Preparation, modification and application of mesoporous silica resin

Abstract

The application discloses synthesis, modification and application of regular spherical porous silica. The preparation method of the modified mesoporous silica in the application is as follows: mesoporous silica is prepared first, then the mesoporous silica is activated by hydrogen peroxide, and then silane coupling agent (3-aminopropyl) trimethoxysilane (APTES) is added in N,N-dimethylformamide (DMF) to synthesize aminosilica SiO2-APTES by deoxidation, and an amidation reaction is performed to stably graft imidophosphoric acid groups and quaternary amine functional groups to the silica. The regular spherical porous silica is prepared by a sol-gel method. The water / oil ratio (cyclohexane / water) in the preparation process can control the size of the silica, the imidophosphoric acid groups and the quaternary amine functional groups are stably grafted to the silica by a mild amidation reaction, and a novel mesostructure-based resin material with high grafting rate and porosity is synthesized, which can exhibit high adsorption performance on target uranium (VI) ions.

Description

Technical Field

[0001] This invention relates to the synthesis, modification, and application of a mesoporous silica resin, particularly the synthesis, modification, and application of a porous silica with regular spherical shapes. Background Technology

[0002] Nuclear energy, as a clean and efficient new energy source, occupies an increasingly important position in the global energy structure. Uranium is the main fuel for nuclear power generation; however, large amounts of uranium-containing wastewater are generated at every stage of the nuclear fuel cycle, including uranium mining, refining, reactor operation, and reprocessing. Once discharged into the environment, this uranium-containing wastewater poses a serious threat to the ecological environment and human health. Among these, the alpha-radioactive wastewater generated by alkaline washing in the Prex process is a key bottleneck in the reprocessing waste management chain. Mesoporous silica materials are a novel type of nanoporous material that has attracted widespread attention in recent years. Its most significant characteristics are a highly ordered pore structure, a large specific surface area, and adjustable pore size. Silica prepared by traditional methods is costly, its morphology is difficult to control, and the uneven distribution of functional sites easily leads to pore blockage, significantly reducing the material's adsorption performance.

[0003] CN118206127A discloses a modified mesoporous silica, its preparation method, and its application. The preparation method involves dissolving ethylene phosphonic acid and the prepared mesoporous silica nanofibers under anaerobic conditions, adding 2,2'-azobisisobutyronitrile, reacting at 40–90°C for 12–24 hours, and separating the solid to obtain the modified mesoporous silica. The modified mesoporous silica is used as an adsorbent for adsorbing uranium from wastewater. According to the disclosed information, this product is a novel mesoporous silica-based material with high phosphonic acid grafting density and abundant pores, exhibiting relatively high rigidity and accelerating the uranium adsorption process. However, the synthesized silica is in the form of irregular, slender fibers. While possessing a large external surface area, the randomly oriented fibrous structure, due to its large aspect ratio, is prone to entanglement and aggregation, and has low mechanical stability, making it more susceptible to breakage under shear forces (such as stirring or grinding). After structural breakage, the originally regular pore structure is destroyed, leading to a decrease in specific surface area or pore blockage. Mesoporous silica with regular spherical particles (especially monodisperse spheres) is considered an "ideal morphology" in the materials field, with its main advantages being excellent flowability and dispersibility, isotropy and higher packing density - which is crucial for applications requiring high volumetric capacity (such as chromatography column packing). Summary of the Invention

[0004] This invention discloses a method for preparing modified mesoporous silica, and the uses of the product prepared by this method, particularly a method for preparing modified mesoporous silica with regular spherical shape, and the uses of the product prepared by this method.

[0005] The present invention provides a method for preparing modified mesoporous silica. First, mesoporous silica is prepared, and then activated with hydrogen peroxide. After activation, a silane coupling agent (3-aminopropyl)trimethoxysilane (APTES) is added and deoxygenated in N,N-dimethylformamide (DMF) to synthesize aminated silica SiO2-APTES. The amidation reaction stabilizes and fixes imine phosphate groups and quaternary ammonium functional groups onto silica.

[0006] Preferably, the method for preparing the modified mesoporous silica of the present invention involves adding SiO2-APTES and N-(phosphorylmethyl)glycine (PRS) to DMF, stirring under an inert atmosphere to allow dehydration condensation between amino and carboxyl groups to form stable amide bonds, and grafting PRS onto silica to form silica PRS@SiO2-APTES modified with imine phosphate functional groups; or, adding SiO2-APTES and carboxyl-N,N,N-trimethylammonium bromide (CTAC) to DMF, stirring under an inert atmosphere to allow dehydration condensation between amino and carboxyl groups to form stable amide bonds, and grafting CTAC onto silica to form silica CTAC@SiO2-APTES modified with quaternary ammonium functional groups.

[0007] Preferably, in the method for preparing modified mesoporous silica of the present invention, regular spherical porous silica is prepared by sol-gel method.

[0008] Preferably, in the method for preparing modified mesoporous silica of the present invention, regular spherical porous silica is prepared by sol-gel method using hexadecyltrimethylammonium bromide (CTAB) and tetraethyl silicate (TEOS) as raw materials and cyclohexane and water as solvents.

[0009] Preferably, in the method for preparing modified mesoporous silica of the present invention, when preparing regular spherical porous silica, the rotation speed is 350 r / min, the reaction temperature is 70-80℃, and the reaction time is 12-13 h. A suitable rotation speed allows for sufficient contact between the aqueous and oil phases, enabling adequate nucleation at the interface between the two phases. Heating accelerates the nucleation of silicon spherical particles. Cyclohexane has a boiling point of approximately 80 degrees Celsius. Therefore, the reaction temperature should be designed to be 70-80℃.

[0010] Preferably, in the method for preparing modified mesoporous silica of the present invention, the concentration of hydrogen peroxide is 30% when preparing amino-modified mesoporous silica. The use of hydrogen peroxide can activate the hydroxyl groups on the silica surface, enhancing the modification activity.

[0011] Preferably, in the preparation method of the modified mesoporous silica of the present invention, the mass ratio of silica to silane coupling agent is 1:3 when preparing amino-modified mesoporous silica. Controlling the amount of amino-modified silane coupling agent added can regulate its pore structure and functional group grafting rate. Excessive silane coupling agent will cause pore blockage, while too little will result in a low grafting rate and poor actual effect.

[0012] Preferably, in the method for preparing modified mesoporous silica of the present invention, the reaction temperature is 120°C and the actual reaction time is 24-25 h; the functionalization of silica with phosphoric acid and quaternary ammonium forms stable amide bonds through the dehydration condensation reaction of amino and carboxyl groups, and the reaction condition of 120°C promotes the forward dehydration reaction.

[0013] Preferably, in the method for preparing modified mesoporous silica of the present invention, the mass ratio of modified silica to grafted functional groups is 3:1 when preparing functionalized mesoporous silica. Controlling a suitable grafting rate can achieve the interaction between pore size and functional groups.

[0014] The modified mesoporous silica prepared by this invention can be used as an adsorbent, especially for adsorbing uranium in complex water bodies, such as uranium extraction from seawater with multiple interfering ions and uranium removal from alkaline radioactive waste liquid.

[0015] This invention uses TEOS as a raw material to prepare uniform spherical silica via a sol-gel method, resulting in low synthesis cost and uniform pore distribution. Furthermore, the mesoporous silica synthesized in this invention has a surface rich in silanol groups, facilitating various functional modifications to introduce specific functional groups, thereby enhancing its adsorption selectivity and capacity for target pollutants and exhibiting excellent versatility.

[0016] This invention prepares regular spherical porous silica by forming stable strong amide bonds through a dehydration reaction, overcoming the uncontrollability of condensation reaction modification. It synthesizes mesoporous silica materials with regular morphology, controllable pores, and easy multifunctionality, and is more suitable for column separation processes.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Regularly shaped spherical porous silica was prepared via a sol-gel method. The size of the silica could be controlled by varying the water-to-oil ratio (cyclohexane / water). A novel mesostructured resin material with high grafting rate and porosity was synthesized by stably imine phosphate groups and quaternary ammonium functional groups onto the silica through a mild amidation reaction. This method has good versatility, and suitable functional groups can be subsequently modified according to actual application requirements.

[0018] 2. The introduction of high-density functional groups endows the material with high adsorption performance for target uranium (VI) ions. The prepared modified mesoporous silica can be used for efficient uranium purification and recovery within a high pH range (1-10). The adsorption capacity exceeds 350 mg / g. Attached Figure Description

[0019] Figure 1 Schematic diagram of the synthesis of functionalized modified mesoporous silica.

[0020] Figure 2 Morphology of mesoporous silica and PRS / CTAC@SiO2-APTES.

[0021] Figure 3 Adsorption properties of mesoporous silica PRS / @SiO2-APTES (left) and CTAC@SiO2-APTES (right). Detailed Implementation

[0022] The preparation of 500 nm uniform spherical mesoporous silica in the technical solution of this invention will be clearly and completely described below with reference to specific embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0023] Unless otherwise specified, the methods described in the various embodiments of this invention are conventional methods. Unless otherwise specified, the materials and reagents used are commercially available. Example

[0024] The route diagram for preparing modified mesoporous silica in this invention is shown in the embodiments below. Figure 1 Specifically, it includes the following steps: 1) Preparation of uniform spherical mesoporous silica Mesoporous silica preparation method: Porous silica was prepared by sol-gel method using hexadecyltrimethylammonium bromide (CTAB) and tetraethyl silicate (TEOS) as raw materials and cyclohexane and water as solvents. Different water-oil ratios (cyclohexane / water) could finely control the size of silica, and different synthesis conditions are listed in Table 1. Taking 500 nm as an example, 4.0 g of CTAB and 2.4 g of urea were dissolved in 120 mL of water. Then, 200 mL of cyclohexane and 3.92 mL of isopropanol were added as pore-forming agents under vigorous stirring, followed by the slow dropwise addition of 10 mL of TEOS. After stirring the mixed solution at room temperature for 60 min, the system was heated to 80 °C and stirred vigorously for 24 h. The white flocculent material was obtained by centrifugation and washed three times with ethanol and water, respectively. Then, the sample was dried under vacuum at 50 °C for 12 h. Calcination in air at 550 °C for 8 h was performed to remove residues, yielding pure white powder solid porous nano-silica with a yield of 58%.

[0025] The table below shows the synthesis conditions of silicon dioxide under different conditions according to the present invention:

[0026] 2) Synthesis of amino-modified silica Preparation method of modified silica: The synthesized porous nano-silica was aminated. First, 1 g of silica was mixed with 100 mL of hydrogen peroxide and stirred in an oil bath at 70 °C for 12 hours to activate the surface hydroxyl groups. Then, the activated silica was poured into N,N-dimethylformamide (DMF), followed by the addition of 3 mL of silane coupling agent (3-aminopropyl)trimethoxysilane (APTES), and three vacuum-nitrogen purgings were performed to ensure synthesis under a nitrogen atmosphere. Finally, the mixture was stirred in an oil bath at 70 °C for 12 hours, cooled, and the solid and liquid phases were separated. The solid was washed three times with DMF, water, and methanol, and dried under vacuum at 70 °C for 12 hours to obtain a white powder solid SiO2-APTES.

[0027] 3) Synthesis of Functionalized Modified Silica Synthesis of silica with imine phosphate functional groups: 1.5 g of SiO2-APTES and 0.5 g of N-(phosphorylmethyl)glycine (PRS) were added to a three-necked flask containing 50 mL of DMF. The mixture was stirred at 120 °C for 24 hours under a nitrogen atmosphere. The dehydration condensation between the amino and carboxyl groups formed stable amide bonds, allowing PRS to be effectively grafted onto silica. The resulting product was then washed three times with DMF, water, and methanol, and finally dried under vacuum at 70 °C for 12 h to obtain a white powder solid PRS@SiO2-APTES.

[0028] Synthesis of quaternary ammonium functional group silica: 1 g of SiO2-APTES and 0.5 g of carboxyl-N,N,N-trimethylammonium bromide (CTAC) were added to a three-necked flask containing 50 mL of DMF. The mixture was stirred at 120 °C for 24 h under a nitrogen atmosphere. The dehydration condensation between the amino and carboxyl groups formed stable amide bonds, allowing CTAC to be effectively grafted onto silica. The resulting product was then washed three times with DMF, water, and methanol, and finally dried under vacuum at 70 °C for 12 h to obtain a white powder solid CTAC@SiO2-APTES.

[0029] Experimental Results and Discussion (I) Morphology and Characterization like Figure 2Electron microscopy analysis showed that the synthesized silica particles had a very uniform size, distributed around 500 nm. The abundant porous structure on the surface of the silica material provided a large number of spatial sites for post-modification and adsorption. Subsequent energy dispersive spectroscopy (EDS) analysis detected that the main elements of SiO2-APTES were C, N, O, and Si, and the main elements of PRS@SiO2-APTES were C, N, O, Si, and P, confirming the modification of aminated silica and the successful grafting of phosphoryl silica. Similarly, as shown by electron microscopy analysis, the main elements of CTAC@SiO2-APTES were C, N, O, Si, and Cl, confirming the successful loading of quaternary ammonium functional groups onto mesoporous silica.

[0030] Infrared spectra of SiO2, SiO2-APTES, PRS@SiO2-APTES, and CTAC@SiO2-APTES were acquired at 400 cm⁻¹ using the KBr pellet method. 1 ~4000 cm -1 The FT-IR spectrum within the range is shown. The characteristic peaks at 473 cm⁻¹, 802 cm⁻¹, and 1100 cm⁻¹ correspond to the asymmetric and symmetric stretching of the Si-O-Si bond, respectively, while the characteristic peak at 1390 cm⁻¹ is generated by the P=O vibration, indicating that the phosphoryl functional group was successfully grafted onto silicon dioxide. Similarly, the peak at 1565 cm⁻¹... -1 and 1465 cm -1 The characteristic peaks at the specified locations are generated by the vibrations of CN and CH, indicating that the quaternary ammonium functional groups were successfully grafted onto silica. The porous structure of SiO2 allows N2 to be easily adsorbed into the pores at very low relative pressures (P / P0), and the N2 adsorption capacity increases rapidly when the relative pressure is >0.7. When phosphoryl functional groups are successfully grafted onto silica, the adsorption and desorption process of N2 on the PRS@SiO2-APTES adsorbent is not significant when the relative pressure (P / P0) is <0.7. When the relative pressure is >0.7, the N2 adsorption capacity is consistent with that of silica, but the N2 adsorption capacity increases, indicating that the adsorption isotherms conform to type IV isotherm curves. The pore size distribution of SiO2 and the PRS@SiO2-APTES adsorbent also shows the successful functionalization modification.

[0031] To investigate the functional group content in the adsorbent, differential thermal-thermogravimetric analysis (TG-DSC) was used to determine the decomposition curves of the adsorbent at a heating rate of 10 °C / min, within a temperature range of 25–800 °C, and in an air atmosphere. SiO2 experienced a 5% heat loss before 100 °C, due to the loss of moisture adsorbed from the air in the pores. The heat losses observed around 300 °C in SiO2-APTES and CTAC@SiO2-APTES were due to the thermogravimetric loss of organic molecules at high temperatures. When the temperature rose to 650 °C, the TG curve reached decomposition equilibrium, indicating that the organic matter had been completely decomposed. Therefore, the content of phosphoryl organic matter in the organic-inorganic silicon-based adsorbent resin was approximately 20 wt%. The three-segment heat loss curves observed in the thermogravimetric analysis indicate the successful modification of aminated silica and the successful grafting of functional groups onto the silica surface. This is consistent with the results of infrared and BET analyses, demonstrating that the functional groups were successfully grafted onto the silica surface, and the material exhibits excellent thermal stability.

[0032] (II) Adsorption Experiment – ​​Uranium Capture After confirming the successful functionalization of silica, the adsorption behavior of the adsorbent in purifying and recovering uranium from nuclear wastewater was studied through batch adsorption experiments. This invention aims to investigate the adsorption behavior of the adsorbent for uranyl carbonate, using an adsorbent concentration of 0.2 g / L to study the uranium capture efficiency under different acidities, contact times, and uranium concentrations. Experimental results are as follows: Figure 3 As shown, UO2 2+ The adsorption efficiency of UO2 shows a significant correlation with the solution pH. Under strongly acidic conditions (pH = 2), the adsorption efficiency is low due to intense competition between a large number of H⁺ and U species. As the pH increases from 2 to 6, the adsorption efficiency of UO2 increases. 2+ The adsorption capacity increased from 100 to 350. This is because, under low acid conditions, the H ions on the P-OH group of the phosphoryl functional group are more easily ionized and UO2 is generated. 2+ Ion exchange occurs, thereby increasing the adsorption capacity. Under alkaline conditions with a pH greater than 8, uranium in the solution primarily exists as [UO2(CO3)3]. 4- In its existing form, the P-OH groups on the phosphoryl functional groups are all converted to PO. - Through CO3 2- Ion exchange is used to adsorb [UO2(CO3)3] 4- For the CTAC@SiO2-APTES cationic adsorbent, [UO2(CO3)3] is adsorbed via electrostatic attraction. 4- The adsorption capacity is not affected by pH and remains stable at around 250 mg / g.

[0033] The functionalized silica adsorbent prepared in this invention is effective against [UO2(CO3)3]. 4-The adsorption of [UO2(CO3)3] exhibited rapid adsorption kinetics, with over 90% of the target substance adsorbed within 30 min and reaching adsorption equilibrium after approximately 2 h. To further quantify the adsorption kinetic parameters, we used pseudo-first-order and pseudo-second-order kinetic models to fit and analyze the experimental data. The results showed that the pseudo-second-order kinetic model had a higher degree of agreement with the experimental data, with a correlation coefficient reaching 0.999, indicating that [UO2(CO3)3]... 4- The adsorption processes of both phosphoryl silica adsorbents and quaternized silica are dominated by chemisorption or surface complexation mechanisms.

[0034] Adsorption isotherm studies provide important evidence for revealing the maximum adsorption capacity, adsorption performance, and adsorption mechanism. In a single system, phosphoryl silica and quaternized silica adsorbents exhibit high adsorption capacity for [UO2(CO3)3] at room temperature (298 K). 4- Both exhibit excellent adsorption capacities. The maximum adsorption capacities are 350 and 260 mg / g, respectively. To gain a deeper understanding of the adsorption process, the adsorption isotherms were fitted using the Langmuir and Freundlich models to establish correlations and validate the experimental data. The results show that the correlation coefficient R² of the Langmuir adsorption isotherms is close to 1. The adsorption behavior conforms to the Langmuir model.

[0035] 3. Conclusion In summary, this invention prepared two functionalized silica adsorbents with regular morphologies for the selective recovery and purification of uranyl ions and uranyl carbonate complex anions in nuclear wastewater. The adsorbents are modified by the dehydration condensation between amino and carboxyl groups to form stable amide bonds, exhibiting strong versatility. Suitable effective groups can be selectively introduced to provide adsorption sites according to practical applications, thereby achieving the removal and recovery of various uranium wastewaters in complex systems. The research results of this invention provide a valuable reference for the development and design of adsorbents for large-scale production in the treatment of uranium-containing wastewater.

[0036] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Parts of the present invention not described in detail are techniques known to those skilled in the art.

Claims

1. A method for preparing modified mesoporous silica, characterized in that... First, mesoporous silica was prepared, and then activated with hydrogen peroxide. After adding silane coupling agent (3-aminopropyl)trimethoxysilane (APTES), it was deoxygenated in N,N-dimethylformamide (DMF) to synthesize aminated silica SiO2-APTES. The amidation reaction stabilized the imine phosphate group and quaternary ammonium functional group and could be grafted onto the silica.

2. The method for preparing modified mesoporous silica according to claim 1, characterized in that... SiO2-APTES and N-(phosphorylmethyl)glycine (PRS) are added to DMF, and stirred under an inert atmosphere to allow dehydration condensation between amino and carboxyl groups to form stable amide bonds. PRS is then grafted onto silica to form silica PRS@SiO2-APTES modified with imine phosphate functional groups. Alternatively, SiO2-APTES and carboxyl-N,N,N-trimethylammonium bromide (CTAC) are added to DMF, and stirred under an inert atmosphere to allow dehydration condensation between amino and carboxyl groups to form stable amide bonds. CTAC is then grafted onto silica to form silica CTAC@SiO2-APTES modified with quaternary ammonium functional groups.

3. The method for preparing modified mesoporous silica according to claim 2, characterized in that... Regularly shaped porous silica was prepared by the sol-gel method.

4. The method for preparing modified mesoporous silica according to claim 1, 2, or 3, characterized in that... Regularly shaped porous silica was prepared by sol-gel method using hexadecyltrimethylammonium bromide (CTAB) and tetraethyl silicate (TEOS) as raw materials and cyclohexane and water as solvents.

5. The method for preparing modified mesoporous silica according to claim 4, characterized in that... When preparing 500 nm silica, the rotation speed inside the three-necked flask is controlled at 350 r / min, the reaction temperature is 70-80℃, and the reaction time is 12-13 h.

6. The method for preparing modified mesoporous silica according to claim 5, characterized in that... The concentration of hydrogen peroxide was 30% when preparing aminated modified mesoporous silica.

7. The method for preparing modified mesoporous silica according to claim 6, characterized in that, When preparing aminated modified mesoporous silica, the mass ratio of silica to silane coupling agent is 1:

3.

8. The method for preparing modified mesoporous silica according to claim 7, characterized in that... When preparing amino-functionalized mesoporous silica, the rotation speed inside the three-necked flask was controlled at 250 r / min, the reaction temperature at 120℃, and the reaction time at 24 h-25 h.

9. The method for preparing modified mesoporous silica according to claim 8, characterized in that... When preparing functionalized mesoporous silica, the mass ratio of modified silica to grafted functional groups is 3:

1.

10. The modified mesoporous silica according to any one of claims 1 to 9 is used as an adsorbent.

11. The modified mesoporous silica according to any one of claims 1 to 9 is used for adsorbing uranium in complex water bodies.

Images