ABSTRACT

Extremely long and thin nanocomposite fibers are prepared by oxidative polymerization of pyrrole (or aniline) around the surfaces of copper hydroxide nanostrands. The individual nanostrands of 2.5 nm are uniformly coated with a polypyrrole layer of 3 to 4 nm, resulting in hybrid core/shell fibers of about 10 nm in diameter and a few micrometers in length, as confirmed by high-resolution electron microscopy. The as-prepared nanocomposite fibers are dispersive in water and can be converted into thin free-standing films by simply filtering a small volume of the aqueous solution using a polycarbonate membrane filter. The films covering the submicrometer pores of the membrane filter have a thickness of a few tens of nanometers, and provide a mechanically stable nanofiber network with abundant pores of a few nanometers. The network is stable in acidic and basic media, and can be used for protein separation under pressures of at least 90 kPa. The permeation rates of cytochrome c, myoglobin, and ferritin were examined by changing the pH around their isoelectric points. It is seen that the nanofibrous free-standing films on the polycarbonate membrane filter show clear size selectivity for the proteins, retaining extremely high filtration rates for water. We demonstrate herein durable mesoporous separation membranes made of organic–inorganic nanocomposite fibers and their outstanding performance.

Natural cellulose sheets can be used as substrates for protein immobilization. Individual cellulose nanofibers are first coated with ultrathin titania layers to enable the chemisorption of biotin, and then streptavidin is anchored. The sheets have a high binding capacity for biomolecules (see the fluorescence micrographs) without deterioration of their mechanical and water-absorbing properties.

Natürliche Celluloseschichten können als Substrate zur Immobilisierung von Proteinen genutzt werden. Einzelne Cellulosenanofasern werden zunächst mit dünnen TiO₂-Schichten ummantelt, um die Chemisorption von Biotin zu ermöglichen, dann wird Streptavidin verankert. Die Schichten binden Biomoleküle (siehe Fluoreszenzbild) mit hoher Kapazität, ohne dass ihre mechanischen und Wasserabsorptionseigenschaften verloren gehen.

Das vollständige Entfernen von interstitiellen Wassermolekülen aus einer Reihe von Schaumfilmen amphiphiler Verbindungen liefert freistehende Doppelschichtmembranen. Die getrockneten Schaumfilme liegen im Mikro- bis Submikrometerbereich (siehe Bild) und sind sogar im Ultrahochvakuum und bei Temperaturen über 100 °C stabil.

Complete removal of interstitial water molecules from various foam films of amphiphilic compounds results in self-standing bilayer membranes. The dried foam films (DFFs) in the micrometer to submicrometer range (see picture) are stable even under ultrahigh-vacuum conditions and at temperatures higher than 100 °C.