An observation method based on photographing a cross-sectional view of a graphene oxide carbon nanotube composite film

Abstract

This invention belongs to the field of materials technology, specifically relating to a method for observing cross-sectional images of graphene oxide / carbon nanotube composite films. The invention involves first immersing the graphene oxide / carbon nanotube composite film in hot water, then immediately transferring it to liquid nitrogen, and repeating this process. In liquid nitrogen, the functional layers of the graphene oxide / carbon nanotube composite film shrink; in hot water, they expand due to heat. This continuous alternation of hot and cold generates stress, leading to numerous spontaneous fractures in the graphene oxide / carbon nanotube composite film. By observing these spontaneous fractures using a scanning electron microscope, a clear and accurate morphological structure of the cross-section of the functional layers of the graphene oxide / carbon nanotube composite film can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to an observation method based on photographing cross-sectional images of graphene oxide / carbon nanotube composite films. Background Technology

[0002] Currently, industrial wastewater with recalcitrant degradation characteristics has seriously affected environmental safety in people's daily lives. Therefore, the development of technologies for the deep purification and reuse of industrial wastewater is imperative. Membrane filtration technology has become the dominant technology for industrial wastewater treatment due to its advantages of high separation performance, low energy consumption, and small footprint. Among membrane filtration technologies, graphene oxide / carbon nanotube composite membranes prepared from two-dimensional materials are gaining increasing application as a new generation of separation membranes. The performance of graphene oxide / carbon nanotube composite membranes is the decisive factor in determining whether they can be applied to industrial wastewater treatment.

[0003] Graphene oxide / carbon nanotube composite films consist of a support layer and a functional layer. The performance of these films depends on the structure of their functional layers. Therefore, effectively characterizing the structure of these functional layers and making targeted improvements is crucial for preparing graphene oxide / carbon nanotube composite films with superior performance. Currently, characterizing the functional layer structure mainly relies on cross-sectional images obtained using scanning electron microscopy (SEM). Since accurately capturing the structural features and morphology of the functional layers in graphene oxide / carbon nanotube composite films is essential for obtaining structural information, the cross-sectional images must be sufficiently accurate and clear.

[0004] Currently, the main methods for photographing functional layers are liquid nitrogen brittle fracture, liquid nitrogen cutting, and FIB ion cutting. However, due to the following reasons, it is impossible to photograph clear and accurate functional layer cross sections.

[0005] The liquid nitrogen brittle fracture method is a commonly used method for photographing cross-sectional images of graphene oxide / carbon nanotube composite films. However, the substrate of graphene oxide / carbon nanotube composite films is usually a non-woven fabric material. Non-woven fabrics are tough and not easily brittle in liquid nitrogen. Therefore, this method cannot photograph the morphology of the cross-section of the functional layer of the graphene oxide / carbon nanotube composite film.

[0006] The liquid nitrogen cutting method can solve the problem that graphene oxide / carbon nanotube composite films cannot be brittlely broken in liquid nitrogen. However, the cut surface of the graphene oxide / carbon nanotube composite film usually exhibits ductile deformation, i.e., bending deformation, or even collapse. It is impossible to quickly find the location of the cut surface, and it may be impossible to observe a neat cross-section. Therefore, it cannot accurately reflect the morphology of the functional layer cross-section.

[0007] FIB (Focused Ion Beam) dicing typically targets higher regions of the graphene oxide / carbon nanotube composite film surface due to their high conductivity, making them easier to observe under a scanning electron microscope (FESEM, Hitachi S5500, Japan). The FIB method uses an emitted ion beam to cut the surface of the graphene oxide / carbon nanotube composite film, resulting in a cleaner cross-section compared to liquid nitrogen dicing. However, a mask is required to protect the cut area. Without a mask, the morphology of the cross-section can be damaged during dicing. Furthermore, the difference in contrast between the mask and the functional layer can obscure the functional layer's cross-section, hindering precise observation. Summary of the Invention

[0008] like Figure 1 As shown, due to the toughness of the nonwoven fabric layer and the high stability of the functional layer, the graphene oxide / carbon nanotube composite film cannot be brittle in liquid nitrogen.

[0009] This invention is achieved through the following technical solution:

[0010] A method for observing the cross-sectional shape of a graphene oxide / carbon nanotube composite film includes: when testing the cross-sectional morphology of the graphene oxide / carbon nanotube composite film, firstly, the graphene oxide / carbon nanotube composite film is taken out and immersed in hot water at 100°C, then immersed in liquid nitrogen, and this process is repeated. After drying, it is placed in a carbon spraying instrument for carbon spraying. After carbon spraying, the graphene oxide / carbon nanotube composite film is taken out and placed in a scanning electron microscope for sample measurement.

[0011] The principle behind this invention includes: even though the graphene oxide / carbon nanotube composite film is not a brittle material, it still cannot withstand continuous alternating hot and cold temperatures. This may be because the functional layer of the graphene oxide / carbon nanotube composite film shrinks in liquid nitrogen, and then expands due to heat when placed in 100-degree hot water. This process generates stress, leading to numerous spontaneous fractures in the graphene oxide / carbon nanotube composite film. By observing these spontaneous fractures using a scanning electron microscope, a clear and accurate morphological structure of the cross-section of the functional layer of the graphene oxide / carbon nanotube composite film can be obtained.

[0012] As a preferred technical solution of the present invention, the sample is immersed in hot water at 100°C for 10 seconds, then immersed in liquid nitrogen for 10 seconds, and this process is repeated more than 5 times.

[0013] As a preferred embodiment of the present invention, the graphene oxide / carbon nanotube composite membrane is prepared in the apparatus of the flat cross-flow filtration membrane comprehensive performance testing system.

[0014] As a preferred embodiment of the present invention, the preparation of the graphene oxide / carbon nanotube composite membrane includes: firstly, dissolving 0.3025g of tris(hydroxymethyl)aminomethane in 170ml of pure water, adding 0.6312g of dopamine to the tris(hydroxymethyl)aminomethane solution, rinsing three times with pure water, stirring rapidly, and adjusting the pH to 8.5. Finally, bringing the volume to 250ml in a volumetric flask with pure water, pouring the solution into a PVDF microfiltration membrane with a pore size of 0.1 micrometers, shaking to equilibrate for 3 minutes, then discarding the dopamine solution on the membrane surface, subsequently rinsing the membrane surface three times with pure water, placing it in a membrane tank rinsed with clean water, and then rinsing with sodium tetraborate solution. Cross-flow filtration was performed on the liquid: 0.3125g of graphene oxide and 0.104g of single-walled carbon nanotubes were poured into 2L of sodium tetraborate solution and sonicated for 10 minutes. The sodium tetraborate solution containing graphene oxide and carbon nanotubes was used as the feed water for membrane filtration. After filtration, the product water was poured back into the feed water tank. This process was repeated 3 times. The last filtration was carried out under a pressure of 1 MPa. The purpose was to firmly attach the graphene oxide and carbon nanotubes to the surface of the PVDF membrane. The membrane was removed, the edges were wiped dry with filter paper, and the four corners were taped to a glass plate. It was dried at 90 degrees Celsius for 2 hours and cooled to room temperature before being removed to obtain the graphene oxide / carbon nanotube composite membrane.

[0015] This method, derived through extensive research, specifically involves the following: The graphene oxide / carbon nanotube composite membrane requires a 90°C heat-drying process during preparation to enhance cross-linking performance and stability. This prevents the functional layer on the surface of the graphene oxide / carbon nanotube composite membrane from detaching during cross-flow filtration. Simultaneously, the 90°C drying process removes water molecules between the graphene oxide / carbon nanotube membrane layers, forming stable carbon-oxygen-boron covalent cross-linking bonds. Therefore, the functional layer of the graphene oxide / carbon nanotube membrane remains stable and undamaged during chemical cleaning (sodium hydroxide / SDS). Due to the complexity and extreme conditions of actual wastewater, graphene oxide / carbon nanotube composite membranes without heat-drying treatment may experience increased flux and decreased rejection rate during application. Furthermore, cross-flow filtration can lead to the detachment of the functional layer, affecting its usability. In addition, no obvious cracks were observed on the surface of the graphene oxide / carbon nanotube composite membrane. Figure 1 Therefore, heat drying is a crucial step. This demonstrates that the graphene oxide / carbon nanotube composite film possesses high stability and can withstand drying at high temperatures.

[0016] As a preferred embodiment of the present invention, the drying method is to dry the food in an oven at 45°C.

[0017] As a preferred technical solution of the present invention, the carbon spraying step includes: placing the carbon spraying instrument, performing a vacuuming operation for 10 minutes (until the vacuum level no longer continues to decrease), and starting carbon spraying for 1-5 minutes.

[0018] As a preferred technical solution of the present invention, the observation angle of the scanning electron microscope is rotated downward by about 15°, at which the cross-section of the functional layer can be clearly observed.

[0019] The advantages of this invention over the prior art include:

[0020] (1) By observing the cross-sectional image of the graphene oxide / carbon nanotube composite film using the alternating hot and cold method of the present invention, and observing the cross-section of the functional layer using a scanning electron microscope, a clear and accurate morphological structure at the cross-section of the functional layer of the graphene oxide / carbon nanotube composite film can be obtained.

[0021] (2) The graphene oxide / carbon nanotube composite membrane needs to be dried at 90° during the preparation process to enhance the cross-linking performance and stability. In this way, the functional layer on the surface of the graphene oxide / carbon nanotube composite membrane will not fall off under cross-flow filtration during the application process. At the same time, the functional layer of the graphene oxide / carbon nanotube composite membrane remains stable and will not be damaged during the chemical cleaning process (sodium hydroxide / SDS).

[0022] (3) Since it is necessary to observe the cross-section of the naturally fractured part after the alternating hot and cold treatment of the membrane surface, the scanning electron microscope is rotated downward by about 15°. At this angle, the cross-section of the functional layer can be clearly observed. Attached Figure Description

[0023] Figure 1 Plan view of the graphene oxide / carbon nanotube composite film;

[0024] Figure 2 Cross-sectional view of the graphene oxide / carbon nanotube composite film of this invention using a hot-cold alternating method;

[0025] Figure 3 Cross-sectional view of existing graphene oxide / carbon nanotube composite film using FIB method;

[0026] Figure 4 Cross-sectional view of existing graphene oxide / carbon nanotube composite film cut by liquid nitrogen method. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments and accompanying drawings, but the present invention is not limited thereto.

[0028] Example 1

[0029] The graphene oxide / carbon nanotube composite membrane was prepared using an optimized self-assembly method in a modified apparatus called the Sterlitech Corporation, USA.

[0030] The preparation method of the graphene oxide / carbon nanotube composite membrane is as follows: First, dissolve 0.3025g of tris(hydroxymethyl)aminomethane in 170ml of pure water, add 0.6312g of dopamine to the tris(hydroxymethyl)aminomethane solution, rinse three times with pure water, stir rapidly, and adjust the pH to 8.5. Finally, dilute to 250ml in a volumetric flask with pure water, pour into a PVDF microfiltration membrane with a pore size of 0.1 micrometers, shake well and equilibrate for 3 minutes, then discard the dopamine solution on the membrane surface. Next, rinse the membrane surface three times with pure water, place it in a membrane tank rinsed with clean water, and perform cross-flow filtration with sodium tetraborate solution: Take 0.3125g... Graphene oxide and 0.104 g of single-walled carbon nanotubes were poured into 2 L of sodium tetraborate solution and sonicated for 10 minutes. The sodium tetraborate solution containing graphene oxide and carbon nanotubes was used as the feed water for membrane filtration. After filtration, the product water was poured back into the feed water tank. This process was repeated 3 times. The final filtration was carried out under a pressure of 1 MPa to firmly attach the graphene oxide and carbon nanotubes to the surface of the PVDF membrane. The membrane was removed, the edges were wiped dry with filter paper, and the four corners were taped to a glass plate. It was dried at 90 degrees Celsius for 2 hours and cooled to room temperature before being removed to obtain the graphene oxide / carbon nanotube composite membrane.

[0031] When testing the cross-sectional morphology of the graphene oxide / carbon nanotube composite film, the graphene oxide / carbon nanotube composite film was first taken out and immersed in 100℃ hot water for 10 seconds, then immersed in liquid nitrogen for 10 seconds, and this process was repeated more than 5 times. Then the graphene oxide / carbon nanotube composite film was placed in a 45℃ oven to dry. After drying, it was placed in a carbon spraying instrument, and after a 10-minute vacuum operation (until the vacuum level no longer decreased), carbon spraying began. The carbon spraying time was 1-5 minutes. After carbon spraying, the graphene oxide / carbon nanotube composite film was taken out and placed in a scanning electron microscope (FESEM, Hitachi S5500, Japan) for sample testing. Since it was necessary to observe the cross-section of the naturally fractured part of the graphene oxide / carbon nanotube composite film surface after the alternating hot and cold treatment, the angle of the scanning electron microscope was rotated downward by about 15°. At this angle, the naturally fractured part of the graphene oxide / carbon nanotube composite film surface, i.e., the functional layer cross-section, could be clearly observed.

[0032] Cross-sectional view of the graphene oxide / carbon nanotube composite film of this invention using the alternating heating and cooling method is shown below. Figure 2 As shown.

[0033] Comparative Example 1

[0034] Alternating between 100-degree hot water and freezing, with other aspects the same as in Example 1: The cooling rate is too slow and cannot effectively achieve rapid changes between hot and cold.

[0035] Comparative Example 2

[0036] The method uses alternating 80-degree hot water and freezing, and is otherwise the same as in Example 1, but requires significantly more alternations than the method in Example 1.

[0037] Comparative Example 3

[0038] The graphene oxide / carbon nanotube composite film of the present invention was observed using the existing FIB method, and the results are as follows: Figure 3 As shown, due to the difference in contrast between the mask and the graphene oxide / carbon nanotube composite film, it is not easy to distinguish the cross-section of the functional layer of the graphene oxide / carbon nanotube composite film, and it is impossible to capture the true morphology of the cross-section of the functional layer of the graphene oxide / carbon nanotube composite film.

[0039] Comparative Example 4

[0040] The graphene oxide / carbon nanotube composite film of the present invention was observed using the existing liquid nitrogen cutting method, and the results are as follows: Figure 4 As shown, due to the bending deformation, it is impossible to effectively and quickly locate the cross-section of the functional layer and to capture the true morphology of the cross-section of the functional layer of the graphene oxide / carbon nanotube composite film.

[0041] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for observing cross-sectional images of graphene oxide / carbon nanotube composite films, characterized in that, include: The preparation of the graphene oxide / carbon nanotube composite membrane includes: first, dissolving 0.3025g of tris(hydroxymethyl)aminomethane in 170ml of pure water, adding 0.6312g of dopamine to the tris(hydroxymethyl)aminomethane solution, rinsing three times with pure water, stirring rapidly, and adjusting the pH to 8.

5. Finally, diluting the solution in a 250ml volumetric flask with pure water, pouring it into a PVDF microfiltration membrane with a pore size of 0.1 micrometers, shaking to equilibrate for 3 minutes, then discarding the dopamine solution on the membrane surface, rinsing the membrane surface three times with pure water, placing it in a membrane tank rinsed with clean water, and performing cross-flow filtration with sodium tetraborate solution to firmly attach the graphene oxide / carbon nanotubes to the PVDF membrane surface. After removing the membrane, wiping the edges dry with filter paper, and attaching it to a glass plate with tape, drying it at 90 degrees Celsius for 2 hours, cooling it to room temperature, and removing it to obtain the graphene oxide / carbon nanotube composite membrane. The cross-flow filtration using sodium tetraborate solution refers to: taking 0.3125g of graphene oxide and 0.104g of single-walled carbon nanotubes and pouring them into 2L of sodium tetraborate solution, and after 10 minutes of ultrasonic treatment, using the sodium tetraborate solution containing graphene oxide and carbon nanotubes as the influent for membrane filtration, and after filtration, pouring the product water back into the influent tank, repeating this process 3 times, with the final filtration performed at a pressure of 1 MPa; When testing the cross-sectional morphology of the graphene oxide / carbon nanotube composite film, the graphene oxide / carbon nanotube composite film was first taken out and immersed in 100℃ hot water for 10 seconds, then immersed in liquid nitrogen for 10 seconds, and this process was repeated more than 5 times. After drying, it was placed in a carbon spraying instrument for carbon spraying. The carbon spraying steps included: placing it in the carbon spraying instrument, performing a vacuum operation for 10 minutes until the vacuum level stopped decreasing, and then starting carbon spraying. The carbon spraying time was 1-5 minutes. After carbon spraying, the graphene oxide / carbon nanotube composite film was taken out and placed in a scanning electron microscope for sample measurement. The angle of the scanning electron microscope was rotated downward by 15°, and a clear functional layer cross-section was observed at this angle.

2. The observation method based on photographing cross-sectional images of graphene oxide / carbon nanotube composite films according to claim 1, characterized in that, The graphene oxide / carbon nanotube composite membrane was prepared in the apparatus of the flat cross-flow filtration membrane comprehensive performance testing system.

3. The observation method based on photographing cross-sectional images of graphene oxide / carbon nanotube composite films according to claim 1, characterized in that, The drying method involves drying the food in an oven at 45°C.

Images