CN115028206B

CN115028206B - Janus two-dimensional magnetic nanoparticle and preparation method and application thereof

Info

Publication number: CN115028206B
Application number: CN202210704470.0A
Authority: CN
Inventors: 华朝; 张健; 唐晓旭; 王秀军; 孙哲; 陈翔宇; 李仕超; 侯胜珍; 王姗姗; 赵春花
Original assignee: Beijing Research Center of CNOOC China Ltd; CNOOC China Ltd
Current assignee: Beijing Research Center of CNOOC China Ltd; CNOOC China Ltd
Priority date: 2022-06-21
Filing date: 2022-06-21
Publication date: 2023-10-31
Anticipated expiration: 2042-06-21
Also published as: CN115028206A

Abstract

The invention discloses Janus two-dimensional magnetic nano particles and a preparation method and application thereof. The preparation method of the Janus two-dimensional magnetic nano-particles comprises the following steps: adding melted paraffin into the aqueous dispersion of the two-dimensional magnetic nano particles, stirring, cooling to room temperature, and collecting and separating by a magnet to obtain paraffin balls with the surfaces adsorbing the two-dimensional magnetic nano particles; dispersing paraffin spheres with two-dimensional magnetic nano particles adsorbed on the surface into an ethanol water solution, regulating the pH value to 8-9, adding n-octyl triethoxysilane for reaction, and separating and dissolving paraffin spheres by a magnet after the reaction is finished to obtain Fe ₃ O ₄ Dispersing @ OTES particles in ethanol water solution, adding N-aminoethyl-gamma-aminopropyl trimethoxysilane for reaction, and separating by magnet after the reaction. The Janus two-dimensional magnetic nano-particles are prepared by an interface protection method, and not only have JanusThe s-shaped material has excellent properties and special magnetic response, so that the s-shaped material is easier to recycle and reuse and reduces the cost after being used for preparing stable emulsion.

Description

Janus two-dimensional magnetic nanoparticle and preparation method and application thereof

Technical Field

The invention relates to Janus two-dimensional magnetic nano particles and a preparation method and application thereof, and belongs to the technical field of nano material preparation.

Background

"Janus" was originally proposed by De genies professor in 1991, and primarily refers to two asymmetric materials of different chemical nature or different composition. The Janus nano material has a broad application prospect due to unique properties, and more researchers are researching the Janus nano material. Janus nanomaterials refer to special materials having an asymmetric structure or property, including asymmetry in the morphology or composition properties of the material. From the aspect of morphology, the asymmetry of morphology gives Janus material a special spatial effect; from a compositional standpoint, two halves of a Janus material have two different properties, and may even be opposite properties, such as hydrophilic-lipophilic, polar-nonpolar, magnetic-nonmagnetic, and the like. The Janus material thus has multiple functionalities and can meet more complex environmental requirements. The main preparation methods include interface protection method, microfluidics method, nucleation control growth method, etc. The preparation of Janus particles by adopting a paraffin interface protection method is reported for the first time from Granich, and the paraffin interface protection method is attracting great interest to students at home and abroad.

The two-dimensional magnetic nano particles have good yield and injection increasing effects, no toxicity, low price and special magnetic responsiveness, and are widely applied to various aspects of oil displacement, demulsification, emulsion stabilization and the like. For Janus magnetic nano-sheets, the Janus magnetic nano-sheets not only have the excellent properties of Janus sheet materials, but also have multiple functions of intelligent oil finding, imbibition, oil film stripping, emulsification viscosity reduction, coalescence oil wall and the like; and the emulsion also has special magnetic responsiveness, and the formed emulsion is easier to recycle and reuse. Therefore, the high-stability Pickering emulsion formed by the Janus magnetic nano-sheet is expected to play a larger role in the fields of chemical oil displacement, recovery efficiency improvement and the like. However, so far, little research is done on preparing high-stability Pickering emulsion by adopting Janus magnetic nano-sheets, and based on the research, a new strategy for constructing high-stability Pickering emulsion by using Janus magnetic nano-sheets is provided.

Disclosure of Invention

The invention aims to provide Janus two-dimensional magnetic nano particles and a preparation method thereof, and the prepared Janus two-dimensional magnetic nano particles have strong magnetic responsiveness, good interfacial activity and strong emulsion stabilizing capability.

The Janus two-dimensional magnetic nano-particle is prepared on the basis of the two-dimensional magnetic nano-particle, and the two-dimensional magnetic nano-particle is prepared according to the following method:

Dropwise adding an aqueous solution of ferrous sulfate heptahydrate into an aqueous solution of sodium hydroxide and sodium acetate, and reacting under the condition of stirring; and after the reaction is finished, collecting and separating the two-dimensional magnetic nano particles by using a magnet.

Specifically, the temperature of the reaction is 50-80 ℃, preferably 60 ℃, and the two-dimensional magnetic nano particles prepared at the temperature are regular in shape, uniform in size and uniform in particle size;

under water bath conditions.

Specifically, the stirring speed is 200 to 600rpm, preferably 500rpm, and the two-dimensional magnetic nanoparticles prepared at the stirring speed have regular shapes, most of which have hexagonal shapes and relatively uniform sizes.

Specifically, the reaction time is 2-3 h, preferably 2h, and most of the two-dimensional magnetic nano particles prepared under the reaction time are hexagonal and regular in shape.

Specifically, the dripping speed of the aqueous solution of the ferrous sulfate heptahydrate is 2-2.4 mL/min, preferably 2.4mL/min, and most of the generated products are of a two-dimensional lamellar structure, regular in shape and uniform in distribution when the aqueous solution is dripped at the speed.

Specifically, in the aqueous solution of the ferrous sulfate heptahydrate, the molar concentration of the ferrous sulfate heptahydrate is 0.096-0.144 mol/L, preferably 0.096mol/L, and the shapes of products prepared under the concentration are two-dimensional sheet structures and are regular.

Specifically, in the aqueous solution of sodium hydroxide and anhydrous sodium acetate, the molar concentration of the sodium hydroxide is 0.18-0.27 mol/L, preferably 0.18mol/L, the particle size of the magnetic nano particles prepared under the concentration is smaller, and the shape of the product is a two-dimensional flaky structure and is regular;

the molar concentration of the anhydrous sodium acetate is 0.9-1.35 mol/L, preferably 0.9mol/L, and the magnetic nano particles prepared under the concentration have regular shape and similar structure.

The thickness of the two-dimensional magnetic nano particles prepared by the method is about 4.2-4.6 nm.

The two-dimensional magnetic nano particles prepared by the method have smooth surfaces and uniform thickness.

The magnetism of the prepared two-dimensional magnetic nano particles is measured by adopting VSM, and at room temperature, the saturation magnetization (Ms) of the magnetic nano sheet is 77.5emu/g, the residual magnetization (Mr) is 11.2emu/g, the coercive force (Hc) is 106.7Oe, and the magnetic nano sheet has good magnetism and can be used as a good magnetic material. Meanwhile, under the action of an external magnetic field, the liquid can be quickly separated from the liquid, so that the recovery and the recycling can be realized, and the cost is reduced.

The two-dimensional magnetic nano particles prepared by the method are determined to be Fe by adopting XRD, HRTEM, XPS, FT-IR to analyze the phase and crystal form structures of the two-dimensional magnetic nano particles ₃ O ₄ The exposed surface is (111), and the synthesized two-dimensional magnetic nano sheet is a regular hexagon, and belongs to anisotropic nano particles.

The preparation method of the Janus two-dimensional magnetic nano-particles provided by the invention comprises the following steps:

s1, adding melted paraffin into the aqueous dispersion liquid of the two-dimensional magnetic nano particles, stirring, cooling to room temperature, and collecting and separating by a magnet to obtain paraffin balls with the surfaces adsorbing the two-dimensional magnetic nano particles;

s2, dispersing paraffin spheres with the two-dimensional magnetic nano particles adsorbed on the surface into an ethanol water solution, regulating the pH value to 8-9, adding n-octyl triethoxysilane (or other silane coupling agents) for reaction, and separating and dissolving the paraffin spheres by a magnet after the reaction is finished to obtain Fe ₃ O ₄ An OTES particle;

s3, mixing the Fe ₃ O ₄ Dispersing the @ OTES particles in an ethanol aqueous solution, adding N-aminoethyl-gamma-aminopropyl trimethoxysilane (or other silane coupling agents) for reaction, and separating by a magnet after the reaction is finished to obtain the Janus two-dimensional magnetic nano particles.

In the preparation method, in the step S1, stirring is carried out at 20-40 ℃;

in the aqueous dispersion, the concentration of the two-dimensional magnetic nano particles is 1-4 mg/mL;

In the steps S2 and S3, the volume fraction of water in the ethanol water solution is 1-2%;

in the step S2, the pH value is regulated by adopting a sodium hydroxide aqueous solution;

the dosage of the n-octyl triethoxysilane is as follows: 1g: 0.5-2 mL of the n-octyl triethoxysilane;

the reaction temperature is 20-40 ℃ and the reaction time is 10-20 h.

In the above preparation method, in step S3, the amount of the N-aminoethyl- γ -aminopropyl trimethoxysilane is as follows: 0.25-1 mL of the N-aminoethyl-gamma-aminopropyl trimethoxysilane;

the reaction temperature is 20-40 ℃ and the reaction time is 10-20 h.

According to the invention, the morphology of the prepared product is analyzed through TEM and HRTEM, and the clear coating thickness is about 3.85nm.

According to the analysis of contact angle and interface properties of the Janus two-dimensional magnetic nano-particles, the Janus two-dimensional magnetic nano-particles can obviously reduce toluene/water interface tension, and the influence of the Janus two-dimensional magnetic nano-particles on an oil/water interface is analyzed.

The magnetism of the Janus two-dimensional magnetic nano-particles is measured by adopting VSM, the saturation magnetization (Ms) of the Janus two-dimensional magnetic nano-particles is 48.9emu/g at room temperature, and the Janus two-dimensional magnetic nano-particles can be separated from liquid within 60 seconds under the action of an external magnetic field.

The Janus two-dimensional magnetic nanoparticle prepared by the method can be used for further preparing Pickering emulsion, and can be prepared according to the following method:

dispersing the Janus two-dimensional magnetic nano particles in a mixed system of an oil phase and a water phase, and obtaining the Janus two-dimensional magnetic nano particles after dispersion;

the volume ratio of the oil phase to the water phase is 1:1 to 2;

in the mixed system, the mass fraction of the Janus two-dimensional magnetic nano particles is 0.5-2 wt%.

The oil phase is dodecane, n-hexane, dichloromethane or butyl butyrate, namely the Janus two-dimensional magnetic nano particles can form stable emulsion with dodecane and n-hexane with weak polarity, and can also form emulsion with dichloromethane even butyl butyrate with slightly strong polarity.

Compared with the prior art, the Janus two-dimensional magnetic nano particles are prepared by an interface protection method, and have the excellent properties of Janus sheet materials and special magnetic responsiveness, so that the formed emulsion is easier to recycle. The high-stability Pickering emulsion formed by Janus two-dimensional magnetic nano particles is expected to play a larger role in the fields of chemical oil displacement, recovery efficiency improvement and the like.

Drawings

FIG. 1 is a TEM image of two-dimensional magnetic nanoparticles at different reaction temperatures (FIG. 1 (a) 40 ℃, FIG. 1 (b) 50 ℃, FIG. 1 (c) 60 ℃, FIG. 1 (d) 70 ℃, FIG. 1 (e) 80 ℃).

FIG. 2 is a graph showing the average particle diameter of two-dimensional magnetic nanoparticles as a function of reaction temperature.

FIG. 3 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different reaction temperatures.

FIG. 4 is a TEM image of two-dimensional magnetic nanoparticles at different stirring speeds (FIG. 4 (a) 200rpm, FIG. 4 (b) 300rpm, FIG. 4 (c) 400rpm, FIG. 4 (d) 500rpm, FIG. 4 (e) 600 rpm).

Fig. 5 is a graph showing the change of the average particle diameter of two-dimensional magnetic nanoparticles with stirring speed.

FIG. 6 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different stirring speeds.

Fig. 7 is a TEM image of two-dimensional magnetic nanoparticles at different reaction times (fig. 7 (a) 1h, fig. 7 (b) 2h, fig. 7 (c) 3h, fig. 7 (d) 4h, fig. 7 (e) 5 h).

Fig. 8 is a graph showing the change of the average particle diameter of two-dimensional magnetic nanoparticles with the reaction time.

FIG. 9 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different reaction times.

FIG. 10 shows the difference of Fe ²⁺ TEM image of two-dimensional magnetic nanoparticles at drop velocity (FIG. 10 (a) 6mL/min, FIG. 10 (b) 4mL/min, FIG. 10 (c) 3mL/min, FIG. 10 (d) 2.4mL/min, FIG. 10 (e) 2 mL/min).

FIG. 11 shows the average particle size of two-dimensional magnetic nanoparticles with Fe ²⁺ A graph of the change in drop acceleration.

FIG. 12 shows the difference of Fe ²⁺ Particle size distribution of two-dimensional magnetic nanoparticles at drop acceleration.

FIG. 13 shows the difference of Fe ²⁺ TEM image of two-dimensional magnetic nanoparticles at concentration (FIG. 13 (a) 0.048mol/L, FIG. 13 (b) 0.096mol/L, FIG. 13 (c) 0.144mol/L, FIG. 13 (d) 0.192 mol/L).

FIG. 14 shows the average particle size of two-dimensional magnetic nanoparticles with Fe ²⁺ Concentration profile.

FIG. 15 shows the difference of Fe ²⁺ Particle size distribution of two-dimensional magnetic nanoparticles at concentration.

FIG. 16 is a TEM image of two-dimensional magnetic nanoparticles at different precipitant concentrations (FIG. 16 (a) 0.09mol/L, FIG. 16 (b) 0.18mol/L, FIG. 16 (c) 0.27mol/L, and FIG. 16 (d) 0.36 mol/L).

Fig. 17 is a graph showing the change of the average particle diameter of two-dimensional magnetic nanoparticles with the concentration of precipitant.

FIG. 18 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different precipitant concentrations.

FIG. 19 is a TEM image of two-dimensional magnetic nanoparticles at different electrostatic stabilizer concentrations (FIG. 19 (a) 0.45mol/L, FIG. 19 (b) 0.9mol/L, FIG. 19 (c) 1.35mol/L, FIG. 19 (d) 1.8 mol/L).

Fig. 20 is a graph of average particle size of two-dimensional magnetic nanoparticles as a function of electrostatic stabilizer concentration.

FIG. 21 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different concentrations of electrostatic stabilizer.

Fig. 22 is an XRD spectrum of two-dimensional magnetic nanoparticles at different stirring speeds.

Fig. 23 is an XRD spectrum of two-dimensional magnetic nanoparticles at different reaction temperatures.

Fig. 24 is a HRTEM image, FFT (upper left corner) and a partial magnified view of two-dimensional magnetic nanoparticles.

FIG. 25 is an XPS spectrum of Fe2p, O1s of two-dimensional magnetic nanoparticles.

FIG. 26 is an infrared spectrum of two-dimensional magnetic nanoparticles.

Fig. 27 is an AFM image of two-dimensional magnetic nanoparticles.

Fig. 28 is the thickness of line segments between the line segments in the AFM graph (between fig. 28 (a) a to B, between fig. 28 (B) C to D, and between fig. 28 (C) E to F).

Fig. 29 is a TEM image of two-dimensional magnetic nanoparticles.

Fig. 30 is an AFM 3D view of two-dimensional magnetic nanoparticles.

Fig. 31 is a hysteresis loop of a two-dimensional magnetic nanoparticle.

FIG. 32 is a photograph of a two-dimensional magnetic nanoparticle magnetic separation process (after 1min of ultrasound in FIG. 32 (a), 15s of magnet separation in FIG. 32 (b), 30s of magnet separation in FIG. 32 (c)).

FIG. 33 is a schematic diagram of Janus two-dimensional magnetic nanoparticle synthesis.

Fig. 34 is an SEM image of paraffin spheres formed of two-dimensional magnetic nanoparticles (6000 x in fig. 34 (b), 12000x in fig. 34 (c)).

Fig. 35 is a TEM image of Janus two-dimensional magnetic nanoparticles.

Fig. 36 is a HRTEM image of Janus two-dimensional magnetic nanoparticles.

FIG. 37 is an infrared spectrum of Janus two-dimensional magnetic nanoparticles.

Fig. 38 shows the elemental distribution and composition of the surface of Janus two-dimensional magnetic nanoparticles.

Fig. 39 is a photograph of the water contact angle of Janus two-dimensional magnetic nanoparticles (fig. 39 (a) hydrophilic side, fig. 39 (b) hydrophobic side).

FIG. 40 is an interfacial tension of Janus two-dimensional magnetic nanoparticles.

FIG. 41 is a graph showing the effect of Janus two-dimensional magnetic nanoparticles on oil-water interface (toluene/water mixture in glass vessel of FIG. 41 (a), janus Fe at toluene/water interface after injection of FIG. 41 (b) ₃ O ₄ FIG. 41 (c) is a view showing the formation of an interface film and a climbing film after shaking; FIG. 41 (d) dichloromethane/water mixture in glass vessel, FIG. 41 (e) Janus Fe at dichloromethane/water interface after injection ₃ O ₄ FIG. 41 (f) is a view showing the formation of an interface film and a climbing film after shaking.

FIG. 42 shows the deformation of an interfacial film formed by Janus two-dimensional magnetic nanoparticles (FIG. 42 (a) inserted into a capillary, FIG. 42 (b) magnet attraction, and FIG. 42 (c) after magnet removal).

Fig. 43 is a hysteresis loop of a Janus two-dimensional magnetic nanoparticle.

FIG. 44 is a photograph of a Janus two-dimensional magnetic nanoparticle magnetic separation process (after 1min of ultrasound in FIG. 44 (a), after 30s of magnet separation in FIG. 44 (b), after 60s of magnet separation in FIG. 44 (c)).

FIG. 45 is an optical microscopy image of Pickering emulsion prepared with Janus two-dimensional magnetic nanoparticles of different mass fractions and dodecane (FIG. 45 (a) 0.5wt%, FIG. 45 (b) 1.0wt%, FIG. 45 (c) 1.5wt%, FIG. 45 (d) 2.0 wt%).

Fig. 46 is an optical microscope image of Pickering emulsion prepared with Janus two-dimensional magnetic nanoparticles and different oil phases (fig. 46 (a) dodecane, fig. 46 (b) n-hexane, fig. 46 (c) dichloromethane, fig. 46 (d) butyl butyrate).

Detailed Description

The experimental methods used in the following examples are conventional methods unless otherwise specified.

Materials, reagents and the like used in the examples described below are commercially available unless otherwise specified.

Example 1 preparation of two-dimensional magnetic nanoparticles

0.4g of sodium hydroxide and 4.1g of anhydrous sodium acetate are weighed into a beaker, 55g of deionized water is added into the beaker to prepare a solution, and the solution is transferred into a four-neck flask after ultrasonic dissolution. The four-neck flask is placed in a water bath kettle with the temperature of 60 ℃, the mechanical stirring rotating speed is set to be 500rpm, the reaction temperature is 60 ℃, and the reaction time is 2 hours. 1.6g FeSO was weighed out ₄ ·7H ₂ O is placed in a beaker, 60g of deionized water is added into the beaker to prepare a solution, the solution is transferred into a 60mL syringe after ultrasonic dissolution, the syringe is placed on a constant flow pump, the dripping time of the constant flow pump is set to be 25min, and the solution is gradually pushed into a four-neck flask. After the reaction is finished, the black two-dimensional magnetic nano particles are collected and separated by a magnet, and the obtained black two-dimensional magnetic nano particles are washed by deionized water and absolute ethyl alcohol for a plurality of times. And (5) placing the product in a freeze dryer, freeze-drying for 24 hours, collecting the product, and measuring.

The reaction temperature, stirring speed, reaction time and Fe were examined below ²⁺ Drop acceleration, fe ²⁺ Influence of concentration, precipitant concentration, electrostatic stabilizer concentration on morphology and size of two-dimensional magnetic nanoparticles.

Example 2 influence of reaction temperature on morphology and size of two-dimensional magnetic nanoparticles

The temperature is an important influencing factor of crystal formation, and as the temperature is continuously increased, the heat supplied per unit time is continuously increased, so that the temperature is beneficial to crossing the reaction energy barrier and accelerating the crystal formation. Under the same conditions (stirring speed 500rpm, reaction time 2h, fe) ²⁺ Dropping speed is 2.4mL/min, fe ²⁺ The concentration is 0.096mol/L, and the concentration of the precipitant0.18mol/L and the concentration of the electrostatic stabilizer is 0.9 mol/L), only the reaction temperature in the preparation process of the two-dimensional magnetic nano-particles is changed, and the two-dimensional magnetic nano-particles are prepared at five different reaction temperatures (40 ℃,50 ℃,60 ℃,70 ℃ and 80 ℃).

Fig. 1 is a transmission electron micrograph of two-dimensional magnetic nanoparticles at different reaction temperatures, and fig. 2 is a graph showing the change of the average particle diameter of the two-dimensional magnetic nanoparticles with the reaction temperature. As can be seen from fig. 1 and 2, the particle size of the two-dimensional magnetic nanoparticles gradually increases with an increase in the reaction temperature. When the reaction temperature was 40 ℃, the resulting product was mostly large agglomerate, and had no regular shape (FIG. 1 (a)). As shown in fig. 1 (b) and 1 (c), with the increasing temperature, hexagonal-shaped nanoplatelets appear, and when the temperature reaches 60 ℃, the two-dimensional magnetic nanoparticles are regular in shape and uniform in size. As the reaction temperature continues to increase, the shape of the two-dimensional magnetic nanoparticles remains mostly hexagonal in structure, but the particle size varies (fig. 1 (d) and fig. 1 (e)). The average particle diameters at 40℃and 50℃and 60℃and 70℃and 80℃correspond to 25.59nm,37.90nm,46.74nm,48.74nm and 50.65nm, respectively, and the change in the average particle diameters can be confirmed again. In order to accurately know the particle size distribution of the nano particles in the system, the particle size is subjected to statistical analysis. The particle size distribution of the two-dimensional magnetic nanoparticles at different reaction temperatures is shown in fig. 3. As seen in fig. 3, the particle size distribution of the nanoparticles gradually increased with increasing reaction temperature, which is consistent with the transmission electron microscope observation.

Through analysis of TEM images and particle size distribution of the two-dimensional magnetic nanoparticles at different reaction temperatures, the two-dimensional magnetic nanoparticles are regular in shape and relatively uniform in particle size at the reaction temperature of 60 ℃, and the reaction temperature is finally determined to be 60 ℃.

Example 3 influence of stirring speed on morphology and size of two-dimensional magnetic nanoparticles

During nucleation of crystals, there is a higher energy barrier. Different stirring speeds can provide different energies in the reaction process, and the input of external energy can accelerate the rapid formation of crystal nuclei, so that stirring is performedSpeed is also an important factor in the formation of crystals. Under the same conditions (reaction temperature 60 ℃, reaction time 2h, fe ²⁺ Dropping speed is 2.4mL/min, fe ²⁺ The concentration was 0.096mol/L, the concentration of the precipitant was 0.18mol/L, and the concentration of the electrostatic stabilizer was 0.9mol/L, and the two-dimensional magnetic nanoparticles were prepared at five different stirring speeds (200 rpm,300rpm,400rpm,500rpm,600 rpm) by changing only the stirring speed during the preparation of the two-dimensional magnetic nanoparticles.

Fig. 4 is a transmission electron micrograph of two-dimensional magnetic nanoparticles at different stirring speeds, and fig. 5 is a graph showing the change of average particle diameter of two-dimensional magnetic nanoparticles with stirring speed. As can be seen from fig. 4 and 5, the particle size of the two-dimensional magnetic nanoparticles overall shows a tendency to gradually decrease with increasing stirring speed. As shown in fig. 4 (a), at a stirring speed of 200rpm, the generated nanoparticles were regular in shape, and the morphology was hexagonal, but different sizes were present, and there were cases where different nanoparticles were grown together. At 300rpm, it can still be seen that the particle size distribution of the two-dimensional magnetic nanoparticles is relatively large, and there is still a case where different nanoparticles are combined together during growth (fig. 4 (b)). As can be seen from fig. 4 (c) and 4 (d), with further increase of the stirring speed, the two-dimensional magnetic nanoparticles were regular in shape and relatively uniform in size at 400,500 rpm, and the particle size distribution of the nanoparticles tended to decrease. As can be seen from fig. 4 (e), when the stirring speed was increased to 600rpm, it was found that the difference in the particle size of the two-dimensional magnetic nanoparticles was further reduced and spherical particles were present. Further, the change of the average particle diameter of the two-dimensional magnetic nanoparticles with stirring speed was examined, and the results are shown in fig. 5. At 200rpm,300rpm,400rpm,500rpm,600rpm, the average particle diameters thereof were respectively 62.88nm,60.50nm,59.09nm,46.74nm,39.12nm. As can be seen from the variation of the average particle size, the average particle size of the magnetic nanoparticles prepared under the variation of the stirring speed is continuously reduced with the increase of the stirring speed. FIG. 6 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different stirring speeds. As can be seen from fig. 6, as the stirring speed increases, the particle size distribution of the two-dimensional magnetic nanoparticles also becomes smaller as it goes up, which is consistent with the result of the transmission electron microscopy.

Overall, with the increase of the stirring rotation speed, the external input energy is continuously increased, and the crystallization rate is accelerated, so that the nano particles are quickly nucleated. Resulting in relatively less nucleation of crystals at low rotational speeds, and therefore larger particle sizes, a broader particle size distribution, and the presence of different nanoparticle growth polymerizations. Therefore, under the condition that the stirring rotation speed is continuously increased, the particle size of the magnetic nano-sheets is gradually reduced, and the particle size distribution is gradually reduced. When the rotation speed reaches a certain degree, the growth crystal face of the nano-particles changes, which is beneficial to the co-growth of each crystal face, thereby leading to the appearance of spherical nano-particles. From the results of analysis of the influence of the stirring speed on the two-dimensional magnetic nanoparticles, it was found that the two-dimensional magnetic nanoparticles were regular in shape at a stirring speed of 500rpm, most of the particles were hexagonal in shape and relatively uniform in size, and finally, the stirring speed was preferably 500rpm.

Example 4 influence of reaction time on morphology and size of two-dimensional magnetic nanoparticles

The reaction time is also an important factor affecting the crystal growth, and as the reaction time increases, there may be an oswald ripening effect, so that the reaction of the nanoparticles between the solid and liquid interfaces is reversible, resulting in a large change in the morphology of the two-dimensional magnetic nanoparticles. Under the same conditions (reaction temperature 60 ℃, stirring speed 500rpm, fe) ²⁺ Dropping speed is 2.4mL/min, fe ²⁺ The concentration is 0.096mol/L, the concentration of the precipitant is 0.18mol/L, the concentration of the electrostatic stabilizer is 0.9mol/L, and the two-dimensional magnetic nano particles are prepared under five different reaction times (1 h,2h,3h,4h and 5 h) by only changing the reaction time in the preparation process of the two-dimensional magnetic nano particles.

Fig. 7 is a transmission electron micrograph of two-dimensional magnetic nanoparticles at different reaction times, and fig. 8 is a graph showing the average particle diameter of two-dimensional magnetic nanoparticles over time. As can be seen from fig. 7 and 8, the particle size of the two-dimensional magnetic nanoparticles overall shows a tendency to gradually increase with increasing reaction time. As can be seen from fig. 7 (a), at a reaction time of 1h, the shape of the produced nanoparticle is relatively regular, and is mostly a hexagonal structure, uniform in size, and smaller in the whole particle, but there are also many products like a rod structure. When the reaction time was 2h, it was found that most of the obtained products were hexagonal in shape, increased in particle size and distribution compared with 1h nanoparticles, and relatively few products were in a rod-like or spherical structure (fig. 7 (b)). As shown in fig. 7 (c), (d), and (e), as the reaction time continues to increase, the particle size of the magnetic nanoparticles gradually increases and the particles are relatively uniform. The resulting product contains a large amount of rod-like, spherical nanoparticles, although nanoparticles with a two-dimensional lamellar structure are present in the product. As shown in FIG. 8, the relationship between the average particle diameter of the two-dimensional magnetic nanoparticles and the reaction time was further examined, and the average particle diameters thereof were 38.29nm,46.74nm,47.67nm,48.74nm and 50.16nm at the reaction times of 1h,2h,3h,4h and 5h, respectively. As can be seen from the change of the average particle size with the reaction time, the average particle size of the magnetic nanoparticles is continuously increased with the increase of the reaction time. When the reaction time is 2 hours, the particle size of the generated magnetic nano particles is obviously increased compared with that of the magnetic nano particles subjected to the reaction for 1 hour, and after the reaction time is 2 hours, the average particle size is still in an increasing trend, but the average particle size is not quite different. FIG. 9 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different reaction times. As shown in fig. 9, the particle size distribution of the two-dimensional magnetic nanoparticles shows a tendency to increase and decrease. When the reaction time reached 3 hours, the particle size distribution was not very different.

According to analysis of a two-dimensional magnetic nanoparticle TEM image and a particle size distribution diagram, when the reaction time is 2h, most of products are hexagonal and regular in shape, and finally the reaction time is 2h, and on the basis, the influence of other conditions on the products is examined.

Example 5, fe ²⁺ Influence of the drop acceleration on the morphology and size of two-dimensional magnetic nanoparticles

In the process of synthesizing the two-dimensional magnetic nano particles, a constant flow pump is adopted to realize the preparation of Fe ²⁺ Accurate drop accelerationAnd (5) controlling. Thus, in addition to considering the conventional influencing factors on nanoparticle formation, fe was also examined ²⁺ Impact of drop acceleration on two-dimensional magnetic nanoparticle growth. Under the same conditions (reaction temperature 60 ℃, stirring speed 500rpm, reaction time 2h, fe) ²⁺ The concentration is 0.096mol/L, the concentration of the precipitant is 0.18mol/L, the concentration of the static stabilizer is 0.9 mol/L), and only Fe in the preparation process of the two-dimensional magnetic nano particles is changed ²⁺ Drop acceleration, at five different Fe ²⁺ Two-dimensional magnetic nanoparticles were prepared at a dropping rate (6 mL/min,4mL/min,3mL/min,2.4mL/min,2 mL/min).

FIG. 10 shows two-dimensional magnetic nanoparticles at different Fe ²⁺ FIG. 2.12 is a transmission electron micrograph of two-dimensional magnetic nanoparticles with average particle size as Fe at the dropping speed ²⁺ A graph of the change in drop acceleration. As shown in fig. 10 and 11, with Fe ²⁺ The decrease in the drop velocity, the particle size of the two-dimensional magnetic nanoparticles as a whole tends to gradually increase. As can be seen from FIG. 10 (a), in Fe ²⁺ When the dropping speed is 6mL/min, the generated magnetic nano particles have different shapes, have a hexagonal structure, also have a triangular structure and a linear structure, and are relatively smaller. When Fe is ²⁺ When the dropping speed was 4mL/min and 3mL/min, it was found that the reaction product was Fe ²⁺ The drop velocity is reduced, and the particle size of the obtained magnetic nanoparticles is increased, but more spherical particles still exist. At Fe ²⁺ When the drop acceleration was 3mL/min, many rod-like structures were present (FIG. 10 (b) and FIG. 10 (c)). With Fe ²⁺ Further reduction of the drop velocity, as can be seen from fig. 10 (d) and 10 (e), the particle size of the magnetic nanoparticles gradually increases, and the resultant product is mostly nanoparticles of two-dimensional lamellar structure, regular in shape, and relatively good in dispersibility. As shown in FIG. 11, the average particle size of two-dimensional magnetic nanoparticles was examined as Fe ²⁺ Change in drop acceleration. At Fe ²⁺ The drop acceleration was 6mL/min,4mL/min,3mL/min,2.4mL/min, and the average particle diameters were 39.41nm,41.87nm,44.21nm,46.74nm, and 48.00nm, respectively, at 2 mL/min. As can be seen from the results of the variation in the average particle diameter, the average particle diameter of the magnetic nanoparticles Diameter along with Fe ²⁺ The drop acceleration decreases and increases continuously. FIG. 12 shows the difference of Fe ²⁺ The particle size distribution of the two-dimensional magnetic nanoparticles at the dropping speed is shown in FIG. 12, and it can be seen that the following Fe ²⁺ The drop acceleration is reduced, and the particle size distribution of the two-dimensional magnetic nanoparticles tends to increase.

From the above results, it can be seen that as Fe ²⁺ Drop acceleration reduction, fe in unit time ²⁺ The concentration decreases, resulting in a decrease in the nucleation rate of the nanoparticles. Less nucleation per unit time, more Fe ²⁺ Acting on already nucleated nanoparticles causes a gradual increase in the particle size and also a larger particle size distribution. With Fe ²⁺ The drop acceleration is reduced, and the formed magnetic nano particles are regular in shape and mostly have a two-dimensional lamellar structure. Overall, when Fe ²⁺ When the dropping speed is 2.4mL/min, the produced product is mostly of a two-dimensional lamellar structure, the shape is regular, the distribution is uniform, and finally Fe is determined ²⁺ The dropping speed was 2.4mL/min.

Example 6, fe ²⁺ Influence of concentration on morphology and size of two-dimensional magnetic nanoparticles

In example 5, fe was found to be involved in ²⁺ The shape and the size of the two-dimensional magnetic nano particles are obviously changed due to the change of the drop acceleration. From this, fe is seen ²⁺ Has larger influence on the morphology and the size of the two-dimensional magnetic nano particles, thus further investigating Fe ²⁺ Effect of concentration on two-dimensional magnetic nanoparticle growth. Under the same conditions (reaction temperature 60 ℃, stirring speed 500rpm, reaction time 2h, fe) ²⁺ The dropping speed is 2.4mL/min, the concentration of the precipitant is 0.18mol/L, the concentration of the static stabilizer is 0.9mol/L, and only Fe in the preparation process of the two-dimensional magnetic nano particles is changed ²⁺ Concentration at four different Fe ²⁺ Two-dimensional magnetic nanoparticles were prepared at concentrations (0.048 mol/L,0.096mol/L,0.144mol/L,0.192 mol/L).

FIG. 13 shows two-dimensional magnetic nanoparticles at different Fe ²⁺ FIG. 14 is a transmission electron micrograph of the average particle diameter of two-dimensional magnetic nanoparticles as Fe at a concentration ²⁺ Concentration profile. As shown in fig. 13 and 14The particle size of the two-dimensional magnetic nanoparticles follows the Fe ²⁺ The increase in concentration showed a tendency to gradually increase. As shown in FIG. 13 (a), when Fe ²⁺ At a concentration of 0.048mol/L, the magnetic nanoparticles produced have relatively small particle diameters and various shapes, and have a certain two-dimensional lamellar structure, but have many rod-like and wire-like structures. As shown in FIG. 13 (b), when Fe ²⁺ When the concentration is 0.096mol/L, the particle size of the obtained magnetic nanoparticles becomes large, and the shape is a two-dimensional lamellar structure and is regular. As shown in FIG. 13 (c) and FIG. 13 (d), when Fe ²⁺ When the concentration is further increased to 0.144 or 0.192mol/L, the particle diameter of the nanoparticle is further increased, and the nanoparticle is different in shape and has a large number of spherical particles. As shown in FIG. 14, in Fe ²⁺ The average particle diameters at the concentrations of 0.048mol/L,0.096mol/L,0.144mol/L and 0.192mol/L were 29.88nm,46.74nm,55.53nm and 59.84nm, respectively. It can be seen that the Fe is different ²⁺ The average particle diameter of the magnetic nano particles prepared under the concentration is along with Fe ²⁺ The concentration increases continuously. Compared with Fe ²⁺ Magnetic nanoparticles formed at a concentration of 0.048mol/L, when Fe ²⁺ When the concentration is 0.096mol/L, the particle size change is larger, the difference of the average particle size is 16.86nm, and the Fe is continuously increased ²⁺ Concentration and particle size change were slowed down. FIG. 15 shows the effect of Fe at different levels ²⁺ As can be seen from FIG. 15, the particle size distribution of the two-dimensional magnetic nanoparticles at the concentration, as Fe ²⁺ The particle size distribution of the two-dimensional magnetic nanoparticles tends to increase with increasing concentration.

By reacting different Fe ²⁺ When the analysis of the TEM image and the particle size distribution image of the two-dimensional magnetic nano particles under the concentration shows that Fe ²⁺ When the concentration is 0.096mol/L, the shape of the product is a two-dimensional lamellar structure, the shape is regular, and finally Fe is determined ²⁺ The concentration was 0.096mol/L.

Example 7 Effect of precipitant concentration on two-dimensional magnetic nanoparticle morphology and size

In the process of crystal formation, the concentration of the precipitant has certain influence on nucleation and growth, and the influence of the concentration of the precipitant on the morphology and the size of the two-dimensional magnetic nano particles is examined in the embodiment. Under the condition that other conditions are the same(reaction temperature 60 ℃, stirring speed 500rpm, reaction time 2h, fe) ²⁺ Dropping speed is 2.4mL/min, fe ²⁺ The concentration is 0.096mol/L, the concentration of the electrostatic stabilizer is 0.9 mol/L), the concentration of the precipitant is only changed in the preparation process of the two-dimensional magnetic nano-particles, and the two-dimensional magnetic nano-particles are prepared under four different precipitant concentrations (0.09 mol/L,0.18mol/L,0.27mol/L and 0.36 mol/L).

Fig. 16 is a transmission electron micrograph of two-dimensional magnetic nanoparticles at different precipitant concentrations, and fig. 17 is a graph of the average particle size of the two-dimensional magnetic nanoparticles as a function of precipitant concentration. As can be seen from fig. 16 and 17, the particle size of the two-dimensional magnetic nanoparticles shows a tendency to gradually decrease with increasing concentration of the precipitant. When the concentration of the precipitant was 0.09mol/L, the magnetic nanoparticles produced had a larger particle diameter and a larger particle diameter distribution than those of nanoparticles under other conditions, and from the electron micrograph, there was a certain two-dimensional lamellar structure, but there was still a large number of spherical structures (FIG. 16 (a)). When the concentration of the precipitant is 0.18mol/L, the particle size of the obtained magnetic nanoparticle becomes small, and the shape is mostly a two-dimensional lamellar structure, and the shape is regular (FIG. 16 (b)). When the concentration of the precipitant was further increased to 0.27, 0.36mol/L, the magnetic nanoparticles continued to show a decreasing trend in particle size and varied in shape, had spherical, flaky, rod-like shapes, and had severe agglomeration (FIGS. 16 (c) and 16 (d)). As shown in FIG. 2.18, the average particle diameters at the precipitant concentrations of 0.09mol/L,0.18mol/L,0.27mol/L and 0.36mol/L were 58.96nm,46.74nm,41.86nm and 36.72nm, respectively. It can be seen that the average particle size of the magnetic nanoparticles decreases with increasing concentration of precipitant. Fig. 18 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different precipitant concentrations, and it can be seen from fig. 18 that the particle size distribution of two-dimensional magnetic nanoparticles gradually decreases with increasing precipitant concentration.

The magnetic nano particles gradually decrease along with the increase of the concentration of the precipitant, and the agglomeration is more and more obvious. When the concentration of the precipitant is low, OH in the solution ^- Relatively less, only part of the metal ions are combined with OH ^- To form crystal nucleus, the rest metal ion acts on the crystal surface, and thenThe growth rate of the fast nanoparticles. At this time, the growth rate is greater than the nucleation rate, and the nanoparticles tend to grow, eventually making the particle size of the nanoparticles larger. Conversely, when the precipitant concentration is relatively high, a large amount of OH ^- The nucleation rate is greater than the growth rate when the nanoparticles tend to nucleate and grow slowly, eventually making the particle size of the nanoparticles smaller. In addition, as the concentration of the precipitant increases, the particle size of the generated magnetic nanoparticles decreases, and the specific surface energy of the magnetic nanoparticles increases, resulting in significant agglomeration. When the concentration of the precipitant is large, OH in the solution ^- More, there is part of OH ^- The magnetic nano particles are adsorbed on the surfaces of the magnetic nano particles, so that the surfaces of the nano particles have certain negative charges, and the possibility of agglomeration of the magnetic nano particles is increased due to the existence of electrostatic action. When the concentration of the precipitant is 0.18mol/L, the particle size of the obtained magnetic nano particles is small, the shape of the product is a two-dimensional lamellar structure, the shape is regular, and the concentration of the precipitant is finally determined to be 0.18mol/L.

Example 8 influence of the concentration of the electrostatic stabilizer on the morphology and size of two-dimensional magnetic nanoparticles

In order to determine the effect of the concentration of the electrostatic stabilizer on the morphology and the size of the magnetic nanoparticles, the present example examined the effect of different electrostatic stabilizer concentrations on the morphology and the size of the two-dimensional magnetic nanoparticles. Under the same conditions (reaction temperature 60 ℃, stirring speed 500rpm, reaction time 2h, fe) ²⁺ Dropping speed is 2.4mL/min, fe ²⁺ The concentration is 0.096mol/L, the concentration of the precipitant is 0.9 mol/L), the concentration of the electrostatic stabilizer in the preparation process of the two-dimensional magnetic nano-particles is only changed, and the two-dimensional magnetic nano-particles are prepared under four different electrostatic stabilizer concentrations (0.45 mol/L,0.9mol/L,1.35mol/L and 1.8 mol/L).

Fig. 19 is a transmission electron micrograph of two-dimensional magnetic nanoparticles at different concentrations of electrostatic stabilizer, and fig. 20 is a graph showing the average particle size of two-dimensional magnetic nanoparticles as a function of the concentration of electrostatic stabilizer. As shown in fig. 19 and 20, the particle size of the two-dimensional magnetic nanoparticles exhibited a change of decreasing followed by increasing with increasing concentration of the electrostatic stabilizer. As shown in FIG. 19 (a), when the electrostatic stabilizer concentration was 0.45mol/L, it was found from the TEM image that the magnetic nanoparticles produced had a larger particle diameter, a relatively small number of two-dimensional plate-like structures, and a large number of spherical structures. As shown in FIG. 19 (b), when the electrostatic stabilizer concentration is 0.9mol/L, the magnetic nanoparticles produced at this time have a large particle size, and the shape is generally a two-dimensional sheet structure and is regular. When the electrostatic stabilizer concentration was further increased to 1.35mol/L, the particle size of the magnetic nanoparticles showed a tendency to decrease, and from the morphology of the magnetic nanoparticles, there were only few two-dimensional platelet particles, mostly spherical particles. When the concentration reached 1.8mol/L, the magnetic nanoparticle particle diameters tended to increase, and the shapes were spherical, with almost no two-dimensional lamellar structure (FIGS. 19 (c) and 19 (d)). As shown in FIG. 20, the average particle diameters at the precipitant concentrations of 0.45mol/L,0.9mol/L,1.35mol/L and 1.8mol/L were 48.04nm,46.74nm,44.55nm and 49.64nm, respectively. It can also be seen from the variation of the average particle size that the average particle size of the two-dimensional magnetic nanoparticles tends to decrease and then increase with increasing concentration of the electrostatic stabilizer.

Fig. 21 is a graph showing the particle size distribution of two-dimensional magnetic nanoparticles at different concentrations of electrostatic stabilizer, and it can be seen from fig. 21 that the particle size distribution of two-dimensional magnetic nanoparticles is not significantly regular as the concentration of electrostatic stabilizer increases. This is because increasing the concentration of the electrostatic stabilizer can increase the nucleation and growth rate of the magnetic nanoparticles. In addition, as the electrostatic stabilizer further increased, the shape of the nanoparticles also changed, and when the concentration reached 1.35mol/L, the growth crystal plane had changed, forming spherical nanoparticles, and when the concentration reached 1.8mol/L, almost all spherical nanoparticles had almost no nanoplatelets formed. This is mainly due to the fact that increasing the concentration of sodium acetate accelerates the growth rate of the two-dimensional magnetic nanoparticles, changes the growth direction of the magnetic nanoparticles, and results in the generation of spherical nanoparticles. According to analysis of the morphology and the particle size of the two-dimensional magnetic nano particles under different electrostatic stabilizer concentrations, when the electrostatic stabilizer concentration is 0.9mol/L, the generated products are regular in shape and similar in structure, and finally the electrostatic stabilizer concentration is 0.9mol/L.

Example 9 two-dimensional magnetic nanoparticle phase and Crystal form structural analysis

(1) X-ray diffraction analysis (XRD)

The above examples examined the effect of different reaction conditions on the morphology and size of two-dimensional magnetic nanoparticles, while defining the optimal preparation conditions. Aiming at the magnetic nano particles synthesized under different conditions, the magnetic nano particles with more sheet structures are selected for XRD test, and further phase analysis is carried out on the two-dimensional magnetic nano particles. Fig. 22 and 23 are XRD patterns of two-dimensional magnetic nanoparticles at different stirring speeds and XRD patterns of two-dimensional magnetic nanoparticles at different reaction temperatures, respectively. As shown in FIGS. 22 and 23, there are eight characteristic diffraction peaks on XRD patterns of two-dimensional magnetic nanoparticles, and the positions and intensities of the respective characteristic diffraction peaks are equal to those of Fe ₃ O ₄ The standard patterns (JCPDS No. 88-0315) of the two-dimensional magnetic nano particles are consistent, wherein eight characteristic diffraction peaks (2 theta = 30.157 degrees, 35.521 degrees, 37.157 degrees, 43.172 degrees, 53.561 degrees, 57.098 degrees, 62.703 degrees, 74.186 degrees) correspond to diffraction crystal faces of the two-dimensional magnetic nano particles which are (220), (311), (222), (400), (422), (511), (440), (533) respectively, no other redundant peaks appear, diffraction characteristic peaks of all samples are strong and sharp, and the purity of the prepared two-dimensional magnetic nano particles is higher, and the prepared two-dimensional magnetic nano particles have better crystallinity.

In addition, the observation of the spectrogram can show that diffraction peaks at different temperatures and different stirring speeds can be well corresponding to the standard spectrogram, which indicates that the magnetic nano particles prepared at different temperatures and different stirring speeds are all Fe ₃ O ₄ . As a whole, as the stirring speed increases, the diffraction characteristic peak is sharper and higher, and when the stirring speed is 500rpm, the diffraction characteristic peak is sharper, and the influence of the reaction temperature on the crystallinity of the magnetic nanoparticles is not obvious.

(2) High Resolution Transmission Electron Microscope (HRTEM)

In the synthesis of bottom-up cubic nanoparticles, the process of growing to form a polyhedron after nucleation is considered to be an important process for initially forming a nanostructure. After nucleation, at different timesThe morphology of the final product obtained is different. Studies have shown that isotropic growth causes concentric rapid growth of the centers of six crystal faces of the crystal nuclei, eventually resulting in disappearance of the crystal faces, thereby forming nanoparticles of spherical structure. Under specific conditions, the (111) face is limited to grow, and finally the product with the (111) face exposed, namely the anisotropic nano-sheet is obtained. In the embodiment, the two-dimensional magnetic nano particles prepared under the optimal condition are selected, and are characterized by adopting HRTEM, and meanwhile, the growth mechanism of the nano sheet is revealed. FIG. 24 is a high resolution transmission electron micrograph (FFT) of two-dimensional magnetic nanoparticles and corresponding fast Fourier transform image (FFT), from which it can be inferred that the lattice spacing of the two-dimensional magnetic nanoparticles formed is about 0.297nm, from which the surface of lattice fringes and Fe can be deduced ₃ O ₄ The crystal faces (220) on the crystal correspond to each other, and further confirm that the synthesized magnetic nano-sheet is Fe ₃ O ₄ . Studies have shown that, in face-centered cubic crystals, all belong to {220} crystal system, six crystal faces are parallel to [111 ]]In the same direction, have the same lattice spacing. And the included angle between adjacent crystal faces is 60 DEG, the direction of the electron beam can point to Fe ₃ O ₄ [111 of (2)]The direction is then the (111) plane. Meanwhile, the synthesized two-dimensional magnetic nano-sheet can be observed to be regular-shaped hexagon from both TEM results and HRTEM results, so that the synthesized two-dimensional magnetic nano-sheet is judged to belong to anisotropic nano-particles.

(3) X-ray photoelectron spectroscopy (XPS)

To further determine the structure and composition of the two-dimensional magnetic nanoparticle composite phase, an X-ray electron spectrometer was used for analysis. The results of the Fe 2p and O1s XPS spectra of the two-dimensional magnetic nanoparticles are shown in FIG. 25. From the figure, fe 2p can be seen _3/2 And Fe 2p _1/2 Binding energies of 710.5eV and 724.6eV, respectively, and O1s of 530.2eV, which are consistent with the data reported in the literatureDetermining the synthesized two-dimensional magnetic nano particles as Fe ₃ O ₄ 。

(4) Infrared spectrum analysis (FT-IR)

FIG. 26 is an infrared spectrum of two-dimensional magnetic nanoparticles. Wherein 580cm ^-1 Characteristic absorption of (C) corresponds to Fe ₃ O ₄ Vibration absorption of the nanoparticle Fe-O. 1605cm ^-1 The water molecules combined on the surface of the product absorb bees, 3433cm ^-1 The absorption peaks in the vicinity are characteristic absorption peaks of water and-OH. In addition to the influence of water molecules, vibration absorption of Fe-O mainly exists in the infrared spectrogram of the two-dimensional magnetic nanoparticles, so that the infrared spectrogram is that the two-dimensional magnetic nanoparticles are Fe ₃ O ₄ Is a powerful demonstration of (a).

Example 10 two-dimensional magnetic nanoparticle thickness analysis

As shown in fig. 27, the thickness of the two-dimensional magnetic nanoparticles was analyzed by means of an atomic force microscope. It can be seen that the surface of the synthesized two-dimensional magnetic nanoparticle is smooth. In order to examine the thicknesses of the two-dimensional magnetic nanoparticles in different ranges, the thicknesses of the nano-sheets on the whole surfaces between A and B are respectively measured, the thicknesses of the nano-sheets between the line segments between C and D and the thicknesses of the nano-sheets between the line segments between E and F penetrating through the whole areas are respectively measured, and the thicknesses of the two-dimensional magnetic nanoparticles are determined by combining the three ranges. As shown in FIG. 28, it can be seen that the distance between A and B is about 4.2nm, the distance between C and D is about 4.6nm, and the distances between the three "steps" between E and F are about 4.5nm, and 4.6nm, respectively. Overall, the thickness of the synthesized two-dimensional magnetic nanoparticles is approximately between 4.2 and 4.6nm.

As shown in fig. 29, the TEM image of the two-dimensional magnetic nanoparticles shows that the thickness of the two inclined nano-sheets is about 4.5nm, and in summary, it can be basically determined that the thickness of the two-dimensional magnetic nanoparticles synthesized by the present invention is about 4.2 to 4.6 nm.

AFM data were further analyzed using NanoScope Analysis software to obtain two-dimensional magnetic nanoparticle surface roughness. In the wide-range (5 μm) AFM image, the root mean square roughness Rq was about 2.18nm, and the surface roughness of the local nanoplatelets was examined, and the root mean square roughness Rq was about 0.28 nm. From the above surface roughness results, it can be seen that the synthesized two-dimensional magnetic nanoparticles were smooth in surface. The AFM 3D diagram is shown in fig. 30. From fig. 30, it can be seen that the thickness of the nano-sheet is uniform, and the height difference of the nano-sheet in the whole area is uniform, which again proves that the surface of the two-dimensional magnetic nano-particle is smooth and the thickness is uniform.

Example 11 two-dimensional magnetic nanoparticle magnetic analysis

Fig. 31 shows the hysteresis loop of two-dimensional magnetic nanoparticles, which exhibits a symmetrical structure. The hysteresis loop was tested in the range-20 k-20k Oe at room temperature. As can be seen from FIG. 31, the saturation magnetization (Ms) of the two-dimensional magnetic nanoparticles is 77.5emu/g, which is close to the saturation magnetization (85-95 emu/g) of the bulk magnetic material, and the saturation magnetization is lower than 85-95 emu/g due to the relatively thin two-dimensional magnetic nanoparticles and the relatively large specific surface area. As can be seen from the partial magnified image, the remanent magnetization (Mr) was 11.2emu/g and the coercivity (Hc) was 106.7Oe, resulting in a two-dimensional magnetic nanoparticle having ferromagnetic behavior. In addition, the coercivity is high, mainly because the anisotropy of the two-dimensional magnetic nanoparticles prevents the crystal from magnetizing in directions other than the easy axis.

FIG. 32 is a photograph of a two-dimensional magnetic nanoparticle magnetic separation process, taking a small amount of two-dimensional magnetic nanoparticles, and fully dispersing them in 4mL of deionized water. Fig. 32 (a) is a photograph of two-dimensional magnetic nanoparticles dispersed in water after shaking and ultrasound for 1min, fig. 32 (b) is a photograph after magnetic separation for 15s, and fig. 32 (c) is a photograph after magnetic separation for 30 s. As can be seen from fig. 32, after the magnet is placed on the right side of the sample dispersion, the two-dimensional magnetic nanoparticles can be attracted to the magnet side quickly, so that the dispersion is clarified, and after the magnet is removed, the vial is gently shaken, and the two-dimensional magnetic nanoparticles are redispersed in the aqueous solution, which indicates that the dispersibility of the two-dimensional magnetic nanoparticles in water is good. The characteristic enables the two-dimensional magnetic nano particles to be rapidly separated from the liquid under the action of an external magnetic field, so that the two-dimensional magnetic nano particles can be recovered and reused, and the cost is reduced.

Example 12 preparation of Janus two-dimensional magnetic nanoparticles

FIG. 33 is a schematic of a synthetic Janus two-dimensional magnetic nanoparticle.

1) The two-dimensional magnetic nano particles synthesized in the example 1 are placed in a reaction vessel, 100mL of water is added, then the two-dimensional magnetic nano particles are placed in an ultrasonic multifunctional experimental machine for ultrasonic treatment for 10min, and after the two-dimensional magnetic nano particles are fully dispersed, the two-dimensional magnetic nano particles are placed in a water bath kettle at 80 ℃, and the mechanical stirring rotating speed is set to 2000rpm. 10g of paraffin wax which had melted was added thereto at this stirring speed, and the above mixed solution was stirred at 80℃and 2000rpm for 20 minutes. And (3) cooling to room temperature, washing with absolute ethyl alcohol for multiple times, washing out the two-dimensional magnetic nano particles which are not adsorbed on the surface of the paraffin ball, and collecting and separating by a magnet to obtain the paraffin ball with the surface adsorbed with the two-dimensional magnetic nano particles.

2) The paraffin pellets thus collected were placed in a reaction vessel, 98mL of ethanol and 2mL of an aqueous solution were added, then the pH of the dispersion was adjusted to 8 to 9 with 0.1mol/L of an aqueous solution of sodium hydroxide, and 2mL of n-octyltriethoxysilane was added in portions at room temperature with a stirring speed of 500rpm, and reacted under these conditions for 20 hours. After the reaction is finished, separating by a magnet, washing with absolute ethyl alcohol for three times, then completely dissolving paraffin balls by cyclohexane, washing with absolute ethyl alcohol for three times again, and collecting a pure sample to obtain Fe ₃ O ₄ @OTES。

3) Fe obtained as described above ₃ O ₄ The @ OTES particles were uniformly dispersed in an aqueous ethanol solution (98 mL of ethanol, 2mL of water), and 1mL of N-aminoethyl-gamma-aminopropyl trimethoxysilane was added in portions at room temperature with stirring at 500rpm, and reacted under these conditions for 20 hours. After the reaction is finished, separating by a magnet, washing for several times by using absolute ethyl alcohol and deionized water successively to obtain Janus two-dimensional magnetic nano particles, and collecting a product to be detected for later use.

1. The present example uses paraffin protection to prepare Janus two-dimensional magnetic nanoparticles. At 80 ℃, the two-dimensional magnetic nano particles can enable paraffin and water to form emulsion, the two-dimensional magnetic nano particles are firmly adsorbed at the oil-water interface of the emulsion, and when the temperature is reduced to room temperature, the two-dimensional magnetic nano particles are distributed on the surface of the solidified paraffin balls. Because the two-dimensional nano particles are sheet-shaped particles, rotation is not easy to occur at an oil-water interface, and therefore, when the paraffin ball is formed, a large cross-sectional area surface is embedded into the paraffin ball, one surface of the nano sheet is protected from being contacted with a modifier, the purpose of selective grafting is achieved, and the Janus two-dimensional magnetic nano particles are finally synthesized.

The present example examined the effect of the amount of two-dimensional magnetic nanoparticles on the surface distribution of paraffin spheres and the microscopic morphology of Janus two-dimensional magnetic nanoparticles.

(1) Influence of the amount of two-dimensional magnetic nanoparticles on the surface distribution of Paraffin spheres

Fig. 34 is a SEM image of paraffin spheres of two-dimensional magnetic nanoparticles and paraffin. The two-dimensional magnetic nano particles and the paraffin balls have stronger contrast, the paraffin balls are relatively darker in color, and the outer layers are lighter and brighter in color, so that the two-dimensional magnetic nano particles are formed. As can be seen from fig. 34, a layer of two-dimensional magnetic nanoparticles is uniformly coated on the surface where the paraffin spheres are formed.

(2) Microscopic morphology analysis of Janus two-dimensional magnetic nanoparticles

FIG. 35 is a TEM image of Janus two-dimensional magnetic nanoparticles, which can be found to have a shell layer with a relatively shallow color, with a thickness of about 3.85nm. Each particle is uniformly coated on a surface with a relatively large cross-sectional area, and the two-dimensional magnetic nano particles are not easy to rotate at an oil-water interface.

Fig. 36 is a high resolution transmission electron micrograph (sem) and corresponding fast fourier transform image (FFT) of Janus two-dimensional magnetic nanoparticles. As can be seen from the partial enlarged view, the lattice spacing of the formed Janus two-dimensional magnetic nano particles is about 0.297nm, and the included angle of the crystal faces is 60 degrees. Positive correspondence with And the included angle between every two planes in the three planes. From this, it can be deduced that the surface of the lattice fringes and Fe ₃ O ₄ The crystal faces (220) on the crystal correspond. The direction of the electron beam may be directed to Fe ₃ O ₄ [111 of (2)]The direction is then the (111) plane. The results obtained in fig. 36 are completely identical to those of two-dimensional magnetic nanoparticles.

2. Analysis of surface chemistry of Janus two-dimensional magnetic nanoparticles

FIG. 37 is an infrared spectrum of Janus two-dimensional magnetic nanoparticles. As can be seen from FIG. 37, 580cm ^-1 The characteristic absorption of the left and right is Fe-O vibration absorption of 1465cm ^-1 C-H bending vibration at 1605cm ^-1 The product surface is water-binding molecule absorbed bee, 2850 cm and 2920cm ^-1 Characteristic absorption at the location corresponds to C-H stretching vibration, 3433cm ^-1 The absorption peaks in the vicinity are characteristic absorption peaks of water and-OH and N-H. By infrared characterization, it can be demonstrated that the silane coupling agent has been successfully grafted onto the two-dimensional magnetic nanoparticles.

And analyzing the Janus two-dimensional magnetic nano-particles by using Mapping element distribution and X-ray energy spectrum, so as to determine the surface chemical composition of the Janus two-dimensional magnetic nano-particles. Fig. 38 is a diagram of element distribution and composition of a Janus two-dimensional magnetic nanoparticle surface. By Mapping scanning, the content distribution of Fe, O, si, C, N element is examined, and as can be seen from fig. 38, the content distribution of C and N before and after the reaction is very obvious, and both can be detected on Janus two-dimensional magnetic nanoparticles. Since the EDX detection depth is about 1 μm, C, N elements are detected on each face. However, it can be seen that C assumes a circular ring shape, while N can be embedded in the ring shape, which is fully compatible with the synthesis and grafting sequence. In the reaction process, firstly, a cap is buckled on the surface with the largest cross-sectional area of the two-dimensional magnetic nano particle, then the N-aminoethyl-gamma-aminopropyl trimethoxysilane is successfully grafted on the other surface, and finally the Janus two-dimensional magnetic nano particle is synthesized. And meanwhile, the N content change of the local point position is inspected by an X-ray energy spectrometer, the N content of the Janus two-dimensional magnetic nano particles is 5.95 percent respectively and is far higher than that of the two-dimensional magnetic nano particles, so that the successful grafting of the N-aminoethyl-gamma-aminopropyl trimethoxysilane to the two-dimensional magnetic nano particles can be deduced. This is also a powerful demonstration of infrared test results. Taken together, it can be demonstrated that Janus two-dimensional magnetic nanoparticles were successfully prepared.

3. Contact angle analysis of Janus two-dimensional magnetic nanoparticles

After the synthesized Janus two-dimensional magnetic nanoparticle dispersion liquid is injected into a toluene/water system and is shaken, the phenomenon that emulsion liquid drops are quickly combined occurs, so that the nano-sheets spontaneously accumulate and an elastic interface film is formed. The amphipathy and the amphiphilicity of the synthesized Janus two-dimensional magnetic nano particles are proved by measuring the contact angle of water. Fig. 39 is a photograph of water contact angle of Janus two-dimensional magnetic nanoparticles, and as can be seen from fig. 39, one side is hydrophilic, the contact angle is about 45 °, and the other side is hydrophobic, and the contact angle is about 117 °. The two sides of the Janus two-dimensional magnetic nanoparticles are significantly different in wettability, indicating that each side of the Janus two-dimensional magnetic nanoparticles has different chemical groups.

4. Interface Properties of Janus two-dimensional magnetic nanoparticles

The interfacial tension of the Janus two-dimensional magnetic nanoparticle is shown in fig. 40. It can be seen that the interfacial tension of toluene and water is about 31.1mN/m, and that Fe is added ₃ O ₄ After that, the interfacial tension was lowered to about 25.2mN/m, indicating Fe ₃ O ₄ Has some influence on the interfacial tension of oil and water. For toluene/water/Janus Fe ₃ O ₄ The system, after toluene droplet formation, follows Janus Fe ₃ O ₄ The interfacial tension is rapidly reduced due to instantaneous assembly at the interface, and then the interfacial tension is reduced at a slow rate, and the final interfacial tension approaches an equilibrium value of 15.1 mN/m. Due to Janus Fe ₃ O ₄ Adsorption at the oil/water interface thus reduces the oil/water interfacial tension more effectively.

Janus two-dimensional magnetic nanoparticles were dropped into oil/water and their effect on the oil/water interface was analyzed. Toluene having a density less than water and methylene chloride having a density greater than water were selected as oil phases, respectively, to exclude the influence of gravity, and the oil phases were stained with sudan III for observation. As shown in fig. 41 (a), 41 (b) and 41 (c), the Janus two-dimensional nanoparticles spontaneously aggregate at the toluene/water interface (fig. 41 (b)) after being dropped into the toluene/water interface, and have a slight wall climbing phenomenon. After shaking, the mixture is stabilized after shaking, and a layer of Janus Fe ₃ O ₄ The thin film of nanoparticles quickly climbs up the inner wall of the container. Janus Fe after equilibration ₃ O ₄ A flat and uniform interfacial film is formed at the toluene/water interface, and the oil-water interface is reducedTension forces the concave levels of toluene and water to a flat level. The main reason is Janus Fe ₃ O ₄ The amphiphilicity and the amphiphilicity of the catalyst reduce the interfacial tension, so that the catalyst spontaneously accumulates at a toluene/water interface to form an interfacial film. Along with Janus Fe ₃ O ₄ The increase in interfacial concentration increases the surface pressure of the toluene/water interface, and the corresponding diffusion pressure pushes the toluene/water interface up to the bottle wall, forming a climbing film (fig. 41 (c)). Further, as shown in FIG. 41 (d), FIG. 41 (e) and FIG. 41 (f), janus Fe was examined ₃ O ₄ Changing the interface between dichloromethane and water, janus Fe ₃ O ₄ After the nano particles are dripped into a dichloromethane/water interface, janus Fe ₃ O ₄ Aggregation occurs at the toluene/water interface (fig. 41 (e)). After being stabilized by light shaking, a layer of Janus Fe ₃ O ₄ The film of the nano particles is wrapped on the outer side of the dichloromethane, and meanwhile, part of the film quickly climbs on the inner wall of the container. Notably, the interfacial film formed at this time is very uniform and continuous, as compared to the hydrophobically modified two-dimensional magnetic nanoparticles, again due to Janus Fe ₃ O ₄ Is related to the amphiphilicity and biplanarity of (F) in FIG. 41.

Further, the strength and deformation characteristics of the interfacial film were examined, and the results are shown in fig. 42. As can be seen from fig. 42 (a), after the capillary tube is inserted, the interfacial film is deformed but not broken, thereby indicating that the interfacial film has a certain elasticity and strength. Fig. 42 (b) shows that the interface film is deformed by the attraction of the magnet, and the interface film is deformed by the attraction of the magnet by being pulled downward, and after the magnet is removed, the interface film is restored to its original shape (fig. 42 (c)). Therefore, the interface film formed by the Janus two-dimensional magnetic nano particles has certain strength and certain elasticity. Meanwhile, the interface film formed by the Janus two-dimensional magnetic nano particles at the oil-water interface still has magnetic responsiveness.

5. Magnetic analysis of Janus two-dimensional magnetic nanoparticles

Fig. 43 is a hysteresis loop of a Janus two-dimensional magnetic nanoparticle. As can be seen from FIG. 43, janus Fe after grafting reaction when the magnetic field strength reaches 20000Oe ₃ O ₄ The saturation magnetization (Ms) of (C) was 48.9emu/g. After two reactions, the silane coupling agent is preparedEven coating on the surface of the two-dimensional magnetic nanoparticle results in reduced saturation magnetization (Ms), and thus it can also be demonstrated that the present invention successfully grafts the silane coupling agent onto the magnetic nanoparticle. Although Janus Fe ₃ O ₄ The nanoplatelets have reduced magnetization but still have strong magnetic properties. As can be seen from the partial enlargement, janus two-dimensional magnetic nanoparticles have a remanent magnetization (Mr) of 6.0emu/g and a coercivity (Hc) of 56.5Oe, which are both reduced due to the surface grafting of the silane coupling agent.

FIG. 44 is a photograph of a magnetic separation process of Janus two-dimensional magnetic nanoparticles, which was taken in small amounts and well dispersed in 4mL of deionized water. Fig. 44 (a) is a photograph of magnetic nanoparticles dispersed in water after shaking and ultrasound for 1min, fig. 44 (b) is a photograph after magnetic separation for 30s, and fig. 44 (c) is a photograph after magnetic separation for 60 s. It can be seen from fig. 44 that after the magnet is placed on the right side of the sample dispersion, the magnetic nanoparticles can be attracted to the magnet side very quickly, thereby clarifying the dispersion. Janus Fe after 60s magnetic separation ₃ O ₄ The dispersion became clear. In conclusion, the Janus two-dimensional magnetic nano particles prepared by the method have good magnetic responsiveness. This characteristic enables Janus two-dimensional magnetic nanoparticles to be rapidly separated from liquid under the action of an external magnetic field.

Example 13 preparation of magnetic Pickering emulsion

Pickering emulsion was prepared by using Janus two-dimensional magnetic nanoparticles prepared in example 12, 0.02g of Janus two-dimensional magnetic nanoparticles were weighed and dispersed into 2mL of dodecane and 2mL of deionized water, and then the mixture was placed in an ultrasonic cleaner for ultrasonic treatment for 25min to form a black emulsion containing magnetic nanoplatelets, and the mass fraction of the nanoparticles and the oil phase (n-hexane, dichloromethane and butyl butyrate) were changed to form the magnetic Pickering emulsion in the same manner.

Investigation of Janus two-dimensional magnetic nanoparticle stable emulsion:

(1) Pickering emulsion formed by Janus two-dimensional magnetic nanoparticles with different mass fractions

FIG. 45 is an optical microscope image of Pickering emulsion prepared with Janus two-dimensional magnetic nanoparticles and dodecane at different mass fractions. As can be seen from fig. 45, the Janus two-dimensional magnetic nanoparticles can form emulsion with dodecane under the condition that the oil-water ratio is 1:1 and the total volume of oil-water is 4 mL. It can also be seen from fig. 45 that as the mass fraction of Janus two-dimensional magnetic nanoparticles increases gradually, the droplets forming the emulsion have a tendency to decrease gradually. Mainly because the Janus two-dimensional magnetic nano-particles are similar to a small molecular surfactant when being used as an emulsifier, the size of emulsion liquid drops can be regulated by using the Janus two-dimensional magnetic nano-particles. When the mass fraction of the Janus two-dimensional magnetic nano particles is 0.5wt%, the Janus two-dimensional magnetic nano particles can form stable emulsion with dodecane, and the emulsion liquid drops are uniformly distributed.

(2) Pickering emulsion formed by Janus two-dimensional magnetic nano particles and different oil phases

FIG. 46 is an optical microscopy image of Pickering emulsion prepared with Janus two-dimensional magnetic nanoparticles at a mass fraction of 0.5wt% and different oil phases. As can be seen from fig. 46, the Janus two-dimensional magnetic nanoparticles can form stable emulsion with dodecane and n-hexane with weak polarity, and can also form emulsion with dichloromethane with slightly stronger polarity and even butyl butyrate with strong polarity. Overall, the liquid droplet size distribution of the Pickering emulsion formed by the Janus two-dimensional magnetic nanoparticles and the oil phases is uniform and stable. This corresponds to the result of the Janus two-dimensional magnetic nanoparticles forming a uniform and continuous interfacial film with methylene chloride in example 12, especially from the emulsion formed with methylene chloride. The Janus two-dimensional magnetic nano-particles can form efficient and stable Pickering emulsion, and the Pickering emulsion is mainly caused by the amphiphilicity and the amphiphilicity of the Janus two-dimensional magnetic nano-particles.

Claims

1. A preparation method of Janus two-dimensional magnetic nano particles comprises the following steps:

s1, adding melted paraffin into aqueous dispersion liquid of two-dimensional magnetic nano particles, stirring, cooling to room temperature, and collecting and separating by a magnet to obtain paraffin balls with surfaces adsorbing the two-dimensional magnetic nano particles;

S2, dispersing paraffin spheres with the two-dimensional magnetic nano particles adsorbed on the surface into an ethanol aqueous solution, regulating the pH value to 8-9, adding n-octyl triethoxysilane for reaction, and separating and dissolving the paraffin spheres by a magnet after the reaction is finished to obtain Fe ₃ O ₄ An OTES particle;

s3, mixing the Fe ₃ O ₄ Dispersing @ OTES particles in an ethanol aqueous solution, adding N-aminoethyl-gamma-aminopropyl trimethoxysilane for reaction, and separating by a magnet after the reaction is finished to obtain Janus two-dimensional magnetic nanoparticles;

the two-dimensional magnetic nanoparticle is prepared according to a method comprising the following steps:

dropwise adding an aqueous solution of ferrous sulfate heptahydrate into an aqueous solution of sodium hydroxide and sodium acetate, and reacting under the condition of stirring; collecting and separating the two-dimensional magnetic nano particles through a magnet after the reaction is finished, wherein the temperature of the reaction is 50-60 ℃;

under the condition of water bath;

the stirring speed is 400-500 rpm;

the reaction time is 2-3 hours;

the dropping speed of the aqueous solution of the ferrous sulfate heptahydrate is 2-2.4 mL/min;

in the aqueous solution of the ferrous sulfate heptahydrate, the molar concentration of the ferrous sulfate heptahydrate is 0.096-0.144 mol/L;

In the aqueous solution of sodium hydroxide and sodium acetate, the molar concentration of sodium hydroxide is 0.18-0.27 mol/L, and the molar concentration of sodium acetate is 0.9-1.35 mol/L.

2. The method of manufacturing according to claim 1, characterized in that: in the step S1, stirring is carried out at 20-40 ℃;

the dosage of the n-octyl triethoxysilane is as follows: 1g of n-octyl triethoxysilane in an amount of 0.5-2 mL;

the reaction temperature is 20-40 ℃ and the reaction time is 10-20 h.

3. The preparation method according to claim 1 or 2, characterized in that: in the step S3, the dosage of the N-aminoethyl-gamma-aminopropyl trimethoxysilane is as follows: 0.25-1 mL of the N-aminoethyl-gamma-aminopropyl trimethoxysilane;

the reaction temperature is 20-40 ℃ and the reaction time is 10-20 h.

4. A Janus two-dimensional magnetic nanoparticle prepared by the method of any one of claims 1-3.

5. The use of the Janus two-dimensional magnetic nanoparticle of claim 4 in the preparation of Pickering emulsion, interfacial catalysis, petroleum industry.

6. A preparation method of Pickering emulsion comprises the following steps:

the oil phase is dodecane, n-hexane, dichloromethane or butyl butyrate;

the volume ratio of the oil phase to the water phase is 1: 1-2;

7. Pickering emulsion prepared by the method of claim 6.