Patent Publication Number: US-2019168298-A1

Title: Graphene and ferroferric oxide@gold composite material and preparation method and application thereof

Description:
TECHNICAL FIELD 
     The disclosure relates to the field of materials, particularly to a graphene and Fe 3 O 4 -Au (also referred to as Fe 3 O 4 @Au composite, and a preparation method and a use thereof. 
     BACKGROUND 
     At present, with the rapid development of nanotechnology, the function of single component materials has great limitations. For example, graphene has a very high dielectric constant, and can be polarized by an external magnetic field in an electromagnetic field; while the electric dipole inside the graphene material relaxes as the electric field moves, thus consuming part of the electrical energy to cause the dielectric itself to emit heat, i.e., generate dielectric loss. A single graphene sheet is easily penetrated by electromagnetic waves and then loses electromagnetic wave absorption capability; meanwhile, the single high dielectric loss may also lead to difficulty in impedance matching. While ferroferric oxide has ferromagnetism and is a good microwave absorber and nuclear magnetic contrast agent. By combining graphene and ferroferric oxide, electromagnetic waves can be hindered by the barrier between quantum dots and the steric hindrance effect after penetrating into the composite, and then the direct penetration of the electromagnetic waves can be delayed, thereby achieving the effect of reducing the frequency of electromagnetic waves. The surface plasmon resonance effect of nano-gold makes it have good optical absorption properties and light-to-heat conversion effects. CN106501235A discloses a method for detecting  vibrio parahaemolyticus  based on enhanced Raman effects of graphene oxide/ferroferric oxide/colloidal gold nanoparticles, wherein the connection system of graphene oxide/ferroferric oxide/colloidal gold nanoparticles is unstable. Therefore, how to prepare a system-stable multifunctional composite is of great significance. 
     SUMMARY 
     Based on this, it is necessary to provide a system-stable graphene and Fe 3 O 4 -(coated)gold composite, and a preparation method and a use thereof. 
     A method of preparing a graphene and Fe 3 O 4 -gold composite is provided, wherein the method includes the following steps:
         (1) preparing a thiol alkyl azide-modified Fe 3 O 4 -Au complex and an alkynylated graphene oxide,   wherein, the preparing a thiol alkyl azide-modified Fe 3 O 4 -Au complex includes the following steps:   dispersing nano-ferroferric oxide in a reductant solution, ultrasonic processing and heating to 65° C. to 75° C., adding chloroauric acid aqueous solution dropwise under stirring, stopping heating after reaction, and then stirring to conduct ripening reaction to obtain a Fe 3 O 4 -Au complex with a core-shell structure; and   placing the Fe 3 O 4 -Au complex and thiol alkyl azide in a first solvent to perform a reaction at 40 to 45° C. under stirring in a protective atmosphere, and then rinsing repeatedly with a second solvent to obtain the thiol alkyl azide-modified Fe 3 O 4 -Au complex;   the preparing an alkynylated graphene oxide includes the following steps:   placing the graphene oxide in an activator to conduct an activating reaction at a condition of 65 to 75° C., and then adding propargyl alcohol to continue reacting for 20 to 28 h to obtain the alkynylated graphene oxide;   (2) preparing a graphene and Fe 3 O 4 -Au composite,   wherein, the thiol alkyl azide-modified Fe 3 O 4 -Au complex and the alkynylated graphene oxide prepared in step (1) are dispersed in a third solvent, a catalyst is added, and the reaction is stirred in a protective atmosphere to collect a product that is the graphene and Fe 3 O 4 -Au composite.       

     In one embodiment, in the step (2), the mass concentration ratio of the thiol alkyl 25 azide-modified Fe 3 O 4 -Au complex to the alkynylated graphene oxide is 30-50:30-50. 
     In one embodiment, in the step (2), the third solvent is dimethylformamide or tetrahydrofuran, and the catalyst is N,N,N,N″,N″-pentamethyldiethylenetriamine and cuprous bromide. 
     In one embodiment, in the step (1); the number of carbon atoms in the thiol alkyl azide is N, wherein 6&lt;N&lt;15; the mass ratio of the Fe 3 O 4 -Au complex to thiol alkyl azide compound is 100:0.4-2 one embodiment, in the step (1), the activator is thionyl chloride, and the activating reaction time of the graphene oxide in the thionyl chloride is 20-28 h. 
     In one embodiment, in the step (1), the first solvent is toluene; the second solvent is a non-polar solvent, and the reaction time of the Fe 3 O 4 -Au complex and the thiol alkyl azide compound is 45-55 h. 
     In one embodiment, in the step (1), the nano-ferroferric oxide is prepared by a process including the following steps: dissolving 1.8-2.2 g of FeCl 3 .6H 2 O in 100±5 mL of distilled water, adding 0.8-1.2 g of FeCl 2 .4H 2 O with stirring in a nitrogen atmosphere, then adding ammonia water or sodium hydroxide solution dropwise until the pH of the reaction solution is raised to 8.8-9.5, heating to 80° C.; to 90° C. for reacting for 20-30 min, and then conducting magnetic separation to obtain the nano-ferroferric oxide; 
     In the steps for preparing the thiol alkyl azide-modified Fe 3 O 4 -Au complex, the reductant is sodium citrate, and the sodium citrate has a mass concentration of 1-3 mg/mL and a volume of 100±5 mL; the mass concentration of the chloroauric acid aqueous solution is 8-12 mg/mL, and its addition volume is 8-12 mL. 
     In one embodiment, in the step (1), the preparation process of the graphene oxide includes the following steps:
         adding 13-17 mL of concentrated sulfuric acid to a mixed system of 0.4-0.6 g of natural graphite and 0.5-0.6 g of sodium nitrate under an ice bath condition, then adding 1.3-1.7 g of potassium permanganate with maintaining the temperature of the reaction system as no higher than 5° C.;   after the addition, heating the reaction system to 28-32° C. to react for 55-65 min, then adding 15-25 mL of deionized water to the reaction system, further heating to 90-99° C. to continue the reaction for 13-17 min, adding 65-75 mL of deionized water, then adding mL of hydrogen peroxide dropwise, removing excess potassium permanganate to get a bright yellow solution; let the solution stand still for one day, then removing the supernatant, and washing the lower layer yellow solid with deionized water repeatedly until there is no acid and sulfate ion in the supernatant, and then freeze-drying to obtain the graphene oxide.       

     A graphene and Fe 3 O 4 -Au composite prepared by the method of preparing a graphene and Fe 3 O 4 -Au composite is provided. 
     Uses of the graphene and Fe 3 O 4 -Au composite in nuclear magnetic imaging, microwave thermoacoustic imaging, photoacoustic imaging and X-ray imaging are also provided. 
     The present disclosure has the following beneficial effects: 
     In the method of preparing the graphene and Fe 3 O 4 -Au composite according to the present disclosure, firstly, the Fe 3 O 4 -Au complex having high content of coated gold is prepared by an one-pot process, and then the thiol alkyl azide-modified Fe 3 O 4 -Au complex is further prepared so that a gold-sulfur bond is formed on the surface of the nano-gold, and the graphene oxide is activated by the activator to allow the carboxyl group on the surface of the graphene oxide to react with the propargyl alcohol to form the alkynylated graphene oxide, and then click reaction of alkynyl group and azide group is carried out between the thiol alkyl azide-modified Fe 3 O 4 —Au complex and the alkylated graphene oxide under the action of a catalyst in a nitrogen atmosphere, thereby the graphene and Fe 3 O 4 -Au composite connected by the organic covalent bond is obtained, wherein the click reaction has a fast reaction speed and a high efficiency. The method of preparing the graphene and Fe 3 O 4 -Au composite according to the present disclosure can be conducted under mild reaction conditions, and the method is simple and reliable. Since the graphene and Fe 3 O 4 -Au composite of the present disclosure is connected by covalent bond, the system of the graphene and Fe 3 O 4 -Au composite is stable, and at the same time, the graphene and Fe 3 O 4 -Au composite has characteristics such as magnetic properties, good microwave absorption property, good plasmon resonance absorption and attenuation of X-ray&#39;s, and can be applied to nuclear magnetic imaging, microwave thermoacoustic imaging, photoacoustic imaging and X-ray imaging. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a transmission electron micrograph image of the Fe 3 O 4 -Au complex prepared in Example 1. 
         FIG. 2  is a concentration-signal response diagram of the graphene and Fe 3 O 4 -Au composite prepared in Example 1 in a nuclear magnetic imaging application; 
         FIG. 3  is a concentration-signal response diagram of the graphene and Fe 3 O 4 -Au composite prepared in Example 1 in a photoacoustic imaging application; 
         FIG. 4  is a concentration-signal response diagram of the graphene and Fe 3 O 4 -Au composite prepared in Example 1 in a microwave thermoacoustic imaging application; 
         FIG. 5  is a concentration-signal response diagram of the graphene and Fe 3 O 4 -Au composite prepared in Example 1 in an X-ray imaging application, 
     
    
    
     DETAILED DISCUSSION OF ILLUSTRATIVE EMBODIMENT 
     The graphene and Fe 3 O 4 -Au composite (G-Fe 3 O 4 -Au or G-Fe 3 O 4 @Au for short) and the preparation method and use thereof will be described in detail below with reference to specific examples. 
     Example 1 
     The present example provides a method of preparing the graphene and Fe 3 O 4 -Au composite, including the following steps: 
     (1) preparing a thiol alkyl azide-modified Fe 3 O 4 -Au complex and an alkynylated graphene oxide: 
     wherein, the thiol alkyl azide-modified Fe 3 O 4 -Au complex was prepared by a process including the following steps: 
     A. Preparing a Colloidal Solution of Nano-Ferroferric Oxide by a Coprecipitation Method. 
     2.703 g of FeCl 3 -6H 2 O was placed in a four-neck reaction flask, dissolved by adding 100 mL of triple distilled water, protected by nitrogen, then added 0.998 g of FeCl 2 .4H 2 O under stirring, and added ammonia water dropwise into the reaction system through the inlet until the pH of the solution was raised to 9.2. After the addition of the ammonia water was stopped, the reaction was continued for 15 min, then heated to 85° C. and continued for 25 min to obtain the colloidal solution of nano-ferroferric oxide. 
     B. Preparing a Nano-Ferroferric Oxide-(Coated)Gold Complex by a Reduction Method. 
     20 mL of the colloidal solution of nano-ferroferric oxide obtained in the step A was magnetically separated to obtain solid particles. The solid particles were washed 3 times with 2 mg/mL of sodium citrate aqueous solution and then dissolved in 100 mL of sodium citrate aqueous solution having a same concentration (i.e., 2 mg/mL), and placed in a ultrasound machine for sonication for 7 h. The sonicated mixed solution was placed in a three-necked flask, heated to 70° C. under stirring, slowly added HAuCl 4  aqueous solution (10 mg/mL, 10 mL) dropwise under stirring, stopped heating after one hour of continuous reaction, followed by 40 min of ripening under stirring, and then stopped reaction to obtain the nano-ferroferric oxide-(coated)gold complex. In this step, an one-pot process was used to prepare the nano-ferroferric oxide-(coated)gold complex, which leads to high coated gold content and high preparation efficiency. 
     The transmission electron micrograph image of the Fe 3 O 4 -Au complex prepared in this step is shown in  FIG. 1 . As can be seen from  FIG. 1 , the nano-Fe 3 O 4 -Au complex has a small average particle size, wherein the particle size is concentrated and the overall dispersion is good. 
     C. Modifying the Fe 3 O 4 -Au Complex with Thiol Alkyl Azide. 
     40 mg of Fe 3 O 4 -Au complex obtained in the step B and 0.2 mg of thiol alkyl azide (i.e., N 3 -(CH 2 ) n —SH, 6&lt;n&lt;15) were placed in toluene, stirred to react for 48 h at 40-45° C. in a nitrogen atmosphere; and then rinsed repeatedly with n-hexane or toluene to remove unnecessary unmodified chain segments. The gold-sulfur bond is formed on the surface of the nano-gold by preparing the thiol alkyl azide-modified Fe 3 O 4 -Au complex. 
     The alkenylated graphene oxide can be prepared by a process including the following steps: 
     0.5 g of natural graphite and 0.55 g of sodium nitrate were placed in a three-necked flask, which was then placed in an ice bath, slowly added 15 mL of concentrated sulfuric acid, stirred constantly, and then slowly added 1.5 g of potassium permanganate to ensure that the temperature in the flask is not higher than 5° C. After addition, the raw materials were reacted at 30° C. for 1 h. Further, 20 mL of deionized water was added to the three-necked flask, and the reaction system was heated to 95° C. and maintained for 15 min. An additional 70 mL of deionized water was added and 2.5 mL of hydrogen peroxide was added dropwise to remove excess potassium permanganate, and at this moment the solution turned bright yellow. The mixture was allowed to stand for one day and the upper layer of acid liquor was poured out. The lower layer of yellow solid was washed by deionized water and centrifuged, discarded the supernatant, and repeated washing several times until there was no acid and sulfate ions in the supernatant. The washed sample was freeze-dried in low temperature by a freeze dryer to obtain the graphene oxide. 
     At a condition of 65-75° C., 1 g of the graphene oxide obtained in the previous step was placed in 0.1 mL of thionyl chloride for activation for 24 h, and then added propargyl alcohol to continue to react for 24 hours to obtain the alkynylated graphene oxide. In this step, the graphene oxide is activated by thionyl chloride to allow the carboxyl group on the surface of the graphene oxide to react with the propargyl alcohol to form the alkynylated graphene oxide. 
     (2) preparing the graphene and Fe 3 O 4 -Au composite: 
     40 mg of the thiol alkyl azide-modified. Fe 3 O 1 -Au complex and 40 mg of the alkynylated to oxide prepared in the above step (1) were added to 20 mL of dimethylformamide or tetrahydrofuran, and added 0.01 mL of N,N,N″,N″-pentamethyldiethylenetriamine and 6 mg of cuprous bromide as catalysts, and stirred to react for 48 hours under a nitrogen atmosphere. In this step, a gold-sulfur bond was formed by the reaction of the sulfhydryl group at one end of the thiol alkyl azide with the surface of the Fe 3 O 4 -Au complex, and a covalent bond was formed by the click reaction of the azide group at the other end with the alkenyl group in the alkynylated graphene oxide. After the reaction was finished, the product was dissolved in dimethylformamide or tetrahydrofuran, and then filtrated and collected to obtain the graphene and Fe 3 O 4 -Au composite, 
     Performance Test 
     According to the relevant test requirements, the graphene and Fe 3 O 4 -Au composite (G-Fe 3 O 4 -Au) prepared in Example 1 was prepared into G-Fe 3 O 4 -Au nanoparticle solutions with concentration gradients of 0 mmol/L, 0.1 mmol/L, 0.2 mmol/L, 0.4 mmol/L, 0.8 mmol/I, and 1 mmol/L, respectively. The solutions were applied in nuclear magnetic imaging, photoacoustic imaging and microwave thermoacoustic imaging, and the concentration-signal response curves are shown in  FIG. 2 ,  FIG. 3  and  FIG. 4 , respectively. 
     As can be seen from  FIG. 2 , at the same [Fe] concentration, in the T2 sequence nuclear magnetic image of the G-Fe 3 O 4 -Au nanoparticles, the color of the response signal gradually deepens with the increase of the concentration of the G-Fe 3 O 4 -Au. 
     As can be seen from  FIG. 3 , the response intensity of the photoacoustic signal gradually increases with the increase of the concentration of G-Fe 3 O 4 -Au, i.e., they are positively correlated. 
     As can be seen from  FIG. 4 , the microwave thermoacoustic signal increases with the increase of the concentration of [Fe] in G-Fe 3 O 4 -Au, and the thermoacoustic signal of G-Fe 3 O 4 -Au is linearly related to the concentration of [Fe] in G-Fe 3 O 4 -Au on the whole. 
     According to the relevant test requirements in X-ray imaging, the graphene and Fe 3 O 4 -Au composite prepared in Example 1 was further prepared into solutions with concentration gradients of 1 mg/mL, 2 mg/mL, 4 mg/mL and 8 mg/mL which gradients correspond to the imaging mark numbers 4, 3, 2 and 1 in the drawing, respectively. The test results are shown in  FIG. 5 . As can be seen from  FIG. 5 , in X-ray imaging, the color depth of the X-ray image deepens with the increase of the mass concentration of G-Fe 3 O 4 -Au. 
     The technical features of the above-described embodiments may be combined arbitrarily. To simplify the description, not all the possible combinations of the technical features in the above embodiments are described. However, all of the combinations of these technical features should be considered as within the scope of the disclosure, as long as such combinations do not contradict with each other. 
     The above embodiments merely represent several embodiments of the present disclosure, and the description thereof is specific and detailed, but it should not be construed as limiting the scope of the present disclosure. It should be noted that, for those skilled in the art, several variations and improvements may be made without departing from the concept of the present disclosure, and those are all within the protection scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the appended claims.