Ion transport performance in nanochannels manipulated by external surface charge
Nanochannel-based ion transport plays an important role in ionic energy conversion and storage,seawater desalination,and ion sensing.The selectivity and net flux of ion transport are strongly affected by the surface charge of the nanochannels.In current studies,the experimental and finite element simulation methods are primarily adopted,but the influence of external surface charge on ion transport performance is rarely investigated from a microscopic perspective.In this study,a molecular dynamics method was adopted to investigate the manipulation mechanism of the external surface charge on ion transport in nanochannels.The results show that the external surface charge exacerbates the space charge imbalance near and inside the nanochannels and reduces the internal potential of the nanochannels,thereby enhancing the Donnan exclusion effect.The external surface charge stabilizes the water X-velocity inside the nanochannel and improves the water X-velocity near the channel center.Moreover,the external surface charge improves the ion velocity in the middle of the nanochannels.Consequently,the externally and internally surface-charged nanochannels exhibit higher Na+ion flux densities,ion selectivity,and ion current under an electric field,and their ionic conductivities are 2.65 times greater than those of the nanochannels with internal surface charges only.This research enriches the microscopic theory of ion transport manipulation,which is important for the precise regulation of ion transport in nanochannels and the design of ionic energy conversion and desalination devices.
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