Graphene from Graphite by Electrochemical Exfoliation

Graphene is an interesting material, but making enough of the stuff to do something useful can be a little tough. That’s why we’re always on the lookout for new methods, like this electrochemical process for producing graphene in bulk.

You probably know that graphene is a molecular monolayer of carbon atoms linked in hexagonal arrays. Getting to that monolayer is a difficult proposition, but useful bits of graphene can be created by various mechanical and chemical treatments of common graphite. [The Thought Emporium]’s approach to harvesting graphene from graphite is a two-step process starting with electrochemical exfoliation. Strips of thin graphite foil are electrolyzed in a bath of ferrous sulfate, resulting in the graphite delaminating and flaking off into the electrolyte. After filtering and cleaning, the almost graphene is further exfoliated in an ultrasonic cleaner. The result is gram quantity yields with very little work and at low cost.

There’s plenty of effort going into new methods of creating graphene these days, whether by barely controlled explosions or superheating soybean oil. But will graphene be the Next Big Thing? The jury is still out on that.

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Solar-Powered Prosthetic Skin

One of the biggest problems for prosthetic users is feel. If you’ve ever tried to hold a pen and write with a numb hand, you’ve realised how important feedback is to the motor control equation. Research is ongoing to find ways to provide feedback from prosthetic limbs, in even a basic format.  The human nervous system is a little more complex than just interfacing with the average serial UART. One of the requirements of many feedback systems is power, which usually would involve bulky batteries or some form of supercapacitors, but a British team has developed a way to embed solar cells in a touch-sensitive prosthetic skin.

The skin relies on everyone’s favourite material of the minute, graphene. A thin layer of graphene allows the prosthetic to feed signals back to the user of both temperature and contact pressure. The trick is that the graphene skin is incredibly transparent, reportedly allowing 98% of light on its surface to pass through. It’s then a simple matter of fitting solar panels beneath this skin, and the energy harvested can then be used to power the sensor system.

The team does admit that some power storage will later be required, as it would be difficult for any prosthetic user if their limbs lost all feedback when they walked into a dark room. The idea of one’s arm losing all feeling upon going to bed isn’t particularly appealing. Check out the paper here (paywalled). Video below the break.
We see a lot of great prosthetic projects cross our desk here at Hackaday – like this 3D printed prosthetic hand. Prosthetics definitely matter, so why not build your own and enter it in the 2017 Hackaday Prize?

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Explosive New Process Produces Graphene by the Gram

You say you need some graphene so you can invent the Next Big Thing, but you can’t be bothered with processes that yield a few measly milligrams of the precious stuff. Luckily for you there’s a new method for producing gram quantities of graphene. Perhaps unluckily, it requires building a controlled fuel-air bomb.

Graphene is all the rage today, promising to revolutionize everything from batteries to supercapacitors to semiconductors. A molecularly-2D surface with unique properties, graphene can be made in very small quantities with such tedious methods as pulling flakes of the stuff off graphite lumps with Scotch tape. Slightly less ad hoc methods involve lasers, microwaves, or high temperatures and nasty chemicals. But all of these methods are batch methods that produce vanishingly small amounts of the stuff.

The method [Chris Sorenson] et al of Kansas State University developed, which involves detonating acetylene and oxygen in a sturdy pressure vessel with a spark plug, can produce grams of graphene at a go. And what’s more, as their patent application makes clear, the method is amenable to a continuous production process using essentially an acetylene-fueled internal combustion engine.

While we can’t encourage our readers to build an acetylene bomb in the garage, the process is so simple that it would be easily replicated. We wonder how far down it could scale for safety and still produce graphene. Obviously, be careful if you choose to replicate this experiment. If you don’t like explosions and can source some soybean oil and nickel foil, maybe try this method instead. Then you’ll have something to mix with your Silly Putty.

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Flexible, Sensitive Sensors from Silly Putty and Graphene

Everyone’s favorite viscoelastic non-Newtonian fluid has a new use, besides bouncing, stretching, and getting caught in your kid’s hair. Yes, it’s Silly Putty, and when mixed with graphene it turns out to make a dandy force sensor.

To be clear, [Jonathan Coleman] and his colleagues at Trinity College in Dublin aren’t buying the familiar plastic eggs from the local toy store for their experiments. They’re making they’re own silicone polymers, but their methods (listed in this paywalled article from the journal Science) are actually easy to replicate. They just mix silicone oil, or polydimethylsiloxane (PDMS), with boric acid, and apply a little heat. The boron compound cross-links the PDMS and makes a substance very similar to the bouncy putty. The lab also synthesizes its own graphene by sonicating graphite in a solvent and isolating the graphene with centrifugation and filtration; that might be a little hard for the home gamer to accomplish, but we’ve covered a DIY synthesis before, so it should be possible.

With the raw materials in hand, it’s a simple matter of mixing and kneading, and you’ve got a flexible, stretchable sensor. [Coleman] et al report using sensors fashioned from the mixture to detect the pulse in the carotid artery and even watch the footsteps of a spider. It looks like fun stuff to play with, and we can see tons of applications for flexible, inert strain sensors like these.

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Graphene Refractions

Researchers recently observed negative refraction of electrons in graphene PN junctions. The creation of PN junctions in graphene is quite interesting, itself. Negative refraction isn’t a new idea. It was first proposed in 1968 and occurs when a wave bends–or refracts–the opposite way at an interface compared to what you would usually expect. In optics, for example, this can allow for refocusing divergent waves and has been the basis for some proposed invisibility cloaking devices.

In theory, negative refraction for electrons should be easy to observe at PN junctions, but in practice, the band gap voltage causes most electrons to reflect at the junction instead of refract. However, a graphene PN junction has no band gap voltage, so it should be ideal. However, previous attempts to find negative refraction in graphene were not successful.

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Making Graphene More Practical

[James Tour] and others at Rice University announced an improved form of graphene that uses nanoscale rivets. The material incorporates carbon nanotubes along with carbon spheres that encase iron nanoparticles. The nanotubes provide strength and higher conductivity overall, while the spheres let the material transfer more easily.

Typically, placing graphene on something involves using chemical vapor deposition on a polymer layer before transferring to another site. The polymer tends to degrade the graphene’s properties. This new material doesn’t require this intermediate step. In addition, the spheres allow interfacing to the graphene more readily.

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Graphene Optical Boom Emits Light with No Diode

When a supersonic aircraft goes faster than the speed of sound, it produces a shockwave or sonic boom. MIT researchers have found a similar optical effect in graphene that causes an optical boom and could provide a new way to convert electricity into light.

The light emission occurs due to two odd properties of graphene: first, light gets trapped on the surface of graphene, effectively slowing it down. In addition, electrons pass through at very high speeds. Interestingly, the speeds are nearly the same–that is, electrons and trapped light travel at almost the same speed. The researchers found a way to make the electrons move faster than the speed of light (in the graphene) and thus created Cerenkov emissions. Because of the structure of graphene, the resulting light is intense and tightly focused.

The researchers speculate that this technique could be important in building graphene-based optical chips. We’ve talked about mixed graphene and semiconductor chips before. Graphene is pretty exotic stuff. It can even fold itself.