Ni-MOF photoanode, preparation method thereof and application of the photoanode in photoelectrocatalytic oxidation of furfural to prepare furfuroic acid

Abstract

This invention discloses a method for preparing and applying a highly selective photoelectrocatalytic oxidation electrode for furfural compounds. Using TEMPO radical-functionalized organic ligands (H2TPDC-TEMPO), benzothiadiazole-functionalized organic ligands (H2BTDB), and nickel salts as raw materials, a Ni-MOF photoanode material is prepared through a one-step solvothermal in-situ growth process. A highly efficient photoelectrocatalytic synergistic catalytic system is constructed. This material can efficiently catalyze the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid under low potential conditions, with a product yield exceeding 90.4% and a Faradaic efficiency of 98.2%. Furthermore, the material exhibits excellent structural stability, maintaining stable catalytic activity even after 10 cycles. This invention provides a simple, environmentally friendly, and efficient new solution for the high-value photoelectrocatalytic conversion of furfural compounds, possessing significant practical application value in the fields of green organic synthesis and biomass resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalytic organic synthesis, specifically relating to a method for preparing a bifunctionalized nickel-based metal-organic framework photoanode of TEMPO radical and benzothiadiazole, and its application in the photoelectrocatalytic oxidation of furfural. Background Technology

[0002] 5-Hydroxymethylfurfural (HMF), derived from sustainable biomass resources, is considered one of the key bio-based platform molecules for producing various value-added chemicals through multi-electron-particulate oxidation reactions, such as 2,5-furanic acid (FDCA), 5-hydroxymethyl-2-furanic acid (HMFCA), and 2,5-dicarboxyfuran (DFF). Among these oxidation products, FDCA can serve as a precursor for the production of bio-based polymers, with wide applications in engineering plastics, pharmaceuticals, and textiles. Typically, FDCA can be obtained from HMF through thermochemical oxidation, chemical oxidation, and electrocatalytic oxidation. More importantly, the electrocatalytic HMF oxidation reaction (HMFOR) can serve as an alternative oxidation half-reaction, replacing the kinetically sluggish oxygen evolution reaction (OER) in alkaline water electrolysis. This can significantly improve the electrocatalytic performance of the hydrogen evolution reaction, with the obtained value-added FDCA as the main oxidation product.

[0003] 2,2,6,6-Tetramethylpiperidin-1-oxy (TEMPO) and its derivatives are stable nitride radicals that have attracted widespread attention due to their excellent stability, high efficiency / selectivity, and high catalytic activity. TEMPO radicals are widely used in the catalytic oxidation of organic functional groups. However, in TEMPO radical-mediated electrocatalytic oxidation of organic functional groups, various problems exist due to its homogeneous role as a co-catalyst, such as large amounts of nitride radicals, low reaction current density, and difficulties in recovery and reuse. Therefore, immobilizing TEMPO radicals on electrocatalytically active supports (such as conductive metal-organic frameworks, carbon-based materials, or functionalized electrodes) to construct heterogeneous electrocatalytic systems holds promise for overcoming the current problems in TEMPO radical-mediated conductive catalytic alcohol oxidation. This could achieve electrocatalytic alcohol oxidation processes with low loading, high current density, excellent stability, and reusability, thus promoting the industrial application of this technology.

[0004] The benzothiadiazole group not only has strong electron-withdrawing ability and good electrochemical stability and reversibility, but also has a certain rigid planar structure and good carrier transport characteristics. At the same time, it can form a donor-acceptor (DA) conjugated structure with electron-donating groups, thereby obtaining a lower band gap, broadening and enhancing the spectral absorption of the material. Therefore, it is widely used in the design and synthesis of various optoelectronic functional materials.

[0005] Metal-organic frameworks (MOFs) are considered promising non-noble metal electrocatalysts, providing structural stability through strong coordination bonds between metal units and organic linkers. Nickel-based metal-organic frameworks (Ni-MOFs) and their derivatives have gained widespread application in electrocatalysis due to their excellent catalytic performance. Therefore, this invention proposes a bifunctionalized Ni-MOF photoanode based on solvothermal synthesis of TEMPO radicals and benzothiadiazole. The benzothiadiazole functionalized ligand optimizes the photoelectric properties of the material, providing efficient photoelectric drive for the reaction. Simultaneously, this catalyst can effectively immobilize TEMPO radicals, exhibiting not only recyclability and high catalytic activity but also excellent structural and electrochemical stability, effectively addressing the technical limitations of traditional homogeneous catalysts. Summary of the Invention

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

[0007] Therefore, the purpose of this invention is to provide a Ni-MOF photoanode material bifunctionalized with TEMPO radicals and benzothiadiazole, which, while heterogeneously immobilizing TEMPO radicals, optimizes the photoelectric conversion and carrier transport performance of the material by relying on benzothiadiazole, thereby achieving the synergistic effect of the two in photoelectrocatalytic organic conversion, and its application in the photoelectrocatalytic oxidation of furfural to prepare furoic acid.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: the treated nickel foam and a certain amount of mixed solution of NiCl2•6H2O, H2TPDC-TEMPO and H2TBDC are placed in a polytetrafluoroethylene-lined high-pressure reactor and reacted at 120°C for 12 hours; after natural cooling to room temperature, the nickel foam is removed, washed with deionized water and ethanol, and vacuum dried to obtain Ni-MOF photoluminescent material.

[0009] This method is used for the efficient photoelectrocatalytic oxidation of furfural compounds, enabling their targeted conversion into high-value-added acidic chemicals. The specific scheme involves using 15 W blue light as the light source; in a single-chamber electrolytic cell, a three-electrode system is employed, with a platinum sheet as the counter electrode, HgO / Hg as the reference electrode, and KOH aqueous solution as the electrolyte solution at a pH range of 10–14. The electrolysis voltage is 1.3 V–1.7 V (vs. RHE), and the reaction is carried out at a constant potential for 30 minutes.

[0010] Significant advantages of this invention: (1) The precise division of labor among the bifunctional groups enables deep synergy in photoelectrocatalysis. Benzothiadiazole is responsible for light energy absorption and carrier separation and transport, providing photo-driven power for electrocatalysis. TEMPO radicals, as highly selective oxidation active centers, directly mediate the electrocatalytic oxidation of organic functional groups. The photoelectric and electrochemical functions do not overlap and reinforce each other, breaking through the bottleneck that it is difficult to achieve both photoelectrochemical and catalytic performance in single-functional materials.

[0011] (2) The TEMPO radical is covalently immobilized in the MOF framework, replacing the traditional homogeneous co-catalytic form, which fundamentally solves the problems of large amount of TEMPO, difficulty in recovery and poor reusability in electrocatalytic organic oxidation.

[0012] (3) The support of nickel foam is conducive to promoting the diffusion of electrolyte and reaction substrate and the release of bubbles, and avoids poisoning of active sites; at the same time, the substrate improves conductivity. These factors synergistically enhance the electrocatalytic ability of the material in electrolyte.

[0013] (4) The catalyst provided by the present invention can be used directly as a working electrode. Under normal temperature and pressure conditions, it can effectively realize the electrocatalytic oxidation of HMF to FDCA, showing excellent HMFOR Faraday efficiency (up to 98.2%), FDCA yield (up to 99.9%) and conversion rate (up to 99.9%).

[0014] (5) The catalyst provided by the present invention has excellent cycle stability when used directly as a working electrode. After 10 cycles, it still maintains a Faraday efficiency of about 98.2% and an FDCA conversion rate of 90.2%.

[0015] (6) This invention provides a Ni-MOF nanosheet photoanode material that has broad application prospects in the field of photoelectrocatalytic oxidation of small biomass molecules. In particular, it has excellent conversion rate, high 2,5-furandicarboxylic acid selectivity, high Faraday efficiency and good stability in the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to prepare 2,5-furandicarboxylic acid (FDCA). Attached Figure Description

[0016] Figure 1 The images show the infrared spectrum (a) and powder X-ray diffraction pattern (b) of the Ni-MOF photoanode in Example 2.

[0017] Figure 2 This is a scanning electron microscope image of the Ni-MOF photoanode in Example 3.

[0018] Figure 3 This is the XPS spectrum of the Ni-MOF photoanode in Example 4.

[0019] Figure 4 This is the ultraviolet-visible diffuse reflectance spectrum of the Ni-MOF photoanode in Example 5.

[0020] Figure 5 This is the transient photocurrent response diagram of the Ni-MOF photoanode in Example 6.

[0021] Figure 6 This is the linear sweep voltammetry curve of the Ni-MOF photoanode in Example 7.

[0022] Figure 7 This is a graph showing the conversion rate and Faraday efficiency of the Ni-MOF photoanode under different voltages in Example 8.

[0023] Figure 8 This is a cyclic stability diagram of the Ni-MOF photoanode in Example 9. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0025] It should be noted that, unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0026] This application provides a method for preparing a TEMPO radical and benzothiadiazole bifunctionalized Ni-MOF photoanode material. This material can effectively reduce the HMF oxidation overpotential, exhibits excellent HMF oxidation catalytic performance, and has high catalyst stability, which has important application value in the field of green organic synthesis.

[0027] [Example 1] Preparation of TEMPO radical functionalized Ni-MOF electrode material Nickel foam was cut into 2 cm × 3 cm pieces, ultrasonically cleaned in ethanol and deionized water for 30 min each, and dried. It was then soaked in 4 M HCl for 60 min, rinsed with deionized water until neutral, and dried under N2. NiCl2•6H2O (28.6 mg, 0.12 mmol) was weighed and dissolved in 2 mL H2O. H2TPDC-TEMPO (20.6 mg, 0.04 mmol) and H2BTDB (15.05 mg, 0.04 mmol) were weighed and dissolved in 6 mL dimethylformamide (DMF). Clear solutions were obtained by ultrasonication. The solutions were mixed thoroughly and transferred to a polytetrafluoroethylene-lined autoclave. The reaction was carried out at 120 °C for 12 hours. After the reaction was completed and the temperature was lowered to room temperature, the nickel foam was removed, washed with deionized water and ethanol, and vacuum dried for later use.

[0028] [Example 2] Infrared and crystal structure analysis of the sample S1: Infrared spectral characterization: such as Figure 1 As shown in a, at 1700 cm⁻¹, two ligands... -1 The strong absorption peak at 1322 cm⁻¹ is attributed to the stretching vibration of the carboxyl group (C=O), while this absorption peak disappears in Ni-MOF, indicating that the ligand has successfully coordinated with the metal; - The absorption peak at position 1 corresponds to the stretching vibration of the NO• bond in the H2TPDC-TEMPO ligand. This absorption peak can still be observed in Ni-MOF, indicating that the ligand H2TPDC-TEMPO has successfully coordinated with the metal.

[0029] S2: Powder X-ray diffraction characterization: its PXRD pattern is as follows Figure 1 As shown in b, distinct diffraction peaks appeared near 5°, 10°, and 15°, which are typical characteristics of MOF materials. Combined XRD patterns and infrared spectral analysis confirmed the successful synthesis of the target material.

[0030] [Example 3] Characterization of sample morphology The morphology of the prepared samples was characterized by SEM, such as... Figure 2 As shown, the prepared photoanode material exhibits a nanoflower morphology, and the nanosheet structure provides a large number of active sites, which increases the effective contact between the electrolyte and the electrode during photoelectrocatalytic oxidation, allowing for sufficient penetration and diffusion of the electrolyte, which plays a key role in enhancing its electrochemical activity.

[0031] [Example 4] Sample XPS spectrum To further understand the elemental composition of the synthesized Ni-MOF samples, X-ray photoelectron spectroscopy (XPS) was performed. The full XPS spectrum revealed the presence of C, N, O, S, and Ni elements in the Ni-MOF, further characterizing the successful synthesis of the material.

[0032]

Example 5

[0033] Further investigation of the optical properties of the samples was conducted using ultraviolet-visible diffuse reflectance spectroscopy, such as... Figure 4As shown in Figure a, the material exhibits a significant light absorption signal in the 200-500 nm wavelength range, with strong absorption in the 200-400 nm ultraviolet region, relatively weaker absorption in the 400-500 nm visible region but still showing a response, and a significant decrease in absorption intensity after 500 nm. This effectively broadens the material's photoresponse range, enabling it to utilize energy in the ultraviolet-visible light band, providing a foundation for the generation of photogenerated carriers in subsequent photoelectrocatalysis processes. Simultaneously, the material's response in the visible light region is compatible with the blue LED light source used in the test, further verifying the compatibility between the material and the photoelectrocatalysis test system. The Et of the material was calculated using the bandgap width. g =2.44 (e.g.) Figure 4 (b) indicates that the bandgap belongs to the category of narrow bandgap semiconductors.

[0034] [Example 6] Transient photocurrent response diagram of the sample Weigh 5 mg of catalyst powder and mix it thoroughly with 1 mL of ethanol and 50 μL of naphthol 117 solution. Sonicate the mixture for 30 minutes. Drop 20 μL of the solution onto a conductive ITO glass plate and dry it under an infrared lamp. A three-electrode system is used: Pt as the counter electrode, saturated Ag / AgCl as the reference electrode, and the prepared ITO as the working electrode. The electrolyte is 0.5 M Na₂SO₄, and a 3 W blue lamp is used as the light source. Figure 5 As shown, this indicates that the material has good photoresponse activity, can quickly generate and separate photogenerated carriers (manifested as current jump); at the same time, the material has excellent photocurrent cycling stability, and the response trend does not show significant decay after multiple switching of light, indicating that its photogenerated carrier generation and transport performance is reliable and suitable for photoelectrocatalysis application scenarios.

[0035] [Example 7] Linear scan voltammetric curve of the sample The experiment was conducted under ambient temperature and pressure conditions, using 1.0 M potassium hydroxide solution as the electrolyte and 100 mM 5-hydroxymethylfurfural as the electrolyte. A three-electrode system was employed, with Ni-MOF as the working electrode, Pt as the counter electrode, and Hg / HgO as the reference electrode, forming a complete electrochemical testing system. A 15 W blue lamp was used as the light source. The experiment was conducted on a Shanghai Chenhua 660e electrochemical workstation at a voltage of 5 mV·s. -1 A linear sweep voltammetric test was performed at the rate of [equation]. According to equation E... RHE =E Hg / HgO +0.098 +0.059 × pH converts the potential to E(vs RHE) in the relative reversible hydrogen electrode potential, where E(vs Hg / HgO) is the relative Hg / HgO electrode potential (V). Linear sweep voltammetry is as follows: Figure 6 As shown in the figure, the Ni-MOF photoanode material exhibits excellent performance in the catalytic oxidation of HMF, with a current density exceeding 100 mA cm⁻¹ at 1.50 V (vs RHE).-2 The current density and onset potential are both superior to those of nickel foam substrates.

[0036] [Example 8] Conversion rate of 5-hydroxymethylfurfural and Faraday efficiency of the sample at 1.3-1.7 V (vs RHE) Catalysis is performed at different voltages, such as Figure 7 As shown, the conversion rate can reach up to 90.4%, and the Faraday efficiency is optimal at 1.5 V (vsRHE), reaching 98.2%, indicating that the synthesized electrode material can efficiently catalyze 5-hydroxymethylfurfural.

[0037] [Example 9] Yield, Faradaic efficiency and cycling stability of 5-hydroxymethylfurfural at 1.5 V (vs RHE) Stability testing was performed at 1.5 V (vs RHE). Figure 8 As shown in the figure, the bar chart represents the conversion rate, the line graph represents the Faraday efficiency, and the horizontal axis represents the number of cycles. The figure shows that the prepared Ni-MOF photoanode material exhibits high photoelectrocatalytic activity and stability for 5-hydroxymethylfurfural. Under the same voltage, multiple cycles consistently demonstrate high FDCA conversion and high Faraday efficiency, indicating that the prepared electrode material possesses the characteristics of high yield and high catalytic stability for the photoelectrocatalytic oxidation of 5-hydroxymethylfurfural.

[0038] The present invention has been described in detail with reference to the foregoing embodiments. For those skilled in the art, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a Ni-MOF photoanode, characterized in that... Using nickel chloride hexahydrate NiCl2•6H2O, TEMPO radical (2,2,6,6-tetramethylpiperidine oxide) functionalized organic ligand (H2TPDC-TEMPO), and benzothiadiazole functionalized ligand 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)benzoic acid (H2BTDB) as raw materials, a photoelectrochemically active Ni-MOF photoanode was grown in situ on nickel foam using solvothermal methods.

2. The method for preparing Ni-MOF photoanodes according to claim 1, characterized in that, The preparation method includes the following steps: S1: Pre-treat the nickel foam by cutting it into 2 cm × 3 cm pieces. Clean the nickel foam with EtOH and deionized water for 30 min each time to remove oil and impurities from the surface. After drying, immerse the nickel foam in 4 M HCl for 60 min to increase its surface roughness. Then rinse with deionized water until neutral to prevent excessive corrosion from residual acid in the nickel foam channels. Dry with N2 for later use. S2: Weigh NiCl2•6H2O (28.6 mg, 0.12 mmol) and dissolve it in 2 mL of H2O; weigh H2TPDC-TEMPO (20.6 mg, 0.04 mmol) and H2BTDB (15.05 mg, 0.04 mmol) and dissolve them in 6 mL of dimethylformamide (DMF); sonicate each solution to obtain a clear solution. S3: After mixing the above solution evenly, transfer it to a polytetrafluoroethylene-lined autoclave and place it in an ultrasonic cleaner for ultrasonic treatment for 10 minutes; then place the cleaned nickel foam (2 cm × 3 cm) diagonally in it and carry out a solvothermal reaction (120℃, 12 h). S4: After the reaction is complete, cool to room temperature, remove the nickel foam, wash with a large amount of deionized water and ethanol, and vacuum dry to obtain the Ni-MOF photoanode material.

3. The method for preparing Ni-MOF photoanodes according to claim 2, characterized in that, The molar ratio of H2TPDC-TEMPO to H2BTDB is 1:

1.

4. The method according to claim 1, characterized in that, The working electrode electrolyte in the electrolytic cell is an aqueous solution containing 5-hydroxymethylfurfural; the concentration of 5-hydroxymethylfurfural in the aqueous solution containing 5-hydroxymethylfurfural is 100 mM.

5. The application of the photoanode material according to claim 1 in photoelectrocatalytic synthesis, characterized in that, This includes: using organic ligands (H2TPDC-TEMPO) and (H2BTDB) with transition metal nickel to form MOF materials in situ on nickel foam as anode catalysts, and obtaining high-value-added chemicals by photoelectrocatalytic oxidation of furfural to acids.

6. The application according to claim 4, characterized in that, The acidic high-value-added chemicals are the potassium salts corresponding to 2,5-furandicarboxylic acid.

7. The application of the photoanode in photoelectrocatalytic synthesis according to claim 4, characterized in that, A 15 W blue lamp was used as the light source; a single-chamber electrolytic cell was used, and the system was a three-electrode system with a platinum sheet as the counter electrode, HgO / Hg as the reference electrode, and the prepared electrode material as the working electrode; the electrolyte solution was KOH aqueous solution with a pH range of 10 to 14, the electrolysis voltage was 1.31 V to 1.71 V (vs. RHE), and the constant voltage reaction was carried out for 30 minutes.

8. The application of the photoanode according to claim 1 in photoelectrocatalytic synthesis, characterized in that, include: The application of the photoanode in photoelectrocatalytic organic synthesis includes, but is not limited to, the oxidation reaction of furfural compounds.

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