A modified molecular sieve based on liquid phase mediation, its preparation method and application

Abstract

This invention discloses a liquid-phase mediated modified molecular sieve, its preparation method, and its application. The preparation method includes the following steps: (1) dissolving an alkaline compound, a fluoride, and sodium chloride in a solvent to obtain a modified solution; (2) adding the molecular sieve to the modified solution and performing crystallization treatment using a hydrothermal method to obtain the liquid-phase mediated modified molecular sieve. This invention uses an alkaline compound, a fluoride, and sodium chloride as the main raw materials to prepare the modified solution. By mixing this solution with the molecular sieve, the number of defect sites in the molecular sieve is significantly reduced, the crystallinity of the molecular sieve is improved, and the adsorption rate of metal ions in heavy metal solutions by the molecular sieve is increased. The modified molecular sieve provided by this invention can maintain its stability and excellent crystallinity even under high temperature conditions, effectively solving the problems of poor adsorption stability, short service life, and high cost of existing molecular sieve adsorbents under extreme conditions.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a modified molecular sieve based on liquid phase mediation, its preparation method, and its application. Background Technology

[0002] Molecular sieves possess selective adsorption and catalytic properties due to their unique pore structure. Through special processing, molecular sieves can achieve more regular pore structures and fewer crystal defects. High-performance molecular sieves, with their superior selective adsorption and catalytic properties, have been introduced into wastewater treatment, petrochemicals, and fine chemicals, showing promising market prospects. However, the synthesis of molecular sieves is affected by the proportion and purity of raw materials, and often results in certain crystal defects. Improper raw material proportions can lead to uneven crystal growth rates and insufficient inter-crystal bonding, while impurities in the raw materials can cause irregular molecular sieve structures, low product purity, and pore blockage.

[0003] To meet the demand for high-performance molecular sieves, defect control and modification are necessary. Industrially, template agents are commonly used for defect control, guiding inorganic precursors to form mesoporous molecular sieves with regular channels around them. Another common method is secondary crystallization, where the molecular sieve is mixed with a modifying solution and hydrothermally crystallized again. Through condensation reactions, defect sites are moved to the crystal surface, reducing the number of internal defect sites. However, current molecular sieve defect control and modification technologies still face several challenges. For example, the use of template agents is generally costly, and the removal of template agents can easily lead to the collapse of the molecular sieve crystal structure, resulting in the reintroduction of defects and poor stability during the removal process. Secondary crystallization methods typically require the addition of a silicon-aluminum source and suffer from high time costs, complex processing methods, and low efficiency. These problems significantly limit the efficient application of molecular sieve defect control and modification technologies.

[0004] In addition, Cs + With Co 2+ These are currently the main heavy metal ions in nuclear power plant wastewater. While current adsorption treatment technologies, such as those using gel spheres and resins, have achieved some success, they generally suffer from complex operating procedures, high costs, long treatment times, and large amounts of waste, limiting their widespread application. Using modified molecular sieves for adsorption is a potential solution that has been extensively studied. For example, modified molecular sieves prepared using acids, alkalis, and organic modifiers are available. However, these processes are complex, cause significant pollution, and consume high energy, limiting their widespread application. Summary of the Invention

[0005] To address the above technical problems, the purpose of this invention is to provide a liquid-phase mediated modified molecular sieve, its preparation method, and its application.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] The first aspect of this invention provides a method for preparing a modified molecular sieve based on liquid phase mediation, comprising the following steps:

[0008] (1) Dissolve an alkaline compound, a fluoride, and sodium chloride in a solvent to obtain a modified solution; the concentration of the alkaline compound in the modified solution is 0.01–1.0 mol / L, the concentration of the fluoride is 0.01–0.2 mol / L, and the concentration of sodium chloride is 0.4–1.5 mol / L.

[0009] (2) Add the molecular sieve to the modified solution obtained in step (1) and crystallize it by hydrothermal method to obtain the modified molecular sieve based on liquid phase mediation.

[0010] This invention utilizes liquid-phase mediated treatment under specific conditions to dissolve some silicon and aluminum elements at defect sites. Simultaneously, hydroxide and fluoride ions in the alkaline modification solution promote the migration of silicate and aluminum ions within the molecular sieve framework, respectively, and modify the defect sites through condensation reactions, causing the original defect sites to move to the crystal edges. Ultimately, this significantly reduces the number of defect sites within the molecular sieve crystal, thereby improving the stability of the molecular sieve. Furthermore, the Na in sodium chloride... + It can undergo ion exchange with the molecular sieve framework, increasing the silica-alumina ratio of the molecular sieve, altering the original pore structure, and thus improving the adsorption rate of the molecular sieve. This modification method is simple, easy to operate and implement, and significantly improves the stability and adsorption performance of various molecular sieves.

[0011] Furthermore, in step (1), the alkaline compound is selected from sodium hydroxide and / or potassium hydroxide. The alkaline compound provides an alkaline environment that dissolves the silicon and aluminum elements in the molecular sieve framework.

[0012] Further, in step (1), the fluoride is selected from one or more of ammonium fluoride, sodium fluoride, aluminum fluoride, and hexafluoroaluminate, preferably ammonium fluoride.

[0013] Furthermore, in step (1), the modified solution also includes a silicon source and / or an aluminum source.

[0014] Furthermore, the concentration of silicon source and / or aluminum source in the modified solution is 0 to 0.015 mol / L.

[0015] Furthermore, the silicon source is preferably sodium silicate, and the aluminum source is preferably sodium aluminate.

[0016] The purpose of adding additional silicon and / or aluminum sources is to increase the concentration of silicon and aluminum in the modification solution, and under the synergistic effect of hydroxide ions and fluoride ions, further promote the migration of silicate and aluminum ions within the molecular sieve framework, significantly shorten the defect modification time, and improve the modification efficiency.

[0017] Furthermore, in step (1), the solvent is preferably water.

[0018] Furthermore, in step (2), the molecular sieve is an LTA type molecular sieve and / or a FAU type molecular sieve.

[0019] Further, in step (2), the solid-liquid ratio of the molecular sieve to the modified solution is 1g:(10-50)mL.

[0020] Furthermore, in step (2), the temperature of the crystallization treatment is 90 to 120°C.

[0021] Furthermore, in step (2), the crystallization treatment time is 3 to 9 hours.

[0022] The second aspect of the present invention provides a modified molecular sieve based on liquid phase mediation obtained by the preparation method described in the first aspect.

[0023] The crystallinity of modified molecular sieves based on liquid phase mediation can be tested after calcination.

[0024] Furthermore, the calcination treatment temperature is 400–1200°C.

[0025] Furthermore, the calcination treatment time is 1 to 5 hours.

[0026] The third aspect of this invention provides the application of the liquid-phase mediated modified molecular sieve described in the second aspect in the adsorption of metal ions, mainly for the adsorption of metal ions in heavy metal solutions.

[0027] Furthermore, the metal ion is a cesium ion (Cs). + ) and / or cobalt ions (Co 2+ ).

[0028] Furthermore, the concentration of metal ions in the heavy metal solution is 100–1000 mg / L.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention utilizes alkaline compounds, fluorides, and sodium chloride as main raw materials to prepare a modified solution. The crystallinity of the molecular sieve after liquid-phase treatment in the modified solution can reach over 99%, and the crystallinity remains essentially unchanged under high-temperature conditions. On one hand, the alkaline modified solution can dissolve some of the silicon and aluminum elements at defect sites; on the other hand, hydroxide ions and fluoride ions in the modified solution can promote the migration of silicate and aluminum ions within the molecular sieve framework, respectively, and modify defect sites through condensation reactions, causing the original defect sites to move to the crystal edge. Ultimately, this significantly reduces the number of defect sites within the molecular sieve crystal, thus improving the stability of the molecular sieve. The sodium chloride in the modified solution contains Na... + It can undergo ion exchange with the molecular sieve framework to change the pore structure of the molecular sieve, thereby improving the adsorption rate of the molecular sieve.

[0031] 2. The raw materials used in the modified solution of this invention—alkaline compounds, fluorides, and sodium chloride—are inexpensive and can be reused. The molecular sieve modification process is conducted under mild conditions, which, compared with existing molecular sieve modification technologies, not only simplifies the production process but also reduces energy consumption and costs.

[0032] 3. The modified molecular sieve provided by this invention has high crystallinity, large micropore capacity, few defect sites, and high stability. It can maintain its stability and excellent crystallinity even at high temperatures, effectively solving the problems of poor adsorption stability, short service life, and high cost of existing molecular sieve adsorbents on the market under extreme conditions. Attached Figure Description

[0033] Figure 1 The images show the XRD patterns of LTA-type molecular sieves, the modified LTA-type molecular sieve prepared in Example 1, and the modified LTA-type molecular sieve prepared in Example 2.

[0034] Figure 2 The images show the XRD patterns of the FAU-type molecular sieve, the modified FAU-type molecular sieve prepared in Example 10, and the modified FAU-type molecular sieve prepared in Example 11.

[0035] Figure 3 The graph shows the crystallinity data of LTA molecular sieves and the modified LTA molecular sieve prepared in Example 2 at different temperatures.

[0036] Figure 4 This is a graph showing the crystallinity data of FAU-type molecular sieves and the modified FAU-type molecular sieve prepared in Example 11 at different temperatures. Detailed Implementation

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0040] Example 1

[0041] A method for preparing modified LTA molecular sieves based on liquid phase mediation includes the following steps:

[0042] (1) Dissolve 0.05g sodium hydroxide, 0.0185g ammonium fluoride and 1.17g sodium chloride in 50mL of deionized water and stir thoroughly to obtain a modified solution. The concentration of alkaline compound in the modified solution is 0.025mol / L, the concentration of fluoride is 0.01mol / L and the concentration of sodium chloride is 0.4mol / L.

[0043] (2) Add 10g of LTA molecular sieve to the modified solution obtained in step (1), and crystallize it in a polytetrafluoroethylene-lined hydrothermal reactor at 90℃ for 5h. Sonicate the obtained modified molecular sieve turbid liquid for 1 minute, centrifuge it to separate the solid and liquid phases and remove the aqueous phase, and dry it in an oven at 80℃ for 16h to obtain the modified LTA molecular sieve.

[0044] Example 2

[0045] A method for preparing modified LTA molecular sieves based on liquid phase mediation includes the following steps:

[0046] (1) Dissolve 0.012g sodium hydroxide, 0.011g ammonium fluoride, 0.76g sodium chloride and 0.012g sodium aluminate in 30mL of deionized water and stir thoroughly to obtain a modified solution. The modified solution contains 0.01mol / L of alkaline compound, 0.01mol / L of fluoride, 0.43mol / L of sodium chloride and 0.0049mol / L of sodium aluminate.

[0047] (2) Add 10g of LTA molecular sieve to the modified solution obtained in step (1), and crystallize it in a polytetrafluoroethylene-lined hydrothermal reactor at 90℃ for 3h. Sonicate the obtained modified molecular sieve turbid liquid for 1 minute, centrifuge it to separate the solid and liquid phases and remove the aqueous phase, and dry it in an oven at 80℃ for 16h to obtain the modified LTA molecular sieve.

[0048] Example 3

[0049] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization time in step (2) is 1 hour.

[0050] Example 4

[0051] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization treatment time in step (2) is 9h.

[0052] Example 5

[0053] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization time in step (2) is 18h.

[0054] Example 6

[0055] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization time in step (2) is 27h.

[0056] Example 7

[0057] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization temperature in step (2) is 50°C.

[0058] Example 8

[0059] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization temperature in step (2) is 120°C.

[0060] Example 9

[0061] A method for preparing modified LTA molecular sieve based on liquid phase mediation is basically the same as that in Example 2, except that the crystallization temperature in step (2) is 180°C.

[0062] Example 10

[0063] A method for preparing modified FAU-type molecular sieves based on liquid phase mediation includes the following steps:

[0064] (1) Dissolve 0.15g sodium hydroxide, 0.167g ammonium fluoride and 0.72g sodium chloride in 50mL of deionized water and stir thoroughly to obtain a modified solution. The concentration of alkaline compound in the modified solution is 0.075mol / L, the concentration of fluoride is 0.09mol / L and the concentration of sodium chloride is 0.245mol / L.

[0065] (2) Add 10g of FAU molecular sieve to the modified solution obtained in step (1), and crystallize it in a polytetrafluoroethylene-lined hydrothermal reactor at 120℃ for 8h. Sonicate the obtained modified molecular sieve turbid liquid for 1 minute, centrifuge it to separate the solid and liquid phases and remove the aqueous phase, and dry it in an oven at 80℃ for 16h to obtain the modified FAU molecular sieve.

[0066] Example 11

[0067] A method for preparing modified FAU-type molecular sieves based on liquid phase mediation includes the following steps:

[0068] (1) Dissolve 0.06g sodium hydroxide, 0.1g ammonium fluoride, 0.43g sodium chloride and 0.0219g sodium silicate in 30mL of deionized water and stir thoroughly to obtain a modified solution. The modified solution contains 0.05mol / L of alkaline compound, 0.09mol / L of fluoride, 0.245mol / L of sodium chloride and 0.006mol / L of sodium silicate.

[0069] (2) Add 10g of FAU molecular sieve to the modified solution obtained in step (1), and crystallize it in a polytetrafluoroethylene-lined hydrothermal reactor at 120℃ for 5h. Sonicate the obtained modified molecular sieve turbid liquid for 1 minute, centrifuge it to separate the solid and liquid phases and remove the aqueous phase, and dry it in an oven at 80℃ for 16h to obtain the modified FAU molecular sieve.

[0070] Comparative Example 1

[0071] A method for preparing a modified LTA molecular sieve is basically the same as that in Example 2, except that: in step (1), ammonium fluoride is not added to the modified solution.

[0072] Comparative Example 2

[0073] A method for preparing a modified LTA molecular sieve is basically the same as that in Example 2, except that in step (1), the concentration of ammonium fluoride in the modified solution is 0.4 mol / L.

[0074] Comparative Example 3

[0075] A method for preparing a modified LTA molecular sieve is basically the same as that in Example 2, except that sodium hydroxide is not added to the modified solution in step (1).

[0076] Comparative Example 4

[0077] A method for preparing a modified LTA molecular sieve is basically the same as that in Example 2, except that in step (1), the concentration of sodium hydroxide in the modified solution is 2.1 mol / L.

[0078] Comparative Example 5

[0079] A method for preparing a modified LTA molecular sieve is basically the same as that in Example 2, except that sodium chloride is not added to the modified solution in step (1).

[0080] Comparative Example 6

[0081] A method for preparing a modified LTA molecular sieve is basically the same as that in Example 2, except that in step (1), the concentration of sodium chloride in the modified solution is 2 mol / L.

[0082] Test Example 1

[0083] The crystal structures of the LTA-type molecular sieve, the modified LTA-type molecular sieve prepared in Example 1, and the modified LTA-type molecular sieve prepared in Example 2 were observed using X-ray diffraction (XRD). Figure 1 As shown, the intensity of the characteristic diffraction peaks of the modified LTA molecular sieve is significantly enhanced, indicating that the modified LTA molecular sieve has better crystallinity. In addition, an appropriate amount of sodium aluminate was added in Example 2, which significantly shortened the modification time.

[0084] The crystal structures of the FAU-type molecular sieve, the modified FAU-type molecular sieve prepared in Example 10, and the modified FAU-type molecular sieve prepared in Example 11 were observed by XRD. Figure 2 As shown, the characteristic diffraction peak intensity of the modified FAU molecular sieve is significantly enhanced, indicating that the modified FAU molecular sieve has better crystallinity. Furthermore, the addition of an appropriate amount of sodium silicate in Example 11 significantly shortened the modification time.

[0085] Test Example 2

[0086] The diffraction intensities of the modified molecular sieves in Examples 1-11 and Comparative Examples 1-6 were measured using an X-ray diffractometer, and their relative crystallinity was calculated using the following formula:

[0087]

[0088] Where X cX0 represents the relative crystallinity of the synthesized product, in %; X0 represents the crystallinity of the molecular sieve standard of this type, in %; I c Ikl represents the diffraction intensity of a certain crystal plane (hkl) of the synthesized molecular sieve; I0 represents the diffraction intensity of a certain crystal plane (hkl) of the standard sample of this type of molecular sieve.

[0089] The relative crystallinity data of the modified LTA molecular sieves prepared in Examples 1-2, the modified FAU molecular sieves prepared in Examples 10-11, and the modified LTA molecular sieves prepared in Comparative Examples 1-6 are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] As shown in Table 1, the crystallinity of both LTA and FAU type silicate-based molecular sieves significantly improved after modification using the liquid-phase mediated treatment method provided by this invention. Data from Examples 1-2 and 10-11 demonstrate that adding appropriate amounts of silicon or aluminum sources to the modification solution can effectively shorten the modification time and improve modification efficiency while maintaining a substantially unchanged modification effect. Comparative examples 2 and 3-9 show that the preferred crystallization temperature is 90-120℃, and the preferred crystallization time is 3-9 hours. Furthermore, comparative examples 2 and 1-6 show that hydroxide ions and fluoride ions alone exhibit almost no modifying ability; only when both are present simultaneously and maintained within a certain concentration range can crystal defects be effectively modified. When the concentration of hydroxide or fluoride ions is too high, it accelerates the dissolution of silicon and aluminum elements in the molecular sieve framework, resulting in a large number of new lattice defects in the molecular sieve and consequently a significant decrease in crystallinity. In Comparative Example 6, when the sodium chloride concentration was too high, the crystallinity of the molecular sieve decreased, indicating that under conditions of excessive sodium ions, aluminum elements in the molecular sieve framework would dissolve excessively, damaging the molecular sieve framework and reducing crystallinity.

[0094] Test Example 3

[0095] 1g of LTA-type molecular sieve (before modification) and the modified LTA-type molecular sieve prepared in Example 2 (after modification) were placed in muffle furnaces and calcined at 500℃, 600℃, 700℃, 800℃, 900℃, and 1000℃ for 3 hours respectively. After cooling, the changes in diffraction intensity were measured by X-ray diffraction, and the relative crystallinity was calculated. The test results are as follows: Figure 3 As shown.

[0096] 1g of FAU-type molecular sieve (before modification) and the modified FAU-type molecular sieve prepared in Example 11 (after modification) were placed in muffle furnaces and calcined at 500℃, 600℃, 700℃, 800℃, 900℃, and 1000℃ for 3 hours respectively. After cooling, the changes in diffraction intensity were measured by X-ray diffraction, and the relative crystallinity was calculated. The test results are as follows: Figure 4 As shown.

[0097] from Figure 3 and Figure 4 As can be seen, both LTA-type and FAU-type molecular sieves show a significant increase in the critical temperature for crystallinity reduction after modification. Compared with the unmodified state, the crystallinity of the molecular sieves at the same temperature is improved, proving that the modification effectively improves the high-temperature stability of the molecular sieves.

[0098] Test Example 4

[0099] The LTA-type molecular sieves, the modified LTA-type molecular sieves prepared in Examples 1-2, and the modified LTA-type molecular sieves prepared in Comparative Examples 1-6 were activated at 200℃ under vacuum for 2 hours. After cooling, the modified LTA-type molecular sieves were mixed with heavy metal solutions at a solid-liquid ratio of 1g:100mL in a container. The heavy metal solutions were 100mg / L, 500mg / L, and 1000mg / L Cs₂CO₃ solutions and 100mg / L, 500mg / L, and 1000mg / L Co(NO₃)₂ solutions, respectively. The container was fixed on a long-axis mixer and mixed for 9 hours to ensure sufficient adsorption. Then, it was immediately filtered through a PES membrane. The filtrate was then diluted 10,000 times with a 2% dilute nitric acid solution to obtain a sample solution. The concentration of metal ions in the sample solution was measured by ICP-OES (or ICP-MS).

[0100] Calculate the metal ion removal efficiency (R) and adsorption capacity Q using the following formulas. e (mg / g) and partition coefficient K d (mL / g).

[0101] The formula for calculating removal efficiency is:

[0102]

[0103] The formula for calculating adsorption capacity is:

[0104]

[0105] Where C i and C e These are the initial and equilibrium concentrations of the heavy metal solution (mg / L), respectively; V is the solution volume (L); and m is the adsorbent mass (g).

[0106] LTA-type molecular sieves, modified LTA-type molecular sieves prepared in Examples 1-2, and modified LTA-type molecular sieves prepared in Comparative Examples 1-6, respectively, were used to treat Cs2CO3 and Co(NO3)2 mixed solutions at concentrations of 100 mg / L, 500 mg / L, and 1000 mg / L. + and Co 2+ The removal rate and adsorption capacity data are shown in Tables 2 to 7:

[0107] Table 2

[0108] <![CDATA[Sample - 100mg / L Cs + > Removal efficiency R (%) <![CDATA[Adsorption capacity Q e (mg / g)]]> LTA type molecular sieve 84.1 257.1 Example 1 99.7 357.3 Example 2 99.8 369.2 Comparative Example 1 90.9 305.7 Comparative Example 2 75.2 226.4 Comparative Example 3 85.1 260.5 Comparative Example 4 72.9 220.9 Comparative Example 5 86.4 268.4 Comparative Example 6 85.1 264.8

[0109] Table 3

[0110]

[0111]

[0112] Table 4

[0113] <![CDATA[Sample - 500mg / L Cs + > Removal efficiency R (%) <![CDATA[Adsorption capacity Q e (mg / g)]]> LTA type molecular sieve 82.9 250.3 Example 1 98.6 352.3 Example 2 98.2 361.8 Comparative Example 1 88.1 298.5 Comparative Example 2 73.8 221.6 Comparative Example 3 84.3 253.2 Comparative Example 4 71.3 216.1 Comparative Example 5 84.7 260.6 Comparative Example 6 83.5 253.2

[0114] Table 5

[0115]

[0116]

[0117] Table 6

[0118] <![CDATA[Sample - 1000mg / L Cs + > Removal efficiency R (%) <![CDATA[Adsorption capacity Q e (mg / g)]]> LTA type molecular sieve 80.7 245.7 Example 1 95.1 347.8 Example 2 95.3 353.2 Comparative Example 1 85.1 288.4 Comparative Example 2 70.6 211.5 Comparative Example 3 80.8 241.8 Comparative Example 4 68.2 202.9 Comparative Example 5 81.4 252.8 Comparative Example 6 80.9 241.3

[0119] Table 7

[0120] <![CDATA[Sample - 1000mg / L Co 2+ > Removal efficiency R (%) <![CDATA[Adsorption capacity Q e (mg / g)]]> LTA type molecular sieve 62.4 161.6 Example 1 81.8 228.3 Example 2 84.1 239.3 Comparative Example 1 73.3 193.1 Comparative Example 2 49.9 126.4 Comparative Example 3 60.5 159.8 Comparative Example 4 50.2 123.9 Comparative Example 5 64.4 164.6 Comparative Example 6 74.7 192.7

[0121] Tables 2-7 show that the modified LTA molecular sieves prepared in Examples 1-2 exhibited resistance to Cs. + and Co 2+Higher adsorption rates were observed in various concentration solutions. In Comparative Example 1, without the addition of fluoride ions, the adsorption effect of the modified molecular sieve was significantly improved, but the lattice defects within the molecular sieve were not effectively repaired, resulting in low crystallinity. In Comparative Example 2, with excess fluoride ions, the crystallinity was good, but the improvement in modification effect was not significant or even decreased. In Comparative Example 3, without an alkali source, the adsorption rate of the molecular sieve remained almost unchanged, indicating that hydroxide ions had little impact on the modification effect. In Comparative Example 4, with excess alkali source, the dissolution rate of silicon and aluminum elements in the molecular sieve framework was greater than the modification rate, resulting in a large number of new lattice defects in the molecular sieve and a decrease in adsorption rate. In Comparative Example 5, without the addition of sodium chloride, the modification effect was not significant. In Comparative Example 6, with excess sodium chloride, both the removal efficiency and adsorption capacity of the modified molecular sieve increased, but the increase was not as significant as that of the modified LTA-type molecular sieves prepared in Examples 1-2.

[0122] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing modified molecular sieves based on liquid phase mediation, characterized in that, Includes the following steps: (1) Dissolve the alkaline compound, fluoride and sodium chloride in a solvent to obtain a modified solution; The modified solution contains an alkaline compound at a concentration of 0.01–1.0 mol / L, a fluoride at a concentration of 0.01–0.2 mol / L, and a sodium chloride at a concentration of 0.4–1.5 mol / L; the alkaline compound is selected from sodium hydroxide and / or potassium hydroxide; the fluoride is selected from ammonium fluoride and / or sodium fluoride. (2) Add the molecular sieve to the modified solution obtained in step (1) and crystallize it by hydrothermal method to obtain the modified molecular sieve based on liquid phase mediation; The molecular sieve is an LTA type molecular sieve and / or a FAU type molecular sieve.

2. The preparation method according to claim 1, characterized in that, In step (1), the modified solution also includes a silicon source and / or an aluminum source.

3. The preparation method according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the molecular sieve to the modified solution is 1 g : (10~50) mL.

4. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the crystallization treatment is 90~120 ℃.

5. The preparation method according to claim 1, characterized in that, In step (2), the crystallization process takes 3 to 9 hours.

6. The modified molecular sieve based on liquid phase mediation obtained by the preparation method according to any one of claims 1 to 5.

7. The application of the liquid-phase mediated modified molecular sieve as described in claim 6 in the adsorption of metal ions.

8. The application according to claim 7, characterized in that, The metal ions are cesium ions and / or cobalt ions.

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