In an effort to combine graphene and nanoparticles, two of the most sought-after and popular technologies available today, a team of scientists from the Department of Chemical Engineering University of Illinois at Chicago have developed a revolutionary synthesis method that enhances the phenomenal properties of these materials without any need to compromise the unique properties of the two.
As the use of graphene, which is believed to be the most powerful and widely studied material on the planet, continues to rise in almost every imaginable industrial application on the market today, its combination with certain nanomaterials, particularly nanoparticles, has been found to offer highly desirable properties.
Due to its unique two-dimensional (2D) honeycomb lattice structure, graphene exhibits unique structural, optical and electronic properties when used on its own, which has allowed for its applications to be found within a variety of industries including electronics, biological devices, photovoltaics, and sensor technology1.
Graphene-nanoparticle hybrid structures, which describes the combination of graphene with a specific type of nanoparticles, has offered an even greater physicochemical advantage for industrial purposes, as the individual properties of these materials provide synergistic effects when presented together.
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Conventional chemical methods used to synthesize these graphene-nanoparticle hybrid structures typically involve covalent bonding techniques such as oxidation, fluorination, sulphonation and chlorination, however, such processes often negatively affect graphene’s hybridization.
Graphene’s trigonal-planar sp2 hybridization accounts for its highly desirable properties of mechanical strength, electricity and heat conductivity, however, such methods of nanoparticle deposition to this material often distort its natural lattice planarity to tetrahedral sp3 hybridization2.
The subsequent delocalization of the p-clouds surrounding the graphene structure will drastically alter its mobility and innate superior properties. While noncovalent bonding methods have been investigated to incorporate nanoparticles onto the surface of graphene while avoiding such deleterious effects, the often-weak van der Waals interactions that exist between the two materials are not sufficient to hold these two structures together.
In their endeavor to develop a method of attaching nanoparticles to functionalized graphene without distorting its native planarity and properties, the group of researchers from the University of Illinois at Chicago, led by Vikas Berry, have utilized a common chemical deposition process using plasmonic silver nanoparticles (AgNP).
In their experimental design, the researchers conducted a chemical vapor deposition (CVD) method within a quartz tube furnace to initially expose the material to chromium hexacarbonyl (Cr(CO)6) powder2. By gradually increasing the interior temperature of the furnace to 130° C and eventually opening the vacuum valve, the vapor phase reaction of Cr(CO)6 with graphene allowed for a monolayer formation of chromium tetracarbonyl (Cr(CO)3) to attach to graphene’s surface without any type of reaction to occur between the two layers.
To allow for the in situ attachment of AgNPs, which was performed by photolithography and etching processes, onto graphene, the researchers utilized the carbonyl functional groups of the attached Cr(CO)3 as anchoring sites for its formation. Raman spectroscopy, a method that is used to provide information on the specific structural components of a particular compound, was used to determine the final arrangement of the newly developed material.
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The hexahapto bonding that resulted from the (h60-graphene)Cr(CO)3 structure allowed for the proper attachment of the AgNPs to the material without compromising the sp2 lattice planarity or high charge carrier mobility of graphene2.
Furthermore, this scalable and nondestructive functionalization method was also found to increase the plasmonic enhancement of graphene by 11-fold, as well as improve graphene’s individual power conversion by 1.24%.
The synthetic process developed by these researchers has the potential to have a wide range of implications on the applications of graphene that are currently found in optoelectronics and photovoltaic systems.
- “Design, Synthesis, and Characterization of Graphene-Nanoparticle Hybrid Materials for Bioapplications” P. Yin, S. Shah, et al. Chemical Reviews. (2014). DOI: 10.1021/cr500537t.
- “Retained Carrier-Mobility and Enhanced Plasmonic-Photovoltaics of Graphene via ring-centered h6 Functionalization and Nanointerfacing” S. Che, K. Jasuja, et al. Nano Letters. (2017). DOI: 10.1021.acs.nanolett.7b01458.