Metal organic framework Mn-MOF single crystal material and nanosheet as well as preparation and application thereof
阅读说明：本技术 金属有机框架Mn-MOF单晶材料及纳米片与制备和应用 (Metal organic framework Mn-MOF single crystal material and nanosheet as well as preparation and application thereof ) 是由 李�灿 章福祥 肖晔珺 于 2019-09-04 设计创作，主要内容包括：本发明提供一种金属有机框架Mn-MOF单晶材料及纳米片与制备和应用。包括以下步骤：将氯化锰和/或四水氯化锰和配体1,3,6,8-四(4-羧基苯)芘(H_4tbapy)溶于N,N-二甲基甲酰胺、1,4-二氧六环和水的混合溶剂中,在程序控温下进行溶剂热反应,反应停止后缓慢降至室温,将析出晶体经过洗涤、抽滤、干燥后得到Mn-MOF单晶材料,随后将所得Mn-MOF晶体加入到乙腈和水的混合溶剂或乙腈溶剂中进行超声处理,得到Mn-MOF纳米片。本发明制备的Mn-MOF纳米片形貌规则、厚度范围可调,相比于本体的Mn-MOF单晶材料具有更高的光催化分解水制氢性能。本发明提供的合成方法具有条件温和、操作简单、催化活性较高等优点。(The invention provides a metal organic framework Mn-MOF single crystal material, a nanosheet, a preparation method and an application thereof. The method comprises the following steps: manganese chloride and/or manganese chloride tetrahydrate and ligand 1,3,6, 8-tetra (4-carboxyphenyl) pyrene (H) 4 tbapy) is dissolved in a mixed solvent of N, N-dimethylformamide, 1, 4-dioxane and water, a solvothermal reaction is carried out at a program controlled temperature, the temperature is slowly reduced to room temperature after the reaction is stopped, a precipitated crystal is washed, filtered and dried to obtain a Mn-MOF single crystal material, and then the obtained Mn-MOF crystal is added into a mixed solvent of acetonitrile and water or an acetonitrile solvent for ultrasonic treatment to obtain the Mn-MOF nanosheet. The Mn-MOF nanosheet prepared by the method is regular in morphology and adjustable in thickness range, and has higher hydrogen production performance by photocatalytic decomposition of water compared with a Mn-MOF single crystal material of the body. The synthesis method provided by the invention has the advantages of mild conditions, simplicity in operation, higher catalytic activity and the like.)
1. A metal organic framework Mn-MOF single crystal material is characterized in that the molecular formula is [ Mn [ ]2(tbapy)(C4H8O2)(H2O)4]Wherein tbapy is organic anion after carboxyl dehydrogenation in 1,3,6, 8-tetra (4-carboxyphenyl) pyrene.
2. The metal-organic framework Mn-MOF single crystal material according to claim 1, wherein the Mn-MOF has a layered structure, belongs to a monoclinic system, P2/m space group, and has a paddle wheel structure as a node, and two Mn (II) metals are respectively coordinated with one water moleculeAnd eight carboxyl oxygen atoms in four ligandsA two-dimensional layered structure is formed under the common coordination action, the Mn-MOF single crystal material is formed by stacking the two-dimensional layered structure, and the interlayer spacing isA single layer thickness of
3. A method for preparing a metal organic framework Mn-MOF single crystal material according to claim 1 or 2, characterized by comprising the following steps:
(1) mixing manganese chloride and/or manganese chloride tetrahydrate with H4tbapy (1,3,6, 8-tetra (4-carboxyphenyl) pyrene) is added into a hydrothermal reaction kettle;
(2) sequentially adding a solvent N, N-dimethylformamide, 1, 4-dioxane and water into the hydrothermal reaction kettle in the step (1);
(3) placing the hydrothermal reaction kettle in the step (2) in an oven, heating the hydrothermal reaction kettle from room temperature to 120-130 ℃ by adopting a program temperature control technology, then preserving the heat for 48-72 h, then cooling the hydrothermal reaction kettle to the room temperature, and collecting precipitates;
(4) washing the precipitate obtained in the step (3) with N, N-dimethylformamide, performing suction filtration, and naturally drying at room temperature.
4. The method according to claim 3, wherein the manganese chloride and/or manganese chloride tetrahydrate of step (1) is/are reacted with H4the molar ratio of tbapy is 1.5-1: 1-0.9.
5. The method according to claim 3, wherein the mixing volume ratio of N, N-dimethylformamide, 1, 4-dioxane and water in the step (2) is 2-2.1:1-1.1: 2-0.5; the dosage of the solvent in the step (2) is every 0.1mmol of H4tbapy used 3.5-5.0 ml.
6. The method according to claim 3, wherein the temperature increase rate in the step (2) is 35 to 40 ℃/h; the cooling rate in the step (2) is 1.5-2 ℃/h.
7. A preparation method of nanosheets based on the Mn-MOF single crystal material is characterized by comprising the following steps: and adding the obtained Mn-MOF crystal into a mixed solvent of acetonitrile and water or an acetonitrile solvent for ultrasonic treatment to obtain the Mn-MOF nanosheet.
8. The method according to claim 7, wherein the ratio of the mixed solvent of acetonitrile and water in the solvent is 1 to 6: 0-1, preferably 4-6: 1; the ultrasonic power is 38-40kHz, the input power is 490-500W, and the ultrasonic time is 2-5 h.
9. Mn-MOF nanosheets obtainable by a process according to claim 8 or 9, wherein the thickness is from 2 to 70 nm.
10. Use of Mn-MOF nanoplates according to claim 9 in photocatalytic water splitting for hydrogen production.
Technical Field
The invention relates to a metal organic framework Mn-MOF single crystal material, a nanosheet, a preparation method and an application thereof, in particular to an MOFs material for photocatalytic water decomposition and a preparation method thereof, and belongs to the field of photocatalytic materials.
Background
The method for producing hydrogen by utilizing sunlight to catalyze water decomposition is a feasible method for solving the current energy problem, and draws wide attention of people. The two-dimensional material has the advantages of ultrathin thickness and larger specific surface area, and thus has unique advantages in the field of photocatalytic water decomposition. The ultra-thin thickness can shorten the migration distance of photogenerated carriers so as to inhibit the recombination process of the carriers, and the larger specific surface area means that more reaction sites are exposed. Therefore, the two-dimensional nanosheet material generally has superior photocatalytic reaction performance compared to a bulk material.
Metal-organic frameworks (MOFs) are an organic-inorganic hybrid crystalline material formed by coordination bonding of Metal ions or clusters and multidentate organic ligands. In recent years, MOFs have advantages of large specific surface area, adjustable structure and function, etc., and thus the corners of the head are gradually exposed in the field of photocatalytic water splitting, such as UO-66 (chem. Eur. J.2010,16,11133), NH2-Ti-MOF (j.phys.chem.c 2012,116,20848), Al-PMOF (angelw.chem.int.ed.2012, 51,7440) and the like. However, poor charge separation efficiency limits further development of MOFs materials in this field, and development of two-dimensional MOF nanosheet materials is expected to change this situation.
The preparation method of the two-dimensional MOF nanosheet material mainly comprises two steps: bottom-up synthesis and top-down stripping. Compared with the synthesis method, the stripping method by ultrasonic treatment is simpler and more effective, and is beneficial to realizing large-scale preparation. However, limited by the stability of the MOFs materials themselves, it is difficult to prepare two-dimensional MOF nanosheets by a method of sonicating MOFs materials having a layered structure. Furthermore, considering the thermodynamic requirements of photocatalytic water splitting, the layered MOFs materials must possess the appropriate band position. Therefore, two-dimensional MOF nanosheets prepared by an ultrasonic stripping method and used as a photocatalyst in the field of photocatalytic water splitting have not been reported in chinese patents.
Disclosure of Invention
The invention aims to provide a metal organic framework Mn-MOF single crystal material with ultrahigh stability and a preparation method thereof.
The invention also aims to provide a nanosheet based on the metal organic framework Mn-MOF single crystal material and a preparation method thereof.
The invention also aims to provide application of the Mn-MOF single crystal material and the Mn-MOF nanosheet in photocatalytic decomposition of water to produce hydrogen.
In order to achieve the purpose, the invention adopts the following technical scheme:
a metal organic framework Mn-MOF single crystal material with a molecular formula of [ Mn [ ]2(tbapy)(C4H8O2)(H2O)4]Wherein tbapy is organic anion after carboxyl dehydrogenation in 1,3,6, 8-tetra (4-carboxyphenyl) pyrene.
Preferably, the Mn-MOF has a layered structure, belongs to a monoclinic system and a P2/m space group, a node is a paddle wheel structure, and two Mn (II) metals are respectively coordinated with one water moleculeAnd eight carboxyl oxygen atoms in four ligandsA two-dimensional layered structure is formed under the common coordination action, the Mn-MOF single crystal material is formed by stacking the two-dimensional layered structure, and the interlayer spacing isA single layer thickness ofThe single crystal structure is shown in fig. 1. Specific crystal data are shown in table 1.
TABLE 1 crystallographic data of Mn-MOF single-crystal materials
The preparation method of the metal organic framework Mn-MOF single crystal material comprises the following steps:
(1) mixing manganese chloride and/or manganese chloride tetrahydrate with H4tbapy (1,3,6, 8-tetra)(4-carboxyphenyl) pyrene) is added into a hydrothermal reaction kettle;
(2) sequentially adding a solvent N, N-dimethylformamide, 1, 4-dioxane and water into the hydrothermal reaction kettle in the step (1);
(3) placing the hydrothermal reaction kettle in the step (2) in an oven, heating the hydrothermal reaction kettle from room temperature to 120-130 ℃ by adopting a program temperature control technology, then preserving the heat for 48-72 h, then cooling the hydrothermal reaction kettle to the room temperature, and collecting precipitates;
(4) washing the precipitate obtained in the step (3) with N, N-dimethylformamide, performing suction filtration, and naturally drying at room temperature.
Preferably, the manganese chloride tetrahydrate of the step (1) is mixed with H4the molar ratio of tbapy is 1.5: 1.
Preferably, the mixing volume ratio of the N, N-dimethylformamide, the 1, 4-dioxane and the water in the step (2) is 2:1: 1; the dosage of the solvent in the step (2) is every 0.1mmol of H4tbapy used 4 ml.
Preferably, the temperature rise rate of the step (2) is 40 ℃/h; the cooling rate in the step (2) is 2 ℃/h.
The invention also provides a Mn-MOF nanosheet and a preparation method thereof, and the Mn-MOF nanosheet is prepared from the metal organic framework Mn-MOF single crystal material serving as a raw material.
The preparation method of the Mn-MOF nanosheet comprises the following steps: and adding the obtained Mn-MOF crystal into a mixed solvent of acetonitrile and water or an acetonitrile solvent for ultrasonic treatment to obtain the Mn-MOF nanosheet.
Preferably, in the above step, the ratio of acetonitrile to water is 1:0, 6:1, 5:1, 4: 1.
Preferably, in the above steps, the ultrasonic power is 40kHz, the input power is 500W, and the ultrasonic time is 2-5 h.
Preferably, in the step, the thickness of the Mn-MOF nano-sheet is 2-70 nm.
The application method of the Mn-MOF single crystal material and the Mn-MOF nanosheet in the aspect of hydrogen production through photocatalytic water decomposition comprises the steps of adding the Mn-MOF single crystal or the Mn-MOF nanosheet into a mixed solution of acetonitrile, triethanolamine and water, taking platinum as a cocatalyst, and irradiating by using a 300W xenon lamp.
Preferably, the addition amount of the Mn-MOF single crystal or Mn-MOF nano sheet is 50mg, the mixed solution is 90ml of acetonitrile, 10ml of triethanolamine and 2ml of water, and the loading amount of platinum is 3 wt%.
The Mn-MOF nanosheet prepared by the method is regular in morphology and adjustable in thickness range, and has higher hydrogen production performance by photocatalytic decomposition of water compared with a Mn-MOF single crystal material of the body. The synthesis method provided by the invention has the advantages of mild conditions, simplicity in operation, higher catalytic activity and the like.
The invention has the advantages that:
1. the invention utilizes metal manganese salt and ligand H4tbapy is self-assembled to form the MOF material with a two-dimensional layered structure, the preparation method of the material is simple and easy to implement, and the prepared Mn-MOF single crystal material has ultrahigh thermal stability and chemical stability.
2. The Mn-MOF nanosheet can be prepared by ultrasonic treatment based on the novel layered Mn-MOF single crystal material, and the preparation method is simple and easy to implement and high in yield.
3. The Mn-MOF nanosheet has good photocatalytic water decomposition hydrogen production performance, and has higher activity compared with a bulk Mn-MOF single crystal material.
Drawings
FIG. 1 is a single crystal structure diagram of a Mn-MOF single crystal material;
FIG. 2 is an XRD pattern of a Mn-MOF single crystal material;
FIG. 3 is a thermogravimetric analysis diagram of a Mn-MOF single crystal material;
FIG. 4a is an XRD pattern of a Mn-MOF single crystal material after soaking in different solvents;
FIG. 4b is an XRD pattern of a Mn-MOF single crystal material after soaking in aqueous solutions with different pH values;
FIG. 5 is a TEM photograph of Mn-MOF nanosheets prepared at different solvent ratios;
FIG. 6 is an XRD pattern of Mn-MOF nanosheets prepared at different solvent ratios;
FIG. 7 is a TEM photograph of Mn-MOF nanosheets prepared at different sonication times;
FIG. 8 is an AFM image and a thickness distribution range of Mn-MOF nanosheets prepared at different ultrasonic times;
FIG. 9 is an XRD pattern of Mn-MOF nanosheets prepared at different sonication times;
FIG. 10 is a graph of activity data of Mn-MOF nanosheets and Mn-MOF single crystal materials prepared under different solvent ratios for photocatalytic water decomposition hydrogen production;
FIG. 11 is a graph of activity data of Mn-MOF nanosheets and Mn-MOF single crystal materials prepared at different ultrasonic times for photocatalytic water decomposition hydrogen production;
FIG. 12 is a graph of activity data of Mn-MOF nanosheets and Mn-MOF single crystal materials for hydrogen production by water decomposition under visible light.
Detailed Description
To further illustrate the present invention, the following examples are set forth without limiting the scope of the invention as defined by the various appended claims.
Example 1: synthesis of metal organic framework Mn-MOF single crystal material
Manganese chloride tetrahydrate (29.7mg, 0.15mmol), H was weighed4tbapy (66.6mg, 0.1mmol) is added into a 25ml polytetrafluoroethylene lining hydrothermal reaction kettle, 2ml of N, N-dimethylformamide, 1ml of 1, 4-dioxane and 1ml of water are sequentially added, the polytetrafluoroethylene lining hydrothermal reaction kettle is transferred into an oven, the temperature is raised from room temperature to 130 ℃ at the heating rate of 40 ℃/H by using a programmed temperature control method, the temperature is kept for 72H, the temperature is lowered to room temperature at the cooling rate of 2 ℃/H to obtain yellow crystals, the yellow crystals are washed by N, N-dimethylformamide and are subjected to suction filtration, and the target material Mn-MOF is obtained by natural drying at room temperature, wherein the yield is about 85% (based on H) (based on H, the ratio of Mn-MOF is about 85 percent)4tbapy calculated). The structure of the prepared metal organic framework Mn-MOF single crystal material is shown in figure 1, the Mn-MOF has a layered structure and belongs to a monoclinic system and a P2/m space group, nodes are in a visible wheel structure, and two Mn (II) metals are respectively coordinated with a water moleculeAnd eight carboxyl oxygen atoms in four ligandsA two-dimensional layered structure is formed under the common coordination action, the Mn-MOF single crystal material is formed by stacking the two-dimensional layered structure, and the interlayer spacingIs composed ofA single layer thickness of
The XRD results are shown in FIG. 2, which shows that the X-ray powder diffraction curve of the measured Mn-MOF material is basically consistent with the simulated curve (Mn-MOF-simulated) of CIF file of X-ray single crystal diffraction, and the crystal has better crystallization degree and high purity, and the difference of the diffraction intensity of the two is caused by the preferred orientation of the crystal.
Thermogravimetric analysis tests were performed on the novel Mn-MOF single crystal material and the results are shown in fig. 3. The thermogravimetric test of the Mn-MOF is carried out in a nitrogen atmosphere, the nitrogen flow rate is 50ml/min, the heating rate is 10 ℃/min, and the heating range is 20-800 ℃. At a temperature range below 200 ℃, the weight loss is about 22 percent, and the weight loss is attributed to water molecules adsorbed on the surface of Mn-MOF and solvent molecules in pore channels. The decomposition of Mn-MOF occurs at about 435 ℃, and the Mn-MOF is completely decomposed at about 520 ℃, which shows that the material has good thermal stability.
The chemical stability of the novel Mn-MOF single crystal material was tested, and the results are shown in FIG. 4. FIG. 4a is an XRD pattern of Mn-MOF after soaking in different solvents, and the test method is as follows: respectively weighing 30mg of Mn-MOF, adding the Mn-MOF into 20ml of acetone, dichloromethane, 1, 4-dioxane, N-dimethylformamide, water and acetonitrile, soaking for 12h, performing suction filtration, naturally drying at room temperature, and then performing XRD test. FIG. 4b is an XRD pattern of a Mn-MOF single crystal material after soaking in aqueous solutions with different pH values, and the test method is as follows: respectively weighing 30mg of Mn-MOF, adding the Mn-MOF into 20ml of aqueous solutions with different pH values, adjusting the acidic condition by using 1mol/L dilute hydrochloric acid, adjusting the alkaline condition by using 1mol/L dilute potassium hydroxide aqueous solution, soaking for 12 hours, performing suction filtration, naturally drying at room temperature, and performing XRD test. As shown in FIG. 4, the intensity and angle of XRD characteristic peaks of Mn-MOF after soaking for 12h under different conditions are not obviously changed, which indicates that the Mn-MOF single crystal material has good chemical stability.
Example 2: preparation of Mn-MOF nanosheet
Weighing 50mg of the Mn-MOF single-crystal material prepared in the example 1, adding the Mn-MOF single-crystal material into a mixed solvent of 3ml of acetonitrile and water in the ratio of 1:0, 6:1, 5:1 and 4:1, namely the acetonitrile and the water are 3ml and 0ml, 2.57ml and 0.43ml, 2.5ml and 0.5ml, 2.4ml and 0.6ml respectively, and carrying out ultrasonic treatment for 2H under the conditions that the ultrasonic frequency is 40kHz and the output power is 500W to obtain Mn-MOF nanosheet samples of Mn-M-2H, Mn-M-H-6-1-2H, Mn-M-H-5-1-2H and Mn-M-H-4-1-2H.
The embodiment mainly inspects the influence of the ratio of acetonitrile and water on the morphology of the prepared Mn-MOF nanosheet. TEM photographs of Mn-MOF nanosheets prepared at different solvent ratios are shown in FIG. 5, which shows that the addition of water has a significant effect on the morphology of the Mn-MOF nanosheets, with samples Mn-M-H-5-1-2H prepared at a ratio of acetonitrile to water of 5:1 having the most regular rectangular morphology. The XRD pattern of the Mn-MOF nanosheets prepared under different solvent ratios is shown in figure 6, which shows that the XRD curve of the Mn-MOF nanosheets prepared in the embodiment is basically consistent with that of Mn-MOF single crystal materials, and shows that the coordination structure of the prepared Mn-MOF nanosheets is not changed and good crystallinity is maintained. The morphology of the Mn-MOF nanosheet can be regulated and controlled by adjusting the solvent ratio.
Example 3: preparation of Mn-MOF nanosheet
Weighing 3ml of a mixed solution of acetonitrile and water prepared by 2.5ml of acetonitrile and 0.5ml of water, weighing 50mg of the Mn-MOF single crystal material prepared in the embodiment 1, adding the Mn-MOF single crystal material into the mixed solution, and respectively carrying out ultrasonic treatment for 2H, 3H, 4H and 5H under the conditions that the ultrasonic frequency is 40kHz and the output power is 500W to obtain Mn-MOF nanosheet samples Mn-M-H-5-1-2H, Mn-M-H-5-1-3H, Mn-M-H-5-1-4H and Mn-M-H-5-1-5H.
This example mainly examines the effect of sonication time on the preparation of Mn-MOF nanosheets at a ratio of acetonitrile to water of 5: 1. TEM photographs of Mn-MOF nanosheets prepared under different ultrasonic times are shown in FIG. 7, which shows that the prepared Mn-MOF nanosheets are all regular rectangular flaky morphologies, and the ultrasonic times have no significant influence on the morphological size of the nanosheets. The thickness of the Mn-MOF nanosheets is tested by AFM, and the distribution range of the thickness of the nanosheets is counted, so that the average thickness of the Mn-MOF nanosheets is reduced from 27nm to 5.5nm along with the extension of the ultrasonic time, and the distribution range response is reduced as shown in FIG. 8. XRD patterns of Mn-MOF nanosheets prepared under different ultrasonic time are shown in figure 9, XRD diffraction peaks of the prepared Mn-MOF nanosheets are consistent with those of Mn-MOF of the bulk, and the results show that the Mn-MOF nanosheets subjected to ultrasonic stripping have no change in coordination structure and maintain good crystallinity. The thickness of the Mn-MOF nanosheet can be regulated and controlled by changing the time of ultrasonic treatment.
Example 4: photocatalytic decomposition of hydrogen in water
50mg of the sample prepared in example 1 or 2 was weighed, added to a mixed solution of 90ml of acetonitrile, 10ml of triethanolamine and 2ml of water, and then 2.0ml of chloroplatinic acid solution (0.74mg/ml in terms of platinum) was added, after the reaction system was evacuated, the reaction system was irradiated with a 300W xenon lamp for 2 hours under the condition of full-spectrum wavelength light, and the content of generated hydrogen was analyzed by gas chromatography sampling.
In the embodiment, the influence of the ratio of acetonitrile to water on the performance of preparing Mn-MOF nanosheets for photocatalytic decomposition of water to produce hydrogen is mainly considered, as shown in FIG. 10, the performance of preparing Mn-MOF nanosheets for photocatalytic decomposition of water to produce hydrogen is improved compared with that of Mn-MOF single crystal materials, wherein Mn-M-H-5-1-2H shows the highest activity of photocatalytic decomposition of water to produce hydrogen.
Example 5: photocatalytic decomposition of hydrogen in water
50mg of the sample prepared in example 1 or 3 was weighed, added to a mixed solution of 90ml of acetonitrile, 10ml of triethanolamine and 2ml of water, and then 2.0ml of chloroplatinic acid solution (0.74mg/ml in terms of platinum) was added, after the reaction system was evacuated, the reaction system was irradiated with a 300W xenon lamp for 2 hours under the condition of full-spectrum wavelength light, and the content of generated hydrogen was analyzed by gas chromatography sampling.
In this example, the effect of the ultrasonic time on the performance of photocatalytic decomposition of water to produce hydrogen for preparing Mn-MOF nanoplates is mainly examined when the ratio of acetonitrile to water is 5:1, and the result is shown in FIG. 11. With the prolonging of the ultrasonic time, the hydrogen production performance of the Mn-MOF nanosheet by photocatalytic water decomposition is increased and then reduced, wherein the Mn-M-H-5-1-3H shows the optimal performance which is 14 times of that of the Mn-MOF single crystal material.
Example 6: photocatalytic decomposition of water under irradiation of visible light to produce hydrogen
Weighing 50mg of the sample prepared in the embodiment 1 or the Mn-M-H-5-1-3H nanosheet, adding the sample or the Mn-M-H-5-1-3H nanosheet into a mixed solution composed of 90ml of acetonitrile, 10ml of triethanolamine and 2ml of water, then adding 2.0ml of chloroplatinic acid solution (0.74mg/ml in terms of platinum), vacuumizing a reaction system, and irradiating for 3H by using a 300W xenon lamp under the condition of full-spectrum wavelength light to perform reduction deposition of metal platinum. And then vacuumizing the reaction system, continuously irradiating for 5 hours by using a 300W xenon lamp provided with an optical filter (L-42, the wavelength is more than or equal to 420nm), and analyzing the content of the generated hydrogen by using gas chromatography sampling every hour.
In the embodiment, the performance of the Mn-MOF single crystal material and the Mn-M-H-5-1-3H nanosheet for hydrogen production by water decomposition under visible light is mainly considered, and the result is shown in FIG. 12. Both can be used as a photocatalyst to catalyze the decomposition hydrogen production reaction of water under the irradiation of visible light, and the hydrogen continuously and linearly increases under the long-time irradiation, which shows that the novel Mn-MOF single crystal material and the Mn-M-H-5-1-3H nano-sheet have good photochemical stability. The activity of the Mn-M-H-5-1-3H nanosheet is about 12 times that of a Mn-MOF single crystal material, and the mixed solvent ultrasonic treatment is used for preparing the nanosheet with a regular morphology, so that the photocatalytic performance of the material is improved.