Electrode material for electrochemical synthesis of nitrogen-containing aromatic compounds, preparation method thereof, and application thereof

Abstract

The present invention discloses an electrode material for electrochemical synthesis of nitrogen-containing aromatic compounds, as well as a preparation method and application thereof. The novel electrocatalytic electrode material is made of a rich copper salt as a raw material, and biomass-derived syringic acid is introduced as a ligand to obtain a novel syringic acid copper-based MOFs nanomaterial, which is applied to the electrocatalytic reaction of aromatics and nitrogen-containing inorganic salts. Under mild conditions, in an aqueous solution, electrochemical C-H activation and C-N coupling reactions are achieved. Moreover, the catalyst exhibits high catalytic activity, selectivity and stability in the electrochemical synthesis of nitrogen-containing aromatic compounds. Therefore, the nanomaterial disclosed in the present invention has broad application prospects in the electrocatalytic synthesis of high-value-added products such as nitrogen-containing aromatic ring compounds, as well as in sewage treatment, lignin solid waste conversion, fuel cells and other energy conversion devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy and environmental treatment, and in particular relates to an electrode material for electrochemically synthesizing nitroaromatic compounds, a preparation method thereof, and an application thereof. Background Art

[0002] Lignin, a naturally occurring polyhydroxyaromatic compound, is a renewable resource second only to cellulose, accounting for approximately a quarter of all terrestrial biomass. However, due to its complex structure and very low utilization rate, its industrial and agricultural applications are limited. Furthermore, approximately 98% of lignin is burned, resulting in the production of large amounts of greenhouse gases and exacerbating the greenhouse effect. Currently, lignin is treated as a waste product from the pulp and paper industry, placing a significant burden on the environment.

[0003] The rapid development of industry and agriculture has led to the depletion of non-renewable fossil energy, the overuse of nitrogen-containing fertilizers, and the massive discharge of industrial wastewater, resulting in nitrates becoming one of the most common pollutants in surface and groundwater. Excessive nitrates in water not only severely disrupt the natural nitrogen cycle but are also easily converted to nitrites by microorganisms in the environment. Once absorbed by the human body, these nitrates can cause liver damage, hyperhemoglobinemia, and even carcinogenic, teratogenic, and mutagenic risks. Consequently, the increasing severity of nitrate contamination in groundwater and surface water threatens human health and ecosystems, and has become an urgent environmental issue that demands resolution.

[0004] Aromatic nitro compounds are an important class of chemical raw materials and synthetic intermediates with widespread applications in production and life. They serve as intermediates for explosives, fragrances, and dyes, and are also important functional groups in many pharmaceuticals and pesticides. Currently, the preparation of aromatic nitro compounds typically involves direct nitration via electrophilic substitution on the aromatic ring, oxidation of aromatic amines, and nitro substitution of aromatic halides. The most classic nitration reaction, in particular, utilizes mixed acids (concentrated nitric acid / concentrated sulfuric acid) as reagents, which presents significant environmental challenges, including the generation of large amounts of waste acid, high equipment corrosion, demanding reaction conditions, and poor atom economy, hindering its development. With increasing demands for environmental and energy resources, the development of green electrochemical synthesis of aromatic nitro compounds will provide a simple, efficient, and renewable pathway for the production of nitrogen-containing chemicals from biomass, significantly expanding the application of biomass resources. In electrocatalytic synthesis, electrode materials are crucial for the electrochemical reaction. Although noble metal catalysts generally exhibit excellent electrocatalytic activity, their high cost and stability limit their practical application. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a simple preparation method and application of an electrocatalyst capable of electrocatalytically synthesizing nitroaromatic compounds and aminoaromatic compounds. To solve the above technical problems, the present invention provides the following technical solution: placing a cleaned conductive substrate electrode in a mixed solution of copper salt, syringic acid and DMF, and stirring the mixed solution evenly; transferring the mixed solution into a 50 mL reactor, reacting under solvent thermal conditions for a period of time, and naturally cooling to room temperature. The obtained sample is washed with anhydrous ethanol and deionized water for more than three times, and then vacuum dried at 60°C overnight to obtain the prepared Cu-based MOFs nanomaterial supported on the conductive substrate.

[0008] As a preferred solution of the present invention, the conductive base electrode material includes one or more of carbon paper, carbon cloth, foamed nickel, foamed copper, and stainless steel mesh.

[0009] As a preferred embodiment of the present invention, the copper salt refers to at least one of nitrate, chloride, sulfate, phosphate, acetate, and carbonate, and can also be expanded to the preparation of nanomaterials corresponding to salts of Mn, Fe, Co, Ni, Cu, and Zn.

[0010] As a preferred embodiment of the present invention, the solvent thermal reaction temperature is 80 to 160 degrees, and the reaction time is more than 10 minutes.

[0011] As a preferred embodiment of the present invention, the solvent may be one or more of N,N-dimethylformamide, methanol, ethanol, ethylene glycol, and isobutanol.

[0012] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of phenol and its derivatives with nitrogen-containing inorganic salt aqueous solutions in the efficient electrocatalytic synthesis of nitroaromatic compounds and aminoaromatic compounds.

[0013] To solve the above technical problems, the present invention provides the following technical solution: using Cu-based MOFs nanomaterials as electrocatalytic catalysts, phenol and its derivatives and nitrogen-containing inorganic salts are efficiently converted into nitroaromatic ring compounds and aminoaromatic compounds through electrocatalytic oxidation and electrocatalytic reduction reactions, thereby converting phenolic substances obtained from lignin into high-value-added chemicals, and providing a green and environmentally friendly electrochemical synthesis method for treating lignin and nitrogen-containing inorganic salt wastewater.

[0014] As a preferred embodiment of the present invention, the phenol and its derivatives include at least one of phenol, 4-methoxyphenol, guaiacol, eugenol, and p-hydroxyphenylpropane, and the concentration thereof is above 0.05M.

[0015] As a preferred embodiment of the present invention, the nitrogen-containing inorganic salt includes one or more of a nitrate aqueous solution, a nitrite aqueous solution, and a NOx-containing salt aqueous solution.

[0016] As a preferred embodiment of the present invention, the high value-added chemicals include one or more of p-aminophenol, p-nitrophenol, o-nitrophenol and their corresponding derivatives.

[0017] As a preferred embodiment of the present invention, the system is a three-electrode system, using an H-type electrolytic cell, a millstone as the counter electrode, HgO / Hg as the reference electrode, the electrolyte solution is a KOH or NaOH aqueous solution, the pH is in the range of 1 to 14, the electrolysis voltage is -3.0V to 3.0V, and the constant voltage reaction is for more than 10 minutes.

[0018] As a preferred solution of the present invention, the electrode material is used in the fields of electrocatalytic organic synthesis, environmental governance, new energy conversion and devices.

[0019] Beneficial effects of the present invention:

[0020] (1) This application provides a nanoflower-like Cu-based MOFs electrode material. This nanomaterial can be rapidly and massively prepared by a solvothermal method, reacting a copper salt with a bio-derived syringic acid ligand. The process is simple, high in yield, minimal environmental pollution, and inexpensive raw materials, resulting in low production costs. The prepared material exhibits excellent performance in the field of electrocatalytic organic synthesis.

[0021] (2) This application provides a method for preparing the aforementioned electrode material. By placing a conductive substrate in a reaction mixture and conducting a rapid reaction under mild conditions via a solvothermal method, the electrode material can be obtained on a large scale. This simple synthesis method and mild conditions facilitate large-scale industrial production.

[0022] (3) This application provides a Cu-based MOFs electrode material that has broad application prospects in the field of electrocatalytic organic synthesis of nitrogen-containing aromatic small molecules, especially in electrocatalytic CN coupling and CH active reactions to synthesize aromatic nitro compounds, aromatic amino groups, amides, nitriles, nitrogen-containing heterocyclic compounds, etc.; it can also be used in electrocatalytic biomass conversion, including lignin, cellulose, hemicellulose, and other fields, as well as electrocatalytic production of hydrogen, ammonia, and fuel cells, with excellent conversion rate, selectivity, high Faradaic efficiency, and good stability. During the entire reaction process, the device is simple, so it has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0024] Figure 1 This is the powder X-ray diffraction pattern of the typical Cu-based MOFs electrode material described in Example 2.

[0025] Figure 2 This is a scanning electron microscope image of the typical Cu-based MOFs electrode material described in Example 3, and the inset is an enlarged image.

[0026] Figure 3 This is the FT-IR spectrum of the Cu-based MOFs electrode material described in Example 4.

[0027] Figure 4 This is a polarization curve diagram of the Cu-based MOFs electrode material described in Example 5 at a scanning rate of 5 mVs-1.

[0028] Figure 5 This is the mass spectrum of the product obtained by catalyzing phenol using Cu-based MOFs as described in Example 6.

[0029] Figure 6 This is the NMR spectrum of the product obtained by catalyzing phenol using Cu-based MOFs as described in Example 7.

[0030] Figure 7 This is the mass spectrum of the product obtained by catalyzing 4-phenoxymethylphenol using Cu-based MOFs as described in Example 8.

[0031] Figure 8 This is the NMR spectrum of the product obtained by catalyzing 4-phenoxymethylphenol using Cu-based MOFs as described in Example 8. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0035] Example 1

[0036] Preparation of Cu-based nanomaterials

[0037] 24cm 2 The nickel foam was ultrasonically treated in 3M HCl for 15 minutes to remove surface oxides, and was ultrasonically treated in acetone for 5 minutes to remove surface organic matter. After rinsing with deionized water, the base electrode was placed in a mixture of 2mmol copper nitrate, 3mmol syringic acid and 15mL DMF and stirred for 30 minutes; the mixture was then transferred to a 50mL reactor, reacted under solvent thermal conditions at 130°C for 30 minutes, and naturally cooled to room temperature. The obtained sample was washed with anhydrous ethanol and deionized water for more than 3 times, and then vacuum dried at 60°C for 10 hours to obtain the prepared Cu-based MOFs nanomaterial supported on a conductive substrate.

[0038] Example 2

[0039] Crystal structure analysis of the sample

[0040] Powder X-ray diffraction was carried out on a D8 X-ray powder diffractometer from Bruker, Germany. The test conditions were a fixed target monochromatic light source Cu-Kα, a wavelength of The scanning range is 5-50°, and the scanning step is 0.02°. Sample 1# is a typical electrode material prepared in Example 1, such as Figure 1 The X-ray diffraction pattern obtained by fitting is consistent with Figure 1 By comparing the patterns obtained by X-ray diffraction test after grinding sample 1# into powder, it can be found that the diffraction peaks of the prepared nanomaterial are consistent with those of the prepared crystalline MOFs, indicating the successful preparation of the nanomaterial with this structure.

[0041] Example 3

[0042] Characterization of sample morphology

[0043] The morphology of the prepared samples was characterized by SEM. Figure 2 The prepared electrode material is a flower-like cluster structure composed of spindle-shaped particles with uniform size. The nanoparticles grow vertically in one dimension, are nanometer-sized, and have a relatively uniform morphology. This morphology of the nanomaterial exposes more reactive sites. The one-dimensional orientation promotes electron and mass transfer during the catalytic process, effectively improving the catalyst's performance.

[0044] Example 4

[0045] The infrared absorption spectrum of sample 1# was measured on a Nicolet 6700 total reflection Fourier transform infrared spectrometer. Figure 3 As shown in the figure, it can be seen that the broad absorption peak of syringic acid ligand is at 3227-3363 cm -1 The peak at 2837cm corresponds to the OH bond. After the ligand and metal combine to form MOF material, the peak disappears, indicating that the unsaturated coordination bond on the ligand is coordinated with the metal. -1 and 617cm -1 The peak at 1110 cm corresponds to the CH vibration. -1 The peak at 1384 cm is attributed to the C-O-C bond, which indicates that the methoxy group still exists on the ligand. -1 and 1665cm -1 The peaks near the α-aminobutyric acid ions correspond to the carboxylate groups (-COO-) between the organic ligands and the metal, which also proves the successful preparation of Cu-based MOFs nanomaterials.

[0046] Example 5

[0047] Polarization curve of electrode material

[0048] The Cu-based MOFs electrode material was used as the working electrode, and the Hg / HgO electrode and the stone mill rod were used as the reference electrode and the counter electrode, respectively. 0.1g phenoxyphenol or phenol (0.08g), 0.2g sodium nitrite were dissolved in 50mL water, and the pH of the solution was adjusted to 13 with concentrated potassium hydroxide solution as the electrolyte and electrolyte. The electrochemical workstation was operated on a Shanghai Chenhua 760E at 5mV·s -1The LSV polarization curve test was performed at a rate of 100 mV / s. Before the linear sweep voltammetry (LSV) test, 20 cycles were scanned at 100 mV / s to reach a steady state, and then the test was performed at a scan rate of 5 mV / s. The potential value was calculated according to the equation E vs RHE = E vs Hg / HgO + 0.098 + 0.059pH, where E vs RHE is the relative reversible hydrogen electrode potential (V) and E vs Hg / HgO is the relative Hg / HgO electrode potential (V). The polarization curve is shown in Figure 2. Figure 4 As shown in the figure, compared with the blank electrode, the Cu-based MOFs nanomaterials as catalysts have excellent performance in catalyzing the nitration of phenol. At the same voltage, the current density is significantly improved, especially at a voltage of 2.0 V (vs RHE), the current density can exceed 100 mA / cm 2 , meeting the industrial current density requirements and can be used in practical industrial production applications.

[0049] Example 6

[0050] Cu-based MOFs nanomaterials were used as catalysts to electrocatalyze 1M potassium hydroxide solution containing 50mM phenol and 50mM sodium nitrite, and the obtained products were characterized by mass spectrometry, such as Figure 5 The figure shows the mass spectrum of the product solution obtained after electrocatalysis. As can be seen from the figure, the CH of phenol is activated by the catalyst, and undergoes a CN coupling reaction with nitrite, and a series of coupling products are obtained through nitration reaction.

[0051] Example 7

[0052] Liquid chromatogram of phenol reaction liquid catalyzed by electrode materials

[0053] Cu-based MOFs nanomaterials were used as catalysts for electrocatalysis of 1 M potassium hydroxide solution containing 50 mM phenol and 50 mM sodium nitrite, and the obtained products were characterized by liquid chromatography, as shown in FIG. Figure 6 Shown is the NMR spectrum after 1 hour of electrocatalytic reaction, confirming that the product is a nitroaromatic compound.

[0054] Example 8

[0055] Cu-based MOFs nanomaterials were used as catalysts to electrocatalyze 1 M potassium hydroxide solution containing 50 mM lignin model compound 4-phenoxymethylphenol and 50 mM sodium nitrite, and the obtained products were characterized by mass spectrometry, such as Figure 7 The mass spectrum of the product solution obtained after electrocatalysis is shown in FIG. As can be seen from the figure, the CH of 4-phenoxymethylphenol is activated by the catalyst and undergoes a CN coupling reaction with nitrite, and a single coupling product is obtained through the nitration reaction. Figure 8The NMR spectra of the resulting products are shown in Figure 2, demonstrating that the catalyst exhibits high activity and selectivity for a variety of substrates. The catalyst is readily available and highly active, facilitating its widespread industrial application. Therefore, this technology has guiding significance for the synthesis of electrocatalytic biomass-based small molecules.

[0056] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. Application of a Cu-based MOFs nanomaterial in the electrochemical synthesis of nitrogen-containing aromatic compounds, characterized by: The Cu-based MOFs nanomaterials synthesize aromatic nitro compounds through electrocatalytic CN coupling and CH active reaction; The application method of the Cu-based MOFs nanomaterial includes: The electrocatalyst material prepared by the solvothermal method is loaded on a conductive substrate and placed in an electrolytic cell containing an aqueous solution of a nitrogen-containing inorganic salt and a phenol-containing substance, and a voltage is applied to carry out an electrocatalytic reaction; The phenol-containing substance in the electrolyte solution of the electrolytic cell is derived from at least one of phenol, 4-methoxyphenol and p-methylphenol.

2. The use according to claim 1, characterized in that: In the application method of the Cu-based MOFs nanomaterial, the electrocatalyst material prepared by the solvothermal method specifically includes mixing a copper salt solution with syringic acid, mixing the mixture with water or an organic solvent respectively with the above solvent, placing the mixture in a polytetrafluoroethylene-lined high-pressure reactor, and reacting at 80-160°C for more than 10 minutes. The final product has a molecular formula of C9H8O5Cu; wherein the organic solvent is one of N,N'-dimethylformamide, methanol, ethanol, and ethylene glycol.

3. The use according to claim 1, characterized in that: In the application method of the Cu-based MOFs nanomaterial, the base electrode of the conductive substrate includes one or more of metal titanium foil, stainless steel, foam copper, foam nickel, carbon felt, carbon paper, and carbon fiber cloth.

4. The use according to claim 1, wherein: In the electrolytic cell of the aqueous solution of the nitrogen-containing inorganic salt and the phenol-containing substance, a voltage is applied for in-situ electrochemical reduction, and the voltage range is -3.0~3.0V against the reversible hydrogen electrode.

5. The use according to any one of claims 1 or 4, characterized in that: In the electrolytic cell containing the aqueous solution of the nitrogen-containing inorganic salt and the phenol-containing substance, the time range for applying voltage to perform in-situ electrochemical reduction is more than 10 minutes.

6. The use according to claim 1, characterized in that: The nitrogen-containing inorganic salts in the electrolyte solution are nitrate, nitrite, and NO x One or more aqueous solutions with a pH range of 1 to 14.

7. The use according to claim 1, wherein: The molar ratio of the phenol-containing substance to the nitrogen-containing inorganic salt in the electrolyte solution is 1:0.01-20.

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