A Ru-modified α-Co(OH) 2 cellulose membrane and its preparation method and application

Abstract

The present invention discloses a Ru-modified α-Co(OH)2 cellulose membrane, a preparation method thereof and an application thereof. The preparation method of the Ru-modified α-Co(OH)2 cellulose membrane includes: first preparing a ZIF-67 / CNF suspension, and then placing it in a reaction kettle for reaction to obtain α-Co(OH)2 / CNF; then taking ruthenium trichloride hydrate and dissolving it in water, adding the obtained α-Co(OH)2 / CNF and a reducing agent for reaction to obtain Ru-modified α-Co(OH)2 / CNF; then taking polyvinyl alcohol and dissolving it in water, adding the obtained Ru-modified α-Co(OH)2 / CNF and a silane coupling agent for reaction, placing it in a mold for cooling and drying to obtain the product. The cellulose membrane of the present invention can be reused, has a high hydrogen production rate for the hydrolysis of metal hydrides and excellent stability.

Description

Technical Field

[0001] The present invention relates to an integral catalyst, and particularly to an Ru-modified α-Co(OH) 2 cellulose membrane and its preparation method and application. Background Art

[0002] Fossil energy is increasingly depleted, and its large-scale consumption has led to a large amount of carbon dioxide emissions, and the greenhouse effect is becoming increasingly serious. To meet the energy needs of mankind, hydrogen energy is considered an ideal energy form in the future due to its high combustion heat and zero carbon dioxide emissions. However, the problem of hydrogen storage has always been an important link hindering the large-scale use of hydrogen energy. Therefore, researchers are committed to discovering and using efficient and safe hydrogen storage materials. Among them, the chemical hydrogen storage material sodium borohydride (NaBH 4 ) has attracted much attention due to its high hydrogen storage capacity (10.57 wt%), the ability to produce high-purity hydrogen even at low temperatures, its high stability in alkaline solutions, and the non-toxic and recyclable hydrolysis by-products.

[0003] Noble metal and transition metal composite catalysts exhibit excellent catalytic performance during the hydrolysis of NaBH 4 . However, most of these catalysts are powder-type catalysts, which often form large aggregates during the reaction, resulting in a low reaction rate and being difficult to recycle after application, which is extremely disadvantageous for industrialization. Therefore, it is very necessary to prepare a high-performance monolithic catalyst to promote the industrial production of hydrogen by NaBH 4 hydrolysis. In the previous research results of the inventor team of this application, a monolithic catalyst of ruthenium-cobalt phosphide-based aerogel supported on graphene oxide (patent for invention with publication number CN115463676A) was designed and prepared. It was obtained by dispersing the powdered Ru-CoP@GO composite material in water, adding chitosan and mixing evenly to obtain solution A, mixing it with solution B obtained by dispersing graphene oxide in water, adding acetic acid, removing bubbles, standing, and then drying. Although the obtained aerogel has high hydrogen production performance, its stability is not ideal enough. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an Ru-modified α-Co(OH) 2 cellulose membrane with a higher hydrogen production rate and better stability for the hydrolysis of metal hydrides, and its preparation method and application.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A preparation method of an Ru-modified α-Co(OH) 2 cellulose membrane, comprising the following steps:

[0007] 1) Take cellulose nanofibers (CNF) and cobalt nitrate hexahydrate and place them in water, disperse them evenly to obtain solution A; dissolve dimethylimidazole in water to obtain solution B; mix solution A and solution B and react to obtain a ZIF-67 / CNF suspension;

[0008] 2) Place the obtained ZIF-67 / CNF suspension in a reaction kettle for reaction. After the reaction is completed, collect the precipitate and wash it to obtain α-Co(OH) 2 / CNF;

[0009] 3) Take ruthenium(III) chloride hydrate (RuCl 3 ·3H 2 O) and dissolve it in water, add α-Co(OH) 2 / CNF, mix evenly and then add a reducing agent for reaction. After the reaction is completed, collect the precipitate and wash it to obtain Ru-modified α-Co(OH) 2 / CNF;

[0010] 4) Take polyvinyl alcohol (PVA) and dissolve it in water, add Ru-modified α-Co(OH) 2 / CNF, mix evenly and then add a silane coupling agent for reaction, and then place it in a mold to cool and dry to obtain a Ru-modified α-Co(OH) 2 cellulose membrane (Ru-modified α-Co(OH) 2 cellulose membrane is also simply referred to as Ru@α-Co(OH) 2 cellulose membrane) in this application.

[0011] In step 1) of the above preparation method, in the obtained ZIF-67 / CNF suspension, the loading amount of ZIF-67 in ZIF-67 / CNF (that is, the weight ratio of ZIF-67 in ZIF-67@CNF) is preferably 30-60 wt%; calculate and weigh the corresponding amounts of cellulose nanofibers, cobalt nitrate hexahydrate, and dimethylimidazole according to this loading amount. Solution A and solution B are usually mixed at room temperature and stirred for reaction for 0.5-2 h to obtain a ZIF-67 / CNF suspension.

[0012] In step 2) of the above preparation method, convert ZIF-67 in ZIF-67 / CNF into α-Co(OH) 2 by hydrothermal reaction to obtain α-Co(OH) 2 / CNF, where the reaction is preferably carried out at 80-140 °C, and the reaction time is preferably 6-12 h; the precipitate collected after the reaction is usually washed with water. The reaction kettle involved is a hydrothermal reaction kettle commonly used in hydrothermal reactions in the prior art, and its inner lining is preferably a polytetrafluoroethylene lining.

[0013] In step 3) of the above preparation method, when α-Co(OH) 2 in α-Co(OH) 2 / CNF, the loading amount (i.e., the weight percentage of α-Co(OH) 2 in α-Co(OH) 2 / CNF) is 15-30 wt%, the concentration of α-Co(OH) 2 / CNF in the system of step 3) is preferably controlled at 0.6-1.2 wt%, and the concentration of ruthenium trichloride trihydrate is preferably controlled at 0.06-0.15 wt%. The applicant found in the experiment that the loading amount of α-Co(OH) 2 in α-Co(OH) 2 / CNF, the concentrations of α-Co(OH) 2 / CNF and ruthenium trichloride trihydrate in the system all have a great influence on the hydrogen production rate of the finally obtained cellulose membrane. Further, it is preferred that the loading amount of α-Co(OH) 2 in α-Co(OH) 2 / CNF is 20-30 wt%, the concentration of α-Co(OH) 2 / CNF in the system is 0.8-1.0 wt%, and the concentration of ruthenium trichloride trihydrate in the system is 0.1-0.12 wt%.

[0014] In step 3) of the above preparation method, the reducing agent is a conventional selection in the prior art, such as sodium borohydride or ascorbic acid, and sodium borohydride is preferably added in the form of an aqueous solution of sodium borohydride. The amount of the reducing agent used is usually in excess relative to the ruthenium element in ruthenium trichloride trihydrate, and is preferably 10-20 times the molar amount of the ruthenium element in ruthenium trichloride trihydrate. In this step, after adding the reducing agent, the reaction is carried out at room temperature, and the reaction time is usually 0.5-1 h; after the reaction is completed, it is washed with water.

[0015] In step 4) of the above preparation method, the concentrations of polyvinyl alcohol and Ru-modified α-Co(OH) 2 / CNF in the system not only affect the hydrogen production rate of the finally obtained cellulose membrane, but more importantly, also affect the stability of the finally obtained cellulose membrane. The applicant's experiment found that under the conditions defined in step 3) above, when the concentration of polyvinyl alcohol in the system of step 4) is controlled at 0.2-0.6 wt% and the concentration of Ru-modified α-Co(OH) 2 / CNF is controlled at 0.6-1.2 wt%, the finally obtained cellulose membrane can obtain a high hydrogen production rate and excellent stability. Further preferably, the concentration of polyvinyl alcohol in the system of step 4) is 0.4-0.5 wt%, and the concentration of Ru-modified α-Co(OH) 2 / CNF is 0.8-1.0 wt%.

[0016] In step 4) of the above preparation method, the addition of the silane coupling agent has a positive effect on the stability of the finally obtained cellulose membrane. The selection and dosage of the silane coupling agent are the same as those in the prior art. Specifically, the silane coupling agent is preferably KH-550 and / or KH-560, and its dosage is preferably 1-5 wt% of the dosage of cellulose nanofibers.

[0017] In step 4) of the above preparation method, from the perspective of facilitating the dissolution of polyvinyl alcohol, it is preferred to use hot water (water with a temperature of 60-90 °C) to dissolve polyvinyl alcohol. After dissolution, it is preferred to add Ru-modified α-Co(OH) 2 / CNF under the water bath condition of 60-90 °C, and stir and mix evenly under the above water bath condition to avoid generating too many bubbles and affecting the hydrogen production rate and cyclic stability of the finally obtained cellulose membrane. After stirring and reacting with the silane coupling agent for ≥3 min, the reaction material can be poured into a mold for cooling, and the cooling and drying can be natural drying, oven drying or freeze drying.

[0018] In this application, the water generally refers to deionized water.

[0019] The present invention further includes Ru-modified α-Co(OH) 2 prepared by the above method

[0020] The present invention further includes the application of the Ru-modified α-Co(OH) 2 cellulose membrane prepared by the above method in the preparation of a hydrogen production catalyst, specifically in the preparation of a metal hydride hydrolysis hydrogen production catalyst.

[0021] Compared with the prior art, the present invention uses ZIF-67 supported on cellulose nanofibers to be hydrothermally converted into α-Co(OH) 2 , and further adds RuCl 3 ·3H 2 O and reduces it to Ru, so that it has a synergistic effect with α-Co(OH) 2 ; combined with the addition of the silane coupling agent and polyvinyl alcohol to produce chemical and physical effects, finally an integral composite catalyst Ru-modified α-Co(OH) 2 cellulose membrane with a higher hydrogen production rate and better stability for metal hydride hydrolysis and capable of being reused is obtained. This catalyst can achieve a high hydrogen production rate and a low activation energy for the hydrolysis of NaBH 4 , and shows high stability during the catalytic process. At the same time, the morphology of the thin film is very convenient during the use and recycling process, which further promotes the catalysis of NaBH 4Industrial application of hydrogen production by hydrolysis. In addition, the cellulose membrane of the present invention can be made into different sizes, shapes and thicknesses according to needs, which is more convenient. Description of the Drawings

[0022] Figure 1 Appearance photograph of the Ru@α-Co(OH) prepared in Example 1 of the present invention 2 of the cellulose membrane, where (a) is the front view of the product and (b) is the side view of the product.

[0023] Figure 2 Appearance photograph of the Ru@α-Co(OH) prepared in Example 1 of the present invention 2 X-ray diffraction pattern of the cellulose membrane.

[0024] Figure 3 Appearance photograph of the Ru@α-Co(OH) prepared in Example 1 of the present invention 2 Electron microscope image of the cellulose membrane.

[0025] Figure 4 Schematic diagram of the water displacement test device used for the stability experiment of hydrogen production by catalytic hydrolysis of NaBH in Example 1 of the present invention 4

[0026] Figure 5 Appearance photograph of the Ru@α-Co(OH) prepared in Example 1 of the present invention 2 Hydrogen production rate and activation energy of cellulose membrane-catalyzed NaBH 4 hydrolysis, where (a) is the hydrogen production volume-time relationship curve and (b) is the hydrogen production rate-temperature relationship curve.

[0027] Figure 6 Appearance photograph of the Ru@α-Co(OH) prepared in Example 1 of the present invention 2 Hydrogen production stability experiment diagram of cellulose membrane-catalyzed NaBH 4 hydrolysis, where (a) is the hydrogen production volume-time relationship curve for 5 times and (b) is the bar chart of hydrogen production rate for 5 times.

[0028] The labels in the figure are:

[0029] 1 Round-bottom flask, 2 Water bath, 3 Gas washing bottle, 4 Square water tank, 5 Electronic balance, 6 Computer. Detailed Description of the Invention

[0030] In order to better explain the technical solution of the present invention, the present invention will be further described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto.

[0031] Example 1

[0032] ​1) Take 0.6 g of CNF and 0.58 g of cobalt nitrate hexahydrate and place them in 50 mL of water. Disperse them evenly to obtain solution A. Take 0.3 g of dimethylimidazole and dissolve it in 20 mL of water to obtain solution B. Mix solution A and solution B and stir at room temperature for 2 h to obtain a ZIF-67 / CNF suspension with a ZIF-67 loading of 50 wt%.

[0033] 2) Place the obtained ZIF-67 / CNF suspension in a polytetrafluoroethylene inner liner with a filling degree of 70%. Then, put the inner liner into the stainless-steel outer shell of the reaction kettle and seal it. Place it in an oven and react at a constant temperature of 120 °C for 12 h. After the reaction is completed, cool it to room temperature. Collect the precipitate in the reaction kettle and wash it with water to obtain α-Co(OH) 2 with a loading of 25 wt% 2 / CNF;

[0034] 3) Take 100 mL of water and add an appropriate amount of RuCl 3 ·3H 2 O and the α-Co(OH) 2 / CNF obtained in step 2). Control the concentration of RuCl 3 ·3H 2 O in the system to be 0.1 wt% and the concentration of α-Co(OH) 2 / CNF to be 0.8 wt%. Mix and stir for 2 h, then dropwise add 5 mL of an aqueous solution with a concentration of 5 wt% of NaBH 4 . Stir and react for 0.5 h. After the reaction is completed, centrifuge, collect the precipitate, and wash it with water to obtain Ru-modified α-Co(OH) 2 / CNF;

[0035] 4) Take 100 mL of water at a temperature of 80 °C. Under a water bath condition of 75 °C, add an appropriate amount of polyvinyl alcohol and the Ru-modified α-Co(OH) 2 / CNF obtained in step 3). Control the concentration of polyvinyl alcohol in the system to be 0.4 wt% and the concentration of Ru-modified α-Co(OH) 2 / CNF to be 0.84 wt%. Stir for 2 h, then add 0.02 g of KH-550 and stir and react for 3 min. Then, pour the reaction material into a mold to cool and vacuum dry it at 60 °C for 12 h to obtain the Ru@α-Co(OH) 2 cellulose membrane.

[0036] The appearance shape of the product obtained in this example is as Figure 1 shown, where (a) is the front view of the product and (b) is the side view of the product. Perform X-ray diffraction and electron microscopy analysis on the product obtained in this example. Its X-ray diffraction pattern and electron microscopy image are respectively as Figure 2 and Figure 3As shown. From Figure 2 it can be seen that the product obtained in this example is determined to be Ru@α-Co(OH) 2 cellulose membrane. From Figure 3 it can be seen that the product obtained in this example exhibits a complex and rough morphology caused by the fibrous structure and has certain pores, which is very beneficial for solute transfer and hydrogen transport during the hydrolysis of sodium borohydride.

[0037] The drainage method was used to test the hydrogen production process of the product Ru@α-Co(OH) 2 cellulose membrane catalyzing the hydrolysis of NaBH 4 . Among them, the schematic diagram of the drainage method test device is as shown in Figure 4 and the test method is as follows:

[0038] Prepare 50 mL of a mixed solution (containing 0.6 wt% NaBH 4 + 0.4 wt% NaOH) in a round-bottom flask 1, immerse it in a water bath 2 at 30 °C, and then take the Ru@α-Co(OH) 2 cellulose membrane (10 mm × 10 mm, length × width) prepared in this example and place it in the above mixed solution. Continuously stir, the catalytic reaction starts, hydrogen is continuously generated, enters the washing bottle 3, and the discharged water is introduced into the square water tank 4 placed on the electronic balance 5. The mass of the discharged water is recorded in real time by the online test system connected to the computer 6 and converted into the drainage volume (i.e., the hydrogen production volume), and the hydrogen production rate is calculated using the following formula.

[0039] Hydrogen production rate = drainage volume / (catalyst mass × catalytic time)

[0040] The experimental results are as shown in Figure 5 . From Figure 5 it can be seen that the hydrogen production rate of the Ru@α-Co(OH) 2 cellulose membrane catalyzing the hydrolysis of NaBH 4 is 4304 mL min -1 g -1 .

[0041] Using the Figure 4 device shown and the above test method to test the stability of the Ru@α-Co(OH) 2 cellulose membrane catalyzing the hydrolysis of NaBH 4 to produce hydrogen, the experimental results are as shown in Figure 6 . The experimental results show that the stability is 80.8%.

[0042] Comparative Example 1

[0043] Repeat Example 1, except that:

[0044] In step 3), the concentration of RuCl 3 ·3H 2 O in the control system is 0.05 wt%, and the concentration of α-Co(OH) 2 / CNF is 0.8 wt%;

[0045] In step 4), the concentration of polyvinyl alcohol in the control system is 0.4 wt%, and the concentration of Ru-modified α-Co(OH) 2 / CNF is 0.82 wt%.

[0046] The product obtained in this comparative example is still Ru@α-Co(OH) 2 cellulose membrane

[0047] Using the same test device and method as in Example 1, the hydrogen production rate and stability of the Ru@α-Co(OH) 2 cellulose membrane catalyzing the hydrolysis of NaBH 4 were tested. The results showed that the hydrogen production rate and stability were 2678 mL min -1 g -1 and 81.3%, respectively.

[0048] Comparative Example 2

[0049] Repeat Example 1, except that:

[0050] In step 3), the concentration of RuCl 3 ·3H 2 O in the control system is 0.16 wt%, and the concentration of α-Co(OH) 2 / CNF is 0.8 wt%.

[0051] The product obtained in this comparative example is still Ru@α-Co(OH) 2 cellulose membrane.

[0052] Using the same test device and method as in Example 1, the hydrogen production rate and stability of the Ru@α-Co(OH) 2 cellulose membrane catalyzing the hydrolysis of NaBH 4 were tested. The results showed that the hydrogen production rate and stability were 4401 mL min -1 g -1 and 74.9%, respectively.

[0053] Example 2

[0054] Repeat Example 1, except that:

[0055] In step 1), ZIF-67@CNF with a ZIF-67 loading of 40 wt% was prepared;

[0056] In step 2), α-Co(OH) is obtained 2 α-Co(OH) with a loading of 20 wt% 2 / CNF;

[0057] In step 3), the concentration of RuCl 3 ·3H 2 O in the system is controlled to be 0.1 wt%, and the concentration of α-Co(OH) 2 / CNF is 0.72 wt%;

[0058] In step 4), the concentration of polyvinyl alcohol in the system is controlled to be 0.4 wt%, and the concentration of Ru-modified α-Co(OH) 2 / CNF is 0.76 wt%.

[0059] The hydrogen production rate and stability of the Ru@α-Co(OH) 2 cellulose membrane obtained in this example for catalyzing the hydrolysis of NaBH 4 are tested using the same test device and method as in Example 1. The results show that the hydrogen production rate and stability are 3015 mL min -1 g -1 and 83.4%, respectively.

[0060] Example 3

[0061] Repeat Example 1, except that:

[0062] In step 1), ZIF-67@CNF with a ZIF-67 loading of 60 wt% is prepared;

[0063] In step 2), α-Co(OH) is obtained 2 α-Co(OH) with a loading of 30 wt% 2 / CNF;

[0064] In step 3), the concentration of RuCl 3 ·3H 2 O in the system is controlled to be 0.1 wt%, and the concentration of α-Co(OH) 2 / CNF is 0.84 wt%;

[0065] In step 4), the concentration of polyvinyl alcohol in the system is controlled to be 0.45 wt%, and the concentration of Ru-modified α-Co(OH) 2 / CNF is 0.88 wt%.

[0066] The hydrogen production rate and stability of the Ru@α-Co(OH) 2 cellulose membrane obtained in this example for catalyzing the hydrolysis of NaBH 4The hydrogen production rate and stability of hydrogen production by hydrolysis. The results show that the hydrogen production rate and stability are 4273 mL min -1 g -1 and 79.7%, respectively.

[0067] Example 4

[0068] Repeat Example 1, except that:

[0069] In step 1), ZIF-67@CNF with a ZIF-67 loading of 30 wt% is prepared;

[0070] In step 2), α-Co(OH) 2 α-Co(OH) with a loading of 15 wt% 2 / CNF is obtained;

[0071] In step 3), the concentration of RuCl 3 ·3H 2 O in the system is controlled to be 0.1 wt%, and the concentration of α-Co(OH) 2 / CNF is 0.69 wt%;

[0072] In step 4), the concentration of polyvinyl alcohol in the system is controlled to be 0.4 wt%, and the concentration of Ru-modified α-Co(OH) 2 / CNF is 0.73 wt%.

[0073] Using the same test device and method as in Example 1 to test the hydrogen production rate and stability of the Ru@α-Co(OH) 2 cellulose membrane catalyzing the hydrolysis of NaBH 4 The results show that the hydrogen production rate and stability are 2704 mL min -1 g -1 and 82.4%, respectively.

Claims

1. A preparation method of Ru-modified α-Co(OH) 2 cellulose membrane It includes the following steps: 1) Take cellulose nanofibers and cobalt nitrate hexahydrate and place them in water, disperse evenly to obtain solution A; dissolve dimethylimidazole in water to obtain solution B; mix solution A and solution B and react to obtain a ZIF-67 / CNF suspension; 2) The obtained ZIF-67 / CNF suspension is placed in a reaction kettle for reaction. After the reaction is completed, the precipitate is collected and washed to obtain α-Co(OH) 2 / CNF; 3) Dissolve ruthenium(III) chloride hydrate in water, add α-Co(OH) 2 / CNF, mix well and then add a reducing agent to react. After the reaction is completed, collect the precipitate, wash it, and obtain Ru-modified α-Co(OH) 2 / CNF; 4) Dissolve polyvinyl alcohol in water, add Ru-modified α-Co(OH) 2 / CNF, mix well and then add a silane coupling agent for reaction, and then place it in a mold to cool and dry to obtain a Ru-modified α-Co(OH) 2 cellulose membrane.

2. According to the preparation method described in claim 1, characterized in that, In step 3), when the loading amount of α-Co(OH) 2 in α-Co(OH) 2 / CNF is 15-30 wt%, the concentration of α-Co(OH) 2 / CNF in the system is 0.6-1.2 wt%, and the concentration of ruthenium trichloride hydrate is 0.06-0.15 wt%.

3. According to the preparation method described in claim 1, characterized in that, In step 3), the reducing agent is sodium borohydride or ascorbic acid.

4. According to the preparation method described in claim 1, characterized in that, In step 4), the concentration of polyvinyl alcohol in the system is 0.2 - 0.6 wt%, and the concentration of Ru-modified α-Co(OH) 2 / CNF is 0.6 - 1.2 wt%.

5. According to the preparation method described in claim 1, characterized in that, In step 4), the silane coupling agent is KH-550 and / or KH-560.

6. According to the preparation method described in any one of claims 1 to 5, characterized in that, In step 1), in the obtained ZIF-67 / CNF suspension, the loading amount of ZIF-67 in ZIF-67 / CNF is 30-60 wt%.

7. According to the preparation method described in claim 1, characterized in that, In step 2), the reaction is carried out under the condition of 80-140 °C.

8. Ru-modified α-Co(OH) prepared by the preparation method according to any one of claims 1 to 7 2 cellulose membrane 9. The Ru-modified α-Co(OH) according to claim 8 2 Use of a cellulose membrane in the preparation of a hydrogen-producing catalyst.

10. According to the application described in claim 9, characterized in that it is an application in the preparation of a catalyst for hydrogen production by sodium borohydride hydrolysis.

Images