Magnetic photocatalyst, preparation method and method for magnetic flocculation photocatalytic water purification

Abstract

The application discloses a magnetic photocatalyst, a preparation method thereof and a method for magnetic flocculation photocatalytic water purification, the magnetic photocatalyst is composed of a magnetic core, a coating layer and a transition layer, the magnetic core is one of iron, Fe3O4 or gamma-Fe2O3, the magnetic core accounts for 50-80% of the total mass fraction of the magnetic photocatalyst, the first coating layer is alpha-Fe2O3, the second coating layer is TiO2, and the transition layer is iron titanate formed by calcining a composite. The flocculant is added to waste water to perform initial flocculation at a low concentration, then the magnetic photocatalyst is put into the water body, degradation of pollutants is performed under irradiation of ultraviolet light, and then the flocculant and a coagulant aid are added to perform magnetic flocculation and magnetic separation operation, so that the water purification and recycling of the catalyst are completed. The application combines the photocatalytic technology and the magnetic flocculation technology, and through synthesis of the magnetic photocatalyst and the water purification method, degradation of pollutants and removal of suspended matters can be efficiently promoted, continuous operation can be realized, the water treatment efficiency is greatly improved, and the catalyst can be separated and recycled by using a magnetic field.

Description

Technical Field

[0001] This invention relates to a magnetic photocatalyst, its preparation method, and its application in magnetic flocculation photocatalytic water purification. Background Technology

[0002] With industrialization and urbanization, wastewater discharge has become a major challenge seriously affecting the environment and human health. Traditional wastewater treatment methods suffer from low efficiency, large equipment requirements, and high costs, thus urgently requiring new, efficient, economical, and environmentally friendly wastewater treatment technologies. Among current water treatment technologies, photocatalysis and magnetic flocculation have attracted significant attention as emerging advanced water treatment methods. Photocatalysis utilizes light energy to excite active species on the catalyst surface, degrading organic pollutants in wastewater. It boasts advantages such as high efficiency, no chemical additives, and broad applicability to various pollutants. However, photocatalysis has limitations in treating suspended and fine particles. Meanwhile, magnetic flocculation is favored for its high efficiency in removing fine particles and suspended solids, but its degradation effect on organic pollutants in wastewater is relatively poor. Against this backdrop, magnetic photocatalysis combined with magnetic flocculation technology has emerged as a promising innovative technology in current research and application. Photocatalysis, as an advanced wastewater treatment technology, possesses unique advantages. Its core idea is to generate active oxygen species, such as hydroxyl radicals (•OH) and superoxide radicals (•O2), through light irradiation of the catalyst. -These processes, such as […], achieve the degradation of organic pollutants and the purification of wastewater. TiO2, as a widely used photocatalyst, is highly favored due to its stability and photocatalytic activity. The photocatalytic activity of α-Fe2O3 allows it to function under visible light conditions, exhibiting strong visible light responsiveness and relative stability in the catalytic reaction; the introduction of ferromagnetic materials does not affect its stability. The combination of α-Fe2O3 and TiO2 to form ferric titanate complements each other's light absorption range, enabling effective absorption of light energy across the entire spectrum. At the heterojunction interface, due to energy level differences, photogenerated electrons and holes are separated, reducing their recombination opportunities and thus extending the lifetime of photogenerated carriers. The presence of the heterojunction helps to hinder direct recombination of electrons and holes, reducing the loss of photogenerated carriers and improving photocatalytic activity. The introduction of magnetic materials provides a more flexible and efficient solution for wastewater treatment. Magnetic materials possess excellent magnetic responsiveness, enabling rapid separation and recovery under the influence of an external magnetic field. This facilitates the application of magnetic photocatalysts in wastewater treatment. Combining photocatalysis and magnetic flocculation technologies represents a novel water treatment technology that promises to overcome the shortcomings of each and achieve synergistic effects. This combined technology, building upon the efficient degradation of organic pollutants through photocatalysis, rapidly removes fine particles and suspended solids from wastewater through magnetic flocculation, thereby improving overall water treatment efficiency. The combination of photocatalysis and magnetic flocculation offers significant advantages, aiming to address the deficiencies of traditional wastewater treatment methods while fully leveraging the strengths of both technologies to achieve a more efficient, environmentally friendly, and sustainable water treatment solution.

[0003] In this study, we combined photocatalysis and magnetic flocculation technologies, introducing magnetic particles into the photocatalytic process to explore the synergistic mechanism and advantages of their combined effects. The hydroxyl and superoxide radicals generated by photocatalysis contribute to the removal of organic pollutants, while magnetic flocculation aggregates small suspended solids in water, forming larger flocs that facilitate subsequent separation and removal. This innovative combination of technologies effectively overcomes their respective limitations, and the designed water purification device enables wastewater recycling, improving the treatment efficiency for complex wastewater.

[0004] This invention provides a magnetic photocatalyst, its preparation method, and its application in magnetic flocculation photocatalytic water purification. We first synthesize a magnetic photocatalyst to photodegrade pollutants in wastewater. Then, we use magnetic flocculation technology to aggregate the catalyst and suspended solids. The resulting magnetic flocs settle under the influence of a magnetic field, followed by magnetic separation to purify the water and recycle the catalyst. Furthermore, we design a highly efficient water purification device capable of continuous water purification and catalyst recycling. The entire process is sustainable, reducing treatment costs and improving purification efficiency.

[0005] Because photocatalytic reactions are influenced by multiple factors, the amount of catalyst, the pH of the water, and the intensity and duration of ultraviolet light irradiation can be controlled to regulate the photocatalytic process. In magnetic flocculation, the type and amount of flocculant must be carefully controlled, and specific requirements are placed on the stirring speed and time. This can improve the aggregation efficiency of magnetic flocs, thereby increasing the removal rate of pollutants and suspended solids. Furthermore, introducing magnetic materials into the catalyst preparation process can replace traditional magnetic powder in magnetic flocculation, giving it photocatalytic properties to enhance pollutant treatment efficiency. It also allows the magnetic catalyst to utilize its inherent properties for separation, recycling, and regeneration, reducing catalyst loss during experimental production and lowering production costs. Due to the continuous nature of the purification system, each process is closely linked to the next; therefore, overall control of the system is necessary to ensure the smooth operation of the purification process. Summary of the Invention

[0006] The purpose of this invention is to provide a magnetic photocatalyst, its preparation method, and its application in magnetic flocculation photocatalytic water purification.

[0007] Magnetic photocatalysts consist of a magnetic core, a coating layer, and a transition layer.

[0008] The magnetic core is one of iron, Fe3O4, or γ-Fe2O3, and accounts for 50-80% of the total mass fraction of the magnetic photocatalyst.

[0009] The first coating layer is α-Fe2O3, which accounts for 10-30% of the total mass fraction of the magnetic photocatalyst, and the second coating layer is TiO2, which accounts for 10-35% of the total mass fraction of the magnetic photocatalyst.

[0010] The transition layer is iron titanate composed of a first coating layer and a second coating layer calcined together, with a thickness of 1-300 nm.

[0011] The magnetic core is spherical or needle-shaped. The diameter of the spherical magnetic core is 0.1-100 μm, and the aspect ratio of the needle-shaped magnetic core is 2-20. Its length is 0.1-100 μm and its diameter is 0.1-10 μm.

[0012] The preparation method of magnetic photocatalyst includes the following steps:

[0013] 1) Take 0.5-10 g of magnetic cores and spread them evenly in a porcelain boat, then place them in a tube furnace and calcine them at a heating rate of 1-20 ℃ / min, at a temperature of 280-580 ℃, for a calcine time of 10-60 min, so that a layer of α-Fe2O3 is formed on its surface.

[0014] 2) Add the material synthesized in 1) to a mixed solution of tetrabutyl titanate and anhydrous ethanol in a volume ratio of 1:(3-10), and disperse ultrasonically for 10-30 min;

[0015] 3) Add a mixture of water and anhydrous ethanol in a volume ratio of 1:(2-10) to the mixed solution in 2), and stir at 40-80℃ for 1-6 h;

[0016] 4) The product from 3) is recovered using a magnet, washed and dried, and then calcined and compounded at 400-550 °C for 1-5 h to prepare a magnetic photocatalyst.

[0017] The saturation magnetic susceptibility of the magnetic photocatalyst is 20-100 emu / g.

[0018] A method for magnetic flocculation and photocatalytic water purification, characterized by comprising the following steps:

[0019] 1) Take 1 L of wastewater, add 1-10 mg / L of flocculant to the wastewater for low-concentration initial flocculation, which can make full use of the pollutants to gather around the catalyst. Then, put the above magnetic photocatalyst into the wastewater and complete the photodegradation process of the wastewater under ultraviolet light irradiation.

[0020] 2) Add 150-500 mg / L of flocculant to the degraded wastewater, stir evenly, and then add 1-10 mg / L of coagulant aid for magnetic flocculation. After the magnetic flocs grow and stabilize, place the water in a magnetic field for sedimentation to complete the separation of the water from the magnetic flocs.

[0021] The flocculant is one or more of aluminum sulfate, ferric chloride and ferrous sulfate, polyaluminum sulfate, polyferric sulfate, polyaluminum chloride, polyferric chloride, polyferric silicate, and polyaluminum ferric sulfate.

[0022] The coagulant is one of cationic polyacrylamide, anionic polyacrylamide, and nonionic polyacrylamide.

[0023] The magnetic photocatalyst can be recycled and reused for the next wastewater purification cycle.

[0024] This invention successfully loads TiO2 onto iron powder, Fe3O4, or γ-Fe2O3, adding photocatalytic performance to traditional magnetic powder. The intermediate layer α-Fe2O3 forms a heterojunction with TiO2, allowing their light absorption ranges to complement each other, enabling effective light energy absorption across the entire spectrum. At the heterojunction interface, due to energy level differences, photogenerated electrons and holes are separated, reducing their recombination opportunities and thus extending the lifetime of photogenerated carriers. The presence of the heterojunction helps to hinder direct recombination of electrons and holes, reducing the loss of photogenerated carriers and improving photocatalytic activity. In the photocatalytic reaction, the efficiency of pollutant photodegradation can be affected by controlling the amount of catalyst, the pH of the water, and the intensity and duration of ultraviolet light irradiation. In the magnetic flocculation process, controlling the type and amount of flocculant and coagulant aid, and adjusting the stirring speed and time, has a significant impact on the growth of magnetic flocs. In addition, introducing magnetic materials into the catalyst preparation process can not only replace the traditional magnetic powder for magnetic flocculation, giving it photocatalytic performance to enhance the efficiency of pollutant treatment, but also enable the magnetic catalyst to be separated, recycled and reused by utilizing the properties of the material itself, thereby reducing the loss of catalyst in the experimental production stage and reducing production costs. Detailed Implementation

[0025] Example 1:

[0026] 1) The magnetic catalyst Fe@α-Fe2O3@TiO2 has a saturation magnetic susceptibility of 58.6 emu / g, the Fe magnetic core is spherical with a diameter of 2 μm, and the coating layers are α-Fe2O3 and TiO2 with a thickness of 0.2 μm each. The magnetic core accounts for 58% of the total mass fraction.

[0027] 2) 0.8 g of Fe magnetic cores were spread evenly in a porcelain boat and then placed in a tube furnace. The furnace was calcined at 480 °C for 30 min at a heating rate of 5 °C / min to generate an α-Fe₂O₃ layer on its surface. The synthesized Fe@α-Fe₂O₃ was then added to a 1:10 volume ratio solution of tetrabutyl titanate and anhydrous ethanol and ultrasonically dispersed for 12 min. A 1:5 volume ratio solution of water and anhydrous ethanol was then added to the Fe@α-Fe₂O₃ mixture and stirred at 80 °C for 3 h. The reacted material was then collected using a magnet, washed, and dried. It was then calcined at 500 °C for 2 h, resulting in a 100 nm thick transition layer of calcined iron titanate composed of the first and second coating layers. This completed the preparation of the catalyst Fe@α-Fe₂O₃@TiO₂.

[0028] 3) The wastewater consisted of a 10 mg / L methylene blue solution and BaSO4 powder with a turbidity of 400 NTU. One L of simulated wastewater was taken, and 5 mg / L of polyferric silicate flocculant was added for low-concentration initial flocculation. Then, the aforementioned magnetic photocatalyst Fe@α-Fe2O3@TiO2 was added to the wastewater, and the photodegradation process was completed under ultraviolet light irradiation. After degradation, 450 mg / L of polyaluminum chloride flocculant was added to the water, followed by 3 mg / L of anionic polyacrylamide as a coagulant aid for magnetic flocculation. After the magnetic flocs grew, the water was placed in a magnetic field for sedimentation, completing the separation of water and sludge. The degradation rate of the 10 mg / L methylene blue solution in the water was 95%, the removal rate of suspended solids in the water reached 97%, and the recovery rate of the magnetic photocatalyst was 96%.

[0029] This invention combines photocatalysis with magnetic flocculation. The photocatalytic reaction removes organic pollutants and pollutants that are difficult to degrade using traditional magnetic flocculation, significantly improving pollutant removal efficiency. Magnetic flocculation involves the aggregation and recovery of suspended solids and catalyst particles in the water. Furthermore, introducing magnetic materials into the catalyst preparation process not only replaces traditional magnetic powder in magnetic flocculation, giving it photocatalytic properties to enhance pollutant treatment efficiency, but also allows the magnetic catalyst to utilize its inherent properties for separation, recovery, and regeneration, thereby reducing catalyst loss during experimental production and lowering production costs.

[0030] Example 2:

[0031] 1) The magnetic catalyst Fe@α-Fe2O3@TiO2 has a saturation magnetic susceptibility of 68.3 emu / g, the Fe core is spherical with a diameter of 2 μm, the coating layer is composed of α-Fe2O3 and TiO2 with a thickness of 0.1 μm, and the magnetic core accounts for 68% of the total mass fraction.

[0032] 2) 0.8 g of Fe magnetic cores were spread evenly in a porcelain boat and then placed in a tube furnace. The furnace was calcined at 420 °C for 30 min with a heating rate of 5 °C / min, resulting in the formation of an α-Fe₂O₃ layer on the surface. The synthesized Fe@α-Fe₂O₃ was then added to a 1:5 volume ratio mixture of tetrabutyl titanate and anhydrous ethanol and ultrasonically dispersed for 12 min. A 1:8 volume ratio mixture of water and anhydrous ethanol was then added to the Fe@α-Fe₂O₃ mixture, and the mixture was stirred at 80 °C for 4 h. The reacted material was then collected using a magnet, washed, and dried. It was then calcined at 550 °C for 3 h, resulting in a transition layer of 160 nm thick iron titanate, a composite of the first and second coating layers. This completed the preparation of the catalyst Fe@α-Fe₂O₃@TiO₂.

[0033] 3) The wastewater was from the secondary sedimentation tank of the sewage treatment plant. One L of wastewater was taken, and 3 mg / L of polyferric silicate flocculant was added for low-concentration initial flocculation. Then, the aforementioned magnetic photocatalyst Fe@α-Fe2O3@TiO2 was added to the wastewater, and the photodegradation process was completed under ultraviolet light irradiation. After degradation, 350 mg / L of polyaluminum ferric flocculant was added to the water, followed by 2 mg / L of cationic polyacrylamide as a coagulant aid for magnetic flocculation. After the magnetic flocs grew, the water was placed in a magnetic field for sedimentation, completing the separation of water and sludge. The removal rates of COD (chemical oxygen demand), TP (total phosphorus), TN (total nitrogen), and SS (suspended solids) in the water reached over 94%.

[0034] Example 3:

[0035] 1) The saturation magnetic susceptibility of the magnetic catalyst γ-Fe2O3@α-Fe2O3@TiO2 is 52.7 emu / g. The magnetic core γ-Fe2O3 is needle-shaped with an aspect ratio of 10. Its length is 2 μm and its diameter is 0.2 μm. The coating layers are α-Fe2O3 and TiO2, each with a thickness of 0.3 μm. The magnetic core accounts for 52% of the total mass fraction.

[0036] 2) Take 5 g of γ-Fe2O3 magnetic cores, spread them evenly in a porcelain boat, and then place it in a tube furnace at 10℃ / min.

[0037] The heating rate was controlled, the calcination temperature was 420 °C, and the calcination time was 40 min, resulting in the formation of an α-Fe₂O₃ layer on the surface. The synthesized γ-Fe₂O₃@α-Fe₂O₃ was then added to a mixed solution of tetrabutyl titanate and anhydrous ethanol at a volume ratio of 1:8 and ultrasonically dispersed for 15 min. Next, a mixture of water and anhydrous ethanol at a volume ratio of 1:8 was added to the γ-Fe₂O₃@α-Fe₂O₃ mixture, and the mixture was stirred at 60 °C for 5 h. The reacted material was then collected using a magnet, washed, dried, and calcined at 550 °C for 2 h. The transition layer was a composite of the first and second coating layers of iron titanate, with a thickness of 100 nm, completing the catalyst process.

[0038] Preparation of γ-Fe2O3@α-Fe2O3@TiO2.

[0039] 3) The wastewater was from the secondary sedimentation tank of a sewage treatment plant. One L of wastewater was taken, and 9 mg / L of polyferric silicate flocculant was added for low-concentration initial flocculation. Then, the aforementioned magnetic photocatalyst γ-Fe₂O₃@α-Fe₂O₃@TiO₂ was added to the wastewater, and the photodegradation process was completed under ultraviolet light irradiation. After degradation, 300 mg / L of polyaluminum chloride flocculant was added to the water, followed by 6 mg / L of anionic polyacrylamide coagulant aid for magnetic flocculation. After the magnetic flocs grew, the water was placed in a magnetic field for sedimentation, completing the separation of water and sludge. The removal rates of COD, TP, TN, and SS in the water reached over 95%.

[0040] This invention combines photocatalysis with magnetic flocculation to treat wastewater, effectively removing COD, TP, TN, and SS, thus significantly improving water treatment efficiency. Furthermore, introducing magnetic materials into the catalyst preparation process not only replaces traditional magnetic powder in magnetic flocculation, giving it photocatalytic properties to enhance pollutant treatment efficiency, but also allows the magnetic catalyst to utilize its inherent properties for separation, recycling, and reuse.

[0041] Example 4:

[0042] 1) The magnetic catalyst Fe3O4@α-Fe2O3@TiO2 has a saturation magnetic susceptibility of 60.4 emu / g. The Fe3O4 magnetic core is spherical with a diameter of 5 μm. The coating layers are α-Fe2O3 and TiO2, each with a thickness of 0.5 μm. The magnetic core accounts for 65% of the total mass fraction.

[0043] 2) 1.2 g of Fe3O4 magnetic cores were spread evenly in a porcelain boat and then placed in a tube furnace. The furnace was calcined at 450 °C for 60 min at a heating rate of 3 °C / min to generate an α-Fe2O3 layer on its surface. The synthesized Fe3O4@α-Fe2O3 was then added to a 1:10 volume ratio solution of tetrabutyl titanate and anhydrous ethanol and ultrasonically dispersed for 15 min. A 1:10 volume ratio solution of water and anhydrous ethanol was then added to the Fe3O4@α-Fe2O3 mixture, and the mixture was stirred at 80 °C for 6 h. The reacted material was then collected using a magnet, washed, and dried. It was then calcined at 470 °C for 2 h, resulting in a transition layer of 80 nm thick iron titanate composed of the first and second coating layers. This completed the preparation of the catalyst Fe3O4@α-Fe2O3@TiO2.

[0044] 3) The wastewater was from the secondary sedimentation tank of a sewage treatment plant. One L of wastewater was taken, and 5 mg / L of polyferric silicate flocculant was added for low-concentration initial flocculation. Then, the aforementioned magnetic photocatalyst Fe3O4@α-Fe2O3@TiO2 was added to the wastewater, and the photodegradation process was completed under ultraviolet light irradiation. After degradation, 450 mg / L of polyaluminum chloride flocculant was added to the water, followed by 6 mg / L of anionic polyacrylamide as a coagulant aid for magnetic flocculation. After the magnetic flocs grew, the water was placed in a magnetic field for sedimentation, completing the separation of water and sludge. The removal rates of COD, TP, TN, and SS in the water reached over 97%.

[0045] This invention combines photocatalysis with magnetic flocculation to treat wastewater, effectively removing COD, TP, TN, and SS, thus significantly improving water treatment efficiency. Furthermore, introducing magnetic materials into the catalyst preparation process not only replaces traditional magnetic powder in magnetic flocculation, giving it photocatalytic properties to enhance pollutant treatment efficiency, but also allows the magnetic catalyst to utilize its inherent properties for separation, recycling, and reuse.

Claims

1. A magnetic photocatalyst, characterized in that, Magnetic photocatalysts consist of a magnetic core, a coating layer, and a transition layer. The magnetic core is made of iron, Fe3O4, or γ-Fe2O3, and accounts for 50-80% of the total mass fraction of the magnetic photocatalyst. The first coating layer is α-Fe2O3, which accounts for 10-30% of the total mass fraction of the magnetic photocatalyst, and the second coating layer is TiO2, which accounts for 10-35% of the total mass fraction of the magnetic photocatalyst. The transition layer is iron titanate composed of a first coating layer and a second coating layer calcined together, with a thickness of 1-300 nm; The combined mass of the magnetic core, coating layer, and transition layer of the magnetic photocatalyst accounts for 100% of the total mass fraction. The method for preparing the magnetic photocatalyst is characterized by comprising the following steps: 1) Take 0.5-10 g of magnetic cores and spread them evenly in a porcelain boat, then place them in a tube furnace and calcine them at a heating rate of 1-20 ℃ / min, at a temperature of 280-580 ℃, for a calcine time of 10-60 min, so that a layer of α-Fe2O3 is formed on its surface. 2) Add the material synthesized in 1) to a mixed solution of tetrabutyl titanate and anhydrous ethanol in a volume ratio of 1:(3-10), and disperse ultrasonically for 10-30 min; 3) Add water and anhydrous ethanol in a volume ratio of 1:(2-10) to the mixture in 2), and stir at 40-80 °C for 1-6 h to obtain the product; 4) The product from 3) is recovered using a magnet, washed and dried, and then calcined and compounded at 400-550 °C for 1-5 h to prepare a magnetic photocatalyst.

2. The magnetic photocatalyst according to claim 1, characterized in that, The magnetic core is spherical or needle-shaped. The diameter of the spherical magnetic core is 0.1-100 μm, and the aspect ratio of the needle-shaped magnetic core is 2-20. Its length is 0.1-100 μm and its diameter is 0.1-10 μm.

3. The magnetic photocatalyst according to claim 1, characterized in that, The saturation magnetic susceptibility of the magnetic photocatalyst is 20-100 emu / g.

4. A method for magnetic flocculation and photocatalytic water purification, characterized in that, Includes the following steps: 1) Take 1 L of wastewater, first add 1-10 mg / L of flocculant to the wastewater for low-concentration initial flocculation, and then add the magnetic photocatalyst described in claim 1 into the wastewater and carry out the wastewater photodegradation process under ultraviolet light irradiation. 2) Add 150-500 mg / L of flocculant to the degraded wastewater, stir evenly, and then add 1-10 mg / L. The coagulant is used to perform magnetic flocculation. After the magnetic flocs grow and stabilize, the water is placed in a magnetic field to settle, thus separating the water from the magnetic flocs. The flocculant is one or more of aluminum sulfate, polyaluminum sulfate, polyferric sulfate, polyaluminum chloride, polyferric chloride, polyferric silicate, and polyaluminum ferric sulfate; The coagulant is one of cationic polyacrylamide, anionic polyacrylamide, and nonionic polyacrylamide.

5. The method for magnetic flocculation photocatalytic water purification according to claim 4, characterized in that, The magnetic photocatalyst can be recycled and reused for the next wastewater purification cycle.