CN111063502B - Magnetic fluid with adjustable stability and preparation and recovery method thereof - Google Patents
Magnetic fluid with adjustable stability and preparation and recovery method thereof Download PDFInfo
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- CN111063502B CN111063502B CN201911314377.3A CN201911314377A CN111063502B CN 111063502 B CN111063502 B CN 111063502B CN 201911314377 A CN201911314377 A CN 201911314377A CN 111063502 B CN111063502 B CN 111063502B
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- H—ELECTRICITY
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- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
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- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
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Abstract
The invention belongs to the field of magnetic nano materials, and discloses a magnetic fluid with adjustable stability and a preparation and recovery method thereof, wherein the magnetic fluid with adjustable stability is mainly formed by dispersing magnetic nano particles modified by cationic polymers in a carrier liquid, and the cationic polymers have amino groups; for the magnetic fluid, the stability of the magnetic fluid can be adjusted by adjusting the pH value of the magnetic nanoparticle-carrier liquid integral solution system. The magnetic fluid is constructed by modifying the magnetic nanoparticles with the cationic polymer, and the magnetic nanoparticles modified with the cationic polymer can be highly dispersed in the carrier liquid; the protonation of the cationic polymer can enable the surface of the magnetic nano particle to be positively charged, and further the agglomeration effect among the particles can be overcome through the electrostatic interaction among the particles, so that the magnetic fluid is kept stable; the stability of the magnetic fluid is adjustable, and the application field of the magnetic fluid can be expanded by adjusting the stability of the magnetic fluid, so that the magnetic fluid is suitable for different application requirements.
Description
Technical Field
The invention belongs to the technical field of magnetic nano materials, and particularly relates to a magnetic fluid with adjustable stability and a preparation and recovery method thereof.
Background
The magnetic fluid is a liquid functional material, is composed of carrier liquid and nano-scale magnetic particles, and has the liquidity of liquid and the magnetism of solid. Compared with common liquid, the magnetic fluid presents a plurality of special magnetic, optical and electric phenomena under the action of an external magnetic field, such as magnetic targeting property, birefringence optical property, high-efficiency heat conduction and enhanced heat transfer, and has wide application prospect in the fields of biology, chemical industry, medical treatment, sealing, mineral separation, pollution control and the like.
Because the magnetic particles in the magnetic fluid are in the nanometer level and have high surface energy, obvious agglomeration phenomenon can occur among the particles to reduce the surface energy, and further the particles are easy to separate out carrier liquid. Therefore, the key to preparing high performance magnetic fluids is how to properly modify the surface of the magnetic particles to improve their stability in the carrier fluid.
In the prior art, the surface energy of the magnetic nano particles is reduced and the steric hindrance of the magnetic nano particles is improved by adsorbing a surfactant on the surfaces of the magnetic nano particles, so that the stability of the magnetic nano particles in a carrier liquid is enhanced. The surfactant is generally a chemical having both hydrophilic and hydrophobic groups, and is selected according to the type of magnetic particles and carrier liquid and the interaction between them. If the carrier liquid is aqueous, the hydrophobic group of the surfactant acts on the surface of the magnetic nano-particle, and the hydrophilic group at the other end can be dissolved with the aqueous carrier liquid; if the carrier liquid is oily, the hydrophilic group of the surfactant acts on the surface of the magnetic nano-particle, and the hydrophobic group at the other end can be dissolved with the oily carrier liquid.
A typical method for preparing a magnetic fluid based on a surfactant is as follows: (1) ball milling method. Adding the magnetic particles, the surfactant and the carrier liquid into a ball mill together, carrying out ball milling for a long time (1 to 3 months), and removing large particles by centrifugation to prepare the magnetic fluid. (2) A thermal decomposition method. The surfactant and the carboxyl metal complex are mixed in the base liquid, and the metal magnetofluid of iron, cobalt, nickel or alloy thereof and the like can be prepared under the heating condition in a closed container.
However, the magnetic fluid prepared by the method has the following obvious defects: one is the non-reversible process of improving the dispersibility of magnetic nanoparticles by the surfactant. That is, although the dispersibility of the surfactant-modified magnetic nanoparticles is improved, the surfactant-modified magnetic nanoparticles are difficult to separate from the carrier liquid, which presents a challenge for some practical applications, such as in the application of magnetic separation and purification of substances, due to this characteristic, the separation system often needs to rely on high magnetic field strength and gradient to achieve effective separation of substances, and the requirement on magnetic field equipment capacity is extremely high. And in the magnetic fluid prepared by using the surfactant through a ball milling method and other methods, the surfactant is not only adsorbed on the magnetic nanoparticles but also exists in the carrier liquid, so that the application of the magnetic fluid in multiple fields of chemical industry, pollution control, biology and the like is not facilitated. For example, in the problem of wastewater treatment, many surfactants such as amine surfactants are contact-harmed to human bodies and cause serious pollution to water bodies when the amount of the surfactants is very small, and secondary pollution is caused if the magnetofluid containing the surfactants and the magnetic nanoparticles modified by the surfactants in the magnetofluid carrier liquid is difficult to recover from the water bodies.
Therefore, the magnetic fluid with adjustable stability has great application value in the aspects of mineral separation, precision grinding and polishing, sewage treatment, separation and purification of protein and nucleic acid and the like. The magnetic fluid has strong stability, can be applied to give full play to the function of the magnetic fluid, and can easily recover the magnetic nanoparticles through an external magnetic field by weakening the stability of the magnetic fluid according to actual needs. Therefore, the problems of requirements on magnetic field equipment capacity in industrial application scenes, secondary pollution in pollution treatment scene application, cytotoxicity in biological scene application and the like can be reduced.
Disclosure of Invention
In view of the above drawbacks or needs for improvement of the prior art, an object of the present invention is to provide a magnetic fluid with adjustable stability and a method for preparing and recovering the same, in which the magnetic fluid is constructed by modifying magnetic nanoparticles with cationic polymers, and the magnetic nanoparticles modified with cationic polymers can be highly dispersed in a carrier liquid; the protonation of the cationic polymer can make the surface of the magnetic nano particle carry positive charges, and further the agglomeration effect among the particles can be overcome through the electrostatic interaction among the particles, so that the magnetic fluid is kept stable. And the stability of the magnetic fluid is adjustable, the stability of the magnetic fluid can be adjusted by adjusting and controlling the pH value of the magnetic nanoparticle-carrier liquid integral solution system, the application field of the magnetic fluid can be expanded, and the magnetic fluid is suitable for different application requirements.
In order to achieve the above object, according to one aspect of the present invention, there is provided a magnetic fluid with adjustable stability, which is characterized in that the magnetic fluid is mainly composed of magnetic nanoparticles modified by cationic polymer having amino groups dispersed in a carrier liquid; for the magnetic fluid, the stability of the magnetic fluid can be adjusted by adjusting the pH value of the magnetic nanoparticle-carrier liquid integral solution system.
As a further preferred of the present invention, the cationic polymer is selected from polylysine, polyglutamic acid derivatives, polyethyleneimine, polypropyleneimine;
preferably, the relative molecular mass of the cationic polymer is in the range of 800Da to 100 kDa.
In a further preferred embodiment of the present invention, the cationic polymer is a branched polyethyleneimine having a relative molecular mass of 25 kDa.
According to another aspect of the present invention, the present invention provides a method for preparing a magnetic fluid with adjustable stability, which is characterized by comprising the following steps:
(1) preparing magnetic nanoparticles in a solution system;
(2) modifying the magnetic nanoparticles by using a cationic polymer in the solution system obtained in the step (1), and dispersing the modified magnetic nanoparticles in a carrier liquid to obtain a magnetic fluid; wherein the cationic polymer has an amino group;
(3) adding an acidic solution into the magnetofluid solution system obtained in the step (2), and enhancing the stability of the magnetofluid through an acidification process;
(4) and (4) processing the solution system obtained in the step (3) by a high-speed centrifugal separation method of not less than 20000rpm, so that the cationic polymer modified magnetic nanoparticles in the solution system are suspended in neutral carrier liquid, and finally obtaining the neutral and stability-adjustable magnetic fluid solution.
In a further preferred embodiment of the present invention, in the step (2), a cationic polymer solution is added to the solution system obtained in the step (1), and the magnetic nanoparticles are modified in an ultrasonic heating environment, so as to obtain the cationic polymer-modified magnetic nanoparticles.
More preferably, in the step (3), an acidic solution is added dropwise to the solution system obtained in the step (2), and the mixture is uniformly mixed and then kept stand for 5-60 min.
As a further preferable aspect of the present invention, in the step (3), the solution system is specifically acidified by an acidic solution until the pH value of the solution is 1 to 5, and then the solution system is left standing for 5 to 60min, and then the obtained solution system is treated by an ultra high speed centrifuge to separate the magnetic nanoparticles from the carrier liquid, and finally the separated magnetic nanoparticles are resuspended in neutral ultrapure water.
In a further preferred aspect of the present invention, in the step (1), the magnetic nanoparticles have a particle size ranging from 1 to 500 nm; preferably, the step (1) is to prepare the ferroferric oxide nanoparticles by an alkali coprecipitation method;
in the step (2), the cationic polymer is branched polyethyleneimine with the relative molecular mass of 25 kDa.
As a further preference of the present invention, the solution systems are all aqueous solution systems;
in the step (2), the carrier liquid is ultrapure water.
According to another aspect of the present invention, the present invention provides a method for recovering the magnetic fluid with adjustable stability, which is characterized in that an alkaline solution is added into a magnetic fluid solution system, and the stability of the magnetic fluid is weakened through an alkalization process, so as to facilitate the recovery of the magnetic nanoparticles in the magnetic fluid.
Compared with the prior art, the magnetic nano particles modified by the cationic polymer are dispersed in the carrier liquid to form the magnetic fluid, so that the stability of the magnetic fluid is improved by acidification for the first time. Taking polylysine, polyglutamic acid derivatives, polyethyleneimine, polypropylene imine and the like as examples of cationic polymers, the cationic polymers contain a large number of amino groups in molecules, the cationic polymers have the effect that protonation can enable the surfaces of the magnetic nanoparticles to be positively charged, and then the agglomeration effect among the particles can be overcome through the electrostatic interaction among the particles, so that the magnetic fluid is kept stable. Meanwhile, the protonation degree of the cationic polymer can be adjusted by adjusting the pH value of the solution, so that the stability degree of the magnetic fluid is changed. The lower the pH value of the solution is, the higher the protonation degree of the cationic polymer is, the stronger the surface electrical property of the magnetic nanoparticles modified by the cationic polymer is, the stronger the dispersity of the magnetic nanoparticles is, and the more stable the corresponding magnetic fluid is. The higher the pH value of the solution is, the lower the protonation degree of the cationic polymer is, the weaker the surface electrical property and the weaker the dispersity of the magnetic nanoparticles modified by the cationic polymer are, and the magnetic nanoparticles in the magnetic fluid can be easily recovered.
The cationic polymer refers to a polymer having a cationic group in the main chain, and the cationic polymer used in the present invention has an amino group; in the case of polylysine, polyglutamic acid and its derivatives, polyethyleneimine, and polypropyleneimine, a common feature of these polymer structures is that they contain many amino groups in the molecule, which easily bind to protons in solution, thereby making the molecule positively charged (this process is also referred to as "protonation"). Furthermore, the lower the pH of the solution, the higher the protonation degree of the polymer and the stronger the electrical properties.
The cationic polymer is adopted to modify the magnetic nanoparticles, the protonation of the cationic polymer can enable the surfaces of the magnetic nanoparticles to carry positive charges, and then the agglomeration effect among the particles can be overcome through the electrostatic interaction among the particles, so that the magnetic fluid with excellent performance is prepared. Moreover, the protonation degree of the polymer can be adjusted by adjusting the pH value of the solution, so that the dispersity of the magnetic nanoparticles in the solution, namely the stability of the magnetic fluid, can be adjusted. The lower the pH value of the solution, the higher the protonation degree of the cationic polymer, the stronger the surface electrical property of the magnetic nanoparticles modified by the cationic polymer, the stronger the dispersibility of the magnetic nanoparticles, and the more stable the corresponding magnetic fluid, so that the magnetic nanoparticles can be applied to various fields. The higher the pH value of the solution is, the lower the protonation degree of the cationic polymer is, the weaker the surface electrical property and the weaker the dispersity of the magnetic nanoparticles modified by the cationic polymer are, and the magnetic nanoparticles in the magnetic fluid can be easily recovered. In addition, the magnetic nanoparticles in the acidic solution are transferred into the neutral solution, so that the magnetic nanoparticles do not lose good dispersibility rapidly, and can be applied to occasions with requirements on the pH value of the solution.
The method for modifying the cationic polymer on the surface of the magnetic nanoparticles can be direct mixing under a mechanical stirring state, or can be used for modifying the magnetic nanoparticles appropriately and then enabling the magnetic nanoparticles to interact with the cationic polymer. The method can particularly modify the cationic polymer on the surfaces of the magnetic nanoparticles by adopting an ultrasonic heating environment, the ultrasonic heating environment is favorable for forming coordinate bonds between the cationic polymer and the magnetic nanoparticles, and the method is simple to operate and convenient to adjust.
Specifically, the present invention can achieve the following advantageous effects:
(1) the prepared magnetic fluid has adjustable stability, and magnetic nano particles in the magnetic fluid can be easily recovered after the magnetic fluid fully plays a role in an application scene so as to avoid the problems of environmental pollution, container adhesion, overhigh requirement on magnetic field parameters and the like. The stability of the magnetic fluid prepared by the method can be adjusted by an acidification process or an alkalization process, the stability of the magnetic fluid can be enhanced by the acidification process, and the stability of the magnetic fluid can be weakened by the alkalization process. For example, the hydrochloric acid solution and the sodium hydroxide solution with the concentration of 0.5M can be respectively selected as the acid solution and the alkaline solution, and the more the dropwise adding amount is, the more obvious the effect of enhancing or weakening the stability of the magnetic fluid is.
(2) The cationic polymer has high adhesiveness and adsorptivity, is easy to combine magnetic nanoparticles, has simple preparation process operation, low requirement on equipment and low production cost, and is beneficial to industrial production.
(3) The prepared magnetic fluid can be easily purified by adjusting the pH value of the solution, and is beneficial to the utilization of a plurality of fields such as chemical industry, pollution control, biology and the like, and the magnetic fluid solution prepared by the traditional method often has residual surfactant, which can cause damage to human bodies and environment.
(4) The prepared magnetic fluid can change the stability degree of the magnetic fluid by adjusting the pH value of the solution, and is beneficial to the utilization of the fields of material purification and separation and the like. The magnetic fluid formed by dispersing the magnetic nano particles modified by the cationic polymer in the carrier fluid has adjustable stability, and the magnetic nano particles can be conveniently separated from the carrier fluid by using alkalization treatment and destroying the stability of the magnetic fluid, so that the requirements on the magnetic field intensity and the gradient of a separation system can be effectively simplified.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
The magnetic fluid with adjustable stability in the embodiment is prepared by the following steps:
1) synthesizing magnetic nano particles by an alkali coprecipitation method.
a) Introducing nitrogen into 100mL of deionized water to remove oxygen;
b) adding FeSO4·7H2O (1.39g, 5mmol) and FeCl3·6H2O(2.70g，10mmol)；
c) Dropwise adding 50mL of ammonia water;
d) after the dropwise addition, the mixture is stirred vigorously and heated in a water bath at 80 ℃ for 30 min;
2) the magnetic nanoparticles are modified with branched polyethyleneimine.
a) To the above solution was added dropwise 50mL of a PEI solution (40 g/L);
b) after the dropwise addition is finished, carrying out ultrasonic treatment, vigorous stirring and water bath heating at 80 ℃ for 30 min;
c) the product was collected, separated with a magnet, washed several times with deionized water, and resuspended in 40mL of deionized water for subsequent handling.
3) Magnetic fluid prepared by acidifying magnetic nanoparticle solution to enhance stability of magnetic nanoparticle solution
a) To the above solution was added dropwise 10mL of 0.5M hydrochloric acid solution (acidified to pH 2);
b) shaking and standing for 10 min.
4) The solution can be further treated by a high-speed centrifugal separation method (the rotating speed adopted by the high-speed centrifugal separation is not lower than 2 ten thousand rpm, and the specific rotating speed value can be flexibly adjusted), so that the cationic polymer modified magnetic nanoparticles in the solution are resuspended in neutral carrier liquid, and finally the neutral and stability-adjustable magnetic fluid solution is obtained.
In the above embodiment, the acidification treatment of the cationic polymer modified magnetic nanoparticles is specifically to adjust the pH value to 2, and then to stand for 10 min; according to actual requirements, other pH values within the range of 1-5 can be selected as the pH value condition, and other time durations (such as 20min and the like) within the range of 5-60 min can be selected as the standing time. If the acidification degree of the solution is too small (the pH value is too high) and the standing time is too short, the cationic polymer is difficult to protonate fully, so that the stability of the magnetic fluid is weak; if the acidification degree of the solution is too large (the pH value is too small) and the standing time is too long, the cationic polymer can fall off from the magnetic nanoparticles, and the magnetic fluid is not beneficial to improvement, so that the specific value of the pH value and the specific time of the standing treatment can be flexibly adjusted according to actual requirements.
The magnetic fluid with adjustable stability obtained in the above embodiment has an aqueous solution as the carrier liquid.
The raw materials used in the present invention, such as branched polyethyleneimine, can be commercially available materials. The magnetic nano particles adopted in the invention are not limited in kind, and can be ferroferric oxide, and can also be ferromagnetic oxides such as Ni, Co and the like. In addition to polyethyleneimine as the cationic polymer, polylysine, polyglutamic acid derivatives, polypropyleneimine, and the like may be used as the cationic polymer.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. The preparation method of the magnetic fluid with adjustable stability is characterized by comprising the following steps:
(1) preparing magnetic nanoparticles in a solution system;
(2) modifying the magnetic nanoparticles by using a cationic polymer in the solution system obtained in the step (1), and dispersing the modified magnetic nanoparticles in a carrier liquid to obtain a magnetic fluid; wherein the cationic polymer has an amino group;
(3) adding an acidic solution into the magnetofluid solution system obtained in the step (2) to acidify the solution system until the pH value of the solution is 1-5, and enhancing the stability of the magnetofluid through an acidification process;
(4) and (4) processing the solution system obtained in the step (3) by a high-speed centrifugal separation method of not less than 20000rpm, so that the cationic polymer modified magnetic nanoparticles in the solution system are suspended in neutral carrier liquid, and finally obtaining the neutral and stability-adjustable magnetic fluid solution.
2. The preparation method according to claim 1, wherein the step (2) is to add a cationic polymer solution to the solution system obtained in the step (1) and modify the magnetic nanoparticles in an ultrasonic heating environment, thereby obtaining the cationic polymer modified magnetic nanoparticles.
3. The preparation method according to claim 1, wherein the step (3) is specifically to drop an acidic solution into the solution system obtained in the step (2), uniformly mix, and then stand for 5-60 min.
4. The preparation method according to claim 1, wherein the step (3) is to acidify the solution system with an acidic solution to a solution pH value of 1-5, then to stand for 5-60 min, then to separate the magnetic nanoparticles from the carrier liquid by treating the obtained solution system with a super high speed centrifuge, and finally to re-suspend the separated magnetic nanoparticles in neutral ultrapure water.
5. The preparation method according to claim 1, wherein in the step (1), the magnetic nanoparticles have a particle size ranging from 1 to 500 nm;
in the step (2), the cationic polymer is branched polyethyleneimine with the relative molecular mass of 25 kDa.
6. The preparation method according to claim 5, wherein the step (1) is to prepare the ferroferric oxide nanoparticles by an alkali coprecipitation method.
7. The method of claim 1, wherein the solution system is an aqueous solution system;
in the step (2), the carrier liquid is ultrapure water.
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| CN100592439C (en) * | 2005-08-08 | 2010-02-24 | 中国人民解放军军事医学科学院毒物药物研究所 | Bio-compatibility magnetic fluid |
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