Supported lipid bilayers on porous platforms offer biomimetic approaches to highly selective separations in dilute aqueous solute systems. Mesoporous silica materials (in the form of particles or thin films) with tunable pore morphology, chemical, thermal stability and ease of organic functionalization, are an ideal support for lipid bilayers. Our previous investigation of lipid bilayer interactions with mesoporous silica particles demonstrated both lipid bilayer enveloping and pore filling of the lipid bilayers as a function of pore size through vesicle fusion and evaporation deposition, respectively. Combining selective permeable lipid bilayers with high surface area silica materials suggests many potential applications for efficient, selective dilute aqueous solute separations. The recovery of aqueous fructose, which can be bound and released by boronic acid carriers, has been chosen as model separation, representing the recovery of carbohydrates from the depolymerization of biomass. The separation of fructose using lipid bilayer supported on mesoporous silica thin film composite membranes is examined, in which the carbohydrate carrier (boronic acid) is immobilized in the bilayer. The selective separation of carbohydrates from biomass hydrolysate mixtures will address significant challenges to the biochemical production of biofuels and chemicals from lignocellulose.
In this work, vertical oriented hexagonally close packed (HCP) silica thin films on macroporous support are used as the lipid layer supports. The composite silica thin film membrane was prepared by dip coating silica membranes on anodic alumina supports using cross-linked poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) (P123) as a temporary pore blocking film. TEM study demonstrated that the silica membrane, synthesized using P123 as a pore template, has ordered pore structure. Furthermore, SEM imaging suggested that a continuous and uniform silica membrane was formed on the top of porous support. Solvent flux of ethanol and permeability of fluorescent molecules through the composite membrane were used to characterize the transport properties of the membrane. Through vesicle fusion, the lipid bilayers containing a lipophilic boronic acid carrier was formed on the single side of the platform. The diffusivity of fructose through the composite membrane before and after the immobilization of boronic acid into lipid bilayer is examined and used to identify the environmental factors to improve the transportation and selectivity for fructose. Specifically, the location of lipid bilayer (lipid filling and lipid enveloping), boronic acid composition and pH gradient are studied.