Utilizing Nanoporous Alumina Membranes for Molecular Transport and Silica Nanotube Synthesis

Alumina-based nanomembranes with pores of ̃200 nanometers in diameter were modified with a variety of different substituted silanes. The transport of ions through these treated membranes was studied using several analytical tools such as ultraviolet-visible and fluorescence spectroscopy. The surface characteristics of the membrane were studied using a scanning electron microscope (SEM) and an atomic force microscope (AFM). Infrared spectroscopy was used to confirm the presence of silane coupling with the alumina membrane. Silanes with variable functional groups, either hydrophobic (isobutyl trimethoxysilane, IBTMS) or hydrophilic (aminopropyltrimethoxysilane, AMPTMS and aldehydtrimethoxysilane, ALDTMS), were examined. Preliminary data demonstrate that the alumina membranes treated with IBTMS and ALDTMS allow low transport compared to blank (untreated) membrane. The addition of a surfactant (dodecylbenzenesulfonate) slightly improves the transport as compared to untreated membranes. The presence of vacuum did not influence the transport rate and a spin coating silanization technique was found to be effective. Microscopy data confirm that the template synthesis of silica nanotubes using a sol-gel technique produces silica nanotubes

Monitoring Transport Across Modified Nanoporous Alumina Membranes

This paper describes the use of several characterization methods to examinealumina nanotubule membranes that have been modified with specific silanes. The functionof these silanes is to alter the transport properties through the membrane by changing thelocal environment inside the alumina nanotube. The presence of alkyl groups, either long(C18) or short and branched (isopropyl) hydrocarbon chains, on these silanes significantlydecreases the rate of transport of permeant molecules through membranes containingalumina nanotubes as monitored via absorbance spectroscopy. The presence of an ionicsurfactant can alter the polarity of these modified nanotubes, which correlates to anincreased transport of ions. Fluorescent spectroscopy is also utilized to enhance thesensitivity of detecting these permeant molecules. Confirmation of the alkylsilaneattachment to the alumina membrane is achieved with traditional infrared spectroscopy,which can also examine the lifetime of the modified membrane. The physical parameters ofthese silane-modified porous alumina membranes are studied via scanning electronmicroscopy. The alumina nanotubes are not physically closed off or capped by the silanesthat are attached to the alumina surfaces