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Posted: May 08, 2014
Patent issued for instantaneous electrodeposition of metal nanostructures on carbon nanotubes
(Nanowerk News) U.S. patent #8,709,226 has been issued to a group of researchers from Texas Southern University for a method comprising: dispersing carbon nanotubes in a solvent; and depositing the carbon nanotubes on a porous, conductive substrate; wherein the porous, conductive substrate is capable of functioning as a filter and a working electrode.
Metallization of carbon nanotubes (CNTs) presents a next-generation nanotechnology for many important applications, such as fuel cells, electrochemical sensors, CNT alignment and patterning, assessment of CNTs' structural defects, electromagnetic interference shielding, and the like. Metallized CNTs (mCNTs) also offer unique solutions to problems encountered in nano-reinforced composites. Further explorations in these areas demand advances in the development of mass-production techniques for the production of mCNTs.
Although the metallization of nanotubes has been accomplished by previous methods, each method has limitations affecting its commercial feasibility. For example, physisorption and electroless plating have both been previously used to deposit metal nanoparticles on CNTs, but both methods utilize an oxidative acid pretreatment step to create additional sidewall defects in the CNTs prior to metal nanoparticle attachment. The additional CNT sidewall defects act as either attachment sites (physisorption) or nucleation sites (electroless plating) to achieve metallization. However, sidewall defects are known to degrade the mechanical and electrical properties of CNTs and the oxidative acid treatment to create the defects is, thus far, a time-consuming and uncontrolled process. In addition, the physisorption technique requires a separate preparation of metal nanoparticles prior to a lengthy sonication process in order to disperse and attach the metal particles onto CNTs.
The electroless plating method often requires a complicated activation-sensitization procedure to prepare the CNT surface for metal depositions. The harsh acid treatment, the extended sonication, the activation-sensitization procedure, and certain galvanic displacement reactions are very disruptive to the intrinsic structure and properties of CNTs. In addition, physisorption and electroless plating processes often result in chunky metal particles (.gtoreq.50 nm in diameter) mounted on the CNT surface, where severe dislodging is often observed due to the large size of the metal particles and the relatively loose attachment.
It remains exceptionally challenging to achieve reliable electrical contact with bulk CNT samples, an important step for accomplishing electrochemical deposition. Previous efforts to solve this problem include growing CNTs on conducting substrates, microlithography, electrophoresis, sputtering, or thermal evaporation. These processes have been largely unsuccessful, especially at producing reliable, large-scale (grams) amounts of metallized CNTs. Therefore, there remains a need for a scalable process which also provides good control of depositing varying morphologies of metal nanostructures on CNTs, from discrete atom clusters to continuous coatings.
In some aspects, embodiments disclosed herein relate to a method that includes: dispersing carbon nanotubes in a solvent and depositing the carbon nanotubes on a porous, conductive substrate. The porous, conductive substrate is capable of functioning both as a filter and a working electrode in an electrochemical cell. In some embodiments, the substrate-bound carbon nanotubes also provide a convenient storage method until such time as they are ready for use in a metallization process.
In some embodiments, further steps in the metallization of carbon nanotubes include engaging the porous, conductive substrate with deposited carbon nanotubes in an electrochemical cell and depositing at least one metallic structure on the surface of the carbon nanotubes from an electrolyte solution to form metallized carbon nanotubes. In some embodiments, the morphology of the metal deposited on the carbon nanotubes depends on a wide variety of conditions, including, for example, the time of deposition. Access to a variety of morphologies, from simple metal atom clusters to entire continuous surfaces, may be achieved through effective contact with the carbon nanotubes.
In yet further embodiments, metallized carbon nanotubes made by the method described herein may be used in a composite. The metallized carbon nanotube can have at least one metallic structure which includes, but is not limited to, a conductive metal atom selected from the group consisting of platinum, gold, silver, nickel, copper, iron, chromium, zinc, lead, and combinations thereof. The composite incorporating the metallized tube may be virtually any desired matrix material including, but not limited to, those selected from the group consisting of epoxies, thermosets, thermoplastics, elastomers, metals, metal matrix composites, ceramics and combinations thereof.
The foregoing has outlined the features of various embodiments in order that the detailed description that follows may be better understood. Additional features and advantages of various embodiments will be described hereinafter which form the subject of the claims of the invention.