A method for in-situ characterization of nanobubbles in a liquid environment

Abstract

The present invention discloses a method for in-situ characterization of nanobubbles in a liquid environment. The method includes the following steps: (1) depositing a graphene film on a metal support grid to obtain a graphene support grid; (2) plating a metal film on the surface of the graphene support grid; (3) heating to melt the metal film and then cooling to form metal nanoparticles on the surface of the graphene support grid; (4) performing surface modification treatment on the obtained graphene support grid; (5) dropping an aqueous solution on the graphene support grid; (6) covering the graphene support grid with another graphene support grid with the graphene film facing downwards to obtain a graphene liquid cell; (7) putting the graphene liquid cell into a transmission electron microscope after vacuum leak detection, generating nanobubbles by electron beam radiolysis of water and performing in-situ characterization on the nanobubbles. This method has the advantages of high time and space resolution and no introduction of other impurities, providing a new research means for exploring nanobubbles and the properties of gas / liquid / solid interfaces, etc.

Description

Technical Field

[0001] The present invention relates to the field of nanomanufacturing and characterization, and particularly to a method for in-situ generation and characterization of nanobubbles in liquid. Background Art

[0002] Bubbles are ubiquitous in our daily life. Nanobubbles generally refer to bubbles with a diameter less than 1 μm, which have great application prospects in mineral flotation, ultrasonic contrast agents, and sewage treatment. In addition, for reactions involving gas, such as fuel cells, water electrolysis for hydrogen evolution, and photocatalysis, etc., at the nanoscale, gas mostly participates in the reaction in the form of nanobubbles. Understanding the physical and chemical properties, kinetic mechanisms, and gas / liquid / solid interfacial properties of nanobubbles is of great significance for the application of nanobubbles and the regulation of gas-involved multiphase reactions. However, due to the limitations of research methods, most of the current research on bubble dynamics has stagnated at the micron and millimeter scales, lacking direct dynamic observation of bubbles at the nanoscale or even atomic scale. There are still many doubts about the bubble nucleation theory and stability mechanism. For example, according to different calculation models, the critical radius of nanobubbles differs by at least one order of magnitude, and the theoretical nucleation rate and nucleation supersaturation are usually higher than the experimental observation values. According to the Young-Laplace equation, for bubbles smaller than 1 μm, due to their high internal pressure, they should quickly shrink and disappear, and the theoretical prediction of their existence time is no more than 0.02 s. However, in 2000, Lou et al. used atomic force microscopy imaging to image nanobubbles and determined that nanobubbles can exist stably. To explain the situation where experimental phenomena are inconsistent with classical theoretical predictions, various nanobubble stability mechanisms have been proposed, including pollutant pinning, electrostatic theory, many-body model, and dynamic equilibrium theory. However, these models have either been proven not to be universal or lack experimental evidence support.

[0003] Currently, the commonly used methods for preparing nanobubbles include solution replacement method, electrochemical method, ultrasonic method, pressure increase and decrease method, immersion self-generation method, etc. These methods cannot achieve high-resolution in-situ characterization of nanobubbles while preparing them. In recent years, a variety of in-situ characterization techniques have been used to study the dynamic behavior of nanobubbles in solution and certain progress has been made, but there are still limitations. For example, in-situ spectroscopy methods cannot obtain the morphological information of nanobubbles; the spatial resolution of in-situ optical imaging methods is relatively low; atomic force microscopy can obtain a relatively high spatial resolution, but its time resolution is limited and it may cause damage to the bubbles. Transmission electron microscopy can obtain ultra-high time and spatial resolutions and can also obtain the chemical composition information of materials, having unique advantages in the characterization of nanomaterials. However, transmission electron microscopy needs to work in a high-vacuum environment and cannot directly characterize liquids or gases. In-situ liquid environmental transmission electron microscopy technology seals liquid samples in liquid cells formed by micro-nano manufacturing technology and then puts them into the transmission electron microscope for observation, achieving many breakthrough results in the field of dynamically studying the growth, etching, self-assembly, and electrochemical properties of nanoparticles in solution. Currently, the commonly used liquid cells are silicon nitride thin film liquid cells and ultra-thin carbon film liquid cells. The window thickness of the silicon nitride thin film liquid cell is generally greater than 10 nm, and the obtained liquid layer is relatively thick, with limited resolution. The ultra-thin carbon film liquid cell can obtain relatively high resolution, but the mechanical properties and stability of the carbon film are poor, it is not resistant to long-term electron beam irradiation, and it is easy to cause solution and gas leakage. Moreover, it is difficult for the ultra-thin carbon film liquid cell to directly seal pure aqueous solutions. In order to improve the success rate, nanoparticles need to be mixed in the solution to form a support to coat the aqueous solution between the upper and lower carbon films. The aqueous solution of nanoparticles prepared by chemical methods inevitably introduces impurities such as surface ligands, affecting the subsequent preparation and characterization of nanobubbles. Therefore, it is of great significance and has wide applications to develop a method with high stability, capable of in-situ generating and high-resolution characterizing nanobubbles. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technologies, the present invention provides a method for in-situ preparing and high-resolution characterizing nanobubbles, and at the same time solves the problem that it is difficult to balance mechanical stability and imaging resolution in the existing liquid cell preparation methods.

[0005] Technical Solution: To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for in-situ characterizing nanobubbles in a liquid environment, the method comprising the following specific steps:

[0007] (1) Select a transmission electron microscope metal carrier grid;

[0008] (2) Deposit a graphene film on the metal carrier grid to obtain a graphene carrier grid;

[0009] (3) Deposit a metal thin film on the surface of the graphene-coated grid;

[0010] (4) Heat to melt the metal thin film and then cool down to form metal nanoparticles on the surface of the graphene-coated grid;

[0011] (5) Place the graphene-coated grid with metal nanoparticles into a plasma surface treatment instrument for surface modification treatment;

[0012] (6) Drop 1 - 5 μL of aqueous solution onto the graphene-coated grid obtained in (5);

[0013] (7) Cover the graphene-coated grid with the dropped aqueous solution with another graphene-coated grid with the graphene film facing downwards, and let it stand for more than 4 hours. A very small amount of aqueous solution is encapsulated in the gap between the upper and lower graphene films supported by the metal nanoparticles, and the excess liquid volatilizes to prepare a graphene liquid cell;

[0014] (8) Put the graphene liquid cell obtained in step (7) into a vacuum leak detection system. If there is no leakage, put it into a transmission electron microscope, turn on the electron gun switch, and make the electron beam interact with the aqueous solution to generate nanobubbles;

[0015] (9) Continuously irradiate the electron beam to perform in-situ characterization of the nanobubbles.

[0016] Among them:

[0017] The metal-coated grid described in step (1) is one of copper mesh, gold mesh, nickel mesh, and molybdenum mesh, and the mesh number of the metal grid is 200 - 800 mesh.

[0018] The graphene film described in step (2) is prepared by chemical vapor deposition, and the number of graphene layers is 1 - 5 layers.

[0019] The metal described in step (3) is gold or platinum.

[0020] The metal thin film described in step (3) is prepared by magnetron sputtering or evaporation, and the thickness of the metal thin film is 1 - 5 nm.

[0021] The heating described in step (4) refers to heating using a heating stage.

[0022] In step (5), oxygen or argon is selected to perform surface modification treatment on the graphene-coated grid with metal nanoparticles, and the treatment time is 10 s.

[0023] The electron beam dose rate described in step (8) is greater than 100 e - / Å 2 ∙s.

[0024] The present invention provides a method for generating nanobubbles by electron beam radiolysis of water and performing in-situ observation.

[0025] Wherein;

[0026] The electron beam is generated by a transmission electron microscope, and the electron beam dose rate is greater than 100 e - / Å 2 ∙s.

[0027] The present invention also provides a graphene liquid cell for characterizing nano-bubbles in a liquid in a transmission electron microscope.

[0028] The liquid is encapsulated within a sandwich structure composed of graphene-metal nanoparticles-graphene by means of the van der Waals force between the upper and lower layers of graphene thin films. Compared with the existing silicon nitride and ultra-thin carbon film liquid cells, the graphene liquid cell has the advantages of both good resolution and mechanical properties.

[0029] The metal nanoparticles act as spacers to support between the two layers of graphene, which can improve the success rate of sealing the liquid. The metal nanoparticles are prepared by a physical method, avoiding impurities introduced by the chemical synthesis method and reducing side reactions caused by electron beam irradiation.

[0030] A method for in-situ characterization of nano-bubbles in a liquid environment provided by the present invention can simultaneously generate and dynamically characterize nano-bubbles, and has important value in the field of studying dynamic behaviors such as nano-bubble nucleation, growth, fusion, and rupture. Its preparation method is simple, applicable to various types of transmission electron microscopes, and has advantages such as high imaging resolution and good stability. Description of the Drawings

[0031] Figure 1 a is a light microscope image of the graphene liquid cell prepared in Example 1 of the present invention, Figure 1 b is a transmission electron microscope image of the nano-bubbles generated in Example 1.

[0032] Figure 2 is a sequence of transmission electron microscope images of the nano-bubble growth process in Example 2 of the present invention.

[0033] Figure 3 is a sequence of transmission electron microscope images of the nano-bubble fusion process in Example 3 of the present invention. Detailed Embodiments

[0034] The present invention provides a method for in-situ generation and characterization of nano-bubbles. In this method, an aqueous solution is sealed in a graphene liquid cell, placed in a transmission electron microscope, and nano-bubbles are generated by electron beam radiolysis of water by the transmission electron microscope, and the nano-bubbles are dynamically characterized. The present invention will be further described below in conjunction with examples and drawings.

[0035] Example 1

[0036] Select a 400-mesh copper grid;

[0037] A single-layer graphene film is formed on a copper support grid by chemical vapor deposition to form a graphene support grid;

[0038] A 3-nm-thick gold film is plated on the surface of the graphene support grid;

[0039] The graphene support grid with the gold film facing up is placed on a heating platform, heated until the gold film melts and then cooled to room temperature to form gold nanoparticles on the surface of the graphene support grid;

[0040] The graphene support grid containing gold nanoparticles is placed in an oxygen plasma surface treatment instrument and treated for 10 s;

[0041] 5 μL of an aqueous solution is dropped onto the graphene support grid treated by the plasma surface treatment instrument;

[0042] Another graphene support grid treated by the plasma surface treatment instrument is covered with the graphene film facing down on the graphene support grid with the aqueous solution dropped, and then left stationary for more than 4 hours until the excess liquid evaporates to obtain a graphene liquid pool;

[0043] The obtained graphene liquid pool is subjected to vacuum leak detection, placed in a transmission electron microscope, the electron gun switch is turned on, the electron beam interacts with the aqueous solution to generate nanobubbles, and the nanobubbles are characterized.

[0044] Example 2

[0045] A 400-mesh molybdenum support grid is selected;

[0046] A double-layer graphene film is formed on a copper support grid by chemical vapor deposition to form a graphene support grid;

[0047] A 3-nm-thick gold film is plated on the surface of the graphene support grid;

[0048] The graphene support grid with the gold film facing up is placed on a heating platform, heated until the gold film melts and then cooled to room temperature to form gold nanoparticles on the surface of the graphene support grid;

[0049] The graphene support grid containing gold nanoparticles is placed in an oxygen plasma surface treatment instrument and treated for 10 s;

[0050] 5 μL of an aqueous solution is dropped onto the graphene support grid treated by the plasma surface treatment instrument;

[0051] Another graphene support grid treated by the plasma surface treatment instrument is covered with the graphene film facing down on the graphene support grid with the aqueous solution dropped, and then left stationary for more than 4 hours until the excess liquid evaporates to obtain a graphene liquid pool;

[0052] The obtained graphene liquid cell was subjected to vacuum leak detection, placed in a transmission electron microscope, the electron gun switch was turned on, the electron beam interacted with the aqueous solution to generate nanobubbles, and the nanobubbles were characterized. The relevant results are shown in Figure 2 。

[0053] Example 3

[0054] A 400-mesh gold grid was selected;

[0055] Five layers of graphene films were deposited on the gold grid by chemical vapor deposition to form a graphene grid;

[0056] A 3-nm-thick platinum film was deposited on the surface of the graphene grid;

[0057] The graphene grid with the platinum film facing up was placed on a heating platform, heated until the platinum film melted and then cooled to room temperature to form platinum nanoparticles on the surface of the graphene grid;

[0058] The graphene grid containing platinum nanoparticles was placed in an oxygen plasma surface treatment instrument and treated for 10 s;

[0059] 5 μL of the aqueous solution was dropped onto the graphene grid treated by the plasma surface treatment instrument;

[0060] Another graphene grid treated by the plasma surface treatment instrument with the graphene film facing down was covered on the graphene grid with the aqueous solution dropped, and then left stationary for more than 4 hours until the excess liquid evaporated to obtain a graphene liquid cell;

[0061] The obtained graphene liquid cell was subjected to vacuum leak detection, placed in a transmission electron microscope, the electron gun switch was turned on, the electron beam interacted with the aqueous solution to generate nanobubbles, and the nanobubbles were characterized. The relevant results are shown in Figure 3 。

Claims

1. A method for in-situ characterization of nanobubbles in a liquid environment, the method comprising the following specific steps: (1) Select a transmission electron microscope metal support grid; (2) Deposit a graphene film on the metal support grid to obtain a graphene support grid; (3) Coat a layer of metal film on the surface of the graphene support grid; (4) Heat to melt the metal film and then cool down to form metal nanoparticles on the surface of the graphene support grid; (5) Place the graphene support grid containing metal nanoparticles into a plasma surface treatment instrument for surface modification treatment; (6) Drop 1-5 μL of aqueous solution onto the graphene support grid obtained in (5); (7) Cover the graphene support grid with the dropped aqueous solution with the graphene film side of another graphene support grid treated in (5) facing downwards, and let it stand for more than 4 hours. A very small amount of aqueous solution is coated in the gap between the upper and lower graphene films supported by the metal nanoparticles, and the excess liquid volatilizes to prepare a graphene liquid cell; (8) Place the graphene liquid cell obtained in (7) into a vacuum leak detection system. After no leakage, put it into a transmission electron microscope, and turn on the electron gun switch to make the electron beam interact with the aqueous solution to generate nanobubbles; (9) The electron beam continues to irradiate for in-situ characterization of the nanobubbles.

2. The method for in-situ characterization of nanobubbles in a liquid environment according to claim 1, characterized in that, the metal support grid in step (1) is one of a copper grid, a gold grid, a nickel grid or a molybdenum grid, and the mesh number of the metal support grid is 200-800 meshes.

3. The method for in-situ characterization of nanobubbles in a liquid environment according to claim 1, characterized in that, the graphene film in step (2) is prepared by chemical vapor deposition, and the number of graphene film layers is 1-5 layers.

4. The method for in-situ characterization of nanobubbles in a liquid environment according to claim 1, characterized in that, the metal film in step (3) is gold or platinum.

5. The method for in-situ characterization of nanobubbles in a liquid environment according to any one of claims 1 and 4, characterized in that, the metal film in step (3) is prepared by magnetron sputtering or evaporation, and the thickness of the metal film is 1 nm - 5 nm.

6. The method for in-situ characterization of nanobubbles in a liquid environment according to claim 1, characterized in that, the heating in step (4) refers to heating using a heating stage.

7. The method for in-situ characterization of nanobubbles in a liquid environment according to claim 1, characterized in that, in step (5), oxygen or argon is selected to perform surface modification treatment on the graphene support grid containing metal nanoparticles, and the treatment time is 10 s.

8. The method for in-situ characterization of nanobubbles in a liquid environment according to claim 1, characterized in that, The electron beam dose rate in step (8) is greater than 100 e - / Å 2 ∙s.

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