Thursday, April 29, 2010

Graphene Nanoribbons Manufactured From Carbon Nanotubes; Diverse Applications Detailed

Scientists at Rice University Smalley Institute for Nanoscale Science and Technology have disclosed patent pending methods for producing macroscopic quantities of graphene nanoribbons and oxidized graphene nanoribbons from multiwalled carbon nanotubes. The nanoribbons may be used in electronics, concrete, polymer composites, separation and filtration membranes, drilling fluids and for the delivery of drugs.  

In U.S. Patent Application 20100105834,  Professor of Mechanical Engineering and Materials Science James M Tour (Bellaire, TX), Dmitry V. Kosynkin (Houston, TX), Amanda Higginbotham (Los Alamos, NM) and Brandi Katherine Price (Houston, TX)  detail their discovery of a room-temperature chemical process that splits, or unzips, carbon nanotubes to make flat nanoribbons. The technique makes it possible to produce the ultrathin ribbons in bulk quantities.

These ribbons are straight-edged sheets of graphene, the single-layer form of common graphite found in pencils. You'd have to place thousands of them side by side to equal the width of a human hair, but tests show graphene is 200 times stronger than steel.

The process involves sulfuric acid and potassium permanganate, which have been in common use since the 1890s. This chemical one-two punch attacks single and multiwalled carbon nanotubes, reacting with the carbon framework and unzipping them in a straight line.

The Rice University methods for preparing graphene nanoribbons take places either in a liquid medium or on a surface. Without being bound by theory or mechanism, it is thought that when a free-standing graphene sheet (in the form of a graphene nanoribbon) is in solution, the excess surface energy may be stabilized by solvation energy such that folding into a carbon nanotube becomes energetically unfavorable (i.e., endothermic). As a result of the solvation energy, the reverse process of longitudinally opening a carbon nanotube into a graphene nanoribbon becomes energetically favorable in an appropriate liquid medium.

FIG. 1 shows an illustrative schematic demonstrating such a longitudinal opening of a carbon nanotube into a graphene nanoribbon.

Electronics Applications:
Reduced graphene nanoribbons are electrically conductive and oxidized graphene nanoribbons are substantially non-conductive or semiconductive, whereas hydrazine-reduced  graphene  nanoribbons display some electrical conductivity.  However, oxidized graphene nanoribbons may be in a semiconducting state and may be used to form semiconducting thin films. Hydrazine-reduced graphene  nanoribbons that have been further annealed in H2 display a still higher electrical conductivity.

Without being bound by theory or mechanism, the inventors believe that the much higher electrical conductivity of the H2-annealed reduced graphene nanoribbons is due to removal of carboxylic acid groups in hydrogen. The electrical conductivity makes the reduced graphene  nanoribbons suitable for use in a variety of electronic devices and thin film electrical conductors. Such electronic devices include, without limitation, transistors, memories, two-terminal electronic devices, three-terminal electronic devices, gated electronic devices, non-gated electronic devices, sensors, field emission cathodes, ultracapacitors and supercapacitors.

Conductive nanoribbons could replace indium tin oxide (ITO), a material commonly used in flat-panel displays, touch panels, electronic ink and solar cells. ITO is very expensive, so lots of organizations are looking for substitutes that will give them transparency with conductivity.  Nanoribbon-coated paper that could become a flexible electronic display, and Tour has already experimented with nanoribbon-infused ink for ink-jet printers. They have printed transistors and radio-frequency identification tags, printing electronics with these inks. 

FIG. 43 shows illustrative SEM images demonstrating the transformation of a MWNT electronic device into an oxidized graphene nanoribbon electronic device

Drilling Fluids:
Drilling fluids are often used in petroleum recovery processes. Drilling fluids may include graphenes and likewise, graphene nanoribbons may be included in drilling fluids.  Graphene nanoribbons may be desirable in drilling fluids, since the permeability of graphene nanoribbon mats falls dramatically as the thickness of the mats increases. 

Graphene nanoribbons may be used as additive in drilling fluids to provide advantageous properties such as low viscosity, high lubricity and high thermal stability as compared to traditional drilling fluid formulations. Likewise, in non-limiting examples, high shear milling or ultrasound treatment of the graphene nanoribbons may be used to produce shortened graphene  nanoribbons of a few hundred nanometers in length. 

Such shortened graphene nanoribbons may also be used in the drilling fluids.  Graphene  nanoribbons and shortened graphene nanoribbons may be particularly advantageous for reducing permeability in drilling fluid applications for rock formations of very fine porosity. Methods for producing such drilling fluids include adding graphene nanoribbons or shortened  graphene nanoribbons to a drilling fluid. 

Ion Exchange Filters:
In various embodiments, graphene nanoribbons may be included in ion exchange filters. The graphene nanoribbons are sometimes oxidized graphene nanoribbons. In other various embodiments, the graphene nanoribbons are reduced graphene nanoribbons containing carboxylic acid groups. As carboxylic acids, oxidized graphene nanoribbons and reduced  graphene nanoribbons may form strong complexes with cationic species that aggregate into macroscopic clumps and precipitate from water.

Ion exchange filters made from graphene nanoribbons may advantageously have higher specific exchange capacities than similar filters made from flake graphite oxide, owing to the higher ratio of edge carbon atoms to total carbon atoms in the graphene  nanoribbons compared to graphite oxide. Accordingly, due to the higher ratio of edge carbons, a larger number of carboxylic acid groups per weight of carbon are available for complexing cationic species.

Narrow graphene nanoribbons derived from single-wall carbon nanotubes are expected to be especially advantageous for use in ion exchange filters, since their ratio of edge carbon atoms to total carbon atoms is particularly high.

Gas Separation Membranes
Gas separation membranes including graphene nanoribbons are described. Disclosure regarding the gas adsorption properties of graphene nanoribbons is set forth in the Experimental Examples. Methods for preparation of gas separation membranes include adding graphene nanoribbons to a membrane are disclosed in the application.  

Water Soluble Graphene Nanoribbon Compositions
Water soluble graphene nanoribbon compositions may be prepared by attaching a plurality of polymer chains or small molecules to the graphene nanoribbons. Water soluble graphene  nanoribbon compositions may be exploited for sequestration of water-insoluble drugs for drug delivery applications. For example, paclitaxel may be incorporated in a water-based formulation using water

Chemical modification of graphene nanoribbons
Chemical modification can make them suitable for selective binding to cells expressing target receptors from diverse cellular dispersions or other biological fluids. Such modified graphene nanoribbons may be fabricated into selective cellular filters or active elements of cellular and chemical sensors. For example, graphene nanoribbons functionalized with antibodies to influenza virus (or any other pathogen) and connecting two conductive leads (i.e., electrode terminals) will change impedance upon antigen binding. The resulting change in electrical properties enables the use of these functionalized graphene nanoribbons in sensors for diagnostic testing of biological fluids. 

Use of Graphene Nanoribbons in Concrete: 
In various embodiments, graphene nanoribbons may be added to concrete to improve the mechanical properties of the concrete after curing and to lower the gas permeability of the concrete. For example, water-soluble graphene nanoribbon compositions can be prepared that may be dispersed with water and used in concrete mixing. Suitable water-soluble graphene nanoribbons include such graphene nanoribbons as those described hereinabove, as well as other water-soluble graphene nanoribbons.

In other embodiments, an aqueous solution of oxidized graphene nanoribbons may be used. The water-soluble graphene nanoribbon compositions may increase load transfer between the concrete and the graphene nanoribbons. In some embodiments the load transfer involves cross-linking.

Wound Dressings:
Wound dressings including graphene nanoribbons are also contemplated by the inventors. The graphene nanoribbons may include oxidized graphene nanoribbons, reduced graphene  nanoribbons or a combination of them that have been grafted or bonded to at least one anti-microbial agent. Such wound dressings advantageously improve infection suppression, provide odor control and inhibit lipophilic toxins from entering the wound. In various embodiments, methods for making wound dressings include adding graphene nanoribbons that have been grafted or bonded to at least one anti-microbial agent to a standard wound dressing. For example, graphene nanoribbons that have been grafted or bonded to at least one anti-microbial agent may be added to ordinary gauze.

Filter Membranes
Graphene nanoribbons may be included in filter membranes. For example, a dispersion of graphene nanoribbons in at least one solvent may be filtered through a porous membrane to form a graphene nanoribbon mat having a porosity and a permeability. Graphene nanoribbon mats may be used to remove at least one dissolved cation from a solution by filtering the solution through the graphene nanoribbon mat. 

The graphene nanoribbons of the filter membranes are further modified with at least one selective complex forming agent. In such embodiments, a species may be removed from a liquid by filtering the liquid through a graphene nanoribbon mat that contains a selective complexing agent that binds the species in the liquid. For example, such graphene nanoribbon filter membranes may be useful in wastewater treatment.

Graphene nanoribbon filter membranes may adsorb hydrophobic organic molecules. Graphene nanoribbon filter membrane may also be used to remove hydrophobic organic molecules from a solution by filtering the solution through the graphene nanoribbon filter membranes. The solution can be in an organic solvent or an aqueous solution, for example. Hydrophobic organic molecules include, for example, aliphatic hydrocarbons, aromatic hydrocarbons, and halogenated organic compounds. In various embodiments, methods of the present disclosure include filtering a solution containing hydrophobic organic molecules through a graphene nanoribbon filter membrane to remove the hydrophobic organic molecules from the solution.

Graphene nanoribbon filter membranes are characterized by a porosity and permeability, which is inversely proportional to the thickness of the graphene nanoribbon mat.

The graphene  nanoribbon mat thickness and, hence, the porosity and permeability can be varied within a wide range of values. At sufficient thicknesses graphene nanoribbon filter membranes may be used to remove micrometer-, submicrometer- and nanometer-sized particles such as protozoa, bacteria, viruses, large proteins, metallic nanoparticles and carbon nanotubes. In various embodiments of the present disclosure, methods for removal of such particles from solution include filtering a solution containing such particles through a graphene nanoribbon filter membrane.

Graphene nanoribbon filter membranes of sufficient porosity and permeability prevent the passage of the particles sizes referenced above. In some embodiments, the graphene nanoribbons may be further modified with at least one selective complex forming agent.

Composite Materials
Graphene nanoribbons may be incorporated into organic and inorganic matrices such as, for example, polymer matrices. The polymer matrices can include, without limitation, thermoplastic and thermosetting polymer matrices. In various embodiments, polymer composite materials having incorporated graphene nanoribbons are described in the present disclosure. Incorporation of graphene nanoribbons may improve mechanical properties of the polymer composites.

In some embodiments, polymer membranes including graphene nanoribbons may be prepared which are useful for fluid separations, antistatic applications, or electromagnetic shielding materials. As a non-limiting example of composite materials, reinforced rubber composites including graphene nanoribbons may be used to manufacture gaskets and seals with improved tolerance to explosive decompression.

In other applications, the graphene nanoribbons are oxidized graphene nanoribbons or the graphene nanoribbons may be reduced graphene nanoribbons. In some embodiments, the graphene nanoribbons are dispersed as individuals in the polymer matrices. In other embodiments, the graphene nanoribbons are aggregated together in two or more layers in the polymer matrices.

In some uses, the graphene nanoribbons are covalently bonded to the polymer matrices. For example, carboxylic acid groups of graphene nanoribbons may be utilized for making cross-linked polymer composites in which the graphene nanoribbons are covalently bonded to the polymer matrix. Other functional groups in the graphene nanoribbons may be utilized as well for making cross-linked polymer composites. In other embodiments, the graphene nanoribbons are not covalently bonded to the polymer matrices.
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Graphene
Graphene typically refers to a material having less than about 10 graphitic layers. The graphitic layers are characterized by an `infinite` two-dimensional basal plane having a hexagonal lattice structure and various edge functionalities, which may include, for example, carboxylic acid groups, hydroxyl groups, epoxide groups and ketone groups. Graphene nanoribbons are a special class of graphene, which are similarly characterized by a two-dimensional basal plane, but with a large aspect ratio of their length to their width. In this regard, graphene nanoribbons bear similarity to carbon nanotubes, which have a comparable large aspect ratio defined by one or more layers of graphene sheets rolled up to form a cylinder.

Graphene nanoribbons possess a number of useful properties, including, for example, beneficial electrical properties. Unlike carbon nanotubes, which can be metallic, semimetallic or semiconducting depending on their chiral geometry and diameter, the electrical properties of graphene nanoribbons are governed by their width and their edge configurations and functionalization.

For example, graphene nanoribbons of less than about 10 nm in width are semiconductors, whereas similar graphene nanoribbons having a width greater than about 10 nm are metallic or semimetallic conductors. The edge configurations of graphene nanoribbons having an "armchair" or "zigzag" arrangement of carbon atoms, along with the terminal edge functional groups, are also calculated to affect the transmission of electron carriers.

Such "armchair" and "zigzag" arrangements are analogous to those defined in the carbon nanotube art. In addition to the aforesaid electrical properties, graphene nanoribbons maintain many of the desirable mechanical properties that carbon nanotubes and graphene sheets also possess. 

This scanning electron microscope image shows a twice-folded, single-layer nanoribbon. Note the smooth edges and uniform width over the entire length.
Credit: Ayray Dimiev/Rice University

Research by the Rice University lab of Professor James Tour was featured on the cover of the April 16, 2009  issue of the journal Nature.   Tour is a co-founder of NanoComposites, Inc. which specializes in nanotube-based composites and he is a co-founder of RJAC-10, LLC, makers of the JAC line of corrosion inhibitor coatings. He also is the founder and principal of NanoJtech Consultants, LLC, performing technology assessments for the prospective investor.

2 comments:

  1. Drilling Fluids are of three types of viz. Oil Based Fluids (OBFs), Water Based Fluids (WBFs) and Synthetic Based Fluids (SBFs). These fluids are used for drilling of natural gas, oils and water wells.

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