A calcium-based MOF crystal material with photoelectric effect, its preparation method and application

Abstract

This invention provides a calcium-based MOF crystal material with photoelectric effect, its preparation method, and its applications. The material uses L-malic acid (L-2-hydroxysuccinic acid) as the organic ligand and calcium ions as the metal center, forming a three-dimensional network structure with an MBR topology. The calcium-based MOF crystal material of this invention exhibits photoelectric effect, displaying a main peak at λex = 440 nm. With a fixed λ_ex = 440 nm, the emission spectrum shows a strong sharp peak at λ_em = 550 nm, with a Stokes shift of Δλ = 125 nm. The excited state exhibits significant lattice relaxation, making it suitable as a fluorescent matrix material for preparing photoexcited materials and devices. The calcium-based MOF crystal material of this invention is prepared using aloe vera as a raw material. The organic components in aloe vera participate in MOF formation as organic ligands. The preparation method is simple, the preparation conditions are mild, and production costs are reduced.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework materials technology, specifically relating to a calcium-based MOF crystal material with photoelectric effect, its preparation method and application. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of crystalline porous materials with periodic network structures, formed by inorganic metal centers (metal ions or metal clusters) connected to organic ligands through coordination networks. 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, MOF materials are mainly prepared through chemical synthesis methods, which are diverse and commonly include hydrothermal / solvothermal synthesis, ultrasonic methods, microwave heating methods, electrochemical synthesis, and mechanochemical synthesis. Although these methods use inexpensive raw materials, the costs of solvents and post-processing are high. Therefore, using plants as raw materials to prepare MOF materials has significant value. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a calcium-based MOF crystal material with photoelectric effect, using L-2-hydroxysuccinic acid (L-malic acid) as an organic ligand and calcium ions as the metal center to form a three-dimensional network structure with an MBR topology.

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

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

[0006] The second mode: A single L-malic acid ligand connects to 5 calcium ions. 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. The other oxygen atom of the carboxyl group is located in the third calcium ion. At the same time, of the two oxygen atoms of its second carboxyl group, one oxygen atom is located in the fourth calcium ion, and the other oxygen atom is bridged and located in the fifth calcium ion.

[0007] In the first mode, the calcium ion forming the five-membered ring is the first calcium ion; the calcium ion coordinated with the other 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; and the calcium ion bridged by the second carboxyl group is the fourth calcium ion; wherein the first calcium ion and the third calcium ion have the same metal center or different metal centers.

[0008] In the second mode, the calcium ion that forms 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 the other 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 bridged 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 a five-membered ring in the first mode, namely the first calcium ion, and the other calcium ion participates in the formation of a five-membered ring in the second mode, namely the fifth calcium ion.

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

[0011] One calcium ion connected to the bridging oxygen atom in the second mode, namely the sixth calcium ion;

[0012] Three calcium ions coordinated with the second carboxyl group in the first mode, i.e., the third calcium ion.

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

[0014] This calcium ion simultaneously satisfies:

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

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

[0017] The calcium-based MOF crystal material exhibiting photoelectric effect has the general chemical formula C0. 12 H 12 Ca3O 15 ·3H2O, the smallest asymmetric unit contains:

[0018] 1) Three 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) One free water molecule, one bridging water molecule, and one coordinated water molecule.

[0021] The calcium-based MOF crystal material exhibiting photoelectric effect has an orthorhombic crystal system with space group P212121 and cell parameters of [missing information]. a = β = γ = 90°, and the unit cell volume is 1973.65 Å. 3 The chemical structural formula 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, including 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 includes the following steps:

[0025] (1) Grind aloe vera leaves into a homogenate in NaCl solution, take the filtrate, and use differential centrifugation to preliminarily separate chloroplasts;

[0026] (2) The chloroplasts described in step (1) are liquefied by a combination of precipitation, freeze-thaw and high temperature and high pressure to obtain chloroplast contents;

[0027] (3) Evaporate the chloroplast contents obtained in step (2) at a constant temperature, collect the surface membrane and dissolve it in water, dialyze it to obtain purified chloroplast contents;

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

[0029] Preferably, the aloe vera leaf in step (1) is a fresh aloe vera leaf with the head and tail 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 taking the filtrate in step (1) is gauze filtration.

[0033] Preferably, the differential centrifugation technique in step (1) includes 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 precipitation freeze-thaw in step (2) involves freezing the aloe vera leaves at 0 to -80°C for 1 to 24 hours and then thawing them to room temperature; more preferably, the precipitation freeze-thaw in step (2) involves freezing the aloe vera leaves at -40°C for 6 hours and then thawing 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 the precipitation freeze-thaw process in step (2), the sample is pre-cooled at 4-8°C for 10-30 minutes.

[0037] Preferably, the precipitation-freeze-thaw combined high-temperature and high-pressure liquefaction chloroplast step (2) is repeated more than once until all chloroplast contents are obtained.

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

[0039] Preferably, the molecular cutoff 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) involves dissolving the gel in 2 to 4 times its mass of water and rotary evaporating until a slightly yellow, flowable gel is obtained.

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

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

[0044] In another aspect, the present invention provides the application 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 exhibits photoelectric effect, showing a main peak at λex = 440 nm. When the emission spectrum is fixed at λex = 440 nm, it shows a strong and sharp peak at λem = 550 nm, and the Stokes shift is Δλ = 125 nm, indicating that there is significant lattice relaxation in the excited state. It can be used as a fluorescent matrix material to prepare photoexcited materials and devices. However, existing calcium malate crystals do not have this characteristic.

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

[0048] Figure 1 C prepared in Example 1 12 H 12 Ca3O 15 • A 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 • A model diagram of the structure of the 3H2O calcium-based MOF crystal material identified by X-ray diffraction;

[0050] Figure 3 This is a chemical structural diagram of a 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 Implementation

[0053] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are not intended to limit the present invention, but only to illustrate the present invention. Unless otherwise specified, the experimental methods used in the following embodiments are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0054] Example 1

[0055] (1) Using fresh leaves of Aloe vera as raw material, first remove the head and tail of the fresh leaves, cut off 15-20cm 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, put them into 150 L of 0.35 mol / L NaCl solution, and grind them into a homogenate using a grinding jar.

[0057] (3) Filter the above homogenate through 6 layers of gauze, take the filtrate, centrifuge at 1000r / min for 5min, discard the precipitate, and take the upper filtrate.

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

[0059] (5) Resuspend the above precipitate with a NaCl solution with a concentration of 0.35 mol / L, centrifuge at 3000 r / min for 20 min, discard the supernatant, and take the chloroplast precipitate;

[0060] (6) Precipitate and freeze chloroplasts: First, pre-cool at 4°C for 30 minutes, then freeze the chloroplasts at a lower temperature (-40°C) for 6 hours.

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

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

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

[0064] (10) Place the completely liquefied chloroplasts in a constant temperature evaporator and evaporate them at 80°C. A film is formed on the surface. Collect the film every 12 hours for a total of 4 times.

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

[0066] (12) The dialyzed liquid was vacuum freeze-dried for 24 hours, then 2 times the mass of water was added to dissolve it, and the liquid was transferred to a rotary evaporator. The pressure was controlled at 2.5 kPa, the temperature at 45°C, the rotation speed at 160 rpm, and the condenser temperature at 5°C. The liquid was rotary evaporated until the water was completely evaporated. At this time, a slightly yellow, flowable gel appeared.

[0067] (13) Transfer the above gel to a cold storage at 4°C and let it stand for 3 days. Crystals begin to precipitate at the bottom of the gel. Collect the crystals on the 10th day of standing, dry them to constant weight, and weigh them as 1.205g.

[0068] Example 2

[0069] (1) Using fresh leaves of Aloe vera as raw material, first remove the head and tail of the fresh leaves, cut off 15-20cm 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, put them into 150 L of 0.1 mol / L NaCl solution, and grind them into a homogenate using a grinding jar.

[0071] (3) Filter the above homogenate through 6 layers of gauze, take the filtrate, centrifuge at 500r / min for 10min, discard the precipitate, and take the upper filtrate.

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

[0073] (5) Resuspend the above precipitate with a 0.35 mol / L NaCl solution, centrifuge at 2500 r / min for 30 min, discard the supernatant, and take the chloroplast precipitate;

[0074] (6) Precipitate and freeze chloroplasts: First, pre-cool at 8℃ for 20 min, then freeze the chloroplasts at a lower temperature (-60℃) for 24 h.

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

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

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

[0078] (10) Place the completely liquefied chloroplasts in a constant temperature evaporator and evaporate them at 70°C. A film is formed on the surface. Collect the film every 12 hours for a total of 4 times.

[0079] (11) Combine the membranes collected from the four collections, add 10 times the volume of water, and dialyze continuously for 48 hours through an 8kDa dialysis bag;

[0080] (12) The dialysis liquid was vacuum freeze-dried for 15 hours, then 3 times the mass of water was added to dissolve it, and the liquid was transferred to a rotary evaporator. The pressure was controlled at 5 kPa, the temperature at 45°C, the rotation speed at 100 rpm, and the condenser temperature at 5°C. The liquid was rotary evaporated until the water was completely evaporated. At this time, a slightly yellow, flowable gel appeared.

[0081] (13) Transfer the above gel to a cold storage at 4°C and let it stand for 3 days. Crystals begin to precipitate at the bottom of the gel. Collect the crystals on the 10th day of standing, dry them to constant weight, and weigh them as 0.963g.

[0082] Example 3

[0083] (1) Using fresh leaves of Aloe vera as raw material, first remove the head and tail of the fresh leaves, cut off 15-20cm 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, put them into 150 L of 1 mol / L NaCl solution, and grind them into a homogenate using a grinding jar.

[0085] (3) Filter the above homogenate through 6 layers of gauze, take the filtrate, centrifuge at 2000r / min for 1min, discard the precipitate, and take the upper filtrate.

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

[0087] (5) Resuspend the above precipitate with a NaCl solution with a concentration of 0.35 mol / L, centrifuge at 4000 r / min for 5 min, discard the supernatant, and take the chloroplast precipitate;

[0088] (6) Freeze the chloroplast precipitate obtained in Example 1: First, pre-cool at 4°C for 10 min, and then freeze the chloroplast into a solid at a lower temperature (-80°C) for 2 h.

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

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

[0091] (9) Repeat steps (1)-(3) of freezing, thawing at room temperature, and high temperature and high pressure operation once to obtain chloroplast contents;

[0092] (10) Place the completely liquefied chloroplasts in a constant temperature evaporator and evaporate them at 100°C. A film is formed on the surface. Collect the film every 12 hours for a total of 4 times.

[0093] (11) Combine the membranes collected from the four collections, add 10 times the volume of water, and dialyze continuously for 48 hours through a 15kDa dialysis bag;

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

[0095] (13) Transfer the above gel to a 0℃ cold storage and let it stand for 3 days. Crystals precipitate at the bottom of the gel. Collect the crystals on the 10th day of standing, dry them to constant weight, and weigh them as 0.872g.

[0096] Referring to the X-ray diffraction method in Part IV, 0451 of the 2020 edition of the Pharmacopoeia of the People's Republic of China, X-ray diffraction was performed on the crystal materials obtained in Examples 1 and 2 using a Rigaku SuperNova X-ray single crystal diffractometer (Japan). 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's structural morphology and X-ray diffraction pattern. The crystal material's structural morphology and formula in Example 1 are as follows: Figure 1 , Figure 2 , Figure 3 As shown, the detection results of Example 2 are the same and will not be repeated.

[0097] The crystalline material of Example 1 is colorless and transparent with a rough surface, exhibiting a blocky structure approximately 0.055 mm long, 0.033 mm wide, and 0.021 mm high. Figure 1 The chemical formula of this material is C2. 12 H 12 Ca3O 15 ·3H2O( Figure 2 and Figure 3 It belongs to the orthorhombic crystal system, with space group P212121 and cell parameters of . a = β = γ = 90°, and the unit cell volume is 1973.65 Å. 3 See Tables 1 and 2 below.

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

[0099]

[0100] Table 2. Fractional coordinates of different space groups for crystal materials

[0101]

[0102] The crystal material uses L-malic acid (2-hydroxysuccinic acid) as an organic ligand, with all hydroxyl and carboxyl groups in the ligand participating in coordination. Its smallest asymmetric unit consists of three calcium ions, three L-malic acids, and three types of water molecules in different environments (free, bridged, and coordinated). The calcium ions form a three-dimensional network structure with an MBR topology through coordination with L-malic acids, constructing a three-dimensional framework composed of irregular channels.

[0103] Calcium ions coordinate in three ways: 1. The first calcium ion is connected to the second calcium ion through two carboxyl groups and a bridging water group, to the third calcium ion through two carboxyl groups, and to the second and third calcium ions through one carboxyl group; 2. The second calcium ion is connected to the first calcium ion in the aforementioned ways, and is also connected to two other second calcium ions through two carboxyl groups; 3. The third calcium ion is connected to two first calcium ions in the aforementioned two ways, and is also connected to one second calcium ion through one carboxyl group, and has a bridging water group. A free water molecule resides in the cavity formed by one first calcium ion and three third calcium ions, forming a hydrogen bond network with their bridging carboxyl groups.

[0104] L-malic acid exhibits two coordination modes: 1. Two oxygen atoms from the hydroxyl and carboxylic acid groups, respectively, coordinate with a third calcium ion to form a five-membered ring. The remaining oxygen atom of this 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 connects a total of 4 calcium ions. 2. An oxygen atom from the carboxylic acid group, together with the oxygen atom of the hydroxyl group, coordinates with a second calcium ion to form a five-membered ring, while also bridging another second calcium ion. The remaining oxygen atom of this carboxyl group coordinates with a 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 connects a total of 5 calcium ions.

[0105] Application examples

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

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that a heat treatment method was used to liquefy the aloe vera gel.

[0109] (1) Using fresh leaves of Aloe vera as raw material, first remove the head and tail of the fresh leaves, cut off 15-20cm 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, put them into 150 L of 0.35 mol / L NaCl solution, and grind them into a homogenate using a grinding jar.

[0111] (3) Filter the above homogenate through 6 layers of gauze, take the filtrate, centrifuge at 1000r / min for 5min, discard the precipitate, and take the upper filtrate.

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

[0113] (5) Resuspend the above precipitate with a NaCl solution with a concentration of 0.35 mol / L, centrifuge at 3000 r / min for 20 min, discard the supernatant, and take the chloroplast precipitate;

[0114] (6) Heat treatment of chloroplast precipitation: The chloroplast precipitate obtained in (5) was continuously stirred at 100r / min for 2h at 60℃ to completely liquefy it.

[0115] (7) When the fully liquefied chloroplasts are placed in a constant temperature evaporator and evaporated at 80°C, no evaporation film is formed on the liquid surface, so MOF crystal materials cannot be obtained.

[0116] Comparative Example 2

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

[0118] (1) Using fresh leaves of Aloe vera as raw material, first remove the head and tail of the fresh leaves, cut off 15-20cm 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, put them into 150 L of 0.35 mol / L NaCl solution, and grind them into a homogenate using a grinding jar.

[0120] (3) Filter the above homogenate through 6 layers of gauze, take the filtrate, centrifuge at 1000r / min for 5min, discard the precipitate, and take the upper filtrate.

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

[0122] (5) Resuspend the above precipitate with a NaCl solution with a concentration of 0.35 mol / L, centrifuge at 3000 r / min for 20 min, discard the supernatant, and take the chloroplast precipitate;

[0123] (6) Heat treatment of chloroplast precipitation: 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 100r / min for 2h to completely liquefy it.

[0124] (7) When the fully liquefied chloroplasts are placed in a constant temperature evaporator and evaporated at 80°C, no evaporation film is formed on the liquid surface, so MOF crystal materials cannot be obtained.

[0125] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A calcium-based MOF crystal material exhibiting photoelectric effect, characterized in that, Using L-2-hydroxysuccinic acid as an organic ligand (L-malic acid), with calcium ions as the metal center, a three-dimensional network structure with an MBR topology is formed. The three-dimensional network structure contains calcium ions in three coordination environments and water molecules in three different forms: free water, bridged water, and coordinated water; wherein, the L-malic acid ligand coordinates with calcium ions through the oxygen atoms of the hydroxyl and carboxyl groups, and there are two coordination modes: First mode: A single L-malic acid ligand connects to four calcium ions. Its hydroxyl oxygen and carboxyl oxygen together form a five-membered ring with the first calcium ion. The other oxygen atom of the carboxyl group is located in the second calcium ion. At the same time, of the two oxygen atoms of the second carboxyl group, one oxygen atom is located in the third calcium ion, and the other oxygen atom is bridged and located in the fourth calcium ion. The second mode: A single L-malic acid ligand connects to 5 calcium ions. Its carboxyl oxygen and hydroxy oxygen together form a five-membered ring with the fifth calcium ion, and the same oxygen atom of the carboxyl group bridges the sixth calcium ion. The other oxygen atom of the carboxyl group is located in the seventh calcium ion. At the same time, of the two oxygen atoms of its second carboxyl group, one oxygen atom is located in the eighth calcium ion, and the other oxygen atom bridges and is located in the ninth calcium ion. The calcium ions in three coordination environments and the water molecules in three different forms include the following (1)-(3): (1) The bridging water connects two calcium ions, one of which participates in the formation of the five-membered ring in the first mode, namely the first calcium ion, and the other calcium ion participates in the formation of the five-membered ring in the second mode, namely the fifth calcium ion; (2) The free water is located in a tetrahedral cavity surrounded by four calcium ions, the four calcium ions being: One calcium ion connected to the bridging oxygen atom in the second mode, namely the sixth calcium ion; Three calcium ions coordinated with the second carboxyl group in the first mode, i.e., the third calcium ion; (3) The coordinated water directly coordinates 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 apex of a tetrahedral cavity formed by free water molecules; The general chemical formula of the calcium-based MOF crystal material exhibiting photoelectric effect is C0. 12 H 12 Ca3O 15 ·3H2O, the smallest asymmetric unit contains: 1) Three calcium ions; 2) Three L-malic acid ligands, two of which are coordinated in the first mode and one in the second mode; 3) One free water molecule, one bridging water molecule, and one coordinated water molecule; Its crystals belong to the orthorhombic crystal system, and its space group is [missing information]. P 212121, with unit cell parameters a=7.71360Å, b=8.74053Å, c=29.2735Å, a=β=γ=90°, and a unit cell volume of 1973.65 ų; its chemical structure is shown in Formula I: Formula I: .

2. The method for preparing the calcium-based MOF crystal material with photoelectric effect as described in claim 1, characterized in that, Using aloe vera as raw material, chloroplasts are extracted, the chloroplast structure is destroyed and the contents are released, the contents are collected, and impurities and crystals are removed; Includes the following steps: (1) Grind aloe vera leaves into a homogenate in NaCl solution, take the filtrate, and use differential centrifugation to preliminarily separate the chloroplasts; (2) The chloroplasts described in step (1) are liquefied by precipitation, freeze-thaw process and high temperature and high pressure to obtain chloroplast contents; (3) Evaporate the chloroplast contents described in step (2) at a constant temperature, collect the surface membrane and dissolve it in water, dialyze it to obtain purified chloroplast contents; (4) The purified chloroplast contents described in step (3) are freeze-dried, rotary evaporated and crystallized at low temperature to obtain calcium-based MOF crystal material with photoelectric effect.

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

4. The method for preparing the calcium-based MOF crystal material with photoelectric effect according to claim 2, characterized in that, Includes at least one of the following (a)-(k): (a) The differential centrifugation technique in step (1) includes the following steps: centrifuge the filtrate at 500-2000 r / min for 1-10 min, discard the precipitate, centrifuge at 2500-4000 r / min for 1-10 min, take the precipitate, resuspend it in NaCl solution, centrifuge at 2500-4000 r / min for 5-30 min, and obtain the chloroplast precipitate; (b) The concentration of the NaCl solution in step (1) is 0.1–1 mol / L; (c) The method of taking the filtrate in step (1) is gauze filtration; (d) Soak the aloe vera leaves described in step (1) for 10–30 h before grinding to remove the epidermis; (e) The precipitation freeze-thaw process in step (2) involves freezing aloe vera leaves at -40°C for 6 hours and then thawing them to room temperature; (f) The temperature for constant-temperature evaporation in step (3) is 70–100°C; (g) The molecular cutoff rate 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) involves dissolving the gel in 2 to 4 times its mass of water and rotary evaporating until a slightly yellow, flowable gel is obtained; (j) The pressure of the rotary evaporation in step (4) is 2.5 to 5 kPa, the temperature is 40 to 65 °C, the rotation speed is 100 to 160 rpm, and the condensation temperature is 0 to 5 °C; (k) The low-temperature static crystallization in step (4) is static at 0 to 4 °C.

5. The application of the calcium-based MOF crystal material with photoelectric effect as described in claim 1 in the preparation of fluorescent materials and devices.

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