Organic-inorganic nanocomposite membranes from highly ordered mesoporous thin films for solubility-based separations

摘要

Solubility-based membrane separation, in which the more soluble speciespreferentially permeates across the membrane, has attracted considerable recent attentiondue to both economic and environmental concerns. This solubility-selective mode isparticularly attractive over a diffusivity-selective mode in applications in which theheavier species are present in dilute concentrations. Examples include the recovery ofvolatile organic components (VOCs) from effluent streams and the removal of higherhydrocarbons from natural gas. Recently, nanocomposites have shown great promise aspossible membrane materials for solubility-selective separations. The chemicalderivatization of inorganic mesoporous substrates has been explored to synthesizeorganic-inorganic nanocomposite membranes. The most exciting feature of thisapproach is that it enables the rational engineering of membrane nano-architecture withindependent control over the free volume and chemistry to create membranes withhighly customizable permselectivity properties. In this study, we synthesized the organic-inorganic nanocomposite membranesby decorating the surfaces of commercially available mesoporous alumina substrates,and surfactant-templated highly ordered mesoporous silicate thin films placed oncommercially available macroporous inorganic substrates, with a selective organicmaterial that is physically or chemically anchored to the porous surfaces.Hyperbranched melamine-based dendrimers, with nanometer dimension and chemicalcomposition designed to target certain components, were used as filling agents. Weevaluated these membranes for several environmentally relevant separations, such as therecovery of the higher hydrocarbon from air and the removal of trace VOCs from air orwater, while exploring the impact of organic oligomer size, chemistry, and surfacecoverage, as well as substrate pore size and structure, on membrane performance. First,we did a model study to verify the feasibility of dendrimer growth inside mesopores byusing ordered mesoporous silica. Alumina-ordered mesoporous silica (alumina-OMS)hybrid membranes were prepared as new inorganic porous substrates. Finally, wesynthesized dendrimer-ceramic nanocomposite membranes by growing severalgenerations of melamine-based dendrimers with diverse functional groups directly offthe commercial alumina membranes. Composite membranes show very highpropane/nitrogen selectivity up to 70.