Preparation of fluorescent functionalized hydrotalcite-based composite material and application of fluorescent functionalized hydrotalcite-based composite material in heavy metal adsorption and in-situ monitoring

Abstract

The invention relates to multifunctional integrated hydrotalcite (MgAlEu-LDH) which has the capabilities of efficient adsorption, oxidation repair and real-time monitoring of heavy metal pollution. According to the material, the adsorption selectivity is enhanced by introducing rare earth element europium (Eu < 3 + >), a dual mechanism of'coordination adsorption-photocatalytic oxidation 'is realized by utilizing the photocatalytic characteristic of the material, and an ultra-stable mineralization structure is constructed. The preparation method comprises the following steps: weighing magnesium chloride, aluminum chloride and europium chloride according to a molar ratio of 2: 1: 0.1 to prepare a salt solution, reacting the salt solution with an alkali solution in a colloid mill, aging, washing and drying to obtain MgAlEu-LDH, and calcining at 350 DEG C to obtain MgAlEu-LDH. The fluorescence characteristic of Eu < 3 + > can be used for monitoring the adsorption process in situ in real time, and the fluorescence intensity of Eu < 3 + > is quenched along with the increase of arsenite adsorption time. Experiments show that the material is high in arsenic adsorption rate, the adsorption process conforms to a Langmuir model, the fluorescence intensity change is related to the adsorption process, and an economic and environment-friendly technical scheme is provided for heavy metal pollution remediation.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrastable mineralization, and specifically relates to a hydrotalcite with "multifunctional integrated" characteristics, which is a composite system with high-efficiency adsorption, oxidation repair and real-time monitoring. Background Art

[0002] Soil is the core of Earth's surface system, the foundation of agricultural production and crucial for ecological balance. However, with accelerating industrialization, heavy metal pollution is rapidly eroding the global soil environment. Heavy metals such as lead, cadmium, and arsenic enter the soil through mining, industrial emissions, and agricultural activities, creating a difficult-to-remediate "chemical time bomb." According to the United Nations, over 30% of the world's arable land is at risk of excessive heavy metal levels. Heavy metal pollution is non-degradable and bioaccumulates, with its ions remaining in the soil for long periods, spreading through the food chain and harming the human nervous system, kidneys, and immune system. For example, arsenic is highly mobile in soil and easily absorbed by plants, converting it into highly toxic methylarsenic, which increases the risk of cancer. Traditional remediation technologies, such as chemical precipitation, ion exchange, and bioremediation, suffer from low treatment efficiency, high risk of secondary contamination, high costs, and limited applicability, making them inadequate for the remediation of complex contaminated sites.

[0003] Layered double hydroxides (LDHs, commonly known as hydrotalcites) have attracted much attention in the treatment of heavy metal pollution due to their unique layered structure and adjustable chemical composition. The main layer is composed of divalent / trivalent metal cations, and the interlayer is filled with exchangeable anions. It has functions such as ion exchange and surface coordination, and performs particularly well in removing heavy metals such as arsenic and lead. However, the adsorption capacity and environmental adaptability of traditional binary LDHs are still limited, and the synergistic effect of their metal ions and the potential for functional expansion have not been fully explored. The introduction of rare earth element europium (Eu 3+ ) can break through the bottleneck. 3+ It has a large coordination space and strong Lewis acidity, and can coordinate with arsenate in a multidentate manner to enhance adsorption selectivity; its 4f electrons generate photogenerated electron-hole pairs under photoexcitation, synergistically promoting the oxidation and fixation of heavy metal ions, forming a dual mechanism of "coordination adsorption-photocatalytic oxidation", which is expected to construct an efficient and stable ultra-stable mineralization structure.

[0004] This study focuses on the design and preparation of europium-doped magnesium-based ternary hydrotalcites (MgMEu-LDHs, M=Al). By regulating the metal ion ratio, interlayer anion type, calcination temperature and light conditions, a new functional material with ultra-stable mineralization ability is constructed. The research content includes material synthesis process optimization, structure-performance relationship analysis, adsorption thermodynamics and kinetics mechanism exploration, and Eu-based 3+Development of an in-situ monitoring system for fluorescence properties. Using colloid milling technology to achieve uniform dispersion and crystal form control of nanosheets, X-ray diffraction, scanning electron microscopy, and other methods revealed the enhanced effect of calcination-induced layer reconstruction on heavy metal capture, and fluorescence spectroscopy was used to track the adsorption process in real time, providing a visualization tool for dynamic monitoring of pollution remediation. On a theoretical level, the functional application of rare earth elements in layered materials was expanded, clarifying the role of Eu 3+ With transition metal ions (Al 3 +), enriching the theoretical system of heavy metal removal by LDHs; at the application level, the developed ultra-stable mineralized structure exhibits excellent heavy metal removal efficiency and cyclic stability in complex soil environments, providing an economical and environmentally friendly technical solution for the remediation of heavy metal contaminated sites. In particular, the in-situ fluorescence monitoring system breaks through the "black box" limitations of the traditional adsorption process and provides an innovative path for the regulation and effect evaluation of remediation processes. Faced with the challenge of increasing global heavy metal pollution in soil, this study is committed to connecting basic theory with engineering applications to provide scientific and technological support for "clean soil and safe grain." In the future, we will deepen the pilot application of materials in actual contaminated sites, combine environmental big data to build a remediation efficiency prediction model, and promote europium-based hydrotalcite materials to a broader field of pollution control. Summary of the Invention

[0005] The present invention provides a hydrotalcite in a MgAlEu system with strong coordination fixation as the main feature and fluorescence signal output as the auxiliary feature. The fluorescence of the material is quenched as the adsorption time of arsenite increases. 3+ Based on the fluorescence characteristics of α-D-glucose phosphate, an in situ real-time monitoring method was developed. By monitoring the changes in fluorescence intensity, the adsorption kinetics process can be tracked intuitively and quantitatively.

[0006] The fluorescence of the product MgAlEu-LDO obtained by calcining MgAlEu-LDH at 350°C is gradually quenched as the adsorption time of arsenite increases to achieve the purpose of in-situ real-time monitoring. The preparation method of the material is as follows:

[0007] (1) Magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O) and europium chloride (EuCl3·6H2O) were accurately weighed according to the molar ratio of magnesium, aluminum and europium in the target product. (MgCl2·6H2O) 2+ :Al 3+ :Eu 3+ The molar ratio can be set to 2:1:0.1 and can be adjusted as needed. Prepare the precipitant by preparing an alkaline solution with sodium hydroxide (NaOH) and deionized water.

[0008] (2) Preparation of salt solution: Add weighed magnesium chloride, aluminum chloride and europium chloride to an appropriate amount of deionized water and stir thoroughly to dissolve them completely to form a mixed salt solution.

[0009] (3) Rubber mill treatment: Slowly inject the mixed salt solution and alkaline solution into the rubber mill simultaneously. Control the speed of the rubber mill to 3000–5000 r / min, maintain the temperature at room temperature, and adjust the feed rate according to the processing capacity of the rubber mill. Thoroughly mix and grind in the rubber mill to allow the metal ions to fully react with the hydroxide ions and chloride ions to form a precipitate. The reaction time is usually 10–20 minutes.

[0010] (4) Aging: The product after the rubber mill treatment is transferred to the reactor and aged at 60-80 ° C for 12-24 hours to promote further crystallization growth of the precipitate.

[0011] (5) Washing and Drying: The aged product was washed twice with deionized water at 4000 rpm in a centrifuge, and then washed twice with ethanol at 5000 rpm in a centrifuge until the pH of the washing solution was close to neutral, thereby removing impurities that interfere with the experiment. The centrifuged product was dried in an oven at 60-80°C for 12-24 hours to obtain the magnesium aluminum europium ternary metal hydrotalcite product, i.e., MgAlEu-LDH.

[0012] (6) Calcination at 350 ° C in a muffle furnace to obtain MgAlEu-LDO

[0013] Beneficial effect: In the MgAlEu-LDH system, Eu 3+ It exhibits unique photoluminescence properties. When excited by light of a specific energy, Eu 3+ It will transition from the ground state to the excited state, and then return to the ground state from the excited state, accompanied by fluorescence emission. 3+ interacts with heavy metal ions on the surface of hydrotalcite, which changes the Eu 3+ The electron cloud structure and its surrounding chemical environment. According to the principle of spectroscopy, changes in the chemical environment will lead to changes in fluorescence parameters such as fluorescence intensity and fluorescence lifetime. For the system of MgAlEu-LDO adsorbing arsenic ions, as arsenic ions continue to adsorb to the surface of hydrotalcite, Eu 3+ The interaction between Eu and arsenic ions is to form coordination bonds, which promotes the 3+ The excited-state energy is more easily dissipated through non-radiative pathways, resulting in a decay in fluorescence intensity. Furthermore, the degree of fluorescence decay correlates with the amount of adsorbed arsenic ions. By monitoring the change in fluorescence intensity over time in real time, information on the adsorption rate of heavy metal ions by the adsorbent can be indirectly obtained, enabling in situ, dynamic monitoring of the adsorption process. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1The Eu-doped magnesium-aluminum layered bimetallic oxide composite materials prepared in Example 1 and Comparative Example 1 and their XRD patterns after calcination at different temperatures.

[0015] Figure 2 These are the Eu-doped magnesium-aluminum layered bimetallic oxide composite materials prepared in Example 1 and Comparative Example 1, and their SEM images after calcination at different temperatures.

[0016] Figure 3 Comparison of EPR spectrum g-value distribution of Eu-doped MgAl-LDO and LDH in Example 1.

[0017] Figure 4 This is the adsorption rate curve of trivalent arsenic by MgAlEu-LDO in Experimental Example 1.

[0018] Figure 5 This is the fitting diagram of the MgAlEu-LDO adsorption capacity of Experimental Example 1.

[0019] Figure 6 The fluorescence intensity of MgAl(Eu)-LDO with different europium doping amounts in Experimental Example 1 varies with wavelength.

[0020] Figure 7 The fluorescence intensity of MgAlEu-LDO with a ratio of 2:1:0.1 in Experimental Example 1 changes with wavelength at different reaction times. DETAILED DESCRIPTION

[0021] Example 1

[0022] (1) According to Mg 2+ :Al 3+ :Eu 3+ The molar ratio of magnesium chloride, aluminum chloride, and europium chloride is set to 2:1:0.1. The corresponding masses of magnesium chloride, aluminum chloride, and europium chloride are accurately weighed and added to an appropriate amount of deionized water. They are stirred thoroughly to completely dissolve them to form a mixed salt solution to obtain solution A. A certain amount of sodium hydroxide (NaOH) is taken to prepare an alkaline solution to obtain solution B.

[0023] (2) Solution A and solution B are slowly injected into the rubber mill at the same time. The speed of the rubber mill is controlled at 3000-5000r / min, the temperature is maintained at room temperature, and the reaction is carried out for 10-20 minutes. The product treated by the rubber mill is transferred to the reactor and aged at 60-80°C for 12-24h to promote further crystallization growth of the precipitate. The aged product is then washed twice with deionized water in a centrifuge at 4000rpm, and then washed twice with ethanol in a centrifuge at 5000rpm until the pH of the washing liquid is close to neutral, thereby removing impurities that interfere with the experiment. The centrifuged product is placed in an oven at 60-80°C and dried for 12-24h to obtain a magnesium aluminum europium ternary metal hydrotalcite product, namely MgAlEu-LDH;

[0024] (3) MgAlEu-LDH was calcined at 350 °C in a muffle furnace to obtain MgAlEu-LDO.

[0025] The XRD pattern, SEM pattern and EPR spectrum of the target product were obtained as follows: Figure 1 、 Figure 2 c and Figure 3 shown.

[0026] Comparative Example 1

[0027] a. According to Mg 2+ :Al 3+ :Eu 3+ The molar ratio of magnesium chloride, aluminum chloride, and europium chloride is set to 2:1:0.1. The corresponding masses of magnesium chloride, aluminum chloride, and europium chloride are accurately weighed and added to an appropriate amount of deionized water. They are stirred thoroughly to completely dissolve them to form a mixed salt solution to obtain solution A. A certain amount of sodium hydroxide (NaOH) is taken to prepare an alkaline solution to obtain solution B.

[0028] b. Slowly inject solution A and solution B into the rubber mill at the same time. Control the speed of the rubber mill at 3000-5000r / min, keep the temperature at room temperature, and react for 10-20 minutes. Transfer the product treated by the rubber mill to the reactor and age it at 60-80℃ for 12-24h to promote further crystallization growth of the precipitate. Then wash the aged product twice with deionized water in a centrifuge at 4000rpm, and then wash the washed product twice with ethanol in a centrifuge at 5000rpm until the pH of the washing liquid is close to neutral, so as to remove impurities that interfere with the experiment. Place the centrifuged product in an oven at 60-80℃ and dry it for 12-24h to obtain a magnesium-aluminum-europium ternary metal hydrotalcite product, namely MgAlEu-LDH;

[0029] c. MgAlEu-LDH was not calcined, and was calcined at 250°C and 450°C in a muffle furnace.

[0030] The XRD pattern of the target product is obtained as follows: Figure 1 As shown, the SEM image and EPR spectrum of uncalcined MgAlEu-LDH are as follows Figure 2 b. Figure 3 According to the SEM images, the specific surface area of ​​the uncalcined MgAlEu-LDH is significantly smaller than that of the one calcined at 350 °C, and it lacks oxygen vacancies (≡Al–O· defects), which reduces the 3+ The synergistic effect of the two components reduces the oxidation-adsorption dual functional activity of the material.

[0031] Experimental Example 1

[0032] To investigate the As(III) removal mechanism, a kinetic model was established based on the time-varying adsorption rate. Experimental results showed that the adsorption reaction rate was extremely high in the initial adsorption stage (t < 15 min), reaching 221.9 mg·(g·h). -1 , 45.2% of As(III) adsorption was completed in just 15 minutes. As the adsorption sites gradually became saturated, the reaction rate showed an exponential decay trend. At t = 5h, the adsorption process gradually approached equilibrium, and the adsorption rate finally reached 88.2%. Figure 4 shown.

[0033] The static adsorption experiment fitting showed that the adsorption isotherm of arsenic on MgAlEu-LDH was consistent with the Langmuir model (R 2 =0.993) is highly consistent, indicating that the adsorption process is mainly monolayer chemical adsorption, such as Figure 5 shown.

[0034] At 25 ° C, 600 r / min shaking conditions, 0.1g MgAl-LDH, MgAlEu-LDH (2:1:0.1) and MgAlEu-LDH (3:1:0.1) were added to 100mL of 100ppm As (III) solution (pH = 7.0). The experimental results showed that MgAlEu-LDH (2:1:0.1) and MgAlEu-LDH (3:1:0.1) exhibited a characteristic fluorescence emission peak at 615nm, while MgAl-LDH did not detect this characteristic peak at this wavelength. This indicates that the doping of europium (Eu) gives the material unique fluorescence properties, and this characteristic fluorescence peak can be attributed to Eu 3+ The electronic transition process of ions (e.g. 5D0→7F2), such as Figure 6 shown.

[0035] At 25°C and 600 r / min oscillation conditions, 0.1 g MgAlEu-LDH (2:1:0.1) was added to 100 mL of 100 ppm As(Ⅲ) solution (pH = 7.0). As the adsorption reaction time prolonged (0 to 4 h), the characteristic fluorescence intensity at 615 nm showed a trend of gradually weakening. Real-time fluorescence spectrum data showed that: at the initial moment of the adsorption reaction (0 min), the fluorescence intensity was 1705 a.u.; it quickly dropped to 1560 a.u. (attenuation 8.5%) at 1 h; it further dropped to 1320 a.u. (attenuation 22.2%) at 2 h; it further dropped to 1080 a.u. (attenuation 18.2%) at 3 h; it dropped to 817 a.u. (attenuation 24.3%) at 4 h, and then stabilized. This shows that in the process of adsorbing As(Ⅲ), Eu 3+ The interaction between Eu and As(Ⅲ) resulted in 3+Therefore, the fluorescence characteristics of Eu in MgAlEu-LDHs can be used to 3+ The 5D0→7F2 transition (615 nm) of As(Ⅲ) was used as a fluorescent probe to construct a real-time fluorescence monitoring system to monitor the adsorption process of As(Ⅲ). Figure 7 shown.

Claims

1. Preparation of a fluorescent functionalized hydrotalcite-based composite material and its application in heavy metal adsorption and in-situ monitoring, the specific steps of the preparation method are: (1) Magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O) and europium chloride (EuCl3·6H2O) were accurately weighed according to the molar ratio of magnesium, aluminum and europium in the target product. (MgCl2·6H2O) 2+ :Al 3+ :Eu 3+ ) The molar ratio is set to 2:1:0 1. Prepare the precipitant, prepare sodium hydroxide (NaOH) into an alkaline solution, and prepare deionized water. (2) Preparation of salt solution: Add weighed magnesium chloride, aluminum chloride and europium chloride to an appropriate amount of deionized water and stir thoroughly to dissolve them completely to form a mixed salt solution. (3) Rubber mill treatment: Slowly inject the mixed salt solution and alkaline solution into the rubber mill simultaneously. Control the speed of the rubber mill at 3000-5000 r / min, maintain the temperature at room temperature, and adjust the feed rate according to the processing capacity of the rubber mill. Thoroughly mix and grind in the rubber mill to allow the metal ions to fully react with the hydroxide ions and chloride ions to form a precipitate. The reaction time is usually 10-20 minutes. (4) Aging: The product after the rubber mill treatment is transferred to the reactor and aged at 60-80 ° C for 12-24 hours to promote further crystallization growth of the precipitate. (5) Washing and Drying: The aged product was washed twice with deionized water at 4000 rpm in a centrifuge, and then washed twice with ethanol at 5000 rpm in a centrifuge until the pH of the washing solution was close to neutral, thereby removing impurities that interfere with the experiment. The centrifuged product was dried in an oven at 60-80°C for 12-24 hours to obtain the magnesium aluminum europium ternary metal hydrotalcite product, i.e., MgAlEu-LDH. (6) Calcination at 350 °C in a muffle furnace to obtain MgAlEu-LDO. The present invention also provides an application of the MgAlEu-LDO material prepared by the method described above in adsorbing heavy metals, wherein the method is: At 25°C and 600 r / min oscillation conditions, 0.1 g MgAlEu-LDH (2:1:0.1) was added to 100 mL of 100 ppm As(III) solution (pH = 7.0). As the adsorption reaction time prolonged (0 to 4 h), the characteristic fluorescence intensity at 615 nm showed a trend of gradually weakening. Real-time fluorescence spectrum data showed that: at the initial moment of the adsorption reaction (0 min), the fluorescence intensity was 1705 a.u.; it quickly dropped to 1560 a.u. (attenuation 8.5%) after 1 h; it further dropped to 1320 a.u. (attenuation 222%) after 2 h; it further dropped to 1080 a.u. (attenuation 18.2%) after 3 h; it dropped to 817 a.u. (attenuation 24.3%) after 4 h, and then tended to be stable. This shows that in the process of adsorbing As(III), Eu 3+ The interaction between Eu and As(III) resulted in 3+ Therefore, the fluorescence characteristics of Eu in MgAlEu-LDHs can be used to 3+ The 5D0→7F2 transition (615 nm) of As(III) was used as a fluorescent probe to construct a real-time fluorescence monitoring system to monitor the adsorption process of As(III).

2. The preparation method according to claim 1, characterized in that Mg in MgAlEu-LDH 2+ :Al 3+ :Eu 3+ The optimal molar ratio is 2:1:0.

1.

3. The preparation method according to claim 1, characterized in that The magnesium, aluminum and europium materials in the synthetic hydrotalcite are all chlorides. According to previous studies, chloride ions are determined to be superior to nitrate ions as interlayer anions.

4. The preparation method according to claim 1, characterized in that The MgAlEu-LDO is a product formed by calcining at 350°C.

5. The preparation method according to claim 1, characterized in that When the MgAlEu-LDO adsorbs As(III), the characteristic fluorescence intensity at 615 nm shows a trend of gradually weakening.

Images