixture for 15 min, add 0.5 mL of methanol, put it into a photoreactor, turn on a 500 W xenon lamp for illumination, and take samples at different time intervals (0 min, 30 min, 60 min, 90 min, 120 min, 150 min), and then perform a full-wavelength scan.

[0082] When Ag ions receive the photo-generated electrons generated by Sn-PTA-MI, the electrons stored in the reduced Ag nanoparticles can induce the silver surface plasmon band (the fluctuating electromagnetic oscillation of the metal coupling charges at the dielectric interface), which can be observed in the range of 350 - 550 nm from the ultraviolet-visible absorption spectrum. It can be seen that with the increase of illumination time, the absorption band shifts upward, which is related to the accumulation of electrons in Ag. However, after the illumination time is extended to 150 min, the absorption band shifts downward, which is attributed to the fact that the electrons stored in Ag are captured by AgNO3 in the solution again. This phenomenon provides strong evidence that Ag nanoparticles can store photo-generated electrons.

[0083] Example 2

[0084] The embodiment of the present invention provides a preparation method of an Ag / double-ligand Sn-MOF composite material, including the following steps:

[0085] Step 1: Weigh 2.5 mmol of phthalic acid (PA) and 0.5 mmol of 4-methylimidazole (4-MI) and dissolve them in a mixed solution of 25 mL of N,N-dimethylformamide and 100 mL of absolute ethanol, stir for 15 min to obtain a ligand solution;

[0086] Step 2: Weigh 6 mmol of SnCl2·2H2O and pour it into the above ligand solution. Stir for 15 min, transfer it to a hydrothermal reactor, react at 150 °C for 12 h, filter, wash the precipitate alternately with ultrapure water and absolute ethanol three times, dry at 60 °C, and grind to obtain Sn-PA-MI;

[0087] Step 3: Weigh 0.06 g of the prepared Sn-PA-MI and ultrasonically disperse it in 20 mL of an aqueous AgNO3 solution with a concentration of 0.2 g / L. After stirring for 15 min, add 0.5 mL of methanol, place it in a photoreactor, turn on the xenon lamp, set the power to 500 W, irradiate for 1 h, filter, wash the solid precipitate with deionized water, dry, and grind to obtain the Ag / Sn-PA-MI composite material.

[0088] Example 3

[0089] The embodiment of the present invention provides a preparation method of an Ag / bis-ligand Sn-MOF composite material, which includes the following steps:

[0090] Step 1: Weigh 2.5 mmol of trimesic acid (H3BTC) and 7.5 mmol of 1,2-dimethylimidazole (1,2-MI) and dissolve them in a mixed solution of 14 mL of N,N-dimethylformamide and 28 mL of absolute ethanol. Stir for 15 min to obtain a ligand solution;

[0091] Step 2: Weigh 5 mmol of SnCl2·2H2O and pour it into the above ligand solution. Stir for 15 min, transfer it to a hydrothermal reactor, react at 150 °C for 12 h, filter, wash the precipitate alternately with ultrapure water and absolute ethanol three times, dry at 60 °C, and grind to obtain Sn-H3BTC-MI;

[0092] Step 3: Weigh 0.15 g of the prepared Sn-H3BTC-MI and ultrasonically disperse it in 20 mL of an aqueous AgNO3 solution with a concentration of 0.3 g / L. After stirring for 15 min, add 0.5 mL of methanol, place it in a photoreactor, turn on the xenon lamp, set the power to 300 W, irradiate for 2 h, filter, wash the solid precipitate with deionized water, dry, and grind to obtain the Ag / Sn-H3BTC-MI composite material.

[0093] Comparative Example 1

[0094] This comparative example provides a preparation method of an Ag / Sn-PTA photocatalytic material, which includes the following steps:

[0095] Step 1: Weigh 2.5 mmol of terephthalic acid (PTA) and dissolve it in a mixed solution of 20 mL of N,N-dimethylformamide and 60 mL of absolute ethanol. Stir for 15 min to obtain a ligand solution;

[0096] Step 2: Weigh 5 mmol of SnCl2·2H2O and pour it into the above ligand solution. Stir for 15 min, transfer it to a hydrothermal reactor, react at 150 °C for 12 h, filter, wash the precipitate alternately with ultrapure water and absolute ethanol 3 times, dry at 60 °C, and grind to obtain Sn-PTA;

[0097] Step 3: Weigh 0.1 g of the Sn-PTA prepared above and ultrasonically disperse it in 20 mL of an aqueous AgNO3 solution with a concentration of 0.25 g / L. After stirring for 15 min, add 0.5 mL of methanol, place it in a photoreactor, turn on the xenon lamp, set the power to 400 W, irradiate for 2 h, filter, wash the solid precipitate with deionized water, dry, and grind to obtain the Ag / Sn-PTA composite material.

[0098] Comparative Example 2

[0099] This comparative example provides a preparation method of a Sn-MI catalytic material, including the following steps:

[0100] Step 1: Weigh 2.5 mmol of 2-methylimidazole (2-MI) and dissolve it in a mixed solution of 20 mL of N,N-dimethylformamide and 60 mL of absolute ethanol. Stir for 15 min to obtain a ligand solution;

[0101] Step 2: Weigh 5 mmol of SnCl2·2H2O and pour it into the above ligand solution. Stir for 15 min, transfer it to a hydrothermal reactor, react at 150 °C for 12 h, filter, wash the precipitate alternately with ultrapure water and absolute ethanol 3 times, dry at 60 °C, and grind to obtain Sn-MI;

[0102] Step 3: Weigh 0.1 g of the Sn-PTA prepared above and ultrasonically disperse it in 20 mL of an aqueous AgNO3 solution with a concentration of 0.25 g / L. After stirring for 15 min, add 0.5 mL of methanol, place it in a photoreactor, turn on the xenon lamp, set the power to 400 W, irradiate for 2 h, filter, wash the solid precipitate with deionized water, dry, and grind to obtain the Ag / Sn-MI composite material.

[0103] Photocatalytic performance test

[0104] 1. Under the illumination environment

[0105] Weigh 0.1 g of the Sn-PTA, Sn-MI, Sn-PTA-MI, Ag / Sn-PTA, Ag / Sn-MI, and Ag / Sn-PTA-MI materials prepared in Example 1 and Comparative Examples 1-2, and add them separately to 50 mL of a methyl orange (MO) solution with a concentration of 20 mg / L. Place them in a photoreactor with condensed water, and conduct a photocatalysis experiment at room temperature. The mixing and stirring speed is 200 r / min. After stirring in the dark environment for 15 min, turn on a 500 W xenon lamp to start the photocatalysis experiment. Take water samples every 15 min. After filtering the water samples, measure the absorbance at a wavelength of 463 nm using a UV-visible spectrophotometer. The results are as Figure 10 shown in Table 2.

[0106] Table 2 Removal rate of MO under light irradiation conditions

[0107]

[0108] Under photocatalytic reaction conditions, the photocatalytic degradation effect of Sn-PTA-MI on MO is better than that of the single-ligand MOF materials Sn-PTA and Sn-MI. After depositing Ag elements on the Sn-PTA, Sn-MI, and Sn-PTA-MI materials, the photocatalytic effect of the composite materials is better than that of the individual MOF materials. Among them, the removal rate of MO by Ag / Sn-PTA-MI reaches 91.77% after 60 min of light irradiation.

[0109] 2. Dark reaction

[0110] Weigh 0.1 g of the Sn-PTA, Sn-MI, Sn-PTA-MI, Ag / Sn-PTA, Ag / Sn-MI, and Ag / Sn-PTA-MI materials prepared in Example 1 and Comparative Examples 1-2. After irradiating with a 500 W xenon lamp for 2 h, add them separately to 50 mL of a methyl orange (MO) solution with a concentration of 20 mg / L. Place them in a photoreactor with condensed water, do not turn on the xenon lamp, and conduct a dark reaction experiment at room temperature. The mixing and stirring speed is 200 r / min. Take water samples every 15 min. After filtering the water samples, measure the absorbance at a wavelength of 463 nm using a UV-visible spectrophotometer. The results are as Figure 11 shown in Table 3.

[0111] Table 3 Removal rate of MO under dark reaction conditions

[0112]

[0113] After the catalyst was excited by light irradiation for 2 h, the degradation of MO solution was carried out under dark reaction conditions. The degradation of pollutants by Sn-PTA, Sn-MI and Sn-PTA-MI was mainly due to adsorption. After 30 min, the pollutants basically no longer decreased. However, Ag / Sn-PTA, Ag / Sn-MI and Ag / Sn-PTA-MI all had a continuous degradation effect on pollutants under dark reaction conditions. Among them, after 60 min under dark reaction conditions, the pollutant removal effect of Ag / Sn-PTA-MI could reach 41.75%, which was 11% higher than that of Sn-PTA-MI. These indicate that on the one hand, Ag element can form a heterostructure with MOF under light irradiation conditions to avoid hole-electron recombination and improve the photocatalytic effect; on the other hand, as an electron trap to capture photo-generated electrons for electron storage, and electrons are released under dark reaction to achieve continuous degradation of pollutants.

[0114] 3. Photocatalytic reaction with alternate light and dark cycles

[0115] Weigh 0.1 g of the Sn-PTA, Sn-MI, Sn-PTA-MI, Ag / Sn-PTA, Ag / Sn-MI, and Ag / Sn-PTA-MI materials prepared in Example 1 and Comparative Examples 1-2. After irradiating with a 500 W xenon lamp for 2 h, add them to 50 mL of methyl orange (MO) solution with a concentration of 20 mg / L respectively, and place them in a photoreactor with condensed water. Conduct a photocatalytic reaction with alternate light and dark cycles at room temperature. The mixing and stirring speed is 200 r / min. First, turn on the 500 W xenon lamp for 15 min of light reaction, then turn off the xenon lamp for 15 min of dark reaction. Perform alternate light and dark cycles every 15 min, and take water samples every 15 min. After filtration, measure the absorbance of the water samples with a UV-visible spectrophotometer at a wavelength of 463 nm. The results are as Figure 12 and Table 4 show.

[0116] Table 4 Removal rate of MO under alternate light and dark conditions

[0117]

[0118] After the catalyst was excited by light irradiation for 2 h and then carried out a photocatalytic reaction with alternate light and dark cycles, Ag / Sn-PTA, Ag / Sn-MI and Ag / Sn-PTA-MI could achieve continuous degradation of pollutants under light and dark conditions; while Sn-PTA, Sn-MI and Sn-PTA-MI could only catalytically degrade pollutants under light irradiation conditions. Among them, Ag / Sn-PTA-MI had the best catalytic effect. After 45 min of the reaction under alternate light and dark conditions, more than 99% of the pollutants could be degraded, which could greatly reduce energy consumption in practical applications.

[0119] 4. Recycling performance

[0120] After the light-dark alternating reaction test, the Ag / Sn-PTA-MI catalyst was recovered by centrifugation. The used catalyst was washed alternately with ethanol and deionized water three times, ground after drying at 60 °C, and reserved. The above process of the light-dark alternating reaction was repeated 5 times, and the results of the MO removal rate are as Figure 13 shown in Table 5.

[0121] Table 5 Recycling performance data

[0122]

[0123] 5. Three-dimensional fluorescence test of water samples

[0124] Preparation of test samples:

[0125] (a) MO solution: Prepare a 20 mg / L methyl orange (MO) solution, take 3 mL of the prepared MO solution for testing;

[0126] (b) Dark reaction: Put 0.1 g of the Ag / Sn-PTA-MI catalyst prepared in Example 1 into the photoreactor, turn on the 500 W xenon lamp and irradiate for 2 h in advance, then put it into 50 mL of the MO solution, turn off the xenon lamp, and react for 60 min under dark conditions. Then take 3 mL of the sample for testing;

[0127] (c) Photocatalytic reaction: Add 0.1 g of the Ag / Sn-PTA-MI catalyst prepared in Example 1 to 50 mL of the MO solution, put it into the photocatalytic reactor, turn on the 500 W xenon lamp, and react for 60 min under photocatalytic conditions. Then take 3 mL of the sample for testing;

[0128] (d) Light-dark alternating reaction: Add 0.1 g of the Ag / Sn-PTA-MI catalyst prepared in Example 1 to 50 mL of the MO solution, put it into the photocatalytic reactor, turn on the 500 W xenon lamp, and alternately perform light and dark catalytic reactions every 15 min. After 60 min, take 3 mL of the sample for testing.

[0129] Turn on the synchronous absorption-three-dimensional fluorescence spectrometer and preheat it for 20 min. Turn on the measurement software, rinse the quartz cuvette with distilled water, take 3 mL of each sample solution and place it in the cuvette, and then put it into the sample cell. The spectral range of this instrument is 230 nm - 800 nm. Set the initial measurement spectrum to 230 nm, the excitation bandwidth to 5 nm, the emission bandwidth to 5 nm, and the grating to 1800 g / mm @ 400 nm. Ensure that the sample is in full contact with the excitation light. Start the measurement program and record the fluorescence spectrum data. The results are as Figure 14 shown.

[0130] As Figure 14 shown in (a), the original MO solution did not show in the effective excitation and emission wavelengths of the three-dimensional fluorescence spectrum. AndFigure 14 (b) After 60 min of the dark reaction of Ag / Sn-PTA-MI for the degradation of MO, a fluorescence peak appeared in the water sample in Region IV. The reason was attributed to the oxidation degradation reaction caused by the release of the electrons stored during the pre-irradiation process of Ag / Sn-PTA-MI. Figure 14 (c) After 60 min of the photoreaction experiment, two main fluorescence peaks were detected in the water sample and were shown in all five regions, indicating that MO was catalytically degraded into more biodegradable small-molecule substances. Figure 14 (d) shows the degradation products after the photo-dark reaction. A fluorescence peak with obvious fluorescence intensity was formed in the four regions, indicating that MO was also degraded into small-molecule products under the photo-dark reaction conditions.

[0131] The Ag / dual-ligand Sn-MOF materials prepared by using other ligands defined in the present invention can all achieve effects basically equivalent to those of Example 1.

[0132] In summary, Ag / Sn-PTA-MI can be photoexcited and continuously catalytically degrade pollutants into biodegradable small-molecule substances in a lightless environment. Fundamentally speaking, memory catalysis is based on the reaction of electrons and O2 to produce active components to oxidize and reduce pollutants, and the stored electrons may also combine with other electron acceptors, thus affecting the degradation effect of pollutants.

[0133] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of an Ag / double-ligand Sn-MOF composite material, characterized in that, It includes the following steps: S1. Dissolve the double organic ligand in an organic solvent to obtain a ligand solution; the double organic ligand includes an aromatic carboxylic acid ligand and an alkylimidazole ligand. S2. Add a soluble tin salt to the ligand solution, mix evenly, carry out a hydrothermal reaction at 120°C to 180°C, wash and dry to obtain an Sn-MOF material; the molar ratio of the soluble tin salt to the total amount of the double organic ligand is 1:0.5 to 1:

2. S3. Disperse the Sn-MOF material in a silver salt solution, add an alcohol solvent, and deposit silver nanoparticles on the surface of the Sn-MOF material by a photoreduction method to obtain an Ag / double-ligand Sn-MOF composite material; the mass ratio of the Sn-MOF material to the silver salt in the silver salt solution is 15:1 to 25:

1.

2. The preparation method of the Ag / double-ligand Sn-MOF composite material according to claim 1, wherein, The aromatic carboxylic acid ligand is terephthalic acid, phthalic acid, isophthalic acid or trimesic acid; and / or The alkylimidazole ligand is 2-methylimidazole, 4-methylimidazole, 1,2-dimethylimidazole or 2,4-dimethylimidazole.

3. The preparation method of the Ag / double-ligand Sn-MOF composite material according to claim 1 or 2, characterized in that, The molar ratio of the aromatic carboxylic acid ligand to the alkylimidazole ligand is 1:0.5 to 1:3; and / or The concentration of the aromatic carboxylic acid ligand in the ligand solution is 20 mmol / L to 60 mmol / L.

4. The preparation method of the Ag / double-ligand Sn-MOF composite material according to claim 1, characterized in that, In S1, the organic solvent is a mixed solution of N,N-dimethylformamide and absolute ethanol with a volume ratio of 1:2 to 1:

4.

5. The preparation method of the Ag / double-ligand Sn-MOF composite material according to claim 1, wherein, In S2, the soluble tin salt is stannous chloride or stannous sulfate.

6. The preparation method of the Ag / double-ligand Sn-MOF composite material according to claim 1, characterized in that, In S2, the time of the hydrothermal reaction is 8 h to 15 h.

7. The preparation method of the Ag / double-ligand Sn-MOF composite material according to claim 1, characterized in that, In S3, the silver salt solution is an aqueous silver nitrate solution with a concentration of 0.20 g / L to 0.30 g / L; and / or In S3, a xenon lamp is used for photoreduction deposition of silver nanoparticles, the power of the xenon lamp is 300 W to 500 W, and the illumination time is 1 h to 2 h.

8. An Ag / double-ligand Sn-MOF composite material, characterized in that, It is prepared by the preparation method of the Ag / double-ligand Sn-MOF composite material according to any one of claims 1 to 7.

9. Application of the Ag / double-ligand Sn-MOF composite material according to claim 8 in degrading organic pollutants in wastewater.

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