Preparation method and application of cobalt-iron-aluminum layered hydroxide-polydopamine composite photo-thermal synergistic catalyst

Abstract

The invention provides a preparation method and application of a composite photo-thermal synergistic catalyst based on cobalt-iron-aluminum layered hydroxide-polydopamine (CoFeAl-LDH (at) PDA). Adding cobalt-iron-aluminum layered hydroxides in different proportions into the alkaline buffer solution, and ultrasonically dispersing uniformly; under the ultrasonic condition, dopamine is continuously added for reaction; and carrying out suction filtration, washing and vacuum drying on the obtained product to obtain the cobalt-iron-aluminum layered hydroxide-polydopamine composite material. According to the cobalt-iron-aluminum layered hydroxide-polydopamine composite material obtained by the preparation method provided by the invention, the hydrogen production performance and the catalytic stability of the cobalt-iron-aluminum layered hydroxide-polydopamine composite material for photo-thermal synergistic catalysis of NaBH4 hydrolysis are remarkably improved compared with those of pure cobalt-iron-aluminum layered hydroxide. The preparation method is simple and easy for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and specifically relates to a preparation method of a cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst and its application in hydrogen production by hydrolysis of NaBH4. Background Art

[0002] Hydrogen production by hydrolysis of NaBH4 is an efficient hydrogen production method. Improving the performance and cyclic stability of catalysts remains a major challenge. The cobalt-iron-aluminum layered hydroxide has relatively high photo-thermal synergistic catalytic activity for hydrogen production from NaBH4, but its cyclic stability is not good. Because the pH of the NaBH4 hydrolysis system is relatively high, it will damage the structure of the cobalt-iron-aluminum layered hydroxide catalyst, resulting in performance degradation.

[0003] Polydopamine (PDA) has become a potential heterojunction interface medium due to its biocompatibility, excellent light response ability, and self-polymerization performance. PDA is formed by in-situ self-polymerization of dopamine under weak alkaline conditions. Dopamine is a PDA monomer containing catechol and amino functional groups. During the polymerization process, PDA will coat on the surface of other materials through the strong bonding force of the catechol functional group. In addition, studies have shown that PDA has a wide absorption range from ultraviolet to near-infrared and can be used for photothermal therapy (ACS Applied Material Interfaces, 2016, 8(18): 11237-11245), which also indicates that PDA has the ability of photothermal conversion. Polydopamine has excellent photothermal conversion ability and coating ability, and can form a stable interface layer through in-situ self-polymerization, providing a new idea for improving the cyclic stability of catalysts. Therefore, the cobalt-iron-aluminum layered hydroxide is polymerized and modified by polydopamine, and by utilizing their respective advantages, a cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst with better performance for hydrogen production by hydrolysis of NaBH4 is prepared. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a highly efficient and catalytically stable cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst and its application in hydrogen production by hydrolysis of NaBH4 in order to overcome the deficiencies and disadvantages existing in the prior art. Different proportions of cobalt-iron-aluminum layered hydroxide are added to an alkaline buffer solution and ultrasonically dispersed evenly, and then dopamine is added and polymerization is continued under ultrasonic conditions. The product is filtered by suction, washed, and dried in vacuum to obtain the CoFeAl-LDH@PDA composite material.

[0005] Preferably, in the above preparation method of the CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance, the molar ratio of cobalt, iron, and aluminum in the cobalt-iron-aluminum layered hydroxide is 6:1:1.

[0006] Preferably, in the above-mentioned CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance and its preparation method, it is characterized in that the weight ratio of CoFeAl-LDH to dopamine is 1:2 - 5:1.

[0007] Preferably, in the above-mentioned CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance and its preparation method, it is characterized in that the buffer solution is glycine-sodium hydroxide buffer solution with a pH of 8.6 - 10.

[0008] Preferably, in the above-mentioned CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance and its preparation method, it is characterized in that the dosage ratio of hydrotalcite to buffer solution is 0.5 - 2 g:1000 mL.

[0009] Preferably, in the above-mentioned CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance and its preparation method, it is characterized in that the post-treatment is suction filtration and washing 3 - 5 times.

[0010] Preferably, in the above-mentioned CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance and its preparation method, it is characterized in that the temperature of vacuum drying is 40 - 60 °C and the time is 2 - 6 h.

[0011] Preferably, the above-mentioned CoFeAl-LDH@PDA composite catalyst with photothermal synergistic catalytic performance is applied to the field of photothermal catalytic decomposition of sodium borohydride for hydrogen production.

[0012] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects: (1) Under ultrasonic conditions, dopamine in-situ polymerizes on the particle surface to form polydopamine coated on the surface of nanoparticles, which can protect CoFeAl-LDH from being immersed in a strong alkaline environment for a long time to a certain extent, thereby weakening the damage of the reaction environment to the catalyst and further improving the stability of the catalyst.

[0013] (2) The PDA coated on the outer layer of CoFeAl-LDH is beneficial to improving the photothermal conversion efficiency on the catalyst surface, realizing that the photothermal performance of the CoFeAl-LDH@PDA composite is superior to that of pure CoFeAl-LDH.

[0014] (3) Active species such as h+, Vo and •OH generated during the photo-thermal synergistic catalytic process can inhibit the electron-hole recombination of the catalyst itself by participating in the hydrolysis reaction of sodium borohydride, thereby improving the photo-thermal catalytic efficiency. Description of the Drawings

[0015] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings: In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art Figure 1 XRD patterns of cobalt-iron-aluminum layered double hydroxide-polydopamine composite photothermal synergistic catalysts obtained with different amounts of dopamine hydrochloride in the present application and the comparative examples; Figure 2 Fourier transform infrared spectra of cobalt-iron-aluminum layered double hydroxide-polydopamine composite photothermal synergistic catalysts obtained with different amounts of dopamine hydrochloride in the present application, (a) CoFeAl-LDH, (b-e) CoFeAl-LDH@PDA samples obtained with different amounts of dopamine hydrochloride Figure 3 Transmission electron microscope image of cobalt-iron-aluminum layered double hydroxide-polydopamine composite photothermal synergistic catalyst obtained with 1.0 g of dopamine hydrochloride in the present application; Figure 4 ESR diagram of cobalt-iron-aluminum layered double hydroxide-polydopamine composite photothermal synergistic catalyst obtained with 1.0 g of dopamine hydrochloride in the present application. (a) V o , (b) •OH and (c) h + Figure 5 Infrared thermal imaging diagrams (a) and relative temperature rise change diagrams (b) of pure PDA, pure CoFeAl-LDH, and CoFeAl-LDH@PDA obtained with 1.0 g of dopamine hydrochloride Figure 6 Hydrogen production volume and blank control under light conditions for CoFeAl-LDH@PDA obtained with 1.0 g of dopamine hydrochloride (a); hydrogen production rates after light irradiation of CoFeAl-LDH@PDA, pure PDA, and pure LDH without external heat sources (b).

[0016] Figure 7 Cyclic stability test of CoFeAl-LDH@PDA obtained with 1.0 g of dopamine hydrochloride Detailed implementation manners

[0017] The following will cooperate with the drawings and embodiments to detail the implementation manners of the present application, so as to fully understand the implementation process of how the present application applies technical means to solve technical problems and achieve technical effects and implement accordingly.

[0018] Step 1: Weigh a certain amount of Co(NO3)2•6H2O, Fe(NO3)3•6H2O, Al(NO3)3•9H2O and urea, dissolve them in deionized water, and stir magnetically to form a purplish-red transparent and clear solution.

[0019] Step 2: Transfer the solution to a stainless-steel autoclave with a polytetrafluoroethylene liner and react at a certain temperature, then cool it to room temperature naturally.

[0020] Step 3: After the reaction, the precipitate is filtered by suction, and the precipitate is washed several times with ethanol and deionized water, dried at a certain temperature and ground to obtain CoFeAl-LDH powder.

[0021] Step 4: Under ultrasonic conditions, add a certain amount of cobalt-iron-aluminum layered hydroxide to the glycine-sodium hydroxide alkaline buffer solution to uniformly disperse the cobalt-iron-aluminum layered hydroxide nanoparticles in the solution.

[0022] Step 5: In the above mixed solution, add a certain amount of dopamine, and continue to react under ultrasonic conditions until the polymerization is complete. The precipitate is filtered by suction, washed, and dried in vacuum to obtain the CoFeAl-LDH@PDA composite material.

[0023] Preparation method of cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst: Example 1: First, prepare CoFeAl-LDH powder by hydrothermal method. Weigh 6 mmol Co(NO3)2•6H2O, 1 mmol Fe(NO3)3•6H2O, 1 mmol Al(NO3)3•9H2O and 40 mmol urea and place them in a beaker. Measure 40 mL of deionized water and add it to the beaker, stir magnetically for 30 min to form a purplish-red transparent and clear solution. Then transfer the well-mixed solution to a 100 mL stainless-steel autoclave with a polytetrafluoroethylene liner and react at 120 °C for 6 h, and then cool it to room temperature naturally. The obtained precipitate is centrifuged and washed several times with ethanol and deionized water until the pH is close to neutral. The solid product obtained by suction filtration is dried at 80 °C for 24 h. Grind it thoroughly to obtain CoFeAl-LDH. From Figure 1 the XRD pattern, it can be seen that cobalt-iron-aluminum layered hydroxide is prepared.

[0024] Weigh 1.0 g of the CoFeAl-LDH powder prepared by the hydrothermal method and transfer it to 1.0 L of glycine-sodium hydroxide buffer solution (pH = 9). Sonicate for 30 min, then add 1 g of dopamine hydrochloride and continue sonication for 30 min. Stir at room temperature on a magnetic stirrer for 24 h, and the solution changes from purplish-red to brownish-black. Vacuum filter, wash the filtered product with deionized water multiple times, dry it in vacuum at 60 °C for 2 h, and grind to obtain a solid powder, which is CoFeAl-LDH@PDA. From Figure 1 XRD, Figure 2 transmission electron microscopy and Figure 3 Fourier transform infrared spectroscopy, it can be seen that a cobalt-iron-aluminum layered hydroxide-polydopamine composite material is prepared. Figure 4 From the ESR diagram of CoFeAl-LDH@PDA, it can be seen that there are Vo, •OH and h+ active species during the photo-thermal synergistic catalytic hydrogen production process.

[0025] Example 2 Weigh 1.0 g of the CoFeAl-LDH powder prepared by the hydrothermal method and transfer it to 1.0 L of glycine-sodium hydroxide buffer solution (pH = 8.5). Sonicate for 30 min, then add 0.5 g of dopamine hydrochloride and continue sonication for 30 min. Stir at room temperature on a magnetic stirrer for 24 h, and the solution changes from purplish-red to brownish-black. Vacuum filter, wash the filtered product with deionized water multiple times, dry it in vacuum at 60 °C for 3 h, and grind to obtain a solid powder, which is CoFeAl-LDH@PDA. From Figure 1 XRD and Figure 3 Fourier transform infrared spectroscopy, it can be seen that a cobalt-iron-aluminum layered hydroxide-polydopamine composite material is prepared.

[0026] Example 3 Weigh 1.0 g of the CoFeAl-LDH powder prepared by the hydrothermal method and transfer it to 1.0 L of glycine-sodium hydroxide buffer solution (pH = 9). Sonicate for 30 min, then add 1.5 g of dopamine hydrochloride and continue sonication for 30 min. Stir at room temperature on a magnetic stirrer for 24 h, and the solution changes from purplish-red to brownish-black. Vacuum filter, wash the filtered product with deionized water multiple times, dry it in vacuum at 65 °C for 2 h, and grind to obtain a solid powder, which is CoFeAl-LDH@PDA x . From Figure 1 XRD and Figure 3 Fourier transform infrared spectroscopy, it can be seen that a cobalt-iron-aluminum layered hydroxide-polydopamine composite material is prepared.

[0027] Example 4 Weigh 1.0 g of the CoFeAl-LDH powder prepared by the hydrothermal method and transfer it to a 1 L glycine-sodium hydroxide buffer solution (pH = 10). Sonicate for 30 min, then add 2 g of dopamine hydrochloride and continue sonication for 30 min. Stir at room temperature on a magnetic stirrer for 24 h. The solution changes from purplish-red to brownish-black. Filter under vacuum, wash the filtered product with deionized water multiple times, dry in vacuum at 60 °C for 4 h, and grind to obtain a solid powder, which is CoFeAl-LDH@PDA x From Figure 1 XRD and Figure 3 Fourier transform infrared spectra, it can be seen that a cobalt-iron-aluminum layered hydroxide-polydopamine composite material was prepared.

[0028] (2) Performance examples of cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalysts Example 5 (Photothermal conversion performance test) Use an infrared thermal imager to quantitatively analyze the thermal effect on the surface of the catalyst. Use a Xe lamp with a 400 nm filter as the light source, and verify the photothermal effect by monitoring the temperature change of the catalytic reaction system. As Figure 5 shown, the surface temperature change of the CoFeAl-LDH@PDA1 composite material is the most significant. After 30 min of illumination, the relative temperature rise of CoFeAl-LDH@PDA1 reaches 51 °C, which is better than that of pure PDA (34.8 °C) and pure CoFeAl-LDH (46.6 °C). This indicates that the photothermal conversion performance of the CoFeAl-LDH@PDA1 composite material is better than that of pure PDA and pure CoFeAl-LDH. The high surface temperature of the catalyst can promote the absorption and activation of reactants, thereby improving the photothermal synergistic catalytic performance of the catalyst.

[0029] Example 6 (Hydrogen production performance test of photothermal synergistic catalyst) First, put 2 mg of the catalyst, 0.3 g of NaBH4, and 1 g of NaOH into the reactor. Inject 30 mL of defoamed deionized water into the reactor through the water injection port and turn on the magnetic stirrer. Carry out a photoreaction with a 100 W LED light source.

[0030] To rule out the interference of the improved hydrogen production performance of the self-hydrolysis of NaBH4 after illumination, we carried out a blank comparison experiment (i.e., testing the hydrogen production volume of the self-hydrolysis of NaBH4 without adding any catalyst). From Figure 6 (a), we can find that compared with the blank experiment without adding a catalyst, CoFeAl-LDH@PDA has better hydrogen production performance under illumination conditions, and the hydrogen production volume of the blank experiment is almost negligible. Figure 6(b) The performance change after the combination of LDH and PDA was investigated by comparing the hydrogen production rates of CoFeAl-LDH@PDA, pure PDA, and pure LDH under illumination without an external heat source. Through experimental verification, it was found that the hydrogen production rate of CoFeAl-LDH@PDA for the photocatalytic and thermocatalytic hydrolysis of sodium borohydride was higher than that of pure PDA and pure LDH. Moreover, when the weight ratio of CoFeAl-LDH to dopamine was 1:1, CoFeAl-LDH@PDA exhibited the best hydrogen production performance. This indicates that the coating of PDA enhanced the photocatalytic and thermocatalytic ability of CoFeAl-LDH@PDA, achieving the expected synergistic effect of 1 + 1 > 2 for the photothermal conversion capabilities of PDA and LDH.

[0031] Example 7 (Testing the hydrogen production cycle stability of the photocatalytic and thermocatalytic catalyst) To study the stability of CoFeAl-LDH@PDA, five-cycle performance tests were conducted on CoFeAl-LDH@PDA. As Figure 7 shown, after five cycles, the hydrogen production amount of CoFeAl-LDH@PDA for the hydrolysis of NaBH4 was 85% of the initial hydrogen production amount, indicating that CoFeAl-LDH@PDA had good stability and a significantly improved stability compared to pure LDH.

[0032] The foregoing description has shown and described several preferred embodiments of the invention. However, as previously mentioned, it should be understood that the invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the above teachings or the techniques or knowledge in related fields. Any alterations and changes made by those skilled in the art without departing from the spirit and scope of the invention shall fall within the protection scope of the appended claims of the invention.

Claims

1. A method for preparing a cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst, characterized in that: Adding cobalt-iron-aluminum layered hydroxides in different proportions to an alkaline buffer solution, and dispersing them uniformly by ultrasonication, and then adding dopamine to continue polymerizing under ultrasonication; The product was filtered, washed, and vacuum dried to obtain the Co6FeAl-LDH@PDA composite material.

2. The method for preparing the cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst according to claim 1, characterized in that: The molar ratio of cobalt, iron and aluminum in the cobalt-iron-aluminum layered hydroxide is 6:1:

1.

3. The method for preparing the cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst according to claim 1, characterized in that: The weight ratio of cobalt-iron-aluminum layered hydroxide to dopamine is 1:2-5:

1.

4. The method for preparing the cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst according to claim 1, characterized in that: The buffer solution is a glycine-sodium hydroxide buffer solution with a pH of 8.6-10.

5. The method for preparing the cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst according to claim 1, characterized in that: The dosage ratio of cobalt-iron-aluminum layered hydroxide to buffer solution is 0.5-2 g:1000 mL.

6. The method for preparing the cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst according to claim 1, characterized in that: The post-treatment includes suction filtration and washing 3-5 times.

7. The method for preparing the cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst according to claim 1, characterized in that: The vacuum drying temperature is 40-60°C and the time is 2-6h.

8. The cobalt-iron-aluminum layered hydroxide-polydopamine composite photothermal synergistic catalyst as described in claim 1 is used in the field of photothermal synergistic catalytic decomposition of sodium borohydride to produce hydrogen.

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