Magnetic visible light photocatalyst ZnFe2O4 / MXene as well as preparation method and application thereof

Abstract

The invention discloses a magnetic visible light photocatalyst ZnFe2O4 / MXene as well as a preparation method and application thereof, and belongs to the technical field of photocatalytic materials. According to the specific technical scheme, the preparation method comprises the following steps: fully dissolving a zinc source and an iron source in a solvent under the ultrasonic action, adding a morphology regulator, and preparing magnetic ZnFe2O4 through a hydrothermal method; then a two-dimensional material MXene with high conductivity is introduced to promote separation and migration of ZnFe2O4 photo-induced electrons and holes and inhibit compounding of the ZnFe2O4 photo-induced electrons and holes, so that the photocatalytic efficiency is improved, and the magnetic visible light photocatalyst ZnFe2O4 / MXene is prepared. The prepared photocatalyst is easy to recover, has the advantage of rapidly degrading organic pollutants, and has a good application prospect in the aspect of treatment of organic wastewater such as dyeing wastewater and medical wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a magnetic visible-light photocatalyst ZnFe2O4 / MXene, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of science and technology and the growth of population, water pollution has become a problem that cannot be ignored. For example, a large amount of dyeing wastewater is generated in industries such as leather making, textile, and dyeing. Most industrial dyes have complex chemical structures, high stability, and are not easily degraded. Direct discharge will have a serious impact on natural water resources and the ecological system. The aromatic amine compounds generated after decomposition have strong carcinogenicity and will also seriously endanger human health. Therefore, it is very necessary to develop green, economical, and efficient organic pollutant treatment technologies.

[0003] Traditional wastewater treatment methods include adsorption, biofilm method, oxidation method, membrane separation, etc. However, these methods will have problems such as incomplete degradation and generation of harmful by-products during the treatment process. Photocatalytic technology is a method that uses renewable solar energy to achieve the purpose of degrading pollutants, and has advantages such as high efficiency, energy saving, economy, and complete degradation of pollutants, so it has attracted much attention. The photocatalytic reaction includes three main steps: (1) the photocatalyst absorbs photons and generates electron-hole carriers; (2) the separation and migration of photo-generated carriers; (3) the redox reaction of photo-generated charges on the surface of the photocatalyst with chemical substances. In this series of processes, whether photo-generated electrons and holes are easily generated and recombined is the key influencing factor leading to photocatalytic efficiency. Therefore, developing excellent photocatalysts has a pivotal position in the field of wastewater treatment by photocatalytic technology.

[0004] ZnFe2O4 is a photocatalyst that is easily excited by visible light, has easy magnetic recovery, and has good photochemical stability, and has good application potential in wastewater treatment. However, its band gap E g is relatively narrow, only 1.9 eV, and the photo-generated electrons and holes generated are easily recombined, which affects its photocatalytic performance and needs to be modified. In existing research, most use precious metals such as Ag and Au and their derivatives as co-catalysts to form Schottky junctions with ZnFe2O4, and then use the formed Schottky barriers to inhibit the recombination of photo-generated electrons and holes, thereby improving the photocatalytic performance. However, the price of precious metals is expensive, and it is difficult to achieve large-scale production. It is urgent to explore other alternative co-catalysts.

[0005] MXene is a newly emerging two-dimensional material etched from titanium aluminum carbide (Ti3AlC2). Structurally, it is composed of alternating stacks of metal ion layers and atomic layers such as carbon or nitrogen. This structure endows it with high conductivity, and MXene can be used instead of precious metals as a co-catalyst. SUMMARY OF THE INVENTION

[0006] Aiming at the problems existing in the prior art, the object of the present invention is to provide a magnetic visible-light photocatalyst ZnFe2O4 / MXene and its preparation method, so as to solve the problem that the photocatalytic efficiency of ZnFe2O4 is low due to the easy recombination of electrons and holes, and the limitation of the high cost of the cocatalyst used in the existing modification technology.

[0007] The present invention is achieved by the following technical solutions: Preparation method of magnetic visible-light photocatalyst ZnFe2O4 / MXene: Add iron source and zinc source into a solvent at the same time. After fully stirring to completely dissolve them, add a morphology regulator to obtain a precursor solution; transfer the above precursor solution to a hydrothermal reaction kettle for reaction. After the reaction is completed, wait until it cools to room temperature, centrifuge to obtain the precipitate, wash it thoroughly and then calcine and grind to obtain ZnFe2O4; add MXene into deionized water and make it fully disperse by means of ultrasonic wave and stirring to obtain a MXene dispersion; add the above ZnFe2O4 into the MXene dispersion, ultrasonic wave and stir to obtain a ZnFe2O4 / MXene dispersion, centrifuge to obtain the precipitate, and grind it after vacuum drying to prepare the magnetic visible-light photocatalyst ZnFe2O4 / MXene.

[0008] Preferably, the specific steps of the preparation method of the above magnetic visible-light photocatalyst ZnFe2O4 / MXene include: (1) Add the iron source and zinc source into a solvent, stir for 5 - 10 min to completely dissolve them; then add a morphology regulator and stir for 10 - 30 min to completely dissolve it to obtain a precursor solution; (2) Pour the precursor solution into a hydrothermal reaction kettle and place it in an oven. After the constant-temperature reaction is completed, cool it to room temperature to obtain a suspension, centrifuge to obtain the precipitate, wash it 4 - 6 times alternately with water and ethanol, calcine and grind to obtain ZnFe2O4; (3) Add MXene into deionized water and stir under ultrasonic action to obtain a MXene dispersion; (4) Directly add ZnFe2O4 into the MXene dispersion, after ultrasonic wave and stirring, centrifuge to obtain the precipitate, vacuum dry it at 50 - 80 °C and grind it to obtain the magnetic visible-light photocatalyst ZnFe2O4 / MXene.

[0009] In the above step (1), the preferred iron source is one of ferric nitrate, ferric chloride, ammonium ferrous sulfate, and ferrous sulfate. The preferred concentration of the iron source is 0.1 - 0.5 mol / L, more preferably 0.2 - 0.4 mol / L; the preferred zinc source is one of zinc nitrate, zinc sulfate, and zinc acetate. The preferred concentration of the zinc source is 0.05 - 0.25 mol / L, more preferably 0.1 - 0.2 mol / L. Higher or lower concentrations of the iron source and zinc source will reduce the yield or productivity of ZnFe2O4. The molar ratio of the iron source to the zinc source is fixed at 2:1. The main reason is that the molar ratio of zinc element to iron element in the product ZnFe2O4 is 2:1. Selecting this ratio can reduce the generation of by-products.

[0010] In the above step (1), the preferred morphology regulator is one or none of the urea / ammonium fluoride mixture, glucose, and oxalic acid. The preferred concentration is 0.2 - 1.5 mol / L. The addition of the morphology regulator is mainly to control the growth direction of ZnFe2O4 crystals. Only by selecting the appropriate type and its concentration can the growth rates of different crystal planes be better controlled, thereby changing its morphology.

[0011] In the above step (2), the preferred temperature of the hydrothermal reaction is 120 - 200 °C, more preferably 160 - 190 °C. The temperature of the hydrothermal reaction can have different effects on the growth rates of each crystal plane of ZnFe2O4, thereby regulating the morphology of ZnFe2O4.

[0012] In the above step (2), the preferred hydrothermal reaction time is 6 - 16 h, more preferably 10 - 15 h. If the hydrothermal reaction time is too short, the integrity and particle size of ZnFe2O4 crystals will be affected. If it is too long, the preparation efficiency will be reduced.

[0013] In the above step (2), the temperature and time of calcination in the muffle furnace are 300 - 500 °C and 2 - 6 h. The preferred temperature is 350 - 450 °C, and the time is 3 - 5 h. Calcining ZnFe2O4 at an appropriate temperature can remove impurities and simultaneously regulate the crystal structure of ZnFe2O4, thereby affecting its surface morphology and changing the catalytic activity. If the temperature is too low or the time is too short, a good effect cannot be achieved. If the temperature is too high or the time is too long, the crystal structure of ZnFe2O4 may be damaged, reducing its stability.

[0014] In the above step (3), the time of ultrasonic stirring is 30 - 90 min, and the preferred time is 50 - 70 min. A lower ultrasonic time will make it difficult for MXene to be completely dispersed in water, while a higher ultrasonic time may damage the structure of MXene and affect its performance.

[0015] The preferred mass percentage concentration of MXene in the above step (3) is 0.01% to 0.15%, and more preferably 0.05% to 0.1%. Too low a concentration will directly reduce the mass percentage concentration of the product and reduce the preparation efficiency; while too high a mass percentage concentration will deteriorate the dispersibility of MXene and affect the subsequent combination with ZnFe2O4.

[0016] In the above step (3), the mass ratio of ZnFe2O4 to MXene is 1:(0.02 ~ 0.3), wherein the preferred mass ratio is 1:(0.075 ~ 0.15). Appropriate MXene content will improve the photocatalytic performance of ZnFe2O4 / MXene, while excessive MXene will inhibit the photocatalytic effect due to light shielding or filtering.

[0017] The preferred ultrasonic time and stirring time in the above step (4) are 4 to 8 h and 10 to 16 h, respectively, and more preferably 5 to 7 h and 12 to 14 h, respectively. Too short ultrasonic time and stirring time cannot fully combine ZnFe2O4 and MXene, while too long time may destroy the original structure of the material and affect its photocatalytic performance.

[0018] The magnetic visible light photocatalyst ZnFe2O4 / MXene prepared by the above preparation method, the introduction of MXene effectively promotes the separation of photogenerated carriers. The photocatalyst has a rapid degradation efficiency for organic pollutants under visible light and can be recycled through magnetic recovery.

[0019] The magnetic visible light photocatalyst ZnFe2O4 / MXene prepared by the above preparation method is used in the degradation of organic pollutants in wastewater, and is suitable for the treatment of dyeing wastewater and medical wastewater.

[0020] The beneficial effects of the present invention are: 1) High-efficiency photocatalytic performance and carrier separation optimization: The present invention significantly improves the photocatalytic performance of ZnFe2O4. By introducing the two-dimensional high conductivity of MXene, it effectively solves the key problem of low catalytic efficiency of ZnFe2O4 due to the easy recombination of photogenerated electrons and holes. In the embodiment, the addition of MXene makes the degradation rate of methylene blue (MB) of ZnFe2O4 / MXene composite material under visible light reach 96.4% within 5 minutes (Example 5), and the catalytic efficiency is improved by more than 2 times compared with the control example without MXene. As an electron transmission channel, MXene significantly accelerates the separation and migration of photogenerated carriers, fundamentally suppresses the recombination phenomenon, and thus greatly improves the photocatalytic activity.

[0021] 2) Magnetic recovery and cycle stability: likeFigure 3 As shown, ZnFe2O4 / MXene can be rapidly recovered by applying an external magnetic field, solving the problem that traditional photocatalysts are difficult to recover and prone to loss, and is particularly suitable for industrial scenarios such as dyeing wastewater and medical wastewater containing high concentrations of organic pollutants.

[0022] 3) Low cost and environmental friendliness: Replacing noble metal cocatalysts (such as Ag, Au) with MXene significantly reduces the raw material cost. Moreover, the preparation process of ZnFe2O4 / MXene does not require complex equipment or high temperature and high pressure conditions, meeting the requirements of green chemical engineering and large-scale production.

[0023] 4) Morphology tunability and structural advantages: By regulating the morphology regulator and hydrothermal reaction parameters, ZnFe2O4 with diverse morphologies such as hollow microspheres and nanoparticles can be prepared, and its specific surface area and light absorption range are significantly optimized, further enhancing the pollutant adsorption and light response capabilities. Description of the Drawings

[0024] Figure 1 SEM images of ZnFe2O4 in Examples 1 to 5.

[0025] Figure 2 Degradation curves of methylene blue for Comparative Example 1, Example 1 and Example 5.

[0026] Figure 3 Schematic diagram of magnetic recovery for Example 1. Detailed Description of the Invention

[0027] The present invention will be further described in detail below in conjunction with specific embodiments, but the implementation manners of the present invention include, but are not limited to, the scope represented by the following embodiments.

[0028] In the present invention, the conductive material MXene is prepared by the following method: Weigh 1.3 g of lithium fluoride, dissolve it in a polytetrafluoroethylene container containing 30 mL of concentrated hydrochloric acid, magnetically stir at room temperature for 5 min to completely dissolve it, slowly add 1.95 g of aluminum carbide titanium within 10 min, then ultrasonically assist mechanical stirring of the mixture at 50 °C for 12 h, cool to room temperature, wash with water and alcohol until the pH value is 6 to remove impurities such as lithium fluoride and hydrochloric acid. Centrifuge (4000 r, 10 min), and vacuum dry and grind into powder at 60 °C for standby.

[0029] Comparative Example 1: 0.8080 g of iron(III) nitrate nonahydrate and 0.2975 g of zinc nitrate hexahydrate were added to deionized water, and stirred for 8 min to completely dissolve them, so that the concentrations of the iron source and the zinc source were 0.1 and 0.05 mol / L respectively; then 5.4 g of glucose was added and stirred for 30 min to completely dissolve it, and the final concentration of glucose was 1.5 mol / L to obtain a precursor solution; the above precursor solution was poured into a hydrothermal reaction kettle and placed in an oven, and reacted at a constant temperature of 180 °C for 6 h, cooled to room temperature to obtain a suspension, the precipitate was collected by centrifugation, washed alternately with water and ethanol 6 times, calcined at 450 °C for 6 h, and ground to obtain ZnFe2O4.

[0030] Example 1: 0.8080 g of iron(III) nitrate nonahydrate and 0.2975 g of zinc nitrate hexahydrate were added to deionized water, and stirred for 8 min to completely dissolve them, so that the concentrations of the iron source and the zinc source were 0.1 and 0.05 mol / L respectively; then 5.4 g of glucose was added and stirred for 30 min to completely dissolve it, and the final concentration of glucose was 1.5 mol / L to obtain a precursor solution; the above precursor solution was poured into a hydrothermal reaction kettle and placed in an oven, and reacted at a constant temperature of 180 °C for 6 h, cooled to room temperature to obtain a suspension, the precipitate was collected by centrifugation, washed alternately with water and ethanol 6 times, calcined at 450 °C for 6 h, and ground to obtain ZnFe2O4; 0.01 g of MXene was added to deionized water, and stirred for 50 min under ultrasonic treatment to obtain a MXene dispersion with a mass percentage concentration of 0.05%; ZnFe2O4 was directly added to the above MXene dispersion, so that the mass ratio of ZnFe2O4 to MXene was 1:0.06, ultrasonicated for 5 h and then stirred for 13 h, the precipitate was collected by centrifugation, vacuum dried at 65 °C and ground to obtain the magnetic visible light photocatalyst ZnFe2O4 / MXene.

[0031] Example 2: 1.082 g of iron(III) chloride hexahydrate and 0.439 g of zinc acetate dihydrate were added to ethylene glycol, and stirred for 6 min until completely dissolved, so that the concentrations of the iron source and the zinc source were 0.2 mol / L and 0.1 mol / L respectively. Subsequently, 2.7 g of glucose was added and stirred for 20 min until completely dissolved, and the final concentration of glucose was 0.75 mol / L to obtain a precursor solution; the above precursor solution was poured into a hydrothermal reaction kettle and placed in an oven, and reacted at a constant temperature of 190 °C for 15 h, cooled to room temperature to obtain a suspension, centrifuged to collect the precipitate, washed alternately with water and ethanol 5 times, calcined at 350 °C for 2 h, and ground to obtain ZnFe₂O₄; 0.002 g of MXene was added to deionized water, and stirred for 30 min under ultrasonic treatment to obtain an MXene dispersion with a mass percentage concentration of 0.01%; ZnFe₂O₄ was directly added to the above MXene dispersion, so that the mass ratio of ZnFe₂O₄ to MXene was 1:0.02, ultrasonicated for 4 h and then stirred for 10 h, centrifuged to collect the precipitate, vacuum dried at 80 °C and ground to obtain the magnetic visible light photocatalyst ZnFe₂O₄ / MXene.

[0032] Example 3: 2.3528 g of ammonium ferrous sulfate and 0.6217 g of zinc sulfate heptahydrate were added to a mixed solution of ethylene glycol / deionized water, and the concentrations of the iron source and the zinc source were 0.3 mol / L and 0.15 mol / L respectively. Stirred for 5 min until completely dissolved, then 0.3602 g of oxalic acid was added and stirred for 10 min until completely dissolved, and the final concentration of oxalic acid was 0.2 mol / L to obtain a precursor solution; the above precursor solution was poured into a hydrothermal reaction kettle and placed in an oven, and reacted at a constant temperature of 120 °C for 12 h, cooled to room temperature to obtain a suspension, centrifuged to collect the precipitate, washed alternately with deionized water and ethanol 6 times, calcined at 400 °C for 5 h, and ground to obtain ZnFe₂O₄; 0.020 g of MXene was added to deionized water, and stirred for 70 min under ultrasonic treatment to obtain an MXene dispersion with a mass percentage concentration of 0.1%; ZnFe₂O₄ was directly added to the above MXene dispersion, so that the mass ratio of ZnFe₂O₄ to MXene was 1:0.15, ultrasonicated for 7 h and then stirred for 14 h, centrifuged to collect the precipitate, vacuum dried at 70 °C and ground to obtain the magnetic visible light photocatalyst ZnFe₂O₄ / MXene.

[0033] Example 4: 2.2241 g of ferrous sulfate heptahydrate and 1.19 g of zinc nitrate hexahydrate were added to deionized water, and stirred for 10 min to completely dissolve them. The concentrations of the iron source and the zinc source were 0.4 and 0.2 mol / L respectively; then 0.3 g of urea and 0.0741 g of ammonium fluoride were added, and stirred for 15 min to completely dissolve them. The final concentration of urea / ammonium fluoride was 0.35 mol / L to obtain a precursor solution; the above precursor solution was poured into a hydrothermal reaction kettle and placed in an oven, and reacted at a constant temperature of 200 °C for 10 h, cooled to room temperature to obtain a suspension, centrifuged to collect the precipitate, washed alternately with water and ethanol 6 times, calcined at 300 °C for 3 h, and ground to obtain ZnFe2O4; 0.015 g of MXene was added to deionized water, and stirred for 40 min under ultrasonic treatment to obtain a MXene dispersion with a mass percentage concentration of 0.075%; ZnFe2O4 was directly added to the above MXene dispersion, so that the mass ratio of ZnFe2O4 to MXene was 1:0.075, ultrasonicated for 6 h and then stirred for 12 h, centrifuged to collect the precipitate, vacuum dried at 60 °C and ground to obtain the magnetic visible light photocatalyst ZnFe2O4 / MXene.

[0034] Example 5: 2.705 g of ferric chloride hexahydrate and 1.4875 g of zinc nitrate hexahydrate were added to ethanol / ethylene glycol, and stirred for 7 min to completely dissolve them. The concentrations of the iron source and the zinc source were 0.5 and 0.25 mol / L respectively to obtain a precursor solution; the above precursor solution was poured into a hydrothermal reaction kettle and placed in an oven, and reacted at a constant temperature of 160 °C for 16 h, cooled to room temperature to obtain a suspension, centrifuged to collect the precipitate, washed alternately with water and ethanol 4 times, calcined at 500 °C for 4 h, and ground to obtain ZnFe2O4; 0.03 g of MXene was added to deionized water, and stirred for 90 min under ultrasonic treatment to obtain a MXene dispersion with a mass percentage concentration of 0.15%; ZnFe2O4 was directly added to the above MXene dispersion, so that the mass ratio of ZnFe2O4 to MXene was 1:0.3, ultrasonicated for 8 h and then stirred for 16 h, centrifuged to collect the precipitate, vacuum dried at 50 °C and ground to obtain the magnetic visible light photocatalyst ZnFe2O4 / MXene.

[0035] Through the specific implementations of Examples 1 to 5 and Comparative Example 1 of the present invention, the significant advantages of the magnetic visible light photocatalyst ZnFe2O4 / MXene in the treatment of organic wastewater were verified.

[0036] High degradation performance: As Figure 2 shown, Figure 2Degradation curves of methylene blue for Comparative Example 1, Example 1 and Example 5. After introducing MXene in Example 1, the degradation rate of ZnFe2O4 / MXene for methylene blue under visible light reached over 90% within 10 minutes, and in Example 5, a degradation rate of 96.4% was achieved within 5 minutes, far exceeding Comparative Example 1 without adding MXene. The two-dimensional highly conductive structure of MXene effectively promoted the separation of photo-generated electrons and holes in ZnFe2O4, significantly inhibited recombination, and thus greatly improved the photocatalytic efficiency.

[0037] Morphology tunability and structural advantages: Figure 1 (a - e) are SEM images of ZnFe2O4 in Examples 1 - 5 respectively, where Examples 1 - 5 correspond to Figure 1 (a - e) in. It can be seen from the figure that ZnFe2O4 with different morphologies can be prepared by adjusting conditions such as the type of raw materials, morphology regulators, and hydrothermal reaction temperature and time, such as hollow microspheres (a), nanospheres (b), micro-rods (c), octahedrons (d), and nanoparticles (e). Figure 1 ZnFe2O4 with different morphologies in shows that by adjusting the type of morphology regulator, hydrothermal temperature and time, the specific surface area and the distribution of active sites of the material can be optimized, further enhancing light absorption and catalytic activity.

[0038] Magnetic recycling and cycle stability: Figure 3 Schematic diagram of magnetic recycling for Example 1. As Figure 3 shown, ZnFe2O4 / MXene can be quickly recycled by an external magnetic field. This characteristic solves the problem of difficult recycling of traditional photocatalysts, reduces the actual application cost, and is especially suitable for large-scale treatment of dyeing wastewater and medical wastewater.

[0039] Low cost and environmental friendliness: Using MXene to replace noble metal co-catalysts can greatly reduce the raw material cost while ensuring performance, and the preparation process of ZnFe2O4 / MXen does not require complex equipment, meeting the requirements of green chemical engineering.

Claims

1. A preparation method of a magnetic visible-light photocatalyst ZnFe2O4 / MXene, characterized in that: (1) Add an iron source and a zinc source to a solvent in a molar ratio of 2:1, stir to completely dissolve it, and then add a morphology regulator to obtain a precursor solution; (2) Perform a hydrothermal reaction on the precursor solution, cool, centrifuge, wash, calcine and grind after the reaction to obtain magnetic ZnFe2O4; (3) Disperse MXene in deionized water to form a MXene dispersion; (4) Mix ZnFe2O4 with the MXene dispersion, and prepare a ZnFe2O4 / MXene composite material after ultrasonic treatment, stirring, centrifugation and drying.

2. The preparation method of a magnetic visible light photocatalyst ZnFe2O4 / MXene according to claim 1, characterized in that, The specific steps are as follows: In the step (1), the iron source is one of iron nitrate, iron chloride, ammonium ferrous sulfate and ferrous sulfate; the zinc source is one of zinc nitrate, zinc sulfate and zinc acetate; the solvent is one of ethylene glycol, ethylene glycol / ethanol mixture, ethylene glycol / deionized water mixture and deionized water.

3. The preparation method according to claim 1, characterized in that: In the step (1), the concentration of the iron source is 0.1 - 0.5 mol / L, the concentration of the zinc source is 0.05 - 0.25 mol / L; the morphology regulator is one or none of a urea / ammonium fluoride mixture, glucose and oxalic acid, and the concentration is 0.2 - 1.5 mol / L.

4. The preparation method according to claim 1, characterized in that: In the step (2), the hydrothermal reaction temperature is 120 - 200 °C, the reaction time is 6 - 20 h, the calcination temperature is 300 - 500 °C, and the calcination time is 2 - 6 h.

5. The preparation method according to claim 1, characterized in that: In the step (3), the mass percentage concentration of MXene is 0.01% - 0.15%, and in the step (4), the mass ratio of ZnFe2O4 to MXene is 1: (0.02 - 0.3).

6. The preparation method according to claim 1, characterized in that: In the step (4), the ultrasonic time is 4 - 8 h, the stirring time is 10 - 16 h, and the drying temperature is 50 - 80 °C.

7. A magnetic visible-light photocatalyst ZnFe2O4 / MXene prepared by the preparation method according to any one of claims 1 - 6.

8. Application of a magnetic visible-light photocatalyst ZnFe2O4 / MXene prepared by the preparation method according to any one of claims 1 - 6 in degrading organic pollutants in wastewater.

9. The application according to claim 8, wherein: The degradation rate of methylene blue by the magnetic visible-light photocatalyst ZnFe2O4 / MXene reaches more than 90% within 10 minutes and is recycled through magnetic recovery.

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