Homogeneous-heterogeneous double-junction coupled photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a homogeneous-heterogeneous double-junction coupled photocatalyst as well as a preparation method and application thereof. The preparation method of the homogeneous-heterogeneous double-junction coupled photocatalyst comprises the following steps: mixing carbon nitride, lithium chloride and potassium chloride to obtain mixed powder, calcining the mixed powder, cooling, washing and drying to obtain a precursor; mixing the precursor, ammonium chloride and sodium thiocyanate, grinding to obtain a mixture, calcining the mixture, cooling, washing, and drying to obtain homojunction carbon nitride; ferric trichloride hexahydrate and sodium acetate are dispersed in ethyl alcohol, H2O is dropwise added, a mixed solution is obtained, homogeneous-junction carbon nitride is added into the mixed solution and subjected to ultrasonic treatment, dispersion liquid is obtained, the dispersion liquid is heated, cooled, washed and dried, the homogeneous-heterogeneous double-junction coupled photocatalyst is obtained, the TC removal rate of the homogeneous-heterogeneous double-junction coupled photocatalyst within 20 min is 99.8%, and the TC removal rate of the homogeneous-heterogeneous double-junction coupled photocatalyst within 20 min is 99.8%. The problem that heterojunction is limited by the pH value is solved, and the pH application range of the photocatalyst is widened.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and in particular relates to a homogeneous-heterogeneous double junction coupled photocatalyst and a preparation method and application thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, the discharge of organic wastewater is becoming increasingly serious. In particular, various pollutants from pharmaceuticals, textiles, agriculture and daily life have caused organic wastewater to contain ingredients such as antibiotics, dyes, endocrine disruptors and personal care products, making it highly toxic and difficult to degrade, seriously affecting water quality and ecosystems. The presence of pollutants not only aggravates water pollution, but may also lead to the emergence of antibiotic-resistant bacteria, threatening public health. At the same time, these pollutants have a negative impact on the growth and reproduction of aquatic organisms, destroy the ecological balance, and may even affect human reproductive health. Therefore, it is urgent to protect water resources and ecosystems, maintain human health and safety, and achieve effective treatment of organic wastewater.

[0003] Advanced oxidation processes (AOPs) are widely recognized for their ease of operation, rapid degradation and mineralization. However, conventional AOPs have disadvantages such as high energy consumption and large dosage of reagents. Photocatalytic molecular oxygen activation technology, as a sustainable and environmentally friendly AOP, uses naturally occurring oxygen molecules as an oxidant to convert oxygen into reactive oxygen species (ROS) groups under the drive of solar energy, thereby degrading pollutants and purifying organic wastewater. It has the advantages of being green and requiring low dosage of reagents. Semiconductor carbon nitride (gC 3 N 4 ) 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 poor catalytic efficiency.

[0004] Although there are literatures (Synergistic enhancement of photocatalytic molecularoxygen activation by nitrogen defect and interfacial photoelectron transferover Z-schemeα-Fe 2 O 3 / gC 3 N 4heterojunction, Applied Catalysis B: Environmental, 335 (2023) 122890) reported that the construction of heterojunctions (such as iron oxide / carbon nitride heterojunctions, manganese oxide / carbon nitride heterojunctions, and indium oxide / carbon nitride heterojunctions) can improve the dissociation of excitons. However, this type of heterojunction is limited by the weak internal electric field of traditional bulk carbon nitride (CN) and the changes in the pH value in the system. It has the disadvantages of poor photocatalytic molecular oxygen activation ability, poor selectivity for the generation of active species, narrow pH application range, and low removal rate of organic pollutants. Summary of the invention

[0005] In view of the deficiencies of the prior art, an object of the present invention is to provide a homogeneous-heterogeneous double junction coupled photocatalyst.

[0006] Another object of the present invention is to provide a method for preparing a homogeneous-heterogeneous double junction coupled photocatalyst.

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

[0008] The purpose of the present invention is achieved through the following technical solutions.

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

[0010] Step 1: Carbon nitride (gC 3 N 4 ), lithium chloride (LiCl) and potassium chloride (KCl) are uniformly mixed to obtain a mixed powder, and the mixed powder is calcined at 540-560°C for 4-5h under an inert gas atmosphere, cooled, washed and dried to obtain a precursor. The ratio of carbon nitride, lithium chloride and potassium chloride is (1.8-2.2): (8.5-9.5): (10.5-11.5) by mass.

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

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

[0013] Step 2: Precursor, ammonium chloride (NH 4Cl) and sodium thiocyanate (NaSCN) are uniformly mixed and ground to obtain a mixture, and the mixture is calcined at 510-530° C. for 4-5 hours under an inert gas atmosphere, cooled, washed, and dried to obtain homogeneous carbon nitride.

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

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

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

[0017] Step 3: Hexahydrate ferric chloride (FeCl 3 6H 2 O) and sodium acetate (CH 3 COONa) was dispersed in ethanol and H 2 O, continue stirring until the sodium acetate is dissolved to obtain a mixed solution, add homojunction carbon nitride to the mixed solution, ultrasonicate to obtain a dispersion, heat the dispersion at 175-190° C. for 12-15 h, cool, wash, and dry to obtain a homo-heterojunction double junction coupled photocatalyst, wherein the ratio of homo-junction carbon nitride, ferric chloride hexahydrate, and sodium acetate is (3-4):11:32 by mass.

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

[0019] In step 3, the mass fraction of ferric chloride hexahydrate, H 2 The ratio of the volume fraction of O to the volume fraction of ethanol is 1.1:2.8:(35-45), the unit of the mass fraction is g, and the unit of the volume fraction is mL.

[0020] In step 3, ferric chloride hexahydrate (FeCl 3 6H 2 O) and sodium acetate (CH 3 COONa) was dispersed in ethanol.

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

[0022] In steps 1 to 3, the washing is performed by washing with water and ethanol at least 3 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 double junction coupled photocatalyst obtained by the above preparation method.

[0025] The application of the above homogeneous-heterogeneous double junction coupled photocatalyst in the degradation of tetracycline.

[0026] In the above technical solution, the homogeneous-heterogeneous double junction coupled photocatalyst promotes O in the degradation of tetracycline. 2 Selective generation of O 2- .

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

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

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

[0030] 1. The homogeneous-heterogeneous double junction coupled photocatalyst of the present invention exhibits super strong photocatalytic oxygen activation performance. Within 20 minutes, the removal rate of TC (tetracycline) is 99.8%, and its degradation rate constant k is 0.1793min -1 .

[0031] 2. The homogeneous-heterogeneous double junction coupled photocatalyst of the present invention greatly broadens the application scope of the photocatalyst. In the range of pH = 4.5 to 9.0, the removal rate of TC is maintained at more than 96%; in the range of pH = 9.0 to 12.0, the removal rate of TC is maintained at more than 83%, and is not affected by interfering ions, and can achieve efficient removal of organic pollutants. It solves the problem that conventional heterojunctions are limited by the influence of the system's pH, greatly broadens the pH application range of the photocatalyst, and is suitable for actual water bodies.

[0032] 3. The homogeneous-heterogeneous double junction coupled photocatalyst of the present invention has a super strong built-in electric field, exhibits super strong charge carrier behavior, greatly weakens the exciton effect, promotes charge-carrier separation and efficient migration, and realizes the directional migration of electrons and holes after exciton dissociation, greatly accelerating the O 2 The activation of O 2 Nearly 100% selective generation of O 2 - This accelerates the degradation of TC, causing it to gradually degrade into non-toxic organic intermediates and eventually be mineralized. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 XRD spectra of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Examples 3 to 4;

[0034] Figure 2 (a) is a transmission electron microscope (TEM) image of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3, Figure 2 (b) is Figure 2 A magnified image of the homojunction carbon nitride in (a). Figure 2 (c) is Figure 2 Magnified image of iron oxide in (a);

[0035] Figure 3 FT-IR spectra of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Example 1 and Comparative Examples 3 to 5;

[0036] Figure 4 The Kelvin probe force microscope (KPFM) surface potential test diagram, wherein (a) is the photocatalyst prepared in Comparative Example 4, (b) is the photocatalyst prepared in Comparative Example 3, and (c) is the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3;

[0037] Figure 5 The photocurrent transient response (TPR) graphs of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Example 1 and Comparative Examples 3 to 5;

[0038] Figure 6 Photoluminescence spectra (PL) of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Examples 4 to 5;

[0039] Figure 7 is the fitting curve of the luminescence peak intensity and temperature of the low-temperature steady-state spectrum, wherein (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 homogeneous-heterogeneous double junction coupled photocatalyst prepared in Examples 1 to 5;

[0041] Fig. 9 The removal rate and degradation rate constant of tetracycline by the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Examples 3 to 5;

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

[0043] Fig.11 The removal effect of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 on tetracycline under different interfering ions, wherein (a) is different concentrations of NO 3 - (b) shows the removal effect under different concentrations of HCO 3 - (c) shows the removal effect of different concentrations of Cl - The removal effect under

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

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

[0046] Fig.14 The electron paramagnetic resonance spectra of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 5 are shown in Figure 1, where (a) is the electron paramagnetic resonance spectrum of ·OH, and (b) is the electron paramagnetic resonance spectrum of ·O 2 - The electron paramagnetic resonance spectrum of 1 O 2 Electron paramagnetic resonance spectrum of

[0047] Fig.15 It is the degradation roadmap of tetracycline;

[0048] Fig.16 for Fig.15 (a) Daphnia magna LD50 and (b) mutagenicity of organic intermediates. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0050] Embodiments 1 to 5

[0051] A method for preparing a homogeneous-heterogeneous double junction coupled photocatalyst comprises 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 raised to 500°C at a rate and calcined at 500°C for 4 h 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. The mixed powder was placed in a tube furnace under a nitrogen atmosphere and heated at 10°C min -1The temperature was raised to 550°C at a rate and calcined at 550°C for 4 hours, naturally cooled to room temperature, washed with water and ethanol for 3 times each, dried in an oven at 60°C for 12 hours, and ground in a mortar after drying to obtain a precursor, in which the ratio of carbon nitride, lithium chloride and potassium chloride was 2:9:11 by mass.

[0053] Step 2: The precursor, ammonium chloride and sodium thiocyanate are mixed evenly, ground in a mortar to obtain a mixture, and the mixture is placed in a tube furnace under a nitrogen atmosphere at 2.5°C·min -1 The temperature was raised to 520°C at a rate and calcined at 520°C for 4 hours, then naturally cooled to room temperature, washed with water and ethanol for 3 times each, dried in an oven at 60°C for 12 hours, and ground in a mortar after drying to obtain homogeneous carbon nitride, wherein the ratio of the precursor, ammonium chloride and sodium thiocyanate was 1:1:2 by mass.

[0054] Step 3: Disperse ferric chloride hexahydrate and sodium acetate in ethanol by ultrasonication for 60 min, and add H 2 O, continue stirring for 30 minutes until the sodium acetate is dissolved to obtain a mixed solution, add homojunction carbon nitride to the mixed solution, ultrasonicate for 6 hours to obtain a dispersion, heat the dispersion in an oven at 180°C for 12 hours, cool naturally to room temperature, wash with water and ethanol three times each, dry in an oven at 60°C for 12 hours, cool naturally to room temperature, and grind in a mortar to obtain a homogeneous-heterogeneous double junction coupled photocatalyst, wherein, by weight, the ratio of homojunction carbon nitride, ferric chloride hexahydrate, and sodium acetate is W, the weight percentage of ferric chloride hexahydrate, H 2 The ratio of the volume fraction of O to the volume fraction of ethanol is 1.1:2.8:40. The unit of mass fraction is g, and the unit of volume fraction is mL.

[0055] The W and serial numbers of the homogeneous-heterogeneous double 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 (code: CN), which is the carbon nitride in Example 1.

[0061] Comparative Example 2

[0062] A photocatalyst (code: HCN) is 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 (code: HCCN) is the homojunction carbon nitride (carbon nitride homojunction) in Example 1.

[0065] Comparative Example 4

[0066] A method for preparing a photocatalyst (code: FO) comprises the following steps:

[0067] Ferric chloride hexahydrate and sodium acetate were dispersed in ethanol by ultrasonication for 60 min, and H 2 O, continue stirring for 30 minutes until sodium acetate is dissolved to obtain a dispersion, heat the dispersion in an oven at 180°C for 12 hours, cool naturally to room temperature, wash with water and ethanol three times each, dry in an oven at 60°C for 12 hours, cool naturally to room temperature, grind in a mortar to obtain a photocatalyst (No.: FO), wherein the ratio of ferric chloride hexahydrate to sodium acetate is 11:32 by mass, the mass fractions of ferric chloride hexahydrate, H 2 The ratio of the volume fraction of O to the volume fraction of ethanol is 1.1:2.8:40. The unit of mass fraction is g, and the unit of volume fraction is mL.

[0068] Comparative Example 5

[0069] A method for preparing a photocatalyst (number: FO / CN) is basically the same as that of comparative example 4, except that the dispersion liquid of comparative example 5 is prepared by dispersing ferric chloride hexahydrate and sodium acetate in ethanol, adding H 2 O, continue stirring for 30 min until the sodium acetate is dissolved to obtain a mixed solution, add the carbon nitride prepared in Comparative Example 1 to the mixed solution, and ultrasonicate for 6 h to obtain a dispersion, wherein the ratio of the carbon nitride prepared in Comparative Example 1, ferric chloride hexahydrate and sodium acetate is 3.228:11:32 by mass.

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

[0071] Figure 2 (a) is a transmission electron microscope (TEM) image of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3. Figure 2 As can be seen from (a), there are clear interface boundaries and layered structures in the TEM image of the homo-heterojunction double junction coupled photocatalyst prepared in Example 3, indicating that the flake iron oxide constructs a heterojunction on the flake homojunction carbon nitride. Figure 2 (b) is Figure 2 Magnified image of homojunction carbon nitride (circle) in (a). Figure 2 (c) is Figure 2 Magnified image of iron oxide (circle) in (a), Figure 2 From (b) and (c), it can be seen that the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 contains homogeneous carbon nitride with a crystal plane of (002) and a lattice fringe of 0.33 nm, and also contains iron oxide with a crystal plane of (104) and a lattice fringe of 0.26 nm, which is consistent with Figure 1 The analysis is consistent with that of , therefore, the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 was successfully prepared.

[0072] Figure 3 FT-IR spectra of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalysts prepared in Comparative Example 1 and Comparative Examples 3 to 5. Figure 3 It can be seen that in the FT-IR spectrum of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3, at 2167.5 cm -1 There is a characteristic peak of cyano at 535.7 cm -1 and 457.8cm -1 The presence of characteristic peaks of Fe-O further verifies the introduction of homojunction carbon nitride and iron oxide.

[0073] The surface potential of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Examples 3 to 4 was detected by Kelvin probe microscopy. The detection results are as follows: Figure 4 As shown by Figure 4 From (a), it can be seen that the surface potential of the photocatalyst prepared in Comparative Example 4 is 36 mV. Figure 4 From (b), it can be seen that the surface potential of the photocatalyst prepared in Comparative Example 3 is 56 mV. Figure 4 It can be seen from (c) that the surface potential of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 is 323 mV, indicating that the heterojunction interface of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 produces a strong surface potential and an ultra-strong built-in electric field, which is conducive to the directional migration of charge carriers.

[0074] Figure 5The photocurrent transient response (TPR) diagram of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 1 and Comparative Examples 3 to 5 is shown in FIG. Figure 5 It can be seen that the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 exhibits a transient photocurrent response far exceeding that of the photocatalysts prepared in Comparative Example 1 and Comparative Examples 3 to 5, indicating that its photogenerated electron-hole separation efficiency is the highest.

[0075] Figure 6 The photoluminescence spectra (PL) of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Examples 4 to 5 are shown in FIG. Figure 6 It can be seen that the spectral intensity of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 is the lowest, indicating that its photogenerated electrons and holes are not easy to recombine. Figure 5 The TPR results remain consistent.

[0076] Figure 7 The fitting curves of the luminescence peak intensity and temperature of the low-temperature steady-state spectrum (the inset is the low-temperature steady-state spectrum), where (a) is the photocatalyst prepared in Comparative Example 5, and (b) is the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3. The fitting curves are obtained by fitting the low-temperature steady-state spectrum in the inset and the exciton binding energy (E b ), the exciton binding energy of the photocatalyst prepared in Comparative Example 5 is 62.4 meV, and the exciton binding energy of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 is 50.5 meV. The results show that the E b Even lower, it proves that the homo-heterojunction coupling strategy effectively promotes the dissociation of excitons, greatly weakens the exciton effect, and promotes 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 ultrasonicated for 2 min to make it dispersed evenly to obtain the test solution. At room temperature of 20-25 °C, oxygen was continuously introduced into the test solution through an air guide tube. 2 The adsorption-desorption equilibrium was reached by stirring for 10 min in the dark. After the adsorption-desorption equilibrium was reached, the adsorption-desorption equilibrium was reached under a light intensity of 0.8 W / m 2 Stir for 20 min under 300W xenon lamp (with filter installed to make the wavelength greater than 420nm) (while irradiating with xenon lamp, continue to pass O 2 ), after stirring for 20 minutes, take 1.5 mL of the test solution, filter it with a 0.22 μm filter membrane, test its tetracycline concentration, and calculate the removal rate. The results are as follows Figure 8 , Fig. 9As shown in Table 2, the catalyst is one of the homogeneous-heterogeneous double junction coupled photocatalysts prepared in Examples 1 to 5 and the photocatalysts prepared in Comparative Examples 3 to 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 , pH of tetracycline solution = 7.0.

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

[0080] Table 2

[0081]

[0082]

[0083] Example 7

[0084] The homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 and the photocatalyst prepared in Comparative Example 5 were used as "catalysts" to carry out the photocatalytic molecular oxygen activation experiment in Example 6 above on 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 values ​​were adjusted by 0.05M dilute sulfuric acid or 0.05M sodium hydroxide aqueous solution. The test results are shown in FIG. Fig.10 As shown by Fig.10 It can be seen that in the range of pH = 3.5 to 12.0, the removal rate of tetracycline by the photocatalyst prepared in Comparative Example 5 fluctuates and is unstable, and maintains a low removal rate, while the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 maintains a degradation effect of more than 83% in the range of pH = 4.5 to 12.0, and the removal rate reaches the maximum at pH = 7.0, which is 99.8%. Therefore, it is suitable for actual sewage applications.

[0085] Example 8

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

[0087] Interference ion group: basically the same as the control group, except that 10 mg of catalyst and sodium salt were put into 50 mL of tetracycline solution, and ultrasonicated for 2 min to disperse them evenly to obtain the test solution, wherein the sodium salt was sodium nitrate (NO was released in the test solution). 3 - as interfering ions), sodium bicarbonate (which releases HCO in the test solution 3 - as interfering ions) and sodium chloride (which releases Cl in the test solution - As one of the interfering ions), the initial concentrations of sodium salt in the test solution were 1mmol / L, 3mmol / L and 5mmol / L, respectively. The removal rates of different sodium salts after stirring for 20 minutes under xenon lamp irradiation are shown in Table 3. The removal effect of sodium salt as sodium nitrate is shown in Table 3. Fig.11 As shown in (a), the removal effect of sodium salt as sodium bicarbonate is as follows Fig.11 As shown in (b), the removal effect of sodium salt as sodium chloride is as follows Fig.11 as shown in (c).

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

[0089] Table 3

[0090]

[0091]

[0092] Example 9

[0093] Free radical quenching experiment: The homogeneous-heterogeneous double junction 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 homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 are as follows: Fig.12 As shown in "0 mM", the test results of the photocatalyst prepared in Comparative Example 5 are as follows Fig.13Indicated by “0 mM”;

[0094] Free radical quenching experiment: It is basically the same as the free radical quenching experiment, except that for the test solution, 10 mg of catalyst and quencher were put into 50 mL of tetracycline solution, and ultrasonicated for 2 min to disperse them evenly to obtain the test solution. The quenchers were p-benzoquinone, L-histidine, disodium ethylenediaminetetraacetate, methanol, isopropanol or catalase. When the quencher was p-benzoquinone or L-histidine, the initial concentrations of the quencher in the test solution were 1.5 mM, When the quencher is disodium ethylenediaminetetraacetate, 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 (·O 2 - ), L-histidine quenches singlet oxygen ( 1 O 2 ), disodium ethylenediaminetetraacetic acid quenches holes (h + ), methanol quenches the hydroxyl radicals (·OH) in the test solution and on the catalyst surface, isopropanol quenches the hydroxyl radicals (·OH) in the test solution, and catalase quenches hydrogen peroxide (H 2 O 2 ) to analyze the active substances produced by the catalyst, Fig.13 It can be seen that with the increase of the concentration of the quencher, the tetracycline removal rate of the photocatalyst prepared in Comparative Example 5 inhibited by benzoquinone, L-histidine, disodium ethylenediaminetetraacetate, methanol and catalase gradually increased, indicating that 2 - , 1 O 2 、h + , ·OH and H on the catalyst surface 2 O 2 The degradation process of tetracycline by the photocatalyst prepared in Comparative Example 5.

[0096] Depend on Fig.12 It can be seen that p-benzoquinone inhibited the tetracycline removal rate of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 by 92.1%, disodium ethylenediaminetetraacetate inhibited the tetracycline removal rate of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 by 94.3%, isopropanol inhibited the tetracycline removal rate of the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 by 27.2%, and L-histidine, methanol and isopropanol all inhibited their tetracycline removal rates by 0%, indicating that2- and h + Play a major role.

[0097] Example 10

[0098] In the degradation process of photocatalyst, there is + Therefore, compared with the photocatalyst prepared in Comparative Example 5, the homogeneous-heterogeneous double junction coupling photocatalyst prepared in Example 3 using the homogeneous-heterogeneous double junction coupling strategy promotes ·O 2- The selective generation of , which in turn promoted the degradation of TC. To further verify whether oxygen can selectively generate a single active species, the following experiment was set up.

[0099] ·O 2 - Experiment: 10 mg of catalyst was put into 50 mL of water and dispersed evenly under ultrasonic for 2 min to obtain a catalyst solution. O was continuously introduced into the catalyst solution through an air guide tube at room temperature of 20-25 °C. 2 The adsorption-desorption equilibrium was reached by stirring for 10 min in the dark. After the adsorption-desorption equilibrium was reached, the adsorption-desorption equilibrium was reached under a light intensity of 0.8 W / m 2 Stir for 20 min under 300W xenon lamp (with filter installed to make the wavelength greater than 420nm) (while irradiating with xenon lamp, continue to pass O 2 ), after stirring for 20 min, 200 μL of the catalyst solution was mixed with 100 μL of the capture agent and 2 mL of methanol to obtain a test solution, and its electron paramagnetic resonance spectrum was detected, wherein the catalyst was the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 ( Fig.14 (b) in "Example 3+0 2 + light") and the photocatalyst prepared in Comparative Example 5 ( Fig.14 (b) "FO / CN+O 2 + light"), the capture agent is 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and the detection results are as follows Fig.14 As shown in (b)

[0100] ·OH experiment: Same as above ·O 2 - The experiments were basically the same, except that the detection solution was stirred for 20 min, and 200 μL of the catalyst solution was mixed with 100 μL of the capture agent and 2 mL of water to obtain the detection solution. The capture agent was 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The results are shown in Fig.14 As shown in (a), Fig.14 (a) in "Example 3+0 2 + light" means the catalyst is Example 3, Fig.14 In (a) "FO / CN+O2 + light" means the catalyst is Comparative Example 5.

[0101] 1 O 2 Experiment: It is basically the same as the above ·OH experiment, except for the capture agent. After stirring for 20 minutes, 200 μL of the catalyst solution was mixed with 20 mg of the capture agent and 2 mL of water to obtain the test solution. The capture agent was 2,2,6,6-tetramethylpiperidinyl oxide (TEMP). The results are shown in Fig.14 As shown in (c), Fig.14 (c) in "Example 3+0 2 + light" means the catalyst is Example 3, Fig.14 (c) "FO / CN+O 2 + light" means the catalyst is Comparative Example 5.

[0102] Depend on Fig.14 It can be seen that the photocatalyst prepared in Comparative Example 5 contains hydroxyl radicals (·OH) and superoxide radicals (·O 2 - ) and singlet oxygen ( 1 O 2 ) three active oxygen species, only the signal peak of superoxide radicals was observed in the electron paramagnetic resonance spectrum of the homo-heterogeneous double junction coupled photocatalyst prepared in Example 3, which proved that the homo-heterogeneous double junction coupled photocatalyst prepared in Example 3 achieved the selective generation of superoxide radicals, and further showed that the homo-heterogeneous double junction coupled photocatalyst prepared in Example 3 had an extremely high charge carrier density on the catalyst surface during the photocatalytic activation of oxygen, that is, it achieved efficient separation of photogenerated electrons and holes.

[0103] Embodiment 11

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

[0105] The toxicity and mutagenicity of each organic intermediate in the above three degradation routes were analyzed by TEST toxicity analysis software, and the results were integrated. Fig.16 As shown, the results show that as the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 degrades tetracycline, the organic intermediates in each degradation route gradually increase in the half-lethal dose of Daphnia magna produced by the degradation of tetracycline, the mutagenicity tends to be negative as a whole, and the toxicity gradually decreases, and finally degrades into carbon dioxide and water, proving that the homogeneous-heterogeneous double junction coupled photocatalyst prepared in Example 3 has excellent detoxification ability.

[0106] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A method for preparing a homogeneous-heterogeneous double junction coupled photocatalyst, characterized in that: The following steps are involved: Step 1, carbon nitride, lithium chloride and potassium chloride are uniformly mixed to obtain a mixed powder, and the mixed powder is calcined at 540-560° C. for 4-5 hours under an inert gas atmosphere, cooled, washed and dried to obtain a precursor, wherein the ratio of carbon nitride, lithium chloride and potassium chloride is (1.8-2.2): (8.5-9.5): (10.5-11.5) by weight; Step 2, the precursor, ammonium chloride and sodium thiocyanate are mixed evenly, ground to obtain a mixture, calcined at 510-530° C. for 4-5 hours under an inert gas atmosphere, cooled, washed and dried to obtain homogeneous carbon nitride; Step 3, dispersing ferric chloride hexahydrate and sodium acetate in ethanol, adding H2O dropwise while stirring, continuing to stir until the sodium acetate is dissolved to obtain a mixed solution, adding homojunction carbon nitride to the mixed solution, ultrasonicating to obtain a dispersion, heating the dispersion at 175-190°C for 12-15h, cooling, washing, and drying to obtain a homo-heterojunction double junction coupled photocatalyst, wherein the ratio of homojunction carbon nitride, ferric chloride hexahydrate, and sodium acetate is (3-4):11:32 by mass.

2. The preparation method according to claim 1, characterized in that: The carbon nitride is obtained by calcining melamine at 480-520° C. for 3.5-4.5 hours.

3. The preparation method according to claim 1, characterized in that: In terms of mass fractions, the ratio of the precursor, ammonium chloride and sodium thiocyanate is (0.8-1.2): (0.8-1.2): (1.8-2.2).

4. The preparation method 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), the unit of the mass fraction is g, and the unit of the volume fraction is mL.

5. A homogeneous-heterogeneous double junction coupled photocatalyst obtained according to the preparation method of any one of claims 1 to 4.

6. A homogeneous-heterogeneous double junction coupled photocatalyst, characterized in that: include: Iron oxide and homojunction carbon nitride, iron oxide and homojunction carbon nitride form a heterojunction.

7. Use of the homogeneous-heterogeneous double junction coupled photocatalyst according to claim 5 or 6 in the degradation of tetracycline.

8. The use according to claim 7, characterized in that: The homogeneous-heterogeneous double junction coupled photocatalyst promotes the selective generation of O2·O in the degradation of tetracycline 2- .

9. The use according to claim 7, characterized in that: The homogeneous-heterogeneous double junction coupled photocatalyst degrades tetracycline under the conditions of light irradiation and oxygen introduction.

10. The use according to claim 7, characterized in that: The wavelength of light is greater than 420nm.

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