Polydopamine / nanosilver / graphene composite aerogel and preparation method and application thereof

Abstract

The present invention relates to a polydopamine / silver nanometer / graphene composite aerogel, a preparation method thereof and an application. The preparation method comprises the following steps: S1. Mix AgNO3, trisodium citrate and deionized water to obtain a silver colloid solution, centrifuge the silver colloid solution and discard the supernatant to obtain silver nanoparticles; S2. Prepare a graphene oxide solution by the Hummer method; S3. Mix the silver nanoparticles and the graphene oxide solution, ultrasonicate and perform a first stirring, adjust the pH to weakly acidic, add a dopamine hydrochloride solution, perform a second stirring in an oxygen-containing environment, carry out a reduction reaction, and finally elute, freeze and dry to obtain a polydopamine / silver nanometer / graphene composite aerogel. Compared with the prior art, the present invention promotes the polymerization of dopamine and the synthesis of reduced graphene oxide aerogel in a weak acid environment, and can also be used as a surface-enhanced Raman substrate. The aerogel structure is fluffy, the mechanical strength is improved, and the specific surface area is further increased.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel preparation, and particularly relates to a polydopamine / nano silver / graphene composite aerogel and a preparation method and application thereof. Background Art

[0002] Graphene aerogel (GA), whose structure is formed by three-dimensional lapping and assembling of graphene sheets, has a three-dimensional continuous porous network structure, inheriting the advantages of graphene and aerogel such as high specific surface area, high porosity, high electrical conductivity, and good thermal conductivity and mechanical strength, and has important application prospects in the fields of energy storage, sensing, adsorption, thermal interface materials, etc.

[0003] Dopamine is easily polymerized without the need for initiators and cross-linking agents. Polydopamine can increase the π-π interaction and hydrophobic interaction of graphene sheets, promote the self-assembly between adjacent graphene sheets, and prepare green and pollution-free dopamine-reduced graphene oxide aerogel by using the self-polymerization and reduction properties of dopamine in water. The pH of traditional dopamine polymerization is usually alkaline, and the polydopamine-reduced graphene oxide aerogel prepared under alkaline conditions has defects such as volume swelling, weak resilience, and easy fragmentation. Summary of the Invention

[0004] The purpose of the present invention is to provide a polydopamine / nano silver / graphene composite aerogel and a preparation method and application thereof in order to overcome the defects of the polydopamine / graphene composite aerogel prepared by the above-mentioned prior art, such as volume swelling, weak resilience, and easy fragmentation. The polydopamine / nano silver / graphene composite aerogel is loaded with silver nanoparticles and is prepared in a weak acid environment.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a preparation method of a polydopamine / nano silver / graphene composite aerogel, including the following steps:

[0007] S1. Mix AgNO3, trisodium citrate, and deionized water to obtain a silver colloid solution, centrifuge the silver colloid solution, and discard the supernatant to obtain silver nanoparticles;

[0008] S2. Prepare graphene oxide solution by the Hummer method;

[0009] S3. Mix the silver nanoparticles obtained in step SI with the graphene oxide solution obtained in step S2, ultrasonicate the mixture and perform a first stirring, adjust the pH to weakly acidic, then add the dopamine hydrochloride solution and perform a second stirring in an oxygen-containing environment, then transfer it to a closed space for a reduction reaction, and finally perform elution, freezing, and drying in sequence to obtain a polydopamine-reduced graphene oxide hydrogel loaded with silver nanoparticles, which is a polydopamine / nano silver / graphene composite aerogel.

[0010] Further, in step S1, the concentration of the AgNO3 solution is (1.0 - 3.0)×10 -4 mol / L, the concentration of the trisodium citrate solution is 8 - 12 g / L, the volume ratio of the AgNO3 solution, the trisodium citrate solution to the silver colloid solution is (1 - 5):(1 - 5):100, and the particle size of the silver nanoparticles is 20 - 50 nm; the mixing temperature is 100 °C and the mixing time is 25 - 35 min;

[0011] In step S3, the concentration of the graphene oxide solution is 2 - 4 mg / mL, and the volume ratio of the graphene oxide solution to the silver colloid solution is (1 - 3):5.

[0012] Further, in step S3, the ultrasonication time is 0.5 - 1 h; the temperature of the first stirring is room temperature and the first stirring time is 1 - 3 h.

[0013] Further, in step S3, use a tris(hydroxymethyl)aminomethane (Tris) solution to adjust the pH to 6.0 - 7.0, and stabilize for 25 - 35 min after adjusting the pH.

[0014] Further, in step S3, the concentration of the dopamine hydrochloride solution is 1.0 - 3.0 mg / mL, and the dopamine hydrochloride solution is added dropwise slowly, where the mass ratio of dopamine hydrochloride to graphene oxide is 1:(5 - 10).

[0015] Further, in step S3, the temperature of the second stirring is room temperature and the second stirring time is 30 - 80 min.

[0016] Further, in step S3, the temperature of the reduction reaction is 120 - 180 °C and the reduction reaction time is 10 - 15 h.

[0017] More preferably, the temperature of the reduction reaction is 150 - 180 °C.

[0018] Further, in step S3, the elution process is: select an ethanol aqueous solution as the eluent, wash at least 3 times, and the washing time for each time is 1 - 3 h, where the volume ratio of ethanol to water in the eluent is 1:(4 - 5); the freezing temperature is -40 °C to -20 °C and the freezing time is 5 - 10 h.

[0019] More preferably, the freezing time is 7 to 8 h.

[0020] The second technical solution of the present invention is to provide a polydopamine / nano silver / graphene composite aerogel based on the preparation method described in the first technical solution above.

[0021] The third technical solution of the present invention is to provide an application of the polydopamine / nano silver / graphene composite aerogel described in the second technical solution above. The polydopamine / nano silver / graphene composite aerogel is used as a substrate for surface-enhanced Raman scattering sensors to detect pollutants in the environment.

[0022] Surface-enhanced Raman scattering (SERS) can obtain a signal enhanced compared to ordinary Raman scattering by adsorbing molecules on the surface of rough metals or metal sol particles. It requires no labeling, has high sensitivity, and good accuracy. The SERS enhancement effect mainly depends on the size, morphology, and uniformity of metal nanostructures. When assembling metal nano-ions in the aerogel, the three-dimensional spatial structure provided by the graphene aerogel can not only form three-dimensionally distributed SERS "hot spots", but also provide a large specific surface area for the adsorption of nanomaterials, thereby providing more SERS "hot spots" and significantly improving the SERS signal of trace analytes.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention provides a synthesis method for initiating the polymerization of dopamine and reducing graphene oxide aerogel in a weak acid environment, and at the same time loading silver nanoparticles, which enhances the conductivity of the aerogel. The prepared aerogel does not show a swelling situation in volume, has a fluffy structure, further increases the specific surface area, and improves the mechanical strength such as good resilience and is not easily broken. The polydopamine-reduced graphene oxide aerogel loaded with silver nanoparticles prepared in a weak acid environment (i.e., polydopamine / nano silver / graphene composite aerogel) has novelty and can expand its application scenarios.

[0025] (2) The polydopamine-reduced graphene oxide aerogel loaded with silver nanoparticles prepared by the present invention can be used as a surface-enhanced Raman substrate. Combining with surface-enhanced Raman technology, it can simultaneously achieve high-selectivity and high-sensitivity detection of substances such as rhodamine (R6G) in complex environments such as water bodies.

[0026] (3) On the one hand, the present invention successfully synthesizes the hydrogel by green chemical reduction. On the other hand, polydopamine can increase the π-π interaction and hydrophobic interaction between graphene sheets, promote the self-assembly between adjacent graphene sheets, form a highly ordered 3D structure, and finally expand its application scope and scenarios by adding silver nanoparticles.

[0027] (4) In the present invention, dopamine hydrochloride is used as a reducing agent and binder, which has the advantages of being safe, environmentally friendly, easy to obtain, inexpensive, mild polymerization reaction conditions, and no need for additional initiators and crosslinking agents, etc.

[0028] (5) The present invention has a high repeatability rate, a simple preparation process, and is suitable for large-scale commercial production. Description of the Drawings

[0029] Figure 1 It is the TEM image of the polydopamine / nanosilver / graphene composite aerogel prepared in Example 1.

[0030] Figure 2 It is the Raman peak spectrum of the polydopamine / nanosilver / graphene composite aerogel prepared in Example 2.

[0031] Figure 3 It is the TEM image of the silver nanoparticles in Example 2.

[0032] Figure 4 It is the SEM image of the polydopamine / nanosilver / graphene composite aerogel prepared in Example 2. Detailed Embodiments

[0033] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0034] In the following examples and comparative examples, unless otherwise specified, the raw materials or treatment techniques are all conventional commercially available raw material products or conventional treatment techniques in the art.

[0035] The graphene oxide solution uses 325-mesh graphite powder as the raw material.

[0036] Example 1:

[0037] The preparation of a polydopamine-reduced graphene oxide aerogel loaded with silver nanoparticles in a weak acid environment includes the following steps:

[0038] (1) Synthesis of silver nanoparticles: Accurately add 1.5 mL of 1×10 -4 mol·L -1 silver nitrate solution (AgNO3) into a clean 50 mL beaker, add deionized water to 50 mL, boil, and then dropwise add 0.5 mL of 8 g / L trisodium citrate, boil for 30 min to obtain a silver colloid solution, and naturally cool to room temperature. Then, after centrifugation, silver nanoparticles are obtained. The TEM of the silver nanoparticles is as Figure 3 shown.

[0039] (2) Add the obtained silver nanoparticles to 20 mL of a 2 mg / mL graphene oxide solution (prepared by the Hummer method), and sonicate for 30 min, then stir for 30 min. The purpose of this step is to allow the silver nanoparticles to come into full contact with the graphene oxide and prevent the silver nanoparticles from aggregating together. Then, slowly add a Tris solution with a concentration of 1 mg / mL while precisely adjusting the pH to between 6 and 7.

[0040] (3) Slowly add 2 mL of a 1 mg / mL hydrochloric acid dopamine solution to step (2), continue stirring for 60 min, then transfer to a high-pressure hydrothermal reactor and carry out a reduction reaction at 180 °C for 12 h. A regular-shaped black cylinder is obtained, which is the graphene hydrogel. Then, naturally cool to room temperature and wash 3 times with an ethanol aqueous solution, with each washing time being 3 h, where the volume ratio of ethanol to deionized water is 1:4.

[0041] (4) After the washing is completed, place it in the freezer compartment of the refrigerator. After freezing for 3 h, put it into a set vacuum freeze-dryer, where the temperature is -40 °C and the vacuum freeze-drying time is 6 h. Finally, a polydopamine-reduced graphene oxide aerogel loaded with silver nanoparticles is obtained, that is, a polydopamine / silver nanometer / graphene composite aerogel, and its TEM image is as Figure 1 shown.

[0042] Example 2:

[0043] Preparation of a polydopamine-reduced graphene oxide aerogel loaded with silver nanoparticles in a weak acid environment, including the following steps:

[0044] (1) Synthesis of silver nanoparticles: Accurately add 1.5 mL of a 1×10 -4 mol·L -1 silver nitrate solution (AgNO3) to a clean 50 mL beaker, add deionized water to 50 mL, boil, and then dropwise add 0.5 mL of an 8 g / L trisodium citrate, boil for 30 min to obtain a silver colloid solution, and naturally cool to room temperature. Then, after centrifugation, silver nanoparticles are obtained.

[0045] (2) Add the obtained silver nanoparticles to 20 mL of a 3 mg / mL graphene oxide solution (prepared by the Hummer method), sonicate for 60 min, and then stir for 30 min. The purpose of this step is to allow the silver nanoparticles to come into full contact with the graphene oxide and prevent the silver nanoparticles from aggregating together. Then, slowly add a Tris solution with a concentration of 1 mg / mL while precisely adjusting the pH to between 6.5 and 6.8.

[0046] (3) Slowly add 2 mL of dopamine hydrochloride solution with a concentration of 2 mg / mL to step (2), continue stirring for 60 min, then transfer it to a high-pressure hydrothermal reactor and carry out a reduction reaction at 180 °C for 12 h. A regular-shaped black cylinder is obtained, which is the graphene hydrogel. Then naturally cool it to room temperature and wash it 3 times with an ethanol aqueous solution, with each washing time being 3 h, where the volume ratio of ethanol to deionized water is 1:4.

[0047] (4) After the washing is completed, place it in the freezer of the refrigerator. After freezing for 3 h, put it into a set vacuum freeze-drying oven, where the temperature is -40 °C and the vacuum freeze-drying time is 6 h. Finally, a polydopamine-reduced graphene oxide aerogel loaded with silver nanoparticles, that is, a polydopamine / nano-silver / graphene composite aerogel, is obtained. Its SEM image is as Figure 4 shown.

[0048] Example 3:

[0049] Compared with Example 1, most of them are the same. The difference is that in step (3), the concentration of the dopamine hydrochloride solution is 2 mg / mL.

[0050] Example 4:

[0051] Compared with Example 1, most of them are the same. The difference is that in step (3), the concentration of the dopamine hydrochloride solution is 3 mg / mL.

[0052] Example 5:

[0053] Compared with Example 1, most of them are the same. The difference is that in step (2), the concentration of the graphene oxide solution is 3 mg / mL.

[0054] Example 6:

[0055] Compared with Example 1, most of them are the same. The difference is that in step (2), the concentration of the graphene oxide solution is 4 mg / mL.

[0056] Example 7:

[0057] Compared with Example 1, most of them are the same. The difference is that in step (1), the concentration of the silver nitrate solution is 2×10 -4 mol·L -1 .

[0058] Example 8:

[0059] Compared with Example 1, most of them are the same. The difference is that in step (3), the temperature of the reduction reaction is 150 °C.

[0060] Example 9:

[0061] Compared with Example 1, most of them are the same. The difference is that in step (3), the reduction reaction time is 14 h.

[0062] Use the prepared polydopamine / nanosilver / graphene composite aerogel as the substrate of the surface-enhanced Raman scattering sensor for the enrichment detection of the analyte. The steps are as follows:

[0063] (1) Standard solution preparation: Prepare a group of standard aqueous solutions of rhodamine B, including rhodamine B solutions with different concentrations (1.0×10 -9 ~1.0×10 -3 mol·L -1 ), and a blank standard sample.

[0064] (2) Immerse the prepared polydopamine / nanosilver / graphene composite aerogel into the rhodamine B solutions with different concentrations respectively for 300 s of enrichment. Then take it out and dry it for SERS detection. Good SERS signals can be detected. Among them: the Raman excitation wavelength is 785 nm, the integration time is 20 s, and the integration intensity is 20.

[0065] As Figure 2 shown, it is the Raman peak diagram of the polydopamine / nanosilver / graphene composite aerogel (labeled as AgNPs / PDA@GOA in the figure) prepared in Example 2. The D-band peak comes from the structural disorder or defect existing in the sp 3 graphite-based material. The G-band peak is related to the bond stretching vibration of sp 2 carbon atoms in the hexagonal carbon skeleton. The intensity ratio of the D peak to the G peak (I D / I C ) is usually used to measure the degree of structural disorder. The higher the value, the higher the degree of disorder. The I D / I C of GO without reduction is usually less than 1. After reduction by PDA, the D peak of GPA increases significantly, and the I D / I C is 1.25, and the value increases significantly. This is because the smaller-sized graphene sheets generated during the reduction process increase the edge effect, resulting in an increase in the disordered structure, and GO is effectively reduced.

[0066] Comparative Example 1:

[0067] Compared with Example 1, most of them are the same. The difference is that silver nanoparticles are not added.

[0068] Comparative Example 2:

[0069] Compared with Example 1, most of them are the same. The difference is that in step (3), dopamine solution is used, and as a result, the specific surface area increases significantly.

[0070] Comparative Example 3:

[0071] Compared with Example 1, most of them are the same. The difference is that the pH value described in step (2) is 7-9 (excluding 7). The obtained poly-dopamine-reduced graphene oxide aerogel loaded with silver nanoparticles presents a flocculent shape, without forming a cylindrical aerogel, and the structure is loose. It is difficult to remove the hydrogen ions generated by the self-polymerization of dopamine under acidic conditions, and the self-polymerization process of dopamine triggered by oxygen will be greatly delayed. When pH = 6-7, the deposition of poly-dopamine will be greatly inhibited. When the pH is under acidic conditions, the polymerization rate of dopamine can be controlled under acidic conditions, so that dopamine is loaded on the graphene sheets without completely covering all the pores.

[0072] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a polydopamine / nano silver / graphene composite aerogel, characterized in that It includes the following steps: S1. Mix AgNO3, trisodium citrate, and deionized water to obtain a silver colloid solution. After centrifuging the silver colloid solution, discard the supernatant to obtain silver nanoparticles; S2. Prepare a graphene oxide solution using the Hummer method; S3. Mix the silver nanoparticles obtained in step S1 with the graphene oxide solution obtained in step S2, ultrasonicate and perform a first stirring, adjust the pH to weakly acidic, then add a dopamine hydrochloride solution and perform a second stirring in an oxygen-containing environment to carry out a reduction reaction. Finally, perform elution, freezing, and drying in sequence to obtain a polydopamine-reduced graphene oxide hydrogel loaded with silver nanoparticles, which is a polydopamine / nano-silver / graphene composite aerogel; Among them, in step S1, the concentration of the AgNO3 solution is (1.0~3.0)×10 -4 mol / L, the concentration of the trisodium citrate solution is 8 - 12 g / L, the volume ratio of the AgNO3 solution, the trisodium citrate solution to the silver colloid solution is (1 - 5):(1 - 5):100, the particle size of the silver nanoparticles is 20~50 nm, the mixing temperature is 100 °C, and the mixing time is 25~35 min; In step S3, the concentration of the graphene oxide solution is 2 - 4 mg / mL, and the volume ratio of the graphene oxide solution to the silver colloid solution is (1 - 3):5; adjust the pH to 6.0 - 7.0 using a tris(hydroxymethyl)aminomethane solution, and keep it stable for 25 - 35 min after adjusting the pH.

2. The preparation method of a polydopamine / nano silver / graphene composite aerogel according to claim 1, characterized in that, In step S3, the ultrasonication time is 0.5 - 1 h; the temperature of the first stirring is room temperature, and the time is 1 - 3 h.

3. The preparation method of a polydopamine / nano silver / graphene composite aerogel according to claim 1, wherein, In step S3, the concentration of the dopamine hydrochloride solution is 1.0 - 3.0 mg / mL, and the addition method of the dopamine hydrochloride solution is slow dropping, where the mass ratio of dopamine hydrochloride to graphene oxide is 1:(5 - 10).

4. The preparation method of a polydopamine / nano silver / graphene composite aerogel according to claim 1, characterized in that In step S3, the temperature of the second stirring is room temperature, and the time is 30 - 80 min.

5. The preparation method of a polydopamine / nano silver / graphene composite aerogel according to claim 1, characterized in that, In step S3, the temperature of the reduction reaction is 120 - 180 °C, and the time is 10 - 15 h.

6. The preparation method of a polydopamine / nano silver / graphene composite aerogel according to claim 1, characterized in that, In step S3, the elution process is: select an ethanol aqueous solution as the eluent, wash at least 3 times, and the washing time for each time is 1 - 3 h. Among them, the volume ratio of ethanol to water in the eluent is 1:(4 - 5); the freezing temperature is -40 °C to -20 °C, and the freezing time is 5 - 10 h.

7. A polydopamine / nanosilver / graphene composite aerogel, characterized in that, Based on the preparation method according to any one of claims 1 - 6.

8. Use of the polydopamine / nano silver / graphene composite aerogel according to claim 7, characterized in that, The polydopamine / nano-silver / graphene composite aerogel is used as a substrate for a surface-enhanced Raman scattering sensor for the detection of pollutants in the environment.

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