A zinc-based prussian blue analogue ammonia-nitrogen adsorbent, a preparation method and application thereof

Abstract

The application relates to a zinc-based prussian blue analogue ammonia nitrogen adsorbent and a preparation method and application thereof, the ammonia nitrogen adsorbent is obtained by mixing a zinc source solution and a ferrocyanide source solution, standing and aging, separating out a precipitate, drying, and then carrying out heat treatment under a protective atmosphere, the protective gas serving as the protective atmosphere is selected from one or more of nitrogen, argon and helium, the target temperature of the heat treatment is 100-200 DEG C, the temperature rising rate is 3-7 DEG C / min, and the heat preservation time is 20-40 min. Compared with the prior art, the application has a fast adsorption rate and a high adsorption capacity for ammonium.

Description

Technical Field

[0001] This invention belongs to the field of material separation technology, and relates to a zinc-based Prussian blue analog ammonia nitrogen adsorbent, its preparation method, and its application. Background Technology

[0002] Nitrogen exhibits a typical dual nature: on the one hand, it is a key strategic resource for maintaining social development and energy transition; on the other hand, excessive emissions constitute serious environmental pollution. Achieving efficient nitrogen recovery and recycling can not only alleviate energy and carbon emission pressures but is also a strategic requirement for promoting sustainable development. Currently, achieving efficient nitrogen recovery from ammonia wastewater is a crucial link in promoting sustainable nitrogen cycle management.

[0003] Adsorption is considered the most promising nitrogen recovery method due to its simplicity and adaptability. However, existing adsorption materials generally suffer from slow kinetics, low adsorption capacity, and insufficient selectivity, making it difficult to meet the needs of engineering applications. Prussian blue (PB) and its analogues (PBAs) rely on metal-cyano bridging bonds to construct a three-dimensional framework, offering the advantages of simple synthesis and low cost. However, the adsorption performance of Prussian blue analogues is not solely determined by the framework structure; the microenvironment within the framework, especially the presence and distribution of moisture, can also profoundly affect ion migration and adsorption.

[0004] Patent CN119430225A discloses a method for preparing Prussian blue and its analogues using a precipitation conversion reaction, comprising: mixing ferricyanide, a transition metal salt, and a solvent in a single step; first, performing a precipitation conversion reaction to generate a precipitate containing the target product; then, washing and drying to obtain the Prussian blue and its analogues. Although this patent discloses a reaction temperature of 0–200 °C and a time of 1–72 h, and a vacuum drying temperature of 30–200 °C and a time of 2–48 h, with a vacuum degree <10 kPa, this patent only provides broad temperature control, rather than active water molecule control and performance regulation based on analysis of the material's thermal stability.

[0005] Patent CN109292795A proposes a heat treatment method using a high-temperature vacuum oven and tubular furnace. Through a calcination step in an inert gas environment, the temperature is gradually increased to remove interstitial water from the material, producing anhydrous Prussian blue analog nanoparticles with uniform particle size and dispersion. While this patent achieves superior battery cathode performance by removing interstitial water, it lacks in-depth control over adsorption performance, and completely eliminating moisture is not conducive to improving adsorption performance.

[0006] Patent CN107486130A discloses a method for preparing Prussian blue-based deammoniation materials and their application in wastewater deammoniation. The chemical formula of the Prussian blue-based compound is A2MFe(CN)6, where A is Na.+ or K + M is Zn 2+ Cu 2+ Ni 2+ Co 2+ or Mn 2+ One method for preparing this material is as follows: A transition metal salt solution and a ferrocyanide complex solution are prepared separately; a certain mass of the corresponding solid chloride is added to the ferrocyanide complex solution to completely dissolve the chloride, resulting in a mixed solution of the ferrocyanide complex and chloride; the transition metal salt solution is gradually added dropwise to the mixed solution while magnetically stirring; after the addition is complete, stirring continues to obtain a white suspension, which is allowed to settle and precipitate. This suspension is then centrifuged to obtain a white solid, which is repeatedly washed with deionized water to remove impurities and dried to obtain the deammonium-removing material. However, this patent only synthesizes Prussian blue-based deammonium-removing materials and lacks further control over the adsorption performance.

[0007] Patent CN121601653A discloses a Prussian blue-based cathode material, its preparation method, and its applications, with the molecular formula A. x M[M'(CN)6] y ·zH₂O, where: A is an alkali metal, M is a transition metal, M' is a transition metal, 1 < x ≤ 2, 0.8 ≤ y < 1, 0 < z ≤ 3; In the water content of Prussian blue cathode materials, interstitial water X b and coordination water X a The mass content ratio is 0.2~5:1, and the adsorbed water X c and coordination water X a The mass content ratio is 0.1~5:1. However, this patent optimizes the content and distribution of different types of water in Prussian blue cathode materials to avoid the problem of poor structural stability caused by water content in the material, rather than actively regulating performance. Summary of the Invention

[0008] The purpose of this invention is to overcome at least one defect of the prior art and provide a zinc-based Prussian blue analog ammonia nitrogen adsorbent, its preparation method, and its application. This invention has a fast adsorption rate and high adsorption capacity for ammonium.

[0009] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of this invention is to provide a zinc-based Prussian blue analog ammonia nitrogen adsorbent, which is obtained by mixing a zinc source solution and a ferrocyanide source solution, allowing them to stand and age, separating the precipitate, drying it, and then heat-treating it under a protective atmosphere followed by drying. The protective gas used as the protective atmosphere is selected from one or more of nitrogen, argon, and helium. The target temperature of the heating heat treatment is 100~200 ℃, the heating rate is 3~7 ℃ / min, and the holding time is 20~40 min.

[0010] As a preferred technical solution, the temperature of the heat treatment is 100~150 ℃.

[0011] One of the technical solutions of the present invention is to provide a method for preparing the zinc-based Prussian blue analog ammonia nitrogen adsorbent, the method comprising the following steps: A zinc source and a chelating agent are dissolved in water to obtain a zinc source solution. The zinc source and the chelating agent combine to form a soluble chelate, which slowly releases zinc ions during the subsequent reaction with the ferrocyanide source, slowing down the crystallization precipitation rate, avoiding explosive nucleation, reducing vacancy defects, improving crystal integrity, reducing lattice water, and enhancing structural stability. The ferrocyanide source is dissolved in water to obtain a ferrocyanide source solution. The ferrocyanide source solution is poured into the zinc source solution to obtain a suspension mixture. The suspension mixture is stirred and allowed to stand for aging to obtain a solid-liquid mixture containing a precipitate. The solid-liquid mixture containing the precipitate is centrifuged to remove the supernatant. The precipitate is washed and dried to obtain a zinc-based Prussian blue analog material. The zinc-based Prussian blue analog material is heat-treated under a protective atmosphere and dried to obtain a zinc-based Prussian blue analog ammonia nitrogen adsorbent.

[0012] First, the influence of water molecules in Prussian blue analogs on ammonia nitrogen adsorption performance was clarified. Then, based on simultaneous thermal analysis, the mapping relationship between heat treatment temperature and water molecule type and content during the temperature rise and weight loss process was established, and the heat treatment temperature was determined. Finally, the zinc-based Prussian blue analog material was heat-treated at the determined heat treatment temperature to obtain a zinc-based Prussian blue analog ammonia nitrogen adsorbent with controlled water molecule state after heat treatment.

[0013] Further, the zinc source is selected from one or more of zinc chloride, zinc nitrate, zinc acetate, and zinc sulfate, the chelating agent is selected from one or more of potassium citrate and sodium citrate, and the molar / volume ratio of zinc source, chelating agent and water in the zinc source solution is 1 mol:(1~1.25 mol):(20~30 L).

[0014] Furthermore, the ferrocyanide source is selected from one or more of potassium ferrocyanide and sodium ferrocyanide, and the molar / volume ratio of the ferrocyanide source to water in the ferrocyanide source solution is 1 mol:(20~30 L).

[0015] Furthermore, the molar ratio of the zinc source to the ferrocyanide source is 1:(0.875~1.125).

[0016] Furthermore, the temperature of the infusion is 10~40 ℃, and the rate is 1~5 mL / s.

[0017] Furthermore, the stirring temperature is 10~40 ℃, the stirring speed is 300~700 rpm, and the stirring time is 20~40 min. The static aging process is carried out at a temperature of 10~40 ℃ for 20~28 h.

[0018] Furthermore, the centrifugation temperature is 10~40 ℃, the speed is 6000~10000 rpm, and the time is 5~15 min. Washing is performed using one or more of water, ethanol, and acetone, and the number of washes is 2 to 5. The drying temperature after washing is 50~70 ℃, and the time is 10~14 h.

[0019] As a preferred technical solution, the drying after washing is carried out by vacuum drying, and the vacuum degree of the vacuum drying is 10~30 kPa.

[0020] Furthermore, the drying temperature after the heat treatment is 90~110 ℃, and the time is 10~14 h.

[0021] As a preferred technical solution, the drying after the heating heat treatment is carried out by vacuum drying, and the vacuum degree of the vacuum drying is 10~30 kPa.

[0022] One of the technical solutions of the present invention is to provide an application of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the separation, removal and enrichment of ammonium in water.

[0023] The synthesis of Prussian blue analogs inevitably generates a large number of Fe(CN)6 vacancies. A sufficient number of these vacancies interconnect to form an expanded microporous network. Furthermore, the Fe(CN)6 vacancies introduce water molecules into the framework of the Prussian blue analogs. Due to the strong retention tendency of coordinated water, well-defined water channels can be formed within the material. Based on Prussian blue analog technology, on the one hand, under high water content conditions, water molecules can promote the diffusion of ammonium in the framework by shielding hydrogen bonds; on the other hand, low water content reduces the number of adsorption sites occupied by water molecules, effectively increasing the adsorption capacity.

[0024] The ammonia nitrogen adsorbent has an adsorption capacity of ≥35 mg / g for ammonium and reaches adsorption equilibrium within ≤30 min.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) Based on the profound influence of the presence and distribution of water molecules on ion migration and adsorption, this invention controls the type and content of water molecules inside the zinc-based Prussian blue analog material through simple heat treatment. The continuity and distribution position of water molecules in the pores are changed, thereby changing the diffusion rate of ammonium in the framework and the occupancy of adsorption sites, thus regulating the transport rate and adsorption capacity of ammonium. The superior ammonium capture performance achieves efficient and rapid adsorption that is difficult to achieve in traditional material systems. Moreover, it has good directional selective adsorption and structural stability for ammonium. (2) The preparation method of the present invention is mild, low-cost and adjustable in performance, which can provide new ideas and solutions for extracting ammonium in complex water bodies, and provide theoretical basis and strong technical support for the application of adsorption technology in the recovery and resource utilization of ammonia nitrogen wastewater. Attached Figure Description

[0026] Figure 1 The image shows the simultaneous thermal analysis (TG-DSC) diagram of the zinc-based Prussian blue analog material in the comparative example of this invention. Figure 2 The X-ray powder diffraction (XRD) spectra of the zinc-based Prussian blue analog material in the comparative examples of the present invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 are shown. Figure 3 Solid-state proton nuclear magnetic resonance spectra of zinc-based Prussian blue analog materials in comparative examples and zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 of this invention. 1 H NMR spectrum; Figure 4 The nitrogen adsorption-desorption curves are shown for the zinc-based Prussian blue analog material in the comparative examples of the present invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3. Figure 5 The pore size distribution diagrams are shown for the zinc-based Prussian blue analog material in the comparative examples of the present invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3. Figure 6 The adsorption kinetics and second-order kinetics fitting curves are shown for the zinc-based Prussian blue analog material in the comparative examples of the present invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3. Figure 7 The adsorption isotherms and Langmuir fitting curves of the zinc-based Prussian blue analog material in the comparative examples of the present invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 are shown. Figure 8 The images show the adsorption isotherms and Freundlich fitting curves of the zinc-based Prussian blue analog materials in the comparative examples of this invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3. Figure 9This is an experimental diagram showing the cation coexistence competition of zinc-based Prussian blue analog materials in the comparative examples of the present invention and zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3. Figure 10 The graphs show the adsorption effects of the zinc-based Prussian blue analog material in the comparative examples of this invention and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 at different initial pH values. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0029] Unless otherwise specified, the following procedures are generally performed at room temperature and atmospheric pressure.

[0030] Comparative example: A zinc-based Prussian blue analog material and its preparation method are described below: 2 mmol of anhydrous zinc chloride (ZnCl2) and 2.25 mmol of potassium citrate monohydrate (K3C6H5O7·H2O) were dissolved in 50 mL of deionized water to obtain a clear zinc chloride solution. Then, 2 mmol of potassium ferrocyanide trihydrate (K4[Fe(CN)6]·3H2O) was dissolved in 50 mL of deionized water to obtain a clear potassium ferrocyanide solution. The potassium ferrocyanide solution was then slowly poured into the zinc chloride solution at a rate of 2.5 mL / s at 25 °C to obtain a suspension. The suspension was continuously and thoroughly stirred at 500 rpm for 30 min at 25 °C and allowed to stand at 25 °C for 24 h to obtain a solid-liquid mixture containing a precipitate. The solid-liquid mixture containing the precipitate was centrifuged at 8000 rpm for 10 min at 25 °C, the supernatant was discarded, and the precipitate was washed three times with deionized water. The precipitate was then subjected to a 20°C incubation period. The zinc-based Prussian blue analog material Zn-PBAs-60 was obtained by drying in a kPa vacuum drying oven for 12 h.

[0031] Example 1: A zinc-based Prussian blue analog ammonia nitrogen adsorbent and its preparation method are described below: The zinc-based Prussian blue analog material Zn-PBAs-60 from the comparative example was transferred to a crucible and heated to 100 °C at a rate of 5 °C / min in a tube furnace under a nitrogen atmosphere. It was then heat-treated at 100 °C for 30 min and cooled to room temperature of 25 °C before being transferred to a vacuum drying oven at 100 °C and 20 kPa for 12 h to obtain the zinc-based Prussian blue analog ammonia nitrogen adsorbent Zn-PBAs-100. The product was stored under dry conditions for later use.

[0032] Example 2: A zinc-based Prussian blue analog ammonia nitrogen adsorbent and its preparation method are described below: The zinc-based Prussian blue analog material Zn-PBAs-60 from the comparative example was transferred to a crucible and heated to 150 °C at a rate of 5 °C / min in a tube furnace under a nitrogen atmosphere. It was then heat-treated at 150 °C for 30 min and cooled to room temperature of 25 °C before being transferred to a vacuum drying oven at 100 °C and 20 kPa for 12 h to obtain the zinc-based Prussian blue analog ammonia nitrogen adsorbent Zn-PBAs-150. The product was stored under dry conditions for later use.

[0033] Example 3: A zinc-based Prussian blue analog ammonia nitrogen adsorbent and its preparation method are described below: The zinc-based Prussian blue analog material Zn-PBAs-60 from the comparative example was transferred to a crucible and heated to 200 °C at a rate of 5 °C / min in a tube furnace under a nitrogen atmosphere. It was then heat-treated at 200 °C for 30 min and cooled to room temperature of 25 °C before being transferred to a vacuum drying oven at 100 °C and 20 kPa for 12 h to obtain the zinc-based Prussian blue analog ammonia nitrogen adsorbent Zn-PBAs-200. The product was stored under dry conditions for later use.

[0034] The above-mentioned Prussian blue analogues were subjected to the following tests or experiments, and the test or experiment results were then analyzed.

[0035] Experimental Example 1: The thermal stability of the zinc-based Prussian blue analogue material in the comparative example was tested by simultaneous thermal analysis (TG-DSC).

[0036] like Figure 1As shown, the zinc-based Prussian blue analog material in the comparative example exhibits at least two overlapping dehydration events with central temperatures of 94 °C and 139 °C. The lower temperature event is attributed to the removal of weakly bound or physically adsorbed water, while the higher temperature event corresponds to the release of more strongly bound aquatic species within the framework. The broad and partially overlapping differential thermogravimetric (DTG) peaks indicate a non-uniform distribution of the aquatic environment, rather than a discrete dehydration process. This result suggests that the total water content of the zinc-based Prussian blue analog material gradually decreases with increasing temperature, mainly due to the removal of adsorbed water and some structural water.

[0037] The mapping relationship between the heating heat treatment temperature and the type and content of water molecules is as follows: the zinc-based Prussian blue analog obtained without heating heat treatment or after drying at 60℃ has a higher adsorbed water content, which is suitable for improving the ammonium migration rate; the zinc-based Prussian blue analog obtained after heat treatment at 100℃ has a lower adsorbed water content and a higher micropore openness, which is suitable for improving the ammonium adsorption capacity; the Prussian blue analog obtained after heat treatment at 150℃ or 200℃ has a further lower adsorbed water content and a relatively higher proportion of bound water, which is suitable for reducing the occupancy of adsorption sites by water molecules.

[0038] Experimental Example 2: The crystal structures of the zinc-based Prussian blue analog materials in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 were characterized by X-ray powder diffraction (XRD).

[0039] like Figure 2 As shown, the zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 all exhibit typical diffraction peaks at 2θ≈16.4°, 19.7°, 21.8°, and 24.5°. These peaks are sharp and have high intensity, indicating that the zinc-based Prussian blue analog has high crystallinity. All diffraction peaks can be accurately matched with the standard card PDF#33-1061 of K2Zn3[Fe(CN)6]2·xH2O, indicating that the crystal framework structure of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples remains stable during heat treatment.

[0040] Experimental Example 3: Using solid-state nuclear magnetic resonance hydrogen spectrum ( 1 The water content of the zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Examples 1 to 3 was characterized by 1H NMR.

[0041] like Figure 3As shown, it can be seen that the signal intensity of the zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Examples 1 to 3 significantly decreased with increasing heat treatment temperature, indicating that the water molecule content in the zinc-based Prussian blue analog decreased; at the same time, 1 The H signal shifts to higher fields and broadens significantly, indicating that adsorbed water on the surface of the zinc-based Prussian blue analogue is gradually removed, and internal components participate in Zn... 2+ The bound water was gradually exposed; this indicates that the heat treatment in the example not only reduced the water content of the zinc-based Prussian blue analog, but also caused the water to change its form, gradually changing from a state in which adsorbed water and bound water coexisted to a state dominated by bound water.

[0042] Experimental Example 4: The specific surface area and pore size distribution of the zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 were tested using nitrogen adsorption-desorption curves.

[0043] like Figure 4 As shown, the zinc-based Prussian blue analogue material in the comparative example has the largest BET specific surface area of ​​76.41 m². 2 / g, the BET specific surface area of ​​the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 1 is 58.62 m² / g. 2 / g, the BET specific surface area of ​​the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 2 is 11.75 m² / g. 2 / g, the BET specific surface area of ​​the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 3 is 10.28 m² / g. 2 / g indicates that the specific surface area of ​​the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples gradually decreases as the heat treatment temperature increases, indicating that the water content of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples significantly affects the specific surface area.

[0044] like Figure 5 As shown, the zinc-based Prussian blue analog material in the comparative example has a pore size of 37.99 nm and a pore volume of 0.0577 cm³. 3 / g, the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 1 has a pore size of 35.03 nm and a maximum pore volume of 0.0819 cm³. 3 / g, the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 2 has a pore size of 38.00 nm and a pore volume of 0.0539 cm³. 3 / g, the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 3 has a maximum pore size of 40.91 nm and a pore volume of 0.0579 cm³. 3 / g indicates that, based on the heat treatment of the zinc-based Prussian blue analog material in the comparative example, the pore volume of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 1 increased, indicating enhanced structural openness. This structural evolution is attributed to the removal of framework-bound water molecules, which previously occupied or blocked parts of the pore network, thus allowing additional ion exchange sites to be exchanged by ammonium ions (NH4+). + Access was improved, thereby increasing the effective utilization of the framework; although the measured pore volume of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in Examples 2 and 3 decreased due to partial framework degradation during heating, the overall accessibility of the adsorption sites was improved by the presence of water-bound water molecules, and the increased pore size led to a higher ammonium ion adsorption capacity.

[0045] Experimental Example 5: The adsorption kinetics of the zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 were tested. The specific steps are as follows: 25 mg of zinc-based Prussian blue analogue was added to a sample vial containing 50 mL of an initial 10 mg / L ammonium chloride (NH4Cl) aqueous solution. The vial was then placed in a constant-temperature shaker at 25°C and shaken at 200 rpm. Subsequently, 2.5 mL of the suspension was aspirated at different time intervals of 0, 30 s, 60 s, 180 s, 300 s, 600 s, and 1800 s using a syringe. After filtration through a 0.22 μm polyethersulfone membrane, an aqueous solution of adsorbed ammonium ions was obtained. The solution was diluted and the ammonium ion concentration was determined. Two parallel tests were performed to ensure accurate adsorption capacity determination.

[0046] like Figure 6 As shown in the figure, the zinc-based Prussian blue analogue material in the comparative example exhibits an exceptionally rapid adsorption rate, reaching kinetic equilibrium within only 30 s, with a second-order rate constant k2 as high as 3.878 × 10⁻⁶. 23 The adsorption rate of zinc-based Prussian blue analog ammonia nitrogen adsorbent was significantly higher than that of zinc-based Prussian blue analog ammonia nitrogen adsorbent in Example 1 (equilibrium within 10 min), Example 2 (equilibrium within 10 min), and Example 3 (equilibrium within 30 min), which was 0.100 g / (mg·min). This indicates that the adsorption rate of zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples gradually decreased with increasing heat treatment temperature, suggesting that the water content of zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples significantly affected the adsorption rate.

[0047] Experimental Example 6: The adsorption isotherms of the zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 were tested. The specific steps are as follows: Ten mg of zinc-based Prussian blue analogue was added to sample vials containing 20 mL of aqueous solutions of ammonium chloride at initial concentrations of 1 mg / L, 5 mg / L, 10 mg / L, 25 mg / L, 50 mg / L, and 100 mg / L. The vials were then placed in a constant-temperature shaker at 25 °C and shaken at 200 rpm for 24 h. After the vials had settled, the supernatant was aspirated using a syringe. The supernatant was filtered through a 0.22 μm polyethersulfone membrane to obtain an aqueous solution of adsorbed ammonium ions. The solution was diluted and the ammonium ion concentration was determined. Two parallel tests were performed to ensure accurate adsorption capacity determination.

[0048] like Figure 7 As shown, based on Langmuir fitting, the theoretical monolayer adsorption capacity Q of the zinc-based Prussian blue analog material for ammonium ions in the comparative example is... max The concentration is 32.1 mg / g, and the adsorption equilibrium constant K is... L The maximum is 0.756 L / mg. The theoretical monolayer adsorption capacity Q of the zinc-based Prussian blue analog ammonia nitrogen adsorbent for ammonium ions in Example 1 is... max The maximum is 76.5 mg / g, and the adsorption equilibrium constant K L The theoretical monolayer adsorption capacity Q of the zinc-based Prussian blue analog ammonia nitrogen adsorbent for ammonium ions in Example 2 is 0.054 L / mg. max The concentration is 65.3 mg / g, and the adsorption equilibrium constant K is... L The theoretical monolayer adsorption capacity Q of the zinc-based Prussian blue analog ammonia nitrogen adsorbent for ammonium ions in Example 3 is 0.074 L / mg. max The concentration is 39.9 mg / g, and the adsorption equilibrium constant K is... L The value was 0.718 L / mg, indicating that the type and content of water molecules in the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples significantly affected the adsorption capacity. Adjusting the state of water molecules by using a suitable heat treatment temperature can significantly improve the adsorption capacity and prevent the zinc-based Prussian blue analog material in the comparative example from being adsorbed to a smaller capacity too quickly.

[0049] like Figure 8 As shown, according to Freundlich fitting, the adsorption capacity constant K of the zinc-based Prussian blue analog material for ammonium ions in the comparative example is... F The adsorption capacity constant K of the zinc-based Prussian blue analog ammonia nitrogen adsorbent for ammonium ions is 0.207, the adsorption strength factor n is 14.03, and the adsorption capacity constant K of the zinc-based Prussian blue analog ammonia nitrogen adsorbent for ammonium ions in Example 1 is 0.207. FThe maximum value is 0.342, and the adsorption strength factor n is 14.24. In Example 2, the zinc-based Prussian blue analog ammonia nitrogen adsorbent exhibits the following adsorption capacity constant K for ammonium ions. F The adsorption capacity constant K of the zinc-based Prussian blue analog ammonia nitrogen adsorbent for ammonium ions in Example 3 is 0.287, and the adsorption strength factor n is 16.22. F The value is 0.213, and the maximum adsorption strength factor n is 17.80, which further proves the relationship between the heat treatment temperature and the adsorption capacity of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples. This indicates that the adsorption of the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples is more consistent with the adsorption of non-uniform surface multilayer molecules, and the adsorption capacity increases with the increase of heat treatment temperature.

[0050] Experimental Example 7: Selective isothermal adsorption tests were conducted on the zinc-based Prussian blue analog materials in the comparative examples and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3. The specific steps are as follows: Different reagents, including sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2), were weighed to prepare mixed ionic solutions with a molar ratio of 1:1 to ammonium chloride, where the ammonium chloride concentration was 10 mg / L. 10 mL of the mixed solution was added to a sample vial, followed by the addition of 10 mg of a zinc-based Prussian blue analogue. The sample vial was placed in a constant-temperature shaker at 25 °C and shaken at 200 rpm for 24 h. After the vial had settled, the supernatant was aspirated using a syringe. The solution was filtered through a 0.22 μm polyethersulfone membrane to obtain an aqueous solution of adsorbed ammonium ions. The solution was diluted and the ammonium ion concentration was determined. Two parallel tests were performed to ensure accurate adsorption capacity determination.

[0051] like Figure 9 As shown, the results indicate that the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples still exhibits a high adsorption capacity when placed in an aqueous solution containing multiple ions such as sodium, potassium, magnesium, and calcium, with almost no adsorption capacity decay. Only potassium ions (K...) show this characteristic. + This results in a slight decrease in the adsorption of ammonium ions, while the influence of other ions is negligible. This selectivity stems from a size sieving mechanism: the 3.2 Å effective pore size of the framework closely matches the 3.31 Å hydration radii of potassium and ammonium ions, allowing them to preferentially diffuse and exchange. The weaker binding force of ammonium ions to water and the hydrogen bonding with the cyano nitrogen on the framework mean that potassium ions only slightly affect the adsorption of ammonium ions rather than directly replacing them. In contrast, larger hydrated ions, such as sodium ions with a hydration radius of 3.58 Å, significantly reduce the adsorption of ammonium ions. + Magnesium ions with a hydration radius of 4.28 Å (Mg) 2+ ), calcium ions with a hydration radius of 4.12 Å (Ca2+ These are directly excluded, minimizing competitive interference; overall, the zinc-based Prussian blue analog ammonia nitrogen adsorbents in the examples exhibit excellent selectivity for the adsorption of ammonium ions.

[0052] Experimental Example 8: The zinc-based Prussian blue analog material in the comparative example and the zinc-based Prussian blue analog ammonia nitrogen adsorbents in Examples 1 to 3 were tested for isothermal adsorption at different initial pH values. The specific steps are as follows: Ten mg of zinc-based Prussian blue analogue was added to sample vials containing 20 mL of aqueous solutions of ammonium chloride with initial concentrations of 10 mg / L and initial pH values ​​of 4, 6, 8, and 10. The vials were then placed in a constant-temperature shaker at 25°C and shaken at 200 rpm for 24 h. After the vials had settled, the supernatant was aspirated using a syringe. The supernatant was filtered through a 0.22 μm polyethersulfone membrane to obtain an aqueous solution of adsorbed ammonium ions. The solution was diluted and the ammonium ion concentration was determined. Two parallel tests were performed to ensure accurate adsorption capacity determination.

[0053] like Figure 10 As shown, the results indicate that the zinc-based Prussian blue analog ammonia nitrogen adsorbent in the examples has excellent adsorption capacity under acidic and weakly alkaline conditions with an initial pH of 4-8, and there is no problem of adsorption capacity decay. Under strongly alkaline conditions with an initial pH of 10, the adsorption capacity is reduced. However, in practical applications, the main application scenario is low-concentration ammonia nitrogen wastewater with a neutral background solution pH. Therefore, it also has application potential in actual wastewater.

[0054] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A zinc-based Prussian blue analog ammonia nitrogen adsorbent, characterized in that, This ammonia nitrogen adsorbent was obtained by mixing a zinc source solution and a ferrocyanide source solution, allowing them to stand and age, separating the precipitate, drying it, and then heat-treating it under a protective atmosphere followed by drying. The protective gas used as the protective atmosphere is selected from one or more of nitrogen, argon, and helium. The target temperature of the heating heat treatment is 100~200 ℃, the heating rate is 3~7 ℃ / min, and the holding time is 20~40 min.

2. A method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent as described in claim 1, characterized in that, The method includes the following steps: A zinc source and a chelating agent are dissolved in water to obtain a zinc source solution; a ferrocyanide source is dissolved in water to obtain a ferrocyanide source solution; the ferrocyanide source solution is poured into the zinc source solution to obtain a suspension mixture; the suspension mixture is stirred and allowed to stand for aging to obtain a solid-liquid mixture containing a precipitate; the solid-liquid mixture containing the precipitate is centrifuged to remove the supernatant, the precipitate is washed and dried to obtain a zinc-based Prussian blue analog material; the zinc-based Prussian blue analog material is heat-treated under a protective atmosphere and dried to obtain a zinc-based Prussian blue analog ammonia nitrogen adsorbent.

3. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The zinc source is selected from one or more of zinc chloride, zinc nitrate, zinc acetate, and zinc sulfate; the chelating agent is selected from one or more of potassium citrate and sodium citrate; and the molar / volume ratio of zinc source, chelating agent, and water in the zinc source solution is 1 mol:(1~1.25 mol):(20~30 L).

4. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The ferrocyanide source is selected from one or more of potassium ferrocyanide and sodium ferrocyanide, and the molar / volume ratio of ferrocyanide source to water in the ferrocyanide source solution is 1 mol:(20~30 L).

5. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The molar ratio of the zinc source to the ferrocyanide source is 1:(0.875~1.125).

6. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The temperature of the infusion is 10~40℃, and the rate is 1~5 mL / s.

7. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The stirring temperature is 10~40 ℃, the stirring speed is 300~700 rpm, and the stirring time is 20~40 min. The static aging process is carried out at a temperature of 10~40 ℃ for 20~28 h.

8. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The centrifugation temperature is 10~40 ℃, the speed is 6000~10000 rpm, and the time is 5~15 min. Washing is performed using one or more of water, ethanol, and acetone, and the number of washes is 2 to 5. The drying temperature after washing is 50~70 ℃, and the time is 10~14 h.

9. The method for preparing a zinc-based Prussian blue analog ammonia nitrogen adsorbent according to claim 2, characterized in that, The drying temperature after the heat treatment is 90~110 ℃, and the time is 10~14 h.

10. The application of the zinc-based Prussian blue analog ammonia nitrogen adsorbent as described in claim 1 in the separation, removal, and enrichment of ammonium in water.

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