Preparation method of functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent and its application in uranium extraction

Abstract

The present invention discloses a preparation method of a functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent and its application in uranium extraction. The "ouzo" effect, that is, after a Tris aqueous solution is mixed with n-propanol, air overflows in the form of nanobubbles due to the difference in solubility. Dopamine oxidatively self-polymerizes to form hollow polydopamine nanospheres while forming a polydopamine coating on the carrier, giving the entire material surface chemical modification advantages. First, the free radicals of polydopamine itself are used to modify the cyanide group based on distillation precipitation free radical polymerization, and then m‑CNTs@H‑PDA‑AO is prepared after amidoximation. The hollow material is constructed based on the "ouzo" effect, which is green and environmentally friendly; and the magnetic carrier gives the adsorbent the characteristic of rapid solid-liquid separation. The adsorption results show that m‑CNTs@H‑PDA‑AO can reach adsorption saturation (50 mL) within 1.0 h, and the maximum adsorption capacity at room temperature is 381.98 mg·g ‑1 ; It has a specific adsorption capacity for uranyl ions, and five cycle regeneration experiments have proved that the adsorption of uranium on its surface is reversible and has good regeneration performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of functional materials for adsorption and separation, and relates to a method for preparing a composite adsorbent suitable for selectively and efficiently enriching uranyl ions (U(VI)) in seawater, and in particular to a method for preparing hollow nanospheres loaded with carbon nanotubes based on a one-step process, and its application in the field of extracting U(VI) from seawater. Background Art

[0002] Energy is the foundation of human survival and development, crucial not only for national industrial production but also for the well-being of the nation. As the world's largest energy consumer, effectively ensuring national energy supply and security is a paramount concern for China's energy development. Humanity has historically relied heavily on fossil fuels, an unsustainable reliance that is a major contributor to global warming, prompting a shift toward renewable, clean energy sources. Nuclear energy, one of the best alternatives to fossil fuels, offers extremely high energy density and virtually zero greenhouse gas emissions. However, conservative estimates suggest that terrestrial U(VI) reserves will only last for less than 100 years for existing nuclear power plants, posing a significant bottleneck to the utilization of nuclear energy as a sustainable energy source. However, U(VI) resources are abundant in seawater, exceeding 1,000 times the terrestrial uranium reserves. Therefore, research on extracting U(VI) from seawater is of vital importance for energy supply and security.

[0003] Over the past few decades, numerous U(VI) extraction methods, such as co-precipitation, ion exchange, electrochemical methods, and adsorption separation, have been developed to address the challenges of ultra-low U(VI) concentrations (3.3 ppb) and the abundance of competing ions encountered during U(VI) extraction from seawater. Among these, considerable progress has been made in the efficient adsorption of U(VI) from seawater using amidoxime-functionalized adsorbents. These adsorbents exhibit good affinity for U(VI) and are reproducible during the adsorption separation process. Furthermore, they offer advantages such as a simple and environmentally friendly preparation process.

[0004] Hollow polymer nanospheres (HPNs) play an important role in the separation field due to their high specific surface area and low density. Furthermore, the introduction of magnetic carriers, "making a whole," not only further improves the material's adsorption performance but also overcomes the difficulty of nanoadsorbents in separation. By grafting functional monomers onto the polymer surface and utilizing the unique spatial structure of amidoxime groups coordinated with U(VI), efficient capture of target ions is achieved.

[0005] Traditional hollow adsorbent preparation methods have defects such as structural destruction caused by hard template elution or environmental pollution caused by the inevitable use of organic emulsifiers during the use of soft templates. In addition, hollow nano-adsorbents have the problem of good adsorption performance but difficult separation. In order to avoid the above situation, it is urgent to study an easily separable hollow nano-sphere-based composite adsorbent for the extraction of U(VI) from seawater. Summary of the Invention

[0006] In order to solve the problems of environmental pollution caused by the use of emulsifiers in the preparation process of traditional hollow nano-adsorbents by the soft template method or the destruction of material structure caused by template elution in the preparation process by the hard template method, as well as the defect that hollow nano-adsorbents are difficult to separate after use, the present invention provides a nano-bubble-based "ouzo" effect-based magnetic hollow nano-composite adsorbent. By utilizing the surface functionalization advantages of polydopamine and grafting high-density amidoxime groups, a high-density amidoxime-functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent (m-CNTs@H-PDA-AO) is prepared.

[0007] The present invention is based on the "ouzo" effect. During the mixing process of a Tris aqueous solution (pH 8.5) and n-propanol, gas overflows in the form of nanobubbles due to changes in solubility. Dopamine oxidatively polymerizes to form hollow nano-polydopamine spheres, which simultaneously coat the carrier with a layer of polydopamine (m-CNTs@H-PDA), giving the entire material surface-modified properties. First, thermally initiated free radical polymerization (FRP) is used to successfully graft cyanide (-CN) groups using double bonds between polydopamine surface free radicals and a functional monomer (2-amino-3,5-divinylbenzonitrile (ADBN)). Finally, amidoxime groups (m-CNTs@H-PDA-AO) are successfully modified by treatment with hydroxylamine hydrochloride. In summary, this work compared the adsorption capacities of the following three adsorbents to evaluate the adsorption performance of the invented composite adsorbent (m-CNTs@H-PDA-AO): CNTs, m-CNTs@H-PDA, and m-CNTs@H-PDA-AO.

[0008] The technical solution adopted in the present invention is:

[0009] The preparation method of a functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent comprises the following steps:

[0010] (1) Synthesis of magnetic carbon nanotubes (m-CNTs)

[0011] S1: Weigh appropriate amounts of anhydrous FeCl3, sodium citrate, sodium acetate, and polyethylene glycol and disperse them in a certain amount of ethylene glycol to obtain a mixed solution A. Place the solution in a water bath at a certain temperature and add CNTs while stirring at an appropriate speed to obtain a mixed solution B. Continue stirring and reacting for a period of time, then centrifuge the mixed solution B and wash it once with pure water.

[0012] S2: Add a mixture of anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol and ethylene glycol in the same amount as the mixed solution A to the centrifugal washing product of step S1 above, ultrasonically disperse it, place it in a reactor and react at a suitable temperature for a period of time, collect, wash and dry it to obtain m-CNTs.

[0013] (2) Synthesis of magnetic carbon nanotube-loaded hollow nanospheres (m-CNTs@H-PDA)

[0014] S1: Weigh an appropriate amount of m-CNTs obtained in step (1), disperse them in a certain amount of n-propanol, perform ultrasonic dispersion, and soak for a period of time to obtain solution C;

[0015] S2: Weigh an appropriate amount of tris(hydroxymethyl)aminomethane (Tris) and disperse it in a certain amount of pure water. Under certain temperature conditions, add solution C while stirring at an appropriate speed. Continue stirring for a period of time and then add a certain amount of dopamine. Polymerize for a period of time, centrifuge, collect, wash several times with pure water, wash several times with anhydrous ethanol, dry with air, and collect the product m-CNTs@H-PDA.

[0016] (3) Synthesis of amidoxime-functionalized m-CNTs@H-PDA-AO

[0017] S1: Weigh the m-CNTs@H-PDA powder obtained in step (2), disperse appropriate amounts of ADBN and AIBN in a certain volume of acetonitrile, place in an oil bath at a certain temperature, and distill until 1 / 3 of the solution remains. Collect, wash with anhydrous ethanol several times, and air dry to collect the product m-CNTs@H-PDA-CN;

[0018] S2: The m-CNTs@H-PDA-CN obtained in S1 in step (3) is dispersed in a mixed solution of pure water and anhydrous ethanol, a certain amount of hydroxylamine hydrochloride is weighed, ultrasonically dispersed, stirred under a certain temperature condition until the hydroxylamine hydrochloride is dissolved, and sodium hydroxide (NaOH) is added to adjust the pH of the solution to the required conditions. The reaction is continued at this temperature for a period of time, collected, washed multiple times with pure water, washed multiple times with anhydrous ethanol, and dried with air to collect the amidoxime functionalized composite adsorbent, i.e., m-CNTs@H-PDA-AO.

[0019] Preferably, in S1 of step (1), the ratio of anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol, ethylene glycol, and CNTs in the mixed solution A is 200-250 mg: 100-150 mg: 1.0-1.5 g: 300-350 mg: 30-40 mL: 20 mg.

[0020] Preferably, in S1 of step (1), the temperature of the water bath and the stirring reaction is 20-30° C., the stirring speed is 1200-1800 rpm, and the stirring time is 12-36 h.

[0021] Preferably, in S2 of step (1), the reaction temperature is 180-200° C., and the reaction time is 10-12 h.

[0022] Preferably, in S1 of step (2), the ratio of m-CNTs to n-propanol in the solution C is 1.2-2.0 mg: 3.0-5.0 mL, and the soaking time is 10 min-24 h.

[0023] Preferably, in step (2) S2, the amount ratio of Tris, pure water, and dopamine is 25-35 mg:45-55 mL:15-30 mg; the reaction temperature is 20-30° C.; the stirring speed is 400-600 rpm; the stirring time is 1.0-3.0 min; and the polymerization time is 90-150 min.

[0024] Preferably, in S1 of step (3), the ratio of m-CNTs@H-PDA, ADBN, AIBN, and acetonitrile is 100 mg: 30-80 mg: 50-100 mg: 20-50 mL; and the oil bath temperature is 110-130°C.

[0025] Preferably, in S2 of step (3), the usage ratio of the m-CNTs@H-PDA-CN, pure water, anhydrous ethanol, and hydroxylamine hydrochloride is 100 mg: 4.0-6.0 mL: 44 mL-46 mL: 2.0 g-2.1 g.

[0026] Preferably, in step (3) S2, the pH of the solution is adjusted to 7.5-8.5, the reaction temperature is 60-80° C., and the reaction time is 6.0-10 h.

[0027] In steps (1)-(3), the drying temperature is 50-70°C and the drying time is 8.0-12 hours.

[0028] The magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent (m-CNTs@H-PDA) or amidoxime-functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent (m-CNTs@H-PDA-AO) prepared by the present invention is used for extracting uranium.

[0029] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0030] Based on nanobubbles induced by the "ouzo" effect, the present invention uses a "one-step" method to construct carbon nanotube-loaded hollow nanospheres, using ADBN as a functional monomer. A composite adsorbent, m-CNTs@H-PDA-AO, containing magnetic carbon nanotube-loaded hollow nanospheres, is prepared, featuring high-density amidoxime adsorption sites, fast mass transfer, high adsorption capacity, and convenient recovery. The composite adsorbent is used to extract U(VI) from seawater. The adsorbent m-CNTs@H-PDA-AO reaches adsorption equilibrium in a U(VI) solution (10 ppm, 10 mL) after 20 minutes of adsorption; it reaches adsorption equilibrium in a U(VI) solution (10 ppm, 50 mL) after 50 minutes of adsorption. Under conditions of 298K, the maximum adsorption capacity of 50 mL of U(VI) solution, pH 7.0, is 381.98 mg g -1 ; 0.1M HNO3 is used as the desorption liquid, 6.0mL, 1.0h, the elution efficiency exceeds 97%, and the adsorbent has good regeneration. The magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent prepared by the present invention also has the following advantages:

[0031] 1) Based on the nanobubbles induced by the "ouzo" effect, the present invention uses a "one-step method" to construct a magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent. This solves the problems of template elution causing material structure damage in the hard template method used in the preparation of traditional hollow nanomaterials, or the use of organic emulsifiers in the soft template method preparation process causing environmental pollution. At the same time, it also overcomes the problem of difficult recovery of hollow nano adsorbents after use.

[0032] 2) Polydopamine, derived from the oxidative self-polymerization of dopamine, is a black, highly cross-linked polymer. It exhibits excellent biocompatibility, and its surface post-modification properties can meet a wide range of surface functionalization requirements. Common functionalization methods utilize amino, imino, and catechol groups on the polydopamine chain, which limits the diversity of polymers that can be attached. However, the free radicals present in the polydopamine chain are also excellent post-modification options. In summary, this system combines the advantages of green and stable nanobubbles with the surface functionalization of polydopamine. Furthermore, the introduction of a magnetic carrier allows for easy material recycling, making the entire preparation process simple and environmentally friendly.

[0033] 3) This material is a composite adsorbent of magnetic carbon nanotubes loaded with hollow nanospheres. Hollow nanomaterials have the advantages of low density, high specific surface area, fast mass transfer, and high adsorption capacity. The introduction of magnetic carriers not only further improves the adsorption capacity of the material, but also solves the problem of difficult recycling of hollow nanomaterials. Therefore, this composite material has great application potential in U(VI) extraction.

[0034] 4) Based on the surface functionalization platform provided by polydopamine, the free radicals of polydopamine and the double bonds of ADBN were utilized to rapidly post-modify the material through FRP under thermal initiation conditions, grafting -CN. Following treatment with hydroxylamine hydrochloride, the amidoxime-functionalized adsorbent m-CNTs@H-PDA-AO was obtained, achieving the goals of fast mass transfer, high adsorption capacity, good selectivity, and easy recovery. In summary, the "ouzo" effect-based nanobubbles were used to construct a composite adsorbent composed of magnetic carbon nanotubes loaded with hollow nanospheres in a one-step process. This method is simple, environmentally friendly, and features a tunable material structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a preparation flow chart of the present invention.

[0036] Figure 2 This is a TEM image of m-CNTs in Example 1(1).

[0037] Figure 3 TEM image of Example 2(2) m-CNTs@H-PDA

[0038] Figure 4 The hysteresis loop diagram of m-CNTs in Example 1 (1) and m-CNTs@H-PDA in Example 2 (2) (a); the infrared spectra of m-CNTs@H-PDA in Example 2 (2) and m-CNTs@H-PDA-CN and m-CNTs@H-PDA-AO in Example 3 (3) (b).

[0039] Figure 5 The pH-adsorption capacity diagram of CNTs and m-CNTs@H-PDA of Example 2(2) (a), and the Zeta potential diagram of m-CNTs@H-PDA in aqueous solutions with different pH values ​​(b).

[0040] Figure 6 The pH-adsorption capacity diagram of the initial solution of m-CNTs@H-PDA-AO in Example 3(3) (a) and the Zeta potential diagram of m-CNTs@H-PDA-AO in aqueous solutions with different pH values ​​(b) are shown.

[0041] Figure 7 This is the time-adsorption capacity diagram of m-CNTs@H-PDA-AO at pH 7.0 in Example 3(3) (a); and the equilibrium concentration-adsorption capacity diagram at 288K, 298K, and 308K temperatures (b).

[0042] Figure 8 This is a test of the selectivity of m-CNTs@H-PDA-AO of Example 3(3) for the target substance U(VI) in simulated seawater.

[0043] Figure 9 This is the time-elution efficiency diagram of m-CNTs@H-PDA-AO in different volumes of 0.1M HNO3 in Example 3(3) (a); the adsorption capacity diagram of m-CNTs@H-PDA-AO after five adsorption-desorption cycles. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0045] like Figure 1 , which is a flow chart of the present invention for preparing functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent.

[0046] Example 1:

[0047] (1) Design and synthesis of magnetic carbon nanotubes (m-CNTs)

[0048] S1: Weigh 200 mg of anhydrous FeCl3, 100 mg of sodium citrate, 1.0 g of sodium acetate, and 300 mg of polyethylene glycol and disperse them in 30 mL of ethylene glycol to obtain a mixed solution A. Place the mixture in a 25°C water bath and stir at 1500 rpm while adding 20 mg of CNTs to obtain a mixed solution B. React for 24 h. After the reaction, collect the mixed solution B by centrifugation and wash once with pure water.

[0049] S2: Add anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol and ethylene glycol in the same amount as the mixed solution A to the centrifugal washing product of step S1 above, ultrasonically disperse, place in a reactor at 200°C, react for 10 hours, collect, wash, and dry at 60°C for 12 hours to obtain m-CNTs.

[0050] (2) Design and synthesis of magnetic carbon nanotube-loaded hollow nanospheres (m-CNTs@H-PDA)

[0051] S1: Weigh 1.2 mg of the m-CNTs obtained in step (1) of Example 1 and disperse them in 3.0 mL of n-propanol, perform ultrasonic dispersion, and soak for 10 min to obtain solution C.

[0052] S2: 25 mg of Tris was dispersed in 45 mL of pure water. Solution C was added while stirring at 20°C and 400 rpm. Stirring was continued for 1.0 min. 15 mg of dopamine was added and the polymerization reaction was carried out for 90 min. The mixture was centrifuged and collected. The mixture was washed several times with pure water and anhydrous ethanol, and dried at 50°C for 12 h to collect the product m-CNTs@H-PDA.

[0053] (3) Design and synthesis of amidoxime functionalized m-CNTs@H-PDA-AO

[0054] S1: Weigh 100 mg of the m-CNTs@H-PDA powder obtained in step (2) of Example 2, 30 mg of ADBN, and 50 mg of AIBN, disperse them in 20 mL of acetonitrile, place them in an oil bath at 110°C, and distill until 1 / 3 of the solution remains. Collect the solution, wash it with anhydrous ethanol several times, and dry it with air to collect the product m-CNTs@H-PDA-CN;

[0055] S2: 100 mg of the m-CNTs@H-PDA-CN obtained in the above S1 was dispersed in a mixed solution of pure water (4.0 mL) and anhydrous ethanol (46 mL), 2.05 g of hydroxylamine hydrochloride was weighed, ultrasonically dispersed, stirred and reacted at 60°C, sodium hydroxide (NaOH) was added to adjust the pH of the solution to 7.5, and the reaction was continued for 10 hours. The product was collected, washed with pure water and anhydrous ethanol several times, and dried with air at 50°C for 12 hours to collect the amidoxime functionalized composite adsorbent, i.e., m-CNTs@H-PDA-AO.

[0056] Figure 2 This is a TEM image of m-CNTs prepared in Example 1(1), where Fe3O4 particles with a size of about 6.0 nm can be seen attached to the surface of the carbon nanotubes.

[0057] Example 2:

[0058] (1) Design and synthesis of magnetic carbon nanotubes (m-CNTs)

[0059] S1: Weigh 200 mg of anhydrous FeCl3, 100 mg of sodium citrate, 1.0 g of sodium acetate, and 300 mg of polyethylene glycol and disperse them in 30 mL of ethylene glycol to obtain a mixed solution A. Place the mixture in a 20°C water bath and stir at 1200 rpm while adding 20 mg of CNTs to obtain a mixed solution B. The mixture was reacted for 12 h. After the reaction, the mixed solution B was collected by centrifugation and washed once with pure water.

[0060] S2: Add anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol and ethylene glycol in the same amount as the mixed solution A to the centrifugal washing product of the above step S1, ultrasonically disperse, place in a reactor at 180°C, react for 12 hours, collect, wash, and dry at 50°C for 12 hours to obtain m-CNTs.

[0061] (2) Design and synthesis of magnetic carbon nanotube-loaded hollow nanospheres (m-CNTs@H-PDA)

[0062] S1: Weigh 1.5 mg of the m-CNTs obtained in step (1) of Example 1 and disperse them in 4.0 mL of n-propanol, perform ultrasonic dispersion, and soak for 24 h to obtain solution C.

[0063] S2: Weigh 30 mg of Tris and disperse it in 50 mL of pure water. Add solution C while stirring at 25°C and 500 rpm. Continue stirring for 2.0 min, add 20 mg of dopamine, and allow polymerization to proceed for 120 min. Centrifuge, collect, wash several times with pure water, wash several times with anhydrous ethanol, and dry with air at 60°C for 12 h to collect the product m-CNTs@H-PDA.

[0064] (3) Design and synthesis of amidoxime functionalized m-CNTs@H-PDA-AO

[0065] S1: Weigh 100 mg of the m-CNTs@H-PDA powder obtained in step (2) of Example 2, 80 mg of ADBN, and 100 mg of AIBN, disperse them in 50 mL of acetonitrile, place them in an oil bath at 130°C, and distill until 1 / 3 of the solution remains. Collect the solution, wash it with anhydrous ethanol several times, and dry it with air to collect the product m-CNTs@H-PDA-CN;

[0066] S2: 100 mg of the m-CNTs@H-PDA-CN obtained in the above S1 was dispersed in a mixed solution of pure water (6.0 mL) and anhydrous ethanol (44 mL), 2.1 g of hydroxylamine hydrochloride was weighed, ultrasonically dispersed, stirred and reacted at 80°C, sodium hydroxide (NaOH) was added to adjust the pH of the solution to 8.5, and the reaction was continued for 6.0 h. The product was collected, washed with pure water and anhydrous ethanol several times, and dried by air drying (60°C) for 12 h to collect the amidoxime functionalized composite adsorbent, i.e., m-CNTs@H-PDA-AO.

[0067] Figure 3 This is the TEM image of m-CNTs@H-PDA prepared in Example 2(2). It can be seen that this composite material has the morphology of uniform hollow nanospheres loaded on magnetic carbon nanotubes. The diameter of the spheres is about 50nm, the hollow morphology is obvious, and the cavity is about 14nm. There are small-sized magnetic nanoparticles on the carbon nanotubes, which facilitates solid-liquid separation after material adsorption.

[0068] Figure 4 (a) is the hysteresis loop of m-CNTs and m-CNTs@H-PDA prepared in Examples 1(1) and 2(2), as well as the magnetic separation photograph of m-CNTs@H-PDA, indicating that the material has magnetic properties.

[0069] Figure 5 (a) is the pH-adsorption capacity diagram of CNTs and m-CNTs@H-PDA in Example 2(2). It can be seen that the maximum adsorption capacity of CNTs is 80.55 mg g at pH 7.0. -1 At pH 6.0, the maximum adsorption capacity of m-CNTs@H-PDA was 105.7 mg g -1; (b) is the pH-Zeta potential diagram of m-CNTs@H-PDA. It can be seen that when pH ≥ 5.0, the material carries a negative charge in the aqueous solution, and thus the electrostatic effect further enhances the adsorption effect under certain pH conditions.

[0070] Example 3:

[0071] (1) Design and synthesis of magnetic carbon nanotubes (m-CNTs)

[0072] S1: Weigh 250 mg of anhydrous FeCl3, 150 mg of sodium citrate, 1.5 g of sodium acetate, and 350 mg of polyethylene glycol and disperse them in 40 mL of ethylene glycol to obtain mixed solution A. Place the mixture in a 30°C water bath and stir at 1800 rpm while adding 20 mg of CNTs to obtain mixed solution B. React for 36 h. After the reaction, collect mixed solution B by centrifugation and wash once with pure water.

[0073] S2: Add anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol and ethylene glycol in the same amount as the mixed solution A to the centrifugal washing product of the above step S1, ultrasonically disperse, place in a reactor at 180°C, react for 10 hours, collect, wash, and dry at 70°C for 8.0 hours to obtain m-CNTs.

[0074] (2) Design and synthesis of magnetic carbon nanotube-loaded hollow nanospheres (m-CNTs@H-PDA)

[0075] S1: Weigh 2.0 mg of the m-CNTs obtained in step (1) of Example 1 and disperse them in 5.0 mL of n-propanol, perform ultrasonic dispersion, and soak for 12 h to obtain solution C.

[0076] S2: Weigh 35 mg of Tris and disperse it in 55 mL of pure water. Add solution C while stirring at 30°C and 600 rpm. Continue stirring for 3.0 min. Add 30 mg of dopamine and allow polymerization to proceed for 150 min. Centrifuge and collect the product. Wash several times with pure water and anhydrous ethanol, and dry it at 70°C for 8.0 h to collect the product m-CNTs@H-PDA.

[0077] (3) Design and synthesis of amidoxime functionalized m-CNTs@H-PDA-AO

[0078] S1: Weigh 100 mg of the m-CNTs@H-PDA powder obtained in step (2) of Example 2, 50 mg of ADBN, and 80 mg of AIBN, disperse them in 30 mL of acetonitrile, place them in an oil bath at 120°C, and distill them until 1 / 3 of the solution remains. Collect the solution, wash it with anhydrous ethanol several times, and dry it with air to collect the product m-CNTs@H-PDA-CN;

[0079] S2: 100 mg of the m-CNTs@H-PDA-CN obtained in the above S1 was dispersed in a mixed solution of pure water (5.0 mL) and anhydrous ethanol (45 mL), 2.0 g of hydroxylamine hydrochloride was weighed, ultrasonically dispersed, stirred and reacted at 70°C, sodium hydroxide (NaOH) was added to adjust the pH of the solution to 8.0, and the reaction was continued for 8.0 h. The product was collected, washed with pure water and anhydrous ethanol several times, and dried by air drying (60°C) for 12 h to collect the amidoxime functionalized composite adsorbent, i.e., m-CNTs@H-PDA-AO.

[0080] Figure 4 (b) is the infrared spectra of m-CNTs@H-PDA prepared in Example 2(2), m-CNTs@H-PDA-CN, and m-CNTs@H-PDA-AO prepared in Example 3(3). The appearance and disappearance of characteristic peaks can prove that the functional groups of the materials have been successfully modified.

[0081] Figure 6 (a) is the pH-adsorption capacity diagram of m-CNTs@H-PDA-AO prepared in Example 3(3). At pH 7.0, the maximum adsorption capacity is 162.5 mg g -1 ; (b) is the pH-Zeta potential diagram of m-CNTs@H-PDA-AO. It can be seen that when pH ≥ 5.0, the materials exist in a charged form.

[0082] Figure 7 (a) is the time-adsorption capacity diagram of the m-CNTs@H-PDA-AO prepared in Example 3(3). It can reach adsorption equilibrium in 20 min after adsorption in U(VI) solution (10 ppm, 10 mL); it can reach adsorption equilibrium in 50 min after adsorption in U(VI) solution (10 ppm, 50 mL). (b) is the equilibrium concentration-adsorption capacity diagram of the m-CNTs@H-PDA-AO prepared in Example 3(3). Under the conditions of 298 K, 50 mL of U(VI) solution, pH 7.0, the maximum adsorption capacity can reach 381.98 mg g -1 .

[0083] Figure 8 This is the selectivity test of m-CNTs@H-PDA-AO prepared in Example 3(3) for the target substance U(VI) in simulated seawater. It can be seen from the figure that it has good selectivity for U(VI).

[0084] Figure 9(a) is the time-desorption efficiency diagram of m-CNTs@H-PDA-AO prepared in Example 3 (3). When 0.1MHNO3 is used as the desorption liquid, the elution efficiency reaches 90% at 3.0 mL and 1.0 h; and the elution efficiency exceeds 97% at 6.0 mL and 1.0 h. (b) is the adsorption capacity diagram of m-CNTs@H-PDA-AO after five adsorption-desorption cycles. The adsorption capacity of the fifth cycle can still reach 145 mg g -1 , indicating good regeneration performance.

Claims

1. A method for preparing a functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent, characterized in that: The steps include: (1) Synthesis of magnetic carbon nanotubes m-CNTs: S1: Weigh appropriate amounts of anhydrous FeCl3, sodium citrate, sodium acetate, and polyethylene glycol and disperse them in a certain amount of ethylene glycol to obtain a mixed solution A. Place the solution in a water bath at a certain temperature and add CNTs while stirring at an appropriate speed to obtain a mixed solution B. Continue stirring and reacting for a period of time, then centrifuge the mixed solution B and wash it once with pure water. S2: Add anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol, and ethylene glycol in the same amount as the mixed solution A to the centrifugal washing product of step S1, disperse by ultrasonication, place in a reactor and react for a period of time at a suitable temperature, collect, wash, and dry to obtain m-CNTs; (2) Synthesis of magnetic carbon nanotube-loaded hollow nanospheres m-CNTs@H-PDA: S1: Weigh an appropriate amount of m-CNTs obtained in step (1), disperse them in a certain amount of n-propanol, perform ultrasonic dispersion, and soak for a period of time to obtain solution C; S2: Weigh an appropriate amount of tris(hydroxymethyl)aminomethane (Tris) and disperse it in a certain amount of pure water. Add solution C while stirring at a suitable speed under certain temperature conditions. Continue stirring for a period of time, then add a certain amount of dopamine. Polymerize for a period of time, centrifuge, collect, wash several times with pure water, wash several times with anhydrous ethanol, dry with air, and collect the product m-CNTs@H-PDA. (3) Synthesis of amidoxime functionalized m-CNTs@H-PDA-AO: S1: Weigh the m-CNTs@H-PDA powder obtained in step (2), disperse appropriate amounts of ADBN and AIBN in a certain volume of acetonitrile, place in an oil bath at a certain temperature, and distill until 1 / 3 of the solution remains. Collect, wash with anhydrous ethanol several times, and air dry to collect the product m-CNTs@H-PDA-CN; S2: The m-CNTs@H-PDA-CN obtained in S1 in step (3) is dispersed in a mixed solution of pure water and anhydrous ethanol, a certain amount of hydroxylamine hydrochloride is weighed, ultrasonically dispersed, stirred under a certain temperature condition until the hydroxylamine hydrochloride is dissolved, and sodium hydroxide (NaOH) is added to adjust the pH of the solution to the required conditions. The reaction is continued at this temperature for a period of time, collected, washed multiple times with pure water, washed multiple times with anhydrous ethanol, and dried with air to collect the amidoxime functionalized composite adsorbent, i.e., m-CNTs@H-PDA-AO.

2. The preparation method according to claim 1, wherein In S1 of step (1), the ratio of anhydrous FeCl3, sodium citrate, sodium acetate, polyethylene glycol, ethylene glycol, and CNTs in the mixed solution A is 200-250 mg: 100-150 mg: 1.0-1.5 g: 300-350 mg: 30-40 mL: 20 mg.

3. The preparation method according to claim 1, wherein In S1 of step (1), the temperature of the water bath and the stirring reaction is 20-30° C., the stirring speed is 1200-1800 rpm, and the stirring time is 12-36 h.

4. The preparation method according to claim 1, wherein In step (1) S2, the reaction temperature is 180-200° C., and the reaction time is 10-12 h.

5. The preparation method according to claim 1, wherein In step (2) S1, in the solution C, the ratio of m-CNTs to n-propanol is 1.2-2.0 mg: 3.0-5.0 mL, and the soaking time is 10 min-24 h.

6. The preparation method according to claim 1, wherein In step (2) S2, the amount ratio of Tris, pure water, and dopamine is 25-35 mg:45-55 mL:15-30 mg; the reaction temperature is 20-30° C.; the stirring speed is 400-600 rpm; the stirring time is 1.0-3.0 min; and the polymerization time is 90-150 min.

7. The preparation method according to claim 1, wherein In step (3) S1, the m-CNTs@H-PDA, ADBN, AIBN, and acetonitrile are used in a ratio of 100 mg: 30-80 mg: 50-100 mg: 20-50 mL; and the oil bath temperature is 110-130°C.

8. The preparation method according to claim 1, wherein In step (3) S2, the ratio of the m-CNTs@H-PDA-CN, pure water, anhydrous ethanol, and hydroxylamine hydrochloride is 100 mg: 4.0-6.0 mL: 44 mL-46 mL: 2.0 g-2.1 g; Adjust the solution pH to 7.5-8.5, the reaction temperature to 60-80°C, and the reaction time to 6.0-10h.

9. The preparation method according to claim 1, wherein In steps (1)-(3), the drying temperature is 50-70°C and the drying time is 8.0-12 hours.

10. Use of the functionalized magnetic carbon nanotube-loaded hollow nanosphere composite adsorbent prepared by the preparation method according to any one of claims 1 to 9 for extracting uranium.

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