A method for preparing underwater adhesive porous hydrogel adsorbent based on liquid-gas droplet reactor

Abstract

The present invention belongs to the technical field of preparation of functional materials for adsorption and separation, and discloses a method for preparing underwater adhesive porous hydrogel uranium extraction adsorbent based on a liquid-gas droplet reactor. Using amidoxime functional groups as selective ligands, and poly(N-isopropylacrylamide-co-acrylic acid) microgel P(NIPAM-co-AAc)-HEMA functionalized with hydroxyethyl methacrylate (HEMA) as a polymer matrix and surfactant, an amidoxime-functionalized porous hydrogel-based adsorbent PAOmgel with underwater adhesion properties was prepared by treatment with a dopamine solution. The present invention achieves efficient and selective extraction of uranyl ions by introducing polyamidooxime functional units. The use of a Pickering liquid-gas droplet reactor provides a clean and effective method for the controllable preparation of porous structures, utilizes the water absorption and porosity of the hydrogel to accelerate the mass transfer kinetics of the adsorbent, and the underwater adhesion characteristics simplify the adsorbent recovery process, solving the problem of difficult recovery of uranium extraction adsorbents.

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 an underwater adhesive porous hydrogel adsorbent based on a liquid-gas droplet reactor, and in particular to a method for preparing an amidoxime-functionalized porous hydrogel adsorbent with underwater adhesion properties using a Pickering liquid-gas droplet reactor, and the use of the method for extracting uranium. Background Art

[0002] Uranium's radiotoxicity, chemical toxicity, and widespread presence in the natural environment pose serious risks to the ecological environment and human health. More importantly, extracting uranium from seawater is more environmentally friendly than extracting it from uranium ore. Therefore, extracting uranium from seawater is of great significance to the future development of nuclear energy.

[0003] However, due to the low concentration of uranium in seawater (approximately 3.3 ppb), competition from a large number of coexisting ions, and the complexity of the environment, extracting uranium from seawater remains a huge challenge. To date, a variety of technologies have been used to extract uranium, including adsorption, ion exchange, photocatalytic reduction, electrocatalytic reduction, membrane filtration, and microbial remediation. Given the need to process large amounts of water samples, adsorption has become the most promising method for extracting uranium from seawater due to its low cost, simple operation, high efficiency, no or minimal secondary pollution, and ease of multifunctionalization and regeneration. However, most of the materials currently developed for effective uranium extraction from seawater are in powder form, which is difficult to fix and recover, hindering their application in the ocean. Therefore, it is necessary to design and manufacture adsorbents with good adsorption selectivity, high adsorption capacity, and high mechanical strength.

[0004] Amidoxime (AO)-functionalized hydrogel adsorbents are considered the most promising for extracting uranium from seawater because their three-dimensional hydrophilic networks can not only disperse and anchor large amounts of amidoxime-functionalized polymers but also provide hydrophilic channels to accelerate adsorption. However, these hydrogels often have weak mechanical strength due to their simple network structure, making them unable to withstand the harsh marine environment for a long time. Furthermore, they lack the traditional controllable porous structure and are difficult to recycle, limiting their adsorption and recovery efficiency for uranyl ions. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to overcome the problems of existing hydrogel preparation, such as the difficulty in balancing porosity and mechanical properties, the difficulty in controlling and adjusting the pore structure, and the difficulty in recycling in practical applications. The present invention provides a method for preparing an amidoxime-functionalized porous hydrogel adsorbent with underwater adhesion properties based on a Pickering liquid-gas-liquid droplet reactor. Using amidoxime functional groups as selective ligands, and hydroxyethyl methacrylate (HEMA)-functionalized poly(N-isopropylacrylamide-co-acrylic acid) microgels (P(NIPAM-co-AAc)-HEMA) as the polymer matrix and surfactant, an amidoxime-functionalized porous hydrogel-based adsorbent (PAOmgel) with underwater adhesion properties was prepared by treating the hydrogel with a dopamine solution.

[0006] In order to achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0007] (1) Preparation of polyacrylamidoxime PAO:

[0008] NH2OH·HCl is added to N,N-methyleneformamide, and the mixture is heated in a water bath to a reaction temperature T1 for a reaction time t1. Na2CO3 and NaOH are then added under stirring, and the resulting mixed solution is stirred for a reaction time t2. Polyacrylonitrile PAN is then added under continuous stirring, and after complete dissolution, the mixture is heated to a reaction temperature T2 and the reaction time t3 is continued. Na2CO3 and NaOH are again added, and the reaction time t4 is continued. The supernatant is collected by centrifugation until no precipitation is produced, and the supernatant is dropped into pure water to collect the produced flocs, which are then freeze-dried to obtain polyacrylonitrile oxime (PAO).

[0009] (2) Preparation of HEMA functionalized poly (N-isopropylacrylamide-co-acrylic acid) microgel P (NIPAM-co-AAc)-HEMA microgel:

[0010] First, N-isopropylacrylamide (NIPAM), acrylic acid (AAc), N,N'-dimethylformamide (BIS), and sodium dodecylsulfonate (SDS) were dissolved in deionized water; excess nitrogen was introduced to remove oxygen; the reaction solution was refluxed under nitrogen protection to a reaction temperature (T3) and continued for a reaction time (t5); then, an aqueous solution of potassium persulfate (KPS) was added to initiate the reaction; after a reaction time (t6), the resulting microgel nanoparticles (P(NIPAM-co-AAc)) were dialyzed against deionized water for a purification time (t7);

[0011] The purified P(NIPAM-co-AAc) dispersion was added with HEMA and EDC, and the reaction was stirred at temperature T4 for time t8. The resulting product was dialyzed with deionized water for time t9 and lyophilized to obtain HEMA-functionalized P(NIPAM-co-AAc) microgels, which were designated as P(NIPAM-co-AAc)-HEMA microgels.

[0012] (3) Preparation of polyamidooxime functionalized underwater adhesive porous hydrogel:

[0013] P(NIPAM-co-AAc)-HEMA microgel was dispersed in NaOH solution of PAO, and photoinitiator Irgacure 1173 was added and stirred for t 10 A water-in-gas Pickering high internal phase liquid-gas droplet reactor is formed, and then the polymerization is initiated by ultraviolet light for a time t 11 Prepare PAO functionalized porous hydrogel, then soak in dopamine DA solution for time t 12 After freeze-drying, amidoxime-functionalized porous hydrogel with underwater adhesion properties was obtained, which was named PAOmgel.

[0014] Preferably, in step (1), the ratio of the total amount of NH2OH·HCl, N,N-methyleneformamide, Na2CO3, the total amount of NaOH and polyacrylonitrile is 50-70 mmol: 35-55 mL: 35-45 mmol: 20-40 mmol: 50-70 mmol;

[0015] The reaction temperature T1 is 30-50°C, and the reaction time t1 is 20-60min;

[0016] The reaction time t2 under stirring is 2.0-4.0h;

[0017] The reaction temperature T2 is 60-85°C, and the reaction time t3 is 12-36h;

[0018] Reaction time t4 is 12-36h;

[0019] The stirring speed is 600-1200 rpm, and the centrifugal speed is 10000-15000 rpm.

[0020] Preferably, in step (2), the amount ratio of NIPAM, AAc, BIS, SDS and deionized water is 1.2-1.6 g: 0.05-0.15 g: 0.01-0.05 g: 0.04-0.08 g: 80-120 mL; the reaction temperature T3 is 50-90 ° C, and the reaction time t5 is 0.5-1.5 h;

[0021] The dosage ratio of NIPAM and KPS is 1.2-1.6 g:0.06-0.1 g; the reaction time t6 is 2.0-6.0 h; the dialysis time t7 is 1-3 weeks, and the water is changed 2-4 times per day;

[0022] The usage ratio of the purified P(NIPAM-co-AAc) dispersion, HEMA and EDC is 30-70 mL: 1.6-2.0 g: 2.2-2.6 g; the temperature T4 is 20-30°C, the reaction time t8 is 2.0-6.0 h, the dialysis time t9 is 5-9 days, and the water is changed 2-4 times a day.

[0023] Preferably, in step (3), the ratio of P(NIPAM-co-AAc)-HEMA microgel, NaOH solution of PAO and initiator Irgacure 1173 is 50-150 mg: 0.5-1.5 mL: 5.0-15 μL,

[0024] Wherein, in the NaOH solution of PAO, the concentration of PAO is 20-40 mg / mL, and the concentration of the NaOH solution is 0.5-1.5 M;

[0025] The stirring speed is 12000-18000rpm, and the stirring time t 10 0.5-1.5min;

[0026] The wavelength of ultraviolet light is 360-400nm, the power is 10-20W, and the polymerization time is t 11 0.5-1.5h;

[0027] The concentration of dopamine DA solution is 0.5-1.5M; the soaking time t 12 0.5-1.5h.

[0028] The amidoxime-functionalized porous hydrogel adsorbent with underwater adhesion properties prepared based on a liquid-gas-liquid droplet reactor of the present invention is used for the selective extraction of uranyl ions in water.

[0029] Beneficial effects of the present invention:

[0030] (1) The present invention selects polyacrylamide oxime as the functional unit for selective extraction of uranyl ions, uses porous hydrogel as the substrate, and dopamine as the adhesion unit. The amidoxime-functionalized porous adsorbent PAOmgel with underwater adhesion properties is prepared using a Pickering liquid-gas droplet reactor, thereby achieving specific adsorption of uranyl ions.

[0031] (2) The present invention prepares a porous hydrogel with underwater adhesion properties and rich in amidoxime functional groups through a Pickering liquid-gas droplet reactor, and uses it for uranium extraction from seawater. The research results show that the mass transfer kinetics of the hydrogel-based uranium extraction adsorbent is improved, the problem of difficult recovery of the uranium extraction adsorbent is solved, the preparation process of the adsorbent is simplified, and the adsorption capacity of the adsorbent is enhanced. The P(NIPAM-co-AAc)-HEMA microgel particles are not only used as a polymer matrix, but also as a Pickering surfactant to stabilize the liquid-gas interface, avoiding the use of molecular surfactants and reducing the pollution caused by the material preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 IR spectra of PAN and PAO in Example 1.

[0033] Figure 2 a and b are the H NMR spectra of P(NIPAM-co-AAc) microgel and P(NIPAM-co-AAc)-HEMA microgel in Example 1, respectively.

[0034] c and d are the water contact angles of P(NIPAM-co-AAc) microgels and P(NIPAM-co-AAc)-HEMA microgels, respectively.

[0035] Figure 3 Figure a is an optical microscope image of the liquid-gas droplet reactor prepared in step (3) of Example 1, and figure b is a SEM image of the prepared PAOmgel hydrogel.

[0036] Figure 4 a is the Fourier transform infrared spectra of P(NIPAM-co-AAc) microgel, P(NIPAM-co-AAc)-HEMA microgel and PAOmgel prepared in Example 1,

[0037] b is the XPS spectrum of PAOmgel prepared in Example 1 and its C1s, N 1s and O1s high-resolution spectra.

[0038] Figure 5 Figure a is the tensile stress-strain curves of the PAOmgel prepared in Example 1 and the comparative material PNAHmgel, and figure b is the underwater adhesion property test results of the PAOmgel prepared in Example 1.

[0039] Figure 6In the figure, a is the effect of pH on the adsorption of uranyl ions by the PAOmgel hydrogel prepared in Example 1, b is the adsorption kinetics of uranyl ions by the PAOmgel hydrogel prepared in Example 1 and its model fitting curve, and c is the effect of temperature on the adsorption equilibrium of uranyl ions by the PAOmgel hydrogel prepared in Example 1 and its model fitting curve.

[0040] Figure 7 Where a is the adsorption selectivity of the PAOmgel hydrogel adsorbent prepared in Example 1, and b is the adsorption regeneration of the PAOmgel hydrogel adsorbent prepared in Example 1 for uranyl ions. DETAILED DESCRIPTION

[0041] In the specific implementation of the present invention, the recognition performance evaluation is performed according to the following method:

[0042] The static adsorption experiment was completed. The adsorption capacity of uranyl ions on 5.0 mg of PAOmgel was tested in the pH range of 3.0-9.0. The uranyl ion content after adsorption was measured using inductively coupled plasma emission spectrometry, and the optimal adsorption pH was determined based on the results. The effect of adsorption time on the adsorption capacity of PAOmgel was then studied. The data were fitted, calculated, and analyzed using both the pseudofirst-order model and the pseudosecond-order model.

[0043] To investigate the maximum adsorption capacity of PAOmgel, we conducted adsorption equilibrium experiments with 5.0 mg of PAOmgel in 50 mL of uranyl ion solution at uranyl ion concentrations ranging from 10 to 80 mg / L. We fitted the adsorption data using the Langmuir model and the Freundlich model, and calculated the adsorption capacity based on the results. We also prepared a simulated seawater solution to study the selective adsorption performance of PAOmgel. Finally, we tested its adsorption regeneration performance.

[0044] The present invention will be further described below with reference to specific implementation examples.

[0045] Example 1:

[0046] (1) Preparation of polyacrylamidoxime PAO:

[0047] In a flask, 60 mmol of NH2OH·HCl was added to 45 mL of N,N-methyleneformamide, and the mixture was heated to 45°C in a water bath for 30 minutes. Then, 27 mmol of Na2CO3 and 18 mmol of NaOH were added under vigorous stirring. The resulting mixed solution was then stirred at 1000 rpm for 3.0 hours. 60 mmol of PAN was then added, and after complete dissolution, the temperature was raised to 65°C and the reaction was continued for 24 hours. 13.5 mmol of Na2CO3 and 9.0 mmol of NaOH were added again, and the reaction was continued for 24 hours. The supernatant was collected by centrifugation at 13000 rpm until no precipitation was produced. The supernatant was dropped into pure water to collect the produced flocs, which were freeze-dried to obtain polyacrylamidoxime (PAO).

[0048] (2) Preparation of HEMA functionalized poly (N-isopropylacrylamide-co-acrylic acid) microgel P (NIPAM-co-AAc)-HEMA microgel:

[0049] 1.400 g NIPAM, 0.101 g AAc, 0.032 g BIS, and 0.058 g SDS were dissolved in 100 mL deionized water and then transferred to a three-necked round-bottom flask equipped with a condenser reflux apparatus and a nitrogen inlet tube. Excess nitrogen was introduced to remove oxygen from the solvent. The reaction solution was heated to 70°C under nitrogen protection and continued to react for 1.0 h. Then, 2.0 mL of an aqueous solution of 0.081 g KPS was added to initiate the reaction. After reacting for 4.0 h, the obtained microgel nanoparticles P(NIPAM-co-AAc) were dialyzed against deionized water for two weeks, with the water changed three times a day.

[0050] Take 50 mL of the purified P(NIPAM-co-AAc) dispersion, add 1.820 g HEMA and 2.390 g EDC, and continue stirring at 25°C for 4.0 h. The obtained product is dialyzed with deionized water for one week, changing the water three times a day. After freeze-drying, HEMA-functionalized P(NIPAM-co-AAc) microgels are obtained, which are recorded as P(NIPAM-co-AAc)-HEMA microgels.

[0051] (3) Preparation of polyamidooxime functionalized underwater adhesive porous hydrogel:

[0052] 100 mg of P(NIPAM-co-AAc)-HEMA microgel was dispersed in 1.0 mL of PAO NaOH solution (PAO concentration was 30 mg / mL, and the concentration of NaOH solution was 1.0 M). 10 μL of photoinitiator Irgacure 1173 was added, and the mixture was stirred at 16,000 rpm for 1.0 min to form a water-in-air Pickering liquid-gas-liquid droplet reactor. The resulting mixture was then irradiated with UV light for 1.0 h to initiate polymerization to prepare a PAO-functionalized porous hydrogel. The hydrogel was then soaked in a 1.0 M DA solution for 1.0 h and freeze-dried to obtain an amidoxime-functionalized porous hydrogel with underwater adhesion properties, which was designated as PAOmgel.

[0053] As a comparative material, the hydrogel material prepared without adding PAO was labeled as PNAHmgel.

[0054] Figure 1 The infrared spectra of PAN and PAO in Example 1 are shown. Compared with the infrared absorption spectrum of PAN, it can be found that the characteristic peak of C≡N in the infrared spectrum of PAO disappears, and the characteristic absorption peaks of the amidoxime functional group (the stretching vibration peak of C=N and the stretching vibration absorption peak of NO) are newly added, indicating that PAN is completely converted into PAO.

[0055] Figure 2 Figures a and b are the H NMR spectra of P(NIPAM-co-AAc) microgel and P(NIPAM-co-AAc)-HEMA microgel in Example 1, respectively. 1 Compared with the H NMR spectra, the P(NIPAM-co-AAc)-HEMA microgels 1 The H NMR spectrum showed new peaks at 6.09 ppm and 5.64 ppm, which were attributed to the hydrogen atoms in the methyl and vinyl groups in HEMA, indicating that the vinyl groups were successfully introduced. The new peaks at 4.20 ppm (-O-CH2-CH2-O-) and 1.86 ppm (-CH3) further confirmed the successful modification of P(NIPAM-co-AAc) microgels by HEMA.

[0056] Figures c and d are the water contact angles of P(NIPAM-co-AAc) microgel and P(NIPAM-co-AAc)-HEMA microgel, respectively. The results show that the water contact angle of the microgel increases after HEMA functionalization. This is because the modification of HEMA introduces more hydrophobic groups (such as C=C) on the surface of the microgel, which also indirectly indicates the successful modification of HEMA.

[0057] from Figure 3 We can find that the liquid-gas droplet reactor prepared under this condition can exist stably, and Figure 3 As shown in b, the prepared polymer is an open-pore porous polymer.

[0058] Figure 4 Figure a is the infrared spectra of P(NIPAM-co-AAc) microgel, P(NIPAM-co-AAc)-HEMA microgel and PAOmgel prepared in Example 1. Compared with the infrared spectrum of P(NIPAM-co-AAc) microgel, the infrared spectrum of P(NIPAM-co-AAc)-HEMA microgel has a new characteristic absorption peak of C=C, indicating the successful modification of HEMA. 1 The results of HNMR tests were consistent. In addition, the infrared spectrum of the hydrogel prepared by adding PAO added a new characteristic absorption peak of NO;

[0059] Figure 4 Figure b is the XPS spectrum of PAOmgel prepared in Example 1 and its C1s, N 1s and O 1s high-resolution spectra, which mainly contain three signal peaks: C1s (284eV), N 1s (398eV) and O1s (530eV). The high-resolution XPS spectrum of C1s can be divided into CC / C=C, CO, C=O and CN / C=N quartet, the high-resolution XPS spectrum of N1s can be divided into C(NH2)=N-OH and -NH- / -N= doublet, and the high-resolution XPS spectrum of O1s can be divided into C(NH2)=N-OH and COOH doublet. The above results prove the successful preparation of PAOmgel.

[0060] Figure 5 The results show that the tensile strength of PAOmgel is stronger than that of PNAHmgel, indicating that the tensile strength of the hydrogel is enhanced due to the entanglement between the chains after the introduction of PAO, and PAOmgel has underwater adhesion, such as Figure 5 b.

[0061] Example 2:

[0062] (1) Preparation of polyacrylamidoxime PAO:

[0063] In a flask, 50 mmol of NH2OH·HCl was added to 35 mL of N,N-methyleneformamide, and the mixture was heated to 30°C in a water bath for 20 minutes. Then, 20 mmol of Na2CO3 and 10 mmol of NaOH were added under vigorous stirring, and the resulting mixed solution was reacted under mechanical stirring at 800 rpm for 2.0 hours. Under continuous stirring, 50 mmol of PAN was added, and after complete dissolution, the temperature was raised to 60°C and the reaction was continued for 12 hours. 15 mmol of Na2CO3 and 10 mmol of NaOH were added again, and the reaction was continued for 12 hours. The supernatant was collected by centrifugation at 10,000 rpm until no precipitation was produced. The supernatant was dropped into pure water to collect the produced flocs, and freeze-dried to obtain polyacrylamide oxime (PAO).

[0064] (2) Preparation of HEMA functionalized poly (N-isopropylacrylamide-co-acrylic acid) microgel P (NIPAM-co-AAc)-HEMA microgel:

[0065] 1.200 g NIPAM, 0.05 g AAc, 0.01 g BIS, and 0.04 g SDS were dissolved in 80 mL deionized water and then transferred to a three-necked round-bottom flask equipped with a condenser reflux apparatus and a nitrogen inlet tube. Excess nitrogen was introduced to remove oxygen from the solvent. The reaction solution was heated to 50°C under nitrogen protection and continued to react for 0.5 h. Then, 1.0 mL of an aqueous solution of 0.06 g KPS was added to initiate the reaction. After reacting for 2.0 h, the obtained microgel nanoparticles P(NIPAM-co-AAc) were dialyzed against deionized water for one week, with the water changed twice a day.

[0066] Take 30 mL of the purified P(NIPAM-co-AAc) dispersion, add 1.6 g HEMA and 2.2 g EDC, and react with continuous stirring at 20°C for 2.0 h. The obtained product is dialyzed against deionized water for 5 days, with the water changed twice a day. After freeze-drying, HEMA-functionalized P(NIPAM-co-AAc) microgels are obtained, which are recorded as P(NIPAM-co-AAc)-HEMA microgels.

[0067] (3) Preparation of polyamidooxime functionalized underwater adhesive porous hydrogel:

[0068] 50 mg of P(NIPAM-co-AAc)-HEMA microgel was dispersed in 0.5 mL of PAO NaOH solution (PAO concentration was 20 mg / mL, and the concentration of NaOH solution was 0.5 M), and 5.0 μL of photoinitiator Irgacure 1173 was added. The mixture was stirred at 12000 rpm for 0.5 min to form a water-in-air Pickering liquid-gas droplet reactor. The PAO-functionalized porous hydrogel was then prepared by ultraviolet light-initiated polymerization for 0.5 h. The microgel was then soaked in 0.5 M DA solution for 0.5 h and freeze-dried to obtain an amidoxime-functionalized porous hydrogel with underwater adhesion properties, which was recorded as PAOmgel.

[0069] Example 3:

[0070] (1) Preparation of polyacrylamidoxime PAO:

[0071] In a flask, 70 mmol NH2OH·HCl was added to 55 mL N,N-methyleneformamide, and the mixture was heated to 50°C in a water bath for 40 min. Then, 30 mmol Na2CO3 and 25 mmol NaOH were added under vigorous stirring, and the resulting mixed solution was reacted under mechanical stirring at 1200 rpm for 4.0 h. Under continuous stirring, 70 mmol PAN was added, and after complete dissolution, the temperature was raised to 85°C and the reaction was continued for 36 h. 15 mmol Na2CO3 and 15 mmol NaOH were added again, and the reaction was continued for 36 h. The supernatant was collected by centrifugation at 15000 rpm until no precipitate was produced. The supernatant was dropped into pure water to collect the produced flocs, and freeze-dried to obtain polyacrylamide oxime (PAO).

[0072] (2) Preparation of HEMA functionalized poly (N-isopropylacrylamide-co-acrylic acid) microgel P (NIPAM-co-AAc)-HEMA microgel:

[0073] 1.600 g NIPAM, 0.15 g AAc, 0.05 g BIS, and 0.08 g SDS were dissolved in 120 mL deionized water and then transferred to a three-necked round-bottom flask equipped with a condenser reflux apparatus and a nitrogen inlet tube. Excess nitrogen was introduced to remove oxygen from the solvent. The reaction solution was heated to 90°C under nitrogen protection and continued to react for 1.5 h. Then, 3.0 mL of an aqueous solution of 0.1 g KPS was added to initiate the reaction. After 6.0 h of reaction, the obtained microgel nanoparticles P(NIPAM-co-AAc) were dialyzed against deionized water for three weeks, with the water changed four times a day.

[0074] Take 70 mL of the purified P(NIPAM-co-AAc) dispersion, add 2.0 g HEMA and 2.6 g EDC, and react with continuous stirring at 30°C for 6.0 h. The obtained product is dialyzed with deionized water for 9 days, with the water changed four times a day. After freeze-drying, HEMA-functionalized P(NIPAM-co-AAc) microgels are obtained, which are recorded as P(NIPAM-co-AAc)-HEMA microgels.

[0075] (3) Preparation of polyamidooxime functionalized underwater adhesive porous hydrogel:

[0076] 150 mg of P(NIPAM-co-AAc)-HEMA microgel was dispersed in 1.5 mL of PAO NaOH solution (PAO concentration was 40 mg / mL, and the concentration of NaOH solution was 1.5 M). 15 μL of photoinitiator Irgacure 1173 was added, and the mixture was stirred at 18,000 rpm for 1.5 min to form a water-in-air Pickering liquid-gas-liquid droplet reactor. The resulting mixture was then irradiated with UV light for 1.5 h to initiate polymerization to prepare a PAO-functionalized porous hydrogel. The hydrogel was then soaked in a 1.5 M DA solution for 1.5 h and freeze-dried to obtain an amidoxime-functionalized porous hydrogel with underwater adhesion properties, which was designated as PAOmgel.

[0077] Performance testing:

[0078] (1) The environmental pH value has a huge impact on the adsorption behavior of metal ions. First, the effect of PAOmgel on the adsorption capacity of uranyl ions in the pH range of 3.0-9.0 was studied.

[0079] like Figure 6 As shown in a, when the pH value is not higher than 6.0, the adsorption capacity of PAOmgel shows a gradual upward trend with the increase of pH value. After the pH value is higher than 6.0, its adsorption capacity decreases with the increase of pH value. When the pH is 6.0, the adsorption capacity of PAOmgel is the largest, which is 47.84 mg / g.

[0080] The adsorption kinetics of uranyl ions on PAOmgel are as follows: Figure 6 As shown in b, the adsorption capacity of PAOmgel increased rapidly in the first 30 minutes and gradually reached a maximum adsorption capacity of 49.43 mg / g. The data were fitted and analyzed using the Pseudo first-order model and the Pseudo second-order model.

[0081] (2) To study the maximum adsorption capacity of PAOmgel, we conducted adsorption equilibrium experiments in the uranyl ion concentration range of 10-80 mg / L, fitted the adsorption data using the Langmuir model and the Freundlich model, and explored the effect of temperature on the adsorption capacity.

[0082] like Figure 6 As shown in Figure c, within the test temperature range, the adsorption capacity increases with increasing temperature. The maximum adsorption capacity reaches 475.3 mg / g at 298 K, 533.7 mg / g at 303 K, and 549.2 mg / g at 308 K.

[0083] (3) Since there are a large number of competing ions in natural seawater, selectivity is considered to be an important factor affecting the practical application of adsorbents. In order to further evaluate the selective adsorption performance of PAOmgel for uranyl ions, the adsorption performance of PAOmgel adsorbent for uranyl ions in a simulated seawater environment was studied.

[0084] The results are as follows Figure 7 As shown in Figure a, at 298K, PAOmgel's adsorption capacity for uranyl ions is much higher than that for other metal ions, reaching 1.44 mg / g, demonstrating excellent selectivity. This is attributed to the strong affinity of the amidoxime functional group for uranyl ions. Because vanadate ions and uranyl ions have similar ionic structures, PAOmgel has a higher adsorption capacity for vanadate ions, but it is still lower than its adsorption capacity for uranyl ions.

[0085] (4) Adsorption regeneration is an important indicator for evaluating the stability of adsorbents during recycling. In this work, a mixed solution of 0.1 M H2O2 and 1.0 M Na2CO3 was selected as the eluent to test the adsorption regeneration performance of PAOmgel.

[0086] like Figure 7 As shown in Figure b, after five adsorption-desorption cycles, the PAOmgel adsorbent still has a high adsorption capacity for uranyl ions, which can reach 32.75 mg / g, which is about 85.3% of the adsorption amount during the first cycle, indicating that it has potential application value in the extraction of uranyl ions.

[0087] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification has described the present invention in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention may still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing underwater adhesive porous hydrogel adsorbent based on a liquid-gas-liquid droplet reactor, characterized in that: The following steps are involved: (1) Preparation of polyacrylamidoxime PAO: NH2OH·HCl is added to N,N-methyleneformamide, and the mixture is heated in a water bath to a reaction temperature T1 for a reaction time t1. Na2CO3 and NaOH are then added under stirring, and the resulting mixed solution is stirred for a reaction time t2. Polyacrylonitrile PAN is then added under continuous stirring, and after complete dissolution, the mixture is heated to a reaction temperature T2 and the reaction time t3 is continued. Na2CO3 and NaOH are added, and the reaction time t4 is continued. The supernatant is collected by centrifugation until no precipitation is produced, and the supernatant is dropped into pure water to collect the produced flocs, which are then freeze-dried to obtain polyacrylonitrile oxime (PAO). (2) Preparation of hydroxyethyl methacrylate (HEMA) functionalized poly (N-isopropylacrylamide-co-acrylic acid) microgel P (NIPAM-co-AAc)-HEMA microgel: First, N-isopropylacrylamide (NIPAM), acrylic acid (AAc), N,N'-dimethylformamide (BIS), and sodium dodecylsulfonate (SDS) were dissolved in deionized water; excess nitrogen was introduced to remove oxygen, and the reaction solution was refluxed under nitrogen protection to a reaction temperature (T3) and continued for a reaction time (t5). Then, an aqueous solution of potassium persulfate (KPS) was added to initiate the reaction. After a reaction time (t6), the obtained microgel nanoparticles (P(NIPAM-co-AAc)) were dialyzed against deionized water for a time (t7). The purified P(NIPAM-co-AAc) dispersion was taken, HEMA and EDC were added, and the reaction was continued at a temperature (T4) with continuous stirring for a reaction time (t8). The obtained product was dialyzed against deionized water for a time (t9) and freeze-dried to obtain HEMA-functionalized P(NIPAM-co-AAc) microgel, which was recorded as P(NIPAM-co-AAc)-HEMA microgel. (3) Preparation of polyamidooxime functionalized underwater adhesive porous hydrogel: P(NIPAM-co-AAc)-HEMA microgel was dispersed in NaOH solution of PAO, photoinitiator Irgacure 1173 was added, and the stirring time was t 10 A water-in-gas Pickering high internal phase liquid-gas droplet reactor is formed, and then the polymerization is initiated by ultraviolet light for a time t 11 Prepare PAO functionalized porous hydrogel, then soak in dopamine DA solution for time t 12 After freeze-drying, amidoxime-functionalized porous hydrogel with underwater adhesion properties was obtained, which was named PAOmgel.

2. The method according to claim 1, wherein In step (1), the ratio of the total amount of NH2OH·HCl, N,N-methyleneformamide, Na2CO3, the total amount of NaOH and polyacrylonitrile is 50-70mmol:35-55mL:35-45mmol:20-40mmol:50-70mmol.

3. The method according to claim 1, wherein In step (1), the reaction temperature T1 is 30-50°C, the reaction time t1 is 20-60 min; the reaction time t2 under stirring is 2.0-4.0 h; the reaction temperature T2 is 60-85°C, the reaction time t3 is 12-36 h; and the reaction time t4 is 12-36 h; The stirring speed is 600-1200 rpm, and the centrifugal speed is 10000-15000 rpm.

4. The method according to claim 1, wherein In step (2), the usage ratio of NIPAM, AAc, BIS, SDS and deionized water is 1.2-1.6 g: 0.05-0.15 g: 0.01-0.05 g: 0.04-0.08 g: 80-120 mL; The reaction temperature T3 is 50-90°C, and the reaction time t5 is 0.5-1.5h.

5. The method according to claim 1, wherein In step (2), the usage ratio of NIPAM and KPS is 1.2-1.6 g:0.06-0.1 g; the reaction time t6 is 2.0-6.0 h; the dialysis time t7 is 1-3 weeks, and the water is changed 2-4 times per day.

6. The method according to claim 1, wherein In step (2), the amount ratio of the purified P(NIPAM-co-AAc) dispersion, HEMA and EDC is 30-70 mL: 1.6-2.0g: 2.2-2.6g; The temperature T4 is 20-30°C, and the reaction time t8 is 2.0-6.0h; The dialysis time t9 is 5-9 days, and the water is changed 2-4 times a day.

7. The method according to claim 1, wherein In step (3), the ratio of P(NIPAM-co-AAc)-HEMA microgel, PAO NaOH solution, and initiator Irgacure 1173 is 50-150 mg:0.5-1.5 mL:5.0-15 μL; Wherein, in the NaOH solution of PAO, the concentration of PAO is 20-40 mg / mL, and the concentration of the NaOH solution is 0.5-1.5M.

8. The method according to claim 1, wherein In step (3), The stirring speed is 12000-18000rpm, and the stirring time t 10 0.5-1.5min; The wavelength of ultraviolet light is 360-400nm, the power is 10-20W; the polymerization time t 11 0.5-1.5h; The concentration of dopamine DA solution is 0.5-1.5M, and the soaking time is t 12 0.5-1.5h.

9. The underwater adhesive porous hydrogel adsorbent prepared by the method according to any one of claims 1 to 8.

10. Use of the underwater adhesive porous hydrogel adsorbent according to claim 9 for selective extraction of uranyl ions in water.

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