CN105771908B - A kind of magnetic silica core-shell composite material and preparation method thereof for heavy metal adsorption - Google Patents

Abstract

The magnetic silica core-shell composite material and preparation method thereof that the invention discloses a kind of for heavy metal adsorption, includes the following steps：(1) coprecipitation prepares CoFe₂O₄Nano particle；(2)Method is to CoFe obtained by step (1)₂O₄Nano particle carries out SiO₂Cladding, obtains CoFe₂O₄@SiO₂；(3) with gained CoFe₂O₄@SiO₂It is raw material with 3 aminopropyl triethoxysilanes, the 4~8h that flows back at 60~100 DEG C obtains black suspension, the CoFe for being dried in vacuo amino modified after separation₂O₄@SiO₂Chain nanocomposite.Technical solution of the present invention technique and easy to operate, it is environmental-friendly, different designs can be carried out for different heavy metals.Such material may be used on the processing of heavy metal containing sewage and radioactive wastewater.

Description

A magnetic silica core-shell composite material for heavy metal adsorption and its preparation method

technical field

The present invention relates to the fields of heavy metal ion adsorption, heavy metal waste liquid treatment and magnetic separation technology, and especially relates to a new technology scheme of amino functionalized magnetic silica core-shell composite material with a certain adsorption capacity designed for the adsorption of heavy metal ions .

Background technique

With the rapid development of the global economy, resources and the environment have become two major problems faced by human beings. Environmental protection and resource conservation have become major issues for human beings. Water is an indispensable element of environmental resources for human production and life. Nowadays, heavy metal pollution has become one of the most serious environmental problems. Heavy metals, unlike organic pollutants, are not biodegradable and tend to accumulate in living organisms. Many heavy metal ions have been proved to be toxic or carcinogenic, which greatly endanger people's daily life. The treatment of heavy metal wastewater is related to people's quality of life and living environment. Reusing qualified water can not only solve the shortage of water resources, but also recycle heavy metals. Therefore, the research on the treatment of heavy metal wastewater and water purification and reuse technology is currently the focus. important topic.

At present, the main heavy metal wastewater treatment technologies include ion exchange method, adsorption method, chemical precipitation method, reverse osmosis method, membrane filtration method, etc., but they all have their own inherent advantages and limitations. The adsorption method has the advantages of low cost, good effect, strong operability, high-quality sewage, desorption and regeneration, etc. It is currently recognized as an effective method for treating heavy metal wastewater.

Traditional adsorbents such as biosorbents (bacteria, fungi, algae, etc.), natural adsorbents (zeolite, diatomaceous earth, kaolin, montmorillonite, etc.), synthetic adsorbents (activated carbon, carbon nanotubes, SiO ₂ , TiO ₂ , ZrO ₂ , etc.). Although these adsorbents have played a certain role in the treatment of heavy metal wastewater. However, some adsorbents, such as nanoparticles, are difficult to separate after adsorbing heavy metals and consume a lot of time, which limits the application of these adsorbents. If these difficult-to-separate adsorbents are combined with magnetic properties, the synthesis of nanocomposites with large specific surface area and magnetic recovery ability will take a big step in application.

The magnetic adsorbent still has the problem of weak adsorption capacity. In order to improve the dispersibility and adsorption performance of the adsorbent, the current research can be roughly summarized into three points: the first is to functionalize the ligand, such as thiol, organic amine Classes, organic sulfides, etc.; the second is to coat magnetic shells on nanoparticles to obtain magnetic adsorbents with large specific surface area and high chemical stability; the third is to connect functional groups on magnetic mesoporous nanoparticles, such as amino groups. , Sulfur base, etc.

Contents of the invention

In order to overcome the shortcomings of the prior art above, the present invention provides an amino-functionalized magnetic silica core-shell composite material with a certain adsorption capacity designed for the adsorption of heavy metal ions and a preparation method thereof.

A method for preparing a magnetic silica core-shell composite material for heavy metal adsorption, comprising the steps of:

(1) Preparation of CoFe ₂ O ₄ nanoparticles by co-precipitation method;

(2) CoFe ₂ O ₄ nanoparticles obtained in step (1) are coated with SiO ₂ to obtain CoFe ₂ O ₄ @SiO ₂ ;

(3) Using the obtained CoFe ₂ O ₄ @SiO ₂ and 3-aminopropyltriethoxysilane as raw materials, reflux at 60-100°C for 4-8 hours to obtain a black suspension, which is separated and vacuum-dried to obtain amino-modified CoFe ₂ O ₄ @SiO ₂ chain nanocomposites.

Based on the existing research and existing problems, the present invention adheres to the principles of low cost, high efficiency and no pollution, and improves the magnetic adsorbent in terms of synthesis method and performance, and obtains a magnetic adsorbent designed for the adsorption of heavy metal ions. A new technology solution for amino-functionalized magnetic silica core-shell composites with a certain adsorption capacity. With spinel ferrite CoFe ₂ O ₄ as the core, this kind of magnetic nanoparticles has high coercive force, moderate saturation magnetization, good mechanical strength and other excellent characteristics. Amorphous SiO ₂ is the shell layer. SiO ₂ can not only protect the inner magnetic core, but also has chemical stability, acid and alkali resistance. The amino-functionalized magnetic silica core-shell composite material has high adsorption capacity, fast separation speed, selective adsorption function, etc. This new technology solution can be designed according to different needs, which will promote the research on heavy metal wastewater treatment and guarantee people's production and life.

The present invention adopts the CoFe ₂ O ₄ magnetic nanoparticles synthesized by the improved co-precipitation method, Synthesized CoFe ₂ O ₄ @SiO ₂ chain nanocomposites with SiO ₂ as the shell and CoFe ₂ O ₄ as the core, and then functionalized it with amino groups by the reflux method. The shell thickness of SiO ₂ can be adjusted as needed, and the surface can also be grafted with corresponding adsorption groups according to different adsorption requirements. The magnetism of CoFe ₂ O ₄ can be adjusted by sintering conditions, and it can maintain strong magnetism, which is beneficial to the separation of adsorbents. The invention has the advantages of simple preparation method and low preparation cost. After the magnetic nanoparticles are combined with _SiO2 , they still have high magnetic properties and can be separated quickly. The adsorbent has a stable structure and a chain-like core-shell structure. After grafting amino groups, it has certain adsorption properties for heavy metal copper ions. The composite modified magnetic adsorbent can be used in the fields of radioactive waste liquid treatment, heavy metal ion removal and the like.

The chain-shaped nanocomposite material prepared by the invention has high magnetization strength and can be separated quickly due to the good contact of the inner magnetic nanoparticles. The long chain has a longer size and a stable structure, which is conducive to its application.

Preferably, the CoFe ₂ O ₄ nanoparticles are prepared by an improved co-precipitation method, including the following steps:

(1) Dissolve the iron source and the cobalt source in deionized water according to the ratio, mix evenly and drop into NaOH solution drop by drop to obtain a reddish-brown suspension, add polyethylene glycol to the obtained brownish-red suspension, mix well and adjust pH to 9-12 to obtain dark brown red suspension;

(2) Transfer the resulting dark brown-red suspension into a three-necked flask, reflux in a boiling water bath for 60-90 minutes to obtain a black suspension, separate it with a magnet to take a black precipitate, wash, dry, grind and sinter in sequence to obtain CoFe ₂ O ₄ nanoparticles.

Further preferably, the iron source is Fe(NO ₃ ) ₃ 9H ₂ O, the cobalt source is Co(NO ₃ ) ₂ 6H ₂ O, and the iron source and cobalt source are in a molar ratio of 1.5-2.5:1, The iron source is calculated as 0.01-0.03mol dissolved in 150mL deionized water; most preferably, the iron source and cobalt source are in a molar ratio of 2:1, and the iron source is calculated as 0.02mol dissolved in 150mL deionized water.

Further preferably, the concentration of the sodium hydroxide dropped in is 1.0-2.0 mol/L, and its volume is adjusted according to the total molar weight of the iron source and the cobalt source, so that the pH of the solution is controlled within the range of 10-11.

The molar ratio of the added amount of PEG to the cobalt source is 2:1.

Further preferably, the drying is drying in a vacuum oven at 80-90° C. for 6-12 hours; most preferably, drying in a vacuum oven at 80° C. for 12 hours.

Further preferably, the sintering is sintering at 300-700°C for 1-7h, most preferably at 600°C for 1h.

In this step, a 1.0-2.0 mol/L NaOH solution is used to adjust the pH.

In the method of the present invention, the amino functionalized magnetic silica microsphere sample is obtained by an improved co-precipitation method, method and vacuum drying method. In the co-precipitation process, ammonia water (25%) is first used as a precipitant, and then used to adjust the pH of the solution, so that iron and cobalt ions are completely precipitated; polyethylene glycol (PEG 6000) is used as a dispersant and template agent to form a dispersed basis of the chain structure.

Most preferably, firstly, 8.08g of Fe(NO ₃ ) ₃ ·9H ₂ O and Co(NO ₃ ) ₂ ·6H ₂ O are dissolved in 150-250mL of deionized water in a molar ratio of 2:1, and stirred evenly at a medium speed; then Add 25-35mL of 1.0-2.0mol/L NaOH solution dropwise to obtain a reddish-brown suspension, then add 2.9697g of PEG to the above suspension; after stirring evenly, use 1.0-2.0mol/L NaOH The solution adjusts the pH of the suspension so that it is in the range of 9-12; the obtained uniform dark brown-red suspension is transferred to a three-neck flask, and it is refluxed in a boiling water bath for 60-90min; the obtained black precipitate is removed by a magnet. Quickly separate, then wash it well until neutral. The wet black precipitate was dried in a vacuum drying oven at 80-90° C. for 6-12 hours to obtain bright black CoFe ₂ O ₄ coarse particles, which were ground to obtain CoFe ₂ O ₄ precursor powder. Finally, the precursor is sintered at different times (1-7h) and at different temperatures (300-700° C.) to obtain CoFe ₂ O ₄ nanoparticles.

The present invention adopts an improved co-precipitation method, on the basis of the original co-precipitation method, PEG is added as a dispersant and a template agent, on the one hand, the dispersibility of nano magnetic particles can be improved, and on the other hand, these particles can be bound on the PEG chain structure, make it form a chain-like core. After adjusting the pH of the suspension, reflux in a boiling water bath for a certain period of time to make the reaction more complete. Preferably, the The method includes the following steps:

Ultrasonically disperse CoFe ₂ O ₄ nanoparticles into the mixture of ethanol and deionized water, adjust the pH to 10-12, add tetraethyl orthosilicate dropwise, stir and react for 4-48 hours, then separate with magnets, and wash the precipitate at 60-90°C Vacuum dried for 6-12 hours to obtain CoFe ₂ O ₄ @SiO ₂ dark gray powder.

Ethanol is absolute ethanol, and the mixing volume ratio of absolute ethanol and deionized water is 1:1-3:1.

Further preferably, the mass volume ratio of CoFe ₂ O ₄ nanoparticles to the mixed solution is 0.5-1.0 g: 150-250 mL.

Further preferably, the ultrasonic time of the CoFe ₂ O ₄ nanoparticles in the mixed liquid is 30-60 min.

In this step, ammonia water (25-28%) is used to adjust the pH to 10-12.

More preferably, CoFe ₂ O ₄ (0.5-1.0g) is ultrasonically dispersed into a 1:1-3:1 mixture of alcohol and deionized water, and 15-25mL ammonia water (25-28% ) to adjust the pH of the solution. When the pH of the solution is 10-12, add 5-10mL tetraethyl orthosilicate (TEOS) dropwise, stir at a certain rate for 4-48h, and separate the dark gray suspension with a magnet, and then use Wash with deionized water several times until neutral. Finally, vacuum-dry at a temperature of 60-90°C for 6-12 hours to obtain CoFe ₂ O ₄ @SiO ₂ dark gray powder.

The invention is Vacuum drying is used in the process of preparing CoFe ₂ O ₄ @SiO ₂ , which is beneficial to maintain the chain-like morphology of the composite material.

Preferably, the mass volume ratio of CoFe ₂ O ₄ @SiO ₂ and 3-aminopropyltriethoxysilane in step (3) is (0.5-1.0) g: (3-6) mL.

Further preferably, 0.5-1.0g CoFe ₂ O ₄ @SiO ₂ is fully washed with pure isopropanol solution to ensure an anhydrous environment, then soaked in 50-100mL pure isopropanol, and stirred at room temperature for 30-60min Add 3-6mL of 3-aminopropyltriethoxysilane (APTES) dropwise, continue to stir for 6h, transfer it to a three-necked flask, reflux at 80°C for 6h, wash with alcohol several times, separate with a magnet, and finally vacuum at 80-90°C Dry for 6-12 hours to obtain CoFe ₂ O ₄ @SiO ₂ -NH ₂ black powder.

In this step, pure isopropanol solution is used as solvent, the first 6h is room temperature stirring, and the last 6h is reflux stirring at 80°C; the amino-functionalized magnetic silica composite material has a higher saturation magnetization (28.09emu/g) , can be quickly separated by a magnet within one minute.

The invention also provides a magnetic silica core-shell composite material for heavy metal adsorption prepared by the preparation method. The magnetic silicon dioxide composite material prepared by the invention has a chain core-shell structure. CoFe ₂ O ₄ nanoparticles are the core with an average grain size of 10-15nm; SiO ₂ is the shell with an average thickness of 50nm. The complex prepared by the invention is used for the adsorption of heavy metals, especially copper ions.

The adsorption process of copper ions is as follows:

Static adsorption experiment of copper: The batch method is mainly used to study the adsorption performance of CoFe ₂ O ₄ @SiO ₂ -NH ₂ magnetic microspheres on copper. The parameters measured in the experiment mainly include the adsorption equilibrium time of the magnetic microspheres on copper in the solution. , Equilibrium adsorption capacity, equilibrium removal rate.

The specific operation method of the experiment: In 20 100mL centrifuge tubes, weigh a certain amount of magnetic composite powder prepared in step (3), pipette 50mL copper nitrate standard solution into the centrifuge tube, cover the lid, put Shake in a water bath thermostatic shaker. Take out a centrifuge tube at the set time, pipette 10mL supernatant for centrifugation, pipette 1mL supernatant into a 10mL centrifuge tube, dilute 10-20 times with deionized water, and use atomic absorption spectrometry Obtain the corresponding absorbance and copper ion concentration, calculate the adsorption amount and removal rate of copper in the solution by this sample, and draw the relationship curve between the adsorption amount, removal rate and adsorption time of CoFe ₂ O ₄ @SiO ₂ -NH ₂ for copper.

According to the special complexation between copper ions and amino groups, the complex prepared in the present invention is functionalized with amino groups. It can also be modified differently according to the characteristics of other heavy metal ions.

The ratio of each component in the magnetic core-shell complex can be specifically adjusted according to the needs, and different modification designs can be made on the material for the selective adsorption of different heavy metal ions.

Adsorption method is widely used, and it has many unique advantages for treating heavy metal sewage. The existing research work on adsorbents shows that the current adsorption technology has disadvantages such as high cost, complicated preparation, low adsorption capacity, and no adsorption selectivity. It is of great significance to prepare low-cost magnetic adsorbents with high adsorption capacity and adsorption selectivity and simple preparation by grafting adsorption groups, strengthening the composite modification of adsorbents, meeting different adsorption conditions to improve its adsorption efficiency.

The invention provides a new technical scheme of amino-functionalized chain-like core-shell nano-magnetic composite materials designed for the adsorption of heavy metal ions. Amino-functionalized magnetic silica nanocomposites were prepared by a modified co-precipitation method, method and vacuum drying method. The shell thickness of SiO ₂ can be adjusted as needed, and the surface can also be grafted with corresponding adsorption groups according to different adsorption requirements. The magnetism of CoFe ₂ O ₄ can be adjusted by sintering conditions, and it can maintain strong magnetism, which is beneficial to the separation of adsorbents. The formation mechanism of this material in each process and the adsorption mechanism of the material to copper ions are given corresponding explanations and theoretical basis. This technical solution has simple process and operation, and is environmentally friendly, and can be designed differently for different heavy metals. Such materials can be applied to the treatment of heavy metal sewage and radioactive wastewater.

Description of drawings

Fig. 1 is the flowchart of preparation method of the present invention.

Figure 2 is a schematic diagram of the formation mechanism of the three products (CoFe ₂ O ₄ NPs, CoFe ₂ O ₄ @SiO ₂ and CoFe ₂ O ₄ @SiO ₂ -NH ₂ ) during the preparation process.

Fig. 3 is the XRD pattern (a) and FTIR pattern (b) of CoFe ₂ O ₄ NPs, CoFe ₂ O ₄ @SiO ₂ and CoFe ₂ O ₄ @SiO ₂ -NH ₂ .

Figure 4 is the SEM images and corresponding TEM images of CoFe ₂ O ₄ NPs, CoFe ₂ O ₄ @SiO ₂ and CoFe ₂ O ₄ @SiO ₂ -NH ₂ .

Figure 5 is the magnetization curve (a) and magnetic field separation effect diagram (b) of CoFe ₂ O ₄ NPs, CoFe ₂ O ₄ @SiO ₂ and CoFe ₂ O ₄ @SiO ₂ -NH ₂ at room temperature.

Figure 6 is a comparison of the morphology of CoFe ₂ O ₄ NPs obtained without adding PEG (6000) (a) and adding PEG (6000) (b).

Fig. 7 is the XRD patterns (a) of CoFe ₂ O ₄ NPs at different sintering temperatures and the corresponding magnetization curves (b) at room temperature.

Fig. 8 is the relationship curve of adsorption amount (b), removal rate (a) and adsorption time of the amino-functionalized magnetic silica nanocomposite material (CoFe ₂ O ₄ @SiO ₂ -NH ₂ ) for the adsorption of copper ions.

Detailed ways

The present invention will be further described below in combination with specific embodiments and accompanying drawings.

Example 1

The process flow is shown in Figure 1.

Step 1: Preparation of _CoFe2O4 Nanomagnetic Particles by Modified Co-precipitation _Method

Dissolve Fe(NO ₃ ) ₃ 9H ₂ O and Co(NO ₃ ) ₂ 6H ₂ O in 150mL deionized water at a molar ratio of 2:1 (where Fe(NO ₃ ) ₃ 9H ₂ O is 0.02mol) , stir well at medium speed. Then 25 mL of 2.0 mol/L NaOH solution was added dropwise to obtain a reddish-brown suspension, and then 0.02 mol PEG 6,000 was added to the above suspension. After stirring evenly, adjust the pH of the suspension with 2.0mol/L NaOH solution to make it within the range of 10-11. The obtained homogeneous dark brown-red suspension was transferred to a three-necked flask, and it was refluxed in a boiling water bath for 90 min. The obtained black precipitate is quickly separated by a magnet, and then it is fully washed with water until it is neutral. The wet black precipitate was dried in a vacuum oven at 80°C for 12 hours to obtain bright black CoFe ₂ O ₄ coarse particles, which were ground to obtain CoFe ₂ O ₄ precursor powder. Finally, the precursor was sintered at 600°C for 1 h to obtain CoFe ₂ O ₄ nanoparticles with an average size of 10-15 nm.

Step 2: Synthesis of _CoFe2O4 @ _SiO2 Magnetic _{Nanocomposite}

The CoFe ₂ O ₄ nanoparticles that step 1 obtains are dispersed in the mixed solution of alcohol and deionized water, and after a while of ultrasonication, add an appropriate amount of ammonia (25%) to adjust the pH of the solution. When the pH of the solution is 10.5-11, drop Add tetraethyl orthosilicate (TEOS), stir at a certain rate for 48h, and the dark gray suspension is separated with a magnet, and then washed several times with deionized water until neutral. Finally, dry at a vacuum temperature of 80° C. for 12 hours to obtain CoFe ₂ O ₄ @SiO ₂ dark gray powder.

Step 3: Synthesis of amino-modified _CoFe2O4 @ _{SiO2 magnetic} nanocomposites

First, fully wash the CoFe ₂ O ₄ @SiO ₂ obtained in step 2 with pure isopropanol to ensure an anhydrous environment, then soak it in 50mL of pure isopropanol, stir at room temperature for a period of time, and then add 3mL of 3- Aminopropyltriethoxysilane (APTES), continue to stir for 6h, transfer it to a three-necked flask, reflux at 80°C for 6h, wash with alcohol several times, separate with a magnet, and vacuum dry at 80°C for 12h to obtain CoFe ₂ O ₄ @SiO ₂ -NH ₂ black powder.

The experimental flow chart and formation mechanism of the product obtained in the above steps 1-3 are shown in Figure 1 and Figure 2 . The phase structure and molecular structure of the product were obtained by XRD and FTIR tests, respectively, as shown in (a) and (b) in Figure 3, where (a) is the XRD pattern and (b) is the FTIR pattern. From the XRD pattern, we can conclude that the spinel structure of CoFe ₂ O ₄ has been formed, and the amorphous peak of SiO ₂ appears after coating. Infrared spectrum results show that there are vibrations of Si-O-Si absorption peaks and -NH vibrations. On the one hand, it shows that the silicon dioxide is successfully coated, and on the other hand, it shows that the amino functionalization is successful.

The product was placed under a scanning electron microscope to observe its surface morphology, and its fine structure was observed under a transmission electron microscope, as shown in Figure 4. (a) in Figure 4 is the SEM image of CoFe ₂ O ₄ NPs, (d) is the TEM image of CoFe ₂ O ₄ NPs, the distribution of CoFe ₂ O ₄ magnetic nanoparticles can be seen in Figure 4 (a) and (d) Uniform, with an average diameter of 10-15nm; SiO ₂ is coated to form a chain-like morphology with a core-shell structure, and the thickness of the coating layer is about 50nm, as shown in (b) and (e) in Figure 4, and in Figure 4 (b) is the SEM image of CoFe ₂ O ₄ @SiO ₂ , (e) is the TEM image of CoFe ₂ O ₄ @SiO ₂ ; the morphology and fine structure have not changed after amino modification, in Figure 4 (c) As shown in and (f), (c) in Figure 4 is the SEM image of CoFe ₂ O ₄ @SiO ₂ -NH ₂ , and (f) is the SEM image of CoFe ₂ O ₄ @SiO ₂ -NH ₂ . Figure 5(a) shows the magnetization curves of CoFe ₂ O ₄ , CoFe ₂ O ₄ @SiO ₂ and CoFe ₂ O ₄ @SiO ₂ -NH ₂ , and their saturation magnetizations are 61.96, 31.41, 23.84 emu /g. The gradual decrease of magnetization is due to the increase of non-magnetic substances, but CoFe ₂ O ₄ @SiO ₂ -NH ₂ is also easily separated by magnet within one minute, as shown in Fig. 5(b).

In addition, the comparative images of CoFe ₂ O ₄ magnetic particles formed without adding PEG (6000) and adding PEG (6000) in step 1 are shown in (a) and (b) in Figure 6, respectively. The agglomeration of the magnetic particles without PEG (6000) is serious, and the dispersibility is better after adding PEG (6000), and there is a certain chain distribution.

In step 1, the magnetic particles are sintered at a certain temperature. The XRD patterns of the magnetic particles obtained at different temperatures are shown in (a) of Figure 7, and the corresponding magnetization curves at room temperature are shown in (b) of Figure 7. As the sintering temperature increases, the crystallinity increases, the particle size becomes larger, and the saturation magnetization increases.

Example 2

The products obtained in steps 2 and 3 in Example 1 were subjected to static adsorption experiments on Cu(II) ions.

Take 20 100mL centrifuge tubes, add the same amount of adsorbent to each volumetric flask, pipette 50mL of the prepared copper nitrate standard solution into the ion tube, and put it into a water bath constant temperature oscillator to vibrate. Take out a centrifuge tube at the set time, pipette 10mL supernatant for centrifugation, pipette 1mL supernatant into a 10mL centrifuge tube, dilute 10 times with deionized water, and obtain the corresponding concentration by atomic absorption spectrometry. Calculate the absorbance and copper ion concentration of the sample, and calculate the adsorption amount and removal rate of copper in the solution, and draw the relationship curve between the adsorption amount, removal rate and adsorption time.

Figure 8 shows the relationship between the adsorption amount, removal rate and adsorption time of the amino-functionalized magnetic silica composite material (CoFe ₂ O ₄ @SiO ₂ -NH ₂ ) on the adsorption of copper ions, and the pH of the solution is fixed for 5. (a) is the relationship curve between removal rate and adsorption time, (b) is the relationship curve between adsorption amount and adsorption time. At the beginning of time, the adsorption rate is very fast. When the adsorption time is 200min, the adsorption becomes slow and basically reaches saturation. The adsorption curve of (CoFe ₂ O ₄ @SiO ₂ ) of the magnetic silica composite material before functionalization is not shown here, because CoFe ₂ O ₄ @SiO ₂ has basically no adsorption on copper ions within 400 min. This indicates that the _-NH2 on the surface after amino functionalization has a special complexing effect on copper ions. This result also illustrates the selective adsorption function of CoFe ₂ O ₄ @SiO ₂ -NH ₂ .

Claims (2)

1. A preparation method for a magnetic silica core-shell composite material for heavy metal adsorption, characterized in that, comprising the steps: (1) Preparation of CoFe ₂ O ₄ nanoparticles by co-precipitation method; Co-precipitation method includes the following steps: (a) Dissolve the iron source and the cobalt source in deionized water according to the ratio, mix evenly and drop into NaOH solution drop by drop to obtain a reddish-brown suspension, add polyethylene glycol to the obtained reddish-brown suspension, mix well and adjust pH to 9-12 to obtain dark brown red suspension; (b) Transfer the resulting dark brown-red suspension into a three-necked flask, reflux in a boiling water bath for 60-90 minutes to obtain a black suspension, separate with a magnet to collect a black precipitate, wash, dry, grind and sinter in sequence to obtain CoFe ₂ O ₄ nanoparticles; the iron source is Fe(NO ₃ ) ₃ 9H ₂ O, the cobalt source is Co(NO ₃ ) ₂ 6H ₂ O, and the molar ratio of iron source and cobalt source is 1.5-2.5:1, Wherein the iron source is calculated as 0.01～0.03moL dissolved in 150mL deionized water; the concentration of sodium hydroxide dropped in is 1.0-2.0mol/L, and the amount is used so that the pH of the solution is within the range of 10-11; Drying in a vacuum oven at 80-90°C for 6-12h; the sintering is sintering at 300-700°C for 1-7h; (2) CoFe ₂ O ₄ nanoparticles obtained in step (1) are coated with SiO ₂ to obtain CoFe ₂ O ₄ @SiO ₂ ; The method includes the following steps: Ultrasonically disperse CoFe ₂ O ₄ nanoparticles into the mixed solution of ethanol and deionized water, adjust the pH to 10-12, then add tetraethyl orthosilicate dropwise, stir and react for 4-48 hours, then separate with the magnet, and wash the precipitate with water for 60-90 hours Vacuum drying at ℃ for 6-12 hours to obtain CoFe ₂ O ₄ @SiO ₂ powder; the mass volume ratio of CoFe ₂ O ₄ nanoparticles to the mixed solution is 0.5-1.0g: 150-250mL; (3) Using the obtained CoFe ₂ O ₄ @SiO ₂ and 3-aminopropyltriethoxysilane as raw materials, reflux at 60-100°C for 4-8 hours to obtain a black suspension, which is separated and vacuum-dried to obtain amino-modified CoFe ₂ O ₄ @SiO ₂ chain core-shell nanocomposite; the mass-volume ratio of CoFe ₂ O ₄ @SiO ₂ and 3-aminopropyltriethoxysilane in step (3) is (0.5-1.0) g: (3-6) mL. 2. A magnetic silica core-shell composite material for heavy metal adsorption prepared by the preparation method according to claim 1.