Preparation method of core-shell structure Au@MnO2 nanoparticles with Raman enhancement capability

Abstract

The application belongs to the technical field of nanometer materials, and specifically discloses a preparation method of a core-shell structure Au@MnO2 nanoparticle with Raman enhancement capability, which comprises the following steps: (1) synthesis of an inner core gold nanoparticle, and (2) synthesis of the Au nanoparticle coated with a MnO2 shell layer. In an alkaline system, the Au@MnO2 catalyst with different shell thicknesses is prepared by adding a reducing agent, fully ice-bathing and regulating the reduction time. By virtue of the extremely strong Raman enhancement capability of the inner core gold, the strategy can be used for detecting the in-situ electro-reduction process of MnO2 in an alkaline electrolyte, observing the phase change of the catalyst in the system and the information of the interfacial water.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterials, and particularly relates to a preparation method of a core-shell structure Au@MnO2 nanoparticle with Raman enhancement capability. BACKGROUND

[0002] As a powerful technology for molecular fingerprint identification, Raman and infrared spectroscopy has been widely applied to in-situ surface analysis. However, infrared spectroscopy is difficult to accurately monitor the low-waveband catalyst bulk structure change and oxygen species information, and is easily interfered by the bulk water in the process of testing the interface water. When a semiconductor participates in an electrocatalytic reaction, it is of great significance to detect the change of the catalyst structure and the molecular structure information of the interface water for revealing the electrocatalytic reaction mechanism and structure-activity relationship.

[0003] Raman spectroscopy, especially surface-enhanced Raman spectroscopy, is a powerful technology with high surface detection sensitivity, which can simultaneously detect the low-waveband catalyst bulk peak change and the high-waveband interface water fingerprint vibration information. However, it is limited to the substrate material, and can only obtain the fingerprint vibration information of the adsorbed species on the rough Au, Ag, Cu and other surfaces. On this basis, the "borrowing" strategy (J. Am. Chem. Soc. 1987, 109, 5113-5119.) has been developed, that is, high-catalytic-activity transition metal nanoparticles are coated on copper, gold and silver with strong Raman signal amplification effect, and through this shell structure, the strong Raman signal of the adsorbed molecules on the transition metal can be obtained. We further develop it to metal oxides for observing the change of the morphology and structure of the catalyst and the interaction of the interface water in the electrocatalysis process, and reveal how the solid-liquid interface of the semiconductor is affected by the interface water in the charge transfer process. SUMMARY

[0004] The purpose of the application is to overcome the defects in the prior art, provide a preparation method of a core-shell structure Au@MnO2 nanoparticle with Raman enhancement capability, realize real-time monitoring of how the catalyst structure changes in the catalytic reaction process, how the interface water and anions in the solution affect the reaction process, and obtain high-quality Raman spectroscopy information by coating the semiconductor catalyst on the surface of the Au nanoparticle with Raman enhancement capability.

[0005] In order to achieve the above purpose, one of the technical solutions of the application is a preparation method of a core-shell structure Au@MnO2 nanoparticle with Raman enhancement capability, which specifically comprises the following steps:

[0006] (1) Synthesis of inner core gold nanoparticles: the precursor solution of Au is heated to boiling, a reducing agent is added, and the condensation reflux is continued for 0.5-1.5 hours, and after cooling, the Au nanoparticle sol with a particle size of 45-100 nm is obtained;

[0007] (2) Synthesis of Au nanoparticles coated with MnO2 shell: take the Au nanoparticle sol of 45-100 nm synthesized in step (1), add a basic solution, then add MnO2 precursor, and then add a reducing agent, stir and react in an ice bath, then centrifuge and clean to obtain Au@MnO2 nanoparticle sol with satellite structure of 2-10 nm in size and Raman enhancement capability.

[0008] In a preferred embodiment of the present application, the precursor of Au used in step (1) is chloroauric acid, and the mass fraction of chloroauric acid is 0.01%-0.2%.

[0009] In a preferred embodiment of the present application, the reducing agent used in step (1) is a sodium citrate solution, and the mass fraction of sodium citrate is 0.5%-2%.

[0010] In a preferred embodiment of the present application, the volume ratio of the precursor to the reducing agent in step (1) is 200:(1-6).

[0011] In a preferred embodiment of the present application, water bath heating is used in step (1), and the reflux time is controlled to be 0.5-1.5 h, and then natural cooling is performed.

[0012] In a preferred embodiment of the present application, the volume ratio of Au nanoparticle sol, basic solution, MnO2 precursor, and reducing agent in step (2) is 1000-3000:3-27:10-100:50-500.

[0013] In a preferred embodiment of the present application, step (2) is performed under alkaline conditions, the basic solution is a KOH solution, and the concentration of the basic solution is 0.05-0.5 M.

[0014] In a preferred embodiment of the present application, the MnO2 precursor used in step (2) is a KMnO4 solution, and the concentration of the MnO2 precursor is 0.1-1.0 M.

[0015] In a preferred embodiment of the present application, the reducing agent used in step (2) is a K2C2O4 solution or a MnSO4 solution, and the concentration of the reducing agent is 0.1-1.0 M.

[0016] In a preferred embodiment of the present application, the whole reaction in step (2) is stirred in an ice bath for 30-120 min.

[0017] In a preferred embodiment of the present application, the centrifugation speed in step (2) is 3000-5000 rpm, and after centrifugation, the product is dispersed in deionized water.

[0018] In order to achieve the above object, the second technical scheme of the present application is: the core-shell structure Au@MnO2 nanoparticle prepared by the above preparation method.

[0019] In order to achieve the above object, the third technical scheme of the present application is: application of the core-shell structure Au@MnO2 nanoparticle in the study of the electro-reduction process.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. The reduction process of manganese dioxide itself is studied for the first time by using the strategy of borrowing force, and the change process of the interface water involving proton insertion is observed, and the change process of the bulk phase of the catalyst in the low wave number region is also observed.

[0022] 2. The semiconductor catalyst is coated on the surface of the Au nanoparticle with Raman enhancement capability, so that the change of the catalyst bulk phase structure in the semiconductor (not limited to manganese dioxide) catalytic reaction process can be monitored in real time, the change of the interface water structure involving proton insertion is also observed, and the influence of the catalyst thickness and the solution concentration on the reaction process is also observed, and high-quality Raman spectrum information is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 TEM image of the Au nanoparticle prepared in Example 1;

[0024] Figure 2 TEM image of the Au@MnO2 with a shell thickness of 2nm prepared in Example 1;

[0025] Figure 3 TEM image of the Au@MnO2 with a shell thickness of 10nm prepared in Example 2;

[0026] Figure 4 Electrochemical Raman spectrum in the low wave number region in the electro-reduction process of the Au@MnO2 in Example 3;

[0027] Figure 5 Electrochemical Raman spectrum in the high wave number region in the electro-reduction process of the Au@MnO2 in Example 3. DETAILED DESCRIPTION

[0028] In order to make the object, technical scheme and advantages of the present application clearer and more apparent, the present application is described in more detail below in combination with the drawings and specific examples, but the protection scope of the present application is not limited to these examples.

[0029] A preparation method of a core-shell structure Au@MnO2 nanoparticle with Raman enhancement capability, specifically comprising the following steps:

[0030] (1) Synthesis of core Au nanoparticles: The precursor solution of Au is heated to boiling, and a reducing agent is added. The condensation reflux is continued for 0.5-1.5 hours. After cooling, Au nanoparticle sol with a particle size of 45-100 nm is obtained.

[0031] (2) Synthesis of Au nanoparticles coated with a MnO2 shell: The Au nanoparticle sol with a particle size of 45-100 nm obtained in step (1) is stirred, and a basic solution is added. Then, a MnO2 precursor and a reducing agent are added. The reaction is stirred in an ice bath, and then centrifuged and washed to obtain Au@MnO2 nanoparticle sol with a satellite structure and a particle size of 2-10 nm, which has Raman enhancement capability.

[0032] The Au precursor used in step (1) is chloroauric acid, and the mass fraction of chloroauric acid is 0.01%-0.2%.

[0033] The reducing agent used in step (1) is sodium citrate, and the mass fraction of sodium citrate is 0.5%-2%.

[0034] The volume ratio of the precursor to the reducing agent in step (1) is 200:(1-6).

[0035] In step (1), water bath heating is used, and the reflux time is controlled to be 0.5-1.5 h. Finally, natural cooling is performed.

[0036] In step (2), the volume ratio of Au nanoparticle sol, basic solution, MnO2 precursor, and reducing agent is 1000-3000:3-27:10-100:50-500.

[0037] Step (2) is performed under basic conditions. The basic solution is KOH solution, and the concentration of the basic solution is 0.05-0.5 M.

[0038] In step (2), the MnO2 precursor is KMnO4 solution, and the concentration of the MnO2 precursor is 0.1-1.0 M.

[0039] In step (2), the reducing agent used is K2C2O4 solution or MnSO4, and the concentration of the reducing agent is 0.1-1.0 M.

[0040] In step (2), the reaction is stirred in an ice bath for 30-120 min.

[0041] In step (2), the centrifugation speed is 3000-5000 rpm. After centrifugation, the product is dispersed in deionized water.

[0042] A core-shell structure Au@MnO2 nanoparticle prepared by the above method.

[0043] The application of a core-shell structure Au@MnO2 nanoparticle in the study of electro-reduction process.

[0044] Example 1

[0045] A core-shell structure Au@MnO2 nanoparticle with Raman enhancement ability is prepared, and the thickness of the MnO2 layer is about 2 nm, and the specific steps are as follows:

[0046] (1) 200 ml of 0.01% HAuCl4 aqueous solution is heated to boiling, 1.4 mL of 1% sodium citrate aqueous solution is quickly added, the solution color changes from the previous light yellow to black after 1 min, and changes to brown red after 3 min, and the whole heating process needs to be condensed reflux with a condenser. The reaction is stopped after 40 min. Water bath cooling, that is, the red 55-60 nm Au nanoparticles are obtained; Figure 1 The TEM image of Au nanoparticles is shown in the figure, and the core Au nanoparticle is 55-60 nm;

[0047] (2) 10 ml of 55 nm Au obtained in step 1) is fully ice-bathed, 170 μl of 0.1 M KOH solution is added under stirring, 0.5 ml of 0.01 M KMnO4 is added, 2.5 ml of 0.01 M K2C2O4 is slowly added (the syringe is slowly pushed), and the reaction is stirred for 60 min under ice-bath. After the reaction is completed, it is dispersed in deionized water after centrifugation, and the centrifugation speed is 4500 rpm, and the Au@MnO2 nanoparticle sol is prepared after centrifugation for 2 times; Figure 2 The TEM image of the prepared Au@MnO2 with a shell thickness of 2 nm is shown in the figure, and the outer MnO2 shell layer is 2 nm, and the Au@MnO2 nanoparticle has a particle size of 60-65 nm.

[0048] Example 2

[0049] A core-shell structure Au@MnO2 nanoparticle with Raman enhancement ability is prepared, and the thickness of the MnO2 layer is about 10 nm, and the specific steps are as follows:

[0050] (1) 200 ml of 0.01% HAuCl4 aqueous solution is heated to boiling, 1.4 mL of 1% sodium citrate aqueous solution is quickly added, the solution color changes from the previous light yellow to black after 1 min, and changes to brown red after 3 min, and the whole heating process needs to be condensed reflux with a condenser. The reaction is stopped after 40 min. Water bath cooling, that is, the red 55-60 nm Au nanoparticles are obtained;

[0051] (2) Take 10 ml of the above step 1) obtained 55 nm Au ice bath, stirring under the addition of 170 μl concentration of 0.1M KOH solution, 0.5 ml concentration of 0.01M KMnO4, slowly (slowly push the syringe) 2.5 ml concentration of 0.01M K2C2O4, ice bath under stirring reaction 60 min, then continue to heat under the condition of 60 °C water bath reaction 5h. After the reaction, centrifuged and dispersed in deionized water, the number of revolutions of centrifugation was 4500 rpm, centrifugation 2 times, prepared Au@MnO2nanoparticle sol; Figure 3 TEM of the prepared thickness of 10 nm Au@MnO2, from the figure can be seen that the outer layer of MnO2 shell is 10 nm, Au@MnO2nanoparticle particle size is 60-65 nm.

[0052] Example 3

[0053] A core-shell structure of Au@MnO2 catalyst with Raman enhancement ability in situ Raman experiment in the process of electrochemical reduction under alkaline conditions:

[0054] (1) take 5uL of the Au@MnO2nanoparticle sol prepared in example 1 drop on the glassy carbon electrode, dry naturally;

[0055] (2) the glassy carbon electrode treated in step (1) is assembled on the in-situ electrolysis cell, the electrolyte solution is 0.1M KOH, first CV activation and impurity removal in the potential range of 1.1v-0.3V vs.RHE, then collect the in-situ Raman spectrum at different reduction potentials (1.10-0.40V(vs.RHE), the potential interval between each spectrum is 0.05V(vs.RHE), and finally-0.40V(vs.RHE) is collected. The low wave number region (200-1200cm -1 ) of the electrochemical Raman spectrum of Au@MnO2 in the process of electrochemical reduction Figure 3 , Raman laser wavelength 638 nm. From Figure 4 , the Raman peak of MnO2 at low wave number-590cm -1 can be observed, with the negative shift of potential, MnO2 is reduced, the change of MnOOH peak in low wave number region can be seen, the reaction of MnO2+e-+H2O→MnOOH+OH - is observed, and the bending vibration of OH around low wave number-800cm -1 . Figure 5 is the high wave number region (3000-3800cm -1) electrochemical Raman spectra, starting from a potential of 1.10 V (vs. RHE) with a potential interval of 0.05 V (vs. RHE) between each spectrum, ending at -0.40 V (vs. RHE). The Raman peak of water at 3488 cm -1 -1 was found at 0.7 V vs. RHE in the figure, and the water peaks at -3423 cm -1 and -3650 cm -1 were found as the potential shifted negatively.

[0056] The preferred embodiments of the present application have been described above with the specific examples, but the present application is not limited to the above examples, and the technical solutions described in the above examples can be modified or some technical features can be replaced by equivalent features, as long as the modifications, replacements, improvements, etc. are within the spirit and principles of the present application.

Claims

1. A method for preparing core-shell Au@MnO2 nanoparticles with Raman enhancement capability, characterized in that: The steps include: (1) Synthesis of core gold nanoparticles: Heat the Au precursor solution to boiling, add a reducing agent, continue heating and condensing under reflux for 0.5-1.5 hours, and after cooling, obtain an Au nanoparticle sol with a particle size of 45-100 nm; (2) Synthesis of Au nanoparticles coated with MnO2 shell: Take the Au nanoparticle sol synthesized in step (1), stir and add alkaline solution, then add MnO2 precursor, and then add reducing agent, stir and react in an ice bath, then centrifuge and wash to obtain Au@MnO2 nanoparticle sol with satellite structure and shell thickness of 2-10 nm with Raman enhancement ability; the volume ratio of Au nanoparticle sol, alkaline solution, MnO2 precursor, and reducing agent is 1000-3000:3-27:10-100:50-500; the alkaline solution is KOH solution, the MnO2 precursor is KMnO4 solution, and the reducing agent is K2C2O4 solution or MnSO4 solution; the stirring reaction time in the ice bath is 30-120 min, and the centrifugal speed is 3000-5000 rpm.

2. The method for preparing the core-shell structured Au@MnO2 nanoparticles according to claim 1, wherein: In the step (1), the Au precursor is chloroauric acid, and the mass fraction of the chloroauric acid in the chloroauric acid aqueous solution is 0.01%-0.2%. In the step (1), the reducing agent is a sodium citrate aqueous solution, and the mass fraction of sodium citrate in the sodium citrate aqueous solution is 0.5%-2%.

3. The method for preparing the core-shell structured Au@MnO2 nanoparticles according to claim 1, wherein: In the step (1), the volume ratio of the Au precursor to the reducing agent is 200:(1-6).

4. The method for preparing the core-shell structured Au@MnO2 nanoparticles according to claim 1, wherein: The heating method in step (1) is water bath heating, and the heating condensation reflux time is continued for 0.5-1.5 hours.

5. The method for preparing the core-shell structured Au@MnO2 nanoparticles according to claim 1, wherein: The concentration of the alkaline solution in step (2) is 0.05-0.5 M.

6. Application of the method for preparing the core-shell Au@MnO2 nanoparticles with Raman enhancement capability according to any one of claims 1 to 5 in the study of electroreduction processes.

Images