GB2590792A

GB2590792A - Method for preparing amidoxime functionalized hollow porous polymer microsphere by using CO2 as emulsion template

Info

Publication number: GB2590792A
Application number: GB2018087.3A
Authority: GB
Inventors: Bai Xue; Pan Jianming; Liu Jinxin
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2019-11-11
Filing date: 2020-05-27
Publication date: 2021-07-07
Anticipated expiration: 2040-05-27
Also published as: CN110961085B; WO2021093306A1; GB202018087D0; CH717047B1; CN110961085A; JP2022511183A; JP7207765B2; GB2590792B

Abstract

The present invention relates to the technical field of adsorption and separation functional materials, and relates to a method for preparing an amidoxime functionalized hollow porous adsorbent by using CO2 as an emulsion template. The method comprises the following steps: first preparing silicon dioxide nanoparticles and MF-HP; adding the MF-HP and PEA to ethanol; passing through an ultrasonic and water bath reaction; washing using water, washing using ethanol, and drying to obtain MF-NH2-HP; adding same to a glutaraldehyde aqueous solution; after passing through a water bath, washing using water, washing using ethanol, and drying, obtaining MF-CHO-HP; then adding same and DAMN to an ethanol solution; passing through a water bath, washing using water, washing using ethanol, and drying to obtain MF-CN-HP; adding same and hydroxylamine hydrochloride to a mixed solution of water and ethanol; and after reacting, washing using water, washing using ethanol, and drying to obtain MF-AO-HPS. By grafting PEA, the present invention provides the possibility for subsequent modification of a large number of action sites as well as combines with a hollow porous structure, thus not only improving the adsorption capacity of adsorption U(VI), but also accelerating mass transfer kinetics.

Description

METHOD FOR PREPARING AMIDOXIME FUNCTIONALIZED HOLLOW

POROUS POLYMER MICROSPHERES USING CO2 AS EMULSION

TEMPLATE

Technical Field

The present invention belongs to the technical field of preparation of adsorption and separation functional materials, and specifically relates to a method for preparing an am doxime functionalized hollow porous sorbent using CO2 as an emulsion template.

Background

As for its special use in the nuclear industry, naturally occurring uranium (U(VI)) has become a key strategic resource for the nuclear industry. Up to now, the proven uranium resource mainly exists in the form of hexavalent uranium (U(VI)) in seawater, which is about 4.5 billion tons, suggesting that seawater is a promising source for uranium exploitation. However, the difficulty in extracting large amounts of uranium from seawater limits its widespread application. In addition, due to its combined radio-and chemo-toxicities, uranium present in seawater is not only harmful to humans and the environment, but also dangerous. Therefore, extracting uranium from seawater is of economically and environmentally beneficial and scientific significance. Until now many kinds of methods have been developed for enriching U(VI) from seawater, such as electrodialysis, liquid-liquid extraction, chemical precipitation, organic-inorganic ion exchange, and adsorption. As a successful technique, adsorption is the most extensively used approach for enriching U(VI) from seawater due to its high extraction efficiency, low preparation cost, low production of secondary pollution and simple operation. However, the enrichment of U(VI) from seawater via adsorption always faces enormous challenges, including an exceptionally low concentration of about 3.3 ppb, a large amount of competitive ions, and complex chemical and biological environments. Thus, an environmentally friendly, highly selective and efficient sorbent is urgently needed to be explored for specific enrichment of U(VI) from seawater.

There are many types of sorbents used for ion extraction, and hollow porous sorbents (HIPS) have aroused great interest of researchers owing to their low density, clear structure, and high carrying capacity. Pickering emulsion template method is one of the most commonly used methods for preparing DIPS. Due to its unique spatial configuration, amidoxime group can achieve selective adsorption with U(VI) through coordination. Using this principle, the surface of the material can be modified with amidoxime groups to give it the ability to selectively adsorb U(VI). The traditional Pickering emulsion template method usually faces many challenges, such as a complicated elution process for the organic solvent in internal phase, the use of large numbers of eluents as a big obstacle to mass production and environmental safety, limited control of size, large size and other deficiencies. The direct participation of functional monomers in polymerization will lead to a large number of functional sites located in the polymer, which not only has a slow mass transfer rate, but also causes unnecessary loss of some functional sites due to their inability to participate in the reaction. In order to avoid the above shortcomings, it is necessary to study a new material for selective extraction of U(VI).

Summary

Aiming at the shortcomings of the prior art, it is an object of the present invention to overcome the problems such as the difficulty of internal phase elution and the difficulty of structure control in the preparation of Pickering emulsion template method. The present invention provides a method for preparing HPS by an amidoxime functionalized gas-in-water emulsion template method using amidoxime groups as selective ligands and a melamine resin as a substrate to prepare an amidoxime functionalized hollow porous sorbent (MF-AO-HPS).

In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows: ( I) Preparation of Si02 nanoparticles A predetermined amount of tetraethyl orthosil cate (TEOS) is added to ethanol (Et0H), and after the temperature of the solution is raised to a predetermined temperature in a water bath, a predetermined amount of a mixed solution of NH3-H20 and H20 is added dropwise. After that, the resulting mixed solution is allowed to react for a period of time under magnetic stirring. After the reaction is completed, the product is collected through centrifugation, washed with deionized water and Et0H three times each, and dried to obtain the Si02 nanoparticles; (2) Preparation of a hollow porous melamine resin The Si02 nanoparticles obtained in step (1) are dispersed in deionized water to obtain an aqueous dispersion of Sift., and then, melamine is added to a mixed solution of a formaldehyde solution and a glutaraldehyde (GA) solution under a predetermined temperature condition, the mixed solution is subjected to pH adjustment and stirred, and allowed to continue to react for a period of time after the solution turns from milky white to clear. After that, the aqueous dispersion of Si02 is added to the solution under a stirring condition for reaction, followed by cooling to a predetermined temperature, and after adjusting pH again, the reaction is carried out. After the reaction, a polymerization reaction is carried out under water bath conditions. Finally, the product is collected by centrifugation, washed with deionized water and ethanol, and dried to obtain a powder sample. The powder sample is added to a hydrofluoric acid (HF) solution for etching the Si02 nanoparticles, and the product collected after centrifugation is washed again with deionized water and ethanol, and collected by centrifugation again and dried to obtain the hollow porous melamine resin which is denoted as MF-HP; (3) The MF-HP prepared in step (2) and polyethylene polyamine (PEA) are dispersed into Et0H to obtain a mixed solution A, and then, the mixed solution A is sonicated and allowed to react in a water bath under magnetic stirring to obtain a product after centrifugation. The obtained product is washed with Et0H, and collected by centrifugation again to obtain amino-grafted hollow porous melamine resin polymer microspheres denoted as MF-NFL-HP. The obtained MF-NEL-HP and glutaraldehyde are added to Et0H to obtain a mixed solution B, and then, the mixed solution B is allowed to react in a water bath under magnetic stirring. After the reaction, the resulting product is washed with deionized water and Et0H, and collected by centrifugation to obtain aldehyde-grafted hollow porous melamine resin polymer microspheres denoted as MF-CHO-HP; (4) The MF-CHO-HP prepared in step (3) and diaminomaleonitrile (DAMN) are suspended in 40-60 mt. of Et0H E to obtain a mixed solution C, and then, the mixed solution C is sonicated, and allowed to react in a water bath under magnetic stirring, followed by centrifugation to obtain a nitrile-grafted hollow porous melamine resin denoted as MF-CN-HP. Finally, Et0H F is added to deionized water to obtain a mixed solution of Et0H and H20, and then, the Aff-CN-HP and NH2011-11C1 are added to the mixed solution, pH-adjusted and then placed in a water bath for reaction. After the reaction, the resulting product is collected by centrifugation, and washed with deionized water and Et0H and dried to obtain amidoxime-functionalized hollow porous melamine resin microspheres denoted as MF-AO-HPS.

Another adsorbent without PEA grafting is obtained using the same method as step (3), except 15 that MF-CHO-IIP is replaced with MF-IIP, and the adsorbent without PEA grafting is denoted as IVIF-nPEA-A0-1IPS.

Preferably, in step (1), the TEOS, Et0H, NH3.H20 and H20 are used in a ratio of 8.0-10 g: 170-190 mL: 9.0-11 mL: 9.0-10 g, and are allowed to react at a reaction temperature of 30-40°C for a reaction time of 2.0-4.0 h. Preferably, the predetermined temperature condition in step (2) is 80-90°C.

Preferably, in step (2), the melamine, the mixed solution of the formaldehyde and GA, and the dispersion of Si02 are used in a ratio of 1.0-2.0 g: 2.0-4.0 mL * 5 0-15 mL, the formaldehyde solution has a volume fraction of 37%, and the GA solution has a volume fraction of 25%, the aqueous dispersion of SiO2 has a concentration of 10 wt%. ;Preferably, in step (2), the pH adjustment is performed by using a Na/CO3 solution to adjust the pH to 9.0-10.0, and the Na2CO3 solution has a concentration of 2.0 M. Preferably, in step (2), the stirring condition is 1200-1600 rpm, the mixed solution is allowed to continue to react for a period of 3.0-5.0 mm, and the aqueous dispersion of Si02 is added for reaction for a period of 10-30 min. Preferably, in step (2), the cooling to the predetermined temperature is cooling to 30-50°C, adjusting the pH again is performed by dropwise adding 2.0 M HCI to adjust the pH to 5.0-6.0, and the reaction after adjusting the pH again is carried out for a period of 10-30 min. Preferably, in step (2), the water bath s ma ntained at a temperature of 30-50°C, the polymerization reaction is carried out for a period of 3.0-5.0 h, and the HE solution has a volume concentration of 2%, and the drying is performed at a temperature of 60-80°C. ;Preferably, in step (3), the MF-HP, PEA and Et0H are used in a ratio of 0.3-0.5 mg 3.0-5.0 g 40-60 mL Preferably, in step (3), the sonication is performed for a period of 5.0-10 min, the water bath for the mixed solution A is maintained at a temperature of 30-40°C for a reaction time of 8.0-i 6 h. Preferably, in step (3), the kW -NH2-HP, GA and Et0H are used in a ratio of 0.2-0.4 mg: 8.0-12 mL: 30-50 mL, and the GA has a volume fraction of 25%. ;Preferably, in step (3), the water bath for the mixed solution B is maintained at a temperature of 20-30°C for a reaction time of 8.0-16 h. Preferably, the MF-CHO-HP, DAMN and Et0H E in step (4) are used in a ratio of 0.2-0.6 mg 0.4-1.2 mg: 40-60 mL. ;Preferably, in step (4), the mixed solution C is sonicated for a period of 5.0-10 mm, the water bath is maintained at a temperature of 20-30°C for a reaction time of 2.0-4.0 h. Preferably, in step (4), the Et0H F and H20 are in a volume ratio of 9:1, and the MF-CN-HP, NH2OHHC1, and the mixed solution of Et0H F and H20 are used in a ratio of 0.2-0.6 mg: 2.0-6.0 g 40-60 mL. ;Preferably, in step (4), the pH adjustment is performed by using 1.0 M NaOH to adjust the pH to 8.0-9.0, and the water bath is maintained at a temperature of 70-90°C for a reaction time of 4.0-8.0 h. Preferably, the drying in step (4) is performed at a temperature of 60-80°C. ;In the above, Et0H E and Et0H F are both Et0H, and the letters E and F are only to distinguish expressions. ;BENEFICIAL EFFECTS OF THE PRESENT INVENTION ;(1) The present invention selects amidoxime group as the selective ligand of U(VI), hollow porous melamine resin as substrates, the amidoxime functionalized hollow porous sorbent (ME-AO-11PS) was prepared through the gas-in-water emulsion template method. ;(2) In the present invention, the hollow porous melamine resin polymer microspheres with rich aldehyde groups on the surface are prepared by the gas-in-water emulsion template method, which shortens the U(V1) diffusion path and improves the mass transfer kinetics, and the aldehyde group contained in itself avoids subsequent unstable binding caused by modification simplifies the preparation process. The grafting of PEA provides the possibility for the modification of high-density sites. The high-density amidoxime sites grafted on the surface of ME-AO-HP can interact with a large amount of U(VI), thereby increasing the adsorption capacity of the adsorbent. Through the experimental results of pH response of MF-AO-HPS and MF-nPEA-AO-HPS, it can be seen that MF-A0-11PS has a higher adsorption capacity of U(VI) than MF-nPEA-AO-HPS under different pH conditions. ;Brief Description of the Drawings ;FIG. I a and b show the SEM images of the MF-HP prepared in Example I; and FIG. I c and d 25 show the TEEM images of the INIF-HP prepared in Example 1. ;FIG. 2 shows the FTIR spectra of ME-HP, MF-NH2-HP, MF-CHO-HP, MF-CN-HP and MF-AO-HPS prepared in Example 1. ;FIG. 3 shows the Zeta potential of IMF-HP, MF-N}12-HP, IMF-AO-BPS and MF-nPEA-AO-HPS prepared in Example I FIG. 4a shows the XPS spectrum of ME-AO-HPS prepared in Example 1; FIG. 4b shows the cure spectra of the C ls core spectrum of IMF-AO-BPS prepared in Example 1; and FIG. 4c shows the cure spectra of the N Is core spectrum of MF-AO-HPS prepared in Example I. FIG. 5 shows the organic element analysis spectra of ME-11P, ME-NH2-HP, MF-CHO-HP, IMF-CN-HP and IMF-A0-1-TPS prepared in Example 1. ;FIG. 6 shows the CP-MAS 12C NMR. spectrum of MF-AO-I-IPS prepared in Example I. FIG. 7 shows the TGA curve of MF-AO-HPS prepared in Example I. FIG. 8 shows the effect of pH on the adsorption capacity of MF-AO-HPS, MF-nPEA-AO-HPS and MF-HP prepared in Example 1. ;FIG. 9 shows the adsorption kinetics of ME-A0-1-IFS prepared in Example 1 and its model fitting curve. ;FIG. 10 shows the influence of temperature on the adsorption equilibrium for uranium of IMF-AO-HIPS prepared in Example 1 and its model fitting curve FIG. ii shows the selective adsorption capacity of the MF-AO-HPS prepared in Example I. FIG. 12 shows the recyclability performance of the MF-AO-HPS prepared in Example I. ;Detailed Description of the Embodiments ;In the specific embodiments of the present invention, the recognition performance evaluation is carried out according to the following method: it is completed by a static adsorption experiment. The adsorption capacity of U(VI) of 2.0 mg ME-A0-14Ps, MF-nPEA-AO-TTPS and ME-HP in the pH range of 3.0-9.0 and the content of U(,11) after adsorption were determined by ICP-OES, and the optimal adsorption pH was determined according to the results. In order to study the maximum adsorption capacity of ME-AU-BPS, the adsorption equilibrium test was carried out in the range of U(VI) concentration of 10-500 mg/L. The Langmuir model and Freundlich model were used to fit the adsorption data, and the adsorption capacity was calculated according to the results. After the adsorption equilibrium, several other substances with the same structure as U(VI) were selected as competing adsorbents to participate in the study of the selective adsorption performance of MF-AO-HPS and its adsorption recyclability performance. ;The present invention is further illustrated by the following specific examples. ;Example I: ;(1) Preparation of Si02 nanoparticles The Si02 nanoparticles were fabricated using the Stober method: 8.735 g of TEOS was added to Et0H (180 mL), after the solution temperature was raised to 35°C under a water bath, a mixture solution of NH34120 (10 mL) and H20 (9.48 g) was added dropwise. The formed mixture solution was reacted for 3.0 h under a slow stirring. Then, the products were collected through centrifugation and washed them with deionized water and Et0H for three times, respectively. After drying, Si02 nanoparticles with diameters of 180-200 nm can be obtained. ;(2) Preparation of hollow porous melamine resin 1.26 g of melamine was added to 3.0 mL of mixed solution of 37% formaldehyde and 25% glutaraldehyde (WV, 2:1) at 85°C. Then, Na2CO3 (2.0 M) was adopted to adjust the pH to 9.5. ;Stirring at 1500 rpm, after the solution turned from white to clear, this solution was reacted at the same condition for another 3.0 min. Subsequently, 10 mL of lOwt% Si02 aqueous solution was added into the solution under stirring and continued to be stirred at the same condition for 20 min. To follow, the solution was cooled to 40°C, HC1 (2.0 M) was added to adjust the pH to 5.5. After additional stirring for 20 mm, the solution was allowed to polymerize at 40°C for 4.0 h without stirring. Finally, the product is collected by centrifugation, washed with deionized water and ethanol, and dried to obtain a powder sample. The powder sample is added to the 2% HE solution for etching the Si02 particles, after centrifugation the collected product was washed with deionized water and ethanol for three times respectively, centrifuged again to collect the product, and dried at 60°C to obtain a hollow porous melamine resin (MF-HP). ;(3) NIP-A0-HPS can get through the following method: Firstly, 0.4 g of as-prepared NTP-HP powders and 4.0 g of PEA were dispersed into 50 mL of Et0H, ultrasonically treat it for 5.0 min. Subsequently, this mixture was reacted at 35°C for 12 h under magnetic stirring. After that, the amino-grafted hollow melamine resin polymer microspheres (MF-NE12-HP) were collected via centrifugation and washed with Et0H for several times. Secondly, the obtained MF-NH2-HP (0.4 g), 10 mL of 25% GA, and 40 mL of Et0H were added into a flask, and this mixture was reacted at 35°C for 12 h under magnetic stirring in the dark environment. Then the collected product was washed with water for three times to remove excess GA and washed with Et0H for two times then the aldehyde-grafted hollow porous melamine resin polymer microsphere (MF-CHO-HP) could be obtained. ;(4) 0.4 g of NW-CHO-HP and 0.8 g of DAMN were suspended in 50 mL of Et0H. After sonicating for 5.0 min, the mixture was reacted at 25°C for 3.0 h under magnetic stirring, and the nitrile-modified hollow melamine resin (MF-CN-HP) can get after the product were collected. Finally, 0.4 g of MF-CN-HP was treated with 4.0 g of NH2OH.HCI in a 50 mL solution of H20/Et0H (VW, 1:9), and the pH of this system was adjusted to 8.0 using NaOH solution (1.0 M). Then the mixture solution was reacted at 80°C for 6.0 h, the amidoxime functionalized hollow porous melamine resin polymer microsphere (ATP-AO-HIPS) could obtained after centrifugation, rinsed with distilled water and Et0H and dried at 60°C. ;Using the same method as step (3), the difference is that MF-CHO-HP is replaced by MF-HP to obtain another adsorbent without PEA grafting, denoted as MF-nPEA-A 0-MPS. ;FIG. 1 shows the SEM and TEM image of MF-HP. From the SEM image we can find that the microsphere is monodispersed, the diameter is about 2.0 pm, the surface is porous, the hollow structure can be seen from the TEM image The graft and chemical modification of MF-A0-1-IPS were studied by FT-IR, XPS and 0EA, Zeta potential and CP-MAS I1C NMR spectra. FIG. 2 shows the FT-IR spectra of MF-HP, MF-NH2-HP, MF-CHO-HP, MF-CN-HP and MF-AO-HPS In the spectra of MF-CN-HP, the bound at 2210 cm" is the characteristic adsorption peak of CEN, which indicates the successful modification with DAMN, and the disappear in the spectra of MF-AO-HPS is due to the react with NH2OH.HC1. ;As shown in FIG. 3, the Zeta potential changes after each reaction, which is because after modifying different substances, the functional groups on the surface of the materials are different, so the Zeta potential displayed is also different. This reflects the success of each step of modification and the successful preparation of each material. ;On the survey XPS spectra of AO-HP-Nff, as shown in Fig. 4a, it exhibits three intense peaks at 284.83 eV, 399.03 eV, and 535.88 eV corresponding to Cis, Nis and Ols core levels, respectively. The Fig. 4b shows the cure spectra of the Cis core spectra, and it can be cure-fitted to three peaks that assigned to C-C, C-H and C=N groups. The N Is spectra of A0-1JP-MF in Fig. 4c is also fitted to three peaks, which are attributed to N-0, C=N and N-H groups. ;FIG. 5 shows the change of carbon (C) and nitrogen (N) element compositions in each product. After calculation, the C content in MF-HP is less than the N. PEA contains more C than N, so the content of C in NW-H-W relatively elevates, while the N content slightly reduces compared with ME-HP, For the same reason, MF-CHO-HP and MP-CN-HP have more carbon than nitrogen, and MF-AO-HPS have more nitrogen than carbon. ;The FIG. 6 displays the 13C CP-MAS NMR spectrum of AO-HP-MF, it contains four main signals at 48.12 ppm, 105.80 ppm, 162.72 ppm and 219.75 ppm, which are attributed to carbon in -C=C-, C=NOH and C=0, respectively. All the above results can prove the successful 25 preparation of ME-AO-HPS. Subsequently, the stability of W-AO-HPS was determined by thermogravimetric analysis (TGA). ;As shown in FIG. 7, it was observed in the MF-AO-BPS curve that the weight between 200°C and 360°C was reduced by 1.75%, which was due to the loss of the surface grafted am doxime group, while the weight between 360°C and 600°C was reduced by 1.60%, which was caused by the loss of PEA grafted. The little weight loss of MF-AO-HPS indicates that it has good stability. ;Example 2: ;(I) Preparation of Si02 nanoparticles The Si02 nanoparticles were fabricated using the StOber method: 8.0 g of TEOS was added to Et0H (170 mL), after the solution temperature was raised to 30°C under a water bath, a mixture solution of NH3.1120 (9 mL) and H20 (9.0 g) was added dropwise. The formed mixture solution was reacted for 2.0 h under a slow stirring. Then, the products were collected through centrifugation and washed them with deionized water and Et0H for three times, respectively. After drying, Si02 nanoparticles with diameters about 200 nm can be obtained. ;(2) Preparation of hollow porous melamine resin 1.0 g of melamine was added to 2.0 mL of mixed solution of 37% formaldehyde and 25% glutaraldehyde (WV, 2:1) at 80°C. Then, Na2C01 (2.0 M) was adopted to adjust the pH to 9.0. ;Stirring at 1200 rpm, after the solution turned from white to clear, this solution was reacted at the same condition for another 4.0 min. Subsequently, 5 0 mL of lOwt% 5i02 aqueous solution was added into the solution under stirring and continued to be stirred at the same condition for 10 min. To follow, the solution was cooled to 30°C, HC1 (2.0 M) was added to adjust the pH to 5.0. After additional stirring for 10 min, the solution was allowed to polymerize at 30°C for 3.0 h without stirring. Finally, the product is collected by centrifugation, washed with deionized water and ethanol, and dried to obtain a powder sample. The powder sample is added to the 2% HE solution for etching the Si02 particles, after centrifugation the collected product was washed with deionized water and ethanol for three times respectively, centrifuged again to collect the product, and dried at 60°C to obtain a hollow porous melamine resin (NW-HP). ;(3) NW-AO-HIPS can get through the following method: Firstly, 0.3 g of as-prepared NW-HP powders and 3.0 g of PEA were dispersed into 40 ml. of Et0H, ultrasonically treat it for 8.0 min. Subsequently, this mixture was reacted at 30°C for 8.0 h under magnetic stirring. After that, the amino-grafted hollow melamine resin polymer microspheres (NW-NH2-11P) were collected via centrifugation and washed with Et0H for several times. Secondly, the obtained NIT-NTF-HP (0.2 g), 8.0 mL of 25% GA, and 30 mL of Et0H were added into a flask, and this mixture was reacted at 30°C for 8.0 h under magnetic stirring in the dark environment. Then the collected product was washed with water for three times to remove excess GA and washed with Et0H for two times then 10 the aldehyde-grafted hollow porous melamine resin polymer microsphere (MF-CHO-HP) could be obtained. ;(4) 0.2 g of MF-CHO-HP and 0.4 g of DAMN were suspended in 40 mL of Et0H. After sonicating for 8.0 min, the mixture was reacted at 20°C for 2.0 h under magnetic stirring, and the nitrile-modified hollow melamine resin (ME-CM-HP) can get after the product were collected. ;Finally, 0.2 g of ME-CM-HP was treated with 2.0 g of NH2OH.HCI in a 40 nit solution of H20/Et0H (VAT, 1:9), and the pH of this system was adjusted to 8.5 using NaOH solution ( 1.0 M). Then the mixture solution was reacted at 70°C for 4.0 h, the amidox me funct onalized hollow porous melamine resin polymer microsphere (NW-AO-UPS) could obtained after centrifugation, rinsed with distilled water and Et0H and dried at 70°C. ;Using the same method as step (3), the difference is that MF-CHO-HP is replaced by MF-HP to obtain another adsorbent without PEA grafting, denoted as MF-nPEA-AO-HPS. ;Example 3: ;(1) Preparation of SiChnanoparticles The SiO2 nanoparticles were fabricated using the StOber method: 10 g of TEOS was added to Et0H (190 mL), after the solution temperature was raised to 40°C under a water bath, a mixture solution of N143.11.20 (11 mL) and 1120 (10 g) was added dropwise. The formed mixture solution was reacted for 4.0 h under a slow stirring. Then, the products were collected through centrifugation and washed them with deionized water and Et0H for three times, respectively. After drying, Si02 nanoparticles with diameters about 200 nm can be obtained. ;(2) Preparation of hollow porous melamine resin 2.0 g of melamine was added to 4.0 mL of mixed solution of 37% formaldehyde and 25% glutaraldehyde (WV, 2:1) at 90°C. Then, Naze(); (2.0 M) was adopted to adjust the pH to 10. ;Stirring at 1600 rpm, after the solution turned from white to clear, this solution was reacted at the same condition for another 5.0 min. Subsequently, 15 mL of lOwt% Si02 aqueous solution was added into the solution under stirring and continued to be stirred at the same condition for 30 min. To follow, the solution was cooled to 50°C, HC1 (2.0 M) was added to adjust the pH to 6.0. After additional stirring for 30 min, the solution was allowed to polymerize at 50°C for 5.0 h without stirring. Finally, the product is collected by centrifugation, washed with deionized water and 15 ethanol, and dried to obtain a powder sample. The powder sample is added to the 2% HE solution for etching the 5i02 particles, after centrifugation the collected product was washed with deionized water and ethanol for three times respectively, centrifuged again to collect the product, and dried at 60°C to obtain a hollow porous melamine resin (MF-HP). ;(3) NIF-AO-HPS can get through the following method: Firstly, 0.5 g of as-prepared NTF-HP powders and 5.0 g of PEA were dispersed into 60 mL of Et0H, ultrasonically treat it for 10 min. Subsequently, this mixture was reacted at 40°C for 16 h under magnetic stirring. After that, the amino-grafted hollow melamine resin polymer microspheres (MF-NE-12-HP) were collected via centrifugation and washed with Et0H for several times. Secondly, the obtained MF-NH2-HP (0.4 g), 12 mL of 25% GA, and 50 mL of Et0H were added into a flask, and this mixture was reacted at 40°C for 16 h under magnetic stirring in the dark environment. Then the collected product was washed with water for three times to remove excess GA and washed with Et0H for two times then the aldehyde-grafted hollow porous melamine resin polymer microsphere (MF-CHO-HP) could be obtained. ;(4) 0.6 g of MF-CHO-HP and 1.2 g of DAMN were suspended in 60 mL of Et0H. After sonicating for 10 min, the mixture was reacted at 30°C for 4.0 h under magnetic stirring, and the nitrile-modified hollow melamine resin (MF-CN-HP) can get after the product were collected. Finally, 0.6 g of MF-CN-HP was treated with 6.0 g of NH2OH*HC1 in a 60 mL solution of H20/'Et0H (VAT, 1:9), and the pH of this system was adjusted to 9.0 using NaOH solution (1.0 M).

Then the mixture solution was reacted at 90°C for 8.0 h, the amidoxime functionalized hollow porous melamine resin polymer microsphere (MF-AO-HPS) could obtained after centrifugation, rinsed with distilled water and Et0H and dried at 80°C.

Using the same method as step (3), the difference is that MF-CHO-HP is replaced by MF-HP to obtain another adsorbent without PEA grafting, denoted as MF-nPEA-A0-1IPS.

PERFORMANCE 1EXT: The pH value of the solution has a great influence on the adsorption behavior of metal ions. Thus, the effect of pH on the adsorption performance of H-MF, NPEA-AO-HP-MF, and AO-HP-MF for U(VI) was investigated in the pH range of 3.0 to 9.0. As shown in Fig. 7a, the results demonstrate that pH has a strong influence on U(VI) adsorption on the NPEA-AO-HP-MF and AO-HP-MF surface. As shown in FIG 8, the adsorption capacities of AO-T-IP-MF and NPEA-AO-HP-MF increase dramatically when the pH value no more than 7.0, then decrease with a further increase in pH value, and the adsorption capacity of MF-AO-HPS is higher than that of MF-NPEA-AO-HPS and MF-HP under any pH condition.

The adsorption kinetics of U(VI) by MF-A0-1IPS is shown in FIG. 9. As shown in FIG. 9, the 25 adsorption capacity increases rapidly in the first 30 m n, and reaches the maximum adsorption in min In order to study the maximum adsorption capacity of MF-AO-HPS, the adsorption equilibrium test was carried out in the range of U(VI) concentration of 10-500 mg/L, the Langmuir model and Freundlich model were used to fit the adsorption data, and the influence of temperature on the adsorption capacity was also explored. As shown in FIG. 10, within the test temperature range, the adsorption capacity increases with the increase of temperature.

The combination of interfering ions and amidoxime groups may have a huge impact on the adsorption capacity of MF-AO-HPS for U(VI) adsorption, so we choose V03-, Co2, Ni-, Cu', Zn', Pb', Ca', Mg', and Na+ as competitive ions for U(VI), and the adsorption behavior of ++ adsorbents in a mixed solution of V02-, Co2 zn2 - , pb2 Nit, Cu', mg2 -, Nat and U(VI) was studied. As shown in FIG. I I, in the presence of numerous interfering ions, MF-AO-T-1PS still has the highest adsorption capacity for U(VI).

Adsorption recyclability is an important index to evaluate the stability of adsorbent during the cycle use. Therefore, we tested the adsorption recyclability performance of I\TF-AO-HPS through 7 adsorption-desorption cycle experiments. As shown in FIG. 12, MF-AO-HPS still has a high adsorption capacity after 7 adsorption-desorption cycles, indicating that it has better adsorption recyclability performance, and it can maintain a good adsorption capacity for U(VI) during recycling.

Note: The above examples are used only to describe the present invention and not to limit the technical scheme described in the present invention. Therefore, although the specification is described in detail with reference to the above examples, ordinary technicians in the field should understand that the present invention may still be modified or equally substituted.

And all technical schemes and improvements not divorced from the spirit and scope of the present invention shall be covered within the scope of the claims of the present invention.

Claims

Claims What is claimed is: I. A method for preparing amidoxime functionalized hollow porous polymer microspheres using CO2 as an emulsion template, characterized by comprising the following steps: (1) preparing Si02 nanoparticles; (2) dispersing the Sift nanoparticles obtained in step (1) in deionized water to obtain an aqueous dispersion of Si02; then, adding melamine to a mixed solution of a formaldehyde solution and a glutaraldehyde (GA) solution under a predetermined temperature condition, subjecting the mixed solution to pH adjustment, followed by stirring and allowing the mixed solution to continue to react for a period of time after the solution turns from milky white to clear; after that, adding the aqueous dispersion of Si02 to the solution under a stirring condition for reaction, followed by cooling to a predetermined temperature, and after adjusting pH again, allowing a reaction to be carried out, and then allowing a polymerization reaction to be carried out under water bath conditions to obtain a product, and finally, collecting the product by centrifugation, washing the product with deionized water and ethanol (Et0H), and drying the product to obtain a powder sample; adding the powder sample to a hydrofluoric acid (HF) solution for etching the Sift nanoparticles to obtain a product, collecting the product by centrifugation, and then washing the product with deionized water and Et0H, collecting the product by centrifugation again, followed by drying to obtain a hollow porous melamine resin denoted as ME-HP, (3) dispersing the ME-HP prepared in step (2) arid polyethylene polyam ne (PEA) in Et0H to obtain a mixed solution A, and then sonicating the mixed solution A, allowing the mixed solution A to react in a water bath under magnetic stirring to obtain a product after centrifugation, washing the obtained product with Et0H and collecting the product by centrifugation again to obtain amino-grafted hollow porous melamine resin polymer microspheres denoted as MF-NH2-HP; and then adding the obtained MF-N112-1-IP and glutaraldehyde to Et0H to obtain a mixed solution B, and then allowing the mixed solution B to react in a water bath under magnetic stirring to obtain a product; and after the reaction, washing the product with deionized water and Et0H, followed by centrifugation to obtain aldehyde-grafted hollow porous melamine resin polymer microspheres denoted as MF-CHO-HP; (4) suspending the MF-CHO-HP prepared in step (3) and diaminomaleonitrile (DAMN) in Et0H E to obtain a mixed solution C, and then sonicating the mixed solution C, allowing the mixed solution C to react in a water bath under magnetic stirring, followed by centrifugation to obtain a nitrile-grafted hollow porous melamine resin denoted as MF-CN-HP; finally, adding Et0H F to deionized water to obtain a mixed solution of Et0H and 1120, and then adding the MF-CN-HP and NH2OHHC1, followed by pH adjustment, and then placing the mixture in a water bath for reaction to obtain a product; and after the reaction, collecting the product by centrifugation, and washing the product with deionized water and Et0H, followed by drying to obtain amidoxime-functionalized hollow porous melamine resin microspheres denoted as ME-AO-BPS.
2. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (2), the predetermined temperature condition is 80-90°C; the melamine, the mixed solution of the formaldehyde and GA, and the dispersion of Si02 are used in a ratio of 1.0-2.0 g: 2.0-4.0 mL 5.0-15 mL; the formaldehyde solution has a volume fraction of 37%, and the GA solution has a volume fraction of 25%; and the aqueous dispersion of SiO2 has a concentration of 10 wt%.
3. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (2), the pH adjustment is performed by using a Na7CO3 solution to adjust the pH to 9.0-10.0; the Na2CO3 solution has a concentration of 2.0 M; the stirring condition is 1200-1600 rpm; the mixed solution is allowed to continue to react for a period of 3.0-5.0 min; and the aqueous dispersion of Si02 is added for reaction for a period of 10-30 min.
4. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (2), the cooling to the predetermined temperature is cooling to 30-50°C; the adjusting of the pH again is performed by dropwise adding 2.0 M HC1 to adjust the pH to 5.0-6.0; the reaction after adjusting the pH again is carried out for a period of 10-30 min; the water bath is maintained at a temperature of 30-50°C; the polymerization reaction is carried out for a period of 3.0-5.0 h; the HF solution has 5 a volume concentration of 2%; and the drying is performed at a temperature of 60-80°C.
5. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (3), the ME-HP, PEA and Et0H are used in a ratio of 0.3-0.5 mg: 3.0-5.0 g: 40-60
6. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (3), the sonicating is performed for a period of 5.0-10 min; and the water bath for the mixed solution A is maintained at a temperature of 30-40°C for a reaction time of 8.0-16 h.
7. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (3), the 15 NH-NI-1241P, GA and Et0H are used in a ratio of 0.2-0.4 mg: 8.0-12 mL: 30-50 mL; the GA has a volume fraction of 25%; and the water bath for the mixed solution B is maintained at a temperature of 20-30°C for a reaction time of 8.0-16 h.
8. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (4), the 20 MF-CHO-HP, DAMN and Et0H E are used in a ratio of 0.2-0.6 mg: 0.4-1.2 mg: 40-60 mL; and the sonicating of the mixed solution C is performed for a period of 5.0-10 min, the water bath is maintained at a temperature of 20-30°C for a reaction time of 2.0-4.0 h.
9. The method for preparing the amidoxime functionalized hollow porous polymer microspheres using CO2 as the emulsion template according to claim 1, characterized in that in step (4), the Et0H F and H20 are in a volume ratio of 9:1; the MF-CN-HP, NH2OHHCI, and the mixed solution of Et0H and H20 are used in a ratio of 0.2-0.6 mg: 2.0-6.0 g: 40-60 mL; the pH adjustment is performed by using 1.0 M NaOH to adjust the pH to 8.0-9.0; the water bath is maintained at a temperature of 70-90°C for a reaction time of 4.0-8.0 h; and the drying is 5 performed at a temperature of 60-80°C.I 0. An amidoxime functionalized hollow porous sorbent prepared by the method according to any one of claims 1-9, which is used for selective adsorption and separation of U(VI) in solution.