A binaphthyl anthracene compound, a synthetic method thereof and application of the compound in preparation of a MOF (30-Zr) for extracting uranium from seawater

Abstract

The application relates to the fields of seawater uranium extraction and new materials, and specifically provides a double-naphthyl anthracene compound, a synthesis method thereof, and application of the double-naphthyl anthracene compound in preparation of seawater uranium extraction MOF (30-Zr). The prepared double-naphthyl anthracene compound is 4-[10-(4-carboxy naphthalene-1-yl) anthracene-9-yl] naphthalene-1-methanoic acid (H2NAN), the H2NAN is used as a ligand, a zirconium-containing compound is used in a one-pot method, and the MOF (30-Zr) with super-high stability is synthesized, the material stability is ensured, the material has very high uranium adsorption capacity, and a new direction is provided for the MOF used as a seawater uranium extraction material.

Description

Technical Field

[0001] This invention relates to the fields of new compounds, new materials, and seawater uranium extraction, specifically to a bisnaphthyl anthracene compound, its synthesis method, and its application in the preparation of the seawater uranium extraction material MOF(30-Zr). Background Technology

[0002] Uranium, a core strategic resource for the nuclear energy industry, is primarily obtained through mining. Although terrestrial uranium reserves are approximately 6.3 million tons, these resources will become scarce due to continuously increasing energy demand. The ocean contains about 4.5 billion tons of uranium, almost 1000 times the total available terrestrial uranium. However, the uranium concentration in seawater is low, at 3.3 ppb. Therefore, developing efficient and economical technologies for extracting uranium from seawater is essential.

[0003] On the other hand, the continuous development of nuclear power also poses potential threats to ecological security and human health. Once released from mining and industrial activities, uranium becomes highly toxic in aqueous solutions. Exposure to uranium increases the risk of cancer and / or liver damage, and long-term ingestion can lead to radiation and chemical toxicity. Therefore, capturing and recovering uranium from aqueous solutions is of great significance to human health, environmental protection, and the sustainable development of nuclear energy. Existing uranium adsorption materials have some drawbacks in practical applications, such as slow adsorption rates, poor regeneration capacity, and poor environmental stability. To address these shortcomings, researchers are constantly exploring new materials and improving processes to enhance the efficiency and safety of uranium adsorption and recovery.

[0004] Metal-organic frameworks (MOFs) are based on molecular recognition and self-assembly, assembled from organic ligands or organic bridging groups containing specific coordinating atoms or functional groups and metals as building blocks. The abundance of organic ligands and the diverse coordination modes with metal ions / clusters offer endless possibilities for MOF design and synthesis. To date, MOFs have attracted attention in many fields due to their structural diversity, unique pore environments, and precisely tunable properties. Although MOF materials possess characteristics such as high selective adsorption, high specific surface area, environmental friendliness, and strong regeneration capabilities, only about 300 of the more than 100,000 MOFs synthesized to date are water-stable. Therefore, designing and synthesizing a MOF material capable of adsorbing uranium under seawater conditions is crucial. Summary of the Invention

[0005] To address the problems of poor water, acid, and alkali stability and difficulty in uranium extraction and utilization from seawater caused by existing metal-organic framework structures, this invention prepares a bis-naphthyl anthracene compound, its synthesis method, and its application in preparing a seawater uranium extraction MOF (30-Zr). The prepared bis-naphthyl anthracene compound, 4,4'-(anthracene-9,10-diyl)bis(1-naphthoic acid) (H2NAN), is used as a ligand in a one-pot synthesis with a zirconium-containing compound to produce a MOF (30-Zr) with ultra-high stability. This ensures that the material has both ultra-high acid-base and thermal stability and high uranium adsorption capacity, providing a new direction for the use of MOFs as seawater uranium extraction materials.

[0006] This invention first provides a novel bis-naphthyl anthracene compound, Chinese name 4-[10-(4-carboxynaphth-1-yl)anthracite-9-yl]naphth-1-carboxylic acid (abbreviated as H2NAN), with the molecular formula C 36 H 22 O4, with a relative molecular mass of 518.57, is a yellow solid with the following chemical structural formula:

[0007]

[0008] This invention further provides a method for preparing the above-mentioned H2NAN, comprising the following steps:

[0009] S1. Weigh 2.7g of methyl 4-bromo-1-naphthoic acid, 2.8g of pinacol diboronic acid, 0.1-0.2g of [1,1-bis(diphenylphosphine)ferrocene]palladium dichloride and 2.9-3.5g of potassium acetate, put them into a 500mL three-necked flask, add 200-300mL of anhydrous dioxane, react at 80-100℃ for 1 day under nitrogen atmosphere, cool to room temperature after reaction, dry by rotary evaporation to obtain crude product, purify crude product by column chromatography to obtain product (1);

[0010] S2. The product (1) obtained in step S1, 1.5 g of 9,10-dibromoanthracene, 0.2 g of tetratriphenylphosphine palladium and 9.8 g of cesium carbonate were placed in a 500 mL three-necked flask, and 200-300 mL of anhydrous dioxane was added. The mixture was reacted at 80-100 °C for 3 days under nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was removed by rotary evaporation to obtain the crude product. The crude product was purified by column chromatography to obtain product (2).

[0011] S3. Add product (2) to a single-necked flask, add 50 mL of 5M sodium hydroxide solution and 100 mL of methanol, reflux at 100°C for 3 days, cool to room temperature after the reaction is complete, remove methanol, continue to add deionized water until the solution is clear, add concentrated hydrochloric acid to the clear solution until pH=1, filter and vacuum dry to constant weight to obtain the target product (3).

[0012] The reaction equation is as follows:

[0013]

[0014] Based on the above-mentioned bis-naphthyl anthracene compounds, this invention also prepared a MOF (30-Zr), the specific steps of which are as follows:

[0015] S1. Add 10 mg of H2NAN, 10 mg of zirconium-containing compound and 100-300 mg of regulator to 5 mL of solvent, then add 30 μL of water and sonicate for 10-30 min to form a homogeneous mixed solution;

[0016] S2. Place the mixed solution obtained in S1 into a 10 mL glass bottle, keep it at 100-130℃ for 24-72 h, filter, and obtain MOF(30-Zr) crystals.

[0017] S3. The crystal obtained from filtering in S2 is obtained by washing, exchanging with acetone, and activating.

[0018] Preferably, the zirconium-containing compound is zirconium chloride or zirconium oxychloride octahydrate, and the modifier includes one or more of hydrochloric acid, acetic acid, formic acid, nitric acid, water, methanol, ethanol, and benzoic acid.

[0019] Preferably, the solvent is N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA).

[0020] Preferably, in step S3, the filtered MOF(30-Zr) crystals are first washed three times with DMF, then three times with ethanol, and then soaked in acetone for 24 hours, with the acetone solution being replaced every 6 hours to complete the acetone exchange of the MOF(30-Zr) crystals.

[0021] As a further preferred option, the MOF(30-Zr) crystals were activated at 120°C for 12 hours after being exchanged with acetone.

[0022] The metal-organic framework material MOF(30-Zr) described in this invention has the molecular formula [Zr6(O)4(OH)4(NAN)6]. n It belongs to the monoclinic crystal system, space group Fm-3m, where Zr is a tetravalent zirconium ion, NAN 2-As a deprotonated H2NAN ligand, the secondary structural unit (SBU) in MOF(30-Zr) is a hexanuclear tetravalent metal cluster [Zr6(O)4(OH)4(COO]. 12 The SBU consists of four O ions and four OH ions that alternately coordinate with three Zr ions to form a hexanuclear Zr metal cluster. The SBU is linked by 12 H2NAN ligands, so the overall structure is very stable.

[0023] In summary, this invention synthesizes a MOF (30-Zr) with ultra-high stability using a one-pot method and applies it to the field of seawater uranium extraction. Based on UiO-68, the ligand is modified with naphthalene-anthracene, ensuring both material stability and high uranium adsorption capacity. Experiments show that under simulated seawater conditions, this MOF exhibits a high uranium adsorption capacity, with an absorption rate reaching 97%, demonstrating extremely high adsorption capacity and providing a new direction for the use of MOFs as seawater uranium extraction materials. Attached Figure Description

[0024] Figure 1 : A simplified structural diagram of the MOF(30-Zr) material prepared in Example 5;

[0025] Figure 1 a: a hexanuclear cluster of Zr;

[0026] Figure 1 b: Organic ligands for the MOF(30-Zr) material prepared in Example 5;

[0027] Figure 1 c: Structural diagram of the MOF(30-Zr) material prepared in Example 5;

[0028] Cyan represents the coordination mode of metal clusters, specifically the connection mode of Zr atoms; blue represents octahedral channels; and yellow represents tetrahedral channels.

[0029] Figure 1 d: Tetrahedral cages of MOF(30-Zr) material prepared in Example 5;

[0030] Figure 1 e: Octahedral cage of MOF(30-Zr) material prepared in Example 5;

[0031] Figure 2 X-ray simulation image and powder X-ray image of the MOF(30-Zr) material prepared in Example 5;

[0032] Figure 3 Thermal stability test diagram of MOF(30-Zr) prepared in Example 5;

[0033] Figure 4: The 1H NMR spectrum of the bisnaphthyl anthracene compound (H2NAN) prepared in Example 1;

[0034] Figure 5 Acid-base stability test of MOF(30-Zr) material prepared in Example 5. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the scope of protection of the present invention.

[0036] Unless otherwise specified, the test methods described in the embodiments are conventional methods; unless otherwise specified, the instruments and materials described are commercially available.

[0037] Example 1

[0038] Preparation method of bisnaphthyl anthracene compounds, 4-[10-(4-carboxynaphth-1-yl)anthraphen-9-yl]naphth-1-carboxylic acid, also known as H2NAN:

[0039] The reaction equation is as follows:

[0040]

[0041] The specific steps are as follows:

[0042] S1. Weigh 2.7g of methyl 4-bromo-1-naphthoic acid, 2.8g of pinacol diboronic acid, 0.1g of [1,1-bis(diphenylphosphine)ferrocene]palladium dichloride and 2.9g of potassium acetate, put them into a 500mL three-necked flask, add 300mL of anhydrous dioxane, and react at 80-100℃ for 1 day under nitrogen. After the reaction is completed, cool to room temperature, and dry by rotary evaporation to obtain crude product. Purify crude product by column chromatography to obtain product (1) 3.05g, yield: 97.8%;

[0043] S2. The product (1) obtained in step S1, 1.5 g of 9,10-dibromoanthracene, 0.2 g of tetra-triphenylphosphine palladium and 9.8 g of cesium carbonate were placed in a 500 mL three-necked flask, and 300 mL of anhydrous dioxane was added. The mixture was reacted at 80-100 °C for 3 days under nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was removed by rotary evaporation to obtain the crude product. The crude product was purified by column chromatography to obtain product (2) 2.3 g, yield: 95.8%.

[0044] S3. Add product (2) to a single-necked flask, add 50 mL of 5M sodium hydroxide solution and 100 mL of methanol, reflux at 100°C for 3 days, cool to room temperature after the reaction is complete, remove methanol, and continue to add deionized water until the solution is clear. Add concentrated hydrochloric acid to the clear solution until pH = 1, filter and vacuum dry to constant weight to obtain the target product H2NAN2.1 g, yield: 96.3%.

[0045] The target product H2NAN was detected by means of... Figure 4 The HNMR spectrum shown confirms the formation of this compound. Its 1H NMR data are as follows: 1H NMR (400MHz, DMSO-d6): 13.36 (s, 2H), 9.07 (d, 2H), 8.39 (d, 2H), 7.73 (d, 2H), 7.70 (t, 2H), 7.41 (t, 2H), 7.33 (m, 8H), 7.23 (d, 2H).

[0046] Example 2

[0047] Preparation of MOF(30-Zr):

[0048] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 100 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0049] (2) The solution was placed in a 10ml glass bottle and kept at 100℃ for 48 hours. After filtration, powdered MOF(30-Zr) was obtained.

[0050] (3) The MOF(30-Zr) was first washed three times with DMF, then washed three times with ethanol, and then soaked in acetone for 24 hours. The acetone solution was changed every 6 hours during this period to complete the acetone exchange of MOF(30-Zr) crystals. After the acetone exchange, the MOF(30-Zr) crystals were activated at 120℃ for 12 hours to obtain MOF(30-Zr).

[0051] Example 3

[0052] Preparation of MOF(30-Zr):

[0053] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 100 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0054] (2) The solution was placed in a 10 ml glass bottle and kept at 110 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0055] Example 4

[0056] Preparation of MOF(30-Zr):

[0057] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 100 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0058] (2) The solution was placed in a 10 ml glass bottle and kept at 120 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0059] Example 5

[0060] Preparation of MOF(30-Zr):

[0061] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 100 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0062] (2) The solution was placed in a 10 ml glass bottle and kept at 130 °C for 48 hours. After filtration, crystalline MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0063] Figure 1 The diagram shows the structure of the MOF(30-Zr) obtained above, with the molecular formula [Zr6(O)4(OH)4(NAN)6]. n It belongs to the monoclinic crystal system, space group Fm-3m. See details... Figure 1 (a), where Zr is a tetravalent zirconium ion, NAN 2- As a deprotonated H2NAN ligand, the secondary structural unit (SBU) in MOF(30-Zr) is a hexanuclear tetravalent metal cluster [Zr6(O)4(OH)4(COO]. 12 The SBU consists of four O ions and four OH ions that alternately coordinate with three Zr ions to form a hexanuclear Zr metal cluster. The SBU is linked by 12 H2NAN ligands, so the overall structure is very stable.

[0064] Figure 2The figures show the simulated single-crystal X-ray image and the powder X-ray image of the MOF(30-Zr) material obtained above. It can be seen from the figures that the peak positions of the simulated and tested curves match, indicating that the material has extremely high purity.

[0065] Figure 3 The figure shows the thermal stability test results of the obtained MOF(30-Zr). The figure indicates a slow decrease in mass within the 30-400℃ range, due to the removal of solvent molecules from the material's pores. After 500℃, there is a rapid decrease in mass due to structural collapse. The figure demonstrates that this material possesses extremely high thermal stability, with its highest thermal stability temperature at 500℃.

[0066] Example 6

[0067] Preparation of MOF(30-Zr):

[0068] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 200 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0069] (2) The solution was placed in a 10 ml glass bottle and kept at 100 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0070] Example 7

[0071] Preparation of MOF(30-Zr):

[0072] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 200 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0073] (2) The solution was placed in a 10 ml glass bottle and kept at 110 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0074] Example 8

[0075] Preparation of MOF(30-Zr):

[0076] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 200 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0077] (2) The solution was placed in a 10 ml glass bottle and kept at 120 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0078] Example 9

[0079] Preparation of MOF(30-Zr):

[0080] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 200 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0081] (2) The solution was placed in a 10ml glass bottle and kept at 130℃ for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0082] Example 10

[0083] Preparation of MOF(30-Zr):

[0084] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 300 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0085] (2) The solution was placed in a 10 ml glass bottle and kept at 100 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0086] Example 11

[0087] Preparation of MOF(30-Zr):

[0088] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 300 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0089] (2) The solution was placed in a 10 ml glass bottle and kept at 110 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0090] Example 12

[0091] Preparation of MOF(30-Zr):

[0092] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 300 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0093] (2) The solution was placed in a 10 ml glass bottle and kept at 120 °C for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0094] Example 13

[0095] Preparation of MOF(30-Zr):

[0096] (1) Add 10 mg of H2NAN, 10 mg of zirconium chloride and 300 mg of benzoic acid to 5 ml of DMF and 30 μL of water, and sonicate for 10 minutes to form a homogeneous mixed solution.

[0097] (2) The solution was placed in a 10ml glass bottle and kept at 130℃ for 48 hours. After filtration, powdered MOF(30-Zr) was obtained. Then, it was washed, solvent exchanged and activated in the same way as in Example 2 to obtain MOF(30-Zr).

[0098] Experimental Example 1

[0099] Water and acid / base stability tests of MOF(30-Zr):

[0100] The activated MOF(30-Zr) from Example 5 was divided into 7 portions (10 mg each) and placed in separate 10 ml glass bottles. 5 mL of aqueous solution (pH adjusted with sodium hydroxide and hydrochloric acid) was added to each bottle for the corresponding pH values ​​(1, 3, 5, 7, 9, 11, 13). The bottles were soaked for 7 days, then centrifuged and dried. Powder X-ray diffraction analysis was performed. The test results are referenced. Figure 5 Experiments show that the peak position and intensity of XRD did not change significantly within the pH range of 1-11, indicating that the material has high stability in water and acid / alkali conditions, with a stability range of pH 1-11.

[0101] Experiment Example 2

[0102] Tests for uranium adsorption on MOF(30-Zr):

[0103] Uranium adsorption experiments were conducted in pure water at pH 7 and simulated seawater at pH 8.3 (30g of sea salt was prepared into 1L of simulated seawater using water).

[0104] In a typical procedure, 10 mg of the MOF (30-Zr) prepared in Example 5 was added to 10 mL of 15 ppm uranyl nitrate hexahydrate solution (prepared with pure water and simulated seawater, respectively). The mixture was magnetically stirred (600 rpm) for 1 h at room temperature (approximately 23°C), the adsorbent was separated by centrifugation, and the uranium concentration in the supernatant was analyzed using a UV-Vis spectrophotometer. Azoarsine III dye, acting as a uranium complexing agent, exhibited a strong absorption band at 652 nm. Specific experimental data are as follows.

[0105]

[0106] Experiments show that under simulated seawater conditions, this MOF has a very high uranium adsorption capacity, with a uranium absorption rate of up to 97%, demonstrating extremely high adsorption capacity.

[0107] It is evident that this invention synthesizes a MOF (30-Zr) with ultra-high stability and applies it to the field of seawater uranium extraction. This material is based on UiO-68 and the ligands are modified to ensure material stability and give the material a high uranium adsorption capacity, providing a new direction for the use of MOF as a seawater uranium extraction material.

[0108] Experimental Example 3

[0109] The MOF(30-Zr) in Example 5 was measured by single-crystal X-ray diffraction. The crystal data, bond lengths, and bond angles of MOF(30-Zr) (Example 5) are shown in Tables 1-3 below. The MOF(30-Zr) structure belongs to the monoclinic crystal system, space group Fm-3m, and its cell parameter is the axis length. Axial angles α = 90.000°, β = 90.000°, γ = 90.000°, and unit cell volume is...

[0110] Table 1: Crystal Data

[0111]

[0112]

[0113] Table 2: Typical bond length data for crystals (unit: )

[0114]

[0115]

[0116] Table 3: Typical bond angle data for crystals (unit: °)

[0117]

[0118]

Claims

1. Use of a bisnaphthylanthracene compound in the preparation of a seawater uranium extraction MOF (30-Zr), characterized in that, The chemical structural formula of the binaphthyl anthracene compound is: The specific steps for synthesizing the MOF (30-Zr) are as follows: S1. 10 mg of the binaphthyl anthracene compound, 10 mg of the zirconium-containing compound and 100-300 mg of the adjusting agent are added into 5 mL of the solvent, and then 30 microliters of water is added, and ultrasonic treatment is performed for 10-30 min to form a uniform mixed solution; The adjusting agent is benzoic acid; the solvent is N,N-dimethylformamide or N,N-dimethylacetamide; S2. The mixed solution obtained in S1 is incubated at 100-130 DEG C for 24-72 h, and then filtered; S3. The crystal obtained in S2 is washed, subjected to acetone exchange and activated to obtain the MOF (30-Zr).

2. Use of the bisnaphthylanthracene compound according to claim 1 for the production of a seawater uranium extraction MOF (30-Zr), characterized in that, The zirconium-containing compound is zirconium chloride or zirconium dichloride oxide octahydrate.

3. Use of the bisnaphthylanthracene compound according to claim 1 or 2 for the production of a seawater uranium extraction MOF (30-Zr), characterized in that, After the MOF (30-Zr) is prepared by the S1 and S2 methods, the MOF (30-Zr) crystal is washed with DMF for three times, washed with ethanol for three times, and then soaked in acetone for 24 h, and the acetone solution is replaced every 6 h during the soaking, so that the acetone exchange of the MOF (30-Zr) crystal is completed.

4. Use of the bisnaphthylanthracene compound according to claim 3 for the production of a seawater uranium extraction MOF (30-Zr), characterized in that, After the MOF (30-Zr) crystal is subjected to the acetone exchange, the MOF (30-Zr) crystal is activated at 120 DEG C for 12 h.

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