A design method for enhancing directional ion transport and inducing separation through a periodically cascaded biconical docking nanopore structure.

Abstract

This invention relates to a design method for enhancing directional ion transport and inducing separation through a periodically cascaded biconical nanopore structure. Under certain flow rate conditions, this method constructs a geometrically asymmetric nanopore unit by controlling key geometric parameters such as the length, pore size ratio, and biconical length ratio of the conical nanopores. Each unit consists of two conical nanopores joined at the smaller end to form a centrally contracting structure. Based on this unit structure, a periodic cascading method is introduced, connecting multiple biconical nanopore units end-to-end along the axial direction to form a multi-level cascaded nanochannel system. By controlling the number of cascaded units, the ion transport path length and interface effects can be adjusted, thereby constructing a periodic geometrically asymmetric nanopore structure. This invention achieves overall optimization of ion transport performance through the synergistic control of the conical channel geometric parameters and the periodically cascaded structure parameters, possessing both good structural designability and controllability.

Description

Technical Field

[0001] This invention relates to the field of nanofluid ion transport regulation and functional membrane materials technology, specifically to a design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure. Background Technology

[0002] With the development of nanofluid transport regulation technology and functional membrane materials, the ion-selective transport and interface regulation mechanisms based on nanopore structures have attracted widespread attention in fields such as ion separation, energy conversion, and nanofluid regulation. Among them, achieving directional migration and selective transport of ions by regulating the interfacial charge effect and geometric constraint effect within nanopores is an important foundation for constructing high-performance functional membranes and ion regulation systems.

[0003] Traditional nanoporous transport systems mostly rely on single-channel structures or regular array structures to achieve ion transport regulation. In actual operation, ion transport behavior is mainly driven by potential and concentration gradients. However, due to the relatively simple channel structure and strong geometric symmetry, the difference between forward and reverse ion transport is limited, resulting in insufficient directional transport regulation capability. Furthermore, local ion enrichment and concentration polarization are prone to occur during long-term operation, thus affecting transport stability and structural reliability.

[0004] Existing research typically enhances ion-selective transport performance by adjusting surface charge density or optimizing the geometry of individual channels. However, due to insufficient structural control dimensions and the lack of multi-channel coupling mechanisms, it is difficult to achieve synergistic control of ion transport directionality and intensity. Furthermore, research on introducing multi-level cascade structures to regulate ion transport response characteristics by addressing the geometric asymmetry of tapered nanopores remains relatively limited. In particular, there is a lack of systematic support for structural design methods that enhance transport response through cascade coupling between channels of different scales.

[0005] Against this backdrop, how to achieve multi-scale synergistic control of ion transport pathways by regulating the geometric parameters and periodic cascade arrangement of conical nanopores, thereby enhancing the directional and selective ion transport capability and transport direction dependence, has become a key issue in improving the ion regulation performance of functional membrane materials. Therefore, a design method based on the geometrically asymmetric structure of conical nanopores and the periodic cascade coupling mechanism is urgently needed to enhance ion directional transport capability and provide a structural basis for ion directional and selective separation and nanofluidic regulation based on direction-dependent transport differences. Summary of the Invention

[0006] To address the aforementioned problems, the main objective of this invention is to provide a design method for enhancing ion directional selective transport characteristics by adjusting the geometric parameters and periodic cascade structure of conical nanopores. This method is then used for ion directional selective separation based on direction-dependent transport differences, unidirectional permeable membrane construction, and nanofluid regulation, through a periodic cascaded biconical docking nanopore structure.

[0007] This invention addresses the aforementioned technical problems through the following technical solution: a design method for enhancing directional ion transport and its induced separation using a periodically cascaded biconical docking nanopore structure. This method is based on constructing an ion transport regulation system using conical nanopores with geometrically asymmetric structures. The conical nanopores have large and small pore ends. The method introduces conical nanopore units with different size parameters and connects two conical nanopore units at their small pore ends to form a biconical docking nanopore unit, thereby constructing a basic transport unit with a central contraction structure. This achieves ordered coupling and ion channel reconstruction between conical channels of different scales. Furthermore, by periodically cascading multiple biconical docking nanopore units along the axial direction, a multi-level cascaded nanochannel structure system is constructed. By controlling the number of cascaded units and their pore geometry parameters, the ion transport path length, interface coupling effect, and local potential distribution can be adjusted.

[0008] The pore geometry parameters include pore length, bicone length ratio, and pore size ratio. Through synergistic regulation, the forward and reverse transport behaviors of ions under different scale conditions are enhanced, thereby improving the directional and selective transport capability of ions in the nanochannel and strengthening the selective differences in the cross-channel transport process.

[0009] Under the coupling effect of multiple physics fields, the structure can enhance the transport differences of ions in different transport directions, thereby realizing the enhancement and controllable adjustment of the ion directional selective separation process caused by the direction-dependent transport differences, and demonstrating the separation enhancement effect based on structural asymmetry.

[0010] In a specific embodiment of the present invention, the specific steps are as follows:

[0011] Step 1: Construction of biconical nanoporous units:

[0012] Based on numerical simulation, a conical nanopore unit model with geometric asymmetry is constructed. The two ends of the conical nanopore are a macropore end and a micropore end, respectively. Two conical nanopores are connected to each other at the micropore end, forming a central contraction structure at the connection interface, thereby constructing a double-cone docking nanopore unit structure. By presetting key geometric parameters such as the channel length, aperture ratio, and double-cone length ratio of the conical nanopore, and by adjusting the surface potential conditions of the pore wall, ion transport unit models with different interface characteristics are constructed to characterize the forward and reverse transport behavior of ions in asymmetric nanochannels.

[0013] Step 2: Construction of periodic cascaded nanoporous structures:

[0014] Based on a single biconical docking nanopore unit, multiple biconical docking nanopore units are periodically cascaded using a head-to-tail docking method to construct a periodically cascaded biconical docking nanopore structure system. By adjusting the number of cascaded units, the overall nanochannel length and the interfacial coupling strength between units can be controlled, thereby constructing a periodic ion transport path structure with multi-scale characteristics. In this structural system, the cascaded units enhance the directional and selective transport capability of ions within the channel through the synergistic effect of geometric asymmetry and interfacial potential distribution, and amplify the transport differences under different transport directions, thus achieving controllable adjustment of the asymmetric characteristics of ion transport.

[0015] Step 3: Evaluation method for asymmetric ion transport characteristics:

[0016] Ion transport performance was analyzed for single-level biconical docking nanopore structures and periodically cascaded biconical docking nanopore structures. Ion current response models under forward and reverse transport driving conditions were established to calculate the transport asymmetry ratio in different structural systems. The transport asymmetry ratio is defined as the ratio of the absolute values ​​of the forward ion current to the reverse ion current, used to characterize the degree of regulation of ion-directed selective transport capability by the nanopore structure. By comparing the changes in the transport asymmetry ratio of single-level and multi-level periodically cascaded structures under the same geometric parameters and interface potentials, the enhancement effect of the periodically cascaded structure on ion-directed selective transport was evaluated, thereby achieving quantitative analysis and optimization design of the ion transport regulation capability of different structural systems. The difference in transport asymmetry reflects the difference in the selective passage capability of ions in different transport directions and embodies an enhancing trend in ion-directed selective transport capability, thus providing a structural basis for the ion-directed selective separation process based on direction-dependent transport differences.

[0017] In a specific embodiment of the present invention, in step one, the radius of the middle constriction hole of the double-cone docking nanopore unit is 50 nanometers, 75 nanometers, or 100 nanometers, the radius of the two end holes is 200 nanometers, and the pore diameter ratio is 4:1, 8:3, or 2:1; the length ratio of the double cones is 1:4, 3:7, or 2:3; and the total length of the double-cone docking nanopore unit is 1500 nanometers, 2000 nanometers, or 2500 nanometers.

[0018] In a specific embodiment of the present invention, in step two, the number of cascaded biconical docking nanopore units in the periodically cascaded biconical docking nanopore structure is 2 to 4.

[0019] In a specific embodiment of the present invention, in step one or two, the inner wall of the biconical docking nanopore unit has a surface charge distribution, and its surface potential ψ is designed to be -25 millivolts.

[0020] In a specific embodiment of the present invention, in step one or two, the material of the conical nanopores is selected from one or more of alumina Al2O3, silicon dioxide SiO2, titanium dioxide TiO2, boron nitride BN, silicon carbide SiC, polymer porous membranes or composite materials thereof.

[0021] In a specific embodiment of the present invention, in step one or two, there is an ionic environment gradient in the nanoporous system caused by a concentration difference, and the concentration difference ΔC is designed to be in the range of 10 to 100 moles per cubic meter, wherein the concentration of one end of the solution is set to be 1 to 5 moles per cubic meter.

[0022] In a specific embodiment of the present invention, in step one or two, there is a temperature difference ΔT in the nanoporous system caused by local heating effect, and the temperature difference ΔT is designed to be 1 to 10 Kelvin.

[0023] In a specific embodiment of the present invention, in step one or two, under the condition of mass conservation, the inlet flow rate of the liquid is set to 1.1 × 10⁻⁶. -6 ~1.78×10 -5 meters per second.

[0024] In a specific embodiment of the present invention, in step three, the ion transport asymmetry characteristic is characterized by the transport asymmetry ratio, which is defined as the ratio of the absolute values ​​of the forward transport ion current to the reverse transport ion current, and its expression is: ,in, For transport asymmetry ratio, Forward transport current, The reverse transport current refers to the forward transport process of ions along the nanopores from the short conical segment to the long conical segment, while the reverse transport refers to the transport process of ions along the nanopores from the long conical segment to the short conical segment.

[0025] The positive and progressive effects of this invention are as follows: The design method for enhancing directional ion transport and inducing separation through a periodically cascaded biconical docking nanopore structure provided by this invention has the following advantages: This invention proposes an ion transport regulation method based on the synergistic design of a biconical docking nanopore structure and a periodically cascaded configuration, achieving the orderly construction of ion transport paths and asymmetric transport characteristics. Under the preset conditions of pore geometry parameters, by adjusting key structural parameters such as pore length, pore size ratio, and biconical length ratio, and in combination with adjusting the number of cascaded units, the synergistic regulation of ion transport directionality and selective transport capability is achieved. Numerical simulation methods are used to analyze the influence of different structural parameters and cascaded methods on the ion current response, achieving systematic optimization of the asymmetric characteristics of ion transport.

[0026] The periodic cascaded biconical docking nanopore structure system constructed in this invention can effectively enhance the asymmetry of the interfacial potential distribution within the pores, amplify the difference between forward and reverse transport, thereby obtaining a more significant transport asymmetry ratio and more stable directional transport behavior, providing a structural basis for ion selective passage.

[0027] This invention optimizes the structural parameters of the biconical docking unit and the periodic cascading method to achieve multi-scale control and selective enhancement of ion transport paths, making the differences in ion throughput under different transport directions more obvious, thereby improving the system's control capability and direction-dependent separation performance in the ion directional selective transport process.

[0028] This invention features a simple structure and flexible control, achieving stable ion-directed selective transport behavior without complex external control conditions. It can be widely applied in fields such as ion-directed selective separation based on direction-dependent transport differences, unidirectional permeable functional membranes, and nanofluid control, providing an effective technical solution for the design of novel functional membrane materials and nanopore transport control structures. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the forward and reverse ion transport of the biconical docking nanopores of the present invention.

[0030] Figure 2 This is a schematic diagram of the periodic cascaded biconical docking nanopore structure of the present invention. Among them, (a), (b) and (c) correspond to the two-unit, three-unit and four-unit periodic cascaded biconical docking nanopore structures, respectively.

[0031] Figure 3 This is a graph showing the relationship between the transport asymmetry ratio and concentration difference under different cycle numbers and bicone length ratios in Example 1, designed based on the method of the present invention. Among them, (a), (b), (c), and (d) correspond to the transport asymmetry ratio changes of single-unit, double-unit, triple-unit, and quadruple-unit bicone-connected nanopore structures under different bicone length ratios, respectively.

[0032] Figure 4 This is a graph showing the relationship between the transport asymmetry ratio and concentration difference under different pore size ratios and bicone length ratios in the three-unit structure designed based on the method of the present invention in Example 1. Among them, (a), (b), and (c) correspond to the changes in the transport asymmetry ratio under different bicone length ratios when the pore size ratios are 4:1, 8:3, and 2:1, respectively.

[0033] Figure 5 This is a graph showing the relationship between the transport asymmetry ratio and the ion concentration difference at both ends of the three-unit periodic cascaded biconical docking nanopore structure designed based on the method of the present invention in Example 1, under different unit lengths and biconical length ratios. Among them, (a), (b), and (c) correspond to the changes in the transport asymmetry ratio under different unit length conditions when the biconical length ratios are 1:4, 3:7, and 2:3, respectively. Detailed Implementation

[0034] The preferred embodiments of the present invention are given below with reference to the accompanying drawings to illustrate the technical solution of the present invention in detail.

[0035] like Figure 1 , Figure 2 As shown, the specific steps of the present invention are as follows: A design method for enhancing directional ion transport and its induced separation through a periodically cascaded biconical docking nanopore structure includes the following steps:

[0036] Step 1: Construct a double-cone docking nanopore unit structure model. Under the condition that the channel geometric parameters are preset, a conical nanopore with geometric asymmetry is constructed, and two conical nanopores are docked with each other at the small end, forming a central contraction structure at the connection interface, thereby forming a double-cone docking nanopore unit. By adjusting parameters such as channel length, aperture ratio, and double-cone length ratio, and combining the surface potential of the pore wall and its distribution characteristics, a microstructure model with specific ion transport behavior is constructed.

[0037] Step 2: Construct a periodic cascaded nanopore structure model. Based on a single biconical docking nanopore unit, multiple units are periodically cascaded by end-to-end docking to form a periodic cascaded biconical docking nanopore structure system. By adjusting the number of cascaded units and their geometric parameters, the overall transport path length and interfacial coupling effect between units can be adjusted. Under the synergistic effect of geometric asymmetry and interfacial potential distribution, ion directional transport paths are constructed and the differences between forward and reverse transport are enhanced.

[0038] Step 3: Based on the above structural model, the ion transport performance of the single-level biconical docking nanopore structure and the periodic cascade structure are analyzed. By establishing ion current response models under forward and reverse transport conditions, the transport asymmetry ratio in different structural systems is calculated. By comparing the changes in the transport asymmetry ratio of different cascade structures under the same geometric parameters and interface potential, quantitative characterization and optimization design of ion transport asymmetry are achieved, thereby evaluating the enhancement effect of the periodic cascade structure on the ability to regulate ion transport asymmetry. Furthermore, the difference in transport asymmetry can be reflected in the difference in the selective passage behavior of ions under different transport directions, thus providing a structural basis for the directional selective separation process of ions caused by direction-dependent transport differences.

[0039] Furthermore, in step one, the material for the tapered nanopores can be selected from materials with stable chemical properties such as alumina (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), boron nitride (BN), silicon carbide (SiC), or polymer materials and their composites.

[0040] Furthermore, in step one, the radius of the middle constriction hole of the double-cone docking nanopore unit is designed to be 50 nanometers, 75 nanometers, or 100 nanometers, and the radius of the two end holes is designed to be 200 nanometers. The aperture ratio is 4:1, 8:3, or 2:1, the length ratio of the double cones is 1:4, 3:7, or 2:3, and the total length of the double-cone docking nanopore unit is designed to be 1500 nanometers, 2000 nanometers, or 2500 nanometers.

[0041] Furthermore, in step two, the number of cascaded biconical docking nanopore units in the periodically cascaded biconical docking nanopore structure is designed to be 2 to 4. The overall length of the nanochannel and the interface coupling effect can be controlled by adjusting the number of cascaded units.

[0042] Furthermore, in step one or two, the inner wall of the biconical nanopore has a surface charge distribution, and its surface potential ψ is designed to be -25 mV. By controlling the surface potential, the selective transport of ions and the rectification performance are enhanced.

[0043] Furthermore, in step one or two, there is an ionic environment gradient in the nanoporous system caused by a concentration difference, and the concentration difference ΔC is designed to be in the range of 10 to 100 moles per cubic meter, with the solution concentration at one end set to 1 to 5 moles per cubic meter.

[0044] Furthermore, in step one or two, there exists a temperature difference ΔT in the nanoporous system caused by local heating effect, and the temperature difference ΔT is designed to be 1 to 10 Kelvin.

[0045] Furthermore, in step one or two, under the condition of mass conservation, the inlet flow rate of the liquid is set to 1.1 × 10⁻⁶. -6 ~1.78×10-5 meters per second.

[0046] Furthermore, in step three, the ion rectification performance is characterized by the transport asymmetry ratio, which is defined as the ratio of the absolute values ​​of the forward transport current to the reverse transport current, and its expression is: ,in, For transport asymmetry ratio, Forward transport current, The forward transport current is the reverse transport current; the forward transport is the transport process of ions along the nanopores from the short cone segment to the long cone segment, and the reverse transport is the transport process of ions along the nanopores from the long cone segment to the short cone segment.

[0047] Furthermore, by selecting a micro / nano fabrication, etching, or self-assembly process for constructing channels, the constructed biconical docking nanochannel units with specific geometric parameters are arranged in an orderly manner in a periodic cascade manner to form a periodic cascaded biconical docking nanochannel structure system, thereby preparing a nanochannel structure system with controllable structure and excellent transport asymmetric regulation capability.

[0048] Example 1

[0049] In the periodic cascaded double-cone docking nanopore structure system constructed in this invention, silicon carbide is preferably used as the structural material of the nanochannel. A double-cone docking nanopore unit array with geometric asymmetry is constructed inside it. By controlling the geometric size parameters of the pore and the potential distribution characteristics of the pore wall surface, an ion-directed transport control channel structure is formed.

[0050] Figure 3 This is a graph showing the relationship between the transport asymmetry ratio and concentration difference under different cycle numbers and bicone length ratios in Example 1, designed based on the method of the present invention. Among them, (a), (b), (c), and (d) correspond to the transport asymmetry ratio changes of single-unit, double-unit, triple-unit, and quadruple-unit bicone-connected nanopore structures under different bicone length ratios, respectively.

[0051] like Figure 3As shown, this invention systematically studies the influence of concentration difference ΔC on transport asymmetry ratio under different period numbers and bicone length ratios. Under conditions of a unit length of 2000 nm and a pore size ratio of 4:1, the transport asymmetry response of different structural systems exhibits tunable characteristics with parameter variations. With increasing cascade period number, the peak value of the transport asymmetry ratio gradually shifts towards lower concentration gradients, indicating that increasing the number of cascade units reduces the driving conditions required for significant transport asymmetry, allowing the structure to exhibit a significant enhancement in ion transport direction dependence even under weaker concentration gradients. As the bicone length ratio increases, the geometric asymmetry of the structure improves, the transport asymmetry response range expands accordingly, and the peak position shifts. In contrast, structures with smaller bicone length ratios show weaker peak position changes and a more concentrated overall response. Under the same period conditions, further increasing the bicone length ratio shifts the concentration difference corresponding to the optimal transport asymmetry state towards higher ΔC, indicating that the system requires higher driving conditions to achieve a stronger transport asymmetry response. By combining the peak values ​​of different structures with their corresponding concentration gradient ranges, it can be found that the three-period cascade structure exhibits superior overall transport asymmetry response capability, achieving a high peak value of transport asymmetry ratio even under medium to low concentration gradient conditions, with a maximum value reaching 75. Furthermore, the structural transport asymmetry response is most significant when the bicone length ratio is 2:3.

[0052] Figure 4 This is a graph showing the relationship between the transport asymmetry ratio and concentration difference under different pore size ratios and bicone length ratios in the three-unit structure designed based on the method of the present invention in Example 1. Among them, (a), (b), and (c) correspond to the changes in the transport asymmetry ratio under different bicone length ratios when the pore size ratios are 4:1, 8:3, and 2:1, respectively.

[0053] like Figure 4 As shown, this invention systematically analyzes the effects of different pore size ratios and bicone length ratios on the transport asymmetry ratio as a function of concentration gradient under a three-unit periodic cascade structure with a unit length of 2000 nm. The results show that, under the same periodic structure, as the pore size increases, the peak position of the transport asymmetry ratio generally shifts towards higher concentration gradients, indicating that increasing the pore size improves the driving conditions required for the system to reach a stronger transport asymmetry state. Among these, a pore size ratio of 4:1 shows the best overall performance, corresponding to the highest peak transport asymmetry ratio, reaching 75. Meanwhile, different structures exhibit varying degrees of response to changes in pore size ratio. Structures with smaller bicone lengths show relatively smooth changes in the peak transport asymmetry ratio, with the peak mainly concentrated in the low to medium concentration gradient range, demonstrating strong stability. However, as the bicone length ratio increases, the transport asymmetry response becomes more sensitive to pore size changes, and the peak fluctuations are enhanced.

[0054] Figure 5This is a graph showing the relationship between the transport asymmetry ratio and the ion concentration difference at both ends of the three-unit periodic cascaded biconical nanopore structure designed based on the method of the present invention in Example 1, under different unit lengths and biconical length ratios. Specifically, (a), (b), and (c) correspond to the changes in the transport asymmetry ratio under different unit length conditions when the biconical length ratios are 1:4, 3:7, and 2:3, respectively. Figure 5 As shown, under a pore size ratio of 4:1, the effects of different total pore lengths and bicone length ratios on the transport asymmetry ratio were further investigated. The results show that as the bicone length ratio increases, the peak position of structures with different total lengths generally shifts towards higher concentration gradients. Simultaneously, some structures exhibit response changes in the low-concentration region, indicating that changes in the ratio of long and short cone segments significantly affect the driving response threshold of the system. Furthermore, as the bicone length ratio increases, the overall peak transport asymmetry ratio shows a decreasing trend, indicating a matching relationship between enhanced structural geometric asymmetry and enhanced transport response. Comprehensive comparison shows that at a bicone length ratio of 1:4, the unit length of 2500 nm performs best, with its transport asymmetry ratio peak appearing in the lower concentration gradient region, reaching a maximum value of 194, significantly superior to other parameter combinations.

[0055] In summary, this invention constructs a periodically cascaded biconical nanopore structure and synergistically regulates the pore geometry and the number of cascaded units to achieve controllable design of ion transport paths and optimization of transport asymmetry performance. The results show that the combined effect of the geometric asymmetry of the pore structure and the periodic cascading effect significantly enhances the difference between forward and reverse ion transport, thereby improving the system's ability to regulate transport asymmetry. This structure represents a designable structural scheme for regulating ion transport in nanofluids. Through flexible configuration of geometric parameters and cascading methods, it enables precise control of ion migration paths and current response characteristics, and provides structural design basis and theoretical support for the construction of unidirectional permeable functional membranes and the directional selective separation and nanofluid transport regulation based on direction-dependent transport differences.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as defined by the appended claims and their equivalents.

Claims

1. A design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure, characterized in that: The design method for enhancing directional ion transport and inducing separation through a periodically cascaded biconical docking nanopore structure is based on constructing an ion transport regulation system using conical nanopores with geometrically asymmetric structures. These conical nanopores have large and small pore ends. The method introduces conical nanopore units with different size parameters and connects two units at their small pore ends to form a biconical docking nanopore unit, thereby constructing a basic transport unit with a central contraction structure. This achieves ordered coupling and ion channel reconstruction between conical channels of different scales. Furthermore, by periodically cascading multiple biconical docking nanopore units along the axial direction, a multi-level cascaded nanochannel structure system is constructed. By controlling the number of cascaded units and their pore geometry parameters, the ion transport path length, interface coupling effect, and local potential distribution can be adjusted. The pore geometry parameters include pore length, bicone length ratio, and pore size ratio. Through synergistic regulation, the forward and reverse transport behaviors of ions under different scale conditions are enhanced, thereby improving the directional and selective transport capability of ions in the nanochannel and strengthening the selective differences in the cross-channel transport process.

2. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 1, characterized in that: The specific steps are as follows: Step 1: Construction of biconical nanoporous units: Based on numerical simulation, a conical nanopore unit model with geometric asymmetry is constructed. The two ends of the conical nanopore are a macropore end and a micropore end, respectively. Two conical nanopores are connected to each other at the micropore end, forming a central contraction structure at the connection interface, thereby constructing a double-cone docking nanopore unit structure. By presetting key geometric parameters such as the pore length, pore diameter ratio, and double-cone length ratio of the conical nanopore, and by adjusting the surface potential conditions of the pore wall, ion transport unit models with different interface characteristics are constructed to characterize the forward and reverse transport behavior of ions in asymmetric nanochannels. Step 2: Construction of periodic cascaded nanoporous structures: Based on a single biconical docking nanopore unit, multiple biconical docking nanopore units are periodically cascaded using a head-to-tail docking method to construct a periodically cascaded biconical docking nanopore structure system. By adjusting the number of cascaded units, the overall nanochannel length and the interfacial coupling strength between units can be adjusted, thereby constructing a periodic ion transport path structure with multi-scale characteristics. In this structure system, the cascaded units enhance the directional and selective transport capability of ions within the channel through the synergistic effect of geometric asymmetry and interfacial potential distribution, and amplify the transport differences under different transport directions, thereby achieving controllable adjustment of the asymmetric characteristics of ion transport. Step 3: Evaluation method for asymmetric ion transport characteristics: Ion transport performance was analyzed for single-level biconical docking nanopore structures and periodically cascaded biconical docking nanopore structures. Ion current response models under forward and reverse transport-driven conditions were established to calculate the transport asymmetry ratio in different structural systems. The transport asymmetry ratio, defined as the ratio of the absolute values ​​of the forward ion current to the reverse ion current, characterizes the degree of regulation of the nanopore structure's ability to selectively transport ions. By comparing the changes in the transport asymmetry ratio of single-level and multi-level periodically cascaded structures under the same geometric parameters and interface potentials, the enhancement effect of the periodically cascaded structure on the selective transport of ions was evaluated, thereby achieving quantitative analysis and optimized design of the ion transport regulation capability of different structural systems. The difference in transport asymmetry is reflected in the difference in the selective passage capacity of ions under different transport directions, and it manifests as an increasing trend in the directional selective transport capacity of ions, thus providing a structural basis for the directional selective separation process of ions caused by the difference in direction-dependent transport.

3. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step one, the radius of the middle constriction pore of the double-cone docking nanopore unit is 50 nm, 75 nm, or 100 nm, the radius of the two end pores is 200 nm, and the pore diameter ratio is 4:1, 8:3, or 2:1; the length ratio of the double cones is 1:4, 3:7, or 2:3; and the total length of the double-cone docking nanopore unit is 1500 nm, 2000 nm, or 2500 nm.

4. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step two, the number of cascaded biconical docking nanopore units in the periodically cascaded biconical docking nanopore structure is 2 to 4.

5. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step one or two, the inner wall of the biconical docking nanopore unit has a surface charge distribution, and its surface potential ψ is designed to be -25 millivolts.

6. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step one or two, the material of the tapered nanopores is selected from one or more of alumina (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), boron nitride (BN), silicon carbide (SiC), polymer porous membranes, or composite materials thereof.

7. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step one or two, there is an ionic environment gradient in the nanoporous system caused by the concentration difference. The concentration difference ΔC is designed to be in the range of 10 to 100 mol per cubic meter, with the solution concentration at one end set to 1 to 5 mol per cubic meter.

8. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step one or two, there is a temperature difference ΔT in the nanoporous system caused by local heating effect, and the temperature difference ΔT is designed to be 1 to 10 Kelvin.

9. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step one or two, under the condition of mass conservation, the inlet flow velocity of the liquid is set to 1.1 × 10⁻⁶. -6 ~1.78×10 -5 meters per second.

10. The design method for enhancing directional ion transport and inducing separation through a periodically cascaded double-cone docking nanopore structure according to claim 2, characterized in that: In step three, the asymmetric characteristics of ion transport are characterized by the transport asymmetry ratio, which is defined as the ratio of the absolute values ​​of the forward transport ion current to the reverse transport ion current, and its expression is: ,in, For transport asymmetry ratio, Forward transport current, This refers to the reverse transport current; forward transport refers to the transport process of ions along the nanopore from the short cone segment to the long cone segment, while reverse transport refers to the transport process of ions along the nanopore from the long cone segment to the short cone segment.

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