Porous silver nanoparticle catalyst for reducing 4-nitrophenol and its preparation and application
By preparing porous silver nanoparticle catalysts, the problems of self-aggregation and low load of silver nanoparticles are solved, and the reduction of efficient catalytic 4-NP is achieved, which reduces production costs and equipment needs, and has high catalytic activity and repeatability.
Patent Information
- Application Number
- CN202211592650.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-13
- Publication Date
- 2024-12-10
- Estimated Expiration
- 2042-12-13
AI Technical Summary
In the prior art, silver nanoparticles (AgNPs) have self-aggregation behavior and low loading capacity during the reduction of 4-nitrophenol (4-NPs), resulting in low catalytic efficiency and requiring expensive instruments and equipment and complex processes. process.
The preparation method of porous silver nanoparticle catalyst was adopted, and the hydrothermal curing reaction of DVB and AIBN was combined with sulfuric acid and nitric acid treatment, followed by reaction with SnCl2 and 2-aldehyde pyridine to form Porous PDVB-PA as a support, and AgNO3 was used for The reduction reaction prepared an efficient porous silver nanoparticle catalyst, which avoided the self-aggregation of silver nanoparticles and increased the load of Ag.
It realizes efficient catalytic reduction of 4-NP under mild conditions, reducing production costs and equipment requirements, and the catalyst has high catalytic activity and excellent repeatability, avoids the self-aggregation of silver nanoparticles and improves catalytic efficiency.
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Figure CN115945221B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of water pollution control, and in particular to a porous silver nanoparticle catalyst for reducing 4-nitrophenol and a preparation method and application thereof. Background Art
[0002] With the progress of civilization, clean water has become an important link between people's lives and sustainable development, playing an extremely important role in places that we are not easy to notice. However, various water pollution problems are emerging in an endless stream. Organic pollutants such as pesticides, herbicides, antibiotics and nitroaromatics are continuously discharged into wastewater by humans and industrial operations, causing serious pollution to water quality and having a huge impact on the ecosystem, further exacerbating water shortages and threatening human health. Among the many pollutants, aromatic nitro compounds, especially 4-nitrophenol (4-NP), are very dangerous chemicals. They are recognized as a priority pollutant because of their non-biodegradability, carcinogenicity, chemical stability, persistence and toxicity to human health and the environment.
[0003] In order to reduce the dangerous impact of 4-NP on the environment and human safety, various technologies have been developed to remove 4-NP from the environment, such as adsorption, photocatalysis and flocculation. However, these technologies currently have the disadvantages of low efficiency and high energy consumption. Compared with various treatment methods, NaBH4-mediated chemical catalytic reduction is a more sustainable, green and efficient method. This method uses a reducing agent to convert 4-NP into 4-aminophenol (4-AP), which has the obvious advantage of converting harmful substances into value-added commodities. The reduction product 4-AP is not only an organic chemical product used to synthesize various analgesic and antipyretic drugs, but also has good product quality and green environmental protection concepts.
[0004] Due to the inertness of the nitro group, it is difficult for the reducing agent to spontaneously reduce 4-NP to 4-AP at room temperature. Therefore, it is necessary to find a low-cost, highly active, and highly selective catalyst to reduce 4-NP. The rapid development of nanotechnology has greatly promoted the development of catalysts. At present, noble metal nanoparticles such as AuNPs, PtNPs, PdNPs, and AgNPs are often used to reduce 4-NP in aqueous solution. AgNPs have always attracted much attention due to their efficient catalytic reduction performance, especially small-sized and highly dispersed AgNPs. In addition, the severe self-aggregation behavior of bare AgNPs greatly restricts their catalytic activity for 4-NP reduction. Therefore, a supporting substrate is needed to constrain the aggregation of AgNPs, thereby stabilizing the nanoparticles and controlling the size of the nanoparticles. Porous organic polymers are potential and excellent supporting materials due to their advantages such as simple synthesis, high specific surface area, and adjustable pore size, and have become the research object of many scholars. Therefore, it is of great practical significance to synthesize high-performance and highly stable porous silver nanoparticles using a low-cost and easy-to-operate method. Summary of the invention
[0005] In view of this, the present application provides a porous silver nanoparticle catalyst for reducing 4-nitrophenol and its preparation and application, which can solve the problems of severe self-aggregation behavior of AgNPs and low Ag loading capacity in the prior art. The prepared catalyst has high efficiency in catalyzing sodium borohydride reduction of 4-NP.
[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions:
[0007] In a first aspect, the present application provides a method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol, comprising the following steps:
[0008] S1. Using DVB and AIBN as raw materials, a hydrothermal curing reaction is carried out at 80-120°C in an organic solvent to obtain Porous PDVB;
[0009] S2. Add Porous PDVB to a mixture of sulfuric acid and nitric acid, stir in an ice bath, and then disperse in pure water to obtain Porous PDVB-NO2;
[0010] S3. Add Porous PDVB-NO2 and SnCl2 to concentrated hydrochloric acid and stir, and then disperse in pure water to obtain Porous PDVB-NH2;
[0011] S4. Dissolve Porous PDVB-NH2 in an organic solvent, then add 2-formylpyridine, and heat under reflux at 80-120°C to obtain Porous PDVB-PA;
[0012] S5. Under the condition of a reducing agent, porous PDVB-PA and AgNO3 are used as raw materials to react to obtain a reduced 4-nitrophenol porous silver nanoparticle catalyst.
[0013] Preferably, in step S1, the organic solvent is one or more of N,N'-dimethylformamide, tetrahydrofuran, acetonitrile and dimethyl sulfoxide.
[0014] Preferably, in step S4, the mass ratio of Porous PDVB-NH2 to 2-aldehyde pyridine is 1:2.3-3.4.
[0015] Preferably, in step S1, the molar ratio of DVB to AIBN is 1:0.002-0.006.
[0016] Preferably, the specific steps of step S5 are: heating the methanol solution of Porous PDVB-PA, then adding AgNO3 solution and stirring, removing the solvent by rotary evaporation, washing to obtain a precipitate, mixing the precipitate with a reducing agent, stirring, and removing impurities to obtain a reduced 4-nitrophenol porous silver nanoparticle catalyst.
[0017] Preferably, in step S3, the mass ratio of Porous PDVB-NO2 and SnCl2 is 1:5-8.
[0018] Preferably, in step S5, the mass ratio of Porous PDVB-PA to AgNO3 is 1:1.16-1.75.
[0019] Preferably, the mass ratio of Porous PDVB to sulfuric acid and nitric acid is 1:25-35:6-10.
[0020] In a second aspect, the present application provides a porous silver nanoparticle catalyst for reducing 4-nitrophenol.
[0021] In a third aspect, the present application provides an application of a porous silver nanoparticle catalyst for reducing 4-nitrophenol in catalyzing sodium borohydride to reduce 4-nitrophenol (4-NP) in water.
[0022] The beneficial effects of this application are as follows:
[0023] 1. The present invention does not require the use of complex and expensive instruments and equipment, is easy to industrialize, and has low-priced reaction monomers, mild reaction conditions, and is easy to control, thereby reducing investment costs.
[0024] 2.Porous PDVB-PA as a carrier material has abundant pores and high nitrogen content, and its inherent porous skeleton controls the size of the nanoparticles.
[0025] 3. High N content is not only Ag + It provides abundant coordination sites, ensures a high loading amount of Ag, and effectively anchors the position of Ag in porous materials, avoiding the self-aggregation behavior of AgNPs.
[0026] 4. The catalyst of the present invention is used as a catalyst for catalyzing the reduction of 4-NP by sodium borohydride, and has high catalytic activity and excellent repeatability. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 For Porous PDVB and Porous AgNPs 13 C NMR spectrum.
[0028] Figure 2The scanning electron microscopy images of Porous PDVB-PA and the projection electron microscopy images of Porous AgNPs.
[0029] Figure 3 This is the specific surface area diagram of Porous PDVB, Porous PDVB-PA and Porous AgNPs.
[0030] Figure 4 XRD patterns of Porous PDVB-PA and Porous AgNPs.
[0031] Figure 5 XPS full spectrum and Ag 3d spectrum of Porous AgNPs.
[0032] Figure 6 Thermogravimetric curves of Porous PDVB-PA and Porous AgNPs.
[0033] Figure 7 This is the UV spectrum of Porous AgNPs catalyzing the reduction of 4-AP by 4-NP.
[0034] Figure 8 This is the reaction rate diagram and cycle number diagram of Porous AgNPs catalyzing 4-NP. DETAILED DESCRIPTION
[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.
[0036] Explanation of terms
[0037] 4-NP (4-nitrophenol);
[0038] DVB (divinylbenzene);
[0039] Porous PDVB (porous polydivinylbenzene);
[0040] PDVB (polydivinylbenzene);
[0041] PA (bis-aldehyde pyridine);
[0042] AIBN (azobisisobutyronitrile);
[0043] AgNPs (silver nanoparticles);
[0044] The present application provides a method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol, comprising the following steps:
[0045] S1. Using DVB and AIBN as raw materials, a hydrothermal curing reaction is carried out in an organic solvent at 80-120°C to obtain Porous PDVB; specifically, DVB is added to 120 ml of an organic solvent at room temperature, and then AIBN is added and stirred for 2-5 hours, and the mixed solution is transferred to a high-pressure reactor, and hydrothermally cured at 80-120°C for 25-72 hours, and then the solution is cooled and filtered to obtain Porous PDVB;
[0046] S2. Add Porous PDVB to a mixture of sulfuric acid and nitric acid, stir in an ice bath, and then disperse in pure water to obtain Porous PDVB-NO2; specifically, take Porous PDVB and add it to a mixed solution of sulfuric acid (98%) and nitric acid (65%), stir in an ice water bath for 12-24h, then disperse the mixed solution in pure water, stir for 30-60min, filter, wash and dry to obtain Porous PDVB-NO2;
[0047] S3. Porous PDVB-NO2 and SnCl2 were added to concentrated hydrochloric acid and stirred, and then dispersed in pure water to obtain Porous PDVB-NH2; specifically, Porous PDVB-NO2 and SnCl2 were added to 60 ml of concentrated hydrochloric acid, stirred at room temperature for 2-4 days, and the mixture was dispersed in pure water, filtered and washed with an organic mixed solvent to obtain Porous PDVB-NH2;
[0048] S4. Porous PDVB-NH2 is dissolved in an organic solvent, and then 2-formaldehyde pyridine is added, and the mixture is heated under reflux at 80-120°C to obtain Porous PDVB-PA; specifically, Porous PDVB-NH2 is added to 100 ml of toluene, and the mixture is stirred at room temperature for 30-60 min, and then 2-formaldehyde pyridine is added, and the mixture is refluxed at 80-120°C for 24-48 h, and the solid sample is filtered and dried to obtain Porous PDVB-PA;
[0049] S5. Under the condition of a reducing agent, Porous PDVB-PA and AgNO3 are used as raw materials to react to obtain a reduced 4-nitrophenol porous silver nanoparticle catalyst; specifically, Porous PDVB-PA is added to a round-bottom flask containing 45 ml of methanol and continuously ultrasonicated for 10-30 minutes. Stir at room temperature for 30-60 minutes, heat the system to 50°C, add AgNO3 solution to the mixture, stir for 120-720 minutes, then rotary evaporate to remove the solvent, and then centrifuge and wash twice with distilled water to remove excess AgNO3. The collected precipitate is redissolved with 30 ml of methanol, and the reducing agent solution is added dropwise, and the precipitate is collected by stirring for 24-48 hours. The precipitate is further washed twice with water and methanol, centrifuged to remove free AgNPs and other impurities, and finally dried in a vacuum oven to obtain the catalyst Porous AgNPs for reducing 4-nitrophenol (4-NP); this process first adsorbs / captures Ag + ions and then reduced to Ag nanoparticles in situ.
[0050] The design idea of this scheme is to first obtain Porous PDVB through the double bond polymerization of DVB, then modify Porous PDVB with amine groups to obtain Porous PDVB-NH2, and then react Porous PDVB-NH2 with 2-aldehyde pyridine (2-PA) to obtain Schiff base-modified Porous PDVB-PA, and finally coordinate and stir Porous PDVB-PA in AgNO3 solution, and use a reducing agent to reduce it in situ to obtain the Porous AgNPs catalyst that reduces 4-NP to 4-AP.
[0051] The scheme does not require the use of complex instruments and equipment, is easy to industrialize, and has low-cost reaction monomers, mild reaction conditions, and is easy to control; the carrier material has abundant pores and high nitrogen content, and its inherent porous skeleton controls the size of the nanoparticles, and the high nitrogen content provides abundant coordination sites, ensuring a high silver loading amount and avoiding the self-aggregation behavior of silver nanoparticles; the catalyst of the present invention, as a catalyst for catalyzing the reduction of 4-NP by sodium borohydride, has high catalytic activity and excellent repeatability.
[0052] In some embodiments, in step S1, the organic solvent is one or more of N,N'-dimethylformamide, tetrahydrofuran, acetonitrile, and dimethyl sulfoxide.
[0053] In some embodiments, in step S4, the mass ratio of Porous PDVB-NH2 to 2-formylpyridine is 1:2.3-3.4.
[0054] In some embodiments, in step S1, the molar ratio of DVB to AIBN is 1:0.002-0.006.
[0055] In some embodiments, in step S3, the mass ratio of Porous PDVB-NO2 and SnCl2 is 1:5-8; the volume of pure water is 1-3L, and the organic mixed solvent is prepared from aminopropane and propanol; the volume ratio of aminopropane and propanol in the organic mixed solvent is 8:2.
[0056] In some embodiments, in step S5, the mass ratio of Porous PDVB-PA and AgNO3 is 1:1.16-1.75; preferably, the concentration of the AgNO3 solution can be 8.75 mg / ml; the reducing agent is at least one of hydrazine hydrate, potassium borohydride, L-ascorbic acid, and sodium citrate; preferably, the solubility of the reducing agent solution is 1 mol / l and the volume is 10 ml.
[0057] In some embodiments, the mass ratio of Porous PDVB to sulfuric acid and nitric acid is 1:25-35:6-10; and the volume of pure water is 1-3L.
[0058] In a second aspect, the present application provides a porous silver nanoparticle catalyst for reducing 4-nitrophenol.
[0059] In a third aspect, the present application provides an application of a porous silver nanoparticle catalyst for reducing 4-nitrophenol in catalyzing sodium borohydride to reduce 4-nitrophenol in water. The experimental steps for catalytic reduction of 4-nitrophenol (4-NP) are as follows:
[0060] At room temperature, NaBH4 was added into a round-bottom flask containing 4-NP solution, and then the prepared catalyst was added to initiate the reduction reaction. The entire reaction process was monitored by the change of the UV absorption peak. The UV spectrum detection range was from 250nm to 500nm.
[0061] It is further explained that after adding NaBH4, 4-nitrophenolate ions are formed in the solution, and at this time there is a maximum absorption peak at 400nm. Then the prepared Porous AgNPs catalyst is added to initiate the reduction reaction, and the reaction process is monitored by the decrease of the absorption peak at 400nm and the increase of the absorption peak at 300nm of the newly added 4-AP.
[0062] The present solution is further described below through specific embodiments.
[0063] Example 1
[0064] A method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol comprises the following steps:
[0065] S1. Add 13 g DVB to 120 ml DMF at room temperature, then add 0.3 g AIBN and continue stirring for 3 h. Transfer the mixed solution to an autoclave, hydrothermally cure at 100 °C for 48 h, cool and filter the solution to obtain Porous PDVB.
[0066] S2, add 5g of Porous PDVB to a mixed solution of 150g of sulfuric acid (98%) and 40g of nitric acid (65%), stir in an ice-water bath for 20h, then disperse the mixed solution into 2L of pure water, stir for 60min, filter, wash, and dry to obtain Porous PDVB-NO2;
[0067] S3, add 2g Porous PDVB-NO2 and 12g SnCl2 to 120ml concentrated hydrochloric acid, stir at room temperature for 2 days, continue to disperse the mixture into 2L pure water, filter and wash with a large amount of 8:2 mixed solvent of aminopropane and propanol to obtain Porous PDVB-NH2;
[0068] S4, add 5g of Porous PDVB-NH2 into 100ml of toluene, stir at room temperature for 60min, then add 30ml of 2-PA, reflux at 120°C for 48h, filter and dry to obtain Porous PDVB-PA;
[0069] S5. Add 75 mg of Porous PDVB-PA to a round-bottom flask containing 45 ml of methanol. After continuous ultrasonic treatment for 30 min, stir at room temperature for 60 min, heat the system to 50 ° C, add 12 ml of AgNO3 solution to the mixture, stir for 360 min, and then remove the solvent by rotary evaporation. Then centrifuge and wash twice with distilled water to remove excess AgNO3. The collected precipitate is redissolved with 30 ml of methanol, 10 ml of hydrazine hydrate solution is added dropwise, and the precipitate is collected by stirring for 48 h. The precipitate is washed twice with water and methanol, and free AgNPs and other impurities are removed by centrifugation. Finally, it is dried in a vacuum oven to obtain the catalyst Porous AgNPs for reducing 4-nitrophenol (4-NP).
[0070] The prepared catalyst was characterized by solid-state nuclear magnetic resonance, scanning / transmission electron microscopy, nitrogen adsorption-desorption instrument, X-ray powder diffractometer, X-ray photoelectron spectrometer and thermogravimetric analyzer.
[0071] exist Figure 1 middle 13The various chemical shifts of the support C can be seen from the 13C NMR spectrum. As shown in the figure, the 41 ppm signal belongs to the chemical shift of the aliphatic chain C1 / 2 in the Porous PDVB backbone; the strong signals at 128 ppm and 145 ppm belong to the chemical shift of the carbon C3 / 4 on the benzene ring; the signals at 114 ppm and 135 ppm belong to the chemical shift of the carbon C5 / 6 in the vinyl group. These two signals are relatively weak, indicating that the degree of polymerization of divinylbenzene in the support is relatively high. Compared with Porous PDVB, Porous AgNPs have an obvious signal at 149 ppm, which belongs to the chemical shift of the carbon C7 / 8 in the C=N bond, proving the formation of Schiff base ligands on Porous PDVB, facilitating the coordination of Ag + , and proving again that the synthesis of the support Porous PDVB-PA is successful.
[0072] In Figure 2 , it can be seen from the scanning electron microscopy (SEM) image that Porous PDVB-PA has abundant and randomly distributed pores, showing a honeycomb-like structure, and the specific surface area behind also proves that it has abundant pore channels. Transmission electron microscopy (TEM) confirmed the existence of roughly spherical AgNPs in the porous support, and widely distributed Ag nanoparticles (black dots) can be clearly observed, indicating that the silver particles are effectively dispersed during the preparation process and do not aggregate into large particles.
[0073] In Figure 3 , the porosity of the samples was studied by nitrogen adsorption tests. The adsorption-desorption isotherms of Porous PDVB, Porous PDVB-PA, and Porous AgNPs all have obvious hysteresis loops at 0.45 < P / P0 < 0.95, indicating that these samples have abundant pore structures. Among them, the specific surface area of Porous PDVB is 568 m 2 / g, and the specific surface areas of Porous PDVB-PA and Porous AgNPs are 328 m 2 / g and 236 m 2 / g respectively. This is due to the repeated modification of the matrix Porous PDVB.
[0074] In Figure 4 , the XRD peaks of Porous PDVB-PA have no characteristics, only a broad peak at 22.5°, indicating that the material presents an amorphous structure. However, the Porous AgNPs sample shows diffraction peaks of the (111), (200), (220), (331), and (222) crystal planes of AgNPs at 38.1°, 44.2°, 64.3°, 77.2°, and 81.5°, proving that AgNPs are successfully encapsulated into the porous Porous PDVB-PA.
[0075] exist Figure 5 XPS measurements further prove that the four elements C, N, O, and Ag coexist in Porous AgNPs, with specific atomic contents of 61.32%, 26.73%, 5.48%, and 6.47%, respectively. The Ag 3d energy level shows two peaks at 367.4eV and 373.4eV, respectively, proving the existence of Ag0 in Porous AgNPs.
[0076] exist Figure 6 In the experiment, TG analysis proved that Porous AgNPs had excellent thermal stability, and compared with Porous PDVB-PA, it still maintained a smaller loss at 800℃.
[0077] From the above analysis, it can be concluded that the prepared catalyst is Porous AgNPs.
[0078] In order to further verify the catalytic reduction performance of the catalyst prepared in this example, the catalyst prepared in this example was used in the sodium borohydride reduction reaction of 4-NP to test its catalytic activity. The specific test process is as follows:
[0079] A 250ml round-bottom flask was filled with 100ml of 5mmol 4-NP solution, and then 50mmol NaBH4 solution was added, and the color of the solution changed from light yellow to yellow-green. Under stirring, 50mg of catalyst was added to initiate the reaction of 4-NP reducing 4-AP. Samples were taken every 2 minutes and the ultraviolet absorption spectrum was measured. The end of the reaction was marked by the solution color gradually approaching colorless, and the value of the absorption peak at 400nm was almost zero. After the reaction was completed, the catalyst was separated and recovered by a centrifuge, and the recovered catalyst was washed 3 times with distilled water and reused.
[0080] from Figure 8 It can be seen that as the reaction proceeds, the degradation rate of 4-NP continues to increase. When the reaction is 14 minutes, the degradation rate of 4-NP is 98.4%, which is basically completely degraded. The results show that the catalytic effect is significant. When investigating the catalytic activity of the prepared catalyst, the recyclability of the catalyst is also an important factor. Six cycle experiments were carried out, and the results showed that the catalytic activity of the catalyst did not decrease significantly, the catalyst was relatively stable, and could be reused many times.
[0081] Example 2
[0082] A method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol, which is different from Example 1 in that the amount of 2-PA is adjusted, and the specific steps are:
[0083] S1. Add 13 g DVB to 120 ml DMF at room temperature, then add 0.3 g AIBN and continue stirring for 3 h. Transfer the mixed solution to an autoclave, hydrothermally cure at 100 °C for 48 h, cool and filter the solution to obtain Porous PDVB.
[0084] S2, add 5g of Porous PDVB to a mixed solution of 150g of sulfuric acid (98%) and 40g of nitric acid (65%), stir in an ice-water bath for 20h, then disperse the mixed solution into 2L of pure water, stir for 60min, filter, wash, and dry to obtain Porous PDVB-NO2;
[0085] S3, add 2g Porous PDVB-NO2 and 12g SnCl2 to 120ml concentrated hydrochloric acid, stir at room temperature for 2 days, continue to disperse the mixture into 2L pure water, filter and wash with a large amount of 8:2 mixed solvent of aminopropane and propanol to obtain Porous PDVB-NH2;
[0086] S4, add 5g of Porous PDVB-NH2 into 100ml of toluene, stir at room temperature for 60min, then add 15ml of 2-PA, reflux at 120°C for 48h, filter and dry to obtain Porous PDVB-PA;
[0087] S5. Add 75 mg of Porous PDVB-PA to a round-bottom flask containing 45 ml of methanol. After continuous ultrasonic treatment for 30 min, stir at room temperature for 60 min, heat the system to 50 ° C, add 12 ml of AgNO3 solution to the mixture, stir for 360 min, and then remove the solvent by rotary evaporation. Then centrifuge and wash twice with distilled water to remove excess AgNO3. The collected precipitate is redissolved with 30 ml of methanol, 10 ml of hydrazine hydrate solution is added dropwise, and the precipitate is collected by stirring for 48 h. The precipitate is washed twice with water and methanol, and free AgNPs and other impurities are removed by centrifugation. Finally, it is dried in a vacuum oven to obtain the catalyst Porous AgNPs for reducing 4-nitrophenol (4-NP).
[0088] The prepared catalyst was further characterized by scanning / transmission electron microscopy, nitrogen adsorption and desorption instrument, X-ray powder diffractometer, X-ray photoelectron spectrometer and thermogravimetric analyzer. The results showed that the loading of Ag decreased, while other structural properties remained basically the same. XPS analysis showed that the contents of C, N, O and Ag were 63.89%, 25.38%, 6.45% and 4.28%, respectively. The main reason is that the free amino group (-NH2) ensures that the N content remains basically unchanged, while the reduction of 2-PA makes the Schiff base ligand content less, which cannot effectively anchor the Ag ions, making Ag easy to be eluted.
[0089] The catalyst prepared in this example was used to catalyze the reduction of 4-NP by potassium borohydride. After 17 minutes of reaction, the degradation rate of 4-NP was 97.6%, and the activity of the catalyst did not decrease significantly after being used for 6 times. The test results show that the material has high catalytic activity and good repeatability.
[0090] Example 3
[0091] A method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol, which is different from Example 1 in that the solvent of reaction S1 is adjusted to generate a different porous PDVB matrix, and the specific steps are:
[0092] S1. Add 13 g DVB to 120 ml THF at room temperature, then add 0.3 g AIBN and continue stirring for 3 h. Transfer the mixed solution to an autoclave, hydrothermally cure at 100 °C for 48 h, cool and filter the solution to obtain Porous PDVB.
[0093] S2, add 5g of Porous PDVB-3 to a mixed solution of 150g of sulfuric acid (98%) and 40g of nitric acid (65%), stir in an ice-water bath for 20h, then disperse the mixed solution into 2L of pure water, stir for 60min, filter, wash, and dry to obtain Porous PDVB-NO2;
[0094] S3, add 2g Porous PDVB-NO2-3 and 12g SnCl2 into 120ml concentrated hydrochloric acid, stir at room temperature for 2 days, continue to disperse the mixture into 2L pure water, filter and wash with a large amount of 8:2 mixed solvent of aminopropane and propanol to obtain Porous PDVB-NH2;
[0095] S4, add 5g of Porous PDVB-NH2 into 100ml of toluene, stir at room temperature for 60min, then add 30ml of 2-PA, reflux at 120°C for 48h, filter and dry to obtain Porous PDVB-PA;
[0096] S5. Add 75 mg of Porous PDVB-PA to a round-bottom flask containing 45 ml of methanol. After continuous ultrasonic treatment for 30 min, stir at room temperature for 60 min, heat the system to 50 ° C, add 12 ml of AgNO3 solution to the mixture, stir for 360 min, and then remove the solvent by rotary evaporation. Then centrifuge and wash twice with distilled water to remove excess AgNO3. The collected precipitate is redissolved with 30 ml of methanol, 10 ml of hydrazine hydrate solution is added dropwise, and the precipitate is collected by stirring for 48 h. The precipitate is washed twice with water and methanol, and free AgNPs and other impurities are removed by centrifugation. Finally, it is dried in a vacuum oven to obtain the catalyst Porous AgNPs for reducing 4-nitrophenol (4-NP).
[0097] The prepared catalyst was further characterized by scanning / transmission electron microscopy, nitrogen adsorption-desorption instrument, X-ray powder diffractometer, X-ray photoelectron spectrometer and thermogravimetric analyzer. The results showed that the morphology and structure of the catalyst were consistent with those in Example 1, with no obvious difference. The Ag particles were anchored in the porous material and did not aggregate into large particles.
[0098] The catalyst prepared in this example was used to catalyze the reduction of 4-NP by potassium borohydride. After 14 minutes of reaction, the degradation rate of 4-NP was 98.2%, and the activity of the catalyst did not decrease significantly after being used for 6 times. The test results show that the material has high catalytic activity and good repeatability.
[0099] Example 4
[0100] A method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol, which is different from Example 1 in that the amount of the reaction initiator is adjusted to generate a porous PDVB matrix with different polymerization degrees, and the specific steps are:
[0101] S1. Add 13 g DVB to 120 ml DMF at room temperature, then add 0.8 g AIBN and continue stirring for 3 h. Transfer the mixed solution to an autoclave, hydrothermally cure at 100 °C for 48 h, cool and filter the solution to obtain Porous PDVB.
[0102] S2, add 5g of Porous PDVB to a mixed solution of 150g of sulfuric acid (98%) and 40g of nitric acid (65%), stir in an ice-water bath for 20h, then disperse the mixed solution into 2L of pure water, stir for 60min, filter, wash, and dry to obtain Porous PDVB-NO2;
[0103] S3, add 2g Porous PDVB-NO2-3 and 12g SnCl2 into 120ml concentrated hydrochloric acid, stir at room temperature for 2 days, continue to disperse the mixture into 2L pure water, filter and wash with a large amount of 8:2 mixed solvent of aminopropane and propanol to obtain Porous PDVB-NH2;
[0104] S4, add 5g of Porous PDVB-NH2 into 100ml of toluene, stir at room temperature for 60min, then add 30ml of 2-PA, reflux at 120°C for 48h, filter and dry to obtain Porous PDVB-PA;
[0105] S5. Add 75 mg of Porous PDVB-PA to a round-bottom flask containing 45 ml of methanol. After continuous ultrasonic treatment for 30 min, stir at room temperature for 60 min, heat the system to 50 ° C, add 12 ml of AgNO3 solution to the mixture, stir for 360 min, and then remove the solvent by rotary evaporation. Then centrifuge and wash twice with distilled water to remove excess AgNO3. The collected precipitate is redissolved with 30 ml of methanol, 10 ml of hydrazine hydrate solution is added dropwise, and the precipitate is collected by stirring for 48 h. The precipitate is washed twice with water and methanol, and free AgNPs and other impurities are removed by centrifugation. Finally, it is dried in a vacuum oven to obtain the catalyst Porous AgNPs for reducing 4-nitrophenol (4-NP).
[0106] In reaction S1, due to the large amount of initiator AIBN, the reaction rate per unit time is increased, a large amount of polymer is formed, and the reaction time is greatly shortened. However, the particle size of the formed polymer increases and overflows the container.
[0107] The prepared catalyst was further characterized by scanning / transmission electron microscopy, nitrogen adsorption-desorption instrument, X-ray powder diffractometer, X-ray photoelectron spectrometer and thermogravimetric analyzer. The results showed that the morphology density of the catalyst was not high and the structure was looser. In the TG test, the thermal stability of the polymer decreased.
[0108] The catalyst prepared in this example was used to catalyze the reduction of 4-NP by potassium borohydride. After 20 minutes of reaction, the degradation rate of 4-NP was 97.2%, and the activity of the catalyst did not decrease significantly after being used for 6 times. The test results show that when synthesizing a matrix material, it is necessary to select a suitable amount of initiator in order to synthesize a stable matrix material.
[0109] The above are only preferred specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.
Claims
1. A method for preparing a porous silver nanoparticle catalyst for reducing 4-nitrophenol, characterized in that: The following steps are involved: S1. Using DVB as raw material and AIBN as initiator, a hydrothermal curing reaction is carried out at 80-120°C in an organic solvent to obtain Porous PDVB; S2. The Porous PDVB is added to a mixture of sulfuric acid and nitric acid, stirred in an ice bath, and then dispersed in pure water to obtain Porous PDVB-NO2; S3. The Porous PDVB-NO2 and SnCl2 were added to concentrated hydrochloric acid and stirred, and then dispersed in pure water to obtain Porous PDVB-NH2; S4. The Porous PDVB-NH2 is dissolved in an organic solvent, and then 2-formylpyridine is added, and heated to reflux at 80-120°C to obtain Porous PDVB-PA; S5. The methanol solution of Porous PDVB-PA is heated, and then AgNO3 solution is added and stirred. After the solvent is removed by rotary evaporation, the solution is washed to obtain a precipitate. The precipitate is mixed and stirred with a reducing agent, and after impurities are removed, a reduced 4-nitrophenol porous silver nanoparticle catalyst is obtained.
2. The preparation method according to claim 1, characterized in that: In step S1, the organic solvent is one or more of N,N-dimethylformamide, tetrahydrofuran, acetonitrile, and dimethyl sulfoxide.
3. The preparation method according to claim 1, characterized in that: In step S4, the mass ratio of Porous PDVB-NH2 to 2-formylpyridine is 1:2.3-3.
4.
4. The preparation method according to claim 1, characterized in that: In step S1, the molar ratio of DVB to AIBN is 1:0.002-0.
006.
5. The preparation method according to claim 1, characterized in that: In step S5, the reducing agent is one or more of hydrazine hydrate, potassium borohydride, L-ascorbic acid, and sodium citrate.
6. The preparation method according to claim 1, characterized in that: In step S3, the mass ratio of Porous PDVB-NO2 and SnCl2 is 1:5-8.
7. The preparation method according to claim 1, characterized in that: In step S5, the mass ratio of the Porous PDVB-PA to AgNO3 is 1:1.16-1.
75.
8. The preparation method according to claim 1, characterized in that: The mass ratio of Porous PDVB to sulfuric acid and nitric acid is 1:25-35:6-10.
9. A porous silver nanoparticle catalyst for reducing 4-nitrophenol obtained by the preparation method according to any one of claims 1 to 8.
10. Use of the porous silver nanoparticle catalyst for reducing 4-nitrophenol as claimed in claim 9 in catalyzing the reduction of 4-nitrophenol in water with sodium borohydride.