pH-regulated electrokinetic ion rectification in SiO2/Al2O3 heterojunction membrane channel

The ion current rectification (ICR) phenomenon is well known due to the diode-like response behavior that attracts increasing research interest. However, most studies focus on the single channel with fixed surface charge, and the dependent ion transport behavior in highly coupled solution-surface-membrane has not been fully studied so far. Herein, a coupled ion transport model in the SiO₂/Al₂O₃ membrane channel is proposed to investigate the asymmetric response behavior. The results show that SiO₂ and Al₂O₃ membrane enable the negative and positive surface charge that forms a heterojunction channel. This leads to significant ion rectification due to the asymmetrical surface charge property. Besides, the surface property of the membrane is highly regulated by solution pH and the acidic environment is more conducive to the enhancement of asymmetric ion transport. Further study shows that the best heterojunction ratio is 1:1 of the lengths of negative charge regions to that of positive charge regions. The research results provide valuable information on ion transport and nanofluidic devices.