Preparation method of super-hydrophobic monatomic Cu porous polymer ammonia separation material

Abstract

The invention discloses a preparation method of a super-hydrophobic monatomic Cu porous polymer ammonia separation material. According to the material, divinyl benzene and 4-vinylpyridine are copolymerized to construct a super-hydrophobic porous framework, and pyridine nitrogen groups are used for anchoring monatomic dispersed copper species to form strong adsorption sites. The preparation method is simple in process and easily available in raw materials. The obtained material has both a super-hydrophobic surface and high-density monatomic copper sites, has extremely high adsorption capacity and selectivity on ammonia gas, particularly can effectively inhibit competitive adsorption of water molecules in a high-humidity environment, keeps excellent ammonia gas trapping performance and cycling stability, and is suitable for industrial production. The method has wide application prospects in the fields of synthesis gas purification, ammonia-containing waste gas treatment, ammonia energy purification and the like.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials and gas adsorption and separation technology, specifically relating to a superhydrophobic single-atom Cu porous polymer ammonia separation material, and its preparation method and application as a moisture-resistant high-performance ammonia adsorbent. Background Technology

[0002] Ammonia (NH3) is an indispensable cornerstone of the chemical industry and an emerging green energy carrier. It is not only an important raw material for the manufacture of fertilizers, food, and pharmaceuticals, but also, due to its high hydrogen content (hydrogen storage density of up to 17.6 wt%), easy liquefaction and storage, and the advantage of not producing carbon dioxide upon combustion, it is considered a carbon-neutral fuel and hydrogen transport medium with great potential. However, NH3 is both an important chemical raw material and a toxic pollutant, posing a threat to the environment and human health. As a major alkaline gas in the atmosphere, NH3 readily reacts with acidic substances (such as SO2) to form ammonium salts, becoming particulate matter (PM2.5). 2.5 Ammonia is a key precursor to nitrogen oxides, not only reducing atmospheric visibility but also harming the ecological environment. For humans, ammonia is irritating and can damage the eyes, skin, and respiratory tract; high-concentration exposure can even be life-threatening. Therefore, achieving efficient and economical capture and separation of ammonia is a crucial step in its resource utilization and pollution control.

[0003] Currently, mainstream ammonia capture technologies include absorption, adsorption, and membrane separation. Among these, adsorption offers advantages such as mild operating conditions, relatively low energy consumption, and ease of recycling, enabling the capture and reuse of ammonia. However, traditional porous adsorbents, such as zeolites, have been widely used in ammonia adsorption due to their diverse pore structures, low cost, and readily available raw materials. However, their ammonia adsorption capacity is limited, and their selectivity is low. The key issue is the lack of effective chemisorption sites on the surface of these materials. Especially in humid environments, water molecules within the pores fiercely compete with ammonia for adsorption sites, leading to a sharp decline in performance and severely limiting practical applications. Metal-organic frameworks (MOFs), as emerging adsorbents, possess advantages such as high porosity and tunable structure, exhibiting excellent initial adsorption performance for ammonia. However, their framework is composed of coordination bonds, resulting in insufficient chemical stability. In high humidity or strongly alkaline ammonia environments, structural collapse or irreversible adsorption easily occurs, leading to short cycle life. Furthermore, they face challenges such as high synthesis costs and difficulties in large-scale preparation. Porous organic polymers (POPs) are a class of novel porous materials mainly composed of light elements such as C, H, O, and N, which have rich pore structures and good stability. These materials have flexible preparation methods, strong structural modifiability, and high structural stability, and can be repeatedly used for ammonia capture. However, since their surfaces usually lack active sites that have strong specific interactions with ammonia molecules, they mainly rely on physical adsorption, so their adsorption capacity and selectivity need to be improved.

[0004] Therefore, it is crucial to develop a novel adsorption material that can overcome the aforementioned defects simultaneously. This invention designs a synergistic strategy combining single-atom copper active sites with a superhydrophobic polymer framework: high-capacity, highly selective chemisorption is achieved by utilizing the strong specific coordination between single-atom copper and ammonia molecules; simultaneously, the superhydrophobic framework composed of divinylbenzene crosslinks effectively repels water molecules, protecting the active sites, thereby ensuring the material's adsorption performance and structural stability in humid environments. Summary of the Invention

[0005] To overcome the problems of drastic performance degradation, low utilization of active sites, and poor stability of existing ammonia adsorption materials under humid environments, this invention provides a method for preparing a superhydrophobic single-atom Cu porous polymer ammonia separation material. This material prevents water molecules from condensing in the pores through a superhydrophobic framework and achieves efficient adsorption of ammonia through strong chemical interactions between single-atom copper sites. It exhibits excellent ammonia separation performance and cycle stability under both dry and humid conditions.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A superhydrophobic single-atom Cu porous polymer ammonia separation material is obtained by copolymerizing divinylbenzene and 4-vinylpyridine monomers to form a superhydrophobic polymer framework, and by coordinating and loading pyridine nitrogen groups with highly dispersed copper species in single-atom form; the specific surface area of ​​the ammonia separation material is 50-350 m². 2 / g, and copper species are dispersed in the polymer channels and skeleton surface in the form of single atoms.

[0007] A method for preparing a superhydrophobic single-atom Cu porous polymer ammonia separation material includes the following steps: (1) Carrier synthesis: Divinylbenzene (DVB), 4-vinylpyridine (VP) and initiator azobisisobutyronitrile (AIBN) were dissolved in an organic solvent and subjected to solvothermal polymerization. After the reaction was completed, the product was first volatilized at room temperature and pressure to remove the solvent, and then dried under vacuum to obtain a superhydrophobic porous polymer carrier with pyridine nitrogen groups. (2) Construction of single-atom copper sites: The support obtained in step (1) and the copper source were placed in anhydrous ethanol solvent and stirred at room temperature to obtain a mixed solution; (3) Post-processing: The mixed solution obtained in step (2) is filtered by vacuum filtration, the resulting solid is washed with anhydrous ethanol, filtered again, and the solid product is placed in a constant temperature drying oven to dry, thus obtaining the superhydrophobic single-atom Cu porous polymer ammonia separation material.

[0008] Furthermore, the method for preparing the superhydrophobic single-atom Cu porous polymer ammonia separation material is characterized in that the organic solvent in step (1) is one of tetrahydrofuran, ethyl acetate, and ethanol, and the mass ratio of DVB, VP, and AIBN is 1:0.5~2:0.03~0.1.

[0009] Furthermore, the preparation method of the superhydrophobic single-atom Cu porous polymer ammonia separation material is characterized in that the temperature of the solvothermal polymerization reaction in step (1) is 100~140 ℃, the reaction time is 24~72 h, the volatilization time is 12~24 h, the vacuum drying temperature is 60~100 ℃, and the vacuum drying time is 12~24 h.

[0010] Furthermore, the method for preparing the superhydrophobic single-atom Cu porous polymer ammonia separation material is characterized in that the copper source in step (2) is selected from one of copper chloride dihydrate, copper sulfate pentahydrate, and copper nitrate trihydrate.

[0011] Furthermore, the preparation method of the superhydrophobic single-atom Cu porous polymer ammonia separation material is characterized in that, in step (2), the mass ratio of the porous organic polymer carrier to the copper source is 0.1~0.5, the amount of anhydrous ethanol solvent is 20~40 mL, and the stirring time is 1~6 h.

[0012] Furthermore, the preparation method of the superhydrophobic single-atom Cu porous polymer ammonia separation material is characterized in that the drying temperature in step (3) is 80~120 ℃ and the drying time is 24~72 h.

[0013] Furthermore, the superhydrophobic single-atom Cu porous polymer ammonia separation material prepared by the above method can be used for the efficient and selective adsorption and separation of ammonia. The adsorption temperature is 25~75 ℃, and the adsorption pressure is 0~1.0 bar; ammonia adsorption and separation are carried out in a humidity range of RH = 50~80%; the ammonia desorption temperature is 120~160 ℃, and the desorption pressure is 0~0.1 bar.

[0014] The advantages of this invention are: (1) By anchoring single-atom copper with pyridine nitrogen groups, a high-density strong coordination adsorption site is formed, which significantly improves the adsorption capacity and selectivity for ammonia. (2) The superhydrophobic framework constructed by divinylbenzene can effectively inhibit the competitive adsorption of water molecules, ensuring the stability of the material's performance in humid environments. (3) Its porous structure and hydrophobicity can be flexibly controlled by the comonomer and synthesis conditions, and the single-atom copper loading process is simple and mild, with good reproducibility and potential for large-scale production. Attached Figure Description

[0015] Figure 1The XRD patterns of adsorbents A to D are shown. Figure 2 The isotherms (a) and pore size distribution diagram (b) of N2 adsorption and desorption for adsorbents A to D at -198 °C are shown. Figure 3 The isotherms for NH3 adsorption and desorption of adsorbents A to E at 25 °C are shown. Figure 4 The breakthrough curve of adsorbent B prepared in Example 2 in NH3 / N2 / H2 mixed gas at 25 °C; Figure 5 The NH3 breakthrough curves of adsorbent B prepared in Example 2 under different environmental conditions. Detailed Implementation

[0016] The specific embodiments of the present invention will be described in detail below. The specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0017] Example 1: (1) Carrier synthesis: 1.0 g divinylbenzene, 2.0 g 4-vinylpyridine, 0.065 g azobisisobutyronitrile, and 20 mL ethyl acetate were weighed and placed in a polytetrafluoroethylene liner. The mixture was stirred at room temperature for 3 h. Then, the polytetrafluoroethylene liner was transferred to a high-pressure reactor and placed in an oven at 120 ℃ for 24 h. After the reaction, the product was placed at room temperature and pressure to evaporate the solvent for 24 h, and then placed in an 80 ℃ vacuum drying oven for 24 h to obtain a superhydrophobic porous polymer carrier with pyridine nitrogen groups. (2) Construction of single-atom copper sites: Weigh 0.30 g of the support obtained in step (1) and 0.80 g of CuCl2·2H2O and disperse them in 30 mL of anhydrous ethanol solvent. After stirring at room temperature for 24 h, a mixed solution is obtained. (3) Post-processing: The mixed solution obtained in step (2) is filtered by suction, the resulting solid is washed with anhydrous ethanol, filtered again, and then placed in an 80 ℃ oven to dry for 24 h. After natural cooling, a superhydrophobic single-atom Cu porous polymer ammonia separation material is obtained, which is denoted as adsorbent A.

[0018] Example 2: (1) Carrier synthesis: 1.0 g divinylbenzene, 2.0 g 4-vinylpyridine, 0.065 g azobisisobutyronitrile, and 20 mL ethyl acetate were weighed and placed in a polytetrafluoroethylene liner. The mixture was stirred at room temperature for 3 h. Then, the polytetrafluoroethylene liner was transferred to a high-pressure reactor and placed in an oven at 120 ℃ for 24 h. After the reaction was completed, the product was placed at room temperature and pressure to evaporate the solvent for 24 h, and then placed in an 80 ℃ vacuum drying oven for 24 h to obtain a superhydrophobic porous polymer carrier with pyridine nitrogen groups. (2) Construction of single-atom copper sites: Weigh 0.30 g of the support obtained in step (1) and 1.20 g of CuCl2·2H2O and disperse them in 30 mL of anhydrous ethanol solvent. After stirring at room temperature for 24 h, a mixed solution is obtained. (3) Post-processing: The mixed solution obtained in step (2) is filtered by vacuum filtration. The resulting solid is washed with anhydrous ethanol and filtered again. It is then placed in an 80 ℃ oven to dry for 24 h. After natural cooling, a superhydrophobic single-atom Cu porous polymer ammonia separation material is obtained, which is denoted as adsorbent B.

[0019] Example 3: (1) Carrier synthesis: 1.0 g divinylbenzene, 2.0 g 4-vinylpyridine, 0.065 g azobisisobutyronitrile, and 20 mL ethyl acetate were weighed and placed in a polytetrafluoroethylene liner. The mixture was stirred at room temperature for 3 h. Then, the polytetrafluoroethylene liner was transferred to a high-pressure reactor and placed in an oven at 120 ℃ for 24 h. After the reaction was completed, the product was placed at room temperature and pressure to evaporate the solvent for 24 h, and then placed in an 80 ℃ vacuum drying oven for 24 h to obtain a superhydrophobic porous polymer carrier with pyridine nitrogen groups. (2) Construction of single-atom copper sites: Weigh 0.30 g of the support obtained in step (1) and 1.60 g of CuCl2·2H2O and disperse them in 30 mL of anhydrous ethanol solvent. After stirring at room temperature for 24 h, a mixed solution is obtained. (3) Post-processing: The mixed solution obtained in step (2) was filtered by suction, and the resulting solid was washed with anhydrous ethanol. After being filtered again, it was placed in an 80 ℃ oven to dry for 24 h. After natural cooling, a superhydrophobic single-atom Cu porous polymer ammonia separation material was obtained, which was denoted as adsorbent C.

[0020] Comparative Example 1: Compared with the preparation method of Example 2, this comparative example did not introduce copper active centers. The steps are as follows: 2.0 g of divinylbenzene, 1.0 g of 4-vinylpyridine, 0.065 g of azobisisobutyronitrile, and 20 mL of ethyl acetate were weighed and placed in a polytetrafluoroethylene (PTFE) liner. The mixture was stirred at room temperature for 3 h, and then the PTFE liner was transferred to a high-pressure reactor and placed in an oven at 120 ℃ for 24 h. After the reaction, the obtained product was allowed to evaporate the solvent at room temperature and pressure for 24 h, and then dried in a vacuum drying oven at 80 ℃ for 24 h to obtain the final product, denoted as adsorbent D.

[0021] Comparative Example 2: Weigh 0.1 g of commercial 13X molecular sieve into an adsorption tube and dry it in an oven at 80 ℃ for 24 h. This is recorded as adsorbent E.

[0022] Characterization: X-ray diffraction (XRD) was performed on an X'Pert3 powder diffractometer, with X-rays derived from Cu Kα radiation (λ = 1.5418 Å), and voltage and current of V = 45 kV and I = 40 mA, respectively. The BET specific surface area and pore volume of various samples were evaluated on a Micromeritics TriStarⅡ3020 system, after degassing at 160 °C for 12 h prior to measurement.

[0023] NH3 static adsorption performance test: The equipment selected for the adsorption reaction performance test is a high-performance corrosive gas adsorption and microporous analyzer (BSD-660MC).

[0024] The Micromeritics Autochem 2920 instrument was used for the performance testing of NH3 dynamic breakthrough. A mass spectrometer (Hiden Analytical, HPR-20 R&D) and an ion source detector were used to detect the outlet gas concentration online. Before testing, the sample was placed in a U-shaped quartz tube and pretreated with high-purity argon gas at 160 °C for 4 h, with an adsorbent dosage of 0.04–0.05 g. The composition of the feed gas in the NH3 dynamic breakthrough was NH3 / N2 / H2 (0.8% / 27.0% / 72.2%) and NH3 / H2O / Ar (0.8% / 1.0% / 98.2%), with a gas flow rate range of 10–40 mL / min and a test temperature of 25 °C.

[0025] Analysis results: The obtained Cu porous polymer ammonia adsorbent was analyzed and tested accordingly: Figure 1 The figures show the wide-angle XRD patterns of adsorbents A through D. From the figures, it can be seen that all adsorbents exhibit XRD patterns at 2θ = 10°. ° ~20 ° Within the range, there is a broad, amorphous diffraction peak without any crystalline characteristics. The intensity of the characteristic diffraction peaks corresponding to adsorbents A, B, and C decreases while the peak width increases with increasing Cu loading. This is due to coordination with polar groups on the porous organic polymer molecular chain of the support, causing Cu species to be anchored in single-atom form on the pores and framework surface of the support and highly dispersed. The high dispersion of single-atom copper is beneficial for maintaining structural integrity and also provides abundant active sites for the ammonia adsorption reaction.

[0026] Figure 2N2 adsorption-desorption isotherms (a) and pore size distribution diagrams (b) of adsorbents A-D at -198 °C. As can be seen from the figure, all adsorbent samples exhibit type-IV isothermal adsorption-desorption curves, and the N2 adsorption amount increases sharply in the range of 0.8 < P / P0 < 1.0, indicating the presence of mesoporous structures in the adsorbents. The specific surface area of all adsorbents decreases with the increase in the amount of added metal Cu, and the pore size distribution of the adsorbents is between 20 and 150 nm. After loading single-atom copper, the material still maintains a developed mesoporous-macroporous structure, which provides channels for the diffusion of ammonia molecules, and at the same time its superhydrophobic surface ensures that these channels are not easily blocked by water in a humid environment.

[0027] Table 1 summarizes the structural parameters of adsorbents A-D. First, the introduction of Cu significantly reduces the specific surface area of the material (comparing adsorbent D with A), which is mainly due to the anchoring of Cu species in the carrier pores. Secondly, when comparing adsorbents A, B, and C loaded with Cu, with the further increase in the Cu doping amount, the specific surface area continues to show a gradually decreasing trend, which is attributed to the increased Cu species (possibly in the form of oxides) occupying more pore space.

[0028] The structural parameters of adsorbent are shown in the following table:

[0029] Figure 3 NH3 adsorption-desorption isotherm diagrams of adsorbents A-E at 25 °C. Adsorbents A-C all show significantly better adsorption performance than comparative examples D and E. It is noteworthy that with the increase in the Cu content, the adsorption capacity of the adsorbent for ammonia also increases, but when the Cu content is too high, the adsorption capacity will decrease. This is attributed to the fact that excessive copper precursors cause some single-atom sites to agglomerate into clusters or oxides that occupy the pores, preventing sufficient contact with ammonia and unable to fully capture ammonia.

[0030] As can be seen from Table 2, although the specific surface area of adsorbent B is relatively low, it shows the best ammonia adsorption capacity. This is mainly attributed to the successful anchoring of highly dispersed single-atom copper active sites on its carrier. The strong chemical interaction between these active sites and ammonia is the dominant factor in enhancing the adsorption capacity, rather than simple physical adsorption. This shows that the ammonia adsorption capacity is mainly affected by the density of moderately and highly dispersed metal active sites, and at the same time, the developed mesoporous-macroporous structure of the carrier is also conducive to the rapid diffusion of ammonia, enabling the full utilization of the internal active sites.

[0031] Table 2 Ammonia adsorption amounts (mmol / g) of adsorbents A-E at 25 °C

[0032] Figure 4The graph shows the breakthrough curve of adsorbent B for the NH3 / H2 / N2 mixture. As can be seen from the graph, adsorbent B achieves almost instantaneous breakthrough for N2 and H2, while the breakthrough time for NH3 is greater than 279 min / g. This demonstrates the high selectivity of adsorbents based on the strong coordination of single-atom copper sites for ammonia in complex gas mixtures, showcasing their application potential in industrial syngas purification, ammonia leak recovery, and ammonia-containing waste gas treatment.

[0033] Figure 5 The graph shows the NH3 breakthrough curves of adsorbent B under different environmental conditions. As can be seen from the graph, compared to dry conditions, the dynamic breakthrough time of adsorbent B hardly decreases under humid conditions. This directly indicates the effective repulsion of water molecules by its superhydrophobic surface, protecting the single-atom copper active sites and enabling it to maintain high adsorption capacity in real humid environments. The single-atom copper in the adsorbent, acting as a Lewis acid, strongly coordinates with the lone pair electrons of the nitrogen atom in ammonia molecules (acting as a Lewis base), forming a stable adsorption complex. This is the main source of its high capacity (dynamic breakthrough capacity of NH3 is 4.93 mmol / g under humidity ranges of 50%–80%) and high selectivity. Simultaneously, the hydrophobic polymer framework effectively inhibits the competitive adsorption and aggregation of water molecules within the pores, thus ensuring stable performance under humid conditions.

[0034] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a superhydrophobic single-atom Cu porous polymer ammonia separation material, characterized in that, The ammonia separation material is obtained by copolymerizing divinylbenzene and 4-vinylpyridine monomers to form a superhydrophobic polymer framework, and then coordinating and loading pyridine nitrogen groups with highly dispersed copper species in single-atom form; the specific surface area of ​​the material is 50-350 m². 2 / g, and copper species are dispersed in the polymer channels and skeleton surface in the form of single atoms.

2. The preparation method of the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 1, characterized in that, Includes the following steps: (1) Carrier synthesis: Divinylbenzene (DVB), 4-vinylpyridine (VP) and initiator azobisisobutyronitrile (AIBN) were dissolved in an organic solvent and subjected to solvothermal polymerization. After the reaction was completed, the product was first volatilized at room temperature and pressure to remove the solvent, and then dried under vacuum to obtain a superhydrophobic porous organic polymer carrier with pyridine nitrogen groups. (2) Construction of single-atom copper sites: The support obtained in step (1) and the copper source were placed in anhydrous ethanol solvent and stirred at room temperature to obtain a mixed solution; (3) Post-processing: The mixed solution obtained in step (2) is filtered by vacuum filtration, the resulting solid is washed with anhydrous ethanol, filtered again, and the solid product is placed in a constant temperature drying oven to dry, thus obtaining the superhydrophobic single-atom Cu porous polymer ammonia separation material.

3. The preparation method of the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 2, characterized in that, The organic solvent mentioned in step (1) is one of tetrahydrofuran, ethyl acetate, and ethanol, and the mass ratio of DVB, VP, and AIBN is 1:0.5~2:0.03~0.

1.

4. The method for preparing the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 2, characterized in that, The temperature of the solvothermal polymerization reaction in step (1) is 100~140 ℃, the reaction time is 24~72 h, the volatilization time is 12~24 h, the vacuum drying temperature is 60~100 ℃, and the vacuum drying time is 12~24 h.

5. The preparation method of the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 2, characterized in that, The copper source mentioned in step (2) is selected from one of copper chloride dihydrate, copper sulfate pentahydrate, and copper nitrate trihydrate.

6. The method for preparing the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 2, characterized in that, In step (2), the mass ratio of the porous organic polymer carrier to the copper source is 0.1 to 0.5, and the stirring time is 1 to 6 hours.

7. The method for preparing the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 2, characterized in that, The drying temperature in step (3) is 80~120 ℃ and the drying time is 24~72 h.

8. The superhydrophobic single-atom Cu porous polymer ammonia separation material prepared by the preparation method according to any one of claims 1-7.

9. The application of the superhydrophobic single-atom Cu porous polymer ammonia separation material according to claim 8 in the selective adsorption and separation of ammonia.

10. The application according to claim 9, characterized in that: The adsorption temperature is 25~75 ℃, and the adsorption pressure is 0~1.0 bar; ammonia adsorption and separation are carried out in a humidity range of RH = 50~80%; the ammonia desorption temperature is 120~160 ℃, and the desorption pressure is 0~0.1 bar.

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