TiO2 (at) cMOF heterojunction photo-anode material and preparation method and application thereof

Abstract

The invention discloses a TiO2 (at) cMOF heterojunction photo-anode material as well as a preparation method and application of the TiO2 (at) cMOF heterojunction photo-anode material. The TiO2 nanorod array photo-anode material TiO2 (at) cMOF coated with a single-metal conductive metal organic framework (cMOF) and a double-metal conductive metal organic framework (cMOF) is prepared by adopting a solvothermal method, and the selectivity for synthesizing glyceraldehyde through photoelectrocatalytic oxidation of glycerol in a neutral medium is high; the photo-anode has a unique core-shell structure, the separation efficiency of photon-generated carriers is enhanced, further the photoelectrocatalytic activity of glycerin is remarkably improved, biomass oriented upgrading of converting glycerin into glyceraldehyde is achieved, meanwhile, the photoelectrocatalytic reaction condition is mild, the problem of C-C bond breakage in the oxidation process of multi-carbon organic matter can be effectively solved, and the photo-anode has a good application prospect. A new thought is provided for high-selectivity preparation of a multi-carbon product.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectrocatalytic materials and organic synthesis, and specifically relates to a TiO2@conductive metal organic framework (cMOF) heterojunction photoanode material with a core-shell structure and a preparation method thereof, as well as an application in the photoelectrocatalytic oxidation of glycerol into glyceraldehyde. Background Art

[0002] Photoelectrocatalytic (PEC) technology, by combining the dual advantages of photoexcitation and electrochemical control, offers an innovative solution for highly selective oxidation reactions. This technology achieves directional migration and efficient separation of photogenerated charge carriers by applying a low bias voltage, effectively suppressing deep oxidation of the reaction substrate while reducing energy consumption and significantly increasing the efficiency of generating semi-oxidized target products. This unique characteristic gives it a unique advantage in the high-value conversion of biomass resources. For example, PEC systems can precisely oxidize glycerol, a major byproduct of biodiesel, to C3 platform compounds (such as glyceraldehyde and 1,3-dihydroxyacetone) under mild conditions, achieving closed-loop value-added in the biorefining process. Glyceraldehyde, a key intermediate with both α-hydroxyaldehyde and polyol functional groups, holds irreplaceable application value in food additives, pharmaceutical synthesis, and fine chemicals. Consequently, the development of semiconductor photoanode materials with broad spectral response, strong interfacial charge transfer, and excellent catalytic stability has become a key breakthrough in advancing the industrialization of PEC glycerol oxidation, holding strategic significance for improving the economic viability and sustainability of the biodiesel industry chain.

[0003] Metal-organic frameworks (MOFs) are a class of porous crystalline materials composed of metal nodes and organic linkers. They have ultra-high porosity and adjustable pore structure and have recently attracted much attention as promising electrocatalysts. Conductive metal-organic frameworks (cMOFs) build on this and overcome the shortcomings of poor conductivity of general MOFs. By virtue of their π-conjugated properties with delocalized electron pathways, they can achieve efficient cross-frame electron transport. The coating morphology of MOFs loaded on the surface of optical semiconductors is a key factor affecting the efficiency of interfacial charge transfer and separation. Previous studies have shown that when MOFs are grown directly on the surface of a semiconductor without the assistance of an intermediate layer, randomly distributed crystals rather than homogeneous films are easily formed. To address this problem, the present invention uses caffeic acid as a coordination bridging agent to construct a TiO2@cMOF photoanode material with a unique core-shell structure, which exhibits excellent catalytic activity and high selectivity for glyceraldehyde (GLD) in the PEC glycerol oxidation reaction. Summary of the Invention

[0004] The present invention provides a TiO2@cMOF heterojunction photoanode material and a preparation method thereof, and applies the material to photoelectrocatalytic oxidation of glycerol into glyceraldehyde, thereby achieving targeted upgrading and conversion of high-value fine chemicals.

[0005] The technical solutions of the present invention are as follows:

[0006] A TiO2@cMOF heterojunction photoanode material, which uses a TiO2 nanorod array as a core and a conductive metal organic framework as a shell to form a composite photoanode material with a core-shell structure;

[0007] The diameter of the TiO2 nanorods is preferably 80 to 120 nm;

[0008] The thickness of the conductive metal organic framework shell coating is preferably 5 to 12 nm;

[0009] The conductive metal-organic framework can be a single metal or multi-metal conductive metal-organic framework, for example, selected from: copper conductive metal-organic framework (Cu-cMOF), iron conductive metal-organic framework (Fe-cMOF), copper iron conductive metal-organic framework (CuFe-cMOF), zinc iron conductive metal-organic framework (ZnFe-cMOF), nickel iron conductive metal-organic framework (NiFe-cMOF) or cobalt iron conductive metal-organic framework (CoFe-cMOF).

[0010] The preparation method of the TiO2@cMOF heterojunction photoanode material of the present invention is:

[0011] The TiO2 nanorod array is immersed in an ethanol solution of caffeic acid at a constant temperature of 30 to 80° C. (preferably 50° C.) for 2 to 5 hours (preferably 3 hours) to obtain a TiO2 nanorod array modified with caffeic acid; the TiO2 nanorod array modified with caffeic acid is placed in a precursor solution of a conductive metal organic framework, reacted at 100° C. for 3 to 12 hours, and then washed and dried to obtain the TiO2@cMOF heterojunction photoanode material;

[0012] The concentration of the caffeic acid ethanol solution is 2 to 10 mg / mL, preferably 5 mg / mL;

[0013] The specific washing and drying operations are as follows: after the reaction is completed, cool to room temperature, take out the photoanode, wash with N,N-dimethylformamide and ethanol, and then soak in acetone (12 hours), and then take out and vacuum dry (60°C, 12 hours) to obtain the TiO2@cMOF heterojunction photoanode material.

[0014] Specifically, the TiO2 nanorod array is prepared as follows:

[0015] Deionized water, concentrated hydrochloric acid (36.5-38 wt%), and tetrabutyl titanate were mixed in an autoclave, added to a cleaned FTO substrate with the conductive surface facing downward, heated to 150°C for hydrothermal reaction for 5 hours, then removed, rinsed, dried, and heated to 450°C in air at a rate of 2°C / min and kept warm for 30 minutes to obtain TiO2 nanorod arrays grown on the FTO substrate;

[0016] The preferred volume ratio of deionized water, concentrated hydrochloric acid, and tetrabutyl titanate is 3:3:0.1.

[0017] Specifically, the precursor solution of the conductive metal-organic framework is prepared as follows:

[0018] Copper acetate and ferrous sulfate were dissolved in N,N-dimethylformamide, which was designated as solution A. 2,5-dihydroxy-1,4-benzoquinone and tetrabutylammonium bromide were added to a mixed solution of N,N-dimethylformamide, ethanol, and ultrapure water, and stirred and dissolved under a nitrogen atmosphere, which was designated as solution B. Solution A and solution B were mixed to prepare a precursor solution of a copper-iron conductive metal-organic framework (CuFe-cMOF).

[0019] Preferably, in solution A, the concentration of copper acetate is 5.6 mg / mL and the concentration of ferrous sulfate is 2.68 mg / mL;

[0020] Preferably, in solution B, the concentration of 2,5-dihydroxy-1,4-benzoquinone is 2 mg / mL, the concentration of tetrabutylammonium bromide is 16.67 mg / mL; the volume ratio of N,N-dimethylformamide, ethanol, and ultrapure water is 4:1:1;

[0021] “Solution A” and “Solution B” have no special meanings. They are marked as “A” and “B” only to distinguish different solution systems.

[0022] Replacing the copper acetate in the above preparation method with zinc acetate, nickel nitrate or cobalt acetate to obtain: a precursor solution of zinc-iron conductive metal-organic framework (ZnFe-cMOF), a precursor solution of nickel-iron conductive metal-organic framework (NiFe-cMOF) or a precursor solution of cobalt-iron conductive metal-organic framework (CoFe-cMOF);

[0023] The copper acetate and ferrous sulfate in the above preparation method are replaced with corresponding single metal salts to obtain: a precursor solution of a copper conductive metal-organic framework (Cu-cMOF) or a precursor solution of an iron conductive metal-organic framework (Fe-cMOF).

[0024] The TiO2@cMOF heterojunction photoanode material described in this invention can be used for the photoelectrocatalytic oxidation of glycerol to glyceraldehyde. Using an H-type electrolytic cell, a platinum sheet serves as the cathode and is assembled with an electrolyte to form a photoelectrolytic cell. Glycerol is added to the electrolyte on the photoanode side. Under the influence of light intensity and bias voltage, glycerol is selectively oxidized to glyceraldehyde on the photoanode catalyst.

[0025] The specific application methods are as follows:

[0026] An H-shaped electrolyzer with a quartz window on one side was used. The cathode and anode compartments were separated by a Nafion 117 proton exchange membrane. A photoelectrocatalytic reaction system was assembled using a TiO2@cMOF heterojunction as the photoanode, platinum as the cathode, Ag / AgCl as the reference electrode, and an aqueous sodium sulfate solution as the electrolyte. Glycerol was added to the electrolyte in the anode compartment. The light source was a xenon lamp (300W) equipped with an AM1.5G filter to simulate sunlight, which was irradiated onto the photoanode through the quartz window. A constant voltage was applied to the electrolytic reaction, resulting in the selective conversion of glycerol to glyceraldehyde.

[0027] The electrolyte sodium sulfate aqueous solution has a concentration of 0.1 to 1 M, preferably 0.5 M;

[0028] In the electrolyte of the anode chamber, the initial concentration of glycerol is 10 to 100 mM, preferably 100 mM;

[0029] The electrolysis potential is 0.8 to 1.2 V vs. RHE, preferably 1.0 V vs. RHE.

[0030] The beneficial effects of the present invention are:

[0031] The present invention provides a TiO2@cMOF heterojunction photoanode material with a unique core-shell structure. By using caffeic acid as a coordination bridging agent, the loading morphology of the conductive metal organic framework on the TiO2 nanorods is effectively regulated, thereby improving the interfacial charge transport behavior and the utilization rate of photogenerated holes, thereby enhancing the photoelectrocatalytic activity of glycerol. The photocurrent density of TiO2@CuFe-cMOF at 1.0V vs. RHE is 1.67mA / cm 2 , which is 3.2 times that of TiO2; the glyceraldehyde yield is 108.0mmol / m 2 / h, is TiO2 (36.5mmol / m 2 / h) is ~3.0 times.

[0032] This invention achieves the targeted upgrading of biomass from glycerol to glyceraldehyde, effectively alleviating the problem of C-C bond cleavage during the oxidation of multi-carbon organic matter and providing a new approach for the highly selective production of multi-carbon products. Furthermore, the mild conditions of the photoelectrocatalytic reaction are of great significance to the green development of the biodiesel industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 : Transmission electron microscopy image of the TiO2@CuFe-cMOF core-shell photoanode material in Example 1.

[0034] Figure 2 : Glyceraldehyde yield of TiO2@CuFe-cMOF photoanode in Example 1 at three electrolysis potentials.

[0035] Figure 3 : Linear sweep voltammogram of the TiO2@bimetallic-cMOF photoanode in Example 2.

[0036] Figure 4 : Graph showing the yield of glyceraldehyde on the TiO2@bimetallic-cMOF photoanode in Example 2.

[0037] Figure 5 : Linear sweep voltammogram of TiO2@single metal-cMOF photoanode in Example 3.

[0038] Figure 6 : Graph showing the yield of glyceraldehyde on the TiO2@single metal-cMOF photoanode in Example 3. DETAILED DESCRIPTION

[0039] To facilitate understanding of the present invention, the present invention will be further described below in conjunction with specific examples. These examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. The professional terms used herein are merely for the purpose of describing specific examples and are not intended to limit the scope of the present invention.

[0040] In the following examples,

[0041] The preparation process of TiO2 nanorod arrays is as follows: 3 mL of deionized water and 3 mL of concentrated hydrochloric acid are mixed and stirred in a 25 mL Teflon-lined stainless steel autoclave. Then 100 μL of tetrabutyl titanate is added and a clean conductive glass (FTO, 1*2.5 cm 2 ) were placed at an angle with the conductive surface facing downward. A hydrothermal reaction was performed at 150°C for 5 hours. After the reaction was complete, the sample was removed, rinsed with deionized water, and air-dried. The sample was then calcined at 450°C for 30 minutes to obtain a TiO2 nanorod array.

[0042] The conductive metal-organic framework (cMOF) precursor solution was prepared as follows: 28 mg of copper acetate and 13.4 mg of ferrous sulfate were dissolved in 5 mL of N,N-dimethylformamide, designated as solution A. Simultaneously, 36 mg of 2,5-dihydroxy-1,4-benzoquinone and 300 mg of tetrabutylammonium bromide were dissolved in a mixture of 12 mL of N,N-dimethylformamide, 3 mL of ethanol, and 3 mL of ultrapure water, and stirred under nitrogen for 15 minutes, designated as solution B. Solution A was then mixed with solution B to obtain a copper-iron conductive metal-organic framework (CuFe-cMOF) precursor solution.

[0043] The preparation methods of the precursor solutions of zinc-iron conductive metal-organic framework (ZnFe-cMOF), nickel-iron conductive metal-organic framework (NiFe-cMOF), and cobalt-iron conductive metal-organic framework (CoFe-cMOF) are the same as above, except that copper acetate is replaced with zinc acetate, nickel nitrate, and cobalt acetate.

[0044] The preparation method of the precursor solution of copper conductive metal organic framework (Cu-cMOF) and iron conductive metal organic framework (Fe-cMOF) is the same as above, except that copper acetate and ferrous sulfate are replaced by the corresponding single metal salts.

[0045] Example 1

[0046] The preparation method of TiO2@CuFe-cMOF photoanode material is as follows:

[0047] (1) The obtained TiO2 nanorod array was placed in an ethanol solution containing 5 mg / mL caffeic acid and soaked at 50°C for 3 hours to obtain TiO2 coordinated with caffeic acid.

[0048] (2) TiO2 was placed in a precursor solution containing 10 mL of a copper-iron conductive metal-organic framework and heated at 100°C for 6 hours. After the reaction was completed, the solution was cooled to room temperature. The photoanode was removed and washed three times with N,N-dimethylformamide and ethanol. The prepared photoanode was then immersed in acetone for 12 hours and vacuum-dried at 60°C for 12 hours to obtain TiO2@CuFe-cMOF.

[0049] Figure 1 This is a transmission electron microscopy image of the prepared TiO2@CuFe-cMOF photoanode. An obvious core-shell structure can be seen from the image. The diameter of TiO2 is 85nm and the thickness of the shell is 8nm.

[0050] An H-type electrolytic cell with a quartz window on one side was used. 15 mL of 0.5 M sodium sulfate aqueous solution was added, and 100 mM glycerol was added to the anode chamber. TiO2@CuFe-cMOF was used as the photoanode, platinum as the cathode, and Ag / AgCl as the reference electrode. A xenon lamp was turned on and irradiated through the quartz window onto the back of the FTO loaded with the photoanode material. Electrolysis was performed for 1 hour at 0.8 V, 1.0 V, and 1.2 V vs. RHE, respectively. After the reaction was completed, 1 mL of the reaction solution was taken and the product was detected by high-performance liquid chromatography. The results are as follows: Figure 2 As shown in Figure 2, the yield of glyceraldehyde on the TiO2@CuFe-cMOF photoanode is higher than that on the pure TiO2 electrode, and the yield is 108.0 mmol / m at 1.0 V vs. RHE. 2 / h(7200mM / m 2 / h), which is ~3.0 times that of TiO2. The photocurrent density of TiO2@CuFe-cMOF at 1.0V vs.RHE is 1.67mA / cm 2 , which is ~3.2 times that of TiO2

[0051] Example 2

[0052] The TiO2@bimetallic-cMOF photoanode material with a core-shell structure was prepared using the same steps as in Example 1. The copper acetate in the precursor solution of the conductive metal organic framework was replaced with 0.15 mmol zinc acetate, 0.15 mmol nickel nitrate, and 0.15 mmol cobalt acetate, while other conditions remained unchanged. The TiO2@ZnFe-cMOF, TiO2@NiFe-cMOF, and TiO2@CoFe-cMOF photoanode materials were obtained, and their linear voltammetric curves were shown in FIG. Figure 3 As shown in the figure, the photocurrent density of TiO2@ZnFe-cMOF, TiO2@NiFe-cMOF and TiO2@CoFe-cMOF are all higher than that of TiO2, among which the photocurrent density of TiO2@ZnFe-cMOF is the highest, 1.0V RHE The photocurrent density at the 2 , which is ~2.7 times that of TiO2.

[0053] The performance of three different bimetallic TiO2@cMOF photoanode materials in photoelectrocatalytic glycerol oxidation reaction is shown in Figure 2. Figure 4 As shown in Figure 2, the best one is TiO2@CoFe-cMOF, with a glyceraldehyde yield of 76.7 mmol / m 2 / h, is TiO2 (36.5mmol / m 2 / h) is 2.1 times.

[0054] Example 3

[0055] The core-shell structure TiO2@single metal-cMOF photoanode material was prepared by the same steps as in Example 1. Only the copper acetate and ferrous sulfate in the precursor solution of the conductive metal organic framework were replaced with single metal salts, copper acetate or ferrous sulfate, and other conditions remained unchanged to obtain TiO2@Cu-cMOF and TiO2@Fe-cMOF. The linear voltammetric curves are shown in Figure 2. Figure 5 As shown in the figure, the photocurrent density of TiO2@Cu-cMOF and TiO2@Fe-cMOF is higher than that of TiO2, among which the photocurrent density of TiO2@Fe-cMOF is the highest, 1.0V RHE The photocurrent density at the 2 , which is ~2.9 times that of TiO2.

[0056] The performance of two different single metal TiO2@cMOF photoanode materials in the photoelectrocatalytic glycerol oxidation reaction is shown in Figure 2. Figure 6 As shown in Figure 2, the best one is TiO2@Cu-cMOF, with a glyceraldehyde yield of 93.2 mmol / m 2 / h, which is ~2.6 times that of TiO2.

Claims

1. A TiO2@cMOF heterojunction photoanode material, characterized in that: A composite photoanode material with a core-shell structure is constructed with TiO2 nanorod arrays as the core and a conductive metal organic framework as the shell. The conductive metal organic framework is selected from the group consisting of a copper conductive metal organic framework, an iron conductive metal organic framework, a copper iron conductive metal organic framework, a zinc iron conductive metal organic framework, a nickel iron conductive metal organic framework or a cobalt iron conductive metal organic framework.

2. The TiO2@cMOF heterojunction photoanode material according to claim 1, wherein The diameter of TiO2 nanorods is 80 to 120 nm.

3. The TiO2@cMOF heterojunction photoanode material according to claim 1, wherein The thickness of the conductive metal organic framework shell coating is 5 to 12 nm.

4. The method for preparing the TiO2@cMOF heterojunction photoanode material according to claim 1, wherein: The preparation method is: The TiO2 nanorod array is immersed in an ethanol solution of caffeic acid at a constant temperature of 30-80°C for 2-5 hours to obtain a TiO2 nanorod array modified with caffeic acid; the TiO2 nanorod array modified with caffeic acid is placed in a precursor solution of a conductive metal-organic framework, reacted at 100°C for 3-12 hours, and then washed and dried to obtain the TiO2@cMOF heterojunction photoanode material.

5. The preparation method according to claim 4, wherein The concentration of the caffeic acid ethanol solution is 2 to 10 mg / mL.

6. The preparation method according to claim 4, wherein TiO2 nanorod arrays were prepared as follows: Deionized water, concentrated hydrochloric acid and tetrabutyl titanate were mixed in an autoclave, added to a cleaned FTO substrate with the conductive surface facing down, heated to 150°C for hydrothermal reaction for 5 hours, then taken out, rinsed and dried, and heated to 450°C in air at a rate of 2°C / min and kept warm for 30 minutes to obtain a TiO2 nanorod array grown on the FTO substrate.

7. The preparation method according to claim 4, wherein The precursor solution of the conductive metal-organic framework was prepared as follows: Copper acetate and ferrous sulfate were dissolved in N,N-dimethylformamide, which was designated as solution A. 2,5-dihydroxy-1,4-benzoquinone and tetrabutylammonium bromide were added to a mixed solution of N,N-dimethylformamide, ethanol, and ultrapure water, and stirred and dissolved under a nitrogen atmosphere, which was designated as solution B. Solution A and solution B were mixed to prepare a precursor solution of a copper-iron conductive metal-organic framework. Replacing the copper acetate in the above preparation method with zinc acetate, nickel nitrate or cobalt acetate to obtain: a precursor solution of a zinc-iron conductive metal-organic framework, a precursor solution of a nickel-iron conductive metal-organic framework or a precursor solution of a cobalt-iron conductive metal-organic framework; The copper acetate and ferrous sulfate in the above preparation method are replaced by corresponding single metal salts to obtain: a precursor solution of a copper conductive metal-organic framework or a precursor solution of an iron conductive metal-organic framework.

8. Use of the TiO2@cMOF heterojunction photoanode material according to claim 1 in the photoelectrocatalytic oxidation reaction of glycerol to glyceraldehyde.

9. The use according to claim 8, characterized in that Here’s how: An H-shaped electrolyzer with a quartz window on one side was used. The cathode and anode compartments were separated by a Nafion 117 proton exchange membrane. A photoelectrocatalytic reaction system was assembled using a TiO2@cMOF heterojunction as the photoanode, platinum as the cathode, Ag / AgCl as the reference electrode, and an aqueous sodium sulfate solution as the electrolyte. Glycerol was added to the electrolyte in the anode compartment. The light source was a xenon lamp equipped with an AM1.5G filter to simulate sunlight, which was irradiated onto the photoanode through the quartz window. A constant voltage was applied to the electrolytic reaction, resulting in the selective conversion of glycerol to glyceraldehyde. The electrolyte sodium sulfate aqueous solution has a concentration of 0.1 to 1 M; In the electrolyte of the anode chamber, the initial concentration of glycerol is 10-100 mM; Electrolysis potential 0.8~1.2V vs.RHE.

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