Specifically, Giaya et al. compared Silicalite-1, an all-silica zeolite having the MFI framework type, a dealuminated zeolite Y (FAU framework), and an AC in terms of their TCE and PCE adsorption behavior, both for the gas phase and for aqueous solution. In addition to observing high uptakes of both species in Silicalite-1 in the ppm range, they also demonstrated that co-adsorption of water affected CE adsorption in the all-silica zeolite much less than in the other two adsorbents, a finding that was attributed to its high hydrophobicity. In an investigation focused on cationic zeolites, Na-containing FAU-type zeolites with low Si/Al ratios (1.2 and 2.4) were found to be efficient adsorbents for the removal of PCE from dry gas streams. However, it was also noted that humidity would have to be removed prior to PCE adsorption, as water adsorption had a detrimental effect on adsorbent performance. Besides adsorptive removal, it was proposed to employ zeolites as catalysts for the oxidative destruction of CEs in the gas phase. A number of other investigations looked at gas-phase CE adsorption in zeolites from a more fundamental point of view. In particular, Mellot, Chihara and co-workers investigated the adsorption of TCE and PCE (along with other chlorinated hydrocarbons) in FAU samples having different Si/Al ratios and obtained via different dealumination routes. The experimental investigations were complemented by molecular simulations (see below). The impact of relative humidity on TCE and PCE adsorption capacities of FAU-type zeolites was also studied. Although it was generally observed that more hydrophobic zeolites (higher Si/Al ratios) possess higher uptake capacities, increasing diffusion limitations in highly siliceous samples were highlighted in one of the studies. Detailed investigations revealed a rather unusual adsorption behavior of PCE in MFI-type zeolites, with the adsorption isotherm showing two steps. Different researchers have attributed this phenomenon to the adsorption of PCE in distinct regions of the pore and to structural transitions of the framework with increasing pressure.