Thorium ion detection-adsorption integrated treatment method based on fluorescence self-indication

Abstract

The invention discloses a thorium ion detection-adsorption integrated treatment method based on fluorescence self-indication. A metal organic framework material Eu-NDC (the chemical formula is [(CH3) 2NH2) 2] [Eu6 (mu3-F) 8 (1, 4-NDC) 6] with the red fluorescence characteristic is used as an adsorbent to be put into thorium-containing wastewater, a detection signal and an adsorption behavior are deeply coupled, and the thorium ions in the thorium-containing wastewater can be detected by utilizing the remarkable fluorescence color conversion from red to blue generated in the thorium ion capturing process of the material. And real-time and visual monitoring of the adsorption progress is realized. According to the invention, dynamic monitoring of the whole adsorption process can be completed without the help of a large-scale analytical instrument; the detection limit of the material to thorium ions is as low as 9.2 nM, the maximum adsorption capacity is as high as 504.3 mg g <-1 >, and the material shows excellent stability in complex ion interference and strong acid radiation environments. The method effectively solves the problems of disjunction of detection and adsorption, invisible state and other pain points in the traditional process, and has important application value in the fields of nuclear wastewater treatment, thorium resource recovery and precise environment restoration.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of radionuclide detection and adsorption, and particularly relates to a thorium ion detection-adsorption integrated processing method based on fluorescence self-indication. BACKGROUND

[0002] Thorium (Th) is a naturally occurring radioactive element, mainly existing in the form of ThO2 in nature. 232 Th has a long half-life and persistent radioactivity, and is widely present in nuclear fuel cycle, rare earth ore mining and smelting processes. Especially in the mining, leaching and separation processes of monazite and other rare earth ores, thorium usually coexists with rare earth elements and uranium and other radionuclides, and enters the leaching solution, wastewater and residue system in the form of tetravalent thorium ions (Th(IV)), causing potential pollution risk to the environment. In addition, thorium and its decay daughter can enter the human body through inhalation, ingestion and other ways, stay in the body for a long time and continuously release alpha rays, which may cause bone tissue damage, liver and lung lesions, and pose a serious threat to human health. The World Health Organization (WHO) has proposed a guideline limit for the safety of thorium in drinking water, and the recommended maximum allowable concentration of Th(IV) ions is 1.06 μM. Therefore, it is of great significance to develop efficient and accurate thorium ion monitoring and separation technologies to ensure nuclear safety and ecological environment.

[0003] At present, the detection methods for thorium ions mainly include laboratory high-precision analysis means such as mass spectrometry (such as inductively coupled plasma-mass spectrometry), spectroscopy (such as spectrophotometry, inductively coupled plasma-atomic emission spectrometry), nuclear activation analysis, etc. Although the detection accuracy is high, there are problems such as expensive equipment, complex operation, tedious sample pretreatment, and difficulty in realizing real-time detection on site. At the same time, rare earth leaching solution and nuclear-related waste liquid usually have complex composition, containing a large amount of transition metal ions, rare earth ions and uranyl ions (UO2 2+ ), which can easily interfere with the detection process. Fluorescence sensing technology is favored in the field of radionuclide detection due to its high sensitivity, fast response and relatively simple operation. However, existing fluorescence sensors mostly rely on the quenching or enhancement of fluorescence intensity, and the signal is easily affected by environmental factors, and most of them still need to rely on auxiliary detection means for quantitative analysis, which limits their practical application.

[0004] In terms of thorium ion removal, adsorption method is the most common treatment method at present due to its simple operation, high efficiency and low risk of secondary pollution. A variety of adsorption materials, such as carbon-based materials, zeolites, clays, covalent organic framework materials and metal organic framework materials, are used to capture thorium ions in water bodies. However, the existing adsorption materials generally have the following shortcomings: first, the selectivity for thorium ions is limited, especially when coexisting with uranium and rare earth elements, it is difficult to effectively distinguish; second, the adsorption capacity is insufficient, resulting in large amount of material consumption and high amount of secondary solid waste; third, the adsorption process lacks intuitive and real-time indication means, usually needs to rely on additional analytical instruments to judge whether the adsorption is saturated, thereby increasing the operation complexity and running cost.

[0005] Metal organic framework materials (MOFs) are a kind of crystalline porous materials self-assembled by metal ions or metal clusters and organic ligands, which have adjustable pore structure, high specific surface area and functionalization ability. In recent years, MOFs have shown great application potential in adsorption, separation and sensing of radionuclides. However, most of the existing MOFs only have single detection or adsorption function, which is difficult to meet the dual needs of detection and adsorption, which greatly limits the application of MOF materials in actual complex environment. Therefore, it is urgent to develop a thorium ion detection-adsorption integrated treatment method, which realizes high selective capture of thorium ions through deep coupling of signal feedback and adsorption behavior of the material, and uses self-indication signal to determine the adsorption progress and saturation endpoint in real time. This has important scientific significance and application value for radionuclide pollution monitoring and treatment. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide a thorium ion detection-adsorption integrated treatment method based on fluorescence self-indication, which makes it possible to visualize detection and synchronous adsorption of thorium ions.

[0007] To achieve the purpose of the present application, the technical scheme of the present application is as follows: A thorium ion detection-adsorption integrated treatment method based on fluorescence self-indication, comprising the following steps: (1) Synthesizing a metal organic framework material with fluorescence, chemical formula is [(CH3)2NH2)2][Eu6( μ 3-F)8(1,4-NDC)6] (abbreviated as Eu-NDC), wherein 1,4-NDC is the deprotonated form of ligand 1,4-naphthalene dicarboxylic acid (1,4-H2NDC); (2) Putting the Eu-NDC material as an adsorbent into a thorium ion-containing aqueous solution for mixing treatment; (3) Use a handheld ultraviolet lamp with a wavelength of 365 nm as the excitation source to irradiate the mixed system in step (1), and monitor the fluorescence signal of the system to realize real-time monitoring of thorium ions in the water. (4) Maintain the contact reaction of the mixed system and use Eu-NDC material to selectively adsorb and separate thorium ions in water; (5) In the thorium ion removal process in step (4), the degree of change of fluorescence color from red to blue in the mixed system is monitored in real time, and the adsorption process of thorium ions in the water and the saturation of Eu-NDC material are determined in real time, thereby realizing the integrated control of thorium ion fluorescence self-indication detection-adsorption.

[0008] Preferably, in step (1), the Eu-NDC material belongs to the cubic crystal system, F m -3 m Space group, cell parameters a=b=c=21.7010(15) Å, α=β=γ=90°, V=10219.73(212) Å 3 .

[0009] Preferably, in step (1), the Eu-NDC material exhibits red fluorescence under ultraviolet wavelength excitation.

[0010] Preferably, in step (1), the solid mass ratio of the Eu-NDC material to the volume ratio of the thorium-containing aqueous solution is 0.5 g / L. –1 The pH value is 3.

[0011] Preferably, in step (3), after the Eu-NDC material comes into contact with thorium ions, the fluorescence gradually changes from red to blue, resulting in a change in proportional fluorescence; Preferably, in step (3), after the Eu-NDC material comes into contact with thorium ions, the ratio of the change in fluorescence intensity ( I 408 / I 612 A quantitative relationship was established between the concentration of thorium ions and the detection limit was as low as 9.2 nM.

[0012] Preferably, in step (4), the Eu-NDC material achieves a thorium ion removal rate of nearly 100% and a maximum adsorption capacity (Q). m The value was 504.3 mg g. –1 .

[0013] Preferably, in step (5), the method for determining the material saturation is to extract the red, green and blue (RGB) values ​​of the fluorescence image of the system and calculate the red / blue (B / R) ratio to indicate the adsorption saturation. When the B / R ratio approaches 4, the material adsorption is determined to have reached the saturation endpoint.

[0014] Preferably, the Eu-NDC material has high selectivity for the detection and separation of thorium ions. The interfering ions include, but are not limited to, main group metals (Mg(II), Al(III) and Ca(II)), rare earth elements (Sc(III), Y(III), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)), uranyl ions (U(VI)) and tetravalent cations (Zr(IV), Hf(IV) and Ce(IV)).

[0015] The present invention has the following beneficial effects: This invention organically integrates thorium ion detection and adsorption removal in aquatic environments, proposing a novel method for real-time thorium ion identification and self-indicating monitoring of the adsorption process based on fluorescence color changes. The fluorescent metal-organic framework material Eu-NDC undergoes a significant transition from red to blue fluorescence upon contact with thorium ions. This fluorescence change can be directly observed with the naked eye under ultraviolet light excitation, thus eliminating the need for complex analytical instruments to determine the presence of thorium ions and the progress of the adsorption process, achieving dynamic and visual monitoring of adsorption behavior.

[0016] Furthermore, the Eu-NDC exhibits excellent selectivity, sensitivity, and adsorption capacity for thorium ions. Even in complex aquatic environments where various rare earth ions, uranyl ions, and other high-valence metal ions coexist, it can still accurately identify and efficiently remove thorium ions, demonstrating good anti-interference ability and environmental adaptability. Compared with the traditional step-by-step approach of "detect first, then treat," the integrated detection-adsorption scheme proposed in this invention effectively avoids problems such as disconnection between detection and treatment processes, response lag, and excessive material addition. It provides a feasible and efficient technical approach for real-time monitoring, precise treatment, and intelligent environmental remediation of radionuclide pollution.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0018] Figure 1 This is the Eu-NDC crystal structure tested in Example 1 of this invention. Color codes: Eu: orange, F: green, O: yellow, C: gray; Figure 2 This is the powder X-ray diffraction pattern of the Eu-NDC crystal material tested in Example 1 of this invention; Figure 3 These are scanning electron microscope images and energy-dispersive X-ray spectra of the Eu-NDC crystal material tested in Example 1 of this invention; Figure 4 This is the thermogravimetric curve of the Eu-NDC crystal material tested in Example 1 of this invention; Figure 5 These are powder X-ray diffraction patterns of Eu-NDC crystal material before and after X-ray irradiation, as tested in Example 1 of this invention. Figure 6 These are the fluorescence excitation and emission spectra of the Eu-NDC crystal material tested in Example 1 of this invention; Figure 7 This is a photoluminescence quantum yield diagram of the Eu-NDC crystal material tested in Example 1 of this invention; Figure 8 This is the fluorescence lifetime diagram of the Eu-NDC crystal material tested in Example 1 of this invention; Figure 9 This is the fluorescence spectrum of the Eu-NDC crystal material tested in Example 2 of the present invention at different thorium ion concentrations; Figure 10 This is a curve showing the fluorescence intensity ratio of the Eu-NDC crystal material tested in Example 2 of the present invention at wavelengths of 408 nm and 612 nm, fitted with the thorium ion concentration. Figure 11 This is the fluorescence spectrum of the Eu-NDC crystal material tested in Example 2 of the present invention in the range of 0-1430 nM thorium ion concentration; Figure 12 This is a curve showing the fluorescence quenching ratio of the Eu-NDC crystal material at 612 nm as a function of thorium ion concentration, as tested in Example 2 of this invention. Figure 13 This is the fluorescence spectrum of the Eu-NDC crystal material reacting with different interfering ions as tested in Example 2 of this invention; Figure 14 The images show the reaction of Eu-NDC crystal material with different interfering ions as tested in Example 2 of this invention, along with bar graphs and fluorescence color photographs of the fluorescence intensity ratio at wavelengths of 408 nm and 612 nm with different ion types. Figure 15 This is the adsorption kinetic model of thorium ions on the Eu-NDC crystal material tested in Example 3 of the present invention; Figure 16 This is the adsorption isotherm model of thorium ions by the Eu-NDC crystal material tested in Example 3 of the present invention; Figure 17These are fluorescence photographs taken at different times during the adsorption of thorium ions by the Eu-NDC crystal material tested in Example 4 of this invention. Figure 18 These are the RGB values ​​extracted from fluorescence photographs taken at different times during the adsorption of thorium ions by the Eu-NDC crystal material tested in Example 4 of this invention. Figure 19 This is a curve showing the change of B / R value over time during the adsorption of thorium ions by the Eu-NDC crystal material tested in Example 4 of this invention. Figure 20 This is a curve showing the fitting relationship between the adsorption amount and the B value during the adsorption of thorium ions by the Eu-NDC crystal material tested in Example 4 of this invention. Detailed Implementation The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] Example 1: Synthesis and Characterization of Basic Properties of Crystal Materials I. Synthesis and Structural Characterization of Crystal Materials The synthesis of the fluorescent metal-organic framework material Eu-NDC in this invention is based on the work of Eddaoudi et al. (J. Am. Chem. Soc., 2015, 137, 5034). The method described in 5040). The simplified synthesis steps are as follows: 0.005 mmol of europium(III) nitrate hexahydrate (Eu(NO3)3·6H2O), 0.005 mmol of 1,4-naphthalenedicarboxylic acid (1,4-H2NDC), and 0.04 mmol of 2-fluorobenzoic acid (2-FBA) solid were weighed and added to 500 μL of N,N'-dimethylformamide (DMF) and 30 μL of 3.5 M nitric acid (HNO3) solution. The mixture was sealed and heated at 130 °C for 48 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature to obtain pale yellow octahedral crystals. The obtained crystals were washed three times with DMF and diethyl ether and dried at room temperature. This mixture is referred to as Eu-NDC. Eu-NDC is a metal-organic framework material constructed using lanthanide metals Eu(III) as metal nodes. Benefiting from the efficient luminescence of lanthanide ions and the high recognition ability of MOFs for target molecules, Eu-NDC is considered a promising fluorescence sensing platform.

[0020] Single-crystal X-ray diffraction showed that Eu-NDC crystallized in the Fm-3m space group with cell parameters a=b=c=21.7010(15) Å, α=β=γ=90°, and V=10219.73(212) Å. 3Eu-NDC is an anionic framework, with two negative charges separated by two dimethylamine cations (CH3)2NH2. + The equilibrium is achieved, thus forming [(CH3)2NH2)2][Eu6( μ 3-F)8(1,4-NDC)6]. Figure 1 This is a schematic diagram of the Eu-NDC structure. Specifically, six Eu(III) ions in the crystal pass through... μ The 3-F coordination is bridged by eight F atoms, forming [Eu6( μ 3-F)8] 10+ Secondary building blocks (SBUs). Each SBU is further connected to multiple 1,4-NDCs. 2– The carboxylic acid ligands coordinate to form a three-dimensional metal-organic framework structure. X-ray powder diffraction (PXRD) verified the crystal phase purity, which was highly consistent with the PXRD pattern obtained from single-crystal simulation. Figure 2 Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) further characterized the elemental analysis, confirming the presence of F and indicating that 2-FBA was involved in the crystal formation process. Figure 3 ).

[0021] II. Stability Testing of Crystal Materials To verify the structural and chemical stability of the fluorescent metal-organic framework material Eu-NDC under actual aquatic environments and detection-adsorption applications, a systematic test was conducted to assess its crystal structure retention under different environmental conditions. The stability of Eu-NDC under different acid and alkaline conditions was investigated. Eu-NDC samples were immersed in aqueous solutions with pH values ​​ranging from 1 to 12 for 24 h (adjusted by pH 1 hydrochloric acid and pH 12 sodium hydroxide). The results showed that Eu-NDC exhibited good structural stability within the pH range of 2-12, meeting the requirements for thorium ion detection and adsorption applications in aquatic environments. Figure 2 The thermal stability of Eu-NDC was measured by thermogravimetric analysis, and it can be maintained up to 300 °C. Figure 4 Furthermore, Eu-NDC exhibits excellent radiation stability, maintaining its crystallinity even after X-ray irradiation with a cumulative dose of 14 kGy. Figure 5 ).

[0022] III. Characterization of Fluorescence Properties of Crystal Materials In this embodiment, ultraviolet light is used as the excitation source for Eu-NDC to collect steady-state fluorescence spectra. The excitation wavelength is in the range of 250-400 nm, preferably 340 nm. Figure 6 As shown, Eu-NDC at 578, 591, 612, 651, and 697 nm (λ) exA clear and sharp characteristic emission peak is observed at 340 nm, corresponding to the Eu(III) ion. 5 D0→ 7 F J (J=0-4) transition. Furthermore, the rigid framework of Eu-NDC effectively suppresses nonradiative decay, achieving a photoluminescence quantum yield (PLQY) of 39.11% and a luminescence lifetime of 0.87 ms (λ). em = 612 nm) Figure 7 and Figure 8 ).

[0023] Example 2: Investigation of fluorescence detection of thorium ions I. Detection range and detection limit of thorium ions by Eu-NDC To verify the fluorescence detection performance of the fluorescent metal-organic framework material Eu-NDC for thorium ions in the aqueous environment, a fluorescence titration method was used to detect thorium ions. The specific process is as follows: (1) In typical experiments, the solid-liquid ratio of the Eu-NDC suspension was maintained at 0.5 g / L. –1 The pH was adjusted to 3. The suspension was stirred at 300 rpm for 3 h on a magnetic stirrer to obtain a homogeneous and stable suspension. 2.5 mL of Eu-NDC suspension was titrated with 10 mM thorium ion solution, controlling the final thorium ion concentration to gradually increase. The emission spectrum of the suspension was recorded three times every 5 minutes under 340 nm UV excitation to calculate the average emission intensity and minimize instrument fluctuations.

[0024] (2) In the steady-state fluorescence spectrum, as the thorium ion concentration increases, the fluorescence intensity of the characteristic emission peak of Eu-NDC at 612 nm gradually decreases, while a new emission peak appears at 408 nm, whose fluorescence intensity increases with the increase of thorium ion concentration. This is due to the interaction between thorium and 1,4-NDC. 2– Fluorescence emission peaks forming new crystals ( Figure 9 ).

[0025] (3) Further, the fluorescence intensity ratio at 408 nm and 612 nm ( I 408 / I 612 Using this as an analytical signal, the concentration of thorium ions was quantitatively analyzed. The results showed that within the range of 0-385 μM, I 408 / I 612 There is a good linear correlation between the concentration of thorium ions and the concentration of thorium ions, which conforms to the equation. I 408 / I612 = 0.00035×C+0.018, Relevance R 2 = 0.9982, which can be used for the quantitative detection of thorium ions ( Figure 10 ).

[0026] (4) To further evaluate the sensitivity of Eu-NDC at environmentally relevant concentrations, thorium ion detection was achieved at the threshold concentration recommended by the World Health Organization (WHO). Figure 11 Using a signal change reaching 3% of the baseline signal as the criterion, the limit of detection (LOD) was calculated to be as low as 9.2 nM, significantly lower than the WHO recommended limit for thorium content in drinking water (1.06 μM), indicating that the material possesses ultra-high sensitivity for thorium ion detection. Figure 12 ).

[0027] II. Exploration of the selectivity of Eu-NDC for thorium ion detection The ion selectivity of Eu-NDC is crucial because environmental samples are often complex and contain a variety of interfering ions. The specific process is as follows: (1) In a typical experiment, Eu-NDC fine powder was dispersed into 23 metal ion solutions of 2 mM (solid-liquid ratio 0.5 g / L). –1 (pH 3). The solutions of each interfering ion were prepared using corresponding high-purity nitrate or chloride reagents. The 23 potential interfering ions included main group metal ions (Mg(II), Al(III) and Ca(II)), rare earth ions (Sc(III), Y(III), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)), uranyl ions (U(VI)), and tetravalent cations (Zr(IV), Hf(IV) and Ce(IV)).

[0028] (2) The emission spectrum of the suspension was collected at an excitation wavelength of 340 nm. For example... Figure 13 As shown, the presence of main group metals, rare earth elements (except Sc(III)), and U(VI) cations has negligible effect on the fluorescence spectrum of Eu-NDC. Sc(III), Zr(IV), Hf(IV), and Ce(IV) induce significant quenching of the red emission of Eu-NDC, accompanied by ligand group fluorescence, which at first glance seems to interfere with the detection of Th(IV). However, comparing the fluorescence color of the suspension after the reaction, Th(IV) exhibits a unique deep blue fluorescence that distinguishes it from other ions. Furthermore, the ligand-metal emission intensity ratio triggered by Th(IV) is significantly different. I408 / I 612 The selectivity of Eu-NDC for Th(IV) ions was approximately 32, 29, 36, and 6 times higher than that for Sc(III), Zr(IV), Hf(IV), and Ce(IV), respectively, indicating the excellent selectivity of Eu-NDC for Th(IV) ions. Figure 14 ).

[0029] Example 3: Investigation of Thorium Ion Adsorption I. An Investigation into the Adsorption Kinetics of Thorium Ions (1) In a typical adsorption kinetics experiment, 45 mg of Eu-NDC fine powder was dispersed in 90 mL of 77 mg / L (0.33 mM) thorium ion aqueous solution for adsorption kinetics experiment (solid-liquid ratio 0.5 g / L). –1 (pH 3). The Eu-NDC suspension was stirred at a constant speed of 300 rpm to ensure homogeneous mixing. Samples were collected using a syringe at fixed time points (0, 3, 5, 10, 20, 40, 60, 90, 120, 180, 300, 420, 540, and 660 min) and filtered through a 0.22 μm aqueous nylon membrane to completely remove the solid adsorbent. The concentration of thorium ions in the filtrate was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The thorium ion removal efficiency was calculated using Equation 1: Formula 1 In Formula 1, C0 (mg L) –1 ( ) represents the initial concentration of thorium ions before the addition of Eu-NDC powder, C t (mg L) –1 ( ) represents the concentration of thorium ions in the solution after different stirring times.

[0030] (2) Adsorption kinetics were fitted to the data using pseudo-first-order kinetics (PFO), pseudo-second-order kinetics (PSO), and double-exponential kinetics models, respectively. The results showed that Eu-NDC could achieve nearly 100% removal of thorium ions within 7 h. The double-exponential kinetics model (R... 2 = 0.9918) compared to the commonly used quasi-first level (R 2 = 0.9253) and quasi-secondary (R 2 = 0.9622) The model better fits the adsorption kinetics of Eu-NDC for thorium ions ( Figure 15 ).

[0031] II. Investigation of the Adsorption Isotherm of Eu-NDC (1) In a typical adsorption isotherm experiment, a series of initial concentrations ranging from 4.6 to 852 mg L were prepared. –1(0.02 to 3.67 mM) thorium ion solutions were added, and the pH of the solutions was adjusted to 3. 6 mg of Eu-NDC fine powder was weighed into several centrifuge tubes, and 12 mL of thorium ion solutions of different concentrations (solid-liquid ratio 0.5 g / L) were added to each tube. –1 The Eu-NDC suspension was stirred at a constant speed of 300 rpm to ensure uniform mixing. After continuous stirring for 24 h, the Eu-NDC was allowed to fully adsorb thorium ions and reach equilibrium. Suspension samples of each component were then collected using a syringe and filtered through a 0.22 μm aqueous nylon membrane to completely remove the solid adsorbent. The equilibrium concentration of residual thorium ions in the filtrate was determined using ICP-OES. The thorium ion adsorption capacity was calculated using Equation 2: Formula 2 In formula 2, Q e (mg g) –1 ) represents the adsorption capacity, C0 (mg / L) –1 C represents the initial concentration of thorium ions in the solution before the addition of Eu-NDC material. e (mg L) –1 ) represents the equilibrium concentration after adsorption of thorium ions, V (L) represents the volume of the thorium ion aqueous solution, and m (g) represents the mass of Eu-NDC powder.

[0032] (2) To further investigate the adsorption mechanism, the experimental data were fitted using the Langmuir model and the Freundlich model, respectively. For example... Figure 16 As shown, the linear fit correlation coefficient (R²) of the Langmuir model is... 2 = 0.9747) is significantly higher than the Freundlich model (R = 0.9747). 2 = 0.8556). This result indicates that the adsorption of thorium ions by Eu-NDC is a monolayer chemisorption. Based on the Langmuir model, the theoretical maximum adsorption capacity Q of Eu-NDC at room temperature is calculated. m 486.13 mg g –1 (2.10 mmol g) –1 (), compared to the experimentally measured maximum adsorption capacity of 504.3 mg g –1 (2.17 mmol g) –1 The results show that Eu-NDC has excellent thorium ion capture performance, which is close to that of other thorium ions.

[0033] Example 4: Thorium ion detection-adsorption integrated experiment (1) This embodiment realizes an integrated process of real-time colorimetric detection and adsorption separation of thorium ions in aqueous solution using Eu-NDC material. In a typical adsorption experiment, 40 mg of Eu-NDC fine powder was dispersed in 80 mL of 210 mg L... –1 (0.9mM) thorium ion solution (solid-liquid ratio 0.5 g / L) –1 (pH 3), and a constant stirring speed of 300 rpm was maintained throughout the experiment to ensure sufficient contact between the adsorbent and thorium ions.

[0034] (2) During the adsorption reaction (0-660 min), the Eu-NDC suspension was excited using a handheld UV lamp with an excitation wavelength of 365 nm. The suspension initially exhibited red fluorescence, which gradually changed from red to purple as the adsorption reaction progressed, eventually stabilizing at blue. Figure 17 Fluorescence images were recorded at predetermined time intervals using a digital camera with fixed imaging parameters, and the red, green, and blue (RGB) values ​​at the center of the images were extracted using Adobe Photoshop. Simultaneously with fluorescence monitoring, suspension samples were collected at regular intervals and filtered through a 0.22 μm aqueous nylon membrane. The concentration of thorium ions in the filtrate was determined using ICP-OES, and the amount of thorium ions adsorbed at different time points was calculated using Equation 2.

[0035] (3) Colorimetric analysis of the Eu-NDC suspension using photographs showed that the blue (B) value intensity increased sharply from 0 to 225 within the first 100 min, and then tended to saturate. In contrast, the red (R) value showed a gradual decreasing trend, while the change in the green (G) value was relatively negligible. Figure 18 Fitting analysis of the relationship between the B / R value and adsorption time revealed that this change process can be well described by a bi-exponential kinetic model, consistent with the observed adsorption kinetics. Figure 19 The B / R ratio is close to saturation, approximately 4, indicating that thorium ions are almost completely adsorbed in the system, and the material's adsorption capacity is near saturation. Furthermore, a linear relationship exists between the adsorption amount and the R value, suggesting that the R value can serve as a reliable indicator for quantifying the amount of thorium ion adsorption. Figure 20 ).

[0036] As can be seen from the above embodiments, the present invention has the following characteristics: (1) The Eu-NDC material described in this invention exhibits extremely sensitive fluorescence response to thorium ions, with a detection limit (LOD) as low as 9.2 nM, far below the drinking water guidance limit set by the World Health Organization (WHO). Simultaneously, this material employs a proportional fluorescence detection mode, measuring the intensity ratio at 408 nm to 612 nm (…). I 408 / I 612 A quantitative relationship is established. This proportional mode effectively eliminates the influence of background noise, sample concentration fluctuations, and unstable excitation light sources on the measurement results, achieving high-precision self-calibration detection.

[0037] (2) The Eu-NDC material described in this invention has excellent thorium ion capture ability, with a maximum adsorption capacity of up to 504.3 mg g. –1 (2.17 mmol g) –1 This material outperforms most currently reported porous adsorbent materials, demonstrating its potential application in nuclear wastewater treatment and thorium resource recovery.

[0038] (3) The Eu-NDC material described in this invention realizes the integrated detection and adsorption of thorium ions based on fluorescence self-indication. During the adsorption process, the B / R fluorescence ratio of the material shows a dynamic relationship with time. When the B / R value tends to saturate, it can be determined that the material is close to adsorption saturation, thereby realizing the self-indication of adsorption state without additional analytical instruments, providing a new technical path for real-time monitoring, accurate separation and environmental remediation of radioactive nuclide pollution.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for integrated thorium ion detection and adsorption based on fluorescence self-indication, characterized in that, Includes the following steps: (1) Synthesize a fluorescent metal-organic framework material with the chemical formula [(CH3)2NH2)2][Eu6( μ [3-F)8(1,4-NDC)6] is abbreviated as Eu-NDC, where 1,4-NDC is the deprotonated form of the ligand 1,4-naphthalenedicarboxylic acid (1,4-H2NDC); (2) The Eu-NDC material is used as an adsorbent and mixed in an aqueous solution containing thorium ions; (3) Use a handheld ultraviolet lamp with a wavelength of 365 nm as the excitation source to irradiate the mixed system in step (1), and monitor the fluorescence signal of the system to realize real-time monitoring of thorium ions in the water. (4) Maintain the contact reaction of the mixed system and use Eu-NDC material to selectively adsorb and separate thorium ions in the water; (5) In the thorium ion removal process in step (4), the degree of change of fluorescence color from red to blue in the mixed system is monitored in real time, and the adsorption process of thorium ions in the water and the saturation of Eu-NDC material are determined in real time, thereby realizing the integrated control of thorium ion fluorescence self-indication detection-adsorption.

2. The processing method according to claim 1, characterized in that, In step (1), the Eu-NDC material belongs to the cubic crystal system, F m -3 m Space group, cell parameters a=b=c=21.7010(15) Å, α=β=γ=90°, V=10219.73(212) Å 3 .

3. The processing method according to claim 1, characterized in that, In step (1), the Eu-NDC material exhibits red fluorescence when excited by ultraviolet wavelength.

4. The processing method according to claim 1, characterized in that, In step (1), the solid mass ratio of the Eu-NDC material to the volume ratio of the thorium-containing aqueous solution is 0.5 g / L. –1 The pH value is 3.

5. The material according to claim 1, characterized in that, In step (3), after the Eu-NDC material comes into contact with thorium ions, the fluorescence gradually changes from red to blue, resulting in a change in proportional fluorescence.

6. The material according to claim 1, characterized in that, In step (3), after the Eu-NDC material comes into contact with thorium ions, the ratio of the change in fluorescence intensity ( I 408 / I 612 A quantitative relationship was established between the concentration of thorium ions and the detection limit was as low as 9.2 nM.

7. The material according to claim 1, characterized in that, In step (4), the Eu-NDC material achieves a thorium ion removal rate of nearly 100% and a maximum adsorption capacity (Q). m The value is 504.3 mg g. –1 .

8. The material according to claim 1, characterized in that, In step (5), the method for determining the material saturation is to extract the RGB values ​​of the three primary colors of red, green and blue from the fluorescence image of the system and calculate the red / blue B / R ratio to indicate the adsorption saturation. When the B / R ratio approaches 4, the material adsorption is determined to have reached the saturation endpoint.

9. The material according to claim 1, characterized in that, The Eu-NDC material exhibits high selectivity for the detection and separation of thorium ions. Interfering ions include, but are not limited to, main group metals (Mg(II), Al(III) and Ca(II)), rare earth elements (Sc(III), Y(III), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)), uranyl ions U(VI)), and tetravalent cations (Zr(IV), Hf(IV) and Ce(IV).

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