Solvent-Extraction and Langmuir-Adsorption-Based Transport in Chemically Functionalized Nanopore Membranes

Abstract

We have investigated the transport properties of nanopore alumina membranes that were rendered hydrophobic by functionalization with octadecyltrimethoxysilane (ODS). The pores in these ODS-modified membranes are so hydrophobic that they are not wetted by water. Nevertheless, nonionic molecules can be transported from an aqueous feed solution on one side of the membrane, through the dry nanopores, and into an aqueous receiver solution on the other side. The transport mechanism involves Langmuir-type adsorption of the permeating molecule onto the ODS layers lining the pore walls, followed by solid-state diffusion along these ODS layers; we have measured the diffusion coefficients associated with this transport process. We have also investigated the transport properties of membranes prepared by filling the ODS-modified pores with the water-immiscible (hydrophobic) liquid mineral oil. In this case the transport mechanism involves solvent extraction of the permeating molecule into the mineral oil subphase confined with the pores, followed by solution-based diffusion through this liquid subphase. Because of this different transport mechanism, the supported-liquid membranes show substantially better transport selectivity than the ODS-modified membranes that contain no liquid subphase.

Diffusivities of Tris(2,2′-bipyridyl)ruthenium inside Silica- Nanochannels Modified with Alkylsilanes

“…The apparent diffusion coefficients of molecules inside alkylsilane-modified nanopores have been reported for several systems: phenol derivatives permeated into octadecyltrimethoxysilane-modified alumina pores with ca. 200 nm in diameter from the aqueous phases (10 -8 to 10 -6 cm 2 s -1 ) 12 and Phenol Blue extracted in octadecylsilyl-modified silica gel (pore diameter, 12 nm) from the water/acetonitrile mixtures (10 -11 to 10 -8 cm 2 s -1 ). 37 These values are also smaller than those in the bulk solution phases.…”

“…1, [12][13][14] Martin and co-workers 1, 12 have studied the diffusivity inside nanopores by observing the mass transport across nanopore membranes. In their studies, they estimated the apparent diffusion coefficients of phenol derivatives in columnar alumina pores modified with octadecyltrimethoxysilane; the order of the estimated values was 10 -8 to 10 -6 cm 2 s -1 .…”

“…In their studies, they estimated the apparent diffusion coefficients of phenol derivatives in columnar alumina pores modified with octadecyltrimethoxysilane; the order of the estimated values was 10 -8 to 10 -6 cm 2 s -1 . 12 For the alumina membrane system, the diffusion coefficients of metal cations (10 -7 to 10 -6 cm 2 s -1 ) in unmodified alumina pores were reported and the surface effect on the diffusion behavior was discussed. 13 Fu et al 14 applied single-molecule fluorescence correlation spectroscopy to estimate an apparent diffusion coefficient of Nile Red in a surfactant-templated mesoporous silica thin film, and found that the diffusion coefficient was very small (∼10 -10 cm 2 s -1 ).…”

Soft and Hard Surface Manipulation of Nanoporous Anodic Aluminum Oxide (AAO)

“…The early work sought to chemically modify the surface using organic acids, thiolates, organosilanes, alkanethiolates, alcohols, amines and carboxylic acids assemblies on AAO-gold-coated surface with the goal of introducing functional groups for specific orientation, functionalities and selectivity. Considerable work has been done involving SAMs focusing on octadecyltrichlorosilane (OTS) that resulted in a rapidly growing body of research [4]. Formation of SAMs from organic acids i.e.…”

A microfluidic chip with poly(ethylene glycol) hydrogel microarray on nanoporous alumina membrane for cell patterning and drug testing

“…Recently, silane treatment has been used for surface modification of alumina [18][19][20]. The fabricated nanoporous alumina membranes were boiled in 30% 7 hydrogen peroxide for 30 min to clean the surface.…”