A method for constructing a polyol-functionalized hollow covalent organic framework and its boron removal application

Abstract

The application belongs to the technical field of preparation of adsorption separation functional materials, and discloses a construction method of polyol functionalized hollow covalent organic framework and boron removal application thereof. The application uses a silicon template method to induce covalent organic framework COFs to deposit and grow on the surface of a silicon medium, and through a reversible covalent bond regulation technology as a core, reaction conditions such as solvents, reaction temperatures and monomers are accurately designed, and through a synergistic strategy, the functionalization and structure optimization of the COFs layer adsorbent are simultaneously realized, and then the silicon template is removed through a reversible bond locking strategy to stabilize the COFs layer, thereby a COFs adsorbent with a hollow structure and a high monomer loading capacity is prepared and used for deep and rapid removal of boron in an aqueous solution. The application proposes a simple strategy that can simultaneously realize the functionalization and reconstruction optimization of COFs, and the prepared adsorbent has novel structure, controllable size, simple preparation process, fast mass transfer rate, large adsorption capacity, easy recovery and good regeneration performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of adsorption separation functional materials, and relates to a method for constructing a polyol functionalized hollow covalent organic framework and boron removal application thereof. BACKGROUND

[0002] Because of its unique chemical stability and electronic properties, boron and its compounds play a key role in semiconductor materials, high-performance composite materials, special glasses, and drug synthesis, and are widely used in building materials, metallurgy, agriculture, medicine, nuclear industry, and many other fields, and are an important cornerstone supporting global technological progress and industrial upgrading. Although boron is an essential trace element in the body, the adaptability of animals, plants, and humans to boron in water is very limited, and excessive intake of boron can cause a series of health problems including physiological metabolic disorders, nervous system damage, and functional damage to the organs of liver and kidney. In recent years, with the rapid development of the boron industry, the amount of boron-containing wastewater discharged has increased year by year, seriously disrupting the boron cycle in the natural environment, threatening the ecological system, and further affecting the human living environment. The continuous improvement of environmental protection requirements is an important trend and key measure to protect the human living environment and social sustainable development, which puts forward more stringent requirements for the rational development of liquid boron resources and the deep treatment technology of boron-containing wastewater in the boron industry. Therefore, establishing a new green and efficient boron removal method with independent intellectual property rights to realize the harmless treatment of boron-containing wastewater is of great significance to maintain the stability of the boron cycle in the natural environment, and is in line with the guiding spirit of the New Pollutant Control Action Plan to strengthen the governance of new pollutants, and is a positive response to the demand of the national green development strategy.

[0003] Currently, the technologies for removing boron from aqueous solution include extraction, acidification precipitation, multi-stage crystallization, and adsorption. Among them, the adsorption method has broad application potential in the field of separation technology due to its simple operation, economic and environmental protection, and renewable advantages, and has attracted widespread attention. Covalent organic framework (COFs) materials have shown wide application prospects in the field of adsorption separation due to their excellent characteristics such as large specific surface area, adjustable pore size, and densely modified sites, and have been favored by the industry. However, as a member of emerging materials, COFs materials still face difficulties in functionalization, poor structural stability, and difficulty in elucidating structure-activity relationships, which limit their performance and application value. Therefore, innovatively developing a new COFs material preparation technology that integrates functionalization, highly ordered structure, and stability is a key way to promote the application of COFs materials in the field of adsorption separation.

[0004] The ordered structure of COFs-based adsorbents, the loading of monomers in the pores, and the morphology, which together affect the interaction efficiency between COFs adsorbents and target molecules, determine their adsorption performance. By precisely designing the functionalization reaction conditions, and by regulating the reversibility of covalent bonds, the release and recombination of COFs basic units can be achieved. When the basic units are released in solution, the accessibility of the modification sites is greatly enhanced. In this process, the functionalization of COFs adsorbents can be achieved. Subsequently, the functionalized COFs basic units are re-stacked due to the conjugation between units, and the covalent bonds are re-formed, achieving micro-level structural optimization.

[0005] Micro-nano materials with hollow structures are widely used in the development of micro-nano adsorbents due to their unique advantages such as lightweight, strong site accessibility, and good dispersion. The introduction of hollow structures is an effective way to regulate the structure-activity relationship of adsorbents and improve the accessibility between target and functional sites. Through the solid template-assisted surface polymerization strategy, COFs material growth is successfully introduced on the template surface, and hollow COFs adsorbents can be obtained by removing the template. Although the strong conjugation interaction between COF units promotes their assembly, there are still challenges in the level of precise control of synthesis, especially in accurately regulating the stacking mode of units. Therefore, most products are mainly in the non-ideal AB stacking mode, which significantly hinders the formation of regular channels inside the COFs material, and thus weakens its structural characteristics and expected functional performance, limiting the potential of COFs materials in high-performance application fields. Therefore, by exploring the structure-activity relationship between the growth process of COFs layers and the design of post-functionalization reaction conditions during the preparation process through the template method, achieving high order structure and high loading of monomers, and constructing hollow structure, the performance of COFs adsorbents can be effectively improved. SUMMARY

[0006] In order to solve the problems of COFs-based boron removal adsorbents such as difficult functionalization, poor structural stability, and low adsorption capacity in the prior art, the present application proposes a method for constructing a multi-alcohol functionalized hollow covalent organic framework (HSPCOF), which is used for rapid boron removal in aqueous solution.

[0007] The present application firstly grows a COFs layer on the surface of a silicon medium by a template method, then through precise control of reaction conditions, anchors a polyol functional group on the basic unit of the COFs by using N,N-dimethylformamide (DMF) as a solvent and meglumine chloride (Cl-NMDG) as a functional monomer, realizes reconstruction of the COFs structure in the functionalization process, and finally realizes preparation of a polyol functionalized hollow COFs adsorbent after stabilization modification and removal of the template. Through precise regulation of the reaction temperature and solvent in the functionalization process, a series of HSPCOF boron removal adsorbents with different monomer loadings and structure optimization degrees are obtained, and their boron adsorption performance is explored.

[0008] To achieve the above technical purposes, the technical scheme adopted by the present application is:

[0009] (1) Preparation of pre-aldehyde group functionalized silica nanosphere template (SiO2-CHONST)

[0010] First, a mixed solution A of anhydrous ethanol, deionized water and ammonia water is prepared, a small amount of tetraethyl orthosilicate (TEOS) is added to the mixed solution A under stirring conditions for the first reaction, centrifugal separation is performed, and the obtained solid is washed with anhydrous ethanol for several times and dispersed with methanol, then an ethanol solution of 3-aminopropyl triethoxysilane (APTES) is added, stirring is performed, and the second reaction is carried out, centrifugal separation is performed, and the obtained solid is washed with anhydrous ethanol for several times and dispersed with methanol, then acetic acid and p-phenylenediamine are added, stirring is performed, and the third reaction is carried out, centrifugal separation is performed, and the obtained solid is washed with ethanol for several times, the obtained solid is SiO2-CHONST, and the obtained solid is vacuum dried for standby use;

[0011] (2) Preparation of covalent organic framework layer (BCOF)

[0012] The SiO2-CHONST prepared in step (1) is placed in a round-bottom flask, then methanol and acetic acid are added, ultrasonic dispersion is performed, and then the mixture is placed in a water bath for stirring, 1,4-dialdehyde-2,5-divinylbenzene (DVA) methanol solution and 1,3,5-tris (4-aminophenyl) benzene (TAPB) methanol solution are added through a syringe at intervals, centrifugal separation is performed after the reaction is completed, and the obtained solid is washed with methanol and anhydrous ethanol for several times to remove residual reagents, and the obtained solid BCOF is vacuum dried for standby use;

[0013] (3) Preparation of polyol functionalized adsorbent (PCOF)

[0014] 1) Epoxy chloropropane and meglumine are dispersed with DMF, stirring reaction is performed, the mixture is extracted with acetone and filtered, a pure white mixture is obtained, vacuum drying is performed to completely remove acetone, and finally Cl-NMDG is obtained as a viscous transparent liquid;

[0015] 2) The BCOF prepared in step (2) is placed in a round-bottom flask and dispersed with DMF, then Cl-NMDG is added, and after ultrasonic dispersion, oxygen is removed by nitrogen blowing under stirring, and then copper chloride dihydrate, pentamethyldiethylene triamine (PMEDTA) and ascorbic acid (AA) are added in sequence, the reaction is sealed and completed, after cooling to room temperature, centrifugal separation is performed, and the obtained solid PCOF is washed with deionized water and ethanol for several times to remove residual reagents, and then vacuum dried for standby use.

[0016] (4) Preparation of polyol functionalized hollow covalent organic framework (HSPCOF)

[0017] 1) The product PCOF obtained in step (3) is dispersed in methanol with terephthalic acid at low temperature, sodium borohydride is slowly added under stirring, and after a reaction time t1, the reaction is continued in an oil bath at a slow temperature rise for a reaction time t2, and then the reaction is naturally cooled to room temperature, centrifugal separation is performed, and the obtained solid SPCOF is washed with deionized water and ethanol for several times to remove residual reagents, and then vacuum dried for standby use;

[0018] 2) The SPCOF is added into a sodium hydroxide solution, and after stirring and reaction, centrifugal separation is performed, and the obtained solid HSPCOF is washed with deionized water and ethanol for several times to remove residual reagents, and then vacuum dried for standby use.

[0019] Preferably, in step (1), the volume ratio of anhydrous ethanol, deionized water and ammonia water in the mixed solution A is 15-45 mL: 2.5-7.5 mL: 1-3 mL;

[0020] The amount ratio of the mixed solution A, the ethanol solution of TEOS, APTES, acetic acid and terephthaldehyde is 18-60 mL: 2-6.5 mL: 2-10 mL: 0.1-0.3 mL: 0.1-0.6 g; wherein, TEOS is added in two times, 5% of the total amount of TEOS is added in the first time, and 95% of the total amount of TEOS is added in the second time after an interval of 0.5-1 h; the concentration of the ethanol solution of APTES is 2.5% (v / v);

[0021] The reaction temperature is 25-35℃, and the stirring speed is 200-400 rpm; the first reaction time is 8-12 h; the second reaction time is 8-12 h; and the third reaction time is 3-6 h;

[0022] Preferably, in step (2), the amount ratio of SiO2-CHONST, methanol, acetic acid, the methanol solution of DVA and the methanol solution of TAPB is 50-150 mg: 25-75 mL: 0.1-0.3 mL: 5-15 mL: 5-15 mL, wherein, the concentration of the methanol solution of DVA is 4.4 g / L, and the concentration of the methanol solution of TAPB is 5.6 g / L.

[0023] The reaction temperature in the water bath is 25-35℃, the stirring speed is 200-400rpm, the interval adding monomer time is 15-20min, the adding amount is 0.2-0.6mL each time, and the reaction time after adding is 24-48h.

[0024] Preferably, in 1) of step (3), the amount ratio of the epichlorohydrin and meglumine is 4.15-12.45mL:9.55-28.65g, the stirring reaction temperature is 45-55℃, and the stirring reaction time is 20-26h.

[0025] Preferably, in 2) of step (3), the amount ratio of the BCOF, Cl-NMDG, copper chloride dihydrate, PMEDTA and AA is 50-150mg:0.2-0.6g:50-150mg:0.1-0.3mL:25-75mg, the stirring speed is 200-300rpm, the sealed reaction temperature is 45-50℃, and the reaction time is 20-26h.

[0026] Preferably, in 1) of step (4), the amount ratio of the PCOF, terephthalic acid and sodium borohydride is 50-150mg:0.12-0.36g:1-3g, the stirring speed is 200rpm, the low temperature is 0 to-18℃, the first reaction time t1 is 100-120min, then the temperature is raised to 30-35℃, and the second reaction time t2 is 20-26h.

[0027] Preferably, in 2) of step (4), the concentration of the sodium hydroxide solution is 2M, the stirring speed is 200-400rpm, the stirring reaction temperature is 30-35℃, the stirring reaction time is 6-8h, and the centrifugal speed is 4000-6000rpm.

[0028] The polyol functionalized hollow covalent organic framework prepared by the application is used for boron removal in aqueous solution. Compared with the prior art, the application has the following beneficial effects:

[0029] The application is based on the template method and reversible regulation of covalent bond, and a hollow polyol functionalized covalent organic framework is prepared and applied to boron removal in aqueous solution. ①The hollow structure of HSPCOF improves the accessibility of adsorption sites, can realize rapid enrichment of boron, and can reach 87.94% of the maximum adsorption capacity within 180min and reach adsorption equilibrium within 5h; ②The functionalization and structure optimization of COFs material can be realized by a simple reaction process, which simplifies the reaction steps of obtaining high-performance COFs material; ③HSPCOF still has good adsorption performance after five cycles, and can realize the enrichment of boron. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The preparation flowchart of the polyol functionalized hollow covalent organic frameworks (HSPCOF) of the present application.

[0031] Figure 2 SEM and TEM images of the materials at each stage in Example 1.

[0032] Figure 3 The infrared spectra of the product BCOF in (2), the product PCOF at different reaction temperatures, and the product SPCOF in Example 1.

[0033] Figure 4 The infrared spectra of the monomer Cl-NMDG in 1) in (3) in Example 1.

[0034] Figure 5 The XRD spectra of the product PCOF at different reaction temperatures in Example 4.

[0035] Figure 6 The elemental analysis data of the product PCOF at different reaction temperatures in Example 4.

[0036] Figure 7 The pH results and Zeta potential analysis of Example 5 are shown.

[0037] Figure 8 The adsorption kinetics experimental results of Example 6 are shown.

[0038] Figure 9 The equilibrium adsorption experimental results of Example 7 are shown.

[0039] Figure 10 The regeneration performance experimental results of HSPCOF in Example 8 are shown. DETAILED DESCRIPTION

[0040] Figure 1 The preparation flowchart of the polyol functionalized hollow covalent organic frameworks (HSPCOF) of the present application.

[0041] Example 1:

[0042] (1) Preparation of pre- aldehyde group functionalized silica nanospheres template (SiO2-CHO NST)

[0043] A 50 mL single neck round bottom flask was charged with 15 mL of anhydrous ethanol, 2.5 mL of deionized water and 1 mL of aqueous ammonia, then 0.1 mL of TEOS was added, stirred at 200 rpm for 0.5 h, then 2 mL of TEOS was added and the reaction was allowed to proceed for a certain period of time. After centrifugation and washing with anhydrous ethanol several times to remove residual reagents, it was dispersed in 15 mL of anhydrous ethanol in a 50 mL single neck round bottom flask, 2 mL of 2.5% vol APTES ethanol solution was added, and the reaction was stirred at 200 rpm for 8 h. After centrifugation, residual reagents were removed by washing with anhydrous ethanol several times, and then dispersed in 25 mL of methanol in a 50 mL single neck round bottom flask, 0.1 mL of acetic acid and 0.1 g of p-xylylene glycol were added, and the reaction was stirred at 200 rpm for 8 h. After centrifugation, residual reagents were removed by washing with ethanol several times, and the obtained solid SiO2-CHO NST was placed in a vacuum oven for drying.

[0044] (2) Preparation of covalent organic framework layer (BCOF)

[0045] A 50 mL single neck round bottom flask was charged with 15 mL of anhydrous ethanol, 2.5 mL of deionized water and 1 mL of aqueous ammonia, then 0.1 mL of TEOS was added, stirred at 200 rpm for 0.5 h, then 2 mL of TEOS was added and the reaction was allowed to proceed for a certain period of time. After centrifugation and washing with anhydrous ethanol several times to remove residual reagents, it was dispersed in 15 mL of anhydrous ethanol in a 50 mL single neck round bottom flask, 2 mL of 2.5% vol APTES ethanol solution was added, and the reaction was stirred at 200 rpm for 8 h. After centrifugation, residual reagents were removed by washing with anhydrous ethanol several times, and then dispersed in 25 mL of methanol in a 50 mL single neck round bottom flask, 0.1 mL of acetic acid and 0.1 g of p-xylylene glycol were added, and the reaction was stirred at 200 rpm for 8 h. After centrifugation, residual reagents were removed by washing with ethanol several times, and the obtained solid SiO2-CHO NST was placed in a vacuum oven for drying.

[0046] (3) Preparation of polyol functionalized adsorbent (PCOF)

[0047] Preparation of Cl-NMDG: 4.15 mL of epichlorohydrin and 9.55 g of meglumine were dispersed with DMF, and the reaction was stirred at 45°C for 20 h. The mixture was extracted with acetone and filtered to obtain a pure white mixture. The mixture was transferred to a vacuum dryer for drying to completely remove acetone, and finally Cl-NMDG was obtained as a viscous transparent liquid for use in the next step.

[0048] The 50 mg of BCOF prepared in step (2) was placed in a 50 mL round-bottom flask, then 20 mL of DMF and 0.2 g of Cl-NMDG were added, after ultrasonic dispersion, stirring was carried out at 50°C with a rotation speed of 200 rpm, nitrogen was introduced for 0.5 h to remove as much oxygen as possible in the reaction system, 50 mg of copper chloride dihydrate, 0.1 mL of PMEDTA and 25 mg of AA were sequentially added, and the reaction was sealed for 24 h, after cooling to room temperature, centrifugal separation was carried out, and the residual reagents were removed by washing with deionized water and ethanol several times, and the obtained solid (PCOF) was placed in a vacuum oven for drying for standby use.

[0049] (4) Preparation of polyol functionalized hollow covalent organic framework (HSPCOF)

[0050] 1) 50 mg of the product PCOF obtained in step (3) was dispersed with 0.12 g of terephthalic acid in 20 mL of methanol at 0°C in a 50 mL round-bottom flask, stirring was carried out at 200 rpm, then 1 g of sodium borohydride was slowly added, after 2 h of reaction, the temperature was slowly increased to room temperature, and the reaction was carried out in a 35°C oil bath for 24 h, and then naturally cooled to room temperature, centrifugal separation was carried out, and the residual reagents were removed by washing with deionized water and ethanol several times, and the obtained solid (SPCOF) was placed in a vacuum oven for drying for standby use.

[0051] 2) 50 mg of the product SPCOF obtained in step 1) was placed in a 50 mL round-bottom flask, 20 mL of 2M sodium hydroxide solution was added, etching was carried out at 200 rpm for 6 h, after centrifugal separation at 5000 rpm, and the residual reagents were removed by washing with deionized water and ethanol several times, and the obtained solid (HSPCOF) was placed in a vacuum oven for drying for standby use.

[0052] Figure 2 The SEM and TEM images of the materials at each stage in Example 1 are shown in FIG. 1, which are the SEM (a-d) and TEM (e-h) images of BCOF, PCOF, SPCOF and HSPCOF, respectively, from which the morphology and structure of the materials can be clearly seen. The COF layer a, e of BCOF shows a larger thickness due to the disorder of the stacking form. After functionalization and structure optimization, the particle size of PCOF is slightly smaller and the thickness is reduced, as shown in b, f, which is due to the change of the stacking form. After stabilization modification, the overall structure does not change significantly, and the hollow structure of HSPCOF can be clearly observed in d, h after etching the template.

[0053] Figure 3 FIG. 1 is an infrared spectrum of the product BCOF in (2) of Example 1, the product PCOF in (3) at different reaction temperatures, and the product SPCOF in (4) 1), and the chlorine is at 735 cm -1The absorption peak at 3370 cm⁻¹ indicates that the Cl-NMDG monomer reacts with the vinyl groups within the channel, anchoring the polyol to the inner wall of the channel. -1 A distinct hydroxyl absorption peak was observed at 1100 cm⁻¹, further confirming the successful modification of the functional group. Furthermore, a peak was observed at 1100 cm⁻¹. -1 The disappearance of the silica absorption peak indicates the complete removal of the silica template.

[0054] Figure 4 This is the infrared spectrum of monomer Cl-NMDG in Example 1 (3), where chlorine (735 cm⁻¹) is present. -1 The presence of ) corresponds to the epoxy portion (910 cm) in epichlorohydrin. -1 The absence of ) and the hydroxyl group (3370cm) in meglumine -1 The significant absorption characteristics of Cl-NMDG indicate its successful synthesis.

[0055] Example 2:

[0056] (1) Preparation of pre-aldehyde-functionalized silica nanosphere templates (SiO2-CHO NST)

[0057] 30 mL of anhydrous ethanol, 5 mL of deionized water, and 2 mL of ammonia were mixed in a 100 mL single-necked round-bottom flask. Then, 0.2 mL of TEOS was added, and the mixture was stirred at 200 rpm for 0.5 h. Another 4 mL of TEOS was added, and the reaction was continued for a certain period. The mixture was collected by centrifugation, and after washing several times with anhydrous ethanol to remove residual reagents, it was dispersed in a 50 mL single-necked round-bottom flask with 20 mL of anhydrous ethanol. 3 mL of 2.5% vol APTES ethanol solution was added, and the mixture was stirred at 200 rpm for 8 h. After centrifugation, the mixture was washed several times with anhydrous ethanol to remove residual reagents. Then, 25 mL of methanol was added to a 50 mL single-necked round-bottom flask to disperse the mixture, followed by 0.1 mL of acetic acid and 0.2 g of terephthalaldehyde. The mixture was stirred at 200 rpm for 8 h. After centrifugation, the mixture was washed several times with ethanol to remove residual reagents. The resulting solid, SiO2-CHO NST, was dried in a vacuum oven for later use.

[0058] (2) Preparation of covalent organic framework layer (BCOF)

[0059] Preparation of Si02-CHO NST: 100 mg of Si02was prepared in step (1) and placed in a 100 mL round bottom flask, then 50 mL of methanol and 0.1 mL of acetic acid were added, after ultrasonic dispersion, it was placed in a water bath at 35°C, stirring at 200 rpm, every 15 minutes, 0.4 mL of DVA methanol solution (44 mg of DVA dissolved in 10 mL of methanol) and 0.4 mL of TAPB methanol solution (56 mg of TAPB dissolved in 10 mL of methanol) were added by syringe, after all the monomers were added, the reaction was maintained for 48 h, centrifuged and washed several times with methanol and anhydrous ethanol to remove residual reagents, the obtained solid (BCOF) was placed in a vacuum oven for drying for standby.

[0060] (3) Preparation of polyol functionalized adsorbent (PCOF)

[0061] Preparation of Cl-NMDG: 8.3 mL of epichlorohydrin and 19.1 g of meglumine were dispersed with DMF, stirring at 50°C for 24 h. The mixture was extracted by acetone and filtered to obtain a pure white mixture. The mixture was transferred to a vacuum dryer for drying to completely remove acetone, and finally Cl-NMDG was obtained as a viscous transparent liquid for use in the next step.

[0062] 100 mg of BCOF prepared in step (2) was placed in a 100 mL round bottom flask, then 40 mL of DMF and 0.4 g of Cl-NMDG were added, after ultrasonic dispersion, stirring was carried out at 50°C with a rotation speed of 200 rpm, nitrogen was introduced for 0.5 h to remove as much oxygen as possible in the reaction system, 100 mg of copper chloride dihydrate, 0.2 mL of PMEDTA and 50 mg of AA were added in turn, sealed for 24 h, after cooling to room temperature, centrifugation and washing with deionized water and ethanol several times to remove residual reagents, the obtained solid (PCOF) was placed in a vacuum oven for drying for standby.

[0063] (4) Preparation of polyol functionalized hollow covalent organic framework (HSPCOF)

[0064] 1) 100 mg of PCOF obtained in step (3) and 0.24 g of terephthalic acid were dispersed in 30 mL of methanol at zero degree in a 50 mL round bottom flask, stirring at 200 rpm, then 2 g of sodium borohydride was slowly added, after reaction for 2 h, the temperature was slowly increased to room temperature, transferred to a 35°C oil bath pot for reaction for 24 h, naturally cooled to room temperature, centrifuged and washed with deionized water and ethanol several times to remove residual reagents, the obtained solid (SPCOF) was placed in a vacuum oven for drying for standby.

[0065] 2) 100 mg of the product obtained in step 1) SPCOF was placed in a 50 mL round bottom flask, 20 mL of 2 M sodium hydroxide solution was added, etched for 6 h at 200 rpm, after centrifugal separation at 5000 rpm, and washed several times with deionized water and ethanol to remove residual reagents, the obtained solid (HSPCOF) was placed in a vacuum oven for drying for standby.

[0066] Example 3:

[0067] (1) Preparation of pre-aldehyde group functionalized silica nanosphere template (SiO2-CHONST)

[0068] A mixture of 45 mL of anhydrous ethanol, 7.5 mL of deionized water and 3 mL of ammonia water was placed in a 100 mL single-neck round-bottom flask, then 0.3 mL of TEOS was added, stirred at 200 rpm for 0.5 h, and then 6 mL of TEOS was added. After centrifugal separation and washing several times with anhydrous ethanol to remove residual reagents, it was dispersed in 60 mL of anhydrous ethanol in a 100 mL single-neck round-bottom flask, 10 mL of 2.5% vol APTES ethanol solution was added, and stirred at 200 rpm for 8 h. After centrifugal separation, washing several times with anhydrous ethanol to remove residual reagents, it was dispersed in 25 mL of methanol in a 50 mL single-neck round-bottom flask, 0.3 mL of acetic acid and 0.6 g of p-phenylenediamine were added, and stirred at 200 rpm for 8 h. After centrifugal separation, the residual reagents were removed by washing several times with ethanol, and the obtained solid SiO2-CHONST was placed in a vacuum oven for drying for standby.

[0069] (2) Preparation of covalent organic framework layer (BCOF)

[0070] 75 mg of SiO2-CHONST prepared in step (1) was placed in a 100 mL round-bottom flask, then 50 mL of methanol and 0.1 mL of acetic acid were added, and after ultrasonic dispersion, it was placed in a water bath at 35°C, stirred at 200 rpm, and every 15 minutes, 0.3 mL of DVA methanol solution (33 mg of DVA dissolved in 7 mL of methanol) and 0.3 mL of TAPB methanol solution (42 mg of TAPB dissolved in 7 mL of methanol) were added by syringe. After all the monomers were added, the reaction was maintained for 48 h, centrifugal separation, and washing several times with methanol and anhydrous ethanol to remove residual reagents, the obtained solid (BCOF) was placed in a vacuum oven for drying for standby.

[0071] (3) Preparation of polyol functionalized adsorbent (PCOF)

[0072] Preparation of Cl-NMDG: 12.45 mL of epichlorohydrin and 28.65 g of meglumine were dispersed with DMF, and the reaction was stirred at 55 °C for 26 h. The mixture was extracted by acetone and filtered to obtain a pure white mixture. The mixture was transferred to a vacuum dryer for complete removal of acetone, and finally Cl-NMDG was obtained as a viscous transparent liquid for use in the next step.

[0073] 100 mg of BCOF prepared in step (2) was placed in a 100 mL round-bottom flask, then 40 mL of DMF and 0.4 g of Cl-NMDG were added, and after ultrasonic dispersion, stirring was carried out at 50 °C with a rotation speed of 300 rpm, and nitrogen was introduced for 0.5 h to remove as much oxygen as possible in the reaction system. 100 mg of copper chloride dihydrate, 0.2 mL of PMEDTA and 50 mg of AA were added in turn, and the reaction was sealed for 24 h. After cooling to room temperature, centrifugal separation was carried out, and the residual reagents were removed by washing with deionized water and ethanol several times. The obtained solid (PCOF) was placed in a vacuum oven for drying for standby use.

[0074] (4) Preparation of polyol functionalized hollow covalent organic framework (HSPCOF)

[0075] 1) 150 mg of PCOF obtained in step (3) and 0.36 g of terephthalic acid were dispersed in 30 mL of methanol at zero degrees in a 50 mL round-bottom flask, and stirring was carried out at 200 rpm, then 3 g of sodium borohydride was slowly added, and after reaction for 2 h, the temperature was slowly increased to room temperature, and the reaction was transferred to a 35 °C oil bath for 24 h, and then naturally cooled to room temperature. The residual reagents were removed by centrifugal separation and washing with deionized water and ethanol several times. The obtained solid (SPCOF) was placed in a vacuum oven for drying for standby use.

[0076] 2) 150 mg of SPCOF obtained in step 1) was placed in a 50 mL round-bottom flask, 30 mL of 2M sodium hydroxide solution was added, and etching was carried out at 200 rpm for 6 h. After centrifugal separation at 5000 rpm, and the residual reagents were removed by washing with deionized water and ethanol several times. The obtained solid (HSPCOF) was placed in a vacuum oven for drying for standby use.

[0077] Example 4: Effect of reaction temperature on adsorbent structure and functional monomer loading

[0078] The 50 mg of BCOF prepared in step (2) of Example 1 was placed in a 100 mL round-bottom flask, then 20 mL of DMF and 0.2 g of Cl-NMDG were added, and after ultrasonic dispersion, stirring was carried out at different temperatures (30, 40, 45, 50, 55, 60°C) at a rotation speed of 300 rpm, and nitrogen was introduced for 0.5 h to remove as much oxygen as possible in the reaction system, and then 100 mg of copper chloride dihydrate, 0.2 mL of PMEDTA, and 50 mg of AA were added in sequence, and the reaction was sealed for 24 h, and after being cooled to room temperature, centrifugal separation was carried out, and the residual reagents were removed by washing with deionized water and ethanol several times, and the obtained solid (PCOF) was placed in a vacuum oven for drying.

[0079] Figure 5 The XRD spectrum of the product PCOF at different reaction temperatures in Example 4 is shown, and according to the XRD analysis, at 318 K to 323 K, the four peaks at 2.84°, 4.85°, 5.65° and 7.37° become more obvious, the peak moves from 2.59° to 2.84° and enhances, and presents the AA stacking mode. It can be seen from the enhancement of the peak that functionalization at the optimal reaction temperature can effectively improve the crystal form of the product.

[0080] Figure 6 The elemental analysis data of the product PCOF at different reaction temperatures in Example 4 is shown, and after grafting modification of the Cl-NMDG monomer, the nitrogen-carbon ratio will change, and the grafting amount and the nitrogen-carbon ratio present a positive correlation, and through the improvement of the nitrogen-carbon ratio, it can be seen that functionalization at the optimal reaction temperature can effectively improve the monomer modification amount of the product.

[0081] Example 5: Effect of solution pH on boron adsorption capacity

[0082] Accurately weigh 6 portions of 5 mg of HSPCOF prepared under the conditions described in Example 1, and add them to 5 mL of boron solution with a pH value of 5, 6, 7, 8, 9, 10, and a concentration of 200 mg / L, respectively, and place them at 25°C for 24 h, then centrifugal separation, and after collecting the solution through a membrane, the concentration of residual boron in the solution is detected by hydrazine-H acid photometry, and three groups of parallel experiments are carried out.

[0083] Figure 7 The pH results and zeta potential analysis of Example 5 are shown, it can be seen that the adsorption capacity of HSPCOF is the largest in the environment with a pH of 9, reaching 114.86 mg g -1 , and the electrostatic effect on this process is small.

[0084] Example 6: Effect of adsorption time on boron adsorption capacity

[0085] Accurately weigh 8 portions of 5 mg HSPCOF prepared under the conditions described in Example 1, and add to 5 mL of a boron solution with a concentration of 200 mg / L and a pH of 9, and place at 25°C. After 5, 15, 30, 60, 120, 180, 240, 300, and 360 min, centrifugal separation is performed, and the solution is collected and passed through a membrane. The remaining boron concentration is detected by the methanimine-H acid photometric method, and three sets of parallel experiments are performed.

[0086] Figure 8 The adsorption kinetics experiment results of Example 6 are shown in Table 2. It can be seen that HSPCOF can achieve rapid enrichment of boron, and 87.94% of the maximum adsorption capacity can be reached within 180 min, and adsorption equilibrium can be reached within 5 h.

[0087] Example 7: Effect of initial boron concentration on adsorption capacity

[0088] Accurately weigh 6 portions of 5 mg HSPCOF prepared under the conditions described in Example 1, and add to 5 mL of a boron solution with concentrations of 100, 200, 300, 500, 700, and 1000 mg / L (pH = 9), respectively, and place at 25°C. After 24 h, centrifugal separation is performed, and the adsorption solution is collected. The same operations are performed at 35°C and 45°C. After passing through a membrane, the remaining boron concentration is detected by the methanimine-H acid photometric method, and three sets of parallel experiments are performed.

[0089] Figure 9 The equilibrium adsorption experiment results of Example 7 are shown in Table 3. It can be seen that as the initial concentration of boric acid increases, the adsorption capacity of HSPCOF gradually increases, and can reach 162.01 mg / g -1 , and the fitting results of the adsorption data are more consistent with the Langmuir model, indicating that the material belongs to a uniform monolayer adsorption.

[0090] Example 8: Effect of adsorbent regeneration on boron adsorption capacity

[0091] Accurately weigh 5 mg of HSPCOF prepared under the conditions described in Example 1, and add to 5 mL of a boron solution with a concentration of 200 mg / L and a pH of 9. After 24 h at 25°C, centrifugal separation is performed, and the solution is removed. After washing with deionized water, 10 mL of 0.1 mol / L hydrochloric acid is added as an eluent, and the mixture is placed for another 24 h. After centrifugal separation, the solution is removed, and washed with deionized water until neutral. This is one cycle, and a total of five cycles are performed. After passing through a membrane, the remaining boron concentration is detected by the methanimine-H acid photometric method, and three sets of parallel experiments are performed.

[0092] Figure 10The regeneration performance of HSPCOF in Example 8 is shown in the experimental results, and it can be seen that HSPCOF still has relatively stable adsorption performance and good regeneration performance after 5 cycles.

Claims

1. A method of constructing a polyol-functionalized hollow covalent organic framework, characterized in that, Comprising the following steps: (1) Preparation of pre-aldehyde group functionalized silica nanosphere template SiO2-CHONST First, prepare a mixed solution A of anhydrous ethanol, deionized water and ammonia water, under stirring conditions, add a small amount of tetraethyl orthosilicate TEOS to the mixed solution A for the first reaction, centrifugal separation, and dispersion after washing with anhydrous ethanol for several times, then add 3-aminopropyl triethoxysilane APTES ethanol solution, stir and react for the second time, centrifugal separation, washing with anhydrous ethanol for several times, methanol dispersion, add acetic acid and p-phenylenediamine, stir and react for the third time, centrifugal separation, ethanol washing for several times, the obtained solid is SiO2-CHONST, vacuum drying for standby; (2) Preparation of covalent organic framework layer BCOF Put the SiO2-CHONST prepared in step (1) into a round-bottom flask, then add methanol and acetic acid, ultrasonic dispersion, then put it in a water bath and stir, every certain time, add 1,4-dialdehyde-2,5-divinylbenzene DVA methanol solution and 1,3,5-tris(4-aminophenyl) benzene TAPB methanol solution through a syringe respectively, after the reaction is completed, centrifugal separation, and washing with methanol and anhydrous ethanol for several times to remove residual reagents, the obtained solid BCOF is vacuum dried for standby; (3) Preparation of polyol functionalized adsorbent PCOF 1) Disperse epichlorohydrin and meglumine with DMF, stir and react, then extract the mixture with acetone and filter to obtain a pure white mixture, vacuum drying to completely remove acetone, and finally obtain Cl-NMDG as a viscous transparent liquid; 2) Put the BCOF prepared in step (2) into a round-bottom flask and disperse it with DMF, then add Cl-NMDG, ultrasonic dispersion, then pass nitrogen to remove oxygen under stirring conditions, then add copper chloride dihydrate, pentamethyl diethylene triamine PMEDTA and ascorbic acid AA in sequence, seal and react, after the reaction is completed, centrifugal separation, and washing with deionized water and ethanol for several times to remove residual reagents, the obtained solid PCOF is vacuum dried for standby; (4) Preparation of polyol functionalized hollow covalent organic framework HSPCOF 1) Disperse the product PCOF obtained in step (3) and terephthalic acid in methanol at low temperature, slowly add sodium borohydride under stirring conditions, react for a time t1, then slowly warm up and continue to react for a time t2 in an oil bath, naturally cool to room temperature, centrifugal separation, and washing with deionized water and ethanol for several times to remove residual reagents, the obtained solid SPCOF is vacuum dried for standby; 2) Add SPCOF to sodium hydroxide solution, stir and react, then centrifugal separation, and washing with deionized water and ethanol for several times to remove residual reagents, the obtained solid HSPCOF is vacuum dried for standby.

2. The construction method of claim 1, wherein In step (1), In the mixed solution A, the volume ratio of anhydrous ethanol, deionized water and ammonia water is 15-45 mL: 2.5-7.5 mL: 1-3 mL; The amount ratio of mixed solution A, ethanol solution of TEOS and APTES, acetic acid and p-phenylenediamine is 18-60 mL:2-6.5 mL:2-10 mL:0.1-0.3 mL:0.1-0.6 g; wherein, TEOS is added twice, 5% of the total amount of TEOS is added first, and 95% of the total amount of TEOS is added after 0.5-1 h; the concentration of the ethanol solution of APTES is 2.5% (v / v); The temperature of the reaction is 25-35℃, and the stirring speed is 200-400 rpm; the time of the first reaction is 8-12 h; the time of the second reaction is 8-12 h; and the time of the third reaction is 3-6 h.

3. The construction method of claim 1, wherein In step (2), the amount ratio of SiO2-CHO NST, methanol, acetic acid, methanol solution of DVA, and methanol solution of TAPB is 50-150 mg:25-75 mL:0.1-0.3 mL:5-15 mL:5-15 mL, wherein the concentration of the methanol solution of DVA is 4.4 g / L, and the concentration of the methanol solution of TAPB is 5.6 g / L.

4. The construction method of claim 1, wherein In step (2), the temperature of the reaction in the water bath is 25-35℃, the stirring speed is 200-400 rpm, the interval between the addition of monomers is 15-20 min, the amount of each addition is 0.2-0.6 mL, and the reaction time after the addition is completed is 24-48 h.

5. The construction method of claim 1, wherein In 1) of step (3), the amount ratio of epichlorohydrin and meglumine is 4.15-12.45 mL:9.55-28.65 g, the temperature of the stirring reaction is 45-55℃, and the time of the stirring reaction is 20-26 h.

6. The construction method of claim 1, wherein In 2) of step (3), the amount ratio of BCOF, Cl-NMDG, copper chloride dihydrate, PMEDTA, and AA is 50-150 mg:0.2-0.6 g:50-150 mg:0.1-0.3 mL:25-75 mg.

7. The construction method of claim 1 wherein, In 2) of step (3), the stirring speed is 200-300 rpm, the temperature of the sealed reaction is 45-50℃, and the time of the reaction is 20-26 h.

8. The construction method of claim 1, wherein, In 1) of step (4), the amount ratio of PCOF, terephthalic acid, and sodium borohydride is 50-150 mg:0.12-0.36 g:1-3 g, the stirring speed is 200 rpm, the low temperature is 0 to -18℃, the time of the first reaction t1 is 100-120 min, then the temperature is raised to 30-35℃, and the time of the second reaction t2 is 20-26 h.

9. The construction method of claim 1 wherein, In 2) of step (4), the concentration of the sodium hydroxide solution is 2M, the stirring speed is 200-400 rpm, the temperature of the stirring reaction is 30-35℃, the time of the stirring reaction is 6-8 h, and the centrifugal speed is 4000-6000 rpm.

10. The polyol-functionalized hollow covalent organic framework prepared by the construction method of any one of claims 1-9 for use in the removal of boron in an aqueous solution.

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