Tag Archives: filter

SEM

Cheap nano-filter scrubs toxic metals from polluted water

Researchers from the RMIT University and University of New South Wales (UNSW) present a new filter technology that harnesses naturally occurring nanostructures that grow on liquid metals. The team also shows that their new creation can filter both oils and heavy metals from water. The filter works over 100 times faster than current ones.

Filter close-up.

Low- (a,b) and high-resolution (c,d) transmisson electron microscope photos of the filter’s layers.
Image credits Ali Zavabeti et al., 2018, AFM.

Not only is this filter way faster than its currently-available counterparts, but it’s also simple to produce and scale up, meaning that it can be deployed rapidly and en masse in areas or situation that require it.

Quick’n’clean

Water contamination and pollution are a significant threat to public health in many areas of the world today. Roughly 1 in 9 people have no clean water close to their homes, the team writes.

“Heavy metal contamination causes serious health problems and children are particularly vulnerable,” says Dr. Ali Zavabeti, a researcher at RMIT and the paper’s lead author. “Our new nano-filter is sustainable, environmentally-friendly, scalable and low cost.”

The filters rely on a unique internal architecture to perform their job. The team drew on liquid metal chemistry to grow differently shaped nano-structures (either as the atomically thin sheets used for the nano-filter or as nano-fibrous structures) in the process of creating the new filters.

Zavabeti’s team created the alloy by combining gallium-based liquid metals with aluminum. When exposed to water, aluminum oxide moves to the surface of the nano-sheets and start ‘growing’, forming aluminum oxide layers. These layers, which start out 100,000 times thinner than a strand of human hair, end up all wrinkled, making them very porous.

The shapes physically stop pollutants from passing through. Lead and other heavy metals have a very high affinity to aluminum oxide so, as the water passes through billions of layers, each one of these lead ions get attracted to one of these aluminium oxide sheets. Lab testing revealed that the nano-filter could remove lead from water even when concentration passed 13 times safe drinking levels, and was also very effective in separating oil from water.

“We’ve shown it works to remove lead and oil from water but we also know it has potential to target other common contaminants. Previous research has already shown the materials we used are effective in absorbing contaminants like mercury, sulfates and phosphates,” Zavabeti explains.

“With further development and commercial support, this new nano-filter could be a cheap and ultra-fast solution to the problem of dirty water.”

The method Zavabeti’s team developed allows them to grow the material either in nano-sheets or as nano-fibers, each with their own characteristics. The ultra-thin sheets used in the nano-filter experiments have high mechanical stiffness, while the nano-fibers are highly translucent. These two flavors of the material can be mixed to create filters with certain properties for applications in fields such as electronics, membranes, optics, and catalysis.

One particularly exciting trait of the manufacturing process is that it “be readily upscaled, the liquid metal can be reused, and the process requires only short reaction times and low temperatures,” according to Zavabeti, which should keep costs down. The manufacturing process generates no waste, requiring only aluminum and water — the liquid metals are reused for each new batch of nano-sheets.

UNSW Professor Kalantar-zadeh, paper co-author, believes the technology could be put to good use in Africa and Asia in places where heavy metal ions in the water are at levels well beyond safe human consumption.

“If you’ve got bad quality water, you just take a gadget with one of these filters with you,” he said. “You pour the contaminated water in the top of a flask with the aluminium oxide filter. Wait two minutes and the water that passes through the filter is now very clean water, completely drinkable.”

“And the good thing is, this filter is cheap.”

There are portable filtration products available that do remove heavy metals from water, but they are comparatively expensive, often costing more than $100. In contrast, the team’s aluminum oxide filters could be produced for as little as 10 cents a piece.

The paper “Green Synthesis of Low-Dimensional Aluminum Oxide Hydroxide and Oxide Using Liquid Metal Reaction Media: Ultrahigh Flux Membranes” has been published in the journal Advanced Functional Materials.

Alan Turing. Credit: Public Domain.

Alan Turing’s final paper inspires new way to desalinate water

Alan Turing. Credit: Public Domain.

Alan Turing. Credit: Public Domain.

Alan Turing is famous as the father of computer science and artificial intelligence, as well as a WWII code breaker. However, Turing was also heavily involved in what was, at the time, an obscure field of science: mathematical biology. In 1952, just two years before his death, the brilliant British scientist published a paper in which he proposed a mathematical model that finally described how embryonic cells turn into complex structures like organs or bones. Now, Chinese researchers have built a unique nanostructure of tubular strands inspired by Turing’s work in mathematical biology. They’ve incorporated the structure into a filter that removes salt from water three times faster than some conventional filters.

Dot-based and tube-based Turing-type membranes (imaged with electron microcope). Credit: Z. Tan et al./Science

Dot-based and tube-based Turing-type membranes (imaged with electron microcope). Credit: Z. Tan et al./Science

Turing structures arise when imbalances in diffusion rates make a stable steady-state system sensitive to small heterogeneous perturbations. For example, Turing patterns occur in chemical reactions when a fast-moving inhibitor controls the motion of a slower-moving activator. The motion causes the inhibitor to push back the activator, causing a pattern of spots or stripes to appear on the product. It’s not clear whether this reaction-diffusion process does indeed take place at the cellular level, but previously scientists have used it to explain zebra stripes, sand ripples, and the movements of financial markets.

Attempts to synthesize such structures have so far been confined to 2D patterns. Now, thanks to the marvels of 3D printing, a team of researchers at Zhejiang University in Hangzhou, China have created a 3D Turing structure out of a polyamid (a material similar to nylon). The substance is the result of the reaction between piperazine and trimesoyl chloride. In typical conditions, trimesoyl chloride diffuses faster than piperazine but not fast enough to result in a Turing structure. The researchers, led by material scientist Lin Zhang, used a nifty trick: they added polyvinyl alcohol to the piperazine, further lowering its diffusion rate and allowing it to act as the activator to the trimesoyl chloride’s inhibitor.

The resulting material is a rough, porous mesh with a nanostructure resembling a Turing pattern. The Chinese researchers were even able to print two variants: dots and tubes. These are the two types of self-organizing structure predicted by Turing’s model.

The primary objective of the new study was to produce 3D Turing structures. However, the researchers were amazed to learn that membranes fashioned this way were incredibly efficient water filters. Due to the filter’s tubular structure, water can pass through a much larger surface area compared to conventional filters. In experiments, the amount of table-salt inside a slightly saline solution passing through the Turing filter was reduced by half. The Turing filter proved much more efficient with other salts: magnesium chloride was reduced by more than 90%, and magnesium sulfate (aka Epsom salt) was reduced by more than 99%, as reported in the journal  Science.

The membranes may be impractical on their own for desalinating seawater due to the rather low effectiveness for this purpose. Zhang, however, says it could be used to pretreat the seawater before eliminating the rest of the salt via reverse osmosis, which would make the overall process much more efficient. The tubular Turin filter could also be useful for purifying brackish water and industrial wastewater. And perhaps, in the future, the tubular Turing structures could be used to fashion artificial veins or bones. Turing would have been so proud!

Glass of water.

Novel graphene filter removes 99% of organic waste in water

Australian researchers have developed a filter which promises to revolutionize how we treat drinking water.

Glass of water.

Image via Pixabay.

Graphene has been making many appearances in science lately, owing to its unique physical properties. Today, it’s making headlines in a rather unexpected field of research: water treatment. Researchers from the University of New South Wales (UNSW) Sydney, working together with Sydney Water, have created a world-first graphene filter that can remove 99% of the natural, organic matter left behind by conventional treatment of drinking water. The team is now working on scaling up their technology.

Sydney Water caters to the H2O needs of about 4.8 million people throughout Sydney proper, the Illawarra, and the Blue Mountains. One problem they’re facing is that the source of this water (nature) doesn’t do a very good job at keeping the water pure. For that, Sydney Water employs direct filtration plants, but there’s still a problem — during periods of heavy rains, small-particle organic matter contaminants negatively impact the performance of these plants, reducing their overall capacity.

No organics allowed

The most common working principle these plants rely on is the use of chemical coagulants, which fuse all the organic material together into goop that settles on the bottom. High enough concentrations of these contaminants interfere with the chemical reactions that produce said goop, meaning the plants need to reduce output to ensure the water’s purity.

The team, led by Dr. Rakesh Joshi of the UNSW, decided to skip the chemicals altogether and rely on good old-fashioned mechanical methods:

“Our advance is to use filters based on graphene — an extremely thin form of carbon. No other filtration method has come close to removing 99% of natural organic matter from water at low pressure,” said lead researcher Dr Rakesh Joshi.

“Our results indicate that graphene-based membranes could be converted into an alternative new option that could in the future be retrofitted in conventional water treatment plants.”

The filters are produced by converting natural graphite into membranes of graphite oxide. At high pressures, these membranes become selectively permeable, allowing water to flow through, but not contaminants.

Currently, the filters have only been used in a prototype, small-scale form inside laboratory settings. However, given the exciting results they’ve had thus far, the UNSW team plans to upgrade the experimental rig to a small pilot plant for field testing.

While water filters don’t seem like headline news, it all has to be viewed in the context of our present situation. Pollution, especially plastic pollution, has been plaguing our waterways for decades now. We’re pumping out a lot of waste into the waterways around us, and it’s not going away as we hoped or wanted to think. There’s even cocaine in there. In later years, the situation has taken a dramatic turn for the worst. Plastic particles have found their way into the water we drink, and it also bears the industrial legacy of toxic metal contamination.

Better water filters could help stop the goop before it ever enters the waters — and until it’s clean again, they will help keep the goop (and plastic) out of our bodies.

The paper “Application of graphene oxide membranes for removal of natural organic matter from water” has been published in the journal Carbon.

New algorithm can detect depression by Instagram photos

It’s a simple principle which could help improve millions of lives.

Valencia vs Inkwell filters, via The Next Web.

Since time immemorial, color has been associated with emotion. Bright colors are associated with positive emotions, while neutral or darker ones are more likely to carry on negative feelings. This simple concept led Harvard’s Andrew Reece and Chris Danforth to believe that they could investigate if someone was suffering from depression only by looking at their Instagram photos.

They recruited some 500 workers from Amazon’s Mechanical Turk, 170 of which agreed to have their Instagram accounts analyzed. Of these, 70 users were clinically depressed.

Overall, researchers identified 40,000 photos, selecting the most recent 100 photos for each volunteer. For depressed individuals, they chose the 100 photographs posted before their diagnosis. They identified some relevant variables, such as hue, color saturation, contrast and so on, while also subjectively rating the “happiness” of a picture from 0 to 5. They also used a face recognition software to identify how many people there were in the photo.

The thing with Instagram is that it makes it very easy to apply filters in a way that’s representative for your mood, and you can greatly influence the aspect of a photo. Researchers quickly noticed that people suffering from depression preferred the ‘Inkwell’ filter, which converts color photographs to black-­and-­white images. They also favored pictures with more black or blue in them, and showed an overall preference towards darker colors.

Meanwhile, non-depressed volunteers preferred the ‘Valencia,’ a filter that lightens photographs. The detection algorithm isn’t perfect, but overall, it boasted a 70% accuracy, which could at the very least highlight people at risk for depression. The fact that this information can be so easily obtained from Instagram could make a big different for the hundreds of millions of users.

“These findings support the notion that major changes in individual psychology are transmitted in social-media use, and can be identified via computational methods,” say Reece and Danforth.

Dutch designer creates device that turns smog into beautiful jewelry

Dutch designer Daan Roosegaarde created a new air purifier that he hopes will be the answer to today’s smog-choked urban environments. All the particles that the device captures are then made into jewelry.

The Smog Free Tower.
Image credits wikimedia user Bic

Not so long ago a Canadian company started raking in money selling canned air in China. Everyone was talking about it, and it seemed to me that most conversations ended along the lines of “poor people, I wouldn’t want to live somewhere like that.” While China is an especially powerful example because the smog over Beijing is terrifying to behold, things aren’t much better in the US either. Air quality in most cities is just terrible — the American Lung Association estimates that about 4 in 10 of its people live in counties with “unhealthy” levels of ozone or particle pollution. In most cases, conditions are only getting worse.

Dutch designer Daan Roosegaarde decided to do something about it. He created the Smog Free Tower, a 7 meter (23 foot) tall, six-sided air purifier. The tower-like structure is intended to be used in parks and acts like a vacuum, sucking in smog at the top and releasing squeaky-clean air through its vents. The device uses 1,400 watts of energy to clean more than 30,000 cubic meters (roughly 1,060,000 cubic feet) of air per hour. According to Roosegaarde:

“By charging the Smog Free Tower with a small positive current, an electrode will send positive ions into the air. These ions will attach themselves to fine dust particles,” the project’s Kickstarter page states.

“A negatively charged surface – the counter electrode – will then draw the positive ions in, together with the fine dust particles. The fine dust that would normally harm us, is collected together with the ions and stored inside of the tower. This technology manages to capture ultra-fine smog particles which regular filter systems fail to do.”

A simple and very effective method; however, the Tower isn’t just a cleaning device — Roosegaarde designed so that the fine carbon particles trapped by the filters can be pressed into tiny “gem stones,” to be embedded in jewelry. Each of the tiny stones is roughly equivalent to 1,000 cubic meters of purified air.

Image credits Daan Roosegaarde.

Roosegaarde got his funding via Kickstarter and spent three years researching and developing the Tower. The first prototype is currently in Rotterdam, but the designer aims to take his towers to Beijing, Mexico City, Paris, and Los Angeles.

Cleaner air and fancy jewelry from the same device? That’s saving two birds with one tower.

Homes lay in ruins after two dams burst, flooding the small town of Bento Rodrigues in Minas Gerais state, Brazil. Photograph: Felipe Dana/AP

Cheap water filter is fantastically efficient: absorbs heavy toxic metals and can recover gold

Water pollution is a big issue, and so far there isn’t one single system capable of reliably filtering toxic heavy metals. These are either too small, or selectively filter certain metals when polluted water often contains a mix. Researchers at ETH Zurich claim they’ve hit a breakthrough. Using cheap, readily available materials they designed a filter that can retain over 99% concentration of mercury, gold cyanide or toxic potassium, to name a few. It can also absorb radioactive waste and help recycle gold.

Homes lay in ruins after two dams burst, flooding the small town of Bento Rodrigues in Minas Gerais state, Brazil. Photograph: Felipe Dana/AP

Homes lay in ruins after two dams burst, flooding the small town of Bento Rodrigues in Minas Gerais state, Brazil.
Photograph: Felipe Dana/AP

In November, ZME Science reported about one of the worst environmental disaster in history. Then, two dams at a Brazilian iron mine collapsed killing two dozen people, and spewing 60 million cubic meters of mining waste into the Rio Doce and, eventually, the Atlantic Ocean some days later. A quarter million people were deprived of clean, drinking water.

Events such as these serve as a stark warning: environmental disasters have far reaching consequences and should be prevented. When they do happen, however, we should also be prepared. It goes without saying that Brazil wasn’t equipped to handle such a situation, but few governments are.

The contaminated water (coloured water in vials) is drawn through the hybrid membrane by negative pressure; the heavy metal ions (red spheres) bind to the protein fibres in the process. The filtered water is of drinking quality. (Graphics: Bolisetty & Mezzenga, Nature Nanotechnology, 2016)

The contaminated water (coloured water in vials) is drawn through the hybrid membrane by negative pressure; the heavy metal ions (red spheres) bind to the protein fibres in the process. The filtered water is of drinking quality. (Graphics: Bolisetty & Mezzenga, Nature Nanotechnology, 2016)

Mitigating water contamination thus sounds like a priority, and the findings at ETH are most welcomed. Raffaele Mezzenga, Professor of Food and Soft Materials at ETH Zurich, and colleague Sreenath Bolisetty devised a hybrid membrane made out of activated charcoal and tough, rigid whey protein fibres. The whey proteins were first turned into amyloid fibrils, so these could stretch easily. Then both materials were applied on a cellulose filter substrate. The mix consists of 2% whey proteins and 98% activated charcol.

Together, the mix traps heavy metals in a non-specific way, including  lead, mercury, gold and palladium. Moreover, it  absorbs radioactive substances, such as uranium or phosphorus-32 — commonly found in nuclear waste, but also byproducts of cancer treatment. One popular mining technique involves treating mining ore with cyanide to extract precious metals. The ETH filter absorbs cyanide from contaminated water. Gold cyanide compounds are also used in the electronics industry to make conductive tracks on circuits. The industry can use this filter to recover and recycle the gold used in the circuit baths. “The profit generated by the recovered gold is more than 200 times the cost of the hybrid membrane,” says Mezzenga.

The setup is very simple: the hybrid membrane, a collection container and a vacuum pump. “A sufficiently strong vacuum could be produced with a simple hand pump,” says Mezzenga, “which would allow the system to be operated without electricity.”

Gold removed and recovered from polluted water. (Photograph: ETH Zurich/R. Mezzenga/S. Bolisetty)

Gold removed and recovered from polluted water. (Photograph: ETH Zurich/R. Mezzenga/S. Bolisetty)

Mezzenga says that the system is infinitely scalable. A filter the size of a truck should work just as well as one the size of a bottle cap.

Tests so far have been very promising. When mercury chloride was added, the concentration in the filtrate fell by 99.5%; 99.98% for potassium gold cyanide; 99.97% for lead salts; 99.4% for radioactive uranium.

“We achieved these high values in just a single pass,” emphasises Bolisetty, co-author of the invention. But even after multiple passes, the filter still proved useful.  The mercury concentration in the filtrate increased by a factor of 10 from 0.4 ppm (parts per millions) to 4.2 ppm after 10 passes. The filter can easily be replaced.  To filter half a litre of contaminated water, the researchers used a membrane weighing just a 10th of a gram, of which seven percent by weight was made up of protein fibres. “One kilo of whey protein would be enough to purify 90’000 litres of water, more than the amount of water needed in a human life time,” says the ETH professor.

The findings were presented in the journal Nature Nanotechnology.

New sugar polymer can purify water in seconds

Scientists have developed a new polymer that can clean water of tiny impurities and pollutants in a matter of seconds. This could revolutionize the water purification industry, not only saving numerous lives, but saving a lot of money and energy in the process.

A porous material made from cup-shaped cyclodextrins, which rapidly bind pollutants and remove them from contaminated water. © Dichtel Group

The team was led by Will Dichtel from Cornell University in the US.

“What we did is make the first high-surface-area material made of cyclodextrin [sugar molecules bound together in a ring],” said Will Dichtel, associate professor of chemistry, “combining some of the advantages of the activated carbon with the inherent advantages of the cyclodextrin.”

Cyclodextrins are produced from starch and are commonly used in foods, pharmaceutical, drug delivery, and chemical industries, as well as agriculture and environmental engineering. This porous form of cyclodextrin has adsorption rates much higher than traditional filters – up to 200 times more.

“What we did is make the first high-surface-area material made of cyclodextrin combining some of the advantages of the activated carbon with the inherent advantages of the cyclodextrin,” Mr Dichtel said. He also mentioned that the material will be extremely quick in cleaning the water. “These materials will remove pollutants in seconds, as the water flows by,” he said.

Not only is the polymer very fast and efficient, but it’s also cheap and recyclable. While most carbon filters must undergo specific heat-treatment for regeneration, this one can simply be washed at room temperature with methanol or ethanol. Even Dichtel was surprised at how efficient it can be.

“We knew that [water filtering] would be a likely application if we were successful,” Dichtel says. “We were definitely pleasantly surprised with just how good the performance is.”

Journal Reference: Alaaeddin Alsbaiee, Brian J. Smith, Leilei Xiao, Yuhan Ling, Damian E. Helbling & William R. Dichtel – Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer. Nature (2015) doi:10.1038/nature16185

Beakers of solution containing mercury and Rhodamine B dye. (Credit: Jeff Fitlow/Rice University)

“Super sand” is five times more purifying than regular one. Turns toxic water into drinkable water

It’s a bird! It’s a plane! No, it’s super sand! *tadam

Researchers from Rice University have managed to develop a new kind of filtering sand, dubbed “super sand”, which has five times the filtering properties of regular sand. The advancement could provide an indispensable, cost-effective solution for the current water crisis in developing countries where millions of people do not have access to clean water.

Simple bed sands have been used to filter water for thousands of years, its effectiveness in removing contaminants in water being dependent on the texture and the thinness of the sand grains. However, its filtering capabilities are highly limited and can prove to be highly undependable, becoming overloaded fairly quickly.

Using nanotechnology, Rice University scientists coated grains of sand with a nanomaterial called graphite oxide (GO), a product in the chemical exfoliation process of graphite (aka pencil lead) that leads to single-atom sheets known as graphene via subsequent reduction. These nanosheets of carbon can be engineered to have either hydrophobic (water-hating) or hydrophilic (water-loving) properties, and when combined with sand, the coatings adhere to the grains and thus exposure of the hydrophilic parts is ensured.

Beakers of solution containing mercury and Rhodamine B dye. (Credit: Jeff Fitlow/Rice University)

Beakers of solution containing mercury and Rhodamine B dye. (Credit: Jeff Fitlow/Rice University)

To test the effectiveness of super sand, Professor Pulickel Ajayan who lead the team of researchers from Rice, together with collaborators from Australia and Georgia conducted experiments to compare this coated sand with plain sand.

Two experimental models were employed, one containing mercury (at 400 parts per billion) and the other Rhodamine B dye (10 parts per million), each tested on plain and graphite oxide sand. After 10 minutes, plain sand became saturated and stopped filtering the mercury. The nano coated sand went on filtering for well over 50 minutes, and the resulting compound contained less than one part per billion of mercury—within the EPA’s safe rating of two parts per billion—and far below the levels left by regular sand. Results for Rhodamine B dye were similar.

The lab is looking at ways to further functionalize graphite oxide shells to enhance contaminant removal. “By attaching different functional moieties onto graphite oxide, we could engineer some form of a ‘super sand’ to target specific contaminants species, like arsenic, trichloroethylene and others,” said Rice graduate student Wei Gao, primary author of the paper.