Hybrid adsorbent materials have been synthesized with thegoal of selective aqueous separations. These materials consist of a highsurface area oxide support (e.g. SiO 2, Al 2O3)with rigidly- and covalently-attached calix(n)arenes, which are intrinsicallycavity-containing small molecules. (Fig. 1) This method of surface attachment allows for a high density of these calixarene sites, which in turn each act as astrong adsorption site. In this sense, these materials are proposed to act asideal Langmuiran adsorbents, where the number of adsorption sites corresponds to the synthesized number of calixarenes. In Fig. 1, the identity of the R groups, the numberof phenol units in the macrocycle (n), the X bridging species, and the surfacedensity of calixarene (s) are all systematicallytuned to optimize uptake from the aqueous phase and to understand the mechanismof uptake. A large library of calixarenes are commercially available and haveknown host-guest chemistry in organic solvents, but have generally not been studiedfor these types of applications, as these hydrophobic calixarenes cannottypically be dispersed in water or the absence of solvent. Here we study separation of n-butanol from water atbinary concentrations relevant to typical fermentation processes (< 0.1 M). Butanol is a renewable energy source that has advantages over other bioalcohols, but separation by distillation is not practical, opening opportunities foradsorption. If able to be made selective, as this methodology forhighly-tailorable adsorbent surfaces promises, adsorbents could also be addeddirectly to fermentation broths for enhanced yield. Adsorption uptake and interaction energies are shown to increasemonotonically with the number of hydrophobic groups at the upper rim, indicating that adsorption on this first class of materials is dominated by vander Waals interactions. The possibility is also floated of more specific OH-p or CH-p,or in some cases, OH-S interactions between butanol and the calixarene cavity. Fractionaluptake is weakly dependent on the surface density of the calixarene adsorptionsites, implying that background effects are small. The net adsorption process (exchange of butanol for water within the calixarene cavity) is net exothermic process witha low heat of adsorption. Equilibrated adsorption is demonstrated by reversibleuptake upon desorption into water or temperature programmed desorption into the vapor. These organic layers on these surfaces are robust and stable up to 250 C, which suggests they may be capable of multiple regeneration cycles. In general, these materials are not suitable onlyfor butanol separations. The synthetic protocols presented here can begeneralized to a wide variety of functionalized calixarenes and supports, potentially enabling the design of new calixarene-based adsorbents, sensors, and other functional materials. (Figure presented).