Research On Nonlinear Ion Transport In Solid Nanopores Of Two-dimensional Metal-organic Framework Materials

Solid-state nanopore technology has been an emerging analysis technique in recent ten years,which utilizes the changes of ion flow caused by the target passing through the nanopore to analyze it with high spatial resolution.Because of its high precision and accuracy,the method can be applied to the field of protein analysis,DNA sequencing,biomimetic material and energy conversion.The theoretic study of ions transport in nanopores is helpful for people to deeply understand the ion channels on the cytomembrane.In addition,the selective transport of ions through nanopores can be applied to the field of biomimics or energy conversion.Due to inconvenient maneuverability,high cost and harsh technical conditions,the development of solid-state nanopores is greatly limited.In order to solve the above problems,we adopt a two-dimensional?2-D?metal-organic framework material?MOFs?with its own pore size as solid-state nanopore,propose a new loading method of composite nanopores based on electrophoresis,discover the nonlinear ion transport phenomenon in MOFs nanopores,and study the mechanism through COMSOL multiphysical field simulation.It is divided into the following two parts in detail.Based on it,my research direction is divided into two aspects as followed:First of all,we introduced electrophoresis method to manufacture 2-D MOFs solid-state nanopores and observe nonlinear ion transport phenomena.The 2-D Zr-BTB-BA nanosheets with ultrathin thickness,subnanometer pore size and long-term water stability were synthesized with zirconium cluster as the central metal,1,3,5-tri?4-carboxyl phenyl?benzene?H₃BTB?as the ligand and benzoic acid as the regulator.The Si N_X substrate was perforated by electrical breakdown,and the pore size was larger than 2 nm.Compared with two electrophoresis,we found that the interface of 2-D MOFs/Si N_x solid-state nanopores was more stable and it showed nonlinear ion transport phenomenon under acidic conditions.The influencing factors on the nonlinear ion transport in Zr-BTB-BA nanopores were studied.By changing the acidity and alkalinity of the solution,it was found that the ion transport in the nanopores was affected by charge effect and hydrophobic effect under different p H conditions.The hydrophobic effect of materials under acidic conditions was the dominant factor,which gave rise to the emergence of I-V curve platform in small voltage and a modest degree of ion rectification.While the leading factor was charge effect of the material and the electrical property changed under basic conditions,contributing to the inversion and enhancement of ICR.Also,the ionic strength had a certain influence on the degree of rectification.By synthesizing 2-D Zr-BTB-FA and Zr-BTB-PABA nanosheets with different hydrophobicity,it was further verified that the appearance of the I-V curve platform was mainly caused by the hydrophobicity of the nanopore while the occurrence of rectification resulted from the effect of charge.At the same time,COMSOL multiphysical field simulation was used to obtain the transport states of cation and anion in the nanopore,and it was found that when changing the amount of charge in 2-D Zr-BTB-BA nanopore,the accumulative degree of the two kinds of ion in the different polarities was disparate,which resulted in ion rectification and reversal of rectification.