Controllable synthesis of europium-doped magnesium-iron ternary hydrotalcite and application of europium-doped magnesium-iron ternary hydrotalcite to oxidation-adsorption synergistic removal of trivalent arsenic

Abstract

The invention belongs to the technical field of adsorption materials, and discloses controllable synthesis of europium-doped magnesium-iron ternary hydrotalcite and application of the europium-doped magnesium-iron ternary hydrotalcite to oxidation-adsorption synergistic removal of trivalent arsenic. According to the method, a colloid mill is adopted to prepare materials, and a metastable-state spinel structure is successfully constructed by optimizing the metal ratio (Mg < 2 + >: Fe < 3 + >: Eu < 3 + > = 5: 1: 0.1), interlayer Cl <-> anions and a 350 DEG C calcination process. Under irradiation of a xenon lamp (lambda > = 450 nm), electron transition of Eu < 3 + > promotes generation of oxygen vacancies, and the adsorption capacity is improved. Thermodynamic fitting shows that adsorption is mainly monomolecular layer chemical adsorption, and dynamics conforms to a quasi-secondary kinetic model. The invention provides a novel, efficient and stable material and a technical scheme for repairing a heavy metal polluted site.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and specifically relates to a controllable synthesis of europium-doped magnesium-iron ternary hydrotalcite and its application in oxidation-adsorption synergistic removal of trivalent arsenic. Background Art

[0002] Arsenic (As) is a common environmental pollutant, widely present in water, soil, and the atmosphere. Trivalent arsenic (As(III)) and pentavalent arsenic (As(V)) are the most common. As(III) is significantly more toxic than As(V), and its carcinogenicity, teratogenicity, and mutagenicity have attracted widespread attention, making it a high-risk pollutant with priority control. As(III) is commonly found in wastewater from mining, smelting, pesticides, glass, and electronics industries. It has strong mobility and bioavailability, and can easily enter the human body through drinking water and other pathways, causing chronic poisoning. As(III) exists primarily in water as the neutral molecule H3AsO3 and is particularly stable in weakly acidic environments below pH 7. This property limits the effectiveness of traditional treatment methods, posing a significant challenge to wastewater treatment. Therefore, the development of efficient and highly selective As(III) removal materials and technologies has become a key research direction in water pollution control.

[0003] In recent years, layered double hydroxides (LDHs) have shown great potential in the field of environmental governance due to their adjustable chemical composition and unique layered structure. LDHs materials have the following significant characteristics when treating heavy metal ions: first, their interlayer anions are exchangeable; second, the selective adsorption of specific heavy metal ions can be achieved by regulating the metal elements of the layer plates; third, the hydroxyl groups rich in the surface of the material can coordinate with metal ions. In addition, by introducing functional groups such as thiol and carboxyl groups for surface modification, its ability to capture heavy metals can be further enhanced. Based on these characteristics, LDHs can efficiently remove heavy metal pollutants from water bodies through various pathways such as surface complexation, ion exchange, and isomorphous substitution.

[0004] Rare earth element europium (Eu 3+ ) plays a dual key role in ternary hydrotalcite, effectively improving its ability to repair arsenic pollution. 3+ [Xe]4f 6 The electronic configuration has a high coordination number (usually 8-9) and strong Lewis acidity, and can form a multidentate coordination with arsenate (AsO2-). According to the hard acid-hard base principle, Eu 3+ The strong electrostatic coupling with AsO2- significantly enhances its selective fixation ability. 2+ , Ca 2+ Divalent ions such as Eu 3+ The higher the charge density, the more stable the chelate system can be constructed in the layered structure. 2-, HCO3- anti-interference is improved by about 40%, and the excellent adsorption performance is maintained in the pH range of 4-9, which is attributed to Eu 3+ –AsO2- has stronger orbital hybridization and higher coordination bond energy (up to 218kJ / mol). Summary of the Invention

[0005] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a method for preparing a europium-doped magnesium-iron ternary hydrotalcite material.

[0006] The second object of the present invention is to provide an application of the MgFeEu-LDO material prepared by the method described above in solving the heavy metal As (III) pollution of water resources.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a europium-doped magnesium-iron ternary hydrotalcite material comprises the following preparation steps:

[0009] a. Accurately weigh 6.10 g of magnesium chloride (MgCl2·6H2O), 2.70 g of ferric chloride (FeCl3·6H2O), and 0.37 g of europium chloride (EuCl3·6H2O), respectively, to achieve a molar ratio of 5:1:0.1 for the target product. Dissolve them in 200 mL of deionized water to obtain Solution A. Prepare a precipitant by dissolving sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution, Solution B.

[0010] b. Slowly inject the mixed salt solution A and alkaline solution B into the rubber mill simultaneously. Control the mill speed at 2600 rpm and maintain the temperature at room temperature. Adjust the feed rate based on the mill's processing capacity. Thoroughly mix and grind the materials in the mill to allow the metal ions to fully react with the hydroxide and chloride ions to form a precipitate. The reaction typically takes 5 minutes.

[0011] c. The product after the rubber mill treatment was transferred to a reactor and aged at 60°C to promote further crystallization of the precipitate. The centrifuged product was placed in an oven at 60°C and dried for 12 hours to obtain magnesium iron europium hydrotalcite (MgFeEu-LDH) with chloride ions as the interlayer anion.

[0012] d. The MgFeEu-LDH was placed in a muffle furnace and calcined at a temperature of 350°C to obtain the MgFeEu-LDO material.

[0013] The present invention also provides an application of the MgFeEu-LDO material prepared by the method described above in solving the heavy metal As(III) pollution of water resources, wherein the method is:

[0014] a. Use the obtained MgFeEu-LDO material for adsorption experiments: Weigh an appropriate amount of the adsorbent material and disperse it in a 100 ppm As(III) solution, pH = 7.0 ± 0.2, T = 25°C. After the desired adsorption time, filter and sample the solution for ICP testing.

[0015] b. An appropriate amount of MgFeEu-LDO material was dispersed in a 100 ppm As(III) solution and adsorbed under xenon lamp irradiation (300 W, λ ≥ 450 nm) for 5 h. After filtration through a 0.22 μm nylon membrane, the residual As(III) concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400).

[0016] c. An appropriate amount of MgFeEu-LDO material was dispersed in an As(III) solution of 50–500 ppm. After adsorption saturation, the solution was filtered through a 0.22 μm nylon membrane. The residual As(III) concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400) to obtain the adsorption capacity of the MgFeEu-LDO material.

[0017] The preparation method of the present invention and the obtained product have the following advantages and beneficial effects:

[0018] (1) The material of the present invention is a europium-doped magnesium-iron ternary hydrotalcite material with high As(III) fixation performance. The composite material has the characteristics of high adsorption efficiency, fast adsorption speed and stability in removing As.

[0019] (2) The material of the present invention can not only efficiently adsorb As in aqueous solution under dark conditions, but also has a better adsorption effect under light.

[0020] (3) The elements contained in the magnesium salt and iron salt used in the present invention are natural components, and the amount of europium used is very small, which has the advantages of low price.

[0021] It is cheap, widely available, and has no environmental pollution.

[0022] (4) The preparation method of the present invention is simple, has mild reaction conditions, low energy consumption, high yield, and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the effect of Eu doping and different magnesium-iron ratios on the adsorption rates of MgFe-LDH and MgFeEu-LDH under the conditions of Example 1 of the present invention.

[0024] Figure 2 These are the XRD patterns of MgFe-LDH, MgFe-LDO, MgFeEu-LDH and MgFeEu-LDO under the conditions of Example 2 of the present invention.

[0025] Figure 3 These are SEM images of MgFe-LDH, MgFe-LDO, MgFeEu-LDH and MgFeEu-LDO under the conditions of Example 2 of the present invention.

[0026] Figure 4 This is the EPR spectrum of the MgFe-based material doped with Eu and calcined under the conditions of Example 2 of the present invention.

[0027] Figure 5 (A) XPS spectrum of Cl 2p orbitals in MgFeEu-LDO under the conditions of Example 2 of the present invention, (B) XPS spectrum of Cl 2p orbitals after arsenic adsorption on MgFeEu-LDO, and (C) XPS spectrum of As 3d orbitals after arsenic adsorption on MgFeEu-LDH.

[0028] Figure 6 (A) XPS spectrum of Fe 2p orbitals in MgFeEu-LDH under the conditions of Example 2 of the present invention; (B) XPS spectrum of Fe 2p orbitals after arsenic adsorption on MgFeEu-LDH.

[0029] Figure 7 This is the effect of different interlayer anions on the adsorption rate of MgFeEu-LDH and MgFeEu-LDO under the conditions of Example 3 of the present invention.

[0030] Figure 8 2. XRD patterns of MgFeEu-LDO at different calcination temperatures under the conditions of Example 3 of the present invention.

[0031] Figure 9 This is the effect of different calcination temperatures on the adsorption rate of MgFeEu-LDO under the conditions of Example 4 of the present invention.

[0032] Figure 10 This is the effect of light on the adsorption rate of MgFeEu-LDO under the conditions of Example 4 of the present invention.

[0033] Figure 11 (A) The adsorption rate curve of trivalent arsenic by MgFeEu-LDO under the conditions of Example 4 of the present invention; (B) The pseudo-second-order kinetic model of trivalent arsenic by MgFeEu-LDO.

[0034] Figure 12 This is a fitting diagram of the adsorption capacity of MgFeEu-LDO under the conditions of Example 5 of the present invention.

[0035] Table 1 is a Langmuir and Freundlich isotherm fitting table of the adsorption capacity of MgFeEu-LDO under the conditions of Example 5 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0037] Example 1

[0038] The present invention provides a controllable synthesis of a europium-doped magnesium-iron ternary hydrotalcite:

[0039] (1) Magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O), and europium chloride (EuCl3·6H2O) were accurately weighed according to the molar ratio of magnesium, iron, and europium in the target product (2:1:0.1, 3:1:0.1, 5:1:0.1, and 6:1:0.1) and dissolved in 200 mL of deionized water to obtain solution A. A precipitant was prepared by dissolving sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0040] (2) Comparative sample: Magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O), and europium chloride (EuCl3·6H2O) were accurately weighed according to the molar ratio of magnesium to iron in the target product (2:1, 3:1, 5:1, and 6:1) and dissolved in 200 mL of deionized water to obtain solution A. Prepare the precipitant by dissolving sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0041] (3) Slowly inject the mixed salt solution A and alkaline solution B into the rubber mill simultaneously. Control the speed of the rubber mill at 2600 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 5 minutes.

[0042] (4) The product after the rubber mill treatment was transferred to a reactor and aged at 60°C to promote further crystallization growth of the precipitate. The centrifuged product was placed in an oven at 60°C and dried for 12 hours to obtain MgFeEu-LDH and MgFe-LDH with chloride as the interlayer anion. 0.1g of the adsorbent material was weighed and dispersed in a solution of As(III) = 100ppm, pH = 7.0 ± 0.2, T = 25°C. After the required adsorption time, the sample was filtered and sampled for ICP testing.

[0043] The effects of Eu doping and different magnesium-iron ratios on the adsorption rates of MgFe-LDH and MgFeEu-LDH were obtained for the target products and the comparative samples, such as Figure 1 shown.

[0044] like Figure 1 As shown, in Mg 2+ :Fe 3+ :Eu 3+In the systematic screening of molar ratios, when the ratio was 5:1:0.1, the removal rate of arsenic by the material reached 86.7%, which was significantly better than other ratios. By comparing the adsorption performance of MgFe-LDH and MgFeEu-LDH, it was found that Eu 3+ The introduction of Eu enhanced the material's ability to remove arsenic. When the initial arsenic concentration was 100 ppm, the equilibrium adsorption rate of MgFeEu-LDHs increased by an average of 5.6% compared to that of undoped MgFe-LDH. This optimization is due to the 3+ Multiple roles: On the one hand, Eu 3+ (ionic radius 0.095nm) and Fe 3+ The synergistic doping of ions (ionic radius 0.0645 nm) regulates the cationic charge density of the layer, making the positive charge distribution of the layer more uniform and enhancing the arsenate (AsO2 — ) electrostatic attraction; on the other hand, Eu 3+ The 4f electron configuration provides abundant coordination active sites, promoting the interaction between As(Ⅲ) and layer metal ions (Mg 2+ 、Fe 3+ 、Eu 3+ ) between ligand exchange reactions.

[0045] Example 2

[0046] Preparation of a europium-doped magnesium-iron ternary hydrotalcite material in the present invention:

[0047] (1) According to the molar ratio of magnesium, iron, and europium in the target product of 5:1:0.1, accurately weigh 10.16, 2.70, and 0.37 g of magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O), and europium chloride (EuCl3·6H2O), respectively, and dissolve them in 200 mL of deionized water to obtain solution A. Prepare the precipitant by dissolving 3.90 g of sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0048] (2) Comparative sample: Accurately weigh 6.10 g of magnesium chloride (MgCl2·6H2O) and 2.70 g of ferric chloride (FeCl3·6H2O) to achieve a molar ratio of 5:1 in the target product and dissolve them in 200 mL of deionized water to obtain solution A. Prepare a precipitant by dissolving 3.84 g of sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0049] (3) Slowly inject the mixed salt solution A and alkaline solution B into the rubber mill simultaneously. Control the speed of the rubber mill at 2600 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 5 minutes.

[0050] (4) The product after the rubber mill treatment was transferred to the reactor and aged at 60°C to promote further crystallization growth of the precipitate. The centrifuged product was placed in a 60°C oven and dried for 12 hours to obtain MgFeEu-LDH and MgFe-LDH with chloride ions as interlayer anions. The product was placed in a muffle furnace and calcined for 3 hours at a temperature of 350°C to obtain MgFeEu-LDO and MgFe-LDO for adsorption experiments. An appropriate amount of adsorption material was weighed and dispersed in an As(III) = 100 ppm solution, pH = 7.0 ± 0.2, T = 25°C. After the required adsorption time, the sample was filtered and sampled for ICP testing.

[0051] The XRD, SEM, EPR and XPS images of the target product and the comparative sample were obtained, as shown in FIG. Figure 2 , 3, 4, 5 and 6 as shown.

[0052] like Figure 2 XRD results show that the (003), (006), and (009) crystal plane diffraction peaks of MgFe-LDH and MgFeEu-LDH are strong, reflecting the characteristics of MgFe-LDH, indicating that MgFe-LDH and MgFeEu-LDH were successfully synthesized. However, the (003), (006), and (009) peaks of MgFe-LDO and MgFeEu-LDO disappeared compared with the uncalcined hydrotalcite, indicating that the layered structure collapsed and calcined into spinel. After doping, the (003) crystal plane diffraction peak intensity of the hydrotalcite increased and the half-peak width narrowed, indicating that Eu 3+ The introduction of improves the crystallinity of the layered structure and provides a more ordered microenvironment for the interlayer adsorption of arsenic ions.

[0053] like Figure 3 SEM results show Figure 3 a shows the typical layered stacking structure of LDH, with uniform layer thickness, close arrangement between layers, smooth surface, and no obvious cracks or holes, which is consistent with the typical microstructure and chemical composition of Mg-Fe hydrotalcite. Figure 3 b is the slight distortion of the laminate after Europium doping, the surface roughness increases, and a small amount of nanoparticles can be seen attached. The introduction of Europium causes the charge density of the laminate to change, and some Mg 2+ Eu 3+ substitution, causing local lattice distortion. Figure 3After calcination at 350°C, the layered structure partially collapses, forming a massive oxide structure with numerous mesopores (pore diameter 2–5 nm) and microcracks on the surface. This is a typical result of the removal of interlayer water molecules and hydroxyl (–OH) groups during LDH calcination. The removal of interlayer hydroxyl (–OH) groups from the original LDH generates H2O and CO2, causing the layers to shrink and reorganize into metal oxides (MgO, Fe2O3). Figure 3 d Due to the “memory effect” of hydrotalcite, it recovers to a layered stacking structure after adsorbing As.

[0054] like Figure 4 EPR results show that the EPR signal g value of MgFeEu-LDO after calcination and europium doping fluctuates greatly (broad peak), which is due to the diversity of oxygen vacancies, Eu 3+ Coordination reconstruction and spin interaction; while the uncalcined LDH has a complete structure and few defects, resulting in a stable signal (narrow peak). This difference directly reflects the optimization mechanism of the adsorption-oxidation performance of the material after calcination.

[0055] like Figure 5 XPS results show that the intensity of Cl 2p peak (binding energy ~198eV) decreased by 75.3%, while As 3d peak (binding energy ~44.5eV corresponding to As(III), ~45.5eV corresponding to As(V)) appeared, indicating that the interlayer Cl – AsO3 3– Substitution (ion exchange dominated).

[0056] like Figure 6 XPS results show that AsO3 is adsorbed 3- Fe was detected in the Fe 2p spectrum. 2+ Characteristic peak (binding energy ~ 709eV), while Fe 3+ The peak (binding energy ~711eV) intensity decreased, indicating that Fe 3+ Reduced to Fe 2+ As 3d spectrum peak fitting shows the simultaneous presence of As 3+ (~44.5eV) and As 5+ (~45.5eV) components, indicating that the redox reaction occurred. 3+ Reduction to Fe 2+ When As 3+ Oxidized to As 5+ This is also one of the reasons why MgFeEu-LDH material has good adsorption performance.

[0057] Example 3

[0058] Preparation of a europium-doped magnesium-iron ternary hydrotalcite material in the present invention:

[0059] (1) According to the molar ratio of magnesium, iron, and europium in the target product of 5:1:0.1, accurately weigh 10.16, 2.70, and 0.37 g of magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O), and europium chloride (EuCl3·6H2O), respectively, and dissolve them in 200 mL of deionized water to obtain solution A. Prepare the precipitant by dissolving 3.90 g of sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0060] (2) Comparative sample: According to the molar ratio of magnesium, iron, and europium in the target product of 5:1:0.1, accurately weigh 12.82, 4.04, and 0.45 g of magnesium nitrate (Mg(NO3)2·6H2O), iron nitrate (Fe(NO3)3·9H2O), and europium (III) nitrate (Eu(NO3)3·6H3O) and dissolve them in 200 mL of deionized water to obtain solution A. Prepare the precipitant by dissolving 3.90 g of sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0061] (3) Slowly inject the mixed salt solution A and alkaline solution B into the rubber mill simultaneously. Control the speed of the rubber mill at 2600 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 5 minutes.

[0062] (4) The product after the rubber mill treatment was transferred to the reactor and aged at 60°C to promote further crystallization growth of the precipitate. The centrifuged product was placed in an oven at 60°C and dried for 12 hours to obtain MgFeEu-LDH with interlayer anions of chloride ions and nitrate ions. It was placed in a muffle furnace and calcined for 3 hours at a calcination temperature of 350°C to obtain MgFeEu-LDO with interlayer anions of chloride ions and nitrate ions. The four materials obtained were subjected to adsorption experiments. Appropriate amounts of adsorbent materials were weighed and dispersed in a solution of As(III) = 100 ppm, pH = 7.0 ± 0.2, T = 25°C. After the required adsorption time, the samples were filtered and sampled for ICP testing.

[0063] The effect of different interlayer anions on the adsorption rate of the target product and the reference sample was obtained, such as Figure 7 shown.

[0064] Figure 7 Comparison of Cl — With NO3 — As the adsorption performance of interlayer anions, Cl — The removal efficiency of arsenic by MgFeEu-LDHs with interlayer anions is higher than that of NO3 — The system is 9.2% higher. This difference is mainly determined by the physical and chemical properties of the anion: Cl— The ionic radius (0.181nm) is smaller than that of NO3 — (0.24nm), the interlayer stacking is tighter, and the unit interlayer space can accommodate more anions, thus providing more exchangeable sites. It is easier to react with AsO2 — Ionic radius 0.245nm) undergoes interlayer exchange; at the same time, Cl — The hydration energy is low (-383kJ / mol), NO3 — (-307kJ / mol), it is easier to break away from the interlayer lattice in aqueous solution, reducing the activation energy of anion exchange, and kinetically more favorable for AsO2 — Fast embedding. In addition, Cl — The presence of common anions in water (such as SO4 2— 、HCO3 — ) competitive adsorption, while NO3 — With AsO2 — The charge density of the two species is similar, which easily leads to competition for adsorption sites and reduces the removal efficiency.

[0065] Example 4

[0066] Preparation of a europium-doped magnesium-iron ternary hydrotalcite material in the present invention:

[0067] (1) According to the molar ratio of magnesium, iron, and europium in the target product of 5:1:0.1, accurately weigh 10.16, 2.70, and 0.37 g of magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O), and europium chloride (EuCl3·6H2O), respectively, and dissolve them in 200 mL of deionized water to obtain solution A. Prepare the precipitant by dissolving 3.90 g of sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B.

[0068] (2) Slowly inject the mixed salt solution A and alkaline solution B into the rubber mill simultaneously. Control the speed of the rubber mill at 2600 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 5 minutes.

[0069] (3) The product after the rubber mill treatment was transferred to a reactor and aged at 60°C to promote further crystallization growth of the precipitate. The centrifuged product was placed in an oven at 60°C and dried for 12 hours. The obtained MgFeEu-LDH was placed in a muffle furnace and calcined for 3 hours at a calcination temperature of 150–550°C to obtain MgFeEu-LDO with different calcination temperatures.

[0070] (4) The obtained material was subjected to adsorption experiment. An appropriate amount of adsorption material was weighed and dispersed in a solution containing As(III) = 100 ppm, pH = 7.0 ± 0.2, and T = 25°C. After the required adsorption time, the sample was filtered and sampled for ICP testing.

[0071] The XRD patterns and adsorption rates of the target products at different calcination temperatures were obtained, such as Figure 8 and 9 shown.

[0072] like Figure 8 As shown by XRD, after calcination at 350℃, the layered structure of hydrotalcite partially collapses and forms a spinel phase (MgFeO4-Eu), which is manifested by the disappearance of the (003) peak and the appearance of the characteristic peaks of spinel such as (220) and (311). When the temperature is too low, only the interlayer free water is removed, and the layer-coordinated water (such as [Mg(OH2)6] 2+ ) is still partially retained, and the interlayer anions (Cl — ) did not desorb. When the temperature is too high, the layer cations undergo deep reconstruction: Mg 2+ with Fe 3+ / Eu 3+ Oxygen ions form a stable spinel structure (MgFe2O4, EuFeO3), significantly enhancing its characteristic XRD peaks (such as 2θ = 31.3° and 36.8°), while the characteristic peak of hydrotalcite ((003) plane at 2θ = 11.6°) completely disappears. The cations in the spinel structure are highly ordered with octahedral / tetrahedral coordination, significantly increasing the metal-oxygen bond energy and forming a thermodynamically stable rigid lattice. This prevents the regeneration of layered hydroxyl compounds through water absorption, completely eliminating the memory effect.

[0073] like Figure 9 It shows that when the calcination temperature is 350℃, the adsorption rate of the material reaches a peak of 94.7%.

[0074] Example 5

[0075] A preparation method of a europium-doped magnesium-iron ternary hydrotalcite material is described with reference to Example 4, except that the calcination temperature is 350°C.

[0076] (1) An appropriate amount of MgFeEu-LDO material was dispersed in a 100 ppm As(III) solution and adsorbed under xenon lamp irradiation (300 W, λ ≥ 450 nm) for 5 h. After filtration through a 0.22 μm nylon membrane, the residual As(III) concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400).

[0077] (2) An appropriate amount of MgFeEu-LDO material was dispersed in an As(III) solution of 50–500 ppm. After adsorption saturation, the solution was filtered through a 0.22 μm nylon membrane, and the residual As(III) concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400).

[0078] The XRD patterns, adsorption rate curves and adsorption capacities of the target products at different calcination temperatures were obtained, such as Figure 10 , as shown in 11 and 12.

[0079] like Figure 10 As shown in Figure 2, xenon lamp irradiation can further improve the adsorption efficiency of MgFeEu LDHs. Under the optimal conditions, the removal rate increased from 92.7% to 94.2%. 3+ The photoresponse characteristics are closely related to: light excites Eu 3+ 4f electron transition ( 7 F0→ 5 D0), generating photogenerated electron-hole pairs, which migrate to the surface of the material and promote the reduction of O2 to generate superoxide radicals (·O2 — ), while the holes react with water to generate hydroxyl radicals (·OH). The generation of free radicals enhances the oxidation reaction on the material surface, causing some As(III) to be oxidized to As(V), which then forms more stable coordination compounds with the metal ions of the laminate.

[0080] like Figure 11 As shown in the figure, in the rapid adsorption stage, the adsorption rate reached 40.16% in the first 5 minutes, with an instantaneous rate of 481.92 mg / (g·h), which was attributed to the high specific surface area of the LDO material and the rapid saturation of surface active sites; in the equilibrium stage, the adsorption rate change rate was <1% / h at 360 minutes, and the adsorption rate was 95.12%, which was consistent with the pseudo-second-order kinetic model.

[0081] like Figure 12 As shown in the static adsorption experiment fitting, it was found that the adsorption isotherm of arsenic by MgFeEu-LDHs was consistent with the Langmuir model (R 2 =0.992) is highly consistent, indicating that the adsorption process is mainly monolayer chemical adsorption and there are uniform specific adsorption sites. Table 1 Langmuir model parameters show that the saturated adsorption capacity (Q m ) is 407 mg / g, which is close to the maximum adsorption capacity (403 mg / g) measured experimentally, verifying the surface active sites of the material for AsO2 — The monolayer coordination adsorption mechanism.

[0082] Table 1

[0083]

Claims

1. A controllable synthesis of europium-doped magnesium-iron ternary hydrotalcite and its application in the oxidation-adsorption synergistic removal of trivalent arsenic. The specific steps of the preparation method are: (1) Accurately weigh the materials containing the corresponding metals according to the molar ratios of magnesium, iron, and europium in the target product (2:1:0.1, 3:1:0.1, 5:1:0.1, and 6:1:0.1) and dissolve them in 200 mL of deionized water to obtain solution A. Prepare a precipitant by dissolving sodium hydroxide (NaOH) in 200 mL of deionized water to prepare an alkaline solution to obtain solution B. (2) Slowly inject the mixed salt solution A and alkaline solution B into the rubber mill simultaneously. Control the speed of the rubber mill at 2600 r / min and maintain the temperature at room temperature. Adjust the feed rate based on 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 5 minutes. (3) The product after the rubber mill treatment was transferred to a reactor and aged at 60°C to promote further crystallization growth of the precipitate. The centrifuged product was placed in an oven at 60°C and dried for 12 hours to obtain magnesium iron europium hydrotalcite (MgFeEu-LDH) with chloride ions as the interlayer anion. (4) MgFeEu-LDH was calcined in a muffle furnace at a temperature of 150–550°C to obtain MgFeEu-LDO for adsorption experiments. An appropriate amount of adsorbent material was weighed and dispersed in a 100 ppm As(III) solution, pH = 7.0 ± 0.2, T = 25°C. After the desired adsorption time, the sample was filtered and sampled for ICP testing. (5) An appropriate amount of MgFeEu-LDO material was dispersed in a 100 ppm As(III) solution and adsorbed under xenon lamp irradiation (300 W, λ ≥ 450 nm) for 5 h. After filtration through a 0.22 μm nylon membrane, the residual As(III) concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400). (6) An appropriate amount of MgFeEu-LDO material was dispersed in an As(III) = 50–500 ppm solution and filtered through a 0.22 μm nylon membrane after adsorption saturation. The residual As(III) concentration was quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400).

2. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, wherein In step (1), the molar ratio of magnesium, iron and europium in the target product is 5:1:0.

1.

3. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, wherein In step (2), the rotation speed of the rubber mill is 2600 r / min.

4. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, wherein In step (1), the metal substances are magnesium chloride (MgCl2·6H2O), ferric chloride (FeCl3·6H2O) and europium chloride (EuCl3·6H2O), weighing 10.16, 2.70 and 0.37 g respectively.

5. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, wherein In step (1), 3.90 g of sodium hydroxide (NaOH) is weighed.

6. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, wherein In step (3), the aging time is 12 hours.

7. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, characterized in that: In step (4), the MgFeEu-LDH is calcined in a muffle furnace for 3 hours at a calcination temperature of 350°C.

8. The method for preparing magnesium-iron-europium hydrotalcite according to claim 1, wherein In steps (5) and (6), the amount of MgFeEu-LDO material used is 0.1 g.

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