Composite photocatalyst with metal oxide wound on carbon nitride wire mesh as well as preparation method and application of composite photocatalyst

Abstract

The invention relates to the field of preparation and photocatalysis application of composite catalysts, in particular to a composite catalyst with a carbon nitride wire mesh wound with metal oxide and a preparation method and application of the composite catalyst. Modifying the metal oxide nanoparticles; preparation of a composite catalyst: respectively dispersing melamine, cyanuric acid and the modified metal oxide nanoparticles in a specified mass ratio in deionized water, stirring for specified time A, adding a cyanuric acid aqueous dispersion solution into the melamine aqueous dispersion solution to obtain a mixed solution, stirring for specified time B at normal temperature, then heating and stirring for specified time C, filtering, washing and drying to obtain the composite catalyst. And raising the temperature of the metal oxide dispersion liquid to the same temperature, adding the mixed liquid, stirring for a specified time D, then carrying out a hydrothermal reaction, after the reaction is finished, standing and cooling, cleaning and drying a precipitate obtained in a container, raising the temperature of the dried precipitate in nitrogen, calcining, and cooling to obtain the composite photocatalyst with the carbon nitride wire mesh wound with the metal oxide.

Description

Technical Field

[0001] The invention relates to the preparation and photocatalytic application fields of composite photocatalysts, and in particular to composite photocatalysts of carbon nitride wire mesh wound with metal oxides, and a preparation method and application thereof. Background Art

[0002] In recent years, antibiotics have been widely used and even abused in the medical field because of their low price and broad-spectrum antibacterial effect. However, this type of drug has high stability and is difficult to biodegrade. Only 30% of antibiotics taken by the human body are absorbed, and the rest are discharged into nature. However, the biodegradation technology used by environmental protection units such as traditional sewage treatment plants is difficult to effectively remove antibiotics, making them emerging pollutants PPCPs (Pharmaceutical and Personal Care Products) that are ubiquitous in soil and water.

[0003] Antibiotics in these environments not only cause pollution, but also induce the generation of resistant microorganisms and resistance genes. These resistance genes will be vertically transferred to subsequent generations of bacteria, continuously damaging the ecological environment and changing the structure and community of microorganisms. Furthermore, when humans and animals consume food and water, these resistance 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 its removal mechanism in the environment. Many researchers have confirmed that advanced oxidation processes (AOPs) are highly efficient in destroying the structure of antibiotics. They attack pollutants by activating oxidants to produce free radicals with strong oxidizing ability (hydroxyl, sulfate, superoxide, etc.), causing pollutants to degrade into small molecules and mineralize into CO2 and H2O. There are many types of oxidants commonly used, including hydrogen peroxide (H2O2) used in Fenton oxidation, peroxymonosulfate (PMS) and peroxydisulfate (PDS) in Fenton-like oxidation, and ozone in ozone oxidation.

[0005] Catalysts are the key to the development of advanced oxidation technology. They directly determine the activation efficiency of the oxidant and indirectly determine the number of active free radicals generated. Metal oxides are the most efficient and commonly used catalysts, especially nano-scale metal oxides with a particle size of tens to hundreds of nanometers, which have stronger catalytic ability. Among nano-metal oxides, magnetic oxides have a wider range of uses because they can be recovered magnetically. 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 graphite phase carbon nitride have attracted extensive attention. They have stable chemical properties and good electron transport properties, and have shown 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, so its reuse rate is low. Summary of the invention

[0007] In order to solve the above-mentioned problems, the purpose of the present invention is to provide a composite photocatalyst of carbon nitride wire mesh wrapped nano metal oxide and its preparation method and application. By preparing modified nano metal oxide, and using supramolecular self-assembly and hydrothermal method to encapsulate nano metal oxide layer by layer in the process of synthesizing carbon nitride precursor, a composite photocatalyst having a special material structure of carbon nitride wire mesh wrapped nano metal oxide is obtained after pyrolysis, which is denoted as M x O y #C3N4.

[0008] The photocatalyst obtained by this preparation method has a unique nanostructure, which can generate a synergistic effect in the photocatalytic process, improve the activation efficiency of the oxidant, and the composite photocatalyst has magnetic recovery performance and a high recovery rate. In addition, due to the synergistic effect and the confinement of the nano-metal oxide, the metal element leaching of the composite photocatalyst is less, the catalyst is highly stable, and the recycling rate is high.

[0009] According to one aspect of the present invention, a method for preparing a composite photocatalyst of a carbon nitride mesh wrapped with a metal oxide is characterized by comprising the following steps: Step 1: Preparation of metal oxide nanoparticles, Step 2: Modification of metal oxide nanoparticles: surface modification of the metal oxide nanoparticles obtained in step 1 is performed by a modifier to obtain modified metal oxide nanoparticles. Step 3: Preparation of a composite photocatalyst. Disperse melamine, cyanuric acid and modified metal oxide nanoparticles in a specified mass ratio in deionized water and stir continuously for a specified time A. Add the cyanuric acid aqueous dispersion to the melamine aqueous dispersion to obtain a mixed solution. Stir at room temperature for a specified time B and then heat 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 stirring for a specified time D and then conduct a hydrothermal reaction. After the reaction is completed and allowed to stand and cool, wash and dry the precipitate obtained in the container several times. Heat and calcine the dried precipitate in a nitrogen atmosphere. After cooling, obtain a composite photocatalyst of carbon nitride mesh wrapped with metal oxide.

[0010] Preferably, the prescribed time A in step 3 is 30 min or more, and the stirring rate is 400-600 rpm, The specified time B in step 3 is 1-2 hours, and the stirring rate is 400-600 rpm, In step 3, the temperature of the heating and stirring is 60°C, the prescribed time C is 0.5-1 hour, and the stirring rate is 300-400 rpm. The prescribed time D in step 3 is 0.5-1 hour, and the stirring rate is 300-400 rpm.

[0011] Preferably, the hydrothermal reaction temperature in step 3 is 200-220° C., and the reaction time is 10-12 hours.

[0012] Preferably, the cleaning method described in step three is washing with methanol 2-3 times and washing with pure water 2-3 times.

[0013] Preferably, the drying method in step three is ordinary air drying or vacuum drying, and the drying temperature is 50°C.

[0014] Preferably, in step three, the calcination temperature is 520-600°C, the calcination time is 4-6 hours, and the heating rate is 2°-10°C / min.

[0015] According to another aspect of the present invention, a composite photocatalyst of a carbon nitride mesh wrapped with a metal oxide is prepared by the aforementioned preparation method. The composite photocatalyst of carbon nitride wire wrapped around metal oxide has a material microstructure of wire wrapped around metal oxide nanoparticles, wherein the diameter of a single carbon nitride wire is 5-300nm, and the size of the wrapped metal oxide nanoparticles is 5-300nm.

[0016] According to another aspect of the present invention, the aforementioned composite photocatalyst of carbon nitride wire mesh wrapped with metal oxide is used to catalyze oxidants to degrade antibiotic wastewater.

[0017] Preferably, the aforementioned oxidant is one or more of hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and peroxydisulfate (PDS).

[0018] Preferably, the aforementioned antibiotic wastewater includes one or more of tetracycline antibiotic wastewater and quinolone antibiotic wastewater. The antibiotic concentration in the antibiotic wastewater is 2 mg / L-100 mg / L.

[0019] Technical effects: The composite photocatalyst of carbon nitride wire mesh wrapped with nano-metal oxide provided by the present invention is used to activate oxidants to treat antibiotic wastewater, and its advantages are: (1) By first encapsulating and then carbonizing, a mesh-like carbon nitride structure is generated, which stably constrains the nano-metal oxides in the carbon nitride matrix, successfully achieving single-particle dispersion of the nano-metal oxides, solving the problem of particle agglomeration, and improving the catalytic efficiency of the oxidant.

[0020] (2) Nano-metal oxides are confined within carbon nitride, and the catalyst size is increased from nanoscale to micron scale, making it easier to separate and improving recovery efficiency.

[0021] (3) Through the synergistic effect of carbon nitride and metal oxide, a catalytic effect far greater than that of either alone is achieved.

[0022] (4) By wrapping the metal oxide around the carbon nitride mesh, the carbon nitride that could not be recovered magnetically can also be recycled.

[0023] (5) The metal leaching rate is greatly reduced by carbon nitride wire mesh winding constraint. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A diagram showing the material morphology of the Fe3O4#C3N4 composite photocatalyst.

[0025] Figure 2 This is the transmission electron microscope-dark field scanning image of the Fe3O4#C3N4 composite photocatalyst and the corresponding C and N element distribution map.

[0026] Figure 3 This is the thermogravimetric diagram of the Fe3O4 content in the Fe3O4#C3N4 composite photocatalyst.

[0027] Figure 4 Comparison of the removal rates of antibiotics by various catalysts.

[0028] Figure 5 It shows the magnetic recovery performance and metal leaching of the composite photocatalyst Fe3O4#C3N4. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and is in no way intended to limit 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 stated, the relative arrangement of the components and steps, numerical expressions, and numerical values, etc., described in these embodiments should be interpreted as being merely exemplary and not as limiting.

[0030] The words “include” or “comprising” and the like used in the present invention mean that the elements before the words include the elements listed after the words, and do not exclude the possibility of also including other elements.

[0031] All terms (including technical terms or scientific terms) used in the present invention have the same meanings as those understood by ordinary technicians in the field to which the present invention belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined in this document.

[0032] Components not described in detail in this section, parameters such as specific models of components, relationships between components, and control circuits may be considered as technologies, methods, and equipment known to ordinary technicians in the relevant fields, but in appropriate cases, such technologies, methods, and equipment should be considered as part of the specification.

[0033] Specific embodiments of the present invention are described below.

[0034] As described in the background technology, metal oxides (oxides of common elements such as iron, copper, manganese, cobalt, nickel, etc.) are the most efficient and most commonly used catalysts, especially nano-scale metal oxides with particle sizes of tens to hundreds of nanometers have stronger catalytic ability. Among nano-metal oxides, magnetic oxides have a wider range of uses because they can be recovered by magnetic force. Nevertheless, nano-metal oxides, especially magnetic nano-metal oxides, still have obvious defects during use. On the one hand, due to magnetic attraction, particles are easy to agglomerate, resulting in active sites not being exposed clearly during the catalytic process, reducing catalytic efficiency. On the other hand, too small particle sizes make them recover slowly after being dispersed in a large reactor and cannot be filtered and separated, resulting in incomplete recovery. Therefore, maintaining the dispersion rate of nano-metal oxides in the catalytic process and improving recovery efficiency are technical difficulties of nano-metal oxides and magnetic nano-metal oxides as PMS activators in actual water treatment applications.

[0035] In contrast, regarding carbon nitride (g-C3N4, C3N4) catalysts, the traditional method uses urea, dicyandiamide, melamine and the like to thermally decompose to generate carbon nitride in block morphology. The carbon nitride generated in this way is in a non-porous block, has a small specific surface area and a high photogenerated electron recombination rate. Currently, block, lamellar, tubular and other morphologies have been developed. Despite this, in current practical applications, the catalytic ability of metal-free carbon nitride for oxidants such as hydrogen peroxide and persulfate is still relatively low, and the metal-free carbon nitride is in powder form and cannot be recovered by magnetic force, resulting in poor recovery efficiency.

[0036] On the other hand, the use of 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, nanoscale 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 of melamine, due to the corrosion of cyanuric acid, the carbon nitride finally formed is no longer a block without pores, but a honeycomb or wire mesh with pores. These pores will cause the carbon nitride to have a low degree of crystallinity, which was originally a defect in the preparation of carbon nitride. However, these research foundations provide the basic conditions for the construction of multifunctional and new nanostructures based on carbon nitride, and provide the possibility for carbon nitride to support metal oxides.

[0037] By adjusting the preparation conditions, the above carbon nitride morphology and pore defects are adjustable. The present invention pioneered the intentional formation of a carbon nitride carrier with pore defects during the preparation stage, overcoming technical prejudices, making the original defects effective properties, and successfully dispersing and constraining nano-scale metal oxides in the carbon nitride carrier.

[0038] Figure 1 The composite photocatalyst M prepared by the preparation method of the present invention is represented by x O y #Diagram of the material structure of C3N4. Figure 1 The carbon nitride shown is in a lamellar shape, but is not limited thereto and can also be prepared into a block, a tube, etc. as required.

[0039] like Figure 1 As shown, in the lamellar carbon nitride, the carbon nitride between the two surface layers is formed into a wire drawing mesh, wherein the diameter of a single carbon nitride wire mesh is 5-300nm. Figure 1 The white spherical granular substance shown in the figure is a metal oxide, which is mounted in the carbon nitride mesh, forming a unique structure in which the carbon nitride mesh is layered and wrapped with nano metal oxide. In addition, it is worth noting that Figure 1 The spherical granular metal oxide shown in the figure is a real scanning electron microscope image of Fe3O4, but the metal oxide is not limited to Fe3O4, and can also be an oxide of other metal elements such as iron, copper, manganese, cobalt, nickel, etc. From the perspective of easy magnetic recovery, magnetic metal oxides such as iron, cobalt, and nickel are more preferred.

[0040] The following detailed description Figure 1 The method for preparing the composite photocatalyst of carbon nitride wire mesh wrapped with metal oxide is shown.

[0041] Step 1: Preparation of Fe3O4 nanoparticles: Weigh a certain mass of FeCl3·6H2O and add it to ethylene glycol solution, stir until completely dissolved, then add sodium acetate, continue stirring for 0.5-1h, then transfer to a hydrothermal reactor, heat to 200℃ and maintain for 10-12h, magnetically recover solid particles, and obtain Fe3O4 nanoparticles after washing and drying.

[0042] The preparation method of Fe3O4 nanoparticles is not limited thereto, as long as nano-scale Fe3O4 nanoparticles can be obtained.

[0043] Step 2: Modification of Fe3O4 nanoparticles: Add the Fe3O4 nanoparticles obtained in step 1 to ethanol, mechanically stir and disperse for 0.5-1h, add ammonia water, adjust the pH to 11, and mechanically stir for 4-6 hours. Recover the solid particles by magnetic force, wash and dry to obtain modified nano Fe3O4.

[0044] By surface modification, Fe3O4 nanoparticles can be better dispersed in the carrier material (carbon nitride) to avoid agglomeration and precipitation. In the present invention, ethanol and ammonia water are used as modifiers for modification, which can introduce hydrophobic functional groups into Fe3O4 nanoparticles, so that they interact with the matrix material, i.e., the carbon nitride carrier, to achieve better dispersibility and loading capacity. However, it is not limited to this, and the modifiers and reaction conditions used can be freely adjusted according to needs.

[0045] Those skilled in the art will appreciate that the surface modification can be carried out by appropriately selecting or adjusting the preparation method, conditions, etc. according to the needs and is not limited to the above-mentioned preparation steps.

[0046] Step 3: Preparation of composite photocatalyst: Disperse melamine, cyanuric acid and modified nano-Fe3O4 in a certain mass ratio in deionized water and continue stirring 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 heat and stir for time C. At the same time, the temperature of the nano-Fe3O4 dispersion is also raised to the same temperature, and then added to the mixed solution, and the mixed solution continues to be mechanically stirred for time D. Transfer the mixed solution to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, stand and cool, and then wash and dry the precipitate obtained in the container several times. Put the dried precipitate into a porcelain boat, cover it, heat it up and calcine it in a nitrogen atmosphere, and obtain the final catalyst after cooling.

[0047] As mentioned above, the carbon nitride prepared using only melamine is in a block shape without pores, but after adding cyanuric acid, pores can be formed in the carbon nitride through the corrosion effect of cyanuric acid, thereby forming the carbon nitride into a mesh shape (refer to Figure 1). By adjusting the raw material ratio, temperature, time and other preparation conditions in step three, the morphology of the wire mesh carbon nitride can be adjusted. The morphology of the wire mesh carbon nitride will determine the catalytic performance of the carbon nitride itself and the supporting performance of the metal oxide, and the supporting performance of the metal oxide will determine the catalytic performance of the metal oxide, as well as the synergistic effect of the two. Therefore, the morphology of the wire mesh carbon nitride, and the loading amount and loading state of the metal oxide in the wire mesh 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 various preparation conditions in the preparation method will be described in detail below.

[0048] Preferably, the mass ratio of FeCl3·6H2O, ethylene glycol and sodium acetate in step 1 is 1:32-35:2-3.

[0049] Preferably, the cleaning method described in step one is ethanol cleaning 2-3 times and pure water cleaning 2-3 times.

[0050] Preferably, the drying method in step 1 is ordinary blast drying or vacuum drying, and the drying temperature is 60-80°C.

[0051] Preferably, the mass ratio of Fe3O4, ethanol and ammonia water in step 2 is 1:30-35:5-10, and the concentration of ammonia water is 25%-28%.

[0052] Preferably, the pH adjustment method in step 2 is to add NaOH solution.

[0053] Preferably, the cleaning method and drying method described in step 2 are consistent with those in step 1.

[0054] 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.

[0055] Here, as mentioned above, the mass ratios of melamine, cyanuric acid, modified nano Fe3O4, and deionized water are different, and the morphology of the formed wire mesh carbon nitride is completely different, and the morphology of carbon nitride determines its own catalytic performance and the supporting performance of metal oxides, and the supporting performance of metal oxides will determine the catalytic performance of metal oxides. In addition, the mass ratio and supporting state of metal oxides relative to carbon nitride affect the synergistic effect of the two, as well as the subsequent magnetic recovery performance. Therefore, the morphology of wire mesh carbon nitride, and the loading amount and supporting state of metal oxides in wire mesh carbon nitride are the key to determining the performance of the composite photocatalyst of the present invention.

[0056] The inventors of the present application have conducted a large number of experiments to explore the optimal mass ratio of melamine, cyanuric acid, modified nano-Fe3O4 and deionized water.

[0057] Experimental conditions: ofloxacin concentration 20 mg / L, catalyst dosage 0.2 g / L, PMS dosage 0.2 g / L, initial pH value 7, temperature 20°C, lighting conditions natural light or 300 watt xenon lamp. The removal rate of ofloxacin was tested at 294 nm using an ultraviolet spectrophotometer for 40 minutes.

[0058] Experimental data 1: only adjust the ratio of cyanuric acid (the mass of melamine is used as the benchmark, the mass ratio of cyanuric acid, modified nano-Fe3O4, and deionized water to melamine):

[0059] According to empirical ratios, carbon nitride can be effectively synthesized when the mass ratio of melamine: cyanuric acid is in the range of 1:0.5-2. Therefore, synthesis experiments with a mass ratio of 1:0.25-3 were carried out, and the catalytic performance of the catalysts obtained under various synthesis conditions was evaluated.

[0060] It can be seen that when the mass ratio of melamine: cyanuric acid is in the range of 1:1-1.05, more than 95% ofloxacin removal can be achieved, especially when the mass ratio is 1:1.02, 99% ofloxacin removal efficiency can be achieved.

[0061] In addition, when the amount of cyanuric acid added is small, the corrosion of cyanuric acid on melamine is insufficient, and sufficient pores cannot be formed in carbon nitride. Therefore, the modified nano-Fe3O4 particles cannot be fully loaded into the pores of carbonized nitrogen. Therefore, as the proportion of cyanuric acid decreases, the removal rate of ofloxacin decreases sharply. When the mass ratio of cyanuric acid is less than 0.25, the carbonized nitrogen formed is close to a block without pores. The prepared composite photocatalyst has the same removal effect on antibiotic drugs as the simple carbonized nitrogen catalyst.

[0062] On the other hand, when the amount of cyanuric acid added is large, its corrosive effect on melamine is too large, and the pores (defects) of the formed carbon nitride are too many. When there are too many pores, the stability of carbonized nitrogen is reduced, and it is difficult to fully constrain and wrap Fe3O4. When the mass ratio of cyanuric acid reaches 3, the solid morphology of carbonized nitrogen can no longer be maintained, and the composite photocatalyst cannot be prepared.

[0063] Through the above experiments, the inventors of the present application found that when the mass ratio of melamine: cyanuric acid is within the range of 1:1-1.05, a composite photocatalyst with stable morphology can be prepared and the best loading performance for Fe3O4 can be obtained. The above experiments are tests for the removal rate of ofloxacin, but as long as the mass ratio of melamine: cyanuric acid is within the range of 1:1-1.05, the best loading performance for Fe3O4 can be ensured. When removing other antibiotics other than ofloxacin, the mass ratio of Fe3O4 can be appropriately adjusted.

[0064] Experimental data 2 only adjusts the ratio of modified nano-Fe3O4 (the mass of melamine is used as the benchmark, the mass ratio of cyanuric acid, modified nano-Fe3O4, and deionized water relative to melamine):

[0065] It can be seen that when the mass ratio of the added modified nano-Fe3O4 is within the range of 0.08-0.12, more than 95% of ofloxacin removal can be achieved. When the amount of modified nano-Fe3O4 is gradually reduced, the synergistic effect of modified nano-Fe3O4 and carbon nitride is insufficient. Moreover, when the amount of modified nano-Fe3O4 is gradually reduced, it can be foreseen that the magnetic recovery performance of the composite photocatalyst will be greatly reduced. When the mass ratio of modified nano-Fe3O4 is within the range of 0.08-0.12, especially around 0.1, the best ofloxacin removal rate can be achieved. When the amount of modified nano-Fe3O4 is too much, for example, reaching 0.2, the synergistic effect of modified nano-Fe3O4 and carbon nitride decreases instead. When the amount of modified nano-Fe3O4 is further increased, it has in fact exceeded the carrying capacity of porous carbonized nitrogen, so the loading amount of modified nano-Fe3O4 cannot be further increased, and it is meaningless to continue to increase the amount of modified nano-Fe3O4. It is worth noting that for different antibiotics, the optimal mass ratio of Fe3O4 is slightly different.

[0066] Experimental data 3 only adjusts the ratio of deionized water (the mass of melamine is used as the benchmark, the mass ratio of cyanuric acid, modified nano-Fe3O4, and deionized water relative to melamine):

[0067] It can be seen that when the mass ratio of the added solvent water is within 20-50, the synthesized catalyst can realize more than 98% of the removal of ofloxacin. When the solvent water is too little, it is inferred that the dispersion rate of melamine, cyanuric acid, and modified nano-Fe3O4 in the solvent water is not ideal, and particularly the dissolution rate of melamine and cyanuric acid in water is lower. When the solvent water is insufficient, melamine and cyanuric acid are easily cemented and cause the dispersion rate to be poor, affecting the quality of the carbon nitride prepared. When the solvent water is too much, the hydrothermal reaction time becomes long, and the defect rate of the carbon nitride prepared becomes high. Therefore, the mass ratio of the solvent water is preferably within the range of 20-50, which can not affect the removal rate of ofloxacin.

[0068] Preferably, the stirring time A in step three is 30 min or more, and the stirring rate is 400-600 rpm.

[0069] Preferably, the stirring time B in step 3 is 1-2 hours, and the stirring rate is 400-600 rpm.

[0070] Preferably, in step 3, the stirring temperature is 60-65° C., the stirring time C is 0.5-1 hour, and the stirring rate is 300-400 rpm.

[0071] Preferably, the stirring time D in step three is 0.5-1 hour, and the stirring rate is 300-400 rpm.

[0072] Preferably, the hydrothermal reaction temperature in step 3 is 200-220° C., and the reaction time is 10-12 hours.

[0073] Preferably, the cleaning method described in step three is washing with methanol 2-3 times and washing with pure water 2-3 times.

[0074] Preferably, the drying method in step three is ordinary air drying or vacuum drying, and the drying temperature is 50°C.

[0075] Preferably, in step three, the calcination temperature is 520-600°C, the calcination time is 4-6 hours, and the heating rate is 2°-10°C / min.

[0076] According to the above steps, the composite photocatalyst of carbon nitride wire mesh wrapped with nano-Fe3O4 described in the patent of the present invention is prepared.

[0077] The composite photocatalyst of carbon nitride wire wrapped nano-Fe3O4 described in the present invention is characterized in that the material microstructure is presented as wire mesh wrapped particles, wherein the diameter of a single carbon nitride wire is between 5-300nm, and the size range of the wrapped nano-Fe3O4 particles is between 5-300nm.

[0078] In this regard, through the preparation conditions of step 1 and step 3, a carbon nitride wire mesh diameter between 5-300 nm and a nano-Fe3O4 particle size between 5-300 nm can be obtained.

[0079] The composite photocatalyst of carbon nitride wire mesh wrapped with nano-Fe3O4 described in the present invention is used for catalyzing oxidants to degrade antibiotic wastewater.

[0080] The oxidant described in the present invention is one or more of H2O2, PMS and PDS.

[0081] The antibiotic wastewater includes tetracycline antibiotics and quinolone antibiotic wastewater, specifically one or more of tetracycline, oxytetracycline, ofloxacin, ciprofloxacin, and norfloxacin.

[0082] The antibiotic concentration in the antibiotic wastewater ranges from 2 mg / L to 100 mg / L.

[0083] The catalytic effects of the composite photocatalysts obtained under different preparation conditions are described below in conjunction with specific examples. Embodiment 1:

[0084] Preparation of Fe3O4 nanoparticles: Weigh 2.0g of FeCl3·6H2O and add it to 70.0g of ethylene glycol solution. After stirring until completely dissolved, add 5.0g of sodium acetate and continue stirring for 0.5h. Transfer it to a hydrothermal reactor with a capacity of 100mL, heat it to 200℃ and keep it for 10h. Recover the solid particles magnetically, wash them twice with anhydrous ethanol and pure water respectively, and dry them in a forced air drying oven at 70℃ for 8h to obtain Fe3O4 nanoparticles.

[0085] Modification of Fe3O4 nanoparticles: 2.0 g of Fe3O4 nanoparticles were added to 60.0 g of ethanol, mechanically stirred and dispersed for 0.5 h, 14.56 g of 25% ammonia water was added, the pH was adjusted to 11, and mechanical stirring was continued for 4 hours. The solid particles were magnetically recovered, washed twice with anhydrous ethanol and pure water, and dried to obtain modified nano-Fe3O4.

[0086] Preparation of composite photocatalyst: 3.0g of melamine, 3.06g of cyanuric acid, and 0.28g of modified nano-Fe3O4 were dispersed in 60mL of deionized water and stirred continuously for 0.5h at a stirring speed of 600 rpm. Then, the cyanuric acid aqueous dispersion solution was added to the melamine aqueous dispersion solution, and mechanically stirred for 1h at room temperature, with the stirring speed unchanged, and then heated to 60℃ and stirred for 0.5h, and the speed was reduced to 300rpm. At the same time, the temperature of the nano-Fe3O4 dispersion was also raised to 60℃, and then added to the mixed solution, and the mixed solution continued to be mechanically stirred for 0.5h. The mixed solution was transferred to a 250mL hydrothermal reactor and kept at 200℃ for 10h for hydrothermal reaction. After the reaction was completed, the precipitate obtained in the container was washed twice with methanol and pure water, and dried at 50℃ for 8h. The dried precipitate was placed in a porcelain boat, covered, and heated to 550°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 4 h. The final catalyst was obtained after cooling.

[0087] The composite photocatalyst prepared by the above method was applied to activate PMS to degrade ofloxacin wastewater, and the reaction conditions were: ofloxacin concentration 20 mg / L, catalyst dosage 0.2 g / L, PMS dosage 0.2 g / L, initial pH value 7, temperature 20 ° C, and illumination conditions of natural light or a 300-watt xenon lamp. At this time, the removal rate of ofloxacin reached 99.1% within 40 minutes. The removal rate of ofloxacin was determined by ultraviolet spectrophotometry at a wavelength of 294 nm. Using magnetic recovery, a catalyst recovery rate of 99.5% was achieved within 2 minutes. Embodiment 2:

[0088] Preparation of Fe3O4 nanoparticles: Weigh 3.0g of FeCl3·6H2O and add it to 105.0g of ethylene glycol solution. Stir until completely dissolved, then add 9.0g of sodium acetate and continue stirring for 1h. The mechanical stirring speed is 600 rpm. The mixed solution is transferred to a 200mL hydrothermal reactor, heated to 200℃ and maintained for 12h. The solid particles are recovered magnetically, washed with anhydrous ethanol and pure water three times each, and dried in a forced air drying oven at 80℃ for 8h to obtain Fe3O4 nanoparticles.

[0089] Modification of Fe3O4 nanoparticles: 3.0 g of Fe3O4 nanoparticles were added to 105.0 g of ethanol, mechanically stirred and dispersed for 1 h, 27.3 g of 28% ammonia water was added, the pH was adjusted to 11, and mechanical stirring was continued for 6 hours. The solid particles were magnetically recovered, washed with anhydrous ethanol and pure water for 3 times each, and then dried to obtain modified nano-Fe3O4.

[0090] Preparation of composite photocatalyst: 5.0g of melamine, 5.1g of cyanuric acid, and 0.5g of modified nano-Fe3O4 were dispersed in 100mL of deionized water and stirred continuously for 0.5h at a speed of 600 rpm. Then the cyanuric acid aqueous dispersion was added to the melamine aqueous dispersion, mechanically stirred for 1h at room temperature, then heated to 60℃ and stirred for 1h, and the speed was reduced to 400rpm. At the same time, the temperature of the nano-Fe3O4 dispersion was also raised to 60℃, and then added to the mixed solution, and the mixed solution continued to be mechanically stirred for 1h. The mixed solution was transferred to a 500mL hydrothermal reactor and kept at 220℃ for 12h for hydrothermal reaction. After the reaction was completed, the precipitate obtained in the container was washed 3 times with methanol and pure water respectively, and vacuum dried at 50℃ for 8h. The dried precipitate was placed in a porcelain boat, covered, and heated to 550°C at a heating rate of 5°C / min in a nitrogen atmosphere and calcined for 5 h. The final catalyst was obtained after cooling.

[0091] The catalyst prepared by the above method was applied to activate H2O2 to degrade norfloxacin wastewater, and the reaction conditions were: norfloxacin concentration 10 mg / L, catalyst dosage 0.1 g / L, H2O2 dosage 0.2 mL / L, initial pH value 7, temperature 20°C, and lighting conditions of natural light or a 300-watt xenon lamp. At this time, the removal rate of norfloxacin reached 95% within 40 minutes. The removal rate of norfloxacin was determined by ultraviolet spectrophotometry at a wavelength of 273 nm. Using magnetic recovery, a catalyst recovery rate of 99% was achieved within 2 minutes. Embodiment 3:

[0092] Preparation of Fe3O4 nanoparticles: Weigh 2.0g of FeCl3·6H2O and add it to 65.0g of ethylene glycol solution. Stir until completely dissolved, then add 4.5g of sodium acetate and continue stirring for 0.5h. The mechanical stirring speed is 500 rpm. Transfer it to a 100mL hydrothermal reactor, heat it to 200℃ and keep it for 10h. Recover the solid particles by magnetic force, wash them twice with anhydrous ethanol and pure water respectively, and dry them in a forced air drying oven at 70℃ for 8h to obtain Fe3O4 nanoparticles.

[0093] Modification of Fe3O4 nanoparticles: 2.0 g of Fe3O4 nanoparticles were added to 60.0 g of ethanol, mechanically stirred and dispersed for 0.5 h, 18.2 g of 25% ammonia water was added, the pH was adjusted to 11, and mechanical stirring was continued for 4 hours. The solid particles were magnetically recovered, washed twice with anhydrous ethanol and pure water, and dried to obtain modified nano-Fe3O4.

[0094] Preparation of composite photocatalyst: 2.0g of melamine, 2.04g of cyanuric acid, and 0.22g of modified nano-Fe3O4 were dispersed in 100mL of deionized water and stirred continuously for 0.5h at a speed of 400 rpm. Then the cyanuric acid aqueous dispersion was added to the melamine aqueous dispersion, mechanically stirred for 1h at room temperature, and then heated to 60℃ and stirred for 0.5h. At the same time, the temperature of the nano-Fe3O4 dispersion was also raised to the same temperature, and then added to the mixed solution, and the mixed solution continued to be mechanically stirred for 0.5h. The mixed solution was transferred to a 500mL hydrothermal reactor and kept at 220℃ for 12h for hydrothermal reaction. After the reaction was completed, the precipitate obtained in the container was washed twice with methanol and pure water, and dried at 50℃ for 8h. The dried precipitate was placed in a porcelain boat, covered, and heated to 600°C at a heating rate of 5°C / min in a nitrogen atmosphere and calcined for 4 h. The final catalyst was obtained after cooling.

[0095] The catalyst prepared by the above method was applied to activate PDS to degrade tetracycline wastewater, and the reaction conditions were: 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 lighting conditions of natural light or a 300-watt xenon lamp. At this time, the removal rate of tetracycline reached 99% within 40 minutes. The tetracycline removal rate was determined by ultraviolet spectrophotometry at a wavelength of 352 nm. Using magnetic recovery, a catalyst recovery rate of 99% was achieved within 3 minutes.

[0096] Next, refer to Figure 1-Figure 5 The morphology and performance data of the composite photocatalyst obtained by the preparation method of the present invention are described.

[0097] Figure 2 The left figure in FIG. 1 shows that the diameter of a single 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 pictures in the figure show the transmission electron microscope-dark field scanning image of the Fe3O4#C3N4 composite photocatalyst and the corresponding C and N element distribution map. When the observation magnification is magnified to 100nm, it is observed that the C and N elements are evenly distributed, forming a straight tube, which indicates the successful construction of the C3N4 wire mesh in the nanostructure.

[0098] Figure 3 The content of Fe3O4 in the composite photocatalyst obtained by the preparation method of the present invention is shown by a thermogravimetric diagram. Figure 3 The thermogravimetric results showed that the actual Fe3O4 content in the prepared Fe3O4#C3N4 composite photocatalyst was 10.8%, achieving a good Fe3O4 loading effect, which was conducive to the formation of a synergistic effect of Fe3O4 and C3N4.

[0099] Figure 4 The catalytic effects of different catalysts are compared. Figure 4 (A) in the figure indicates the adsorption capacity of ofloxacin by Fe3O4, C3N4, and Fe3O4#C3N4 based on adsorption alone. Figure 4 (B) in the figure shows the degradation efficiency of ofloxacin by Fe3O4, Fe3O4+C3N4, and Fe3O4#C3N4.

[0100] Test conditions: ofloxacin concentration 20 mg / L, total catalyst amount for a 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, the PMS dosage is 0.2 g / L, and the lighting conditions are natural light or a 300-watt xenon lamp.

[0101] Figure 4 The results of (A) show that the removal rates of pure adsorption of ofloxacin by Fe3O4, C3N4, and Fe3O4#C3N4 are all less than 10%, while Figure 4 The various data in (B) all show higher removal rates, which indicates that the contribution of adsorption to the removal rate of ofloxacin by each catalyst is limited, and photocatalysis is the main factor at work.

[0102] from Figure 4 From the results of (B), it can be seen that at the same proportion of Fe3O4 weight, the catalytic effect of Fe3O4#C3N4 is obviously far superior to the other catalysts, about 2.9 times that of pure Fe3O4 and 5.1 times that of pure C3N4. This shows that the construction of the special nanostructure greatly improves the catalytic activity, and a 1+1>2 synergistic effect 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 cycle of Fe during the catalytic reaction, which is beneficial to the catalysis of PMS. This result shows that the composite photocatalyst provided by the present invention can achieve higher catalytic efficiency and active site utilization at the same Fe3O4 content.

[0103] Figure 5 The magnetic recovery performance and metal leaching of the composite photocatalyst Fe3O4#C3N4 are shown. Figure 5 (A) shows the recovery rate of the catalyst recovered by magnetic force 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) shows the leaching of Fe element from Fe3O4 and Fe3O4#C3N4 when the amount of Fe3O4 is constant during five cycles of use. Figure 4 (B) Consistent.

[0104] from Figure 5 (A) It can be seen that since pure C3N4 is non-magnetic, the recovery rate is 0. The side magnetic recovery rate of Fe3O4 is 89.3%, and there is still more than 10% loss. The recovery rate of Fe3O4#C3N4 catalyst reaches 99.5%. This is because, under the same magnetic conditions, 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 of micron level, which is more conducive to macroscopic recovery, resource saving and multiple recycling. In particular, the structure of the metal oxide wrapped with carbon nitride mesh allows the carbon nitride that was originally unrecoverable to be recovered, greatly improving the utilization efficiency of the catalyst.

[0105] Figure 5 (B) The results 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 shows that the formation of special nanostructures can constrain Fe3O4 through the wire mesh structure and increase the stability of the catalyst. Therefore, the catalytic efficiency of the recycled catalyst can be maintained well and it has strong reusability.

[0106] 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 substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a composite photocatalyst of carbon nitride mesh wrapped with metal oxide, characterized in that The following steps are involved: Step 1: Preparation of metal oxide nanoparticles, Step 2: Modification of metal oxide nanoparticles: surface modification of the metal oxide nanoparticles obtained in step 1 is performed by a modifier to obtain modified metal oxide nanoparticles. Step 3: Preparation of a composite catalyst. Disperse melamine, cyanuric acid and modified metal oxide nanoparticles in a specified mass ratio in deionized water and continue stirring 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 and stir for a specified time C. At the same time, increase the temperature of the metal oxide dispersion solution to the same temperature and add it to the mixed solution. Continue stirring for a specified time D and then conduct a hydrothermal reaction. After the reaction is completed and allowed to stand and cool, wash and dry the precipitate obtained in the container several times. Heat and calcine the dried precipitate in a nitrogen atmosphere. After cooling, obtain a composite photocatalyst of carbon nitride mesh wrapped with metal oxide.

2. The preparation method according to claim 1, characterized in that: The specified time A in step 3 is 30 minutes or more, and the stirring rate is 400-600 rpm. The specified time B in step 3 is 1-2 hours, and the stirring rate is 400-600 rpm, In step 3, the temperature of the heating and stirring is 60°C, the prescribed time C is 0.5-1 hour, and the stirring rate is 300-400 rpm. The prescribed time D in step 3 is 0.5-1 hour, and the stirring rate is 300-400 rpm.

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

4. The preparation method according to claim 1, characterized in that: The cleaning method described in step three is to use methanol for 2-3 times and pure water for 2-3 times.

5. The preparation method according to claim 1, characterized in that: The drying method described in step 3 is ordinary air drying or vacuum drying, and the drying temperature is 50°C.

6. The preparation method according to claim 1, characterized in that: 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 of carbon nitride mesh wrapped with metal oxide, prepared by the preparation method according to any one of claims 1 to 6, in, The composite photocatalyst of carbon nitride wire wrapped with metal oxide has a material microstructure of wire wrapped with metal oxide nanoparticles, wherein the diameter of a single carbon nitride wire is 5-300nm, and the size of the wrapped metal oxide nanoparticles is 5-300nm.

8. Use of a composite photocatalyst of carbon nitride wire wrapped with metal oxide according to claim 7 in the degradation of antibiotic wastewater by catalytic oxidants.

9. The use of the composite photocatalyst of carbon nitride wire mesh wrapped with metal oxide according to claim 8, characterized in that: The oxidant is one or more of hydrogen peroxide, peroxymonosulfate, and peroxydisulfate.

10. The use of the composite photocatalyst of carbon nitride mesh wrapped with metal oxide according to claim 8, characterized in that: The antibiotic wastewater is antibiotic wastewater containing one or more of tetracycline antibiotics and quinolone antibiotics. The antibiotic concentration in the antibiotic wastewater is 2 mg / L-100 mg / L.

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