Preparation method of uranium electro-adsorbent of sulfonic acid-functionalized N, P and B co-doped carbon material

Abstract

The present invention discloses a preparation method of a sulfonic acid-functionalized N, P, and B co-doped carbon material uranium electro-adsorbent. In the present invention, a polyphosphazene-derived heteroatom co-doped carbon material is used as a precursor, and through hydrothermal reaction with sulfuric acid, a sulfonated heteroatom co-doped carbon material uranium electro-adsorbent BNPCs-SO3H is prepared. The heteroatoms in the carbon material lay the foundation for the adsorption of uranyl ions. The number of heteroatoms and the synergistic effect brought about by the co-doping between heteroatoms can further enhance the electrochemical reaction activity of the material, while the introduction of sulfonic acid groups can provide more adsorption sites on the surface of the adsorbent, improving the adsorption capacity. The preparation method of the sulfonated heteroatom co-doped carbon material uranium electro-adsorbent is simple, has a clear structure, and good stability, and can be used for the selective and efficient electro-adsorption of uranyl ions, with good application prospects. The present invention not only provides new ideas for the design and regulation of adsorbent precursors, but also provides a new approach for the preparation of efficient uranium electro-adsorbents.

Description

Technical Field

[0001] The present invention relates to the field of preparation of carbon material uranium adsorbents, and in particular to a preparation method of a sulfonic acid-functionalized N, P and B co-doped carbon material uranium electro-adsorbent. Background Art

[0002] Uranium is a heavy metal and a primordial radionuclide, and is a key element of nuclear fuel. With the development and utilization of global nuclear energy, more and more uranium is released into the water environment, posing a major threat to human health and the ecosystem. The mining and processing of uranium ore and subsequent fuel processing generate a large amount of radioactive waste and wastewater, which contain various radionuclides. These uranium (VI) can accumulate through the food chain and eventually enter the circulatory system of organic life forms. Thus, it poses a serious threat to the lives of aquatic organisms and humans. Excessive radioactive substances will directly affect people's health, especially for infants, the elderly and pregnant women, because the immune capabilities of such groups decline and their resistance to the outside world is also weak, and they are more harmed by radioactive substances. Therefore, there is an urgent need to develop new materials and processes to remove wastewater before it is discharged into the environment.

[0003] Capacitive deionization (CDI) technology is a beneficial method widely used in the field of water treatment. By electro-adsorbing charged ions in the electrical double layer (EDLs) of the electrode, pure water is expected to be produced. Under the action of the electric field force, cations and anions in the aqueous solution are transferred to the electrodes with opposite charges. The separated ions can be stored in the electrical double layer on the electrode surface. Electrode regeneration can be achieved by changing the voltage or short-circuiting the electrode, thereby releasing the adsorbed ions back into the solution. Compared with traditional methods, CDI technology has the advantages of operating at normal temperature and low pressure, being environmentally friendly and having convenient electrode regeneration.

[0004] The performance of electro-adsorption mainly depends on the electrodes used. Carbon materials (such as activated carbon, carbon fiber, carbon aerogel, carbon nanotube and graphene) are often used as electrode materials due to their high electrical conductivity, large specific surface area, excellent porous structure and economy. However, due to their low selectivity and adsorption capacitance, these carbon materials perform relatively poorly in CDI performance. The capacitive behavior of carbon materials is mainly affected by the accessible specific surface area and surface functional groups. The microscopic morphology and physicochemical properties of porous carbon materials significantly affect their electrochemical characteristics. Introducing heteroatoms into carbon materials can optimize the electron distribution and local bonding on the material surface, thereby achieving excellent electrochemical performance. In addition, the number of heteroatoms and the co-doping effect can further enhance the electro-chemical reaction activity of carbon materials. In addition, functionalization can improve the surface structure of the electrode and increase the adsorption sites for U(VI). Previous studies have shown that sulfonic acid groups can be used as effective functional groups for uranium adsorption due to their excellent hydrophilic properties. Therefore, heteroatom doping and functional group modification are key strategies to enhance the performance of carbon materials.

[0005] In view of this, the present invention intends to combine heteroatom co-doped carbon materials with sulfonic acid groups and apply them to the electro-adsorption of uranyl ions in wastewater to improve their application performance. Summary of the Invention

[0006] The present invention aims to provide a preparation method of a uranium electro-adsorbent based on a sulfonic acid-functionalized N, P, and B co-doped carbon material. The carbon material used in the present invention is a heteroatom-doped carbon material derived from polyphosphazene, which is then subjected to a hydrothermal reaction with sulfuric acid to prepare a sulfonated heteroatom co-doped carbon material uranium electro-adsorbent BNPCs-SO3H. The heteroatoms in the carbon material lay the foundation for the adsorption of uranyl ions. The number of heteroatoms and the synergistic effect brought about by the co-doping between heteroatoms can further enhance the electrochemical reaction activity of the material, while the introduction of sulfonic acid groups can provide more adsorption sites on the surface of the adsorbent, further enhancing the adsorption capacity. The preparation method of the sulfonated heteroatom co-doped carbon material uranium electro-adsorbent in the present invention is simple, has a clear structure, and good stability, and can be used for the selective and efficient electro-adsorption of uranyl ions, having good application prospects. The present invention can not only provide new ideas for the design and regulation of adsorbent precursors, but also provide a new approach for the preparation of high-efficiency uranium electro-adsorbents.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a preparation method of a uranium electro-adsorbent based on a sulfonic acid-functionalized N, P, and B co-doped carbon material, comprising the following steps:

[0009] 1) Preparation of heteroatom co-doped carbon material: First, hexachlorocyclotriphosphazene and phenylboronic acid are added to acetonitrile and dissolved and stirred to be named solution A. Secondly, solution A is transferred to an ultrasonic bath and kept at a constant temperature of 80 °C for 3 h;

[0010] The reaction solution is vacuum filtered, washed with acetonitrile and absolute ethanol, and dried for 12 h to obtain a white powder of polyphosphazene. The uniformly ground polyphosphazene is placed in a muffle furnace and calcined at a constant temperature of 750 °C for 2 h to obtain a heteroatom-doped carbon material.

[0011] 2) Preparation of sulfonated heteroatom co-doped carbon material uranium electro-adsorbent: The heteroatom co-doped carbon material prepared in step 1) is dispersed in a concentrated sulfuric acid solution. After ultrasonic treatment for 15 min, the solution is placed in a stainless steel autoclave and reacted at a constant temperature of 160 °C for 8 h. After the reaction, the product is washed with absolute ethanol and deionized water until the solution is neutral. After drying, a sulfonated heteroatom-doped carbon microsphere material uranium electro-adsorbent BNPCs-SO3H is obtained.

[0012] Preferably, the volume of acetonitrile used in step 1) is 200 mL.

[0013] Preferably, the mass ratio of the hexachlorocyclotriphosphazene described in step 1) to the mass of benzenediboronic acid is 0.1859 g: 0.2943 g.

[0014] Preferably, the mass ratio of the heteroatom co-doped carbon material in step 2) to the volume of concentrated sulfuric acid used is 10 mg: 8 ml.

[0015] The present invention also provides the application of the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H prepared by the above method in the adsorption of uranyl ions.

[0016] Add the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H to the solution to be treated containing uranyl ions, and use a three-electrode system to react at room temperature for a corresponding time under a certain voltage.

[0017] Furthermore, before the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H is mixed with the solution to be treated containing uranyl ions, its pH needs to be adjusted to 2.0 - 8.0 using a pH regulator; preferably, the pH value is 5.5.

[0018] Furthermore, the adsorption time of the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H and the solution to be treated containing uranyl ions is 3 - 60 min; preferably, the adsorption time is 22 min.

[0019] Furthermore, the concentration range of the solution to be treated containing uranyl ions is 40 - 200 mg / L; preferably, the solution concentration is 140 mg / L;

[0020] Furthermore, the applied potential of the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H and the solution to be treated containing uranyl ions is 0.0 - 0.9 v; preferably, the applied potential is 0.9 v.

[0021] Furthermore, after the electroadsorption process of the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H and the solution to be treated containing uranyl ions ends, filter it using filter paper and measure the remaining uranyl ion content through a UV spectrophotometer.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The present invention synthesizes the sulfonated heteroatom co-doped carbon material uranium electroadsorbent BNPCs-SO3H by a hydrothermal method, which has the advantages of simple preparation method, low cost, and strong stability.

[0024] (2) The uranium electro-adsorbent BNPCs-SO3H of the sulfonated heteroatom co-doped carbon material prepared by the present invention. The number of heteroatoms and the synergistic effect brought about by the co-doping between heteroatoms can further enhance the electrochemical reaction activity of the material. The introduction of sulfonic acid groups improves the surface structure of the co-doped carbon material, provides more sites for the adsorption of uranyl ions, and thus improves the adsorption performance.

[0025] (3) The uranium electro-adsorbent BNPCs-SO3H of the sulfonated heteroatom co-doped carbon material prepared by the present invention has good stability, high electro-adsorption capacity, fast adsorption kinetics and high selectivity, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the synthesis of BNPCs-SO3H of the present invention;

[0027] Figure 2 It is a Fourier transform infrared spectrum diagram of BNPCs-SO3H and BNPCs-SO3H-U of the present invention;

[0028] Figure 3 It is a SEM diagram of BNPCs-SO3H of the present invention;

[0029] Figure 4 It is an XRD diagram of BNPCs-SO3H of the present invention;

[0030] Figure 5 It is a diagram showing the effect of pH value on the performance of BNPCs-SO3H in adsorbing uranyl ions;

[0031] Figure 6 It is a diagram showing the effect of adsorption time on the performance of BNPCs-SO3H in adsorbing uranyl ions;

[0032] Figure 7 It is a diagram showing the effect of uranium solution concentration on the performance of BNPCs-SO3H in adsorbing uranyl ions;

[0033] Figure 8 It is a diagram showing the effect of applied potential on the performance of BNPCs-SO3H in adsorbing uranyl ions;

[0034] Figure 9 It is a diagram showing the selective adsorption of BNPCs-SO3H for coexisting metal ions;

[0035] Figure 10 It is a CV curve diagram of BNPCs-SO3H. DETAILED DESCRIPTION OF THE INVENTION

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with embodiments. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0037] Example 1: Preparation method and property characterization of a uranium electro-adsorbent BNPCs-SO3H, a sulfonic acid-functionalized N, P, and B co-doped carbon material:

[0038] Solution A: Measure 200 mL of acetonitrile, add 0.1859 g of hexachlorocyclotriphosphazene and 0.2943 g of terephthalic acid diborate, stir evenly, then transfer the solution to an ultrasonic bath and keep it at a constant temperature of 80 °C for 3 h. Finally, filter the reaction solution by vacuum filtration, wash it 3 times with acetonitrile and absolute ethanol, and dry it for 12 h to obtain a white powder of polyphosphazene. Put the evenly ground polyphosphazene into a muffle furnace, under a N2 atmosphere, with a heating rate of 4 °C / min, calcine it at a constant temperature of 750 °C for 2 h to obtain a black solid powder (heteroatom co-doped carbon material).

[0039] Further, take 10 mg of BNPCs and put it into 8 mL of concentrated sulfuric acid. After ultrasonic treatment for 15 min, put the solution into a stainless-steel autoclave and react at a constant temperature of 160 °C for 8 h. After the reaction, wash the product with absolute ethanol and deionized water until the solution is neutral. Dry it for 12 h. After cooling to room temperature, carefully grind the material into fine particles with a mortar to obtain a black solid powder (BNPCs-SO3H).

[0040] Figure 1 is a schematic diagram of the synthesis route of BNPCs-SO3H.

[0041] Figure 2 is the Fourier transform infrared (FT-IR) spectra of BNPCs-SO3H and BNPCs-SO3H-U. The peaks that obviously appear at 1321 cm -1 , 1478 cm -1 and 1234 cm -1 are the absorption peaks of B-O bond, C-N bond, and C-C bond respectively. Related to SO3H, the new peaks that appear at 1034 cm -1 and 1178 cm -1 are respectively the asymmetric stretching vibration peak and symmetric stretching vibration peak of S=O in the sulfonic acid group, and the new peak at 725 cm -1 is the bending vibration peak of O-H in the sulfonic acid group. After electro-adsorption, in the infrared spectrum of BNPCs-SO3H-U, at 883 cm −1The new peak at [location] belongs to the stretching vibration peaks of O=U=O and S=O, and the intensity of the stretching vibration peak of S=O has decreased, indicating that there is chemical bonding between U(VI) and BNPCs-SO3H.

[0042] Figure 3 This is the SEM image of BNPCs-SO3H. Many large pores with different structures appear on the surface of BNPCs-SO3H, which is beneficial to increasing the pore volume to form more binding sites.

[0043] In the range of 20 - 80°, XRD analysis was performed on the crystals of BNPCs-SO3H. From Figure 4 it can be seen that for BNPCs-SO3H, the graph has a strong diffraction peak and a weak diffraction peak at approximately 29° and 43° respectively, corresponding to the 002 plane representing the ordered stacked graphene structure and the 100 plane representing the disordered structure. In the spectrum of BNPCs-SO3H, the 002 plane moves from 27° to 29°, the intensity decreases, and the full width at half maximum broadens; the full width at half maximum of the 100 plane narrows and the intensity increases. These indicate that functionalization increases the degree of disorder of the structure and provides more abundant pore structures for the material.

[0044] Example 2: Adsorption of uranyl ions by sulfonated heteroatom-doped carbon material uranium electroadsorbent BNPCs-SO3H

[0045] The pH value of the solution will affect the species and morphology of uranyl ions, and even lead to the formation of polynuclear complexes, thereby affecting the adsorption performance of the adsorbent. The pH value of the solution was adjusted in the range of 2.0 - 8.0 using 1 mol / L HNO3 or NaOH solution. In 30 mL of uranium solution with a concentration of 100 mg / L, the three-electrode system was operated for 1 h, filtered with filter paper, and the content of remaining uranyl ions in the filtrate was measured using a UV spectrophotometer to calculate the adsorption capacity of the uranium adsorption carbon microsphere composite material BNPCs-SO3H for uranyl ions. Figure 5 This is the change in the adsorption performance of BNPCs-SO3H in the range of pH value from 2.0 to 8.0. The adsorption process shows a strong correlation with the pH value. The electroadsorption amount of BNPCs-SO3H increases with the increase of pH, reaching a maximum value of 389.48 mg / g at pH = 5.5. The electroadsorption capacity of the material decreases with the further increase of the pH value, which may be due to the fact that the pH value affects the charge on the surface of the adsorbent and the protonation of oxygen-containing groups, resulting in the precipitation and formation of low-affinity uranyl substances. The sharp decrease in the electroadsorption capacity of BNPCs-SO3H after reaching the maximum value proves that it is more sensitive to the pH value, indicating that the adsorption mechanism is mainly complexation. Therefore, 5.5 was selected as the optimal pH value for the studied adsorbent.

[0046] As Figure 6, keeping other conditions unchanged, the adsorption kinetics of uranyl ions on BNPCs-SO3H at different adsorption times (3 - 60 min) was studied. The pH value of the uranium solution was adjusted to 5.5 with 1 mol / L HNO3 or NaOH solution. Samples were taken after working in a three-electrode system for different times in 30 mL of uranium solution with a concentration of 100 mg / L. After filtering with filter paper, the content of residual uranyl ions in the filtrate was measured using a UV spectrophotometer, and the adsorption capacity of BNPCs-SO3H for uranyl ions was calculated. The adsorption kinetic curve of BNPCs-SO3H for uranyl ions was plotted. The kinetic mechanism of the adsorbent for uranyl ions depends on the rate of transfer of uranyl ions from the bulk phase to the binding sites. As time increases, the electro-adsorption capacity of BNPCs-SO3H reaches a maximum of 373.58 mg / g within 22 min. This can be explained by the increase in the binding sites associated with U(VI) ions over time until the binding sites are completely occupied.

[0047] As Figure 7 , keeping other conditions unchanged, the effect of the initial concentration of uranyl ions on the adsorption amount was investigated, and the optimal adsorption amount of BNPCs-SO3H under ideal conditions was estimated. The pH value of the uranium solution was adjusted to 5.5 with 1 mol / L HNO3 or NaOH solution. In 30 mL of uranium solutions with different concentrations (40 - 200 mg / L), after working in a three-electrode system for 1 h, samples were filtered with filter paper, and the content of residual uranyl ions in the filtrate was measured using a UV spectrophotometer, and the adsorption capacity of BNPCs-SO3H for uranyl ions was calculated. The electro-adsorption ability of BNPCs-SO3H increases with the increase of the initial concentration and reaches 626.37 mg / g at 140 mg / L. The electro-adsorption capacity of BNPCs-SO3H increases with the change of the initial concentration, and the maximum electro-adsorption capacity is much higher than that of BNPCs, indicating that sulfonic acid functionalization can greatly improve the electro-adsorption performance of BNPCs.

[0048] As Figure 8 , keeping other conditions unchanged, the effect of different applied potentials on the adsorption amount was studied. When the DC regulated power supply is open circuit (0 V), BNPCs-SO3H can spontaneously adsorb U(VI) ions in the solution and reach equilibrium within a certain period of time. As the applied potential increases, the electro-adsorption capacity of BNPCs-SO3H gradually increases and reaches a maximum of 387.84 mg / g at 0.9 V. It is speculated that a higher applied potential can provide more electric field force to promote the binding of U(VI) ions to the adsorbent.

[0049] Example 3: Selective adsorption of uranyl ions by the sulfonated heteroatom-doped carbon material uranium electro-adsorbent BNPCs-SO3H.

[0050] In actual aqueous solutions, there are various metal ions, which will affect the binding efficiency of U(VI) with the adsorbent. In a 30 mL mixed solution containing 100 mg / L of uranyl ions and interfering metal ions of the same concentration, the three-electrode system was operated for 1 h, filtered with filter paper, and the content of remaining uranyl ions in the filtrate was measured by inductively coupled plasma mass spectrometry to calculate the adsorption capacity of BNPCs-SO3H for uranyl ions, and test the effects of Mg 2+ 、Cu 2+ 、Ca 2+ 、Pb 2+ 、Th 4+ 、Fe 2+ and Eu 3+ metal ions on the adsorption of uranyl ions by BNPCs-SO3H. Figure 9 , Figure 10 Among them, in the presence of the other 7 metal ions, BNPCs-SO3H still has a high electro-adsorption capacity for U(VI), indicating that BNPCs-SO3H has a high selectivity for U(VI). The above results show that the sulfonated heteroatom-doped carbon material uranium electro-adsorbent BNPCs-SO3H prepared by the method of the present invention has the advantages of simple preparation method, good stability, good adsorption performance, and strong anti-interference ability, and can be used as a potential adsorbent for the treatment of U(VI)-containing wastewater.

[0051] The present invention uses a polyphosphazene-derived heteroatom co-doped carbon material as a precursor, and synthesizes a sulfonated heteroatom co-doped carbon material uranium electro-adsorbent BNPCs-SO3H by hydrothermal reaction with sulfuric acid, which has the advantages of simple preparation method, low cost, and strong stability;

[0052] For the sulfonated heteroatom-doped carbon material uranium electro-adsorbent BNPCs-SO3H prepared by the present invention, the introduction of sulfonic acid groups increases the porosity of the heteroatom-doped carbon material, provides more sites for the adsorption of uranyl ions, and thus improves the adsorption performance.

[0053] The sulfonated heteroatom-doped carbon material uranium electro-adsorbent BNPCs-SO3H prepared by the present invention has good stability, high adsorption capacity and high selectivity, and has good application prospects.

[0054] The embodiments described above only represent several preferred embodiments of the present invention, and the description thereof is relatively specific and detailed, but is not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may have various changes and modifications, and any modifications, equivalent replacements, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a sulfonic acid-functionalized N, P and B co-doped carbon material uranium electroadsorbent, characterized in that, It includes the following steps: a. Preparation of heteroatom co-doped carbon materials: First, hexachlorocyclotriphosphazene and phenylboronic acid are added to acetonitrile for dissolution and stirring, and it is named solution A. Secondly, solution A is transferred to an ultrasonic bath and kept at a constant temperature of 80 °C for 3 h; The reaction solution is vacuum filtered, washed with acetonitrile and absolute ethanol, and dried for 12 h to obtain white powder polyphosphazene. The uniformly ground polyphosphazene is placed in a muffle furnace and calcined at a constant temperature of 750 °C for 2 h to obtain heteroatom-doped carbon materials; b. Preparation of sulfonated heteroatom co-doped carbon microsphere material uranium electro-adsorbent: The heteroatom co-doped carbon materials prepared in step a are dispersed in concentrated sulfuric acid solution. After ultrasonic treatment for 15 min, the solution is placed in a stainless steel autoclave and reacted at a constant temperature of 160 °C for 8 h; After the reaction, the product is washed with absolute ethanol and deionized water until the solution is neutral, and dried to obtain sulfonated heteroatom-doped carbon material uranium electro-adsorbent BNPCs-SO3H.

2. The preparation method of a sulfonic acid-functionalized N, P, and B co-doped carbon material uranium electro-adsorbent according to claim 1, characterized in that, In step a, the volume of acetonitrile used is 200 mL.

3. The preparation method of a sulfonic acid-functionalized N, P, and B co-doped carbon material uranium electro-adsorbent according to claim 1, characterized in that, In step a, the mass ratio of hexachlorocyclotriphosphazene to phenylboronic acid is 0.1859 g:0.2943 g.

4. The preparation method of a sulfonic acid-functionalized N, P and B co-doped carbon material uranium electro-adsorbent according to claim 1, characterized in that, In step b, the mass ratio of the heteroatom co-doped carbon materials to the volume of concentrated sulfuric acid used is 10 mg:8 ml.

5. The preparation method of a sulfonic acid-functionalized N, P and B co-doped carbon material uranium electroadsorbent according to any one of claims 1-4, characterized in that, For the prepared sulfonated heteroatom-doped carbon material uranium electro-adsorbent, an electrochemical workstation is used in a three-electrode system, and constant voltage polarization is used for the electro-adsorption process in the solution to be treated containing uranyl ions.

6. The preparation method of a uranium electro-adsorbent of a sulfonic acid-functionalized N, P, and B co-doped carbon material according to claim 5, characterized in that, Before the sulfonated heteroatom-doped carbon material uranium electro-adsorbent is mixed with the solution to be treated containing uranyl ions, its pH needs to be adjusted to 2.0 - 8.0 using a pH regulator.

7. The preparation method of a sulfonic acid-functionalized N, P, and B co-doped carbon material uranium electroadsorbent according to claim 5, characterized in that The adsorption time of the sulfonated heteroatom-doped carbon material uranium electro-adsorbent and the solution to be treated containing uranyl ions is 3 - 60 min.

8. The preparation method of a uranium electro-adsorbent of a sulfonic acid-functionalized N, P and B co-doped carbon material according to claim 5, characterized in that, The solution concentration range of the sulfonated heteroatom-doped carbon material uranium electro-adsorbent and the solution to be treated containing uranyl ions is 40 - 200 mg / L.

9. The preparation method of a sulfonic acid-functionalized N, P and B co-doped carbon material uranium electroadsorbent according to claim 5, characterized in that, The applied potential of the sulfonated heteroatom-doped carbon material uranium electro-adsorbent and the solution to be treated containing uranyl ions is 0.0 - 0.9 v; After the electro-adsorption process of the sulfonated heteroatom co-doped carbon material uranium electro-adsorbent and the solution to be treated containing uranyl ions is completed, it is filtered using filter paper and the remaining uranyl ion content is measured by an ultraviolet spectrophotometer.

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