Adsorption-activated nanovalve

A polycrystalline MFI zeolite layer, which was prepared with two types of pores, behaves as a adsorption-activated and chemically-specific nanometer-sized valve. The layer consists of zeolite crystals with ~0.6 nm zeolite pores and larger pores (0.6 - 4 nm) that are the spaces between the crystals. Most gas and liquid flow is through these larger pores, which reversibly close and open due to adsorption in and desorption from the zeolite pores, respectively. The valve closing is chemically specific and highly sensitive: 0.2% n-hexane, which adsorbs in the 0.6-nm zeolite pores, expands the zeolite crystals and this expansion shrinks the larger pores. Thus, n-hexane decreased the flow of 2,2-dimethylbutane, a molecule that could only fit into the larger pores, by 2 orders of magnitude. In contrast benzene, which also adsorbs in the zeolite pores, had a negligible effect on the larger pores, even at high concentrations. A combination of vapor- and liquid-feed permeation measurements, for both single components and binary mixtures, clearly demonstrate this behavior.