Site-selective functionalization of periodic mesoporous organosilica (PMO) with macrocyclic host for specific and reversible recognition of heavy metal

Abstract

A novel kind of macrocyclic-host-functionalized periodic mesoporous organosilica (PMO) with excellent and reversible recognition of Pb(II) was developed. The macrocyclic host molecule cis-dicyclohexano[18]crown-6, with strong affinity to Pb(II), was carefully modified as a bridged precursor to build the PMO material. To break down the limit of the functionalization degree for PMOs incorporated with large-sized moieties, a site-selective post-functionalization method was proposed to further decorate the external surface of the PMO material. The selective recognition ability of the upgraded PMO material towards Pb(II) was remarkably enhanced without destroying the mesoporous ordering. Solid-state (13)C and (29)Si NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), XRD, TEM, and nitrogen adsorption-desorption isotherm measurements were utilized for a full characterization of the structure, micromorphology, and surface properties. Reversible binding of Pb(II) was realized in the binding-elution cycle experiments. The mechanism of the supramolecular interaction between the macrocyclic host and metal ion was discussed. The synthetic strategy can be considered a general way to optimize the properties of PMOs as binding materials for practical use while preserving the mesostructure.