Preparation method and application of cuprous oxide / cobaltosic oxide heterojunction composite material

Abstract

The invention provides a preparation method of a cuprous oxide / cobaltosic oxide heterojunction composite material. The preparation method comprises the following steps: S1) growing cobaltous hydroxide on the surface of a carrier in situ; s2) calcining the cobaltous hydroxide, so as to obtain cobaltosic oxide; and S3) carrying out electroreduction deposition on the cobaltosic oxide in a mixed solution containing a copper source and an electrolyte to obtain the cuprous oxide / cobaltosic oxide heterojunction composite material. In the reduction reaction of electro-catalysis of 5-hydroxymethylfurfural, the prepared composite material serves as a catalyst, cuprous oxide serves as a main catalytic site for catalyzing reduction of HMF into DHMF, the capacity of generating active hydrogen through water dissociation is promoted due to existence of a cobaltosic oxide substrate, and therefore the selectivity of the product DHMF is improved; meanwhile, the composite material prepared by the invention shows excellent electrochemical catalysis performance and good cycling stability, and has a great application prospect in an HMF electroreduction reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of 2,5 - dihydroxymethylfuran, and particularly relates to a preparation method and application of a copper oxide / cobalt tetroxide heterojunction composite material. Background Art

[0002] As a renewable non - fossil resource, biomass is considered a potential alternative to meet the strict requirements of environmental protection and sustainable development. 5 - Hydroxymethylfurfural (HMF), as an important biomass - based platform compound, can be obtained by acid - catalyzed dehydration of C6 carbohydrates and can be catalytically reduced to hydrogenated deoxygenated chemicals; 2,5 - Dihydroxymethylfuran (DHMF) is a value - added chemical for synthesizing resins, pharmaceuticals, man - made fibers, and functional polymers. Currently, the conversion of HMF to DHMF mainly occurs under high - temperature and high - pressure conditions, with H2 as the main hydrogenation source in the catalytic process. Therefore, there is an urgent need to develop a mild catalytic method to achieve efficient hydrogenation of HMF to DHMF.

[0003] Recent progress has shown that electrochemical reduction driven by renewable electricity generated from solar energy, wind energy, tides, etc. is a sustainable alternative to thermochemical hydrogenation. In recent years, due to the fact that proton donors such as buffer salts have a medium degree of proton dissociation and may promote the reduction of HMF to DHMF, the research on the electro - reduction of HMF in a protonic acid buffer salt system has received extensive attention. However, during the electrolysis process, H2O can also act as a proton donor to generate active hydrogen species (*H) through the Volmer step for the electro - catalytic hydrogenation (ECH) of HMF. Therefore, it is necessary to consider introducing H2O dissociation sites into the catalyst to accelerate the rate of H2O dissociation to generate active hydrogen species *H. Although noble metals such as Ru, Rh, Ag, Pd have good water - dissociation ability and some works have been published successively. However, due to the high price of noble metals, it is more practically significant to use non - noble - metal - based catalysts to achieve highly selective electro - reduction of HMF under neutral conditions. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a preparation method of a copper oxide / cobalt tetroxide heterojunction composite material. The copper oxide / cobalt tetroxide heterojunction composite material prepared in this application, as a catalyst for the electrochemical reduction of 5 - hydroxymethylfurfural, can highly selectively prepare 2,5 - dihydroxymethylfuran.

[0005] This application provides a preparation method of a copper oxide / cobalt tetroxide heterojunction composite material, including the following steps:

[0006] S1) Mix a cobalt source, an etching agent, and urea in water to obtain a mixed aqueous solution; perform a hydrothermal reaction on the mixed aqueous solution and a carrier to obtain cobalt hydroxide loaded on the surface of the carrier;

[0007] S2) Calcinate the cobaltous hydroxide to obtain cobalt tetroxide;

[0008] S3) Electrochemically reduce and deposit the cobalt tetroxide in a mixed solution containing a copper source and an electrolyte to obtain a cuprous oxide / cobalt tetroxide heterojunction composite material.

[0009] Preferably, in step S1), the etchant includes ammonium fluoride, the cobalt source includes one or more of cobaltous nitrate hexahydrate, cobaltous sulfate heptahydrate, cobaltous chloride hexahydrate, and cobalt acetate, and the carrier is nickel foam.

[0010] Preferably, in step S1), the hydrothermal reaction is carried out in a high-pressure reactor, the temperature of the hydrothermal reaction is 80-140 °C, and the time is 1-3 h.

[0011] Preferably, in step S2), the calcination is carried out in an air atmosphere, the temperature of the calcination is 250-450 °C, and the time of the calcination is 1-5 h.

[0012] Preferably, in step S3), the copper source includes copper sulfate, and the electrolyte includes sodium sulfate; the concentration of the copper source in the mixed solution is 5-18 mM, and the concentration of the electrolyte is 60-100 mM.

[0013] Preferably, in step S3), the electroreductive deposition is carried out under a constant current condition, the current of the electroreductive deposition is -15 to -30 mA, and the time is 5-15 min.

[0014] Preferably, before the hydrothermal reaction, it further includes:

[0015] Clean the carrier with ethanol and hydrochloric acid.

[0016] Preferably, in the cuprous oxide / cobalt tetroxide heterojunction composite material, cubic cuprous oxide particles are dispersed on the cobalt tetroxide nanosheet carrier.

[0017] This application also provides a method for electroreductively preparing 2,5-dihydroxymethylfuran from 5-hydroxymethylfurfural, including the following steps:

[0018] Add 5-hydroxymethylfurfural to the cathode and carry out electrolysis in a three-electrode system of a reference electrode, a counter electrode, and a working electrode and an electrolyte solution to obtain 2,5-dihydroxymethylfuran;

[0019] The material of the working electrode is the cuprous oxide / cobalt tetroxide heterojunction composite material prepared by the preparation method according to any one of claims 1 to 8.

[0020] Preferably, the reference electrode is a silver / silver chloride electrode, the counter electrode is a platinum sheet, the electrolyte solution is 0.1 M sodium sulfate solution, and the electrolysis time is 2 h.

[0021] The present application provides a method for preparing a cuprous oxide / cobalt tetroxide heterojunction composite material. First, a cobalt source, an etchant, and urea are mixed in water to obtain a mixed aqueous solution. Then, the mixed aqueous solution and a carrier are subjected to a hydrothermal reaction. The cobalt hydroxide loaded on the surface of the carrier is calcined to obtain cobalt tetroxide with a flaky structure. Then, the cobalt tetroxide is subjected to electroreductive deposition in a mixed solution containing a copper source and an electrolyte to obtain a cuprous oxide / cobalt tetroxide heterojunction composite material. The cuprous oxide / cobalt tetroxide heterojunction composite material prepared in the present application is used as a catalyst for electrocatalytic preparation of 2,5-dihydroxymethylfuran (DHMF) from 5-hydroxymethylfurfural (HMF). Among them, cuprous oxide is the main catalytic site for catalyzing the reduction of HMF to DHMF. The presence of the cobalt tetroxide substrate promotes the ability of H2O to dissociate to produce active hydrogen, increases the coverage of active hydrogen on the surface of the composite material, thereby inhibiting the formation of by-product BHH, improving the selectivity of DHMF, and realizing the process of highly selective electroreduction of HMF to DHMF by a non-noble metal-based catalyst under neutral conditions. Description of the Drawings

[0022] Figure 1 Scanning electron microscope image of the Cu2O / Co3O4 heterojunction composite material prepared in Example 1;

[0023] Figure 2 Transmission electron microscope image of the Cu2O / Co3O4 heterojunction composite material prepared in Example 1;

[0024] Figure 3 EDS image of the Cu2O / Co3O4 heterojunction composite material prepared in Example 1;

[0025] Figure 4 X-ray diffraction patterns of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0026] Figure 5 Raman spectra of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0027] Figure 6 High-resolution XPS spectra of the Co 2p region of the materials prepared in Example 1 and Comparative Example 1;

[0028] Figure 7 High-resolution XPS spectra of the Cu 2p region of the materials prepared in Example 1 and Comparative Example 2;

[0029] Figure 8High-resolution XPS Auger electron spectra of the materials prepared in Example 1 and Comparative Example 2 in the Cu LMM region;

[0030] Figure 9 Performance comparison chart of HMF conversion rate and DHMF selectivity of the Cu2O / Co3O4 heterojunction composite material prepared in Example 1 at different voltages;

[0031] Figure 10 Performance comparison chart of HMF conversion rate and DHMF selectivity of the Cu2O / Co3O4 heterojunction composite material prepared in Example 1 and the materials of Comparative Example 1 and Comparative Example 2 at a voltage of -1.2 V vs. Ag / AgCl;

[0032] Figure 11 HPLC spectrum of the Cu2O / Co3O4 composite material prepared in Example 1;

[0033] Figure 12 Performance chart of 10-cycle tests of the Cu2O / Co3O4 composite material prepared in Example 1. Detailed implementation manners

[0034] To further understand the present invention, the preferred implementation manners 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] Two major problems existing in the electrocatalysts for HMF electroreduction in the prior art limit their large-scale application: (1) The catalysts mainly focus on noble metals such as Ru, Rh, Ag, Pd, etc., resulting in high costs; (2) The HMF electroreduction system focuses on protonic acid buffer salt systems, while water as a hydrogen source has more practical application prospects. In view of the above problems, the present application provides a preparation method of a cuprous oxide / cobalt tetroxide heterojunction composite material. In the prepared cuprous oxide / cobalt tetroxide heterojunction composite material, Cu2O is the main catalytic site for catalyzing the reduction of HMF to DHMF, and the presence of the Co3O4 substrate promotes the ability of H2O to dissociate to produce active hydrogen, increasing the coverage of active hydrogen on the surface of the composite material, thereby inhibiting the generation of by-product BHH and improving the selectivity of DHMF, realizing the process of highly selective electroreduction of HMF to DHMF by a non-noble metal-based catalyst under neutral conditions. Specifically, the present application provides a preparation method of a cuprous oxide / cobalt tetroxide heterojunction composite material, including the following steps:

[0036] S1) Mix a cobalt source, an etchant, and urea in water to obtain a mixed aqueous solution;

[0037] Perform a hydrothermal reaction on the mixed aqueous solution and a carrier to obtain cobalt hydroxide loaded on the surface of the carrier;

[0038] S2) Calcinate the cobaltous hydroxide to obtain cobalt tetroxide;

[0039] S3) Electrochemically reduce and deposit the cobalt tetroxide in a mixed solution containing a copper source and an electrolyte to obtain a cuprous oxide / cobalt tetroxide heterojunction composite material.

[0040] In the preparation method of the cuprous oxide / cobalt tetroxide heterojunction composite material, the present application first prepares a substrate cobalt tetroxide. First, a cobalt source, an etchant, and urea are mixed in water to obtain a mixed aqueous solution. The mixed aqueous solution and a carrier are subjected to a hydrothermal reaction to obtain cobaltous hydroxide loaded on nickel foam; in the above process, the cobalt source is selected from cobalt sources well-known to those skilled in the art. By way of example, the cobalt source includes one or more of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, cobalt chloride hexahydrate, and cobalt acetate. More specifically, the cobalt source is selected from one of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, cobalt chloride hexahydrate, and cobalt acetate; the etchant is used to etch the carrier to facilitate the formation of flaky cobaltous hydroxide, and the etchant specifically uses ammonium fluoride; the urea is used to provide a weakly alkaline environment for the reaction. In the present application, it is preferred to clean the carrier with ethanol and 1M hydrochloric acid to remove organic substances and oxides on the surface of the carrier; the carrier is conducive to the in-situ formation of flaky cobaltous hydroxide, and in the present application, it specifically includes nickel foam. The hydrothermal reaction is carried out in a high-pressure reaction kettle, the temperature of the hydrothermal reaction is 80-140°C, and the time is 1-3 h; specifically, the temperature of the hydrothermal reaction is 100-140°C, and the time is 1-2 h. The above hydrothermal reaction grows cobaltous hydroxide in-situ on the surface of the carrier.

[0041] The present application then calcines the above cobaltous hydroxide to obtain cobalt tetroxide; the calcination is preferably carried out in a muffle furnace, the calcination is carried out in an air atmosphere, the temperature of the calcination is 250-450°C, and the time of the calcination is 1-5 h; specifically, the temperature of the calcination is 300-450°C, and the time of the calcination is 1-3 h.

[0042] According to the present invention, the obtained cobalt tetroxide is then subjected to electroreductive deposition in a mixed solution containing a copper source and an electrolyte to obtain a cuprous oxide / cobalt tetroxide heterojunction composite material. The copper source is used to provide copper ions in the cuprous oxide in the heterojunction composite material, and it is selected from compounds well-known to those skilled in the art. In some specific embodiments, the copper source includes copper sulfate. The electrolyte is used to provide a neutral electrolyte environment. In some specific embodiments, the electrolyte is selected from sodium sulfate. In the mixed solution, the concentration of copper sulfate is 5-18 mM. In some specific embodiments, the concentration of copper sulfate is 5-15 mM; the concentration of sodium sulfate is 50-100 mM. In some specific embodiments, the concentration of sodium sulfate is 50-55 mM. The electroreductive deposition is carried out under a constant current condition, the current is -15 to -30 mA, and the time is 5-15 min. In some specific embodiments, the current is -15 mA to -28 mA, and the time is 5-12 min.

[0043] The cuprous oxide / cobalt tetroxide heterojunction composite material was prepared according to the above method, in which cubic cuprous oxide particles are dispersed on a cobalt tetroxide nanosheet support. The cuprous oxide / cobalt tetroxide heterojunction composite material prepared in this application can be used as a catalyst for the electroreduction of 5-hydroxymethylfurfural as an electrode material.

[0044] This application also provides a method for preparing 2,5-bis(hydroxymethyl)furan by electroreduction of 5-hydroxymethylfurfural, including the following steps:

[0045] Adding 5-hydroxymethylfurfural to the cathode, and performing electrolysis in a three-electrode system of a reference electrode, a counter electrode and a working electrode and an electrolyte solution to obtain 2,5-bis(hydroxymethyl)furan;

[0046] The material of the working electrode is the cuprous oxide / cobalt tetroxide heterojunction composite material prepared by the preparation method described in the above scheme.

[0047] In the process of preparing 2,5-bis(hydroxymethyl)furan, the reference electrode is a silver / silver chloride electrode, and the counter electrode is a platinum sheet; the electrolyte solution is a 0.1 M sodium sulfate solution, and the electrolysis time is 2 h; during the electrolysis, water serves as a proton donor.

[0048] The method for preparing 2,5-bis(hydroxymethyl)furan by electroreduction of 5-hydroxymethylfurfural in this application is more specifically:

[0049] (a) Electroreduction was carried out in a standard three - electrode system, where the silver / silver chloride electrode was used as the reference electrode, the platinum sheet was used as the counter electrode, and the as - prepared cuprous oxide / cobalt ferrite heterojunction composite material was used as the working electrode. A 0.1 M sodium sulfate solution was used as the electrolyte solution. The foam of the working electrode was cut into a size of 1.0 cm×3 cm, and the geometric surface area for electrocatalytic testing was 2 cm -2 (1.0 cm×2.0 cm);

[0050] (b) Electrochemical tests were carried out on an electrochemical workstation (760e, Shanghai Chenhua Instrument Co., Ltd., China), and all measurements were performed in an H - type (30 mL / cavity) electrolytic cell with a Nafion117 membrane; each time the test was carried out, both chambers were filled with 18 mL of 0.1 M sodium sulfate as the electrolyte, and 10 mM HMF was added to the cathode part, and electrolysis was carried out for 2 h;

[0051] (c) The electrolyzed liquid sample was collected, diluted with deionized water, and analyzed using a high - performance liquid chromatograph (HPLC, LC - 16, Shimadzu Corporation, Japan) equipped with an ultraviolet - visible dual - wavelength detector (SPD - 16); the chromatographic column was (ZORBAXEclipse Plus C18, 4.6×250 mm, 5 μm), the column temperature was 35 °C, water and acetonitrile were used as the mobile phase, and the flow rate was 0.6 mLmin -1 , and the volume fraction of acetonitrile increased from the initial 15% (v / v) to 60% at 4 - 5 min, remained at 60% from 5 - 7 min, and then decreased to 15% from 7 - 8 min; the detection wavelength of the ultraviolet detector was 240 nm; among them, DHMF and HMF were eluted and peaked at about 6.0 and 7.2 min respectively. The concentrations of HMF and DHMF after the reaction were calculated by using the peak area of HPLC and the standard curve, and further calculation could obtain the HMF conversion rate and DHMF selectivity of the catalyst.

[0052] When the Cu - based catalyst is applied to the reduction and hydrogenation reaction of HMF with H2O as the proton donor, due to the instability of the intermediate keto - radical, dimerization reaction occurs, resulting in the production of by - product BHH. Since the hydrogenation of HMF is usually an adsorption - hydrogen - dependent process, the applicant believes that when the surface H* concentration of the material increases, its coupling reaction may be inhibited, and the selectivity of DHMF may be improved. After experiments, the applicant considered introducing metal oxides near Cu to promote the activation of H2O to generate *H, regulate the surface *H coverage, and then regulate the HMF conversion activity of the material.

[0053] The Cu2O / Co3O4 heterojunction composite material prepared by the present invention has the characteristics of multi-functional active sites, where Cu2O is the main catalytic site for catalyzing the reduction of HMF to DHMF, and the presence of the Co3O4 substrate promotes the ability of the catalyst to dissociate H2O to generate active hydrogen. The tandem active site mechanism constructed by the heterojunction interface produces a synergistic effect, which helps to increase the coverage of active hydrogen on the material surface, thereby inhibiting the formation of by-product BHH and improving the selectivity of the main product DHMF. At the same time, based on the in-situ growth method of the material on the surface of nickel foam, the catalyst exhibits excellent cycle stability, providing guarantee for the efficient catalysis of the catalyst.

[0054] The Cu2O / Co3O4 heterojunction composite material prepared by the present invention exhibits high electroreduction catalytic efficiency for HMF under neutral conditions. Its synthesis method is simple, the cost is low, and the stability is excellent, having broad industrial application prospects. The Cu2O / Co3O4 heterojunction composite material provided by this application realizes the process of highly selective electroreduction of HMF to DHMF in a neutral electrolyte through the construction of heterojunction catalytic sites, providing a new idea for the design of novel electrocatalysts.

[0055] To further understand the present invention, the preparation method and application of the copper oxide / cobalt tetroxide heterojunction composite material provided by the present invention will be described in detail below in conjunction with examples. The protection scope of the present invention is not limited by the following examples.

[0056] Example 1

[0057] Dissolve 0.436 g of cobalt nitrate hexahydrate, 0.111 g of ammonium fluoride, and 0.45 g of urea in 50 mL of water and stir to form a clear mixed solution; clean nickel foam (1 cm × 2.5 cm) with ethanol and 1 M HCl to remove surface organic substances and oxides;

[0058] Transfer the mixed solution and nickel foam to a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, seal it, and keep it at 110 °C for 1.5 h. After cooling to room temperature, take out the nickel foam and rinse it several times with pure water to obtain cobalt hydroxide supported on the surface of nickel foam;

[0059] Anneal cobalt hydroxide in a muffle furnace at 623 K in air for 2 h to obtain cobalt tetroxide; after preparing cobalt tetroxide, place it in a solution containing 10 mM copper sulfate and 50 mM sodium sulfate in 80 mL, and carry out a deposition process for 9 min under a constant current condition of -25 mA. The finally obtained Cu2O / Co3O4 heterojunction composite material is used as an electrode material.

[0060] Example 2

[0061] Dissolve 0.422 g of cobalt(II) sulfate heptahydrate, 0.111 g of ammonium fluoride, and 0.45 g of urea in 50 mL of water and stir to form a clear mixed solution; clean the nickel foam (1 cm × 2.5 cm) with ethanol and 1 M HCl to remove surface organic substances and oxides;

[0062] Transfer the mixed solution and the nickel foam to a 100 mL stainless steel autoclave with a Teflon liner, seal it, maintain it at 120 °C for 1.5 h, after cooling to room temperature, take out the nickel foam, rinse it several times with pure water to obtain cobalt(II) hydroxide;

[0063] Anneal the cobalt(II) hydroxide in a muffle furnace at 723 K in air for 3 h to obtain cobalt(II,III) oxide; after preparing the cobalt(II,III) oxide, place it in a solution of 80 mL containing 5 mM copper sulfate and 60 mM sodium sulfate, and carry out a deposition process for 10 min under a constant current condition of -20 mA. Finally, the obtained Cu2O / Co3O4 heterojunction composite material is used as the electrode material.

[0064] Example 3

[0065] Dissolve 0.357 g of cobalt(II) chloride hexahydrate, 0.111 g of ammonium fluoride, and 0.45 g of urea in 50 mL of water and stir to form a clear mixed solution; clean the nickel foam (1 cm × 2.5 cm) with ethanol and 1 M HCl to remove surface organic substances and oxides;

[0066] Transfer the mixed solution and the nickel foam to a 100 mL stainless steel autoclave with a Teflon liner, seal it, maintain it at 100 °C for 2 h, after cooling to room temperature, take out the nickel foam, rinse it several times with pure water to obtain cobalt(II) hydroxide;

[0067] Anneal the cobalt(II) hydroxide in a muffle furnace at 673 K in air for 3 h to obtain cobalt(II,III) oxide; after preparing the cobalt(II,III) oxide, place it in a solution of 80 mL containing 15 mM copper sulfate and 50 mM sodium sulfate, and carry out a deposition process for 5 min under a constant current condition of -28 mA. Finally, the obtained Cu2O / Co3O4 heterojunction composite material is used as the electrode material.

[0068] Example 4

[0069] Dissolve 0.266 g of cobalt(II) acetate, 0.111 g of ammonium fluoride, and 0.45 g of urea in 50 mL of water and stir to form a clear mixed solution; clean the nickel foam (1 cm × 2.5 cm) with ethanol and 1 M HCl to remove surface organic substances and oxides;

[0070] Transfer the mixed solution and nickel foam into a 100 mL stainless-steel autoclave with a PTFE liner, seal it, and maintain it at 140 °C for 1 h. After cooling to room temperature, take out the nickel foam and rinse it several times with pure water to obtain cobaltous hydroxide;

[0071] Anneal the cobaltous hydroxide in a muffle furnace at 573 K in air for 2 h to obtain cobalt tetroxide; after preparing the cobalt tetroxide, place it in a solution of 80 mL containing 5 mM copper sulfate and 100 mM sodium sulfate, and perform a deposition process for 12 min under a constant current condition of -15 mA. The finally obtained Cu2O / Co3O4 heterojunction composite material is used as the electrode material.

[0072] Comparative Example 1

[0073] Dissolve cobalt nitrate hexahydrate, ammonium fluoride, and urea in 50 mL of water and stir to form a clear mixed solution; clean the nickel foam (1 cm × 2.5 cm) with ethanol and 1 M HCl to remove surface organic substances and oxides;

[0074] Transfer the mixed solution and nickel foam into a 100 mL stainless-steel autoclave with a PTFE liner, seal it, and maintain it at 110 °C for 1.5 h. After cooling to room temperature, take out the nickel foam and rinse it several times with pure water to obtain cobaltous hydroxide; anneal the cobaltous hydroxide in a muffle furnace at 623 K in air for 2 h to obtain Co3O4 material.

[0075] Comparative Example 2

[0076] First, mix 170 mL of water with 10 mL of 0.68 M copper sulfate and 3.0 g of polyvinylpyrrolidone (k = 30, MW = 30000) in a round-bottom glass bottle; stir the obtained mixture for 15 - 20 minutes, then add a mixed solution of 10 mL of 0.74 M sodium citrate and 1.2 M anhydrous sodium carbonate dropwise to the above mixture. After about 10 min, slowly add 10 mL of 1.4 M glucose solution dropwise. Keep the obtained solution in a water bath at 80 °C for 2 h, and then naturally cool it to room temperature; filter off the brick-red precipitate, wash it several times with distilled water and absolute ethanol, and finally dry it in vacuum at 60 °C for 8 h. Ultrasonically disperse 10 mg of the prepared Cu2O in 0.8 mL of ethanol, add 20 μL of Nafion (5 wt%), and then drop-coat it on the nickel foam to form a Cu2O material.

[0077] Morphology and structure characterization of the Cu2O / Co3O4 heterojunction composite material prepared in Example 1:

[0078] First, corresponding morphology characterizations of the material were carried out by SEM and TEM: As Figure 1As shown, the scanning electron microscope (SEM) photograph of the Cu2O / Co3O4 heterojunction composite material shows that cubic particles are uniformly dispersed on the nanosheet support. Figure 2 The high-resolution transmission electron microscope (HRTEM) results show that in the Cu2O / Co3O4 heterojunction material, the side length of the Cu2O cube is about 1 μm, and the Co3O4 nanosheet is thin enough in the field of view. In addition, Figure 3 The energy-dispersive X-ray spectroscopy analysis results also further prove that cobalt and copper are distributed on the sheet and cube respectively, confirming that the cube is Cu2O and the sheet is Co3O4.

[0079] From Figure 4 the XRD results, it can be seen that Cu2O (JCPDS No. 65-3288) and Co3O4 (JCPDS No. 76-1802) phases exist in Cu2O / Co3O4, where the peaks of Co3O4 are partially covered by Cu2O and weakened during the electrodeposition process, thus confirming that the synthesized Cu2O is the Cu2O phase. In addition, Figure 5 The Raman spectra of the three materials were recorded. In the figure, the Raman shifts at 184, 458, 503, 595, 654 cm -1 in the Co3O4 spectrum are attributed to the F12g, Eg, F22g, F32g, A1g modes of crystalline Co3O4, and the peaks at 144, 213, 405, 630 cm -1 correspond to the Raman vibration modes of Cu2O. Compared with Co3O4, the peak position of Co3O4 in Cu2O / Co3O4 shows a blue shift, indicating that Co3O4 may experience compressive strain or electron transfer under the induction of Cu2O.

[0080] X-ray photoelectron spectroscopy (XPS) was used to investigate the valence states of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. As Figure 6 , Figure 7 shown, the peaks of Co 2p 3 / 2 and 2p 3 / 2 in Cu2O / Co3O4 are located at 781.4 eV and 932.1 eV respectively. Compared with Co3O4, the peak of Co 2p 3 / 2 shifts towards higher binding energy; while compared with Cu2O, the peak of Cu 2p 3 / 2 shifts towards lower binding energy; the shift of the binding energy indicates that the surface of Cu in Cu2O / Co3O4 becomes electron-rich and there is a charge redistribution effect between Co and Cu. The spectrum of Cu 2p3 / 2 can be split into two peaks, corresponding to Cu + (932.1 eV, 951.9 eV) and Cu 2+ (934.1 eV, 953.8 eV), which may be due to oxidation in the air. In the Cu LMM Auger spectrum Figure 8Among them, the peaks located at ~917 eV and ~918 eV are attributed to Cu(I) and Cu(II) respectively. For the Cu in Cu2O / Co3O4, part (I) shifts towards lower kinetic energy, indicating a change in the chemical environment. These results show that there is an obvious charge transfer at the composite interface between Cu and Co, further proving the successful synthesis of the Cu2O / Co3O4 heterojunction.

[0081] Example 5

[0082] The Cu2O / Co3O4 composite material prepared in Example 1, the Co3O4 prepared in Comparative Example 1, and the Cu2O material prepared in Comparative Example 2 were used as catalysts for the electrochemical HMF reduction reaction respectively.

[0083] Taking Example 1 as an example, the specific method of using this heterojunction material as a catalyst for electrochemical testing is as follows:

[0084] The electrochemical reduction reaction was carried out on an electrochemical workstation (760e, Shanghai Chenhua Instrument Co., Ltd., China), and all measurements were carried out in an H-type (30 mL / cavity) cell with a Nafion117 membrane. The three-electrode system consisted of a solid-state Ag / AgCl electrode, a Pt counter electrode, a working electrode, and the catalyst material prepared above. The foam of the working electrode was cut into a size of 1.0 cm × 3 cm, and the geometric surface area for electrocatalytic testing was 2 cm -2 (1.0 cm × 2.0 cm). Each time a test was carried out, 18 mL of 0.1 M sodium sulfate was used as the electrolyte in both chambers, 10 mM HMF was added to the cathode half-cell part, and electrolysis was carried out for 2 h. After the reaction ended, the solution after the reaction was sampled and tested.

[0085] Example 6

[0086] At room temperature, the catalytic performance of the Cu2O / Co3O4 catalyst was characterized:

[0087] The catalysts prepared in Example 1 and Comparative Examples 1 - 2 were used for the HMF electroreduction reaction. Figure 9 shows the HMF conversion rate and DHMF selectivity shown by Example 1 at different potentials. Among them, when the test voltage is -1.2 V vs. Ag / AgCl, the Cu2O / Co3O4 composite material catalyst shows the best catalytic performance. Figure 10 is a performance comparison chart of Example 1, Comparative Example 1, and Comparative Example 2 at a test voltage of -1.2 V vs. Ag / AgCl. The specific HMF conversion rate and DHMF selectivity can be seen in Table 1;

[0088] Table 1 Comparison of the catalytic performance of different catalysts

[0089]

[0090]

[0091] As can be seen from the table, the Cu2O / Co3O4 heterojunction composite material exhibits the most excellent performance. Compared with each individual component, the combination of Cu2O and Co3O4 greatly improves the selectivity of DHMF.

[0092] The liquid chromatograms of the initial and final samples of different catalysts are as Figure 11 shown. It can be seen from the figure that the unknown peaks appearing in the Cu2O chromatogram are determined to be two isomers of 5,5'-dihydroxymethylfurfural (BHH) through liquid chromatography-mass spectrometry (LC-MS) analysis. The Cu2O / Co3O4 heterojunction composite material present on the Co3O4 substrate can significantly inhibit the generation of by-products and improve the selectivity of DHMF.

[0093] Stability is one of the most important properties of a catalyst. The Cu2O / Co3O4 heterojunction composite material obtained in Example 1 was used as a catalyst for 10 cyclic electrolysis tests; Figure 12 is the performance diagram of the 12-cycle test of the catalyst. The results show that during the 10 cycles of use, the conversion rate of HMF and the selectivity of DHMF of the catalyst both remained above 90%. This shows that the Cu2O / Co3O4 heterojunction composite material synthesized in this example has relatively excellent stability and recyclability as a catalyst.

[0094] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0095] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a cuprous oxide / cobalt tetroxide heterojunction composite material, comprising the following steps: S1) Mix a cobalt source, an etchant, and urea in water to obtain a mixed aqueous solution; perform a hydrothermal reaction on the mixed aqueous solution and a carrier to obtain cobalt hydroxide supported on the surface of the carrier; S2) Calcinate the cobalt hydroxide to obtain cobalt tetroxide; S3) Perform electroreductive deposition of the cobalt tetroxide in a mixed solution containing a copper source and an electrolyte to obtain a cuprous oxide / cobalt tetroxide heterojunction composite material.

2. The preparation method according to claim 1, characterized in that, In step S1), the etchant includes ammonium fluoride, the cobalt source includes one or more of cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, cobalt chloride hexahydrate, and cobalt acetate, and the carrier is nickel foam.

3. The preparation method according to claim 1, characterized in that, In step S1), the hydrothermal reaction is carried out in a high-pressure reaction kettle, the temperature of the hydrothermal reaction is 80-140 °C, and the time is 1-3 h.

4. The preparation method according to claim 1, characterized in that, In step S2), the calcination is carried out in an air atmosphere, the temperature of the calcination is 250-450 °C, and the time of the calcination is 1-5 h.

5. The preparation method according to claim 1, characterized in that, In step S3), the copper source includes copper sulfate, and the electrolyte includes sodium sulfate; the concentration of the copper source in the mixed solution is 5-18 mM, and the concentration of the electrolyte is 60-100 mM.

6. The preparation method according to claim 1, wherein In step S3), the electroreductive deposition is carried out under a constant current condition, the current of the electroreductive deposition is -15 to -30 mA, and the time is 5-15 min.

7. The preparation method according to claim 1, characterized in that, Before performing the hydrothermal reaction, it further includes: Clean the carrier with ethanol and hydrochloric acid.

8. The preparation method according to claim 1, characterized in that, In the cuprous oxide / cobalt tetroxide heterojunction composite material, cubic cuprous oxide particles are dispersed on a cobalt tetroxide nanosheet carrier.

9. A method for electroreductive preparation of 2,5-dihydroxymethylfuran from 5-hydroxymethylfurfural, comprising the following steps: Add 5-hydroxymethylfurfural to the cathode, and perform electrolysis in a three-electrode system of a reference electrode, a counter electrode, and a working electrode and an electrolyte solution to obtain 2,5-dihydroxymethylfuran; The material of the working electrode is the cuprous oxide / cobalt tetroxide heterojunction composite material prepared by the preparation method according to any one of claims 1-8.

10. The method according to claim 9, characterized in that, The reference electrode is a silver / silver chloride electrode, the counter electrode is a platinum sheet, the electrolyte solution is a 0.1 M sodium sulfate solution, and the electrolysis time is 2 h.

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