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John O | June 2017

Graphene research continues with 3-D printed foam and new chemical method


researchers at the university of illinois-chicago have developed a new chemical method to attach nanomaterials onto graphene without changing the properties and the arrangement of the carbon atoms, which retains the material’s electron-mobility, according to a report on the school’s website.

 


laser sintering was used to 3-d print objects made of graphene foam, a 3-d version
of atomically thin graphene.  (tour group/rice university)

 

the article explained, “instead of adding molecules to the individual carbon atoms of graphene, [the] new method adds metal atoms, such as chromium or molybdenum, to the six atoms of a benzoid ring. unlike carbon-centered bonds, this bond is delocalized, which keeps the carbon atoms’ arrangement undistorted and planar, so that the graphene retains its unique properties of electrical conduction.”

 

this new method could expand the range of applications for graphene and allow the material to interface with a wider range of technologies, including solar cells, high-speed electronics, and industrial processes.

 

the work was published in nano letters. the abstract stated:

 

“binding graphene with auxiliary nanoparticles for plasmonics, photovoltaics, and/or optoelectronics, while retaining the trigonal-planar bonding of sp2 hybridized carbons to maintain its carrier-mobility, has remained a challenge.

 

“the conventional nanoparticle-incorporation route for graphene is to create nucleation/attachment sites via “carbon-centered” covalent functionalization, which changes the local hybridization of carbon atoms from trigonal-planar sp2to tetrahedral sp3. this disrupts the lattice planarity of graphene, thus dramatically deteriorating its mobility and innate superior properties.

 

“here, we show large-area, vapor-phase, “ring-centered” hexahapto (η6) functionalization of graphene to create nucleation-sites for silver nanoparticles (agnps) without disrupting its sp2 character. this is achieved by the grafting of chromium tricarbonyl [cr(co)3] with all six carbon atoms (sigma-bonding) in the benzenoid ring on graphene to form an (η6-graphene)cr(co)3 complex.

 

“this nondestructive functionalization preserves the lattice continuum with a retention in charge carrier mobility (9% increase at 10 k); with agnps attached on graphene/n-si solar cells, we report an ∼11-fold plasmonic-enhancement in the power conversion efficiency (1.24%).”

 

researchers at rice university (dallas, texas) and tianjin (china) university have also been studying graphene and have developed a means for fabricating centimeter-sized objects through 3-d laser printing of graphene foams from non-graphene starting materials, according to a report on the rice website.

 

this new process was conducted at room temperature, required no molds and used starting materials of powdered sugar and nickel powder.

 

“3-d laser printers work differently than the more familiar extrusion-based 3-d printers, which create objects by squeezing melted plastic through a needle as they trace out two-dimensional patterns,” the article explained. “in 3-d laser sintering, a laser shines down onto a flat bed of powder. wherever the laser touches powder, it melts or sinters the powder into a solid form. the laser is rastered, or moved back and forth, line by line to create a single two-dimensional slice of a larger object. then a new layer of powder is laid over the top of that layer and the process is repeated to build up three-dimensional objects from successive two-dimensional layers.”

 

when the laser shown on the sugar and nickel powder, the sugar would melt with the nickel acting as a catalyst. graphene formed as the mixture cooled. the article noted, “the foam created by the process is a low-density, 3-d form of graphene with large pores that account for more than 99 percent of its volume.”

 

the research was recently published in acs nano. the abstract stated:

 

“an automated metal powder three-dimensional (3d) printing method for in situ synthesis of free-standing 3d graphene foams (gfs) was successfully modeled by manually placing a mixture of ni and sucrose onto a platform, and then using a commercial co2 laser to convert the ni/sucrose mixture into 3d gfs.

 

“the sucrose acted as the solid carbon source for graphene and the sintered ni metal acted as the catalyst and template for graphene growth. this simple and efficient method combines powder metallurgy templating with 3d printing techniques, and enables direct in situ 3d printing of gfs with no high-temperature furnace or lengthy growth process required.

 

“the 3d printed gfs show high porosity (~ 99.3%), low density (~ 0.015 g cm-3), high quality and multi-layered graphene features. the gfs have an electrical conductivity of ~ 8.7 s cm-1, remarkable storage modulus of ~ 11 kpa, as well as high damping capacity of ~ 0.06.

 

“these excellent physical properties of 3d printed gfs indicate potential applications in fields requiring rapid design and manufacturing of 3d carbon materials; for example, energy storage devices, damping materials, and sound absorption.”

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