A composite photocatalyst of carbon nitride wire-wound metal oxide, its preparation method and application

Abstract

The present invention relates to the field of preparation and photocatalytic application of composite catalysts, and particularly to a composite catalyst of carbon nitride wire mesh wound with metal oxide, and a preparation method and application thereof. The method includes the steps of: preparing metal oxide nanoparticles; modifying the metal oxide nanoparticles; preparing the composite catalyst. Melamine, cyanuric acid, and the modified metal oxide nanoparticles in a specified mass ratio are each dispersed in deionized water and stirred for a specified time A. The aqueous dispersion solution of cyanuric acid is added to the aqueous dispersion solution of melamine to obtain a mixed solution, which is stirred at room temperature for a specified time B and then heated and stirred for a specified time C. The temperature of the metal oxide dispersion is raised to the same temperature and added to the mixed solution. After stirring for a specified time D, a hydrothermal reaction is carried out. After the reaction ends and the mixture is allowed to stand and cool, the precipitate obtained in the container is washed and dried. The dried precipitate is calcined by heating under nitrogen, and after cooling, a composite photocatalyst of carbon nitride wire mesh wound with metal oxide is obtained.

Description

Technical Field

[0001] The present invention relates to the field of preparation and photocatalytic application of composite photocatalysts, and particularly to a composite photocatalyst of carbon nitride wound around metal oxide, and a preparation method and application thereof. Background Art

[0002] In recent years, due to their low price and broad-spectrum antibacterial properties, antibiotic drugs have been widely used, even overused, in the medical field. However, such drugs have high stability and are difficult to biodegrade. Only 30% of the antibiotic drugs taken by the human body are absorbed, and the rest are discharged into the natural environment. However, the biodegradation technology adopted by traditional environmental protection units such as sewage treatment plants is difficult to effectively remove antibiotic drugs, which thus become emerging pollutants PPCPs (Pharmaceutical and Personal Care Products) commonly present in soil and water bodies.

[0003] These antibiotic drugs in the environment not only cause pollution, but also induce the generation of resistant microorganisms and resistant genes. These resistant genes can be vertically transferred to the offspring bacteria, continuously damaging the ecological environment and changing the microbial structure and community. Furthermore, during the process of humans and animals ingesting food and water, these resistant genes may also be horizontally transferred to other organisms, endangering public health throughout the food chain.

[0004] In order to fundamentally solve this threat, it is necessary to study the removal mechanism of antibiotic drugs in the environment. Many researchers have confirmed that advanced oxidation processes (AOPs) are highly efficient in destroying the structure of antibiotics. AOPs attack pollutants by activating oxidants to generate free radicals with strong oxidation ability (hydroxyl, sulfate, superoxide, etc.), promoting the degradation of pollutants into small-molecule substances and mineralizing them into CO2 and H2O. Currently, there are many types of oxidants commonly used, including hydrogen peroxide (H2O2) used in Fenton oxidation, peroxymonosulfate (PMS) and persulfate (PDS) used in Fenton-like oxidation, and ozone used in ozone oxidation.

[0005] Catalysts are the key to the development of advanced oxidation technologies, directly determining the activation efficiency of oxidants and indirectly determining the generation quantity of active free radicals. Metal oxides are the most efficient and commonly used catalysts, especially nano-scale metal oxides with particle sizes in the range of dozens to hundreds of nanometers, which have stronger catalytic ability. Among nano-metal oxides, magnetic oxides have a wider range of applications because they can be magnetically recovered. Nevertheless, as a common feature of oxides, metal leaching during the reaction process and weak recovery efficiency in large-scale reactors are still inevitable defects in use.

[0006] New non-metallic organic semiconductor materials represented by graphitic carbon nitride have attracted extensive attention. It has stable chemical properties, good electron transport performance, and shows great application potential in the field of photocatalysis. However, carbon nitride has weak catalytic ability for oxidants such as hydrogen peroxide and persulfate, and powdered carbon nitride cannot be recovered by magnetic force, resulting in low reuse rate. Summary of the Invention

[0007] To solve the above problems, the purpose of the present invention is to provide a composite photocatalyst of carbon nitride wire-wound nano metal oxide, its preparation method and application. By preparing modified nano metal oxide and using supramolecular self-assembly and hydrothermal method to encapsulate the nano metal oxide layer by layer during the synthesis of carbon nitride precursor, a composite photocatalyst with a special material structure of carbon nitride wire-wound nano metal oxide is obtained after pyrolysis, denoted as M x O y #C3N4.

[0008] The photocatalyst obtained by this preparation method has a unique nanostructure, can generate a synergistic effect during the photocatalysis process, improve the activation efficiency of oxidants, and the composite photocatalyst has magnetic recovery performance and high recovery rate. In addition, due to the generation of synergistic effect and the confinement of nano metal oxide, the leaching of metal elements from the composite photocatalyst is less, the catalyst has high stability and high recycling rate.

[0009] According to one aspect of the present invention, a preparation method of a composite photocatalyst of carbon nitride wire-wound metal oxide is characterized by including the following steps:

[0010] Step 1: Prepare metal oxide nanoparticles,

[0011] Step 2: Modify the metal oxide nanoparticles, and surface-modify the metal oxide nanoparticles obtained in Step 1 with a modifier to obtain modified metal oxide nanoparticles.

[0012] Step 3: Prepare the composite photocatalyst. Disperse melamine, cyanuric acid, and the modified metal oxide nanoparticles in deionized water according to a specified mass ratio and continuously stir for a specified time A. Then add the cyanuric acid aqueous dispersion solution to the melamine aqueous dispersion solution to obtain a mixed solution. Stir at room temperature for a specified time B and then heat up and stir for a specified time C. At the same time, raise the temperature of the metal oxide dispersion to the same temperature and add it to the mixed solution. Continue to stir for a specified time D and then carry out a hydrothermal reaction. After the reaction ends and it is left to stand and cool, wash the precipitate obtained in the container multiple times and dry it. Heat the dried precipitate in a nitrogen atmosphere and calcine it. After cooling, a composite photocatalyst of carbon nitride wire-wound metal oxide is obtained.

[0013] Preferably, the specified time A in step three is 30 min or more, and the stirring rate is 400 - 600 rpm.

[0014] The specified time B in step three is 1 - 2 hours, and the stirring rate is 400 - 600 rpm.

[0015] The temperature for heating and stirring in step three is 60 °C, the specified time C is 0.5 - 1 hour, and the stirring rate is 300 - 400 rpm.

[0016] The specified time D in step three is 0.5 - 1 hour, and the stirring rate is 300 - 400 rpm.

[0017] Preferably, the hydrothermal reaction temperature in step three is 200 - 220 °C, and the reaction time is 10 - 12 hours.

[0018] Preferably, the cleaning method in step three is to clean with methanol 2 - 3 times and clean with pure water 2 - 3 times.

[0019] Preferably, the drying method in step three is ordinary blast drying or vacuum drying, and the drying temperature is 50 °C.

[0020] Preferably, the calcination temperature in step three is 520 - 600 °C, the calcination time is 4 - 6 hours, and the heating rate is 2° - 10 °C / min.

[0021] According to another aspect of the present invention, a composite photocatalyst of carbon nitride wire-wound metal oxide is prepared by the foregoing preparation method.

[0022] Among them, the composite photocatalyst of carbon nitride wire-wound metal oxide has a microscopic structure of a substance with metal oxide nanoparticles wire-wound by carbon nitride wire. The single diameter of the carbon nitride wire is 5 - 300 nm, and the size of the wire-wound metal oxide nanoparticles is 5 - 300 nm.

[0023] According to another aspect of the present invention, the foregoing composite photocatalyst of carbon nitride wire-wound metal oxide is applied to catalytic oxidation of antibiotic wastewater for degradation.

[0024] Preferably, the foregoing oxidant is one or more of hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and persulfate (PDS).

[0025] Preferably, the foregoing antibiotic wastewater includes one or more of tetracycline antibiotics and quinolone antibiotic wastewater.

[0026] The concentration of antibiotics in the antibiotic wastewater is 2 mg / L - 100 mg / L.

[0027] Technical effects:

[0028] The composite photocatalyst of carbon nitride wire-wound nano metal oxide provided by the present invention is used to activate the oxidant to treat antibiotic wastewater, and its advantages are as follows:

[0029] (1) By first wrapping and then carbonizing, a wire-mesh carbon nitride structure is generated, which stably confines the nano metal oxide in the carbon nitride matrix, successfully realizing the single-particle dispersion of the nano metal oxide, solving the problem of particle agglomeration, and improving the catalytic efficiency of the oxidant.

[0030] (2) The nano metal oxide is confined in the carbon nitride, and the size of the catalyst is increased from the nano level to the micron level, which is easier to separate and the recovery efficiency is improved.

[0031] (3) Through the synergistic effect of carbon nitride and metal oxide, a catalytic effect far greater than that of the two alone is achieved.

[0032] (4) By winding the carbon nitride wire around the metal oxide, the carbon nitride that could not be magnetically recovered originally can also be recycled.

[0033] (5) Through the confinement of the carbon nitride wire winding, the metal leaching rate is greatly reduced. Description of the Drawings

[0034] Figure 1 It shows the morphological map of the Fe3O4#C3N4 composite photocatalyst.

[0035] Figure 2 It is the transmission electron microscope-dark field scanning image of the Fe3O4#C3N4 composite photocatalyst and the corresponding C and N element distribution maps.

[0036] Figure 3 It is the thermogravimetric diagram of the content of Fe3O4 in the Fe3O4#C3N4 composite photocatalyst.

[0037] Figure 4 It shows the comparison of the removal rates of various catalysts for antibiotic drugs.

[0038] Figure 5 It shows the magnetic recovery performance and metal leaching situation of the composite photocatalyst Fe3O4#C3N4. Detailed Embodiments

[0039] Various exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and in no way limits the present invention and its application or use. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the present invention thorough and complete and to fully convey the scope of the present invention to those skilled in the art. It should be noted that: unless otherwise specified, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments should be construed as merely exemplary and not as limitations.

[0040] As used in the present invention, words such as "comprising" or "including" mean that the elements before this word cover the elements listed after this word, and do not exclude the possibility of also covering other elements.

[0041] All terms used in the present invention (including technical terms or scientific terms) have the same meaning as understood by those of ordinary skill in the art to which the present invention pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary should be understood to have a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such herein.

[0042] For components not described in detail in this part, specific model parameters of the components, the mutual relationships between the components, and the control circuit, they can be considered as technologies, methods, and devices known to those of ordinary skill in the relevant art. However, in appropriate cases, the said technologies, methods, and devices should be regarded as part of the specification.

[0043] The following describes the specific embodiments of the present invention.

[0044] As described in the background art, metal oxides (oxides of common elements such as iron, copper, manganese, cobalt, nickel, etc.) are the most efficient and commonly used catalysts, especially nano-scale metal oxides with particle sizes in the range of dozens to hundreds of nanometers have stronger catalytic capabilities. Among nano-metal oxides, magnetic oxides have a wider range of uses because they can be magnetically recovered. Nevertheless, nano-metal oxides, especially magnetic nano-metal oxides, still have obvious defects during use. On the one hand, due to magnetic attraction, the particles are prone to agglomeration, resulting in the active sites not being significantly exposed during the catalytic process, reducing the catalytic efficiency. On the other hand, the too small particle size makes them disperse slowly and cannot be filtered and separated after being dispersed in a large reactor, and there is an incomplete recovery situation. Therefore, maintaining the dispersion rate of nano-metal oxides during the catalytic process while improving the recovery efficiency is a technical difficulty for nano-metal oxides and magnetic nano-metal oxides as PMS activators in practical water treatment applications.

[0045] In contrast, regarding carbon nitride (g-C3N4, C3N4) catalysts, traditional methods use pyrolysis of urea, dicyandiamide, melamine, etc. to generate carbon nitride with a bulk morphology. The carbon nitride thus generated presents a pore-free bulk, with a small specific surface area and a high recombination rate of photo-generated electrons. Currently, morphologies such as bulk, sheet-like, and tubular have been developed. Nevertheless, in current practical applications, the catalytic ability of metal-free carbon nitride for oxidants such as hydrogen peroxide and peroxymonosulfate is still relatively low, and metal-free carbon nitride is in powder form and cannot be recycled by magnetic force, with poor recycling efficiency.

[0046] On the other hand, using melamine and cyanuric acid to mix and prepare carbon nitride can generate a precursor in the form of supramolecular self-assembly, and then pyrolyze to generate carbon nitride. By adjusting the preparation conditions of the precursor, nano-level regulation of the morphology and structure of carbon nitride can be achieved, and different morphologies can be obtained after pyrolysis. This is because, during the pyrolysis process of melamine, due to the corrosion of cyanuric acid, the finally formed carbon nitride is no longer a pore-free bulk, but a honeycomb-like or wire-mesh-like structure with pores. For carbon nitride, these pores will result in a lower crystallinity, which was originally a defect in the preparation of carbon nitride. However, these research bases provide the basic conditions for constructing multifunctional and novel nanostructures based on carbon nitride, and provide the possibility for loading metal oxides on carbon nitride.

[0047] Through the adjustment of the preparation conditions, the above-mentioned morphology and pore defects of carbon nitride have become adjustable. The present invention creatively forms a carbon nitride carrier with pore defects intentionally during the preparation stage, overcomes the technical prejudice, makes the original defects become effective properties, and successfully disperses and confines nano-level metal oxides in the carbon nitride carrier.

[0048] Figure 1 Denote the composite photocatalyst M prepared by the preparation method of the present invention x O y #Substance structure diagram of C3N4. Figure 1 The shown carbon nitride is sheet-like, but not limited thereto, and can also be prepared into a bulk, tubular, etc. according to requirements.

[0049] Such as Figure 1 As shown, in the sheet-like carbon nitride, the carbon nitride between the two surface layers is formed into a wire-mesh shape. The single diameter of the carbon nitride wire mesh is 5 - 300 nm. Figure 1 The white spherical granular substance shown in is metal oxide, which is mounted in the carbon nitride wire mesh, forming a unique structure in which the carbon nitride wire mesh wraps and coats the nano-metal oxide layer by layer. In addition, it is worth noting that Figure 1The physical scanning electron microscope image of the spherical granular metal oxide shown is that of Fe3O4. However, the metal oxide is not limited to Fe3O4 and can also be oxides of other metal elements such as iron, copper, manganese, cobalt, nickel, etc. From the perspective of facilitating magnetic recovery, metal oxides with magnetism such as iron, cobalt, and nickel are more preferred.

[0050] The following is a detailed description Figure 1 The preparation method of the composite photocatalyst of carbon nitride wire-wound metal oxide shown.

[0051] Step 1: Preparation of Fe3O4 nanoparticles: Weigh a certain mass of FeCl3·6H2O and add it to an ethylene glycol solution. After stirring until completely dissolved, add sodium acetate, continue stirring for 0.5 - 1 h, then transfer it to a hydrothermal reaction kettle, heat it to 200 °C and maintain for 10 - 12 h, magnetically recover the solid particles, wash and dry them to obtain Fe3O4 nanoparticles.

[0052] The preparation method of Fe3O4 nanoparticles is not limited to this, as long as nanoscale Fe3O4 nanoparticles can be obtained.

[0053] Step 2: Modification of Fe3O4 nanoparticles: Add the Fe3O4 nanoparticles obtained in Step 1 to ethanol, mechanically stir and disperse for 0.5 - 1 h, add ammonia water, adjust the pH to 11, and then mechanically stir for 4 - 6 hours. Magnetically recover the solid particles, wash and dry them to obtain modified nano-Fe3O4.

[0054] Through surface modification, the Fe3O4 nanoparticles can be better dispersed in the carrier material (carbon nitride), avoiding aggregation and precipitation. In the present invention, ethanol and ammonia water are used as modifiers for modification, which can introduce hydrophobic functional groups into the Fe3O4 nanoparticles, enabling them to interact with the matrix material, namely the carbon nitride carrier, thus achieving better dispersibility and loadability. However, it is not limited to this, and the modifiers and reaction conditions used can be freely adjusted according to requirements.

[0055] Those skilled in the art can understand that the surface modification can appropriately select or adjust the preparation method, conditions, etc. according to requirements, and is not limited to the above preparation steps.

[0056] Step 3: Preparation of the composite photocatalyst: Disperse melamine, cyanuric acid, and modified nano-Fe3O4 with a certain mass ratio in deionized water and continuously stir for time A. Then add the cyanuric acid aqueous dispersion solution to the melamine aqueous dispersion solution, mechanically stir at room temperature for time B, and then raise the temperature and stir for time C. At the same time, also raise the temperature of the nano-Fe3O4 dispersion to the same temperature, and then add it to the mixed solution, and the mixed solution continues to be mechanically stirred for time D. Transfer the mixed solution to a hydrothermal reaction kettle for hydrothermal reaction. After the reaction ends, let it stand and cool, and then wash the precipitate obtained in the container multiple times and dry it. Put the dried precipitate into a porcelain boat, cover it, and calcine it under a nitrogen atmosphere by heating, and then cool to obtain the final catalyst.

[0057] As described above, the carbon nitride prepared only using melamine presents a non-porous block shape, while after adding cyanuric acid, through the etching effect of cyanuric acid, pores can be formed in the carbon nitride, thereby forming the carbon nitride into a wire mesh shape (refer to Figure 1 ). By adjusting the preparation conditions such as the raw material ratio, temperature, and time in Step 3, the morphology of the wire mesh-shaped carbon nitride can be adjusted. The morphology of the wire mesh-shaped carbon nitride will determine the catalytic performance of the carbon nitride itself and the loading performance on the metal oxide, and the loading performance on the metal oxide will in turn determine the catalytic performance of the metal oxide and the synergistic effect between the two. Therefore, the morphology of the wire mesh-shaped carbon nitride, as well as the loading amount and loading state of the metal oxide in the wire mesh-shaped carbon nitride, are the key to determining the performance of the composite photocatalyst of the present invention. The inventors of the present application have verified the preparation conditions of the composite photocatalyst with the best morphology through a large number of experiments. The following will detail each preparation condition in the preparation method.

[0058] Preferably, the mass ratio of FeCl3·H2O, ethylene glycol, and sodium acetate described in Step 1 is 1:32-35:2-3.

[0059] Preferably, the cleaning method described in Step 1 is to clean with ethanol 2-3 times and then clean with pure water 2-3 times.

[0060] Preferably, the drying method described in Step 1 is ordinary blowing drying or vacuum drying, and the drying temperature is 60-80°C.

[0061] Preferably, the mass ratio of Fe3O4, ethanol, and ammonia water described in Step 2 is 1:30-35:5-10, and the concentration of the ammonia water is 25%-28%.

[0062] Preferably, the method of adjusting the pH described in Step 2 is to add a NaOH solution.

[0063] Preferably, the cleaning method and drying method described in Step 2 are the same as those in Step 1.

[0064] Preferably, the mass ratio of melamine, cyanuric acid, modified nano-Fe3O4, and deionized water in step three is 1:1.02:0.02-0.1:20-50.

[0065] Here, as described above, when the mass ratio of melamine, cyanuric acid, modified nano-Fe3O4, and deionized water is different, the morphology of the silk-like carbon nitride formed is completely different. The morphology of carbon nitride determines its own catalytic performance and the loading performance on metal oxides, and the loading performance on metal oxides will in turn determine the catalytic performance of metal oxides. Moreover, the mass ratio and loading state of metal oxides relative to carbon nitride affect the synergistic effect between the two and the subsequent magnetic recovery performance. Therefore, the morphology of the silk-like carbon nitride and the loading amount and loading state of metal oxides in the silk-like carbon nitride are the key to determining the performance of the composite photocatalyst of the present invention.

[0066] The inventors of the present application conducted a large number of experiments to explore the optimal mass ratio of melamine, cyanuric acid, modified nano-Fe3O4, and deionized water.

[0067] Experimental conditions: The concentration of ofloxacin is 20 mg / L, the dosage of the catalyst is 0.2 g / L, the dosage of PMS is 0.2 g / L, the initial pH value is 7, the temperature is 20 °C, and the light condition is natural light or a 300-watt xenon lamp. The removal rate of ofloxacin at 40 min of reaction was measured at 294 nm using an ultraviolet spectrophotometer.

[0068] Experimental data 1: Only adjust the proportion of cyanuric acid (taking the mass of melamine as the benchmark, and the mass ratios of cyanuric acid, modified nano-Fe3O4, and deionized water relative to melamine):

[0069]

[0070] According to the empirical ratio, the mass ratio of melamine to cyanuric acid in the range of 1:0.5-2 can effectively synthesize carbon nitride. Therefore, synthesis experiments were carried out with a mass ratio in the range of 1:0.25-3, and the catalytic performance of the catalysts obtained under various synthesis conditions was evaluated.

[0071] It can be seen that when the mass ratio of melamine to cyanuric acid is in the range of 1:1-1.05, the removal rate of ofloxacin can reach more than 95%. Especially when the mass ratio is 1:1.02, the removal efficiency of ofloxacin can reach 99%.

[0072] In addition, when the dosage of cyanuric acid is small, due to the insufficient corrosion effect of cyanuric acid on melamine, sufficient pores cannot be formed in carbon nitride. Therefore, the modified nano-Fe3O4 particles cannot be fully loaded into the pores of carbon nitride. As a result, with the decrease in the proportion of cyanuric acid, the removal rate of ofloxacin decreases sharply. When the mass ratio of cyanuric acid is less than 0.25, the formed carbon nitride is close to a poreless block, and the prepared composite photocatalyst has the same removal effect on antibiotic drugs as the pure carbon nitride catalyst.

[0073] On the other hand, when the dosage of cyanuric acid is large, its corrosion effect on melamine is too strong, and the formed carbon nitride has too many pores (defects). When there are too many pores, the stability of carbon nitride decreases, and it is difficult to fully confine and wrap Fe3O4. When the mass ratio of cyanuric acid reaches 3, the solid morphology of carbon nitride cannot be maintained, and the composite photocatalyst cannot be prepared.

[0074] Through the above experiments, the inventors of this application found that when the mass ratio of melamine to cyanuric acid is in the range of 1:1 - 1.05, not only can a composite photocatalyst with a stable morphology be prepared, but also the best loading performance for Fe3O4 can be obtained. The above experiments were carried out for the removal rate of ofloxacin. However, as long as the mass ratio of melamine to cyanuric acid is in the range of 1:1 - 1.05, the best loading performance for Fe3O4 can be ensured. When removing other antibiotic drugs other than ofloxacin, the mass ratio of Fe3O4 can be appropriately adjusted.

[0075] Experimental data 2: Only adjust the proportion of modified nano-Fe3O4 (the mass of melamine is used as the benchmark, and the mass ratios of cyanuric acid, modified nano-Fe3O4, and deionized water relative to the mass of melamine):

[0076]

[0077] It can be seen that when the mass ratio of the incorporated modified nano-Fe3O4 is within the range of 0.08 - 0.12, the removal rate of ofloxacin can reach over 95%. When the dosage of the modified nano-Fe3O4 gradually decreases, the synergistic effect between the modified nano-Fe3O4 and carbon nitride is insufficient. Moreover, when the dosage of the modified nano-Fe3O4 gradually decreases, it can be predicted that the magnetic recovery performance of the composite photocatalyst will be greatly reduced. When the mass ratio of the modified nano-Fe3O4 is within the range of 0.08 - 0.12, especially near 0.1, the optimal ofloxacin removal rate can be achieved. When the dosage of the modified nano-Fe3O4 is excessive, for example, reaching 0.2, the synergistic effect between the modified nano-Fe3O4 and carbon nitride instead decreases. When the dosage of the modified nano-Fe3O4 is further increased, it actually exceeds the loading capacity of the porous carbon nitride. Therefore, the loading amount of the modified nano-Fe3O4 cannot be further increased, and it is meaningless to continue increasing the dosage of the modified nano-Fe3O4. It should be noted that for different antibiotic drugs, the optimal mass ratio of Fe3O4 is slightly different.

[0078] Experimental data three: Only adjust the proportion of deionized water (taking the mass of melamine as the benchmark, the mass ratios of cyanuric acid, modified nano-Fe3O4, and deionized water relative to melamine):

[0079]

[0080] It can be seen that when the mass ratio of the added solvent water is within 20 - 50, the synthesized catalyst can achieve an ofloxacin removal rate of over 98%. When the solvent water is too little, it is speculated that the dispersion rates of melamine, cyanuric acid, and modified nano-Fe3O4 in the solvent water are not ideal. Especially, the dissolution rates of melamine and cyanuric acid in water are relatively low. When the solvent water is insufficient, melamine and cyanuric acid are prone to agglomeration, resulting in poor dispersion rates and affecting the quality of the prepared carbon nitride. When the solvent water is too much, the hydrothermal reaction time becomes longer, and the defect rate of the prepared carbon nitride becomes higher. Therefore, it is preferably that the mass ratio of the solvent water is within the range of 20 - 50, which can not affect the ofloxacin removal rate.

[0081] Preferably, the stirring time A in step three is 30 min or more, and the stirring rate is 400 - 600 rpm.

[0082] Preferably, the stirring time B in step three is 1 - 2 hours, and the stirring rate is 400 - 600 rpm.

[0083] Preferably, the temperature for heating and stirring in step three is 60 - 65 °C, the stirring time C is 0.5 - 1 hour, and the stirring rate is 300 - 400 rpm.

[0084] Preferably, the stirring time D in step 3 is 0.5 - 1 hour, and the stirring rate is 300 - 400 rpm.

[0085] Preferably, the hydrothermal reaction temperature in step 3 is 200 - 220 °C, and the reaction time is 10 - 12 hours.

[0086] Preferably, the cleaning method in step 3 is to clean with methanol 2 - 3 times and then clean with pure water 2 - 3 times.

[0087] Preferably, the drying method in step 3 is ordinary blow - air drying or vacuum drying, and the drying temperature is 50 °C.

[0088] Preferably, the calcination temperature in step 3 is 520 - 600 °C, the calcination time is 4 - 6 hours, and the heating rate is 2° - 10 °C / min.

[0089] The composite photocatalyst of carbon nitride wire - wound nano - Fe3O4 described in the present invention is prepared according to the above steps.

[0090] The composite photocatalyst of carbon nitride wire - wound nano - Fe3O4 described in the present invention is characterized in that the microscopic structure of the substance presents as wire - wound particles. Among them, the diameter of a single carbon nitride wire is between 5 - 300 nm, and the size range of the wound nano - Fe3O4 particles is between 5 - 300 nm.

[0091] In this regard, through the preparation conditions of step 1 and step 3, a carbon nitride wire diameter between 5 - 300 nm and a nano - Fe3O4 particle size between 5 - 300 nm can be obtained.

[0092] The application range of the composite photocatalyst of carbon nitride wire - wound nano - Fe3O4 described in the present invention is to catalyze oxidants to degrade antibiotic wastewater.

[0093] The oxidant described in the present invention is one or more of H2O2, PMS, and PDS.

[0094] The range of the antibiotic wastewater includes tetracycline - type antibiotics and quinolone - type antibiotic wastewater, specifically one or more of tetracycline, oxytetracycline, ofloxacin, ciprofloxacin, and norfloxacin.

[0095] The concentration range of antibiotics in the antibiotic wastewater is 2 mg / L - 100 mg / L.

[0096] The following combines specific examples to illustrate the catalytic effects of the composite photocatalysts obtained under different preparation conditions. Example 1:

[0097] Preparation of Fe3O4 nanoparticles: Weigh 2.0 g of FeCl3·6H2O and add it to 70.0 g of ethylene glycol solution. Stir until completely dissolved, then add 5.0 g of sodium acetate. Continue stirring for 0.5 h, transfer to a 100 mL hydrothermal reaction kettle, heat up to 200 °C and maintain for 10 h. Magnetically recover the solid particles, wash them twice with absolute ethanol and pure water respectively, and dry them in a blast drying oven at 70 °C for 8 h to obtain Fe3O4 nanoparticles.

[0098] Modification of Fe3O4 nanoparticles: Take 2.0 g of the obtained Fe3O4 nanoparticles and add them to 60.0 g of ethanol. Mechanically stir and disperse for 0.5 h, add 14.56 g of 25% ammonia water, adjust the pH to 11, and then mechanically stir for 4 hours. Magnetically recover the solid particles, wash them twice with absolute ethanol and pure water respectively, and dry them to obtain modified nano-Fe3O4.

[0099] Preparation of composite photocatalyst: Take 3.0 g of melamine, 3.06 g of cyanuric acid, and 0.28 g of modified nano-Fe3O4, disperse them in 60 mL of deionized water respectively and continuously stir for 0.5 h, with a stirring speed of 600 rpm. Then add the cyanuric acid aqueous dispersion solution to the melamine aqueous dispersion solution, mechanically stir at room temperature for 1 h with the stirring speed unchanged, then heat up to 60 °C and stir for 0.5 h, and the speed is reduced to 300 rpm. At the same time, raise the temperature of the nano-Fe3O4 dispersion to 60 °C, and then add it to the mixture. The mixture continues to be mechanically stirred for 0.5 h. Transfer the mixture to a 250 mL hydrothermal reaction kettle and carry out hydrothermal reaction at 200 °C for 10 h. After the reaction is completed, let it stand and cool. Wash the precipitate obtained in the container twice with methanol and pure water respectively, and dry it in a blast drying oven at 50 °C for 8 h. Put the dried precipitate into a porcelain boat, cover it, and calcine it at a heating rate of 5 °C / min to 550 °C in a nitrogen atmosphere for 4 h, and cool to obtain the final catalyst.

[0100] Apply the composite photocatalyst prepared by the above method to activate PMS to degrade ofloxacin wastewater. The reaction conditions are as follows: ofloxacin concentration is 20 mg / L, catalyst dosage is 0.2 g / L, PMS dosage is 0.2 g / L, initial pH value is 7, temperature is 20 °C, and the light condition is natural light or using a 300-watt xenon lamp. At this time, the removal rate of ofloxacin reaches 99.1% within 40 min. The ofloxacin removal rate is measured by ultraviolet spectrophotometry at a measurement wavelength of 294 nm. Use magnetic recovery to achieve a catalyst recovery rate of 99.5% within 2 min. Example 2:

[0101] Preparation of Fe3O4 nanoparticles: Weigh 3.0 g of FeCl3·6H2O and add it to 105.0 g of ethylene glycol solution. After stirring until completely dissolved, add 9.0 g of sodium acetate, and continue stirring for 1 h with a mechanical stirring speed of 600 rpm. Transfer the mixed solution to a hydrothermal reaction kettle with a capacity of 200 mL, heat it to 200 °C and maintain for 12 h. Magnetically recover the solid particles, wash them 3 times each with absolute ethanol and pure water, and dry them in a blast drying oven at 80 °C for 8 h to obtain Fe3O4 nanoparticles.

[0102] Modification of Fe3O4 nanoparticles: Take 3.0 g of the obtained Fe3O4 nanoparticles and add them to 105.0 g of ethanol. Mechanically stir and disperse for 1 h, add 27.3 g of 28% ammonia water, adjust the pH to 11, and then mechanically stir for 6 hours. Magnetically recover the solid particles, wash them 3 times each with absolute ethanol and pure water, and dry them to obtain modified nano-Fe3O4.

[0103] Preparation of composite photocatalyst: Take 5.0 g of melamine, 5.1 g of cyanuric acid, and 0.5 g of modified nano-Fe3O4, and disperse them in 100 mL of deionized water respectively and continuously stir for 0.5 h with a speed of 600 rpm. Then add the cyanuric acid aqueous dispersion solution to the melamine aqueous dispersion solution, mechanically stir at room temperature for 1 h, then heat up to 60 °C and stir for 1 h, and reduce the speed to 400 rpm. At the same time, raise the temperature of the nano-Fe3O4 dispersion liquid to 60 °C, and then add it to the mixed solution. The mixed solution continues to be mechanically stirred for 1 h. Transfer the mixed solution to a hydrothermal reaction kettle with a capacity of 500 mL, and carry out hydrothermal reaction at 220 °C for 12 h. After the reaction ends, let it stand and cool. Wash the precipitate obtained in the container 3 times each with methanol and pure water, and dry it in vacuum at 50 °C for 8 h. Put the dried precipitate into a porcelain boat, cover it, and calcine it at a heating rate of 5 °C / min to 550 °C in a nitrogen atmosphere for 5 h, and cool it to obtain the final catalyst.

[0104] Apply the catalyst prepared by the above method to activate H2O2 to degrade norfloxacin wastewater. The reaction conditions are as follows: norfloxacin concentration is 10 mg / L, catalyst dosage is 0.1 g / L, H2O2 dosage is 0.2 mL / L, the initial pH value is 7, the temperature is 20 °C, and the light condition is natural light or using a 300-watt xenon lamp. At this time, the removal rate of norfloxacin reaches 95% within 40 min. The removal rate of norfloxacin is measured by ultraviolet spectrophotometry at a measurement wavelength of 273 nm. Use magnetic recovery to achieve a 99% catalyst recovery rate within 2 min. Example 3:

[0105] Preparation of Fe3O4 nanoparticles: Weigh 2.0 g of FeCl3·6H2O and add it to 65.0 g of ethylene glycol solution. Stir until completely dissolved, then add 4.5 g of sodium acetate. Continue stirring for 0.5 h with a mechanical stirring speed of 500 rpm. Transfer it to a 100 mL hydrothermal reaction kettle, heat up to 200 °C and maintain for 10 h. Magnetically recover the solid particles, wash them twice with anhydrous ethanol and pure water respectively, and dry them in a blast drying oven at 70 °C for 8 h to obtain Fe3O4 nanoparticles.

[0106] Modification of Fe3O4 nanoparticles: Take 2.0 g of the obtained Fe3O4 nanoparticles and add them to 60.0 g of ethanol. Mechanically stir and disperse for 0.5 h, add 18.2 g of 25% ammonia water to adjust the pH to 11, and then mechanically stir for 4 hours. Magnetically recover the solid particles, wash them twice with anhydrous ethanol and pure water respectively, and dry them to obtain modified nano-Fe3O4.

[0107] Preparation of composite photocatalyst: Take 2.0 g of melamine, 2.04 g of cyanuric acid, and 0.22 g of modified nano-Fe3O4, and disperse them in 100 mL of deionized water respectively and continuously stir for 0.5 h with a rotation speed of 400 rpm. Then add the cyanuric acid aqueous dispersion solution to the melamine aqueous dispersion solution, mechanically stir at room temperature for 1 h, and then heat up to 60 °C and stir for 0.5 h. At the same time, also raise the temperature of the nano-Fe3O4 dispersion liquid to the same temperature, and then add it to the mixed solution. The mixed solution continues to be mechanically stirred for 0.5 h. Transfer the mixed solution to a hydrothermal reaction kettle with a volume of 500 mL, and carry out hydrothermal reaction at 220 °C for 12 h. After the reaction ends, let it stand and cool, wash the precipitate obtained in the container twice with methanol and pure water respectively, and dry it in a blast drying oven at 50 °C for 8 h. Put the dried precipitate into a porcelain boat, cover it, and calcine it at a heating rate of 5 °C / min to 600 °C in a nitrogen atmosphere for 4 h, and cool to obtain the final catalyst.

[0108] Apply the catalyst prepared by the above method to activate PDS to degrade tetracycline wastewater. The reaction conditions are: tetracycline concentration 20 mg / L, catalyst dosage 0.3 g / L, PDS dosage 0.3 g / L, initial pH value 7, temperature 20 °C, and the light condition is natural light or using a 3 kW xenon lamp. At this time, the removal rate of tetracycline reaches 99% within 40 min. The removal rate of tetracycline is measured by ultraviolet spectrophotometry at a measurement wavelength of 352 nm. Use magnetic recovery to achieve a 99% catalyst recovery rate within 3 min.

[0109] Next, refer to Figures 1 - 5 Describe the morphology and performance data of the composite photocatalyst obtained by the preparation method of the present invention.

[0110] Figure 2The left figure in [ref] shows that the single diameter of the C3N4 wire mesh in Fe3O4#C3N4 obtained by the preparation method of the present invention is in the order of 5 - 300 nm. In addition, Figure 2 The middle and right figures in [ref] show the transmission electron microscopy-dark field scanning image of the Fe3O4#C3N4 composite photocatalyst and the corresponding distribution maps of C and N elements. When the observation magnification is enlarged to 100 nm, it is observed that C and N elements are evenly distributed, forming a straight tube, which indicates the successful construction of the C3N4 wire mesh in the nanostructure.

[0111] Figure 3 The thermogravimetric diagram in [ref] shows the content of Fe3O4 in the composite photocatalyst obtained by the preparation method of the present invention. Figure 3 The thermogravimetric result shows that the actual proportion of Fe3O4 in the prepared Fe3O4#C3N4 composite photocatalyst is 10.8%, achieving a good Fe3O4 loading effect and facilitating the formation of the synergistic effect between Fe3O4 and C3N4.

[0112] Figure 4 shows the comparison of the catalytic effects of different catalysts. Among them, Figure 4 (A) in [ref] represents the ofloxacin adsorption capacity of Fe3O4, C3N4, and Fe3O4#C3N4 relying only on adsorption. Figure 4 (B) in [ref] represents the degradation efficiency of Fe3O4, Fe3O4 + C3N4, and Fe3O4#C3N4 for ofloxacin.

[0113] Test conditions: ofloxacin concentration 20 mg / L, total amount of catalyst per single reaction 0.2 g / L, initial pH value 7, test solution 200 mL, reaction time 40 min; the amount of Fe3O4 in the catalyst in Figure B is constant at 0.0216 g / L, PMS dosage 0.2 g / L, and the light condition is natural light or a 300-watt xenon lamp.

[0114] Figure 4 The results of (A) show that the removal rates of pure adsorption of ofloxacin by Fe3O4, C3N4, and Fe3O4#C3N4 are all lower than 10%, while Figure 4 All kinds of data in (B) show higher removal rates. This indicates that for the removal rate of ofloxacin by each catalyst, the contribution of the adsorption effect is limited, and the photocatalysis mainly plays a role.

[0115] From Figure 4As can be seen from the results of (B), at the same proportion of Fe3O4 by weight, obviously the catalytic effect of Fe3O4#C3N4 far exceeds that of the other catalysts, about 2.9 times that of pure Fe3O4 and 5.1 times that of pure C3N4. This indicates that the construction of the special nanostructure greatly improves the catalytic activity, and a synergistic effect of 1 + 1 > 2 is generated between the nano Fe3O4 and the C3N4 wire mesh (the removal rate of pure Fe3O4 is about 45%, the removal rate of pure C3N4 is about 21%, and the removal rate of Fe3O4#C3N4 is close to 100%). This is because the unique structure of the present invention accelerates the valence state cycle of Fe during the catalytic reaction process, which is beneficial to the catalytic PMS. This result shows that the composite photocatalyst provided by the present invention can achieve higher catalytic efficiency and active site utilization rate at the same Fe3O4 content.

[0116] Figure 5 Shows the magnetic recovery performance and metal leaching of the composite photocatalyst Fe3O4#C3N4. Figure 5 (A)represents the recovery rate of the catalyst recovered magnetically from the side within 2 min (test conditions: 1800 mL of solution and 0.36 g of catalyst were loaded into a reactor with a diameter of 12 cm and a height of 20 cm); Figure 5 (B)represents the Fe element leaching of Fe3O4 and Fe3O4#C3N4 when the amount of Fe3O4 is constant during five cycles of use. The reaction conditions are the same as Figure 4 (B).

[0117] From Figure 5 (A), it can be seen that since pure C3N4 has no magnetism, the recovery rate is 0. The magnetic recovery rate of Fe3O4 from the side is 89.3%, and there is still a loss of more than 10%. The recovery rate of the Fe3O4#C3N4 catalyst reaches 99.5%. This is because, under the same magnetic force, the C3N4 catalyst in the present invention is no longer a nano-scale powder, and the Fe3O4 catalyst is no longer a nano-scale particle. The two are organically combined into a larger particle size at the micron scale, which is more conducive to macroscopic recovery, resource conservation, and multiple recycling. In particular, through the structure of winding the metal oxide with the carbon nitride wire mesh, the originally unrecoverable carbon nitride can also be recovered, greatly improving the utilization efficiency of the catalyst.

[0118] Figure 5 The results of (B) show that when the iron element is constant, the metal leaching of the composite photocatalyst Fe3O4#C3N4 is only about 10% of that of pure Fe3O4, which can be regarded as almost no loss. This indicates that the generation of the special nanostructure can restrict Fe3O4 through the wire mesh structure, increasing the stability of the catalyst. Therefore, the catalytic efficiency of the recovered catalyst can be maintained well, and the reusability is strong.

[0119] The above describes the embodiments of the present invention, but is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A preparation method of a composite photocatalyst of carbon nitride wire-wound iron oxide, characterized in that It includes the following steps: Step 1: Prepare magnetite nanoparticles. Step 2: Modify the magnetite nanoparticles. Add the magnetite nanoparticles obtained in Step 1 into ethanol, mechanically stir for a specified time E, add ammonia water, adjust the pH to 11, then mechanically stir for a specified time F, magnetically recover the solid particles, wash and dry them to obtain modified magnetite nanoparticles. Step 3: Prepare the composite catalyst. Disperse melamine, cyanuric acid, and the modified magnetite nanoparticles in deionized water at a specified mass ratio and continuously stir for a specified time A. Then add the cyanuric acid aqueous dispersion solution into the melamine aqueous dispersion solution to obtain a mixed solution. Stir at room temperature for a specified time B and then heat up and stir for a specified time C. At the same time, raise the temperature of the magnetite dispersion to the same temperature and add it into the mixed solution. Continue to stir for a specified time D and then carry out a hydrothermal reaction. After the reaction ends and it is left to stand and cool, wash the precipitate obtained in the container multiple times and dry it. Heat the dried precipitate to calcine in a nitrogen atmosphere and cool it to obtain a composite photocatalyst with carbon nitride wire mesh wrapped around magnetite. The mass ratio of melamine, cyanuric acid, and modified magnetite nanoparticles is 1:1 - 1.05:0.02 - 0.

1.

2. The preparation method according to claim 1, wherein in Step 2, the specified time E is 0.5 - 1 hour, and the specified time F is 4 - 6 hours. in Step 3, the specified time A is 30 min or more, and the stirring rate is 400 - 600 rpm. in Step 3, the specified time B is 1 - 2 hours, and the stirring rate is 400 - 600 rpm. in Step 3, the temperature for heating and stirring is 60°C, the specified time C is 0.5 - 1 hour, and the stirring rate is 300 - 400 rpm. in Step 3, the specified time D is 0.5 - 1 hour, and the stirring rate is 300 - 400 rpm.

3. The preparation method according to claim 1, wherein in Step 3, the hydrothermal reaction temperature is 200 - 220°C, and the reaction time is 10 - 12 hours.

4. The preparation method according to claim 1, wherein the cleaning method in Step 3 is to wash 2 - 3 times with methanol and 2 - 3 times with pure water.

5. The preparation method according to claim 1, wherein the drying method in Step 3 is ordinary blow-drying or vacuum drying, and the drying temperature is 50°C.

6. The preparation method according to claim 1, wherein in Step 3, the calcination temperature is 520 - 600°C, the calcination time is 4 - 6 hours, and the heating rate is 2 - 10°C / min.

7. A composite photocatalyst with carbon nitride wire mesh wrapped around magnetite is prepared by the preparation method according to any one of claims 1 - 6. Among them, The composite photocatalyst with carbon nitride wire mesh wrapped around magnetite has a microscopic structure of a substance with carbon nitride wire mesh wrapped around magnetite nanoparticles, wherein the single diameter of the carbon nitride wire mesh is 5 - 300 nm, and the size of the magnetite nanoparticles wrapped is 5 - 300 nm.

8. Use of a composite photocatalyst of carbon nitride wire-wound around magnetite in the degradation of antibiotic wastewater by a catalytic oxidant.

9. Use of the composite photocatalyst of carbon nitride wire-wound around magnetite according to claim 8, characterized in that the oxidant is one or more of hydrogen peroxide, peroxymonosulfate, and persulfate.

10. Use of the composite photocatalyst of carbon nitride wire-wound around magnetite according to claim 8, characterized in that the antibiotic wastewater is antibiotic wastewater comprising one or more of tetracycline antibiotics and quinolone antibiotics, and the concentration of antibiotics in the antibiotic wastewater is 2 mg / L - 100 mg / L.

Images