Catalyst for realizing efficient mineralization of perfluorinated pollutants by solar photo-thermal conversion, preparation method and application thereof

Abstract

This invention discloses a catalyst for the efficient mineralization of perfluorinated pollutants using solar photothermal conversion, its preparation method, and its application. The process includes: preparing a spinning solution containing nickel ions; forming a precursor membrane from the spinning solution using electrospinning; pre-oxidizing the precursor membrane to obtain a pre-oxidized membrane; and heat-treating the pre-oxidized membrane to obtain a catalyst membrane. The catalyst membrane is used to catalyze the oxidative degradation of perfluorinated compounds in water using solar photothermal conversion. The catalyst membrane is placed in a light-illuminating environment, with a concentrator element positioned above it to focus light onto the surface of the catalyst membrane. The water containing perfluorinated pollutants to be treated comes into contact with the surface of the catalyst membrane, catalyzing the oxidative degradation of perfluorinated compounds in the light-illuminating environment. The catalyst preparation process provided by this invention is simple, can be achieved at low cost and on a large scale using electrospinning technology, and can efficiently perform photothermal conversion, increasing the surface reaction temperature and accelerating the degradation reaction rate.

Description

Technical Field

[0001] This invention relates to the field of organic pollutant degradation technology, specifically to the preparation and application of a catalyst for the efficient mineralization of perfluorinated pollutants using solar energy. Background Technology

[0002] Perfluorinated compounds are widely used in various consumer products and industrial production due to their oil and water resistance, high temperature resistance and extremely high chemical stability. However, they are highly toxic, persistent and bioaccumulative. With the discharge of industrial wastewater, they enter the environment in large quantities, causing lasting damage to humans and the ecological environment.

[0003] Water treatment technologies for perfluorinated pollutants in water can be divided into three main categories: physical removal technologies, chemical degradation technologies, and biological treatment technologies. The core of physical removal technologies is to separate perfluorinated compounds from water through adsorption, membrane separation, etc., without destroying their molecular structure. However, these technologies require subsequent treatment (such as adsorbent incineration) to avoid secondary pollution. However, both physical and biological removal technologies have poor selectivity for short-chain perfluorinated compounds. Furthermore, adsorbent regeneration is difficult and prone to secondary pollution; membrane modules are expensive, require high-pressure operation, and consume a lot of energy; membranes are also susceptible to fouling and clogging, requiring frequent cleaning or replacement. Biological treatment technologies rely on enzymes secreted by specific microorganisms (such as bacteria and fungi) to gradually break the C-C or CF bonds in perfluorinated compound molecules, ultimately mineralizing them. This technology is environmentally friendly and low-cost, but its degradation efficiency is low, the cycle is long, and conditions are strict due to the biological inertness of perfluorinated compounds. For example, microbial growth requires specific temperature, pH, and nutrient conditions, and is easily inhibited by heavy metals and toxic substances in water; therefore, its application is currently immature. Chemical degradation technologies break the CF bonds of perfluorinated compounds through oxidation, reduction, and other reactions, decomposing them into harmless F-C bonds. - CO2 and H2O are the core technological directions for the complete elimination of perfluorinated compounds. Among them, advanced oxidation technologies generate hydroxyl radicals (·OH) and sulfate radicals (SO42-). - Strong oxidizing agents such as hydroxyl radicals (·) attack perfluorinated compound molecules. However, these technologies have extremely low degradation efficiency: the traditional hydroxyl radical redox potential (approximately 2.8 V) is insufficient to effectively break the CF bond, only degrading side chain groups and failing to achieve complete mineralization; the removal rate for typical perfluorinated compounds such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) is typically less than 30%. Simultaneously, intermediate products are easily generated: the oxidation process may produce shorter-chain perfluorinated compounds that are more difficult to degrade, increasing the difficulty of subsequent treatment. Operating costs are high: the consumption of oxidants (such as ozone and hydrogen peroxide) is large, and ultraviolet photocatalysis has high energy consumption.

[0004] In addition to the methods mentioned above, high-temperature incineration / pyrolysis technology can completely decompose perfluorinated compound molecules under high-temperature (typically >1200℃), oxygen-rich or oxygen-deficient conditions, producing CO2, H2O and F.- This type of method is often used to treat waste containing high concentrations of perfluorinated compounds, such as adsorbents and concentrates. However, this method is extremely energy-intensive: maintaining a high-temperature incinerator requires a large amount of fuel, resulting in high treatment costs. It also easily produces toxic byproducts: if the incineration temperature is insufficient or the oxygen supply is uneven, highly toxic gases such as dioxins and hydrogen fluoride may be generated, requiring a matching exhaust gas treatment system. Furthermore, it is not suitable for low-concentration wastewater, which must be concentrated and enriched first.

[0005] In summary, existing technologies for degrading perfluorinated compounds still suffer from problems such as high cost and energy consumption, complex processes, and difficulty in completely degrading short-chain perfluorinated compounds. Summary of the Invention

[0006] To address the problems existing in the background art, this invention provides a catalyst for the efficient mineralization of perfluorinated pollutants using solar photothermal conversion, its preparation method, and its application. The catalyst prepared by this invention can be produced on a large scale, has low operating costs, produces no secondary pollution, and exhibits a fast mineralization rate. Furthermore, by replacing traditional high-temperature incineration / pyrolysis technology with solar photothermal conversion technology, it achieves efficient mineralization of perfluorinated pollutants with extremely low energy consumption.

[0007] The technical solution adopted in this invention is: I. A method for preparing a catalyst that utilizes solar photothermal conversion to achieve efficient mineralization of perfluorinated pollutants. The preparation method includes the following steps: Step S1: Prepare a spinning solution containing nickel ions and a polymeric solute.

[0008] The concentration of nickel ions in the spinning solution is 6.6 mmol / L to 267 mmol / L, and the concentration of the polymeric solute is 0.1 g / mL to 0.12 g / mL.

[0009] The high molecular weight solute is selected from polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone and sodium alginate.

[0010] Preferably, the raw material for the nickel ions is nickel nitrate hexahydrate, the polymeric solute is polyacrylonitrile with a molecular weight of 100,000 to 200,000, and the mass ratio of nickel nitrate hexahydrate to polyacrylonitrile is 0.018 to 0.73:1.

[0011] The solvent of the spinning solution is a volatile organic solvent. The volatile organic solvent includes, but is not limited to, N,N-dimethylformamide (DMF), acetone, ethanol, etc., or a mixed solvent formed by mixing the above solvents in a certain proportion, such as a mixed solvent formed by mixing N,N-dimethylformamide and acetone in a volume ratio of 3:1 to 5:1.

[0012] Step S2: The spinning solution is used to prepare a precursor membrane by electrospinning.

[0013] In step S2, the distance between the syringe needle and the receiving roller must be maintained at 14~17 cm, the voltage during the spinning process is 17~18 kV, the injection flow rate of the spinning solution is 0.3~0.8 mL / h, the receiving roller must be kept at a constant speed, and the rotation speed of the receiving roller is 100~150 rpm.

[0014] Step S3: Pre-oxidize the precursor membrane to obtain a pre-oxidized membrane.

[0015] In step S3, the pre-oxidation conditions are as follows: under an air atmosphere, the temperature is gradually increased to 230-250°C at a heating rate of 1-3°C / minute, held at that temperature for 1.5-4 hours, and then naturally cooled to room temperature.

[0016] Step S4: Perform high-temperature heat treatment on the pre-oxidized film to obtain a catalyst film.

[0017] In the catalyst film, the mass percentage of metallic nickel (Ni) is 0.5% to 19.4%.

[0018] In step S4, the conditions for high-temperature heat treatment are as follows: under an inert gas atmosphere, the temperature is gradually increased to 900℃~1100℃ at a heating rate of 3℃ / min~6℃ / min, held for 1.5~4 hours, and then naturally cooled to room temperature.

[0019] II. A catalyst membrane prepared using the aforementioned preparation method.

[0020] 3. The catalyst membrane is used to utilize solar photothermal conversion to oxidize and degrade perfluorinated compounds in water.

[0021] The application method includes the following steps: Step D1: Place the catalyst membrane in a light environment and arrange a light-concentrating element above the catalyst membrane so that the light is focused onto the surface of the catalyst membrane by the light-concentrating element.

[0022] Preferably, the light intensity on the surface of the catalyst film is 8 kW / m². 2 Or more.

[0023] Step D2: Bring the water containing perfluorinated pollutants to be treated into contact with the surface of the catalyst membrane, and catalyze the oxidation and degradation of perfluorinated compounds in the water under light.

[0024] In step D2, the water is brought into contact with the surface of the catalyst membrane in any of the following ways: a) Spray the water containing perfluorinated pollutants to be treated onto the surface of the catalyst membrane; the preferred spraying density is 0.04 mL / cm³. 2 After maintaining the spray position for 1 minute, proceed with the next spraying. The spraying methods include, but are not limited to, spraying and coating. b) Allow the water containing perfluorinated pollutants to be treated to flow over the surface of the catalyst membrane.

[0025] The perfluorinated contaminants are perfluorooctanoic acid (PFOA) C8 and its corresponding short-chain compounds, including trifluoroacetic acid (C2), perfluoropropionic acid (C3), perfluorobutyric acid (C4), perfluorovalerate (C5), perfluorohexanoic acid (C6), and perfluoroheptanoic acid (C7).

[0026] The beneficial effects of this invention are: 1. Existing catalytic reactions based on pure metallic Ni often require precise design of the catalyst structure and preparation under strictly controlled processes and conditions, such as stacking metallic Ni in the channels to form a metal plasmon effect. In contrast, the loading and preparation process of metallic Ni in this invention is simple, the loading requirement is relatively low, and low-cost, large-scale preparation can be achieved using electrospinning technology.

[0027] 2. The catalyst prepared by the method of this invention has a light absorption rate of over 90% across the entire solar spectrum, enabling efficient photothermal conversion and increasing the reaction temperature on the catalyst surface, thereby accelerating the degradation rate of perfluorinated pollutants. Furthermore, upon photoexcitation, the charge carriers in the catalyst interact to generate hot charge carriers, directly activating the CF bonds in the perfluorinated pollutants, lowering the reaction energy barrier, and achieving efficient mineralization of the perfluorinated pollutants.

[0028] 3. The aqueous solution of perfluorinated compounds prepared by the method of the present invention contains a high concentration of single fluoride ions after treatment, which can be recovered as raw materials for chemical reactions. The above process does not require external energy and can directly utilize solar energy to achieve efficient defluorination and fluorine recovery in one system. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation process of the catalyst of the present invention; Figure 2 The images show X-ray diffraction (XRD) patterns of the catalysts prepared in Examples 1, 2, 3, 4 and the comparative examples of this invention. Figure 3 The images are scanning electron microscope (SEM) images of the catalysts prepared in Example 3 and the comparative example of the present invention; wherein, a is the CNFs catalyst prepared in the comparative example of the present invention, and b is the Ni-CNFs-2 catalyst prepared in Example 3 of the present invention. Figure 4 This is a transmission electron microscope (TEM) image of the catalyst Ni-CNFs-2 prepared in Example 3 of this invention; Figure 5 The UV-Vis-NIR absorption spectra of the catalysts prepared in Examples 1, 2, 3, 4 and the comparative examples of this invention are shown. Figure 6 The graphs show the photothermal conversion performance of the catalysts prepared in Examples 1, 2, 3, 4 and the comparative examples of this invention. Figure 7 The removal curves of perfluorooctanoic acid by the catalysts prepared in Examples 1, 2, 3, 4 and the comparative examples of the present invention using solar photothermal degradation are shown. Figure 8 The catalyst prepared in Example 3 of this invention exhibits removal curves for perfluorooctanoic acid (PFOA) under different light intensities using solar photothermal degradation. Figure 9 The defluorination rate curves of the catalysts prepared in Examples 1, 2, 3, 4 and the comparative examples of the present invention for the degradation of perfluorooctanoic acid by solar photothermal energy are shown. Figure 10 This is a bar chart showing the defluorination rate of different perfluorinated compounds by the catalyst prepared in Example 3 of this invention using solar photothermal degradation. Figure 11 The N1s spectrum is shown in the X-ray photoelectron spectroscopy of the catalyst prepared in Example 3 of this invention. Figure 12 This is a schematic diagram of the reaction unit designed in Embodiment 5 of the present invention; Figure 13 This is a schematic diagram of the outdoor experimental device constructed according to Embodiment 6 of the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 This is a flowchart of the catalyst preparation process for the present invention. First, a homogeneous solution is obtained by magnetic stirring; then, an electrospinning film is formed; and finally, pre-oxidation and high-temperature calcination are performed.

[0032] The preparation principle of the catalyst in this invention is explained below: The present invention selects volatile organic solvents and polymeric solutes because during the electrospinning process, the solvent needs to evaporate rapidly within a very short time under the stretching jet of the electric field, allowing the polymer to quickly solidify into fibers. This is necessary for the catalyst to form a film better and possess a certain mechanical strength, which is essential for subsequent large-scale outdoor applications. The pre-oxidation step after spinning helps the fibers to further cross-link and form a film, making the catalyst less likely to be destroyed into powder, which is more conducive to catalytic reactions under sunlight and large-scale applications. At the same time, it can prevent the loss of some elements (such as C, N, etc.) during the subsequent high-temperature heat treatment process. The principle of high-temperature heat treatment is to reduce metallic nickel to nanoparticles through high-temperature carbonization. At the same time, the heat-treated fibers will change (for example, the diameter will decrease, exposing the metal nanoparticles to form catalytic sites for better catalytic reactions), creating confined reaction conditions to increase the adsorption of perfluorinated pollutants, and making it less likely to be damaged by dissolution and other problems during water treatment.

[0033] Based on the above principles, this invention proposes a method for preparing a catalyst that utilizes solar photothermal conversion to achieve efficient mineralization of perfluorinated pollutants.

[0034] The preparation method of this invention includes the following steps: Step S1: Prepare a spinning solution containing nickel ions and a polymeric solute.

[0035] In the spinning solution, the concentration of nickel ions ranges from 6.6 mmol / L to 267 mmol / L, and the concentration of the polymeric solute ranges from 0.1 g / mL to 0.12 g / mL.

[0036] The polymeric solute is selected from polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, and sodium alginate. Preferably, the molecular weight of the polymeric solute is between 100,000 and 200,000.

[0037] Preferably, the raw material for nickel ions is nickel nitrate hexahydrate, the polymeric solute is polyacrylonitrile with a molecular weight of 100,000 to 200,000, and the mass ratio of nickel nitrate hexahydrate to polyacrylonitrile is 0.018 to 0.73:1.

[0038] The solvent of the spinning solution is a volatile organic solvent, including but not limited to N,N-dimethylformamide, acetone, ethanol, etc., or a mixed solvent formed by mixing the above solvents in a certain proportion, such as N,N-dimethylformamide and acetone mixed in a volume ratio of 3:1 to 5:1.

[0039] Step S2: The spinning solution is used to prepare a precursor membrane by electrospinning.

[0040] In step S2, the distance between the syringe needle and the receiving roller must be maintained at 14 cm to 17 cm, the voltage during the spinning process is 17 kV to 18 kV, the injection flow rate of the spinning solution is 0.3 mL / h to 0.8 mL / h, the receiving roller must be kept at a constant speed, and the rotation speed of the receiving roller is 100 rpm to 150 rpm.

[0041] Step S3: Pre-oxidize the precursor membrane to obtain a pre-oxidized membrane.

[0042] In step S3, the pre-oxidation conditions are as follows: under an air atmosphere, the temperature is gradually increased to 230-250°C at a heating rate of 1-3°C / min, held at that temperature for 1.5-4 hours, and then naturally cooled to room temperature.

[0043] Step S4: Perform high-temperature heat treatment on the pre-oxidized film to obtain the catalyst film.

[0044] In step S4, the conditions for high-temperature heat treatment are as follows: under an inert gas atmosphere, the temperature is gradually increased to 900-1100°C at a heating rate of 3-6°C / min, held for 1.5-4 hours, and then naturally cooled to room temperature.

[0045] The present invention also provides a catalyst membrane prepared by the above-described preparation method. In the catalyst membrane, the mass percentage of metallic nickel (Ni) is 0.5% to 19.4%.

[0046] This invention also provides an application of the above-described catalyst membrane. The catalyst membrane prepared by the above method can be used to catalyze the oxidative degradation of perfluorinated compounds in water using solar photothermal conversion.

[0047] The present invention also provides a method for applying the above-mentioned catalyst membrane, specifically including the following steps: Step D1: Place the catalyst membrane in a light-illuminated environment and place a concentrating element above the catalyst membrane so that the light is focused onto the surface of the catalyst membrane through the concentrating element.

[0048] The preferred light intensity on the surface of the catalyst film is 8 kW / m 2 Or more.

[0049] Step D2: Bring the water containing perfluorinated pollutants to be treated into contact with the surface of the catalyst membrane, and catalyze the oxidation and degradation of perfluorinated compounds in the water under light.

[0050] In step D2, the water can be brought into contact with the surface of the catalyst film in any of the following ways: a) Spray the water containing perfluorinated pollutants to be treated onto the surface of the catalyst membrane; the spraying density is 0.04 mL / cm³. 2After maintaining the spray position for 1 minute, proceed with the next spraying. Spraying methods include, but are not limited to, spraying and coating. b) The water containing perfluorinated pollutants to be treated is continuously flowed through the surface of the catalyst membrane at a flow rate of 0.2 mL / h to 1 mL / h.

[0051] The perfluorinated pollutants are perfluorooctanoic acid (C8) and its corresponding short-chain compounds (trifluoroacetic acid C2, perfluoropropionic acid C3, perfluorobutyric acid C4, perfluorovalerate C5, perfluorohexanoic acid C6, and perfluoroheptanoic acid C7).

[0052] Specific embodiments of the present invention are as follows: Example 1 In this embodiment, the catalyst film Ni-CNFs-0.1 was prepared through the following process: (1) Under magnetic stirring, 0.1 mmol of nickel nitrate hexahydrate and 1.6 g of polyacrylonitrile (PAN) were dissolved in 15 mL of N,N-dimethylformamide (DMF) solution to form a homogeneous spinning solution. The molecular weight of polyacrylonitrile (PAN) was 150,000.

[0053] (2) The spinning solution was used for electrospinning technology. The distance between the syringe needle and the receiving roller was set to 15cm, the voltage was set to 17~18 kV, the flow rate was set to 0.6 mL / h, and the rotation speed was set to 120 rpm, so that the spun filaments could be evenly covered on the receiving roller to obtain the precursor film.

[0054] (3) Tear the precursor film off the receiving roller and cut it into 5 cm × 5 cm sizes. Pre-oxidize it in a muffle furnace at 240°C for 3 hours with a heating rate of 2°C / min. Then, fire it at high temperature in a tube furnace at 1000°C for 3 hours with a heating rate of 5°C / min to obtain the catalyst film Ni-CNFs-0.1.

[0055] In the catalyst film Ni-CNFs-0.1, the proportion of metallic nickel (Ni) is 0.5% wt.

[0056] The Ni-CNFs-0.1 catalyst membrane was placed in a photochemical reactor. 1 mL of simulated wastewater (500 mg / L) prepared with perfluorooctanoic acid was dripped onto the 3 cm × 3 cm catalyst membrane. The photochemical reactor was placed under sunlight, and the light was focused using a Fresnel lens. The intensity of the focused sunlight was approximately 8 kW / m². 2 Under these conditions, the reaction is carried out for 1 hour to degrade perfluorinated pollutants in the water.

[0057] Comparative Example 1 The difference between this embodiment and Example 1 is that the amount of nickel nitrate hexahydrate in step (1) is 0 mmol, resulting in a catalytic membrane containing only pure carbon and nitrogen, denoted as CNFs. Everything else is the same as in Example 1.

[0058] Example 2 The difference between this embodiment and Example 1 is that the amount of nickel nitrate hexahydrate in step (1) is 1 mmol, resulting in a catalyst material with a nickel content of 5.3% in the composite catalyst, denoted as Ni-CNFs-1. Everything else is the same as in Example 1.

[0059] Example 3 The difference between this embodiment and Example 1 is that the amount of nickel nitrate hexahydrate in step (1) is 2 mmol, resulting in a catalytic material with a nickel content of 10.8% in the composite catalyst, denoted as Ni-CNFs-2. Everything else is the same as in Example 1.

[0060] Example 4 The difference between this embodiment and Example 1 is that the amount of nickel nitrate hexahydrate in step (1) is 4 mmol, resulting in a catalyst material with a nickel content of 19.4% in the composite catalyst, denoted as Ni-CNFs-4. Everything else is the same as in Example 1.

[0061] Figure 2 These are X-ray diffraction patterns of the catalysts prepared in Examples 1, 2, 3, 4, and the comparative example of this invention. Figure 2 It can be seen that as the loading of metallic Ni nanoparticles increases, the characteristic peaks of the three crystal planes of metallic Ni appear, and the intensity increases with the increase of loading.

[0062] Figure 3 These are scanning electron microscope (SEM) images of the CNFs and Ni-CNFs-2 catalysts prepared in Example 3 and the comparative example of this invention. Figure 3 Image 'a' is a scanning electron microscope image of the CNFs catalyst obtained in the comparative example; compared to... Figure 3 a, from Figure 3 In the scanning electron microscope image of the catalyst Ni-CNFs-2 obtained in Example 3 of the present invention shown in b, it can be clearly seen that metallic Ni nanoparticles are loaded on the catalyst.

[0063] Figure 4 This is a transmission electron microscope (TEM) image of the Ni-CNFs-2 catalyst prepared in Example 3 of this invention. It can be clearly seen from the image that not only are metallic Ni nanoparticles distributed on the surface of the nanofibers, but metallic Ni nanoparticles also exist inside the nanofibers.

[0064] Figure 5These are the UV-Vis and near-infrared absorption spectra of the catalysts Ni-CNFs-0.1, Ni-CNFs-1, Ni-CNFs-2, Ni-CNFs-4, and CNFs prepared in Examples 1, 2, 3, 4, and the comparative example of this invention. The figures show that all catalysts exhibit good absorption across the entire solar spectrum. Furthermore, the addition of metallic nickel (Ni) has little impact on the absorption spectrum of the catalysts, still achieving an average absorption rate of over 90% across the entire solar spectrum.

[0065] Figure 6 The graphs show the photothermal conversion performance of the catalysts prepared in Examples 1, 2, 3, 4 and the comparative examples of this invention. All catalysts exhibit good photothermal conversion performance with little difference between them; as the intensity of sunlight increases, the temperature of the catalyst surface increases from the initial 350 K (1 sun) to 520 K (8 sun).

[0066] Figure 7 The catalysts Ni-CNFs-0.1, Ni-CNFs-1, Ni-CNFs-2, Ni-CNFs-4, and CNFs prepared in Examples 1, 2, 3, 4, and the comparative examples of this invention are used in 8 kW / m 2 The removal curves of perfluorooctanoic acid (PFOA) by solar photothermal degradation under (8 sun) light intensity are shown. It is evident that the loading of Ni nanoparticles has a significant impact on catalytic performance. When the proportion of metallic Ni in the composite catalyst is 0.5%~19.4%, the catalytic activity first increases and then tends to stabilize with increasing loading. Among them, the catalytic effect is optimal when the proportion of metallic Ni in the composite catalyst is 10.8% (Example 3). When the loading is further increased to 19.4%, the catalytic performance decreases slightly without significant improvement. This is because the loading of metallic Ni has reached saturation for this catalytic reaction; simply increasing the loading of metallic Ni cannot improve the catalytic performance, and may even prevent the carbon substrate from effectively absorbing solar energy to generate excited-state electrons, thus hindering the catalytic reaction.

[0067] Figure 8 The catalyst Ni-CNFs-2 prepared in Example 3 of this invention is used under different light intensities (1 kW / m²). 2=1sun) Removal curve of perfluorooctanoic acid (PFOA) by solar photothermal degradation. It can be seen that with the increase of light intensity, the degradation performance of the catalyst Ni-CNFs-2 on PFOA precursor increased from 10% to 100%, and the degradation kinetics were significantly improved, achieving complete decomposition of PFOA precursor within 20 minutes. The reasons are: (1) With the increase of light intensity, the photothermal conversion causes the catalyst surface temperature to rise continuously, reaching 520K at 8sun, which can greatly improve the reaction kinetics; (2) Under high light intensity, the number of excited state electrons generated increases significantly, which can better activate PFOA molecules, making more molecules activated and easier to break bonds and decompose.

[0068] Figure 9 The catalysts CNFs, Ni-CNFs-0.1, Ni-CNFs-1, Ni-CNFs-2, and Ni-CNFs-4 prepared in Examples 1, 2, 3, 4, and Comparative Examples 5 of this invention, and CNFs, were used at 8 kW / m 2 The defluorination rate curve of perfluorooctanoic acid (PFOA) degradation by solar photothermal energy under a light intensity of (8 sun) is shown. It is evident that the loading of Ni nanoparticles has a significant impact on catalytic performance. The optimal catalytic mineralization effect is observed when the proportion of metallic Ni in the composite catalyst reaches 10.8% (Example 3). Further increasing the loading to 19.4% results in a slight decrease in catalytic performance, without a significant improvement. This is because the loading of metallic Ni has reached saturation for this catalytic reaction; simply increasing the loading of metallic Ni cannot improve catalytic performance. In fact, excessive nickel content may prevent the carbon substrate from effectively absorbing solar energy to generate excited-state electrons, thus hindering the catalytic reaction.

[0069] Figure 10 The catalyst Ni-CNFs-2 prepared in Example 3 of this invention is at 8 kW / m 2 A bar chart showing the defluorination rates of different perfluorinated pollutants (PFOS, GenX, C6H2FO4, C4F9O3H, 6:2FTSA, 5:3FTCA) under solar photothermal degradation at an intensity of (8 suns). It is evident that this catalyst can achieve high defluorination rates for perfluorinated pollutants of different structures and types, indicating that this method has a certain degree of universality rather than being targeted at a specific single perfluorinated pollutant.

[0070] Figure 11 This is the N1s spectrum of the Ni-CNFs-2 catalyst prepared in Example 3 of this invention. It can be seen that metallic Ni and N form a Ni-N coordination structure, and the Ni and CN substrate are connected through the Ni-N form. This allows for better stabilization of the Ni valence state through electron transfer, thereby protecting metallic Ni from oxidation and deactivation.

[0071] Finally, the mechanism of photothermal catalysis in this invention is explained based on the above results: pass Figure 5 It can be seen that the catalyst prepared by the present invention achieves high absorption rate across the entire solar energy spectrum, and can make full use of solar energy in almost all wavelengths. Its solar energy utilization rate is higher than that of commonly reported photocatalysts (which generally use specific ultraviolet wavelengths, such as 254 nm UV light). pass Figure 6 It can be concluded that the catalyst prepared in this invention has good photothermal conversion performance and can achieve certain thermocatalytic degradation of perfluorinated compounds without an external heat source. pass Figure 7 , Figure 9 The comparison of degradation performance shows that perfluorooctanoic acid exhibits better degradation and mineralization performance in the presence of nickel catalyst, indicating that nickel plays a role in accelerating the degradation of perfluorooctanoic acid during photothermal catalytic oxidation. at the same time, Figure 9 This indicates that when the amount of nickel added reaches 2 mmol / 15 mL (i.e., catalyst Ni-CNFs-2), the mineralization rate of perfluorooctanoic acid is close to 100%, supporting the parameters such as the amount of metal added in this invention.

[0072] Carbon-based materials, under sunlight, excite electrons to an excited state. These excited electrons generate heat through relaxation, thereby increasing the catalyst surface temperature. Simultaneously, some excited electrons directly activate perfluorinated compound molecules, lowering the bond-breaking energy barrier and facilitating the catalytic bond-breaking reaction. This reaction is essentially an oxidative decomposition of perfluorinated compounds under oxygen conditions. However, under conventional conditions (no heating, no specific wavelength of light, no oxidant, etc.), this reaction is difficult to occur, hence perfluorinated compounds are recognized as recalcitrant pollutants. The catalyst prepared using this invention can effectively absorb the full spectrum of solar energy, achieving better photothermal conversion performance and increasing the reaction temperature on the catalyst surface. Furthermore, the excited electrons generated during this process can directly activate perfluorinated compound molecules, lowering the bond-breaking reaction barrier and making them more easily catalytically oxidized and decomposed by metallic nickel at lower temperatures.

[0073] Example 5 In this embodiment, the catalyst membrane prepared in Example 3 was used to construct the reaction unit of an outdoor experimental device for treating industrial wastewater containing C2~C7 perfluoroalkyl carboxylic acids (PFCA). The reaction unit adopts a flow-type design, which facilitates wastewater treatment and catalyst membrane cleaning.

[0074] Figure 12This is a schematic diagram of the reaction unit designed in this embodiment. As can be seen, the catalyst membrane is placed inside the stainless steel reaction unit, with a transparent calcium fluoride window above it; the inlet and outlet water pipes are located below the reaction unit, connected to the wastewater storage tank and the treated collection unit via PE conveying pipes. Each reaction unit can be arranged closely together, reducing space utilization and increasing the number of catalyst membranes that can be placed.

[0075] The specific design is as follows: (1) Constructing a catalyst membrane reaction unit: The catalyst membrane prepared in Example 3 has an area of ​​3×3~5×5cm. 2 Each catalyst membrane is placed within a cubic stainless steel reaction unit, with a calcium fluoride window at the top for receiving sunlight (e.g., Figure 12 (As shown).

[0076] (2) Setting up spraying components: A flow spraying design is adopted. A water inlet nozzle and a water outlet are set below each reaction unit. The water inlet nozzle is placed 3 cm above the catalyst membrane, which can realize that the wastewater is evenly sprayed on the surface of the catalyst membrane. After rapid reaction, it condenses on the stainless steel metal wall and finally gathers at the water outlet and flows out through the water outlet pipe for collection.

[0077] Tests revealed that the concentrations of various perfluorinated compounds in the collected industrial wastewater were 285.98 mg / L (trifluoroacetic acid C2), 16.84 mg / L (perfluoropropionic acid C3), 66.78 mg / L (perfluorobutyric acid C4), 128.52 mg / L (perfluorovalerate C5), 18.23 mg / L (perfluorohexanoic acid C6), 0.52 mg / L (perfluoroheptanoic acid C7), and 82.05 mg / L (GenX).

[0078] Example 6 The outdoor experimental device constructed in this embodiment is adapted to the reaction unit designed in Example 5 and the catalyst membrane prepared in Example 3, and is used to treat industrial wastewater containing C2~C7 perfluoroalkyl carboxylic acids (PFCA).

[0079] Figure 13 This is a schematic diagram of the outdoor experimental setup constructed in this embodiment. The diagram shows a 16×16 matrix combination used for treating fluoride-containing wastewater under real sunlight.

[0080] In this embodiment, the device adopts a modular design, which facilitates outdoor installation, debugging, and maintenance. The specific setup is as follows: The site selection is to choose a flat and open area within the wastewater treatment plant of the fluorochemical industrial park, avoiding areas with flammable and explosive materials, strong electromagnetic interference, and areas prone to rainwater accumulation. The site should be well-ventilated to facilitate wastewater transportation and discharge of treated effluent. At the same time, a maintenance access channel with a width of not less than 1.2m should be reserved. Main device construction: Based on the reaction unit designed in Example 5, the reaction array is arranged in array combination, including but not limited to matrix forms such as 16×16 and 20×20. The combined reaction array is fixed on the support. The device support is made of stainless steel and the angle can be adjusted within the range of 30° to 60° to facilitate all-weather reception of sunlight according to the actual movement and direction of the sun throughout the day. Wastewater storage and transportation unit construction: A 500L corrosion-resistant PE material storage tank is selected, with a flow rate adjustment range of 0.5~2m. 3 The variable frequency circulating pump with a capacity of / h is connected through a PE conveying pipe with a diameter of 5 mm. The outer wall of the PE conveying pipe is wrapped with an insulation layer to prevent outdoor temperature changes from affecting the stability of sewage conveying. At the same time, a clean water flushing pipe and a clean water storage tank are reserved for nighttime cleaning of sewage or precipitated inorganic anions and cations remaining on the catalyst membrane surface or inside the reaction unit. Set up a detection and control unit: Install water quality detection sensors in the water storage tank, the main water inlet and the main water outlet of the device to quickly detect fluoride ion concentration, pH value and turbidity. These water quality detection sensors are all connected to the outdoor control cabinet for communication or electrical connection, so as to display the detection data in real time. At the same time, an automatic alarm device is set up. When the fluoride ion concentration of the outlet water is too low or close to the fluoride ion concentration of the inlet water, the alarm is automatically triggered and the spraying flow rate is adjusted. Set up an effluent collection unit: Set up a PE collection tank below the catalyst membrane reaction unit to collect the treated wastewater. The collection tank is connected to the industrial park's wastewater treatment network through a pipe. At the same time, a sampling port is reserved to facilitate regular sampling and testing.

[0081] Example 7 This embodiment describes the treatment process and parameters of an outdoor experimental device for treating industrial wastewater containing C2-C7 perfluoroalkyl carboxylic acids (PFCA). The specific process is as follows: The collected industrial wastewater is stored in a water storage tank, connected to a circulating pump and the device reaction unit. The flow rate is set according to the reaction unit (the flow rate of each reaction unit is 0.2 mL / h to 1 mL / h) so that the wastewater can be evenly sprayed onto the catalyst membrane. Under outdoor sunlight, the orientation and tilt angle of the outdoor device need to be adjusted constantly according to the movement of the sun to ensure that the sunlight spots always cover the windows of all reaction units; If salt spots appear on the catalyst membrane due to changes in the concentration of anions and cations in the wastewater, the catalyst membrane can be flushed at night by switching the influent to a clean water storage tank and using a high flow rate to dissolve the precipitated inorganic anions and cations, thus maintaining the catalytic performance of the catalyst membrane.

[0082] Tests showed that the concentrations of various perfluorinated compounds in the collected treated wastewater were all lower than those detected by the instrument, indicating that the mineralization rate was close to 100%.

[0083] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

[0084] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A method for preparing a catalyst that utilizes solar photothermal conversion to achieve efficient mineralization of perfluorinated pollutants, characterized in that, Includes the following steps: Step S1: Prepare a spinning solution, wherein the spinning solution contains nickel ions and a polymeric solute; Step S2: Prepare a precursor membrane from the spinning solution using electrospinning. Step S3: Pre-oxidize the precursor membrane to obtain a pre-oxidized membrane; Step S4: Heat-treat the pre-oxidized film to obtain a catalyst film.

2. The method for preparing the catalyst for efficient mineralization of perfluorinated pollutants by utilizing solar photothermal conversion according to claim 1, characterized in that: The concentration of nickel ions in the spinning solution is 6.6 mmol / L to 267 mmol / L, and the concentration of the polymeric solute is 0.1 g / mL to 0.12 g / mL.

3. The method for preparing the catalyst for efficient mineralization of perfluorinated pollutants using solar photothermal conversion according to claim 2, characterized in that: The high molecular weight solute is selected from polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone and sodium alginate.

4. The method for preparing the catalyst for efficient mineralization of perfluorinated pollutants by utilizing solar photothermal conversion according to claim 1, characterized in that: In the catalyst film, the mass percentage of metallic nickel (Ni) is 0.5% to 19.4%.

5. The method for preparing the catalyst for efficient mineralization of perfluorinated pollutants by utilizing solar photothermal conversion according to claim 1, characterized in that: In step S2, the distance between the syringe needle and the receiving roller is 14 cm to 17 cm, the voltage during the spinning process is 17 kV to 18 kV, the injection flow rate of the spinning solution is 0.3 mL / h to 0.8 mL / h, the receiving roller is kept at a constant speed, and the rotation speed of the receiving roller is 100 rpm to 150 rpm.

6. The method for preparing the catalyst for efficient mineralization of perfluorinated pollutants by utilizing solar photothermal conversion according to claim 1, characterized in that: In step S3, the pre-oxidation conditions are as follows: under an air atmosphere, the temperature is gradually increased to 230-250°C at a heating rate of 1-3°C / min, held at that temperature for 1.5-4 hours, and then naturally cooled to room temperature. In step S4, the heat treatment conditions are as follows: under an inert gas atmosphere, the temperature is gradually increased to 900-1100°C at a heating rate of 3-6°C / min, held for 1.5-4 hours, and then naturally cooled to room temperature.

7. A catalyst membrane prepared by any one of the preparation methods described in claims 1 to 6.

8. An application of the catalyst membrane as described in claim 7, characterized in that: It is used to utilize solar photothermal conversion to oxidize and degrade perfluorinated compounds in water.

9. The application according to claim 8, characterized in that: The application method includes the following steps: Step D1: Place the catalyst membrane in a light environment and arrange a light-concentrating element above the catalyst membrane so that the light is focused onto the surface of the catalyst membrane by the light-concentrating element. Step D2: Bring the water containing perfluorinated pollutants to be treated into contact with the surface of the catalyst membrane, and catalyze the oxidation and degradation of perfluorinated compounds in the water under light.

10. The application according to claim 9, characterized in that: In step D2, the water is brought into contact with the surface of the catalyst membrane in any of the following ways: a) Spray the water containing perfluorinated pollutants to be treated onto the surface of the catalyst membrane; b) Allow the water containing perfluorinated pollutants to be treated to flow over the surface of the catalyst membrane.

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