Rare earth doped hydrotalcite-like catalyst and preparation method and application thereof

Abstract

The invention discloses a rare earth doped hydrotalcite-like catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The method provided by the invention avoids high-temperature and high-pressure conditions, reduces energy consumption and potential safety hazards, promotes uniform dispersion of metal ions, and significantly improves the crystallinity and purity of the product. The preparation method comprises the following steps: dissolving Co (NO3) 2.6 H2O, Fe (NO3) 3.9 H2O, Eu (NO3) 3.6 H2O, ammonium fluoride and urea in absolute methanol, and violently stirring at room temperature for at least 2 hours to obtain a clear mixed salt solution; and slowly dropwise adding the NaOH solution into the mixed salt solution under magnetic stirring until the pH value of the solution reaches 9-10, then aging, washing and centrifuging at room temperature to collect brown solid precipitates, drying and grinding to obtain the rare earth doped hydrotalcite-like catalyst. The oxygen vacancy concentration and the electron transfer capability are regulated and controlled through rare earth doping, so that the antibiotic degradation performance of the catalyst is improved, including environmental applicability, broad spectrum, stability and recyclability.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts. Specifically, it relates to a rare earth doped hydrotalcite catalyst; it also relates to a preparation method of the rare earth doped hydrotalcite catalyst; it also relates to the application of the rare earth doped hydrotalcite catalyst. Background Art

[0002] As a class of chemical substances produced by microorganisms or animals and plants, antibiotics play an important role in the prevention and treatment of human and animal diseases and the promotion of animal growth. However, with their widespread application, antibiotic pollution incidents occur frequently, attracting wide social attention. Antibiotics in water mainly come from the discharge of pharmaceutical, medical, domestic and aquaculture wastewater. Most of them are excreted in the body in the form of the original form or metabolites and finally flow into water bodies. Antibiotics are substances that are difficult to biodegrade, with high biological activity, persistence and bioaccumulation. Although the residue level is at a trace level, through accumulation and food chain transmission, they pose a serious threat to the ecological system and human health, including increased bacterial drug resistance, affected growth and reproduction of animals and plants, and chronic poisoning of the human body. In view of this, exploring low-cost and highly efficient methods for the deep treatment of antibiotic residues has become an urgent task in the field of environmental protection.

[0003] Existing preparation methods of rare earth doped hydrotalcite, such as co-precipitation method, hydrothermal method, ion exchange method and urea decomposition method, each have their own advantages and disadvantages. The co-precipitation method is simple to operate and has low cost, but the crystallinity is not high and the reaction conditions need to be strictly controlled; although the hydrothermal method can prepare products with high crystallinity, it relies on high temperature and high pressure environment, with high energy consumption and low efficiency; the ion exchange method can regulate the interlayer anions, but the steps are cumbersome and are easily affected by impurities; the urea decomposition method has mild reaction, but takes a long time and the crystallinity of the product is low. These traditional methods often have difficulty in taking into account the product quality, preparation efficiency and operation convenience. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a rare earth doped hydrotalcite catalyst and its application in activating peroxymonosulfate to treat antibiotic wastewater.

[0005] The preparation method of the present invention realizes the efficient synthesis of rare earth doped hydrotalcite at room temperature by introducing methanol as a solvent and combining the slow dropping of NaOH and controlling the pH value. The method of the present invention avoids high temperature and high pressure conditions, reduces energy consumption and potential safety hazards, and at the same time promotes the uniform dispersion of metal ions, significantly improving the crystallinity and purity of the product. In addition, simplifying subsequent treatment steps, such as direct centrifugal washing and low-temperature drying, further shortens the preparation cycle and reduces the cost.

[0006] The advantages of the method of the present invention lie in its ability to overcome many defects of traditional preparation techniques, not only improving the doping efficiency of rare earth ions, but also enhancing the functionality and stability of the product. The method of the present invention makes the preparation of rare earth-doped hydrotalcite-like materials more efficient, economical and environmentally friendly, providing strong support for their large-scale application in the fields of catalysis, photo-electromagnetism, etc.

[0007] The present invention synthesized a rare earth-doped hydrotalcite-like material (CoFeEu-LDHs). By introducing rare earth element (Eu), the activity of the catalyst was significantly enhanced. The synergistic effect between the 4f electron configuration of rare earth elements and the metal ions in the LDHs layer is the key to improving the catalytic performance.

[0008] In the persulfate (PMS) activation system, CoFeEu-LDHs exhibited excellent catalytic performance and was able to efficiently generate sulfate radicals (SO4 - ·) and singlet oxygen ( 1 O2), realizing the rapid degradation of antibiotic pollutants such as tetracycline hydrochloride (TC-HCl). The catalyst of the present invention showed good environmental applicability under different water quality conditions (such as high-salt, wastewater containing complex anions), and still maintained high degradation performance after multiple cycle experiments, with strong structural stability. The degradation performance of the antibiotic wastewater (such as tetracycline hydrochloride) in the persulfate (PMS) activation system, including degradation efficiency, reaction conditions (such as pH value, temperature) and environmental applicability. The present invention regulates the oxygen vacancy concentration and electron transfer ability through rare earth doping, thereby improving the stability and recyclability of the catalyst.

[0009] The present invention systematically verified the synergistic mechanism of SO4 - · and 1 O2 through electron spin resonance (ESR), quenching experiments combined with density functional theory (DFT) calculations, and revealed the catalytic degradation mechanism of TC-HCl, providing theoretical support for the rational design of the catalyst.

[0010] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0011] The purpose of the present invention is to provide a preparation method of a rare earth-doped hydrotalcite-like catalyst, comprising the following steps:

[0012] Dissolve Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Eu(NO3)3·6H2O, ammonium fluoride and urea in anhydrous methanol, and stir vigorously at room temperature for at least 2 h to obtain a clear mixed salt solution;

[0013] Under magnetic stirring, the NaOH solution was slowly dropped into the mixed salt solution until the pH value of the solution reached 9 - 10. Subsequently, it was aged at room temperature, washed, centrifuged to collect the brown solid precipitate, dried and then ground to obtain the rare earth - doped hydrotalcite - like catalyst.

[0014] Furthermore, it is defined that the mass - to - volume ratio of Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Eu(NO3)3·6H2O, ammonium fluoride and urea to anhydrous methanol is 0.87359 g∶0.4040 g∶(0.4342 g - 1.7368 g)∶0.1 g∶1.261 g∶30 mL.

[0015] Furthermore, it is defined that the concentration of the NaOH solution is 0.04 g / mL

[0016] Furthermore, it is defined that the dropping rate is 1 mL / min.

[0017] Furthermore, it is defined that the aging time is 24 h.

[0018] Furthermore, it is defined that the washing process is as follows: the above suspension is first washed once with deionized water, and then immediately washed once with absolute ethanol. This washing - replacement process is alternately repeated for 3 cycles. After each washing, centrifugal separation is carried out at a speed of 8000 r / min to collect the brown solid precipitate at the bottom of the centrifuge tube. The obtained precipitate is transferred to a constant - temperature oven and dried at 80 °C for more than 12 h (overnight) to ensure complete drying of the sample.

[0019] The purpose of the present invention is to provide the rare earth - doped hydrotalcite - like catalyst prepared by any of the above methods.

[0020] The structure of the rare earth - doped hydrotalcite - like catalyst of the present invention belongs to a stacked layered structure; Eu, Co, Fe, C, and O co - exist and are uniformly distributed in the rare earth - doped hydrotalcite - like catalyst.

[0021] The present invention relates to the application of the rare earth - doped hydrotalcite - like catalyst in treating antibiotic wastewater in an activated persulfate system.

[0022] Existing persulfate (PMS) wastewater treatment technologies rely on homogeneous or heterogeneous transition metals (such as Co 2+ , Fe 2+ ) for activation, but there are problems such as environmental toxicity (such as Co 2+ pollution) or being greatly affected by pH (such as Fe 2+) The problem is as follows. The present invention innovatively introduces rare earth-doped layered double hydroxides (CoFeEu-LDHs) as catalysts. By utilizing the synergistic effect between the unique 4f electron configuration of rare earth elements (Eu) and the metal ions in the LDHs lamellar, the catalytic performance is significantly enhanced. Experiments show that CoFeEu-LDHs can achieve complete degradation of tetracycline hydrochloride (TC-HCl) within 15 minutes, far exceeding the efficiency of traditional catalysts.

[0023] Although traditional LDHs materials have adsorption and photocatalytic functions in wastewater treatment, they are easily affected by water quality conditions (such as the type of anions, pH value), and the catalyst stability is insufficient. The present invention regulates the oxygen vacancy concentration and electron transfer ability of LDHs through rare earth doping (such as CoFeEu-LDHs having more oxygen vacancies), which not only improves the applicability of the catalyst in different water qualities (such as high-salt, wastewater containing complex anions), but also significantly enhances its cyclic stability. After five cyclic experiments, the catalyst still maintains high degradation performance, and X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analyses confirm its structural stability.

[0024] Existing technologies mostly focus on the contribution of a single active species (such as SO4 - ·), while the present invention, through electron spin resonance (ESR) and quenching experiments, systematically verifies for the first time the synergistic mechanism of sulfate radicals (SO4 - ·) and singlet oxygen ( 1 O2). Combining density functional theory (DFT) calculation and analysis, it further reveals the catalytic degradation mechanism of TC-HCl, providing theoretical support for the rational design of the catalyst. This breakthrough at the mechanism level not only improves the degradation efficiency of the current technology, but also provides a scientific basis for extending to the treatment of other antibiotic wastewater.

[0025] In summary, the present invention realizes a comprehensive improvement in the treatment efficiency, environmental applicability and stability of antibiotic wastewater through the synergistic catalytic system of rare earth-doped layered double hydroxides and peroxymonosulfate, providing an important innovation for the application of advanced oxidation technologies.

[0026] Compared with the existing technologies, the present invention has the following beneficial effects:

[0027] 1. Significantly improved catalytic efficiency:

[0028] Existing peroxymonosulfate (PMS) wastewater treatment technologies rely on homogeneous or heterogeneous transition metals (such as Co 2+ , Fe 2+ ) activation, but there are environmental toxicities (such as Co 2+ pollution) or are significantly restricted by pH conditions (such as Fe 2+Limited activity), and the overall degradation efficiency is poor. The present invention innovatively proposes a preparation scheme of rare earth-doped layered double hydroxides (CoFeEu-LDHs). Through the synergistic effect of rare earth elements (Eu) and lamellar metal ions, a leapfrog improvement in catalytic performance has been achieved. Experimental data shows that compared with traditional catalysts, CoFeEu-LDHs can achieve complete degradation and efficient mineralization of tetracycline hydrochloride (TC-HCl) within 15 minutes, and both the degradation rate and mineralization rate reach unprecedented heights, demonstrating significant technical advantages.

[0029] 2. Stronger environmental applicability and stability:

[0030] Although traditional LDHs materials have adsorption and photocatalytic functions in wastewater treatment, they are easily affected by water quality conditions (such as the type of anions, pH value), and the catalyst stability is insufficient. The present invention regulates the oxygen vacancy concentration and electron transfer ability of LDHs through rare earth doping (such as CoFeEu-LDHs having more oxygen vacancies), not only improving the applicability of the catalyst in different water qualities (such as high-salt, wastewater containing complex anions), but also significantly enhancing its cyclic stability. After five cyclic experiments, the catalyst still maintains high degradation performance, and X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analyses confirm its structural stability.

[0031] 3. Breakthrough at the mechanism level, guiding practice with theory:

[0032] Existing technologies mostly focus on the contribution of a single active species (such as SO4 - ·), while the present invention, through electron spin resonance (ESR) and quenching experiments, for the first time systematically verifies the synergistic mechanism of sulfate radicals (SO4 - ·) and singlet oxygen ( 1 O2). Combining density functional theory (DFT) calculation and analysis, it further reveals the catalytic degradation mechanism of TC-HCl, providing theoretical support for the rational design of the catalyst. This breakthrough at the mechanism level not only improves the degradation efficiency of the current technology, but also provides a scientific basis for extending to the treatment of other antibiotic wastewaters.

[0033] 4. Higher technical economy:

[0034] The present invention reduces costs, improves the lifespan and cyclic use performance of the catalyst by optimizing the catalyst preparation process and reaction conditions, and is more economical than traditional technologies. At the same time, although the introduction of rare earth elements increases the initial material cost, due to its significantly improved catalytic performance and stability, the long-term operating cost is lower.

[0035] In summary, the present invention shows significant advantages in terms of catalytic efficiency, environmental applicability, stability, mechanism revelation and technical economy, providing an important innovation for the field of antibiotic wastewater treatment.

[0036] To further understand the features and technical content of the present invention, please refer to the following detailed description of the present invention and the attached drawings. However, the attached drawings are only for reference and illustration purposes and are not used to limit the present invention. Description of the Drawings

[0037] Figure 1 is the SEM image of the Co3Fe1Eu1-LDHs catalyst, (a) Scanning electron microscope image of Co3Fe1Eu1-LDHs, (b-g) Element mapping distribution diagrams of Co3Fe1Eu1-LDHs;

[0038] Figure 2 is the XRD patterns of CoFe-LDHs, CoEu-LDHs and CoFeEu x -LDHs;

[0039] Figure 3 is the Fourier transform infrared spectra of CoFe-LDHs, CoEu-LDHs and CoFeEu x -LDHs;

[0040] Figure 4 is the (a) N2 adsorption-desorption isotherm and (b) pore size distribution of CoFe-LDHs, CoEu-LDHs and CoFeEu x -LDHs;

[0041] Figure 5 is the XPS spectra of CoFe-LDHs and Co3Fe1Eu1-LDHs, (a) Total XPS spectrum, (b) Co 2p, (c) Fe2p, (d) Eu 3d, (e) O 1s, (f) C 1s;

[0042] Figure 6 is the surface electrical property analysis of Co3Fe1Eu1-LDHs;

[0043] Figure 7 is the ESR spectrum of oxygen vacancies in Co3Fe1Eu1-LDHs;

[0044] Figure 8 is the effect of catalysts with different metal ratios on the activation of PMS by CoFeCe-LDHs for the degradation of tetracycline;

[0045] Figure 9 is the effect of catalyst dosage on the degradation of TC-HCl, (a) Effect of catalyst dosage, (b) Pseudo-first-order kinetic constant;

[0046] Figure 10It is the influence of PMS concentration on the degradation of TC-HCl, (a) influence of PMS concentration, (b) pseudo-first-order kinetic constant, (c) influence of different oxidants, (d) consumption of PMS in the system;

[0047] Figure 11 It is the influence of the initial pollutant concentration on the degradation of TC-HCl, (a) influence of the initial pollutant concentration, (b) pseudo-first-order kinetic constant;

[0048] Figure 12 It is the influence of different initial pH on the degradation of TC-HCl, (a) influence of the system pH value, (b) pseudo-first-order kinetic constant;

[0049] Figure 13 It is the influence of temperature on the degradation of TC-HCl, (a) influence of the reaction temperature, (b) pseudo-first-order kinetic constant;

[0050] Figure 14 It is the influence of different reaction systems on the degradation effect of tetracycline, (a) influence of different reaction systems, (b) pseudo-first-order kinetic constant;

[0051] Figure 15 It is to investigate the influence of various environmental anions on the degradation of tetracycline (TC-HCl) by the CoFeEu-LDHs / PMS system, (a) influence of different anions, (b) pseudo-first-order kinetic constant;

[0052] Figure 16 It is to test the catalytic performance of the CoFeEu-LDHs / PMS system with typical pollutants, (a) influence of different pollutants, (b) pseudo-first-order kinetic constant;

[0053] Figure 17 It is shown by the degradation performance test of TC-HCl in mixed pollutants, (a) influence of different pollutants; (b) pseudo-first-order kinetic constant;

[0054] Figure 18 It is the influence of different water qualities on the degradation of TC-HCl, (a) influence of different water qualities; (b) pseudo-first-order kinetic constant;

[0055] Figure 19 It is the evaluation of the cyclic stability and environmental friendliness of the CoFeEu-LDHs / PMS system, (a) cyclic experiment, (b) pseudo-first-order kinetic constant, (c) leaching of Co and Fe ions, (d) XRD before and after the reaction, (e) FT-IR before and after the reaction, (f) TOC removal rate;

[0056] Figure 20 It is the adsorption energy of PMS on CoFeEu-LDHs. Specific implementation manners

[0057] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention for patent, and at the same time, the present invention is not limited in any form. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention for patent, several modifications and improvements can still be made. These all fall within the protection scope of the present invention for patent.

[0058] Example 1: The preparation method of the rare earth doped hydrotalcite Co3Fe1Eu1 in this example is achieved through the following steps:

[0059] Weigh Co(NO3)2·6H2O (0.87359 g), Fe(NO3)3·9H2O (0.4040 g), Eu(NO3)3·6H2O (0.4342 g), ammonium fluoride (0.1 g) and urea (1.261 g) and dissolve them in 30 mL of anhydrous methanol. Stir vigorously at a speed of 700 revolutions per minute at room temperature for two hours to obtain a clear mixed salt solution.

[0060] At the same time, weigh 1.6 g of NaOH and dissolve it in 40 mL of deionized water. Stir evenly with a glass rod to make it fully dissolve for subsequent use.

[0061] Using an acid-base titrant, slowly drip the NaOH solution into the mixed salt solution at a dropping speed of 1 mL / min under magnetic stirring until the pH of the solution reaches 9 - 10, and then age it at room temperature for 24 h.

[0062] After that, first wash the above suspension with deionized water once, and then immediately wash it with absolute ethanol once. This washing - replacement process is alternately repeated for 3 cycle periods. After each washing, centrifuge at a speed of 8000 r / min to collect the brown solid precipitate at the bottom of the centrifuge tube. Transfer the obtained precipitate to a constant temperature oven and dry it at 80 °C for more than 12 h (overnight) to ensure that the sample is completely dry.

[0063] Finally, grind the dried sample with a mortar to obtain a brown powdery solid (rare earth doped hydrotalcite catalyst Co3Fe1Eu1), and store it in the dark for subsequent experimental use.

[0064] Example 2: The preparation method of the rare earth doped hydrotalcite Co3Fe1Eu 0.5 in this example is achieved through the following steps:

[0065] Weigh Co(NO3)2·6H2O (0.87359 g), Fe(NO3)3·9H2O (0.4040 g), Eu(NO3)3·6H2O (0.2171 g), ammonium fluoride (0.1 g) and urea (1.261 g), dissolve them in 30 mL of anhydrous methanol, and stir vigorously at a speed of 700 revolutions per minute for two hours at room temperature to obtain a clear mixed salt solution.

[0066] Meanwhile, weigh 1.6 g of NaOH, dissolve it in 40 mL of deionized water, stir it evenly with a glass rod to make it fully dissolved for subsequent use.

[0067] Slowly drip the NaOH solution into the mixed salt solution under magnetic stirring at a dripping speed of 1 mL / min until the pH of the solution reaches 9 - 10, and then age it at room temperature for 24 h.

[0068] After that, wash the above suspension with deionized water once first, and then immediately wash it with anhydrous ethanol once. This washing - displacement process is alternately repeated for 3 cycle periods. After each washing, centrifuge at a speed of 8000 r / min to collect the brown solid precipitate at the bottom of the centrifuge tube. Transfer the obtained precipitate to a constant - temperature oven and dry it at 80 °C for more than 12 h (overnight) to ensure that the sample is completely dry.

[0069] Finally, grind the dried sample with a mortar to obtain a brown powdery solid, and store it away from light for subsequent experimental use.

[0070] Example 3: The preparation method of the rare - earth - doped hydrotalcite Co3Fe1Eu4 in this example is achieved through the following steps:

[0071] Weigh Co(NO3)2·6H2O (0.87359 g), Fe(NO3)3·9H2O (0.4040 g), Eu(NO3)3·6H2O (1.7368 g), ammonium fluoride (0.1 g) and urea (1.261 g), dissolve them in 30 mL of anhydrous methanol, and stir vigorously at a speed of 700 revolutions per minute for two hours at room temperature to obtain a clear mixed salt solution.

[0072] Meanwhile, weigh 1.6 g of NaOH, dissolve it in 40 mL of deionized water, stir it evenly with a glass rod to make it fully dissolved for subsequent use. Slowly drip the NaOH solution into the mixed salt solution under magnetic stirring at a dripping speed of 1 mL / min until the pH of the solution reaches 9 - 10, and then age it at room temperature for 24 h.

[0073] After that, the above suspension was first washed once with deionized water and then immediately washed once with absolute ethanol. This washing-replacement process was alternately repeated for 3 cycle periods. After each washing, centrifugation was performed at a speed of 8000 r / min, and the brown solid precipitate at the bottom of the centrifuge tube was collected. The obtained precipitate was transferred to a constant temperature oven and dried at 80 °C for more than 12 h (overnight) to ensure complete drying of the sample.

[0074] Finally, the dried sample was ground in a mortar to obtain a brown powdery solid (rare earth-doped hydrotalcite catalyst Co3Fe1Eu4), which was stored in the dark for subsequent experiments.

[0075] Scanning electron microscopy (SEM)

[0076] The SEM image of the prepared Co3Fe1Eu1-LDHs catalyst is as Figure 1 shown, and its structure belongs to a stacked layered structure. In addition, the corresponding element mapping images of Co3Fe1Eu1-LDHs were also detected to determine the distribution of specific elements. As Figure 1 (c-g) shows, multiple elements such as Eu, Co, Fe, C, and O coexist and are uniformly distributed within the Co3Fe1Eu1-LDHs material, indicating the successful synthesis of the Co3Fe1Eu1-LDHs material.

[0077] X-ray diffraction (XRD)

[0078] Through the XRD analysis of CoFe-LDHs, CoEu-LDHs, and CoFeEu x -LDHs ( Figure 2 ), it is shown that the diffraction peaks of CoFe-LDHs and CoEu-LDHs match the standard cards JCPDS No. 50-0235 and 34-0392 respectively; CoFeEu x -LDHs has no impurity peaks, indicating that Eu doping does not change the main structure of CoFe-LDHs; the diffraction peak of CoFeEu x -LDHs shifts to the right compared to Eu2O3 at 28.4°, proving the chemical interaction between Eu and the lamellar; with the increase of Eu doping amount, the diffraction peak intensity decreases significantly (attributed to the decrease in crystallinity caused by surface defects); the calculation by Bragg's formula shows that the interlayer spacing of the (006) crystal plane decreases to 0.319 nm and the lattice constant increases to 0.4782 nm, indicating that the average distance between atoms shortens and the particle size increases, which helps to optimize the electronic structure, increase the active sites, and surface reaction activity.

[0079] Fourier transform infrared spectroscopy (FT-IR)

[0080] Figure 3The functional group characteristics of CoFe-LDHs, CoEu-LDHs and CoFeEu x -LDHs were analyzed by FT-IR. There are characteristic peaks of CO3 -1 intercalated into the interlayer at 1387 cm 2- for all three materials, and the bending vibration peak of adsorbed water is at 1668 cm -1 . The vibration peaks of CoFeEu -1 -LDHs in the range of 400 - 1000 cm x correspond to M-O / M-OH bonds, among which 662, 591, and 514 cm -1 are attributed to the bending vibrations of Co-O, Eu-O, and Fe-O respectively. The broad and strong peak at ~3456 cm -1 indicates that the -OH content in the layered structure is significantly higher than that of the other two materials. After introducing Eu, the M-O peak position of CoFeEu x -LDHs shifts, which is due to the lattice distortion caused by the large ionic radius of Eu, consistent with the XRD results. As the Eu content increases, the characteristic peak intensity first increases and then decreases, also in line with the XRD conclusion.

[0081] Specific surface area (BET) analysis

[0082] To gain an in-depth understanding of the pore structure of rare earth hydrotalcites, specific surface area analysis was carried out on CoFeEu x -LDHs, and the nitrogen adsorption-desorption curves and pore size distribution results are as Figure 4 shown. The type-IV isotherm and pore size distribution results of CoFeEu x -LDHs indicate that this material is mainly composed of mesopores and has an H3-type hysteresis isotherm. From the BET results, the specific surface area of Co3Fe1Eu1-LDHs (47.2828 m 2 / g) is much larger than that of CoFe-LDHs (8.7884 m 2 / g) and CoEu-LDHs (16.0798 m 2 / g), and as the Eu content increases, the specific surface area of CoFeEu x -LDHs also gradually increases. This difference may be attributed to the larger atomic radius of the rare earth metal Eu in CoFeEu x -LDHs, which increases the pore size and interlayer spacing of CoFeEu x -LDHs, and thus increases the specific surface area of CoFeEu x -LDHs.

[0083] X-ray photoelectron spectroscopy (XPS)

[0084] XPS analysis shows that ( Figure 5): CoFe-LDHs contains Co, Fe, C, and O elements, while Co3Fe1Eu1-LDHs adds Eu element (a). The Co 2p spectrum shows 781.4 / 797.2 eV (Co 3+ ), 784.5 / 798.7 eV (Co 2+ ), and satellite peaks (b); in the Fe 2p spectrum, 710.7 / 720.5 eV (Fe 2+ ), 713.7 / 725.4 eV (Fe 3+ ), and its satellite peaks confirm the existence of multiple valence states of Fe (c); the Eu 3d 5 / 2 peak is located at 1135.11 eV (d), confirming the successful doping of Eu 3+ . The deconvolution of the O 1s spectrum shows 532.3 eV (OA), 531.9 eV (OV), and 530.6 eV (OL). Among them, the proportion of OV in Co3Fe1Eu1-LDHs reaches 81.23%, which is significantly higher than that of Co3Fe1Eu1-LDHs (75.38%) (e). In the C 1s spectrum, the characteristic peaks of 289.3 eV (C=O), 286.1 eV (C-O), and 284.8 eV (C=C) and the O 1s peak all show a red shift, which is attributed to the change in electron cloud density caused by the lattice charge rearrangement due to Eu doping (f). This result, together with the EDS element distribution, verifies the successful preparation of the catalyst.

[0085] Surface electrical property analysis

[0086] To deeply understand the surface charge properties of Co3Fe1Eu1-LDHs, as Figure 6 shown, the isoelectric point of Co3Fe1Eu1-LDHs is 7.26. This means that when the pH value of the environment is higher than 7.26, the surface of Co3Fe1Eu1-LDHs will carry negative charges; conversely, if the pH value is lower than 7.26, its surface will carry positive charges.

[0087] Oxygen vacancy analysis

[0088] The ESR spectrum shows ( Figure 7 ), the resonance signal intensity of Co3Fe1Eu1-LDHs at g = 2.003 is significantly higher than that of CoFe-LDHs, confirming that it has richer oxygen vacancies (OVs). These OVs originate from lattice defects, surface undercoordinated oxygen ions, and weakly coordinated oxygen species, which can capture electrons to promote charge transfer and provide active sites for the reduction of high-valent metal ions.

[0089] Performance study of CoFeCe-LDHs activating PMS for tetracycline degradation

[0090] 1. Influence of reaction conditions on the activation of PMS by CoFeCe-LDHs for tetracycline degradation

[0091] 1) Determination of catalyst ratio

[0092] To explore the optimal molar ratio of Co, Fe, and Eu metal elements, six catalysts with different metal ratios were prepared. A 30 mg / L tetracycline hydrochloride solution was prepared, and a catalytic degradation experiment was carried out under the condition that the pH value of the solution was 7. The results are as Figure 8 shown. It can be seen that when the molar ratio of Co, Fe, and Eu = 3:1:1, 3:1:2, and 3:1:3, the removal rate of TC-HCl can reach 91% within 30 min. From the perspective of economic evaluation, after comprehensive consideration, the optimal feeding molar ratio of Co, Fe, and Eu elements was finally determined to be 3:1:1. For the convenience of subsequent description, the composite material under this ratio is abbreviated as CoFeEu-LDHs.

[0093] 2) Influence of catalyst dosage on the degradation of TC-HCl

[0094] Figure 9 a shows that as the dosage of CoFeEu-LDHs increased from 15 to 100 mg / L, the degradation efficiency of TC-HCl increased, but the growth rate slowed down when it was 50-100 mg / L. It is speculated that this is due to the competitive consumption of active free radicals and diffusion limitation. Therefore, 50 mg / L was selected as the optimal economic dosage. Kinetic fitting ( Figure 9 b) shows that the reaction rate constant increased with the increase of the dosage, which was consistent with the degradation trend.

[0095] 3) Influence of PMS concentration on the degradation of TC-HCl

[0096] Figure 10 a shows that as the PMS concentration increased from 0.1 to 0.3 g / L, TC-HCl was completely degraded within 15 min, and the reaction rate constant increased from 0.26968 to 0.34204 min -1 ( Figure 10 b). Excessive PMS (>0.2 g / L) will generate unstable free radicals and inhibit the oxidation potential of ·SO4 - / ·OH. Comparing the oxidant systems ( Figure 10 c), the degradation rate of H2O2 reached 58% within 1 min (73.3% after 15 min), and the catalyst strengthened its decomposition by reducing the activation energy; while PDS was difficult to activate due to its symmetrical structure, and only 18% was degraded in 20 min. Figure 10 d shows that the PMS residue in the CoFeEu-LDHs catalytic system was only 9.2%, which was significantly lower than that of CoFe-LDHs (29.3%) and CoEu-LDHs (34.6%). It is speculated that its abundant oxygen vacancies accelerated the decomposition of PMS.

[0097] 4) Influence of initial pollutant concentration on the degradation of TC-HCl

[0098] From Figure 11 it can be seen that as the concentration of TC-HCl in the system gradually increases, the degradation efficiency of TC-HCl shows a downward trend. This is because the intermediate products generated during the degradation process will compete with TC-HCl for the active sites on the surface of the catalyst. In addition, a higher concentration of TC-HCl requires more ROS consumption, which further inhibits the degradation efficiency of TC-HCl.

[0099] 5) Influence of initial pH value on the degradation of TC-HCl

[0100] Figure 12 shows the influence of different initial pH values on the degradation of TC-HCl. CoFeEu-LDHs maintains high degradation ability in the pH range of 5-9, indicating its good pH adaptability. When pH = 3, excessive H + inhibits free radical generation by stabilizing HSO5 - and leads to a decrease in the degradation rate. The activation rate of PMS reaches the peak at pH = 7. Under strong alkaline conditions (pH = 11), electrostatic repulsion occurs between the catalyst surface and PMS, significantly weakening the degradation effect on TC-HCl.

[0101] 6) Influence of reaction temperature on the degradation of TC-HCl

[0102] Figure 13 The influence of temperature on the degradation of TC-HCl was studied. The results show that TC-HCl can be completely degraded within 15 minutes at each temperature, but the reaction rate increases significantly with the increase of temperature (the rate constant is 0.26968 min-1 at 298K and increases to 0.35311 min-1 at 313K). Increasing the temperature accelerates the reaction by promoting the generation of ·SO4 - free radicals and enhancing molecular thermal motion. However, considering the energy consumption cost comprehensively, 298K was selected as the optimal temperature. Based on the Arrhenius equation, the activation energy of this system was calculated to be 12.304 kJ / mol, which is significantly lower than that of the CoFeCe-LDHs system (25.9 kJ / mol), indicating that the CoFeEu-LDHs / PMS system has lower energy consumption and higher catalytic efficiency.

[0103] 2. Influence of different reaction systems on the degradation effect of tetracycline

[0104] Figure 14It shows that the adsorption efficiency of TC-HCl alone is extremely low (the removal rate is 11.2% in 15 min) because the ability of PMS alone to activate ROS is limited. When CoFe-LDHs / PMS or CoEu-LDHs / PMS is added, the degradation rate is still lower than 85%, indicating that the single-metal system is difficult to effectively activate PMS. The CoFeEu-LDHs / PMS system exhibits a synergistic effect and achieves complete degradation within 15 min (k = 0.26968 min-1), which is due to the multi-metal synergistic promotion of ROS generation. Although the physical mixture nitrate / PMS system can achieve a removal rate of 94.7%, the reaction rate is significantly reduced (k = 0.16651 min-1), and the dissolution of nitrate causes ion pollution and difficulty in recycling. In contrast, constructing a hydrotalcite-like structure can inhibit the dissolution of metal ions and has both high degradation efficiency (100%) and environmental friendliness characteristics.

[0105] 3. Exploration of the environmental applicability of CoFeEu-LDHs

[0106] 1) Influence of common anions in water on the degradation of TC-HCl

[0107] This study investigated the influence of various environmental anions on the degradation of tetracycline (TC-HCl) by the CoFeEu-LDHs / PMS system ( Figure 15 ). The experiments showed that SO4 2- and NO3 - had little inhibition on degradation because they hardly reacted with reactive oxygen species (ROS); Cl - produced an inhibitory effect by reacting with the ·SO4 - free radical; while CO3 2- / HCO3 - showed significant inhibition because they reacted with ·SO4 - to form the less reactive ·CO3 - . Nevertheless, under the conditions containing CO3 2- / HCO3 - , the system still maintained a high degradation efficiency (82.56% and 79.2% respectively), which benefited from the continuous activation of PMS by the abundant oxygen vacancies (OVs) of the material to generate active substances, and the non-radical mechanism mainly based on 1 O2 having strong anti-interference ability.

[0108] 2) Compound pollution

[0109] To evaluate the applicability of the CoFeEu-LDHs / PMS system, the study selected typical pollutants such as rhodamine B (Rh B), oxytetracycline (OTC), doxycycline (DOCX), norfloxacin (OFL), carbamazepine (CBZ), and sulfamethoxazole (SEX) to test their catalytic performance ( Figure 16)。The results showed that the system achieved complete degradation of dye wastewater (such as Rh B) within 8 min, indicating its broad-spectrum applicability to dye pollutants. At the same time, the system showed significant oxidation selectivity towards different pollutants, which was consistent with the non-free radical-dominated mechanism. This selectivity could reduce the ineffective consumption of PMS on non-target organic matters, thereby improving the utilization efficiency of PMS.

[0110] The degradation efficiency of TC-HCl over time was measured by mixing several pollutants, and the results are as Figure 17 shown.

[0111] The degradation rates of TC-HCl in CoFeEu-LDHs / PMS in TC+Rh B, TC+OTC, TC+DOCX, TC+OFL, TC+CBZ, TC+SXM, and TC+RhB+OTC+DOCX+OFL+CBZ+SXM solutions within 15 min were 100%, 91.3%, 94.6%, 82.5%, 75.8%, 67.38%, and 59.6%, respectively. This may be because after mixing the pollutants, there may be similar degradation pathways during the degradation process, thus competing for the active substances required for degradation, which may lead to a reduction in the degradation resources obtained by TC-HCl, thereby reducing its degradation efficiency.

[0112] 3) Influence of different water qualities on the degradation of TC-HCl

[0113] Taking tap water, purified water, industrial wastewater, and domestic sewage as the research objects, the influence of different water qualities on the degradation of TC-HCl was investigated, and the results are as Figure 18 shown. As expected, the degradation effect of TC-HCl in distilled water was the best. Under different water quality conditions, the degradation efficiency of TC-HCl within 15 min was in the order of distilled water > tap water > purified water > industrial wastewater > domestic sewage. The possible reason is that the TOC and Cl - contents in industrial wastewater and domestic sewage are relatively high, and Cl - may react with reactive oxygen species. In addition, these components may occupy the reaction sites on the catalyst surface, hindering the contact between the catalyst and PMS.

[0114] 4) Exploration of the stability of CoFeEu-LDHs

[0115] The evaluation of the cyclic stability and environmental friendliness of the CoFeEu-LDHs / PMS system showed that ( Figure 19 ):After 5 cycles, the 15-minute degradation rate of TC-HCl still remained above 86.5%, showing excellent reusability ( Figure 19 (a-b)). The metal leaching test showed that ( Figure 19 (c), Co in the first cycle2+ (0.47 mg / L) and Fe 2+ (0.24 mg / L) had relatively low concentrations, which further decreased to 0.29 mg / L and 0.13 mg / L after five cycles. It was speculated that this was due to the release of weakly bound metals on the surface through PMS oxidation. XRD and FT-IR analyses showed no obvious changes in the characteristic peaks of the catalyst before and after the reaction ( Figure 19 (d - e)), corroborating its structural stability. Meanwhile, the system achieved a TOC removal rate of 63.7% within 15 minutes ( Figure 19 (f)), indicating that the pollutants were effectively mineralized. This catalyst combines high stability, low metal leaching, and high mineralization ability, showing potential for practical applications.

[0116] 4. Theoretical Calculation of CoFeEu-LDHs Activating PMS for Degrading TC-HCl

[0117] Through adsorption energy analysis ( Figure 20 ), it was found that Eu in CoFeEu-LDHs had the strongest adsorption energy for PMS (-1.21 eV), significantly higher than that of Co (-0.72 eV), indicating a strong interaction between Eu and PMS. At the same time, Eu transferred 0.97 eV of charge to PMS, demonstrating excellent electron supply ability and promoting PMS activation. The OVs in the composite material acted as electron traps: the OVs of CoFeEu / PMS captured -0.96 eV electrons. By comparison, both the adsorption energy and charge transfer ability of Eu in the composite material were better than those of the single Co component. It was speculated that the synergistic effect between elements improved the catalytic performance.

[0118] The adsorption model analysis showed that after PMS was adsorbed on the surface of CoFeEu, the S - O bond length changed from to with a relatively large contraction; at the same time, the O - O bond length changed from to with a significant change. This more drastic bond length reconstruction phenomenon indicated that there was a stronger interaction between CoFeEu and PMS, which might promote subsequent catalytic reactions by significantly changing the structure of the peroxide ion. This phenomenon originated from the characteristics of the electronic structure and chemical properties of the CoFeEu surface, revealing the interaction mechanism between its active sites and PMS, and providing a theoretical basis for the directional design of the catalyst.

[0119] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A preparation method of a rare earth doped hydrotalcite-like catalyst, characterized in that, It includes the following steps: Dissolve Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Eu(NO3)3·6H2O, ammonium fluoride and urea in anhydrous methanol, and stir vigorously at room temperature for at least 2 h to obtain a clear mixed salt solution; Slowly drop the NaOH solution into the mixed salt solution under magnetic stirring until the pH value of the solution reaches 9 - 10, then age at room temperature, wash, centrifuge to collect the brown solid precipitate, dry and grind to obtain the rare earth doped hydrotalcite-like catalyst.

2. The preparation method according to claim 1, wherein, The mass ratio of Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Eu(NO3)3·6H2O, ammonium fluoride and urea to the volume of anhydrous methanol is 0.87359 g∶0.4040 g∶(0.4342 g - 1.7368 g)∶0.1 g∶1.261 g∶30 mL.

3. The preparation method according to claim 1, wherein The concentration of the NaOH solution is 0.04 g / mL.

4. The preparation method according to claim 1, wherein The dropping rate is 1 mL / min.

5. The preparation method according to claim 1, characterized in that, The aging time is 24 h.

6. The preparation method according to claim 1, characterized in that, The washing is carried out according to the following steps: Step 1: First wash once with deionized water, centrifuge at a speed of 8000 r / min, and then immediately wash once with anhydrous ethanol and centrifuge at a speed of 8000 r / min; Step 2: Repeat the operation in Step 1 at least 3 times.

7. A rare earth doped hydrotalcite-like catalyst prepared by the method according to any one of claims 1 - 6.

8. The rare earth-doped hydrotalcite catalyst according to claim 7, wherein The structure of the rare earth doped hydrotalcite-like catalyst belongs to a stacked layered structure.

9. The rare earth-doped hydrotalcite catalyst according to claim 7, characterized in that, Eu, Co, Fe, C, and O coexist and are uniformly distributed in the rare earth doped hydrotalcite-like catalyst.

10. An application of the rare earth doped hydrotalcite-like catalyst prepared by the method according to any one of claims 1 - 6 or the rare earth doped hydrotalcite-like catalyst according to any one of claims 7 - 9 in treating antibiotic wastewater in an activated persulfate system.

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