Polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel, and preparation method and application thereof

Abstract

The application provides a polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel and a preparation method and application thereof, and belongs to the field of adsorption materials. The polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel (CBCS) is prepared, and is used for high-selectivity adsorption of uranium in seawater. The results show that the CBCS has good adsorption performance on uranium in the pH range of 5.0-8.0, the theoretical maximum adsorption capacity of the CBCS on U(VI) is 496.049 mg / g (288K, pH=6.0), the adsorption of the CBCS on uranium is a spontaneous exothermic reaction, the hydroxyl group, the amino group and the C=N bond on the surface of the CBCS directly participate in the adsorption of uranium, the dense pores on the surface of the CBCS play an important role in the adsorption of uranium, and the CBCS has excellent uranium adsorption selectivity. In addition, the CBCS has good cyclic regeneration performance, and the adsorption rate of the CBCS on uranium can still reach more than 98% after 7 adsorption-desorption cycles.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorption materials, and particularly relates to a polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel and a preparation method and application thereof. BACKGROUND

[0002] There are 4.5 billion tons of uranium resources in seawater, but due to the extremely low concentration (3.3 ug / L) of uranium in seawater, the existence of uranium in the form of [UO2(CO3)3]4- and the competition of many metal ions (vanadium, calcium, magnesium, iron and sodium, etc.) coexisting with uranium for adsorption sites, uranium extraction from seawater for nuclear fuel still faces great challenges. 4-

[0003] Although the prior art discloses adsorbents containing amine oxime groups and the like for adsorbing uranium, due to the competitive adsorption of various metal ions, especially vanadium ions, not only the limited adsorption sites on the adsorbents are competed for, but also the uranium adsorption capacity is greatly reduced, the adsorbents are not easy to elute, the adsorption sites are occupied for a long time, the cycle efficiency of the adsorbents is reduced, and there is still a long way to go for the industrialization of uranium extraction from seawater. Therefore, it is urgent to develop an adsorbent with excellent adsorption selectivity for uranium. SUMMARY

[0004] Therefore, the present application aims to provide a polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel and a preparation method and application thereof. The hydrogel prepared by the present application has excellent uranium adsorption selectivity and good uranium adsorption effect.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel, comprising the following steps:

[0007] Mixing 1-butyl-3-methyl imidazole nitrate with water to obtain a 1-butyl-3-methyl imidazole nitrate solution;

[0008] Mixing the 1-butyl-3-methyl imidazole nitrate solution with carbon nanotubes to obtain ion liquid immobilized carbon nanotubes;

[0009] Mixing the ion liquid immobilized carbon nanotubes, a polyvinyl alcohol solution and chitosan, and then drying to obtain the polyvinyl alcohol-imidazole-containing ionic liquid carbon nanotube / chitosan hydrogel.

[0010] Preferably, the mass ratio of 1-butyl-3-methyl imidazole nitrate in the 1-butyl-3-methyl imidazole nitrate solution to carbon nanotubes is 0.5-1.5:1. ​

[0011] Preferably, the mass fraction of 1-butyl-3-methylimidazolium nitrate in the 1-butyl-3-methylimidazolium nitrate solution is 3-10%.

[0012] Preferably, the mass ratio of polyvinyl alcohol, carbon nanotubes with supported ionic liquid, and chitosan in the polyvinyl alcohol solution is 0.8–1:4–6:1–7.

[0013] Preferably, the polyvinyl alcohol solution contains 2.5% to 10% polyvinyl alcohol by mass.

[0014] Preferably, after mixing the 1-butyl-3-methylimidazolium nitrate solution with carbon nanotubes, the mixture is further subjected to a process of standing and drying, wherein the standing time is 8-12 hours and the drying temperature is 100-150°C for 8-14 hours.

[0015] Preferably, the drying process includes freeze-drying and oven drying in sequence, wherein the freeze-drying temperature is -10 to -30°C and the time is 18 to 24 hours, and the oven drying temperature is 20 to 50°C and the time is 18 to 24 hours.

[0016] The present invention also provides a polyvinyl alcohol-imidazolium ionic liquid-containing carbon nanotube / chitosan hydrogel prepared by the preparation method described above.

[0017] This invention also provides the application of the polyvinyl alcohol-imidazolium ionic liquid-carbon nanotube / chitosan hydrogel described above in the field of uranium adsorption.

[0018] Preferably, the application includes the following steps:

[0019] The polyvinyl alcohol-imidazolium ionic liquid-containing carbon nanotube / chitosan hydrogel was added to a uranium solution with a pH of 5.0 to 8.0.

[0020] This invention provides a method for preparing polyvinyl alcohol-imidazolium ionic liquid-carbon nanotube / chitosan hydrogel (CBCS), comprising the following steps: mixing 1-butyl-3-methylimidazolium nitrate with water to obtain a 1-butyl-3-methylimidazolium nitrate solution; mixing the 1-butyl-3-methylimidazolium nitrate solution with carbon nanotubes to obtain carbon nanotubes immobilized with the ionic liquid; mixing the carbon nanotubes immobilized with the ionic liquid, the polyvinyl alcohol solution, and chitosan, and then drying the mixture to obtain the polyvinyl alcohol-imidazolium ionic liquid-carbon nanotube / chitosan hydrogel.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The polyvinyl alcohol-imidazolium ionic liquid-containing carbon nanotube / chitosan hydrogel prepared in this invention is used for highly selective adsorption of uranium from seawater. Results from the examples show that CBCS exhibits good adsorption performance for uranium in the pH range of 5.0–8.0, making it suitable for application under seawater pH conditions. Kinetic and thermodynamic experiments show that the theoretical maximum adsorption capacity of CBCS for U(VI) is 496.049 mg / g (288 K, pH = 6.0), which is a spontaneously exothermic reaction. Mechanistic analysis indicates that the hydroxyl, amino, and C=N bonds on the CBCS surface directly participate in uranium adsorption, and the dense pores on the CBCS surface provide channels for uranyl ion transport, playing a crucial role in uranium adsorption. Competitive adsorption experiments demonstrate that CBCS possesses excellent uranium adsorption selectivity. CBCS exhibits good reusability; after seven adsorption-desorption cycles, the uranium adsorption rate of CBCS can still reach over 98%. Therefore, CBCS has good potential for extracting uranium from seawater. Attached Figure Description

[0023] Figure 1 The effect of initial solution pH on uranium adsorption by CBCS;

[0024] Figure 2 The removal rates of uranium solution with an initial concentration of 10 mg / L were calculated using 10, 20, 30, and 45 mg of hydrogel adsorbent.

[0025] Figure 3 (a) shows the effect of contact time on uranium adsorption by CBCS, (b) shows the adsorption isotherm of uranium by CBCS at 288 K, (c) shows the adsorption isotherm of uranium by CBCS at 298 K, and (d) shows the adsorption isotherm of uranium by CBCS at 308 K.

[0026] Figure 4 In the figure, (a) is the partition coefficient of CBCS adsorbing competing ions, (b) is the recycling performance of CBCS, (c) is the infrared spectrum of the desorbed material, and (d) is the SEM image of the desorbed material.

[0027] Figure 5 In the figure, (a) is the SEM spectrum of CBCS before adsorption, (b) is the SEM spectrum of CBCS after adsorption; (c), (d), (e), and (f) are the elemental distribution diagrams of C, O, N, and U, respectively.

[0028] Figure 6 EDS image of CBCS after adsorption;

[0029] Figure 7 In the image, (a) shows the infrared images of C, CB, CBCS, and CBCS-U, and (b), (c), (d), (e), and (f) show the XPS images of CBCS and CBCS-U. Detailed Implementation

[0030] This invention provides a method for preparing a polyvinyl alcohol-imidazolium-containing ionic liquid carbon nanotube / chitosan hydrogel, comprising the following steps:

[0031] 1-Butyl-3-methylimidazolium nitrate was mixed with water to obtain a 1-butyl-3-methylimidazolium nitrate solution;

[0032] The 1-butyl-3-methylimidazolium nitrate solution was mixed with carbon nanotubes to obtain carbon nanotubes with immobilized ionic liquids.

[0033] The carbon nanotubes with the immobilized ionic liquid, the polyvinyl alcohol solution, and the chitosan were mixed and dried to obtain the polyvinyl alcohol-imidazolium-containing carbon nanotube / chitosan hydrogel.

[0034] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0035] In this invention, 1-butyl-3-methylimidazolium nitrate is mixed with water to obtain a 1-butyl-3-methylimidazolium nitrate solution.

[0036] In this invention, the mass fraction of 1-butyl-3-methylimidazolium nitrate in the 1-butyl-3-methylimidazolium nitrate solution is preferably 3-10%, more preferably 3-5%.

[0037] In this invention, the water is preferably deionized water.

[0038] After obtaining a 1-butyl-3-methylimidazolium nitrate solution, the present invention mixes the 1-butyl-3-methylimidazolium nitrate solution with carbon nanotubes to obtain carbon nanotubes (CB) with immobilized ionic liquid.

[0039] In this invention, the mass ratio of 1-butyl-3-methylimidazolium nitrate to carbon nanotubes in the 1-butyl-3-methylimidazolium nitrate solution is preferably 0.5 to 1.5:1, more preferably 1:1.

[0040] In this invention, the mixing of the 1-butyl-3-methylimidazolium nitrate solution with carbon nanotubes preferably further includes allowing the resulting mixture to stand and dry sequentially. The standing time is preferably 8-12 hours, more preferably 9-10 hours, and the temperature is preferably room temperature. The drying temperature is preferably 100-150°C, more preferably 110-120°C, and the drying time is preferably 8-14 hours, more preferably 10-12 hours.

[0041] In this invention, the 1-butyl-3-methylimidazolium nitrate solution is added dropwise to carbon nanotubes, and stirred until the 1-butyl-3-methylimidazolium nitrate solution covers the carbon nanotubes. The resulting mixture is left at room temperature for 10 hours, then dried at 120°C for 12 hours, and pulverized to obtain the carbon nanotubes with the ionic liquid immobilized.

[0042] After obtaining carbon nanotubes immobilized with ionic liquid, the present invention mixes the carbon nanotubes immobilized with ionic liquid, polyvinyl alcohol solution and chitosan and dries them to obtain the polyvinyl alcohol-imidazolium-containing carbon nanotube / chitosan hydrogel.

[0043] In this invention, the mass ratio of polyvinyl alcohol, carbon nanotubes with immobilized ionic liquid, and chitosan in the polyvinyl alcohol solution is preferably 0.8-1:4-6:1-7, more preferably 0.8:4:6, 1:6:4, 1:6:1, 1:6:6, 1:4:6, or 1:6:7.

[0044] In this invention, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is preferably 2.5-10%, more preferably 3-5%. Preferably, the polyvinyl alcohol (PVA) is added to a 1 wt% acetic acid solution and heated at 120°C for 2 hours to obtain the polyvinyl alcohol solution. In a specific embodiment of this invention, 1 g of polyvinyl alcohol is added to 30 mL of a 1 wt% acetic acid solution and heated at 120°C for 2 hours to obtain a PVA solution. The polyvinyl alcohol solution is preferably allowed to cool naturally to room temperature before use.

[0045] In this invention, the drying process preferably includes freeze-drying and oven drying in sequence. The freeze-drying temperature is preferably -10 to -30°C, more preferably -20 to -30°C, and the time is preferably 18 to 24 hours, more preferably 20 to 24 hours. The oven drying temperature is preferably 20 to 50°C, more preferably 30 to 40°C, and the time is preferably 18 to 24 hours, more preferably 20 to 24 hours.

[0046] In this invention, the freeze-drying is preferably carried out in a refrigerator, and the drying is preferably carried out in an oven.

[0047] The present invention also provides a polyvinyl alcohol-imidazolium ionic liquid-containing carbon nanotube / chitosan hydrogel prepared by the preparation method described above.

[0048] This invention also provides the application of the polyvinyl alcohol-imidazolium ionic liquid-carbon nanotube / chitosan hydrogel described above in the field of uranium adsorption.

[0049] In this invention, the application preferably includes the following steps:

[0050] The polyvinyl alcohol-imidazolium ionic liquid-containing carbon nanotube / chitosan hydrogel is added to a uranium solution, wherein the pH value of the uranium solution is preferably 5.0 to 8.0, more preferably 8.0.

[0051] In this invention, the uranium solution is preferably seawater.

[0052] In this invention, the preferred ratio of the polyvinyl alcohol-imidazolium ionic liquid-carbon nanotube / chitosan hydrogel to seawater is 10-45 mg: 90 mL.

[0053] In this invention, the polyvinyl alcohol-imidazolium ionic liquid-carbon nanotube / chitosan hydrogel is preferably recycled. The recycling process preferably includes desorption, and the desorption solution is preferably a mixture of 1 mol / L sodium chloride solution and 2.5 g / L sodium bicarbonate solution.

[0054] In this invention, the number of times the cycle is used is preferably 5 to 7 times.

[0055] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0056] Example 1

[0057] CBCS preparation:

[0058] Carbon nanotubes immobilized with ionic liquid: 1-Butyl-3-methylimidazolium nitrate ionic liquid was dissolved in deionized water to obtain a 5 wt% solution. The prepared solution (containing 5 g of 1-butyl-3-methylimidazolium nitrate ionic liquid) was added dropwise to 5 g of carbon nanotubes, and stirred until the solution covered the carbon nanotubes. The mixture was left to stand at room temperature for 10 h, and then dried at 120 °C for 12 h. After pulverization, carbon nanotubes immobilized with ionic liquid (CB) were obtained.

[0059] Hydrogel preparation: 1 g of polyvinyl alcohol was added to 30 mL of 1 wt% acetic acid solution and heated at 120 °C for 2 h to obtain a PVA solution. 4 g of CB and 6 g of chitosan were added to the cooled PVC solution and mixed thoroughly. The mixture was frozen for 24 h and then dried in an oven at 30 °C for 24 h to obtain a dried hydrogel (CBCS).

[0060] Effect of initial pH value

[0061] pH is a crucial factor affecting uranium adsorption. The speciation of uranium and the binding strength between the adsorbent and uranium are both influenced by pH, and the optimal pH for uranium adsorption determines the application range of the adsorbent. This invention studies the adsorption performance of CBCS on a 10 mg / L uranium solution within the pH range of 5.0–9.0 ± 0.02. Figure 1 As shown, the initial pH value has a significant effect on the adsorption performance of CBCS. The adsorption rate can reach over 90% in the range of 5–8, with the optimal pH being 6.0 and the adsorption capacity being 29.63 mg·g⁻¹. -1 The conditions are suitable for uranium extraction from seawater. At a low initial pH, uranium in the solution primarily exists as UO2. 2+ It exists in a form that gradually hydrolyzes into UO2(OH) as the pH value increases. + UO2 2+ (UO2)2(OH)2 2+ and (UO2)3(OH) 5+ As the pH value increases further, the main form of uranium is UO2(OH). 3- (UO2)3(OH) 7 The adsorption rate decreases due to the presence of UO2(OH)2.

[0062] The low adsorption capacity of CBCS in uranium solutions with pH ≤ 4.0 may be due to uranium ions (i.e., UO2). 2+ The adsorption of uranyl ions is inhibited by electrostatic repulsion between the positively charged CBCS adsorbent surface and the limited adsorption sites between uranyl ions and protons. As pH increases, the negative charge on the CBCS surface increases, making it easier to adsorb positively charged substances and increasing the adsorption capacity. However, at pH ≥ 8.0, the number of uranium ions adsorbed on CBCS decreases due to the formation of soluble and stable uranium-carbonate complexes. In summary, pH has a significant impact on the adsorption performance of CBCS, with the optimal adsorption effect at pH 6.0. Therefore, subsequent experiments will be conducted under pH 6.0 conditions.

[0063] The removal rates of uranium solution with an initial concentration of 10 mg / L were experimentally investigated using 10, 20, 30, and 45 mg of hydrogel adsorbent. Figure 2 As shown, the removal rate increases linearly with the increase of adsorbent mass. When the adsorbent mass is 30 mg, the removal rate of CBCS reaches 96.11%. When the adsorbent mass is further increased, the removal rate tends to level off. Considering all factors, 30 mg is selected as the optimal adsorbent mass for subsequent experiments.

[0064] Adsorption kinetics

[0065] Adsorption kinetics curves were plotted using the adsorption capacity of CBCS for a 10 mg / L uranium solution as a function of adsorption time.Figure 3 (a) shows the effect of contact time on uranium adsorption by CBCS. Figure 3 (a) shows the effect of contact time on uranium adsorption by CBCS; (b) shows the adsorption isotherm of uranium by CBCS at 288 K; (c) shows the adsorption isotherm of uranium by CBCS at 298 K; and (d) shows the adsorption isotherm of uranium by CBCS at 308 K. Figure 3 It can be seen that the CBCS adsorption reaction is divided into a rapid adsorption stage and an ion adsorption equilibrium stage. In the first 3 hours, the adsorption sites of the adsorbent are abundant and have not been filled, so the adsorption rate increases rapidly. As the reaction proceeds, the adsorption sites gradually decrease, the adsorption rate decreases, and the removal rate gradually stabilizes, reaching adsorption equilibrium.

[0066] To elucidate the kinetics of the adsorption reaction, pseudo-first-order and pseudo-second-order kinetic models of uranium adsorption by CBCS were fitted. Figure 3 Table (a) and Table 1 show the kinetic fitting results. The linear regression correlation coefficient (R0) is included in the kinetic parameters of Table 1. 2 The values ​​indicate that the pseudo-second-order kinetic model better describes the CBCS adsorption kinetics, suggesting that chemical reactions dominate the CBCS adsorption and uranium capture process. Temperature and initial uranium concentration in the solution control the chemisorption process.

[0067] Table 1 Dynamic parameters

[0068]

[0069] Adsorption isotherms and thermodynamic analysis

[0070] Adsorption isotherms can assess the adsorption capacity of an adsorbent, reflect the interaction between adsorbents, and calculate the theoretical maximum adsorption capacity. To evaluate the adsorption capacity of the prepared CBCS, the initial concentration of the uranium solution was gradually changed from 5 mg / L to 600 mg / L within the temperature range of 288–308 K to determine the adsorption isotherms. Adsorption was fitted using the Freundlich and Langmuir models, and the results are as follows: Figure 3 As shown in (b), (c), (d) and Table 2, the higher the initial concentration of the uranium solution, the greater the adsorption capacity of the CBCS adsorbent for uranium. When the concentration is greater than 100 mg / L, the rate of increase in adsorption capacity gradually decreases. Based on the linear correlation coefficient R of the Langmuir model in Table 2... 2 The adsorption capacity of CBCS for uranium is greater than that of the Freundlich model, indicating that the uranium adsorption reaction of CBCS is more in line with the Langmuir model. The maximum adsorption capacity of CBCS for uranium at 288 K is 496.049 mg / g, which is a monolayer adsorption mode. The adsorption sites are identical and independent of each other, and there is no interaction force between the adsorbate molecules on the surface of the adsorbent.

[0071] Table 2 Isothermal Adsorption Parameters

[0072]

[0073] Adsorption experiments were conducted in the temperature range of 288–308 K, and the distribution coefficient K of uranium on the CBCS was calculated using equation (1). d K d Multiply by 1000 to get the distribution coefficient K for the same unit. C Thermodynamic parameters are shown in Table 3. The adsorption capacity decreases with increasing temperature, ΔH 0 <0 indicates that the uranium adsorption process of CBCS is an exothermic reaction. ΔS 0 A value greater than 0 indicates that the surface randomness and disorder between the solid and liquid increase during adsorption. ΔG 0 A negative value indicates that the adsorption of uranium by CBCS is spontaneous and thermodynamically feasible. In conclusion, the adsorption of uranium by CBCS is spontaneous and exothermic.

[0074]

[0075] Where C0 represents the initial concentration of the uranium solution, C e V represents the equilibrium concentration, V represents the solution volume, and m represents the dry weight of the adsorbent CBCS.

[0076] Table 3 Thermodynamic parameters at different temperatures

[0077]

[0078] The influence of competing ions

[0079] The complex composition of seawater affects the adsorption efficiency of uranium. This study investigates the selective adsorption of uranium by CBCS under the influence of coexisting ions. Adsorption experiments were conducted on CBCS in a simulated seawater solution containing uranium, calcium, magnesium, zinc, sodium, vanadium, and copper ions. The concentrations of the metal ions were as follows: Figure 4 As shown in (a), Figure 4 (a) shows the partition coefficient of competing ions adsorbed by CBCS, (b) shows the recycling performance of CBCS, (c) shows the infrared spectrum of the desorbed material, and (d) shows the SEM image of the desorbed material. Competition between uranium and vanadium ions has always been a major obstacle to uranium extraction from seawater. Under simulated seawater conditions, the partition coefficient of CBCS for U exceeds that of vanadium by approximately 12 times, indicating that CBCS has a superior U removal effect. The adsorption behavior of calcium, magnesium, sodium, and vanadium ions has little effect, demonstrating the excellent adsorption selectivity of CBCS and its great potential for uranium extraction from seawater.

[0080] Cyclic adsorption and desorption

[0081] The cyclic regeneration performance of CBCS was verified through adsorption and desorption experiments. CBCS adsorbed a uranium solution with a concentration of 10 mg / L under the conditions of pH 6 and 298 K. Desorption experiments were conducted at 313 K using 1 mol / L sodium chloride and 2.5 g / L sodium bicarbonate as desorption solutions. The adsorption capacity and desorption rate of CBCS for uranium in each cycle are shown below. Figure 4 As shown in (b). The SEM and infrared spectra of the desorbed material are shown in [Figure 1]. Figure 4 As shown in (d) and (c) SEM images, after seven cycles of desorption, dense pores still exist on the surface of CBCS, and no obvious uranium peaks are observed in the infrared spectrum, indicating that the composition of CBCS has not been significantly damaged. After seven cycles of adsorption and desorption, the adsorption rate of uranium by CBCS can still be maintained above 98%, and the uranium desorption rate can still be maintained above 91%, indicating that it has good reusability.

[0082] Adsorption mechanism study

[0083] Figure 5 In the image, (a) shows the SEM spectrum of CBCS before adsorption, (b) shows the SEM spectrum of CBCS after adsorption, and (c), (d), (e), and (f) are the elemental distribution diagrams of C, O, N, and U, respectively. Figure 6 EDS images of CBCS after adsorption, such as Figures 5-6 As shown, before adsorption, CBCS has a dense porous surface; after adsorption, the surface pores of CBCS are filled, and the surface becomes smooth. BET analysis revealed that the specific surface area of ​​CBCS is 27.313 m². 2 The material has an average pore size of 39.718 nm, classified as mesoporous. EDS analysis of the elemental composition of the CBCS surface after the adsorption reaction revealed that carbon (C) was the most abundant element, followed by oxygen (O) and nitrogen (N). In addition to the presence of nitrogen, oxygen, and carbon in the material itself, uranium (U) was also detected. This indicates that, with the participation of functional groups within the CBCS, uranium was effectively attached to the material surface, and carbon, oxygen, nitrogen, and uranium were distributed on the surface of the CBCS or accumulated in its pores.

[0084] Figure 7 (a) shows the infrared images of C, CB, CBCS, and CBCS-U; (b), (c), (d), (e), and (f) show the XPS images of CBCS and CBCS-U. The infrared spectra of carbon nanotubes (C), carbon nanotubes (CB) with immobilized ionic liquids, CBCS, and CBCS-U composite materials are also presented. Figure 7 As shown in (a), the infrared spectra of CB and C differ at 1383 cm⁻¹. -1 The presence of -CH bending vibrations at 1167 and 1256 cm⁻¹ indicates that the ionic liquid is well immobilized on the carbon nanotubes. -1The peaks observed at these locations confirm the successful immobilization of the ionic liquid within the carbon nanotubes. These peaks correspond to the CH stretching vibrations (aromatic) and CN stretching vibrations (aromatic). CBCS peaks at 2921 and 2854 cm⁻¹... -1 The corresponding peaks at 3448 cm⁻¹ represent the asymmetric and symmetric stretching vibrations of -CH₂, reflecting the -[CH₂]⁻ group in polyvinyl alcohol. C, CB, and CBCS peak at 3448 cm⁻¹ -1 There is a gradually increasing peak representing -OH at 893 cm⁻¹, and the nearby absorption band shows a trend of broadening towards lower frequency regions, possibly due to the superposition of interactions between -OH and -NH₂ functional groups. Furthermore, CBCS-U shows a peak at 893 cm⁻¹. -1 The presence of the O=U=O peak at this point proves that uranium has been adsorbed on the CSCB-U material.

[0085] The modification mechanism of the material prepared by XPS Research Institute. The total scanning spectra of CBCS before and after adsorption are shown below. Figure 7 As shown in (c), the emission peaks at 398.11 and 400.73 eV in the N1s spectrum are attributed to the presence of C=N and NH, further proving the effective binding of the ionic liquid in the material. At binding energies of 286.93, 285.02, and 283.43 eV, the C1s spectrum can be distinguished into three peaks, corresponding to carbon atoms in the CC / CH, CN, and C=N functional groups, respectively. An O1s peak was observed at 531.31 eV, confirming the presence of the hydrophilic hydroxyl group in CBCS. After uranium adsorption, the XPS spectrum of O1s showed a significant change in peak intensity, with a new peak appearing at 531.04 eV. This is attributed to the formation of O=U=O bonds by uranium adsorption in the material, and the shift of the hydroxyl peak to a lower binding energy, indicating a reaction of the hydroxyl group. After uranium extraction, the C=N group peak shifted to a higher binding energy (+1.05 eV), indicating a complexation reaction between nitrogen atoms and uranyl ions. Compared to before adsorption, in… Figure 7 In (b), two characteristic peaks of the U4f uranium ion can be clearly seen, namely U4f... 7 / 2 (392.54eV) and U4f 5 / 2 (381.26 eV, splitting degree ~11.28 eV, these two peaks indicate that free uranium is effectively adsorbed by CBCS, and there are covalent bonds between functional groups and uranium. The results show that hydroxyl, amino and C=N bonds in ionic liquids directly participate in uranium adsorption, and the dense pores on the CBCS surface also play an important role in uranium adsorption.)

[0086] Example 2

[0087] CBCS preparation:

[0088] The preparation of carbon nanotube-supported ionic liquids is the same as in Example 1.

[0089] Hydrogel preparation: 1 g of polyvinyl alcohol was added to 30 mL of 1 wt% acetic acid solution and heated at 120 °C for 2 h to obtain a PVA solution. 6 g of CB and 6 g of chitosan were added to the cooled PVC solution and mixed thoroughly. The mixture was frozen for 24 h and then dried in an oven at 30 °C for 24 h to obtain a dried hydrogel.

[0090] An adsorption and removal experiment was conducted on a uranium solution with an initial concentration of 10 mg / L using 30 mg of the hydrogel prepared in Example 2. The uranium removal rate reached 93.35%.

[0091] Example 3

[0092] CBCS preparation:

[0093] The preparation of carbon nanotube-supported ionic liquids is the same as in Example 1.

[0094] Hydrogel preparation: 0.8 g of polyvinyl alcohol was added to 30 mL of 1 wt% acetic acid solution and heated at 120 °C for 2 h to obtain a PVA solution. 4 g of CB and 6 g of chitosan were added to the cooled PVC solution and mixed thoroughly. The mixture was frozen for 24 h and then dried in an oven at 30 °C for 24 h to obtain a dried hydrogel.

[0095] An adsorption and removal experiment was conducted on a uranium solution with an initial concentration of 10 mg / L using 30 mg of the hydrogel prepared in Example 3. The uranium removal rate reached 92.17%.

[0096] Example 4

[0097] CBCS preparation:

[0098] The preparation of carbon nanotube-supported ionic liquids is the same as in Example 1.

[0099] Hydrogel preparation: 1 g of polyvinyl alcohol was added to 30 mL of 1 wt% acetic acid solution and heated at 120 °C for 2 h to obtain a PVA solution. 6 g of CB and 7 g of chitosan were added to the cooled PVC solution and mixed thoroughly. The mixture was frozen for 24 h and then dried in an oven at 30 °C for 24 h to obtain a dried hydrogel.

[0100] An adsorption and removal experiment was conducted on a uranium solution with an initial concentration of 10 mg / L using 30 mg of the hydrogel prepared in Example 4. The uranium removal rate reached 97.35%.

[0101] In summary, this invention prepared a novel composite hydrogel (CBCS). The maximum adsorption capacity of CBCS at pH 6.0 and 288 K was 496.049 mg / g. Dynamic and isotherm experiments showed that the adsorption process was mainly chemisorption, exhibiting monolayer adsorption. Thermodynamic parameters revealed the spontaneous endothermic nature of CBCS. Mechanistic analysis indicated that the hydroxyl and amino groups on the CBCS surface and the C=N bonds in the IL played a crucial role in uranium adsorption. Competitive adsorption experiments showed that the partition coefficient of CBCS for uranium was significantly higher than that for vanadium and other metal ions. CBCS can be recycled more than 5 times, maintaining its excellent uranium adsorption rate even after 5 cycles. Therefore, CBCS is an ideal uranium adsorbent material with great development potential.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing polyvinyl alcohol- imidazole-containing ionic liquid-carbon nanotube / chitosan hydrogel, characterized in that, The method comprises the following steps: mixing 1-butyl-3-methylimidazolium nitrate with water to obtain a 1-butyl-3-methylimidazolium nitrate solution; mixing the 1-butyl-3-methylimidazolium nitrate solution with carbon nanotubes to obtain carbon nanotubes with immobilized ionic liquid; mixing the carbon nanotubes with immobilized ionic liquid, a polyvinyl alcohol solution and chitosan, and then drying to obtain the polyvinyl alcohol-1-butyl-3-methylimidazolium nitrate-containing carbon nanotube / chitosan hydrogel; the mass ratio of 1-butyl-3-methylimidazolium nitrate in the 1-butyl-3-methylimidazolium nitrate solution to the carbon nanotubes is 1:1; the mass ratio of polyvinyl alcohol in the polyvinyl alcohol solution to the carbon nanotubes with immobilized ionic liquid and chitosan is 0.8-1:4-6:1-7.

2. The production method according to claim 1, characterized by, the mass fraction of 1-butyl-3-methylimidazolium nitrate in the 1-butyl-3-methylimidazolium nitrate solution is 3-10%.

3. The preparation method according to claim 1, characterized in that, the mass fraction of polyvinyl alcohol in the polyvinyl alcohol solution is 2.5-10%.

4. The method of claim 1, wherein, after mixing the 1-butyl-3-methylimidazolium nitrate solution with the carbon nanotubes, the obtained mixture is sequentially subjected to standing and drying, the standing time is 8-12 h, and the drying temperature is 100-150°C, and the time is 8-14 h.

5. The preparation method according to claim 1, characterized in that, the drying comprises sequentially performing freeze drying and oven drying, the freeze drying temperature is -10 to -30°C, and the time is 18-24 h, the oven drying temperature is 20-50°C, and the time is 18-24 h.

6. The polyvinyl alcohol-1-butyl-3-methylimidazolium nitrate-containing carbon nanotube / chitosan hydrogel prepared by the preparation method of any one of claims 1-5.

7. The use of the polyvinyl alcohol-1-butyl-3-methylimidazolium nitrate-containing carbon nanotube / chitosan hydrogel of claim 6 in the field of uranium adsorption.

8. Use according to claim 7, characterized in that, The use comprises the following steps: adding the polyvinyl alcohol-1-butyl-3-methylimidazolium nitrate-containing carbon nanotube / chitosan hydrogel to a uranium solution, and the pH value of the uranium solution is 5.0-8.0.

Images