Seawater initiation preparation method of metal wet gel and aerogel and application of seawater initiation preparation method in electro-catalysis

Abstract

The invention discloses a seawater initiation preparation method of metal wet gel and aerogel and application of the seawater initiation preparation method in electro-catalysis ethylene glycol oxidation. Comprising the following steps: 1) sequentially adding a metal salt, sodium citrate and a reducing agent into pure water, 2) adding seawater into a reaction solution to obtain wet gel, and 3) washing and drying the wet gel to obtain the aerogel. Seawater can be used for replacing expensive drugs used in a large amount in a salting-out method and an excessive sodium borohydride method, so that the metal nanoparticle solution is unstable, the metal aerogel material is prepared, and the preparation cost of the metal aerogel is greatly reduced. The metal aerogel obtained by the invention shows excellent catalytic performance in the application of electro-catalysis of ethylene glycol oxidation.

Description

Technical Field

[0001] The invention belongs to the field of aerogels and relates to a seawater-initiated preparation method of a metal wet gel and an aerogel and application thereof in electrocatalytic ethylene glycol oxidation. Background Art

[0002] Metal aerogels are porous materials constructed entirely of metal nanostructures. Their metal composition covers most elements in the periodic table (about 90 species), significantly expanding the scope of aerogels. By combining the optical, electrical, and magnetic properties of different metals, we can further explore the new physical and chemical properties of aerogels and expand their potential in various application fields. However, metals and classical aerogels (oxide aerogels, carbon aerogels, etc.) differ greatly in terms of structural unit properties. The synthesis of metal aerogels involves new processes such as atomic migration, the formation and fusion of metal nanoparticles (NPs). Therefore, in order to achieve controllable preparation of metal aerogels, it is necessary to have a deep understanding of the gelation process of the metal system and then develop effective regulation strategies.

[0003] The main preparation method of metal aerogel is the sol-gel method. In 2009, Bigall et al. first used the sodium borohydride (NaBH4) reduction method to prepare a dilute solution of metal NPs. After concentration, the solution was induced to gel with an oxidant or a poor solvent to produce gold (Au), silver (Ag), platinum (Pt), Au-Ag and other gels (DOI: 10.1002 / anie.200902543). In 2019, Du Ran et al. used the salting-out method to destabilize the metal nanoparticle solution with an inorganic salt 555 times the amount of the metal precursor to prepare a metal wet gel (DOI: 10.1126 / sciadv.aaw4590); in 2020, Du Ran et al. directly used an excess reducing agent to prepare a metal aerogel, expanding the composition space of metal aerogels to almost all common single-component noble metals (Au, Ag, Pd, Pt, ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir) and two-component noble metals (Au-Ir, Au-Ru, Au-Rh, Au-Pd-Pt, etc.) (DOI:10.1038 / s41467-020-15391-w). However, both the preparation method involving sodium borohydride and the salting-out method have inevitable defects. Sodium borohydride itself is relatively expensive, and sodium borohydride can only remain stable under alkaline conditions. However, most metal ions will be consumed by hydrolysis under alkaline conditions, which further increases the cost of preparation. The content of inorganic salts used in the salting-out method is too high, and the preparation cost is extremely expensive, making it unsuitable for industrial production. Therefore, finding an efficient and low-cost method for preparing metal aerogels is an essential part of the industrialization of this material.

[0004] On the other hand, ethylene glycol, one of the decomposition products of polyethylene terephthalate (PET), is an important chemical raw material. Its oxidation products, such as glycolic acid, can be used to synthesize biodegradable plastics (PGA / PLGA), enabling the high-value conversion of waste polyethylene terephthalate (PET) plastics with significant economic and environmental benefits. However, the ethylene glycol oxidation reaction is a complex multi-step proton-coupled electron transfer process with disadvantages such as slow reaction rate and poor selectivity. The key to solving this problem lies in the development of new and efficient catalysts. Metal aerogels combine the excellent catalytic activity of nanometals with the high specific surface area of aerogels, making them highly promising catalysts for ethylene glycol oxidation reactions. Summary of the Invention

[0005] To address the high cost of chemicals required by the existing excess sodium borohydride and salting-out methods, as well as the poor performance of traditional ethylene glycol oxidation catalysts, the present invention aims to provide a seawater-initiated method for preparing wet metal gels and aerogels. This method uses seawater to replace the expensive chemicals used in the salting-out and excess sodium borohydride methods, destabilizing the metal nanoparticle solution and thus producing aerometallic materials. The resulting aerometallic materials combine the excellent catalytic activity of nanometals with the high specific surface area of aerogels, demonstrating their potential for application in industrial chemical applications.

[0006] The present invention adopts the following technical solution: a method for preparing metal wet gel and aerogel by seawater initiation, comprising the following steps:

[0007] (1) Add a metal salt precursor, sodium citrate dihydrate and a reducing agent to pure water in sequence, and mix them at a certain temperature.

[0008] (2) Add seawater to the solution obtained in step (1) and mix uniformly at a certain temperature.

[0009] (3) The suspension obtained in step (2) is allowed to stand for a certain period of time to obtain a gel (i.e., wet gel), which is then washed and a portion of the sample is subjected to solvent exchange.

[0010] (4) freeze-drying the wet gel obtained in step (3) to obtain a metal aerogel.

[0011] (5) The metal aerogel obtained in step (4) was added to a certain solution and ultrasonicated for 30 minutes, and then the uniform dispersion was dropped onto the surface of a clean and dry current collector prepared in advance and dried. As the working electrode, a Pt sheet and a Hg / HgO electrode were used as the counter electrode and the reference electrode, respectively, and electrochemical testing was carried out in an electrolyte under a certain atmosphere saturation.

[0012] The metal salt described in step (1) is one or more of tetrachloroauric acid trihydrate, silver nitrate, potassium tetrachloropalladate, potassium chloroplatinite, and ammonium hexachlororhodate, and the metal salt concentration is 0.2 mM; the reaction temperature is 10-40° C.; and the mixing method can be stirring, ultrasound, or the like.

[0013] The reducing agent described in step (1) is one or more of sodium borohydride, potassium borohydride, hydrazine hydrate and ferrous sulfate.

[0014] The molar ratio of the metal salt, sodium citrate dihydrate and reducing agent in step (1) is 1:10:(0.5-5).

[0015] The seawater content in step (2) is 1% to 10% of the total solution volume.

[0016] The washing in step (3) is specifically performed by washing with pure water 2 to 6 times, each time interval being 1 to 12 hours. The solvent replacement is specifically performed by exchanging with tert-butyl alcohol 3 to 5 times, each time interval being 1 to 12 hours.

[0017] The freeze drying described in step (4) is specifically: freezing at -196°C for 2 to 20 minutes, followed by freeze drying for 4 to 48 hours (cold trap temperature -80°C to -20°C).

[0018] The solution described in step (5) is a mixed solution of isopropanol and Nafion solution, and the aerogel concentration is 1-5 mg / mL; the current collector is a glassy carbon electrode, a graphite electrode, carbon cloth or carbon paper; the atmosphere is argon or nitrogen; and the electrolyte is 1M potassium hydroxide + 1M ethylene glycol.

[0019] The beneficial effects of the present invention are embodied in:

[0020] (1) In the previous process of preparing metal aerogels using the excess sodium borohydride method and the salting-out method, only extremely high concentrations of sodium borohydride or inorganic salts can be used, which is extremely costly. In the present invention, a seawater-initiated preparation method is adopted, and natural seawater is used instead of sodium borohydride and inorganic salts. The inorganic salts in natural seawater are used to destabilize the metal nanoparticle solution, thereby initiating a reaction to prepare a high specific surface area metal gel; through subsequent purification and freeze-drying, a metal aerogel with a clean surface and a multi-level structure can be obtained. The method of the present invention avoids the use of large amounts of sodium borohydride and inorganic salts, effectively solves the problem of high preparation costs, and provides a feasible way for the industrial preparation of high-quality metal aerogels.

[0021] (2) The method of the present invention has wide applicability and can be used to prepare a variety of metal aerogels (chemical compositions include but are not limited to gold (Au), silver (Ag), palladium (Pd), gold-rhodium (AuRh), gold-silver-palladium (AuAgPd), etc.). It has high universality and feasibility and is expected to promote the further industrial production of metal aerogel materials.

[0022] (3) The metal aerogel material prepared by the method of the present invention can effectively catalyze the electrochemical ethylene glycol oxidation reaction, and its performance is far superior to that of commercial precious metal catalysts. In addition, it is foreseeable that by further adjusting its chemical composition, it can also be used as a catalyst for other important electrochemical reactions (such as ethanol oxidation reaction, hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, etc.). Therefore, the present invention has important application significance in energy conversion, new energy development and other application fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are scanning electron microscope photos of gold aerogels prepared by initiating seawater with different contents.

[0024] Figure 2 This is an optical photograph of gold aerogel prepared by initiating the reaction with 10% volume fraction seawater.

[0025] Figure 3 These are scanning electron microscope images of silver aerogel and palladium aerogel prepared by initiating 10% volume fraction seawater.

[0026] Figure 4 This is a scanning electron microscope image of multi-metal aerogel prepared by initiating the reaction with 10% volume fraction of seawater.

[0027] Figure 5 This is a transmission electron microscope photograph of multi-metal aerogel prepared by initiating the reaction with 10% volume fraction of seawater.

[0028] Figure 6 Cyclic voltammograms of electrocatalytic ethylene glycol oxidation of AuPd aerogel, AgPd aerogel, AuAgPd aerogel, and commercial Pd / C. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to specific examples, but the preparation formula, chemical composition of the metal, applicable catalytic reaction, etc. used in the present invention are not limited thereto.

[0030] Example 1: 33.3 μL of a 30 mM aqueous solution of tetrachloroauric acid trihydrate and 25 μL of a 0.4 M aqueous solution of sodium citrate dihydrate were added to 4.922 mL of pure water and mixed thoroughly. Subsequently, 50 μL of a 0.1 M ferrous sulfate solution was added to the solution and mixed thoroughly. This yielded a red Au nanoparticle solution. 50 μL of seawater was further added to the Au nanoparticle solution and allowed to stand for 24 hours to produce an Au wet gel. The prepared wet gel was washed six times with copious amounts of water for a total of three days to remove any residues. The gel was then exchanged with tert-butanol five times, with intervals of 1 hour, 2 hours, 5 hours, and 12 hours. The gel was then flash-frozen with liquid nitrogen and held at -196°C for approximately 10 minutes. Finally, the frozen sample was freeze-dried at -80°C for 10 hours to produce a dark-brown Au aerogel. Figure 1 a is a scanning electron microscope image of the black-brown Au aerogel obtained in Example 1. Figure 2 This is an optical image of the black-brown Au aerogel obtained in Example 1.

[0031] Example 2: 33.3 μL of a 30 mM aqueous solution of tetrachloroauric acid trihydrate and 25 μL of a 0.4 M aqueous solution of sodium citrate dihydrate were added to 4.922 mL of pure water and mixed thoroughly. Subsequently, 50 μL of a 0.1 M ferrous sulfate solution was added to the solution and mixed thoroughly. This yielded a red Au nanoparticle solution. 500 μL of seawater was further added to the Au nanoparticle solution and allowed to stand for 24 hours to produce an Au wet gel. The prepared wet gel was then washed six times with copious amounts of water for a total of three days to remove any residues. The gel was then exchanged with tert-butanol five times, with intervals of 1 hour, 2 hours, 5 hours, and 12 hours. The gel was then flash-frozen with liquid nitrogen and held at -196°C for approximately 10 minutes. Finally, the frozen sample was freeze-dried at -80°C for 10 hours to produce a dark-brown Au aerogel. Figure 1 c is a scanning electron microscope image of the black-brown Au aerogel obtained in Example 2.

[0032] Example 3: 33.3 μL of a 30 mM silver nitrate aqueous solution and 25 μL of a 0.4 M sodium citrate dihydrate aqueous solution were added to 4.922 mL of pure water and mixed thoroughly. Subsequently, 50 μL of a 0.1 M ferrous sulfate solution was added to the solution and mixed thoroughly. This yielded a yellow Ag nanoparticle solution. 500 μL of seawater was further added to the Ag nanoparticle solution and allowed to stand for 24 hours to produce a wet Ag gel. The resulting wet gel was washed six times with copious amounts of water for a total of three days to remove any residues. The gel was then exchanged with tert-butanol five times, with intervals of 1 hour, 2 hours, 5 hours, and 12 hours. The gel was then flash-frozen with liquid nitrogen and held at -196°C for approximately 10 minutes. Finally, the frozen sample was freeze-dried at -80°C for 10 hours to produce a black Ag aerogel. Figure 3a is a scanning electron microscope image of the black Ag aerogel obtained in Example 3.

[0033] Example 4: 16.7 μL of a 30 mM aqueous solution of tetrachloroauric acid trihydrate, 16.7 μL of a 30 mM aqueous solution of potassium tetrachloropalladate, and 25 μL of a 0.4 M aqueous solution of sodium citrate dihydrate were added to 4.922 mL of pure water and mixed thoroughly. Subsequently, 50 μL of a 0.1 M ferrous sulfate solution was added to the solution and mixed thoroughly. This yielded a brown AuPd nanoparticle solution. 500 μL of seawater was further added to the AuPd nanoparticle solution and allowed to stand for 24 hours to obtain an AuPd wet gel. The prepared wet gel was washed six times with copious amounts of water for a total of three days to remove any residues. The gel was then exchanged with tert-butanol five times, with intervals of 1 hour, 2 hours, 5 hours, and 12 hours. The gel was then quickly frozen with liquid nitrogen and held at -196°C for approximately 10 minutes. Finally, the frozen sample was freeze-dried at -80°C for 10 hours to obtain a black AuPd aerogel. Figure 4 c is a scanning electron microscope image of the black AuPd aerogel obtained in Example 4. Figure 5 a is a projection electron microscope image of the black AuPd aerogel obtained in Example 4.

[0034] Example 5: 11.1 μL of a 30 mM aqueous solution of tetrachloroauric acid trihydrate, 11.1 μL of a 30 mM aqueous solution of silver nitrate, 11.1 μL of a 30 mM aqueous solution of potassium tetrachloropalladate, and 25 μL of a 0.4 M aqueous solution of sodium citrate dihydrate were added to 4.922 mL of pure water and mixed thoroughly. Subsequently, 50 μL of a 0.1 M ferrous sulfate solution was added to the solution and mixed thoroughly. This yielded a black AuAgPd nanoparticle solution. 500 μL of seawater was further added to the AuAgPd nanoparticle solution and allowed to stand for 24 hours to obtain an AuAgPd wet gel. The prepared wet gel was washed six times with copious amounts of water for a total of three days to remove any residues. The gel was then exchanged with tert-butanol five times, with intervals of 1 hour, 2 hours, 5 hours, and 12 hours. The gel was then quick-frozen with liquid nitrogen and held at -196°C for approximately 10 minutes. Finally, the frozen sample was freeze-dried at −80 °C for 10 h to obtain black AuAgPd aerogel. Figure 4 f is a scanning electron microscope image of the black AuAgPd aerogel obtained in Example 5. Figure 5 c is a projection electron microscope image of the black AuAgPd aerogel obtained in Example 5.

[0035] Example 6: 1.0 mg of catalyst (AuPd aerogel, AgPd aerogel, AuAgPd aerogel, commercial Pd / C) was dispersed in 425 μL of isopropanol and 75 μL of Nafion (1 wt.%) and sonicated for approximately 30 min to obtain a uniform dispersion. 10 μL of the dispersion was then dropwise added to the surface of a clean, dry glassy carbon electrode prepared in advance and allowed to volatilize at room temperature. After the solvent evaporated, a film was formed, which served as the working electrode. A Pt sheet and a Hg / HgO electrode were used as the counter and reference electrodes, respectively. Cyclic voltammetry was performed in an argon-saturated electrolyte (1 M potassium hydroxide + 1 M ethylene glycol) over a voltage range of 0.4 to 1.3 V at a scan rate of 50 mV / s. Figure 6 Cyclic voltammograms for the electrocatalytic oxidation of ethylene glycol using AuPd aerogel, AgPd aerogel, AuAgPd aerogel, and commercial Pd / C. The current density of the forward scan curve for the AuAgPd aerogel in the methanol oxidation reaction is 7.49 times higher than that of commercial Pd / C, demonstrating superior catalytic performance.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing metal wet gel and aerogel by seawater initiation, characterized in that: The steps include: (1) Add a metal salt precursor, sodium citrate dihydrate and a reducing agent to pure water in sequence, and mix them at a certain temperature. (2) Add seawater to the solution obtained in step (1) and mix uniformly at a certain temperature. (3) The suspension obtained in step (2) is allowed to stand for a certain period of time to obtain a gel (i.e., wet gel), which is then washed and a portion of the sample is subjected to solvent exchange. (4) freeze-drying the wet gel obtained in step (3) to obtain a metal aerogel.

2. The preparation method according to claim 1, characterized in that The metal salt described in step (1) is one or more of tetrachloroauric acid trihydrate, silver nitrate, potassium tetrachloropalladate, potassium chloroplatinite, and ammonium hexachlororhodate, and the metal salt concentration is 0.2 mM; the reaction temperature is 10-40° C.; and the mixing method can be stirring, ultrasound, or the like.

3. The preparation method according to claim 1, characterized in that The reducing agent described in step (1) is one or more of sodium borohydride, potassium borohydride, hydrazine hydrate and ferrous sulfate.

4. The preparation method according to claim 1, characterized in that The reducing agent described in step (1) is one or more of sodium borohydride, potassium borohydride and hydrazine hydrate.

5. The preparation method according to claim 1, characterized in that The molar ratio of the metal salt, sodium citrate dihydrate and reducing agent in step (1) is 1:10:(0.5-5).

6. The preparation method according to claim 1, characterized in that The seawater content in step (2) is 1% to 10% of the total solution volume.

7. The preparation method according to claim 1, characterized in that The washing in step (3) is specifically performed by washing with pure water 2 to 6 times, each time interval being 1 to 12 hours. The solvent replacement is specifically performed by exchanging with tert-butyl alcohol 3 to 5 times, each time interval being 1 to 12 hours.

8. The preparation method according to claim 1, characterized in that The freeze drying described in step (4) is specifically: freezing at -196°C for 2 to 20 minutes, followed by freeze drying for 4 to 48 hours (cold trap temperature -80°C to -20°C).

9. A metal wet gel and aerogel, characterized in that: The metal gel material obtained by the preparation method according to claims 1 to 9.

10. The metal gel (AuPd, AgPd, AuAgPd gel) obtained by the preparation method of claim 1 can be used as an excellent electrocatalytic ethylene glycol oxidation catalyst.

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