A nano silver-based composite material and its preparation method and application

Abstract

This invention belongs to the technical field of nano-silver-based composite materials, and discloses a nano-silver-based composite material, its preparation method, and its application. The preparation method is as follows: using straw residue as a matrix, drying and pulverizing it, followed by sequential carbonization, activation, and sulfonation treatments to obtain modified biochar; dispersing the modified biochar in a solution containing silver salt, adding a reducing agent to obtain a mixed solution; subjecting the mixed solution to a hydrothermal reaction to in-situ coating of the modified biochar with a layer of nano-silver; after solid-liquid separation, freeze-drying the solid phase component to obtain the nano-silver-based composite material. The preparation method of this invention is easy to operate, and the prepared material has good and stable catalytic performance, which is conducive to its widespread use.

Description

Technical Field

[0001] This invention relates to the field of nano-silver-based composite materials technology, and in particular to a nano-silver-based composite material, its preparation method, and its application. Background Technology

[0002] Noble metal catalysts are widely used in industrial catalysis, new energy research materials, and catalytic hydrogen production due to their high catalytic activity, as well as their advantages such as high temperature resistance, oxidation resistance, and corrosion resistance.

[0003] However, the high price of precious metals hinders their widespread use. Therefore, those skilled in the art have proposed using nickel, silver, and their alloys to replace platinum and gold. While nickel possesses excellent electrocatalytic performance, it gradually dissolves in acidic electrolytes during the catalytic process, leading to decreased stability of the catalytic material and consequently a decline in its hydrogen evolution performance. Silver itself exhibits good catalytic activity, and existing technologies have proposed that reducing silver nitrate to silver nanoparticles significantly improves its catalytic performance. However, the small size of silver nanoparticles makes them difficult to recycle, resulting in poor reusability.

[0004] To address the aforementioned technical issues, existing technologies propose combining silver nanoparticles with other materials (such as carbon materials) to increase the volume of silver nanoparticles and thus improve their reusability. However, silver nanoparticles tend to agglomerate in solution, resulting in poor bonding between them and other materials. During catalysis, they are prone to detaching from other materials, thus failing to effectively improve the catalytic performance of the material and ensure its stability.

[0005] Therefore, the present invention provides a nano-silver-based composite material, its preparation method, and its application. Summary of the Invention

[0006] To address the problem in the prior art where nano-silver is prone to aggregation, resulting in poor bonding with other materials and easy detachment during catalysis, making it difficult to prepare highly efficient and stable catalytic materials and severely limiting the application of nano-silver in catalytic materials, this invention provides a nano-silver-based composite material, its preparation method, and its application.

[0007] The present invention provides a nano-silver-based composite material, its preparation method, and its application, which are achieved through the following technical solutions:

[0008] The first objective of this invention is to provide a method for preparing a nano-silver-based composite material, comprising the following steps:

[0009] Step 1: Using straw residue as a matrix, dry and crush it, then perform carbonization, activation and sulfonation treatments in sequence to obtain modified biochar.

[0010] Step 2: Disperse the modified biochar in a solution containing silver salt, add a reducing agent, and obtain a mixed solution;

[0011] Step 3: The mixed solution is subjected to a hydrothermal reaction to coat the modified biochar surface with a layer of nano-silver in situ. After solid-liquid separation, the solid phase component is freeze-dried to obtain the nano-silver-based composite material.

[0012] Furthermore, the silver salt is silver nitrate; the reducing agent is any one of triethylamine, glucose, ascorbic acid, ferrous sulfate, and citric acid.

[0013] Furthermore, the mass ratio of the modified biochar to the silver salt is 1:0.5~1.5;

[0014] Furthermore, the concentration of the silver salt in the mixed solution is 3~5 g / L.

[0015] Furthermore, the molar ratio of the reducing agent to the silver salt is 1~1.5:1.

[0016] Furthermore, in step 1, the carbonization temperature is 400~500℃ and the carbonization time is 1~3h.

[0017] Further, in step 1, the activation treatment steps are as follows:

[0018] Ferric nitrate and zinc chloride are uniformly dispersed in an aqueous solution to obtain an impregnation solution;

[0019] The carbonized product is impregnated in an impregnation solution for 6-24 hours, and the solid and liquid are separated to obtain the solid phase component. The solid phase component is then activated at 550-650°C for 1-3 hours to obtain the biochar.

[0020] The impregnation solution contains ferric nitrate at a concentration of 10-30 g / L and zinc chloride at a concentration of 30-70 g / L.

[0021] Further, in step 1, the sulfonation treatment is performed as follows:

[0022] The biochar is placed in sulfuric acid and soaked and sulfonated under stirring to achieve sulfonation treatment and obtain modified biochar.

[0023] The sulfuric acid to the biochar solid-liquid ratio is 1g:10~20mL; the sulfuric acid has a mass fraction of 98%.

[0024] The stirring process is carried out at a temperature of 140-160℃, for a stirring time of 8-16 hours, and at a stirring rate of 150-250 r / min.

[0025] The second objective of this invention is to provide a nano-silver-based composite material prepared by the above-described preparation method.

[0026] A third objective of this invention is to provide an application of the above-mentioned nano-silver-based composite material in electrocatalytic materials.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] This invention preferentially uses abundant agricultural waste biomass straw residue as the base carbon source, which not only reduces costs but also enables the high-value utilization of waste biomass, reducing environmental pollution and playing a role in environmental protection. Furthermore, this invention obtains biochar with a rich specific surface area by carbonizing and activating the straw residue. The biochar undergoes sulfonation treatment to introduce sulfonate groups, which helps increase the proportion of active sites. This allows the biochar to chemically bond with silver ions through sulfonate groups, enhancing the binding force between the biochar and nano-silver and solving the problems of easy detachment and poor reusability of nano-silver. Simultaneously, the modified biochar improves its role as a carrier, allowing nano-silver to form a film structure on its surface during subsequent reactions. This prevents the nano-silver from agglomerating and increases the volume of the catalytic material, thereby increasing the effective contact area of ​​the nano-silver during use, improving its catalytic performance, and facilitating recycling due to the increased volume of the catalytic material.

[0029] This invention involves uniformly dispersing modified biochar in a silver salt solution, ensuring sufficient contact between the modified biochar and silver ions in the solution. This facilitates the bonding of sulfonate groups on the surface of the modified biochar with silver ions, resulting in a uniform distribution of silver ions on the surface of the modified biochar. Then, a reducing agent is added. During the hydrothermal reaction, the reducing agent reduces the silver ions to elemental silver, thereby achieving a uniform coating of nano-silver particles on the surface of the modified biochar. Simultaneously, the porous and rough structure of the modified biochar acts as a seed crystal, promoting the in-situ precipitation of nano-silver on its surface. This strengthens the bond between the nano-silver and the modified biochar, making the nano-silver less prone to detachment and thus improving the stability of the material's catalytic performance.

[0030] The preparation method of the present invention is easy to operate, the raw material cost is lower than that of precious metals, and the prepared material has good and stable catalytic performance, which is conducive to its widespread use. Attached Figure Description

[0031] Figure 1 This is a SEM image of the silver nanoparticle-based composite material prepared in Example 1.

[0032] Figure 2 The change in absorbance of the characteristic absorption peak (at 400 nm) of p-nitrophenol aqueous solution over time after treatment with the nano-silver-based composite materials prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0033] Figure 3 The conversion rate of the nano-silver-based composite material of Example 1 at different cycle numbers. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0035] This invention provides a nano-silver-based composite material, and its preparation method is as follows:

[0036] Step 1, Preparation of modified biochar

[0037] Using straw residue as a matrix, the residue is dried and crushed, and then subjected to carbonization, activation and sulfonation treatments in sequence to obtain modified biochar.

[0038] It should be noted that the present invention preferably uses abundant agricultural waste biomass straw residue (the straw residue can be selected from any one of corn straw residue, rice straw residue and wheat straw residue) as the base carbon source, which can not only reduce costs, but also make high-value utilization of waste biomass, reduce environmental pollution, and play a role in protecting the environment.

[0039] To facilitate subsequent processing of the straw residue, this invention preferably involves drying it at a temperature of 80-105°C for 4-8 hours to remove moisture. Subsequently, it is pulverized using a crushing device until it can pass through an 80-mesh sieve, thereby increasing its surface area and facilitating carbonization and activation treatment.

[0040] To obtain a porous material with a high specific surface area, this invention first carbonizes pulverized straw residue at 400-500℃ for 1-3 hours. Then, ferric nitrate and zinc chloride are uniformly dispersed in an aqueous solution to obtain an impregnation solution (the concentration of ferric nitrate in the impregnation solution is 10-30 g / L, and the concentration of zinc chloride is 30-70 g / L). The carbonized product is then impregnated in the impregnation solution for 6-24 hours, followed by solid-liquid separation to obtain the solid phase component, which is then activated at 550-650℃ for 1-3 hours to obtain biochar. The biochar prepared by this invention through the above steps has a high specific surface area.

[0041] It should also be noted that this invention, by sulfonating the obtained biochar to introduce sulfonate groups, increases the proportion of its active sites. This, in turn, allows the modified biochar to chemically bond with silver ions in subsequent processes via sulfonate groups, thereby enhancing the binding force between the modified biochar and nano-silver and solving the problems of easy detachment and poor reusability of nano-silver. Simultaneously, the modified biochar acts as a carrier, enabling the formation of a film structure of nano-silver on its surface during subsequent reactions. This prevents the nano-silver from agglomerating and increases the effective contact area of ​​the nano-silver during use, thus improving its electrocatalytic performance. Furthermore, the present invention performs sulfonation treatment through the following steps: placing the biochar in sulfuric acid and soaking and sulfonating it under stirring to obtain sulfonated biochar; wherein, the solid-liquid ratio of sulfuric acid to the biochar is 1g:10~20mL, and the mass fraction of sulfuric acid is 98%; the stirring temperature is 140~160℃, the stirring time is 8~16h, and the stirring rate is 150~250r / min to obtain modified biochar.

[0042] Step 2: Disperse the modified biochar in a solution containing silver salt, add a reducing agent to obtain a mixed solution; subject the mixed solution to a hydrothermal reaction to in situ coat a layer of nano-silver on the surface of the modified biochar; after solid-liquid separation, freeze-dry the solid phase component to obtain the nano-silver-based composite material.

[0043] It should be noted that, for ease of operation and to improve the contact effect between modified biochar and silver ions, this invention first uniformly disperses silver salt in an aqueous solvent using ultrasound to obtain a silver salt solution with uniformly distributed silver ions. Then, the modified biochar prepared above is uniformly dispersed in the silver salt solution using ultrasound, ensuring sufficient contact between the modified biochar and the silver ions in the solution. Under ultrasound, the sulfonate groups on the surface of the modified biochar can bond with the silver ions, resulting in a uniform distribution of silver ions on the surface of the modified biochar. Next, a reducing agent is added. During the hydrothermal reaction, the reducing agent reduces the silver ions to metallic silver, thereby achieving a uniform coating of nano-silver particles on the surface of the modified biochar. Simultaneously, the porous and rough structure of the modified biochar acts as a seed crystal, facilitating the in-situ precipitation of nano-silver on the surface of the modified biochar, strengthening the bonding force between the nano-silver and the modified biochar, making the nano-silver less prone to detachment, and thus improving the stability of the material's catalytic performance.

[0044] This invention does not limit the specific type of silver salt, as long as it can increase the silver ion concentration; silver nitrate can be selected as an example. Furthermore, the reducing agent of this invention is any one of triethylamine, glucose, ascorbic acid, ferrous sulfate, and citric acid, preferably citric acid.

[0045] This invention involves separating the solid and liquid phases of the hydrothermal reaction product through filtration, then washing the obtained solid phase product until the washing liquid is neutral to remove surface impurities. Following this, the product undergoes freeze-drying to remove surface moisture while preserving the original porous structure of the material. The freeze-drying temperature of this invention is -80 to -50°C, and the drying time is 4 to 24 hours.

[0046] Example 1

[0047] This embodiment provides a nano-silver-based composite material, and its preparation method is as follows:

[0048] 1) After drying the corn stalks at 90℃ for 6 hours, crush them with a pulverizer and pass them through an 80-mesh sieve to obtain corn stalk powder.

[0049] 2) Carbonize the corn stalk powder obtained above at 450℃ for 2 hours, and then cool it to room temperature to obtain biochar precursor.

[0050] 3) Ferric nitrate and zinc chloride are uniformly dispersed in an aqueous solution to prepare an impregnation solution with a concentration of 20 g / L for ferric nitrate and 50 g / L for zinc chloride. The biochar precursor obtained above is then impregnated in the solution, ensuring that the impregnation solution covers the surface of the biochar precursor. After impregnation at room temperature for 12 h, the solution is filtered, and the obtained solid phase is activated at 600 °C for 2 h to obtain biochar.

[0051] 4) According to the ratio of sulfuric acid to biochar solid-liquid ratio of 1g:15mL, the biochar obtained above is placed in the corresponding volume of 98% sulfuric acid. The temperature is raised to 140~160℃ under the stirring action of 150~250r / min, and the reaction is carried out at 140~160℃ for 10h. The obtained solid phase component is the modified biochar.

[0052] 5) Place silver nitrate in deionized water and sonicate for 10 min to fully dissolve and disperse it evenly to obtain a silver nitrate solution. Then, add modified biochar of the same mass as silver nitrate to the silver nitrate solution and continue sonicating for 30 min. Then add sodium citrate with a molar amount of 1.5 times that of silver nitrate and sonicate for 1 min. Transfer to a polytetrafluoroethylene liner, pack into a reactor, and hydrothermally treat at 200℃ for 12 h. After cooling to room temperature, filter and wash until the pH of the washing solution is neutral. Then freeze-dry to obtain the nano-silver-based composite material.

[0053] Example 2

[0054] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0055] In this embodiment, the mass ratio of modified biochar to silver salt is 1:0.5, and the concentration of silver salt in the mixed solution is 3 g / L.

[0056] Example 3

[0057] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0058] In this embodiment, the mass ratio of modified biochar to silver salt is 1:1.5, and the concentration of silver salt in the mixed solution is 5 g / L.

[0059] Example 4

[0060] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0061] In this embodiment, the hydrothermal reaction temperature is 150°C and the reaction time is 24 hours.

[0062] Example 5

[0063] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0064] In this embodiment, the hydrothermal reaction temperature is 250°C and the reaction time is 8 hours.

[0065] Example 6

[0066] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0067] In this embodiment, the molar ratio of the reducing agent to the silver salt is 1.5:1.

[0068] Example 7

[0069] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0070] In this embodiment, the molar ratio of the reducing agent to the silver salt is 1.3:1.

[0071] Example 8

[0072] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0073] In this embodiment, the carbonization temperature is 400°C and the carbonization time is 3 hours.

[0074] Example 9

[0075] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0076] In this embodiment, the carbonization temperature is 500°C and the carbonization time is 1 hour.

[0077] Example 10

[0078] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0079] In this embodiment, the activation temperature is 550°C and the activation time is 3 hours.

[0080] Example 11

[0081] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0082] In this embodiment, the activation temperature is 650°C and the activation time is 1 hour.

[0083] Example 12

[0084] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0085] In this embodiment, during the activation treatment, the concentration of ferric nitrate in the impregnation solution is 10 g / L, and the concentration of zinc chloride is 30 g / L.

[0086] Example 13

[0087] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0088] In this embodiment, during the activation treatment, the concentration of ferric nitrate in the impregnation solution is 30 g / L, and the concentration of zinc chloride is 70 g / L.

[0089] Example 14

[0090] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0091] In this embodiment, during the sulfonation treatment, the solid-liquid ratio of sulfuric acid to biochar was 1g:10mL; and the stirring temperature was 140℃, the stirring time was 16h, and the stirring rate was 150r / min.

[0092] Example 15

[0093] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0094] In this embodiment, during the sulfonation treatment, the solid-liquid ratio of sulfuric acid to biochar was 1g:20mL; and the stirring temperature was 160℃, the stirring time was 8h, and the stirring rate was 250r / min.

[0095] Example 16

[0096] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0097] In this embodiment, triethylamine is used as a reducing agent.

[0098] Example 17

[0099] This embodiment provides a nano-silver-based composite material, and its preparation method differs from that of Example 1 only in that:

[0100] In this embodiment, wheat straw is used as straw residue.

[0101] Comparative Example 1

[0102] The only difference between this comparative example and Example 1 is that:

[0103] Without sulfonation, the activated biochar is directly placed in a silver salt solution for hydrothermal reaction.

[0104] Comparative Example 2

[0105] The only difference between this comparative example and Example 1 is that:

[0106] The product obtained from the hydrothermal reaction was dried using a conventional drying method, namely, in an oven at 60°C for 6 hours.

[0107] Experimental Section

[0108] (a) SEM testing

[0109] This invention takes the nano-silver-based composite material prepared in Example 1 as an example, and performs SEM testing on it. The test results are as follows: Figure 1 As shown.

[0110] Figure 1 The image shows the SEM image of the silver nanoparticle-based composite material prepared in Example 1. It can be seen that silver nanoparticles are uniformly loaded on the surface of the modified biochar, indicating that the silver nanoparticle-based composite material prepared by the method of the present invention can make silver nanoparticles uniformly formed on the surface of the modified biochar.

[0111] (II) Catalytic performance testing

[0112] This invention evaluates the catalytic ability and reusability of the catalytic reduction reaction of p-nitrophenol.

[0113] A 10 mmol / L aqueous solution of p-nitrophenol was prepared as the catalytic solution, and a 30 mmol / L aqueous solution of sodium borohydride was prepared as the reducing agent.

[0114] Then, three groups of 0.2 mL of the above-mentioned p-nitrophenol aqueous solution were separately labeled as Group #1, Group #2, and Group #3. 10 mg of the nano-silver-based composite material prepared in Example 1, Comparative Example 1, and Comparative Example 2 was added to Group #1, Group #2, and Group #3, respectively. After mixing, 20 mL of the above-mentioned sodium borohydride aqueous solution was added to each group and mixed again. At 0 min, 1 min, 2 min, 3 min, 4.5 min, 6.5 min, 8 min, and 10 min after adding 20 mL of the sodium borohydride aqueous solution, 2 mL of the mixed solution was taken, and the absorbance of the characteristic absorption peak of nitrophenol (at 400 nm) was measured over time using a spectrophotometer (UV-2450 spectrophotometer). The results were recorded as follows. Figure 2 As shown.

[0115] Depend on Figure 2 It can be seen that the nano-silver-based composite material prepared in Example 1 of this invention has the best catalytic effect on the catalytic reduction of p-nitrophenol, followed by Comparative Example 2, and the worst in Comparative Example 1. This indicates that the sulfonation treatment of biochar is a key step in improving its catalytic performance, and the drying treatment method also has an important influence on its catalytic performance. This shows that the catalytic performance of the nano-silver-based composite material prepared in this invention is not improved by a single step, but is improved by each step being carried out sequentially.

[0116] To further test the stability of its catalytic performance, the nano-silver-based composite material of Example 1 after the above experiment was recovered (i.e., the nano-silver-based composite material of Example 1 was recovered by filtering the solution after the above reaction and drying the solid). The recovered nano-silver-based composite material was then subjected to the above experiment again, and the characteristic absorption peak of p-nitrophenol at 400 nm was measured after 10 min of treatment. This was repeated five times, and the corresponding conversion rate was calculated based on the measured absorbance. The conversion rate is calculated as follows: Conversion rate = [(1.6 - measured absorbance) / 1.6] × %, where 1.6 is the initial absorbance of the p-nitrophenol aqueous solution. The conversion rate results are shown below. Figure 3 As shown, after 5 cycles, the conversion rate of Example 1 is still less than 95%, indicating that the nano-silver-based composite material prepared by the present invention has strong stability.

[0117] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a nano-silver-based composite material, characterized in that, Includes the following steps: Step 1: Using straw residue as a matrix, dry and crush it, then perform carbonization, activation and sulfonation treatments in sequence to obtain modified biochar. Step 2: Disperse the modified biochar in a solution containing silver salt, add a reducing agent, and obtain a mixed solution; The mixed solution is subjected to a hydrothermal reaction to coat a layer of nano-silver on the surface of the modified biochar in situ. After solid-liquid separation, the solid phase component is freeze-dried to obtain the nano-silver-based composite material. The activation process involves the following steps: Ferric nitrate and zinc chloride are uniformly dispersed in an aqueous solution to obtain an impregnation solution; The carbonized product is impregnated in an impregnation solution for 6-24 hours, and the solid and liquid are separated to obtain the solid phase component. The solid phase component is then activated at 550-650°C for 1-3 hours to obtain the biochar. The impregnation solution contains ferric nitrate at a concentration of 10-30 g / L and zinc chloride at a concentration of 30-70 g / L. The sulfonation process involves the following steps: The biochar was placed in sulfuric acid and soaked and sulfonated under stirring. The solid-liquid ratio of the biochar to sulfuric acid is 1g:10~20mL; the mass fraction of the sulfuric acid is 98%. The stirring process is carried out at a temperature of 140~160℃, for a stirring time of 8~16h, and at a stirring rate of 150~250r / min. The hydrothermal reaction is carried out at a temperature of 150~250℃ for 8~24h.

2. The preparation method according to claim 1, characterized in that, The silver salt is silver nitrate; The reducing agent is any one of triethylamine, glucose, ascorbic acid, ferrous sulfate, and citric acid.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the modified biochar to the silver salt is 1:0.5~1.5; Furthermore, the concentration of the silver salt in the mixed solution is 3~5 g / L.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the reducing agent to the silver salt is 1~1.5:

1.

5. The preparation method according to claim 1, characterized in that, in step 1, the carbonization temperature is 400~500℃ and the carbonization time is 1~3h.

6. A nano-silver-based composite material prepared by the preparation method according to any one of claims 1-5.

7. The application of the nano-silver-based composite material according to claim 6 in the catalytic reduction reaction of p-nitrophenol.

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