{"id":12169,"date":"2017-04-25T11:26:23","date_gmt":"2017-04-25T11:26:23","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=12169"},"modified":"2017-04-25T11:26:23","modified_gmt":"2017-04-25T11:26:23","slug":"graphene-holds-high-pressure","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/graphene-holds-high-pressure\/","title":{"rendered":"Graphene holds up under high pressure"},"content":{"rendered":"

Used in filtration membranes, ultrathin material could help make desalination more productive.<\/strong><\/em><\/span><\/p>\n

\"\"
On the left, an atomic-force microscopy image shows a nanoporous graphene membrane after a burst test at 100 bars. The image shows that failed micromembranes (the dark black areas) are aligned with wrinkles in the graphene. On the right, two zoomed-in scanning electron microscopy images of graphene membranes show the before (top) and after of a burst test at pressure difference of 30 bars. The images illustrate that membrane failure is associated with intrinsic defects along wrinkles.
Courtesy of the researchers<\/figcaption><\/figure>\n

CAMBRIDGE, Mass. —\u00a0A single sheet of graphene, comprising an atom-thin lattice of carbon, may seem rather fragile. But engineers at MIT have found that the ultrathin material is exceptionally sturdy, remaining intact under applied pressures of at least 100 bars. That\u2019s equivalent to about 20 times the pressure produced by a typical kitchen faucet.<\/span><\/p>\n

The key to withstanding such high pressures, the researchers found, is pairing graphene with a thin underlying support substrate that is pocked with tiny holes, or pores. The smaller the substrate\u2019s pores, the more resilient the graphene is under high pressure.<\/span><\/p>\n

Rohit Karnik, an associate professor in MIT\u2019s Department of Mechanical Engineering, says the team\u2019s results, reported today in the journal<\/span> Nano Letters<\/a><\/em> serve as a guideline for designing tough, graphene-based membranes, particularly for applications such as desalination, in which filtration membranes must withstand high-pressure flows to efficiently remove salt from seawater.<\/span><\/p>\n

\u201cWe\u2019re showing here that graphene has the potential to push the boundaries of high-pressure membrane separations,\u201d Karnik says. \u201cIf graphene-based membranes could be developed to do desalination at high pressure, then it opens up a lot of interesting possibilities for energy-efficient desalination at high salinities.\u201d<\/span><\/p>\n

Karnik\u2019s co-authors are lead author and MIT postdoc Luda Wang, former undergraduate student Christopher Williams, former graduate student Michael Boutilier, and postdoc Piran Kidambi.<\/span><\/p>\n

Water stressed<\/strong><\/span><\/p>\n

Today\u2019s existing membranes desalinate water via reverse osmosis, a process by which pressure is applied to one side of a membrane containing saltwater, to push pure water across the membrane while salt and other molecules are prevented from filtering through.<\/span><\/p>\n

Many commercial membranes desalinate water under applied pressures of about 50 to 80 bars, above which they tend to get compacted or otherwise suffer in performance. If membranes were able to withstand higher pressures, of 100 bars or greater, they would enable more effective desalination of seawater by recovering more fresh water. High-pressure membranes might also be able to purify extremely salty water, such as the leftover brine from desalination that is typically too concentrated for membranes to push pure water through.<\/span><\/p>\n

\u201cIt\u2019s pretty clear that the stress on water sources is not going away any time soon, and desalination forms a major source of fresh water,\u201d Karnik says. \u201cReverse osmosis is among the most efficient methods of desalination in terms of energy. If membranes could operate at higher pressures, this would allow higher water recovery at high energy efficiency.\u201d<\/span><\/p>\n

Turning the pressure up<\/strong><\/span><\/p>\n

Karnik and his colleagues set up experiments to see how far they could push graphene\u2019s pressure tolerance. Previous simulations have predicted that graphene, placed on porous supports, can remain intact under high pressure. However, no direct experimental evidence has supported these predictions until now.<\/span><\/p>\n

The researchers grew sheets of graphene using a technique called<\/span> chemical vapor deposition<\/a>, then placed single layers of graphene on thin sheets of porous polycarbonate. Each sheet was designed with pores of a particular size, ranging from 30 nanometers to 3 microns in diameter.<\/span><\/p>\n

To gauge graphene\u2019s sturdiness, the researchers concentrated on what they termed \u201cmicromembranes\u201d \u2014 the areas of graphene that were suspended over the underlying substrate\u2019s pores, similar to fine meshwire lying over Swiss cheese holes.<\/span><\/p>\n

The team placed the graphene-polycarbonate membranes in the middle of a chamber, into the top half of which they pumped argon gas, using a pressure regulator to control the gas\u2019 pressure and flow rate. The researchers also measured the gas flow rate in the bottom half of the chamber, reasoning that any increase in the bottom half\u2019s flow rate would indicate that parts of the graphene membrane had failed, or \u201cburst,\u201d from the pressure created in the top half of the chamber.<\/span><\/p>\n

They found that graphene, placed over pores that were 200 nanometers wide or smaller, withstood pressures of 100 bars \u2014 nearly twice that of pressures commonly encountered in desalination. As the size of the underlying pores decreased, the researchers observed an increase in the number of micromembranes that remained intact. Karnik says the this pore size is essential to determining graphene\u2019s sturdiness.<\/span><\/p>\n

\u201cGraphene is like a suspension bridge, and the applied pressure is like people standing on that bridge,\u201d Karnik explains. \u201cIf five people can stand on a short bridge, that weight, or pressure, is OK. But if the bridge, made with the same rope, is suspended over a larger distance, it experiences more stress, because a greater number of people are standing on it.\u201d<\/span><\/p>\n

Porous design<\/strong><\/span><\/p>\n

\u201cWe show graphene can withstand high pressure,\u201d says lead author Luda Wang. \u201cThe other part that remains to be shown on large scale is, can it desalinate?\u201d<\/span><\/p>\n

In other words, can graphene tolerate high pressures while selectively filtering out water from seawater? As a first step toward answering this question, the group fabricated nanoporous graphene to serve as a very simple graphene filter. The researchers used a technique they had previously developed to etch nanometer-sized pores in sheets of graphene. Then they exposed these sheets to increasing pressures.<\/span><\/p>\n

In general, they found that wrinkles in the graphene had a lot to do with whether micromembranes burst or not, regardless of the pressure applied. Parts of the porous graphene that lay along wrinkles failed or burst, even at pressures as low as 30 bars, while those that were unwrinkled remained intact at pressures up to 100 bars. And again, the smaller the underlying substrate\u2019s pores, the more likely micromembranes in the porous graphene were to survive, even in wrinkled regions.<\/span><\/p>\n

\u201cAs a whole, this study tells us single-layer graphene has the potential of withstanding extremely high pressures, and that 100 bars is not the limit \u2014 it\u2019s comfortable in a sense, as long as the pore sizes on which graphene sits are small enough,\u201d Karnik says.<\/span><\/p>\n

This research was supported, in part, by the MIT Energy Initiative and the U.S. Department of Energy.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

Used in filtration membranes, ultrathin material could help make desalination more productive. CAMBRIDGE, Mass. —\u00a0A single sheet of graphene, comprising an atom-thin lattice of carbon, may seem rather fragile. But engineers at MIT have found that the ultrathin material is exceptionally sturdy, remaining intact under applied pressures of at least 100 bars. That\u2019s equivalent to […]<\/p>\n","protected":false},"author":6,"featured_media":12170,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-12169","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0-150x150.jpg",150,150,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0-300x200.jpg",300,200,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",600,400,false],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",600,400,false],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",540,360,false],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",95,63,false],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",639,426,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",96,64,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2017\/04\/MIT-Graphene-Pressure_0.jpg",150,100,false]},"author_info":{"info":["Amrita Tuladhar"]},"category_info":"Research<\/a>","tag_info":"Research","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/12169","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=12169"}],"version-history":[{"count":0,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/12169\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/12170"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=12169"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=12169"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=12169"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}