Zif-8 / algal powder-based composite aerogel and preparation method and application thereof

Abstract

The ZIF-8 / algae powder-based composite aerogel, preparation method and application thereof relate to the field of environmental engineering and material science technology. A novel chitosan / ZIF-8 / algae powder (ZIF-8 / CP / CS) composite adsorbent is synthesized for efficient adsorption of uranium ions in seawater. The results show that the adsorbent has good adsorption performance for uranium in the pH range of 4.0-8.0, and the adsorption rate is all above 89%. Mechanism analysis shows that the hydroxyl, amino, phosphoric acid groups on the surface of ZIF-8 / CP / CS and the C=N bond in ZIF-8 play a key role in the adsorption of uranium, and the quaternary phosphonium salt improves the competitiveness of the adsorbent for uranium. The competitive adsorption experiment shows that compared with the original ZIF-8 and ZIF-8 / C / CS without immobilized ionic liquid, the uranium vanadium ratio of ZIF-8 / CP / CS is increased by 20 times and 6 times respectively. The real uranium tailing pond wastewater is treated by adsorption, and the uranium content of the wastewater is reduced to 40 μg / L, so the adsorbent has good potential for extracting uranium from seawater and good application prospect for recovering uranium from uranium tailing wastewater.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and materials science, and in particular to a ZIF-8 / algae powder-based composite aerogel, its preparation method, and its application. Background Technology

[0002] As a substitute for traditional fossil fuels, nuclear energy faces increasing challenges in its supply of uranium, a raw material for nuclear reactions, due to its growing use. The ocean's uranium reserves are 1000 times greater than those on land, making uranium extraction from unconventional resources like seawater a significant focus. However, the complex marine environment and the low uranium concentration in seawater (3.3 µg / L) raise the bar for uranium extraction from real seawater. Furthermore, the lack of highly selective uranium separation and enrichment technologies in nuclear industry wastewater results in PPM-level uranium resources that urgently require treatment and recycling. This lack of technology generates large quantities of uranium-containing wastewater, the spread of which poses a threat to human health and the nuclear ecosystem.

[0003] To address this problem, methods for extracting uranium from seawater and treating uranium-containing wastewater have been developed, including ion exchange, electrochemistry, coprecipitation, and adsorption. Among these, adsorption has broad application prospects in seawater uranium extraction and wastewater treatment due to its advantages such as simple operation, recyclability, high efficiency, and easy availability. To date, various materials have been used for seawater uranium extraction, such as polymers, metal-organic frameworks, and hydrogels.

[0004] However, many traditional adsorbents exhibit low adsorption efficiency in low-concentration uranium environments, making it difficult to meet the demands of large-scale uranium extraction from seawater. Furthermore, seawater and wastewater contain numerous coexisting metal ions (such as vanadium, calcium, magnesium, and copper) that compete with uranium for adsorption sites, often hindering the high selectivity of traditional adsorbents for uranium. Moreover, some materials suffer from insufficient stability under long-term use or extreme conditions, affecting the sustainability of their practical applications. Additionally, the performance of certain materials fluctuates significantly under different pH values ​​or temperatures, limiting their application in variable environments. Therefore, exploring and developing highly efficient and selective adsorbents is a meaningful task for more effectively extracting uranium from seawater and treating and recovering low-concentration uranium-containing wastewater. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing ZIF-8 / algae powder-based composite aerogel that can improve the adsorption efficiency of uranium.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing ZIF-8 / algae powder-based composite aerogel, comprising the following steps:

[0007] (1) Preparation of ZIF-8 / algae powder: Add the protein core Chlorella powder to the zinc nitrate hexahydrate solution, then add 2-methylimidazole solution, stir the reaction at room temperature, centrifuge to obtain the precipitate, and then wash and dry to obtain ZIF-8 / algae powder;

[0008] (2) Preparation of ZIF-8 / algae powder supported quaternary phosphonium salt ionic liquid: Trihexyl (tetradecyl)phosphonium chloride was dissolved in methanol to prepare an ionic liquid of a certain concentration. ZIF-8 / algae powder was added to the ionic liquid and stirred until the solution just covered ZIF-8 / algae powder. The solution was allowed to stand at room temperature and dried to obtain ZIF-8 / algae powder supported quaternary phosphonium salt ionic liquid.

[0009] (3) Preparation of ZIF-8 / algae powder-based composite aerogel: Add deionized water to a beaker containing myricetin and stir to dissolve it completely. Then add an appropriate amount of chitosan, ZIF-8 / algae powder-supported quaternary phosphonium salt ionic liquid and an appropriate amount of glacial acetic acid. Continue stirring until the chitosan is completely dissolved. Then add glutaraldehyde solution and shake in a constant temperature shaker until the sol ages. Then freeze dry to obtain ZIF-8 / algae powder-based composite aerogel.

[0010] Preferably, in step (1), the washing and drying methods are as follows: wash three times with ethanol and deionized water, and dry at 80°C for 12 h.

[0011] More preferably, in step (2), the concentration of the ionic liquid is 5%.

[0012] More preferably, in step (2), the method of standing and drying at room temperature is: standing at room temperature for 10 h, and then drying in an oven at 80°C for 12 h.

[0013] More preferably, in step (3), the concentration of the glutaraldehyde solution is 0.1%.

[0014] More preferably, in step (3), the sol is shaken in a constant temperature shaking box at 150 r / min and 45°C for 24 hours until it ages, and then freeze-dried for 48 hours.

[0015] In addition, this invention also provides a ZIF-8 / algae powder-based composite aerogel, which is prepared using the above-described method for preparing ZIF-8 / algae powder-based composite aerogel. This ZIF-8 / algae powder-based composite aerogel can be used for extracting uranium from seawater and recovering uranium from uranium tailings wastewater.

[0016] Compared with existing technologies, the present invention exhibits excellent adsorption performance for uranium within a pH range of 4.0 to 8.0, with adsorption rates exceeding 89%. When adsorbing uranium from real seawater, the adsorption capacity is 114.2 mg / kg. When treating real uranium tailings wastewater, the uranium content in the wastewater is reduced to 40 μg / L. Therefore, the ZIF-8 / algae powder-based composite aerogel prepared by this invention has good potential for uranium extraction from seawater and also shows promising application prospects in the treatment of uranium tailings wastewater. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the effect of pH value on the adsorption of uranium by the composite aerogel.

[0018] Figure 2 A schematic diagram showing the effect of different times and uranium concentrations on the rate of uranium adsorption on ZIF-8 / CP / CS;

[0019] Figure 3 The partition coefficients of different metal ions after adsorption and the infrared spectra of the material after desorption are shown.

[0020] Figure 4 Images (a), (b), and (c) show the adsorption of UO2 detected by SEM and EDS. 2+ Surface morphology and elemental distribution of ZIF-8 / CP / CS; (d) and (e) are TEM images of ZIF-8 and ZIF-8 / CP / CS, respectively;

[0021] Figure 5 This is a mapping image of the material surface obtained after scanning the SEM area;

[0022] Figure 6 (a) shows the FTIR spectra of ZIF-8, ZIF-8 / C, ZIF-8 / CP, and ZIF-8 / CP / CS; (b) is a schematic diagram of the thermal stability evaluation results of ZIF-8 / CP / CS by thermogravimetric analysis.

[0023] Figure 7 The images show the C1s spectra before and after adsorption.

[0024] Figure 8 The images show the spectra of each adsorbent material. Detailed Implementation

[0025] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0026] In this embodiment, the raw materials included 2-methylimidazole (PubChem CID: 12749), trihexyl(tetradecyl)phosphonium chloride (PubChem CID: 11375816), and chitosan (CS) from Macklin Reagents. Analytical grade zinc nitrate hexahydrate, glutaraldehyde, glacial acetic acid, and tannic acid were purchased from domestic companies. All reagents were AR grade.

[0027] The specific steps for preparing ZIF-8 / algae powder-based composite aerogel are as follows:

[0028] (1) Preparation of ZIF-8 / algae powder: Take 0.2 g Chlorella pyrenoidosa powder, 100 mL of Zn(NO3)2·6H2O solution with a concentration of 100 mmol / L and 100 mL of 2-methylimidazole solution with a concentration of 400 mmol / L in a beaker, stir at room temperature for 5 h, centrifuge to obtain precipitate, wash with ethanol and deionized water 3 times, dry at 80℃ for 12 h to obtain ZIF-8 / algae powder (ZIF-8 / C).

[0029] (2) Preparation of ZIF-8 / algae powder supported quaternary phosphonium salt ionic liquid: Trihexyl (tetradecyl)phosphonium chloride was dissolved in methanol to prepare an ionic liquid with a concentration of 5%. ZIF-8 / algae powder was added to the ionic liquid and stirred until the solution just covered ZIF-8 / algae powder. The solution was left to stand at room temperature for 10 h and then dried in an oven at 80℃ for 12 h to obtain ZIF-8 / algae powder supported quaternary phosphonium salt ionic liquid (ZIF-8 / CP).

[0030] (3) Preparation of ZIF-8 / algae powder-based composite aerogel: 60 mL of deionized water was added to a beaker containing 0.3 g of myricetin and stirred for 2 h to completely dissolve it. Then, 0.3 g of chitosan and 0.3 g of ZIF-8 / algae powder-supported quaternary phosphonium salt ionic liquid were added to the mixture, followed by 0.6 mL of glacial acetic acid. The mixture was stirred for another 2 h. After the chitosan was completely dissolved, 1 mL of 0.1% glutaraldehyde solution was added. The mixture was shaken in a constant temperature shaking oven (150 r / min, 45℃) for 24 h until the sol aged. The mixture was then freeze-dried for 48 h to obtain ZIF-8 / algae powder-based composite aerogel (ZIF-8 / CP / CS).

[0031] Adsorption test

[0032] Adsorption experiments were conducted using 10 mg of adsorbent in 90 mL of uranium solution or simulated seawater with various ion concentrations to investigate the effects of pH (4–9), contact time (30 min–12 h), initial uranium concentration (5–150 mg / L), and temperature (15–35 °C) on the adsorption capacity of the adsorbent for uranium ions. The pH of the solution was adjusted using Na₂CO₃ and HNO₃. All adsorption experiments were performed in a constant-speed oscillator at 175 r / min. After the reaction, the solution was filtered through filter paper to achieve solid-liquid separation, and the uranium concentration before and after adsorption was measured using a UV-Vis spectrophotometer. Multiple parallel experiments were conducted, and the experimental error was controlled to be less than 1.0%.

[0033] The uranium removal rate (R, %) and equilibrium adsorption capacity (q) were calculated using formulas (1)-(3) respectively. e (mg / g) and partition coefficient (K) d (mL / g).

[0034]

[0035]

[0036]

[0037] Where C0 and C e (mg / L) represents the initial and equilibrium concentrations of metallic uranium ions, respectively; V(L) is the volume of the adsorption solution; and m(g) is the dry weight of the adsorbent.

[0038] Characterization

[0039] Fourier transform infrared spectroscopy (FTIR) was used in the wavelength range of 4000-500 cm⁻¹ -1 The surface functional groups of the adsorbent before and after adsorption were determined within a certain range. The specific surface area and pore size of the material were analyzed using BET. The morphology of the samples was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the composition and distribution of the material were observed using energy-dispersive X-ray spectroscopy (EDS) and a mapping analysis system. X-ray photoelectron spectroscopy (XPS) was used to analyze and record scans of the U4f, O1s, N1s, and C1s regions. The stability of the adsorbent in aqueous solution was analyzed using the Zeta potential method, and the selective adsorption performance of uranium was analyzed using inductively coupled plasma atomic emission spectrometry (ICP).

[0040] Experimental results

[0041] 1. Effect of pH value. The initial pH value of the solution has a significant impact on the adsorption of uranium and the surface charge distribution of the adsorbent. Figure 1The effect of pH on the adsorption of uranium by the composite aerogel was demonstrated. As the pH increased from 4.0 to 9.0, the zeta potential of ZIF-8 / CP / CS decreased, reaching its isoelectric point at pH 7.5. ZIF-8 / CP / CS maintained a high adsorption rate for uranium in the pH range of 5.0–7.0, with the maximum adsorption capacity at pH 6. At pH < 4, due to the high protonation of the amino and imidazole groups, the surface charge of ZIF-8 / CP / CS was positive, and U(VI) was mainly adsorbed as UO2. 2+ The uranium exists in the form of precipitates, therefore, there is a strong electrostatic repulsion between them, resulting in low adsorption capacity. As the pH value increases, the functional groups on the adsorbent surface deprotonate, the electrostatic repulsion gradually decreases, and the adsorption rate for uranium gradually increases. When pH ≥ 8.0, the precipitate (UO2)3(OH) forms. 7- and (UO2)2(OH)2 2+ As pH increases, the adsorption rate decreases. However, at pH=9, the adsorption rate can still reach 80%.

[0042] 2. Adsorption Kinetics. Under the condition of an initial uranium concentration of 10 mg / L, the effect of contact time on the adsorption rate of uranium on ZIF-8 / CP / CS was investigated. Figure 2 As shown in part (a), the adsorption of uranium by ZIF-8 / CP / CS is initially rapid and then slows down. The adsorption rate of uranium reaches over 90% within 2 hours, and gradually reaches adsorption equilibrium after 4 hours. This is because at the initial stage of adsorption, there are a large number of free uranyl ions in the solution. At this time, ZIF-8 / CP / CS has abundant adsorption sites, and particle motion enables the adsorbent to quickly capture a large number of uranyl ions. As the contact time increases, the number of uranyl ions and adsorption sites decreases, and the adsorption rate gradually decreases until a dynamic equilibrium is reached.

[0043] This embodiment fitted pseudo-first-order and pseudo-second-order kinetic models of uranium adsorption on ZIF-8 / CP / CS. Table 1 shows the relevant parameters of the models. A high linear regression correlation coefficient (R0) indicates a high kinetic performance. 2 The results and approximate adsorption amounts indicate that the kinetics of uranium adsorption on ZIF-8 / CP / CS can be better described by a pseudo-second-order kinetic model. This implies that U(VI) adsorption is a chemisorption process, occurring through electron transfer between U(VI) and the active groups of the adsorbent. This is consistent with the results regarding the effect of solution pH.

[0044] Table 1 Kinetic parameters of uranium adsorption by ZIF-8 / CP / CS.

[0045]

[0046] 3. Adsorption Thermodynamics. To evaluate the maximum adsorption capacity of the adsorbent, adsorption isotherms were tested in this example. From Figure 2 Parts (b), (c), and (d) clearly show that the adsorption capacity of the adsorbent increases with increasing uranyl ion concentration. The adsorption capacity of ZIF-8 / CP / CS increases with increasing temperature.

[0047] To better reveal the relationship between uranium and materials, the experimental data in this embodiment were fitted using Freundlich, Langmuir, and Sips isotherm models. The relevant isotherm parameters are shown in Table 2. The experimental fitting results show that the correlation coefficient Rs of the Sips model is... 2 The values ​​are greater than those of the Freundlich and Langmuir models, and both are greater than 0.98, indicating that it exhibits monolayer adsorption characteristics at high U(VI) concentrations and multilayer adsorption characteristics at low U(VI) concentrations. The maximum theoretical adsorption capacities of ZIF-8 / CP / CS calculated by the Sips model at 308 K, 298 K, and 288 K are 873 mg / g, 861 mg / g, and 849 mg / g, respectively.

[0048] Table 2 Uranium adsorption isotherm parameters of ZIF-8 / CP / CS

[0049]

[0050] The adsorption thermodynamics of U(VI) on ZIF-8 / CP / CS at different temperatures (298 K, 308 K, and 318 K) was studied, and ΔS0 (J / mol / K), ΔH0 (kJ / mol), and ΔG0 (kJ / mol) were calculated. The relevant parameters are listed in Table 3. A positive ΔH0 indicates that the adsorption is an endothermic process, with high temperatures favoring adsorption, and that chemisorption is predominant, with the adsorption capacity increasing with increasing temperature. A negative ΔG0, which decreases with increasing temperature, indicates that the adsorption of uranium by ZIF-8 / CP / CS is a spontaneous process. A positive ΔS0 reflects the high affinity of ZIF-8 / CP / CS for U(VI), indicating an increase in disorder in the solid / liquid system during adsorption.

[0051] Table 3 Uranium adsorption thermodynamic parameters of ZIF-8 / CP / CS

[0052]

[0053] 4. Influence of Competing Ions. Due to the complex composition of seawater, the presence of coexisting ions significantly affects uranium adsorption. Therefore, studying the selective adsorption of uranium by ZIF-8 / CP / CS is crucial. In this example, adsorption experiments were conducted on ZIF-8 / CP / CS in a simulated seawater solution containing Ca, Mg, Na, Ni, Cu, Fe, U, and V. Figure 3 (a) shows the partition coefficients of different metal ions after adsorption, indicating that ZIF-8 / CP / CS has excellent adsorption selectivity for uranium in simulated seawater. Ni, Cu, and Fe have almost no effect on the adsorption of uranium on ZIF-8 / CP / CS. The adsorbent material preferentially captures cations with higher valence states and smaller radii. V(V) and U(VI) have similar ionic radii, and the competition between uranium and vanadium ions is the main obstacle to uranium extraction from seawater. Figure 3 The results show that the addition of algal powder increased the uranium adsorption rate of ZIF-8 / C by 30% compared to ZIF-8. The addition of chitosan and tannic acid also increased the adsorption rate. Furthermore, the addition of quaternary phosphonium salt ionic liquid improved the selectivity of the adsorbent for uranyl ions. The Kd of ZIF-8 / CP / CS for uranium was 21 times that of vanadium, while that of ZIF-8 / C / CS was 15 times that of vanadium, indicating that the selectivity of ZIF-8 / CP / CS for uranium is significantly superior to that of ZIF-8 / C / CS. Therefore, ZIF-8 / CP / CS has broad application prospects in seawater uranium extraction.

[0054] 5. Cyclic Desorption. This embodiment verifies the recovery performance of ZIF-8 / CP / CS through adsorption and desorption experiments. ZIF-8 / CP / CS adsorbs a uranium solution with a concentration of 10 mg / L under conditions of pH=6 and 25℃. Desorption experiments are conducted at 45℃ using 1.5 mol / L sodium chloride and 1.5 g / L ammonium carbonate as desorption solutions. The adsorption capacity and desorption rate of ZIF-8 / CP / CS for uranium in each cycle are shown in Figure S2. The infrared spectrum of the desorbed material is shown in Figure S2. Figure 3 As shown in (b), after three cycles of desorption, the infrared spectrum of ZIF-8 / CP / CS showed no obvious uranium peaks, and the infrared spectrum was similar to that before adsorption, indicating that the composition of ZIF-8 / CP / CS was not significantly damaged. After the first desorption, nearly 80% of the uranium was eluted from ZIF-8 / CP / CS. After three cycles of adsorption and desorption, the adsorption rate of ZIF-8 / CP / CS for uranium remained above 80%, and its desorption rate was still 90%. ZIF-8 / CP / CS can still maintain stable adsorption capacity, indicating its reusability.

[0055] 6. Real Seawater. To further explore the practical application effect of ZIF-8 / CP / CS, this embodiment conducted an adsorption experiment using real seawater sourced from the Bohai Sea coast of Liaoning Province. 1 L of seawater was adsorbed with 10 mg of ZIF-8 / CP / CS at 25℃. After adsorption, the ZIF-8 / CP / CS was digested, and the adsorbed uranium and vanadium content in the material was tested using ICP. The test results showed that the adsorption capacity of ZIF-8 / CP / CS for uranium was 114.2 mg / kg, and the adsorption capacity for vanadium was 72 mg / kg. This indicates that ZIF-8 / CP / CS has high selectivity for uranium. Furthermore, this embodiment also investigated the adsorption effect of ZIF-8 / CP / CS on uranium in actual wastewater. The tailings pond wastewater is characterized by low uranium concentration and large volume. The wastewater has a pH of 6 and a uranium concentration of 1.17 mg / L. After 12 h of adsorption, the uranium content in the wastewater decreased to 40 μg / L. The uranium removal rate of ZIF-8 / CP / CS reached 96%, which meets the limit requirement of uranium concentration in wastewater discharge (≤50 μg / L) in the "Regulations on Radiation Protection and Environmental Protection in Uranium Mining and Metallurgy". This indicates that ZIF-8 / CP / CS has good application prospects in the treatment of uranium tailings wastewater.

[0056] 7. Adsorption Mechanism. Pump pressure analysis results show that the specific surface area of ​​ZIF-8 / CP / CS is 3.645 m². 2 / g, with an average pore size of 57.210 nm. For example... Figure 4 As shown in (a), 4(b), and 4(c), the adsorbed UO2 was detected by SEM and EDS. 2+ The surface morphology and elemental distribution of ZIF-8 / CP / CS after adsorption. After adsorption of U(VI), the morphology of the adsorbent did not change significantly and remained a plate-like structure. A white deposit was formed on the surface of the adsorbent after adsorption. Figure 4 (d) and (e) are TEM images of ZIF-8 and ZIF-8 / CP / CS, respectively.

[0057] After scanning the SEM area, a mapping image of the material surface is obtained, which is... Figure 5 It can be seen that uranyl ions are uniformly distributed in the two-dimensional space of the scanning region, and this distribution is related to elements such as C, N, O, and P in the adsorbent. This confirms the successful adsorption of U(VI) by ZIF-8 / CP / CS.

[0058] In addition, thermogravimetric analysis was used in this embodiment to evaluate the thermal stability of ZIF-8 / CP / CS. The results are as follows: Figure 6As shown in (b). The experimental results indicate that the initial weight loss of ZIF-8 / CP / CS occurs between 30°C and 200°C. This stage is likely due to the evaporation or removal of any volatile components present in the sample. These may include water or other small molecules that are easily evaporated at low temperatures. The relatively small weight loss indicates that ZIF-8 / CP / CS has good hydrophilicity. Subsequently, a greater weight loss was observed between 250°C and 350°C compared to the initial stage, which may be due to the loss of functional groups such as amino, hydroxyl, and carbonyl groups in the biomaterial. The third stage occurs between 400°C and 700°C, with a weight loss of only 15.33%, which may correspond to the further decomposition of smaller units generated in the previous stage. The final stage occurs between 700°C and 800°C, with a relatively small weight loss compared to the previous stages, which corresponds to the combustion of any remaining organic matter in the sample.

[0059] The FTIR spectra of ZIF-8, ZIF-8 / C, ZIF-8 / CP, and ZIF-8 / CP / CS are as follows: Figure 6 As shown in (a), the peak values ​​mainly appear at 2923, 2854, 1658, 1566, 1422, 1311, 1149, 995, and 757 cm⁻¹. -1 3140 cm -1 and 2923 cm -1 The absorption peaks at 1566 cm⁻¹ belong to the stretching vibrations of the C-H bonds in the methyl and imidazole rings, respectively. -1 and 1149 cm -1 The characteristic absorption peak at 1422 cm⁻¹ is attributed to the tensile vibrations of C═N and C─N. Furthermore, at 1422 cm⁻¹... -1 The peak observed at 757 cm⁻¹ was assigned to the tensile vibration peak of C═N─H in imidazole. -1 The peak at 421 cm is attributed to out-of-plane bending motion, while the peak at 421 cm is attributed to out-of-plane bending motion. -1 The bands discovered are related to Zn-N stretching vibrations. Compared to ZIF-8, the addition of algal powder resulted in the appearance of protein characteristic peaks, with ZIF-8 / C at 1658 cm⁻¹. -1 The infrared spectrum shows a stretching vibration peak of C-O bond and a bending peak of N-H bond for amide I, and a stretching vibration peak of C-N bond for amide II. Compared with the infrared spectrum of ZIF-8 / C, the infrared spectrum of ZIF-8 / CP shows a peak at 2854 cm⁻¹. -1 The newly added band is caused by the stretching vibration of the C-H bond, and it is located at 1216 cm⁻¹. -1The appearance of a peak representing the P═O tensile vibration indicates that the quaternary phosphonium salt ionic liquid is effectively immobilized on ZIF-8 / C to form ZIF-8 / CP. After crosslinking and curing ZIF-8 / CP with chitosan and tannic acid, ZIF-8 / CP / CP retains undamaged -OH and -NH2 active groups, making this material suitable for uranium ion adsorption. Figure 3 (b) ZIF-8 / CP / CP-U at 900cm -1 A new O-U-O peak appeared, confirming the adsorption of uranium by the ZIF-8 / CP / CP-U composite material.

[0060] The mechanism of uranyl ion adsorption was further revealed through chemical analysis and XPS comparison of ZIF-8 / CP / CS before and after adsorption. Figure 7 The C1s spectra before and after adsorption are shown. Figure 7 (a) It can be seen that the binding energies are 284.63 eV, 286.09 eV, and 288.09 eV, respectively. These peaks are caused by the C─C, C═O, and C═N structures in ZIF-8 / CP / CS, revealing the existence forms of carbon and oxygen atoms in ZIF-8 / CP / CS. After the adsorption of uranyl ions, the C peaks all shift to the direction with higher binding energies, indicating that these functional groups participate in the adsorption of uranium. Figure 8 In (a), the O1s spectrum at 532.42 eV and 530.94 eV represents -OH and P═O, respectively. After adsorption, a new peak appears at 533.18 eV, which is attributed to the formation of O═U═O bonds due to uranium adsorption in the material. Figure 8 In the P2p spectrum of (b), the peak at 132.31 eV represents the P═O peak, confirming that the quaternary phosphonium salt ionic liquid was successfully immobilized on the material. After U adsorption, the intensity of the P═O peak weakened and shifted to 132.81 eV, indicating that the phosphate group participated in the U complexation. Figure 8 (c) shows the N1s spectrum. Before adsorption, the binding energies of the N peaks are 399.00 eV and 400.12 eV, representing C─N and C═N, respectively. These two peaks mainly originate from the imidazole ring of ZIF-8. After adsorption, the two peaks are clearly seen appearing at higher binding energies, indicating that the nitrogen atom has undergone a complexation reaction with the uranyl ion. Compared with before adsorption, in Figure 8 In (i), two characteristic peaks of the U4f uranium ion can be clearly seen, namely U4f... 7 / 2 (392.79 eV) and U4f 5 / 2 The peaks (381.72 eV) and splitting degree (~11.07 eV) indicate that uranyl ions are effectively adsorbed by ZIF-8 / CP / CS, and that there are covalent bonds between the functional groups and uranium. The results show that the ZIF-8 / CP / CS surface contains a large number of hydroxyl, amino, carbon-nitrogen double bonds, and phosphate groups, which are beneficial for uranium removal.

[0061] The above experiments demonstrate that the ZIF-8 algae powder-based composite aerogel prepared in this invention exhibits high adsorption selectivity and capacity for uranium, and strong adsorption effect on uranyl ions over a wide pH range (pH 4-8). The maximum adsorption capacity of ZIF-8 / CP / CS at pH 6.0 and 308 K is 873 mg / g. Dynamic and isotherm experiments show that the adsorption process is mainly chemisorption, exhibiting monolayer adsorption characteristics at high U(VI) concentrations and multilayer adsorption characteristics at low U(VI) concentrations. Thermodynamic parameters reveal the spontaneous endothermic properties of ZIF-8 / CP / CS. Mechanistic analysis indicates that the hydroxyl, amino, and P=O bonds on the surface of ZIF-8 / CP / CS, as well as the C=N bonds in ZIF-8, play a key role in uranium adsorption. Competitive adsorption experiments showed that the partition coefficient of ZIF-8 / CP / CS for uranium was significantly higher than that for vanadium and other metal ions. When adsorbed onto real seawater, the adsorption capacity for uranium was 114.2 mg / kg. When used to treat wastewater from a low-concentration uranium tailings pond, the uranium concentration was reduced to 40 μg / L. This indicates that ZIF-8 / CP / CS has broad application prospects in uranium extraction from seawater and in the treatment and recovery of low-concentration uranium-containing wastewater.

[0062] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified. The above embodiments are preferred implementations of this invention. In addition, this invention can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this invention.

Claims

1. A method for preparing ZIF-8 / algae powder-based composite aerogel, characterized in that, Includes the following steps: (1) Preparation of ZIF-8 / algae powder: Add the protein core Chlorella powder to the zinc nitrate hexahydrate solution, then add 2-methylimidazole solution, stir the reaction at room temperature, centrifuge to obtain the precipitate, and then wash and dry to obtain ZIF-8 / algae powder; (2) Preparation of ZIF-8 / algae powder supported quaternary phosphonium salt ionic liquid: Trihexyl (tetradecyl)phosphonium chloride was dissolved in methanol to prepare an ionic liquid of a certain concentration. ZIF-8 / algae powder was added to the ionic liquid and stirred until the solution just covered ZIF-8 / algae powder. The solution was allowed to stand at room temperature and dried to obtain ZIF-8 / algae powder supported quaternary phosphonium salt ionic liquid. (3) Preparation of ZIF-8 / algae powder-based composite aerogel: Add deionized water to a beaker containing myricetin and stir to dissolve it completely. Then add an appropriate amount of chitosan, ZIF-8 / algae powder-supported quaternary phosphonium salt ionic liquid and an appropriate amount of glacial acetic acid. Continue stirring until the chitosan is completely dissolved. Then add glutaraldehyde solution and shake in a constant temperature shaker until the sol ages. Then freeze dry to obtain ZIF-8 / algae powder-based composite aerogel.

2. The preparation method of ZIF-8 / algae powder-based composite aerogel according to claim 1, characterized in that: In step (1), the washing and drying methods are as follows: wash three times with ethanol and deionized water, and dry at 80°C for 12 h.

3. The preparation method of ZIF-8 / algae powder-based composite aerogel according to claim 1, characterized in that: In step (2), the concentration of the ionic liquid is 5%.

4. The preparation method of ZIF-8 / algae powder-based composite aerogel according to claim 1, characterized in that: In step (2), the method of standing and drying at room temperature is as follows: stand at room temperature for 10 h, and then dry in an oven at 80℃ for 12 h.

5. The preparation method of ZIF-8 / algae powder-based composite aerogel according to claim 1, characterized in that: In step (3), the concentration of the glutaraldehyde solution is 0.1%.

6. The preparation method of ZIF-8 / algae powder-based composite aerogel according to claim 1, characterized in that: In step (3), the sol is shaken in a constant temperature shaking box at 150 r / min and 45℃ for 24 hours until it ages, and then freeze-dried for 48 hours.

7. A ZIF-8 / algae powder-based composite aerogel, characterized in that: The ZIF-8 / algae powder-based composite aerogel was prepared using the preparation method described in any one of claims 1-6.

8. An application of the ZIF-8 / algae powder-based composite aerogel according to claim 7, characterized in that: Used for extracting uranium from seawater and recovering uranium from uranium tailings wastewater.

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