Calcium-based MOF (Metal Organic Framework) crystal material with photoelectric effect as well as preparation method and application of calcium-based MOF crystal material

Abstract

The invention provides a calcium-based MOF (Metal Organic Framework) crystal material with a photoelectric effect as well as a preparation method and application of the calcium-based MOF crystal material. According to the material, levo-2-hydroxysuccinic acid (L-malic acid) is taken as an organic ligand, calcium ions are taken as a metal center, and a three-dimensional network structure with an mbr topology type is formed. The calcium-based MOF crystal material disclosed by the invention has a photoelectric effect, shows a main peak at lambda ex = 440nm, shows a strong sharp peak at lambda em = 550nm when an emission spectrum is fixed to lambda ex = 440nm, has Stokes shift of delta lambda = 125nm and has remarkable lattice relaxation in an excited state, and can be used as a fluorescent matrix material for preparing light-excited materials and devices; the calcium-based MOF crystal material is prepared by adopting aloe as a raw material, organic components in the aloe serve as organic ligands to participate in MOF formation, the preparation method is simple, the preparation conditions are mild, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal organic framework materials, and specifically relates to a calcium-based MOF crystal material with a photoelectric effect, and a preparation method and application thereof. Background Art

[0002] Metal-organic frameworks (MOFs) are a class of crystalline porous materials with a periodic network structure formed by inorganic metal centers (metal ions or metal clusters) connected to organic ligands through a coordination network. Due to their high crystallinity, porosity, and designability, they have attracted widespread attention and development in fields such as gas adsorption and separation, catalysis, and sensing. Currently, MOFs are mainly prepared through chemical synthesis methods. There are many common synthesis methods, including hydrothermal / solvothermal synthesis, ultrasonication, microwave heating, electrochemical synthesis, and mechanochemical synthesis. Although the raw materials of these methods are cheap, the solvent and post-processing costs are high. Therefore, using plants as raw materials to prepare MOFs materials is of great value. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides a calcium-based MOF crystal material with a photoelectric effect, which uses L-hydroxysuccinic acid (L-malic acid) as an organic ligand and calcium ions as metal centers to form a three-dimensional network structure with an MBR topological type;

[0004] The three-dimensional network structure contains three types of calcium ions in coordination environments and three different forms of water molecules: free water, bridging water, and coordinated water. Among them, the L-malic acid ligand coordinates with the calcium ion through the oxygen atoms of the hydroxyl and carboxyl groups, and there are two coordination modes:

[0005] The first mode: A single L-malic acid ligand connects to four calcium ions. Its hydroxyl oxygen and carboxyl oxygen groups jointly form a five-membered ring with one calcium ion. The other oxygen atom of the carboxyl group is coordinated to the second calcium ion. At the same time, one of the two oxygen atoms of the second carboxyl group is coordinated to the third calcium ion, and the other oxygen atom is bridged to the fourth calcium ion.

[0006] The second mode: a single L-malic acid ligand is connected to 5 calcium ions, and its carboxyl oxygen and hydroxyl oxygen together form a five-membered ring with one calcium ion, and the same oxygen atom of the carboxyl group bridges another calcium ion, and the other oxygen atom of the carboxyl group is coordinated to the third calcium ion; at the same time, of the two oxygen atoms of the second carboxyl group, one oxygen atom is coordinated to the fourth calcium ion, and the other oxygen atom is bridged and coordinated to the fifth calcium ion.

[0007] In the first mode, the calcium ion forming a five-membered ring is the first calcium ion; the calcium ion coordinated with another oxygen atom of the first carboxyl group is the second calcium ion; the calcium ion directly coordinated with the second carboxyl group is the third calcium ion; the calcium ion bridged and coordinated by the second carboxyl group is the fourth calcium ion; wherein, the first calcium ion and the third calcium ion are the same metal center or different metal centers.

[0008] In the second mode, the calcium ion forming a five-membered ring is the fifth calcium ion; the calcium ion bridged by the same carboxyl oxygen atom is the sixth calcium ion; the calcium ion coordinated with another oxygen atom of the first carboxyl group is the seventh calcium ion; the calcium ion directly coordinated with the second carboxyl group is the eighth calcium ion; and the calcium ion coordinated by the second carboxyl group is the ninth calcium ion.

[0009] The bridging water connects two calcium ions, one of which participates in the formation of the five-membered ring of the first mode, namely the first calcium ion, and the other calcium ion participates in the formation of the five-membered ring of the second mode, namely the fifth calcium ion.

[0010] The free water is located in a tetrahedral cavity surrounded by four calcium ions, wherein the four calcium ions include:

[0011] 1 calcium ion connected to the bridging coordinated oxygen atom in the second mode, i.e., the sixth calcium ion;

[0012] Three calcium ions coordinated to the second carboxyl group in the first pattern, namely the third calcium ions.

[0013] The coordinated water molecules are directly coordinated with the five-membered ring calcium ion participating in the second coordination mode of L-malic acid, and

[0014] The calcium ion also meets the following requirements:

[0015] 1) connected by the bridging oxygen atom of the second carboxyl group of L-malic acid;

[0016] 2) Located at the vertices of the tetrahedral cavity formed by free water molecules.

[0017] The calcium-based MOF crystal material with photoelectric effect has a chemical formula of C 12 H 12 Ca3O 15 3H2O, the smallest asymmetric unit contains:

[0018] 1) 3 calcium ions;

[0019] 2) three L-malic acid ligands, two of which are coordinated in the first mode and one in the second mode;

[0020] 3) 1 free water molecule, 1 bridging water molecule and 1 coordinated water molecule.

[0021] The calcium-based MOF crystal material with photoelectric effect belongs to the orthorhombic system, the space group is P212121, and the unit cell parameters are a=β=γ=90°, the unit cell volume is 1973.65A 3 ; The chemical structure is shown in Formula I:

[0022]

[0023] On the other hand, the present invention provides a method for preparing the above-mentioned calcium-based MOF crystal material with photoelectric effect, comprising the steps of using aloe vera as raw material, extracting chloroplasts, destroying the chloroplast structure and releasing the contents, collecting the contents, removing impurities and crystallizing.

[0024] Preferably, the preparation method specifically comprises the following steps:

[0025] (1) Grind aloe leaves in a NaCl solution and homogenize them. Take the filtrate and perform preliminary separation using differential centrifugation to obtain chloroplast precipitate.

[0026] (2) liquefying the chloroplasts described in step (1) by freeze-thawing and precipitation combined with high temperature and high pressure to obtain chloroplast contents;

[0027] (3) evaporating the chloroplast contents in step (2) at a constant temperature, collecting the surface membrane and dissolving it in water, and dialyzing to obtain purified chloroplast contents;

[0028] (4) The purified chloroplast contents in step (3) are freeze-dried, rotary evaporated, and crystallized at low temperature to obtain a calcium-based MOF crystal material with a photoelectric effect.

[0029] Preferably, the aloe leaves in step (1) are fresh aloe leaves with their heads and tails removed.

[0030] Preferably, the aloe vera leaves in step (1) are soaked for 10 to 30 hours before grinding to remove the epidermis.

[0031] Preferably, the concentration of the NaCl solution in step (1) is 0.1 to 1 mol / L.

[0032] Preferably, the method of obtaining the filtrate in step (1) is gauze filtration.

[0033] Preferably, the differential centrifugation technique in step (1) comprises the following steps: centrifuging the filtrate at 500-2000 r / min for 1-10 min, discarding the precipitate, centrifuging at 2500-4000 r / min for 1-10 min, taking the precipitate, resuspending it in NaCl solution, and centrifuging at 2500-4000 r / min for 5-30 min to obtain the chloroplast precipitate.

[0034] Preferably, the freeze-thaw precipitation in step (2) is to freeze the aloe leaves at 0-80°C for 1-24 hours and then thaw them to room temperature; more preferably, the freeze-thaw precipitation in step (2) is to freeze the aloe leaves at -40°C for 6 hours and then thaw them to room temperature.

[0035] Preferably, the high temperature and high pressure conditions in step (2) are: 101-103.4 kPa, 121-132° C., and 15-30 min.

[0036] Preferably, before starting the freeze-thawing of the precipitate in step (2), it is pre-cooled at 4-8°C for 10-30 minutes.

[0037] Preferably, the freeze-thawing of the precipitation combined with the high temperature and high pressure liquefaction of chloroplasts in step (2) is cycled for more than one time until all the chloroplast contents are obtained.

[0038] Preferably, the temperature of the constant temperature evaporation in step (3) is 70-100°C.

[0039] Preferably, the molecular retention rate of the dialysis in step (3) is 8 kDa to 15 kDa.

[0040] Preferably, the freeze-drying in step (4) is vacuum freeze-drying for 15 to 30 hours.

[0041] Preferably, the rotary evaporation in step (4) is performed by dissolving the solution in 2 to 4 times the mass of water, and rotary evaporating until a light yellow, flowable gel is obtained;

[0042] Preferably, the rotary evaporation in step (4) has a pressure of 2.5 to 5 KPa, a temperature of 40 to 65° C., a rotation speed of 100 to 160 rpm, and a condensation temperature of 0 to 5° C.

[0043] Preferably, the low-temperature standing crystallization in step (4) is standing at 0 to 4°C.

[0044] On the other hand, the present invention provides the use of the calcium-based MOF crystal material with photoelectric effect in the preparation of fluorescent materials and devices.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The calcium-based MOF crystal material of the present invention has a photoelectric effect, showing a main peak at λex = 440nm. When the emission spectrum is fixed at λex = 440nm, it shows a strong sharp peak at λem = 550nm, and the Stokes shift is Δλ = 125nm, indicating that there is significant lattice relaxation in the excited state. It can be used as a fluorescent matrix material to prepare light-excited materials and devices. Existing calcium malate crystals do not have this property.

[0047] 2. The calcium-based MOF crystal material with photoelectric effect of the present invention is prepared using aloe vera as a raw material. The organic components in aloe vera participate in the formation of MOF as organic ligands. The preparation method is simple, the preparation conditions are mild, and the production cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 C prepared in Example 1 12 H 12 Ca3O 15 Photograph of 3H2O calcium-based MOF crystal material under an optical microscope;

[0049] Figure 2 C prepared in Example 1 12 H 12 Ca3O 15 Model diagram of the structure of 3H2O calcium-based MOF crystal material identified by X-ray diffraction;

[0050] Figure 3 The chemical structure diagram of calcium-based MOF crystal material;

[0051] Figure 4 C prepared in Example 1 12 H 12 Ca3O 15 Photoluminescence (PL) emission spectrum of 3H2O calcium-based MOF crystal material;

[0052] Figure 5 C prepared in Example 1 12 H 12 Ca3O 15 Time-resolved fluorescence lifetime (TRPL) spectrum of 3H2O calcium-based MOF crystal material. DETAILED DESCRIPTION

[0053] The present invention will be further described in detail below with reference to specific examples. The following examples are not intended to limit the present invention but are merely intended to illustrate the present invention. The experimental methods used in the following examples are generally based on conventional conditions unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified.

[0054] Example 1

[0055] (1) Using fresh Aloe vera leaves as raw materials, first remove the head and tail of the fresh leaves, chop off 15-20 cm from the front end, remove the tail, rinse with clean water, and soak in purified water for 24 hours;

[0056] (2) Wash the aloe vera leaves soaked in purified water, dry them, remove the epidermis, weigh 50 kg, place them in 150 L of 0.35 mol / L NaCl solution, and grind them into a homogenate using a grinding jar;

[0057] (3) Filter the homogenate through 6 layers of gauze, collect the filtrate, centrifuge at 1000 rpm for 5 min, discard the precipitate, and collect the upper filtrate;

[0058] (4) Centrifuge the upper filtrate at 3000 rpm for 5 min and collect the precipitate;

[0059] (5) Resuspend the precipitate in 0.35 mol / L NaCl solution, centrifuge at 3000 rpm for 20 min, discard the supernatant, and collect the chloroplast precipitate;

[0060] (6) Freezing treatment of chloroplast pellet: first pre-cool at 4°C for 30 minutes, then freeze the chloroplast into a solid state at a lower temperature (-40°C) for 6 hours;

[0061] (7) Transfer the frozen chloroplast pellet to room temperature and thaw until the chloroplasts return to room temperature to accelerate the liquefaction of the chloroplasts;

[0062] (8) The chloroplast precipitate restored to room temperature was subjected to high temperature and high pressure treatment at 103.4 kPa and 121°C for 30 min to further accelerate the liquefaction of the chloroplasts;

[0063] (9) Repeat steps (6) to (8) of freezing, thawing at room temperature, and high temperature and high pressure for three cycles to obtain chloroplast contents;

[0064] (10) Place the completely liquefied chloroplasts in a constant temperature evaporation tank and evaporate at 80°C. A film will form on the surface. Collect the film every 12 hours for 4 consecutive times.

[0065] (11) Combine the membranes collected four times, add 10 times the volume of water, and dialyze continuously for 48 h using a 10 kDa dialysis bag;

[0066] (12) The dialyzed liquid was freeze-dried in vacuum for 24 h, then dissolved by adding twice the mass of water, and transferred to a rotary evaporator. The pressure was controlled to 2.5 KPa, the temperature was 45 °C, the speed was 160 rpm, and the condenser temperature was 5 °C. The liquid was evaporated by rotary evaporation until the water was completely evaporated, and a slightly yellow, flowable gel appeared.

[0067] (13) The gel was transferred to a 4°C cold storage and allowed to stand for 3 days. Crystals began to precipitate from the bottom of the gel. The crystals were collected on the 10th day and dried to a constant weight, which was 1.205 g.

[0068] Example 2

[0069] (1) Using fresh Aloe vera leaves as raw materials, first remove the head and tail of the fresh leaves, chop off 15-20 cm from the front end, remove the tail, rinse with clean water, and soak in purified water for 10 hours;

[0070] (2) Wash the aloe vera leaves soaked in purified water, dry them, remove the epidermis, weigh 50 kg, place them in 150 L of 0.1 mol / L NaCl solution, and grind them into a homogenous slurry using a grinding jar;

[0071] (3) Filter the homogenate through 6 layers of gauze, collect the filtrate, centrifuge at 500 rpm for 10 min, discard the precipitate, and collect the upper filtrate;

[0072] (4) Centrifuge the upper filtrate at 2500 rpm for 10 min and collect the precipitate;

[0073] (5) Resuspend the precipitate in 0.35 mol / L NaCl solution, centrifuge at 2500 rpm for 30 min, discard the supernatant, and collect the chloroplast precipitate;

[0074] (6) Freezing treatment of chloroplast precipitate: first pre-cool at 8°C for 20 min, then freeze the chloroplast into a solid state at a lower temperature (-60°C) for 24 h;

[0075] (7) Transfer the frozen chloroplast pellet to room temperature and thaw until the chloroplasts return to room temperature to accelerate the liquefaction of the chloroplasts;

[0076] (8) The chloroplast precipitate returned to room temperature was subjected to a high temperature and high pressure treatment at 101 kPa and 132°C for 15 min to further accelerate the liquefaction of the chloroplasts;

[0077] (9) Repeating steps (6) to (8) of freezing, thawing at room temperature, and high temperature and high pressure twice to obtain chloroplast contents;

[0078] (10) Place the completely liquefied chloroplasts in a constant temperature evaporation tank and evaporate at 70°C. A film will form on the surface. Collect the film every 12 hours for 4 consecutive times.

[0079] (11) Combine the membranes collected four times, add 10 volumes of water, and dialyze continuously for 48 h using an 8 kDa dialysis bag;

[0080] (12) The dialyzed liquid was freeze-dried in vacuum for 15 h, then dissolved by adding 3 times the mass of water, and transferred to a rotary evaporator. The pressure was controlled to 5 kPa, the temperature was 45 °C, the speed was 100 rpm, and the condenser temperature was 5 °C. The liquid was evaporated by rotary evaporation until the water was completely evaporated, and a slightly yellow, flowable gel appeared.

[0081] (13) The gel was transferred to a 4°C cold storage and allowed to stand for 3 days. Crystals began to precipitate from the bottom of the gel. The crystals were collected on the 10th day and dried to a constant weight, which was 0.963 g.

[0082] Example 3

[0083] (1) Using fresh Aloe vera leaves as raw materials, first remove the head and tail of the fresh leaves, chop off 15-20 cm from the front end, remove the tail, rinse with clean water, and soak in purified water for 30 hours;

[0084] (2) Wash the aloe vera leaves soaked in purified water, dry them, remove the epidermis, weigh 50 kg, place them in 150 L of 1 mol / L NaCl solution, and grind them into a homogenous slurry using a grinding jar;

[0085] (3) Filter the homogenate through 6 layers of gauze, collect the filtrate, centrifuge at 2000 rpm for 1 min, discard the precipitate, and collect the upper filtrate;

[0086] (4) Centrifuge the upper filtrate at 4000 rpm for 1 min and collect the precipitate;

[0087] (5) Resuspend the precipitate in 0.35 mol / L NaCl solution, centrifuge at 4000 rpm for 5 min, discard the supernatant, and collect the chloroplast precipitate;

[0088] (6) The chloroplast precipitate obtained in Example 1 was frozen: first, pre-cooled at 4°C for 10 min, and then the chloroplasts were frozen into a solid state at a lower temperature (-80°C) for 2 h;

[0089] (7) Transfer the frozen chloroplast pellet to room temperature and thaw until the chloroplasts return to room temperature to accelerate the liquefaction of the chloroplasts;

[0090] (8) The chloroplast precipitate restored to room temperature was subjected to high temperature and high pressure treatment at 103.4 kPa and 121°C for 30 min to further accelerate the liquefaction of the chloroplasts;

[0091] (9) Repeating steps (1) to (3) of freezing, thawing at room temperature, and high temperature and high pressure for one cycle to obtain chloroplast contents;

[0092] (10) Place the completely liquefied chloroplasts in a constant temperature evaporation tank and evaporate at a constant temperature of 100°C. A film will form on the surface. Collect the film every 12 hours for 4 consecutive times.

[0093] (11) Combine the membranes collected four times, add 10 volumes of water, and dialyze continuously for 48 h using a 15 kDa dialysis bag;

[0094] (12) The dialyzed liquid was freeze-dried in vacuum for 30 h, and then 4 times the mass of water was added to dissolve it. The liquid was transferred to a rotary evaporator, and the pressure was controlled to 4 kPa, the temperature to 45 °C, the speed to 130 rpm, and the condenser temperature to 0 °C. The liquid was rotary evaporated until the water was completely evaporated, and a slightly yellow, flowable gel appeared.

[0095] (13) The gel was transferred to a cold storage at 0°C and allowed to stand for 3 days. Crystals precipitated from the bottom of the gel. The crystals were collected on the 10th day and dried to a constant weight, which was 0.872 g.

[0096] With reference to the Pharmacopoeia of the People's Republic of China 2020 edition Part IV 0451 X-ray diffraction method, the crystal materials obtained in Examples 1 and 2 were subjected to X-ray diffraction using a Rigaku SuperNova X-ray single crystal diffractometer. The detection conditions were: Cu target Ka ray, wavelength Voltage 50kV, current 0.8mA The morphology was observed using an optical microscope to obtain the crystal material structure and X-ray diffraction pattern. The crystal material structure and formula of Example 1 are as follows: Figure 1 、 Figure 2 、 Figure 3 As shown, the test results of Example 2 are the same and will not be repeated.

[0097] The crystal material of Example 1 is colorless and transparent, with a rough surface and a block structure of about 0.055 mm in length, about 0.033 mm in width, and about 0.021 mm in height ( Figure 1 ), the chemical formula of the material is C 12 H 12 Ca3O 15 ·3H2O( Figure 2 and Figure 3 ), belongs to the orthorhombic system, the space group is P212121, and the unit cell parameters are a=β=γ=90°, the unit cell volume is 1973.65A 3 , see Table 1 and Table 2 below.

[0098] Table 1 Crystallographic data of different space groups of crystalline materials

[0099]

[0100] Table 2 Fractional coordinates of different space groups of crystalline materials

[0101]

[0102] This crystal material uses L-hydroxybutanedioic acid (L-malic acid) as an organic ligand, and all the hydroxyl and carboxyl groups in the ligand participate in coordination. Its minimum asymmetric unit is composed of three calcium ions, three L-malic acid and three water molecules in different environments (free, bridged and coordinated). The calcium ions form a three-dimensional network structure with an MBR topology type through coordination with the L-malic acid, constructing a three-dimensional framework composed of irregular channels.

[0103] Calcium ions are coordinated through three coordination mechanisms: 1. The first calcium ion is linked to the second calcium ion via two carboxyl groups and a bridging coordinated water, is linked to the third calcium ion via two carboxyl groups, and is linked to the second and third calcium ions via one carboxyl group. 2. The second calcium ion is linked to the first calcium ion in the aforementioned manner and is also linked to two other second calcium ions via two carboxyl groups. 3. The third calcium ion is linked to two first calcium ions via the aforementioned two means and is also linked to one second calcium ion via one carboxyl group and has one coordinated water. A free water molecule resides in the cavity surrounded by the first calcium ion and three third calcium ions, forming a hydrogen bond network with their coordinated carboxyl groups.

[0104] L-malic acid exhibits two coordination modes: 1. Two oxygen atoms from the hydroxyl and carboxylic acid groups coordinate with a third calcium ion to form a five-membered ring, while the remaining oxygen atom of the carboxyl group coordinates with another first or second calcium ion. When the two oxygen atoms of the second carboxyl group simultaneously coordinate with a first or third calcium ion, one of the oxygen atoms also bridges another third or first calcium ion. This malic acid ligand is connected to a total of four calcium ions. 2. One oxygen atom from the carboxylic acid group, together with the hydroxyl oxygen atom, coordinates with the second calcium ion to form a five-membered ring and also bridges another second calcium ion. The remaining oxygen atom of the carboxyl group coordinates with the first calcium ion. When the two oxygen atoms of the second carboxyl group simultaneously coordinate with a second calcium ion, one of the oxygen atoms also bridges a first calcium ion. This malic acid ligand is connected to a total of five calcium ions.

[0105] Application Examples

[0106] The optical properties of the crystal materials of Examples 1 and 2 were tested using a steady-state fluorescence spectrometer. The test results of the crystal material prepared in Example 1 are shown in FIG. Figure 4 PL spectra and Figure 5 The TRPL spectrum of Example 2 is the same as the detection result of the crystal material prepared in Example 1, indicating that the MOF crystal materials prepared in Examples 1 and 2 show a main peak at λex=440nm, and the emission spectrum shows a strong sharp peak at λem=550nm when λex=440nm is fixed, and the Stokes shift is Δλ=125nm, indicating that there is significant lattice relaxation in the excited state, which proves that the MOF crystal materials prepared in Examples 1 and 2 have potential value in the field of photocatalysis.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that the aloe vera gel is liquefied by a heat treatment method.

[0109] (1) Using fresh Aloe vera leaves as raw materials, first remove the head and tail of the fresh leaves, chop off 15-20 cm from the front end, remove the tail, rinse with clean water, and soak in purified water for 24 hours;

[0110] (2) Wash the aloe vera leaves soaked in purified water, dry them, remove the epidermis, weigh 50 kg, place them in 150 L of 0.35 mol / L NaCl solution, and grind them into a homogenate using a grinding jar;

[0111] (3) Filter the homogenate through 6 layers of gauze, collect the filtrate, centrifuge at 1000 rpm for 5 min, discard the precipitate, and collect the upper filtrate;

[0112] (4) Centrifuge the upper filtrate at 3000 rpm for 5 min and collect the precipitate;

[0113] (5) Resuspend the precipitate in 0.35 mol / L NaCl solution, centrifuge at 3000 rpm for 20 min, discard the supernatant, and collect the chloroplast precipitate;

[0114] (6) Heat treatment of chloroplast precipitate: The chloroplast precipitate obtained in (5) was stirred continuously at 100 rpm for 2 h at 60°C to completely liquefy it;

[0115] (7) The completely liquefied chloroplasts were placed in a constant temperature evaporation tank and evaporated at a constant temperature of 80°C. No evaporation film was formed on the liquid surface, and MOF crystal materials could not be obtained.

[0116] Comparative Example 2

[0117] The difference between this comparative example and Example 1 is that a chemical method is used to accelerate the liquefaction of aloe vera gel.

[0118] (1) Using fresh Aloe vera leaves as raw materials, first remove the head and tail of the fresh leaves, chop off 15-20 cm from the front end, remove the tail, rinse with clean water, and soak in purified water for 24 hours;

[0119] (2) Wash the aloe vera leaves soaked in purified water, dry them, remove the epidermis, weigh 50 kg, place them in 150 L of 0.35 mol / L NaCl solution, and grind them into a homogenate using a grinding jar;

[0120] (3) Filter the homogenate through 6 layers of gauze, collect the filtrate, centrifuge at 1000 rpm for 5 min, discard the precipitate, and collect the upper filtrate;

[0121] (4) Centrifuge the upper filtrate at 3000 rpm for 5 min and collect the precipitate;

[0122] (5) Resuspend the precipitate in 0.35 mol / L NaCl solution, centrifuge at 3000 rpm for 20 min, discard the supernatant, and collect the chloroplast precipitate;

[0123] (6) Heat treatment of chloroplast precipitate: The chloroplast precipitate obtained in (5) was mixed with 20% (v / v) ethanol solution at a mass ratio of 1:5 and stirred continuously at 100 r / min for 2 h to completely liquefy it;

[0124] (7) The completely liquefied chloroplasts were placed in a constant temperature evaporation tank and evaporated at a constant temperature of 80°C. No evaporation film was formed on the liquid surface, and MOF crystal materials could not be obtained.

[0125] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A calcium-based MOF crystal material with photoelectric effect, characterized in that: With L-malic acid as the organic ligand and calcium ion as the metal center, a three-dimensional network structure with the mbr topology type is formed; The three-dimensional network structure contains three types of calcium ions in coordination environments and three different forms of water molecules: free water, bridging water, and coordinated water. Among them, the L-malic acid ligand coordinates with the calcium ion through the oxygen atoms of the hydroxyl and carboxyl groups, and there are two coordination modes: The first mode: A single L-malic acid ligand connects to four calcium ions. Its hydroxyl oxygen and carboxyl oxygen groups jointly form a five-membered ring with one calcium ion. The other oxygen atom of the carboxyl group is coordinated to the second calcium ion. At the same time, one of the two oxygen atoms of the second carboxyl group is coordinated to the third calcium ion, and the other oxygen atom is bridged to the fourth calcium ion. The second mode: a single L-malic acid ligand is connected to 5 calcium ions, and its carboxyl oxygen and hydroxyl oxygen together form a five-membered ring with one calcium ion, and the same oxygen atom of the carboxyl group bridges another calcium ion, and the other oxygen atom of the carboxyl group is coordinated to the third calcium ion; at the same time, of the two oxygen atoms of the second carboxyl group, one oxygen atom is coordinated to the fourth calcium ion, and the other oxygen atom is bridged and coordinated to the fifth calcium ion.

2. The calcium-based MOF crystal material with photoelectric effect according to claim 1, characterized in that: In the first mode, the calcium ion forming a five-membered ring is the first calcium ion; the calcium ion coordinated with another oxygen atom of the first carboxyl group is the second calcium ion; the calcium ion directly coordinated with the second carboxyl group is the third calcium ion; the calcium ion bridged and coordinated by the second carboxyl group is the fourth calcium ion; wherein, the first calcium ion and the third calcium ion are the same metal center or different metal centers.

3. The calcium-based MOF crystal material with photoelectric effect according to claim 1, characterized in that: In the second mode, the calcium ion forming a five-membered ring is the fifth calcium ion; the calcium ion bridged by the same carboxyl oxygen atom is the sixth calcium ion; the calcium ion coordinated with another oxygen atom of the first carboxyl group is the seventh calcium ion; the calcium ion directly coordinated with the second carboxyl group is the eighth calcium ion; and the calcium ion coordinated by the second carboxyl group is the ninth calcium ion.

4. The calcium-based MOF crystal material with photoelectric effect according to claim 1, characterized in that: Include at least one of the following (1)-(3): (1) The bridging water connects two calcium ions, one of which participates in the formation of the five-membered ring of the first mode, i.e., the first calcium ion, and the other calcium ion participates in the formation of the five-membered ring of the second mode, i.e., the fifth calcium ion; (2) The free water is located in a tetrahedral cavity surrounded by four calcium ions, the four calcium ions including: 1 calcium ion connected to the bridging coordinated oxygen atom in the second mode, i.e., the sixth calcium ion; 3 calcium ions coordinated to the second carboxyl group in the first pattern, i.e., the third calcium ion; (3) The coordinated water molecule is directly coordinated with the five-membered ring calcium ion participating in the second coordination mode of L-malic acid, and the calcium ion simultaneously satisfies: 1) connected by the bridging oxygen atom of the second carboxyl group of L-malic acid; 2) Located at the vertices of the tetrahedral cavity formed by free water molecules.

5. The calcium-based MOF crystal material with photoelectric effect according to claim 1, characterized in that: The chemical formula is C 12 H 12 Ca3O 15 3H2O, the smallest asymmetric unit contains: 1) 3 calcium ions; 2) three L-malic acid ligands, two of which are coordinated in the first mode and one in the second mode; 3) 1 free water molecule, 1 bridging water molecule and 1 coordinated water molecule; Its crystal belongs to the orthorhombic system, the space group is P212121, and the unit cell parameters are a=β=γ=90°, the unit cell volume is 1973.65A 3 ; The chemical structure is shown in Formula I:

6. The method for preparing the calcium-based MOF crystal material with photoelectric effect according to claim 1, characterized in that: The method comprises the steps of using aloe vera as raw material, extracting chloroplasts, destroying the chloroplast structure and releasing the contents, collecting the contents, removing impurities and crystallizing.

7. The method for preparing a calcium-based MOF crystal material having a photoelectric effect according to claim 6, characterized in that: The specific steps include: (1) Grind aloe leaves in a NaCl solution and homogenize them. Take the filtrate and perform preliminary separation using differential centrifugation to obtain chloroplast precipitate. (2) liquefying the chloroplasts described in step (1) by freeze-thawing and precipitation combined with high temperature and high pressure to obtain chloroplast contents; (3) evaporating the chloroplast contents in step (2) at a constant temperature, collecting the surface membrane and dissolving it in water, and dialyzing to obtain purified chloroplast contents; (4) The purified chloroplast contents in step (3) are freeze-dried, rotary evaporated, and crystallized at low temperature to obtain a calcium-based MOF crystal material with a photoelectric effect.

8. The method for preparing the calcium-based MOF crystal material according to claim 7, characterized in that: Include at least one of the following (a)-(d): (a) the freeze-thaw step of the precipitation in step (2) is combined with the high temperature and high pressure chloroplast liquefaction step for more than one cycle until all the chloroplast contents are obtained; (b) The freeze-thaw precipitation in step (2) is to freeze the aloe leaves at 0-80°C for 1-24 hours and thaw them to room temperature; (c) The high temperature and high pressure conditions of step (2) are: 101-103.4 kPa, 121-132° C., and 15-30 min; (d) Before starting the freeze-thawing of the precipitate in step (2), pre-cool it at 4-8°C for 10-30 minutes.

9. The method for preparing a calcium-based MOF crystal material having a photoelectric effect according to claim 8, characterized in that: Include at least one of the following (a)-(k): (a) The differential centrifugation technique of step (1) comprises the following steps: centrifuging the filtrate at 500-2000 r / min for 1-10 min, discarding the precipitate, centrifuging at 2500-4000 r / min for 1-10 min, taking the precipitate, resuspending it in a NaCl solution, and centrifuging at 2500-4000 r / min for 5-30 min to obtain the chloroplast precipitate; (b) the concentration of the NaCl solution in step (1) is 0.1 to 1 mol / L; (c) the filtrate is collected by filtering through gauze in step (1); (d) soaking the aloe leaves in step (1) for 10 to 30 hours before grinding to remove the epidermis; (e) The freeze-thaw precipitation in step (2) is to freeze the aloe leaves at -40°C for 6 hours and thaw them to room temperature; (f) The temperature of the constant temperature evaporation in step (3) is 70-100° C.; (g) the molecular cutoff of the dialysis in step (3) is 8 kDa to 15 kDa; (h) the freeze drying in step (4) is vacuum freeze drying for 15 to 30 hours; (i) The rotary evaporation in step (4) is performed by dissolving the mixture in water 2 to 4 times its mass and rotary evaporating the mixture until a slightly yellow, flowable gel is obtained; (j) The rotary evaporation in step (4) is performed at a pressure of 2.5 to 5 kPa, a temperature of 40 to 65° C., a rotation speed of 100 to 160 rpm, and a condensation temperature of 0 to 5° C.; (k) The low-temperature standing crystallization in step (4) is standing at 0 to 4°C.

10. Use of the calcium-based MOF crystal material with photoelectric effect according to claim 1 in the preparation of fluorescent materials and devices.

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