A method for constructing micro-nano structure containing holes by using electrolyte phase change

Abstract

The application provides a method for constructing a micro-nano structure with a hole by using a change of a state of an electrolyte, and belongs to the technical field of micro-nano processing. The method is as follows: in an electrodeposition process, freezing and solidification and melting and other operations are performed on the electrolyte by increasing and decreasing the temperature, so that the state of the electrolyte (solid and liquid) is changed, and then the concentration of the electrolyte, the ion transmission direction, the pH and the medium temperature and other variables in the system are changed, and a micro-nano structure with a hole, such as a through hole, a half-through hole, a double-wall / multi-wall shell opening and the like, is constructed on the surface of a conductive base. The method provided by the application can quickly and efficiently adjust the mass transfer and charge transfer variables closely related to the construction of the micro-nano structure with a hole by using only a simple change of the state of the electrolyte, and provides a mild and rapid condition to make up for the shortcomings of traditional preparation technologies of the micro-nano structure with a hole. The micro-nano structure constructed has a good application prospect in aspects of adsorption filtration, energy, photoelectric catalysis, chemical sensing, latent imaging, drug / gene carrying diagnosis and treatment and the like.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication technology, specifically relating to a method for constructing porous micro-nano structures by utilizing changes in the state of electrolyte to interfere with the mass and charge transfer process. Background Technology

[0002] Pore ​​design technology is a key issue in the field of micro / nanostructure fabrication. Porous structures can add additional voids, which provide additional attachment sites and specific surface area for other foreign substances, thus endowing materials with superior properties in many applications. For example, porous materials play an important role in gas adsorption and filtration, energy conversion, photoelectrocatalysis, chemical sensing, stealth imaging, drug / gene delivery, and diagnostics, thus attracting many researchers to design porous micro / nanostructures. Through more than 30 years of efforts, porous micro / nanostructure design has gradually developed four types of construction technology routes based on template-assisted strategies, Oswald ripening mechanisms, Kirkendall effects, or electrochemical displacement reactions. These existing technologies have greatly facilitated the application of porous structures in various fields. However, the pore design process may require cumbersome and time-consuming processing steps, demanding experimental conditions, or difficulties in constructing various complex small-sized pores. Therefore, developing new rapid and mild design methods for small-sized pore fabrication will be an important supplement to existing technologies. Summary of the Invention

[0003] The purpose of this invention is to rapidly and gently design complex porous micro / nano structures by utilizing the changes in the state of the electrolyte during the electrodeposition process, thus overcoming the shortcomings of existing technologies.

[0004] The technical solution provided by this invention is as follows: a method for constructing porous micro / nano structures by utilizing changes in the physical state of an electrolyte. The method is as follows: during the electrodeposition process, the electrolyte is subjected to freezing and melting operations by raising or lowering the temperature, causing a change in the physical state (solid to liquid) of the electrolyte. This simply and quickly interferes with the mass transfer and charge transfer related variables (electrolyte concentration, ion transport direction, pH, and medium temperature) during the reaction process, thereby constructing a porous micro / nano structure on the surface of a conductive substrate.

[0005] Preferably, the electrolyte is a silver nitrate solution containing boric acid. The silver nitrate solution is the main electrodeposition solution, and the concentrations of both silver nitrate and boric acid are >0.001M.

[0006] Preferably, the state transition (solid-liquid) occurs during the electrodeposition process, achieved through operations such as freezing and thawing of the electrolyte by raising or lowering the temperature. The purpose of these temperature adjustments is to rapidly change the reaction concentration, ion transport direction, pH, and medium temperature within the electrolyte system. Applying a temperature below the electrolyte's freezing point using a refrigerator or liquid nitrogen achieves the purpose of cooling to achieve freezing; subsequently, applying a temperature above the electrolyte's freezing point using a heating platform or at room temperature achieves the purpose of heating to achieve thawing.

[0007] Preferably, the mass and charge transfer related variables include electrolyte concentration, ion transport direction, pH, and medium temperature. Rapid changes in these variables will significantly interfere with the transformation process of solution ions into deposited products on the working electrode during electrodeposition. During electrodeposition, when the electrolyte concentration drops sharply, the ions required for the formation of deposited products on the working electrode are difficult to replenish with the rapidly decreasing ions in the electrolyte, disrupting the complete growth mode of the micro / nano structure and resulting in pores that cannot fill the complete structure. When the ion transport direction in the system shifts away from the micro / nano structure, pores tend to form. When the electrolyte is acidic, electro-corrosion is likely to occur during electrodeposition, forming pores. When the electrolyte medium temperature decreases, the mass and charge transfer rate in the solution slows down, and the replenishment of ions near the working electrode is not timely, making it easy to deposit micro / nano structures containing pores.

[0008] Preferably, the freezing and thawing operations can interfere with mass and charge transfer related variables. This is because as the electrolyte freezes from a liquid to a solid state, the frozen electrolyte acts as an "electrolyte concentration concentration pocket." When the frozen electrolyte thaws, the electrolyte concentration in the initially thawed liquid is much higher than that in the later thawed liquid. Therefore, by freezing and thawing the electrolyte, a huge concentration gradient can be provided for pore formation. In addition, freezing and thawing near the freezing point provides a relatively low temperature environment, which slows down the mass and charge transfer rate in the solution. During the deposition of silver nitrate electrolyte or silver nitrate electrolyte containing boric acid, the acidic medium also has the effect of electro-corrosion of the structure as the temperature rises and the pH decreases. The two work together to accelerate pore formation.

[0009] Preferably, the method can be used to prepare porous micron- and nanoscale structures, including through-holes, semi-through-holes, and double-walled / multi-walled shell openings, etc. Different types of porous structures can be constructed by changing the voltage application time, magnitude, direction, application gap, and number of cycles during the freeze-thaw process.

[0010] Compared with the prior art, the advantages of the present invention are as follows:

[0011] 1. By introducing a frozen and thawed electrolyte, spontaneous and rapid modulation of electrolyte concentration, ion transport direction, pH and medium temperature is achieved, which can quickly interfere with the mass and charge transfer process of the deposition reaction, providing a mild and rapid porous design environment and making up for the shortcomings of traditional technologies.

[0012] 2. By simply adjusting the deposition and environmental parameters using the method provided by this invention, various complex porous structures can be flexibly designed, such as multi-shell structures where the number of shells is positively correlated with the number of depositions, internally closed hollow pores, through-holes, and semi-through-holes. The method is easy to operate and can significantly improve the pore design resolution of the obtained micro / nano structures. The resulting pores have great potential in fields such as gas adsorption and filtration, energy conversion, photoelectrocatalysis, chemical sensing, stealth imaging, drug / gene delivery, and diagnosis. Attached Figure Description

[0013] Figure 1 For example 1 of the present invention, during electrodeposition: (a) a schematic diagram of the melting of frozen electrolyte; (b) a diagram of the change in electrolyte concentration during the melting process; (c) a schematic diagram of electro-corrosion under a local electric field during the deposition process; (df) a cross-sectional view of the porous micro / nano structure and part of the structure on the surface of the working electrode;

[0014] Figure 2 Scanning electron microscope (SEM) images of porous micro / nano structures under different electrodeposition conditions in Example 2 of this invention: (a) Deposition at 5V for 120s; (b) Deposition at 7V for 120s; (c) Deposition at 20V for 120s; (d) Deposition at 5V for 600s; (e) Deposition at 3V for 120s followed by deposition at 20V for 120s.

[0015] Figure 3 The following are examples of multi-shell open-pore micro / nano structures obtained under different electrodeposition conditions after introducing molten frozen electrolyte in Example 3 of the present invention: (a) Schematic diagram; (bg) Formation process of double-walled / multi-walled shells; (hj) Porous micro / nano structures with four-walled shells with different orientations;

[0016] Figure 4 In Example 4 of this invention, after introducing a melted cryo-electrolyte, various multi-shell open-cell micro / nano structures were constructed by interfering with changes in ion transport in the system by applying different reduction voltages: (ac) Three-shell open-cell micro / nano structures with different interlayer spacings obtained under different reduction voltages; (d) Schematic diagram of the effect of interfering with ion transport on the final pore structure after applying different potentials in the melted cryo-electrolyte system; (ef) Six-shell open-cell micro / nano structures with different interlayer spacings obtained under different reduction voltages. Detailed Implementation

[0017] The present invention will be described in detail below through embodiments.

[0018] Example 1

[0019] (1) Cut a gold-plated silicon wafer to a size of 1cm x 1.5cm. 2 The size was used as the working electrode, and the obtained working electrode was ultrasonically cleaned for 3 minutes in ethanol and deionized water, respectively.

[0020] (2) Dissolve boric acid H3BO3 and silver nitrate AgNO3 in deionized water to prepare an AgNO3 solution containing supporting electrolyte H3BO3 (the concentration here is 0.06M AgNO3 and 0.16M H3BO3 electrolyte).

[0021] (3) Construct a two-electrode deposition system, using the electrode prepared in (1) as the working electrode, with a working area of ​​1*1cm. 2 The working area is 1*0.5cm. 2 The carbon paper is used as the counter electrode. The working electrode and the counter electrode are respectively attached to the wall of the square quartz cylinder with tape, maintaining a distance of 4cm. The cylinder is then placed in a refrigerator below 0℃ (set to -8℃ here) and frozen until solid.

[0022] (4) Take the quartz tank deposition tank out of the refrigerator and place it in the air at 25°C to melt for a certain period of time (30s here). After observing the liquid water film on the surface, conduct electricity to deposit it. Figure 1 a is a schematic diagram of the melting of frozen electrolyte. Figure 1 Figure b shows the concentration changes of each electrolyte during the melting process. As can be seen from the figure, after freezing and melting the electrolyte, a sharp drop in concentration occurs in the system. The ions required for the formation of deposits on the working electrode are difficult to replenish with the rapidly decreasing ions in the electrolyte, disrupting the complete growth mechanism of the micro / nano structure. It is expected that pores that cannot be filled will appear. Furthermore, since the melted frozen layer accounts for only a very small amount of the total electrolyte, the system has a temperature far lower than the room temperature during normal deposition. This low temperature inhibits the ion charge transport rate in the electrolyte. Based on the ionization equilibrium law supporting the electrolyte boric acid (H3BO3), it is known that as melting progresses, the temperature of the micro-region increases slightly compared to the initial melting stage, leading to ionization towards H2O. + The directional shift of the electrodeposition process causes a decrease in pH within the deposition system. According to earlier research (Adv. Mater. 2018, 30, 1805686), in systems using silver nitrate as the electrolyte, electrodeposition is accompanied by pH-dependent electro-corrosion. When the pH in the system decreases, coupled with the etching of molecules (such as ionization products B(OH)4) under a locally enhanced electric field, the process becomes more efficient. - The presence of ) leads to electro-corrosion phenomena in the local vicinity of micro / nano structures, forming pores (see Figure 1 (See diagram c). Figure 1Micro- and nanostructures with different concentration gradients in different micro-regions on the working electrode were obtained by deposition at 10V and 120s. As can be seen from the cross-sectional views in figures 1d and 1e, the gradient caused by this electrolyte phase change can construct pores with various internal structures (through-hole or semi-through-hole). Furthermore, due to the inconsistent concentration diffusion in the horizontal and vertical directions, pores with different internal structures can also be fabricated in different micro-regions. Figure 1 Different sizes / types of porous micro / nano structures in f.

[0023] Example 2

[0024] (1) Cut a gold-plated silicon wafer to a size of 1cm x 1.5cm. 2 The size was used as the working electrode, and the obtained working electrode was ultrasonically cleaned for 3 minutes in ethanol and deionized water, respectively.

[0025] (2) Dissolve boric acid H3BO3 and silver nitrate AgNO3 in deionized water to prepare an AgNO3 solution containing supporting electrolyte H3BO3 (the concentration here is 0.06M AgNO3 and 0.16M H3BO3 electrolyte).

[0026] (3) Construct a two-electrode deposition system, using the electrode prepared in (1) as the working electrode, with a working area of ​​1*1cm. 2 The working area is 1*0.5cm. 2 The carbon paper is used as the counter electrode. The working electrode and the counter electrode are respectively attached to the wall of the square quartz cylinder with tape, maintaining a distance of 4cm. The cylinder is then placed in a refrigerator below 0℃ (set to -8℃ here) and frozen until solid.

[0027] (4) The quartz deposition tank was removed from the refrigerator and placed in air at 25°C to melt for a certain period of time (30s in this case). After observing a liquid water film on the surface, an electric current was applied to deposit the solution. By introducing the frozen and thawed electrolyte, different deposition voltages or deposition times were selected to obtain porous micro / nano structures of different shapes. Figure 2 ae are scanning electron microscope images of porous micro / nano structures prepared under various conditions: (a) deposition at 5V for 120s; (b) deposition at 7V for 120s; (c) deposition at 20V for 120s; (d) deposition at 5V for 600s; (e) deposition at 3V for 120s followed by deposition at 20V for 120s.

[0028] Example 3

[0029] (1) Cut a gold-plated silicon wafer to a size of 1cm x 1.5cm. 2 The size was used as the working electrode, and the obtained working electrode was ultrasonically cleaned for 3 minutes in ethanol and deionized water, respectively.

[0030] (2) Dissolve boric acid H3BO3 and silver nitrate AgNO3 in deionized water to prepare an AgNO3 solution containing supporting electrolyte H3BO3 (the concentration here is 0.06M AgNO3 and 0.16M H3BO3 electrolyte).

[0031] (3) Construct a two-electrode deposition system, using the electrode prepared in (1) as the working electrode, with a working area of ​​1*1cm. 2 The working area is 1*0.5cm. 2 The carbon paper is used as the counter electrode. The working electrode and the counter electrode are respectively attached to the wall of the square quartz cylinder with tape, maintaining a distance of 4cm. The cylinder is then placed in a refrigerator below 0℃ (set to -8℃ here) and frozen until solid.

[0032] (4) The quartz deposition tank was removed from the refrigerator and placed in air at 25°C to melt for a certain period of time (30s in this case). After observing a liquid water film on the surface, electrolysis was performed to deposit the material. Since the gradually melting frozen electrolyte layer can provide a huge concentration gradient difference, the concentration gradient difference can be mitigated by pausing deposition, while accelerating the diffusion of corrosive substances from the electrode to the surface of the micro / nano structure, thereby corroding the fabricated structure. Using this principle, the ions and corrosive substances in the system are redistributed by continuously pausing and depositing. Growth and corrosion occur continuously when electrolysis is applied, and the micro / nano structure is corroded when electrolysis is paused. After several cycles, a multi-shell porous micro / nano structure with the same number of shells as the number of electrolysis pauses can be prepared. Figure 3 a is a schematic diagram of a multi-shell open-pore micro / nano structure obtained under multiple pauses and re-energizations of electrodeposition after the introduction of a gradually melting cryogenic electrolyte; Figure 3 bg represents the formation process of double-walled / multi-walled porous micro / nano structures corresponding to the re-energization cycle; Figure 3 hj is a scanning electron microscope image of a porous micro / nano structure with four-walled shells, obtained after four rounds of re-energizing.

[0033] Example 4

[0034] (1) Cut a gold-plated silicon wafer to a size of 1cm x 1.5cm. 2 The size was used as the working electrode, and the obtained working electrode was ultrasonically cleaned for 3 minutes in ethanol and deionized water, respectively.

[0035] (2) Dissolve boric acid H3BO3 and silver nitrate AgNO3 in deionized water to prepare an AgNO3 solution containing supporting electrolyte H3BO3 (the concentration here is 0.06M AgNO3 and 0.16M H3BO3 electrolyte).

[0036] (3) Construct a two-electrode deposition system, using the electrode prepared in (1) as the working electrode, with a working area of ​​1*1cm. 2 The working area is 1*0.5cm. 2The carbon paper is used as the counter electrode. The working electrode and the counter electrode are respectively attached to the wall of the square quartz cylinder with tape, maintaining a distance of 4cm. The cylinder is then placed in a refrigerator below 0℃ (set to -8℃ here) and frozen until solid.

[0037] (4) Remove the quartz cylinder deposition tank from the refrigerator and place it in air at 25°C for a certain period of time (30s in this case) to melt it. After observing the liquid water film on the surface, electrolysis is performed to deposit the liquid water. Apply voltage (such as oxidation voltage and different reduction voltages) to the system. Apply different types of voltage according to the different number of open shell layers to obtain multi-walled open shell micro / nano structures. Figure 4 The image shows scanning electron microscope (SEM) images of various multi-shell open-pore micro / nano structures constructed by applying different numbers and magnitudes of reduction voltages during the growth process after applying oxidation voltage. As can be seen from the images, the number of shells can be controlled by the number of reduction voltages applied, and the spacing between shells can be controlled by the magnitude of the reduction voltage. The image shown is a three-shell open-pore micro / nano structure with different layer spacing. Figure 4 Figure d illustrates the effect of different applied voltages on the regulation of ion transport in the final porous micro / nanostructure in this embodiment. The gradually melting frozen electrolyte during deposition provides a low-temperature occlusion environment. Compared to mass transfer in room-temperature solutions, the ion migration rate is more significantly affected by potential. By applying an oxidation voltage and a reduction voltage with opposite electric field directions, the direction of ion transport in the electrolyte changes. When an oxidation voltage is applied to the working electrode, silver ions and hydrogen ions are repelled by the electric field and continuously replenished, tending to grow the micro / nanostructure. However, when a reduction voltage (generally smaller) is applied in the opposite direction, silver ions are difficult to reduce, while hydrogen ions accumulate near the bottom of the micro / nanostructure near the working electrode surface, intensifying the corrosion of the micro / nanostructure and ultimately forming a porous multi-shell micro / nanostructure. Figure 4 ef represents the multi-shell porous micro / nano structures obtained under different voltages. During the oxidation process, six small reduction voltages were applied intermittently, resulting in a clear and visible scanning image of the six-shell porous micro / nano structure.

[0038] The present invention has been illustrated with the above embodiments to explain the detailed method of the invention. However, the present invention is not limited to the detailed method described above, that is, it does not mean that the present invention must rely on the detailed method described above to be implemented. Those skilled in the art should understand that any improvements to the present invention or different modifications based on the above description fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for constructing porous micro / nano structures using electrolyte phase changes, characterized in that, The method is as follows: Boric acid (H3BO3) and silver nitrate (AgNO3) are dissolved in deionized water to prepare an electrolyte with concentrations of 0.06 mM AgNO3 and 0.16 mM H3BO3. A two-electrode deposition system is constructed using a gold-plated silicon wafer as the working electrode and carbon paper as the counter electrode. The electrolyte is frozen to a solid state in a refrigerator at -8 ℃, then removed from the refrigerator and placed in air at 25 ℃ to thaw for 30 seconds. After observing a liquid water film on the surface, an electric current is applied for deposition. By utilizing the solid-liquid transition of the electrolyte, the mass and charge transfer variables in the reaction process are simply and quickly interfered with, thus constructing a porous micro / nano structure on the surface of a conductive substrate.

2. The method according to claim 1, characterized in that, Voltage is applied to the working electrode by adjusting the voltage application time, magnitude, direction, application gap, and number of cycles.

3. The method according to claim 1, characterized in that, The mass and charge transfer related variables include electrolyte concentration, ion transport direction, pH, and electrolyte medium temperature.

4. The method according to claim 1, characterized in that, The porous micro / nanostructure includes micron- and nanoscale structures composed of through holes, semi-through holes, and double-walled / multi-walled shell openings.

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