A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system

Abstract

The present invention discloses a method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, belonging to the technical field of water pollution control; the model pollutant methylene blue (MB) and the toxic organic pollutant phenol are selected as target pollutants, and the nano-composite Fe3O4 / g-C3N4 photocatalyst is added to a thermostatic reactor containing the target pollutant solution. The thermostatic reactor is placed in an ultrasonic cleaner for ultrasonic treatment, taken out, and then placed in a dark environment and left standing to achieve the adsorption and desorption equilibrium of the pollutants. The thermostatic reactor is placed in a photo-magnetic coupling system for pollutant degradation experiments. At regular intervals, samples are taken. After centrifuging and separating the catalyst, a UV-visible spectrophotometer and high-performance liquid chromatography are used to measure the concentration of pollutants in the samples and calculate their degradation rates. Within 300 minutes of reaction time, the degradation rates of MB and phenol can reach 99.23% and 92.84% respectively. Compared with pure g-C3N4 and nano-composite Fe3O4 / g-C3N4 under single photocatalytic conditions, the degradation rates of pollutants are greatly improved.

Description

Technical Field

[0001] The present invention relates to a method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, belonging to the technical field of water pollution control. Background Art

[0002] Semiconductor photocatalysis is developed based on the solid energy band theory, covering research fields of multiple interdisciplinary subjects such as semiconductor physics, material chemistry, catalytic chemistry, and photoelectrochemistry. Due to the advantages of semiconductor photocatalysis technology such as simple operation, mild reaction conditions, no secondary pollution, easy coupling with other environmental treatment technologies, and low requirements for equipment, photocatalysis technology has great potential in environmental governance. As an emerging visible light-driven photocatalyst, g-C3N4 is a semiconductor material composed of C and N elements hybridized by sp 2 hybridization into a kind of aromatic ring-like and two-dimensional layered structure, with C-N and C=N existing, and the bond lengths and bond angles being the same. The highly delocalized π-conjugated system of g-C3N4 endows it with photocatalytic properties. The positions of the conduction band and valence band of g-C3N4 are -1.3 and 1.4 eV, and the band gap is 2.7 eV, which can meet the thermodynamic requirements of O2 reduction to produce free radicals and various energy reactions including H2O decomposition to produce H2, nitrogen fixation, and CO2 reduction. In addition, g-C3N4 also has the advantages of visible light response characteristics, stable chemical properties, non-toxicity, low cost, easy reaction control, acid and alkali resistance, and easy structure modification, and has been proven to be a photocatalyst with good application prospects and application values. However, the g-C3N4 photocatalyst still has disadvantages such as a relatively low specific surface area, rapid recovery of photo-excited e - / h + pairs, poor visible light absorption, low photo-quantum yield, and difficulty in separation and reuse, which greatly limit its wide application in the field of photocatalysis. In recent years, aiming at these limiting factors of g-C3N4, to improve its photocatalytic activity and solve the problem of its difficulty in separation, recovery, and reuse, it can be started from both internal and external aspects. One is to composite g-C3N4 with other co-catalysts to improve its photocatalytic performance; the other is to promote the separation of e - / h + pairs by applying special external energy to improve the photocatalytic property.

[0003] At present, there are many studies on the combination of g-C3N4 with different compounds to improve photocatalytic activity. Among them, the combination of g-C3N4 with magnetic Fe3O4 nanoparticles can not only enhance photocatalytic performance but also facilitate the magnetic recycling of the catalyst. Due to the difference in the conduction band and valence band positions of the two, the electrons or holes generated by photoexcitation in g-C3N4 transfer to the conduction band or valence band of Fe3O4, realizing the separation of electron-hole pairs, reducing the recombination rate, and expanding the light absorption range, so that the active particles generated by photoexcitation can be utilized more efficiently. Therefore, the combination of g-C3N4 with magnetic Fe3O4 nanoparticles has gradually attracted the attention of researchers. For example, in the article "Mesoporousmagnetic g-C3N4 nanocomposites for photocatalytic environmental remediationunder visible light" on pages 111-147 of Volume 205 of "Ecotoxicology and Environmental Safety" in 2020, g-C3N4 was combined with magnetic Fe3O4 nanoparticles to form a composite material and used for the degradation of the dye Rhodamine B. The results showed that the photocatalytic activity of the composite material was greatly improved, and the degradation rate of Rhodamine B in water reached 97.6% after 4 hours of visible light irradiation. The main drawbacks of this study are: (1) Only a common dye, Rhodamine B, was selected as the target pollutant, which has low practical significance for the degradation of pollutants in the environment; (2) During the photocatalytic process, additional mechanical stirring conditions are required to make the reaction system mix evenly, resulting in high maintenance costs.

[0004] In addition, there are also some studies on improving photocatalytic activity by applying an external physical field during the photocatalysis process. Among them, the use of an external magnetic field can inhibit the recombination of photo-generated electrons and holes. The generated Lorentz force can also induce rapid mass transfer and ion condensation at the reaction sites, which can improve the photocatalytic performance. The external magnetic field can be easily realized by means of a permanent magnet or an electromagnet. This process is energy-saving and environmentally friendly. Therefore, the photo-magnetic coupling technology not only has important research value, but also has great application value and broad development prospects. For example, in the article "Enhanced photo-induced carrier separation of CdS / MoS2 via micro-potential of Mo micro sheet derived from electromagnetic induction" on pages 126 - 972 of Volume 404 of "Chemical Engineering Journal" in 2021, a nano CdS / MoS2 / Mo composite photocatalytic material was designed and synthesized by a one-step hydrothermal method. Moreover, in a rotating magnetic field, the CdS / MoS2 / Mo composite material can form a motional electromotive force with the relative motion of the magnetic field. This in-situ magnetic field-derived micro-potential provides a wireless electric field for further inhibiting the recombination of electrons and holes in the catalyst. Therefore, the photocatalytic activity of CdS / MoS2 / Mo can be significantly enhanced. The deficiencies of this study are as follows: (1) This study only considered the photocatalytic hydrogen evolution performance of the composite photocatalyst under a rotating magnetic field and did not evaluate its performance in photocatalytic degradation of organic compounds; (2) This system uses a permanent magnet magnetic field and rotates the material to cut the magnetic field lines through an external mechanical force, which is not applicable to the removal of pollutants in water; (3) The magnetic field intensity of the permanent magnet cannot be adjusted, and the flexibility is poor. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system. The magnetic induction intensity of this system is flexibly variable, which not only enhances the photocatalytic performance of nano-composite Fe3O4 / g-C3N4, but also realizes mixing without mechanical external force stirring, achieving rapid mixing of the photocatalytic material and pollutants. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system greatly improves the photocatalytic degradation activity of the catalyst. The material is easy to recycle, and mechanical transmission stirring equipment is avoided, saving maintenance costs.

[0006] The above objective of the present invention is achieved through the following technical solutions:

[0007] A nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, comprising a photocatalytic system and a magnetic field generating system. The photocatalytic system includes a simulated sunlight source, a constant temperature reactor, a lifting platform, and a low-temperature coolant circulation pump. The simulated sunlight source is connected to the lifting platform and is placed directly above the constant temperature reactor. The constant temperature reactor is connected to the low-temperature coolant circulation pump to ensure a constant temperature inside the reactor. The magnetic field generating system includes a three-phase alternating excitation device, a voltage regulator, and an ammeter. The constant temperature reactor is placed inside the three-phase alternating excitation device, and the three-phase alternating excitation device is connected to the voltage regulator.

[0008] Preferably, the voltage regulator is connected to a 380V three-phase power supply.

[0009] Preferably, the ammeter is connected to one phase circuit between the three-phase alternating excitation device and the voltage regulator to monitor the current.

[0010] Preferably, the constant temperature reactor is connected to the low-temperature coolant circulation pump through a silica gel tube.

[0011] Preferably, the three-phase alternating excitation device is connected to the voltage regulator through a three-phase circuit.

[0012] Preferably, the simulated sunlight source uses a Perfectlight PLS-SXE300UV xenon lamp source with a total light power of 50W, a spectral range of 320 - 780nm, an average light emission angle of 6°, and a spot diameter of 30 - 60mm according to the irradiation distance.

[0013] Preferably, the constant temperature reactor is a customized jacketed beaker with an outer diameter of 85mm, an inner diameter of 60mm, an inner height of 150mm, and the water inlet and outlet nozzles are opposite to each other and are both located at the upper part of the beaker.

[0014] Preferably, the model of the low-temperature coolant circulation pump is DLSB-5 / 20, and the manufacturer is Gongyi Yuhua Instrument Co., Ltd.

[0015] Another object of the present invention is to propose a method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system in view of the problems that g-C3N4 has low photocatalytic activity under visible light and g-C3N4 is in powder form and difficult to recycle; Fe3O4 and g-C3N4 are compounded to form a magnetic composite material, and a rotating alternating magnetic field is applied outside the photocatalytic system to form a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system. The magnetic induction intensity of this system is flexibly variable, which not only enhances the photocatalytic performance of nano-composite Fe3O4 / g-C3N4, but also realizes the rapid mixing of the photocatalytic material and the pollutants without mechanical external stirring; the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system greatly improves the photocatalytic degradation activity of the catalyst, the material is easy to recycle, and mechanical transmission stirring equipment is avoided, saving maintenance costs.

[0016] The above object of the present invention is achieved by the following technical solutions:

[0017] A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, the specific steps are as follows:

[0018] 1. Construction of the photo-magnetic coupling system

[0019] (1) Composition of the photocatalytic system

[0020] The photocatalytic system mainly includes a simulated sunlight source, a constant temperature reactor, a lifting platform, and a low-temperature coolant circulation pump; the simulated sunlight source is connected to the lifting platform, and the simulated sunlight source is placed directly above the constant temperature reactor; the constant temperature reactor is connected to the low-temperature cooling circulation system through a silica gel tube to ensure a constant temperature inside the reactor;

[0021] (2) Construction of the magnetic field generating system

[0022] The externally applied magnetic field is a rotating alternating magnetic field, which is excited by three-phase alternating current and includes a three-phase alternating excitation device, an ammeter, and a voltage regulator. The constant temperature reactor is placed inside the three-phase alternating excitation device. The three-phase alternating excitation device is connected to the voltage regulator. A current with a frequency of 50 Hz is input to the coil through the voltage regulator, and the magnitude of the excitation current is adjusted to adjust the magnetic field intensity generated by the magnetic field generating system. The ammeter is connected to one phase circuit between the three-phase alternating excitation device and the voltage regulator to monitor the current;

[0023] (3) Preparation of the photocatalyst

[0024] ① Preparation of g-C3N4;

[0025] ② Preparation of Fe3O4 / g-C3N4 nano-composite material;

[0026] 2. Method for Degrading Water Pollutants by Nano-Composite Fe3O4 / g-C3N4 Photomagnetic Coupling System

[0027] Select the model pollutant methylene blue (MB) and the toxic organic pollutant phenol as the target pollutants. Add the Fe3O4 / g-C3N4 nanocomposite prepared in step (3) of step 1 to a thermostatic reactor containing the target pollutant solution. Place the thermostatic reactor in an ultrasonic cleaner for ultrasonic treatment, take it out, and then place it in a dark environment and let it stand to achieve adsorption and desorption equilibrium. Place the thermostatic reactor in a photomagnetic coupling system for pollutant degradation experiments. At regular intervals, take samples. After centrifuging and separating the catalyst, use an ultraviolet-visible spectrophotometer and high-performance liquid chromatography to measure the concentration of pollutants in the samples and calculate their degradation rates.

[0028] Preferably, the simulated sunlight light source uses a Perfectlight PLS-SXE300UV xenon lamp light source with a total light power of 50 W; the spectral range is 320 - 780 nm; the average emission angle of the light source is 6°, and the spot diameter is 30 - 60 mm according to the irradiation distance.

[0029] Preferably, the thermostatic reactor is a customized jacketed beaker with an outer diameter of 85 mm, an inner diameter of 60 mm, an inner height of 150 mm, and the inlet and outlet nozzles are opposite and both are located at the upper part of the beaker; the model of the low-temperature coolant circulation pump is DLSB-5 / 20, and the manufacturer is Gongyi Yuhua Instrument Co., Ltd.

[0030] Preferably, the specific steps for preparing g-C3N4 in step ① of step (3) are as follows: Put the precursor melamine into a quartz boat. In a tubular furnace, under a N2 atmosphere, heat it at a heating rate of 2.3 °C·min -1 to 550 °C and keep heating. Then, keep passing N2 in the tubular furnace and let it cool naturally. Then, grind and collect the cooled material through an agate mortar to obtain light yellow powdery g-C3N4.

[0031] Preferably, the specific steps for preparing the Fe3O4 / g-C3N4 nanocomposite in step ② of step (3) are as follows: Add the prepared g-C3N4 to a 200 mL mixed solution of ethanol and water with a volume ratio of 1:2, and ultrasonicate it for 3 h at room temperature for standby; Mix FeCl3·6H2O and FeCl2·4H2O according to the molar ratio of Fe 3+ : Fe 2+Dissolve in distilled water that has been purged with N₂ for 10 min at a ratio of 2:1, and then add the mixture to the ultrasonicated g-C₃N₄ suspension. Stir the mixture at 80 °C under a N₂ atmosphere for 30 min. Then, add 10% ammonia water dropwise to the mixture to adjust the solution pH > 10, and stir for another 30 min. Then, allow the solution to cool naturally. Separate the obtained Fe₃O₄ / g-C₃N₄ nanocomposite from the solution using a magnetic field, and wash it several times with ethanol and water. Finally, dry the material at 60 °C, grind it, and collect it to obtain the Fe₃O₄ / g-C₃N₄ nanocomposite.

[0032] The present invention adopts the above technical solutions and mainly has the following effects:

[0033] 1. The nanocomposite Fe₃O₄ / g-C₃N₄ photo-magnetic coupling system constructed by the present invention has good water pollutant degradation effect. Under simulated sunlight (300 W xenon lamp) irradiation and a rotating alternating magnetic field with a frequency of 50 Hz and a current of 2 A, 0.1 g of the prepared nanocomposite Fe₃O₄ / g-C₃N₄ photocatalyst is respectively dispersed in 100 mL of 20 mg / L MB and 5 mg / L phenol solutions. Within 300 min of reaction time, the degradation rates of methylene blue (MB) and phenol can reach 99.23% and 92.84% respectively. Compared with pure g-C₃N₄ and nanocomposite Fe₃O₄ / g-C₃N₄ without applying an external magnetic field, the degradation rate of pollutants has been greatly improved.

[0034] 2. In the nanocomposite Fe₃O₄ / g-C₃N₄ photo-magnetic coupling system constructed by the present invention, after the photocatalyst is magnetically separated and recycled 4 times, the degradation rates of 20 mg / L MB and 5 mg / L phenol solutions are still 92.32% and 88.48% respectively within 300 min of reaction time.

[0035] 3. The nanocomposite Fe₃O₄ / g-C₃N₄ photo-magnetic coupling system constructed by the present invention can omit the mechanical stirring structure in the traditional photocatalytic system, with simple operation and low maintenance cost.

[0036] The present invention will be further described below through specific embodiments and drawings, but it does not mean limiting the protection scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the nanocomposite Fe₃O₄ / g-C₃N₄ photo-magnetic coupling system of Example 1 of the present invention.

[0038] Figure 2-1 Effect of Fe₃O₄ / g-C₃N₄ with different composite ratios on the degradation of water pollutants (MB) by the nanocomposite Fe₃O₄ / g-C₃N₄ photo-magnetic coupling system of Example 1 of the present invention.

[0039] Figure 2-2 Effect of Fe3O4 / g-C3N4 with different composite ratios in Example 1 of the present invention on the degradation of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system.

[0040] Figure 3-1 Effect of different addition amounts of Fe3O4 / g-C3N4 in Example 2 of the present invention on the degradation of water pollutants (MB) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system.

[0041] Figure 3-2 Effect of different addition amounts of Fe3O4 / g-C3N4 in Example 2 of the present invention on the degradation of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system.

[0042] Figure 4-1 Effect of different magnetic field intensities in Example 3 of the present invention on the degradation of water pollutants (MB) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system.

[0043] Figure 4-2 Effect of different magnetic field intensities in Example 3 of the present invention on the degradation of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system.

[0044] Figure 5 Distribution of magnetic induction intensity in the reactor of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system under different excitation current amplitudes in Example 3 of the present invention (a: 1A, b: 2A, c: 3A).

[0045] Figure 6-1 Degradation diagram of water pollutants (MB) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system in Example 4 of the present invention.

[0046] Figure 6-2 Degradation diagram of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system in Example 4 of the present invention.

[0047] Figure 7 FTIR diagrams of FC20, g-C3N4, and Fe3O4 in Example 1 of the present invention.

[0048] Figure 8 XRD diagrams of FC20, g-C3N4, and Fe3O4 in Example 1 of the present invention.

[0049] Figure 9SEM images of FC20, g-C3N4, and Fe3O4 in Example 1 of the present invention (a: FC20, b: g-C3N4, c: Fe3O4). Detailed implementation manners

[0050] Unless otherwise specified, the reagents involved in the following examples are all conventional reagents that can be purchased on the market, and the methods used are all common methods in the technical field; the unit is the weight unit.

[0051] Example 1

[0052] A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, comprising the following steps:

[0053] 1. Construction of the photocatalytic system

[0054] (1) Composition of the photocatalytic system

[0055] The photocatalytic system mainly includes: a simulated sunlight light source, a constant temperature reactor, a lifting platform, and a low-temperature coolant circulation pump; the simulated sunlight light source uses a PXFEL PLS-SXE300UV xenon lamp light source, with a total light power of 50W; the spectral range is 320 - 780nm; the average light source emission angle is 6°, and the spot diameter is 30 - 60mm according to the irradiation distance; the constant temperature reactor is a customized jacketed beaker with an outer diameter of 85mm, an inner diameter of 60mm, and an inner height of 150mm, and the water inlet and outlet nozzles are opposite to each other and are both located at the upper part of the beaker; the model of the low-temperature coolant circulation pump is DLSB-5 / 20, and the manufacturer is Gongyi Yuhua Instrument Co., Ltd. The simulated solar light source is adjusted in height by a lifting platform and placed directly above the constant temperature reactor; the constant temperature reactor is connected to the low-temperature cooling circulation system through a silica gel tube to ensure a constant temperature inside the reactor;

[0056] (2) Preparation of the photocatalyst

[0057] ① Preparation of g-C3N4

[0058] g-C3N4 is prepared by the thermal polycondensation method: 10g of the precursor melamine is placed in a quartz boat, and in a tubular furnace, under a N2 atmosphere, it is heated to 550°C at a heating rate of 2.3°C·min -1 and kept heated for 4h. Then, N2 is continuously introduced into the tubular furnace and it is allowed to cool naturally. Then, the cooled material is ground and collected through an agate mortar to obtain pale yellow powdery g-C3N4;

[0059] ② Preparation of the Fe3O4 / g-C3N4 nanocomposite

[0060] Add 1 g of the prepared g-C3N4 to 200 mL of a mixed solution of ethanol and water with a volume ratio of 1:2, and ultrasonicate for 3 h at room temperature for later use. Dissolve FeCl3·6H2O and FeCl2·4H2O in 20 mL of distilled water that has been purged with N2 for 10 min according to the molar ratio of Fe 3+ :Fe 2+ = 2:1, and then add the mixed solution to the ultrasonically treated g-C3N4 suspension. Stir the mixed solution at 80 °C under a N2 atmosphere for 30 min. Then, add 10% ammonia water to the mixture to adjust the solution pH > 10, and stir for another 30 min. Then, allow the solution to cool naturally. Separate the obtained Fe3O4 / g-C3N4 nanocomposite from the solution using a magnetic field, and wash it several times with ethanol and water. Finally, dry the material at 60 °C and grind it for collection to obtain the Fe3O4 / g-C3N4 nanocomposite; for comparison purposes, prepare Fe3O4 / g-C3N4 nanocomposites with Fe3O4 contents of 10, 20, 30, 40, and 50 wt%, named FC10, FC20, FC30, FC40, and FC50 respectively. The specific reagent addition amounts are shown in Table 1;

[0061] Table 1 Reagent amounts required for the synthesis of materials with different composite ratios

[0062] Material Name <![CDATA[g-C3N4 / g]]> <![CDATA[FeCl3·6H2O / g]]> <![CDATA[FeCl2·4H2O / g]]> FC10 1 0.2600 0.0955 FC20 1 0.5951 0.2189 FC30 1 0.9738 0.3582 FC40 1 1.5689 0.5771 FC50 1 2.3263 0.8557

[0063] 2. Construction of the magnetic field generation system

[0064] The magnetic field generation system is a rotating alternating magnetic field, excited by three-phase alternating current, and includes a three-phase alternating excitation device, an ammeter, and a voltage regulator. Input a current with a frequency of 50 Hz into the coil through the voltage regulator, and adjust the magnitude of the excitation current (2 A) to thereby adjust the magnetic field strength generated by the magnetic field generation system; adjust the height of the simulated solar light source using a lifting platform and place it directly above the thermostatic reactor; place the thermostatic reactor inside the three-phase alternating excitation device. The three-phase alternating excitation device is connected to the voltage regulator through a three-phase circuit. The voltage regulator is connected to a 380 V three-phase power supply, and the ammeter is connected to one phase of the circuit between the alternating excitation device and the voltage regulator to monitor the current;

[0065] 3. Method for degrading water pollutants using the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system

[0066] Add the nano-composite Fe3O4 / g-C3N4 photocatalyst to a thermostatic reactor containing 100 mL of the target pollutant solution (20 mg / L MB and 5 mg / L phenol respectively), place the thermostatic reactor in an ultrasonic cleaner and ultrasonicate for 30 min, take it out, and then place it in a dark environment and let it stand for 30 min to achieve adsorption and desorption equilibrium; then, place the thermostatic reactor in the photo-magnetic coupling system (as Figure 1As shown in the figure, degradation is carried out. At regular intervals, samples are taken. After centrifuging to separate the catalyst, an ultraviolet-visible spectrophotometer and high-performance liquid chromatography are used to measure the concentration of pollutants in the sample and calculate its degradation rate; as Figure 1 shown, it is a schematic diagram of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system of Example 1 of the present invention; as Figure 2-1 shown, it is the influence of different composite ratios of Fe3O4 / g-C3N4 of the present invention on the degradation of water pollutants (MB) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system; as Figure 2-2 shown, it is the influence of different composite ratios of Fe3O4 / g-C3N4 of the present invention on the degradation of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system; it can be seen that: the nano-composite Fe3O4 / g-C3N4 photocatalyst FC20 containing 20% (w / w) Fe3O4 has the best effect on the degradation of MB and phenol in the photo-magnetic coupling system, and FC20 is used for experiments in subsequent examples.

[0067] Example 2

[0068] A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, comprising the following steps:

[0069] 1. The same as 1 in Example 1;

[0070] 2. The same as 2 in Example 1;

[0071] 3. Add nano-composite Fe3O4 / g-C3N4 photocatalysts with different masses (0.05, 0.10, 0.15, 0.20, 0.25 g) to a thermostatic reactor filled with 100 mL of target pollutant solutions (20 mg / L MB and 5 mg / L phenol respectively). Place the thermostatic reactor in an ultrasonic cleaner, ultrasonicate for 30 min, take it out, and then place it in a dark environment and let it stand for 30 min to achieve adsorption and desorption equilibrium; then, place the thermostatic reactor in a photo-magnetic coupling system (as Figure 1 shown), carry out the degradation experiment. At regular intervals, samples are taken. After centrifuging to separate the catalyst, an ultraviolet-visible spectrophotometer and high-performance liquid chromatography are used to measure the concentration of pollutants in the sample and calculate its degradation rate; as Figure 3-1 shown, it is the influence of different addition amounts of Fe3O4 / g-C3N4 of the present invention on the degradation of water pollutants (MB) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system; as Figure 3-2As shown in the figure, it is the influence of different Fe3O4 / g-C3N4 addition amounts of the present invention on the degradation of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system. It can be seen that when the Fe3O4 / g-C3N4 addition amount is 1 g / L, the degradation effects of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system on MB and phenol are the best. In subsequent experiments, the addition concentration of Fe3O4 / g-C3N4 is 1 g / L.

[0072] Example 3

[0073] A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, comprising the following steps:

[0074] 1. The same as step 1 in Example 1;

[0075] 2. The same as step 2 in Example 1;

[0076] 3. Add the nano-composite Fe3O4 / g-C3N4 photocatalyst to a thermostatic reactor filled with 100 mL of target pollutant solution (20 mg / L MB and 5 mg / L phenol respectively). After ultrasonicating the thermostatic reactor in an ultrasonic cleaner for 30 min, take it out, and then place it in a dark environment and let it stand for 30 min to achieve adsorption and desorption equilibrium. Then, place the thermostatic reactor in the photo-magnetic coupling system (as Figure 1 shown). By adjusting the voltage regulator to adjust the excitation current (1 A, 2 A, 3 A), change the magnetic induction intensity under the composite Fe3O4 / g-C3N4 system, and conduct a degradation experiment. Sample at regular intervals. After centrifuging to separate the catalyst, use an ultraviolet-visible spectrophotometer and high-performance liquid chromatography to measure the concentration of pollutants in the sample and calculate its degradation rate. By establishing a two-dimensional time-step finite element model for the three-phase alternating excitation device and the aqueous phase distribution region containing the nano-composite Fe3O4 / g-C3N4, use ANSYS software to simulate and calculate to determine the magnetic induction intensity under the spatial system of the magnetic nano-composite material. As Figure 4-1 shown, it is the influence of different magnetic field intensities in Example 3 of the present invention on the degradation of water pollutants (MB) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system; as Figure 4-2 shown, it is the influence of different magnetic field intensities in Example 3 of the present invention on the degradation of water pollutants (phenol) by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system; as Figure 5As shown, it is the distribution of magnetic induction intensity in the reactor of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system under different excitation current amplitudes in Example 3 of the present invention (a: 1A, b: 2A, c: 3A); it shows the distribution of magnetic induction intensity in the reactor of this nano-composite material photo-magnetic coupling system under different excitation currents by two-dimensional time-step finite element simulation; it can be seen that: as the magnetic induction intensity in the constant-temperature reactor increases, the efficiency of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system in degrading water pollutants also gradually increases; under the experimental conditions of Example 3, the current amplitudes with the best degradation effects on MB and phenol are 2A and 3A respectively; for unified comparison, a current amplitude of 2A is used in subsequent experiments.

[0077] Example 4

[0078] A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, comprising the following steps:

[0079] 1. The same as 1 in Example 1;

[0080] 2. The same as 2 in Example 1;

[0081] 3. Add the nano-composite Fe3O4 / g-C3N4 photocatalyst to a constant-temperature reactor containing 100 mL of target pollutants (20 mg / L MB and 5 mg / L phenol respectively), place the constant-temperature reactor in an ultrasonic cleaner and ultrasonicate for 30 min, take it out, and then place it in a dark environment and let it stand for 30 min to achieve adsorption and desorption equilibrium; then, place the constant-temperature reactor in the photocatalytic system and the photo-magnetic coupling system respectively for degradation. At regular intervals, take samples, centrifuge to separate the catalyst, and use an ultraviolet-visible spectrophotometer and high-performance liquid chromatography to measure the concentration of pollutants in the samples and calculate their degradation rates; As Figure 6-1 shown, it is the degradation graph of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system of the present invention for water pollutants (MB) in Example 4; As Figure 6-2 shown, it is the degradation graph of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system of the present invention for water pollutants (phenol) in Example 4. Example 4 compares the degradation results under the optimized conditions with the photocatalytic degradation of FC20 under no magnetic field conditions, the photocatalytic degradation of pure g-C3N4 under rotating alternating magnetic fields with and without, and the photocatalytic degradation of pure Fe3O4 under rotating alternating magnetic fields with and without. The experimental results are as Figure 6-1 and Figure 6-2As shown in the figure, the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system can achieve 99.23% and 92.84% degradation of 20 mg / L MB and 5 mg / L phenol within 300 min. Compared with pure g-C3N4, pure Fe3O4, and FC20 without external magnetic field, the degradation effect of water pollutants has been greatly improved.

[0082] Vibrating sample magnetometry shows that the saturation magnetization intensity of FC20 is 20 emu / g, enabling magnetic separation. After the nano-composite Fe3O4 / g-C3N4 photocatalyst is magnetically separated and recycled 4 times, the removal rates of 20 mg / L MB and 5 mg / L phenol within 300 min under this photo-magnetic coupling system are 92.32% and 88.48% respectively.

[0083] Experimental results

[0084] Example 1 studied the effect of different composite ratios of Fe3O4 / g-C3N4 on the degradation of water pollutants by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system. The experimental results are as Figure 2-1 and Figure 2-2 shown. It can be seen that the nano-composite Fe3O4 / g-C3N4 photocatalyst FC20 containing 20% (w / w) Fe3O4 has the best effect on the degradation of MB and phenol in the photo-magnetic coupling system. FC20 was used in subsequent examples for experiments; Example 2 studied the effect of different addition amounts of Fe3O4 / g-C3N4 on the degradation of water pollutants by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system. The experimental results are as Figure 3-1 and 3-2 shown. It can be seen that when the addition amount of Fe3O4 / g-C3N4 is 1 g / L, the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system has the best effect on the degradation of MB and phenol. The addition concentration of Fe3O4 / g-C3N4 in subsequent experiments is 1 g / L; Example 3 studied the effect of different excitation current amplitudes on the degradation of water pollutants by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system. The experimental results are as Figure 4-1 and 4-2 shown; Figure 5 shows the magnetic induction intensity distribution of the reactor under different excitation currents in the photo-magnetic coupling system of this nano-composite material by two-dimensional time-step finite element simulation. It can be seen that: with the increase of the magnetic induction intensity in the reactor, the efficiency of the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system for degrading water pollutants also gradually increases; under the experimental conditions of Example 3, the optimal current amplitudes for the degradation of MB and phenol are 2 A and 3 A respectively; for unified comparison, a current amplitude of 2 A is used in subsequent experiments.

[0085] Examples 1-3 verified that in the above-mentioned nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, under the experimental conditions of selecting FC20 with a Fe3O4 mass percentage of 20%, a nano-composite Fe3O4 / g-C3N4 addition amount of 1.0 g / L, and an excitation current amplitude of 2 A, better removal effects of MB and phenol could be obtained. Example 4 compared the degradation results under this optimized condition with the photocatalytic degradation of FC20 under no magnetic field condition, the photocatalytic degradation of pure g-C3N4 under the presence and absence of a rotating alternating magnetic field, and the photocatalytic degradation of pure Fe3O4 under the presence and absence of a rotating alternating magnetic field. The experimental results are as Figure 6-1 and 6-2 shown. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system can achieve 99.23% and 92.84% degradation of 20 mg / L MB and 5 mg / L phenol within 300 min. Compared with pure g-C3N4, pure Fe3O4, and FC20 without an externally applied magnetic field, the degradation effect of water pollutants has been greatly improved.

[0086] Vibrating sample magnetometry tests showed that the saturation magnetization intensity of FC20 was 20 emu / g, enabling magnetic separation. After the nano-composite Fe3O4 / g-C3N4 photocatalyst was magnetically separated and recycled 4 times, the removal rates of 20 mg / L MB and 5 mg / L phenol within 300 min under this photo-magnetic coupling system were 92.32% and 88.48% respectively.

[0087] FTIR, XRD, and SEM measurements were carried out on the nano-composite Fe3O4 / g-C3N4 photocatalyst FC20, Fe3O4, and g-C3N4. The experimental results are as Figure 7-9 shown. As Figure 7 shown, the strong signal absorption at 550 cm -1 -650 cm -1 was the stretching vibration of Fe-O, the signal absorption at 3100 cm -1 was attributed to the stretching vibration of N-H, the strong absorption band from 1200 to 1650 cm -1 belonged to the typical stretching vibration of C-N heterocycles (C-N, C≡N), and the absorption at 809 cm -1 was related to the vibration of the s-triazine ring. The above indicated that the characteristic peaks of g-C3N4 and Fe3O4 were retained in the Fe3O4 / g-C3N4 nano-composite material.

[0088] As Figure 8As shown, the prominent diffraction peaks of Fe3O4 nanoparticles correspond well to the JCPDS card of Fe3O4 (19-0629), and the diffraction peaks appear at 2θ = 30.25°, 35.58°, 43.21°, 54.39°, 57.09°, 62.92° and 75.19°. In the spectrum of g-C3N4, the two characteristic peaks at 13.04 and 27.58° correspond to the (100) and (002) crystal planes of g-C3N4, which respectively indicate the interlayer structure stacking of g-C3N4 and the stacking between the characteristic planes of the aromatic system. It can be seen that it also exists in the spectrum of the Fe3O4 / g-C3N4 nanocomposite. In addition, no other impurity phases are seen, indicating that the nano Fe3O4 / g-C3N4 is a two-phase composite.

[0089] As Figure 9 shown in Figure 9 Figures b and Figure 9 c, g-C3N4 presents an irregular sheet-like stacked structure, and Fe3O4 presents an irregularly shaped granular structure. As

[0090] Although the above has elaborated on the purpose concept and embodiments of the present invention in detail, those of ordinary skill in the art can recognize that various improvements and transformations can still be made to the present invention without departing from the scope defined by the claims, and such improvements and transformations should still fall within the protection scope of the present invention.

Claims

1. A nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, characterized in that: It includes a photocatalytic system and a magnetic field generating system. The photocatalytic system includes a simulated sunlight light source, a constant temperature reactor, a lifting platform, and a low-temperature coolant circulation pump. The simulated sunlight light source is connected to the lifting platform and placed directly above the constant temperature reactor. The constant temperature reactor is connected to the low-temperature coolant circulation pump. The magnetic field generating system includes a three-phase alternating excitation device, a voltage regulator, and an ammeter. The constant temperature reactor is placed inside the three-phase alternating excitation device, and the three-phase alternating excitation device is connected to the voltage regulator through a three-phase circuit. The magnetic field generating system generates a rotating alternating magnetic field with a frequency of 50 Hz.

2. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 1, wherein: The voltage regulator is connected to a 380V three-phase power supply.

3. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 1, characterized in that: The ammeter is connected to one phase circuit between the three-phase alternating excitation device and the voltage regulator to monitor the current.

4. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 1, wherein: The constant temperature reactor is connected to the low-temperature coolant circulation pump through a silica gel tube.

5. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 1, characterized in that: The simulated sunlight light source uses a Perfectlight PLS-SXE300UV xenon lamp light source with a total light power of 50W. The spectral range is 320 - 780 nm. The average emission angle of the light source is 6°, and the spot diameter is 30 - 60 mm according to the irradiation distance.

6. The nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 1, wherein: The constant temperature reactor is a customized jacketed beaker with an outer diameter of 85 mm, an inner diameter of 60 mm, and an inner height of 150 mm. The water inlet and outlet nozzles are opposite and both are located at the upper part of the beaker.

7. A method for degrading water pollutants based on a nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system, the specific steps are as follows: (1) Construction of the photo-magnetic coupling system 1) Construction of the photocatalytic system The photocatalytic system mainly includes a simulated sunlight light source, a constant temperature reactor, a lifting platform, and a low-temperature coolant circulation pump. The simulated sunlight light source is connected to the lifting platform and placed directly above the constant temperature reactor. The constant temperature reactor is connected to the low-temperature cooling circulation system through a silica gel tube. 2) Construction of the magnetic field generating system The applied magnetic field is a rotating alternating magnetic field, excited by three-phase alternating current, including a three-phase alternating excitation device and a voltage regulator. A current with a frequency of 50 Hz is input into the excitation coil through the voltage regulator, and the current magnitude is adjusted to thereby adjust the magnetic field intensity generated by the magnetic field generating system. 3) Preparation of the photocatalyst ① Preparation of g-C3N4; ② Preparation of Fe3O4 / g-C3N4 nano-composite material; (2) Method for degrading water pollutants by the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system Select the model pollutant methylene blue and the toxic organic pollutant phenol as the target pollutants. Add the nano-composite Fe3O4 / g-C3N4 photocatalyst to the constant temperature reactor filled with the target pollutant solution. Place the constant temperature reactor in an ultrasonic cleaner for ultrasonic treatment, take it out, and then place it in a dark environment and let it stand to achieve adsorption and desorption equilibrium. Place the constant temperature reactor in the photo-magnetic coupling system for the pollutant degradation experiment. At regular intervals, take samples. After centrifuging and separating the catalyst, use an ultraviolet-visible spectrophotometer and high-performance liquid chromatography to measure the concentration of pollutants in the samples and calculate their degradation rates.

8. The method for degrading water pollutants based on the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 7, wherein: The simulated sunlight light source adopts the Perfect Light PLS-SXE300UV xenon lamp light source, with a total light power of 50 W; the spectral range is 320 - 780 nm; the average emission angle of the light source is 6°, and the spot diameter is 30 - 60 mm according to the irradiation distance; the constant temperature reactor is a customized jacketed beaker with an outer diameter of 85 mm, an inner diameter of 60 mm, an inner height of 150 mm, and the water inlet and outlet nozzles are opposite to each other and are both located at the upper part of the beaker.

9. The method for degrading water pollutants based on the nano-composite Fe3O4 / g-C3N4 photo-magnetic coupling system according to claim 8, characterized in that: Step 3) ① The specific steps for preparing g-C3N4 are as follows: Put the precursor melamine into a quartz boat. In a tubular furnace, under a N2 atmosphere, heat it at a heating rate of 2.3 °C·min -1 to 550 °C and keep heating. Then, keep introducing N2 in the tubular furnace and let it cool naturally. Then, grind and collect the cooled material through an agate mortar to obtain yellowish powder-like g-C3N4; Step 3) ② The specific steps for the preparation of Fe3O4 / g-C3N4 nanocomposites are as follows: Add the prepared g-C3N4 into a 200 mL mixed solution of ethanol and water with a volume ratio of 1:2, and ultrasonicate for 3 h at room temperature for standby. Dissolve FeCl3·6H2O and FeCl2·4H2O in 20 mL of distilled water purged with N2 for 10 min according to the molar ratio of Fe 3+ :Fe 2+ = 2:1, then add the mixed solution to the ultrasonically treated g-C3N4 suspension. Stir the mixed solution at 80 °C under a N2 atmosphere for 30 min. Then, add 10% ammonia water to the mixture to adjust the solution pH > 10, and stir for another 30 min. Then, let the solution cool naturally. Separate the obtained Fe3O4 / g-C3N4 nanocomposites from the solution with the aid of a magnetic field, and wash them with ethanol and water multiple times. Finally, dry the material at 60 °C, grind it, and collect it to obtain the Fe3O4 / g-C3N4 nanocomposites.

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