Preparation method and application of a long-lasting and stable advanced oxidation catalyst without aeration

Abstract

The present invention discloses a method for preparing a durable and stable advanced oxidation catalyst without aeration and its application. x ) as a carrier, and the oxygen-rich polymer was introduced as a structure-directing agent to soften the CN X , then implement CN X MOF-derived cobalt tetroxide (V O ‑M‑Co3O4) coating, making V O ‑M‑Co3O4 is highly dispersed and has a large number of catalytic active sites, which can solve the problem of V O The catalyst exhibits good reaction stability, sufficient visible light absorption capacity and strong peroxymonosulfate (PMS) activation ability, achieving efficient degradation of atrazine (ATZ), a difficult-to-remove organic pollutant. From an application perspective, unlike traditional O2-dependent degradation systems, V O ‑M‑Co3O4@CN x The efficiency of ATZ degradation under anaerobic conditions was much higher than that under aerobic conditions, indicating that V O ‑M‑Co3O4@CN x ATZ catalytic degradation can be achieved without aeration, greatly reducing water treatment costs and having potential practical application value in the field of advanced oxidation wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the fields of advanced oxidation wastewater treatment and photocatalytic nanocomposite material technology, and in particular to a preparation method and application of a durable and stable advanced oxidation catalyst that does not require aeration. Background Art

[0002] Pesticides have the function of preventing and controlling crop diseases and ensuring the normal growth of crops. They are widely used in agricultural and food industry production to meet the growing food demand brought about by the world's population explosion. However, the large-scale use of various pesticides has brought about various environmental problems. Taking the widely used atrazine (ATZ) as an example, due to its stable s-triazine structure, long half-life, low biodegradability, it will still remain toxic and residual in the ecological environment in trace amounts, posing a high risk to human health and the ecosystem, and restricting the sustainable development of agriculture. Therefore, it is crucial to seek an effective and sustainable treatment technology to eliminate the ecological and environmental risks of ATZ in the water environment. The Fenton-like process based on peroxymonosulfate (PMS) produces reactive oxygen species (ROS) by catalytic activation of PMS, and has been proven to be a clean and effective technology for the treatment of persistent organic pollutants. Among them, the asymmetric structure (HO-OSO3 - ) and PMS with longer OO bonds can be catalyzed by external field energy (heat, light, ultrasound, microwave, etc.), transition metal ions / compounds (Co 2+ 、Fe 2+ , Co3O4, etc.) and metal-free materials (carbon-based, boron-based, and sulfur-based). Among the above activation methods, photocatalysts can continuously generate abundant photogenerated electrons under light irradiation and are considered to be a more effective and cost-effective strategy for activating PMS. It has been reported that there is no significant difference in the removal efficiency of pollutants under aerobic and anaerobic conditions in Fenton-like degradation systems. This may be because the O in the active oxygen species is not derived from dissolved oxygen but from PMS. It is well known that in traditional photocatalytic degradation systems, the O in the active oxygen species is often overly dependent on oxygen (O2) atmosphere and forced convection of air, which greatly limits their large-scale industrial application. Traditional photo-Fenton-like degradation systems rely heavily on the transport of O2 and the energy consumption of forced convection, which will significantly increase treatment costs. According to statistics, aeration accounts for 35-51% of the total energy consumption in wastewater treatment processes, with an annual energy consumption of 500-750 million kWh. Therefore, the design and development of aeration-free photocatalyst-like photo-Fenton systems to effectively promote the activation of PMS and remove persistent organic pollutants has become crucial and has great application prospects.

[0003] Graphitic carbon nitride (CN) is composed of abundant elements on the earth and has attracted widespread attention from researchers in the field of environmental remediation due to its suitable band gap (2.7 eV), visible light response and PMS activation ability. It is reported that CNs with different degrees of defects were prepared by thermal polymerization of several precursors (melamine, thiourea and their mixtures). These structural defects are formed due to the inevitable loss of nitrogen atoms in the CN framework during the thermal polymerization process. As a special internal defect of CN, N vacancies have been confirmed to be beneficial to light-assisted PMS activation. After the loss of N atoms, lone pairs of electrons are presented, making it easy to accept electrons or interact with electron-rich substances, and easily attract negatively charged PMS or interact with PMS (Science of The Total Environment, (2021, 756: 144139). In addition, CN is 1 It exhibits high activity in the degradation of pollutants using O2-based non-radicals and exhibits good resistance to interference from coexisting substances. The donor-acceptor engineered g-C3N4 designed by Weng et al. (Journal of Hazardous Materials, 2023, 448:130869) selectively removes ATZ via PMS photocatalytic activation, maintaining nearly unchanged ATZ removal performance under aerobic and anaerobic conditions. This suggests that constructing a CN-based photocatalyst-activated PMS-like Fenton system for the removal of organic pollutants is feasible and promising. However, for single-component photocatalysts, the slow PMS activation kinetics, poor photoabsorption performance, and rapid photoinduced electron-hole pair recombination result in far less than satisfactory pollutant degradation activity. In recent years, S-type heterojunctions have been developed, which exhibit unique charge migration pathways and strong photoredox capabilities, as electrons and holes generated by photoexcited heterojunctions accumulate in the more negative conduction band (CB) and more positive valence band (VB), respectively. At present, the excellent performance of CN-based S-type heterojunction photocatalytic system in photocatalytic degradation of environmental pollutants has been demonstrated (Science China Materials 2024, 67(2): 444-472). Cobalt-based Fenton process has been proven to be an effective means of activating PMS, which can rely on PMS to act as both electron donor and acceptor to generate ROS to attack organic pollutants. Among the candidate materials for constructing heterojunction, Co3O4 has a narrow band gap of 1.7-2.0eV, which can be activated by Co III / Co IIReduction induces PMS activation at active sites and is considered a promising PMS activator. However, cobalt ions in Co₃O₄ easily escape from the Co₃O₄, leading to secondary contamination and reduced catalytic activity. The pollutant degradation performance of Co₃O₄@C-500 prepared by Sheng et al. (Chemical Engineering Journal, 2023, 471:143945) dropped from 100% to 64% after four cycles.

[0004] In summary, the existing technology has the following problems:

[0005] (1) Traditional Fenton-like photocatalytic degradation systems rely heavily on the energy consumption of O2 transport and forced convection, which greatly increases treatment costs. The harsh reaction conditions and high energy consumption are not conducive to the practical application of advanced oxidation treatment technologies in the wastewater field;

[0006] (2) Although Co-based catalysts have shown a certain ability to activate PMS, due to structural instability and the complexity of the operating environment, they are inevitably accompanied by a large amount of cobalt leaching. Co ions easily accumulate in the environment, which has a significant impact on the ecological environment and human health;

[0007] (3) Fenton-like photocatalysts have low absorption and utilization rates of visible light in sunlight, high recombination rates of photogenerated electron-hole pairs, few active sites for catalytic reactions, and slow activation rates of PMS, resulting in low catalytic degradation efficiency. Summary of the Invention

[0008] The technical problems to be solved by the present invention are as follows:

[0009] (1) The present invention designs and constructs a novel carbon nitride-based S-type heterojunction Fenton-like photocatalyst with dual defect sites. It does not require aeration to the reaction system, has low energy consumption, and is simple and easy to prepare. It is conducive to the large-scale application of advanced oxidation treatment technology in the field of wastewater. This solves the problem of high energy consumption of the current traditional photo-Fenton-like technology for treating difficult-to-degrade organic pollutants.

[0010] (2) Cobalt ions in Co3O4 can easily escape, causing secondary environmental pollution, reducing catalytic activity and showing poor PMS activation ability. On the one hand, the present invention selects porous zeolite imidazolate framework (ZIF-67) as a precursor, and pyrolyzes V in an inert atmosphere and air respectively. O -M-Co3O4 photocatalyst improves its stability and conductivity, in which the obtained V O-M-Co3O4 oxygen vacancies (Vo) provide abundant active sites, increase the speed of electron generation, accelerate PMS activation and thus enhance the generation of ROS; on the other hand, the present invention introduces oxygen-rich polymer PEG as a structure-directing agent to soften the nitrogen-defective carbon nitride CN x carrier, realize CN x V O -M-Co3O4 coating makes V O -M-Co3O4 is highly dispersed and has a large number of PMS activation sites to solve the V O -M-Co3O4 is prone to agglomeration and environmental problems caused by Co ion leaching.

[0011] (3) Currently, photo-Fenton-like catalysts have fewer active sites, resulting in reduced PMS activation performance and low Fenton-like photocatalytic degradation efficiency. The carbon nitride-based S-type heterojunction Fenton-like photocatalyst material with double defect sites prepared by the present invention can coordinate the directional migration path of photogenerated carriers to the surface under the action of built-in electric field and Coulomb attraction, thereby improving PMS activation performance and accelerating the reaction rate, thereby greatly enhancing its catalytic degradation efficiency.

[0012] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0013] A method for preparing a durable and stable advanced oxidation catalyst without aeration and its application, wherein V is prepared by introducing an oxygen-rich polymer-assisted hydrothermal method O -M-Co3O4@CN x The advanced oxidation catalyst specifically comprises the following steps:

[0014] Step 1: Weigh 8-12g of urea into a 50-150mL covered ceramic crucible and calcine at a certain temperature and a certain heating rate. The ambient temperature is 25-35°C and the relative humidity is about 65-85%. The obtained catalyst is named CN x ;

[0015] Step 2: Dissolve 750-900 mg of Co(NO₃)₂·6H₂O and 1200-2000 mg of 2-methylimidazole in methanol. Stir the mixture rapidly and allow to age at room temperature. Wash the resulting precipitate with ethanol and dry it overnight at 50-80°C to obtain the precursor ZIF-67.

[0016] Step 3: After drying, the ZIF-67 precursor is kept at a certain temperature for a certain time under the protection of high-purity N2, cooled to room temperature with the furnace, and then calcined in air at a certain temperature for a certain time. The obtained catalyst is named V O -M-Co3O4;

[0017] Step 4: Set a certain proportion of V O -M-Co3O4 was prepared into a water dispersion and sealed with plastic wrap, ultrasonicated, and then stirred at a certain temperature for a period of time using a magnetic stirrer. At the same time, a certain amount of CN x Mix with oxygen-containing polymer, dilute with a certain volume of deionized water, stir for 5-20 minutes, and then add different volumes of V O -M-Co3O4 solution to a certain volume. Subsequently, the composite solution was stirred for 0.5-2h, transferred to a reactor, and subjected to hydrothermal treatment. After cooling to room temperature, it was washed with deionized water and anhydrous ethanol, and dried at 50-80°C overnight to obtain a composite material named Y%V O -M-Co3O4@CN x ,Y represents V O -Theoretical addition amount of M-Co3O4.

[0018] As an improvement, the calcination conditions in step 1 are calcined at 450-600℃ for 2℃min -1 ,4h.

[0019] As an improvement, the aging time in step 2 is 20-40 hours.

[0020] As an improvement, the heating rate in step 3 is 1-5℃min -1 The first calcination temperature is 450-550℃, the holding time is 10-50min, the second calcination temperature is 300-400℃, and the holding time is 1-5h.

[0021] As an improvement, in step 4, the oxygen-containing polymer is polyethylene glycol (PEG), the hydrothermal reaction conditions are 100-200° C., the reaction time is 8-20 h, and the value of Y is 1-10 wt %.

[0022] The catalyst obtained by the above preparation method is applied in the field of advanced oxidation synergistic photocatalysis to treat organic pollutants in wastewater without aeration, thereby achieving efficient removal thereof.

[0023] Beneficial effects:

[0024] Compared with the prior art, the preparation method of a durable and stable advanced oxidation catalyst without aeration and its application of the present invention have the following advantages:

[0025] (1) The present invention uses carbon nitride CN containing nitrogen defects x As a carrier, the oxygen-rich polymer PEG was introduced to assist in the preparation of an S-type heterojunction V with double defects. O -M-Co3O4@CN x Catalyst, increase its reaction active sites, greatly improve the pollutant removal efficiency, especially 5% VO -M-Co3O4@CN x , the degradation efficiency reaches 0.12min under air conditions -1 , is pure CN catalyst (0.011min -1 )10.9 times, which is V O -M-Co3O4 removes 5 times more organic pollutants. This shows that the technology provided by the present invention can greatly enhance the catalytic removal efficiency of pollutants;

[0026] (2) To solve the problems of easy escape of cobalt ions in Co3O4, causing secondary environmental pollution, easy reduction of catalytic activity and poor PMS activation ability. On the one hand, the present invention selects porous zeolite imidazolate framework (ZIF-67) as a precursor, and pyrolyzes it under atmosphere to obtain Vo-M-Co3O4 photocatalyst to improve its stability and conductivity, wherein the oxygen vacancies (V O ) provides abundant active sites, increases the speed of photogenerated electron generation, accelerates PMS activation and thus enhances the generation of ROS; on the other hand, the present invention introduces oxygen-rich polymer PEG as a structure-directing agent to soften the nitrogen-defective carbon nitride CN X carrier, realize CN x V O -M-Co3O4 coating makes Vo-M-Co3O4 highly dispersed, which is conducive to the efficient activation of PMS;

[0027] (3) The present invention constructs a novel catalytic system for activating PMS to degrade organic pollutants using a carbon nitride-based S-type heterojunction advanced oxidation catalyst with dual defect sites that does not require aeration. The preparation process is simple and easy, and there is no need to aerate the reaction system, the energy consumption is low, and it is suitable for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Monomer CN prepared in different examples x and V O -M-Co3O4 and different proportions of V O -M-Co3O4 added amount of composite sample V O -M-Co3O4@CN x XRD spectra of the catalysts, wherein (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Example 5;

[0029] Figure 2 Monomer CN prepared by different methods x and V O -M-Co3O4 and V O -M-Co3O4@CN xTransmission electron microscopy (TEM) images of the catalysts, wherein (a) is Example 1, (b) is Example 2, and (c) is Example 4;

[0030] Figure 3 (A) with Figure 3 (B) are respectively V prepared in Example 1 and Example 4 of the present invention O -M-Co3O4@CN x High-resolution XPS spectra of C1s and N 1s in situ and ex situ XPS spectra, where (a) is Example 1 and (b) is Example 4;

[0031] Figure 3 (C) with Figure 3 (D) is V prepared in Examples 2 and 4 of the present invention O -M-Co3O4@CN x High-resolution XPS spectra (C) In-situ and ex-situ XPS spectra of Co 2p and O 1s, where (a) is Example 2 and (b) is Example 4;

[0032] Figure 4 (A) is the monomer CN prepared by different methods of the present invention x and V O -M-Co3O4 and different proportions of V O -M-Co3O4 added amount of composite sample V O -M-Co3O4@CN x Linear graph showing the change in the rate of degradation of organic pollutants by the catalysts in a photocatalytic and synergistic manner with PMS activation, wherein (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Example 5;

[0033] Figure 4 (B) is the monomer CN prepared by different methods of the present invention x and V O -M-Co3O4 and different proportions of V O -M-Co3O4 added amount of composite sample V O -M-Co3O4@CN x A bar graph showing the rate of photocatalytic degradation of organic pollutants by synergistic PMS activation using a catalyst, wherein (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Example 5;

[0034] Figure 5 CN prepared in Example 1 and Example 4 of the present invention x and V O -M-Co3O4@CN xLinear graphs showing the changes in the degradation rates of organic pollutants by photocatalysis in combination with PMS activation under air (aerobic) and argon (anaerobic) conditions, where (a) is Example 1 and (b) is Example 4;

[0035] Figure 6 V prepared in Example 4 of the present invention O -M-Co3O4@CN x A histogram of the degradation rate of organic pollutants by photocatalysis synergistically activated by PMS after 6 cycles of the catalyst and a graph of Co ion concentration leaching during the cyclic reaction;

[0036] Figure 7 The monomer CN prepared by different methods of the present invention x and V O -M-Co3O4 and different proportions of V O -M-Co3O4 added amount of composite sample V O -M-Co3O4@CN x Catalyst UV-visible absorption spectrum (DRS) diagram, where (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Example 5;

[0037] Figure 8 V under different methods of the present invention O -M-Co3O4@CN x Photocurrent response diagram of the catalyst, where (a) is Example 1, (b) is Example 2, and (c) is Example 4. DETAILED DESCRIPTION

[0038] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0039] Example 1CN x Catalyst preparation

[0040] Weigh 10g of urea and put it into a 100mL ceramic crucible with a lid, and heat it at 550℃ at a rate of 2℃min. -1 The catalyst was synthesized under the conditions of calcination for 4 hours, ambient temperature of 25-35°C, and relative humidity of about 65-85%. x .

[0041] Example 2VO Preparation of -M-Co3O4 catalyst

[0042] 875 mg of Co(NO₃)₂·6H₂O and 1600 mg of 2-methylimidazole were dissolved in 20 mL of methanol. The mixture was then rapidly stirred and aged at room temperature. The resulting precipitate was washed with ethanol and dried overnight at 50-80°C to obtain the ZIF-67 precursor. The dried ZIF-67 precursor was heated at 550°C for 30 minutes under high-purity nitrogen, then cooled to room temperature in the furnace and calcined in air at 350°C for 2 hours.

[0043] Example 3 1% V O -M-Co3O4@CN x Catalyst preparation

[0044] 2mgV O -M-Co3O4 was prepared into an aqueous solution and sealed with plastic wrap, ultrasonicated, and then stirred at a certain temperature for a period of time using a magnetic stirrer. At the same time, 200 mg of CN x Mix with 2 mL PEG, dilute with a certain volume of deionized water, stir for 10 minutes, and then add different volumes of V O -M-Co3O4 solution to a certain volume. Subsequently, the composite solution was stirred for 1 hour, transferred to a reactor, and hydrothermally treated at 140℃ for 12 hours. After cooling to room temperature, it was washed with deionized water and anhydrous ethanol three times, and dried at 50-80℃ overnight to obtain a composite material named 1% V O -M-Co3O4@CN x , where V O -The addition amount of M-Co3O4 is 1wt%.

[0045] Example 4 5% V O -M-Co3O4@CN x Preparation of photocatalysts

[0046] 10mgV O -M-Co3O4 was prepared into an aqueous solution and sealed with plastic wrap, ultrasonicated, and then stirred at a certain temperature for a period of time using a magnetic stirrer. At the same time, 200 mg of CN x Mix with 2 mL PEG, dilute with a certain volume of deionized water, stir for 10 minutes, and then add different volumes of V O -M-Co3O4 solution to a certain volume. Subsequently, the composite solution was stirred for 1 hour, transferred to a reactor, and hydrothermally treated at 140℃ for 12 hours. After cooling to room temperature, it was washed with deionized water and anhydrous ethanol three times, and dried at 50-80℃ overnight to obtain a composite material named 5% V O -M-Co3O4@CNx , where V O -The addition amount of M-Co3O4 is 5wt%.

[0047] Example 5 10% V O -M-Co3O4@CN x Preparation of photocatalysts

[0048] 20mgV O -M-Co3O4 was prepared into an aqueous solution and sealed with plastic wrap, ultrasonicated, and then stirred at a certain temperature for a period of time using a magnetic stirrer. At the same time, 200 mg of CN x Mix with 2 mL PEG, dilute with a certain volume of deionized water, stir for 10 minutes, and then add different volumes of V O -M-Co3O4 solution to a certain volume. Subsequently, the composite solution was stirred for 1 hour, transferred to a reactor, and hydrothermally treated at 140℃ for 12 hours. After cooling to room temperature, it was washed with deionized water and anhydrous ethanol three times, and dried at 50-80℃ overnight to obtain a composite material named 10% V O -M-Co3O4@CN x , where V O -The addition amount of M-Co3O4 is 10wt%.

[0049] Morphology and characterization testing

[0050] 1. Material Characterization

[0051] 1.XRD analysis

[0052] Figure 1 The XRD patterns of the different catalysts prepared in Examples 1-5 are: Figure 2 a is the composition of different initial masses V O -M-Co3O4@CN x X-ray diffraction (XRD) pattern of the sample. O -M-Co3O4@CN x The crystal structure of (100) and (002) planes corresponds to two CN x Diffraction peaks. Among them, the weaker and broader peak appearing on the (100) plane is attributed to CN x There are nitrogen vacancies (V N ), this is due to CN x The long-range order of the in-plane structure filling is low. By comparing with the Co3O4 standard card (JCPDS.42-1467) as a reference, it is found that V O -M-Co3O4 peaks are in good agreement with the standard mode spectrum, indicating that V O-M-Co3O4 formation. Among them, the characteristic peaks of the XRD spectrum of the material at 2θ=19.0°, 31.2°, 36.8°, 44.8°, 59.4° and 65.3° correspond to (111), (220), (311), (400), (511) and (440) crystal planes respectively. It can be found that V O -M-Co3O4@CN x The XRD patterns of the samples contain CN x and V O -The entire diffraction peak of M-Co3O4 indicates that CN x and V O -M-Co3O4 coexistence. Figure 1 It can be seen that V O -M-Co3O4@CN x The (002) peak of V O -M-Co3O4 shows a small displacement to a higher angle, indicating that the introduction of PEG causes the CN interlayer to shrink.

[0053] 2. Morphology Analysis

[0054] Further analysis of the morphological characteristics of the catalyst materials prepared by the research, Figure 2 (a) is the TEM image of the sample prepared in Example 1, showing that the synthesized photocatalyst has a lamellar morphology. Figure 2 (b) TEM image of the composite sample prepared in Example 3 shows that with the help of oxygen-containing polymer PEG, V O -M-Co3O4 species through softening of CN x The morphological structure makes it well covered, and V O -M-Co3O4 in CN x High degree of dispersion in .

[0055] 3.XPS analysis

[0056] Ex-situ XPS can characterize the material composition, valence state and defects of photocatalytic materials. Figure 3 (A) is the XPS C 1s graph of the samples prepared in Example 1 and Example 4, the original CN x The high-resolution C1s XPS spectrum (a) shows that CN x The CC(sp 2 ), CO / C-NH2 and sp 2 Hybridized carbon has three obvious peaks at 288.10, 286.19 and 284.79 eV respectively. O -M-Co3O4@CN x(b) shifts 0.10 eV in the negative direction. Figure 3 (B) Original CN x The N1s XPS spectrum of the α-HNO3O3 can be well decomposed into four peaks at 404.30, 400.98, 399.30 and 398.48 eV (a), which are attributed to CN x π excitation, CNH, N-(C3) and C=NC peaks. O -M-Co3O4@CN x The π excitation peak corresponding to sample (b) showed a positive shift of 0.1eV, while CNH, N-(C3) and C=NC showed negative shifts of 0.2eV, 0.2eV and 0.1eV respectively. x of 0.98 increases to V O -M-Co3O4@CN x 1.07, higher than CN x The theoretical value is 0.75. x Nitrogen vacancies (V N ) is formed due to the thermal polymerization process of CN x The loss of nitrogen atoms in the framework, and V O -M-Co3O4@CN x Medium V N The increase is due to the V O -M-Co3O4 coupling.

[0057] Figure 3 (C) is the XPS of the samples prepared in Example 2 and Example 4. Through high-resolution Co 2p XPS spectra, V O The Co 2p spectrum of -M-Co3O4(a) consists of two asymmetric peaks, namely: Co 2+ (2p 1 / 2 :795.91eV; 2p 3 / 2 :780.80eV) and Co 3+ (2p 1 / 2 :794.30eV); 2p 3 / 2 :779.26eV), while the peaks at 803.51eV and 787.29eV may be V O -M-Co3O4 satellite peaks. In addition, the Co 2+ / Co 3+ The atomic ratio of V is 1.86, which is significantly deviated from the theoretical value of 0.5. O -M-Co3O4@CN x (b) The atomic ratio in the sample increases to 1.87. According to the law of electrical neutrality, it can be inferred that the excess Co 2+ In VO -M-Co3O4 and V O -M-Co3O4@CN x There is V O This conclusion is further confirmed by its O1s spectrum. Figure 3 (D) is the O1s XPS spectra of the samples prepared in Example 2 and Example 4; the three characteristic peaks at 532.61, 531.7 and 529.50 eV are caused by the adsorption of oxygen (O) by residual / physical adsorbed water molecules in the polluted organic carbon. ads ), 531.1eV surface chemically adsorbed oxygen (O S ) and metal-oxygen bond lattice oxygen (O L ) caused by. Consider O S / O L The ratio of surface oxygen vacancies (V O ) relative amount, the higher the ratio, the higher the surface V O The calculation results show that V O The relative amount of oxygen vacancies on the surface of M-Co3O4 is 44%, indicating that V O -M-Co3O4 is rich in V O . V O -M-Co3O4@CN x The higher O S / O L The value is as high as 0.66%, indicating that there are more V O , which may be due to the higher Co 2+ / Co 3+ Increased V O concentration. In addition, with V O -M-Co3O4(a) compared with V O -M-Co3O4@CN x (b) The Co 2p spectrum and O1s spectrum of the sample also shift toward the direction of lower binding energy, indicating that V O -M-Co3O4 and CN x There is a strong interfacial interaction between them, which is beneficial to electron transfer and the construction of S-type heterostructures.

[0058] Figure 3 The in-situ XPS (b+ light) spectrum of the sample prepared in Example 4 can be seen due to V O -M-Co3O4@CN x A strong interaction is shown at the interface, and the migration of photoexcited electrons is monitored by in situ XPS under xenon lamp illumination, demonstrating an S-type charge transfer route. Figure 3 As shown in (AB), V O -M-Co3O4@CNx The peak positions of C1s and N1s of the heterojunction are positively shifted relative to those in the ex situ spectrum, while V O -M-Co3O4@CN x The O1s of the heterojunction undergoes a negative shift toward the direction of greater binding energy ( Figure 3 (D)). The shift in binding energy indicates that CN x The electron density of V O -M-Co3O4 has an increased electron density, indicating that CN x The photoexcited electrons in the CB migrate to V under light O -M-Co3O4 VB follows the proposed S-type charge transfer route.

[0059] Performance Testing

[0060] 1. Test method for Fenton-type photocatalytic performance in aerobic systems

[0061] A 250mL double-jacketed beaker was used as the reactor for the pollutant degradation performance test. Circulating cooling water was introduced into the jacket of the double-jacketed beaker to eliminate the heat generated by the light source during the catalytic reaction, thereby ensuring that the photocatalytic water decomposition hydrogen production performance test was carried out at room temperature and pressure. O -M-Co3O4@CN x The photocatalytic performance of the S-type heterojunction was tested by adding 10 mg of photocatalyst to 50 mL of ATZ solution (10 mg L -1 ). First, the reaction mixture was equilibrated in the dark for 30 minutes to reach adsorption-desorption equilibrium. After adsorption equilibrium, 0.6 mM PMS was added and the light source was turned on. Every 6 minutes, 0.8 mL of the degradation solution was removed and filtered through a 0.22 μm nylon membrane. The reaction was then immediately stopped with 200 μL of methanol. During the reaction, degradation products were analyzed using a liquid chromatography-mass spectrometry (LC-MS) system.

[0062] 2. Test method for Fenton photocatalytic performance of anaerobic system catalysis

[0063] Anaerobic system: Except for changing the continuous air pump to continuous Ar flow into the catalytic system to remove dissolved oxygen or generate oxygen during the reaction process, other test methods remain unchanged.

[0064] Figure 4 The catalysts prepared in Examples 1-5 were used to study the photocatalytic activity of V in a Fenton-like system under forced convection atmospheric conditions. O -M-Co3O4@CN xThe ability of the pollutant ATZ (10 mg / L) to be degraded by activating PMS under visible light irradiation. Figure 4 (A) reflects the efficiency of different catalysts in degrading organic pollutants with the illumination time. It can be seen that V O -M-Co3O4@CN x exhibited excellent photoactivation capability of PMS, with V O -M-Co3O4 and CN x Compared with the above, the removal efficiency of ATZ is significantly improved. O -M-Co3O4@CN x The removal rate of ATZ was the highest, reaching 97.80% degradation rate within 30 minutes. Figure 4 Based on the data (A), the reaction rate (k) of ATZ degradation by catalyst was calculated according to the pseudo-first-order kinetic model, as shown in Figure 4 (B) As shown. Pure CN prepared by Example 1 x V prepared in Example 2 O -M-Co3O4 reaction rate is only 0.011 and 0.024min -1 , V prepared by Examples 3-5 O -M-Co3O4@CN x At 1wt%, 5wt% and 10wt% V O -M-Co3O4 addition, the reaction rates were 0.063, 0.12, and 0.11 min, respectively -1 , combined with Figure 4 (A) It can be found that the catalytic activity of the catalyst in Example 4 is the highest, reaching 0.12 min -1 .

[0065] Figure 5 The catalysts prepared in Example 1 and Example 4 were evaluated for V under an oxygen-free atmosphere (Ar). O -M-Co3O4@CN x The Fenton-like photocatalytic performance was used to support the construction of the aeration-free system. x With V O -M-Co3O4@CN x The degradation of ATZ was not only not inhibited, but was significantly improved, proving that the system can efficiently degrade pollutants without the presence of oxygen, and successfully constructed a new aeration-free catalytic system for activating PMS to degrade organic pollutants.

[0066] Figure 6 The activity diagram of the visible light synergistic PMS catalytic degradation of pollutants and the Co ion leaching experiment during the reaction process of the sample prepared in Example 4 after 6 cycles of experiments are shown as follows: Figure 6As shown, it was found that V O -M-Co3O4@CN x After 6 cycles of testing, it showed excellent photocatalytic durability and repeatability, and the leaching amount of Co ions was less than 0.4 mg / L, indicating that V O -M-Co3O4@CN x The catalyst has high stability and low Co ion leaching and is environmentally friendly.

[0067] Photoelectrochemical characterization

[0068] Figure 7 The DRS diagrams of the catalysts prepared in Examples 1, 2, 3, 4 and 5 show that V O -The introduction of M-Co3O4 can enhance the x Visible light absorption intensity, thereby improving the absorption and utilization rate of visible light in sunlight.

[0069] Figure 8 The photocurrent response comparison diagram of the photocatalysts of Example 1, Example 2, and Example 4 shows that V O -M-Co3O4@CN x The photocatalyst has a higher separation and migration rate of photogenerated carriers, which indicates that V O The introduction of M-Co3O4 inhibits the x The recombination of photogenerated electron-hole pairs indicates that the construction of S-type heterojunction greatly improves the CN x Catalytic degradation efficiency.

[0070] In summary, the present invention discloses a preparation method and application of a carbon nitride-based S-type heterojunction Fenton-like photocatalyst with double defect sites. Characterization results show that the lamellar structure of nitrogen-defective carbon nitride CN X As a carrier, an oxygen-rich polymer was introduced as a structure-directing agent to soften CN X , then implement CN X MOF-derived V O -M-Co3O4 coating, showing extremely high stability and reusability during the reaction process, and the degradation efficiency under air conditions reached 0.12min -1 , is pure CN catalyst (0.011min -1 )10.9 times, which is V O -M-Co3O4(0.024min -1 ) can remove 5 times more organic pollutants. The increase in the rate of hydrogen production from water can be attributed to the effective separation and migration of photogenerated charges and the enhanced activation ability of PMS. In addition, from an application perspective, unlike traditional O2-dependent degradation systems, V O-M-Co3O4@CN x The efficiency of ATZ degradation through multiple synergistic pathways under anaerobic conditions is much higher than that under aerobic conditions, indicating that V O -M-Co3O4@CN X ATZ catalytic degradation can be achieved without aeration, greatly reducing water treatment costs and having potential practical application value in the field of advanced oxidation wastewater treatment.

[0071] The above description is only a preferred specific embodiment of the present invention, and the protection scope of the present invention is not limited thereto. Any simple change or equivalent replacement of the technical solution that can be obviously obtained by any technician familiar with this technical field within the technical scope disclosed in the present invention falls within the protection scope of the present invention.

Claims

1. A method for preparing a carbon nitride-based S-type heterojunction Fenton-like photocatalyst with dual defect sites without aeration, characterized in that: Preparation of V by introducing oxygen-rich polymer-assisted hydrothermal method O -M-Co3O4@CN X The advanced oxidation catalyst specifically comprises the following steps: Step 1: Weigh 8-12 g of urea into a 50-150 mL ceramic crucible with a lid and heat at 450-600 °C for 2 °C min. -1 The catalyst was synthesized under the conditions of calcination at a heating rate of 4 h, an ambient temperature of 25-35 ° C, and a relative humidity of 65-85%; the obtained catalyst was named CN x ; Step 2: Weigh 750-900 mg of Co(NO3)2∙6H2O and 1200-2000 mg of 2-methylimidazole and dissolve them in methanol solution. The mixed solution was then rapidly stirred and aged at room temperature; the resulting precipitate was washed with ethanol and then dried at 50-80°C overnight to obtain the precursor ZIF-67; Step 3: The dried ZIF-67 precursor was kept at 450-550°C for 10-50 min under high-purity nitrogen protection, cooled to room temperature, and then calcined in air at 300-400°C for 1-5 h. The resulting catalyst was named V O -M-Co3O4; Step 4: Set a certain proportion of V O -M-Co3O4 was prepared into aqueous solution and sealed with plastic wrap and ultrasonicated. Then, a magnetic stirrer was used to stir at a certain temperature for a period of time. At the same time, a certain amount of CN x Mix with oxygen-containing polymer, dilute with a certain volume of deionized water, stir for 5-20 minutes, and then add different volumes of V O -M-Co3O4 solution to a certain volume; then, the composite solution was stirred for 0.5-2h, transferred to a reactor, and subjected to hydrothermal treatment; after cooling to room temperature, it was washed with deionized water and anhydrous ethanol, and dried at 50-80℃ overnight to obtain a composite material named Y% V O -M-Co3O4@CN x ,Y% is expressed as V O -The theoretical addition amount of M-Co3O4; the oxygen-containing polymer is polyethylene glycol, the hydrothermal reaction conditions are 100-200 ℃, and the reaction time is 8-20 h.

2. The preparation method according to claim 1, characterized in that The aging time in step 2 is 20-40 h.

3. The preparation method according to claim 1, characterized in that The heating rate in step 3 is 1-5 ℃ min -1 .

4. The preparation method according to claim 1, characterized in that The value of Y% in step 3 is 1-10 wt%.

5. Application of a carbon nitride-based S-type heterojunction Fenton-like photocatalyst with dual defect sites prepared by any one of the preparation methods of claims 1-4, which does not require aeration, in the field of advanced oxidation synergistic photocatalysis for treating organic pollutants in wastewater without aeration.

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