A photocatalyst, a preparation method and application thereof

Abstract

The application provides a photocatalyst and a preparation method and application thereof. The photocatalyst comprises a complex of ReO 2‑x , CN4 and Re(CO3)(OH), wherein Re comprises a rare earth element, 0 3‑y The photocatalyst has abundant oxygen and carbon vacancies and a unique double S-type heterojunction. The combination of the vacancies and the special heterojunction structure significantly improves the catalytic performance of the photocatalyst and widens the light response range of the photocatalyst, so that the photocatalyst can be widely applied to degradation of pollutants.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysis, and relates to a photocatalyst and a preparation method and application thereof. BACKGROUND

[0002] Antibiotics refer to a kind of secondary metabolites with anti-pathogen activity produced by microorganisms in life activities, and are widely used in the treatment of various diseases. However, the large-scale use of antibiotic drugs leads to excessive antibiotic content in water bodies. Antibiotics in water bodies can induce DNA and RNA variation of bacteria, so that the bacteria have stronger drug resistance, and have great potential harm to the ecological environment, and antibiotics have been identified as new pollutants. However, due to the variety of antibiotics, stable physicochemical properties and difficulty in degradation, the environmental pollution caused by antibiotics has persistence. Therefore, it is imminent to develop a new technology for efficiently removing antibiotic pollutants in environmental water bodies.

[0003] At present, the main methods for removing antibiotics include biological method, physical method and advanced oxidation method. The biological method refers to the use of microorganisms in aerobic or anaerobic state to realize the oxidative decomposition of antibiotics, but the degradation efficiency of this technology is often low, and a large amount of harmful drug-resistant microorganisms are produced. Physical treatment technologies include adsorption method and membrane filtration method, both of which belong to pure physical separation technology. Although the two methods have a certain removal effect on antibiotics, they only transfer or separate the residual antibiotics in water bodies to another phase, and there is a risk of secondary pollution.

[0004] The advanced oxidation method has attracted widespread attention due to its good oxidation effect, rapid and complete reaction and other advantages. This technology can rapidly degrade macromolecular antibiotics into small molecular substances, and even mineralize them into carbon dioxide, water and inorganic ions; for example, CN116693039A discloses a method for preparing photoelectrocatalytic anode and synergistically degrading antibiotics, which realizes efficient and harmless treatment of refractory antibiotics to reduce the harm of antibiotics to the ecological environment and human health. The method is as follows: 1. preparation of photocatalyst material; 2. preparation of photocatalytic electrode; 3. pretreatment of carbon brush electrode and cation exchange membrane; 4. assembly of photoelectrocatalytic reactor; 5. directional domestication of biological anode functional microorganisms; 6. operation of photoelectrocatalytic coupling anaerobic microbial degradation of typical antibiotic system; that is, by combining the advantages of fast degradation speed of advanced oxidation method and complete degradation of biological method, the method realizes the maximum degradation of refractory antibiotics in wastewater, and converts the chemical energy in wastewater into electrical energy.

[0005] Photocatalysis, a technology in advanced oxidation processes, directly utilizes sunlight to irradiate the surface of a semiconductor photocatalyst, generating photogenerated electron-hole pairs. These generate highly reactive free radicals such as superoxide radicals and hydroxyl radicals, which attack antibiotic pollutants in water, ultimately mineralizing the antibiotics into non-toxic and harmless carbon dioxide, water, and inorganic ions. The entire process requires no additional energy and is characterized by its green, high-efficiency, and environmentally friendly nature, showing great promise for treating antibiotic pollutants in water.

[0006] Rare earth elements, due to their unique 4f electronic structure, are widely used in military, chemical, metallurgical, and glass ceramic fields. Furthermore, the special band structure and electronic level structure of rare earth elements give rare earth compounds very unique optical properties. For example, lanthanide compounds can absorb low-energy infrared light and convert it into high-energy ultraviolet light, thereby effectively expanding their photoresponse range, improving the utilization rate of sunlight by the catalyst, and enhancing photocatalytic efficiency. Therefore, rare earth materials have a wide range of applications in the field of photocatalysis.

[0007] Based on the above research, there is a need to provide a photocatalyst with excellent photocatalytic performance, which can efficiently degrade pollutants. Summary of the Invention

[0008] The purpose of this invention is to provide a photocatalyst, its preparation method, and its application, particularly relating to a photocatalyst rich in oxygen, carbon vacancies, and a double S-type heterojunction, its preparation method, and its application. The photocatalyst possesses abundant oxygen and carbon vacancies and a unique double S-type heterojunction. Through the combination of the aforementioned vacancies and the special heterojunction structure, the catalytic performance of the photocatalyst is significantly improved, and the photoresponse range of the photocatalyst is broadened, enabling the photocatalyst to be widely used in the degradation of pollutants.

[0009] To achieve this objective, the present invention employs the following technical solution:

[0010] In a first aspect, the present invention provides a photocatalyst, the photocatalyst comprising ReO 2-x C 3-y A complex of N4 and Re(CO3)(OH), wherein Re includes rare earth elements, 0 < x < 2, for example, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7 or 1.9, and 0 < y < 3, for example, 0.1, 0.5, 1, 1.5, 2, 2.5 or 2.9, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] The photocatalyst described in this invention is CeO₂ with abundant oxygen and carbon vacancies and a unique double S-type heterojunction. 2-x / C 3- yThe N4 / Ce(CO3)(OH) photocatalyst has abundant oxygen and carbon vacancy structures, which can effectively reduce the band gap of the photocatalyst, further expand the light response range, and the unique double S-type heterojunction can selectively recombine the weakly reductive electrons and weakly oxidizing holes generated by the photocatalyst, so that the holes and electrons with strong oxidation and reduction capacity are retained, further generating high-activity free radicals, further enhancing the photocatalytic performance of the photocatalyst, and realizing efficient oxidative degradation of antibiotic pollutants in water.

[0012] In the application, x and y are in the range of 0

[0013] Preferably, the rare earth element includes Ce and / or La, preferably Ce.

[0014] The rare earth element in the application is preferably Ce, because Ce 4+ / Ce 3+ The existence of the redox cycle provides theoretical support for the formation of oxygen vacancies and provides an active electronic environment for the photocatalytic process.

[0015] In a second aspect, the application provides a preparation method of the photocatalyst as described in the first aspect, and the preparation method comprises the following steps:

[0016] (1) mixing and heating a rare earth salt, a non-metallic element source and a solvent to obtain a precursor material;

[0017] (2) calcining the precursor material of step (1) to obtain an intermediate;

[0018] (3) calcining the intermediate of step (2) in a reducing atmosphere to obtain the photocatalyst.

[0019] In the application, the heterojunction precursor is first prepared, then the CeO2 / C3N4 intermediate is obtained by calcination, and finally the oxygen and carbon vacancies are generated in the intermediate by calcination in a reducing atmosphere, thereby forming the photocatalyst with abundant oxygen and carbon vacancies and a unique double S-type heterojunction.

[0020] Preferably, the mass ratio of the rare earth salt to the non-metallic element source in step (1) is (0.065-0.53):1, which can be 0.065:1, 0.1:1, 0.15:1, 0.20:1, 0.25:1, 0.30:1, 0.35:1, 0.4:1, 0.45:1 or 0.53:1, but is not limited to the listed values, and other values not listed in the value range are also applicable, preferably (0.17-0.53):1, and further preferably (0.17-0.35):1.

[0021] Preferably, the mass of the rare earth salt in step (1) is 0.347-2.610 g, for example, it can be 0.347 g, 0.5 g, 1 g, 1.5 g, 2.5 g or 2.610 g, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 0.870-2.610 g, further preferably 0.870-1.740 g.

[0022] Preferably, the non-metallic element source in step (1) comprises melamine.

[0023] Preferably, the solvent in step (1) comprises deionized water.

[0024] Preferably, the heating in step (1) comprises heating and evaporating dry treatment using a graphite heating plate.

[0025] Preferably, the temperature of the heating in step (1) is 130-180℃, for example, it can be 130℃, 140℃, 150℃, 160℃, 170℃ or 180℃, but is not limited to the listed values, other values not listed in the value range are also applicable.

[0026] Preferably, the temperature of the calcination in step (2) is 450-550℃, for example, it can be 450℃, 480℃, 500℃, 525℃ or 550℃, and the time is 3-5h, for example, it can be 3h, 4h or 5h, but is not limited to the listed values, other values not listed in the value range are also applicable.

[0027] Preferably, the atmosphere of the calcination in step (2) comprises an air atmosphere.

[0028] Preferably, the intermediate in step (2) comprises a composite of CeO2 and C3N4.

[0029] Preferably, the temperature of the calcination in step (3) is 400-800℃, for example, it can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 400-600℃.

[0030] The calcination temperature of the CeO2 / C3N4 intermediate in the present application will affect the catalytic performance of the photocatalyst, if the calcination temperature is too low, the reducing property of the H2 / Ar mixed gas in the tube furnace is weak, and it is difficult to effectively form oxygen and carbon vacancy structure, thereby affecting the photocatalytic activity, if the calcination temperature is too high, the reducing property of the H2 / Ar mixed gas in the tube furnace is too strong, and the CeO2 / C3N4 intermediate is excessively reduced, thereby it is difficult to form the required double S-type heterojunction structure, and the present application further preferably has a calcination temperature of 400-600℃.

[0031] Preferably, the calcination time in step (3) is 0.5-4h, for example, it can be 0.5h, 1h, 2h, 3h or 4h, but is not limited to the listed values, and other values not listed in the value range are also applicable, and preferably 0.25-2h.

[0032] The calcination time of the CeO2 / C3N4 intermediate in the present application will also affect the catalytic performance of the photocatalyst, if the calcination time is too short, the CeO2 / C3N4 intermediate is not reduced sufficiently, and it is also difficult to effectively produce oxygen and carbon vacancies, if the calcination time is too long, the CeO2 / C3N4 intermediate is excessively reduced, and it is also difficult to form the required double S-type heterojunction structure, and the present application further preferably has a calcination time of 0.25-2h.

[0033] Preferably, the reducing atmosphere in step (3) includes hydrogen and inert gas.

[0034] Preferably, the content of hydrogen in the reducing atmosphere in step (3) is 0-15vol%, but does not include 0vol%, for example, it can be 1vol%, 3vol%, 7vol%, 9vol%, 11vol%, 13vol% or 15vol%, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0035] If the content of hydrogen is too low during the calcination in step (3), it will have a certain effect on the formation of oxygen and carbon vacancies on the surface of the photocatalyst, if the content of hydrogen is too high, it will affect the components of the photocatalyst, and it is difficult to form the required double S-type heterojunction.

[0036] As a preferred technical solution of the preparation method of the present application, the preparation method comprises the following steps:

[0037] (1) mixing a rare earth salt, a non-metallic element source and a solvent, and then evaporating to dryness by heating with a graphite heating plate at 130-180℃ to obtain a precursor material;

[0038] The mass ratio of the rare earth salt to the non-metallic element source is (0.065-0.53):1; the non-metallic element source includes melamine;

[0039] (2) calcining the precursor material of step (1) in an air atmosphere at a temperature of 450-550 DEG C for 3-5 h to obtain an intermediate, the intermediate comprising a composite of CeO2 and C3N4;

[0040] (3) calcining the intermediate of step (2) in a mixed gas atmosphere of hydrogen and inert gas at a temperature of 400-800 DEG C for 0.5-4 h to obtain the photocatalyst;

[0041] In the mixed gas atmosphere, the content of hydrogen is 0-15 vol%, but not including 0 vol%.

[0042] In a third aspect, the application provides an application of the photocatalyst as described in the first aspect, the application comprising being used for photocatalytic degradation of quinolone antibiotic wastewater.

[0043] Compared with the prior art, the application has the following beneficial effects:

[0044] The photocatalyst has abundant oxygen and carbon vacancies and a unique double S-type heterojunction, the existence of the double S-type heterojunction effectively avoids the recombination of photo-generated holes and electrons with strong redox ability, and the CeO 2-x The existence of oxygen vacancies and carbon vacancies in C 3-y The existence of oxygen vacancies and carbon vacancies in C BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 XRD patterns of the photocatalysts described in Examples 1-3 of the application;

[0046] Figure 2 XRD patterns of the photocatalysts described in Comparative Examples 1-2 of the application;

[0047] Figure 3 XRD patterns of the photocatalysts described in Comparative Examples 3-5 of the application;

[0048] Figure 4 Scanning electron microscope image of the photocatalyst described in Example 2 of the application at a scale of 1 mu m;

[0049] Figure 5 Scanning electron microscope image of the photocatalyst described in Example 2 of the application at a scale of 500 nm;

[0050] Figure 6Transmission electron microscopy image of the photocatalyst according to Example 2 of the present invention at a scale of 200 nm;

[0051] Figure 7 Transmission electron microscopy image of the photocatalyst according to Example 2 of the present invention at a scale of 50 nm;

[0052] Figure 8 High resolution transmission electron microscopy image of the photocatalyst according to Example 2 of the present invention at a scale of 2 nm;

[0053] Figure 9 High resolution transmission electron microscopy image of the photocatalyst according to Example 2 of the present invention at a scale of 2 nm;

[0054] Figure 10 High resolution N1s XPS spectrum of the photocatalyst according to Examples 1-3 and Comparative Example 2 of the present invention;

[0055] Figure 11 High resolution N1s XPS spectrum of the photocatalyst according to Comparative Examples 1 and 3-5 of the present invention;

[0056] Figure 12 High resolution O1s XPS spectrum of the photocatalyst according to Examples 1-3 of the present invention;

[0057] Figure 13 High resolution O1s XPS spectrum of the photocatalyst according to Comparative Examples 3-5 of the present invention;

[0058] Figure 14 EPR spectrum of the photocatalyst according to Example 2 and Comparative Examples 1-2 of the present invention;

[0059] Figure 15 Degradation of enrofloxacin curve of the photocatalyst according to Examples 1-3 and Comparative Examples 1-5 of the present invention;

[0060] Figure 16 Degradation of enrofloxacin curve of the photocatalyst according to Example 2 of the present invention;

[0061] Figure 17 DMPO-·O2 - spin-trapped ESR spectrum;

[0062] Figure 18 DMPO-·OH spin-trapped ESR spectrum of the photocatalyst according to Example 2 of the present invention;

[0063] Figure 19 Radical quenching curve of the photocatalyst according to Example 2 of the present invention for the photocatalytic degradation of enrofloxacin;

[0064] Figure 20The PL (steady-state fluorescence spectrum) spectrum of the photocatalyst according to the present application Example 2, Comparative Example 1-2 and Comparative Example 4 is shown in the following figure.

[0065] Figure 21 The solid UV-visible diffuse reflectance absorption spectrum of the photocatalyst according to the present application Example 2, Comparative Example 1-2 and Comparative Example 4 is shown in the following figure.

[0066] Figure 22 The band gap of the photocatalyst according to the present application Example 2, Comparative Example 1-2 and Comparative Example 4 is shown in the following figure. DETAILED DESCRIPTION

[0067] The technical solutions of the present application are further illustrated by the following specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations to the present application.

[0068] Example 1

[0069] The present embodiment provides a photocatalyst, which comprises a composite of CeO 2-x , C 3-y N4 and Ce(CO3)(OH), i.e. CeO 2-x / C 3-y N4 / Ce(CO3)(OH), wherein there are oxygen and carbon vacancies in the CeO 2-x / C 3-y N4 / Ce(CO3)(OH).

[0070] The preparation method of the photocatalyst comprises the following steps:

[0071] (1) 5 g of melamine is dispersed in 270 mL of deionized water, heated and stirred until clear, and then 30 mL of an aqueous solution of 0.870 g of Ce(NO3)3·6H2O is added, stirred uniformly to obtain a mixed solution, and the mass ratio of Ce(NO3)3·6H2O to melamine is 0.174:1;

[0072] The obtained mixed solution is transferred to a graphite heating plate, and after evaporation at 160℃, a precursor material is obtained;

[0073] (2) The precursor material of step (1) is transferred to a muffle furnace, calcined at 550℃ for 4 h to obtain CeO2 / C3N4.

[0074] (3) The CeO2 / C3N4 obtained in step (2) is transferred to a tube furnace, calcined at 600℃ for 2 h under a mixed gas of H2 and Ar with a H2 content of 5 vol% to obtain the photocatalyst.

[0075] Example 2

[0076] This example provides a photocatalyst, which is the same as in example 1 except that in the preparation method, the mass of Ce(N03)3-6H20 in step (1) is 1.740 g, and the mass ratio of Ce(N03)3-6H20 to melamine is 0.348: 1, and the resulting photocatalyst is changed adaptively.

[0077] Example 3

[0078] This example provides a photocatalyst, which is the same as in example 1 except that in the preparation method, the mass of Ce(N03)3-6H20 in step (1) is 2.61 g, and the mass ratio of Ce(N03)3-6H20 to melamine is 0.522: 1, and the resulting photocatalyst is changed adaptively.

[0079] Example 4

[0080] This example provides a photocatalyst, which is the same as in example 1 except that in the preparation method, the mass of Ce(N03)3-6H20 in step (1) is 0.347 g, and the mass ratio of Ce(N03)3-6H20 to melamine is 0.069: 1, and the resulting photocatalyst is changed adaptively.

[0081] Example 5

[0082] This example provides a photocatalyst, which is the same as in example 1 except that in the preparation method, the mass of Ce(N03)3-6H20 in step (1) is 0.275 g, and the mass ratio of Ce(N03)3-6H20 to melamine is 0.055: 1, and the resulting photocatalyst is changed adaptively.

[0083] Example 6

[0084] This example provides a photocatalyst, which is the same as in example 1 except that in the preparation method, the mass of Ce(N03)3-6H20 in step (1) is 3 g, and the mass ratio of Ce(N03)3-6H20 to melamine is 0.6: 1, and the resulting photocatalyst is changed adaptively.

[0085] Example 7

[0086] This example provides a photocatalyst, which is the same as in example 4 except that in the preparation method, the temperature of calcination in step (3) is 400°C, and the resulting photocatalyst is changed adaptively.

[0087] Example 8

[0088] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the temperature of the calcination in step (3) is 700°C, which results in an adaptive change in the photocatalyst.

[0089] Example 9

[0090] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the temperature of the calcination in step (3) is 500°C, which results in an adaptive change in the photocatalyst.

[0091] Example 10

[0092] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the temperature of the calcination in step (3) is 800°C, which results in an adaptive change in the photocatalyst.

[0093] Example 11

[0094] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the time of the calcination in step (3) is 0.5h, which results in an adaptive change in the photocatalyst.

[0095] Example 12

[0096] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the time of the calcination in step (3) is 4h, which results in an adaptive change in the photocatalyst.

[0097] Example 13

[0098] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the time of the calcination in step (3) is 0.25h, which results in an adaptive change in the photocatalyst.

[0099] Example 14

[0100] This example provides a photocatalyst which is the same as example 4 except that in the preparation method, the time of the calcination in step (3) is 3h, which results in an adaptive change in the photocatalyst.

[0101] Comparative Example 1

[0102] This comparative example provides a photocatalyst which is C3N4.

[0103] The preparation method of the photocatalyst is the same as that of Example 1, except that Ce(NO3)3·6H2O is not added in step (1) and the calcination in step (3) is not performed.

[0104] Comparative Example 2

[0105] This comparative example provides a photocatalyst, which is C 3-y N4, and the C 3-y N4 has a carbon vacancy.

[0106] The preparation method of the photocatalyst is the same as that of Example 1, except that Ce(NO3)3·6H2O is not added in step (1).

[0107] Comparative Example 3

[0108] This comparative example provides a photocatalyst, which is CeO2 / C3N4.

[0109] The preparation method of the photocatalyst is the same as that of Example 1, except that the calcination in step (3) is not performed.

[0110] Comparative Example 4

[0111] This comparative example provides a photocatalyst, which is CeO2 / C3N4.

[0112] The preparation method of the photocatalyst is the same as that of Example 2, except that the calcination in step (3) is not performed.

[0113] Comparative Example 5

[0114] This comparative example provides a photocatalyst, which is CeO2 / C3N4.

[0115] The preparation method of the photocatalyst is the same as that of Example 3, except that the calcination in step (3) is not performed.

[0116] Comparative Example 6

[0117] This comparative example provides a photocatalyst, which is CeO2 / C3N4.

[0118] The preparation method of the photocatalyst is the same as that of Example 4, except that the calcination in step (3) is not performed.

[0119] The XRD pattern of the photocatalyst described in Examples 1-3 is shown in Figure 1 The high-resolution O1s XPS spectrum is shown in Figure 12 The scanning electron microscope image of the photocatalyst described in Example 2 at a scale of 1 μm is shown in Figure 4The scanning electron microscope image at a scale of 500 nm is shown in Figure 1. Figure 5 The transmission electron microscope image at a scale of 200 nm is shown in Figure 2. Figure 6 The transmission electron microscope image at a scale of 50 nm is shown in Figure 3. Figure 7 The high resolution transmission electron microscope image at a scale of 2 nm is shown in Figure 4. Figure 8 The high resolution transmission electron microscope image at a scale of 2 nm is shown in Figure 5. Figure 9 The cyclic degradation of enrofloxacin curve is shown in Figure 6. Figure 16 The DMPO-·O2 - The spin-trapping ESR spectrum is shown in Figure 7. Figure 17 The DMPO-·OH spin-trapping ESR spectrum is shown in Figure 8. Figure 18 The radical quenching curve of photocatalytic degradation of enrofloxacin is shown in Figure 9. Figure 19 The XRD pattern of the photocatalyst described in Comparative Example 1-2 is shown in Figure 10. Figure 2 The XRD pattern of the photocatalyst described in Comparative Examples 3-5 is shown in Figure 11. Figure 3 The high resolution N1s XPS spectrum of the photocatalyst described in Examples 1-3 and Comparative Example 2 is shown in Figure 12. Figure 10 The high resolution N1s XPS spectrum of the photocatalyst described in Comparative Example 1 and Comparative Examples 3-5 is shown in Figure 13. Figure 11 The high resolution O1s XPS spectrum of the photocatalyst described in Comparative Examples 3-5 is shown in Figure 14. Figure 13 The EPR spectrum of the photocatalyst described in Example 2 and Comparative Examples 1-2 is shown in Figure 15. Figure 14 The degradation of enrofloxacin curve of the photocatalyst described in Examples 1-3 and Comparative Examples 1-5 is shown in Figure 16. Figure 15 The PL spectrum of the photocatalyst described in Example 2, Comparative Examples 1-2 and Comparative Example 4 is shown in Figure 17. Figure 20 The solid-state UV-Vis diffuse reflectance absorption spectrum is shown in Figure 18. Figure 21 The band gap of the photocatalyst is shown in Figure 19. Figure 22

[0120] ​The photocatalysts obtained in the above examples and comparative examples were subjected to performance testing for photocatalytic degradation of antibiotics. The testing method included: using a 500W xenon lamp light source, performing photocatalytic degradation experiments on a CEL-LB70 rotary photochemical reactor. 50mg of photocatalyst was dispersed in 50mL of antibiotic solution (10mg / L), and the pH was adjusted to 7. Before light irradiation, the mixture was stirred in the dark for 30min to ensure that the photocatalyst reached adsorption-desorption equilibrium. During the photocatalytic degradation reaction, the suspension was taken at a certain time point, and after removing the photocatalyst in the suspension using a 0.22 micron Millipore filter, the absorbance of the ENR (enrofloxacin) solution at the maximum absorption wavelength (271nm) was tested using a UV-visible spectrophotometer, and the concentration was converted according to the established standard curve, and the degradation rate was calculated. The results are shown in Table 1.

[0121] Table 1

[0122]

[0123]

[0124] As can be seen from Table 1, with the increase of the constant temperature calcination temperature of the tubular furnace, the photocatalytic degradation rate of the sample on ENR showed a trend of first increasing and then decreasing. Similarly, with the increase of the calcination time of the tubular furnace, the photocatalytic degradation rate of the sample on ENR also showed a trend of first increasing and then decreasing. The sample of Example 2, which was calcined at 600°C for 2h in a 5% H2 / Ar mixed gas, had a higher ENR degradation rate, and Example 2 had the best kinetic reaction rate on ENR. As can be seen from Examples 1, 5-6, 9-10, and 13-14, the amount of added cerium nitrate, the calcination temperature and time of step (3) all affect the performance of the photocatalyst.

[0125] The photocatalysts described in Examples 1-3 were subjected to performance testing for photocatalytic degradation of ENR at different pH values. The testing method included: using a 500W xenon lamp light source, performing photocatalytic degradation on a CEL-LB70 rotary photochemical reactor. 50mg of photocatalyst was dispersed in 50mL of antibiotic solution (10mg / L), and the pH was adjusted to 2, 4, 6, 7, 8. Before light irradiation, the mixture was stirred in the dark for 30min to ensure that the photocatalyst reached adsorption-desorption equilibrium. During the photocatalytic degradation reaction, the suspension was taken at a certain time point, and after removing the photocatalyst in the suspension using a 0.22 micron Millipore filter, the absorbance of the ENR at the maximum absorption wavelength (271nm) was tested using a UV-visible spectrophotometer, and the concentration was converted according to the established standard curve, and the degradation rate was calculated. The results are shown in Table 2.

[0126] Table 2

[0127]

[0128] As can be seen from Table 2, the application exhibits excellent photocatalytic degradation ENR efficiency on ENR in the pH value range of 4-6, and the degradation rates of ENR of Examples 1-3 all decrease to different degrees when the pH value is 2, which may be related to the poor stability of Ce(CO3)(OH) in the acidic system, indicating that CeO 2-x / C 3-y The suitable optimal pH range of the N4 / Ce(CO3)(OH) photocatalytic system is 4-6.

[0129] The sample prepared in Example 2 was subjected to performance test of photocatalytic degradation of different antibiotics, and the test method included: using a 500W xenon lamp light source, and performing photocatalytic degradation antibiotic experiment on a CEL-LB70 rotary photochemical reactor. 50mg of catalyst was dispersed in 50mL of antibiotic solution (10mg / L), and the pH was adjusted to 6. Before light irradiation, the photocatalyst was stirred in the dark for 30min to ensure adsorption-desorption equilibrium. During the photocatalytic degradation reaction, the suspension was taken at a certain time point, and after removing the photocatalyst in the suspension using a 0.22 micron Millipore filter, the absorbance of the antibiotic at the maximum absorption wavelength (ofloxacin, norfloxacin, ciprofloxacin and gatifloxacin, respectively, 288nm, 272nm, 270nm and 284nm) was tested using a UV-visible spectrophotometer, and the concentration was converted according to the established standard curve, and the degradation rate was calculated, and the results are shown in Table 3.

[0130] Table 3

[0131] Antibiotic name Degradation rate (%) Norfloxacin 98.02 Ofloxacin 95.75 Ciprofloxacin 99.15 Gatifloxacin 89.01

[0132] As can be seen from Table 3, the sample prepared in Example 2 has good photocatalytic efficiency on ofloxacin, norfloxacin, ciprofloxacin and gatifloxacin, indicating that the photocatalyst prepared in Example 2 can effectively remove quinolone antibiotics in water, and has very broad application prospects.

[0133] As the application Figures 1-3As shown, the XRD patterns of Comparative Example 1 and Comparative Example 2 show two distinct diffraction peaks at 13.0° and 27.5°, respectively, corresponding to the (100) and (002) crystal planes of C3N4. The XRD patterns of Comparative Examples 3-5 show diffraction peaks at 28.6°, 33.1°, 47.5°, 56.3°, 59.1°, 69.4°, 76.7°, and 79.1°, which correspond to the (111), (200), (220), (311), (222), (400), (331), and (420) crystal planes of CeO2 (PDF#34-0394), respectively. For the XRD patterns of Examples 1-3, in addition to observing the presence of C3N4 and CeO2, Ce(CO3)(OH)(PDF#01-084-7543) and CeO2 can also be found. 2-x The presence of the (PDF#00-049-1415) diffraction peaks suggests that the main reason for this change may be attributed to the reduction effect of step (3) on the sample, thereby causing some of the CeO2 to be removed. 4+ Restored to Ce 3+ CeO 2-x Simultaneously, Ce(CO3)(OH) is generated, which is beneficial for the formation of CeO. 2-x / C 3-y The N4 / Ce(CO3)(OH) double S-type heterojunction is crucial.

[0134] The morphology and microstructure of each sample were analyzed using scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. Figures 4-9 It can be seen that all samples exhibit a layered structure, forming loose micron-sized aggregates with nanosheets as the basic unit. This is significant for increasing the specific surface area of ​​the photocatalyst. In the TEM image of Example 2, although the sample surface is wrinkled, a clear sheet-like structure can still be observed, indicating that Example 2 has an extremely thin two-dimensional layered structure. Furthermore, CeO... 2-x Ce(CO3)(OH) nanoparticles were well dispersed on the surface of Example 2. HRTEM further confirmed the phase composition of Example 2. Figure 8 In Example 2, the approximately 0.339 nm wide lattice fringes correspond to CeO. 2-x The (222) crystal plane, Figure 9 The lattice fringes with a spacing of 0.248 nm correspond to the (230) crystal plane of Ce(CO3)(OH). Through Figure 8 and Figure 9 CeO confirmed 2-x / C 3-y N4 and C 3-yThe formation of N4 / Ce(CO3)(OH) interface indicates that the photocatalytic heterojunction has been constructed and there is a strong interface interaction between them.

[0135] As shown in Figure 11 , the high-resolution N1s XPS spectrum can be fitted into two peaks, respectively at 398.7 eV and 401.2 eV, corresponding to C-N-C and C-N3 peaks of the sample without carbon vacancy, while a new peak at about 399.9 eV can be clearly observed from Figure 10 , which is attributed to the absence of tertiary carbon, indicating the presence of carbon vacancy structure in the samples of Comparative Example 2 and Examples 1-3. In addition, Figure 12 , the high-resolution O1s XPS spectrum of Examples 1-3 shows that, in addition to the corresponding peaks at 529.0 eV (lattice oxygen) and 531.6 eV (chemisorbed oxygen species), a new peak at 530.0 eV appears, which indicates that the sample has an oxygen vacancy structure.

[0136] As shown in Figure 14 , the electron paramagnetic resonance spectrum (EPR) of the sample further proves that the prepared sample has abundant oxygen vacancy and carbon vacancy structures, and the EPR intensity of Comparative Example 2 and Example 2 gradually increases compared with Comparative Example 1, which provides direct evidence for the existence of carbon vacancy and oxygen vacancy. Based on the above analysis, the samples prepared in Examples 1-3 have abundant oxygen vacancy and carbon vacancy, which provides an important basis for reducing the band gap of the sample, extending its light response range, and promoting the photocatalytic performance of the sample.

[0137] Figure 15 The performance curves of the prepared samples in the degradation of ENR by each material under full spectrum illumination are shown. Comparative Example 1 only shows a degradation rate of 25.66% within 240 min at a pH of 6, while after introducing CeO2 into Comparative Example 1, the samples show relatively high activity (Comparative Example 3: 56.71%, Comparative Example 4: 57.49%, Comparative Example 5: 63.54%), which may be attributed to the formation of heterojunction between CeO2 and C3N4, which inhibits the recombination of photo-generated carriers with strong redox ability. When double S-type heterojunction and atomic vacancies are introduced into the sample, the corresponding ENR photocatalytic degradation performance is significantly improved (Example 1: 91.99%, Example 2: 93.58%, Example 3: 92.11%).

[0138] In addition, the reusability of the photocatalyst is also an important indicator for evaluating its performance, which is crucial for the practical application of the photocatalyst, therefore, the stability of the sample prepared in Example 2 was tested by cyclic photodegradation of ENR experiment Figure 16), the results showed that the ENR photodegradation efficiency of the first, second, third, fourth and fifth cycles were 92.11%, 94.36%, 89.05%, 82.34% and 73.58%, respectively. It can be seen that the first three times of ENR photodegradation efficiency decreased slightly, but overall change was not large, while the photocatalytic activity of the sample in the fourth and fifth cycles decreased significantly, which may be due to the consumption of a certain amount of photocatalyst in the recycling and washing process during the recycling stability test. Although the activity decreased, the ENR degradation rate still remained at 73.58% in the fifth cycle experiment, which confirmed its potential application in the degradation of ENR actual wastewater.

[0139] Subsequently, spin-trapping ESR spectroscopy was used to determine the active species involved in the photocatalytic ENR decomposition process. Figures 17-18 The ESR characteristic peaks were very weak in the dark environment, but DMPO-·O2 - adduct (peak intensity ratio: 1:1:1:1) and DMPO-·OH adduct (peak intensity ratio: 1:2:2:1) ESR signals proved the existence of ·O2 - and ·OH in the photocatalytic process, plus the photogenerated holes (h + ) produced in the photocatalytic reaction, it can be determined that ·O2 - , ·OH and h + play a major role in the photocatalytic degradation of ENR. Therefore, active species quenching experiments were carried out, using benzoquinone (BQ), isopropyl alcohol (IPA) and disodium EDTA (EDTA-2Na) to capture ·O2 - , ·OH and h + , respectively. It can be seen from Figure 19 that the ENR photodegradation activity showed a significant downward trend, and the corresponding degradation efficiency was 33.24%, 82.37% and 8.04%, respectively, indicating that ·O2 - and h + are the main active species in the ENR photodegradation process. Isopropyl alcohol has little effect on the photodegradation activity, indicating that ·OH plays a minor role in the ENR photodegradation reaction.

[0140] To explore the micro origin of the enhanced ability of photocatalysts to degrade antibiotics, PL spectroscopy was first tested. As Figure 20As shown, the PL peak of Comparative Example 1 is the strongest in all samples, which is a manifestation of the fast recombination of photo-generated electrons and holes under photo-excitation. In contrast, Comparative Example 2 has a weaker fluorescence emission intensity, indicating that carbon vacancies can inhibit the recombination of photo-generated electrons and holes to some extent, while the emission peak of Example 2 is the weakest, indicating that the recombination of photo-generated electrons and holes is effectively inhibited. The PL spectrum results prove the introduction of carbon and oxygen defects, and the heterojunction formed by the appropriate proportion of CeO2 and C3N4 two semiconductors can promote the transfer of photo-generated electrons and improve the photocatalytic performance of the material. Subsequently, solid UV-Vis diffuse reflectance absorption spectrum test was carried out. Compared with 470 nm of Comparative Example 1, the absorption edge of Comparative Example 2 with carbon vacancy-rich red shifts to 484 nm Figure 21 ), and the absorption edge of Example 2 also red shifts compared with the absorption edge of Comparative Example 4.

[0141] As shown in Figure 22 , the band gap (E g ) of each sample was calculated, which was 2.64 eV (Comparative Example 1), 2.56 eV (Comparative Example 2), 2.60 eV (Comparative Example 4) and 2.54 eV (Example 2), respectively. Compared with Comparative Example 1 and Comparative Example 4, it was found that the Eg of Comparative Example 2 and Example 2 was much narrower, indicating that Example 2 had a wider light response range, which helped to expand the use of longer wavelength light in the ENR photo-degradation process. In addition, when Ce(CO3)(OH) is closely combined with C 3-y N4 and C 3-y N4 / CeO 2-x , the ground state electrons in Ce(CO3)(OH) will spontaneously migrate to the surface of C 3-y N4, while the ground state electrons in C 3-y N4 will spontaneously transfer to the surface of CeO 2-x , until their Fermi levels tend to be balanced, and two internal electric fields are formed on the two interfaces, respectively, which are from Ce(CO3)(OH) to C 3-y N4 and C 3-y N4 to CeO 2-x , which in turn drives the selective recombination of photo-generated electrons in the C 3-y N4 conduction band and photo-generated holes in the Ce(CO3)(OH) valence band and the selective recombination of photo-generated electrons in the CeO 2-x conduction band and photo-generated holes in the C 3-y N4 valence band, and the result of this double S-type charge transfer path will make the photo-generated electrons with strong reducing property in Ce(CO3)(OH) and the photo-generated holes with strong oxidizing property in CeO 2-x remain, providing strong driving force for the degradation of antibiotics.

[0142] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes and replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. Application of a photocatalyst in photocatalytic degradation of quinolone antibiotic wastewater, characterized in that, The photocatalyst is CeO 2-x , C 3-y N4 and Ce(CO3)(OH) complex, wherein 0 < x < 2, 0 < y < 3; The photocatalyst is prepared by a preparation method comprising the following steps: (1) mixing Ce(NO3)3.6H2O, a non-metallic element source and a solvent, and then heating and evaporating dry under the action of a graphite heating plate at 130-180°C to obtain a precursor material; The mass ratio of the Ce(NO3)3.6H2O to the non-metallic element source is (0.065-0.53):1; the non-metallic element source comprises melamine; (2) calcining the precursor material of step (1) in an air atmosphere at a temperature of 450-550°C for 3-5h to obtain an intermediate, the intermediate comprising a composite of CeO2 and C3N4; (3) calcining the intermediate of step (2) in a mixed atmosphere of hydrogen and an inert gas at a temperature of 400-800°C for 0.5-4h to obtain the photocatalyst; In the mixed atmosphere, the content of hydrogen is 0-15vol%, but does not include 0vol%.

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