A flexible MOFs material with reversible water-induced amorphous transformation and its preparation and photoregulatory application

Abstract

A flexible MOFs material with reversible water-induced amorphous transformation, which is a crystal prepared by the in-situ self-assembly of a main ligand, a flexible auxiliary ligand, and metal ions; the main ligand provides N coordination sites, and the flexible auxiliary ligand provides O coordination sites. The preparation method is as follows: A metal salt, a main ligand, and a flexible auxiliary ligand are put into the solvent DMF for reaction; they are fully dispersed to obtain a suspension, and colorless hexagonal plate-like crystals appear after heating at 92-95 °C for 48-72 h; they are washed with DMF, and the crystals are recovered to obtain the product. The long-range order of the crystals of the material changes under different degrees of water perturbation and recovery states, which is manifested as a change in transparency. Through the ordered-disordered transformation of the crystal structure, the regulation and control of light are achieved. The material of the present invention exhibits fast reversible frustrated framework flexibility under the perturbation of H2O molecules, realizing the rapid transformation of crystal-amorphous-crystal. In addition, Cd-MOFs also show a rapid transformation from the amorphous state to another crystalline state in DMF.

Description

(I) Technical field:

[0001] The invention relates to MOFs materials, in particular to a flexible MOFs material capable of reversible water-induced amorphous transformation and its preparation and light-regulated application. (II) Background technology:

[0002] Metal-organic frameworks (MOFs) with crystalline structures are coordination compounds that span two-dimensional or three-dimensional coordination entities. For many years, research on MOFs has mostly focused on their long-range order range. Now, it is widely recognized that inherent disorder can give materials special properties. Therefore, there has been a recent surge in interest in amorphous CP / MOF materials with completely disordered systems. Currently, the more common methods for transforming amorphous MOFs are melt quenching and mechanical grinding, that is, introducing structural disorder into the entire material through thermal excitation and mechanical stimulation. However, the preparation of amorphous MOFs by this method not only requires a high temperature environment, but also the destruction of crystalline MOFs by this method is irreversible. Therefore, it is crucial to develop new methods for preparing mild and reversible amorphous MOFs. H2O molecular perturbation plays an important role in the preparation of amorphous MOFs and glassy MOFs. Many scholars have proposed the use of H2O molecular coordination and heat removal to induce MOFs serialization, which is milder than melt quenching and mechanical grinding, and also provides an opportunity to achieve reversible transformation. Based on the above research and analysis, we regulated and synthesized a flexible MOFs material with water-induced structural transformation. Under water induction, the MOFs material achieved a transformation from crystalline to amorphous state. When immersed back in DMF, the material changed from amorphous state to another crystalline state. (III) Summary of the invention:

[0003] The purpose of the present invention is to provide a flexible MOFs material with reversible water-induced amorphous transformation and its preparation and light-regulated application, which can fill the gap in the current disordered material processing technology. The present invention uses 1,3,5-tri(4-pyridyl)benzene (TPB) combined with flexible dicarboxylic acid 4,4′-diphenyl ether dicarboxylic acid (H2OBA) to construct a MOFs framework with water-induced transformation from crystalline to amorphous state. When it is placed in DMF again, the material recovers from the amorphous state to another crystalline state; the material realizes the transformation from crystal to amorphous at room temperature and pressure through H2O molecular perturbation, and the perturbation is reversible; the preparation of the material provides a new method for the preparation and regulation of amorphous materials, which has certain reference significance.

[0004] The technical solution of the present invention is a flexible MOFs material with reversible water-induced amorphous transformation, which is a crystal prepared by in-situ self-assembly of a main ligand, a flexible auxiliary ligand and a metal ion; the main ligand provides an N coordination site, and the flexible auxiliary ligand provides an O coordination site; the transparency of the crystal will decrease after being induced by an inducing solvent, and can also quickly recover to a transparent state in a recovery solvent.

[0005] The molecular formula of the flexible MOFs material capable of reversible water-induced amorphous transformation is C 28 H 19 CdN2O5, which is a colorless hexagonal plate-like crystal; the crystal belongs to the R-3 space group, the coordination mode of the metal Cd center is 6-coordination, and the smallest asymmetric unit is composed of a cadmium (II) ion, a flexible auxiliary ligand and two one-third TPB molecules.

[0006] The main ligand is 1,3,5-tri(4-pyridyl)benzene (TPB).

[0007] The flexible auxiliary ligand is 4,4'-diphenyl ether dicarboxylic acid (H2OBA).

[0008] The metal ion is a transition metal ion cadmium (Cd).

[0009] The metal ions are metal ions in metal salts, and the metal salts are nitrates.

[0010] The induction solvent is water molecules, and the recovery solvent is DMF.

[0011] The molar ratio of the main ligand: the flexible auxiliary ligand: the metal ion is 1: (1-2): (2-3).

[0012] A method for preparing the above-mentioned flexible MOFs material with reversible water-induced amorphous transformation, characterized in that it comprises the following steps:

[0013] (1) taking a metal salt, a primary ligand and a flexible auxiliary ligand in proportion, and placing them in a solvent DMF for reaction;

[0014] (2) ultrasonically treating the reaction mixture until the components are fully dispersed to obtain a suspension, and heating at 92-95° C. for 48-72 h to produce colorless hexagonal plate-like crystals;

[0015] (3) After cooling to room temperature, the crystals are washed with DMF and recovered to obtain flexible MOFs materials.

[0016] A method for inducing conversion of the above-mentioned flexible MOFs material with reversible water-induced amorphous conversion, characterized in that it comprises the following steps:

[0017] (1) A room temperature in situ H2O-induced conversion method is used, the induction solvent used is H2O, and the recovery solvent is DMF;

[0018] (2) immersing the crystals in H2O to ensure that the crystals are completely immersed below the H2O liquid surface, thereby obtaining a MOF framework disturbed by water; and obtaining MOFs with different degrees of disturbance by controlling the immersion time;

[0019] (3) The disturbed MOF is re-immersed in DMF to ensure that all the crystals are immersed below the DMF liquid surface to obtain a restored MOF.

[0020] An application of a flexible MOFs material with reversible water-induced amorphous transformation, characterized in that the crystal disorder of the material under different water disturbance degrees and recovery states is manifested as changes in transparency, thereby achieving regulation and control of light in a variety of environments.

[0021] The advantages of the present invention are as follows: (1) The present invention provides a TPB-based Cd-MOFs, which exhibits rapid and reversible frustrated framework flexibility under H2O molecular perturbation, and realizes a rapid transition from crystal to amorphous to crystal. This transition originates from local water molecule coordination. In addition, Cd-MOFs also show rapid recovery of amorphous state to another crystalline state in DMF. (2) The present invention deepens the understanding of water-induced amorphization of MOFs to a certain extent. While exploring the optical properties of amorphous MOFs, it also provides a new idea for the functional application of amorphous MOFs. (IV) Description of the drawings:

[0022] Figure 1 The schematic diagram is a preparation diagram of a flexible MOFs material capable of reversible water-induced amorphous transformation according to the present invention.

[0023] Figure 2 The schematic diagram of the induced transformation and recovery of a flexible MOFs material with reversible water-induced amorphous transformation according to the present invention.

[0024] Figure 3 This is a schematic diagram of the original crystal structure of a flexible MOFs material with reversible water-induced amorphous transformation involved in the present invention (O: red; N: blue; Cd: dark green; C atoms are omitted).

[0025] Figure 4 This is a schematic diagram of the recovered crystal structure of a flexible MOFs material with reversible water-induced amorphous transformation according to the present invention (O: red; N: blue; Cd: dark green; C atoms are omitted).

[0026] Figure 5The XRD spectra of the original state c-Cd-MOF, the water-perturbed amorphous state p-Cd-MOF and the restored state r-Cd-MOF of the flexible MOFs material with reversible water-induced amorphous transformation involved in the present invention.

[0027] Figure 6 This is a transparency change diagram of different states of a flexible MOFs material with reversible water-induced amorphous transformation according to the present invention.

[0028] Figure 7 This is a pair distribution function G(r) diagram of different states of a flexible MOFs material with reversible water-induced amorphous transformation according to the present invention.

[0029] Figure 8 The transmittance spectrum of different states of a flexible MOFs material with reversible water-induced amorphous transformation involved in the present invention. (V) Specific implementation methods:

[0030] The present invention is further explained below through specific embodiments, but it is not intended to limit the protection scope of the present invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the protection scope of the present invention.

[0031] Embodiment: A flexible MOFs material with reversible water-induced amorphous transformation, characterized in that it is a crystal prepared by in-situ self-assembly of a main ligand, a flexible auxiliary ligand and a metal ion; the main ligand provides an N coordination site, and the flexible auxiliary ligand provides an O coordination site; the crystal is a molecular formula C 28 H 19 CdN2O5, the morphology is colorless hexagonal flake crystals.

[0032] The main ligand is 1,3,5-tri(4-pyridyl)benzene (TPB).

[0033] The flexible auxiliary ligand is 4,4'-diphenyl ether dicarboxylic acid (H2OBA).

[0034] The metal ion is a transition metal ion cadmium (Cd).

[0035] The molar ratio of the main ligand: the flexible auxiliary ligand: the metal ion is 1: (1-2): (2-3).

[0036] A method for preparing the above-mentioned flexible MOFs material with reversible water-induced amorphous transformation comprises the following steps, and its preparation schematic diagram is shown as follows: Figure 1 As shown:

[0037] (1) Using the solvothermal method, Cd(NO3)2·4H2O (0.05 mmol, 15.4 mg), TPB (0.025 mmol, 7.7 mg) and H2OBA (0.025 mmol, 6.5 mg) were accurately weighed in a 10 mL glass screw-cap vial, and then 2 mL of DMF solvent was added.

[0038] (2) The reaction mixture was sonicated until the components were fully dispersed. After sonication for 5 min, a suspension was obtained, which was heated at 92-95° C. for 48-72 h.

[0039] (3) After cooling to room temperature, the crystals were washed with DMF solvent and filtered to obtain a product having a molecular formula of C 28 H 19 The colorless hexagonal plate-like crystals of CdN2O5 are denoted as c-Cd-MOF. The schematic diagram of the crystal structure is shown in Figure 3 shown.

[0040] In the step (3), the crystals are washed with fresh DMF three times, and the crystals (hexagonal colorless transparent flakes) are recovered with a yield of (65% (based on TPB)).

[0041] A method for inducing conversion of the above-mentioned flexible MOFs material with reversible water-induced amorphous conversion comprises the following steps, and the schematic diagram of the inducing conversion is as follows: Figure 2 As shown:

[0042] (1) The induced conversion method is a room temperature in situ H2O induced conversion method, the induction solvent used is H2O, and the recovery solvent is DMF;

[0043] (2) Obtaining a water-perturbed MOFs framework: Soak the c-Cd-MOF in H2O to ensure that the c-Cd-MOF is fully exposed to H2O. After soaking for 25-30 minutes, a white, opaque, completely water-perturbed amorphous p-Cd-MOF is obtained; by controlling the soaking time, we can obtain MOFs with different degrees of perturbation;

[0044] (3) Obtaining the restored MOFs framework: The recovery process is opposite to the disturbance process. The p-Cd-MOF that has been completely disturbed by water (immersion time is 25-30 min) is placed back in DMF to ensure that the p-Cd-MOF is fully exposed to DMF. The crystal gradually changes from an opaque state to a transparent state. After immersion for 10 min, the crystal remains in a transparent state and no longer changes. The restored r-Cd-MOF is obtained. The schematic diagram of the restored crystal structure is shown in Figure 4 .

[0045] Changes in MOFs framework between original and restored states:

[0046] The original crystal structure diagram is as follows Figure 3 The schematic diagram of the crystal structure of the restored state is shown in Figure 4 As shown. Compared with the original c-Cd-MOF structure, the coordination mode of the metal Cd center changes from a single 6-coordination to a mixed coordination configuration consisting of 6-coordination and 7-coordination (pink polyhedron: 6-coordination; purple polyhedron: 7-coordination). In addition, the restored r-Cd-MOF produces a very obvious shrinkage phenomenon. Figure 3 and Figure 4 As shown in the figure, the distance between the bimetallic centers Cd-Cd has shrunk from the original Shrink to The flexible dicarboxylic acid H2OBA also shrank, as shown by the COC angle changing from 127.28° to 118.78°. Figure 5 The XRD patterns of the original c-Cd-MOF, water-perturbed amorphous p-Cd-MOF and restored r-Cd-MOF are shown. Compared with c-Cd-MOF, p-Cd-MOF has amorphous characteristics and lacks Bragg diffraction peaks. The peak shape of r-Cd-MOF is also different from that of c-Cd-MOF.

[0047] Dynamic response of transparency of amorphous p-Cd-MOF to water disturbance:

[0048] Select a complete c-Cd-MOF crystal and place it on a glass slide. Add H2O to one side of the c-Cd-MOF and absorb the solution with filter paper on the other side to ensure that the crystal is always immersed in the H2O solution. Use the camera function of the microscope to record the state of the crystal at different times. Figure 6 The crystal states under different H2O disturbance times and DMF recovery were recorded (H2O: 3min, 6min; DMF: 4min, 7min, 9min). The dynamic response of crystal transparency can be observed intuitively. When c-Cd-MOF is immersed in water, the crystal gradually changes from a transparent state to an opaque state. When the immersion time reaches 6min, the crystal becomes completely opaque. When re-immersed in DMF solvent, the crystal returns to its original transparent state, and the complete recovery time takes 9min.

[0049] Tracking the disorder degree of water-perturbed amorphous p-Cd-MOF:

[0050] Pair distribution function (PDF) analysis is to use SC-XRD to record XRD data at different times and then further restore it to atomic pair distribution data using PDFget. max The value is 7, q min The value is 0, q maxinstThe value is 7 and the rpoly value is 0.7. Figure 7 The G(r) graphs are the H2O perturbation time (10min, 15min, 25min, 35min, 45min, 55min) and the recovery after adding DMF (5min, 10min). The G(r) graph shows the change of the overall disorder degree in the long range and reflects the change of the core ligand atoms in the short range. Figure 7 As shown in the figure, within a short water disturbance time (25 min), the long-range order of p-Cd-MOF G(r) decreases with the increase of water disturbance time. When the disturbance time exceeds 25 min, the long-range order of p-Cd-MOF increases with the increase of water disturbance time. When re-immersed in the recovery solvent DMF, the crystals quickly return to an ordered state after a certain period of disorder.

[0051] Light transmittance test and its application in light regulation:

[0052] Select a crystal and use a transmittance instrument to test and calculate the transmittance of c-Cd-MOF, p-Cd-MOF and r-Cd-MOF. The transmittance at different wavelengths is as follows: Figure 8 As shown. It can be clearly observed from the figure that the transmittance of p-Cd-MOF at different wavelengths after disturbance is significantly reduced, while the transmittance of r-Cd-MOF in the restored state is significantly restored. This flexible MOFs material with reversible water-induced crystalline to amorphous transition characteristics, its innovative water-induced preparation process, and its clever use in light regulation applications enable the material to achieve precise control of light transmittance through the orderly and disordered conversion of the crystal structure under different water molecule action times. This feature provides a new solution for smart windows, optical sensors, and light modulation technology.

Claims

1. A flexible MOFs material with reversible water-induced amorphous transformation, characterized in that The crystal is prepared from a main ligand, a flexible auxiliary ligand and a metal ion; the main ligand is 1,3,5-tri(4-pyridyl)benzene; the flexible auxiliary ligand is 4,4'-diphenyl ether dicarboxylic acid; the metal ion is a transition metal ion cadmium; the main ligand provides an N coordination site, and the flexible auxiliary ligand provides an O coordination site; the molecular formula of the flexible MOFs material is C 28 H 19 CdN2O5 is a colorless hexagonal plate-like crystal; the molar ratio of the main ligand: the flexible auxiliary ligand: the metal ion is 1:(1-2):(2-3).

2. A flexible MOFs material with reversible water-induced amorphous transformation according to claim 1, characterized in that The metal ions are metal ions in metal salts, and the metal salts are nitrates.

3. A flexible MOFs material with reversible water-induced amorphous transformation according to claim 1, characterized in that The transparency of the crystal will decrease after being induced by the inducing solvent, and will return to a transparent state in the restoring solvent.

4. A flexible MOFs material with reversible water-induced amorphous transformation according to claim 3, characterized in that The induction solvent is water molecules, and the recovery solvent is DMF.

5. A method for preparing a flexible MOFs material with reversible water-induced amorphous transformation according to claim 1, characterized in that It includes the following steps: (1) taking a metal salt, a primary ligand and a flexible auxiliary ligand in proportion, and placing them in a solvent DMF for reaction; (2) ultrasonically treating the reaction mixture until the components are fully dispersed to obtain a suspension, and colorless hexagonal plate-like crystals appear after heating; (3) After cooling to room temperature, the crystals are washed with DMF and recovered to obtain flexible MOFs materials.

6. The method for preparing a flexible MOFs material with reversible water-induced amorphous transformation according to claim 5, characterized in that In the step (2), after heating at 92-95° C. for 48-72 hours, colorless hexagonal plate-like crystals appear.

7. A method for inducing conversion of the flexible MOFs material capable of reversible water-induced amorphous conversion according to claim 1, characterized in that It includes the following steps: (1) A room temperature in situ H2O-induced conversion method is used, the induction solvent used is H2O, and the recovery solvent is DMF; (2) immersing the crystals in H2O to ensure that the crystals are completely immersed below the H2O liquid surface, thereby obtaining a MOF framework disturbed by water; and obtaining MOFs with different degrees of disturbance by controlling the immersion time; (3) The disturbed MOF is re-immersed in DMF to ensure that all the crystals are immersed below the DMF liquid surface to obtain a restored MOF.

8. An application of the flexible MOFs material capable of reversible water-induced amorphous transformation according to claim 1, characterized in that The crystal disorder of the material under different water disturbance degrees and recovery states is manifested as changes in transparency, thereby achieving regulation and control of light.

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