A homojunction-heterojunction dual junction coupled photocatalyst, a preparation method and application thereof

Abstract

The application discloses a homogenous-heterogeneous dual junction coupled photocatalyst and a preparation method and application thereof. The preparation method of the homogenous-heterogeneous dual junction coupled photocatalyst comprises the following steps: mixing carbon nitride, lithium chloride and potassium chloride to obtain mixed powder, calcining the mixed powder, cooling and washing, and drying to obtain a precursor; mixing the precursor, ammonium chloride and sodium thiocyanate, grinding to obtain a mixture, calcining the mixture, cooling and washing, and drying to obtain homogenous junction carbon nitride; dispersing ferric chloride hexahydrate and sodium acetate in ethanol, adding H2O drop by drop to obtain a mixed solution, adding the homogenous junction carbon nitride into the mixed solution, ultrasonicating to obtain a dispersion liquid, heating the dispersion liquid, cooling and washing, and drying to obtain the homogenous-heterogeneous dual junction coupled photocatalyst; and the removal rate of the homogenous-heterogeneous dual junction coupled photocatalyst to TC is 99.8% within 20 min, the problem that the heterojunction is limited by the influence of acid and alkalinity is solved, and the pH application range of the photocatalyst is widened.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a homogeneous-heterogeneous dual-junction coupled photocatalyst, its preparation method, and its application. Background Technology

[0002] With rapid industrialization and urbanization, the discharge of organic wastewater has become an increasingly serious problem. In particular, various pollutants from pharmaceuticals, textiles, agriculture, and daily life result in organic wastewater containing antibiotics, dyes, endocrine disruptors, and personal care products, making it highly toxic and difficult to degrade, severely impacting water quality and ecosystems. The presence of pollutants not only exacerbates water pollution but may also lead to the emergence of antibiotic-resistant bacteria, threatening public health. Simultaneously, these pollutants negatively impact the growth and reproduction of aquatic organisms, disrupting ecological balance and potentially affecting human reproductive health. Therefore, protecting water resources and ecosystems, safeguarding human health and safety, and achieving effective treatment of organic wastewater are urgently needed.

[0003] Advanced oxidation technologies (AOPs) are widely recognized for their ease of operation and rapid degradation and mineralization. However, conventional AOPs suffer from drawbacks such as high energy consumption and large reagent dosages. Photocatalytic molecular oxygen activation technology, as a sustainable and environmentally friendly AOP, utilizes naturally occurring oxygen molecules as an oxidant, converting oxygen into reactive oxygen species (ROS) groups under solar energy, thereby degrading pollutants and purifying organic wastewater. It offers advantages such as being green and requiring low reagent additions. Semiconductor carbon nitride (g-C3N4) has been widely used in photocatalytic molecular oxygen activation technology due to its excellent photoelectric properties. However, its weak dielectric shielding severely inhibits the generation and migration of free charge carriers, resulting in poor utilization of photogenerated electrons and catalytic efficiency.

[0004] Although existing literature (Synergistic enhancement of photocatalytic molecular oxygen activation by nitrogen defect and interfacial photoelectron transferover Z-schemeα-Fe2O3 / g-C3N4heterojunction, Applied Catalysis B: Environmental, 335(2023)122890) reports that constructing heterojunctions (such as iron oxide / carbon nitride heterojunctions, manganese oxide / carbon nitride heterojunctions, and indium oxide / carbon nitride heterojunctions) can improve exciton dissociation, these heterojunctions are limited by the weak internal electric field of traditional bulk carbon nitride (CN) and by changes in pH within the system. They suffer from drawbacks such as poor photocatalytic molecular oxygen activation ability, poor selectivity for active species formation, narrow pH application range, and low removal rate of organic pollutants. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a homogeneous-heterogeneous dual-junction coupled photocatalyst.

[0006] Another objective of this invention is to provide a method for preparing a homogeneous-heterogeneous dual-junction coupled photocatalyst.

[0007] Another object of the present invention is to provide the application of a homo-heterogeneous dual-junction coupled photocatalyst in the degradation of tetracycline.

[0008] The objective of this invention is achieved through the following technical solutions.

[0009] A method for preparing a homogeneous-heterogeneous dual-junction coupled photocatalyst includes the following steps:

[0010] Step 1: Mix carbon nitride (g-C3N4), lithium chloride (LiCl) and potassium chloride (KCl) evenly to obtain a mixed powder. Calcinate the mixed powder at 540-560℃ for 4-5 hours under an inert gas atmosphere. Cool, wash, and dry to obtain the precursor. The mass ratio of carbon nitride, lithium chloride, and potassium chloride is (1.8-2.2):(8.5-9.5):(10.5-11.5).

[0011] In step 1, melamine is calcined at 480–520°C for 3.5–4.5 h to obtain carbon nitride.

[0012] In step 1, the temperature is 5–10 °C / min. -1 The temperature is increased to T1 at a rate of 8–10 °C / min, and then from T1 at a rate of 8–10 °C / min. -1The temperature is increased at a rate to T2, where T1 = 480–520℃ and T2 = 540–560℃.

[0013] Step 2: Mix the precursor, ammonium chloride (NH4Cl) and sodium thiocyanate (NaSCN) evenly, grind them to obtain a mixture, calcine the mixture at 510-530℃ for 4-5 hours under an inert gas atmosphere, cool, wash and dry to obtain homogeneous carbon nitride.

[0014] In step 2, the ratio of the precursor, ammonium chloride, and sodium thiocyanate by mass is (0.8–1.2):(0.8–1.2):(1.8–2.2).

[0015] In step 2, the temperature is 2-3℃·min -1 The temperature is increased at a rate of 510–530°C.

[0016] In steps 1 and 2, the inert gas atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0017] Step 3: Disperse ferric chloride hexahydrate (FeCl3·6H2O) and sodium acetate (CH3COONa) in ethanol. Add H2O dropwise while stirring, and continue stirring until the sodium acetate dissolves to obtain a mixed solution. Add homojunction carbon nitride to the mixed solution and sonicate to obtain a dispersion. Heat the dispersion at 175-190℃ for 12-15 h, cool, wash, and dry to obtain a homo-heterojunction dual-junction coupled photocatalyst. The ratio of homojunction carbon nitride, ferric chloride hexahydrate, and sodium acetate by mass is (3-4):11:32.

[0018] In step 3, the preferred ratio of homogeneous carbon nitride, ferric chloride hexahydrate, and sodium acetate by mass is (3-3.3):11:32.

[0019] In step 3, the ratio of the mass fraction of ferric chloride hexahydrate, the volume fraction of H2O, and the volume fraction of ethanol is 1.1:2.8:(35-45), where the mass fraction is in g and the volume fraction is in mL.

[0020] In step 3, ferric chloride hexahydrate (FeCl3·6H2O) and sodium acetate (CH3COONa) are dispersed in ethanol by sonication for 40–60 min.

[0021] In step 3, the ultrasonication time after adding homogeneous carbon nitride to the mixed solution is 5-6 hours.

[0022] In steps 1 to 3, the washing involves washing with water and ethanol at least three times each.

[0023] In steps 1 to 3, the drying temperature is 60 to 70°C and the drying time is 10 to 14 hours.

[0024] The homogeneous-heterogeneous dual-junction coupled photocatalyst obtained by the above preparation method.

[0025] The application of the above-mentioned homo-heterogeneous dual-junction coupled photocatalyst in the degradation of tetracycline.

[0026] In the above technical solution, the homogeneous-heterogeneous dual-junction coupled photocatalyst promotes the selective generation of O2·O2 during the degradation of tetracycline. 2- .

[0027] In the above technical solution, the homogeneous-heterogeneous dual-junction coupled photocatalyst degrades tetracycline under light irradiation and oxygen introduction conditions.

[0028] In the above technical solution, the light wavelength is greater than 420nm.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The homogeneous-heterogeneous dual-junction coupled photocatalyst of the present invention exhibits superior photocatalytic oxygen activation performance, achieving a 99.8% removal rate of TC (tetracycline) within 20 min, with a degradation rate constant k of 0.1793 min. -1 .

[0031] 2. The homogeneous-heterogeneous dual-junction coupled photocatalyst of the present invention significantly broadens the applicable range of photocatalysts. In the pH range of 4.5 to 9.0, the removal rate of TC remains above 96%; in the pH range of 9.0 to 12.0, the removal rate of TC remains above 83%, and it is not affected by interfering ions. It can achieve efficient removal of organic pollutants, solve the problem that conventional heterojunctions are limited by the pH of the system, and greatly broaden the pH applicable range of photocatalysts, making them suitable for actual water bodies.

[0032] 3. The homo-heterojunction coupled photocatalyst of this invention possesses an ultra-strong built-in electric field, exhibiting superior charge carrier behavior. This significantly weakens the exciton effect, promotes charge carrier separation and efficient migration, and simultaneously achieves the directional migration of electrons and holes after exciton dissociation. This greatly accelerates O2 activation and achieves near 100% selective generation of O2. - This accelerates the degradation of TC, causing it to gradually degrade into non-toxic organic intermediates and eventually be mineralized. Attached Figure Description

[0033] Figure 1 XRD patterns of the homo-heterogeneous double-junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 3-4;

[0034] Figure 2 Image (a) is a transmission electron microscope (TEM) image of the homo-heterogeneous double-junction coupled photocatalyst prepared in Example 3. Figure 2 (b) is Figure 2 (a) is an enlarged view of the homojunction carbon nitride. Figure 2 (c) is Figure 2 Enlarged view of iron oxide in (a);

[0035] Figure 3 The FT-IR spectra of the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 1 and 3-5 are shown.

[0036] Figure 4 The images show surface potential measurements obtained using Kelvin probe force microscopy (KPFM), where (a) is the photocatalyst prepared in Comparative Example 4, (b) is the photocatalyst prepared in Comparative Example 3, and (c) is the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3.

[0037] Figure 5 The instantaneous photocurrent response (TPR) diagrams are shown for the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 1 and 3-5.

[0038] Figure 6 The photoluminescence (PL) spectra of the homo-heterogeneous double-junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 4 and 5 are shown.

[0039] Figure 7 The curves showing the intensity of the emission peak and temperature in the low-temperature steady-state spectrum are shown. (a) is the photocatalyst prepared in Comparative Example 5, and (b) is the homogeneous-heterogeneous double-junction coupled photocatalyst prepared in Example 3.

[0040] Figure 8 The removal rate and degradation rate constant of tetracycline by the homo-heterojunction coupled photocatalysts prepared in Examples 1-5;

[0041] Figure 9 The removal rate and degradation rate constant of tetracycline by the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 3-5;

[0042] Figure 10 The removal rates of tetracycline by the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 5 at different pH values;

[0043] Figure 11The photocatalyst prepared in Example 3 is shown to remove tetracycline under different interfering ions. Among them, (a) shows the removal effect of different concentrations of NO3. - The removal effect is shown in (b), which shows the removal effect of HCO3 at different concentrations. - The removal effect is shown in (c), which represents different concentrations of Cl. - The removal effect below;

[0044] Figure 12 The removal rate of tetracycline by the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 under different quenchers;

[0045] Figure 13 The removal rate of tetracycline by the photocatalyst prepared in Comparative Example 5 under different quenchers;

[0046] Figure 14 The electron paramagnetic resonance (EPR) spectra of the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 5 are shown, where (a) is the EPR spectrum of ·OH and (b) is the EPR spectrum of ·O2. - The electron paramagnetic resonance spectrum, (c) is 1 Electron paramagnetic resonance spectrum of O2;

[0047] Figure 15 This is a degradation route diagram for tetracycline;

[0048] Figure 16 for Figure 15 (a) Median lethal dose (LD50) and (b) mutagenicity of organic intermediates in fleas. Detailed Implementation

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0050] Examples 1-5

[0051] A method for preparing a homogeneous-heterogeneous dual-junction coupled photocatalyst includes the following steps:

[0052] Step 1: Place melamine in a crucible and heat it in a muffle furnace at 10°C / min. -1 The temperature was rapidly increased to 500℃ and calcined at 500℃ for 4 hours to obtain blocky carbon nitride. Carbon nitride, lithium chloride, and potassium chloride were mixed and ground in a mortar to obtain a uniformly mixed powder. Under a nitrogen atmosphere, the mixed powder was placed in a tube furnace and heated at 10℃·min⁻¹. -1The temperature was rapidly increased to 550℃ and calcined at 550℃ for 4 hours. After natural cooling to room temperature, the sample was washed three times each with water and ethanol, and dried in an oven at 60℃ for 12 hours. After drying, the sample was ground in a mortar to obtain the precursor, wherein the ratio of carbon nitride, lithium chloride and potassium chloride by mass parts was 2:9:11.

[0053] Step 2: Mix the precursor, ammonium chloride, and sodium thiocyanate thoroughly, grind them in a mortar to obtain a mixture, and place the mixture in a tube furnace under a nitrogen atmosphere at 2.5℃·min. -1 The temperature was rapidly increased to 520℃ and calcined at 520℃ for 4 hours. After natural cooling to room temperature, the mixture was washed three times each with water and ethanol, and then dried in an oven at 60℃ for 12 hours. After drying, the mixture was ground in a mortar to obtain homogeneous carbon nitride, wherein the ratio of the precursor, ammonium chloride, and sodium thiocyanate by mass was 1:1:2.

[0054] Step 3: Disperse ferric chloride hexahydrate and sodium acetate in ethanol by sonication for 60 min. Add H2O dropwise while stirring, and continue stirring for 30 min until sodium acetate dissolves to obtain a mixed solution. Add homojunction carbon nitride to the mixed solution and sonicate for 6 h to obtain a dispersion. Heat the dispersion in an oven at 180℃ for 12 h, cool naturally to room temperature, wash three times each with water and ethanol, dry in an oven at 60℃ for 12 h, cool naturally to room temperature, and grind in a mortar to obtain a homo-heterojunction coupled photocatalyst. The mass ratio of homojunction carbon nitride, ferric chloride hexahydrate, and sodium acetate is W, and the mass ratio of ferric chloride hexahydrate to the volume ratio of H2O to ethanol is 1.1:2.8:40. The mass fraction is in g and the volume fraction is in mL.

[0055] The W and numbering of the homo-heterogeneous dual-junction coupled photocatalysts prepared in Examples 1 to 5 are shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] Comparative Example 1

[0060] A photocatalyst (number: CN) is carbon nitride, as described in Example 1.

[0061] Comparative Example 2

[0062] A photocatalyst (number: HCN) is used as the precursor in Example 1. The photocatalyst prepared in Comparative Example 2 is used as a precursor to synthesize the photocatalyst prepared in Comparative Example 3.

[0063] Comparative Example 3

[0064] A photocatalyst (number: HCCN) is the homojunction carbon nitride (carbon nitride homojunction) in Example 1.

[0065] Comparative Example 4

[0066] A method for preparing a photocatalyst (No. FO) includes the following steps:

[0067] Ferric chloride hexahydrate and sodium acetate were dispersed in ethanol by sonication for 60 min. H2O was added dropwise while stirring, and stirring was continued for 30 min until the sodium acetate dissolved to obtain a dispersion. The dispersion was heated in an oven at 180℃ for 12 h, and then naturally cooled to room temperature. It was washed three times each with water and ethanol, dried in an oven at 60℃ for 12 h, and then naturally cooled to room temperature. It was then ground in a mortar to obtain the photocatalyst (number: FO). The mass ratio of ferric chloride hexahydrate to sodium acetate was 11:32, and the mass ratio of ferric chloride hexahydrate to H2O to ethanol was 1.1:2.8:40. The mass parts are in g and the volume parts are in mL.

[0068] Comparative Example 5

[0069] A method for preparing a photocatalyst (No. FO / CN) is basically the same as that for Comparative Example 4, except for the dispersion. The dispersion for Comparative Example 5 is prepared by dispersing ferric chloride hexahydrate and sodium acetate in ethanol, adding H2O dropwise while stirring, and continuing to stir for 30 min until the sodium acetate dissolves to obtain a mixed solution. Carbon nitride prepared in Comparative Example 1 is then added to the mixed solution and sonicated for 6 h to obtain a dispersion. The mass ratio of carbon nitride, ferric chloride hexahydrate, and sodium acetate prepared in Comparative Example 1 is 3.228:11:32.

[0070] Figure 1 The XRD patterns of the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 3-4 are shown below. Figure 1 It can be seen that in the XRD pattern of the photocatalyst prepared in Comparative Example 3, a diffraction peak at 26.6° corresponds to the (002) crystal plane of the homojunction carbon nitride. In the XRD pattern of the photocatalyst (iron oxide) prepared in Comparative Example 4, diffraction peaks at 33.1° and 35.6° correspond to the (104) and (110) crystal planes of iron oxide, respectively. The diffraction peaks in the XRD pattern of the homojunction-heterojunction coupled photocatalyst prepared in Example 3 correspond to the homojunction carbon nitride and iron oxide, respectively. Since the homojunction carbon nitride doping amount is low, the diffraction peak shape is not obvious.

[0071] Figure 2Image (a) is a transmission electron microscope (TEM) image of the homo-heterojunction coupled photocatalyst prepared in Example 3. Figure 2 As can be seen from (a), the TEM image of the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 shows clear interface boundaries and layered structures, indicating that the sheet-like iron oxide is constructed as a heterojunction on the sheet-like homojunction carbon nitride. Figure 2 (b) is Figure 2 A magnified view of the homojunction carbon nitride (circles) in (a). Figure 2 (c) is Figure 2 A magnified view of iron oxide (circles) in (a), by Figure 2 As shown in (b) and (c), the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 contains homojunction carbon nitride with a crystal plane of (002) and lattice fringes of 0.33 nm, as well as iron oxide with a crystal plane of (104) and lattice fringes of 0.26 nm. This is consistent with... Figure 1 The analysis is consistent with the results, therefore, the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 was successfully prepared.

[0072] Figure 3 The FT-IR spectra of the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 1 and 3-5 are shown below. Figure 3 It can be seen that in the FT-IR spectrum of the homo-heterojunction coupled photocatalyst prepared in Example 3, at 2167.5 cm⁻¹... -1 The characteristic peak of the cyano group is present at 535.7 cm⁻¹. -1 and 457.8cm -1 The presence of characteristic Fe-O peaks further confirms the introduction of homojunction carbon nitride and iron oxide.

[0073] The surface potentials of the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 3 and 4 were detected using a Kelvin probe microscope. The results are as follows: Figure 4 As shown, by Figure 4 As shown in (a), the surface potential of the photocatalyst prepared in Comparative Example 4 is 36 mV. Figure 4 As shown in (b), the surface potential of the photocatalyst prepared in Comparative Example 3 is 56 mV. Figure 4 As shown in (c), the surface potential of the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 is 323mV, indicating that the heterojunction interface of the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 generates a strong surface potential and has an ultra-strong built-in electric field, which is beneficial to the directional migration of charge carriers.

[0074] Figure 5The transient photocurrent response (TPR) diagrams are shown for the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 1 and 3-5. Figure 5 It can be seen that the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 exhibits a transient photocurrent response that is far superior to that of the photocatalysts prepared in Comparative Examples 1 and 3-5, indicating that it has the highest photogenerated electron-hole separation efficiency.

[0075] Figure 6 The photoluminescence (PL) spectra of the homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 4 and 5 are shown below. Figure 6 It can be seen that the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 has the lowest spectral intensity, indicating that its photogenerated electrons and holes are not easily recombine. Figure 5 The TPR results remained consistent.

[0076] Figure 7 The figures show the fitting curves of the emission peak intensity and temperature of the low-temperature steady-state spectrum (inset shows the low-temperature steady-state spectrum), where (a) is the photocatalyst prepared in Comparative Example 5, and (b) is the homo-heterojunction coupled photocatalyst prepared in Example 3. The fitting curves were obtained by fitting the low-temperature steady-state spectrum in the inset, and the exciton binding energy (E) was calculated. b The exciton binding energy of the photocatalyst prepared in Comparative Example 5 was 62.4 meV, while that of the homo-heterojunction coupled photocatalyst prepared in Example 3 was 50.5 meV. The results indicate that the exciton binding energy of the homo-heterojunction coupled photocatalyst prepared in Example 3 was significantly higher than that of the photocatalyst prepared in Comparative Example 5. b The lower values ​​confirm that the homo-heterogeneous dual-junction coupling strategy effectively promotes exciton dissociation, significantly weakens the exciton effect, and facilitates the separation of photogenerated electrons and holes.

[0077] Example 6

[0078] Photocatalytic molecular oxygen activation experiment: 10 mg of catalyst was added to 50 mL of tetracycline solution and sonicated for 2 min to disperse it evenly, obtaining the test solution. O2 was continuously introduced into the test solution through a gas delivery tube at room temperature (20–25 °C), and the solution was stirred in the dark for 10 min to reach adsorption-desorption equilibrium. After adsorption-desorption equilibrium was reached, the solution was then subjected to a light intensity of 0.8 W / m². 2 The solution was stirred for 20 minutes under irradiation with a 300W xenon lamp (with a filter installed to ensure a wavelength greater than 420nm) (O2 was continuously introduced during xenon lamp irradiation). After stirring for 20 minutes, 1.5 mL of the test solution was taken, filtered through a 0.22 μm filter membrane, and the tetracycline concentration was tested. The removal rate was calculated, and the results are as follows: Figure 8 , Figure 9As shown in Table 2, the catalyst is one of the homo-heterogeneous dual-junction coupled photocatalysts prepared in Examples 1-5 and the photocatalysts prepared in Comparative Examples 3-5. The tetracycline solution is a mixture of tetracycline (TC) and water, and the initial concentration of tetracycline in the tetracycline solution is 20 mg·L⁻¹. -1 The pH of the tetracycline solution is 7.0.

[0079] Depend on Figure 8 , Figure 9 As shown in Table 2, the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 had the highest removal rate of 99.8%, and its degradation rate constant (k) was 0.1793 min. -1 The degradation rate constant of the photocatalyst prepared in Comparative Example 3 is 46 times that of the photocatalyst prepared in Comparative Example 4, 9 times that of the photocatalyst prepared in Comparative Example 5, and 12 times that of the photocatalyst prepared in Comparative Example 5. This shows that the homogeneous-heterogeneous dual-junction coupling strategy of the present invention achieves super-strong charge carrier separation and thus realizes rapid degradation of TC.

[0080] Table 2

[0081]

[0082]

[0083] Example 7

[0084] The homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 5 were used as "catalysts" to perform the photocatalytic molecular oxygen activation experiment in Example 6 with tetracycline solutions of different pH values. The pH values ​​of the tetracycline solutions were 3.5, 4.5, 7.0, 9.0, 11.0, and 12.0, respectively. The pH was adjusted by adding 0.05M dilute sulfuric acid or 0.05M sodium hydroxide aqueous solution. The test results are as follows: Figure 10 As shown, by Figure 10 It can be seen that, within the pH range of 3.5–12.0, the photocatalyst prepared in Comparative Example 5 exhibited fluctuating and unstable removal rates for tetracycline, consistently maintaining low removal rates. In contrast, the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 maintained a degradation effect of over 83% within the pH range of 4.5–12.0, with the removal rate reaching its maximum of 99.8% at pH 7.0. Therefore, it is suitable for practical wastewater applications.

[0085] Example 8

[0086] Control group: Following the photocatalytic molecular oxygen activation experiment in Example 6, the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 was used as the "catalyst" to degrade tetracycline solution (pH = 7.0). After xenon lamp irradiation, 1.5 mL of the test solution was taken every 4 minutes to test the tetracycline concentration. The removal effect was as follows: Figure 11 As indicated by "0 mmol / L", the removal rate was 99.8% after stirring for 20 minutes under xenon lamp irradiation.

[0087] Interfering ion group: basically the same as the control group, except for the test solution. 10 mg of catalyst and sodium salt were added to 50 mL of tetracycline solution and sonicated for 2 min to disperse them evenly, thus obtaining the test solution. The sodium salt was sodium nitrate (which releases NO3 in the test solution). - As interfering ions), sodium bicarbonate (which releases HCO3- in the test solution). - (as interfering ions) and sodium chloride (Cl- is released in the test solution). - As one of the interfering ions, the initial concentrations of sodium salt in the test solution were 1 mmol / L, 3 mmol / L, and 5 mmol / L. The removal rates after 20 minutes of stirring under xenon lamp irradiation with different sodium salts are shown in Table 3. The removal effect of sodium nitrate as the sodium salt is as follows: Figure 11 As shown in (a), the removal effect of sodium bicarbonate as the sodium salt is as follows: Figure 11 As shown in (b), the removal effect of sodium chloride as the sodium salt is as follows: Figure 11 As shown in (c).

[0088] From Table 3 and Figure 11 It can be seen that, in the presence of interfering ions, the removal efficiency of tetracycline by the homo-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 did not decrease significantly, indicating that it has strong anti-interference ability and wide applicability.

[0089] Table 3

[0090]

[0091]

[0092] Example 9

[0093] Radical-free quenching experiment: The homo-heterojunction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 5 were used as "catalysts" to degrade tetracycline solution (pH = 7.0) according to the "photocatalytic molecular oxygen activation experiment in Example 6". The test results of the homo-heterojunction coupled photocatalyst prepared in Example 3 are as follows: Figure 12 As shown in the figure, “0mM”, the test results of the photocatalyst prepared in Comparative Example 5 are as follows. Figure 13 As shown in "0mM";

[0094] Free radical quenching experiment: This is essentially the same as the free radical-free quenching experiment, except for the test solution. 10 mg of catalyst and quencher are added to 50 mL of tetracycline solution and sonicated for 2 min to disperse them evenly, yielding the test solution. The quenchers can be p-benzoquinone, L-histidine, disodium ethylenediaminetetraacetate, methanol, isopropanol, or catalase. When the quencher is p-benzoquinone or L-histidine, the initial concentration of the quencher in the test solution is 1.5 mM. When the quencher is disodium EDTA at 3.0 mM and 4.5 mM, the initial concentrations of the quencher in the test solution are 0.1 mM, 0.2 mM, and 0.3 mM, respectively. When the quencher is methanol or isopropanol, the initial concentrations of the quencher in the test solution are 0.5 mM, 1.0 mM, and 1.5 mM, respectively. When the quencher is catalase, the initial concentrations of the quencher in the test solution are 2.0 mM, 4.0 mM, and 8.0 mM, respectively.

[0095] By quenching superoxide radicals (·O2) with benzoquinone - L-histidine quenches singlet oxygen ( 1 O2), disodium ethylenediaminetetraacetate quenches holes (h) + The active substances produced by the catalyst are analyzed by quenching hydroxyl radicals (·OH) on the surface of the test solution and catalyst with methanol, quenching hydroxyl radicals (·OH) in the test solution with isopropanol, and quenching hydrogen peroxide (H2O2) with catalase. Figure 13 It can be seen that with the increase of the concentration of the added quencher, the tetracycline removal rate of the photocatalyst prepared by the combination of p-benzoquinone, L-histidine, disodium ethylenediaminetetraacetate, methanol, and catalase inhibition in Comparative Example 5 gradually increased, indicating that O2 - , 1 O2, h + The ·OH and H2O2 on the catalyst surface participate in the degradation process of tetracycline by the photocatalyst prepared in Comparative Example 5.

[0096] Depend on Figure 12 It can be seen that p-benzoquinone inhibited the tetracycline removal rate of the homo-heterojunction photocatalyst prepared in Example 3 by 92.1%, disodium ethylenediaminetetraacetate inhibited the tetracycline removal rate of the homo-heterojunction photocatalyst prepared in Example 3 by 94.3%, and isopropanol inhibited the tetracycline removal rate of the homo-heterojunction photocatalyst prepared in Example 3 by 27.2%, while L-histidine, methanol, and isopropanol all inhibited the tetracycline removal rate by 0%, indicating that... 2- and h + It plays a major role.

[0097] Example 10

[0098] During the degradation process of photocatalysts, h exists +It is inevitable that, therefore, compared with the photocatalyst prepared in Comparative Example 5, the homo-heterojunction coupled photocatalyst prepared in Example 3 using the homo-heterojunction coupling strategy promotes the development of O2. 2- The selective generation of oxygen promotes the degradation of TC. To further verify whether oxygen can selectively generate a single active species, the following experiment was set up.

[0099] ·O2 - Experiment: 10 mg of catalyst was added to 50 mL of water and sonicated for 2 min to disperse it evenly, obtaining a catalyst solution. O2 was continuously introduced into the catalyst solution through a gas delivery tube at room temperature (20–25 °C), and the solution was stirred for 10 min in the dark to reach adsorption-desorption equilibrium. After adsorption-desorption equilibrium was reached, the solution was further stirred under a light intensity of 0.8 W / m². 2 The catalyst solution was stirred for 20 minutes under irradiation with a 300W xenon lamp (with a filter installed to ensure a wavelength greater than 420nm) (O2 was continuously introduced during xenon lamp irradiation). After stirring for 20 minutes, 200μL of the catalyst solution was mixed with 100μL of scavenging agent and 2mL of methanol to obtain the detection solution. Its electron paramagnetic resonance spectrum was then detected. The catalyst was the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3. Figure 14 (b) "Example 3 + O2 + Light" and the photocatalyst prepared in Comparative Example 5 ( Figure 14 In (b) of the above, one of the following is used: FO / CN+O2+light irradiation. The scavenging agent is 5,5-dimethyl-1-pyrrolidone-N-oxide (DMPO). The detection results are as follows: Figure 14 As shown in (b)

[0100] ·OH experiment: Similar to the above ·O2 experiment - The experiments were basically the same, the difference being in the detection solution. After stirring for 20 min, 200 μL of catalyst solution was mixed with 100 μL of scavenging agent and 2 mL of water to obtain the detection solution. The scavenging agent was 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO). The results are as follows: Figure 14 As shown in (a), Figure 14 In (a), "Example 3 + O2 + Light Irradiation" represents the catalyst as in Example 3. Figure 14 In (a), “FO / CN+O2+light” represents the catalyst as in Comparative Example 5.

[0101] 1 O2 Experiment: This experiment is basically the same as the ·OH experiment described above, except for the trapping agent. After stirring for 20 minutes, 200 μL of catalyst solution was mixed with 20 mg of trapping agent and 2 mL of water to obtain the detection solution. The trapping agent was 2,2,6,6-tetramethylpiperidine oxide (TEMP). The results are as follows: Figure 14 As shown in (c), Figure 14In (c), "Example 3 + O2 + Light Irradiation" represents that the catalyst is Example 3. Figure 14 In (c), “FO / CN+O2+light” represents the catalyst as in Comparative Example 5.

[0102] Depend on Figure 14 It can be seen that the test solution of the photocatalyst prepared in Comparative Example 5 contains hydroxyl radicals (·OH) and superoxide radicals (·O2). - ) and singlet oxygen ( 1 Of the three reactive oxygen species (O2), only the superoxide radical signal peak was observed in the electron paramagnetic resonance spectrum of the homo-heterojunction coupled photocatalyst prepared in Example 3. This proves that the homo-heterojunction coupled photocatalyst prepared in Example 3 achieves selective generation of superoxide radicals. It also further shows that the homo-heterojunction coupled photocatalyst prepared in Example 3 has an extremely high charge carrier density on the catalyst surface during the photocatalytic activation of oxygen, that is, it achieves efficient separation of photogenerated electrons and holes.

[0103] Example 11

[0104] The homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3 was used as a "catalyst" to perform the photocatalytic molecular oxygen activation experiment in tetracycline solution (pH = 7.0) as described in Example 6. After xenon lamp irradiation, 3 mL of the test solution was taken every 5 min, and the presence of organic intermediates (P1-P14) in the test solution was measured using high performance liquid chromatography-mass spectrometry (LC-MS). The organic intermediates were analyzed, and the TC degradation route was finally obtained, as follows: Figure 15 As shown, by Figure 15 It can be seen that, in the process of tetracycline degradation by the homogeneous-heterogeneous dual-junction coupled photocatalyst prepared in Example 3, it is speculated that its degradation route is divided into three types ( Figure 15 In Pathway I, Pathway II, and Pathway III, tetracycline gradually degrades into smaller molecules and is eventually mineralized.

[0105] The toxicity and mutagenicity of each organic intermediate in the three degradation routes were analyzed using TEST toxicity analysis software. The results were then integrated, as follows: Figure 16 As shown, the results indicate that with the degradation of tetracycline by the homo-heterojunctional double-junctional photocatalyst prepared in Example 3, the half-lethal dose of the organic intermediates generated by the degradation of tetracycline gradually increases, the overall mutagenicity tends to be negative, the toxicity gradually decreases, and finally it is degraded into carbon dioxide and water, proving that the homo-heterojunctional double-junctional photocatalyst prepared in Example 3 has excellent detoxification ability.

[0106] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. The application of a homogeneous-heterogeneous dual-junction coupled photocatalyst in the degradation of tetracycline, characterized in that, The homo-heterojunction coupled photocatalyst degrades tetracycline under light irradiation and oxygen introduction conditions. The preparation method of the homo-heterojunction coupled photocatalyst includes the following steps: Step 1: Mix carbon nitride, lithium chloride, and potassium chloride evenly to obtain a mixed powder. Calcinate the mixed powder at 540~560℃ for 4~5 hours under an inert gas atmosphere. Cool, wash, and dry to obtain the precursor. The mass ratio of carbon nitride, lithium chloride, and potassium chloride is (1.8~2.2):(8.5~9.5):(10.5~11.5). Step 2: Mix the precursor, ammonium chloride and sodium thiocyanate evenly, grind them to obtain a mixture, calcine the mixture at 510~530℃ for 4~5h under an inert gas atmosphere, cool, wash and dry to obtain homogeneous carbon nitride. Step 3: Disperse ferric chloride hexahydrate and sodium acetate in ethanol. Add H2O dropwise while stirring, and continue stirring until sodium acetate dissolves to obtain a mixed solution. Add homojunction carbon nitride to the mixed solution and sonicate to obtain a dispersion. Heat the dispersion at 175~190℃ for 12~15h, cool, wash, and dry to obtain a homo-heterojunction coupled photocatalyst. The ratio of homojunction carbon nitride, ferric chloride hexahydrate, and sodium acetate by mass is (3~3.3):11:

32.

2. The application according to claim 1, characterized in that, Melamine was calcined at 480-520°C for 3.5-4.5 hours to obtain the carbon nitride.

3. The application according to claim 1, characterized in that, The ratio of precursor, ammonium chloride and sodium thiocyanate by mass parts is (0.8~1.2):(0.8~1.2):(1.8~2.2).

4. The application according to claim 1, characterized in that, The ratio of the mass fraction of ferric chloride hexahydrate, the volume fraction of H2O, and the volume fraction of ethanol is 1.1:2.8:(35~45), where the mass fraction is in g and the volume fraction is in mL.

5. The application according to claim 1, characterized in that, The homo-heterogeneous dual-junction coupled photocatalyst comprises iron oxide and homojunction carbon nitride, which together form a heterojunction.

6. The application according to claim 1, characterized in that, The homo-heterogeneous dual-junction photocatalyst promoted the selective generation of O2 and O2 during the degradation of tetracycline. 2- .

7. The application according to claim 1, characterized in that, The wavelength of the light is greater than 420nm.

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