Investigations of the transport properties of gold nanotubule membranes

We have developed a new class of synthetic membranes that consist of a poro us polymeric support that contains an ensemble of gold nanotubules that spa n the complete thickness of the support membrane. The support is a commerci ally available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls; i.e., the pores acts as templates for the nanotubules. We have shown that by controlling the Au deposition time, Au nanotubules t hat have effective inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. In ad dition, because these membranes are composed of an electronically conductiv e material, excess charge can be applied to the tubules by electrochemical charging in an electrolyte solution. We have shown that this allows for con trol of ion-transport selectivity in these membranes. Finally, because the tubules are composed of gold, well-known Au-thiol chemistry can be used to change the chemical environment within the tubules. Via this route chemical transport selectivity can be introduced into these membranes. This paper r eviews progress on size-based, charge-based, and chemical-interaction-based transport selectivity in this new class of membranes.