Composite photo-Fenton catalyst for in-situ H2O2 supply, preparation method and application thereof

Abstract

The present invention belongs to the field of Fenton reagents and wastewater treatment, specifically relating to a composite photo-Fenton catalyst for in-situ H₂O₂ supply, a preparation method, and its application in wastewater treatment. The composite photo-Fenton catalyst disclosed in the present invention comprises glucose oxidase immobilized on a mesoporous Fe-g-C₃N₄ carrier, wherein the mesopores of the Fe-g-C₃N₄ carrier have a pore size of 10 to 30 nm; the molecular weight of the glucose oxidase is 300 to 3000. The composite photo-Fenton catalyst Fe‑g‑C3N4 / GOD of the present invention can catalyze glucose in wastewater to produce H2O2 in situ for photo-Fenton degradation under light conditions. It not only has high photocatalytic degradation efficiency, but also maintains high catalytic activity in a wide pH (3-11) and temperature (20°C-50°C) range. It is suitable for treating a wide range of wastewater types and has low pretreatment requirements for wastewater, without the need for additional H2O2 addition. Less sludge is generated after sewage treatment, and Fe‑g‑C3N4 / GOD is easy to recycle and reuse, greatly reducing the cost of sewage treatment by traditional Fenton methods.

Description

Technical Field

[0001] The present invention belongs to the field of photo-Fenton reagents and sewage treatment, and in particular relates to a composite photo-Fenton catalyst for in-situ supply of H2O2, a preparation method and application thereof in wastewater treatment. Background Art

[0002] Since the French scientist Fenton discovered Fenton's reagent in 1984, it has been widely used in wastewater treatment. + In the presence of ferric iron and H2O2, it is oxidized to trivalent iron and generates ·OH, which can quickly degrade various organic matter.

[0003] Based on the Fenton reagent, researchers have discovered that exposure to ultraviolet and near-ultraviolet wavelengths enhances its oxidative capacity, significantly accelerating the degradation of organic matter and, to a certain extent, reducing the amount of H₂O₂ used. Therefore, photo-Fenton oxidation technology, as a new and highly efficient oxidation technology, has been widely studied and applied in the degradation of pollutants in water.

[0004] The aforementioned Fenton and photo-Fenton processes essentially use iron ions (dissolved iron salts) as catalysts, belonging to homogeneous Fenton. Their pH range is limited to pH 3-5, and homogeneous catalysts are prone to loss, resulting in waste. In recent years, researchers have been committed to developing heterogeneous Fenton and heterogeneous photo-Fenton systems (both using insoluble iron-containing materials as catalysts) to overcome the limitations of traditional homogeneous photo-Fenton reagents and improve their pollutant degradation performance. For example, by combining iron oxides with semiconductor catalysts, the catalytic activity and iron stability of photo-Fenton have been significantly improved.

[0005] Researchers such as Li et al. (Li KY, Liang Y, Yang H, et al. New insight into the mechanism of enhanced photoFenton reaction efficiency for Fe-doped semiconductors: A case study of Fe / gC3N4[J]. Catalysis Today, 2021, 371: 58-63.) have studied and compared the photocatalytic activity of Fe / g-C3N4 under photo-Fenton and dark-Fenton reaction conditions. XPS spectral analysis found that the Fe of Fe / g-C3N4 catalyst 2+ / Fe 3+ The ratio remains unchanged during the light-Fenton reaction. This is consistent with the Fe 2+ / Fe 3+The ratio gradually decreases to form a direct contrast. Under visible light, Fe 3+ Capable of capturing photogenerated electrons from semiconductors and reducing them to Fe 2+ , thereby maintaining the catalytic activity of the photo-Fenton reaction. This new mechanistic insight will guide the design and optimization of high-performance catalysts for advanced oxidation processes by immobilizing transition metal ions in semiconductors.

[0006] Guo et al. (Guo T, Wang K, Zhang GK, et al. A novel alpha-Fe2O3@g-C3N4 catalyst: Synthesis derived from Fe-based MOF and its superior photo-Fenton performance [J]. Applied Surface Science, 2019, 469: 331-339) proposed a Z-scheme heterostructure α-Fe2O3@gC3N4 by co-calcination of melamine and iron-based MOF. The photo-Fenton activity of the catalyst was investigated by degradation of tetracycline (TC) using a visible light / H2O2 system. The optimal composite material FOCN-0.45 degraded about 92% of TC within 60 minutes. The prepared FOCN-0.45 composite material exhibited excellent performance and high stability over a wide pH range.

[0007] Ji et al. (Ji SY, Yang YL, Zhou ZW, et al. Photocatalysis-Fenton of Fe-doped g-C3N4 catalyst and its excellent degradation performance towards RhB[J]. Journal of Water Process Engineering, 2021, 40: 101804) used a two-step calcination-thermal polymerization method to prepare iron-doped graphitic carbon nitride (g-C3N4) nanocomposites with different iron contents (5%, 10%, 15%), and used them as efficient heterogeneous photo-Fenton composites for removing rhodamine B (RhB) in visible light / H2O2 system. In the photo-Fenton system, when the Fe doping amount is 10wt.% (10% Fe-g-C3N4), the degradation rate of RhB can reach more than 90% within 45min.

[0008] In summary, although researchers have prepared a large number of heterogeneous photo-Fenton catalysts that can address some of the challenges of the traditional Fenton reaction, such as improving H₂O₂ utilization, reducing iron sludge in wastewater, and broadening the reaction pH range, heterogeneous photo-Fenton methods all require the external addition of large amounts of H₂O₂ reagents. Besides the high costs and associated safety risks associated with storage and transportation, H₂O₂ production relies on anthraquinone oxidation / reduction, a method that is energy-intensive and prone to environmental hazards. Furthermore, in actual industrial wastewater treatment, the cost of H₂O₂ accounts for over two-thirds of the total cost of the Fenton oxidation process, making the application of Fenton technology very costly. Furthermore, the synergistic photocatalytic-Fenton system also faces challenges such as low reactivity and poor stability. Therefore, the development of photo-Fenton catalysts that combine high activity, low cost, and high stability is crucial for the sustainable development of this classic technology. Summary of the Invention

[0009] To address the problems of the prior art, the present invention aims to provide a composite photo-Fenton catalyst capable of in-situ H2O2 supply, a preparation method, and its application in wastewater treatment. In the presence of glucose, the composite photo-Fenton catalyst can enzymatically convert glucose into H2O2 in situ, eliminating the need for the addition of H2O2 chemical reagents, which can lead to high costs and re-contamination. Compared to traditional Fenton reagents, the composite photo-Fenton catalyst maintains high catalytic activity across a wide pH range (3-11) and temperature range (20°C-50°C). Furthermore, the catalyst produces less sludge after wastewater treatment, making it easy to recycle and reuse, significantly reducing the cost of traditional Fenton wastewater treatment.

[0010] Based on the above purpose, the technical solution adopted by the present invention is as follows:

[0011] In the first aspect, the present invention provides a composite photo-Fenton catalyst for in-situ supply of H2O2, which is made of glucose oxidase (GOD) immobilized on a mesoporous Fe-g-C3N4 carrier, the mass fraction of Fe element in the mesoporous Fe-g-C3N4 carrier is 2%; the pore size of the mesopores in the mesoporous Fe-g-C3N4 carrier is 10 to 30 nm; the molecular weight of glucose oxidase is 300 to 3000.

[0012] The composite photo-Fenton catalyst of the present invention is prepared by immobilizing glucose oxidase (GOD) on a mesoporous Fe-g-C3N4 carrier, and further defines the molecular weight of GOD and the pore size of the mesoporous Fe-g-C3N4 carrier. This is because the pore size of the carrier has a direct impact on the adsorption capacity, enzyme activity and stability of the immobilized enzyme. Fe-g-C3N4, which is rich in excellent mesopores with a pore size of 10 to 30 nm, is an ideal carrier for loading glucose oxidase with a molecular weight of 300 to 3000. The mesoporous Fe-g-C3N4 carrier not only has a physical adsorption effect on glucose oxidase, but also has -OH and -NH2 groups on its surface connected to GOD through chemical bonds. While GOD is immobilized on the mesoporous Fe-g-C3N4, the catalytic activity of GOD itself is not affected.

[0013] The composite photo-Fenton catalyst of the present invention can achieve effective photo-Fenton degradation by reacting with glucose to generate H2O2 in situ. Glucose is widely present in almost all types of wastewater. Therefore, when used for wastewater treatment, the composite photo-Fenton catalyst of the present invention can generate H2O2 in situ, greatly reducing the application cost of existing photo-Fenton catalysts.

[0014] The bio-enzyme catalytic reaction of glucose oxidase (GOD) can generate sufficient H2O2 from glucose substrate under mild conditions. If GOD is directly used as a consumable reagent, the cost is too high and the recyclability is poor. The present invention realizes the loading of GOD through a mesoporous Fe-g-C3N4 carrier, thereby catalyzing the in situ production of H2O2 for biodegradation of glucose in wastewater. The loaded GOD is easy to recover and reuse, greatly reducing the application cost of sewage treatment.

[0015] In a second aspect, the present invention provides a method for preparing the composite photo-Fenton catalyst with in-situ H2O2 supply, comprising the following steps:

[0016] Glucose oxidase and mesoporous Fe-g-C3N4 carrier powder are mixed and dissolved in water. After stirring and loading, the precipitate is collected by centrifugation and dried. Glucose oxidase is immobilized on the mesoporous Fe-g-C3N4 carrier to prepare a composite photo-Fenton catalyst that supplies H2O2 in situ.

[0017] Preferably, the mass ratio of glucose oxidase to mesoporous Fe-g-C3N4 carrier powder is 1:1.

[0018] Preferably, the stirring rate of the stirring load is 280 to 350 rpm, and the stirring time is 120 to 150 min.

[0019] Preferably, the centrifugal speed is 10000-12000 rpm.

[0020] Preferably, the drying temperature is 45-60° C., and the drying time is 12-16 hours.

[0021] Preferably, the mesoporous Fe-g-C3N4 carrier powder is prepared by the following method:

[0022] According to the mass fraction of Fe element in the mesoporous Fe-g-C3N4 catalyst carrier being 2%, melamine and potassium ferrocyanide were weighed, melamine and potassium ferrocyanide were mixed and heated to 550°C at a rate of 5°C / min, and kept warm for 4 hours. After the reaction product was cooled to room temperature, it was ground into powder to obtain a mesoporous Fe-g-C3N4 carrier powder with an Fe mass fraction of 2%.

[0023] The preferred carrier for immobilizing GOD in the present invention is a mesoporous Fe-g-C3N4 carrier containing 2% Fe, because the mesoporous Fe-g-C3N4 carrier containing 2% Fe is itself a photocatalytic Fenton material and has a high catalytic efficiency.

[0024] In a third aspect, the present invention provides the use of the above-mentioned composite photo-Fenton catalyst for in-situ supply of H2O2 in wastewater treatment.

[0025] Preferably, the composite photo-Fenton catalyst that supplies H2O2 in situ does not require additional addition of H2O2 when treating wastewater.

[0026] Glucose is not only a natural decomposition product of polysaccharides / cellulose, but also a major external carbon source for wastewater biochemical treatment. It is widely present in almost all types of wastewater. The composite photo-Fenton catalyst of the present invention can react with glucose to generate H2O2 in situ to achieve effective photo-Fenton degradation. Therefore, the composite photo-Fenton catalyst of the present invention can biochemically treat a wide range of wastewater types.

[0027] Preferably, when the composite photo-Fenton catalyst with in-situ H2O2 is used to treat the wastewater, the pH range of the wastewater is 3 to 11 and the temperature range is 20 to 50°C.

[0028] Compared with traditional Fenton reagents, the composite photo-Fenton catalyst of the present invention maintains high catalytic activity over a wide pH range (3-11) and a wide temperature range (20°C-50°C), has lower requirements for wastewater pretreatment, and produces less sludge after sewage treatment, which is easy to recycle and reuse. No additional H2O2 needs to be added during the treatment process, which greatly reduces the cost of traditional Fenton method for sewage treatment. Therefore, the composite photo-Fenton catalyst of the present invention has great application prospects in wastewater treatment.

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

[0030] (1) The present invention discloses a composite photo-Fenton catalyst for in-situ H2O2 supply, wherein Fe-g-C3N4 rich in excellent mesopores with a pore size of 10 to 30 nm is used as a carrier for loading glucose oxidase. The mesoporous Fe-g-C3N4 carrier not only has a physical adsorption effect on glucose oxidase, but also has -OH and -NH2 groups on its surface connected to GOD through chemical bonds. While GOD is immobilized on the mesoporous Fe-g-C3N4, the catalytic activity of GOD itself is not affected. Moreover, after loading GOD, the pore structure in the Fe-g-C3N4 / GOD catalyst is still largely maintained in the range of 9 to 24 nm, which is beneficial to the effective mass transfer of the subsequent chemical reaction. Therefore, the composite photo-Fenton catalyst of the present invention not only has high catalytic efficiency, but also has a stable structure and can be recycled and reused.

[0031] (2) The composite photo-Fenton catalyst for in-situ H2O2 supply disclosed in the present invention reacts with glucose to generate H2O2 in situ to achieve effective photo-Fenton degradation. It not only has high photocatalytic degradation efficiency, but also maintains high catalytic activity over a wide pH range (3-11) and a wide temperature range (20°C-50°C). It is suitable for treating a wide range of wastewater types and has low pretreatment requirements for wastewater. No additional H2O2 is required. Less sludge is generated after sewage treatment, which is easy to recycle and reuse, greatly reducing the cost of traditional Fenton method for sewage treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 XRD patterns and FTIR patterns of g-C3N4, Fe-g-C3N4, GOD and Fe-g-C3N4 / GOD;

[0033] Figure 2 is the VSM hysteresis loop of Fe-g-C3N4 / GOD;

[0034] Figure 3 The UV-visible absorption spectra, Kubelka-Munk function curves, XPS valence band spectra and band structures of Fe-g-C3N4 and Fe-g-C3N4 / GOD are shown;

[0035] Figure 4 The photocurrent response, electrochemical impedance spectroscopy and photoluminescence spectra of Fe-g-C3N4 and Fe-g-C3N4 / GOD are shown;

[0036] Figure 5 The curves showing the changes of the catalytic degradation performance of Fe-g-C3N4 and Fe-g-C3N4 / GOD with H2O2, light, pH value, temperature and other factors;

[0037] Figure 6 The degradation effect of Fe-g-C3N4 / GOD on refractory coking wastewater;

[0038] Figure 7 OH and O2 - EPR spectrum and schematic diagram of the photosensitization mechanism of Fe-g-C3N4 / GOD;

[0039] Figure 8 The cycling stability of Fe-g-C3N4 / GOD. DETAILED DESCRIPTION

[0040] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below with reference to specific examples. Those skilled in the art will appreciate that the specific examples described herein are intended only to illustrate the present invention and are not intended to limit the present invention. The experimental methods used in the examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available unless otherwise specified.

[0041] Example 1

[0042] This embodiment provides a method for preparing a composite photo-Fenton catalyst (Fe-g-C3N4 / GOD) with in-situ H2O2 supply, comprising the following steps:

[0043] (1) Preparation of mesoporous Fe-g-C3N4 carrier

[0044] A mesoporous Fe-C3N4 support with a 2% Fe content was prepared by heating melamine and potassium ferrocyanide in still air. According to the calculated iron mass percentage, 8.49 g of melamine and 1.51 g of potassium ferrocyanide were weighed and mixed in a covered crucible. After mixing evenly, the mixture was placed in a muffle furnace and heated at 5 °C min -1 The solid was then heated to 550°C at a rate of 0.5°C and held for 4 hours. The solid was then naturally cooled to room temperature and removed. The resulting solid was ground into powder to obtain a mesoporous Fe-g-C3N4 carrier powder with an Fe content of 2% by mass for further use.

[0045] (2) Preparation of composite photo-Fenton catalyst with in-situ H2O2 supply

[0046] 1g of GOD and 1g of mesoporous Fe-g-C3N4 support powder were mixed and dissolved in 50ml of deionized water. The mixture was stirred at 280 rpm on a stirrer at room temperature for 120 minutes. After stirring, the solution was poured into a sample tube and centrifuged at 10,000 rpm to collect the sample. Finally, the collected sample was dried in a vacuum oven at 45°C for 12 hours to achieve the immobilization of GOD on the mesoporous Fe-g-C3N4 support, which is designated as Fe-g-C3N4 / GOD.

[0047] Performance testing

[0048] 1. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR)

[0049] X-ray diffraction, as an effective means of analyzing particle crystal structure, is widely used to clarify the chemical structure composition of the material surface. Figure 1 Figure a shows the XRD patterns of g-C3N4, Fe-g-C3N4, GOD, and Fe-g-C3N4 / GOD. The XRD pattern of g-C3N4 exhibits two typical peaks at 27.5° and 13.1°, which are the characteristic (002) peak of the aromatic system interlayer stacking and the (100) peak corresponding to interfacial separation. Compared with GOD, Fe-g-C3N4 / GOD does not show the characteristic peaks of GOD, indicating that GOD is uniformly distributed in the Fe-g-C3N4 support and does not crystallize.

[0050] In order to further analyze the surface functional group characteristics of g-C3N4, Fe-g-C3N4, GOD and Fe-g-C3N4 / GOD, the samples were characterized by Fourier transform infrared spectroscopy (FTIR). Figure 1 As shown in b. The broad peak is at 3000~3500cm -1 The peaks are caused by the breathing vibration of the -OH group at the aromatic ring defect and the stretching vibration of the terminal -NH2 and =NH amine groups. Compared with Fe-g-C3N4, this broad peak is significantly weakened in Fe-g-C3N4 / GOD, indicating that the terminal -NH2 on g-C3N4 may serve as the original site for connection to the -OH group on GOD through oxidative amination. 1200-1700 cm -1 The absorption peaks in the range are typical stretching modes of aromatic carbon nitride heterocycles. GOD is at 3350~3600cm -1 The main characteristic peak at appears in the spectrum of Fe-gC3N4 / GOD, indicating that GOD is successfully immobilized on the surface of Fe-g-C3N4.

[0051] 2. Analysis of magnetic recovery performance of Fe-g-C3N4 / GOD

[0052] Since the recyclability of the catalyst is also an important aspect in evaluating its performance, we analyzed the vibrating sample magnetometer (VSM) magnetic properties of the Fe-g-C3N4 / GOD material at room temperature in the magnetic field range of -20000 to +20000 Oe. Figure 2As shown, the hysteresis loop of Fe-g-C3N4 / GOD shows that the magnetization curve is consistent with the demagnetization curve, and the remanent magnetization and coercivity tend to zero. This indicates that Fe-g-C3N4 / GOD has typical superparamagnetic properties and is very similar to superparamagnetic Fe3O4. Due to the very low iron content in Fe-g-C3N4 / GOD, the synthesized Fe3O4 nanoparticles are also relatively small. Although the saturation magnetization of Fe-g-C3N4 / GOD is 0.5 emu / g, this result still supports the magnetic recovery of catalysts in water treatment applications.

[0053] 3. Pore structure characteristics of Fe-g-C3N4 / GOD

[0054] Specific surface area and pore structure are often important indicators of a material's reactivity and adsorption capacity. Table 1 shows the specific surface area and pore volume parameters for Fe-g-C3N4 and Fe-g-C3N4 / GOD. Fe-g-C3N4 is rich in high-quality mesoporosity (approximately 20 nm), which provides an ideal location and channel for GOD loading and catalysis. Even after loading with GOD, the pore structure in the Fe-g-C3N4 / GOD material remains largely within the 9-24 nm range, facilitating efficient mass transfer in subsequent chemical reactions.

[0055]

[0056] 4. Band structure analysis

[0057] Since light absorption and energy band structure have a great influence on catalytic performance, the UV-visible diffuse reflectance spectrum (UV-vis DRS) of the material was tested and analyzed within the scanning range of 200-800 nm. Figure 3 As shown in Figure a, the absorption edge of pristine g-C3N4 is approximately 456 nm. As the iron content in the catalyst increases, the adsorption range of the catalyst significantly red-shifts. Compared to pristine g-C3N4, the absorption edge of Fe-g-C3N4 red-shifts to 478 nm, indicating that the light absorption capacity of the Fe-g-C3N4 carrier has been improved. When loaded with GOD enzyme, the adsorption edge of Fe-g-C3N4 / GOD further red-shifts to 487 nm. This may be due to the material's large specific surface area and pore structure, which enhances its light harvesting and absorption capabilities.

[0058] according to Figure 3 The band gaps of g-C3N4, Fe-g-C3N4, and Fe-g-C3N4 / GOD estimated from the Kubelka-Munk function curve in (b) are approximately 2.72 eV, 2.60 eV, and 2.55 eV, respectively. Compared with pure g-C3N4, the relatively narrow band gaps of Fe-g-C3N4 and Fe-g-C3N4 / GOD enable them to absorb more light energy over a wider spectral range.

[0059] Since the positions of the conduction band and valence band are also very important for determining the possible reaction paths in the photocatalytic process, the band gap values calculated by UV-vis DRS, the valence band edge potential (EVB) measured by XPS valence spectrum and the conduction band edge potential (ECB) of the samples were analyzed and compared. Figure 3 c~ Figure 3 As shown in d, the conduction band potentials of Fe-g-C3N4 and Fe-g-C3N4 / GOD are more negative than that of pristine g-C3N4, indicating that the catalyst can effectively promote the generation of photogenerated electron-hole pairs (e - -h + ). The optimized band positions indicate that Fe-g-C3N4 / GOD can generate not only hydroxyl radicals but also superoxide radicals. These results demonstrate that the Fe-g-C3N4 / GOD composite catalyst has strong photocatalytic oxidation potential.

[0060] 5. Electrochemical analysis

[0061] Since the separation rate of photogenerated electron-hole pairs is the key to evaluating the performance of photo-Fenton catalysts, we tested and analyzed the electron-carrier pairs under light excitation through photoluminescence experiments. Figure 4 a The transient photocurrent response of the material is analyzed. As shown in the figure, the photocurrent response of Fe-g-C3N4 is significantly enhanced compared with g-C3N4, confirming that Fe-g-C3N4 has a lower recombination rate of photogenerated electron-hole pairs and a higher separation rate. Figure 4 b The conductivity and photogenerated charge separation rate of the material were analyzed by electrochemical impedance spectroscopy (EIS). The results showed that the Nynquist curve radius of Fe-g-C3N4 was significantly smaller than that of g-C3N4, indicating that Fe-g-C3N4 has a better electron-hole pair separation efficiency. Figure 4 The photoluminescence (PL) intensity of Fe-g-C3N4 in c is significantly reduced, again indicating a low recombination rate of photogenerated electron-hole pairs in the Fe-g-C3N4 catalyst. Furthermore, the Fe-g-C3N4 / GOD catalyst largely retains the electrochemical properties of the Fe-g-C3N4 host, indicating that the GOD-loaded Fe-g-C3N4 / GOD composite catalyst still possesses good photoelectrochemical stability.

[0062] Example 2

[0063] This example analyzes the photo-Fenton performance of the Fe-g-C3N4 / GOD composite photo-Fenton catalyst, its treatment effect on coking wastewater, its reaction mechanism, cyclic stability, and application cost, and comprehensively analyzes the application effect of the Fe-g-C3N4 / GOD composite photo-Fenton catalyst in wastewater treatment. The specific method and results are as follows:

[0064] 1. Analysis of photo-Fenton performance of Fe-g-C3N4 / GOD composite photo-Fenton catalyst

[0065] Glucose oxidase (GOD) is a biological enzyme that can directly generate H2O2 by enzymatic reaction with glucose as substrate. Glucose is not only a natural decomposition product of polysaccharides / cellulose, but also the main external carbon source for wastewater biochemical treatment, so it is widely present in almost all types of wastewater. The byproduct of this reaction, gluconic acid, can also be used as a Fe 3+ and Fe 2+ The Fe-g-C3N4 / GOD catalyst can act as a spontaneous photo-Fenton system in the presence of glucose substrate without the need for external addition of H2O2.

[0066] After the Fe-g-C3N4 and Fe-g-C3N4 / GOD catalysts completed the adsorption-desorption equilibrium of 20 mg / L organic pollutant tetracycline (TC) in the dark reaction stage in the photocatalytic reactor, an appropriate amount of 30% H2O2 was added to the solution and a visible light source provided by a 500W xenon lamp was turned on to carry out a photocatalytic degradation experiment. The photo-Fenton performance of the Fe-g-C3N4 and Fe-g-C3N4 / GOD catalysts was evaluated by monitoring the TC concentration using a spectrophotometer. The results are shown in Figure 2. Figure 5 As shown, Figure 5 a is the removal effect of TC by Fe-g-C3N4 and Fe-g-C3N4 / GOD catalysts in the presence of H2O2. It can be seen that under the condition of adding external H2O2, Fe-g-C3N4 and Feg-C3N4 / GOD as photo-Fenton catalysts both showed high degradation efficiency in the degradation process. Figure 5In Figure 2b, in the absence of external H₂O₂ but in the presence of glucose, the GOD, g-C₃N₄, and Fe-g-C₃N₄ control groups showed negligible degradation of pollutants. Only the Fe-g-C₃N₄ / GOD experimental group exhibited some degradation, with the remaining pollutant concentration less than 60% after 3 hours of reaction. Therefore, the experiments confirm that only in the presence of Fe-g-C₃N₄ / GOD and glucose can the Fe-g-C₃N₄ / GOD composite photo-Fenton catalyst generate H₂O₂ in situ through its reaction with glucose to achieve effective photo-Fenton degradation.

[0067] In order to better analyze the reaction principle, we measured the generation of H2O2 under different reaction conditions. Figure 5 As shown in Figure c, a large amount of H2O2 is produced only when both Fe-g-C3N4 / GOD catalyst and glucose substrate are present, while no H2O2 is produced when Fe-g-C3N4 / GOD exists alone or when g-C3N4 and Fe-g-C3N4 catalysts coexist with glucose substrate.

[0068] from Figure 5 d It can be seen that in the presence of glucose substrate, the introduction of light radiation can further enhance the catalytic activity of Fe-g-C3N4 / GOD catalyst for TC. Figure 5 e~ Figure 5 f also explored the effect of Fe-g-C3N4 / GOD catalyst on pollutant removal efficiency under different pH and temperature conditions. Figure 5 As shown, Fe-g-C3N4 / GOD maintains high catalytic activity under a wide pH range (pH = 3-11) and temperature range (t = 20-50°C). Compared with the homogeneous Fenton process, which can only operate under pH = 3-4, the Fe-g-C3N4 / GOD enzyme-assisted novel photo-Fenton system of the present invention has a wider range of applicability.

[0069] 2. Treatment effect of Fe-g-C3N4 / GOD composite photo-Fenton catalyst on coking wastewater

[0070] Coking wastewater is a type of refractory organic phenolic wastewater produced during the coking process and contains a large amount of highly toxic and carcinogenic cyclic organic compounds. Due to the low biodegradability of these compounds and their high chemical oxygen demand (COD), coking wastewater must be treated by advanced oxidation technologies such as Fenton before it can be biologically treated. The biodegradability of coking wastewater is generally assessed by the BOD5 / COD ratio, where BOD5 represents biological oxygen demand. When the BOD5 / COD ratio is greater than 0.3, the wastewater can be considered biotreatable. In this study, the degradation ability of the Fe-g-C3N4 / GOD catalyst and glucose system in actual coking wastewater was further evaluated.

[0071] like Figure 6 As shown in Figure a, the initial BOD5 / COD ratio of the coking plant wastewater was 0.22, far below the biodegradable threshold of 0.30, making it unsuitable for direct biotreatment. After four hours of treatment with the Fe-g-C3N4 / GOD catalyst in the presence of glucose, the BOD5 / COD ratio increased to 0.35, significantly improving the wastewater's biodegradability. As a control group, the water sample treated with the Fe-g-C3N4 catalyst under the same conditions for four hours had a BOD5 / COD ratio of 0.27, below the threshold of 0.30 and therefore unsuitable for biotreatment.

[0072] Figure 6 b shows the physical appearance of coking wastewater after treatment with different catalysts. From left to right, the color of the coking wastewater gradually becomes clearer. Compared to the original wastewater color, the wastewater treated with the Fe-g-C3N4 catalyst and glucose substrate showed no degradation effect. However, the enzyme-assisted heterogeneous photo-Fenton system composed of the Fe-g-C3N4 / GOD catalyst and glucose substrate not only effectively decolorizes the wastewater, but also allows the catalyst to settle to the bottom after the reaction, making it easy to recover and reuse, while minimizing catalyst costs. Although the traditional Fenton process with external addition of H2O2 shows significant degradation and decolorization effects, the traditional Fenton process not only requires a suitable acidic environment (pH = 3-4) for application, but also produces a large amount of reddish-brown Fe(OH)3 sludge precipitate after the reaction terminates. Therefore, the novel enzyme-assisted photo-Fenton system Fe-g-C3N4 / GOD provided by the present invention has better application and economic benefits than the homogeneous Fenton reaction.

[0073] 3. Study on the reaction mechanism of Fe-g-C3N4 / GOD composite photo-Fenton catalyst

[0074] In order to analyze the active species types in the Fe-g-C3N4 / GOD enzyme-assisted photo-Fenton reaction, we used 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) as a capture agent and detected the electron paramagnetic resonance (EPR) signals of the catalyst in aqueous dispersion under different conditions. Figure 7 As shown, Figure 7 a is the EPR spectrum of OH, Figure 7 b is O2 - The EPR spectrum of Figure 7 c is a schematic diagram of the photosensitization mechanism of Fe-g-C3N4 / GOD composite photo-Fenton catalyst.

[0075] like Figure 7 a. Figure 7 As shown in b, in the absence of glucose substrate, no free radical signal of active substances was observed in Fe-g-C3N4 / GOD. When glucose was added, DMPO·OH and DMPO·O2 were clearly observed in the Fe-g-C3N4 / GOD system. - The spin adduct signal peaks of ·OH and ·O2 have a peak intensity ratio of 1:2:2:1 and 1:1:1:1 respectively. - The characteristic peak intensity is significantly enhanced. Under the coexistence of glucose substrate and Fe-g-C3N4 / GOD, glucose will first undergo enzymatic reaction with GOD on the Fe-g-C3N4 / GOD catalyst to produce H2O2. At the same time, Fe 2+ Can react with H2O2 to produce a large amount of O2 - The above results show that glucose is the active substance of ·OH and ·O2 in the Fe-g-C3N4 / GOD enzyme-assisted photo-Fenton system. - It is a necessary condition for the large-scale production of these active substances, and light can further promote the production of these active substances.

[0076] Figure 7 c The unique photoenzymatic catalytic process of Fe-g-C3N4 / GOD composite photo-Fenton catalyst and glucose under visible light was investigated in this experiment, and the possible reaction mechanism of the Fe-g-C3N4 / GOD enzymatic catalytic process using glucose as a H2O2 precursor was inferred. In the first step, H2O2 can be generated in situ by the enzymatic reaction of glucose oxidation catalyzed by glucose oxidase (GOD). In the second step, the Fe3O4 grains in the Fe-g-C3N4 / GOD catalyst can release Fe 2+ , the Fe 2+ Directly contact with H2O2 generated in situ to produce Fenton reaction, generating a large amount of ·OH and ·O2 -In the third step, Fe-g-C3N4 / GOD catalyst can generate photoinduced electron-hole pairs (e - -h + ), photogenerated electrons can accelerate Fe 3+ Fe 2+ The conversion cycle produces Fe 2+ You can continue with H 2 O 2 The reaction continuously releases ·OH and ·O2 - , thereby achieving continuous and efficient degradation of pollutants.

[0077] 4. Cyclic Stability Analysis of Fe-g-C3N4 / GOD Composite Photo-Fenton Catalyst

[0078] Whether the catalyst can always maintain its performance (such as activity, selectivity and stability) during the reaction process is an important factor to be considered in practical applications. Therefore, the performance of the Fe-g-C3N4 / GOD composite catalyst was evaluated by repeated use. Figure 8 As shown. Figure 8 a is the cyclic stability of the Fe-g-C3N4 / GOD composite catalyst. It can be seen that the degradation ability of the Fe-g-C3N4 / GOD composite photo-Fenton catalyst is slightly reduced after 4 cycles, but it still maintains a high degradation ability overall. Figure 8 b~ Figure 8 (d) XRD, FT-IR, and UV-vis DRS characterizations compare the physical structure and optical properties of the virgin and four-cycle Fe-g-C3N4 / GOD composite catalysts. The spectra show negligible changes in the physical and optical properties of the Fe-g-C3N4 / GOD catalyst even after four cycles, further confirming the stability of this composite photo-Fenton catalyst system. Compared to conventional homogeneous Fenton processes, where reagents cannot be recycled, the recyclability and long-term stability of the Fe-g-C3N4 / GOD catalyst further reduce costs.

[0079] 5. Application cost analysis of Fe-g-C3N4 / GOD composite photo-Fenton catalyst

[0080] The present invention solves the problems of high cost and high energy consumption in the practical application of the traditional homogeneous Fenton process by using an enzyme-assisted photo-Fenton system. Therefore, a brief estimate of the operating cost of the Fe-g-C3N4 / GOD composite photo-Fenton catalyst is made. First, the glucose oxidase (GOD) immobilized on the Fe-g-C3N4 carrier can in situ decompose the free glucose substrate widely present in the wastewater to produce H2O2 in situ, which greatly reduces the storage and transportation cost of H2O2 and improves safety. Secondly, based on the fact that the Fe-g-C3N4 efficient photocatalyst can provide sufficient photogenerated electron-hole pairs under light conditions, the electrons can continuously promote the Fe 2+ and Fe 3+ The effective circulation of FeSO4 reagents and the generation of iron sludge waste are greatly reduced. Finally, the Fe-g-C3N4 / GOD composite photo-Fenton catalyst system can work effectively in a wide pH range (pH = 3 to 11) and temperature range (t = 20 ° C to 50 ° C), thereby reducing the loss of acid and base reagents required in the early acidification and later neutralization processes. Considering the extremely low cost of food-grade GOD and the g-C3N4 matrix derived from cheap melamine or urea precursors, and the fact that the Fe-g-C3N4 / GOD composite photo-Fenton catalyst can be recycled, the total cost of materials and chemical reagents in the new system is almost less than 10% of the traditional homogeneous Fenton reaction.

[0081] Based on the above analysis, the present invention proposes and preliminarily verifies a novel enzyme-assisted photo-Fenton system, namely the Fe-g-C3N4 / GOD composite photo-Fenton catalyst, which can supply H2O2 in situ, based on the mechanism of the enzymatic reaction between glucose and glucose oxidase (GOD) to produce a large amount of H2O2. To immobilize GOD, an Fe-g-C3N4 catalyst with excellent pore structure and photo-Fenton performance was first synthesized to serve as a carrier for loading GOD. The approximately 20nm mesoporous structure of the Fe-g-C3N4 matrix and the abundant amino and hydroxyl functional groups on its surface are crucial for the formation of the highly stable Fe-g-C3N4 / GOD photo-Fenton catalyst.

[0082] As an abundant and free natural resource in wastewater, glucose replaces external H2O2, eliminating the safety risks and high costs of traditional Fenton or photo-Fenton reactions. Experimental results show that in the presence of glucose substrate, Fe-gC3N4 / GOD can effectively degrade pollutants over a wide pH range (pH = 3 to 11) and temperature (t = 20 to 50°C), and exhibits good cyclic stability and recyclability.

[0083] The Fe-g-C₃N₄ / GOD composite photo-Fenton catalyst of the present invention can also increase the BOD₅ / COD ratio of actual coking wastewater from 0.22 to 0.35, thereby achieving biodegradable treatment of coking wastewater. Compared with traditional Fenton systems already used in industry, the composite photo-Fenton catalyst of the present invention significantly reduces costs and chemical reagent usage, thus becoming a simple, efficient, and sustainable alternative solution for wastewater treatment.

Claims

1. A composite photo-Fenton catalyst for in-situ H2O2 supply, characterized in that: The composite photo-Fenton catalyst is made by immobilizing glucose oxidase on a mesoporous Fe-g-C3N4 carrier, and the mass ratio of glucose oxidase to mesoporous Fe-g-C3N4 carrier powder is 1:

1. The composite photo-Fenton catalyst that supplies H2O2 in situ does not require additional H2O2 when treating wastewater. The mass fraction of the Fe element in the mesoporous Fe-g-C3N4 carrier is 2%; the pore size of the mesopores in the mesoporous Fe-g-C3N4 carrier is 10 to 30 nm; and the molecular weight of the glucose oxidase is 300 to 3000.

2. A method for preparing the composite photo-Fenton catalyst with in-situ H2O2 supply according to claim 1, characterized in that: The method comprises the following steps: mixing glucose oxidase and mesoporous Fe-g-C3N4 carrier powder and dissolving the mixture in water; after stirring and loading, collecting the precipitate by centrifugation and drying the precipitate to prepare a composite photo-Fenton catalyst for in-situ H2O2 supply.

3. The method according to claim 2, characterized in that The stirring rate of the stirring load is 280-350 rpm, and the stirring time is 120-150 min.

4. The method according to claim 2, characterized in that The centrifugal speed is 10000-12000 rpm.

5. The method according to claim 2, characterized in that The drying temperature is 45-60° C., and the drying time is 12-16 hours.

6. The method according to claim 2, characterized in that The mesoporous Fe-g-C3N4 carrier powder is prepared by the following method: melamine and potassium ferrocyanide are weighed according to the mass fraction of Fe element in the mesoporous Fe-g-C3N4 catalyst carrier being 2%, melamine and potassium ferrocyanide are mixed and heated to 550°C at a rate of 5°C / min, and the mixture is kept warm for reaction for 4 hours. After the reaction product is cooled to room temperature, it is ground into powder to obtain a mesoporous Fe-g-C3N4 carrier powder with an Fe mass fraction of 2%.

7. Use of the composite photo-Fenton catalyst for in-situ H2O2 supply according to claim 1 in wastewater treatment.

8. The use according to claim 7, characterized in that When the composite photo-Fenton catalyst that in situ supplies H2O2 is used to treat the wastewater, the pH range of the wastewater is 3 to 11 and the temperature range is 20 to 50°C.

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