Preparation of a composite catalyst of MnFe-LDH / g-C3N4 for rapid removal of antibiotics from water

Abstract

The application discloses a preparation method of a high-activity MnFe-LDH / g-C3N4 composite catalyst, and the MnFe-LDH / g-C3N4 can efficiently activate peroxymonosulfate (PMS) and quickly remove antibiotics in water. The method mainly comprises the following two steps: in the first step, an ultrathin g-C3N4 nanosheet is prepared by using a two-step calcination method; and in the second step, the MnFe-LDHs / g-C3N4 is prepared by using a coprecipitation method: a mixed solution of Mn(NO3)2.4H2O and Fe(NO3)3.9H2O with a molar ratio of 2:1 and x mg g-C3N4 (x=0, 30, 60, 90) is prepared and is denoted as A liquid; a mixed solution of NaOH and Na2CO3 is prepared and is denoted as B liquid. The B liquid is added drop by drop into the A liquid, and heating treatment is carried out at 65 DEG C for 4 h; after the obtained precipitate is centrifuged, washed, dried and ground, the MnFe-LDH / g-C3N4 composite catalyst is obtained. The MnFe-LDH / g-C3N4 composite catalyst provided by the application has excellent PMS adsorption and activation performance, can quickly remove antibiotics in water through a non-free radical path dominated by an electron transfer path, and the removal efficiency of tetracycline can reach 86.2% within 20 min; and the raw material is low in price, non-toxic and harmless, and has high practical value and application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing a highly active MnFe-LDH / g-C3N4 composite catalyst, wherein the MnFe-LDH / g-C3N4 can efficiently activate peroxymonosulfate (PMS) and rapidly remove antibiotics from water via a non-radical pathway dominated by direct electron transfer. Background Technology

[0002] Antibiotics are widely used to treat diseases in humans and animals, but they are difficult to metabolize and are excreted into water bodies, posing a serious threat to environmental sustainability and public health. Therefore, there is an urgent need for effective antibiotic remediation strategies in aquatic environments. Advanced oxidation technologies (AOPs), including photocatalytic oxidation, persulfate (PS) oxidation, Fenton oxidation, ozone oxidation, and electrochemical oxidation, are considered a range of effective techniques for treating antibiotics in wastewater. Among them, PS oxidation technology has attracted widespread attention due to its advantages of fast oxidation rate, high throughput, and high reaction selectivity. Its activation methods include ultraviolet activation, thermal activation, electrochemical activation, carbon material activation, photocatalytic activation, and transition metal ion activation.

[0003] One effective method for treating antibiotics is the activation of peroxymonosulfate (PMS) with transition metals. Based on the activation method, it can be divided into homogeneous catalysis and heterogeneous catalysis. Homogeneous catalysis uses transition metal ions to react directly with PMS. This method is prone to metal ion leakage; improper handling can result in large amounts of metal ions remaining in the solution, causing secondary pollution and affecting recycling. Furthermore, metal ions in homogeneous catalysis readily form hydrates with water in acidic environments and precipitates in alkaline environments, both of which affect catalytic efficiency. Heterogeneous catalysis, on the other hand, exists in solid particle form, thus largely avoiding these drawbacks. It also possesses advantages such as high catalytic activity and good chemical stability. Currently, researchers commonly use heterogeneous catalysis to treat pollutants.

[0004] Layered double hydroxides (LDHs) are a class of two-dimensional layered clays composed of metal cation layers and interlayer anions. They possess advantages such as simple preparation, high stability, tunable structural band structures, and low cost. Furthermore, among various LDH materials, MnFe-LDH is a rare, environmentally friendly LDH that does not contain heavy metals and is widely used in water treatment. Therefore, MnFe-LDH was chosen as a transition metal support to activate polymethyl methacrylate (PMS) and employ a heterogeneous catalytic process to treat antibiotics in water. However, currently reported MnFe-LDHs all utilize transition metal ions to activate PMS and degrade antibiotics via a free radical pathway. But free radicals (·OH, ·SO4)... -The low steady-state concentration, short half-life, rapid consumption, and poor resistance to interference of hydrotalcite make its catalytic degradation of antibiotics less effective. In contrast, non-radical pathways offer advantages such as high selectivity, good resistance to interference, and high PMS utilization compared to free radical pathways. Therefore, by introducing g-C3N4 into MnFe-LDH, the chemical environment of Mn and Fe elements in hydrotalcite is effectively improved, enhancing the adsorption of PMS at metal sites and forming metal-PMS complexes. This allows for the rapid removal of antibiotics from water via a non-radical pathway dominated by electron transfer. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a highly active MnFe-LDH / g-C3N4 composite catalyst. The composite catalyst is characterized by its ability to efficiently activate PMS and rapidly remove antibiotics from water via a non-radical pathway dominated by direct electron transfer. The composite catalyst achieves a tetracycline removal efficiency of 86.2% within 20 minutes, while pure MnFe-LDH only achieves a tetracycline removal efficiency of 59.1%. The composite catalyst significantly improves the tetracycline removal efficiency.

[0006] To achieve the above objectives, embodiments of the present invention provide a method for preparing a MnFe-LDH / g-C3N4 composite catalyst, comprising the following steps:

[0007] (1) A two-step calcination method was adopted, using melamine as raw material, which was placed in a crucible and then transferred to a muffle furnace for calcination. The heating rate was 2.3℃ / min, and the temperature was maintained at 550℃ for 4 hours.

[0008] (2) Grind the powder obtained in step (1), transfer it to a muffle furnace again for calcination, with a heating rate of 5℃ / min, and keep it at 550℃ for 2h to obtain ultrathin g-C3N4 nanosheets.

[0009] (3) Weigh out manganese nitrate tetrahydrate (Mn(NO3)2·4H2O) and ferric nitrate nonahydrate (Fe(NO3)3·9H2O) according to a manganese (Mn) and iron (Fe) molar ratio of 2:1 and dissolve them in water. Then disperse the g-C3N4 nanosheets obtained in step (2) in the above solution and stir continuously for 30 minutes.

[0010] (4) Weigh out sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) and dissolve them in water, stirring continuously for 30 minutes;

[0011] (5) Add the solution obtained in step (4) dropwise to the solution obtained in step (3), sonicate the mixture for 30 minutes, and then heat it at 65°C for 4 hours;

[0012] (6) After centrifuging, washing, drying and grinding the precipitate obtained in step (5), the MnFe-LDH / g-C3N4 composite catalyst is obtained.

[0013] The embodiments of the present invention have the following advantages:

[0014] The MnFe-LDH / g-C3N4 composite catalyst provided in this invention has superior PMS adsorption and activation performance, and can rapidly remove antibiotics from water through a non-radical pathway dominated by electron transfer. The removal efficiency of tetracycline can reach 86.2% within 20 minutes, which solves the shortcomings of existing MnFe-LDH catalysts that degrade antibiotics through the free radical pathway, such as low steady-state concentration of free radicals, poor anti-interference ability, short half-life, and rapid consumption. Moreover, the raw materials of the MnFe-LDH / g-C3N4 composite catalyst are inexpensive, non-toxic and harmless, and have high practical value and application prospects. Attached Figure Description

[0015] Figure 1 X-ray diffraction pattern of the MnFe-LDH / g-C3N4 composite catalyst provided in the embodiments of the present invention.

[0016] Figure 2 Transmission electron microscopy (TEM) image of the MnFe-LDH / g-C3N4 composite catalyst provided in the embodiments of the present invention.

[0017] Figure 3 The graph shows the performance of the MnFe-LDH / g-C3N4 composite catalyst for degrading tetracycline provided in the embodiments of the present invention.

[0018] Figure 4 The image shows the capture performance of the MnFe-LDH / g-C3N4 composite catalyst provided in the embodiments of the present invention.

[0019] Figure 5 The open-circuit potential diagram of the MnFe-LDH / g-C3N4 composite catalyst provided in the embodiments of the present invention.

[0020] Figure 6 The degradation mechanism diagram of the MnFe-LDH / g-C3N4 composite catalyst provided in the embodiments of the present invention. Detailed Implementation

[0021] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0022] Example 1

[0023] Place 3g of melamine in a muffle furnace, adjust the controller to heat to 550℃ at a heating rate of 2.3℃ / min, and hold at that temperature for 4 hours. Remove the melamine when the temperature drops to room temperature. Grind the resulting solid powder and place it back into the muffle furnace. Adjust the controller to heat to 500℃ at a heating rate of 5℃ / min, hold at that temperature for 2 hours, and remove the melamine when the temperature drops to room temperature. Grind the resulting powder for later use.

[0024] Example 2

[0025] MnFe-LDHs / g-C3N4 was prepared by coprecipitation: 1 mmol Fe(NO3)3·9H2O and 2 mmol Mn(NO3)2·4H2O were dissolved in 100 mL of water and stirred continuously for 30 min. Then, 30 mg g-C3N4 was added to the above solution, denoted as solution A. 0.035 mol NaOH and 0.015 mol Na2CO3 were dissolved in 100 mL of water and stirred continuously for 30 min, denoted as solution B. Solution B was added dropwise to solution A. During the addition, the pH of the solution was controlled to be stable between 10.4 and 10.7 using a pH meter. After the addition was complete, the mixed solution containing brown flocculent precipitate was sonicated for 30 min. After homogenization, it was transferred to a three-necked flask, a heating mantle was attached, and it was heated at 65 °C for 4 h. After the reaction was complete, the three-necked flask was allowed to cool naturally to room temperature. The liquid was then washed by centrifugation with anhydrous ethanol and deionized water at 8000 rpm for 10 min using a high-speed centrifuge, repeated four times. The resulting precipitate was dried and ground. This MnFe-LDHs / g-C3N4 composite catalyst is labeled LCN30.

[0026] Example 3

[0027] The experimental procedure was the same as in Example 2, except that 60 mg of g-C3N4 was weighed and added to solution A. The corresponding MnFe-LDHs / g-C3N4 composite catalyst was obtained and labeled LCN60.

[0028] Example 4

[0029] The experimental procedure was the same as in Example 2, except that 90 mg of g-C3N4 was weighed and added to solution A. The corresponding MnFe-LDHs / g-C3N4 composite catalyst was obtained and labeled LCN90.

[0030] Example 5

[0031] The experimental procedure was the same as in Example 2, except that g-C3N4 was not added to solution A. Granular MnFe-LDH was obtained.

[0032] Example 6

[0033] The phase composition of the MnFe-LDH / g-C3N4 composite catalyst was characterized using a Bruker AXS D8 ADVANCE X-ray diffractometer (Germany). Figure 1 The image shows the X-ray diffraction pattern of the prepared MnFe-LDH / g-C3N4 composite catalyst. Figure 1 As can be seen, the characteristic diffraction peaks at 2θ of MnFe-LDH at 24.2°, 31.4°, 37.5°, 41.4°, 45.1°, and 51.5° correspond to the (012), (104), (110), (113), (202), and (018) crystal planes, respectively. Meanwhile, the characteristic diffraction peaks at 2θ of g-C3N4 at 13.0° and 27.6° can be indexed to the (100) and (002) crystal planes, respectively. The presence of characteristic diffraction peaks of both MnFe-LDH and g-C3N4 in the composite sample, with the diffraction intensity of g-C3N4 gradually increasing with increasing mass content, indicates the successful preparation of the composite catalyst.

[0034] Example 7

[0035] The microstructure of the MnFe-LDH / g-C3N4 composite catalyst was characterized using a Hitachi H-81002 transmission electron microscope (TEM). Figure 2 Transmission electron microscopy (TEM) image of the prepared MnFe-LDH / g-C3N4 composite catalyst. From... Figure 2 As can be seen, granular MnFe-LDH is uniformly distributed on the surface of lamellar ultrathin g-C3N4.

[0036] Example 8

[0037] Degradation experiments were conducted using a Phchem photocatalytic reactor manufactured by Beijing Newbit Technology Co., Ltd. Figure 3 The performance of the prepared MnFe-LDH / g-C3N4 composite catalyst in degrading tetracycline is shown in the figure. The catalyst dosage was 10 mg, the tetracycline concentration was 50 mg / L, and the PMS concentration was 0.4 mM. Figure 3 It can be seen that, compared with pure MnFe-LDH and g-C3N4, all MnFe-LDH / g-C3N4 composite catalysts showed improved performance in the degradation of tetracycline. Among them, LCN60 exhibited the highest catalytic activity, achieving a degradation efficiency of 86.2% for TC within 20 min.

[0038] Example 9

[0039] The capture experiment was conducted using a Phchem photocatalytic reactor manufactured by Beijing Newbit Technology Co., Ltd. Figure 4The image shows the capture performance of the prepared MnFe-LDH / g-C3N4 composite catalyst. Tert-butanol (TBA), ethanol (EtOH), p-benzoquinone (p-BQ), and L-histidine were selected to capture ·OH and ·SO4 from the solution, respectively. - O2 - and 1 O2. Furthermore, nitrobenzene (NB) was selected to capture the ·OH on the catalyst surface, and phenol (Phenol) was selected to simultaneously capture both ·OH and ·SO4 on the catalyst surface. - .

[0040] Example 10

[0041] The open-circuit potential (OCP) of the MnFe-LDH / g-C3N4 composite catalyst was measured using a CHI-760E electrochemical workstation manufactured by Shanghai Chenhua Co., Ltd. Figure 5 The image shows the OCP curve of the prepared MnFe-LDH / g-C3N4 composite catalyst. (From...) Figure 5 As can be seen, the OCP of the composite sample increased significantly after the addition of PMS, while the OCP decreased after the addition of TC, indicating that there is a direct electron transfer process between the catalyst, PMS and TC, which is a non-radical degradation pathway.

[0042] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. The application of a MnFe-LDH / g-C3N4 composite catalyst in the rapid degradation of antibiotics in water, characterized in that, The MnFe-LDH / g-C3N4 composite catalyst effectively adsorbs and activates peroxymonosulfate, and its degradation pathway is mainly a non-radical degradation pathway dominated by electron transfer. The specific steps for preparing the MnFe-LDH / g-C3N4 composite catalyst are as follows: (1) A two-step calcination method was adopted, using melamine as raw material, which was placed in a crucible and then transferred to a muffle furnace for calcination. The heating rate was 2.3℃ / min, and the temperature was maintained at 550℃ for 4h. (2) Grind the powder obtained in step (1), transfer it to a muffle furnace again for calcination, with a heating rate of 5℃ / min, and keep it at 550℃ for 2h to obtain ultrathin g-C3N4 nanosheets. (3) Weigh out manganese nitrate tetrahydrate and ferric nitrate nonahydrate in water according to a manganese to iron molar ratio of 2:1, then disperse the g-C3N4 nanosheets obtained in step (2) in the above solution and stir continuously for 30 minutes. (4) Weigh out sodium hydroxide and sodium carbonate and dissolve them in water, stirring continuously for 30 minutes; (5) Add the solution obtained in step (4) dropwise to the solution obtained in step (3), sonicate the mixture for 30 minutes, and then heat it at 65°C for 4 hours; (6) After centrifuging, washing, drying and grinding the precipitate obtained in step (5), the MnFe-LDH / g-C3N4 composite catalyst is obtained.

2. The application as described in claim 1, characterized in that, The amount of g-C3N4 added in step (3) is 30-90mg.

3. The application as described in claim 1, characterized in that, In step (4), the final concentration of sodium hydroxide is 0.35 mol / L and the final concentration of sodium carbonate is 0.15 mol / L.

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