Tag Archives: water purification

Understanding nanotechnology with Timbits; a peculiarly Canadian explanation

For the uninitiated, Timbits are also known as donut holes. Tim Hortons, founded by ex-National Hockey League player Tim Horton who has since deceased, has taken hold in the Canada’s language and culture such that one of our scientists trying to to explain nanotechnology thought it would be best understood in terms of Timbits. From a Jan. 14, 2017 article (How nanotechnology could change our lives) by Vanessa Lu for thestar.com,

The future is all in the tiny.

Known as nanoparticles, these are the tiniest particles, so small that we can’t see them or even imagine how small they are.

University of Waterloo’s Frank Gu paints a picture of their scale.

“Take a Timbit and start slicing it into smaller and smaller pieces, so small that every Canadian — about 35 million of us — can hold a piece of the treat,” he said. “And those tiny pieces are still a little bigger than a nanoparticle.”

For years, consumers have seen the benefits of nanotechnology in everything from shrinking cellphones to ultrathin televisions. Apple’s iPhones have become more powerful as they have become smaller — where a chip now holds billions of transistors.

“As you go smaller, it creates less footprint and more power,” said Gu, who holds the Canada research chair in advanced targeted delivery systems. “FaceTime, Skype — they are all powered by nanotechnology, with their retina display.”

Lu wrote a second January 14, 2017 article (Researchers developing nanoparticles to purify water) for thestar.com,

When scientists go with their gut or act on a hunch, it can pay off.

For Tim Leshuk, a PhD student in nanotechnology at the University of Waterloo, he knew it was a long shot.

Leshuk had been working with Frank Gu, who leads a nanotechnology research group, on using tiny nanoparticles that have been tweaked with certain properties to purify contaminated water.

Leshuk was working on the process, treating dirty water such as that found in Alberta’s oilsands, with the nanoparticles combined with ultraviolet light. He wondered what might happen if exposed to actual sunlight.

“I didn’t have high hopes,” he said. “For the heck of it, I took some beakers out and put them on the roof. And when I came back, it was far more effective that we had seen with regular UV light.

“It was high-fives all around,” Leshuk said. “It’s not like a Brita filter or a sponge that just soaks up pollutants. It completely breaks them down.”

Things are accelerating quickly, with a spinoff company now formally created called H2nanO, with more ongoing tests scheduled. The research has drawn attention from oilsands companies, and [a] large pre-pilot project to be funded by the Canadian Oil Sands Innovation Alliance is due to get under way soon.

The excitement comes because it’s an entirely green process, converting solar energy for cleanup, and the nanoparticle material is reuseable, over and over.

It’s good to see a couple of articles about nanotechnology. The work by Tim Leshuk was highlighted here in a Dec. 1, 2015 posting titled:  New photocatalytic approach to cleaning wastewater from oil sands. I see the company wasn’t mentioned in the posting so, it must be new; you can find H2nanO here.

Discussion of a divisive topic: the Oilsands

As for the oilsands, it’s been an interesting few days with the Prime Minister’s (Justin Trudeau) suggestion that dependence would be phased out causing a furor of sorts. From a Jan. 13, 2017 article by James Wood for the Calgary Herald,

Prime Minister Justin Trudeau’s musings about phasing out the oilsands Friday [Jan. 13, 2017] were met with a barrage of criticism from Alberta’s conservative politicians and a pledge from Premier Rachel Notley that the province’s energy industry was “not going anywhere, any time soon.”

Asked at a town hall event in Peterborough [Ontario] about the federal government’s recent approval of Kinder Morgan’s Trans Mountain pipeline expansion, Trudeau reiterated his longstanding remarks that he is attempting to balance economic and environmental concerns.

“We can’t shut down the oilsands tomorrow. We need to phase them out. We need to manage the transition off of our dependence on fossil fuels but it’s going to take time and in the meantime we have to manage that transition,” he added.

Northern Alberta’s oilsands are a prime target for environmentalists because of their significant output of greenhouse gas emissions linked to global climate change.

Trudeau, who will be in Calgary for a cabinet retreat on Jan. 23 and 24 [2017], also said again that it is the responsibility of the national government to get Canadian resources to market.

Meanwhile, Jane Fonda, Hollywood actress, weighed in on the issue of the Alberta oilsands with this (from a Jan. 11, 2017 article by Tristan Hopper for the National Post),

Fort McMurrayites might have assumed the celebrity visits would stop after the city was swept first by recession, and then by wildfire.

Or when the provincial government introduced a carbon tax and started phasing out coal.

And surely, with Donald Trump in the White House, even the oiliest corner of Canada would shift to the activist back burner.

But no; here comes Jane Fonda.

“We don’t need new pipelines,” she told a Wednesday [Jan. 11, 2017] press conference at the University of Alberta where she also dismissed Prime Minister Justin Trudeau as a “good-looking Liberal” who couldn’t be trusted.

Saying that her voice was joined with the “Indigenous people of Canada,” Fonda explained her trip to Alberta by saying “when you’re famous you can help amplify the voices of people that can’t necessarily get a lot of press people to come out.”

Fonda is in Alberta at the invitation of Greenpeace, which has brought her here in support of the Treaty Alliance Against Tar Sands Expansion — a group of Canadian First Nations and U.S. tribes opposed to new pipelines to the Athabasca oilsands.

Appearing alongside Fonda, at a table with a sign reading “Respect Indigenous Decisions,” was Grand Chief Stewart Phillip, who, as leader of the Union of B.C. Indian Chiefs, has led anti-pipeline protests and litigation in British Columbia.

“The future is going to be incredibly litigious,” he said in reference to the approved expansion of the Trans-Mountain pipeline.

The event also included Grand Chief Derek Nepinak of the Assembly of Manitoba Chiefs, which is leading a legal challenge to federal approval of the Line 3 pipeline.

Although much of Athabasca’s oil production now comes from “steam-assisted gravity drainage” projects that requires minimal surface disturbance, on Tuesday Fonda took the requisite helicopter tour of a Fort McMurray-area open pit mine.

As you can see, there are not going to be any easy answers.

Oil spill cleanup nanotechnology-enabled solution from A*STAR

A*STAR (Singapore’s Agency for Science Technology and Research) has developed a new technology for cleaning up oil spills according to an Oct. 11, 2016 news item on Nanowerk,

Oceanic oil spills are tough to clean up. They dye feathers a syrupy sepia and tan fish eggs a toxic tint. The more turbulent the waters, the farther the slick spreads, with inky droplets descending into the briny deep.

Now technology may be able to succeed where hard-working volunteers have failed in the past. Researchers at the A*STAR Institute of Bioengineering and Nanotechnology (IBN) are using nanotechnology to turn an oil spill into a floating mass of brown jelly that can be scooped up before it can make its way into the food chain.

“Nanoscience makes it possible to tailor the essential structures of materials at the nanometer scale to achieve specific properties,” says chemist Yugen Zhang at IBN, who is developing some of the technologies. “Structures and materials in the nanometer size range often take on distinctive properties that are not seen in other size ranges,” adds Huaqiang Zeng, another chemist at IBN.

An Oct. 11, 2016 A*STAR press release, which originated the news item, describes some of problematic solutions before describing the new technology,

There are many approaches to cleaning an oil spill, and none are completely effective. Fresh, thick grease can be set ablaze or contained by floating barriers for skimmers to scoop out. The slick can also be inefficiently hardened, messily absorbed, hazardously dispersed, or slowly consumed by oil-grazing bacteria. All of these are deficient on a large scale, especially in rough waters.

Organic molecules with special gelling abilities offer a cheap, simple and environmentally friendly alternative for cleaning up the mess. Zeng has developed several such molecules that turn crude oil into jelly within minutes.

To create his ‘supergelators’, Zeng designed the molecules to associate with each other without forming physical bonds. When sprayed on contaminated seawater, the molecules immediately bundle into long fibers between 40 and 800 nanometers wide. These threads create a web that traps the interspersed oil in a giant blob that floats on the water’s surface. The gunk can then be swiftly sieved out of the ocean. Valuable crude oil can later be reclaimed using a common technique employed by petroleum refineries called fractional distillation.

Zeng tested the supergelators on four types of crude oil with different densities, viscosities and sulfur levels in a small round dish. The results were impressive. “The supergelators solidified both freshly spilled crude oil and highly weathered crude oil 37 to 60 times their own weight,” says Zeng. The materials used to produce these organic molecules are cheap and non toxic, which make them a commercially viable solution for managing accidents out at sea. Zeng hopes to work with industrial partners to test the nanomolecules on a much larger scale.

Zeng and his colleagues have developed other other ‘water’ applications as well,

Unsalty water

Scientists at IBN are also using nanoscience to remove salt from seawater and heavy metals from contaminated water.

With dwindling global fresh and ground water reserves, many countries are looking to desalination as a viable source of drinking water. Desalination is expected to meet 30 per cent of the water demand of Singapore by 2060, which will mean tripling the country’s current desalination capacity. But desalination demands huge energy consumption and reverse osmosis, the mainstream technology it depends on, has a relatively high cost. Reverse osmosis works by using extreme pressures to squeeze water molecules through tightly knit membranes.

An emerging alternative solution mimics the way proteins embedded in cell membranes, known as aquaporins, channel water in and out. Some research groups have even created membranes made of fatty lipid molecules that can accommodate natural aquaporins. Zeng has developed a cheaper and more resilient replacement.

His building blocks consist of helical noodles with sticky ends that connect to form long spirals. Water molecules can flow through the 0.3 nanometer openings at the center of the spirals, but all the other positively and negatively charged ions that make up saltwater are too bulky to pass. These include sodium, potassium, calcium, magnesium, chlorine and sulfur oxide. “In water, all of these ions are highly hydrated, attached to lots of water molecules, which makes them too large to go through the channels,” says Zeng.

The technology could lead to global savings of up to US$5 billion a year, says Zeng, but only after several more years of testing and tweaking the lipid membrane’s compatibility and stability with the nanospirals. “This is a major focus in my group right now,” he says. “We want to get this done, so that we can reduce the cost of water desalination to an acceptable level.”

Stick and non-stick

Nanomaterials also offer a low-cost, effective and sustainable way to filter out toxic metals from drinking water.

Heavy metal levels in drinking water are stringently regulated due to the severe damage the substances can cause to health, even at very low concentrations. The World Health Organization requires that levels of lead, for example, remain below ten parts per billion (ppb). Treating water to these standards is expensive and extremely difficult.

Zhang has developed an organic substance filled with pores that can trap and remove toxic metals from water to less than one ppb. Each pore is ten to twenty nanometers wide and packed with compounds, known as amines that stick to the metals.

Exploiting the fact that amines lose their grip over the metals in acidic conditions, the valuable and limited resource can be recovered by industry, and the polymers reused.

The secret behind the success of Zhang’s polymers is the large surface area covered by the pores, which translates into more opportunities to interact with and trap the metals. “Other materials have a surface area of about 100 square meters per gram, but ours is 1,000 square meters per gram,” says Zhang. “It is 10 times higher.”

Zhang tested his nanoporous polymers on water contaminated with lead. He sprinkled a powdered version of the polymer into a slightly alkaline liquid containing close to 100 ppb of lead. Within seconds, lead levels reduced to below 0.2 ppb. Similar results were observed for cadmium, copper and palladium. Washing the polymers in acid released up to 93 per cent of the lead.

With many companies keen to scale these technologies for real-world applications, it won’t be long before nanoscience treats the Earth for its many maladies.

I wonder if the researchers have found industrial partners (who could be named) to bring these solutions for oil spill cleanups, desalination, and water purification to the market.

Nanopores and a new technique for desalination

There’s been more than one piece here about water desalination and purification and/or remediation efforts and at least one of them claims to have successfully overcome issues such as reverse osmosis energy needs which are hampering adoption of various technologies. Now, researchers at the University of Illinois at Champaign Urbana have developed another new technique for desalinating water while reverse osmosis issues according to a Nov. 11, 2015 news item on Nanowerk (Note: A link has been removed) ,

University of Illinois engineers have found an energy-efficient material for removing salt from seawater that could provide a rebuttal to poet Samuel Taylor Coleridge’s lament, “Water, water, every where, nor any drop to drink.”

The material, a nanometer-thick sheet of molybdenum disulfide (MoS2) riddled with tiny holes called nanopores, is specially designed to let high volumes of water through but keep salt and other contaminates out, a process called desalination. In a study published in the journal Nature Communications (“Water desalination with a single-layer MoS2 nanopore”), the Illinois team modeled various thin-film membranes and found that MoS2 showed the greatest efficiency, filtering through up to 70 percent more water than graphene membranes. [emphasis mine]

I’ll get to the professor’s comments about graphene membranes in a minute. Meanwhile, a Nov. 11, 2015 University of Illinois news release (also on EurekAlert), which originated the news item, provides more information about the research,

“Even though we have a lot of water on this planet, there is very little that is drinkable,” said study leader Narayana Aluru, a U. of I. professor of mechanical science and engineering. “If we could find a low-cost, efficient way to purify sea water, we would be making good strides in solving the water crisis.

“Finding materials for efficient desalination has been a big issue, and I think this work lays the foundation for next-generation materials. These materials are efficient in terms of energy usage and fouling, which are issues that have plagued desalination technology for a long time,” said Aluru, who also is affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.

Most available desalination technologies rely on a process called reverse osmosis to push seawater through a thin plastic membrane to make fresh water. The membrane has holes in it small enough to not let salt or dirt through, but large enough to let water through. They are very good at filtering out salt, but yield only a trickle of fresh water. Although thin to the eye, these membranes are still relatively thick for filtering on the molecular level, so a lot of pressure has to be applied to push the water through.

“Reverse osmosis is a very expensive process,” Aluru said. “It’s very energy intensive. A lot of power is required to do this process, and it’s not very efficient. In addition, the membranes fail because of clogging. So we’d like to make it cheaper and make the membranes more efficient so they don’t fail as often. We also don’t want to have to use a lot of pressure to get a high flow rate of water.”

One way to dramatically increase the water flow is to make the membrane thinner, since the required force is proportional to the membrane thickness. Researchers have been looking at nanometer-thin membranes such as graphene. However, graphene presents its own challenges in the way it interacts with water.

Aluru’s group has previously studied MoS2 nanopores as a platform for DNA sequencing and decided to explore its properties for water desalination. Using the Blue Waters supercomputer at the National Center for Supercomputing Applications at the U. of I., they found that a single-layer sheet of MoS2 outperformed its competitors thanks to a combination of thinness, pore geometry and chemical properties.

A MoS2 molecule has one molybdenum atom sandwiched between two sulfur atoms. A sheet of MoS2, then, has sulfur coating either side with the molybdenum in the center. The researchers found that creating a pore in the sheet that left an exposed ring of molybdenum around the center of the pore created a nozzle-like shape that drew water through the pore.

“MoS2 has inherent advantages in that the molybdenum in the center attracts water, then the sulfur on the other side pushes it away, so we have much higher rate of water going through the pore,” said graduate student Mohammad Heiranian, the first author of the study. “It’s inherent in the chemistry of MoS2 and the geometry of the pore, so we don’t have to functionalize the pore, which is a very complex process with graphene.”

In addition to the chemical properties, the single-layer sheets of MoS2 have the advantages of thinness, requiring much less energy, which in turn dramatically reduces operating costs. MoS2 also is a robust material, so even such a thin sheet is able to withstand the necessary pressures and water volumes.

The Illinois researchers are establishing collaborations to experimentally test MoS2 for water desalination and to test its rate of fouling, or clogging of the pores, a major problem for plastic membranes. MoS2 is a relatively new material, but the researchers believe that manufacturing techniques will improve as its high performance becomes more sought-after for various applications.

“Nanotechnology could play a great role in reducing the cost of desalination plants and making them energy efficient,” said Amir Barati Farimani, who worked on the study as a graduate student at Illinois and is now a postdoctoral fellow at Stanford University. “I’m in California now, and there’s a lot of talk about the drought and how to tackle it. I’m very hopeful that this work can help the designers of desalination plants. This type of thin membrane can increase return on investment because they are much more energy efficient.”

Here’s a link to and a citation for the paper,

Water desalination with a single-layer MoS2 nanopore by Mohammad Heiranian, Amir Barati Farimani, & Narayana R. Aluru. Nature Communications 6, Article number: 8616 doi:10.1038/ncomms9616 Published 14 October 2015

Graphene membranes

In a July 13, 2015 essay on Nanotechnology Now, Tim Harper provides an overview of the research into using graphene for water desalination and purification/remediation about which he is quite hopeful. There is no mention of an issue with interactions between water and graphene. It should be noted that Tim Harper is the Chief Executive Officer of G20, a company which produces a graphene-based solution (graphene oxide sheets), which can desalinate water and can purify/remediate it. Tim is a scientist and while you might have some hesitation given his fiscal interests, his essay is worthwhile reading as he supplies context and explanations of the science.

The Gaza is running out of water by 2016 if the United Nations predictions are correct

If the notion that people are in imminent danger of dying from thirst isn’t compelling enough, there’s this account of the situation and a possible solution in an August 24, 2015 posting by observers, Abou Assi and Majdi Fathi, with journalist, Dorothée Myriam Kellou for observers.france24.com,

Each year, Gaza’s population uses 180 million cubic metres of water but only has capacity for 60 million cubic metres of water usage per year. Running out of water is a constant fear for Gazans.

To understand the context of the crisis, we first spoke to our Observer Majdi Fathi, a photographer who lives in Gaza. He described the daily struggles of living in a place with a shortage of potable water.

The water that comes out of the taps in Gaza is too salty to drink. We only use it for washing. We have to buy bottled water to drink. Each family goes to water vendors. [Editor’s note : Often, families buy water from private companies who run desalination plants with little regulation. Though the water quality is often criticised, it’s still very expensive]. People frequently pay about $2 for 500 litres of water. There are ten people in my family and we can live on 500 litres for about 25 days. Though the authorities give some free water to the very poorest, it’s not enough.

We are all worried about the water shortage. Often, the taps run dry and we end up having to use the drinking water that we purchased for cleaning. Buying water from vendors is not a long-term, sustainable solution!

In a June 25, 2013 posting, I included (in an update) some information about the Gaza situation in the context of water issues in Israel and a special project with the University of Chicago designed to address those issues,

ETA June 27, 2013: There is no hint in the University of Chicago news releases that these water projects will benefit any parties other than Israel and the US but it is tempting to hope that this work might also have an impact in Palestine given its current water crisis there as described in a June 26, 2013 news item in the World Bulletin (Note: Links have been removed),

A tiny wedge of land jammed between Israel, Egypt and the Mediterranean sea, the Gaza Strip is heading inexorably into a water crisis that the United Nations says could make the Palestinian enclave unliveable in just a few years.

With 90-95 percent of the territory’s only aquifer contaminated by sewage, chemicals and seawater, neighbourhood desalination facilities and their public taps are a lifesaver for some of Gaza’s 1.6 million residents.

But these small-scale projects provide water for only about 20 percent of the population, forcing many more residents in the impoverished Gaza Strip to buy bottled water at a premium.

“There is a crisis. There is a serious deficit in the water resources in Gaza and there is a serious deterioration in the water quality,” said Rebhi El Sheikh, deputy chairman of the Palestinian Water Authority (PWA).

A NASA study of satellite data released this year showed that between 2003 and 2009 the region lost 144 cubic km of stored freshwater – equivalent to the amount of water held in the Dead Sea – making an already bad situation much worse.

But the situation in Gaza is particularly acute, with the United Nations warning that its sole aquifer might be unusable by 2016, with the damage potentially irreversible by 2020.

Abou Assi, a Palestinian engineer, thinks he may have a solution (from the observers.france24.com Aug. 24, 2015 posting),

The water table, which is the main source of drinking water in Gaza, is being over-exploited and is also polluted by both nitrates used in agriculture and by sea water. Gaza’s groundwater could run out as soon as next year, according to the United Nations.

While I was working on my masters in engineering at the Islamic University in Gaza, I started looking for a radical solution to the problem. Seeing as Gaza is located on the shores of the Mediterranean, I started considering a filtration system that could desalinate sea water.

There are seven different desalination plants in Gaza. They each produce between 45 and 80 cubic metres of water an hour. The problem is that all of these factories use the reverse osmosis procedure [Editor’s note: This is a water purification system that uses a semipermeable membrane to remove larger particles, including salt molecules, from water molecules].

Even though the method is ingenious, it requires a lot of energy. This is a problem in Gaza, because we also have a major energy shortage. Our power plant, which provides Gaza with about a third of its energy, regularly stops working due to fuel shortages.

My team and I conducted 170 experiments in 14 months before we managed to create a machine that reduced the salinity of the seawater enough to make it drinkable.

The machine is very simple: it pumps sea water very quickly through iron pipes. The water passes through electrical boxes that push the water through membranes made from nanomaterials. The membranes have tiny, microscopic pores that block the sodium chloride (salt) molecules but allow the water molecules to go through. After the water is filtered, the useful minerals are re-injected. After all this, the water that comes out of the taps is clean enough to drink!

With this machine, it’s possible to treat one cubic metre of water per day, using 60% less energy than with the old system. The water meets the quality standards of the World Health Organisation, which puts limits on a number of substances, including chlorine, limestone, lead, nitrates, pesticides and bacteria. For now, some so-called “drinkable” water in Gaza has nitrate levels that can reach up to 220 mg per litre even though the WHO recommends a limit of 50 mg per litre. Poorly treated drinking water can cause many health problems, especially for children. [Editor’s note: The WHO recently noted an increase in cases of children with diarrhea in Gaza].

Assi has gone into debt to finance his research despite the fact he has received grants for this work (from the observers.france24.com Aug. 24, 2015 posting),

In order to transition from the prototype to a practical application, I need more financial support. I would like to create a model of a smaller version that could be put into people’s homes in Gaza. In order to develop this, all I need is about $20,000.

That said, in order to really resolve the drinking water crisis across Gaza, we would need to build a desalination plant that uses this technique. That would be expensive — about $300,000 million – and there would always be the fear that the plant would be bombed, like with the power plant.

We have attempted to discuss our ideas with officials in both Gaza and Ramallah but, for the time being, we have received no response. We hope for support both from Palestinian institutions and from the international community.

There doesn’t yet seem to be a website or Facebook page or other means of contacting and/or lending other kinds of support to Assi. Hopefully, he will have something soon.

In a February 24, 2014 posting, I featured a nanotechnology laboratory in Oman where they were studying and working to develop desalination technologies. (I noticed that Assi received a grant for his work from the  Middle East Desalination Research Center in Oman.)

Slingshot; a movie about a water purification system

Thanks to David Bruggeman of the Pasco Phronesis blog for his Aug. 2, 2015 posting about Slingshot, which is both a water purification system and a documentary about Dean Kamen, inventor, and his system.  From the Slingshot (movie) About page,

SlingShot focuses on Segway inventor Dean Kamen, his fascinating life, and his work to solve the world’s water crisis.

Iconoclast, Kamen, is a modern hero. His inventions, mostly medical devices, help people in need and ease suffering. Several documentaries have been produced about the world’s dire water challenges. SlingShot is a film about an indomitable man who just might have enough passion, will, and innovative thinking to create a solution for a crisis that affects billions.

A quirky genius with a sharp wit and a provocative worldview, Kamen is our era’s Thomas Edison. He takes on the world’s grand challenges one invention at a time. Best known for his Segway Human Transporter, Kamen has reconceived kidney dialysis, engineered an electric wheelchair that can travel up stairs (the iBot), reworked the heart stent, built portable insulin pumps, founded FIRST robotics to inspire young students, and on and on. Holder of over 440 U.S. and foreign patents, Kamen devotes himself to dreaming up products that improve people’s lives. For the last 15 years, he has relentlessly pursued an effective way to clean up the world’s water supply.

Fifty percent of all human illness is the result of water borne pathogens. Dean Kamen has invented an energy efficient vapor compression distiller that can turn any unfit source of water (seawater, poisoned well water, river sludge, etc.) into potable, safe water without any need for chemical additives or filters. Kamen has nicknamed his device the SlingShot as in the David and Goliath story. In Kamen’s imagining, undeveloped countries are filled with little Davids, and just like the biblical slingshot and stone, the SlingShot device is the tiny piece of technology that is going to take down the gigantic Goliath of bad water.

David lists upcoming US screenings of the documentary and speculates as to a possible market for the system in the US. From David’s Aug. 2, 2015 posting,

It’s worth noting that while Kamen’s target markets for the Slingshot device are in the developing world, the drought in the Western United States may generate additional demand for the Slingshot.  The water conservation tips on the film’s website are worth following, and perhaps some enterprising (or desperate) local government may try to address its water troubles through judicious use of technology like the Slingshot.

You can check the Slingshot documentary Upcoming webpage for US and international screenings, as well as, a list of screenings stretching back to March 2014. Should you wish to host a screening, there’s the Host a Screening webpage.

Unfortunately, I was not able to find any technical details, additional to those on the About page, regarding Kamen’s vapor compression distiller (Slingshot).

Sealing graphene’s defects to make a better filtration device

Making a graphene filter that allows water to pass through while screening out salt and/or noxious materials has been more challenging than one might think. According to a May 7, 2015 news item on Nanowerk, graphene filters can be ‘leaky’,

For faster, longer-lasting water filters, some scientists are looking to graphene –thin, strong sheets of carbon — to serve as ultrathin membranes, filtering out contaminants to quickly purify high volumes of water.

Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak.

Now engineers at MIT [Massachusetts Institute of Technology], Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair these leaks, filling cracks and plugging holes using a combination of chemical deposition and polymerization techniques. The team then used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through.

A May 8, 2015 MIT news release (also on EurkeAlert), which originated the news item, expands on the theme,

Combining these two techniques, the researchers were able to engineer a relatively large defect-free graphene membrane — about the size of a penny. The membrane’s size is significant: To be exploited as a filtration membrane, graphene would have to be manufactured at a scale of centimeters, or larger.

In experiments, the researchers pumped water through a graphene membrane treated with both defect-sealing and pore-producing processes, and found that water flowed through at rates comparable to current desalination membranes. The graphene was able to filter out most large-molecule contaminants, such as magnesium sulfate and dextran.

Rohit Karnik, an associate professor of mechanical engineering at MIT, says the group’s results, published in the journal Nano Letters, represent the first success in plugging graphene’s leaks.

“We’ve been able to seal defects, at least on the lab scale, to realize molecular filtration across a macroscopic area of graphene, which has not been possible before,” Karnik says. “If we have better process control, maybe in the future we don’t even need defect sealing. But I think it’s very unlikely that we’ll ever have perfect graphene — there will always be some need to control leakages. These two [techniques] are examples which enable filtration.”

Sean O’Hern, a former graduate research assistant at MIT, is the paper’s first author. Other contributors include MIT graduate student Doojoon Jang, former graduate student Suman Bose, and Professor Jing Kong.

A delicate transfer

“The current types of membranes that can produce freshwater from saltwater are fairly thick, on the order of 200 nanometers,” O’Hern says. “The benefit of a graphene membrane is, instead of being hundreds of nanometers thick, we’re on the order of three angstroms — 600 times thinner than existing membranes. This enables you to have a higher flow rate over the same area.”

O’Hern and Karnik have been investigating graphene’s potential as a filtration membrane for the past several years. In 2009, the group began fabricating membranes from graphene grown on copper — a metal that supports the growth of graphene across relatively large areas. However, copper is impermeable, requiring the group to transfer the graphene to a porous substrate following fabrication.

However, O’Hern noticed that this transfer process would create tears in graphene. What’s more, he observed intrinsic defects created during the growth process, resulting perhaps from impurities in the original material.

Plugging graphene’s leaks

To plug graphene’s leaks, the team came up with a technique to first tackle the smaller intrinsic defects, then the larger transfer-induced defects. For the intrinsic defects, the researchers used a process called “atomic layer deposition,” placing the graphene membrane in a vacuum chamber, then pulsing in a hafnium-containing chemical that does not normally interact with graphene. However, if the chemical comes in contact with a small opening in graphene, it will tend to stick to that opening, attracted by the area’s higher surface energy.

The team applied several rounds of atomic layer deposition, finding that the deposited hafnium oxide successfully filled in graphene’s nanometer-scale intrinsic defects. However, O’Hern realized that using the same process to fill in much larger holes and tears — on the order of hundreds of nanometers — would require too much time.

Instead, he and his colleagues came up with a second technique to fill in larger defects, using a process called “interfacial polymerization” that is often employed in membrane synthesis. After they filled in graphene’s intrinsic defects, the researchers submerged the membrane at the interface of two solutions: a water bath and an organic solvent that, like oil, does not mix with water.

In the two solutions, the researchers dissolved two different molecules that can react to form nylon. Once O’Hern placed the graphene membrane at the interface of the two solutions, he observed that nylon plugs formed only in tears and holes — regions where the two molecules could come in contact because of tears in the otherwise impermeable graphene — effectively sealing the remaining defects.

Using a technique they developed last year, the researchers then etched tiny, uniform holes in graphene — small enough to let water molecules through, but not larger contaminants. In experiments, the group tested the membrane with water containing several different molecules, including salt, and found that the membrane rejected up to 90 percent of larger molecules. However, it let salt through at a faster rate than water.

The preliminary tests suggest that graphene may be a viable alternative to existing filtration membranes, although Karnik says techniques to seal its defects and control its permeability will need further improvements.

“Water desalination and nanofiltration are big applications where, if things work out and this technology withstands the different demands of real-world tests, it would have a large impact,” Karnik says. “But one could also imagine applications for fine chemical- or biological-sample processing, where these membranes could be useful. And this is the first report of a centimeter-scale graphene membrane that does any kind of molecular filtration. That’s exciting.”

De-en Jiang, an assistant professor of chemistry at the University of California at Riverside, sees the defect-sealing technique as “a great advance toward making graphene filtration a reality.”

“The two-step technique is very smart: sealing the defects while preserving the desired pores for filtration,” says Jiang, who did not contribute to the research. “This would make the scale-up much easier. One can produce a large graphene membrane first, not worrying about the defects, which can be sealed later.”

I have featured graphene and water desalination work before  from these researchers at MIT in a Feb. 27, 2014 posting. Interestingly, there was no mention of problems with defects in the news release highlighting this previous work.

Here’s a link to and a citation for the latest paper,

Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene by Sean C. O’Hern, Doojoon Jang, Suman Bose, Juan-Carlos Idrobo, Yi Song §, Tahar Laoui, Jing Kong, and Rohit Karnik. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.5b00456 Publication Date (Web): April 27, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Egypt steps it up nanowise with a Center for Nanotechnology

Dec. 16, 2014 Egypt’s Prime Minister Ibrahim Mahlab along with other ministers and Dr. Ahmed Zewail, Chairman of the board of Zewail City of Science and Technology (this seems to be a campus with a university and a number of research institutes), announced Egypt’s Center for Nanotechnology (from a Zewail City of Science and Technology Dec. 16, 2014 press release),

The Center, funded by the National Bank of Egypt, cost over $ 100 Million and is, till this moment, the biggest research Center Egypt has seen. This center is hailed as a turning point in the development of scientific research in Egypt as it will allow researchers to develop nanoparticles and nanostructured applications that will improve, even revolutionize, many technology and industry sectors including: information technology, energy, environmental science, medicine, and food safety among many others.

During the visit, Dr. Zewail gave Mahlab and the Cabinet members a brief introduction about the City’s constituents, achievements, and how it is going to improve Egypt’s economic development.

Impressed by the magnitude of Zewail City, Mahalab expressed his excitement about the effect this project is going to have on the future of scientific research in Egypt.

Following the opening ceremony, they all moved to the construction site of the soon-to-be Zewail City new premises, in Hadayk October, to evaluate the progress of the construction process. This construction work is the result of the presidential decree issued on April 9, 2014 to allocate 200 acres for Zewail City in 6th of October City. The construction work is expected to be done by the end of 2015, and will approximately cost $ 1.5 billion.

The end of 2015 is a very ambitious goal for completion of this center but these projects can sometimes inspire people to extraordinary efforts and there seems to be quite a bit of excitement about this one if the video is any indication. From a Dec. 22, 2014 posting by Makula Dunbar, which features a CCTV Africa clip, on AFKInsider,

I was interested to learn from the clip that Egypt’s new constitution mandates at least 1% of the GDP (gross domestic product) must be earmarked for scientific research.

As for Ahmed Zewail, in addition to being Chairman of the board of Zewail City of Science and Technology, he is also a professor at the California Institute of Technology (CalTech). From his CalTech biography page (Note: A link has been removed),

Ahmed Zewail is the Linus Pauling Chair professor of chemistry and professor of physics at the California Institute of Technology (Caltech). For ten years, he served as the Director of the National Science Foundation’s Laboratory for Molecular Sciences (LMS), and is currently the Director of the Moore Foundation’s Center for Physical Biology at Caltech.

On April 27, 2009, President Barack Obama appointed him to the President’s Council of Advisors on Science and Technology, and in November of the same year, he was named the First United States Science Envoy to the Middle East.

The CalTech bio page is a bit modest, Zewail’s Wikipedia entry gives a better sense of this researcher’s eminence (Note: Links have been removed),

Ahmed Hassan Zewail (Arabic: أحمد حسن زويل‎, IPA: [ˈæħmæd ˈħæsæn zeˈweːl]; born February 26, 1946) is an Egyptian- American scientist, known as the “father of femtochemistry”, he won the 1999 Nobel Prize in Chemistry for his work on femtochemistry and became the first Egyptian scientist to win a Nobel Prize in a scientific field. …

If you watched the video, you may have heard a reference to ‘other universities’. The comment comes into better focus after reading about the dispute between Nile University and Zewail City (from the Wikipedia entry),

Nile University has been fighting with Zewail City of Science and Technology, established by Nobel laureate Ahmed Zewail, for more than two years over a piece of land that both universities claim to be their own.

A March 22, 2014 ruling turned down challenges to a verdict issued in April 2013 submitted by Zewail City. The court also ruled in favour of the return of Nile University students to the contested buildings.

In a statement released by Nile University’s Student Union before Saturday’s decision, the students stated that the verdict would test the current government’s respect to the judiciary and its rulings.

Zewail City, meanwhile, stressed in a statement released on Saturday that the recent verdict rules on an urgent level; the substantive level of the case is yet to be ruled on. Sherif Fouad, Zewail City’s spokesman and media adviser, said the verdict “adds nothing new.” It is impossible for Zewail City to implement Saturday’s verdict and take Nile University students into the buildings currently occupied by Zewail City students, he said.

If I understand things rightly, the government has pushed forward with this Zewail City initiative (Center for Nanotechnology) while the ‘City’ is still in a dispute over students and buildings with Nile University. This should make for some interesting dynamics (tension) for students, instructors, and administrators of both the institutions and may not result in those dearly hoped for scientific advances that the government is promoting. Hopefully, the institutions will resolve their conflict in the interest of promoting good research.

Gold nanoparticles as catalysts for clear water and hydrogen production

The research was published online May 2014 and in a July 2014 print version,  which seems a long time ago now but there’s a renewed interest in attracting attention for this work. A Dec. 17, 2014 news item on phys.org describes this proposed water purification technology from Singapore’s A*STAR (Agency for Science Technology and Research), Note: Links have been removed,

A new catalyst could have dramatic environmental benefits if it can live up to its potential, suggests research from Singapore. A*STAR researchers have produced a catalyst with gold-nanoparticle antennas that can improve water quality in daylight and also generate hydrogen as a green energy source.

This water purification technology was developed by He-Kuan Luo, Andy Hor and colleagues from the A*STAR Institute of Materials Research and Engineering (IMRE). “Any innovative and benign technology that can remove or destroy organic pollutants from water under ambient conditions is highly welcome,” explains Hor, who is executive director of the IMRE and also affiliated with the National University of Singapore.

A Dec. 17, 2014 A*STAR research highlight, which originated the news item, describes the photocatalytic process the research team developed and tested,

Photocatalytic materials harness sunlight to create electrical charges, which provide the energy needed to drive chemical reactions in molecules attached to the catalyst’s surface. In addition to decomposing harmful molecules in water, photocatalysts are used to split water into its components of oxygen and hydrogen; hydrogen can then be employed as a green energy source.

Hor and his team set out to improve an existing catalyst. Oxygen-based compounds such as strontium titanate (SrTiO3) look promising, as they are robust and stable materials and are suitable for use in water. One of the team’s innovations was to enhance its catalytic activity by adding small quantities of the metal lanthanum, which provides additional usable electrical charges.

Catalysts also need to capture a sufficient amount of sunlight to catalyze chemical reactions. So to enable the photocatalyst to harvest more light, the scientists attached gold nanoparticles to the lanthanum-doped SrTiO3 microspheres (see image). These gold nanoparticles are enriched with electrons and hence act as antennas, concentrating light to accelerate the catalytic reaction.

The porous structure of the microspheres results in a large surface area, as it provides more binding space for organic molecules to dock to. A single gram of the material has a surface area of about 100 square meters. “The large surface area plays a critical role in achieving a good photocatalytic activity,” comments Luo.

To demonstrate the efficiency of these catalysts, the researchers studied how they decomposed the dye rhodamine B in water. Within four hours of exposure to visible light 92 per cent of the dye was gone, which is much faster than conventional catalysts that lack gold nanoparticles.

These microparticles can also be used for water splitting, says Luo. The team showed that the microparticles with gold nanoparticles performed better in water-splitting experiments than those without, further highlighting the versatility and effectiveness of these microspheres.

The researchers have provided an illustration of the process,

Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water. © 2014 A*STAR Institute of Materials Research and Engineering

Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water.
© 2014 A*STAR Institute of Materials Research and Engineering

Here’s a link to and a citation for the research paper,

Novel Au/La-SrTiO3 microspheres: Superimposed Effect of Gold Nanoparticles and Lanthanum Doping in Photocatalysis by Guannan Wang, Pei Wang, Dr. He-Kuan Luo, and Prof. T. S. Andy Hor. Chemistry – An Asian Journal Volume 9, Issue 7, pages 1854–1859, July 2014. Article first published online: 9 MAY 2014 DOI: 10.1002/asia.201402007

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

Earth Day, Water Day, and every day

I’m blaming my confusion on the American Chemical Society (ACS) which seemed to be celebrating Earth Day on April 15, 2014 as per its news release highlighting their “Chemists Celebrate Earth Day” video series  while in Vancouver, Canada, we’re celebrating it on April 26, 2014 and elsewhere it seems to be on April 20, this year. Regardless, here’s more about how chemist’s are celebrating from the ACS news release,

Water is arguably the most important resource on the planet. In celebration of Earth Day, the American Chemical Society (ACS) is showcasing three scientists whose research keeps water safe, clean and available for future generations. Geared toward elementary and middle school students, the “Chemists Celebrate Earth Day” series highlights the important work that chemists and chemical engineers do every day. The videos are available at http://bit.ly/CCED2014.

The series focuses on the following subjects:

  • Transforming Tech Toys– Featuring Aydogan Ozcan, Ph.D., of UCLA: Ozcan takes everyday gadgets and turns them into powerful mobile laboratories. He’s made a cell phone into a blood analyzer and a bacteria detector, and now he’s built a device that turns a cell phone into a water tester. It can detect very harmful mercury even at very low levels.
  • All About Droughts – Featuring Collins Balcombe of the U.S. Bureau of Reclamation: Balcombe’s job is to keep your drinking water safe and to find new ways to re-use the water that we flush away everyday so that it doesn’t go to waste, especially in areas that don’t get much rain.
  • Cleaning Up Our Water – Featuring Anne Morrissey, Ph.D., of Dublin City University: We all take medicines, but did you know that sometimes the medicine doesn’t stay in our bodies? It’s up to Anne Morrissey to figure out how to get potentially harmful pharmaceuticals out of the water supply, and she’s doing it using one of the most plentiful things on the planet: sunlight.

Sadly, I missed marking World Water Day which according to a March 21, 2014 news release I received was being celebrated on Saturday, March 22, 2014 with worldwide events and the release of a new UN report,

World Water Day: UN Stresses Water and Energy Issues 

Tokyo Leads Public Celebrations Around the World

Tokyo — March 21 — The deep-rooted relationships between water and energy were highlighted today during main global celebrations in Tokyo marking the United Nations’ annual World Water Day.

“Water and energy are among the world’s most pre-eminent challenges. This year’s focus of World Water Day brings these issues to the attention of the world,” said Michel Jarraud, Secretary-General of the World Meteorological Organization and Chair of UN-Water, which coordinates World Water Day and freshwater-related efforts UN system-wide.

The UN predicts that by 2030 the global population will need 35% more food, 40% more water and 50% more energy. Already today 768 million people lack access to improved water sources, 2.5 billion people have no improved sanitation and 1.3 billion people cannot access electricity.

“These issues need urgent attention – both now and in the post-2015 development discussions. The situation is unacceptable. It is often the same people who lack access to water and sanitation who also lack access to energy, ” said Mr. Jarraud.

The 2014 World Water Development Report (WWDR) – a UN-Water flagship report, produced and coordinated by the World Water Assessment Programme, which is hosted and led by UNESCO – is released on World Water Day as an authoritative status report on global freshwater resources. It highlights the need for policies and regulatory frameworks that recognize and integrate approaches to water and energy priorities.

WWDR, a triennial report from 2003 to 2012, this year becomes an annual edition, responding to the international community’s expression of interest in a concise, evidence-based and yearly publication with a specific thematic focus and recommendations.

WWDR 2014 underlines how water-related issues and choices impact energy and vice versa. For example: drought diminishes energy production, while lack of access to electricity limits irrigation possibilities.

The report notes that roughly 75% of all industrial water withdrawals are used for energy production. Tariffs also illustrate this interdependence: if water is subsidized to sell below cost (as is often the case), energy producers – major water consumers – are less likely to conserve it.  Energy subsidies, in turn, drive up water usage.

The report stresses the imperative of coordinating political governance and ensuring that water and energy prices reflect real costs and environmental impacts.

“Energy and water are at the top of the global development agenda,” said the Rector of United Nations University, David Malone, this year’s coordinator of World Water Day on behalf of UN-Water together with the United Nations Industrial Development Organization (UNIDO).

“Significant policy gaps exist in this nexus at present, and the UN plays an instrumental role in providing evidence and policy-relevant guidance. Through this day, we seek to inform decision-makers, stakeholders and practitioners about the interlinkages, potential synergies and trade-offs, and highlight the need for appropriate responses and regulatory frameworks that account for both water and energy priorities. From UNU’s perspective, it is essential that we stimulate more debate and interactive dialogue around possible solutions to our energy and water challenges.”

UNIDO Director-General LI Yong, emphasized the importance of water and energy for inclusive and sustainable industrial development.

“There is a strong call today for integrating the economic dimension, and the role of industry and manufacturing in particular, into the global post-2015 development priorities. Experience shows that environmentally sound interventions in manufacturing industries can be highly effective and can significantly reduce environmental degradation. I am convinced that inclusive and sustainable industrial development will be a key driver for the successful integration of the economic, social and environmental dimensions,” said Mr. LI.

Rather unusually, Michael Bergerrecently published two Nanowerk Spotlight articles about water (is there theme, anyone?) within 24 hours of each other. In his March 26, 2014 Spotlight article, Michael Berger focuses on graphene and water remediation (Note: Links have been removed),

The unique properties of nanomaterials are beneficial in applications to remove pollutants from the environment. The extremely small size of nanomaterial particles creates a large surface area in relation to their volume, which makes them highly reactive, compared to non-nano forms of the same materials.

The potential impact areas for nanotechnology in water applications are divided into three categories: treatment and remediation; sensing and detection: and pollution prevention (read more: “Nanotechnology and water treatment”).

Silver, iron, gold, titanium oxides and iron oxides are some of the commonly used nanoscale metals and metal oxides cited by the researchers that can be used in environmental remediation (read more: “Overview of nanomaterials for cleaning up the environment”).

A more recent entrant into this nanomaterial arsenal is graphene. Individual graphene sheets and their functionalized derivatives have been used to remove metal ions and organic pollutants from water. These graphene-based nanomaterials show quite high adsorption performance as adsorbents. However they also cause additional cost because the removal of these adsorbent materials after usage is difficult and there is the risk of secondary environmental pollution unless the nanomaterials are collected completely after usage.

One solution to this problem would be the assembly of individual sheets into three-dimensional (3D) macroscopic structures which would preserve the unique properties of individual graphene sheets, and offer easy collecting and recycling after water remediation.

The March 27, 2014 Nanowerk Spotlight article was written by someone at Alberta’s (Canada) Ingenuity Lab and focuses on their ‘nanobiological’ approach to water remediation (Note: Links have been removed),

At Ingenuity Lab in Edmonton, Alberta, Dr. Carlo Montemagno and a team of world-class researchers have been investigating plausible solutions to existing water purification challenges. They are building on Dr. Montemagno’s earlier patented discoveries by using a naturally-existing water channel protein as the functional unit in water purification membranes [4].

Aquaporins are water-transport proteins that play an important osmoregulation role in living organisms [5]. These proteins boast exceptionally high water permeability (~ 1010 water molecules/s), high selectivity for pure water molecules, and a low energy cost, which make aquaporin-embedded membrane well suited as an alternative to conventional RO membranes.

Unlike synthetic polymeric membranes, which are driven by the high pressure-induced diffusion of water through size selective pores, this technology utilizes the biological osmosis mechanism to control the flow of water in cellular systems at low energy. In nature, the direction of osmotic water flow is determined by the osmotic pressure difference between compartments, i.e. water flows toward higher osmotic pressure compartment (salty solution or contaminated water). This direction can however be reversed by applying a pressure to the salty solution (i.e., RO).

The principle of RO is based on the semipermeable characteristics of the separating membrane, which allows the transport of only water molecules depending on the direction of osmotic gradient. Therefore, as envisioned in the recent publication (“Recent Progress in Advanced Nanobiological Materials for Energy and Environmental Applications”), the core of Ingenuity Lab’s approach is to control the direction of water flow through aquaporin channels with a minimum level of pressure and to use aquaporin-embedded biomimetic membranes as an alternative to conventional RO membranes.

Here’s a link to and a citation for Montemagno’s and his colleague’s paper,

Recent Progress in Advanced Nanobiological Materials for Energy and Environmental Applications by Hyo-Jick Choi and Carlo D. Montemagno. Materials 2013, 6(12), 5821-5856; doi:10.3390/ma6125821

This paper is open access.

Returning to where I started, here’s a water video featuring graphene from the ACS celebration of Earth Day 2014,

Happy Earth Day!

Water desalination by graphene and water purification by sapwood

I have two items about water. The first concerns a new technique from MIT (Massachusetts Institute of Technology) for desalination using graphene and sapwood, respectively*. From a Feb. 25, 2014 news release by David Chandler on EurekAlert,

Researchers have devised a way of making tiny holes of controllable size in sheets of graphene, a development that could lead to ultrathin filters for improved desalination or water purification.

The team of researchers at MIT, Oak Ridge National Laboratory, and in Saudi Arabia succeeded in creating subnanoscale pores in a sheet of the one-atom-thick material, which is one of the strongest materials known. …

The concept of using graphene, perforated by nanoscale pores, as a filter in desalination has been proposed and analyzed by other MIT researchers. The new work, led by graduate student Sean O’Hern and associate professor of mechanical engineering Rohit Karnik, is the first step toward actual production of such a graphene filter.

Making these minuscule holes in graphene — a hexagonal array of carbon atoms, like atomic-scale chicken wire — occurs in a two-stage process. First, the graphene is bombarded with gallium ions, which disrupt the carbon bonds. Then, the graphene is etched with an oxidizing solution that reacts strongly with the disrupted bonds — producing a hole at each spot where the gallium ions struck. By controlling how long the graphene sheet is left in the oxidizing solution, the MIT researchers can control the average size of the pores.

A big limitation in existing nanofiltration and reverse-osmosis desalination plants, which use filters to separate salt from seawater, is their low permeability: Water flows very slowly through them. The graphene filters, being much thinner, yet very strong, can sustain a much higher flow. “We’ve developed the first membrane that consists of a high density of subnanometer-scale pores in an atomically thin, single sheet of graphene,” O’Hern says.

For efficient desalination, a membrane must demonstrate “a high rejection rate of salt, yet a high flow rate of water,” he adds. One way of doing that is decreasing the membrane’s thickness, but this quickly renders conventional polymer-based membranes too weak to sustain the water pressure, or too ineffective at rejecting salt, he explains.

With graphene membranes, it becomes simply a matter of controlling the size of the pores, making them “larger than water molecules, but smaller than everything else,” O’Hern says — whether salt, impurities, or particular kinds of biochemical molecules.

The permeability of such graphene filters, according to computer simulations, could be 50 times greater than that of conventional membranes, as demonstrated earlier by a team of MIT researchers led by graduate student David Cohen-Tanugi of the Department of Materials Science and Engineering. But producing such filters with controlled pore sizes has remained a challenge. The new work, O’Hern says, demonstrates a method for actually producing such material with dense concentrations of nanometer-scale holes over large areas.

“We bombard the graphene with gallium ions at high energy,” O’Hern says. “That creates defects in the graphene structure, and these defects are more chemically reactive.” When the material is bathed in a reactive oxidant solution, the oxidant “preferentially attacks the defects,” and etches away many holes of roughly similar size. O’Hern and his co-authors were able to produce a membrane with 5 trillion pores per square centimeter, well suited to use for filtration. “To better understand how small and dense these graphene pores are, if our graphene membrane were to be magnified about a million times, the pores would be less than 1 millimeter in size, spaced about 4 millimeters apart, and span over 38 square miles, an area roughly half the size of Boston,” O’Hern says.

With this technique, the researchers were able to control the filtration properties of a single, centimeter-sized sheet of graphene: Without etching, no salt flowed through the defects formed by gallium ions. With just a little etching, the membranes started allowing positive salt ions to flow through. With further etching, the membranes allowed both positive and negative salt ions to flow through, but blocked the flow of larger organic molecules. With even more etching, the pores were large enough to allow everything to go through.

Scaling up the process to produce useful sheets of the permeable graphene, while maintaining control over the pore sizes, will require further research, O’Hern says.

Karnik says that such membranes, depending on their pore size, could find various applications. Desalination and nanofiltration may be the most demanding, since the membranes required for these plants would be very large. But for other purposes, such as selective filtration of molecules — for example, removal of unreacted reagents from DNA — even the very small filters produced so far might be useful.

“For biofiltration, size or cost are not as critical,” Karnik says. “For those applications, the current scale is suitable.”

Dexter Johnson in a Feb. 26,2014 posting provides some context for and insight into the work (from the Nanoclast blog on the IEEE [Institute of Electrical and Electronics Engineers]), Note: Links have been removed,

About 18 months ago, I wrote about an MIT project in which computer models demonstrated that graphene could act as a filter in the desalination of water through the reverse osmosis (RO) method. RO is slightly less energy intensive than the predominantly used multi-stage-flash process. The hope was that the nanopores of the graphene material would make the RO method even less energy intensive than current versions by making it easier to push the water through the filter membrane.

The models were promising, but other researchers in the field said at the time it was going to be a long road to translate a computer model to a real product.

It would seem that the MIT researchers agreed it was worth the effort and accepted the challenge to go from computer model to a real device as they announced this week that they had developed a method for creating selective pores in graphene that make it suitable for water desalination.

Here’s a link to and a citation for the paper,

Selective Ionic Transport through Tunable Subnanometer Pores in Single-Layer Graphene Membranes by Sean C. O’Hern, Michael S. H. Boutilier, Juan-Carlos Idrobo, Yi Song, Jing Kong, Tahar Laoui, Muataz Atieh, and Rohit Karnik. Nano Lett., Article ASAP DOI: 10.1021/nl404118f Publication Date (Web): February 3, 2014

Copyright © 2014 American Chemical Society

This article is behind a paywall.

The second item is also from MIT and concerns a low-tech means of purifying water. From a Feb. 27, 2014 news item on Azonano,

If you’ve run out of drinking water during a lakeside camping trip, there’s a simple solution: Break off a branch from the nearest pine tree, peel away the bark, and slowly pour lake water through the stick. The improvised filter should trap any bacteria, producing fresh, uncontaminated water.

In fact, an MIT team has discovered that this low-tech filtration system can produce up to four liters of drinking water a day — enough to quench the thirst of a typical person.

In a paper published this week in the journal PLoS ONE, the researchers demonstrate that a small piece of sapwood can filter out more than 99 percent of the bacteria E. coli from water. They say the size of the pores in sapwood — which contains xylem tissue evolved to transport sap up the length of a tree — also allows water through while blocking most types of bacteria.

Co-author Rohit Karnik, an associate professor of mechanical engineering at MIT, says sapwood is a promising, low-cost, and efficient material for water filtration, particularly for rural communities where more advanced filtration systems are not readily accessible.

“Today’s filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily,” Karnik says. “The idea here is that we don’t need to fabricate a membrane, because it’s easily available. You can just take a piece of wood and make a filter out of it.”

The Feb. 26, 2014 news release on EurekAlert, which originated the news item, describes current filtration techniques and the advantages associated with this new low-tech approach,

There are a number of water-purification technologies on the market today, although many come with drawbacks: Systems that rely on chlorine treatment work well at large scales, but are expensive. Boiling water to remove contaminants requires a great deal of fuel to heat the water. Membrane-based filters, while able to remove microbes, are expensive, require a pump, and can become easily clogged.

Sapwood may offer a low-cost, small-scale alternative. The wood is comprised of xylem, porous tissue that conducts sap from a tree’s roots to its crown through a system of vessels and pores. Each vessel wall is pockmarked with tiny pores called pit membranes, through which sap can essentially hopscotch, flowing from one vessel to another as it feeds structures along a tree’s length. The pores also limit cavitation, a process by which air bubbles can grow and spread in xylem, eventually killing a tree. The xylem’s tiny pores can trap bubbles, preventing them from spreading in the wood.

“Plants have had to figure out how to filter out bubbles but allow easy flow of sap,” Karnik observes. “It’s the same problem with water filtration where we want to filter out microbes but maintain a high flow rate. So it’s a nice coincidence that the problems are similar.”

The news release also describes the experimental procedure the scientists followed (from the news release),

To study sapwood’s water-filtering potential, the researchers collected branches of white pine and stripped off the outer bark. They cut small sections of sapwood measuring about an inch long and half an inch wide, and mounted each in plastic tubing, sealed with epoxy and secured with clamps.

Before experimenting with contaminated water, the group used water mixed with red ink particles ranging from 70 to 500 nanometers in size. After all the liquid passed through, the researchers sliced the sapwood in half lengthwise, and observed that much of the red dye was contained within the very top layers of the wood, while the filtrate, or filtered water, was clear. This experiment showed that sapwood is naturally able to filter out particles bigger than about 70 nanometers.

However, in another experiment, the team found that sapwood was unable to separate out 20-nanometer particles from water, suggesting that there is a limit to the size of particles coniferous sapwood can filter.

Finally, the team flowed inactivated, E. coli-contaminated water through the wood filter. When they examined the xylem under a fluorescent microscope, they saw that bacteria had accumulated around pit membranes in the first few millimeters of the wood. Counting the bacterial cells in the filtered water, the researchers found that the sapwood was able to filter out more than 99 percent of E. coli from water.

Karnik says sapwood likely can filter most types of bacteria, the smallest of which measure about 200 nanometers. However, the filter probably cannot trap most viruses, which are much smaller in size.

The researchers have future plans (from the news release),

Karnik says his group now plans to evaluate the filtering potential of other types of sapwood. In general, flowering trees have smaller pores than coniferous trees, suggesting that they may be able to filter out even smaller particles. However, vessels in flowering trees tend to be much longer, which may be less practical for designing a compact water filter.

Designers interested in using sapwood as a filtering material will also have to find ways to keep the wood damp, or to dry it while retaining the xylem function. In other experiments with dried sapwood, Karnik found that water either did not flow through well, or flowed through cracks, but did not filter out contaminants.

“There’s huge variation between plants,” Karnik says. “There could be much better plants out there that are suitable for this process. Ideally, a filter would be a thin slice of wood you could use for a few days, then throw it away and replace at almost no cost. It’s orders of magnitude cheaper than the high-end membranes on the market today.”

Here’s a link to and a citation for the paper,

Water Filtration Using Plant Xylem by Michael S. H. Boutilier, Jongho Lee, Valerie Chambers, Varsha Venkatesh, & Rohit Karnik. PLOS One Published: February 26, 2014 DOI: 10.1371/journal.pone.0089934

This paper is open access.

One final observation, two of the researchers (Michael S. H. Boutilier & Rohit Karnik) listed as authors on the graphene/water desalination paper are also listed on the low-tech sapwood paper solution.*

* The first sentence of the this post originally stated both items were graphene-related, it has been changed to say 1… using graphene and sapwood, respectively*’ on May 8, 2015.

The last sentence of this post was changed from

‘One final observation, two of the researchers listed as authors on the graphene/water desalination paper are also listed on the low-tech sapwood paper (Michael S. H. Boutilier & Rohit Karnik).’

to this

‘One final observation, two of the researchers (Michael S. H. Boutilier & Rohit Karnik) listed as authors on the graphene/water desalination paper are also listed on the low-tech sapwood paper solution.*’ for clarity on May 8, 2015.