Preparation and application of modified carbon nitride material for uranium separation

Abstract

The application discloses a preparation and application of a modified carbon nitride material for uranium separation, and comprises the following steps: dissolving dicyandiamide and NaCl in deionized water, stirring, freezing, drying, and then putting into a tube furnace, heating and keeping warm under an argon gas flow, and obtaining a yellow block after cooling; grinding the yellow block into powder, immersing the powder into deionized water, stirring, filtering, washing, and drying to obtain a cyan-modified carbon nitride material; immersing the cyan-modified carbon nitride material into a mixed aqueous solution of NH2OH·HCl and NaOH, heating and keeping warm, filtering, washing, and drying to obtain a modified carbon nitride material modified by amidoxime groups, namely AO-C3N4. The application constructs amidoxime groups on the carbon nitride material, that is, the carbon nitride material can effectively adsorb uranium as a U(VI) binding site, and the visible light absorption capacity and the carrier separation efficiency are improved through the introduction of defect levels, so that the uranium extraction capacity of the AO-C3N4 is improved. Meanwhile, ROS generated under light endows the AO-C3N4 with excellent antibacterial performance, and prevents serious marine biofouling from limiting the uranium extraction performance of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of uranium separation, and more particularly, relates to a preparation and application of a modified carbon nitride material for uranium separation. BACKGROUND

[0002] Nuclear energy is essential for future sustainable energy supply due to its unparalleled efficiency and low carbon emission. As the basis resource for nuclear energy, the uranium reserves on land can only meet the demand of nuclear power generation for less than a century, while the uranium reserves in seawater are 1000 times more than that on land. In this case, it is essential to extract uranium from seawater, which is considered as one of the seven chemical separations that can change the world. Among all the current feasible strategies, the extraction of uranium from seawater through adsorption materials seems to be the most promising way. However, the extremely low concentration (3.3 ppb) of soluble uranium (uranyl ion) in seawater is saturated by strong binding ligand carbonate ions to form uranyl carbonate. Therefore, the uranium extraction capacity of adsorption materials is mainly determined by the thermodynamic equilibrium established between the adsorbed uranyl ions and the uranyl carbonate in seawater, and it is the development trend of seawater uranium extraction adsorption materials to improve the binding strength of adsorption sites to uranyl ions and the number of adsorption sites.

[0003] As the most advanced uranyl ion binding site, amine oxime groups have been widely constructed on various adsorption materials to selectively capture uranyl ions. However, the number of amine oxime groups that can be constructed in adsorption materials is very limited, which has become a major factor restricting the uranium extraction performance. Fortunately, uranium is a redox-active metal element. The soluble hexavalent uranium (U(VI)) in uranyl ions can be reduced to insoluble tetravalent uranium (U(IV)) and further form neutral nanoparticles, releasing uranyl binding sites. In particular, the reduction method based on semiconductor photocatalysis can also produce reactive oxygen species (ROS) to destroy the organic components of biological entities, thereby avoiding the serious marine biological fouling that limits the uranium extraction performance of adsorption materials. In addition, the inexhaustible solar energy can guarantee the energy input of this method. For example, the composite of black phosphorus and polyacrylamide oxime fiber (BP-PAO) extracts 11.76 mg / g of uranium from natural seawater after 8 weeks of simulated sunlight irradiation, which is 1.5 times that of the original polyacrylamide oxime fiber. Unfortunately, the interface energy barrier of the composite structure will cause the loss of electrons in the transmission process, further limiting the U(VI) reduction performance, and the currently used semiconductors are expensive, which is not conducive to practical application. Therefore, it is an effective strategy to directly construct amine oxime groups on inexpensive semiconductors (such as carbon nitride) for light-assisted extraction of uranium from seawater, but it is still a great challenge. SUMMARY

[0004] An object of the present application is to solve at least the above problems and / or disadvantages and provide at least the advantages described later.

[0005] To achieve these objects and other advantages and in accordance with the purpose of the application, as embodied and broadly described herein, there is provided a method for preparing a modified carbon nitride material for uranium separation, comprising the steps of:

[0006] Step one, dissolving dicyandiamide and NaCl in deionized water, stirring for 9-11 hours, then freeze-drying the solution to obtain a mixture of dicyandiamide and NaCl;

[0007] Step two, placing the mixture of dicyandiamide and NaCl obtained in step one into a tube furnace, heating under argon gas flow, and keeping warm for 3-5 hours, after cooling, obtaining a yellow block, grinding into powder; immersing the obtained yellow block powder into deionized water, stirring for 1-3 hours, removing water-soluble impurities by filtering and washing; then drying the product at 50-70℃ to obtain a cyan-modified g-C3N4, namely C-C3N4.

[0008] Step three, dissolving NH2OH·HCl and NaOH in deionized water, then immersing C-C3N4 into the above solution, heating and keeping warm, then filtering and washing to remove water-soluble impurities, drying at 50-70℃ to obtain a modified carbon nitride material, namely AO-C3N4.

[0009] Preferably, in step one, the mass-volume ratio of dicyandiamide, NaCl and deionized water is 1g:4-6g:40-60mL.

[0010] Preferably, in step two, the volume-mass ratio of deionized water to dicyandiamide is 40-60mL:1g.

[0011] Preferably, in step two, the heating rate under argon gas flow is 2-3℃ / min, and the heating temperature is 500-600℃.

[0012] Preferably, in step three, the mass-volume ratio of NH2OH·HCl, NaOH, C-C3N4 and deionized water is 5-7g:3-4g:1g:40-60mL.

[0013] Preferably, in step three, the heating temperature is 70-90℃, and the keeping warm time is 9-11 hours.

[0014] Preferably, in step two, it further comprises: treating the obtained C-C3N4 with a low-temperature plasma treatment instrument for 1-3 minutes.

[0015] Preferably, the atmosphere of the low-temperature plasma treatment instrument is nitrogen or ammonia; the frequency of the low-temperature plasma treatment instrument is 35-55KHz, the power is 200-400W, and the pressure of the atmosphere is 30-40Pa.

[0016] The application further provides application of the modified carbon nitride material prepared by the preparation method in uranium separation, characterized in that the modified carbon nitride material is added into seawater containing uranium, a photocatalytic reaction is carried out under the condition of xenon lamp simulating sunlight, the modified carbon nitride material after the reaction is ultrasonically treated in a mixed solution of Na2CO3 and H2O2 for 2-4 h, and then is washed with deionized water for 2-3 times, and after drying, the modified carbon nitride material is recycled again.

[0017] Preferably, the concentration of the Na2CO3 solution is 0.05-0.15 mol / L, and the concentration of the H2O2 solution is 0.05-0.15 mol / L.

[0018] Preferably, the step three further comprises: treating the obtained AO-C3N4 by using a low-temperature plasma treatment instrument for 3-5 min; the atmosphere of the low-temperature plasma treatment instrument is nitrogen or ammonia; the frequency of the low-temperature plasma treatment instrument is 35-55 KHz, the power is 200-400 W, and the pressure of the atmosphere is 30-40 Pa.

[0019] The application at least has the following beneficial effects: the modified carbon nitride material (AO-C3N4) prepared by constructing amidoxime groups on the cyan-modified g-C3N4 is used for uranium separation. The amidoxime groups not only effectively adsorb uranium as U(VI) binding sites, but also significantly improve the visible light absorption capacity and carrier separation efficiency by introducing defect levels, which opens up a new carrier decay path for AO-C3N4, so that the adsorbed U(VI) can capture carriers faster, thereby improving the uranium extraction capacity of AO-C3N4. In addition, the active oxygen (ROS) generated under light endows AO-C3N4 with excellent antibacterial performance, preventing serious marine biofouling from limiting the uranium extraction performance of the material. Thanks to these excellent performances, the mass of uranium extracted from natural seawater by AO-C3N4 after one week of sunlight is 850 μg / g, which is 1.73 times that after one week without light. The application not only provides a cheap photocatalyst for efficient extraction of uranium from seawater, but also opens up a new way for the development of amidoxime group semiconductors.

[0020] Other advantages, objects, and features of the application will be apparent from the following specification, and will be appreciated by those skilled in the art. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 XRD patterns of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2;

[0022] Figure 2FTIR spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2;

[0023] Figure 3 Solid state NMR spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2; 13 C magic angle spinning nuclear magnetic resonance (NMR) spectra;

[0024] Figure 4 Full XPS spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2;

[0025] Figure 5 C K-edge XAS spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2;

[0026] Figure 6 N K-edge XAS spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2;

[0027] Figure 7 Plot of uranium extraction versus time in the dark and under illumination for AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2;

[0028] Figure 8 Plot of uranium extraction versus time in the dark and under illumination for AO-C3N4 prepared in Example 1, AO-C3N4-1 prepared in Example 2 and AO-C3N4-2 prepared in Example 3;

[0029] Figure 9 Uranium extraction and uranium extraction mass for AO-C3N4 prepared in Example 1 under illumination at different initial uranium concentrations (0.5-200 mg / L);

[0030] Figure 10 Uranium extraction for AO-C3N4 prepared in Example 1 under illumination at different pH (1-10);

[0031] Figure 11 Uranium extraction for AO-C3N4 prepared in Example 1 under illumination in the presence of ionic interference;

[0032] Figure 12 Uranium extraction for AO-C3N4 prepared in Example 1 under illumination for five consecutive cycles;

[0033] Figure 13 Uranium extraction efficiency of AO-C3N4 prepared for Example 1 from spiked natural seawater with 8 mg / L U(VI) in the dark and under illumination;

[0034] Figure 14 UV-Vis diffuse reflectance spectra of AO-C3N4 prepared for Example 1, P-C3N4 prepared for Comparative Example 1 and C-C3N4 prepared for Comparative Example 2;

[0035] Figure 15 Sample images of AO-C3N4 prepared for Example 1 (A), P-C3N4 prepared for Comparative Example 1 (B) and C-C3N4 prepared for Comparative Example 2 (C);

[0036] Figure 16 Transient photocurrent effect of AO-C3N4 prepared for Example 1, P-C3N4 prepared for Comparative Example 1 and C-C3N4 prepared for Comparative Example 2;

[0037] Figure 17 Steady state PL spectra of AO-C3N4 prepared for Example 1, P-C3N4 prepared for Comparative Example 1 and C-C3N4 prepared for Comparative Example 2;

[0038] Figure 18 Full XPS spectra of AO-C3N4, AO-C3N4-U-Dark and AO-C3N4-U-Light;

[0039] Figure 19 U 4f XPS spectra of AO-C3N4-U-Dark and AO-C3N4-U-Light;

[0040] Figure 20 XRD patterns of AO-C3N4 and AO-C3N4-U-Light;

[0041] Figure 21 EPR spectra of hydroxyl radicals (·OH) of AO-C3N4 prepared for Example 1 in the dark and under illumination;

[0042] Figure 22 EPR spectra of superoxide radicals (·O2 - ) of AO-C3N4 prepared for Example 1 in the dark and under illumination;

[0043] Figure 23 EPR spectra of singlet oxygen (1 1 O2) of AO-C3N4 prepared for Example 1 in the dark and under illumination;

[0044] Figure 24 Colony growth photographs of AO-C3N4 prepared for Example 1 in the dark and under illumination;

[0045] Figure 25 Extraction yield of various species (U, V, Fe, Zn, Cu) in natural seawater by AO-C3N4 prepared in Example 1 after one week in the dark and under light; DETAILED DESCRIPTION

[0046] The present application will be further described in conjunction with the drawings, so that those skilled in the art can implement the present application according to the description and the drawings.

[0047] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0048] Example 1

[0049] A preparation method of a modified carbon nitride material for uranium separation, comprising the following steps:

[0050] Step one, 10g dicyandiamide and 50g NaCl are dissolved in 500mL deionized water, stirred for 10h, and then the solution is freeze-dried to obtain a dicyandiamide and NaCl mixture;

[0051] Step two, the dicyandiamide and NaCl mixture obtained in step one is placed in a tube furnace, heated to 550℃ at a heating rate of 2.3℃ / min under an argon gas stream, and kept for 4h, and after cooling, a yellow block is obtained, which is ground into a powder; the obtained yellow block powder is immersed in 500mL deionized water, stirred for 2h, and water-soluble impurities are removed by filtration and washing; then the product is dried at 60℃ to obtain a cyan-modified g-C3N4, namely C-C3N4.

[0052] Step three, 6g NH2OH·HCl and 3.5g NaOH are dissolved in 50mL deionized water, then 1g C-C3N4 is immersed in the above solution and heated to 80℃, kept for 10h, then filtered, washed to remove water-soluble impurities, and dried at 60℃ to obtain a modified carbon nitride material, namely AO-C3N4.

[0053] Example 2

[0054] A preparation method of a modified carbon nitride material for uranium separation, comprising the following steps:

[0055] Step one, 10g dicyandiamide and 50g NaCl are dissolved in 500mL deionized water, stirred for 10h, and then the solution is freeze-dried to obtain a dicyandiamide and NaCl mixture;

[0056] Step two, the mixture of dicyandiamide and NaCl obtained in step one was put into a tube furnace, heated to 550℃ under argon gas flow at a heating rate of 2.3℃ / min, and kept for 4h, after cooling, a yellow block was obtained, which was ground into powder; the yellow block powder obtained was immersed in 500mL deionized water, stirred for 2h, and water-soluble impurities were removed by filtration and washing; then the product was dried at 60℃ to obtain cyano-modified g-C3N4, namely C-C3N4; the obtained C-C3N4 was treated for 2min using a low-temperature plasma treatment instrument, to obtain cyano-modified g-C3N4, namely C-C3N4-1; the atmosphere of the low-temperature plasma treatment instrument was ammonia; the frequency of the low-temperature plasma treatment instrument was 45KHz, the power was 300W, and the pressure of the atmosphere was 35Pa.

[0057] Step three, 6g NH2OH·HCl and 3.5g NaOH were dissolved in 50mL deionized water, then 1g C-C3N4-1 was immersed in the above solution and heated to 80℃, kept for 10h, then filtered, washed to remove water-soluble impurities, and dried at 60℃ to obtain a modified carbon nitride material, namely AO-C3N4-1.

[0058] Example 3

[0059] A method for preparing a modified carbon nitride material for uranium separation, comprising the following steps:

[0060] Step one, 10g dicyandiamide and 50g NaCl were dissolved in 500mL deionized water, stirred for 10h, and then the solution was freeze-dried to obtain a mixture of dicyandiamide and NaCl;

[0061] Step two, the mixture of dicyandiamide and NaCl obtained in step one was put into a tube furnace, heated to 550℃ under argon gas flow at a heating rate of 2.3℃ / min, and kept for 4h, after cooling, a yellow block was obtained, which was ground into powder; the yellow block powder obtained was immersed in 500mL deionized water, stirred for 2h, and water-soluble impurities were removed by filtration and washing; then the product was dried at 60℃ to obtain cyano-modified g-C3N4, namely C-C3N4; the obtained C-C3N4 was treated for 2min using a low-temperature plasma treatment instrument, to obtain cyano-modified g-C3N4, namely C-C3N4-1; the atmosphere of the low-temperature plasma treatment instrument was ammonia; the frequency of the low-temperature plasma treatment instrument was 45KHz, the power was 300W, and the pressure of the atmosphere was 35Pa.

[0062] Step three, 6g NH2OH·HCl and 3.5g NaOH were dissolved in 50mL deionized water, then 1g C-C3N4-1 was immersed in the above solution and heated to 80℃ for 10h, then filtered, washed to remove water-soluble impurities, and dried at 60℃ to obtain a modified carbon nitride material, namely AO-C3N4; the obtained AO-C3N4 was treated for 4min using a low-temperature plasma treatment instrument; the atmosphere of the low-temperature plasma treatment instrument was ammonia; the frequency of the low-temperature plasma treatment instrument was 45KHz, the power was 300W, and the pressure of the atmosphere was 35Pa.

[0063] Comparative example 1

[0064] The preparation method of P-C3N4 includes the following steps:

[0065] 10g dicyandiamide was placed in a tube furnace and heated to 550℃ at a heating rate of 2.3℃ / min under an argon gas stream for 4h, and after cooling, a yellow block was obtained, which was ground into powder to obtain the original g-C3N4, namely P-C3N4;

[0066] Comparative example 2

[0067] The preparation method of C-C3N4 includes the following steps:

[0068] Step one, 10g dicyandiamide and 50g NaCl were dissolved in 500mL deionized water and stirred for 10h, then the solution was freeze-dried to obtain a dicyandiamide and NaCl mixture;

[0069] Step two, the dicyandiamide and NaCl mixture obtained in step one was placed in a tube furnace and heated to 550℃ at a heating rate of 2.3℃ / min under an argon gas stream for 4h, and after cooling, a yellow block was obtained, which was ground into powder; the obtained yellow block powder was immersed in 500mL deionized water and stirred for 2h, and water-soluble impurities were removed by filtration and washing; then the product was dried at 60℃ to obtain a cyan-modified g-C3N4, namely C-C3N4.

[0070] Figure 1X-ray diffraction (XRD) patterns of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2 are shown. It can be seen that the obvious diffraction peaks of P-C3N4 are located at 27.3° (002) and 13.0° (100), belonging to the interlayer stacking of g-C3N4 and the in-plane stacking of heptazine units, respectively. For C-C3N4 and AO-C3N4, no peaks attributable to the (100) plane were observed, indicating that the ordered structure of the in-plane heptazine units was disrupted by cyano and amine oxime groups, respectively. Furthermore, the peaks of the (002) plane of both C-C3N4 and AO-C3N4 are located at 27.7°. Compared with P-C3N4, the (002) plane degree of C-C3N4 and AO-C3N4 is higher, indicating a reduced interlayer stacking distance.

[0071] Fourier transform infrared (FTIR) spectroscopy was used to study the molecular structures of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2. Figure 2 As shown, 3500–3000, 1800–1200, and 808cm -1 The peaks at these locations originate from the stretching mode of the NH / OH bond, the out-of-plane bending mode of the heptaazine unit, and the 2167 cm⁻¹ heptaazine unit, respectively. C-C₃N₄ at 2167 cm⁻¹... -1 A strong cyano characteristic peak appeared at 2167 cm⁻¹, and AO-C3N4 showed a peak at 2167 cm⁻¹. -1 No obvious peak was observed at 931 cm⁻¹, but at 931 cm⁻¹... -1 A new ON bond signal appeared, indicating that the cyano group in C-C3N4 was successfully converted into the amine oxime group in AO-C3N4. Solid-state reactions were performed on AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2. 13 The results of the C-magic-angle rotating nuclear magnetic resonance (NMR) spectroscopy experiment are as follows: Figure 3 As shown, the three samples 13 The C NMR spectra both showed two main peaks at 164.7 and 157.7 ppm, corresponding to NCN(NH4+) and N2O, respectively. x The chemical shifts of the C atom in C-C3N were observed. For C-C3N4, two additional peaks corresponding to the C atom in the cyano group and the neighboring C atom were observed at 122.6 and 172.1 ppm, respectively. For AO-C3N4, two additional new peaks centered at 151.5 and 173.2 ppm were attributed to the chemical shifts of the C atom in the amylopyrime group and the neighboring C atom, respectively, consistent with the FTIR analysis.

[0072] X-ray photoelectron spectroscopy (XPS) and synchrotron radiation soft X-ray absorption (XAS) spectroscopy were used to analyze the electronic structure of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2. Figure 4 For the full XPS spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2, it can be seen that C-C3N4 contains a strong peak of Na 1s at 1071.1 eV, and no signal of Cl 2p is observed, indicating that Na is doped into C-C3N4, which is also the reason for the presence of cyanogroup. In addition, for AO-C3N4, there is almost no peak of Na 1s, and a strong signal is observed at 532.1 eV corresponding to O 1s, indicating that the doped Na is combined with the cyanogroup of C-C3N4 and is released after the cyanogroup is converted into the amidoxime group of AO-C3N4. Figure 5 For the C K-edge XAS spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2, the two characteristic peaks at ~ 285.8 and ~ 288.3 eV correspond to the π* band of out-of-plane C=C and the π* band of N=C-N caused by N defects of heptazine units. Compared with P-C3N4 and C-C3N4, AO-C3N4 exhibits higher peak intensity at ~ 285.8 eV and lower peak intensity at ~ 288.3 eV, and the decrease of N=C-N peak indicates the disorder of ordered structure, indicating that the introduction of cyanogroup and amidoxime group seriously destroys the ordered in-plane structure, resulting in a large number of N defects and enhancing the interlayer bonding. The same conclusion can also be analyzed from the N K-edge XAS spectrum as shown in Figure 6 As shown, the three peaks at ~ 399.9, ~ 402.7, and ~ 405.8 eV are attributed to the π* band of C-N=C, the π* band of N-3C, and the σ* band of out-of-plane C-N. Similarly, the peak intensity of C-N=C of C-C3N4 and AO-C3N4 is much smaller than that of P-C3N4, and the peak intensity of out-of-plane C-N is significantly greater than that of P-C3N4. The above results show that the precursor rich in cyanogroup is successfully synthesized, and AO-C3N4 rich in amidoxime group is further obtained.

[0073] Uranium extraction experiments were carried out on AO-C3N4 prepared in Example 1, AO-C3N4-1 prepared in Example 2, AO-C3N4-2 prepared in Example 3, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2: all samples were used as adsorbents for light-assisted uranium extraction, a certain amount of UO2(NO3)2·6H2O was dissolved in deionized water to prepare a U(VI) solution (100 mg / L), unless otherwise specified, the pH value of the U(VI) solution was adjusted to 5, the glass reactor was filled at a solid-liquid ratio of 0.5 g / L under ambient conditions, each reaction was carried out in an air atmosphere, no sacrificial agent was used, and the glass reactor was illuminated in the dark and using a 2 kW / m 2 of xenon lamp to simulate sunlight, respectively. After solid-liquid separation, the U(VI) concentration was analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES) and azoarsenite III spectrophotometry at a wavelength of 652 nm. The uranium extraction rate (%) was calculated as [(C0-C) / C0]x100%, and the uranium extraction mass (mg / g) was calculated as (C0-C)xV / m, where C is the final concentration of U(VI) (mg / L), C0is the initial concentration of U(VI) (mg / L), V is the volume of the solution (L), and m is the mass of the sample (g).

[0074] The relationship between the uranium extraction rate and time of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2 under dark and light conditions is shown in Figure 7 Under dark conditions, the uranium extraction rates of P-C3N4 and C-C3N4 after 120 min were 9.4% and 14.2%, respectively. Compared with P-C3N4 and C-C3N4, AO-C3N4 showed stronger adsorption capacity, and the uranium extraction rate reached 47.3% after 120 min. When a 2 kW / m 2 of xenon lamp was used to simulate sunlight as a light source, the light-assisted uranium extraction capacity of P-C3N4 was similar to that without light, and the uranium extraction rates of C-C3N4 and AO-C3N4 under light were significantly improved, reaching 57.9% and 94.2% after 120 min, respectively, indicating that AO-C3N4 has superior performance in light-assisted uranium extraction. The relationship between the uranium extraction rate and time of AO-C3N4 prepared in Example 1, AO-C3N4-1 prepared in Example 2 and AO-C3N4-2 prepared in Example 3 under dark and light conditions is shown in Figure 8 The uranium extraction rates of AO-C3N4-1 and AO-C3N4-2 were higher than that of AO-C3N4 under dark and light conditions, and the uranium extraction rate of AO-C3N4-2 under light was the highest, reaching 97.8%, indicating that treating C-C3N4 and AO-C3N4 with a low-temperature plasma processor is beneficial to improving the uranium extraction capacity of the material.

[0075] The AO-C3N4 prepared in Example 1 was subjected to uranium extraction experiments in different initial concentrations of U(VI) solution under light, and the results are shown in Figure 9 When the initial uranium concentration was in the range of 0.5-200 mg / L, AO-C3N4 had excellent uranium extraction rate, and the mass of light-assisted uranium extraction of AO-C3N4 was as high as 334.4 mg / g in the unsaturated case. The AO-C3N4 prepared in Example 1 was subjected to uranium extraction experiments in different pH values of U(VI) solution under light, and the results are shown in Figure 10 The light-assisted uranium extraction rate of AO-C3N4 was very good when the pH value was 3-10, and AO-C3N4 showed the highest uranium extraction capacity at pH 5. The AO-C3N4 prepared in Example 1 was subjected to uranium extraction experiments under ion interference under light, using 10 mg / L U(VI) solution, and the concentration of interfering ions was 100 mg / L, and the results are shown in Figure 11 AO-C3N4 maintained significant light-assisted uranium extraction capacity in the presence of various cations (including K + , Na + , Mg 2+ , Fe 3+ , Zn 2+ and Cu 2+ ).

[0076] The AO-C3N4 prepared in Example 1 was subjected to stability and reusability experiments, and the powder was collected after the uranium extraction experiment, and was ultrasonically treated in 0.1 mol / L Na2CO3 and 0.1 mol / L H2O2 solution for 3 h, and then the powder was washed with deionized water for the next cycle, Figure 12 The uranium extraction rate of AO-C3N4 prepared in Example 1 under light for five consecutive cycles. It can be seen that after 120 minutes of the fifth cycle, the light-assisted uranium extraction rate of AO-C3N4 was still 88.2%. Figure 13 The uranium extraction rate of AO-C3N4 prepared in Example 1 from spiked natural seawater with 8 mg / L U(VI) under darkness and light, it can be seen that more than 85.1% of uranium was extracted after 12 hours under light, which indicates that AO-C3N4 has extraordinary potential for light-assisted uranium extraction from seawater.

[0077] Figure 14 The UV-Vis diffuse reflectance spectra of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1 and C-C3N4 prepared in Comparative Example 2, wherein AO-C3N4 showed the strongest absorption intensity and the widest absorption range, which was also consistent with the color of all samples, P-C3N4, C-C3N4 and AO-C3N4 were light yellow, dark yellow and orange yellow, respectively, as shown in Figure 15A is P-C3N4, B is C-C3N4, and C is AO-C3N4.

[0078] To evaluate the photoelectric conversion of all samples, the photocurrent signals of AO-C3N4 prepared in Example 1, P-C3N4 prepared in Comparative Example 1, and C-C3N4 prepared in Comparative Example 2 were measured by photoelectrochemical method, in which the light was turned on and off every 30 seconds, and the results are shown in Figure 16 As shown, the photocurrent signals can be clearly observed, in which AO-C3N4 exhibits the largest current density, up to ~0.5 mA / cm 2 In addition, the carrier separation efficiency of the obtained samples was analyzed using photoluminescence (PL) spectra, Figure 17 For the steady-state PL spectra, it can be seen that C-C3N4 and AO-C3N4 show much smaller PL intensity than P-C3N4, indicating that the electron-hole recombination is suppressed.

[0079] AO-C3N4 after the uranium extraction experiment under dark and light conditions was collected and named as AO-C3N4-U-Dark and AO-C3N4-U-Light, respectively. Figure 18 For the complete XPS spectra of AO-C3N4, AO-C3N4-U-Dark, and AO-C3N4-U-Light, the U 4f signal can be clearly observed. In addition, the U 4f XPS spectra were fitted with four constituent peaks, as shown in Figure 19 corresponding to U(VI) at 381.8 and 392.4 eV and U(IV) at 381.0 and 391.8 eV, respectively, indicating that the main form of uranium in AO-C3N4-U-Dark is U(VI). AO-C3N4-U-Light has a mixed form of U(IV) and U(VI), indicating that part of the uranium was reduced during the photo-assisted extraction process of AO-C3N4. AO-C3N4-U-Light was further measured by XRD to analyze the enrichment product, and the results are shown in Figure 20 As shown, the diffraction peaks of uranyl peroxide dihydrate ((UO2)O2·2H2O) and uranyl peroxide tetrahydrate ((UO2)O2·4H2O) are clearly observed in the XRD pattern of AO-C3N4-U-Light. (UO2)O2·2H2O and (UO2)O2·4H2O are formed from the oxidation of U(IV) by ROS, and the U(IV) in AO-C3N4-U-Light is amorphous, so no diffraction peaks can be observed.

[0080] Severe biofouling in natural seawater limits the uranium extraction performance of adsorbent materials. Semiconductor photocatalysts can generate biotoxic reactive oxygen species (ROS) under photo-irradiation, destroying the organic components of biological organisms, thus exhibiting good anti-biofouling activity and uranium extraction performance. Electron paramagnetic resonance (EPR) spin trapping technology is used to detect ROS generation, including... Figure 21 Hydroxyl radicals (·OH) in Figure 22 superoxide radicals (·O2) - )and Figure 23 Singlet oxygen in 1 O2). No effective signal of AO-C3N4 was observed under dark conditions, while ·OH and ·O2 appeared in the EPR spectrum of AO-C3N4 under illumination. - and 1 A strong O2 signal indicates the generation of a large amount of ROS. To evaluate the antifouling activity of AO-C3N4, antifouling experiments were conducted using bacteria as targets, employing common Gram-negative bacteria *Escherichia coli* and Gram-positive bacteria *Staphylococcus aureus*, as well as a complex of marine bacteria cultured from natural seawater. First, 5 mg of AO-C3N4 was added to 5 mL of a solution containing 10... 6 CFU / mL of bacterial lysogenic broth (LB) was added, and then the resulting LB medium was hydrated with 1 kW / m³ of water. 2 Xenon lamps were used to simulate sunlight for 1 hour, followed by incubation at 37°C in a constant-temperature shaker for 6 hours. As a control, a similar procedure was used to obtain bacterial cultures containing AO-C3N4 in the absence of light. After incubation, 100 μL of each 10-fold diluted solution was evenly spread onto LB solid medium. Finally, the obtained LB solid medium was incubated at 37°C for 24 hours, and then photographed. Figure 24 As shown, AO-C3N4 significantly inhibited the growth of Gram-negative bacteria *Escherichia coli* and Gram-positive bacteria *Staphylococcus aureus* under light irradiation, exhibiting excellent antibacterial activity. Furthermore, due to the effect of AO-C3N4 under light irradiation, the growth of marine bacterial complex colonies was almost completely inhibited. Therefore, AO-C3N4 exhibits broad-spectrum antibacterial activity and can resist biofouling by marine bacteria. To further evaluate the uranium extraction capability of AO-C3N4 in natural seawater, the experiment used sunlight as the sole light source. 20 L of natural seawater containing 10 mg AO-C3N4 was exposed to continuous sunny days for one week as a control. Another 20 L of natural seawater containing 10 mg AO-C3N4 was placed in darkness for one week. The solids were collected and digested. The concentration of each element (U, V, Fe, Zn, Cu) was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The results are shown below. Figure 25As shown, the uranium extraction capacity of AO-C3N4 from natural seawater is 492 μg / g after one week in the dark, and the uranium extraction capacity of AO-C3N4 is significantly improved under light, reaching 850 μg / g after one week, which is 1.73 times that in the dark after one week, and AO-C3N4 also shows high selectivity for uranium in seawater under light.

[0081] While embodiments of the application have been disclosed in connection with the above specification, it will be apparent to those skilled in the art that many modifications, extensions, substitutions, and alterations of the present application are possible, and that the scope of the present application extends beyond the specifically disclosed embodiments without departing from the spirit or essential characteristics thereof, and it is therefore intended that the disclosure be taken in a non-limiting sense.

Claims

1. A method for producing a modified carbon nitride material for uranium separation, characterized by, The method comprises the following steps: Step 1: Dissolve dicyandiamide and NaCl in deionized water, stir for 9-11 hours, and then freeze-dry the solution to obtain a mixture of dicyandiamide and NaCl; Step 2: Put the mixture of dicyandiamide and NaCl obtained in step 1 into a tube furnace, heat under an argon gas stream, and keep warm for 3-5 hours. After cooling, a yellow block is obtained, which is ground into powder. The yellow block powder is immersed in deionized water, stirred for 1-3 hours, and then filtered and washed to remove water-soluble impurities. Then, the product is dried at 50-70°C to obtain a cyan-modified g-C3N4, namely C-C3N4; Step 3: Dissolve NH2OH·HCl and NaOH in deionized water, then immerse C-C3N4 in the above solution, heat and keep warm, then filter and wash to remove water-soluble impurities, and dry at 50-70°C to obtain a modified carbon nitride material, namely AO-C3N4; the mass-volume ratio of NH2OH·HCl, NaOH, C-C3N4 and deionized water is 5-7g:3-4g:1g:40-60mL; the heating temperature is 80-90°C, and the holding time is 9-11h; In step 2, the obtained C-C3N4 is treated by a low-temperature plasma treatment instrument for 1-3 minutes; In step 3, the obtained AO-C3N4 is treated by a low-temperature plasma treatment instrument for 3-5 minutes; The atmosphere of the low-temperature plasma treatment instrument is ammonia gas, the frequency is 35-55KHz, the power is 200-400W, and the pressure of the atmosphere is 30-40Pa.

2. A process for the preparation of a modified cyanamide material for uranium separation according to claim 1, characterized in that, In step 1, the mass-volume ratio of dicyandiamide, NaCl and deionized water is 1g:4-6g:40-60mL.

3. A process for the preparation of a modified carbon nitride material for uranium separation as claimed in claim 1, wherein, In step 2, the volume-mass ratio of deionized water to dicyandiamide is 40-60mL:1g.

4. The method for preparing a modified carbon nitride material for uranium separation as described in claim 1, characterized in that, In step 2, the heating rate under the argon gas stream is 2-3°C / min, and the heating temperature is 500-600°C.

5. Use of a modified carbon nitride material prepared according to the method of any one of claims 1 to 4 in the separation of uranium, characterized in that, The modified carbon nitride material is added to seawater containing uranium, and a photocatalytic reaction is carried out under xenon lamp simulated sunlight conditions. The modified carbon nitride material after the reaction is ultrasonically treated in a mixed solution of Na2CO3 and H2O2 for 2-4 hours, washed with deionized water for 2-3 times, dried, and then recycled.

6. Use of a modified cyanamide material for the separation of uranium according to claim 5, characterized in that The concentration of the Na2CO3 solution is 0.05-0.15mol / L, and the concentration of the H2O2 solution is 0.05-0.15mol / L.

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