Study Of The Ion Transportation In Single Conical Nanopores

Study of the ion transportation in single conical nanoporesWei Junzhe?Condensed Matter Physics?Directed by Professor Du GuanghuaDue to the symmetry breaking,single conical nanopores show characteristics of ioncurrent rectification,which has a great potential in applications to ion separation,power supplier and chemical valve.It is of great importance to study the electrical properties of nanopores and the modification methods of conical nanopores in order to understand the ion transport properties in nanoscale structures and to improve the application performance of conical nanopores.In this thesis,we used polyethylene terephthalate?PET?film bombarded by single high energy heavy ion in the Lanzhou Interdisciplinary Heavy Ion Microbeam?LIHIM?,and the single latent ion track was chemical etched to prepare the single conical nanopores.Then the ions transport of single conical nanopores in different electrolyte solutions was studied by their I-V properties.The measurement shows the rectification of single conical nanopores in the solution of KCl,NaCl,LiCl,MgCl₂ and CaCl₂.The current rectification coefficient ? first increased and then decreased with the electrolyte concentration from 0.0001 M to 1 M.In bivalent solution the ? reached its maximum at a lower concentration than in monovalent solutions,and the maximum of rectification coefficient in the bivalent solution is larger than that in the monovalent solution.In order to explain the observed experimental phenomena we proposed a model of ion transportation in single conical nanopores using potential well change with ion concentration,applied voltage and anion enrichment.Furthermore,we studied the ion selectivity in single conical nanopores.We tested the unidirectional transport of ions in single conical nanopores,and evaluated the anion or cation selectivity of single conical nanopores by current measurement.We found that the surface of single conical nanopores in PET film can be transformed from a negatively charged state to a positively charged state by the immersion in the multivalent cation solution,which resulted in the change of the ion selectivity of the nanopore from cation to anion selectivity.The surface charge inversion is mainly caused by the adsorption of multivalent cations on the nanopores wall,and it is dependent on the concentration of electrolyte solution.The data showed that the inversion concentration is lower for trivalent ions than for bivalent ions,but no charge inversion was observed in monovalent ion solutions.