Graphene uranyl ion sensor material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of waste liquid detection, and particularly discloses a graphene uranyl ion sensor material as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) compounding COQDs and UiO-66-NH2 < + > type MOF to form COQDs (at) MOF; and 2) carrying out surface functional modification on the COQDs (at) MOF by using 8-hydroxyquinoline to obtain the GQDs (at) MOF (at) 8-HQ composite material. By optimizing the preparation process, high-sensitivity and high-selectivity detection of uranyl ions is realized, so that the sensor has the advantages of low detection limit, wide linear range, high photobleaching resistance and the like, can be effectively applied to detection of low-concentration uranyl ions, and provides a new technical means for environmental monitoring and nuclear waste management.

Description

Technical Field

[0001] This invention relates to the field of waste liquid detection technology, specifically disclosing a graphene-based uranyl ion sensor material, its preparation method, and its application. Background Technology

[0002] Uranium is an important fuel for nuclear energy production, but it possesses both chemical and radiotoxic properties. During the nuclear fuel cycle, liquid uranium waste may be released into the environment, posing a threat to humans and other organisms. Uranyl ions (UO2) 2+ Uranium ions are the most common form of uranium, exhibiting good solubility and easily polluting the environment. Currently, methods for detecting uranium ions include colorimetry, ultraviolet-visible absorption spectrophotometry, and fluorescence analysis. However, these methods have the following limitations when detecting low concentrations of uranium ions: 1. Insufficient detection sensitivity: The detection limit of traditional fluorescent materials is usually at the ppb level, which is difficult to meet the detection requirements of low-concentration uranium waste liquid (such as nuclear laboratory discharge liquid).

[0003] 2. Poor selectivity: Coexisting ions in complex matrices (such as Th) 4+ 、Sr 4+ (etc.) are easily interfered with the detection results, and the existing methods have limited anti-interference capabilities.

[0004] 3. Low material stability: Some nanomaterials are prone to agglomeration or failure during long-term storage or in complex environments, resulting in poor detection repeatability.

[0005] Graphene-based nanomaterials are considered promising fluorescent sensing materials due to their unique physicochemical properties, such as high specific surface area, excellent optical properties, and good chemical stability. However, the application of existing graphene-based nanomaterials in uranyl ion detection still faces challenges such as complex preparation processes and room for improvement in detection performance. Summary of the Invention

[0006] This invention provides a graphene-based uranyl ion sensor material, its preparation method, and its application, to solve the problems of low sensitivity, poor selectivity, and low material stability in the detection of low-concentration uranyl ions in the prior art.

[0007] This invention is achieved through the following technical solution: In a first aspect, a method for preparing a graphene-based uranyl ion sensor material is provided, comprising the following steps: 1) Mix COQDs with UiO-66-NH 2+ MOF composites are formed to create COQDs@MOFs; 2) COQDs@MOF was surface functionalized with 8-hydroxyquinoline to obtain GQDs@MOF@8-HQ composite material.

[0008] In this invention, COQDs are synthesized as follows: glucose is hydrothermally reacted at 150-200℃ for 5-7 hours, followed by ultrasonic treatment with a water-ethanol mixed solvent (volume ratio 3:1) for 1-2 hours. The resulting COQDs are then obtained through dialysis and lyophilization. This method can prepare COQDs with uniform size (2-5 nm), improving the quantum dot size uniformity to ±0.3 nm, and enriching the surface with active sites such as hydroxyl and carboxyl groups. Furthermore, noble metal nanoparticles (such as Au and Ag) can be modified onto the surface of the COQDs to enhance the fluorescence signal using surface plasmon resonance, achieving a quantum yield ≥7%. This results in graphene-like nanomaterials with abundant functional groups and a uniform size distribution, enabling highly sensitive and selective detection of uranyl ions.

[0009] In this invention, in step 1), a COQDs dispersion is mixed with ZrCl4 and 2-aminoterephthalic acid, and reacted at 100-150℃ for 20-28 hours to grow an MOF shell in situ via a solvothermal method. Modifying COQDs with a metal-organic framework (MOF) enhances the material's adsorption capacity and stability.

[0010] In this invention, the mass ratio of COQDs, ZrCl4, and 2-aminoterephthalic acid is 0.5-1.5:5:3.

[0011] In this invention, in step 2), 8-hydroxyquinoline is dissolved in ethanol, ultrasonically mixed with COQDs@MOF, and reacted under microwave conditions for 5-7 hours. 8-hydroxyquinoline, as a uranium-specific chelating agent, is covalently grafted onto the surface of COQDs via an amidation reaction, thereby enhancing the material's resistance to photobleaching and its stability.

[0012] In this invention, the mass ratio of 8-hydroxyquinoline to COQDs@MOF is 1:1-2, the microwave frequency is 2400-2500MHz, and the microwave power is 100W. Introducing microwave radiation can shorten the reaction time from 3 days to approximately 6 hours and increase the yield to 72%.

[0013] In this invention, the COQDs have a size of 2-5 nm, a surface carboxyl group content of ≥8 mmol / g, and a specific surface area of ​​MOF ≥1200 m². 2 / g, with an 8-hydroxyquinoline loading ≥0.5mmol / g.

[0014] Secondly, a graphene-based uranyl ion sensor material prepared by the above-described preparation method is provided.

[0015] Thirdly, a uranyl ion sensor is provided, comprising a fluorescent probe made from the aforementioned graphene-based uranyl ion sensor material.

[0016] Fourthly, a graphene-based uranyl ion sensor material and / or the application of a uranyl ion sensor in uranyl ion detection are provided.

[0017] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention optimizes the composite process of graphene quantum dots (GQDs) and metal-organic frameworks (MOFs), and combines it with functionalization modification using the specific chelating agent 8-hydroxyquinoline (8-HQ) to prepare a core-shell structured composite material (GQDs@MOF@8-HQ). This sensor material has a detection limit as low as 0.006 μmol / L (approximately 0.8 ppb), a linear range of 0.01-1 μM, and a response retention rate ≥95% in the presence of 100 times the concentration of interfering ions. It also exhibits excellent resistance to photobleaching (fluorescence intensity decay <5% after 1 hour of continuous irradiation), making it suitable for rapid and high-precision detection of low-concentration uranyl ions in complex systems such as nuclear waste liquids and environmental water bodies.

[0018] This invention achieves highly sensitive and selective detection of uranyl ions through optimized preparation processes. The sensor possesses advantages such as low detection limit, wide linear range, and strong resistance to photobleaching, and can be effectively applied to the detection of low-concentration uranyl ions in various complex waste liquid systems, providing a new technical means for environmental monitoring and nuclear waste management. Attached Figure Description

[0019] Figure 1 The fluorescence titration curve of GQDs@MOF@8-HQ against uranyl ions provided in Example 1 of this invention (including image under UV light irradiation).

[0020] Figure 2 The fluorescence titration curve and concentration fitting curve of GQDs@MOF@8-HQ for uranyl ions provided in Example 1 of this invention are shown.

[0021] Figure 3 The images shown are TEM and AFM characterization diagrams of GQDs@MOF@8-HQ provided in Embodiment 1 of the present invention. a is the HRTEM image (inset: particle size distribution diagram) with a scale bar of 50 nm, b is the HRTEM image (inset: magnified image) with a scale bar of 10 nm, and ce is the AFM image.

[0022] Figure 4 TEM and AFM characterization images of GQDs@MOF@8-HQ provided for comparison: a is the HRTEM image (inset: particle size distribution), and b is the AFM image. Figure 5 This is a comparison diagram of the fluorescence response of GQDs@MOF@8-HQ to different ions provided in Example 1 of the present invention.

[0023] Figure 6The graph shows the change in fluorescence intensity of GQDs@MOF@8-HQ as a function of xenon lamp irradiation time, as provided in Example 1 of this invention. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0025] Example 1 A method for preparing a graphene-based uranyl ion sensor material includes the following steps: 1) Synthesis of COQDs: 5 g of glucose was dissolved in 50 mL of water and hydrothermally reacted at 180℃ for 6 h. Then, it was ultrasonically treated with a mixed solvent of water and ethanol with a volume ratio of 3:1 for 2 h. After dialyzing and lyophilization, fluorescent COQDs were obtained. The size of COQDs was 2-5 nm and the surface carboxyl content of COQDs was ≥8 mmol / g. 2) COQDs@MOF composite: 0.1 g COQDs were dispersed in DMF to obtain a COQDs dispersion, which was then mixed with 0.5 g ZrCl4 and 0.3 g 2-aminoterephthalic acid and reacted at 120℃ for 24 h to form COQDs@MOF. The specific surface area of ​​the MOF was ≥1200 m². 2 / g; 3) Functionalization modification: 0.1 g of 8-hydroxyquinoline was dissolved in ethanol and ultrasonically mixed with 0.2 g of COQDs@MOF. The mixture was reacted under microwave conditions of 2450 MHz and 100 W for 6 h. After centrifugation and washing, GQDs@MOF@8-HQ composite material was obtained with an 8-hydroxyquinoline loading of ≥0.5 mmol / g.

[0026] Example 2 A method for preparing a graphene-based uranyl ion sensor material includes the following steps: 1) Synthesis of COQDs: 5 g of glucose was dissolved in 50 mL of water and hydrothermally reacted at 150℃ for 5 h. Then, it was ultrasonically treated with a mixed solvent of water and ethanol with a volume ratio of 3:1 for 1 h. After dialyzing and lyophilization, fluorescent COQDs were obtained. The size of COQDs was 2-5 nm and the surface carboxyl content of COQDs was ≥8 mmol / g. 2) COQDs@MOF composite: 0.1 g COQDs were dispersed in DMF to obtain a COQDs dispersion, which was then mixed with 0.5 g ZrCl4 and 0.3 g 2-aminoterephthalic acid and reacted at 100℃ for 28 h to form COQDs@MOF. The specific surface area of ​​the MOF was ≥1200 m². 2 / g; 3) Functionalization modification: 0.1 g of 8-hydroxyquinoline was dissolved in ethanol and ultrasonically mixed with 0.2 g of COQDs@MOF. The mixture was reacted under microwave conditions of 2400 MHz and 100 W for 7 h. After centrifugation and washing, GQDs@MOF@8-HQ composite material was obtained with an 8-hydroxyquinoline loading of ≥0.5 mmol / g.

[0027] Example 3 A method for preparing a graphene-based uranyl ion sensor material includes the following steps: 1) Synthesis of COQDs: 5 g of glucose was dissolved in 50 mL of water and hydrothermally reacted at 200℃ for 5 h. Then, it was ultrasonically treated with a mixed solvent of water and ethanol with a volume ratio of 3:1 for 1.5 h. After dialyzing and lyophilization, fluorescent COQDs were obtained. The size of COQDs was 2-5 nm and the surface carboxyl content of COQDs was ≥8 mmol / g. 2) COQDs@MOF composite: 0.1 g COQDs were dispersed in DMF to obtain a COQDs dispersion, which was then mixed with 0.5 g ZrCl4 and 0.3 g 2-aminoterephthalic acid and reacted at 150℃ for 20 h to form COQDs@MOF. The specific surface area of ​​the MOF was ≥1200 m². 2 / g; 3) Functionalization modification: 0.1 g of 8-hydroxyquinoline was dissolved in ethanol and ultrasonically mixed with 0.2 g of COQDs@MOF. The mixture was reacted under microwave conditions of 2500 MHz and 100 W for 5 h. After centrifugation and washing, GQDs@MOF@8-HQ composite material was obtained with an 8-hydroxyquinoline loading of ≥0.5 mmol / g.

[0028] Example 4 The difference between this embodiment and Example 1 is that the mass ratio of COQDs, ZrCl4, and 2-aminoterephthalic acid is 0.5:5:3, and the mass ratio of 8-hydroxyquinoline to COQDs@MOF is 1:1.

[0029] Example 5 The difference between this embodiment and Example 1 is that the mass ratio of COQDs, ZrCl4, and 2-aminoterephthalic acid is 1.5:5:3, and the mass ratio of 8-hydroxyquinoline to COQDs@MOF is 1:1.5.

[0030] Comparative Example The difference between this comparative example and Example 1 is that a methyl end-capping agent (methyl methacrylate) was added during the hydrothermal reaction stage in the synthesis of COQDs.

[0031] Performance Testing 1. Fluorescence performance test: The GQDs@MOF@8-HQ composite materials prepared in Example 1 and the comparative example were dispersed in DMF solution, and their fluorescence emission intensity was measured to investigate their response performance to uranyl ions.

[0032] The test method was optimized based on the "Test Procedure for Liquid Samples" in the standard "Determination of Fluorescence Properties of Nanomaterials by Fluorescence Spectrophotometer" (GB / T 30706-2014). The test data are as follows: Table 1. Fluorescence performance test results

[0033] Figure 1 The fluorescence titration curve of GQDs@MOF@8-HQ for uranyl ions in Example 1 is shown in the photo under UV light: Under 365nm UV light, the blank test solution showed yellow-green fluorescence, and the fluorescence was gradually quenched to near colorless as uranyl ions were added. Figure 2 The fluorescence titration curve and concentration fitting curve of GQDs@MOF@8-HQ for uranyl ions are shown in Example 1.

[0034] According to Table 1 and Figures 1-2 It can be seen that the detection limit of GQDs@MOF@8-HQ for uranyl ions is as low as 0.006 μmol / L (1.4 ppb), which is far lower than that of traditional graphene quantum dots (detection limit 2.4 × 10⁻⁶). -9 (mol / L, approximately 0.58 ppb, but with a narrow linear range) and carbon dots (detection limit 8.2 × 10⁻⁶). -6 The concentration is approximately 1.97 μmol / L, and the linear range is 0.04–0.45 μmol / L, covering the detection requirements of low-concentration uranyl ions (typically 0.01–1 μmol / L) in nuclear waste liquids. The COQDs@MOF core-shell structure (specific surface area ≥1200 m² / L) in this invention... 2 The adsorption of uranyl ions is enhanced by a chelating agent (8-hydroxyquinoline (8-HQ) with a loading of ≥0.5 mmol / g), and specific binding is achieved. The two work synergistically to improve the fluorescence response sensitivity, thus solving the problem of detecting low-concentration uranyl ions.

[0035] Figure 3 The images show the TEM and AFM characterization of GQDs@MOF@8-HQ in Example 1. a is the HRTEM image (inset: particle size distribution), scale bar 50 nm; b is the HRTEM image (inset: magnified image), scale bar 10 nm; ce is the AFM image. According to... Figure 3 It can be seen that the particle size of GQDs@MOF@8-HQ is 3.9±0.1nm and the thickness is <2nm, indicating that the GQDs@MOF@8-HQ in the embodiments of the present invention have uniform size.

[0036] Figure 4 The images show the TEM and AFM characterizations of GQDs@MOF@8-HQ in comparison. a is the HRTEM image (inset: particle size distribution), and b is the AFM image. According to... Figure 4 It can be seen that the composite material prepared in the comparative example has a slightly smaller particle size (1.7±0.5 nm) and lacks the salicylaldehyde imine structure (-OH and C=N coordinating site). This is because the methyl end-capping agent inhibits the formation of hydroxyl groups (-OH) on the COQD surface through a competitive reaction, ultimately resulting in a GQDs@MOF@8-HQ composite material with "no -OH functional groups on the surface." Furthermore, the GQDs@MOF@8-HQ composite material prepared in the comparative example shows no fluorescence quenching response to uranyl ions.

[0037] 2. Selectivity test: The selectivity of GQDs@MOF@8-HQ for uranyl ions was tested in a solution containing multiple competing ions.

[0038] Reagents and Samples: Competing ion solutions: Prepare Na+ solutions separately. + (Sodium nitrate), K + (Potassium nitrate), Cs + (cesium nitrate), Sr 2+ (Strontium nitrate), Co 2+ (Cobalt nitrate hexahydrate), Yb 3+ (Ytterbium nitrate hydrate), Lu 3+ (lutetium nitrate), Th 4+ The DMF solutions of thorium nitrate were all at a concentration of 420 μmol / L (100 times the concentration of uranyl ions). Test solution: Disperse 5 mg GQDs@MOF@8-HQ in 10 mL LDM and sonicate for 30 min to form a homogeneous mother solution. Take 15 μL of the mother solution and add it to 2 mL LDM for dilution. Then add 10 μL of 4.2 μmol / L uranyl ion solution, mix well, and let stand to obtain the test solution.

[0039] Test steps: a. Blank group: Measure the fluorescence intensity of the 0.2 μmol / L uranyl ion-GQDs@MOF@8-HQ mixture (denoted as F1); b. Interference group: Add an equal volume of competing ion solution (final competing ion concentration 420 μmol / L) to the above mixture, mix well and let stand for 5 min, then measure the fluorescence intensity (recorded as F2). c. Calculate the response retention rate: Response retention rate = (F2 / F1) × 100%, and repeat the test 3 times for each ion.

[0040] Table 2 Response retention rate test results

[0041] Figure 5 The graph shows the fluorescence response of GQDs@MOF@8-HQ to different ions. The horizontal axis represents the ion type, and the vertical axis represents the relative fluorescence intensity. The fluorescence quenching of the uranyl ion group is the most significant, while the fluorescence intensity of other ion groups is basically maintained at more than 95% of that of the blank group.

[0042] According to Table 2 and Figure 5 It can be seen that at a concentration of 100 times that of competing ions (especially Th ions with chemical properties similar to uranyl ions), 4+ In the presence of uranyl ions, the response retention rate is ≥95%, indicating that the recognition of uranyl ions by the GQDs@MOF@8-HQ composite material of this invention is not affected by coexisting ions. Specifically, 8-HQ forms a stable five-membered chelate with uranyl ions (binding constant >10). 10 L / mol), and has weak binding ability with other metal ions (binding constant <10). 5 The material exhibits high anti-interference properties (L / mol), achieving selective recognition and solving the problem of interference from complex matrices. This is because the GQDs@MOF@8-HQ prepared in Example 1 contains -OH and C=N coordinating sites, allowing it to form a stable five-membered chelate with uranyl ions (binding constant > 10). 10 The fluorescence quenching is significant (L / mol). In contrast, the GQDs@MOF@8-HQ synthesized in the comparative proportion showed no fluorescence quenching response. This comparison directly proves that "the -OH functional group is the key to high-selectivity detection." Therefore, it can be concluded that synthesizing COQDs using the method of this invention can improve the high selectivity of the material for uranyl ions.

[0043] 3. Photobleaching resistance test: GQDs@MOF@8-HQ were continuously irradiated for 1 hour, and the change in fluorescence intensity was measured to evaluate the photobleaching resistance.

[0044] Test solution: Disperse 5 mg GQDs@MOF@8-HQ in 10 mL LDM and sonicate for 30 min to form a homogeneous stock solution. Take 15 μL of the stock solution and add 2 mL LDM to dilute to obtain the test solution.

[0045] Test steps: a. Initial fluorescence intensity: The initial fluorescence intensity of the test solution at λex=405nm and λem=520nm (maximum emission wavelength) (denoted as F0); b. Continuous irradiation: Turn on the xenon lamp (100W) to continuously irradiate the test solution, and record the fluorescence intensity (denoted as F) every 10 minutes. x The total irradiation time was 1 hour. c. Calculate the fluorescence decay rate: Fluorescence decay rate = (F0 - F x ) / F0×100%.

[0046] Table 3 Fluorescence intensity detection results

[0047] Figure 6 The graph shows the change in fluorescence intensity of GQDs@MOF@8-HQ with xenon lamp irradiation time. The horizontal axis represents irradiation time, and the vertical axis represents fluorescence intensity. The curve is basically stable, and the decay rate is <5% after 60 min.

[0048] According to Table 3 and Figure 6 It can be seen that the fluorescence decay rate is only 3.54% after continuous irradiation for 1 hour, which is much lower than that of traditional quantum dots (such as CdTe quantum dots, which decay by more than 20% after 1 hour). This indicates that the material of the present invention has a stable fluorescence signal during long-term detection and can be reused. Specifically, the MOF shell of the material of the present invention encapsulates COQDs, which reduces quantum dot aggregation and photo-oxidation. At the same time, the hydroxyl and carboxyl functional groups on the surface of graphene quantum dots enhance photostability.

[0049] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene-based uranyl ion sensor material, characterized in that, Includes the following steps: 1) Mix COQDs with UiO-66-NH 2+ MOF composites are formed to create COQDs@MOFs; 2) COQDs@MOF was surface functionalized with 8-hydroxyquinoline to obtain GQDs@MOF@8-HQ composite material.

2. The method for preparing graphene-based uranyl ion sensor material according to claim 1, characterized in that, The synthesis method of COQDs is as follows: glucose is hydrothermally reacted at 150-200℃ for 5-7 hours, then ultrasonically treated with a mixed solvent of water and ethanol with a volume ratio of 3:1 for 1-2 hours, and fluorescent COQDs are obtained by dialysis and lyophilization.

3. The method for preparing graphene-based uranyl ion sensor material according to claim 1, characterized in that, In step 1), the COQDs dispersion is mixed with ZrCl4 and 2-aminoterephthalic acid and reacted at 100-150℃ for 20-28h to grow the MOF shell in situ by solvothermal method.

4. The method for preparing graphene-based uranyl ion sensor material according to claim 3, characterized in that, The mass ratio of COQDs, ZrCl4, and 2-aminoterephthalic acid is 0.5-1.5:5:

3.

5. The method for preparing graphene-based uranyl ion sensor material according to claim 1, characterized in that, In step 2), 8-hydroxyquinoline is dissolved in ethanol, mixed with COQDs@MOF by ultrasound, and reacted under microwave conditions for 5-7 hours.

6. The method for preparing graphene-based uranyl ion sensor material according to claim 5, characterized in that, The mass ratio of 8-hydroxyquinoline to COQDs@MOF is 1:1-2, the microwave frequency is 2400-2500MHz, and the microwave power is 100W.

7. The method for preparing graphene-based uranyl ion sensor material according to claim 1, characterized in that, COQDs have a size of 2-5 nm, a surface carboxyl group content ≥8 mmol / g, and a specific surface area of ​​MOF ≥1200 m². 2 / g, with an 8-hydroxyquinoline loading ≥0.5mmol / g.

8. A graphene-based uranyl ion sensor material prepared by the preparation method according to any one of claims 1-7.

9. A uranyl ion sensor, characterized in that, This includes fluorescent probes made from the graphene-based uranyl ion sensor material of claim 8.

10. The application of the graphene-based uranyl ion sensor material according to claim 8 and / or the uranyl ion sensor according to claim 9 in uranyl ion detection.

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