External control of ion transport in nanoporous membranes with surfaces modified with self-assembled monolayers

We investigated the effect of external pH, ionic strength, and applied volt age to control the transport of ions through porous PCTE/Au/acid thiol memb ranes with pore radii of 4.0-5.9 nm. Electroless gold was deposited on the inside surfaces of the nanopores of the membrane. The thiols 11-mercaptound ecanoic acid (HSC10H20COOH) and 3-mercapto-1-propanesulfonic acid (HSC3H6SO 3H) were used to form self-assembled monolayers (SAMs) on the gold surfaces of the pores. The ionic permeant through the pores of the membranes was th e organic ion benzene sulfonate (BS). The transport of benzene sulfonate in porous membranes modified with SAMs of the HSC10H20COOH weak acid thiol wa s highly affected by external variation of the pH; the BS flux could be cha nged by a factor of 100. However, transport of benzene sulfonate in membran es modified with SAMs of the HSC3H6SO3H strong acid thiol was influenced le ss by external pH than transport in membranes modified with SAMs of the HSC 10H20COOH weak acid thiol. Increasing the ionic strength of the bulk soluti on caused the flux of benzene sulfonate to increase due to the decrease of the Debye length. Application of a voltage to the membrane has a significan t influence on the benzene sulfonate flux through the porous membrane. Cont rolling the pH and the applied potential can lead to flux changes as large as a factor of 170.