METHOD FOR PREPARING METAL ORGANIC FRAMEWORKS USING MICROWAVE-ASSISTED SYNTHESIS AND METAL ORGANIC FRAMEWORKS PREPARED THEREOF

Abstract

The present invention relates to a method for preparing a metal-organic framework, comprising using microwave-assisted synthesis to induce the reaction of a mixture containing a metal precursor and polyethylene terephthalate plastic. The present invention also relates to a metal-organic framework prepared from said method. The method for preparing a metal-organic framework according to the present invention can utilize polyethylene terephthalate plastic waste, which can help to alleviate environmental problems. Furthermore, the method can be carried out easily without requiring cumbersome and complicated steps, and can also save energy during preparation.

Description

[Technical field]

[0001] The chemistry relates to methods for preparing metal-organic frameworks using microwave-assisted synthesis and to metal-organic frameworks prepared therefrom. [Background technology]

[0002] Plastics are synthetic materials that play an important role in daily life and tend to be used more and more due to their desirable properties, cheap price, and ability to be molded into various shapes. Therefore, plastic products are now widely used, and as a result, plastic waste is increasing year by year. Some plastic wastes are materials that do not self-decompose or take hundreds of years to decompose, which causes environmental impacts and problems in the management of plastic waste.

[0003] Polyethylene terephthalate (PET) is one of the plastics commonly used to make products such as beverage bottles, packaging boxes, or bags because it is lightweight, transparent, sticky, and has good impact resistance. However, most of the polyethylene terephthalate plastic waste currently produced is usually buried in landfills or burned in incinerators. Only a small amount is recycled because the recycling process is complex and consists of many steps, starting from sorting the components of the product by type of plastic, cleaning them, subjecting them to chemical processes to break down the chemical components, and molding them into new products. All of these steps not only use a lot of energy, but also have the potential to release harmful chemicals into the environment. Therefore, in order to reduce the impact on the environment, attempts are being made to find approaches to add value to polyethylene terephthalate plastic waste and maximize its use.

[0004] One way of utilizing polyethylene terephthalate plastic waste that is currently being investigated is to use it in the synthesis of metal-organic frameworks. Polyethylene terephthalate consists of a major component that is converted to terephthalic acid (BDC), and therefore can be used as a source of organic linkers in the synthesis of metal-organic frameworks.

[0005] Examples of prior art relating to the application of polyethylene terephthalate plastic waste to the synthesis of metal-organic frameworks are as disclosed in the following patent documents:

[0006] Patent Document 1 discloses a method for preparing metal-organic frameworks by decomposing polyester plastic waste such as PET using polyacid. The method includes the steps of adding a polyacid precursor to a sodium acetate buffer and mixing it until it becomes transparent, adding polyester plastic waste pieces and mixing thoroughly for 60-80 hours using a temperature in the range of 170-190°C, and then cooling, washing and drying it to obtain the product of metal-organic frameworks.

[0007] US Patent No. 5,999,366 discloses a method for preparing metal-organic frameworks using polyethylene terephthalate plastic waste, which involves the solvothermal reaction of Zn(NO3)2·6H2O and polyethylene terephthalate plastic waste at a temperature of 150°C for 24 hours, followed by washing the resulting reaction solution with N-methylpyrrolidone and methanol solutions and drying it under vacuum.

[0008] US Patent No. 5,999,336 discloses the preparation of metal-organic frameworks from plastic waste using mechanochemical synthesis, which was carried out by grinding the reaction mixture by controlling relevant variants such as impact, grinding time, grinding ball size, temperature range, and pressure.

[0009] However, in addition to the aforementioned prior art, there remains a need for the development of the utilization of polyethylene terephthalate plastic waste in the preparation of metal organic frameworks, in particular for the development of a method for the preparation of metal organic frameworks from polyethylene terephthalate plastics that can be conveniently carried out in simple steps and that can save energy and preparation time. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] China Patent Application Publication No. 110283353A [Patent Document 2] China Patent Application Publication No. 108676174A [Patent Document 3] US Patent Application Publication No. 2021122898A1 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide a method for preparing metal-organic frameworks from polyethylene terephthalate plastic waste, which can be easily carried out without cumbersome and complicated steps, and can save energy and preparation time. In particular, the present invention aims to develop a method for preparing metal-organic frameworks from polyethylene terephthalate plastic waste, which does not require terephthalic acid isolation and terephthalic acid purification steps before carrying out the synthesis of the metal-organic frameworks.

[0012] Another object of the present invention is to provide a method for preparing metal organic frameworks from polyethylene terephthalate plastic waste, which can be easily carried out with significantly reduced processing times as compared to commonly available methods for preparing metal organic frameworks from polyethylene terephthalate plastic waste. [Means for solving the problem]

[0013] In one aspect, the present invention relates to a method for preparing a metal organic framework, the method comprising using microwave assisted synthesis to cause a reaction of a mixture comprising a metal precursor and a polyethylene terephthalate plastic.

[0014] In another aspect, the present invention relates to a metal-organic framework prepared from the method according to the present invention.

[0015] The method for preparing metal-organic frameworks using microwave-assisted synthesis according to the present invention can be easily and conveniently carried out with simple steps, saving energy and requiring short processing time while maintaining high yield, and the obtained metal-organic framework products are of similar quality to those produced from the conventional preparation method using purified terephthalic acid as a reactant in the synthesis of metal-organic frameworks. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 shows powder X-ray diffraction (PXRD) patterns of example metal-organic frameworks prepared according to the method of the present invention, and the PXRD pattern of UiO-66 according to theory from a database. [Diagram 2] FIG. 2 is a graph showing N2 adsorption isotherms of example metal-organic frameworks prepared according to the methods of the present invention. [Diagram 3] FIG. 1 is a graph showing thermogravimetric analysis (TGA) of example metal-organic frameworks prepared from polyethylene terephthalate plastic samples obtained from three different sources. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Any embodiment shown in this specification is intended to encompass applications to other embodiments of the invention as well, unless expressly stated otherwise.

[0018] Technical and scientific terms used herein have the meanings understood by those of ordinary skill in the art unless otherwise defined.

[0019] Throughout this invention, the term "about" is used to indicate that any value appearing or indicated herein may vary or deviate. Such variations or deviations are caused by the error of the device or the method used to determine the value.

[0020] The terms "consist of," "comprise," "have," "contain," and "include" are open-ended verbs. For example, any method that "consists of," "includes," "has," "contains," or "includes" an element or elements, or a step or steps, is not limited to only the element or step, or steps or elements, but also encompasses unspecified elements or steps.

[0021] Any tools, devices, methods, materials, or chemicals referred to herein mean tools, devices, methods, materials, or chemicals commonly used or practiced by those of skill in the art, unless otherwise specified.

[0022] All components and / or methods disclosed and claimed in the present invention are intended to include aspects of the present invention that are not specifically described in the claims, but that, according to the judgment of a person skilled in the art, do not require substantially different experiments from the present invention, and that provide the characteristics and usefulness of the aspects of the present invention and provide the same effects as the aspects of the present invention, resulting from the operation, implementation, modification or alteration of any factor. Therefore, substitutes or similarities of the aspects of the present invention, and any slight modifications or changes that are obvious to a person skilled in the art, are considered to be within the spirit, scope and concept of the present invention.

[0023] As used herein, the term "polyethylene terephthalate plastic" encompasses any plastic or copolymer having polyethylene terephthalate as a component, e.g., polyethylene terephthalate plastic that essentially comprises polyethylene terephthalate and may have additives as additional components. For example, polyethylene terephthalate plastic may comprise 80-100 wt%, 85-100 wt%, 85-95 wt%, 80-95 wt%, or 80-90 wt% polyethylene terephthalate based on the total weight of the polyethylene terephthalate plastic. Polyethylene terephthalate plastic according to the present invention may be obtained from different sources, e.g., plastic bottles, plastic fibers, plastic sheets, plastic waste, plastic chips in products, etc.

[0024] The above mentioned objects of the present invention can be achieved by a method for preparing a metal-organic framework, characterized as follows:

[0025] In accordance with the present invention, a method for preparing a metal organic framework comprises using microwave-assisted synthesis to cause the reaction of a mixture comprising a metal precursor and a polyethylene terephthalate plastic.

[0026] In a particular embodiment, the method for preparing a metal-organic framework according to the present invention comprises the steps of: (i) providing a size-reduced polyethylene terephthalate plastic; (ii) providing a mixture comprising a metal precursor and a size-reduced polyethylene terephthalate plastic in a solvent; (iii) reacting the mixture of step (ii) using microwave assisted synthesis; and (iv) separating the reaction product obtained from step (iii), washing the reaction product with a solvent and drying the reaction product; Includes.

[0027] In an alternative embodiment, the method for preparing a metal-organic framework according to the present invention may further comprise a step of microwave-assisted treatment of the size-reduced polyethylene terephthalate plastic under acidic, basic, or neutral conditions prior to carrying out step (ii).

[0028] More specifically, the method for preparing the metal organic framework may further comprise, prior to carrying out step (ii), a step of microwave assisted heating of the size-reduced polyethylene terephthalate plastic for 5 to 30 minutes at a temperature in the range of 150 to 250° C. Preferably, the step of microwave assisted heating of the size-reduced polyethylene terephthalate plastic is carried out under acidic conditions.

[0029] The process for preparing the metal-organic framework according to the present invention is carried out such that the entire reaction is a one-pot synthesis, without the need to separate and purify the terephthalic acid obtained therefrom prior to the microwave-assisted synthesis of the metal-organic framework in step (iii).

[0030] According to the present invention, the size reduced polyethylene terephthalate plastic in step (i) has a particle size of less than 1 cm, such as a particle size in the range of 0.01 to 1 cm, or such as 0.05 to 1 cm.

[0031] In another preferred aspect, the size reduced polyethylene terephthalate plastic in step (i) has a particle size of less than 0.05 cm, such as a particle size in the range of 0.01 to 0.05 cm.

[0032] The polyethylene terephthalate plastic is reduced in size by crushing, cutting, mechanochemical approaches, shearing, tearing, or a combination thereof.

[0033] According to the present invention, a method for preparing a metal organic framework can be achieved by using microwave assisted synthesis to induce the reaction of a mixture comprising a metal precursor and a polyethylene terephthalate plastic. Preferably, the mixture has a weight ratio of metal precursor to polyethylene terephthalate plastic in the range of 0.2-0.6:1.

[0034] In another preferred embodiment, the mixture further comprises an acid. Specifically, the mixture in step (ii) comprises a metal precursor, a size-reduced polyethylene terephthalate plastic, and an acid.

[0035] Preferably, the mixture has a weight ratio of metal precursor to acid in the range of 0.01 to 0.03:1.

[0036] More preferably, the mixture has a weight ratio of polyethylene terephthalate plastic to acid in the range of 0.02 to 0.07:1.

[0037] Examples of acids used in the present invention are nitric acid, hydrochloric acid, sulfuric acid, and mixtures thereof, preferably nitric acid.

[0038] According to the invention, the metal precursor is selected from the group consisting of salts of zirconium (IV), chromium (III), iron (III) and mixtures thereof. Preferably, the metal precursor is a salt of zirconium (IV).

[0039] The zirconium(IV) salt is selected from the group consisting of zirconium tetrachloride (ZrCl4), zirconium oxychloride (ZrOCl2), zirconium oxychloride octahydrate (ZrOCl2·8H2O), zirconium acrylate (Zr(CH2CHCO2)4), and mixtures thereof.

[0040] According to the present invention, the method for preparing metal organic frameworks can be achieved by microwave assisted synthesis using microwave frequencies of 2,450 MHz and above.

[0041] Specifically, the microwave assisted synthesis is carried out by heating the mixture using a power in the range of 100-400 watts at a temperature in the range of 80-160° C. for 10-240 minutes. Preferably, the microwave assisted synthesis is carried out by heating the mixture using a power in the range of 100-400 watts at a temperature in the range of 100-140° C. for 30-90 minutes, more preferably 45-60 minutes.

[0042] As an example, a solvent selected from the group consisting of dimethylformamide, diethylformamide, water, dimethylsulfoxide, and mixtures thereof can be used to carry out step (ii).

[0043] Also, the solvent for washing in step (iv) is selected from the group consisting of acetone, ethyl acetate, methanol, ethanol, and mixtures thereof.

[0044] The separation of the reaction product in step (iv) may be carried out by filtration or centrifugation, and the drying in step (iv) is carried out at a temperature in the range of 80 to 160° C. Preferably, the drying is carried out under vacuum.

[0045] In certain embodiments, the polyethylene terephthalate plastic includes an additive selected from the group consisting of dipentyl phthalate (DPP), di-(2-ethylhexyl) adipate (DEHA), di-octyl adipate (DOA), diisobutyl phthalate (DEP), and mixtures thereof.

[0046] In certain embodiments, the polyethylene terephthalate plastic comprises polyethylene terephthalate in the range of 80-100% by weight of the polyethylene terephthalate plastic.

[0047] The metal-organic framework prepared from the method according to the present invention can be used as a heavy metal pollutant adsorbent, for example, it is used to adsorb arsenic, mercury, or palladium, etc.

[0048] Working Example The present invention will now be described in more detail with reference to the experimental examples and the accompanying drawings, which, however, are not intended to limit the scope of the invention.

[0049] 1. Methods for preparing metal-organic frameworks An example of a metal-organic framework according to the present invention is a UiO-66 material prepared from used polyethylene terephthalate plastic bottles and zirconium salts to determine the preferred conditions as detailed below.

[0050] 1) Cut used polyethylene terephthalate plastic bottles into small pieces of about 0.5-0.7 cm. Then, powder them into particles with a size of less than 425 μm to obtain powdered polyethylene terephthalate plastic.

[0051] 2) A specified amount of nitric acid (HNO3) is added to the powdered polyethylene terephthalate plastic sample and incubated in a container (EasyPrep Plus vessel) for 5 to 30 minutes.

[0052] 3) The mixture obtained from 2) is subjected to microwave irradiation at a temperature of 150°C (power in the range of 100-400 watts) for 5 minutes.

[0053] 4) Add the specified amount of solvent (DMF) and zirconium salt.

[0054] 5) The mixture obtained from 4) is subjected to ultrasonic treatment for 10 minutes and to microwave irradiation (power in the range of 100-400 watts) at a specified temperature for a specified time.

[0055] 6) The obtained metal-organic framework is separated by centrifugation and washed with the solvents DMF and methanol, respectively.

[0056] 7) The resulting metal-organic framework product is dried at a temperature of 80° C. for 12 hours.

[0057] The prepared example metal-organic framework products are further analyzed using powder X-ray diffraction (PXRD) techniques (results shown in FIG. 1); BET specific surface area and pore volume, and N2 adsorption isotherms (results shown in FIG. 2); and thermogravimetric analysis (TGA) (results shown in FIG. 3).

[0058] 2. Investigation of favorable conditions for the preparation of metal-organic frameworks In the present invention, experiments were carried out to investigate the effect of acid content, temperature and time in microwave-assisted synthesis on the synthesized metal-organic framework product, as detailed below.

[0059] 1) Investigation into the effect of acid content Experiments were conducted by preparing metal-organic frameworks according to the method described above using weight ratios of polyethylene terephthalate plastic (hereinafter referred to as "PET") to nitric acid (HNO3) of about 0.02:1, 0.04:1, and 0.07:1, and weight ratios of zirconium tetrachloride (ZrCl4) to nitric acid of about 0.01:1 (10 and 15 ml of HNO3) and 0.03:1 (5 ml of HNO3). The experimental results are shown in Figure 1 and Table 1.

[0060] [Table 1]

[0061] Notes: a Treatment of polyethylene terephthalate plastic with acid using microwaves was carried out at a temperature of 150° C. for 5 min before the addition of -ZrCl4. -Microwave-assisted synthesis of metal-organic framework was carried out at a temperature of 120 °C for 120 min. b HNO3 has a concentration of 65% and a density of 1.39 g / ml. c The percent yield was calculated relative to the initial amount of zirconium.

[0062] The experimental results in FIG. 1 show that the metal-organic frameworks (Examples 1-3) prepared from polyethylene terephthalate plastic samples using the method of the present invention have properties that correspond to and are consistent with the PXRD pattern of UiO-66 according to theory from the database.

[0063] It was further found that yields increased by increasing the weight ratio of polyethylene terephthalate plastic to acid from 0.02:1 (Example 3, 15 ml HNO3) to 0.04:1 (Example 2, 10 ml HNO3) and 0.07:1 (Example 1, 5 ml HNO3), respectively, and by increasing the weight ratio of zirconium tetrachloride to acid from 0.01:1 (Example 2, 10 ml HNO3 and Example 3, 15 ml) to 0.03:1 (Example 1, 5 ml HNO3). Yields of over 70% and up to 84% can be achieved using a weight ratio of polyethylene terephthalate plastic to nitric acid of 0.07:1 and a weight ratio of zirconium tetrachloride to nitric acid of 0.03:1 (Example 3).

[0064] 2) Investigation of the effects of temperature and time in microwave-assisted synthesis Experiments were conducted by preparing metal-organic frameworks according to the method described above using a weight ratio of polyethylene terephthalate plastic to nitric acid of 0.04:1, and a weight ratio of zirconium tetrachloride to nitric acid of 0.01:1, and the results are shown in Figure 1 and Table 2.

[0065] [Table 2]

[0066] Notes: a Treatment of polyethylene terephthalate plastic with acid using microwaves was carried out at a temperature of 150° C. for 5 min before the addition of -ZrCl4. In preparing the examples, about 500 g of powdered polyethylene terephthalate plastic example, about 200 g of zirconium tetrachloride, and 10 ml of nitric acid were used. b The percent yield was calculated relative to the initial amount of zirconium.

[0067] FIG. 1 shows that the metal-organic framework prepared from a polyethylene terephthalate plastic sample using the method of the present invention has properties that correspond to and are consistent with the PXRD pattern of UiO-66 according to theory from the database.

[0068] From the experimental results in Table 2, it was found that, with the same synthesis time (120 min), increasing the temperature of the microwave-assisted synthesis step from 100°C to 120°C and 140°C, respectively, slightly increased the yield, and a yield of 75% or more could be achieved (Examples 2, 4 and 5).

[0069] It was found that at the same synthesis temperature (120 °C), a maximum yield of 50% could be achieved with a synthesis time of only 30 minutes. Increasing the synthesis time from 30 to 60 minutes significantly increased the yield from 50% to 83%, respectively. However, increasing the synthesis time from 60 to 90 minutes reduced the yield percentage from 83% to 73%, respectively.

[0070] 3) Examples of polyethylene terephthalate plastic Experiments were conducted by preparing metal-organic frameworks according to the method described above using examples of polyethylene terephthalate plastic bottle waste from three different sources, with a weight ratio of polyethylene terephthalate plastic to nitric acid of 0.04:1, and a weight ratio of zirconium tetrachloride to nitric acid of 0.01:1, and the experimental results are shown in Figure 3.

[0071] The graph in FIG. 3 shows the thermogravimetric analysis (TGA) of metal-organic frameworks prepared from polyethylene terephthalate plastic waste from different sources. In FIG. 3, it was found that the metal-organic framework products prepared according to the method of the present invention using polyethylene terephthalate plastic samples from three sources showed decomposition corresponding to weight loss percentage of 85.02% (source 1), 86.11% (source 2) and 86.38% (source 3), respectively, and incomplete decomposition with residual ash of 14.98% (source 1), 13.89% (source 2) and 13.62% (source 3). Such experimental results indicate that the metal-organic frameworks from the three sources have similar thermal stability and purity. Therefore, the method for preparing metal-organic frameworks according to the present invention is an effective method because it can be applied to general polyethylene terephthalate plastic waste regardless of the source.

[0072] All of the above experimental results indicate that the method for preparing metal-organic frameworks from polyethylene terephthalate plastic waste according to the present invention can not only help to alleviate environmental issues, but also help to shorten the synthesis time while maintaining a high yield % compared to commonly available methods.

[0073] Best Mode for Carrying Out the Invention The best mode of the present invention is described in the detailed description of the present invention.

Claims

1. 1. A method for preparing a metal organic framework, the method comprising: using microwave assisted synthesis to cause a reaction of a mixture comprising a metal precursor and a polyethylene terephthalate plastic.

2. (i) providing a size-reduced polyethylene terephthalate plastic; (ii) providing a mixture comprising a metal precursor and a size-reduced polyethylene terephthalate plastic in a solvent; (iii) reacting said mixture of step (ii) using microwave assisted synthesis; and (iv) separating the reaction product obtained from step (iii), washing said reaction product with a solvent and drying it; The method of claim 1 , comprising:

3. 3. The method of claim 2, further comprising the step of microwave assisted heating of the size-reduced polyethylene terephthalate plastic at a temperature in the range of 150-250° C. for 5-30 minutes prior to carrying out step (ii).

4. 4. The method of claim 3, wherein the step of microwave assisted heating the size-reduced polyethylene terephthalate plastic is carried out under acidic conditions.

5. The method of any one of claims 2 to 4, wherein the size-reduced polyethylene terephthalate plastic has a particle size of less than 1 cm.

6. 6. The method of claim 5, wherein the size-reduced polyethylene terephthalate plastic has a particle size of less than 0.05 cm.

7. 7. The method of any one of claims 2 to 6, wherein the polyethylene terephthalate plastic is reduced in size by crushing, cutting, mechanochemical approaches, shearing, tearing, or combinations thereof.

8. The method of claim 1 or 2, wherein the mixture has a weight ratio of metal precursor to polyethylene terephthalate plastic in the range of 0.2 to 0.6:

1.

9. The method of claim 1 or 2, wherein the mixture further comprises an acid.

10. The method of claim 9, wherein the mixture has a weight ratio of metal precursor to acid in the range of 0.01 to 0.03:

1.

11. 10. The method of claim 9, wherein the mixture has a weight ratio of polyethylene terephthalate plastic to acid in the range of 0.02 to 0.07:

1.

12. 12. The method of any one of claims 4 or 9 to 11, wherein the acid is nitric acid, hydrochloric acid, sulfuric acid, or a mixture thereof.

13. 11. The method of any one of claims 1, 2, 8 or 10, wherein the metal precursor is selected from the group consisting of salts of zirconium (IV), chromium (III), iron (III), and mixtures thereof.

14. The salt of zirconium (IV) is zirconium tetrachloride (ZrCl ４ ), zirconium oxychloride (ZrOCl ２ ), zirconium oxychloride octahydrate (ZrOCl ２ ・8H ２ O), zirconium acrylate (Zr(CH ２ CHCO ２ ) ４ 14. The method of claim 13, wherein the compound is selected from the group consisting of:

15. 3. The method according to claim 1 or 2, wherein the microwave-assisted synthesis is carried out by using a microwave frequency of 2,450 MHz or higher.

16. 16. The method of any one of claims 1, 2 or 15, wherein the microwave assisted synthesis is carried out by heating the mixture at a temperature in the range of 80-160°C using a power in the range of 100-400 watts for a period of 10-240 minutes.

17. 17. The method of claim 16, wherein the microwave assisted synthesis is carried out by heating the mixture at a temperature in the range of 100-140° C. using a power in the range of 100-400 watts for a period of 30-90 minutes.

18. 3. The method of claim 2, wherein the solvent in step (ii) is selected from the group consisting of dimethylformamide, diethylformamide, water, dimethylsulfoxide, and mixtures thereof.

19. 3. The method of claim 2, wherein the solvent in step (iv) is selected from the group consisting of acetone, ethyl acetate, methanol, ethanol, and mixtures thereof.

20. 3. The method of claim 2, wherein the separation of the reaction products in step (iv) is carried out by filtration or centrifugation.

21. 3. The method of claim 2, wherein the drying in step (iv) is carried out at a temperature in the range of 80 to 160°C.

22. The method of any one of claims 1 to 21, wherein the polyethylene terephthalate plastic comprises an additive.

23. 23. The method of claim 22, wherein the additive is selected from the group consisting of dipentyl phthalate (DPP), di-(2-ethylhexyl) adipate (DEHA), di-octyl adipate (DOA), diisobutyl phthalate (DEP), and mixtures thereof.

24. 23. The method of any one of claims 1 to 8, 11 or 22, wherein the polyethylene terephthalate plastic comprises polyethylene terephthalate in the range of 80-100 wt% of the polyethylene terephthalate plastic.

25. A metal-organic framework prepared from the method of any one of claims 1 to 24.

26. 26. The metal-organic framework according to claim 25 for use as an adsorbent for heavy metal pollutants.

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