Electric field-controlled ion transport in TiO₂ nanochannel

On the basis of biological ion channels, we constructed TiO₂ membranes with rigid channels of 2.3 nm to mimic biomembranes with flexible channels; an external electric field was employed to regulate ion transport in the confined channels at a high ionic strength in the absence of electrical double layer overlap. Results show that transport rates for both Na⁺ and Mg²⁺ were decreased irrespective of the direction of the electric field. Furthermore, a voltage-gated selective ion channel was formed, the Mg²⁺ channel closed at -2 V, and a reversed relative electric field gradient was at the same order of the concentration gradient, whereas the Na⁺ with smaller Stokes radius and lower valence was less sensitive to the electric field and thus preferentially occupied and passed the channel. Thus, when an external electric field is applied, membranes with larger nanochannels have promising applications in selective separation of mixture salts at a high concentration.