β-Cyclodextrin-based macroporous monoliths: One-pot oil-in-oil emulsion templating and adsorption

The ability of β-cyclodextrin (β-CD) to form a host–guest complex with relatively hydrophobic molecules such as bisphenol A (BPA), a common wastewater contaminant, has inspired the development of β-CD-containing polymers for adsorption applications. For the most part, these polymers are powders, which can limit their applicability. Here, low-density (~0.1 g cm⁻³), macroporous monoliths based on unmodified β-CD were synthesized using emulsion templating. The relatively simple, one-pot, polyurethane synthesis took place within the external phase of oil-in-oil (o/o) high internal phase emulsions (HIPEs) that contained β-CD and a diisocyanate. The combination of o/o emulsions and a polyurethane reaction enabled the incorporation of relatively high β-CD contents (up to 63 wt%) and limited the occurrence of the water–isocyanate urea reaction. The resulting open-cell porous structures varied from an average pore size of 5.0 μm (lower surfactant content) to the typical structure associated with polyHIPEs (higher surfactant content), voids of ~50 μm and interconnecting holes ranging from submicrometer to ~2 μm. The compressive mechanical behaviors of the easily handled monoliths were similar to those of flexible foams, reaching strains of 70% without failure. The BPA adsorption capacities, up to 117.7 mg g⁻¹, may make these monoliths advantageous for adsorption applications.