Preparation method of copper oxide / nickel oxide heterojunction material and method for preparing 2, 5-furandicarboxylic acid

Abstract

The invention provides a preparation method of a copper oxide / nickel oxide heterojunction material, which comprises the following steps: S1) soaking foamed nickel in a copper salt solution, and drying and cleaning the obtained modified foamed nickel; and S2) carrying out heat treatment on the modified foamed nickel obtained in the step S1) to obtain the copper oxide / nickel oxide heterojunction material. The invention further provides a method for preparing 2, 5-furandicarboxylic acid through electro-catalysis of 5-hydroxymethylfurfural. In the electrooxidation reaction of the 5-hydroxymethylfurfural, nickel oxyhydroxide generated after reaction reconstruction is a main active site of the reaction, and the generation capacity of the active site and the adsorption and desorption capacity of a substrate and a product can be enhanced by introducing copper oxide, so that the nickel oxyhydroxide can be used as a catalyst for the electrooxidation reaction of the 5-hydroxymethylfurfural. The copper oxide / nickel oxide heterojunction material prepared by the invention shows excellent electrooxidation performance and cycling stability of 5-hydroxymethylfurfural, and shows great application potential in high-value conversion of 5-hydroxymethylfurfural.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of 2,5-furandicarboxylic acid, and in particular to a method for preparing a copper oxide / nickel oxide heterojunction material and a method for preparing 2,5-furandicarboxylic acid. Background Art

[0002] 2,5-Furandicarboxylic acid (FDCA) is a key raw material for the synthesis of polyethylene furanoate (PEF). Due to its unique molecular structure, FDCA imparts excellent biodegradability to PEF. Compared to non-biodegradable polyethylene terephthalate (PET), FDCA, or PEF, can effectively reduce the long-term environmental pollution caused by plastic waste. With the growing demand for environmentally friendly materials, FDCA presents a promising market prospect in the bio-based chemical sector.

[0003] The preparation method of 2,5-furandicarboxylic acid generally adopts a thermal catalytic method, which needs to be carried out under the action of a noble metal-based catalyst under a high temperature and high pressure environment. Its energy consumption is high and has many limitations. In recent years, the electrocatalytic oxidation method that has attracted much attention can achieve high selectivity and high yield production of 2,5-furandicarboxylic acid at room temperature and pressure using a non-noble metal-based catalyst. It is a mild reaction condition, green, and efficient method. However, the existing technology faces problems such as complex catalyst synthesis, poor stability, high cost, and low substrate treatment concentration, which limits the large-scale application of this process. Therefore, developing an efficient, stable and economical electrocatalyst has become the key.

[0004] Metal foam electrodes are commonly used as catalyst supports for electrochemical reactions due to their three-dimensional structure and low cost. Modification methods for metal foams include multi-step hydrothermal, sulfurization, and phosphating. However, the catalysts obtained by these methods suffer from complex and time-consuming synthesis methods, high catalyst costs, low substrate concentrations, and poor catalyst stability, which significantly limit the large-scale production of FDCA. Therefore, there is an urgent need to provide a catalyst with excellent performance, simple synthesis methods, and high stability for the preparation of 2,5-furandicarboxylic acid. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a method for preparing a copper oxide / nickel oxide heterojunction material. The copper oxide / nickel oxide heterojunction material prepared in the present application has excellent HMF conversion rate, FDCA selectivity and catalyst material cycle stability as a catalyst for the electrooxidation of 5-hydroxymethylfurfural.

[0006] In view of this, the present application provides a method for preparing a copper oxide / nickel oxide heterojunction material, comprising the following steps:

[0007] S1) immersing the nickel foam in a copper salt solution, and drying and cleaning the obtained modified nickel foam;

[0008] S2) heat-treating the modified nickel foam obtained in step S1) to obtain a copper oxide / nickel oxide heterojunction material.

[0009] In some specific embodiments, before step S1), the method further includes:

[0010] The nickel foam is firstly subjected to ultrasonic treatment with a hydrochloric acid solution, and then subjected to ultrasonic treatment with ethanol and water respectively.

[0011] In some specific embodiments, the copper salt solution is a 30-80 mM copper salt solution.

[0012] In some specific embodiments, the copper salt in the copper salt solution is copper sulfate, copper chloride or copper nitrate.

[0013] In some specific embodiments, the immersion time is 5 to 60 minutes; and / or the drying temperature is 50 to 80° C. and the drying time is 10 to 15 hours.

[0014] In some specific embodiments, the heating rate of the heat treatment is 1-10° C. / min; and / or the temperature of the heat treatment is 300-500° C.; and / or the time of the heat treatment is 20-120 min.

[0015] In some embodiments, the heat treatment is performed in an air atmosphere.

[0016] The present application also provides a method for preparing 2,5-furandicarboxylic acid by electrocatalysis of 5-hydroxymethylfurfural, comprising:

[0017] The 5-hydroxymethylfurfural solution is electro-oxidized in a three-electrode system, wherein the working electrode of the three-electrode system is the copper oxide / nickel oxide heterojunction material prepared by the preparation method described in the above scheme.

[0018] In some specific embodiments, in the three-electrode system, the reference electrode is a mercury / mercuric oxide electrode, and the counter electrode is a platinum sheet; and / or the electrolyte solution is a 0.5-3 M potassium hydroxide solution; and / or the electro-oxidation is carried out in an H-type electrolytic cell with a Nafion membrane.

[0019] In some specific embodiments, the concentration of the 5-hydroxymethylfurfural solution is 5-10 mM, and / or the voltage of the electro-oxidation is 1.35-1.60V.

[0020] The present application provides a method for preparing a copper oxide / nickel oxide heterojunction material, which comprises first immersing nickel foam in a copper salt solution, causing ion exchange between Cu and Ni to displace Cu into the nickel foam, and then heat-treating the obtained modified nickel foam to obtain a copper oxide / nickel oxide heterojunction composite material; in the process of electrooxidation of 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid, the copper oxide / nickel oxide heterojunction material is used as a catalyst, wherein the nickel oxide is reconstructed during the electrooxidation process to generate nickel oxyhydroxide as a reaction site, and the introduction of copper oxide can enhance the generation capacity of active sites and further enhance the substrate adsorption and product desorption capabilities, thereby improving the electrooxidation performance of the copper oxide / nickel oxide heterojunction material; further, because the copper sites enter the nickel foam skeleton through metal substitution to activate the nickel sites on the nickel foam surface, the copper oxide / nickel oxide heterojunction material can be ensured to have excellent cycle stability and can still maintain excellent electrooxidation performance during long-term operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The scanning electron microscope images of the catalyst materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are shown;

[0022] Figure 2 This is a high-resolution transmission electron micrograph of the catalyst material prepared in Example 1 of the present invention;

[0023] Figure 3 This is an EDS image of the catalyst material prepared in Example 1 of the present invention;

[0024] Figure 4 High-resolution XPS spectra of the Ni 2p region of the catalyst materials prepared in Example 1 of the present invention and Comparative Example 1;

[0025] Figure 5 The high-resolution XPS spectra of the Cu 2p region of the catalyst materials prepared in Example 1 and Comparative Example 2 of the present invention are shown;

[0026] Figure 6 Linear sweep voltammetry curves of the catalyst materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention in a mixed solution containing 10 mM 5-hydroxymethylfurfural and 1 M potassium hydroxide;

[0027] Figure 7 The performance graph of 5-hydroxymethylfurfural conversion, 2,5-furandicarboxylic acid product selectivity and Faraday efficiency of the catalyst material prepared in Example 1 of the present invention at different voltages;

[0028] Figure 8A performance comparison chart of the conversion of 5-hydroxymethylfurfural as a reaction substrate, 2,5-furandicarboxylic acid production capacity, and Faradaic efficiency of the catalyst materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 at 1.45 V vs. RHE;

[0029] Figure 9 This is a graph showing the relationship between the concentrations of reactants, products, and intermediates in the constant potential electrolysis of 5-hydroxymethylfurfural and the transferred charge in the catalyst material prepared in Example 1 of the present invention;

[0030] Figure 10 This is a performance diagram of the 5-hydroxymethylfurfural conversion rate and 2,5-furandicarboxylic acid Faraday efficiency in 100 cycle tests of the catalyst prepared in Example 1 of the present invention.

[0031] Figure 11 A comparison of the selectivity and conversion efficiency of 2,5-furandicarboxylic acid with 5-hydroxymethylfurfural as the reaction substrate at 1.45 V vs. RHE for the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 of the present invention;

[0032] Figure 12 A comparison of the selectivity and conversion efficiency of 2,5-furandicarboxylic acid using 5-hydroxymethylfurfural as a reaction substrate under 1.45 V vs. RHE conditions for the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 7, and Comparative Example 8 of the present invention;

[0033] Figure 13 This is a comparison chart of the selectivity and conversion efficiency of 2,5-furandicarboxylic acid with 5-hydroxymethylfurfural as the reaction substrate under 1.45V vs. RHE conditions for the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 9 and Comparative Example 10 of the present invention. DETAILED DESCRIPTION

[0034] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0035] In view of the requirements of the prior art for the electro-oxidation of 5-hydroxymethylfurfural (HMF) to produce 2,5-furandicarboxylic acid (FDCA) for catalyst cycle stability, HMF conversion rate and FDCA selectivity, the present application provides a method for preparing a copper oxide / nickel oxide heterojunction material. In the copper oxide / nickel oxide heterojunction material prepared by this method, in the electro-oxidation reaction, the nickel oxyhydroxide produced after the reaction reconstruction is the main active site of the reaction, wherein the introduction of copper oxide can enhance the generation ability of the active site and the adsorption and desorption ability of the substrate and product, thereby achieving excellent HMF conversion rate, FDCA selectivity and catalyst cycle stability. Specifically, an embodiment of the present invention discloses a method for preparing a copper oxide / nickel oxide heterojunction material, comprising the following steps:

[0036] S1) immersing the nickel foam in a copper salt solution, and drying and cleaning the obtained modified nickel foam;

[0037] S2) heat-treating the modified nickel foam obtained in step S1) to obtain a copper oxide / nickel oxide heterojunction material.

[0038] In the preparation method of the copper oxide / nickel oxide heterojunction material, the present application first immerses the nickel foam in a copper salt solution, and the obtained modified nickel foam is dried and cleaned; during this process, the nickel foam is preferably pretreated to remove metal objects and oil stains on the surface of the nickel foam, that is, the nickel foam is first ultrasonically treated with a hydrochloric acid solution, and then ultrasonically treated with ethanol and water respectively; during the above pretreatment process, the concentration of the hydrochloric acid solution is 1 to 3M, the ultrasonic treatment time of the hydrochloric acid solution is 10 to 15 minutes, and the ultrasonic treatment time of the ethanol and water is 5 to 10 minutes respectively. After the nickel foam is pretreated, it is immersed in a copper salt solution, and Cu and Ni undergo ion exchange, so that Cu is replaced in the skeleton of the nickel foam; the copper salt solution can be a copper sulfate solution, a copper chloride solution, or a copper nitrate solution. In a specific embodiment, the copper salt solution is a copper sulfate solution. The concentration of the copper salt solution is 30 to 80 mM, specifically, the concentration of the copper salt solution is 40 to 70 mM, more specifically, the concentration of the copper salt solution is 50 to 60 mM; the immersion time is 0 to 60 min, specifically, the immersion time is 5 to 60 min, more specifically, the immersion time is 10 to 30 min; the drying temperature is 50 to 80° C., and the drying time is 10 to 15 h, specifically, the drying temperature is 60 to 70° C., and the drying time is 12 to 14 h.

[0039] The present application then heat-treats the modified nickel foam to obtain a copper oxide / nickel oxide heterojunction material; during this process, the nickel foam is converted into nickel oxide, and the copper ions are converted into copper oxide, thereby obtaining a copper oxide / nickel oxide heterojunction material. The heat treatment can be carried out in a muffle furnace or in a heating furnace, and this application has no particular restrictions on this; the heat treatment is carried out in an air atmosphere, and the temperature rise rate of the heat treatment is 1 to 10°C / min, the temperature is 300 to 500°C, and the time is 20 to 120min; specifically, the temperature rise rate of the heat treatment is 3 to 8°C / min, the temperature is 350 to 450°C, and the time is 30 to 100min; specifically, the temperature rise rate of the heat treatment is 5 to 6°C / min, the temperature is 380 to 400°C, and the time is 35 to 45min.

[0040] Furthermore, the present application also provides a method for electrocatalytically preparing 2,5-furandicarboxylic acid from 5-hydroxymethylfurfural, comprising:

[0041] The 5-hydroxymethylfurfural solution is electro-oxidized in a three-electrode system, wherein the working electrode of the three-electrode system is the copper oxide / nickel oxide heterojunction material prepared by the preparation method described in the above scheme.

[0042] In the process of preparing 2,5-furandicarboxylic acid, the electrooxidation is carried out in an H-type electrolytic cell of a Nafion membrane. In a three-electrode system, the reference electrode is a mercury / mercury oxide electrode, the counter electrode is a platinum sheet, and the working electrode is a copper oxide / nickel oxide heterojunction composite material prepared according to the above scheme; the electrolyte solution is a 0.5-3M potassium hydroxide solution, the concentration of the 5-hydroxymethylfurfural solution is 5-10mM, and the voltage of the electrooxidation is 1.35-1.60V; specifically, the electrolyte solution is a 1-2M potassium hydroxide solution, the concentration of the 5-hydroxymethylfurfural solution is 8-10mM, and the voltage of the electrooxidation is 1.45-1.60V.

[0043] In some specific embodiments, the copper oxide / nickel oxide heterojunction material prepared above is used as a working electrode, and a method for electrocatalytically preparing 2,5-furandicarboxylic acid from 5-hydroxymethylfurfural is performed, and electrochemical testing is performed, specifically as follows:

[0044] (a) Electrochemical tests were performed in a standard three-electrode system with a mercury / mercuric oxide electrode as the reference electrode, a platinum sheet as the counter electrode, a copper oxide / nickel oxide heterojunction material as the working electrode, and a 1 M potassium hydroxide solution as the electrolyte.

[0045] (b) Electrochemical tests were performed on an electrochemical workstation (760e, Shanghai Chenhua Instrument Co., Ltd., China). All measurements were performed in an H-type electrolytic cell (30 mL / chamber) with Nafion 117 membrane. In each test, 18 mL of 1 M potassium hydroxide was used as the electrolyte in both chambers, and 10 mM HMF was added to the anode. The charge transfer temperature during the electrolysis process was controlled at 103 °C.

[0046] (c) Liquid samples were collected, neutralized, and analyzed using a high performance liquid chromatograph (HPLC, LC-16, Shimadzu Corporation, Japan) with a chromatographic column (ZORBAX Eclipse Plus C18, 4.6×250 mm, 5 μm), a column temperature of 35°C, methanol and 5 mM ammonium acetate solution as the mobile phase, a flow rate of 0.6 mL / min, and a UV detector with a detection wavelength of 265 nm. 5-Hydroxymethylfurfural and 2,5-furandicarboxylic acid elute at 13.5 min and 3.2 min, respectively. The concentrations of HMF and FDCA after the reaction were calculated using the HPLC peak area and the standard curve. Further calculations revealed the HMF conversion rate, FDCA selectivity, and Faraday efficiency of the catalyst.

[0047] The present application provides a method for preparing a copper oxide / nickel oxide heterojunction material. The target catalyst copper oxide / nickel oxide heterojunction material can be obtained through a simple impregnation and heat treatment method. In the electrocatalytic oxidation reaction of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, nickel oxide can be reconstructed during the electrooxidation process to generate nickel oxyhydroxide, which can serve as the active site of the reaction. The introduction of copper oxide can enhance the generation capacity of the active sites. In addition, it can further enhance the substrate adsorption and product desorption capabilities, thereby improving the electrooxidation performance of the catalyst. At the same time, because the copper sites in this method enter the skeleton of the nickel foam through metal substitution to activate the nickel sites on the surface of the nickel foam, this method can ensure that the catalyst has excellent cyclic stability and can still maintain excellent electrooxidation performance during long-term operation.

[0048] The copper oxide / nickel oxide heterojunction material prepared by the present invention has the advantages of simple synthesis method, low cost, easy large-scale preparation, and excellent stability, and has broad industrial application prospects. At the same time, the copper oxide / nickel oxide heterojunction material focuses on the electrocatalytic reaction of 5-hydroxymethylfurfural, a typical biomass platform compound molecule, and converts it into 2,5-furandicarboxylic acid, a biological agent plastic monomer, in a targeted high-value manner, which has potential economic benefits. In addition, the heterojunction material prepared by the present invention has obvious synergistic effects, providing new ideas for the design of new electrocatalysts.

[0049] In order to further understand the present invention, the preparation method and application of the copper oxide / nickel oxide heterojunction material provided by the present invention are described in detail below in conjunction with the examples. The protection scope of the present invention is not limited by the following examples.

[0050] Example 1

[0051] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0052] The treated nickel foam was immersed in 50 mM CuSO4 solution for 15 min, and Cu / NF material was obtained due to the ion exchange between Cu and Ni;

[0053] The Cu / NF material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 30 minutes in an air atmosphere to obtain a CuO / NiO catalyst.

[0054] Comparative Example 1

[0055] Nickel foam was ultrasonically treated with 1 M HCl, ethanol, and water for 10 min, 5 min, and 5 min, respectively, to remove metal oxides and oil stains on its surface;

[0056] The treated nickel foam was dried at 60°C for 12 h, calcined in a muffle furnace at a heating rate of 5°C / min, and kept at 400°C for 30 min to finally obtain a NiO catalyst.

[0057] Comparative Example 2

[0058] The copper foam was ultrasonically treated with 1 M HCl, ethanol, and water for 10 min, 5 min, and 5 min, respectively, to remove metal oxides and oil stains on its surface;

[0059] The treated nickel foam was dried at 60° C. for 12 h, calcined in a muffle furnace at a heating rate of 5° C. / min, and kept at 400° C. for 30 min, to finally obtain a CuO catalyst.

[0060] Comparative Example 3

[0061] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0062] The treated nickel foam was immersed in 50 mM CuSO4 solution for 5 min, and Cu / NF-2 material was obtained due to the ion exchange between Cu and Ni;

[0063] The Cu / NF-2 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 30 minutes in an air atmosphere to obtain a CuO / NiO-2 catalyst.

[0064] Comparative Example 4

[0065] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0066] The treated nickel foam was immersed in 50 mM CuSO4 solution for 30 min, and Cu / NF-3 material was obtained due to the ion exchange between Cu and Ni;

[0067] The Cu / NF-3 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 30 minutes in an air atmosphere to obtain a CuO / NiO-3 catalyst.

[0068] Comparative Example 5

[0069] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0070] The treated nickel foam was immersed in 50 mM CuSO4 solution for 45 min, and Cu / NF-4 material was obtained due to the ion exchange between Cu and Ni;

[0071] The Cu / NF-4 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 30 minutes in an air atmosphere to obtain a CuO / NiO-4 catalyst.

[0072] Comparative Example 6

[0073] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0074] The treated nickel foam was immersed in 50 mM CuSO4 solution for 60 min, and Cu / NF-5 material was obtained due to the ion exchange between Cu and Ni;

[0075] The Cu / NF-5 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 30 minutes in an air atmosphere to obtain a CuO / NiO-5 catalyst.

[0076] Comparative Example 7

[0077] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0078] The treated nickel foam was immersed in 50 mM CuSO4 solution for 15 min, and Cu / NF-6 material was obtained due to the ion exchange between Cu and Ni;

[0079] The Cu / NF-6 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 60 minutes in an air atmosphere to obtain a CuO / NiO-6 catalyst.

[0080] Comparative Example 8

[0081] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0082] The treated nickel foam was immersed in 50 mM CuSO4 solution for 15 min, and Cu / NF-7 material was obtained due to the ion exchange between Cu and Ni;

[0083] The Cu / NF-7 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 120 min in an air atmosphere to obtain a CuO / NiO-7 catalyst.

[0084] Comparative Example 9

[0085] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0086] The treated nickel foam was immersed in 50 mM CuCl2 solution for 15 min, and Cu / NF-8 material was obtained due to the ion exchange between Cu and Ni;

[0087] The Cu / NF-8 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 30 minutes in an air atmosphere to obtain a CuO / NiO-8 catalyst.

[0088] Comparative Example 10

[0089] The nickel foam was ultrasonically treated with 1M HCl for 10 minutes to remove metal oxides and oil stains on its surface, and then ultrasonically treated with ethanol and water for 5 minutes respectively to obtain the treated nickel foam.

[0090] The treated nickel foam was immersed in 50 mM Cu(NO3)2 solution for 15 min, and Cu / NF-9 material was obtained due to the ion exchange between Cu and Ni;

[0091] The Cu / NF-9 material was placed in a muffle furnace at a heating rate of 5°C / min and kept at 400°C for 60 min in an air atmosphere to obtain a CuO / NiO-9 catalyst.

[0092] Example 2

[0093] Morphology and structural characterization of the CuO / NiO heterojunction catalyst material prepared in Example 1:

[0094] like Figure 1 As shown, Figure 1 The scanning electron microscope images of CuO / NiO, NiO and CuO prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are shown; Figure 1 It can be seen that the NiO prepared in Comparative Example 1 presents a relatively smooth surface (as shown in Figure b), the CuO surface prepared in Comparative Example 2 shows a rough and uneven characteristic (as shown in Figure c), and the CuO / NiO prepared in Example 1 greatly increases the roughness of the material surface (as shown in Figure a), thereby increasing the active area of CuO / NiO.

[0095] Furthermore, HRTEM provides direct evidence for the existence of abundant heterogeneous interfaces between two closely contacting crystal planes. Figure 2 The lattice fringe spacing of 0.214 nm corresponds to the (111) crystal plane of CuO, and the lattice fringe spacing of 0.206 nm and 0.242 nm can well correspond to the (111) and (200) crystal planes of NiO. In addition, Figure 3 The energy dispersive spectroscopy (EDS) spectrum of CuO / NiO shows a uniform distribution of Ni, Cu and O, which further indicates the successful formation of the CuO / NiO heterojunction catalyst.

[0096] In order to further explore the valence distribution of metallic Cu and Ni elements in the catalyst and the electronic interaction between the two, the Cu 2p and Ni 2p of the CuO / NiO catalyst prepared in Example 1, the Ni 2p of the NiO catalyst prepared in Comparative Example 1, and the Cu 2p of the CuO catalyst in Comparative Example 2 were compared and analyzed. The results showed that there is obvious charge transfer between Cu and Ni. Specifically, for the Ni element, the binding energy of the heterojunction catalyst is shifted by 0.4 eV toward the high field direction relative to that of NiO alone, and it tends to lose electrons (such as Figure 4 ), for copper, the binding energy of the heterojunction catalyst shifts 0.9eV toward the low field direction relative to the binding energy of CuO alone, tending to gain electrons (such as Figure 5 These results indicate that there is an obvious charge transfer between the composite interface of Cu and Ni, which further proves the successful synthesis of CuO / NiO heterojunction.

[0097] Example 3

[0098] Polarization curve tests were performed using the CuO / NiO catalyst prepared in Example 1, the NiO prepared in Comparative Example 1, and the CuO catalyst prepared in Comparative Example 2, respectively. The specific method was as follows: using an electrochemical workstation (760e, Shanghai Chenhua Instrument Co., Ltd., China), in a typical three-electrode H-type electrolytic cell with 1 M potassium hydroxide electrolyte solution on both sides, and a 10 mM 5-hydroxymethylfurfural solution added to one side of the working electrode, a linear sweep voltammetry test was performed in the voltage range of 1.2 to 1.8 V relative to the standard hydrogen electrode, at a sweep rate of 5 mV / s.

[0099] like Figure 6 As shown in the figure, compared with NiO and CuO catalysts, the CuO / NiO catalyst with heterojunction structure exhibits a lower starting potential and a larger current density, indicating that it has better electrooxidation activity for 5-hydroxymethylfurfural.

[0100] Example 4

[0101] Characterization of the catalytic performance of CuO / NiO heterojunction catalyst at room temperature:

[0102] The catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 were used to selectively electrooxidize 5-hydroxymethylfurfural to produce 2,5-furandicarboxylic acid according to the method of Example 3. Figure 7 The 5-hydroxymethylfurfural conversion rate, 2,5-furandicarboxylic acid selectivity and Faradaic efficiency shown in Example 1 at different potentials show the highest catalytic performance at 1.45 V, where the conversion rate reaches 100%, and the selectivity and Faradaic efficiency are 99.7%. Figure 8 Table 1 shows the conversion, selectivity, and Faradaic efficiency of Example 1, Comparative Example 1, and Comparative Example 2 at a test voltage of 1.45 V. The results show that the CuO / NiO heterostructure catalyst exhibits the best electrooxidation activity, with its HMF conversion and FDCA selectivity far exceeding those of the CuO and NiO alone, further demonstrating the superiority of the heterojunction.

[0103] Table 1 Comparative data of catalytic performance of different catalysts

[0104] Group catalyst HMF conversion rate / % FDCA selectivity / % FE / % Example 1 CuO / NiO 100 99.7 99.7 Comparative Example 1 NiO 43.7 33.6 50.4 Comparative Example 2 CuO 33.1 30.1 44.9

[0105] Figure 9A graph showing the relationship between the concentrations of reactants, reactants, products, and intermediates as a function of transferred charge during the constant potential electrolysis of the CuO / NiO heterojunction catalyst prepared in Example 1 at a potential of 1.45 V vs. RHE. The figure shows that the concentrations of the intermediates HMFCA and FFCA remain low throughout the electrolysis process, indicating that the heterostructured catalyst has excellent kinetic activity.

[0106] Stability is one of the most important properties of a catalyst. The CuO / NiO catalyst prepared in Example 1 was subjected to 100 cycles of electrolysis testing. Figure 10 The figure shows the performance of the catalyst after 100 cycles of testing. The results show that during the 100 cycles, the HMF conversion rate and FDCA selectivity of the catalyst were maintained above 95%, indicating that the CuO / NiO catalyst prepared in this application has relatively excellent stability and recycling performance.

[0107] Example 5

[0108] The effects of different impregnation times on catalyst performance were further compared: the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5 and Comparative Example 6 were used to selectively electrooxidize 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid according to the method of Example 3. Figure 11 The figure shows a comparison of the 5-hydroxymethylfurfural conversion rate and 2,5-furandicarboxylic acid selectivity under different impregnation conditions. The results show that the impregnation of Cu salt can effectively improve the 5-hydroxymethylfurfural oxidation performance of the catalyst. The performance improvement is the best when the impregnation is 15 minutes, at which time the conversion rate reaches 100% and the selectivity is 99.7%.

[0109] Example 6

[0110] The effect of calcination time on catalyst performance was further compared: the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 7 and Comparative Example 8 were used to selectively electrooxidize 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid according to the method of Example 3. Figure 12 The figure shows the comparison of 5-hydroxymethylfurfural conversion and 2,5-furandicarboxylic acid selectivity under different calcination conditions. The results show that the performance is best when the calcination time is 30 minutes, and the conversion rate and selectivity can reach 100% and 99.7% respectively.

[0111] Example 7

[0112] The modification effects of different copper salts were further compared: the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 9 and Comparative Example 10 were used to selectively electrooxidize 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid according to the method of Example 3. Figure 13The figure shows a comparison of the 5-hydroxymethylfurfural conversion rate and 2,5-furandicarboxylic acid selectivity under different copper salt modifications. The results show that copper salt modification can significantly improve the oxidation performance of NiO, among which CuSO4 has the best modification effect, with the conversion rate and selectivity reaching 100% and 99.7% respectively.

[0113] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0114] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a copper oxide / nickel oxide heterojunction material, comprising the following steps: S1) immersing the nickel foam in a copper salt solution, and drying and cleaning the obtained modified nickel foam; S2) heat-treating the modified nickel foam obtained in step S1) to obtain a copper oxide / nickel oxide heterojunction material.

2. The preparation method according to claim 1, characterized in that Before step S1), the method further includes: The nickel foam is firstly subjected to ultrasonic treatment with a hydrochloric acid solution, and then subjected to ultrasonic treatment with ethanol and water respectively.

3. The preparation method according to claim 1, characterized in that The copper salt solution is a 30-80 mM copper salt solution.

4. The preparation method according to claim 1 or 3, characterized in that The copper salt in the copper salt solution is copper sulfate, copper chloride or copper nitrate.

5. The preparation method according to claim 1, characterized in that The immersion time is 5 to 60 minutes; and / or the drying temperature is 50 to 80° C. and the drying time is 10 to 15 hours.

6. The preparation method according to claim 1, characterized in that The heating rate of the heat treatment is 1 to 10° C. / min; and / or the temperature of the heat treatment is 300 to 500° C., and / or the time of the heat treatment is 20 to 120 min.

7. The preparation method according to claim 1, characterized in that The heat treatment is performed in an air atmosphere.

8. A method for electrocatalytically preparing 2,5-furandicarboxylic acid from 5-hydroxymethylfurfural, comprising: The 5-hydroxymethylfurfural solution is electro-oxidized in a three-electrode system, wherein the working electrode of the three-electrode system is the copper oxide / nickel oxide heterojunction material prepared by the preparation method according to any one of claims 1 to 7.

9. The preparation method according to claim 8, characterized in that In the three-electrode system, the reference electrode is a mercury / mercuric oxide electrode, and the counter electrode is a platinum sheet; and / or the electrolyte solution is a 0.5-3M potassium hydroxide solution; and / or the electro-oxidation is carried out in an H-type electrolytic cell with a Nafion membrane.

10. The preparation method according to claim 9, characterized in that The concentration of the 5-hydroxymethylfurfural solution is 5-10 mM, and / or the voltage of the electro-oxidation is 1.35-1.60V.

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