MgAl-LDH / AlOOH catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a MgAl-LDH / AlOOH catalyst, which comprises the following steps: taking urea, magnesium sulfate and aluminum nitrate nonahydrate as raw materials, taking ultrapure water as a solvent, and preparing the target product MgAl-LDH / AlOOH catalyst through a one-step hydrothermal method. The invention also discloses an application of the MgAl-LDH / AlOOH catalyst in catalytic treatment of antibiotic wastewater. The MgAl-LDH / AlOOH catalyst is prepared by adopting a one-step hydrothermal method, urea, magnesium sulfate and aluminum nitrate nonahydrate are selected as raw materials, hydroxyl generated by urea decomposition in the hydrothermal process is utilized, the MgAl-LDH / AlOOH catalyst with different surface Lewis acid sites is generated by adjusting the magnesium-aluminum ratio, activation of PMS and generation of active oxygen species are regulated and controlled, and the PMS-LDH / AlOOH catalyst with different surface Lewis acid sites is obtained. The efficient degradation and safe conversion of antibiotics are improved. In addition, magnesium and aluminum serve as raw materials and are cheap and easy to obtain, and the hydrothermal method is simple in preparation process and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of MgAl-LDH / AlOOH catalyst preparation. More specifically, this invention relates to a MgAl-LDH / AlOOH catalyst, its preparation method, and its applications. Background Technology

[0002] In recent years, the increased bacterial resistance caused by the overuse of antibiotics has posed a significant threat to ecosystems and human health, making the safe disposal of antibiotics and other organic pollutants in water of paramount importance. Currently, commonly used treatment technologies include physical methods, biological methods, and chemical oxidation methods. Physical methods (such as nanofiltration and adsorption) can only separate antibiotics from water, requiring further treatment and cannot fundamentally solve the antibiotic pollution problem. Because antibiotics are biotoxic to microorganisms, traditional biological treatment methods are difficult to effectively degrade them. Chemical oxidation methods, especially advanced oxidation technologies, can generate highly reactive free radicals to oxidize and degrade target pollutants. Traditional advanced oxidation technologies, such as Fenton oxidation, photocatalysis, and electrocatalysis, are often limited by acidic conditions, require additional energy (heat and visible light irradiation), and involve waste of specialized equipment and reagents, thus restricting their widespread application.

[0003] To address organic pollution caused by emerging pollutants such as antibiotics in water, persulfate oxidation technology has become a research hotspot in the field of advanced oxidation technology in recent years due to its advantages such as strong oxidizing power, stable properties, low cost, environmental friendliness, and ease of transportation and storage. Persulfate activation methods include light, heat, electricity, alkali, ultrasound, carbon-based and transition metal-based catalysts, generating •OH and SO4. •- and 1 O2 and other reactive oxygen species possess extremely strong pollutant removal capabilities. Transition metals, in particular, have attracted widespread attention due to their high catalytic efficiency and low cost; however, transition metals and their oxides suffer from high ion leaching, leading to secondary pollution. Magnesium and aluminum are abundant in nature and environmentally friendly, receiving increasing attention in the field of advanced oxidation, but research on magnesium-aluminum minerals in advanced oxidation technologies has progressed slowly. Recent studies have found that specific functional groups on the catalyst surface, such as oxygen vacancies and Lewis acid-base sites, play a crucial role in activating PMS to generate reactive oxygen species, providing theoretical support for research on magnesium-aluminum minerals in advanced oxidation technologies. The regulation of acidic sites on the surface of magnesium-aluminum minerals and the construction of surface electron transport pathways are extremely critical to catalyst performance, requiring not only controlled preparation costs but also a simple preparation process.

[0004] MgAl-LDH / AlOOH is a widely available and inexpensive catalyst made from magnesium and aluminum salts. Its layered structure provides a large specific surface area and controllable surface acid-base sites. Currently, most research on composite materials focuses on stepwise synthesis methods, which are costly. Reports on the one-step hydrothermal preparation of MgAl-LDH / AlOOH catalysts are relatively rare. Summary of the Invention

[0005] To achieve these objectives and other advantages according to the present invention, in one aspect, a preferred embodiment of the present invention provides a method for preparing a MgAl-LDH / AlOOH catalyst, comprising the following steps: The target product, MgAl-LDH / AlOOH catalyst, was prepared by a one-step hydrothermal method using urea, magnesium sulfate, and aluminum nitrate nonahydrate as raw materials and ultrapure water as solvent.

[0006] Preferably, the preparation method of the MgAl-LDH / AlOOH catalyst includes the following steps: S1. Select urea, magnesium sulfate, and aluminum nitrate nonahydrate according to the above proportions and dissolve them in water to obtain a mixed solution; S2. Transfer the mixed solution obtained in S1 to carry out a hydrothermal reaction; S3. The product after reaction S2 is washed, dried and ground to obtain the target product MgAl-LDH / AlOOH catalyst.

[0007] Preferably, the molar ratio of urea to metal ions is 3:1, and the metal ions include magnesium ions and aluminum ions; the molar ratio of magnesium sulfate and aluminum nitrate nonahydrate is (0.3-2):1.

[0008] Preferably, the above hydrothermal reaction is carried out in a sealed high-pressure reactor lined with polytetrafluoroethylene, at a temperature of 120 °C for 24 h.

[0009] Preferably, the cleaning in S3 above specifically involves alternating washing with ethanol and deionized water until neutral; the drying temperature is 60-80 ℃ and the time is 8-12 h.

[0010] On the other hand, another technical solution of the present invention provides a MgAl-LDH / AlOOH catalyst, which is prepared by the method described above.

[0011] On the other hand, another technical solution of the present invention provides an application of the MgAl-LDH / AlOOH catalyst in the catalytic treatment of antibiotic wastewater.

[0012] Preferably, the antibiotic is any one or more of ofloxacin, ciprofloxacin, sulfamethoxazole, and tetracycline hydrochloride.

[0013] Preferably, the catalytic degradation treatment method is as follows: the MgAl-LDH / AlOOH catalyst is dispersed in the wastewater containing antibiotics, and after adsorption-desorption equilibrium is reached, PMS is added for degradation.

[0014] The present invention has at least the following beneficial effects: This invention employs a one-step hydrothermal method to prepare MgAl-LDH / AlOOH catalyst, using urea (CO(NH2)2), magnesium sulfate (MgSO4), and aluminum nitrate nonahydrate (Al(NO3)2). 3` Using 9H2O as a raw material, this method utilizes the hydroxide ions generated during the hydrothermal process of urea decomposition. By adjusting the magnesium-aluminum ratio, MgAl-LDH / AlOOH catalysts with different Lewis acid sites on their surfaces are generated. This regulates the activation of PMS and the generation of reactive oxygen species, thereby improving the efficient degradation and safe conversion of antibiotics. Furthermore, magnesium and aluminum are inexpensive and readily available raw materials, and the hydrothermal preparation process is simple, making it suitable for large-scale industrial production.

[0015] The MgAl-LDH / AlOOH catalyst prepared in this invention exhibits excellent catalytic activity in the activated PMS degradation of ofloxacin system and can effectively degrade a variety of antibiotic pollutants.

[0016] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0017] Figure 1 X-ray diffraction (XRD) patterns of different samples in Examples 1-3; Figure 2 Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) images of the samples prepared in Examples 2 and 3; Figure 3 The degradation curves of ofloxacin by different catalysts in Example 4 are shown. Figure 4 The degradation curves of ofloxacin by the MgAl-LDH / AlOOH catalyst in Example 4 under different pH conditions are shown. Figure 5 The graph shows the degradation curves of different organic pollutants by the MgAl-LDH / AlOOH catalyst in Example 4. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0019] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious modifications will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention. Example 1

[0020] The steps for preparing MgAl-LDH / AlOOH (MgAl-0.5) in this embodiment are as follows: Weigh 0.6756 g of urea (CO(NH2)2), 0.1504 g of magnesium sulfate (MgSO4), and 0.9378 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in 30 mL of ultrapure water, and accelerate the complete dissolution by ultrasound. The molar ratio of urea to metal ions is 3:1. Transfer the dissolved mixture to a 100 mL high-pressure reactor with a polytetrafluoroethylene inner liner, and react at a constant temperature of 120 ℃ for 24 h, then allow it to cool naturally to room temperature. Filter and wash the precipitate in the inner liner repeatedly with deionized water and ethanol 2-4 times, then dry it thoroughly in a 60 ℃ oven to obtain MgAl-0.5 of this embodiment. Example 2

[0021] The steps for preparing MgAl-LDH / AlOOH (MgAl-1) in this embodiment are as follows: The steps are the same as in Example 1, except that in Example 2, while keeping the amount of aluminum nitrate nonahydrate unchanged, the amount of magnesium is adjusted so that the molar ratio of Mg / Al is 1. Example 3

[0022] The steps for preparing MgAl-LDH / AlOOH (MgAl-0.3) in this embodiment are as follows: The steps are the same as in Example 1, except that in Example 3, while keeping the amount of aluminum nitrate nonahydrate unchanged, the amount of magnesium is adjusted so that the molar ratio of Mg / Al is 0.3.

[0023] Comparative Example 4 The steps for preparing MgAl-LDH (MgAl-2) in this embodiment are as follows: Weigh 1.3513 g of urea (CO(NH2)2), 0.6018 g of magnesium sulfate (MgSO4), and 0.9378 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in 30 mL of ultrapure water, and accelerate the complete dissolution by ultrasound. The molar ratio of urea to metal ions is 3:1. Transfer the dissolved mixture to a 100 mL high-pressure reactor with a polytetrafluoroethylene inner liner, and react at a constant temperature of 120 ℃ for 24 h, then allow it to cool naturally to room temperature. Filter and wash the precipitate in the inner liner repeatedly with deionized water and ethanol 2-4 times, then dry it thoroughly in a 60 ℃ oven to obtain MgAl-2 of this embodiment.

[0024] Comparative Example 5 The steps for preparing AlOOH in this embodiment are as follows: Weigh 0.4505 g of urea (CO(NH2)2) and 0.9378 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in 30 mL of ultrapure water, and accelerate the complete dissolution by ultrasound. The molar ratio of urea to metal ions is 3:1. Transfer the dissolved mixture to a 100 mL high-pressure reactor with a polytetrafluoroethylene inner liner, and react at a constant temperature of 120℃ for 24 h, then allow it to cool naturally to room temperature. Filter and wash the precipitate in the inner liner repeatedly with deionized water and ethanol 2-4 times, then dry it thoroughly in a 60℃ oven to obtain AlOOH of this embodiment. X-ray diffraction phase analysis was performed on MgAl-0.5, MgAl-0.3, and MgAl-1 prepared in Examples 1-3, MgAl-2 prepared in Comparative Example 1, and AlOOH prepared in Comparative Example 2. The results are as follows: Figure 1 As shown, the diffraction peaks of MgAl-2 are consistent with the standard card of magnesium aluminum layered double hydroxide (JCPDS: 89-0460), indicating that MgAl-2 is a pure magnesium aluminum layered double hydroxide phase. MgAl-0.3, MgAl-0.5, and MgAl-1 all exhibit mixed phase characteristics. In addition to the diffraction peaks corresponding to magnesium aluminum layered double hydroxide (JCPDS: 89-0460), their diffraction peaks also show aluminum hydroxide diffraction peaks matching the standard card of boehmite (JCPDS: 88-2112). Further observation revealed that as the Mg / Al molar ratio in the sample decreased, the diffraction peak intensity of magnesium aluminum hydrotalcite gradually weakened, while the diffraction peak intensity of aluminum hydroxide gradually increased. This indicates that the Mg / Al molar ratio is the key factor determining the phase composition of MgAl type samples. Only when the Mg / Al ratio reaches 2 can a pure magnesium aluminum hydrotalcite phase be formed. When the Mg / Al ratio is lower than 2, it is accompanied by the formation of boehmite impurity phase. Moreover, the higher the Al content, the higher the proportion of boehmite phase and the lower the proportion of hydrotalcite phase.

[0025] Scanning electron microscope (SEM) images of MgAl-0.5, MgAl-0.3, and MgAl-1 prepared in Examples 1-3, and MgAl-2 prepared in Comparative Example 1, and energy dispersive spectroscopy (EDS) spectra of the MgAl-0.5 catalyst prepared in Example 1 are shown below. Figure 2 As shown, Figure 2 ad represents MgAl-0.5, MgAl-0.3, MgAl-1, and MgAl-2, respectively. Figure 2 Eh represents the elemental distribution and content table of MgAl-0.5. The figure shows that MgAl-2, as a pure hydrotalcite phase, exhibits a flower-like structure composed of petals. MgAl-1 also shows a layered structure of hydrotalcite, but compared to MgAl-2, the platy structure is stacked. As the magnesium content continues to decrease, MgAl-0.3 and MgAl-0.5 exhibit clump-like and irregular shapes, respectively. The layered structure aggregates on its surface, becomes unevenly distributed, and decreases accordingly. This corresponds to the gradually weakening diffraction peaks of hydrotalcite shown by XRD.

[0026] Experimental catalytic treatment of antibiotic wastewater The catalytic performance of the MgAl-LDH / AlOOH catalyst was tested using the following method: 30 mg of the MgAl-0.5 catalyst, MgAl-0.3 catalyst, and MgAl-1 catalyst prepared in Examples 1-3 were dispersed in 100 mL of ofloxacin (OFX) solution at a concentration of 10 mg / L. After adsorption-desorption equilibrium was reached in 30 min, 0.3 g / L permonosulfate (PMS) was added to initiate the degradation reaction. At each given time interval, 4 mL of the sample was filtered through a 0.45 μm microporous membrane, and the absorbance was measured at 289 nm. The concentration at each time point was determined by the OFX standard curve, and the degradation rate was calculated.

[0027] This embodiment sets up different comparative degradation experiments, in which: In control group 1, no MgAl-0.5 catalyst was added, and the remaining steps were the same as in Example 1. In this case, only PMS was involved in the degradation catalysis process. In control group 2, the AlOOH catalyst prepared in Example 5 was used to replace the MgAl-0.5 catalyst, and the remaining steps were the same as in Example 1. In this case, PMS and AlOOH catalysts were present in the degradation catalysis process. In control group 3, no PMS was added, and the remaining steps were the same as in Example 1. In this case, only MgAl-0.5 catalyst was used in the degradation catalysis process.

[0028] After each experiment, the catalyst was filtered, washed, and dried in an oven at 60 °C, and then stability and repeatability experiments were conducted under the same catalytic conditions.

[0029] According to the Lambert-Beer law, the concentration of ofloxacin solution is directly proportional to the magnitude of its absorbance at the characteristic absorption wavelength. Therefore, the catalytic degradation rate can be quantitatively analyzed by detecting the change in absorbance at the absorption peak of the solution during the degradation process, and then the catalytic effect of the catalyst can be measured by the degradation rate (R).

[0030] R = [(A0-A) / A0] × 100% In the formula, A0 is the absorbance of the absorption peak before the addition of PMS; A is the absorbance of the absorption peak at degradation time t.

[0031] Figure 3 The figure shows the degradation kinetics of ofloxacin by different catalysts (AlOOH, MgAl-LDH, and MgAl-LDH / AlOOH). The figure reveals two main points: First, (control group 1) PMS alone showed almost no removal effect on ofloxacin, indicating that the oxidizing capacity of PMS itself is insufficient to effectively degrade ofloxacin without a catalyst, thus confirming the necessity of the catalyst in this advanced oxidation process. Second, under the premise of reaching adsorption-desorption equilibrium at 30 min, the degradation efficiency of ofloxacin in the system using only AlOOH (control group 2) did not show a significant improvement after the addition of PMS. This phenomenon directly indicates that there is no effective interaction between AlOOH and PMS, and that AlOOH cannot activate PMS to generate highly oxidizing active species (such as •OH, SO42-). •- (etc.), and cannot enhance degradation through synergistic effects, thus failing to achieve the catalytic oxidation of ofloxacin. In stark contrast, the magnesium-aluminum based catalysts prepared in Examples 1-3 exhibited superior catalytic performance: the system using only MgAl-LDH (Comparative Example 1) showed an increase in the degradation efficiency of ofloxacin to 59.36% within 180 min after the addition of PMS, demonstrating that the pure magnesium-aluminum hydrotalcite structure of MgAl-LDH can activate PMS through its own structural characteristics, thereby initiating the catalytic degradation reaction; while the catalytic effect of the MgAl-LDH / AlOOH composite system (taking MgAl-0.5 from Example 1 as an example) was further enhanced. The adsorption efficiency of this MgAl-LDH / AlOOH system for ofloxacin alone was only 14.97%, but in the presence of PMS, the degradation efficiency increased significantly to 81.46% within 180 min, which was not only significantly higher than the MgAl-LDH system alone, but also far exceeded the AlOOH system. This is because the Mg(II)-OH sites on the surface of MgAl-0.5 form Mg(II)-(HO)OSO3 with PMS. - The complex has its O / O bonds stretched, but does not generate SO4. •-Instead, it generates SO4 after receiving electrons from pollutants. 2- The localized electron acceptance causes an imbalance in the overall electron distribution of the catalyst. Therefore, some electrons may be transported through two electron transport pathways to ensure a balanced electron distribution on the MgAl-0.5 surface. One pathway involves the LDH layer acting as an electron transfer medium to transport electrons to the Lewis basic sites Al-SO5 in MgAl-LDH. - Another location is Al-SO5, which reaches AlOOH through the amorphous layer between MgAl-LDH and AlOOH. - Both methods ultimately break the HS bonds of the PMS bonded at its location, resulting in SO5. •- And singlet oxygen.

[0032] In summary, the MgAl-LDH / AlOOH composite catalyst can effectively improve the degradation performance of ofloxacin. This improvement is not due to the superposition of the effects of a single component, but rather stems from the possible synergistic effect between MgAl-LDH, AlOOH, and PMS, which ultimately leads to a breakthrough in the degradation efficiency of ofloxacin. AlOOH alone cannot react effectively with PMS and therefore lacks catalytic ability, further highlighting the key promoting role of the composite structure in catalytic performance.

[0033] Figure 4 The figure shows the effect of pH on the degradation process of ofloxacin by the above-mentioned MgAl-0.5 catalyst. As can be seen from the figure, the MgAl-0.5 catalyst has a good degradation effect in a wide pH range of 5-9. This is because the buffering capacity of MgAl-0.5 can adjust the initial pH of the ofloxacin degradation system from 5-9 to near neutral, and the near neutral environment is conducive to the degradation.

[0034] Figure 5 The graph shows the degradation curves of ciprofloxacin (CIP), rhodamine B (RhB), tetracycline (TC), and sulfamethoxazole (SMX) by the above-mentioned MgAl-0.5 catalyst. As can be seen from the graph, the catalyst can achieve a degradation rate of 93.50% for TC, 87.36% for CIP, and 58.28% and 64.91% for SMX and RhB, respectively. These results demonstrate that MgAl-0.5 not only has a high efficiency in degrading specific pollutants (such as ofloxacin), but can also overcome the limitations of pollutant types and can be widely used in the degradation of other pollutants.

[0035] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a MgAl-LDH / AlOOH catalyst, characterized in that, Includes the following steps: The target product, MgAl-LDH / AlOOH catalyst, was prepared by a one-step hydrothermal method using urea, magnesium sulfate, and aluminum nitrate nonahydrate as raw materials and ultrapure water as solvent.

2. The method for preparing the MgAl-LDH / AlOOH catalyst according to claim 1, characterized in that, Includes the following steps: S1. Select urea, magnesium sulfate, and aluminum nitrate nonahydrate according to the above proportions and dissolve them in water to obtain a mixed solution; S2. Transfer the mixed solution obtained in S1 to carry out a hydrothermal reaction; S3. The product after reaction S2 is washed, dried and ground to obtain the target product MgAl-LDH / AlOOH catalyst.

3. The method for preparing the MgAl-LDH / AlOOH catalyst according to claim 1, characterized in that, The molar ratio of urea to metal ions is 3:1, and the metal ions include magnesium ions and aluminum ions; the molar ratio of magnesium sulfate and aluminum nitrate nonahydrate is (0.3-2):

1.

4. The method for preparing the MgAl-LDH / AlOOH catalyst according to claim 2, characterized in that, The above hydrothermal reaction was carried out in a sealed high-pressure reactor lined with polytetrafluoroethylene, at a temperature of 120°C for 24 hours.

5. The method for preparing the MgAl-LDH / AlOOH catalyst according to claim 2, characterized in that, The cleaning in S3 above specifically involves alternating washing with ethanol and deionized water until neutral; the drying temperature is 60-80 ℃ and the time is 8-12 h.

6. A MgAl-LDH / AlOOH catalyst, characterized in that, Prepared by the method described in any one of claims 1-5.

7. The application of the MgAl-LDH / AlOOH catalyst as described in claim 6 in the catalytic treatment of antibiotic wastewater.

8. The application according to claim 7, characterized in that, The antibiotic is any one or more of ofloxacin, ciprofloxacin, sulfamethoxazole, and tetracycline hydrochloride.

9. The application according to claim 7, characterized in that, The catalytic treatment method is as follows: the MgAl-LDH / AlOOH catalyst is dispersed in the wastewater containing antibiotics, and after adsorption-desorption equilibrium is reached, PMS is added for degradation.

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