Preparation method of spherical Fe3O4 (at) ZnO nanosheet photocatalyst

Abstract

The invention relates to the technical field of semiconductor photocatalytic materials, in particular to a preparation method of a spherical Fe3O4 (at) ZnO nanosheet photocatalyst. According to the method, in an ethylene glycol solvent, Fe < 3 + > is used as an iron source, sodium acetate is used as a precipitator, PEG-1000 is used as a morphology guiding agent, and monodisperse spherical Fe3O4 is prepared through a hydrothermal method; then dispersing the spherical Fe3O4 into an aqueous solution containing PEG-20000 and PVP (Polyvinyl Pyrrolidone), and growing a ZnO nanosheet precursor on the surface of the spherical Fe3O4 through hydrothermal reaction again by taking zinc acetate as a zinc source and urea as a homogeneous precipitator; and finally performing high-temperature calcination to obtain a final product. Through the synergistic effect of the two-step hydrothermal method and the surfactant, tight heterojunction compounding of Fe3O4 and ZnO is realized, and the prepared catalyst has high specific surface area, rich active sites and superparamagnetism. The catalyst disclosed by the invention shows excellent photocatalytic degradation activity and cycling stability to organic pollutants under visible light, can be quickly separated and recycled by utilizing an external magnetic field, and has a wide application prospect in the field of wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of semiconductor photocatalytic materials technology, specifically to a method for preparing spherical Fe3O4@ZnO nanosheet photocatalysts. Background Technology

[0002] With the increasing prominence of energy crises and environmental pollution, semiconductor photocatalysis technology, with its advantages of solar energy drive and environmental friendliness, has shown broad application prospects in the field of organic pollutant degradation. Zinc oxide, as a typical wide-bandgap semiconductor photocatalytic material, is widely used in photocatalysis due to its readily available raw materials, abundant surface active sites, strong photogenerated hole oxidation ability, and unique size effect and crystal facet dependence. Zinc oxide nanosheets, with their large specific surface area and specific polar crystal facet exposure characteristics, can promote photogenerated carrier separation and enhance reactant adsorption and activation efficiency by controlling the built-in electric field strength. However, pure zinc oxide photocatalysts have inherent defects: firstly, the rapid recombination rate of photogenerated electron-hole pairs leads to low quantum efficiency; secondly, they are non-magnetic, making it difficult to separate and recover them after the reaction using simple methods, easily causing secondary pollution and material waste; thirdly, single zinc oxide has poor selectivity for target reactions, easily leading to excessive oxidation of products, limiting its practical application.

[0003] To address the aforementioned issues, constructing heterojunction composite materials has become a core strategy for photocatalyst modification. Fe3O4, as a semiconductor material with excellent superparamagnetic properties, can not only achieve efficient catalyst recovery and recycling through magnetic separation, reducing usage costs, but also, when combined with zinc oxide to form a heterojunction, construct energy-level-matched charge transfer channels, significantly suppressing photogenerated carrier recombination and improving charge separation and transfer efficiency. Simultaneously, the active sites on the Fe3O4 surface can synergistically regulate reaction pathways with zinc oxide, promoting the growth of reactive oxygen species (such as ·OH and ·O2). - The generation of ·OOH enhances the catalyst's activation ability for inert molecules and its reaction selectivity.

[0004] Morphology control is a key method for optimizing the photocatalytic performance of Fe3O4@ZnO composites. Spherical Fe3O4 nanosheets offer advantages such as good dispersibility, controllable specific surface area, and uniform magnetic response, while the polar crystal facet exposure of ZnO nanosheets can further enhance the built-in electric field effect. The synergistic morphology of these two materials can maximize the heterojunction contact area, increase active sites, and improve light absorption and catalytic reaction efficiency. Currently, existing methods for preparing Fe3O4@ZnO composites still have shortcomings, such as loose heterojunction bonding, easy particle agglomeration, and poor morphological uniformity, leading to hindered charge transfer, insufficient stability of catalytic performance, and difficulty in simultaneously achieving synergistic optimization of catalytic activity, selectivity, and recovery performance.

[0005] Based on this, developing a spherical Fe3O4@ZnO nanosheet photocatalyst that can be prepared on a large scale, has controllable morphology, and synergistically optimized performance has important research value and practical significance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing spherical Fe3O4@ZnO nanosheet photocatalysts, so as to solve the problems that existing Fe3O4@ZnO composite materials cannot simultaneously achieve catalytic activity, stability and recyclability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a spherical Fe3O4@ZnO nanosheet material, wherein spherical Fe3O4 is loaded on ZnO nanosheets.

[0008] A method for preparing spherical Fe3O4@ZnO nanosheets is disclosed, wherein a ZnO nanosheet precursor is grown on the surface of spherical Fe3O4, and then calcined to obtain spherical Fe3O4@ZnO nanosheets.

[0009] Furthermore, with Fe 3+ Using iron as the source, monodisperse spherical Fe3O4 is obtained through hydrothermal reaction under the action of reducing agent, precipitant and morphology guiding agent.

[0010] Furthermore, the iron source includes FeCl3; the reducing agent includes ethylene glycol; the precipitant includes sodium acetate; and the morphology guiding agent includes PEG-1000.

[0011] Furthermore, in the spherical Fe3O4 dispersion, Zn 2+ Using zinc as the source, ZnO nanosheet precursors are grown on the surface of spherical Fe3O4 through a hydrothermal reaction under the action of morphology-regulating dispersants and homogenizing precipitants.

[0012] Furthermore, the spherical Fe3O4 is dispersed in an aqueous solution containing PEG-20000 to obtain a spherical Fe3O4 dispersion.

[0013] Furthermore, the zinc source includes zinc acetate; the morphology-regulating dispersant includes PVP; and the homogenizing precipitant includes urea.

[0014] Furthermore, the calcination temperature is 400~600℃, and the calcination time is 1~3h.

[0015] Application of spherical Fe3O4@ZnO nanosheets as photocatalysts.

[0016] The beneficial effects of this invention are:

[0017] 1. The spherical Fe3O4@ZnO nanosheet photocatalyst of the present invention uses zinc oxide nanosheets as a carrier and loads spherical Fe3O4 on its surface. Spherical Fe3O4 is a magnetic material that can be absorbed by a magnet, so it can be quickly separated from wastewater by a permanent magnet method, which is convenient for recycling. 2. This invention uses a two-stage hydrothermal synthesis method to prepare spherical Fe3O4 with adjustable size, and then prepares spherical Fe3O4@ZnO nanosheet photocatalysts; this method is simple, efficient, low-cost, has high photocatalytic activity, and fast degradation rate; 3. In the spherical Fe3O4@ZnO nanosheet photocatalyst of the present invention, spherical Fe3O4 and ZnO nanosheets are combined to form a heterojunction, constructing an energy-level matched charge transfer channel and improving charge separation capability; at the same time, the combination of the two can maximize the contact area, increase the number of active sites, and promote the development of reactive oxygen species (such as ·OH, ·O2). - The generation of , OOH, etc., together promotes visible light absorption, maintains good photocatalytic activity, improves catalytic reaction efficiency, and can efficiently and rapidly degrade various organic pollutants in industrial and domestic wastewater; 4. The preparation method of this invention uses readily available raw materials, has a simple process, is pollution-free, has a high yield, and produces materials with stable structure, making it suitable for long-term operation and with broad prospects for production applications. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the spherical Fe3O4@ZnO nanosheets of this invention. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0020] This invention employs a two-step hydrothermal method to prepare spherical Fe3O4@ZnO nanosheets.

[0021] First, in ethylene glycol solvent, with Fe 3+ Using sodium acetate as a precipitant and PEG-1000 as the iron source, monodisperse spherical Fe3O4 nanoparticles with PEG-1000 surface modification were synthesized via a hydrothermal method; wherein, Fe... 3+ As an iron source, ethylene glycol is the core raw material for the formation of Fe3O4; as a solvent, ethylene glycol also has reducing properties, which can remove some of the Fe. 3+ Reduced to Fe 2+ To generate Fe3O4 (containing Fe) 2+ and Fe 3+The high boiling point of the solution provides the necessary conditions for the hydrothermal reaction to proceed stably at 200°C. Anhydrous sodium acetate acts as a precipitant, providing acetate ions to allow iron ions to form hydroxide precipitates. It also acts as a mineralizer, adjusting the pH of the solution and promoting the formation and growth of Fe3O4 crystal nuclei, thus helping to generate spherical particles with uniform particle size. Polyethylene glycol 1000 (PEG-1000) acts as a surfactant, adsorbing onto the surface of Fe3O4 particles to prevent particle agglomeration, ensure monodispersity, and regulate particle growth, thus assisting in the formation of spherical morphology.

[0022] Secondly, Fe3O4 particles were ultrasonically dispersed in water. The suspension was stabilized by the synergistic dispersion and steric hindrance of PEG-20000 and PVP. Then, using zinc acetate as the zinc source and urea as the homogenizing precipitant, a hydrothermal reaction was carried out to generate a plate-like ZnO precursor, allowing spherical Fe3O4 particles to adhere in situ to the surface of the ZnO plates. PEG-20000, as a dispersant, formed steric hindrance on the Fe3O4 particle surface due to its long-chain structure, further stabilizing the suspension, preventing precipitation, and enhancing the interfacial bonding between Fe3O4 and the ZnO precursor, providing conditions for subsequent adhesion. Polyvinylpyrrolidone (PVP), as a dispersant and morphology modifier, was adsorbed onto the ZnO particles. 2+ The surrounding environment controls the growth direction of the ZnO precursor, promotes the formation of lamellar structures, and stabilizes the Fe3O4 suspension, preventing its aggregation or sedimentation during the reaction. Urea acts as a homogeneous precipitant, slowly hydrolyzing and releasing OH- under hydrothermal conditions. - This causes the solution pH to rise uniformly, allowing Zn to... 2+ The zinc hydroxide precursor is gradually generated, and local high pH is avoided to prevent rapid precipitation of ZnO, thus ensuring the uniform growth of the plate-like structure.

[0023] Finally, the organic coating agent was removed by high-temperature calcination, which simultaneously promoted the crystallization of the ZnO precursor, ultimately yielding spherical Fe3O4@ZnO nanosheets with both magnetic and semiconductor properties. In particular, the muffle furnace calcination decomposed and removed residual organic coating agents such as PEG and PVP at high temperatures, purified the product surface, and promoted the dehydration and crystallization of the ZnO precursor, forming highly crystalline sheet-like ZnO and enhancing the interfacial bonding between Fe3O4 and ZnO.

[0024] Scanning electron microscope image of the spherical Fe3O4@ZnO nanosheets of this invention is shown below. Figure 1 As shown, the surface morphology of the spherical Fe3O4@ZnO nanosheets of the present invention can be clearly seen.

[0025] Example 1 (1) Preparation of spherical Fe3O4 Using FeCl3·6H2O as the iron source (0.01 mol) and ethylene glycol (40 mL) as the solvent, the mixture was sonicated for 30 min. Then, anhydrous sodium acetate (0.04 mol) and polyethylene glycol 1000 (1.0 g) were added, and the mixture was magnetically stirred at high speed for 30 min to obtain the first mixture.

[0026] The first mixture was transferred to a 50mL high-pressure reactor (a stainless steel reactor with a polytetrafluoroethylene liner) and sealed tightly. Then it was placed in an oven and crystallized at 200℃ for 12 hours. After the reaction was completed, it was allowed to cool naturally to room temperature (25℃) in the oven.

[0027] The product was separated from the reaction solution using a permanent magnet. The resulting solid product was washed three times with anhydrous ethanol and dried at 60°C for 6 hours to obtain spherical Fe3O4.

[0028] (2) Preparation of ZnO precursor The spherical Fe3O4 (0.5g) prepared in step (1) was placed in a round-bottom flask, and 60mL of deionized water was added. The mixture was ultrasonically dispersed to obtain a black suspension. Under stirring, 5mL of 20% polyethylene glycol 20000 aqueous solution and 10mL of 0.5mol / L zinc acetate solution were added sequentially, and the mixture was stirred for 1h to obtain a second mixture.

[0029] Add 0.5 g of polyvinylpyrrolidone (PVP) to the second mixture above, stir for 15 min, and then add 10 mL of 1 mol / L urea solution (slowly added dropwise with a disposable dropper) while stirring. Transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, place it in a drying oven, and heat at 180 °C for 12 h. After naturally cooling to room temperature, filter the mixture, and wash the product repeatedly with distilled water and ethanol (at least three times). Then dry at 120 °C for 6 h to obtain a solid product.

[0030] (3) Post-processing The obtained solid product was placed in a muffle furnace equipped with a PID temperature controller and heated to 500℃ at a heating rate of 10℃ / min. After calcination for 2 hours, spherical Fe3O4@ZnO nanosheet photocatalysts were obtained.

[0031] To verify the performance of this photocatalyst, a degradation test was conducted on a 10 mg / L Rhodamine B (RhB) solution under simulated visible light irradiation (λ≥420 nm). During the process, 50 mg / L of spherical Fe3O4@ZnO nanosheets were added under stirring. The results are as follows: First, the spherical Fe3O4@ZnO nanosheets can degrade RhB by 99.8% within 60 min, which is much higher than that of pure ZnO nanosheets (63.7%) and pure spherical Fe3O4 (27.9%), demonstrating high catalytic activity.

[0032] Secondly, after five cycles of degradation experiments, the degradation rate of RhB by the catalyst remained at 99.2%; after each cycle, the catalyst was recovered by an external permanent magnet, and the average mass recovery rate was 97.8%, indicating that it has excellent cycle stability and convenient magnetic separation and recovery performance.

[0033] Furthermore, bioactive species capture experiments confirmed that ·OH and ·O2 - It is the main active species, indicating that the heterojunction effectively promotes the separation of photogenerated carriers and the generation of reactive oxygen species.

[0034] This invention successfully prepared a spherical Fe3O4@ZnO nanosheet composite photocatalyst through a two-step hydrothermal method combined with high-temperature calcination. This catalyst not only significantly improves the photogenerated carrier separation efficiency and enhances photocatalytic activity and selectivity through its heterojunction structure, but also achieves rapid magnetic separation and recovery of the catalyst thanks to the superparamagnetism of Fe3O4, overcoming the shortcomings of pure ZnO photocatalysts such as easy aggregation, difficult recovery, and poor stability. Experiments show that this catalyst has a high efficiency in degrading organic pollutants and excellent recycling performance, demonstrating broad application prospects in environmental remediation fields such as wastewater treatment.

[0035] This invention is not limited to the preferred embodiments described above. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes made to their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A spherical Fe3O4@ZnO nanosheet material, characterized in that: Spherical Fe3O4 is loaded on ZnO nanosheets.

2. A method for preparing spherical Fe3O4@ZnO nanosheets, characterized in that: ZnO nanosheet precursors were grown on the surface of spherical Fe3O4, and then calcined to obtain spherical Fe3O4@ZnO nanosheets.

3. The method for preparing spherical Fe3O4@ZnO nanosheets according to claim 2, characterized in that: With Fe 3+ Using iron as the source, monodisperse spherical Fe3O4 is obtained through hydrothermal reaction under the action of reducing agent, precipitant and morphology guiding agent.

4. The method for preparing spherical Fe3O4@ZnO nanosheets according to claim 3, characterized in that: The iron source includes FeCl3; the reducing agent includes ethylene glycol; the precipitant includes sodium acetate; and the morphology guiding agent includes PEG-1000.

5. The method for preparing spherical Fe3O4@ZnO nanosheets according to claim 2, characterized in that: In a spherical Fe3O4 dispersion, with Zn 2+ Using zinc as the source, ZnO nanosheet precursors are grown on the surface of spherical Fe3O4 through a hydrothermal reaction under the action of morphology-regulating dispersants and homogenizing precipitants.

6. The method for preparing spherical Fe3O4@ZnO nanosheets according to claim 5, characterized in that: The spherical Fe3O4 was dispersed in an aqueous solution containing PEG-20000 to obtain a spherical Fe3O4 dispersion.

7. The method for preparing spherical Fe3O4@ZnO nanosheets according to claim 5, characterized in that: The zinc source includes zinc acetate; the morphology-regulating dispersant includes PVP; and the homogenizing precipitant includes urea.

8. The method for preparing spherical Fe3O4@ZnO nanosheets according to claim 2, characterized in that: The calcination temperature is 400~600℃, and the calcination time is 1~3h.

9. The application of the spherical Fe3O4@ZnO nanosheet material according to any one of claims 1-8 as a photocatalyst.

Images