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Experiment and molecular simulation are used to investigate adsorption in heterogeneous porous media consisting of hierarchical solids (combining different porosity scales) or composite solids (such as silver nanoparticles adsorbed at the external surface of zeolite). It is shown that adsorption in such heterogeneous materials can be written as a linear combination of the adsorption isotherms in its different domains (i.e. porosity scales for the hierarchical sample and constituents for the composite sample). In the case of the composite material, we also show that the linear combination can be used with weighing parameters obtained for a different adsorbate. Such a superimposition principle , which is validated using well-characterized experimental samples, is of interest for characterization purpose as well as industrial applications as they can be used to determine accurately the amount of phases in a given sample (volume corresponding to a given porosity scale or constituent). In contrast, significant departure between the experimental adsorption isotherm and the linear combination can be used to detect coupling effects between the different domains or restrained access to a given domain type. Such a characterization strategy of complex heterogeneous media is complementary to other experiments, such as those probing capillary hysteresis shapes, scanning curves and subloops, which allow determining the distribution of domains within the framework of the independent domain theory. [ABSTRACT FROM AUTHOR]

Selective Xe adsorption on regenerable porous materials such as activated carbons, MOFs and zeolites has been found to be promising and economically attractive. The beneficial effect of silver doping of zeolites on Xe adsorption and Xe/Kr separation has been studied for numerous zeolites such as Ag-ZSM-5, Ag-mordenite and Ag-chabazite. Among them, we had shown that Ag-exchanged ZSM-5 is the most effective material for atmospheric Xe capture and selective separation at very low pressure (ppm level). A linear tendency was observed with a ratio of 2 mol of Ag for 1 mol of strong adsorption sites. Based on this observed tendency, we hypothesize that increasing the number of exchangeable sites by lowering the Si/Al ratio could be an approach to improve silver loading and selective xenon adsorption. The aim of this study is to evaluate the impact of desilication of ZSM-5 zeolites on decreasing their Si/Al ratio and increasing the concentration of sodium-exchanged sites and, possibly, strong silver-based adsorption sites. We have shown here that light desilication of this parent ZSM-5 makes it possible to significantly increase xenon uptake at very low pressure. The desilication creates a larger concentration of Al in the zeolite and thus enables a larger concentration of silver to be loaded. Yet we found that for severe desilication, decreased xenon uptake is observed, likely due to the facilitated formation of silver particles in which the core atoms are not accessible for xenon uptake. It appears that a concentration of 0.5 mmol g−1 of strong adsorption sites is a maximum achievable value for the Ag-ZSM-5 system. Surprisingly, we found that the parent ZSM-5 zeolite prepared by organic templating yields Ag-ZSM-5 with a similar concentration of strong adsorption sites but at higher silver loading. We could hypothesize that silanol defects present in commercial zeolites may be responsible for the stabilization of silver clusters. [Display omitted] • Higher xenon adsorption capacity for xenon atmospheric capture (ppm level). • Light desilication of ZSM-5 increases the concentration of adsorption sites. • Silanol defects present in commercial zeolites may stabilize silver clusters. • Severe desilication decreases Xe uptake due to the formation of larger silver NPs. [ABSTRACT FROM AUTHOR]