A Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 and a preparation method and application thereof

Abstract

This invention discloses a Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 This relates to the field of catalyst technology, specifically BaFe in heterojunction catalysts. 12 O 19 The mass ratio of the catalyst to SrTiO3 was 10wt%–30wt%, and the average pore size of the catalyst was 14.413 nm. This method addresses the problems of low reaction efficiency and slow reaction kinetics in the photocatalytic activation of PMS for tetracycline degradation, achieving a degradation efficiency of 96.1% within 60 s and a reaction kinetic constant of 0.241 s. ‑1 Moreover, the metal ions do not leach out, the stability is strong, and it can be reused.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe. 12 O 19 Its preparation methods and applications. Background Technology

[0002] High concentrations of antibiotics in the environment, especially in water, can breed antibiotic-resistant bacteria and viruses. Over time, these can evolve into superbugs and superviruses, causing global diseases, threatening human health, and even leading to economic recession. TC antibiotics (tetracyclines) are the second most widely produced antibiotics in the world, with thousands of tons produced annually. Due to their stable chemical structure and low biodegradability, they are frequently found in various water sources, including drinking water. If TC antibiotics are discharged into natural waterways without sufficient degradation, they will not only promote the emergence of drug-resistant bacteria or viruses but will also directly enter our food chain. Therefore, research on the complete degradation of TC antibiotics is essential.

[0003] While various methods such as coagulation, membrane separation, adsorption, and biodegradation can remove total cholesterol (TC), these methods are costly and have low removal efficiency, hindering their widespread application. Advanced oxidation processes (AOPs) can improve reaction efficiency by generating a strong oxidant, such as ·OH, O3, or O2. ·- SO4 ·- To date, advanced oxidation processes involve Fenton or Fenton-like reactions, ozone or catalytic oxidation, electrochemical oxidation and ionizing radiation, photocatalytic oxidation, and advanced oxidation processes using sulfate radicals. Fenton oxidation is limited to acidic conditions and tends to produce iron sludge that is difficult to treat. Although heterogeneous Fenton or Fenton-like processes can avoid the generation of iron sludge, the reaction efficiency remains low due to the low redox potential of the active substances in the reaction system. Ozone oxidation or catalytic ozone oxidation is expensive. Furthermore, ozone cannot oxidize persistent organic substances such as chloroform, and ozone oxidation alone cannot completely oxidize stubborn macromolecules into smaller molecules like carbon dioxide and water. Electrochemical oxidation and ionizing radiation both have high energy consumption and are unsuitable for large-scale applications.

[0004] Photocatalytic oxidation technology, utilizing inexhaustible solar energy, has been widely used for the degradation of tetracycline. Chen et al. found that a BaSO4 / CuS heterostructure could degrade 96.8% of TC within 120 min under visible light. Under visible light, the degradation efficiency of TC reached 83.16% after 30 min of the double S-type Ag2CO3 / Bi4O5I2 / g-C3N4 reaction. Visible light-driven photocatalysis on a CuAl2O4 / g-C3N4 pn heterojunction achieved a TC degradation efficiency of 90.0% after 60 min (Applied Catalysis B: Environmental, 3072022 121182). Other application examples studied by the applicant in the past two years are shown in Table 1. By examining the reaction time and efficiency, it is easy to see that the main problems currently encountered by photocatalytic technology are low reaction efficiency and slow reaction kinetics.

[0005] Table 1 Comparative Analysis of Visible Light-Driven Photocatalytic Degradation of TC in the Past Two Years

[0006]

[0007] The relatively high reaction efficiency of sulfate-based advanced oxidation processes is due to SO4· - Compared to ·OH, it exhibits higher oxidation potential, longer lifetime, and wider pH adaptability. Homogeneous and heterogeneous activation of PMS with transition metals or transition metal complexes both result in metal ion leaching, easily leading to secondary pollution. Carbon-based materials, including transition metal oxides or complexes coated with biochar, are excellent choices for PMS activators, reducing metal ion leaching, but sacrificing catalytic efficiency due to indirect electron transfer. Furthermore, J. Dou et al. (J. Dou, Environmental Science & Technology, 2023) pointed out that the degradation of pollutants by carbon-based end-capping materials is merely due to adsorption and aggregation caused by the high surface area of ​​the carbon material, rather than true mineralization.

[0008] Therefore, the main problems currently faced in the degradation of tetracycline by photocatalytic activation of PMS are: 1. the leaching of metal ions, leading to secondary pollution; 2. the problems of low reaction efficiency and slow reaction kinetics. Moreover, as can be seen from Table 1, although existing studies have improved the reaction efficiency of tetracycline degradation through photoactivation of PMS, none of them have been able to achieve ultra-fast degradation. Summary of the Invention

[0009] In view of this, the purpose of this invention is to address the shortcomings of the prior art by providing a Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe. 12 O 19This method addresses the issues of low reaction efficiency and slow reaction kinetics in the photocatalytic activation of PMS for tetracycline degradation, achieving a degradation efficiency of 96.1% within 60 seconds and a reaction kinetic constant of 0.241 s. -1 Moreover, the metal ions do not leach out, it has strong stability, can be reused, and is resistant to interference.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 BaFe in heterojunction catalysts 12 O 19 The mass ratio of the catalyst to SrTiO3 is 10wt%-30wt%, and the average pore size of the catalyst is 14.413nm.

[0012] Furthermore, the BaFe 12 O 19 The (114) crystal plane of SrTiO3 forms a heterojunction by being in close contact with the (110) crystal plane of SrTiO3.

[0013] A Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 The preparation method includes the following steps:

[0014] (1) Add Sr(NO3)2 and citric acid to an appropriate amount of ionized water and stir to obtain a uniform mixed solution A; mix ethylene glycol and tetrabutyl titanate to form solution B, wherein the molar ratio of Sr(NO3)2, citric acid, tetrabutyl titanate and ethylene glycol is 0.01:0.015:0.01:0.03-0.04;

[0015] (2) Mix solution A and solution B to form a mixed solution, and adjust the pH of the mixed solution to 6 with ammonia under heating and stirring conditions; add BaFe 12 O 19 Add to the mixed solution, heat in a constant temperature water bath at 80°C with mechanical stirring until a sol is formed; then dry the formed sol in a drying oven at 120°C for 3 hours until a gel is formed; the BaFe 12 O 19 The mass ratio of SrTiO3 is 10wt%-30wt%;

[0016] (3) The gel was calcined at 700℃ for 3 h to obtain SrTiO3 / BaFe 12 O 19 .

[0017] A Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12O 19 Application in photocatalytic activation of PMS for the degradation of tetracycline.

[0018] Furthermore, the reaction conditions for the application test were as follows: the initial TC concentration was controlled at 5-25 mg / L, the initial solution pH was 3-11, the amount of PMS added was 0.1 mM-0.4 mM, and the amount of catalyst added was 0.025-0.1 g.

[0019] Furthermore, the reaction conditions for the application test were as follows: the initial TC concentration was controlled at 15 mg / L, the initial solution pH was 6, the amount of PMS added was 0.1 mM, and the amount of catalyst added was 0.1 g.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention discloses a Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 On the one hand, BaFe 12 O 19 The (114) crystal plane of BaFeO3 forms a heterojunction with the (110) crystal plane of SrTiO3. This heterojunction interface forms the direction of electron migration and electric field. Under illumination, the built-in electric field can stimulate the migration and separation of photoinduced charge carriers and induce BaFeO3 to move and separate. 12 O 19 Photoinduced electrons from the CB flow into the VB of SrTiO3 and further combine with photoinduced holes on the SrTiO3 VB, retaining electrons with strong reducing power on the SrTiO3 CB and holes with strong oxidizing power on the Ba ferrite VB, thus giving this application excellent photocatalytic performance; on the other hand, BaFe 12 O 19 The introduction of [the catalyst] reduces the band gap of SrTiO3 and increases its absorption range; moreover, the photocatalyst of this application is a mesoporous material with an average pore size of 14.413 nm, which has a large specific surface area and is more conducive to catalytic reactions.

[0022] 2. The preparation process of this application is simple and easy to control, with low cost, and produces a high-purity Z-type magnetic heterojunction photocatalyst with uniform morphology and large specific surface area, which is suitable for large-scale production.

[0023] 3. The catalyst of this application photocatalytically activates PMS to degrade tetracycline (TC), achieving a degradation efficiency of 96.1% within 60 s and a reaction kinetic constant of 0.241 s. -1 It can achieve ultra-fast degradation.

[0024] 4. High-resolution XPS spectra analysis before and after the reaction, combined with energy changes, proved that Ba, Fe, Ti, and Sr did not directly participate in the activation of PMS. Therefore, the activation of PMS is mainly based on the photocatalysis of the heterojunction, thus this application does not have the problem of secondary pollution caused by metal leaching, making it more environmentally friendly.

[0025] 5. The residual magnetization and saturation magnetization of the catalyst are 1.20 emu / g and 2.98 emu / g, respectively, which meet the requirements for additional magnet-assisted recovery. After being reused 5 times, the degradation efficiency of TC is still higher than 94.0%, indicating that the catalytic system has high reusability and stability.

[0026] 6. After anti-interference testing, except for H2PO4... - Besides humic acid (HA), Cl - NO3 - HCO3 - The ions have no effect on the catalytic efficiency of the catalytic system for the degradation of TC, and the catalytic system has high anti-interference ability.

[0027] 7. SrTiO3 / BaFe 12 O 19 The PMS / Vis catalytic system exhibits lower developmental toxicity to TC degradation intermediates than TC itself; even P1, P2, and P5 are non-toxic. All intermediates show lower mutagenicity than TC, significantly reducing its toxicity. Therefore, the catalytic system of this application greatly reduces the toxicity of TC. Attached Figure Description

[0028] Figure 1 The self-degradation curve of TC under visible light;

[0029] Figure 2 SrTiO3 / BaFe prepared in Examples 1-3 12 O 19 The degradation of TC by the PMS / Vis catalytic system and its reaction kinetics curves;

[0030] Figure 3 SrTiO3 and SrTiO3 / BaFe 12 O 19 The FTIR curves (a), XRD patterns (b), UV-DRS (c), and corresponding band gap energies (d) are shown.

[0031] Figure 4 SEM image of SrTiO3 (a), SrTiO3 / BaFe 12 O 19 SEM image b), TME image c) of SrTiO3, SrTiO3 / BaFe 12 O19 d) TME image of SrTiO3, e) HRTEM image of SrTiO3 / BaFe 12 O 19 HRTEM image f), SrTiO3 / BaFe 12 O 19 EDS element diagram g);

[0032] Figure 5 SrTiO3 / BaFe 12 O 19 EDS spectrum;

[0033] Figure 6 SrTiO3 / BaFe 12 O 19 XPS total spectra a, b) and SrTiO3, BaFe 12 O 19 and SrTiO3 / BaFe 12 O 19 High-resolution XPS (cf) images of Sr3d, Ti2p, Ba3d, Fe2p and O1s in the sample;

[0034] Figure 7 SrTiO3 / BaFe 12 O 19 N2 isothermal adsorption curves, average pore size distribution, and static adsorption curves;

[0035] Figure 8 The effects of catalyst dosage (a, b) and PMS dosage (c, d) on TC degradation and the corresponding reaction kinetic diagrams are shown.

[0036] Figure 9 The effects of TC concentration (a, b) and pH (c, d) on TC degradation and the corresponding reaction kinetics are shown in the figure.

[0037] Figure 10 SrTiO3 / BaFe 12 O 19 ζ potential under different pH conditions;

[0038] Figure 11 The ionization fraction of TC under variable pH conditions;

[0039] Figure 12 SrTiO3 / BaFe 12 O 19 The degradation efficiency of TC in different catalytic systems under visible light irradiation (a) and corresponding reaction kinetics (b) hysteresis loop (c) and reuse performance (d) are compared.

[0040] Figure 13SrTiO3 / BaFe 12 O 19 TOC removal curves of TC by the PMS / Vis catalytic system;

[0041] Figure 14 To the SrTiO3 / BaFe before and after the reaction 12 O 19 XPS total spectrum;

[0042] Figure 15 To the SrTiO3 / BaFe before and after the reaction 12 O 19 XRD patterns;

[0043] Figure 16 This is a diagram from an anti-interference experiment.

[0044] Figure 17 SrTiO3 / BaFe 12 O 19 High-resolution XPS images of Ba3d and O1s before and after the reaction;

[0045] Figure 18 SrTiO3 / BaFe 12 O 19 High-resolution XPS images of Fe2p, Sr3d, and Ti2p before and after the reaction;

[0046] Figure 19 The electrostatic potential (a) of the SrTiO3110 surface, BaFe 12 O 19 (114) face b), SrTiO3 / BaFe 12 O 19 heterojunction interface (c), SrTiO3 (110) and BaFe 12 O 19 (114) charge density difference and corresponding structure diagram;

[0047] Figure 20 SrTiO3a,b) and BaFe 12 O 19 UPS spectra of c, d);

[0048] Figure 21 Schematic diagram of band structure: a) before contact b) in darkness c) light contact with SrTiO3 / BaFe 12 O 19 The corresponding photogenerated carrier transfer process in the system.

[0049] Figure 22 For TC in SrTiO3 / BaFe 12 O 19Degradation pathways on the / PMS / Vis system. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0051] Example 1

[0052] (1) Add 2.12 g (0.01 mol) Sr(NO3)2 and 3.15 g (0.015 mol) citric acid to 10 mL of ionized water and stir to obtain a homogeneous mixed solution A; mix 2 mL of ethylene glycol with 3.4 mL (0.01 mol) tetrabutyl titanate to form solution B;

[0053] (2) Mix solution A and solution B to form a mixed solution, and adjust the pH of the mixed solution to 6 with ammonia under heating and stirring conditions; add 0.18g BaFe 12 O 19 (Barium ferrite) is added to the mixed solution, heated in a constant temperature water bath at 80°C and mechanically stirred until a sol is formed;

[0054] (3) The formed sol was dried in a drying oven at 120°C for 3 hours until a gel was formed; finally, the gel was calcined in a muffle furnace at 700°C for 3 hours to obtain the Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe. 12 O 19 (10wt.% BaFe) 12 O 19 In this embodiment, BaFe 12 O 19 The mass ratio of SrTiO3 to SrTiO3 is 10%, and the product is...

[0055] Example 2

[0056] BaFe in Example 2 12 O 19 The amount added is 0.36g. In this example, BaFe 12 O 19 The mass ratio of BaFe to SrTiO3 is 20%, i.e., 20 wt.% BaFe 12 O 19 .

[0057] Example 3

[0058] BaFe in Example 2 12 O 19 The amount added is 0.54g. In this example, BaFe 12 O 19 The mass ratio of BaFe to SrTiO3 is 30%, i.e., 30 wt.% BaFe 12 O19 .

[0059] Comparative Example 1

[0060] Comparative Example 1 without BaFe 12 O 19 Therefore, the product prepared is SrTiO3.

[0061] Performance characterization and application testing

[0062] The experimental procedure was as follows: Experiments were conducted in batches in a mechanically stirred photocatalytic reactor, with the solution temperature controlled at 20℃ using flowing condensate. Due to the rapid reaction kinetics, the step of TC adsorption equilibrium on the catalyst was omitted. Under continuous stirring, the pH of the mixed solution was adjusted, and a certain amount of PMS (2KHSO5·KHSO4·K2SO4) and a certain amount of catalyst were added to 100 mL of TC solution to initiate the degradation reaction. Simultaneously, a 300W xenon lamp with an ultraviolet cutoff filter was turned on to simulate visible light irradiation (λ > 420 nm, light intensity 1000 mW·cm). -2 At a given irradiation time interval, a 3 mL sample of the reaction solution was taken from the middle of the reactor. The TC concentration was measured using ultra-high performance liquid chromatography (UPLC, Waters). C / C0 represents the photodegradation rate, where C0 is the initial solution concentration and C is the concentration of the reaction solution after different reaction times. The degradation efficiency was calculated as (1 - C / C0) × 100%. ln(C0 / C) = k·t was used to fit and calculate the reaction rate constant (k).

[0063] I. Photocatalytic degradation tests of products in Examples 1-3

[0064] Autodegradation of TC under visible light, under the condition that [TC] = 15 mg / L, results are shown in [link to results]. Figure 1 Examples 1-3 products (10wt.% BaFe) 12 O 19 20wt.% BaFe 12 O 19 30wt.% BaFe 12 O 19 Photocatalytic degradation experiment, conditions: [TC] = 15 mg / L, [PMS] = 0.3 mM, [catalyst] = 0.1 g, [pH] = 7, results are shown below. Figure 2 .

[0065] Figure 1 This indicates that the self-degradation of TC under visible light is negligible. Under the same conditions, 10 wt.% BaFe 12 O 19The heterojunction catalyst exhibited a degradation efficiency of 89.7% for TC, with a reaction kinetics of 0.211 s⁻¹. -1 The catalytic efficiency and reaction kinetics are higher than those of 20 wt.% and 30 wt.% BaFe. 12 O 19 Proportion( Figure 2 ).

[0066] Considering the need for magnetically assisted recovery, the following characterization and application experiments all selected samples with high reaction kinetics (0.211 s⁻¹). -1 10 wt.% BaFe 12 O 19 Proportional heterojunction photocatalyst (SrTiO3 / BaFe) 12 O 19 The following research will be conducted.

[0067] II. Performance Characterization

[0068] The following characterization experiments were conducted on the Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe prepared in Example 1. 12 O 19 (10wt.% BaFe) 12 O 19 SrTiO3 is the SrTiO3 used in Comparative Example 1 without the addition of BaFe. 12 O 19 High-purity SrTiO3 was prepared.

[0069] 1. FTIR curves, XRD, UV-DRS, and bandgap energy characterization

[0070] like Figure 3 As shown in a, 2937cm -1 and 1445cm -1 The absorption at 3278 cm⁻¹ can be attributed to the stretching and deformation vibrations of the OH bonds, respectively. The absorption peak at 3278 cm⁻¹ is due to water adsorption on the sample surface. This indicates that the sample is hydrophilic, which promotes the photocatalytic reaction between photoinduced holes and H₂O. (581 cm⁻¹) -1 and 413cm -1 The two signals at that location are attributed to Ti-O(H) and Ti-O, respectively. 861cm -1 The adsorption peak at that location originates from the Sr-O bond.

[39] Due to BaFe 12 O 19 The peak intensity is relatively small or coupled with the broad absorption peak of the Ti-O bond, therefore it is in the range of 450–600 cm⁻¹. -1 No characteristic peaks were observed within the range.

[0071] The peaks at 2θ = 32.45°, 40.03°, 46.55°, 57.90°, 67.96°, and 77.35° correspond to the (110), (111), (200), (211), (220), and (310) crystal planes of SrTiO3 (PDF#84-0443). The characteristic peaks at 2θ = 31.91° and 33.87° are attributed to BaFe. 12 O 19 The (107) and (114) crystal planes (PDF#78-0132). Characteristic peaks of SrTiO3 appeared in the XRD pattern of the heterojunction catalyst, but BaFe... 12 O 19 The characteristic peaks are not obvious. Figure 3 b) Because the intensity of the characteristic peak of SrTiO3 is higher than that of BaFe. 12 O 19 The characteristic peaks are much stronger.

[0072] UV-DRS curves show that the heterojunction catalyst exhibits stronger absorption intensity in the UV-Vis region, particularly in the visible light region, compared to pure SrTiO3. This indicates that BaFe 12 O 19 The introduction of [something] enhances the light absorption intensity of SrTiO3. Figure 3 c). Clearly, the heterojunction is a darker color than pure SrTiO3. The calculated band gaps for SrTiO3 and the heterojunction are 3.09 eV and 2.84 eV, respectively. Figure 3 d). Therefore, BaFe 12 O 19 The introduction of [a specific ingredient] reduces the band gap of SrTiO3 and increases its absorption range. These results can preliminarily indicate that BaFe [a specific ingredient] [is a potential adjunct to SrTiO3]. 12 O 19 The existence of.

[0073] 2. Characterization by SEM, TME, HRTEM, and EDS

[0074] Pure SrTiO3 and the heterojunction showed almost identical SEM patterns, indicating that BaFe 12 O 19 The introduction of [the substance] did not change the morphology of SrTiO3. Figure 4 a, b). For example Figure 4 As shown in c and d, the TEM images of the heterojunction show more dark spots, which may also indicate that BaFe 12 O 19 The existence of BaFe. 12 O 19 The atomic number of BaFe is higher than that of pure SrTiO3. Therefore, BaFe 12 O 19It scatters electrons more effectively and involves fewer electrons in bright-field images, resulting in darker corresponding locations in the TEM image. The HRTEM image is processed using Fourier and inverse Fourier transforms to obtain the lattice fringe widths, thereby determining the crystal planes.

[0075] The calculated interplanar spacings of 0.276 nm and 0.295 nm are attributed to the (110) plane of SrTiO3 and BaFe, respectively. 12 O 19 110 crystal plane ( Figure 4 c, d). EDS spectrum ( Figure 5 ) and EDS elemental spectra of heterojunctions ( Figure 4 g) The presence of the desired elements, such as Fe, Ba, Sr, Ti, and O, was confirmed. These results confirm the presence of BaFe. 12 O 19 The existence of BaFe. At the same time, BaFe 12 O 19 The presence is also confirmed by total XPS measurements and high-resolution XPS maps ( Figure 6 This has been confirmed. Therefore, the above characterization demonstrates that the heterostructure has been successfully prepared.

[0076] 3. XPS spectral characterization

[0077] Through high-resolution XPS maps ( Figure 6 The analysis in (a) further confirmed the chemical states of all elements. The binding energies at 133 eV and 134 eV of Ca are attributed to the Sr 3d 5 / 2 and Sr 3d 3 / 2 states, respectively. Figure 6 b). The fitting peaks at ca 458 eV and 464 eV can be attributed to the Ti 2p 3 / 2 and Ti 2p 1 / 2 states, respectively. Figure 6 c)

[42] The two characteristic peaks at approximately 780 eV and 750 eV belong to the Ba 3d 5 / 2 and Ba 3d 3 / 2 states, respectively. Figure 6 d). The fitting peaks appear at ca 711 eV and 724 eV, representing the Fe 2p 3 / 2 and Fe 2p 1 / 2 states, respectively. Figure 6 e). The O1s spectra centered at Ca 529 eV, 531 eV, and 536 eV can be attributed to lattice oxygen, adsorbed oxygen, and oxygen adsorbed from H2O. Figure 6 f). For pure SrTiO3 and Ba ferrite, the binding energies of these elements in the heterojunction exhibit different degrees of blue shift or red shift, which implies the presence of electron transfer at the heterojunction interface and chemical interactions between SrTiO3 and Ba ferrite.

[0078] 4. Characterization by isothermal adsorption and desorption curves

[0079] The N2 isothermal adsorption and desorption curves belong to type III curves. Figure 7 a) The narrow pores formed by the accumulation of layered particles lead to the formation of hysteresis loops during desorption, which is consistent with the layered structure of hexagonal barium ferrite. The average pore size distribution of 14.413 nm proves that the heterostructure is a mesoporous material. Figure 7 b). Static adsorption curve ( Figure 7 c) indicates that small molecules can accumulate in layers on the surface of the heterojunction by means of van der Waals forces, which facilitates subsequent catalytic reactions.

[0080] III. Application Test

[0081] 1. Condition optimization experiment

[0082] (1) The effects of catalyst dosage (a, b) and PMS dosage (c, d) on TC degradation and the corresponding reaction kinetic experiments are described in [reference]. Figure 8 .

[0083] Conditions for a: [TC] = 15 mg / L, [PMS] = 0.3 mM, [pH] = 7; Conditions for c: [TC] = 15 mg / L, [catalyst] = 0.1 g, [pH] = 7.

[0084] (2) The effects of TC concentration (a, b) and pH (c, d) on TC degradation and the corresponding reaction kinetics experiments are described in [reference needed]. Figure 9 .

[0085] Conditions for a: [catalyst] = 0.1 g, [PMS] = 0.1 mM, [pH] = 7; Conditions for c: [TC] = 15 mg / L, [catalyst] = 0.1 g, [PMS] = 0.1 mM.

[0086] Analysis showed that as the initial TC concentration increased from 5 mg / L to 25 mg / L, the degradation efficiency decreased from 86.8% to 80.9%, and the reaction kinetics changed from 0.271 s⁻¹ to 0.271 s⁻¹. -1 It dropped to 0.0273s -1 This is a common phenomenon. Even with an initial TC concentration of 15 mg / L, it can still maintain its effect for 0.210 seconds. -1 The reaction kinetics were high. In practical applications, it is necessary to consider the removal of trace amounts of antibiotics; therefore, we chose an initial concentration of 15 mg / L as the subsequent test condition. If high concentrations of TC are encountered in practical applications, they can be diluted to this concentration to obtain the optimal degradation efficiency.

[0087] In the PMS photocatalytic activation degradation of TC reaction system, the pH of the solution can affect many aspects, such as the ionization of PMS, the electronegativity of the catalyst surface, the form of TC, and the lifetime of free radicals. The zeta potential shows ( Figure 10 The catalyst is negatively charged throughout the acidity, which may lead to its reaction with HSO₄. 5- Electrostatic repulsion and with TC (TCH2 and TCH3) + The electrostatic attraction of TC is observed. The reaction kinetics remain high from pH 3 to 11, but are fastest at pH 6 (0.192 s⁻¹). Using reaction solutions alone at pH 9 and 11, the degradation efficiency decreased from 86.9% (pH 6) to 82.3% and 81.4%, respectively. On the one hand, this catalytic system adapts well to acidity and alkalinity. On the other hand, at pH 6, TC exists as electrically neutral TCH₂. Figure 11 It can be electrostatically attracted by the negatively charged catalyst surface. Furthermore, it is shown that whether organic matter can be attracted to the catalyst surface is crucial in the photocatalytic degradation of organic matter, possibly because photogenerated electrons and holes can directly react with the target. Therefore, pH=6 was chosen as the optimal condition.

[0088] As the catalyst dosage increased from 0.025 g to 0.10 g, the degradation efficiency increased from 82.2% to 86.8%, and the reaction kinetics increased from 0.0632 s⁻¹. -1 Increased to 0.192s -1 As the catalyst dosage increased, the reaction efficiency and kinetics decreased slightly because more catalyst interfered with light penetration into the reaction solution, a relatively common phenomenon in photocatalytic reactions. Therefore, 0.1 g of catalyst was determined to be the optimal amount. Furthermore, the degradation efficiency did not further increase with increasing catalyst dosage, indicating that PMS activation in this reaction system is primarily mediated by photocatalysis.

[0089] As the PMS dosage increased from 0.1 mM to 0.4 mM, the degradation efficiency remained at approximately 86.0%, although the reaction kinetics also increased from 0.173 s⁻¹. -1 Increased to a maximum of 0.192s -1 Considering application costs, 0.1 mM PMS was determined to be the optimal dosage. When the PMS dosage increased from 0.4 mM to 0.5 mM, the degradation efficiency decreased from 86.6% to 84.6%, and the reaction kinetics changed from 0.192 s⁻¹ to 0.5 s⁻¹. -1 It dropped to 0.174s -1 Excessive PMS causes SO4 to rise. ●- Sudden quenching leads to SO5 ●- Low activity.

[0090] Therefore, the optimal reaction conditions are 0.1 g catalyst, 0.1 mM PMS, initial TC concentration of 15 mg / L, and initial solution pH = 6.

[0091] 2. Degradation test

[0092] See Figure 12 The conditions for a and d are: [TC] = 15 mg / L, [PMS] = 0.1 mM, [catalyst] = 0.1 g, [pH] = 6;

[0093] Analysis showed that PMS could degrade 12.0% of TC, indicating that visible light can activate some PMS, but the efficiency is low. Pure barium ferrite can hardly degrade TC under visible light. On Ba ferrite / PMS / Vis, the degradation efficiency of TC reached 16.3%, with a reaction kinetic of 0.0163 s⁻¹. -1 Barium ferrites exhibit very weak photocatalytic activity for PMS activation, primarily due to the faster recombination of photogenerated charges within the barium ferrite.

[0094] The SrTiO3 / PMS / Vis catalytic system can degrade 69.0% of TC, with a reaction kinetics of 0.132 s⁻¹. -1 SrTiO3 / BaFe 12 O 19 The PMS / Vis catalytic system can degrade 96.1% of TC, with a corresponding reaction kinetic of 0.241 s⁻¹. -1 The efficiency was 1.83 times higher than that of the SrTiO3 / PMS / Vis catalytic system. On one hand, the formation of the heterojunction improved the separation efficiency of photogenerated charges, thus increasing the photocatalytic efficiency; on the other hand, the photocatalytic activation of PMS produced a coexistence system of various active substances, including ·OH and O2. ·- SO4 ·- and 1 O2, etc., are beneficial to the degradation of organic matter. Furthermore, the TOC removal rate of TC reaches approximately 40.0% after 30 minutes of reaction. Figure 13 As shown (conditions: [TC] = 15 mg / L, [PMS] = 0.1 mM, [catalyst] = 0.1 g, [pH] = 6).

[0095] 3. Repeatability, stability and anti-interference tests

[0096] The introduction of magnetic components not only promotes the formation of heterojunctions but also facilitates magnet-assisted recovery of the catalyst. The residual magnetization and saturation magnetization of the heterojunction catalyst are 1.20 emu / g and 2.98 emu / g, respectively, meeting the requirements for additional magnet-assisted recovery. Figure 12 c).

[0097] Even after the heterojunction catalyst was reused five times, the degradation efficiency of TC remained above 94.0%. Figure 12 d) indicates that the catalytic system has high reusability.

[0098] XPS general spectrum ( Figure 14 ) and XRD patterns ( Figure 15 The presence of elemental and physical phases was revealed before and after the heterojunction catalyst reaction, respectively, indicating the high structural stability of the heterojunction catalyst.

[0099] Anti-interference experiments were conducted on the catalytic system under the following reaction conditions: [TC] = 15 mg / L, [PMS] = 0.1 mM, [Catalyst] = 0.1 g, [pH] = 6, [NaHCO3] = 15 mM, [NaCl] = 15 mM, [NaNO3] = 15 mM, [NaH2PO4] = 115 mM, [HA] = 5 mM. The results are as follows: Figure 16 As shown. The black color of humic acid itself affects the penetration of light into the solution, thus affecting photocatalysis. H2PO4 - Captured ·OH and SO4· - And may destroy O2· - The generated main chain. This phenomenon, in turn, may indicate that in this catalytic system, O2· - The primary source is not the reaction between photogenerated electrons and dissolved oxygen, because photogenerated electrons are easily captured by PMS. Besides H2PO4... - Besides humic acid (HA), Cl - NO3 - HCO3 - The ions had no effect on the catalytic efficiency of the catalytic system in degrading TC, which also indicates the high anti-interference ability of the catalytic system.

[0100] 4. SrTiO3 / BaFe 12 O 19 High-resolution XPS before and after the elemental reaction

[0101] By comparing the high-resolution XPS spectra of elements in the catalyst before and after the reaction, such as... Figure 17 and 18 As shown, it can be determined whether multivalent transition metal elements directly activate PMS through electron transfer. After the reaction, the binding energies of the Ba 3d 5 / 2 and Ba 3d 3 / 2 states increased by only 0.3 eV and 0.4 eV, respectively, compared to before the reaction. The binding energies of lattice oxygen and adsorbed oxygen in O1s remained unchanged before and after the reaction. After the reaction, Fe... 2+The binding energy decreased by only 0.4 eV. Compared with the binding energy before the reaction, the binding energies of the Sr3d 5 / 2 and Sr3d 3 / 2 states decreased by only 0.04 eV and 0.01 eV respectively after the reaction, and the binding energies of the Ti 2p 3 / 2 and Ti 2p 1 / 2 states increased by only 0.2 eV and 0.1 eV respectively after the reaction. These negligible changes in binding energy prove that Ba, Fe, Ti, and Sr did not directly participate in the activation of PMS. Therefore, the activation of PMS is mainly based on the photocatalysis of the heterojunction, which solves the problem of secondary pollution caused by metal leaching, and these elements were not detected in the solution after the reaction.

[0102] 5. Toxicity assessment

[0103] Figure 22 A degradation pathway for TC was proposed. The LUMO and HOMO of TC are mainly located around the N atom, thus enabling easy deamidation and deamination reactions. First, photogenerated h... + Direct oxidation of TCH2 to form TCH2 + It will react with dissolved oxygen and reactive H substances, causing the benzene ring to add, thus opening reaction pathway I. Photogenerated H + O2 ·- The ·OH then reacts with TC to produce deamidation, deoxygenation, ring opening, and hydroxylation. Pathway II opens the same reaction as described above, but in a different order.

[0104] The toxicity of TC and its TP was evaluated based on five key indicators: LC50-96hr, oral LD50 in rats, bioconcentrating factor, developmental toxicity, and mutagenicity. As shown in Table 2, the LC50-96hr values ​​of all intermediates were greater than that of TC. Except for P6 and P7, the oral LD50 values ​​of all intermediates in rats were greater than that of TC. Although the bioconcentrating factors of all intermediates except P8 were higher than those of TC, the developmental toxicity of all intermediates was lower than that of TC, and even P1, P2, and P5 were non-toxic, the mutagenicity of all intermediates was lower than that of TC. Therefore, SrTiO3 / BaFe 12 O 19 The PMS / Vis catalytic system significantly reduces the toxicity of TC through degradation.

[0105] Table 2. Toxicological analysis of degradation intermediates using T·E·S·T software.

[0106]

[0107] IV. Catalytic Mechanism

[0108] Figure 19 a and b show the (110) crystal plane of SrTiO3 and BaFe.12 O 19 The calculated work functions (Φ) of the (114) crystal plane are 5.82 eV and 9.26 eV, respectively. Therefore, electrons will be drawn from the (110) crystal plane (W) of SrTiO3, which has a low work function and a high Fermi level. f = -3.56eV) migrates to the (114) crystal plane W of Ba ferrite, which has a high work function and a low Fermi level. f = -3.15eV). As a result, an electric field was established at the heterostructure interface pointing from the SrTiO3 (110) surface to the Ba ferrite (114) surface. Furthermore, the formation of the heterojunction interface reduced the work function (Φ = 4.48eV) and increased the Fermi level (W). f =-0.43eV)( Figure 19 c) promotes electron overflow and increases the activity of active sites. The differential charge density at the heterojunction interface confirms the electron migration direction and the corresponding electric field direction between the SrTiO3(110) surface and the Ba ferrite(114) surface. Figure 19 d).

[0109] To construct the band structure of the heterojunction and further verify the conclusions of the theoretical calculations, the ultraviolet photoelectron spectroscopy (UPS) of the sample was analyzed. Figure 20 To determine the band structure. First, SrTiO3 and BaFe 12 O 19 The band gap values ​​(Eg) are 3.09 eV ( Figure 3 d) and 1.87eV.

[0110] By subtracting the band edges of SrTiO3 and Ba ferrite (18.34 eV and 17.00 eV, respectively) from the excitation energy (21.22 eV), Figure 20 (a) and (c) the test work function (Φ) of SrTiO3 and Ba ferrite is estimated to be 2.86 eV and 4.22 eV, respectively. Therefore, the Fermi levels (Ef) of SrTiO3 and Ba ferrite are -2.86 eV and 4.22 eV, respectively. The valence band (VB) and energy (Ef) of SrTiO3 and Ba ferrite are also given. VB The estimated values ​​are -4.44 eV and 4.89 eV, E f The energy levels of SrTiO3 and Ba ferrite are 1.58 eV and 0.67 eV, respectively. Figure 20 b, d). Therefore, the conduction band (CB) energies (E) of SrTiO3 and Ba ferrites are estimated using EVB-Eg. CB The values ​​are 1.35 eV and -1.79 eV, respectively.

[0111] Although there is a certain deviation between the experimentally measured work function and the theoretically calculated work function, the trend in their magnitudes remains unchanged and does not affect the judgment of electron transfer. However, since the experimentally measured work function is the average of the work functions of several crystal surfaces, the result is more accurate. Therefore, the experimentally measured work function is used to construct band structures, such as... Figure 21 The band structure is shown. The band structures of SrTiO3 and Ba ferrite are interleaved. Figure 21 a). Meanwhile, the Wf value of SrTiO3 (2.86 eV) is lower than that of Ba ferrite (4.22 eV), indicating that electrons in SrTiO3 are more likely to escape. Therefore, as a heterojunction forms between the SrTiO3 and Ba ferrite phases, electrons in the SrTiO3 phase will transfer to the Ba ferrite phase. This spontaneous electron transfer process promotes the generation of an internal electric field, the direction of which is from the SrTiO3 phase to the Ba ferrite phase (a). Figure 21 b). Under illumination, the built-in electric field can stimulate the migration and separation of photoinduced charge carriers. These factors induce photoinduced electrons on the Ba ferrite CB to flow into the SrTiO3 VB, and further bind with photoinduced holes on the SrTiO3 VB. Figure 21 c). Therefore, the heterojunction retains the electrons with strong reducing ability on the CB of SrTiO3 and the holes with strong oxidizing ability on the VB of Ba ferrite. Thus, compared to pure SrTiO3 and Ba ferrite, the heterojunction exhibits higher photocatalytic activity.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 Its application in the photocatalytic activation of PMS for the degradation of tetracycline is characterized by: BaFe in heterojunction photocatalyst 12 O 19 The mass ratio of the catalyst to SrTiO3 is 10wt%-30wt%, and the average pore size of the catalyst is 14.413nm.

2. The Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe according to claim 1 12 O 19 Its application in the photocatalytic activation of PMS for the degradation of tetracycline is characterized by: The BaFe 12 O 19 The (114) crystal plane of SrTiO3 forms a heterojunction by being in close contact with the (110) crystal plane of SrTiO3.

3. The Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe according to claim 1 12 O 19 Its application in the photocatalytic activation of PMS for the degradation of tetracycline is characterized by: The Z-type magnetic heterojunction photocatalyst SrTiO3 / BaFe 12 O 19 The preparation method includes the following steps: (1) Add Sr(NO3)2 and citric acid to an appropriate amount of ionized water and stir to obtain a uniform mixed solution A; mix ethylene glycol and tetrabutyl titanate to form solution B, wherein the molar ratio of Sr(NO3)2, citric acid, tetrabutyl titanate and ethylene glycol is 0.01:0.015:0.01:0.03-0.04; (2) Mix solution A and solution B to form a mixed solution, and adjust the pH of the mixed solution to 6 with ammonia under heating and stirring conditions; add BaFe 12 O 19 Add to the mixed solution, heat in a constant temperature water bath at 80°C and mechanically stir until a sol is formed; then dry the formed sol in a drying oven at 120°C for 3 hours until a gel is formed; the BaFe 12 O 19 The mass ratio of SrTiO3 is 10wt%-30wt%; (3) The gel was calcined at 700°C for 3 hours to obtain SrTiO3 / BaFe. 12 O 19 .

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