Ni-mof / nife2o4 heterojunction prepared from waste plastics and application thereof

Abstract

The application relates to a Ni-MOF / NiFe2O4 heterojunction prepared by using waste plastics and an application thereof, and belongs to the technical field of electrocatalysts. The preparation method of the Ni-MOF / NiFe2O4 heterojunction is as follows: a mixed aqueous solution of FeCl3.6H2O and NiCl2.6H2O is uniformly mixed with a DMF dispersion solution of waste plastic PET, a solid obtained after hydrothermal reaction is repeatedly washed with ethanol and deionized water for multiple times, and the solid is dried to obtain the Ni-MOF / NiFe2O4 heterojunction. The mass ratio of the sum of FeCl3.6H2O and NiCl2.6H2O to waste plastic PET is 1:1, and the hydrothermal reaction temperature is 180 DEG C. The Ni-MOF / NiFe2O4 heterojunction is used as an anode catalyst to improve OER performance. Under the premise of the same loading amount of the single-phase material, the catalytic activity of the heterojunction Ni-MOF / NiFe2O4 is significantly improved, which is manifested as a reduction of overpotential, so that the oxygen evolution reaction efficiency is improved; the application uses waste plastics as a MOF matrix, realizes high-value recycling of the waste plastics, reduces environmental pollution, accords with the green and sustainable development concept, the waste plastics are widely sourced and low in cost, traditional high-purity raw materials are replaced, and the MOF synthesis cost is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, and more particularly to a Ni-MOF / NiFe2O4 heterojunction prepared using waste plastics and its applications. Background Technology

[0002] Oxygen evolution reaction (OER) is a key anodic half-reaction in electrochemical energy conversion technologies (such as water splitting and CO2 electroreduction). It involves four electron transfers, exhibits slow intrinsic kinetics, high overpotentials, and significant energy loss, becoming a bottleneck restricting the overall efficiency of devices. Heterogeneous structures can couple the advantages of different components, breaking through the activity limits of single materials, and are considered an ideal approach to achieving high-efficiency OER. Metal-organic frameworks (MOFs) have attracted considerable attention in the field of OER catalysis in recent years due to their high specific surface area and abundant metal sites; however, conventional preparation routes for MOF-based heterojunctions generally suffer from cumbersome steps, time consumption, and high energy consumption, leading to difficulties in scale-up production and high costs, thus limiting their practical application.

[0003] On the other hand, global cumulative plastic production has exceeded 8.3 billion tons, of which polyethylene terephthalate (PET) accounts for approximately 70 million tons annually. The vast majority of this material ends up as waste, causing "white pollution" and potential carbon emissions. Traditional incineration, landfilling, or mechanical recycling all suffer from drawbacks such as high energy consumption, secondary pollution, or product degradation. Chemical recycling can directionally convert PET into 1,4-phthalic acid (H2BDC), and H2BDC is one of the most commonly used organic ligands for synthesizing MOFs. Therefore, waste PET is considered a cheap and sustainable precursor resource for large-scale MOF production.

[0004] In summary, developing a Ni-MOF / NiFe2O4 heterojunction that uses waste PET as a ligand source and is constructed through a simple and low-energy-consumption method to reduce the cost of OER catalysts and realize the high-value utilization and green energy conversion of waste plastics has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a Ni-MOF / NiFe2O4 heterojunction prepared using waste plastics. PET is used as the MOF matrix material, and the mixture is prepared by hydrothermal reaction with FeCl3·6H2O and NiCl2·6H2O. This heterojunction improves the oxygen evolution reaction efficiency, reduces overpotential, and enhances catalytic activity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing Ni-MOF / NiFe2O4 heterojunctions, using waste plastic PET as ligand raw material, mixing it with soluble iron salt and soluble nickel salt and then carrying out a hydrothermal reaction, and the product is post-processed to obtain the Ni-MOF / NiFe2O4 heterojunction.

[0008] Optionally, the soluble iron salt is ferric chloride; the soluble nickel salt is nickel chloride hydrate.

[0009] Furthermore, the molar ratio of the soluble iron salt to the soluble nickel salt is 1:(0.5~4).

[0010] Furthermore, the sum of the amounts of the soluble iron salt and the soluble nickel salt is in a 1:1 ratio to the amount of waste PET plastic.

[0011] Furthermore, the hydrothermal reaction is carried out at a temperature of 180°C for 24 hours.

[0012] Furthermore, before mixing the raw materials, the process includes a step of dispersing the waste plastic PET in DMF.

[0013] Furthermore, the post-processing includes the steps of centrifugation for solid-liquid separation and drying the resulting solid product.

[0014] Furthermore, the drying temperature is 60°C and the drying time is 12 hours.

[0015] The present invention also provides a method for preparing the Ni-MOF / NiFe2O4 heterojunction and the Ni-MOF / NiFe2O4 heterojunction.

[0016] The present invention also provides an application of the Ni-MOF / NiFe2O4 heterojunction as an OER catalyst.

[0017] Compared with the prior art, the present invention has at least the following technical effects:

[0018] 1. This invention uses waste plastics as the MOF matrix to achieve high-value reuse of waste plastics, reduce environmental pollution, and conform to the concept of green and sustainable development. Waste plastics are widely available and inexpensive, and can replace traditional high-purity raw materials, significantly reducing the cost of MOF synthesis, enhancing conductivity and stability, further optimizing catalytic activity, reducing secondary pollution caused by plastic incineration or landfill, and promoting the circular economy model of "waste plastics → functional materials".

[0019] 2. This invention can prepare MOF-based heterojunctions through a simple hydrothermal reaction in one step. Compared with common heterojunction preparation methods, it does not require high-temperature annealing or multi-step composite. The process is simple, energy-efficient, and time-saving. The simplified process leads to a simultaneous reduction in equipment investment and operating costs, and has the prospect of rapid industrialization.

[0020] 3. In this invention, the Ni-MOF / NiFe2O4 heterojunction is used as an OER catalyst, which significantly improves the catalytic activity by reducing the overpotential, thereby improving the oxygen evolution reaction efficiency. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a comparison chart of the OER properties of the materials in Comparative Example 1 and Example 1;

[0023] Figure 2 This is a comparison chart of the OER performance of materials in Comparative Example 1 and Example 2;

[0024] Figure 3 This is a comparison chart of the OER properties of the materials in Comparative Example 1 and Example 3;

[0025] Figure 4 Comparison chart of OER performance of materials in Comparative Example 2 and Examples 1-3;

[0026] Figure 5 The Nyquist plots are for Examples 1-3. Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] This invention provides a method for preparing Ni-MOF / NiFe2O4 heterojunctions. Waste plastic PET is selected as the ligand raw material, and it is mixed with soluble iron salt and soluble nickel salt and subjected to hydrothermal reaction. The product is then post-processed to obtain the Ni-MOF / NiFe2O4 heterojunction.

[0033] In an optional embodiment, the soluble iron salt is ferric chloride; the soluble nickel salt is nickel chloride.

[0034] In some embodiments of the present invention, the preparation method of the Ni-MOF / NiFe2O4 heterojunction specifically includes the following steps: mixing a mixed aqueous solution of FeCl3·6H2O and NiCl2·6H2O with a DMF dispersion solution of waste plastic PET, performing a hydrothermal reaction, and then repeatedly washing the resulting solid with ethanol and deionized water, followed by drying to obtain the Ni-MOF / NiFe2O4 heterojunction.

[0035] PET is a linear polymer formed by the condensation polymerization of terephthalic acid (PTA, HOOC-C6H4-COOH) and ethylene glycol (EG, HOCH2CH2OH) through ester bonds (-O-CO-), with its repeating unit being [-OCH2CH2OCO-C6H4-CO-]. The key reaction site is the ester bond in the PET backbone, which is highly polar and easily broken by nucleophiles (such as water and hydroxyl groups). This is the core basis for PET's participation in hydrothermal reactions.

[0036] Some water molecules dissociate or generate reactive species such as hydroxyl radicals (・OH) and hydroxide ions (OH⁻), providing nucleophiles for ester bond cleavage. High temperature and pressure significantly increase the kinetic energy of water molecules, allowing them to break through the dense layer of the PET surface and penetrate into the amorphous regions of the polymer chain (even defects in some crystalline regions). Water molecules form hydrogen bonds with oxygen atoms in the PET backbone, weakening the van der Waals forces between polymer chains, causing PET to swell (increase the intersegmental spacing), exposing more ester bond sites, creating conditions for subsequent reactions, and ultimately degrading the polymeric PET into oligomers or monomers (PTA, EG).

[0037] In some embodiments of the present invention, the molar ratio of the soluble iron salt to the soluble nickel salt is further 1:(0.5~4).

[0038] In some embodiments of the present invention, the sum of the amounts of the soluble iron salt and the soluble nickel salt is in a 1:1 ratio to the amount of waste PET plastic.

[0039] In some embodiments of the present invention, the hydrothermal reaction is carried out at a temperature of 180°C for 24 hours.

[0040] In some embodiments of the present invention, the step of dispersing the waste plastic PET in DMF is further included before mixing the raw materials.

[0041] In some embodiments of the present invention, the post-processing includes the steps of centrifugation for solid-liquid separation and drying the resulting solid product.

[0042] In some embodiments of the present invention, the drying temperature is 60°C and the drying time is 12 hours.

[0043] This invention also provides a method for preparing the Ni-MOF / NiFe2O4 heterojunction.

[0044] This invention also provides an application of the Ni-MOF / NiFe2O4 heterojunction as an OER catalyst.

[0045] The room temperature in this invention refers to 25±2℃.

[0046] Example 1:

[0047] A Ni-MOF / NiFe2O4 heterostructure is used as an OER catalyst, and the preparation method is as follows:

[0048] Weigh out 8 mmol FeCl3·6H2O and 4 mmol NiCl2·6H2O respectively;

[0049] Dissolve the above reactants in 15 mL of deionized water and stir magnetically until a homogeneous solution A is formed;

[0050] Weigh out 2.3g (12mmol) of waste plastic PET and disperse it in 30mL of DMF, and stir it magnetically to form solution B;

[0051] Mix the above homogeneous solutions A and B, and stir magnetically until a homogeneous mixture C is formed;

[0052] Transfer C to a 100 mL high-pressure reactor, heat to 180 °C, and maintain at this temperature for 24 h;

[0053] After the reaction, allow it to cool naturally to room temperature, collect the solid by centrifugation, and wash it repeatedly with ethanol and deionized water.

[0054] The collected solids were transferred to an oven at 60°C and dried for 12 hours to obtain Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=30%).

[0055] Example 2:

[0056] A Ni-MOF / NiFe2O4 heterostructure is used as an OER catalyst, and the preparation method is as follows:

[0057] Weigh out 4 mmol FeCl3·6H2O and 8 mmol NiCl2·6H2O respectively;

[0058] Dissolve the above reactants in 15 mL of deionized water and stir magnetically until a homogeneous solution A is formed;

[0059] Weigh out another 2.3g of waste PET plastic and disperse it in 30ml of LDMF, and stir it magnetically to form solution B;

[0060] Mix the above homogeneous solutions A and B, and stir magnetically until a homogeneous mixture C is formed;

[0061] Transfer C to a 100 mL high-pressure reactor, heat to 180 °C, and maintain at this temperature for 24 h;

[0062] After the reaction, allow it to cool naturally to room temperature, collect the solid by centrifugation, and wash it repeatedly with ethanol and deionized water.

[0063] The collected solids were transferred to an oven at 60°C and dried for 12 hours to obtain Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=66%).

[0064] Example 3:

[0065] A Ni-MOF / NiFe2O4 heterostructure is used as an OER catalyst, and the preparation method is as follows:

[0066] Weigh out 2.4 mmol FeCl3·6H2O and 9.6 mmol NiCl2·6H2O respectively;

[0067] Dissolve the above reactants in 15 mL of deionized water and stir magnetically until a homogeneous solution A is formed;

[0068] Weigh out 2.3g of waste PET plastic and disperse it in 30mL of DMF, then stir it magnetically to form solution B;

[0069] Mix the above homogeneous solutions A and B, and stir magnetically until a homogeneous mixture C is formed;

[0070] Transfer C to a 100 mL high-pressure reactor, heat to 180 °C, and maintain at this temperature for 24 h;

[0071] After the reaction, allow it to cool naturally to room temperature, collect the solid by centrifugation, and wash it repeatedly with ethanol and deionized water.

[0072] The collected solids were transferred to an oven at 60°C and dried for 12 hours to obtain Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=80%).

[0073] Comparative Example 1

[0074] A single-phase material, NiFe2O4, is prepared by the following method:

[0075] Weigh out 8 mmol FeCl3·6H2O and 4 mmol NiCl2·6H2O respectively;

[0076] Dissolve the above reactants in 15 mL of H2O and 30 mL of LDMF, and stir magnetically until a homogeneous solution is formed.

[0077] The above solution was transferred to a 100 mL high-pressure reactor, heated to 180 °C, and maintained at this temperature for 24 h.

[0078] After the reaction, allow it to cool naturally to room temperature, collect the solid by centrifugation, and wash it repeatedly with ethanol and deionized water.

[0079] The collected solids were transferred to an oven and dried at 60°C for 12 hours to obtain NiFe2O4.

[0080] Comparative Example 2

[0081] A Ni-MOF / NiFe2O4 heterostructure is used as an OER catalyst, and the preparation method is as follows:

[0082] Weigh out 4 mmol FeCl3·6H2O and 8 mmol NiCl2·6H2O respectively;

[0083] Dissolve the above reactants in 15 mL of deionized H2O and stir magnetically until a homogeneous solution A is formed;

[0084] Weigh out 1.99 g (12 mmol) of terephthalic acid and disperse it in 30 mL of DMF, and stir it magnetically to form solution B;

[0085] Mix the above homogeneous solutions A and B, and stir magnetically until a homogeneous mixture C is formed;

[0086] Transfer C to a 100 mL high-pressure reactor, heat to 180 °C, and maintain at this temperature for 24 h;

[0087] After the reaction, allow it to cool naturally to room temperature, collect the solid by centrifugation, and wash it repeatedly with ethanol and deionized water.

[0088] The collected solids were transferred to an oven at 60°C and dried for 12 hours to obtain Ni-Fe-MOFs.

[0089] Test case

[0090] Weigh 3 mg of NiFe2O4 from Comparative Example 1, mix it with 3 mg of carbon powder and dissolve it in a mixed solution containing 450 μL of deionized water, 150 μL of isopropanol and 20 μL of naphthol, and sonicate for 0.5 h; take 200 μL of the above solution and coat it evenly on the treated carbon paper to be used as the working electrode to be tested.

[0091] Weigh 3 mg of Ni-MOF / NiFe2O4 obtained in Examples 1-3, mix it with 3 mg of carbon powder and dissolve it in a mixed solution containing 450 μL of deionized water, 150 μL of isopropanol and 20 μL of naphthol, and sonicate for 0.5 h; take 200 μL of the above solution and coat it evenly on the cleaned carbon paper as the working electrode to be tested.

[0092] In standard water electrolysis tests, it was found that, compared to the single-phase material NiFe2O4, the heterojunction constructed by introducing waste plastics showed varying degrees of improved activity. Figure 1 It can be seen that Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=30%) at 10 mAcm -2 The overpotential at that point decreased by 60mV, due to Figure 2It can be seen that Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=66%) at 10 mAcm -2 The overpotential at that point decreased by 182mV, due to Figure 3 It can be seen that Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=80%) at 10 mAcm -2 The overpotential at the point was reduced by 169 mV. The heterojunction Ni-MOF / NiFe2O4 outperforms the single-phase NiFe2O4 structure, achieving optimal performance at Ni / (Fe+Ni) = 66%.

[0093] Figure 4 This is a comparison chart of the OER performance of Examples 1-3 and Comparative Example 2, provided by... Figure 4 It can be seen that all four catalysts are highly stable. The order of OER performance is: Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=66%) is stronger than Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=80%), which is stronger than Ni-Fe-MOFs, which is stronger than Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=30%). This indicates that the heterojunction catalyst in Example 2 has the best catalytic conductivity.

[0094] Figure 5 The Nyquist plots for Examples 1-3 show that a smaller semicircle radius indicates lower mass transfer resistance and better electrical conductivity in the solution. Figure 5 It can be seen that Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=66%) has the best electrical conductivity.

[0095] Application examples

[0096] Take 3 mg of the product Ni-MOF / NiFe2O4 (Ni / (Fe+Ni)=66%) from Example 2, mix it with 3 mg of carbon powder, add 450 μL of deionized water, 150 μL of isopropanol (dispersant), and 20 μL of Nafion solution, and sonicate for 30 min to form a uniform conductive ink. Then, take 50 mL of this ink and drop it onto a surface with an area of ​​1 cm². 2 The catalyst was dried on hydrophilic carbon paper and the process was repeated four times to form a catalyst loading of 0.967 mg per square centimeter on the carbon paper. 1M KOH was used as the electrolyte, Hg / HgO as the standard reference electrode, and a platinum sheet electrode as the counter electrode. The OER electrolysis reaction was tested using a Chenhua 660E electrochemical workstation with a test range of 0~0.8V (vs. Hg / HgO) and a scan rate of 5mV. When the scan point reached the reaction start point, bubbles were generated continuously in the electrolytic cell. As the scan potential increased, the rate of bubble generation in the electrolytic cell became more intense, to the point that the bubbles adhered to the electrode surface. It was necessary to stir the electrolyte to allow the bubbles to escape and thus improve the contact between the electrode and the electrolyte.

[0097] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a Ni-MOF / NiFe2O4 heterojunction, characterized in that, Waste plastic PET is used as a ligand raw material, and is mixed with soluble iron salt and soluble nickel salt and subjected to hydrothermal reaction. The product is then post-processed to obtain the Ni-MOF / NiFe2O4 heterojunction. The soluble iron salt is selected from ferric chloride; the soluble nickel salt is selected from nickel chloride hydrate. The molar ratio of the soluble iron salt to the soluble nickel salt is 1:(0.5~4). The hydrothermal reaction was carried out at a temperature of 180°C for 24 hours. The process also includes a step of dispersing the waste plastic PET in DMF before mixing the raw materials.

2. The method for preparing Ni-MOF / NiFe2O4 heterojunction according to claim 1, characterized in that, The sum of the amounts of the soluble iron salt and the soluble nickel salt is in a 1:1 ratio with the amount of waste PET plastic.

3. The method for preparing Ni-MOF / NiFe2O4 heterojunction according to claim 1, characterized in that, The post-processing includes centrifugation for solid-liquid separation and drying of the resulting solid product.

4. The method for preparing Ni-MOF / NiFe2O4 heterojunction according to claim 3, characterized in that, The drying temperature is 60°C and the time is 12 hours.

5. A Ni-MOF / NiFe2O4 heterojunction prepared by the method of any one of claims 1-4.

6. The application of the Ni-MOF / NiFe2O4 heterojunction as described in claim 5 as an OER catalyst.

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