Filtration and Chemical Transport Selectivity in the Au Nanotubule Membranes

MOLECULAR FILTRATION AND CHEMICAL TRANSPORT SELECTIVITY IN THE AU NANOTUBULE MEMBRANES 

The work discussed above shows that the Au nanotubule membranes can have one important type of transport selectivity—charge-based selectivity. It occurred to us that because the Au nanotubules can be of molecular dimensions, these membranes might show molecular size-based transport selectivity as well [72]. Finally, the thiol chemisorption chemistry introduced above provides a route for introducing chemically based transport selectivity [85]. Hence, the Au nanotubule membranes should, in principle, be able to show all three of the important transport selectivity paradigms— 

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The idea of using membranes to filter molecules on the basis of size is not without precedent. Dialysis is used routinely to separate low molecular weight species from macromolecules [105]. In addition, nanofiltration membranes are known for certain small molecule separations (such as water purification), but such membranes typically combine both size and chemical transport selectivity and are particularly designed for the separation involved. Hence, in spite of the importance of the concept, synthetic membranes that contain a collection of monodisperse, molecule-sized pores that can be used as molecular filters to separate small molecules on the basis of size are currently not available. 

The electroless plating method described above was used to prepare membranes that contain cylindrical gold nanotubules, which span the complete thickness of the membrane. As before, polycarbonate filtration membranes with cylindrical, monodisperse pores (Poretics, 6 [im thick, pore dia. = 30 nm) were used as the templates. The inside diameter (i.d.) of the nanotubules can be varied by varying the plating time (Fig. 14). At sufficiently long plating times, Au nanotubules with i.d.s of molecular dimensions ( 1 nm) are obtained [106], 

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V. Molecular Filtration and Chemical Transport Selectivity in the Au Nanotubule Membranes... 

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