Nanofabricated synthetic channels have been able to mimic the transport properties of their biological counterparts. But it is still nontrivial to make artificial ion pumps. Recent research on conical pores with charged surfaces has demonstrated significant ionic current rectification, which suggests the possibility of employing conical pores for pumping ions. In this work, salt pumping through conical pores driven by an external potential is studied including a consideration of both static and dynamic surface charges. Because of asymmetry of the structure and a charged inner surface, even conical pores with static surface charges are able to selectively pump ions whose charge is opposite the surface charge. Consequently, a mixture of both negatively and positively charged conical pores is able to pump salt (both cations and anions) with an oscillating external potential. Moreover, if the surface charge can be controlled dynamically, more efficient salt pumping can be achieved and the pumping flux is several times larger than that for cylindrical pores with fixed charges. We also find a reverse rectification effect when the length of the conical pore is shortened and angle is sufficiently large. The origin of reverse rectification is explained by evolution of the concentration profile at the tip side of the cone, with the rectification ratio depending on length and angle of the pore. Numerical simulations also suggest that the radius of the pore should be designed carefully to balance the net pumping flux and pumping-leakage ratio.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films