Sunday, November 22, 2009

Carbon Nanotube Mediated Membrane Extraction

New Jersey Institute of Technology scientists Kamilah Hylton and Somenath Mitra have developed a method for fabricating nanotube immobilized membranes (NIM). They consists of a substrate and carbon nanotubes introduced into and substantially immobilized within the  substrate. NIM are used in separation processes such as membrane distillation, membrane based extraction, supported liquid membrane extraction, pervaporation, desalination, gas separation and liquid-liquid membrane extraction, according to U.S. Patent Application 20090283475.

Prior to introduction into the substrate, the carbon nanotubes takes the form of a dispersion of carbon nanotubes; wherein the dispersion is selected from the group consisting of aqueous, non-aqueous, polymeric and monomeric dispersions. Functionalized CNTs may be readily immobilized into the pore structure of a polymeric membrane, which can dramatically improve the performance of the membrane or NIM ("nanotube immobilized membrane"). This was accomplished by injecting or introducing an aqueous dispersion of the CNTs through a polypropylene hollow fiber under pressure. The CNTs were trapped and held within the pores, and served as sorbents facilitating solute exchange from the donor to the acceptor phase. The effectiveness of the exemplary CNT mediated process was then studied by micro-scale membrane extraction via direct solvent enrichment of non-polar organics, and also by selective extraction of organic acids via a supported liquid membrane. In both cases, the enrichment factor (measured as the ratio of concentrations in the acceptor to the donor phases) could be increased by more than 200%.

New Jersey Institute of Technology's (NJIT) disclosure provides an improved membrane or substrate with carbon nanotubes introduced and/or immobilized therein,  The patent also shows an improved method for introducing and/or immobilizing carbon nanotubes in membranes or substrates. More particularly, the disclosure provides for improved systems and methods for fabricating membranes or substrates with carbon nanotubes immobilized therein. The disclosure provides for systems and methods for introducing and/or immobilizing functionalized carbon nanotubes into the pore structure of a polymeric membrane or substrate, thereby dramatically improving the performance of the polymeric membrane or substrate, according to U.S. Patent Application 20090283475

The schematic below is a representation of NIM extraction according to the NJIT disclosure, wherein the solute first adsorbs to the CNT and then it is desorbed by the organic extractant that fills the pores and lumen of the NIM.

A NIM may be fabricated by percolating and/or injecting a CNT dispersion through a membrane or substrate (e.g., a porous polymeric membrane or a porous substrate). For example, the fabricated NIMs may be utilized for liquid phase extraction or the like. In general, the present disclosure provides for methods to immobilize CNTs in the membrane or substrate pores, without substantially encapsulating the CNTs in a polymer or film so that the surface of the CNTs remains substantially free and/or available for active solute transport or exchange.

NJIT SEM image of a membrane with PVDF/MWNTs (more than 50 nm diameter) composite  used in making a carbon nanotube mediated membrane                                         

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