Preparation method of oxygen-containing heterocyclic functionalized hierarchical pore fiber adsorbent and application of oxygen-containing heterocyclic functionalized hierarchical pore fiber adsorbent in selective cesium separation

Abstract

The invention belongs to the technical field of preparation of ion identification adsorption separation functional materials, and discloses a preparation method of an oxygen-containing heterocyclic ring functionalized hierarchical pore fiber adsorbent and application of the oxygen-containing heterocyclic ring functionalized hierarchical pore fiber adsorbent in selective cesium separation. Aiming at the structural characteristics of Cs (I), a microporous fiber carrier is prepared through a kinetically controlled single micelle self-assembly process, an active carboxyl group is introduced to the surface of the fiber by adopting a nitric acid oxidation method, and then a crown ether oxygen-containing heterocyclic compound is covalently grafted to the surface of the fiber through an amidation reaction, so that the composite material is obtained. Therefore, the fiber adsorbent with specific recognition and separation capability on Cs (I) is successfully prepared. The prepared oxygen-containing heterocyclic ring copolymer microporous fiber has excellent selectivity and environmental adaptability to a target object Cs (I).

Description

Technical Field

[0001] This invention belongs to the field of ion recognition adsorption separation functional material preparation technology, specifically involving a method for preparing an oxygen-containing heterocyclic functionalized fiber adsorbent and its application in selectively separating Cs(Ⅰ). Background Technology

[0002] Cesium (Cs) is the most metallic alkali metal element in nature, primarily existing in its combined state. Cesium compounds are widely used in photodetectors, specialty glasses, pharmaceuticals, and catalysis due to their excellent photoelectric properties, catalytic activity, and biocompatibility. In my country, cesium resources are mainly found in two carriers: solid ores and salt lake brine. Extracting cesium from ores typically requires high-temperature roasting and strong acid leaching, resulting in high energy consumption, heavy pollution, and poor economic efficiency, failing to meet the requirements of green and low-carbon development. In contrast, cesium extraction from salt lake brine has the potential for a relatively simple process and low environmental impact. However, due to the extremely low Cs(I) concentration and severe ion interference, the development of a green and efficient cesium extraction technology suitable for complex systems with high salt and low concentrations is crucial for the efficient separation and utilization of cesium resources. Currently, the main methods for separating and extracting cesium from aqueous solutions include chemical precipitation, membrane separation, solvent extraction, and adsorption. Adsorption methods offer advantages such as ease of operation, environmental friendliness, and high design flexibility. However, given the extremely low Cs(I) concentration and significant background ion interference in actual salt lake brines, traditional adsorption materials such as zeolites, Prussian blue analogs, and ion exchange resins still suffer from problems such as low accessibility of active sites, slow mass transfer, and insufficient selectivity in complex systems, making it difficult to achieve efficient adsorption. Currently, studies have reported that precisely controlling the pore structure of adsorbents can effectively enhance the thermodynamic driving force of adsorption, thereby improving mass transfer efficiency. Simultaneously, porous structures not only provide highly accessible active surfaces but also enrich Cs(I) in local spaces through confinement effects, overcoming the bottleneck of insufficient adsorption driving force in low-concentration environments. Therefore, developing novel adsorption functional materials based on pore engineering is of great significance for promoting the practical application of cesium extraction from salt lake brines.

[0003] Micelle assembly is a soft-template method based on the directional self-assembly of amphiphilic molecules in solution to form supramolecular aggregates, enabling the precise construction of functional materials with hierarchical pores and tunable surface properties. This strategy guides amphiphilic molecules to aggregate into micelles of specific morphology through molecular design and external condition control, further transforming them into stable porous structures, thus providing an ideal material platform for applications such as adsorption, catalysis, and separation. In the field of porous adsorption materials, fibrous structures exhibit significant industrial potential due to their ease of processing and large-scale preparation. In particular, porous nanofiber materials prepared based on micelle assembly can achieve porosities exceeding 90%, greatly increasing active sites and significantly promoting ion mass transfer efficiency within the material, providing a superior structural basis for efficient adsorption and separation. However, unfunctionalized fibrous materials lack specific recognition ability for Cs(I). Although selective functional groups can be introduced through surface modification, existing modification methods generally face problems such as complex processes, uneven functional group distribution, and insufficient binding stability. Therefore, developing a novel fiber adsorbent that combines high selectivity, excellent mass transfer capability, and good stability is key to achieving efficient recovery of cesium resources from salt lake brine.

[0004] Oxygen-containing heterocyclic ligands possess cyclic structures with multiple oxygen atoms as heteroatoms. Crown ethers, due to their unique cyclic cavity structure and coordination characteristics, are considered ideal functional groups for achieving highly selective recognition of Cs(I). In particular, 18-crown-6 and its derivatives, with their cavity size highly matched to the radius of the Cs(I) ion, can form stable host-guest complexes through ion-dipole interactions, thus exhibiting excellent selectivity in complex alkali metal ion coexistence systems. Therefore, by covalently grafting or loading crown ethers onto the surface of fiber carriers, and simultaneously controlling the microstructure of the fiber carriers to achieve efficient, stable, and uniform functionalization of the crown ether groups, nanofiber adsorbents can be prepared. This, combined with the high porosity and rapid mass transfer advantages of fiber materials, simultaneously enhances the high-recognition separation and enrichment effect of Cs(I). Summary of the Invention

[0005] To address the problems of poor selectivity and insufficient mass transfer efficiency of existing adsorbent materials in salt lake brine systems, this invention provides a method for preparing an oxygen-containing heterocyclic polymer microporous fiber adsorbent, which can achieve efficient and highly selective adsorption and separation of cesium ions in salt lake brine.

[0006] This invention aims to overcome the shortcomings of traditional adsorbents, such as poor accessibility and abundance of active sites, and insufficient recognition selectivity, resulting in poor adsorption performance. To this end, a kinetically driven single-micelle self-assembly technique is employed to construct a microporous fiber framework with one-dimensional orientation. This fiber material possesses a high specific surface area and abundant pore structure, providing an ideal matrix for subsequent functionalization. By grafting oxygen-containing heterocyclic functional groups with specific coordination ability for Cs(I) onto its surface, its adsorption capacity and selectivity for Cs(I) are significantly improved.

[0007] Specifically, the preparation method of the present invention includes the following steps: First, using triblock copolymer F127 as a structure directing agent, a kinetically controlled single-micelle self-assembly process is employed. Second, a thermopolymerizable methyl phenolic resin oligomer (Resol-P) is synthesized, which can form a three-dimensional covalent cross-linked network. Next, the two components are mixed, and a uniform composite single-micelle dispersion system is formed under stirring. Subsequently, the system is induced to undergo directional self-assembly and polymerization at low temperature to obtain a polymer fiber precursor (HSF) with a stable microporous structure. The obtained product is freeze-dried and subjected to high-temperature carbonization treatment to finally obtain a carbon-based fiber carrier (CF) with a microporous structure. Simultaneously, by systematically controlling key parameters such as polymerization reaction time, monomer feed ratio, and reaction temperature, precise control of the fiber morphology and pore structure can be achieved. In the functionalization stage, active carboxyl groups (CF-O) were introduced onto the fiber surface using nitric acid oxidation. Then, 4'-aminobenzo-18-crown-6 was covalently grafted onto the fiber surface through an amidation reaction, thus successfully preparing a fiber adsorbent (CF-OC) with specific recognition and separation capabilities for Cs(I).

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows:

[0009] This invention provides a method for preparing a micelle self-assembled oxygen-containing heterocyclic functionalized fiber adsorbent, and evaluates the selective adsorption and separation performance of the oxygen-containing heterocyclic functionalized fiber adsorbent for cesium ions using a salt lake brine solution. The method includes the following steps: (1) Preparation of Resol-P: At the initial temperature, phenol was dissolved in sodium hydroxide solution in proportion, followed by the addition of formaldehyde solution. The mixture was heated to the final reaction temperature and mixed. After the reaction was completed, the pH was adjusted with hydrochloric acid, and the phenolic resin precursor solution Resol-P was obtained by freeze drying. (2) Preparation of CF: Resol-P, F127, and hexamethylenetetramine (HMT) were continuously added to deionized water in a specific ratio. After stirring at room temperature, the mixture was placed in a reactor for hydrothermal reaction. After the reaction was completed and cooled to room temperature, the solid was centrifuged to obtain a yellow solid. The solid was washed several times with deionized water and ethanol and then vacuum dried to obtain HSF fiber. The HSF was preheated to a preheating temperature at a certain heating rate under a nitrogen atmosphere, and then heated to a calcination temperature to finally obtain CF fiber with high specific surface area. (3) Preparation of CF-OC: First, a reflux condensation operation was performed at a certain temperature, and CF was dissolved in nitric acid. Then, deionized water was added, and a reflux condensation reaction was carried out. After the reaction was completed, the mixture was neutralized with a large amount of deionized water. The mixture was centrifuged to obtain a black solid, which was washed several times with deionized water and ethanol, and then dried under vacuum to obtain CF-O fiber with carboxyl groups. Subsequently, the vacuum-dried CF-O was dispersed in ethanol, and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was added, followed by amidation grafting with N-hydroxysuccinimide (NHS), and then 4'-aminobenzo-18-crown-6(4'-AB) was added. 18 C6) is reacted at a certain temperature, centrifuged to obtain a black solid, washed several times with deionized water and ethanol, and vacuum dried to obtain CF-OC fiber with crown ether amidation graft, namely oxygen-containing heterocyclic functionalized hierarchical porous fiber adsorbent.

[0010] In step (1), the ratio of phenol, sodium hydroxide solution and formaldehyde solution in the phenolic resin precursor solution is 1.0 g:(0.2-0.3) g:(1.6-1.8) g, wherein the concentration of sodium hydroxide solution is 30 wt% and the concentration of formaldehyde solution is 13 mol / L.

[0011] The initial temperature is 30-50℃, the final reaction temperature is 60℃-80℃, the reaction time is 0.5-1.5 h, and the pH is adjusted to 6-8.

[0012] In step (2), the ratio of Resol-P, F127, hexamethylenetetramine (HMT) and deionized water is 1.0 mL: (0.05-0.07) mg: (0.01-0.03) g: (12.5-14.5) mL.

[0013] The stirring temperature is 15-35℃, and the stirring time is 1.0-3.0 h; The hydrothermal reaction is carried out at a temperature of 130-150℃ for 12-36 hours.

[0014] In step (2), a tube furnace is used for calcination, the heating rate is 0.5-1.5℃ / min, the preheating temperature is 250-450℃, and the calcination temperature is 700-900℃.

[0015] In step (3), the mass ratio of CF, nitric acid and deionized water is 1.0g:(70-90)mL:(70-90)mL, wherein the concentration of nitric acid is 14-16 mol / L.

[0016] The condensation reflux reaction is carried out at a temperature of 95~115℃ for 3.0-5.0 h.

[0017] In step (3), the CF-O, ethanol, EDC, NHS, and 4'-AB... 18 The dosage ratio of C6 is 1.0 g : (200-400) mL : (1.0-3.0) g : (1.0-3.0) g : (0.5-0.7) g; The amidation grafting time is 15-20 min.

[0018] The reaction temperature is 15-35℃ and the time is 12-36 h.

[0019] The vacuum drying temperature described in the technical solution is 45℃.

[0020] The oxygen-containing heterocyclic functionalized fiber adsorbent prepared in this invention is used for the selective separation of Cs(I) from salt lakes.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention targets the structural characteristics of Cs(I) and prepares a microporous fiber carrier through a kinetically controlled single-micelle self-assembly process. Active carboxyl groups are introduced onto the fiber surface using nitric acid oxidation, followed by a amidation reaction to covalently graft crown ether-based oxygen-containing heterocyclic compounds onto the fiber surface. This successfully produces a fiber adsorbent with specific recognition and separation capabilities for Cs(I). The prepared oxygen-containing heterocyclic copolymer microporous fibers exhibit excellent selectivity and environmental adaptability to the target analyte Cs(I). Attached Figure Description

[0022] Figure 1 SEM images of the HSF(a1-a2), CF(b1-b2), CF-O(c1-c2) and CF-OC(d1-d2) nanofibers prepared in Example 1.

[0023] Figure 2 The water contact angles of HSF(a), CF(b), CF-O(c) and CF-OC(d) prepared in Example 1 are shown.

[0024] Figure 3The thermogravimetric analysis (TGA) diagrams of HSF and CF prepared in Example 1 are shown.

[0025] Figure 4 BET analysis of HSF(a), CF(b), CF-O(c), and CF-OC(d) prepared in Example 1.

[0026] Figure 5 The effect of pH on CF-OC adsorption in Experiment Example 1 Figure 6 The kinetic data and model fitting curves for the adsorption of Cs(I) by CF-OC prepared in Experimental Example 2 at 298.15 K are shown.

[0027] Figure 7 The equilibrium data and model fitting curves for the adsorption of Cs(I) by CF-OC prepared in Experimental Example 3 at 288.15, 298.15 and 308.15 K are shown.

[0028] Figure 8 The results show the adsorption of Na(Ⅰ), K(Ⅰ), Rb(Ⅰ) and Mg(Ⅱ) by the CF-OC prepared in Experimental Example 4. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0030] In a specific embodiment of the present invention, performance evaluation is performed according to the following method: The ratio of phenolic resin precursor and block copolymer to solvent, as well as the hydrothermal time and temperature for polymer formation, were optimized, and the fiber adsorbent prepared from them was subjected to comparative adsorption studies under the same conditions.

[0031] 5.0 mL of Cs(I) solutions with initial concentrations of 20 mg / L, 50 mg / L, and 150 mg / L were added to 10 mL centrifuge tubes. A certain amount of CF-OC fiber adsorbent was added, and the solutions were removed at specific time intervals. The adsorption capacity was calculated based on the results to study the kinetic performance of the CF-OC adsorbent. Alternatively, 5.0 mL of a Cs(I) solution of a certain concentration (solvent: deionized water at pH 9) was added to 10 mL centrifuge tubes. A certain amount of CF-OC fiber adsorbent was added, and the tubes were placed in constant-temperature water baths at different temperatures and shaken for a certain period. The adsorption was then measured using a microporous nitrocellulose membrane (pore size 0.22). The filtrate was filtered at μm, and the concentration of Cs(I) in the filtrate was detected by ICP-OES. The adsorption capacity was calculated based on the results and used to study the thermodynamic properties of the CF-OC adsorbent. Several ions with similar structures and properties to Cs(I), such as rubidium ions (Rb(I)), sodium ions (Na(I)), potassium ions (K(I)) and magnesium ions (Mg(II))), were selected as selective adsorption molecules to study the selective discrimination performance of the adsorbent.

[0032] The invention will be further explained below with reference to specific implementation examples.

[0033] Example 1

[0034] (1) Preparation of Resol-P: 0.61 g of phenol was melted in a 100 mL flask at 40 °C, and then mixed with 0.13 g of 30 wt% NaOH aqueous solution at 300 rpm. After 10 min, formalin (37 wt%, 1.05 g) containing formaldehyde (13.0 mmol) was added dropwise, and the mixture was stirred at 70 °C for 1.0 h. After cooling to room temperature, the pH was adjusted to approximately 7.0 with 0.6 M hydrochloric acid solution. After freeze-drying at -50 °C to remove water, the final product was redissolved in ethanol (20 wt% ethanol solution) for further use. The concentration of the ethanol solution was approximately 0.8 g / mL.

[0035] (2) Preparation of CF: Using HMT as the curing agent and phenolic resin as the carbon source, the synthesis route includes three steps: (I) Preparation of F127 / resin single micelles (II) Subsequently, the composite single micelles were self-assembled into polymer fibers with a hierarchical porous structure. (III) Convert polymer fibers into CF.

[0036] Typically, in the first step, 4.0 mL of Resol-P, 0.24 g of F127, and 0.05746 g of HMT are continuously added to a 200 mL flask. While stirring at 300 rpm, 54 mL of deionized water is added, and the mixture is stirred continuously at room temperature for 2.0 h. The mixture is then transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 140 °C for 24 h. After cooling to room temperature, the polymer fibers are separated by centrifugation, washed multiple times with deionized water, and freeze-dried to obtain HSF. Finally, the polymer composite material is preheated at 350 °C for 3.0 h, and then held at 800 °C for 2.0 h at a heating rate of 1 °C / min under a nitrogen atmosphere to obtain hierarchical porous polymer fibers.

[0037] (3) Preparation of CF-OC: The reaction was carried out under reflux at 105 °C. 0.05 g of CF was dissolved in 4.0 mL of 68% nitric acid in a 50 mL three-necked flask. After five minutes, 4.0 mL of deionized water was added in the same proportion. The mixture was refluxed at 300 rpm for 4.0 h. After the reaction was complete, the mixture was neutralized with a large amount of deionized water, centrifuged to obtain a black solid, washed several times with deionized water and ethanol, and vacuum dried to obtain carboxyl-containing fibers, i.e., CF-O. Subsequently, 50 mg of vacuum-dried CF-O was dispersed in 15 mL of anhydrous ethanol, and 100 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was added. After 5.0 min, 100 mg of N-hydroxysuccinimide (NHS) was added for activation. After 15 min, 30 mg of 4'-aminobenzo-18-crown-6(4'-AB) was added. 18 C6) was reacted at room temperature for 24 hours, and centrifuged to obtain a black solid. The solid was washed several times with deionized water and ethanol, and then vacuum dried to obtain fibers with crown ether amidation grafts, namely CF-OC.

[0038] Figure 1 SEM images of the HSF(a1,a2), CF(b1,b2), CF-O(c1,c2), and CF-OC(d1,d2) nanofibers prepared in Example 1. From... Figure 1 The formation of HSF fibers can be seen in a1 and a2. Fibers containing hierarchical pores are obtained through high-temperature calcination (see...). Figure 1 (b1 and b2), through nitric acid oxidation, the resulting hierarchical porous nanofibers become increasingly coarse (see...) Figure 1 c1 and c2), from Figure 2 As can be seen from d1 and d2, after crown ether amidation grafting, the surface has a large number of polymer particles.

[0039] Figure 2 The figures show the water contact angles of HSF(a), CF(b), CF-O(c), and CF-OC(d) prepared in Example 1. As can be seen from the figures, the water contact angle of the HSF nanofibers is 70°, the water contact angle of the CF nanofibers after high-temperature calcination is 136°, and the water contact angle of the CF nanofibers after high-temperature calcination increases to 66°. This is mainly because after high-temperature calcination, the evaporation of water and the removal of surfactants leave behind an inorganic framework, leading to an increase in the water contact angle of CF. In contrast, the oxidation process uses nitric acid, which grafts a large number of polar groups such as carboxyl groups onto the inorganic framework, increasing chemical hydrophilicity and reducing the water contact angle of CF-O to 28°. The crown ether amidation reaction converts carboxylic acids (-COOH) into amides and attaches an aryl-containing crown ether unit. The presence of polar amide / ether oxygen (hydrogen bonding sites with water) and non-polar aryl groups (reducing surface energy) on the fiber surface increases the water contact angle of CF-OC to 101°. Compared to CF after only high-temperature calcination, CF-OC has more surface-accessible sites, and the crown ether ring size allows for "ion sieve" separation in complex ionic backgrounds. This is more conducive to the dispersion of the adsorbent in aqueous solution and the rapid mass transfer of Cs(I).

[0040] Figure 3 The thermogravimetric analysis (TGA) diagrams of HSF and CF prepared in Example 1 are shown. HSF initially loses approximately 7.8% of its mass in the temperature range from room temperature to 200°C, mainly due to the volatilization of surface-adsorbed water and light components. Subsequently, it undergoes severe thermal decomposition in the 200-800°C range, with a cumulative weight loss of up to 45.7%, indicating that the main organic matter underwent thermal decomposition within this temperature range. In contrast, CF, due to its high-temperature calcination pretreatment, exhibits significantly enhanced thermal stability. Its initial weight loss is minimal, and it maintains almost constant mass below 400°C, only showing slow weight loss in the 600-800°C range, ultimately achieving a residual rate of 87.9%. This comparison confirms that the calcination process effectively removes 36.1% of the unstable organic volatiles from HSF, transforming it into a CF material with a dense inorganic framework structure.

[0041] Figure 4 BET analysis of HSF(a), CF(b), CF-O(c), and CF-OC(d) prepared in Example 1 is shown. The figure reveals that CF-OC possesses a hierarchical porous structure, with micropores, mesopores, and macropores having pore volumes of 0.008 cm³. 3 / g, 0.044 cm 3 / g and 0.010 cm 3 / g, specific surface area S BET 30.51 m 2 / g, the specific surface area decreases significantly from CF to CF-OC, from 674.56m² / g for CF. 2 / g decreased to 30.51 m2 / g, which indirectly proves the successful grafting of crown ether on the fiber surface.

[0042] Example 2

[0043] (1) Preparation of Resol-P: 0.61 g of phenol was melted in a 100 mL flask at 30 °C, and then mixed with 0.13 g of a 20 wt% NaOH aqueous solution at 300 rpm. After 10 min, formalin (37 wt%, 0.976 g) containing formaldehyde (13.0 mmol) was added dropwise, and the mixture was stirred at 60 °C for 0.5 h. After cooling to room temperature, the pH was adjusted to approximately ~6.0 with 0.6 M hydrochloric acid solution. After freeze-drying at -50 °C to remove water, the final product was redissolved in ethanol (20 wt% ethanol solution) for further use. The concentration of the ethanol solution was approximately 0.8 g / mL.

[0044] (2) Preparation of CF: HMT was used as the curing agent and phenolic resin as the carbon source. The synthetic route consisted of three steps: (I) preparation of F127 / resin single micelles, (II) subsequent self-assembly of the composite single micelles into a hierarchical porous polymer fiber, and (III) conversion of the polymer fiber into CF. Typically, in the first step, 4.0 mL of Resol-P, 0.20 g of F127, and 0.04 g of HMT were continuously added to a 200 mL flask, and 50 mL of deionized water was added while stirring at 300 rpm. The stir bar was 2.0 cm long. After continuous stirring at 15 °C for 1.0 h, the mixture was transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 130 °C for 12 h. After cooling to room temperature, the polymer fiber was separated by centrifugation, washed several times with deionized water, and freeze-dried to obtain HSF. Finally, the polymer composite material was preheated at 250℃ for 3.0 h, and then held at 700℃ for 2.0 h in a nitrogen atmosphere at a heating rate of 0.5℃ / min to obtain hierarchical porous polymer fibers.

[0045] (3) Preparation of CF-OC: The reaction was carried out under reflux at 95°C. 0.05 g of CF was dissolved in 3.5 mL of 68% nitric acid in a 50 mL three-necked flask. After five minutes, 3.5 mL of deionized water was added in the same proportion. The mixture was refluxed at 300 rpm for 3.0 h with stirring. After the reaction was complete, the mixture was neutralized with a large amount of deionized water, centrifuged to obtain a black solid, washed several times with deionized water and ethanol, and vacuum dried to obtain carboxyl-containing fibers, i.e., CF-O. Subsequently, 50 mg of vacuum-dried CF-O was dispersed in 10 mL of anhydrous ethanol, and 50 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was added. After 5.0 min, 50 mg of N-hydroxysuccinimide (NHS) was added for activation. After 15 min, 25 mg of 4'-aminobenzo-18-crown-6(4'-AB) was added. 18 C6) was reacted at room temperature for 12 h, and centrifuged to obtain a black solid. The solid was washed several times with deionized water and ethanol, and then vacuum dried to obtain fibers with crown ether amidation grafts, namely CF-OC.

[0046] Example 3

[0047] (1) Preparation of Resol-P: 0.61 g of phenol was melted in a 100 mL flask at 50 °C, and then mixed with 0.13 g of 40 wt% NaOH aqueous solution at 300 rpm. After 10 min, formalin (37 wt%, 1.098 g) containing formaldehyde (13.0 mmol) was added dropwise, and the mixture was stirred at 80 °C for 1.5 h. After cooling to room temperature, the pH was adjusted to approximately ~8.0 with 0.6 M hydrochloric acid solution. After freeze-drying at -50 °C to remove water, the final product was redissolved in ethanol (20 wt% ethanol solution) for further use. The concentration of the ethanol solution was approximately 0.8 g / mL.

[0048] (2) Preparation of CF: HMT was used as the curing agent and phenolic resin as the carbon source. The synthetic route consisted of three steps: (I) preparation of F127 / resin single micelles, (II) subsequent self-assembly of the composite single micelles into a hierarchical porous polymer fiber, and (III) conversion of the polymer fiber into CF. Typically, in the first step, 4.0 mL of Resol-P, 0.28 g of F127, and 0.12 g of HMT were continuously added to a 200 mL flask, and 66 mL of deionized water was added while stirring at 300 rpm. The stir bar was 2.0 cm long. After continuous stirring at 35 °C for 3.0 h, the mixture was transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 150 °C for 36 h. After cooling to room temperature, the polymer fiber was separated by centrifugation, washed several times with deionized water, and freeze-dried to obtain HSF. Finally, the polymer composite material was preheated at 450℃ for 3.0 h, and then held at 900℃ for 2.0 h in a nitrogen atmosphere at a heating rate of 1.5℃ / min to obtain hierarchical porous polymer fibers.

[0049] (3) Preparation of CF-OC: The reaction was carried out under reflux at 115°C. 0.05 g of CF was dissolved in 4.5 mL of 68% nitric acid in a 50 mL three-necked flask. After five minutes, 4.5 mL of deionized water was added in the same proportion. The mixture was refluxed at 300 rpm for 5.0 h. After the reaction was complete, the mixture was neutralized with a large amount of deionized water, centrifuged to obtain a black solid, washed several times with deionized water and ethanol, and vacuum dried to obtain carboxyl-containing fibers, i.e., CF-O. Subsequently, 50 mg of vacuum-dried CF-O was dispersed in 20 mL of anhydrous ethanol, and 150 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was added. After 5.0 min, 150 mg of N-hydroxysuccinimide (NHS) was added for activation. After 15 min, 35 mg of 4'-aminobenzo-18-crown-6(4'-AB) was added. 18 C6) was reacted at room temperature for 36 h, and centrifuged to obtain a black solid. The solid was washed several times with deionized water and ethanol, and then dried under vacuum to obtain fibers with crown ether amidation grafts, namely CF-OC.

[0050] Experimental Example 1: 5.0 mg of the product CF-OC from step (3) of Example 1 was added to a 10 mL centrifuge tube, followed by 5.0 mL of Cs(I) solution with a concentration of 50 mg / L and pH values ​​of 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0. The centrifuge tubes were then placed in a constant temperature water bath with shaking for static adsorption for 12 h. After adsorption, the adsorbent was separated by centrifugation, and the supernatant was filtered through a microporous nitrocellulose membrane. The Cs(I) concentration in the filtrate was determined by ICP-OES. Three parallel experiments were performed using the above steps, and the equilibrium adsorption capacity was calculated. Q e (mg / g).

[0051] Depend on Figure 5 As shown, the adsorption capacity of CF-OC increases as the solution pH increases from 3.0 to 9.0. Q e The adsorption capacity gradually increased, reaching a maximum of 30.08 mg / g. However, when the pH was between 9.0 and 10.0... Q e The adsorption capacity decreased, reaching a maximum of 46.80 mg / g. This is because the large amount of H₂ in the solution at low pH values... +Cs(I) will compete with Cs(I) for adsorption, occupying most of the adsorption sites on the CF-OC surface. As the pH increases, Cs(I) becomes dominant in the adsorption process. However, during the experiment, when pH > 10.0, CF-OC may deprotonate and become negatively charged, generating electrostatic repulsion with Cs(I). Furthermore, hydroxyl groups in the solution may form weak complexes with Cs(I), further reducing the adsorption capacity, which will affect the evaluation of the adsorption performance of CF-OC. Therefore, the following experiments selected pH = 9.0 as the optimal adsorption condition to study the adsorption capacity of CF-OC for Cs(I).

[0052] Experimental Example 2

[0053] 5.0 mL of Cs(I) solutions with initial concentrations of 20, 50, and 150 mg / L were added to centrifuge tubes (solvent: deionized water, pH 9.0). 5.0 mg of CF-OC was added as the adsorbent, and static adsorption was performed under shaking conditions in a 25°C water bath. The solutions were filtered through a microporous nitrocellulose membrane (0.22 μm pore size) at time points of 5.0, 10, 20, 30, 40, 50, 60, and 120 min. The residual Cs(I) concentration in the supernatant was determined by ICP-OES. Three parallel experiments were performed, and the concentrations were calculated. Q t (mg / g), and based on the results, we obtained Figure 6 The results showed that the adsorption process can be divided into approximately three stages. In the initial stage (approximately 5.0–10 min), the adsorption capacity increases rapidly; in the transition stage (10–30 min), the increase in adsorption capacity slows significantly; and finally, in the adsorption equilibrium stage (approximately 30–120 min), the active sites on the adsorbent reach saturation. Q e20 =12.29 mg / g Q e50 =22.32 mg / g Q e150 =32.01 mg / g). The adsorption kinetic data were fitted using a quasi-first-order kinetic model and a quasi-second-order kinetic model. The fitting coefficient of the quasi-second-order kinetic model for the adsorption process was [value missing]. R 2 2 The first-order dynamic model is compared with the R 1 2 high, Q e,c and Q e,e The results are quite close, indicating that the quasi-second-order kinetic model is applicable to the adsorption kinetics of Cs(I) by CF-OC, which is dominated by chemisorption.

[0054] Experimental Example 3

[0055] 5.0 mg of the product CF-OC from step (3) of Example 1 was added to 5.0 mL of Cs(I) solution (50 mg / L, pH=9.0) and adsorbed at 288.15 K, 298.15 K, and 308.15 K for 2.0 h. The mixture was then filtered through a nitrocellulose membrane, and the residual Cs(I) concentration in the supernatant was determined by ICP-OES. Three parallel experiments were performed using the above steps, and the equilibrium adsorption capacity was calculated. Q e (mg / g). For example... Figure 8 As shown, when the temperature increases from 288.15 K to 308.15 K, the adsorption capacity of CF-OC increases from 37.835 mg / g to 53.184 mg / g.

[0056] By studying the adsorption isotherms of adsorbents, the adsorption characteristics of the adsorbents can be evaluated, which helps to understand the adsorption mechanism between CF-OC and Cs(I). The adsorption isotherm curves are shown below. Figure 7 As shown, the adsorption capacity of CF-OC increases significantly with increasing initial Cs(I) concentration, eventually reaching adsorption saturation. In this study, the Langmuir and Freundlich models were used to fit and analyze the equilibrium adsorption process. The fitting coefficient R1 of the Langmuir model was [value missing] at different temperatures. 2 The results were all higher than those of the Freundlich model, indicating that the Langmuir model can better describe the adsorption process, which is monolayer adsorption and mainly depends on the chemical interaction between the grafted crown ether and Cs(I).

[0057] Test Example 4

[0058] Take 5.0 mg of the product CF-OC from step (3) of Example 1 and add it to a mixed solution (5.0 mL) of K(Ⅰ), Rb(Ⅰ), Mg(Ⅱ), Cs(Ⅰ) and Na(Ⅰ) with an ion concentration of 300 mg / L. Adsorb at 25℃ for 2.0 h, centrifuge, take the supernatant and filter it through a membrane. Detect the residual Cs(I) concentration using ICP-OES. Perform three parallel experiments using the above steps and calculate the adsorption capacity for different metal ions using the formula. Q e (mg / g). For example... Figure 8 As shown, in a mixed solution of K(Ⅰ), Mg(Ⅱ), Na(Ⅰ), Rb(Ⅰ) and Cs(I) (pH=9.0, 300 mg / L), the adsorption capacity of CF-OC for Cs(I) was 39.38 mg / g, which was consistent with the adsorption capacity of the single Cs(Ⅰ) solution. Moreover, the adsorption capacity for other ions was extremely low, indicating that CF-OC has excellent competitive adsorption capacity for Cs(Ⅰ).

[0059] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing an oxygen-containing heterocyclic functionalized hierarchical porous fiber adsorbent, characterized in that, Includes the following steps: (1) Preparation of Resol-P: At the initial temperature, phenol was dissolved in sodium hydroxide solution in proportion, followed by the addition of formaldehyde solution. The mixture was heated to the final reaction temperature and mixed. After the reaction was completed, the pH was adjusted with hydrochloric acid, and the phenolic resin precursor solution Resol-P was obtained by freeze drying. (2) Preparation of CF: Resol-P, F127, and hexamethylenetetramine (HMT) were continuously added to deionized water in a specific ratio. After stirring at room temperature, the mixture was placed in a reactor for hydrothermal reaction. After the reaction was completed and cooled to room temperature, the solid was centrifuged to obtain a yellow solid. The solid was washed several times with deionized water and ethanol and then vacuum dried to obtain HSF fiber. The HSF was preheated to a preheating temperature at a certain heating rate under a nitrogen atmosphere, and then heated to a calcination temperature to finally obtain CF fiber with high specific surface area. (3) Preparation of CF-OC: First, a reflux condensation operation was performed at a certain temperature, and CF was dissolved in nitric acid. Then, deionized water was added, and a reflux condensation reaction was carried out. After the reaction was completed, the mixture was neutralized with a large amount of deionized water. The mixture was centrifuged to obtain a black solid, which was washed several times with deionized water and ethanol, and then dried under vacuum to obtain CF-O fiber with carboxyl groups. Subsequently, the vacuum-dried CF-O was dispersed in ethanol, and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) was added, followed by amidation grafting with N-hydroxysuccinimide (NHS), and then 4'-aminobenzo-18-crown-6(4'-AB) was added. 18 C6) is reacted at a certain temperature, centrifuged to obtain a black solid, washed several times with deionized water and ethanol, and vacuum dried to obtain CF-OC fiber with crown ether amidation graft, namely oxygen-containing heterocyclic functionalized hierarchical porous fiber adsorbent.

2. The preparation method according to claim 1, characterized in that, In step (1), the ratio of phenol, sodium hydroxide solution and formaldehyde solution in the phenolic resin precursor solution is 1.0 g:(0.2-0.3) g:(1.6-1.8) g, wherein the concentration of sodium hydroxide solution is 30 wt% and the concentration of formaldehyde solution is 13 mol / L.

3. The preparation method according to claim 1, characterized in that, In step (1), the initial temperature is 30-50℃, the final reaction temperature is 60℃-80℃, the reaction time is 0.5-1.5 h, and the pH is adjusted to 6-8.

4. The preparation method according to claim 1, characterized in that, In step (2), the ratio of Resol-P, F127, hexamethylenetetramine (HMT), and deionized water is 1.0 mL: (0.05-0.07) mg: (0.01-0.03) g: (12.5-14.5) mL; The stirring temperature is 15-35℃ and the time is 1.0-3.0 h; the hydrothermal reaction temperature is 130-150℃ and the time is 12-36 h.

5. The preparation method according to claim 1, characterized in that, In step (2), a tube furnace is used for calcination, the heating rate is 0.5-1.5℃ / min, the preheating temperature is 250-450℃, and the calcination temperature is 700-900℃.

6. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of CF, nitric acid and deionized water is 1.0g:(70-90)mL:(70-90)mL, wherein the concentration of nitric acid is 14-16 mol / L.

7. The preparation method according to claim 1, characterized in that, In step (3), the temperature of the condensation reflux reaction is 95~115℃ and the time is 3.0-5.0 h.

8. The preparation method according to claim 1, characterized in that, In step (3), the CF-O, ethanol, EDC, NHS, and 4'-AB... 18 The dosage ratio of C6 is 1.0 g : (200-400) mL : (1.0-3.0) g : (1.0-3.0) g : (0.5-0.7) g.

9. The preparation method according to claim 1, characterized in that, In step (3), the amidation grafting time is 15-20 min; the reaction temperature is 15-35℃ and the time is 12-36 h.

10. The use of the oxygen-containing heterocyclic functionalized hierarchical porous fiber adsorbent prepared by the preparation method according to any one of claims 1 to 9 for the selective separation of Cs(I) in salt lakes.

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