Halloysite composite material for catalytically degrading tetracycline as well as preparation method and application of halloysite composite material

Abstract

The invention discloses a halloysite composite material for catalytically degrading tetracycline as well as a preparation method and application of the halloysite composite material, and belongs to the technical field of environmental material preparation. According to the FeS2 / HNTs composite material prepared by the preparation method disclosed by the invention, a bidirectional diffusion channel is provided by assembling halloysite nanotubes into FeS2 microspheres, so that diffusion of tetracycline or persulfate to active sites in the FeS2 microspheres is enhanced, and the degradation capability of a catalytic material on tetracycline is improved. The preparation method is simple, convenient and efficient to operate, and the prepared halloysite composite material can activate and degrade tetracycline.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental material preparation, and particularly relates to a halloysite composite material for catalytic degradation of tetracycline, a preparation method and application thereof. Background Art

[0002] Iron sulfide (Fe x S y ) usually exists in a variety of forms, including pyrite (FeS 2 ), pyrrhotite (Fe 1-x S), pyrite (FeS) and amorphous FeS, etc. The iron and sulfur in iron sulfide are usually in a low valence state, so they have strong electron donating ability and can effectively reduce organic pollutants or activate various oxidants. The current effect between sulfur and iron can effectively accelerate the electron transfer process, and the low valence sulfur can also induce Fe 3+ Pyrite is one of the most widely distributed iron-containing minerals in the earth's crust and has also been proven to be the most catalytically active natural iron ore for persulfate (PS). Its weak acidity is conducive to Fe 2+ Slow dissolution of FeS 2 As a heterogeneous catalyst, the surface has abundant active sites as the active centers required for adsorption and catalytic reactions, which can effectively activate PS to generate reactive oxygen species (ROS). 2 When used alone, there are often problems such as being easily oxidized and losing activity, iron ions being easily dissolved and released into the water, and poor dispersibility. 2 The micrometer-scale size results in a small specific surface area, and the reaction sites inside it cannot effectively contact with pollutants or PS. Summary of the invention

[0003] In view of the deficiencies of the prior art, the present invention provides a halloysite composite material for catalytic degradation of tetracycline and a preparation method and application thereof. The prepared halloysite composite material can effectively improve the degradation ability of the oxidant persulfate on tetracycline. The present invention adopts the following technical scheme:

[0004] In a first aspect of the present invention, a method for preparing a halloysite composite material for catalytic degradation of tetracycline is provided, wherein halloysite nanotubes are assembled into FeS 2 FeS 2 / HNTs composites.

[0005] By assembling HNTs onto FeS 2 The microspheres provide a bidirectional diffusion channel to enhance the diffusion of tetracycline or persulfate to FeS 2 The diffusion of active sites inside the microspheres improves the degradation ability of the catalytic material on tetracycline.

[0006] Furthermore, a method for preparing a halloysite composite material for catalytic degradation of tetracycline comprises the following steps:

[0007] dispersing the halloysite nanotubes in an organic solvent to obtain a halloysite nanotube suspension;

[0008] Evenly mixing ferrous sulfate, urea and sulfur in an organic solvent to obtain a mixed solution;

[0009] Mixing the halloysite nanotube suspension and the mixed solution, and performing vacuum treatment to obtain a mixed suspension;

[0010] The mixed suspension is heated, and a black product is collected, washed, and dried to obtain a halloysite composite material.

[0011] Furthermore, the mass ratio of the halloysite nanotubes, the ferrous sulfate, and the sulfur element is (1.58-19.73):1:1.37.

[0012] Furthermore, ferrous sulfate and urea are dissolved in an organic solvent, and sulfur is added and mixed to obtain the mixed solution.

[0013] Furthermore, the vacuum treatment step includes: vacuuming at room temperature, standing, releasing pressure, stirring, and the vacuum treatment is repeated several times.

[0014] Optionally, the ferrous sulfate is at least one of anhydrous ferrous sulfate and a hydrate of ferrous sulfate.

[0015] Furthermore, the organic solvent is at least one of dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), ethylene glycol, methanol, ethanol, and n-pentanol. Preferably, the organic solvent in the halloysite nanotube suspension is at least one of ethylene glycol, methanol, ethanol, and n-pentanol; the organic solvent in the mixed solution is at least one of dimethylformamide (DMF), dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO).

[0016] Furthermore, the heating temperature is 120-200° C., and the heating time is 6-24 h. Preferably, the heating temperature is 180° C., and the heating time is 12 h.

[0017] Preferably, the elemental sulfur is sublimated sulfur.

[0018] The second aspect of the present invention provides a halloysite composite material prepared by the above method.

[0019] The third aspect of the present invention provides use of the halloysite composite material in catalytic degradation of tetracycline.

[0020] The fourth aspect of the present invention provides a method for catalytic degradation of tetracycline using the halloysite composite material.

[0021] Furthermore, the halloysite composite material is used to catalyze the degradation of tetracycline by persulfate; the mass ratio of the halloysite composite material to persulfate is (1-5): (4.76-9.52). Preferably, FeS 2 The dosage of / HNTs was 0.05 g / L, and the dosage of PS was 5 mM.

[0022] Preferably, the initial pH value of tetracycline is 3-9.

[0023] FeS 2 In the degradation system of / HNTs+PS, tetracycline was mainly converted into some small molecular organic substances through demethylation, ring opening, dihydroxylation and hydroxyl rearrangement. With the extension of degradation time, the mutagenicity and developmental toxicity of the intermediates showed a downward trend. 2 The overall toxicity of the intermediate products in the / HNTs+PS degradation system is low.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The raw materials used in the present invention are common, easily available, low-cost, and the preparation method is simple, which is convenient for large-scale production.

[0026] (2) The halloysite composite material prepared by the present invention is prepared by assembling HNTs onto FeS 2 The microspheres provide a bidirectional diffusion channel to enhance the diffusion of tetracycline or PS to FeS 2 The diffusion of active sites inside the microspheres improves the degradation ability of the catalytic material on tetracycline.

[0027] (3) The halloysite composite material prepared by the present invention effectively improves its ability to activate PS to degrade tetracycline. It still exhibits good catalytic activity at a low dosage and has a strong adaptability to the initial concentration of tetracycline (10-60 mg / L) and the initial pH value of tetracycline (3-9). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FeS 2 Effect of HNTs dosage on FeS 2 / HNTs activation of PS to degrade tetracycline, where a is the effect of catalyst dosage on FeS 2 / HNTs activated PS to degrade tetracycline; b is the corresponding rate constant;

[0029] Figure 2PS dosage on FeS 2 / HNTs activated PS to degrade tetracycline, where a is the effect of PS dosage on FeS 2 / HNTs activated PS to degrade tetracycline; b is the corresponding rate constant;

[0030] Figure 3 is the initial concentration of tetracycline on FeS 2 / HNTs activated PS to degrade tetracycline, where a is the effect of initial tetracycline concentration on FeS 2 / HNTs activated PS to degrade tetracycline, b is the corresponding rate constant;

[0031] Figure 4 The initial pH value of tetracycline affects FeS 2 / HNTs activated PS degradation of tetracycline, where a is the initial pH value of tetracycline on FeS 2 / Effect of HNTs activation on PS degradation of tetracycline, b corresponding rate constant;

[0032] Figure 5 Methanol, tert-butyl alcohol, p-benzoquinone and L-histidine as and , , and The quencher of FeS 2 / HNTs activated PS system to degrade tetracycline;

[0033] Figure 6 The EPR test results are shown in Figure 1, where a is the EPR spectrum of OH and captured by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a capture agent, b is the EPR spectrum captured by DMPO as a capture agent, and c is the EPR spectrum captured by 2,2,6,6-tetramethyl-4-piperidone hydrochloride (TEMP) as a capture agent. EPR spectrum of

[0034] Figure 7 FeS 2 / Total organic carbon (TOC) removal rate of HNTs activated PS system;

[0035] Figure 8 is the product identification result of different reaction times by LC-MS, where a is FeS 2 Total ion chromatograms of degradation products of PS activated by / HNTs at different reaction times (0, 5, 30 and 60 min), bf are mass spectra at different retention times of 0, 5, 30 and 60 min;

[0036] Fig. 9FeS 2 / The possible degradation pathways of tetracycline in the HNTs-activated PS system and the chemical structures of the intermediates;

[0037] Fig.10 The results of using the toxicity assessment software TEST to predict the acute toxicity, mutagenicity and developmental toxicity of tetracycline and 21 intermediates to Daphnia magna and fathead minnow, where a is the acute toxicity of tetracycline and its intermediates to Daphnia magna (LC 50 -48 h), b is the acute toxicity of tetracycline and its intermediates to bighead carp (LC 50 -96 h), c is the mutagenicity of tetracycline and its intermediates, d is the developmental toxicity of tetracycline and its intermediates;

[0038] Fig.11 For HNTs, FeS 2 and FeS 2 / XRD spectrum of HNTs;

[0039] Fig.12 FeS 2 and FeS 2 SEM images of / HNTs, where a and b are FeS 2 SEM image of FeS 2 / SEM images of HNTs;

[0040] Fig.13 In order to analyze FeS by TEM and EDS 2 / HNTs transmission structure and element distribution images, where a is FeS 2 TEM images of / HNTs, bf is FeS 2 / EDX surface scanning images of Al, Si, Fe and S in HNTs;

[0041] Fig.14 To utilize N 2 Adsorption-desorption method for FeS 2 and FeS 2 The test results of specific surface area and pore size distribution characteristics of HNTs, where a is FeS 2 and FeS 2 N / HNTs 2 Adsorption-desorption isotherm, b is FeS 2 and FeS 2 / pore size distribution of HNTs;

[0042] Fig.15 FeS under different conditions 2 / HNTs degradation effect on tetracycline, where a is the removal performance of tetracycline by different reaction systems, and b is the degradation rate of tetracycline removal by different reaction systems (reaction conditions: [TC] = 20 mg / L, initial pH = 5.5, catalyst dosage = 0.1 g / L, PS concentration = 5 mM);

[0043] Fig.16 FeS 2 and FeS 2 / HNTs activated PS to degrade tetracycline. DETAILED DESCRIPTION

[0044] To further illustrate the technical means and effects of the present invention, the present invention is further described below in conjunction with the embodiments and drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention, rather than to limit the present invention.

[0045] The present invention combines halloysite nanotubes with FeS 2 FeS 2 / HNTs composite materials are used for catalytic degradation of tetracycline and improving the degradation ability of catalytic materials on tetracycline.

[0046] The present invention also provides a method for preparing a halloysite composite material for catalytic degradation of tetracycline, comprising the following steps:

[0047] dispersing the halloysite nanotubes in an organic solvent to obtain a halloysite nanotube suspension;

[0048] Evenly mixing ferrous sulfate, urea and sulfur in an organic solvent to obtain a mixed solution;

[0049] Mixing the halloysite nanotube suspension and the mixed solution, and performing vacuum treatment to obtain a mixed suspension;

[0050] The mixed suspension is heated, and a black product is collected, washed, and dried to obtain a halloysite composite material.

[0051] In some examples, the mass ratio of the halloysite nanotubes, ferrous sulfate, and elemental sulfur is (1.58-19.73):1:1.37.

[0052] Optionally, the ferrous sulfate is anhydrous ferrous sulfate or a hydrate of ferrous sulfate.

[0053] In some examples, the organic solvent is at least one of dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), ethylene glycol, methanol, ethanol, and n-pentanol. Preferably, the organic solvent in the halloysite nanotube suspension is at least one of ethylene glycol, methanol, ethanol, and n-pentanol; the organic solvent in the mixed solution is at least one of dimethylformamide (DMF), dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO).

[0054] In some examples, the heating temperature is 120-200° C., and the heating time is 6-24 h.

[0055] Preferably, the drying temperature is 60° C., and the drying time is 12 h.

[0056] In some examples, the persulfate is at least one of sodium persulfate, potassium persulfate, and ammonium persulfate.

[0057] The reagents and materials described in the following examples, unless otherwise specified, can be obtained from commercial sources, and halloysite nanotubes (HNTs) were purchased from Yuanxin Nanotechnology Co., Ltd. The detection and verification methods in the following examples, unless otherwise specified, all adopt conventional methods.

[0058] Example 1: FeS 2 Preparation of HNTs materials

[0059] The preparation method of the halloysite composite material provided in this embodiment comprises the following steps:

[0060] (1) Disperse 1 g of HNTs in 30 mL of ethylene glycol, stir for 10 min, and then ultrasonically disperse for 1 h to ensure that the HNTs are evenly dispersed to obtain an HNTs suspension.

[0061] (2) Weigh 0.2317 g of FeSO 4 7H 2 O and 0.2503 g of urea were added to 40 mL of DMF and stirred until completely dissolved. Then, 0.1737 g of sublimated sulfur was added thereto. After stirring for 10 min, ultrasonic dispersion was performed for 1 h to fully disperse the sublimated sulfur to obtain a mixed solution.

[0062] (3) Then pour the HNTs suspension into the above mixed solution and continue stirring for 30 min. Transfer the mixture to a vacuum drying oven and evacuate the pressure to below 0.01 atm at room temperature. At this time, small bubbles can be observed to gradually float up from the bottom of the suspension and make a sizzling sound, and then the number of bubbles gradually increases, and the suspension reaches a boiling state. After maintaining the vacuum for 30 min, close the vacuum valve and vacuum pump, let the suspension stand in a vacuum environment for 30 min, slowly vent the air to restore the normal pressure, take it out, stir for 10 min, and repeat the vacuum treatment step twice. Then transfer the suspension to a 100 mL PPL reactor liner, load it into a stainless steel high-pressure reactor, and react at 180 ° C for 12 h.

[0063] (4) After the reactor is cooled to room temperature naturally, the black product is collected and washed with deionized water and ethanol by centrifugation for 3 times each, and then dried in a vacuum oven at 60°C for 12 h to obtain FeS 2 / HNTs materials.

[0064] Example 2: FeS 2 Preparation of HNTs materials

[0065] The preparation method of the halloysite composite material provided in this embodiment is different from that in embodiment 1 in that the HNTs, FeSO 4 7H 2 The mass ratio of O and sublimated sulfur is 1.58:1:1.37.

[0066] Example 3: FeS 2 Preparation of HNTs materials

[0067] The preparation method of the halloysite composite material provided in this embodiment is different from that in embodiment 1 in that the HNTs, FeSO 4 7H 2 The mass ratio of O and sublimated sulfur is 19.73:1:1.37.

[0068] Example 4: FeS 2 Factors affecting the degradation of tetracycline by PS activated by HNTs

[0069] This embodiment provides FeS 2 The influencing factors of tetracycline degradation in the HNTs+PS system are FeS 2 / HNTs dosage, PS dosage, initial tetracycline concentration and initial pH value of tetracycline.

[0070] PS in this embodiment is sodium persulfate.

[0071] (1) FeS 2 / HNTs dosage

[0072] Usually the amount of catalyst has the most direct impact on the degradation efficiency of the reaction, so the FeS 2 The effect of the dosage of FeS / HNTs in the range of 0.025-0.125 g / L on the catalytic degradation of tetracycline was investigated. 2 / HNTs to FeS 2 / HNTs+PS system, explore FeS 2 The effect of the dosage of HNTs on the degradation efficiency of tetracycline is shown in the following figure. Figure 1 shown.

[0073] Depend on Figure 1 It can be seen that the removal efficiency of tetracycline increases with the increase of catalyst dosage in the stage without adding activating substances. This is because the addition of more catalyst will provide more adsorption sites and reaction active sites. 2 When the dosage of FeS / HNTs is 0.025, 0.05, 0.075, 0.1 and 0.125 g / L 2 / HNTs+PS system for tetracycline degradation efficiency and rate constant ( Figure 1 -b) were 79.58% (0.0217 min -1 )、83.01%(0.0207 min -1 )、84.31%(0.0203min -1 )、85.13%(0.0187 min -1 ) and 86.27% (0.0203 min -1 ). It can be seen that FeS 2 / HNTs can effectively activate PS to degrade tetracycline at a low dosage of 0.025 g / L, and the degradation rate is the highest at this time, which is of great significance for reducing operating costs in practical applications. 2 / HNTs can effectively remove tetracycline through the strong oxidizing property of the adsorbent. In subsequent experiments, 0.1 g / L FeS 2 / HNTs.

[0074] (2) PS dosage

[0075] PS, as the main source of ROS in the reaction system, plays a vital role in the degradation of tetracycline. Therefore, the effect of increasing the PS dosage from 0.05 mM to 10 mM on the degradation of FeS 2 / HNTs+PS system, the results are as follows Figure 2 shown.

[0076] Depend on Figure 2 -a, when the PS concentration is 0.05 mM, the degradation efficiency of tetracycline is only 46.73%. As the PS concentration increases to 5 mM, the degradation efficiency of tetracycline in this system increases to 85.13%. This is because more PS added means more ROS can be activated and generated. As the PS concentration continues to increase to 10 mM, FeS 2 The degradation efficiency of tetracycline in the / HNTs+PS system was only increased by 0.65%. This may be because at a certain catalyst dosage, there are no more surface active sites to provide more PS. The change in reaction rate is consistent with the change in degradation efficiency ( Figure 2 -b), sort the PS dosage from high to low according to tetracycline degradation efficiency: 0.005 mM (0.0022 min -1 )>0.5 mM(0.0135 min -1 )>2 mM(0.0168 min -1 )>5 mM(0.0187 min -1 )>10 mM(0.0196min -1 ). For cost considerations, the PS addition amount selected in subsequent experiments was 5 mM.

[0077] (4) Initial concentration of tetracycline

[0078] Effect of initial tetracycline concentration on degradation efficiency Figure 3 -a, FeS 2 The degradation efficiency of the FeS / HNTs+PS system for tetracycline solutions with initial concentrations of 10, 20, 40, 60 and 100 mg / L was 87.58%, 85.135%, 81.99%, 80.77% and 73.50%, respectively. It can be found that with the increase of the initial concentration of tetracycline, the degradation efficiency of FeS 2 The degradation efficiency of tetracycline in the / HNTs+PS system gradually decreased. This is because as the initial concentration of tetracycline increased, FeS 2 / The molar ratio between HNTs and tetracycline decreased, which means that a certain amount of FeS 2 / HNTs acted on more tetracycline. In the adsorption stage before adding PS, FeS 2 The removal efficiency of tetracycline by HNTs decreased significantly with the increase of tetracycline concentration. The degradation rate of the catalytic degradation stage was observed separately, and it was found that the degradation rate increased first and then decreased. When the initial concentration of tetracycline was 60 mg / L, the degradation rate was the fastest, and its degradation rate constant was 0.0233 min -1 In general, FeS2 / HNTs+PS degradation system has a relatively high adaptability to 10~60 mg / L tetracycline contaminated liquid.

[0079] (5) Initial pH value of tetracycline

[0080] In the process of catalytic degradation of organic pollutants, the adsorption of catalysts, the activation of PS and the oxidation of ROS are all strongly dependent on the pH value of the solution. 2 The degradation efficiency and corresponding degradation rate in the / HNTs + PS degradation system are shown in the following table. Figure 4 shown.

[0081] Depend on Figure 4 It can be seen that when the initial pH values ​​are 3, 5.5, 7, 9 and 11, the degradation efficiency and degradation rate of tetracycline are 81.93% (0.0197 min -1 )、85.13%(0.0187 min -1 )、83.39%(0.0204 min -1 )、82.63%(0.0216 min -1 ) and 34.36% (0.0052 min -1 ). As the pH value of the solution increases, FeS 2 / HNTs+PS system's degradation efficiency of tetracycline first increases and then decreases, and the degradation efficiency is optimal when pH=5.5. 2 / HNTs +PS system can be applied in a wide pH range (3~9), which makes FeS 2 / HNTs catalysts have certain potential in practical applications.

[0082] Example 5: FeS 2 Degradation mechanism and pathway of tetracycline by PS activated by HNTs

[0083] This embodiment provides FeS 2 The degradation mechanism and pathway of tetracycline degradation by / HNTs+PS system were analyzed, and the active oxygen species, intermediates, degradation pathways and toxicity of intermediates generated during the degradation process were analyzed.

[0084] PS in this embodiment is sodium persulfate.

[0085] 1. Analysis of Reactive Oxygen Species

[0086] In order to further optimize the degradation experiment and design a catalytic system with better performance, FeS 2 The degradation mechanism of FeS / HNTs+PS system was discussed.2 The degradation capacity of tetracycline in the FeS / HNTs+PS system is highly dependent on the ROS generated in the system. 2 / HNTs+PS system, methanol, tert-butyl alcohol, p-benzoquinone and L-histidine were selected as the ROS respectively. and , , and By analyzing their effects on tetracycline degradation, we can identify the possible ROS in the reaction system. Figure 5 shown.

[0087] Depend on Figure 5 It can be seen that with the increase of methanol dosage, the degradation efficiency of tetracycline gradually decreased, which shows that the addition of methanol has a significant effect on FeS 2 / HNTs+PS system has a significant inhibitory effect on the degradation effect, which indicates that there is or The generation of Figure 5 -b, the degree of inhibition of tetracycline degradation did not change significantly with the increase of tert-butyl alcohol addition, indicating that in this reaction system does not play a dominant role. Adding different amounts of p-benzoquinone ( Figure 5 -c) and L-histidine ( Figure 5 -c) also has a certain inhibitory effect on the degradation efficiency of tetracycline, which means that there is also and The addition of p-benzoquinone has a significant inhibitory effect on the degradation efficiency of tetracycline. When the addition amount of p-benzoquinone reaches 15 mM, FeS 2 The degradation efficiency of tetracycline by the / HNTs+PS system was reduced to 40.85%, which indicates that It plays a key role in the degradation process.

[0088] In order to further verify the above experimental results, EPR was used to identify the ROS that may appear in the reaction system. , and The capture agent, TEMP was used for capture. 2 The EPR spectrum of the / HNTs+PS system 5 min after adding PS is as follows: Figure 6 shown.

[0089] exist Figure 6 The quartet intensity of DMPO-·OH (ratio of 1:2:2:1) and DMPO- The five-fold split signal peaks indicate that there is and . Figure 6 -b also shows DMPO- The expected 1:1:1:1 quartet intensity ratio indicates that β-hydroxyl groups are also generated during the activation process. .exist Figure 6 -c temp- The expected 1:1:1 triplet intensity ratio is also clearly visible, indicating that the system contains This is consistent with the above quenching experiment results. Tetracycline is , , and Combined with the experimental results, FeS 2 The activation and degradation processes of ROS in the / HNTs+PS system were inferred. 2 It interacts with Fe(Ⅱ) on the catalyst surface to generate active degradation and , while Fe(II) is converted to Fe(III) (Formulas 1 and 2). Interaction with water Formula 3), It is also possible that the surface of the catalyst is transformed into (Formula 4). , , and The combined effects cause tetracycline to be degraded into other intermediates and CO 2 and H 2 O (Formula 5).

[0090] Formula 1:

[0091] Formula 2:

[0092] Formula 3:

[0093] Formula 4:

[0094] Formula 5:

[0095] FeS 2 The degradation of tetracycline by the PS activated by / HNTs can be summarized as follows: FeS 2 / HNTs adsorption of tetracycline, FeS 2The redox ability of FeS / HNTs can significantly affect the degradation of tetracycline, and the ROS activated after the addition of PS can further rapidly degrade tetracycline. 2 / HNTs activated PS system, and the TOC changes in the reaction system over time were measured using a total organic carbon analyzer. Figure 7 It can be seen that FeS 2 The TOC removal rate of the PS system activated by / HNTs was 20.47%. This indicates that tetracycline was not completely mineralized, but was converted into other small molecular intermediates that remained in the solution. It is worth noting that when PS was not added to the reaction, the TOC in the system was removed by 21.25%, and within 5 minutes after the addition of PS, the remaining TOC value in the solution increased. This may be because after the addition of PS, the ROS generated by activation attacked the adsorbed on FeS 2 / HNTs surface tetracycline or other intermediates, so that it is from FeS 2 / HNTs and released back into the solution.

[0096] 2. FeS 2 Analysis of intermediate products and degradation pathways of tetracycline degradation by PS activated by HNTs

[0097] In order to confirm that FeS 2 / HNTs activated PS degradation system in the catalytic degradation process and explore the possible degradation pathways. LC-MS was used to identify the products at different reaction times. The results are as follows Figure 8 As shown,

[0098] Figure 8 -a is the total ion chromatogram obtained by measuring the samples at 0, 5, 30 and 60 min of reaction. It can be seen that the peak at the retention time of 3.87~4.02 min corresponds to the tetracycline molecule. It can be seen that when the reaction reaches 0 min, the intensity of the peak is still very high. After adding PS for 5 min, the signal intensity at this point is very weak. This indicates that most of the tetracycline has been destroyed and converted into intermediates with other structural forms when the reaction reaches this point. Figure 8 -b to 8-f are the mass spectra of the intermediate products obtained at the corresponding retention times under these four reaction times. Based on this, the possible molecular structures of the intermediate products were analyzed and a reasonable degradation pathway was proposed.

[0099] 2. FeS 2 / HNTs activated PS degradation pathway for tetracycline

[0100] like Fig. 9 As shown in the figure, the yellow arrow indicates the reaction time from -30 to 0 min, which means that only FeS is added to the system.2 / HNTs degradation pathway. First, tetracycline molecules are degraded by FeS 2 The reducing ability of FeS / HNTs was directly reduced to generate P1 (m / z=304.13) and P2 (m / z=101.08). 2 / HNTs may also open the six-membered ring of tetracycline to obtain P3 (m / z=361.12). 2 / HNTs donate electrons to further attack, and the amino group and hydroxyl group will be lost to transform into P4 (m / z=318.11). The methyl group on the ring that has been opened in P4 is further removed to transform into P5 (m / z=304.09). The aldehyde group connected to the six-membered ring on P5 is attacked and removed, and the hydroxyl group is converted into a ketone carbonyl group to obtain the intermediate product P6 (m / z=274.08). Then PS is introduced into the reaction system, so that a large amount of ROS is generated in the reaction to further degrade tetracycline and the intermediates that have been produced. In the rapid reaction stage of 0-5 min, tetracycline loses the amino group and hydroxyl group under the attack of ROS to transform into P7 (m / z=369.10). P4 is further attacked and deeply opened to transform into P8 (m / z=159.10). The carbonyl group of P5 is removed and further opened to transform into P9 (m / z=278.12). Then the ethyl and hydroxyl groups connected to the six-membered ring in P9 were removed to obtain P11 (m / z=233.08). P11 may be converted into P10 (m / z=174.07), P13 (m / z=164.08) and P14 (m / z=148.05) under the attack of ROS. The aldehyde and carboxyl groups on P10 were further removed to convert into P12 (m / z=142.08). Within 5-30 minutes of the reaction, the types of intermediates did not change significantly. The residual tetracycline was mainly removed from the hydroxyl group to convert into P15 (m / z=396.17). The aldehyde group on P3 was reduced and removed to convert into P16 (m / z=347.14). In the later stage of the reaction, the intermediates were further degraded to intermediates with smaller molecular weights. The benzene ring of P8 was attacked and converted into P17 (m / z=115.01). The hydroxyl group of P6 was removed and converted into P18 (m / z=258.09), which was then further ring-opened and converted into P19 (m / z=218.09), P20 (m / z=148.05) and P21 (m / z=204.12).

[0101] 3. Toxicity analysis of intermediate products

[0102] Whether the intermediates produced during the degradation process have potential environmental risks is also one of the issues that researchers have always been concerned about. Therefore, the QSAR module of the toxicity assessment software T·E·S·T was used to predict the acute toxicity, mutagenicity and developmental toxicity of tetracycline and 21 intermediates to large water fleas and fathead minnows. The results are as follows: Fig.10 As shown,

[0103] Depend on Fig.10 -a shows that LC 50 -48 h refers to the dose of toxic substances that kill more than 50% of large Daphnia within 48 hours. When the dose is less than 1 mg / L, the substance is considered "toxic"; when it is greater than 1 mg / L and less than 100 mg / L, it is considered a "harmful" substance; when it is greater than 100 mg / L, it is generally considered "harmless". The LC of tetracycline 50 -48 h value is 5.44 mg / L, which is harmful to Daphnia magna. 50 Except for P12 (4.2 mg / L), P16 (44.46 mg / L), P19 (33.53 mg / L) and P20 (4.76 mg / L), which were slightly lower than tetracycline, the LC values ​​of the other intermediates at -48 h were 50 -48 h were higher than tetracycline, and the acute toxicity of most intermediates to Daphnia magna was reduced.

[0104] Fig.10 -b shows the dosage of tetracycline and 21 intermediates that killed more than 50% of fathead minnows within 96 hours. When the dosage is less than 1 mg / L, the substance is considered "extremely toxic"; when it is greater than 1 mg / L and less than 10 mg / L, it is considered "toxic"; when it is greater than 10 mg / L and less than 100 mg / L, it is generally considered "harmful"; and when it is greater than 100 mg / L, it is considered "harmless". The LC of tetracycline 50 -96 h value was 0.9 mg / L, which is "highly toxic" to bighead carp. Except for P18 (0.75 mg / L), the LC values ​​of all other intermediates were 50 -96 h value is higher than that of tetracycline, but it is still a "toxic" substance to fathead minnow. 50 -96 h value reached 471.09 mg / L, which is basically "harmless" to fathead minnows. It can be seen that as the degradation reaction proceeds, the acute toxicity of the intermediates first decreases, but some intermediates with smaller molecular structures are comparable to tetracycline in toxicity. Fig.10-c shows the mutagenicity of tetracycline and its intermediates. Tetracycline is shown as "mutagenic positive". It can be seen that intermediates with larger molecular weight tend to show "mutagenic positive", while intermediates with smaller molecular weight tend to be "mutagenic negative". The developmental toxicity of the intermediates is shown as ( Fig.10 -d), except for P20 (0.44) which was “non-developmentally toxic”, the other intermediates were all “developmentally toxic”, but most of them were less toxic than tetracycline.

[0105] Comparative Example 1: FeS 2 Preparation of materials

[0106] This comparative example provides FeS 2 The material is different from Example 1 in that no HNTs are added, and the final product is FeS 2 Materials and steps are as follows:

[0107] Weigh 0.2317 g of FeSO 4 7H 2 O and 0.2503 g of urea were added to 40 mL of DMF and stirred until completely dissolved. Then, 0.1737 g of sublimated sulfur was added thereto. After stirring for 10 min, ultrasonic dispersion was performed for 1 h to fully disperse the sublimated sulfur to obtain a mixed solution.

[0108] Then the mixed solution was transferred to a vacuum drying oven and vacuumed to reduce the pressure to below 0.01 atm at room temperature. After continuous vacuuming for 30 min, the vacuum valve and vacuum pump were closed, and the mixed solution was allowed to stand in a vacuum environment for 30 min, then slowly vented to restore the pressure to normal and taken out. After stirring for 10 min, the vacuuming treatment was repeated twice. Then the mixed solution was transferred to a 100 mL PPL reactor liner, placed in a stainless steel high-pressure reactor and reacted at 180 °C for 12 h.

[0109] After the reactor was cooled to room temperature naturally, the product was collected, washed with deionized water and ethanol by centrifugation for 3 times each, and dried in a vacuum oven at 60 °C for 12 h to obtain FeS 2 .

[0110] Comparative Example 2: FeS 2 + Preparation of HNTs materials

[0111] This comparative example provides FeS 2 +HNTs material, which is different from Example 1 in that: the FeS prepared by the HNTs of Example 1 and Comparative Example 1 2 The mixture was prepared by simple mechanical mixing in a mass ratio of 10:1, that is, 1g of HNTs and 1g of FeS 2 is 0.1g.

[0112] Test Example: FeS of Example 1 2 / HNTs, FeS of Comparative Example 1 2 Materials and Comparative Example 2 FeS 2 +HNTs materials, characterization, morphology and degradation performance test of HNTs on tetracycline

[0113] 1. Phase analysis

[0114] To confirm the prepared FeS 2 Microspheres and FeS 2 The crystal structure and phase composition of FeS / HNTs prepared in Example 1 were analyzed by XRD. 2 / HNTs material, HNTs, FeS prepared in Comparative Example 2 2 , 7Å Halloysite Standard Card (JCPDS: 09-0453) and FeS 2 The standard card (JCPDS: 01-1295) was used for characterization, and the results were as follows Fig.11 shown.

[0115] It can be seen from the figure that the diffraction peak of the HNTs selected as the carrier is basically consistent with the standard card of 7Å halloysite (JCPDS: 09-0453), and there are no other diffraction peaks. This shows that the HNTs selected are 7Å HNTs with higher purity. 2 The diffraction peaks appear at 2θ=28.6º(111), 33.2º(200), 37.1º(210), 40.8º(211), 56.4º(311), 59.2º(220), 61.8º(230), 64.2º(321), 76.8º(331) and 79.1º(420), which are consistent with FeS 2 The standard card (JCPDS: 01-1295) of FeS 2 There are no other diffraction peaks in the XRD spectrum, indicating that FeS with high purity has been synthesized. 2 .FeS 2 / HNTs composites in the presence of FeS 2 In addition to the same diffraction peaks, the diffraction peaks of HNTs are also retained. This shows that the solvothermal method does not change the crystal structure of HNTs, and FeS 2 / HNTs contain only FeS 2 and HNTs.

[0116] 2. Microscopic morphology analysis

[0117] The FeS prepared in Example 1 was observed by SEM. 2 / HNTs and FeS prepared in Comparative Example 1 2 The surface morphology of Fig.12 shown.

[0118] from Fig.12 -a and Fig.12 -b can clearly see the prepared FeS 2 Microspheres are micron-sized spherical structures with a diameter of about 2 to 5 μm, with a rough surface and composed of a large number of nano-sheet structures. Fig.12 -c and Fig.12 -d can be seen that FeS 2 The size of the microspheres remains basically unchanged, and HNTs are assembled into FeS 2 Inside the microsphere, some HNTs are inserted into the sphere, while others are exposed outside. Some HNTs also penetrate the entire FeS 2 The microspheres are either embedded in the FeS 2 On microspheres.

[0119] The FeS prepared in Example 1 was characterized by TEM and EDS. 2 The transmission structure and element distribution of / HNTs were observed. Fig.13 shown.

[0120] from Fig.13 -a shows that due to FeS 2 The microspheres are large in size and the accelerating voltage of TEM cannot penetrate them, so a black ball with high contrast appears on the screen. 2 / HNTs edge information, FeS 2 The edges of the microspheres show an uneven flake structure, indicating that FeS 2 The microspheres are made of FeS 2 This is consistent with the conclusion drawn from the SEM images. Fig.13 -b shows that FeS 2 The HNTs in the HNTs are inserted into FeS 2 In addition, from Fig.13 -c to 13-f, it can be clearly seen that in FeS 2 The distribution of S and Fe in HNTs is different from that of FeS 2 In addition to the consistent morphology of the microspheres, a small amount of Fe and S signals were also detected at the location showing the unique distribution shape of Si and Al elements in HNTs. This indicates that a certain amount of FeS is also formed on HNTs. 2 .

[0121] 3. Specific surface area and pore size analysis

[0122] Using N 2 The FeS prepared in Example 1 was tested by adsorption-desorption method. 2 / HNTs and FeS prepared in Comparative Example 1 2 The specific surface area and pore size distribution of Fig.14 shown.

[0123] from Fig.14 It can be seen that FeS 2 The specific surface area and average pore size are 1.15 m 2 / g and 13.98 nm. FeS 2 The adsorption isotherm of FeS / HNTs belongs to type IV, and the hysteresis loop is H3 type, which is a typical mesoporous capillary condensation with narrow and long pores. 2 The specific surface area of ​​HNTs is 20.74 m 2 / g, and the average pore size is 13.26 nm. 2 , FeS 2 / The specific surface area of ​​HNTs has increased a lot, and this increase is brought about by HNTs.

[0124] 4. Test on the degradation performance of tetracycline

[0125] By comparing the degradation effects of the catalysts on tetracycline under different conditions, the FeS prepared in Example 1 was investigated. 2 / HNTs, FeS prepared in Comparative Example 2 2 +HNTs and HNTs activation effect on persulfate (PS), the results are as follows Fig.15 shown.

[0126] PS in this test example is sodium persulfate.

[0127] from Fig.15 It can be seen that HNTs, FeS 2 / HNTs and FeS 2 +HNTs without adding PS ( Fig.15 -a and Fig.15 -c), the removal efficiency and removal rate of tetracycline were 14.54% (0.0016 min -1 )、36.60%(0.0045 min -1 ) and 32.03% (0.0044 min -1 ), where FeS 2 / HNTs have the best removal effect. The removal of tetracycline by HNTs comes from its own adsorption capacity. 2 / HNTs and FeS 2 The degradation of tetracycline by +HNTs may be partly due to adsorption and partly due to FeS2 The redox ability of HNTs and FeS 2 / HNTs and FeS 2 +HNTs activates PS to degrade tetracycline. When only PS is added to the tetracycline-contaminated liquid, there is almost no degradation of tetracycline. The removal efficiency of tetracycline by the HNTs+PS system is 13.07%, which is basically the same as the removal efficiency of tetracycline when only HNTs are added. This shows that HNTs have no ability to activate PS, and the removal of tetracycline at this time is basically from the adsorption of HNTs. FeS 2 / HNTs and FeS 2 After adding PS, the degradation efficiency of tetracycline in the +HNTs system was improved to varying degrees. 2 The degradation efficiency of tetracycline by the / HNTs+PS system reached 85.13%, and its degradation rate (k=0.0187 min -1 ) is FeS 2 +HNTs+PS(k=0.0089 min -1 ) degradation system, the introduction of HNTs greatly improved the FeS 2 The activation ability of the microspheres on PS. This may be due to the fact that FeS 2 / HNTs surface area increase and FeS insertion 2 The HNTs inside the microspheres provide PS and pollutants for diffusion into the FeS 2 Internal pathways enhance the capabilities of electron transfer and ion diffusion.

[0128] 5. FeS 2 / Stability and long-term use of HNTs

[0129] In practical applications, catalytic materials with good stability and reusability are beneficial to saving costs and improving economic benefits. 2 / HNTs and FeS of Comparative Example 2 2 +HNTs were used for five consecutive cycles to evaluate the change in tetracycline degradation efficiency to evaluate the cycle life of the catalyst. After each experiment, the catalytic material was collected by centrifugation, washed once with deionized water, and placed in a vacuum drying oven to dry thoroughly before being put into use in the next cycle.

[0130] like Fig.16 As shown, FeS 2 / HNTs+PS and FeS 2The degradation efficiency of tetracycline in the first cycle of the FeS + HNTs + PS system was 83.50% and 53.92%, respectively. As the number of cycles increased, the degradation efficiency of tetracycline in the two systems showed a trend of gradual decrease. 2 / HNTs+PS and FeS 2 The degradation efficiency of tetracycline in the +HNTs+PS system was reduced by 16.34% and 31.7% respectively compared with the first cycle reaction. 2 The degradation efficiency of tetracycline in the composite material was not only improved, but the introduction of HNTs also enhanced the degradation of FeS 2 Cyclic stability and reusability.

[0131] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a halloysite composite material for catalytic degradation of tetracycline, characterized in that: FeS2 / HNTs composites were obtained by assembling halloysite nanotubes into FeS2.

2. A method for preparing a halloysite composite material for catalytic degradation of tetracycline, characterized in that: The following steps are involved: dispersing the halloysite nanotubes in an organic solvent to obtain a halloysite nanotube suspension; Evenly mixing ferrous sulfate, urea and sulfur in an organic solvent to obtain a mixed solution; Mixing the halloysite nanotube suspension and the mixed solution, and performing vacuum treatment to obtain a mixed suspension; The mixed suspension is heated, and the black product is collected, washed, and dried to obtain a halloysite composite material.

3. The method for preparing a halloysite composite material for catalytic degradation of tetracycline according to claim 2, characterized in that: The mass ratio of the halloysite nanotubes, ferrous sulfate and elemental sulfur is (1.58-19.73):1:1.

37.

4. The method for preparing a halloysite composite material for catalytic degradation of tetracycline according to claim 2, characterized in that: The mixed solution is obtained by dissolving ferrous sulfate and urea in an organic solvent, adding sulfur and mixing evenly.

5. The method for preparing a halloysite composite material for catalytic degradation of tetracycline according to claim 2, characterized in that: The steps of vacuuming treatment include: vacuuming at room temperature, standing, releasing pressure, stirring, and the vacuuming treatment is repeated several times.

6. The method for preparing a halloysite composite material for catalytic degradation of tetracycline according to claim 2, characterized in that: The heating temperature is 120-200° C., and the heating time is 6-24 h.

7. A halloysite composite material prepared by the method according to any one of claims 1 to 6.

8. Use of the halloysite composite material as claimed in claim 7 in catalytic degradation of tetracycline.

9. A method for catalytically degrading tetracycline using the halloysite composite material according to claim 7.

10. The method for catalytic degradation of tetracycline by a halloysite composite material according to claim 9, characterized in that: The halloysite composite material is used to catalyze persulfate to degrade tetracycline; the mass ratio of the halloysite composite material to persulfate is (1-5): (4.76-9.52).

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