Self-assembly of a silica–surfactant nanocomposite in a porous alumina membrane

Abstract

A mesoporous membrane composed of nanochannels with a uniform diameter has a potential use for precise size-exclusive separation of molecules. Here, we report a novel method to form a hybrid membrane composed of silica-surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible. The nanocomposite formed inside each columnar alumina pore was an assembly of surfactant-templated silica-nanochannels with a channel diameter of 3.4 nm; the channel direction being predominantly oriented along the wall of the columnar alumina pore. Molecules could be transported across the membrane including the silica-surfactant nanocomposite with a capability of nanometre-order size-exclusive separation. Our proposed membrane system has a potential use not only for separation science, but also catalysis and chip technologies.

Permeation Flux of Organic Molecules through Silica-surfactant Nanochannels in a Porous Alumina Membrane

“…26 A mixture of ethanol (7.68 g), TEOS (11.57 g) and 1 ml of HCl aqueous solution (2.8 mM) was refluxed at 60˚C for 90 min. Then, ethanol (15 g), 4 ml of HCl solution (55 mM) and CTAB (1.52 g) were added to the refluxed solution, which was stirred for 30 min to give the precursor solution.…”

“…Therefore, it is likely that not only anion-exchange but also other interactions are concerned with the extraction of solutes. Other extraction processes such as formation of ionpairs 26,27 may occur at the same time.…”

“…As a consequence of uniform pore size and permeability, the NAM can be utilized for nanometerorder size-exclusive separation membranes. 26 Only small molecules can enter the columnar pore and interact with the interior of the channels. 27 The transport velocity of small molecules in the channels is thought to depend on the interaction with the interior.…”

“…15,19 Recently, a porous anodic alumina membrane with a perpendicularly oriented silica-surfactant nanochannel assembly membrane (NAM) was synthesized. 26 The porous anodic alumina membrane has a packed array of columnar pores ranging from tens to hundreds of nanometers in diameter, and the channel direction of the columnar pores is perpendicular to the membrane.When a precursor solution containing cetyltrimethylammonium bromide (CTAB) surfactant and tetraethyl orthosilicate (TEOS) as a silica source is introduced into the alumina pores, highly ordered hexagonally arranged silica-surfactant nanochannels with pores of 3.4 nm diameter are assembled inside the alumina pores. The channel direction of mesoporous silica is predominantly oriented along the columnar alumina pores.…”

“…15,19 Recently, a porous anodic alumina membrane with a perpendicularly oriented silica-surfactant nanochannel assembly membrane (NAM) was synthesized. 26 The porous anodic alumina membrane has a packed array of columnar pores ranging from tens to hundreds of nanometers in diameter, and the channel direction of the columnar pores is perpendicular to the membrane.…”