An aluminum material covered with a nanometer alumina layer and its preparation method and application

Abstract

This invention provides an aluminum material with a surface covered by a nano-alumina layer, its preparation method, and its application, belonging to the technical field of nano-metal oxide materials. The preparation method involves electrolytically oxidizing a polished aluminum sheet in hydrochloric acid, followed by cleaning and drying. Using the prepared aluminum material with the nano-alumina layer as a cathode, and using 2-phenylthiophene as a raw material, direct current electrolysis in an organic solvent yields the corresponding hydrogenated product, 2-phenyltetrahydrothiophene. The conversion rate, yield, and Faraday efficiency of this reaction can all reach over 90%. By avoiding the use of transition metal catalysts, the disadvantage of the difficulty in hydrogenating sulfur-containing heterocycles is overcome, thus realizing the synthesis and preparation of saturated sulfur-containing compounds.

Description

Technical Field

[0001] This invention belongs to the field of nano-metal oxide materials technology, specifically an aluminum material with a surface covered by a nano-alumina layer, its preparation method, and its application. Background Technology

[0002] Aluminum is the third most abundant element in the Earth's crust, after oxygen and silicon, making it the most abundant metallic element. Metallic aluminum is a silvery-white, lightweight metal with good ductility. Its electrical conductivity is about 60% that of copper; however, on a per-unit-mass basis, aluminum's conductivity exceeds that of copper, making it a frequent substitute for copper in long-distance transport. It is widely used due to its light weight, excellent electrical and thermal conductivity, high reflectivity, and oxidation resistance. Because of its good electrical conductivity, metallic aluminum can be used as an electrode in electrochemical reactions, often as a sacrificial anode in electrochemical synthesis. Metallic aluminum can also be used as a cathode, but due to its low overpotential, it is prone to hydrogen evolution reactions, limiting its application in electrochemical synthesis.

[0003] Oxidized aluminum can form an oxide film with a thickness of approximately 5–20 micrometers on its surface. This film has high hardness, good heat resistance and insulation, and higher corrosion resistance than chemically oxidized films. It is porous and has good adsorption capacity, but it loses its conductivity and is unsuitable for electrochemical reactions. Electron tunneling refers to the phenomenon where electrons travel from a high potential region to a low potential region, breaking through the classical forbidden region. A significant electron tunneling effect occurs when the insulating layer is only a few nanometers thick, turning a material that should be an insulator into a conductor.

[0004] Based on the above research, this invention provides an aluminum electrode material with a surface covered with nano-alumina, its preparation method, and its application. Summary of the Invention

[0005] To address the issue that aluminum is prone to hydrogen evolution reaction when used as a cathode, thus limiting its application in electrochemical synthesis, this invention provides an aluminum material with a surface covered by nano-alumina, its preparation method, and its application, overcoming the limitations of existing aluminum material electrodes in terms of variety and scarcity of applications.

[0006] This invention provides a method for preparing aluminum materials with a surface covered by a nano-alumina layer. The method involves placing a polished aluminum sheet in hydrochloric acid for electrolytic oxidation, followed by cleaning and drying to obtain an aluminum electrode material with a surface covered by a nano-alumina layer containing chlorine.

[0007] Furthermore, the aluminum sheet is made of pure aluminum with a purity of 99% or higher.

[0008] Furthermore, the thickness of the aluminum sheet is greater than 0.5 mm.

[0009] Furthermore, the polishing method is sandpaper or abrasive wheel polishing.

[0010] Furthermore, the concentration of the hydrochloric acid is 1M-2M.

[0011] Furthermore, the electrolysis time is 1-2 hours, and the electrolysis current is 10mA-15mA.

[0012] Furthermore, the thickness of the nano-alumina layer is 2-4 nm, and it has a porous three-dimensional network structure.

[0013] The aluminum material prepared by the method of this invention can be used as the cathode of the reaction electrode in the electrochemical hydrogenation reduction of 2-phenylthiophene. Specifically, the prepared aluminum material with a surface covered by nano-alumina is used as the cathode, and 2-phenylthiophene is used as a raw material. The reaction is carried out in an organic solvent via direct current electrolysis to obtain the corresponding hydrogenated product, 2-phenyltetrahydrothiophene. The conversion rate, yield, and Faraday efficiency of this reaction can all reach over 90%. By avoiding the use of transition metal catalysts, the disadvantage of the difficulty in hydrogenating sulfur-containing heterocycles is overcome, and the synthesis of saturated sulfur-containing compounds is realized. Within the preparation conditions of this invention, the activity of the nano-alumina layer in catalyzing the electrochemical hydrogenation of 2-phenylthiophene is basically consistent.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1) This invention uses pure aluminum as the aluminum material substrate. After removing the surface alumina by grinding, it is placed in a hydrochloric acid solution of a certain concentration for electrolytic oxidation. The nano-alumina layer formed on the surface of the metallic aluminum contains chlorine. This invention uses hydrochloric acid as the electrolyte instead of the commonly used dilute sulfuric acid in industry. During the electrolysis process, the morphology and thickness of the surface oxide film can be better controlled, and chlorine can be introduced onto the surface to obtain Lewis acidic catalytic ability.

[0016] 2) The aluminum oxide generated on the surface of the aluminum material in this invention is at the nanoscale, which has better conductivity compared to the traditional micron-scale aluminum oxide.

[0017] 3) The nano-alumina layer generated on the surface of the aluminum material in this invention has a porous three-dimensional network structure with a large specific surface area, and has a good adsorption effect when used as an electrode.

[0018] 4) The nano-alumina layer on the surface of the aluminum material in this invention has a strong ability to inhibit hydrogen evolution, which can effectively reduce the HER side reaction in the cathode reaction process.

[0019] 5) This invention combines the in-situ generation of Lewis acid sites containing chlorinated aluminum bonds on the surface of aluminum materials to achieve electrocatalytic capability.

[0020] 6) When the aluminum material with a nano-alumina layer on its surface is prepared as the cathode of the reaction electrode in this invention, it has a good effect on the electrochemical hydrogenation reduction of 2-phenylthiophene. Attached Figure Description

[0021] Figure 1 The images shown are scanning electron microscope (SEM) images of the chlorine-containing nano-alumina layer prepared in Example 1 of this invention, where a) is in the 10 μm range and b) is in the 2 μm range.

[0022] Figure 2 The surface elemental characterization of the chlorine-containing nano-alumina layer prepared in Example 1 was performed using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS-mapping), where a) is the full SEM image; b) is the X-ray energy dispersive X-ray spectrum of aluminum; c) is the X-ray energy dispersive X-ray spectrum of oxygen; and d) is the X-ray energy dispersive X-ray spectrum of chlorine.

[0023] Figure 3 The images show a comparison of X-ray diffraction patterns of different aluminum materials, where a) is 5052-Al; b) is the chlorine-containing nano-alumina layer prepared in Example 1 of the invention; and c) is metallic aluminum.

[0024] Figure 4 This is an XPS depth profile of the aluminum material with nano-alumina coating on its surface, as shown in Example 1 of the present invention.

[0025] Figure 5 The figures show a comparison of interfacial resistance tests for different aluminum-based materials, where a) is the surface of a chlorine-containing nano-alumina layer; b) is polished metallic aluminum; and c) is 5052-Al.

[0026] Figure 6 The image shows a comparison of the linear scan voltammogram and Tafel slope diagram of the aluminum material with nano-alumina surface prepared in Example 1 and the polished metallic aluminum in Comparative Example 1, where a) is the linear scan voltammogram and b) is the Tafel slope diagram.

[0027] Figure 7 The bar charts show the conversion rate, yield, and Faraday efficiency of 2-phenylthiophene electrocatalytic hydrogenation in Example 1 and Comparative Example 1 of this invention, where a) is an aluminum material covered with a nano-chlorinated alumina layer; and b) is polished metallic aluminum as the cathode. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to specific embodiments. The embodiments described below are for illustrative purposes only and should not be construed as limiting the present invention itself. Various changes in form and detail may be made to the present invention without departing from the spirit and scope thereof.

[0029] Materials used in the examples and comparative examples: 99% pure metallic aluminum and hydrochloric acid were sourced from Sinopharm Group, with the metallic aluminum having a thickness of 0.8 mm. 2-Phenylenol was sourced from Adamas with a purity of 99%. It should be noted that materials and reagents from other suppliers will have the same effect as long as their purity is similar. The aluminum material covering the micron-sized alumina, i.e., 5052-Al, was sourced from Sinopharm Group, with an alumina film thickness of 3 microns.

[0030] Example 1

[0031] 1) This embodiment provides a method for preparing aluminum material with a nano-alumina layer on the surface. The steps are as follows: A pure aluminum sheet (99% pure metallic aluminum) with a size of 1.5 cm * 1 cm * 0.8 mm is cut, and its surface is carefully polished with sandpaper, with a polishing area of ​​1 cm * 1 cm. Then, it is fixed with an electrode clamp, and the polished part is subjected to oxidation electrolysis in 1 M dilute hydrochloric acid. The anode is the polished aluminum sheet, the cathode is a graphite felt (immersed in the solution 1 cm * 1 cm * 2 mm), the current is 10 mA, and the electrolysis time is 2 h. After electrolysis, the obtained aluminum material is washed with deionized water, and then sonicated in deionized water for 3 min to clean the surface (to remove any residual hydrochloric acid and a small amount of particulate aluminum and alumina). Finally, it is dried with nitrogen gas. The obtained material is an aluminum material with a nano-alumina layer on the surface.

[0032] 2) The prepared aluminum material was subjected to an electro-reaction as follows:

[0033] Add tetraethylammonium chloride (67.0 mg, 0.4 mmol) and 2-phenylthiophene (32 mg, 0.2 mmol) to a 10 mL transparent three-necked reaction flask. Seal the two necks of the flask with rubber stoppers containing an anode (graphite felt, immersion volume 1 cm * 1 cm * 2 mm) and a cathode (aluminum material with nano-alumina surface prepared in the example, immersion area 1 cm * 1 cm). Add 5 mL of N,N-dimethylformamide through the middle neck. Then purge the air in the reaction flask with 100 μL of ethanol using a microsyringe and ammonia gas. After removing the air from the reaction flask, seal the middle neck with a rubber stopper and insert an ammonia balloon. Place the reaction flask on a magnetic stirrer, connect the electrodes, set the current to 10 mA, and stir the reaction for 2.14 hours. After the reaction is complete, extract the reaction product with ethyl acetate, wash the organic phase with saturated brine, dry with anhydrous sodium sulfate, filter, and evaporate the filtrate to dryness. Column chromatography with 300-400 mesh silica gel as the stationary phase was used. The sample was loaded dry and eluted with petroleum ether. The eluent was detected by GC-MS. The collected chromatogram was concentrated to obtain 29.5 mg of the product 2-phenyltetrahydrothiophene.

[0034] Example 2

[0035] The electrode material preparation steps and electroreaction steps were the same as in Example 1, except that 2-phenylthiophene (32 mg, 0.2 mmol) was replaced with 2-p-tolylthiophene (34.8 mg, 0.2 mmol). A final yield of 28.5 mg of the product 2-p-tolyltetrahydrothiophene was obtained.

[0036] Example 3

[0037] The electrode material preparation steps and electroreaction steps were the same as in Example 1, except that 2-phenylthiophene (32 mg, 0.2 mmol) was replaced with 2-p-fluorophenylthiophene (35.6 mg, 0.2 mmol). A final yield of 29.5 mg of the product 2-p-fluorophenyltetrahydrothiophene was obtained.

[0038] Example 4

[0039] The electrode material preparation and electroreaction steps were the same as in Example 1, except that 2-phenylthiophene (32 mg, 0.2 mmol) was replaced with biphenyl (30.8 mg, 0.2 mmol), the electrolysis time was 4 hours, and the electrolysis current was 12.5 mA. Finally, 19.2 mg of the product cyclohexylbenzene was obtained.

[0040] Comparative Example 1

[0041] Polished aluminum was used as the cathode material for the electroreaction, and the electroreaction steps were the same as in Example 1. A total of 12.7 mg of the product 2-phenyltetrahydrothiophene was finally obtained.

[0042] Comparative Example 2

[0043] An electrochemical reaction was carried out using aluminum material with a surface-coated nano-alumina layer (with a hydrochloric acid concentration of 12M), following the same steps as in Example 1. 13.7 mg of the product 2-phenyltetrahydrothiophene was ultimately obtained.

[0044] Comparative Example 3

[0045] An electrochemical reaction was carried out using aluminum material with a surface-coated nano-alumina layer (the electrolysis time for preparing the material was 4 hours), following the same steps as in Example 1. 14.3 mg of the product 2-phenyltetrahydrothiophene was ultimately obtained.

[0046] The aluminum material with a surface covered with nano-alumina prepared in Example 1, its SEM ( Figure 1 The surface morphology images (10 μm and 2 μm sizes) of the aluminum material coated with nano-alumina show a porous three-dimensional network structure. The aluminum material with nano-alumina surface prepared in Example 1, EDS-mapping (… Figure 2The X-ray diffraction pattern shows that the nano-alumina layer covering the surface of the material contains chlorine, oxygen, and aluminum, meaning that the nano-alumina layer covering the surface of the aluminum material is a chlorine-containing alumina layer. Figure 3 The surface elemental composition of the aluminum material with nano-alumina coating prepared in Example 1 is similar to that of alumina, but significantly different from that of metallic aluminum.

[0047] Figure 4 The XPS depth profile (0–10 nm) of the aluminum material with surface-coated nano-alumina prepared in Example 1 of this invention is shown. X-ray photoelectron etching spectrum can be used to test the thickness of the nano-layer. The analysis shows that the thickness of the chlorine-containing alumina layer is 2–4 nm.

[0048] Figure 5 The graph shows a comparison of electrical resistance tests between the aluminum material with nano-alumina coating prepared in Example 1, the polished metallic aluminum in Comparative Example 1, and the aluminum material with micron-sized alumina coating. Figure 5 As can be seen from the above, the aluminum material with nano-alumina coating on the surface of Embodiment 1 of the present invention has a resistance much greater than that of metallic aluminum and micron-sized alumina, and also has good conductivity.

[0049] Figure 6 This is a comparison of the linear scanning voltammogram and Tafel slope diagram of the aluminum material with nano-alumina surface prepared in Example 1 and the polished metallic aluminum in Comparative Example 1. Figure 6 It can be seen that, compared with polished aluminum, aluminum materials with a nano-alumina layer on the surface have a higher reduction rate in the hydrogen evolution reaction and a larger Tafel slope, which proves that aluminum materials with a nano-alumina layer on the surface have a good inhibitory effect on the hydrogen evolution reaction (HER).

[0050] Figure 7 The bar chart shows the electrocatalytic hydrogenation performance comparison of 2-phenylthiophene in Example 1 and Comparative Example 1 of this invention. The electrochemical reduction performance results of Example 1 and Comparative Examples 1 to 3 are shown in Table 1.

[0051] Table 1

[0052]

[0053] Table 1 shows that the conversion rate, yield, and Faraday efficiency of the reaction are more than twice higher when using aluminum materials with a nano-alumina coating compared to polished aluminum. Compared to polished aluminum, aluminum materials with a nano-alumina coating have a larger specific surface area, a higher Tafel slope, and stronger Lewis acidity. These factors are beneficial for the electron-acquiring reduction process of 2-phenylthiophene on the electrode surface, enabling the reaction to achieve a 95% conversion rate, 90% yield, and Faraday efficiency, far superior to polished aluminum electrodes. Changing the electrolysis current and the concentration of hydrochloric acid used in the electrolysis will worsen the material's performance.

[0054] Table 2 shows that aluminum materials with nano-alumina coatings on their surface have good effects on the conversion of various thiophene compounds, and this material can also be used for the reductive hydrogenation of biphenyl.

[0055] Table 2

[0056]

[0057] The molecular structure of the product 2-phenyltetrahydrothiophene from Example 1 is as follows:

[0058]

[0059] NMR spectrum of product 2-phenyltetrahydrothiophene from Example 1: 1 H NMR (400 MHz, Chloroform-d) δ7.44 (d, J = 7.4 Hz, 2H), 7.33 (t, J = 7.5 Hz, 2H), 7.25 (t, J = 7.3 Hz, 1H),4.61 – 4.49 (m, 1H), 3.14 – 3.25 (m, 1H), 3.02- 3.07 (m, 1H), 2.39- 2.44 (m,1H), 2.27- 2.34 (m, 1H), 2.16 – 1.92 (m, 2H). 13 C NMR (101 MHz, CDCl3) δ143.0, 128.4, 127.6, 126.9, 52.7, 40.5, 33.4, 31.0.

[0060] The molecular structure of product 2-p-tolyltetrahydrothiophene from Example 2 is as follows:

[0061]

[0062] NMR spectrum of product 2-p-tolyltetrahydrothiophene from Example 2: 1H NMR (400 MHz, Chloroform-d)δ 7.34 (d, J = 8.1 Hz, 2H), 7.15 (d, J = 7.8 Hz, 2H), 4.71 – 4.41 (m, 1H), 3.22 – 3.14 (m, 1H), 3.07 – 3.01 (m, 1H), 2.46 – 2.38 (m, 1H), 2.36 (s, 3H), 2.34 – 2.27 (m, 1H), 2.11 – 1.91 (m, 2H). 13 C NMR (101 MHz, CDCl3) δ 139.9,136.6, 129.1, 127.5, 52.5, 40.5, 33.4, 31.0, 21.0.

[0063] The molecular structure of product 2-p-fluorophenyltetrahydrothiophene from Example 3 is as follows:

[0064]

[0065] NMR spectrum of product 2-p-fluorophenyltetrahydrothiophene from Example 3: 1 H NMR (400 MHz, Chloroform-d)δ 7.45 – 7.35 (m, 2H), 7.03 – 6.98 (m, 2H), 4.57 – 4.48 (m, 1H), 3.21 – 3.13(m, 1H), 3.07 – 3.00 (m, 1H), 2.44 – 2.36 (m, 1H), 2.32 – 2.24 (m, 1H), 2.08 – 1.86 (m, 2H). 13 C NMR (101 MHz, Chloroform-d) δ 161.8 (d, J = 245.1 Hz), 138.7 (d, J = 3.1 Hz), 129.1 (d, J = 7.9 Hz), 115.1 (d, J = 21.3 Hz), 52.0, 40.7, 33.4, 30.9.

[0066] The molecular structure of the product cyclohexylbenzene in Example 4 is as follows:

[0067]

[0068] NMR spectrum of the product cyclohexylbenzene in Example 4: 1H NMR (400 MHz, Chloroform-d) δ 7.37 –7.30 (m, 2H), 7.29 – 7.18 (m, 3H), 2.63 – 2.48 (m, 1H), 1.98 – 1.75 (m, 5H),1.53 – 1.38 (m, 4H), 1.36 – 1.23 (m, 1H). 13 C NMR (101 MHz, CDCl3) δ 148.1,128.3, 126.8, 125.8, 44.6, 34.5, 26.9, 26.2.

Claims

1. Use of an aluminum material surface-coated with a nanometric layer of aluminum oxide in the electrochemical hydrogenative reduction of 2-phenylthiophene, characterized in that, The method for preparing the aluminum material is as follows: A polished aluminum sheet is placed in hydrochloric acid for electrolytic oxidation, then cleaned and dried to obtain an aluminum electrode material with a nano-alumina layer on its surface. The nano-alumina layer contains chlorine and has a thickness of 2-4 nm and a porous three-dimensional network structure. The concentration of the hydrochloric acid is 1 M-2 M. The electrolysis time is 1-2 h and the electrolysis current is 10 mA-15 mA.

2. The application according to claim 1, characterized in that, The aluminum sheet is made of pure aluminum with a purity of 99% or higher.

3. The application according to claim 1, characterized in that, The thickness of the aluminum sheet is greater than 0.5 mm.

4. The application according to claim 1, characterized in that, The polishing method is sandpaper or abrasive wheel polishing.

5. The application according to claim 1, characterized in that, The aluminum material is used to prepare the cathode of the electrochemical hydrogenation reduction reaction electrode.

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