When it comes to science and technology fields, nanotech has always been something of a misunderstood outsider. While telecoms and the social Web are equivalent to Hollywood blockbusters, nanotechnology has been the arthouse independent: ahead of its time, but considered a little too complicated for the mainstream to pay much attention to. If ever there was a contender for an IT world sleeper hit, however, nanotechnology would be it, because for all its seeming complexity, it really can change the world as we know it.
To get an idea of the scale researchers are working on, imagine taking one millimetre and slicing it up into a million equal pieces. Now you've entered the realm of nanometres (nm), where atoms and molecules can be individually manipulated to create materials with powerful new capabilities. A nanoparticle is considered any piece of material smaller than 100 nanometres. To put things into perspective, a single human hair is about 80 000nm thick.
At this infinitesimal scale, materials start acting differently. Breaking them up into such tiny pieces means the surface area is multiplied by a factor of millions, making them far more reactive. They display unique properties they may not possess in bulk form, such as becoming stronger or more conductive. Solids like gold, for example, turn into liquids at room temperature while silver takes on anti-bacterial properties, and is now used in everything from Band-aids to hospital gowns.
This undetected ability to make amazing things possible is a quality shared by the country's scientists, who are quietly developing world-class applications on home soil. With this in mind, the National Research Foundation recently held a tour, in partnership with the Nanotechnology Public Engagement Initiative and the South African Agency for Science and Technology Advancement, to demonstrate some of the cutting-edge work going on in SA's nanotech labs.
Inside the National Centre for Nanostructure Materials, situated at the Council for Scientific and Industrial Research (CSIR) in Pretoria, researchers are working on solutions to some of the country's most pressing problems, including energy supply, water quality and healthcare. The Department of Science and Technology has allocated more than R120 million to nanotechnology R&D in the current financial year, identifying it as a significant player in meeting SA's five grand challenges.
Bundles of energy
With the demand for energy expected to increase by more than 50% by 2025, one of the hot topics in nanotech research is finding new ways to capture, store and transfer energy. As an example, the CSIR's Dr Gerald Malgas demonstrated some of the thin film solar cells they've developed for use in smaller applications, which could be produced more affordably than the silicon type dominating the market.
Widely used crystalline silicon PV cells are created by sawing thin wafers off a chunk of silicon and sandwiching them between plates of glass. They boast higher efficiency rates (about half to two-thirds the theoretical maximum), but require expensive material and manufacturing techniques. The less popular thin film PV cells are made by depositing layers of semiconductor material on a substrate like glass or stainless steel, and while they have lower efficiencies, they're cheaper to make.
Thin film cells based on organic materials can't compete with their conventional cousins at efficiency level, but they do offer far more flexibility, and can be printed on a variety of materials. The idea is to eventually use roll-to-roll technologies to mass produce goods integrated with solar panels, such as rooftops, toys, consumer devices and books.
Malgas points to a collection of organic thin film cells, the now-mottled slides having served as test cases in order to make improvements. One sample, a thin piece of material that looks like an overhead transparency, seems satisfyingly flexible, but Malgas says it's only 50% transmittant, providing less energy bang for your buck.
Ultimately, these types of cells could be used in smaller devices such as phones or tablets, or even in clothing items that warm up by themselves. But there's still a way to go before self-heating jackets make their debut, says Malgas. “Perhaps in the next 10 to 20 years.”
Even if we improve the efficiency by 10%, if they're not stable you can't sell them commercially.
Dr Gerald Malgas, CSIR
Shelf-life is another bugbear. “The big problem with organic solar cells is that they degrade in sunlight like ordinary plastic, so we have to optimise and encapsulate them in something,” says Malgas. “Even if we improve the efficiency by 10%, if they're not stable you can't sell them commercially.” The cells currently have an efficiency of around 1%, while silicon's is up to 24%.
Malgas doesn't seem too worried about their lacklustre performance, however. “We're not trying to compete with silicon because the applications we want to use these cells for are different.”
Another area receiving great attention is that of printed electronics, whereby various nano-based inks are printed onto flat surfaces. A team at the University of Cape Town's NanoSciences Innovation Centre has managed to develop techniques for printing silicon semiconductors on any material, including fabrics and paper, using conventional printing methods.
While this could be used to print solar cells, UCT professors David Britton and Margit Harting are commercialising what they consider one of the technology's most promising applications: temperature sensors. As Britton explains, electronic temperature sensors are usually small devices that can only measure temperature at a specific point. The ability to print nanoparticle-based inks on any substrate, however, means a 'sensor sheet' can be printed onto surfaces like freight containers or even fridges to measure the average temperature over a large volume.
Once one starts delving into the myriad ways nanotechnology can be harnessed, the possibilities seem endless. Ntombizodwa Mathe, for example, is a candidate researcher looking at using platinum nanoparticles as a catalyst in hydrogen fuel cells, an area in which governments and companies have invested major resources.
“Fuel cells are coming up as an important topic in the alternative energy space,” notes Mathe.
Platinum group metals (PGMs) are widely used as a catalysts in hydrogen fuel cells, and SA, with 75% of the world's known PGM reserves, hopes to capitalise on this emerging industry. The country has adopted a 15-year R&D and innovation strategy around the development of hydrogen technologies, with one of the main goals being to capture 25% of the global demand for PGM in hydrogen energy technologies.
As an energy carrier, hydrogen emits no harmful greenhouse gas emissions at the point of use, and is even cleaner if carrying energy generated via renewables. Its only by-product is water. Given these promising attributes, scientists are now exploring ways to make hydrogen fuel cells more efficient.
One method is replacing regular fuel cell membranes, which allow hydrogen ions to pass through the cell wall and prevent the entry of other atoms or ions, with nanofabricated ones. These would enable hydrogen ions to flow through more easily, allowing for the creation of smaller, lighter, and longer-lasting fuel cells that are less expensive to produce.
Researchers are also looking at using nanoparticles of platinum to enhance its effectiveness and so reduce the amount needed, or combining it with other metals to make for more affordable catalysts. Other options include eliminating the need for platinum altogether by using non-precious metal catalysts that have nanostructured surfaces which equal or surpass the catalytic power of platinum.
Hydrogen fuel cells could also improve or replace the batteries in small electronic devices (no more constant charging) and the lithium-ion batteries currently used in electric vehicles. A team at Stanford University, for example, has found a way to use silicon nanowires to increase the power of conventional batteries used in laptops, cellphones and other devices 10-fold. Researchers at MIT managed similar gains using carbon nanotubes.
Move aside Brita
In a country where an estimated 5.7 million people lack access to basic water services, nanotechnology could have major impacts in providing safe, clean water and preventing disastrous water-related risks in future.
There are multiple ways nanotechnology can help purify water, from using filters to improve water quality, to developing specialised sensors that detect water-borne diseases.
Due to their small size, nano-based filters are capable of removing pathogens such as cholera, and pollutants like toxic heavy metals and organic and inorganic solutes. These microscopic filters and membranes are created from various nanomaterials, such as carbon nanotubes, and are more efficient thanks to their increased surface area, as well as easier to clean.
MSc student Keletso Mphahlele is working on the creation of carbon nanotubes containing iron and silver nanoparticles to destroy bacteria in water supplies. These nanotubes - essentially rolled-up sheets of carbon - boast a substantial surface area, meaning Mphahlele can 'dose' them with various particles which can be activated to soak up and remove water-borne nasties.
“What we like about carbon nanotubes is that the carbon molecule itself, at a nanoscale, exhibits unique properties...which make them attractive for numerous applications, including nanofilters for water purification, super-sensitive sensors for gas sensors, and catalytic support.”
To alleviate the time and cost involved in transporting grimy water elsewhere to remove contaminants, nanocatalysts have been developed as a way of treating water on-site. They contain particles with catalytic properties that can chemically break down pollutants.
“The work I'm doing involves loading certain metals on the nanotubes: iron for its magnetic properties and silver for its anti-bacterial properties. I put them in a composite and use it as a nanofilter,” explains Mphahlele.
Nanomaterials also allow for several clean-up jobs to be done with a single filter. “We are trying to find better ways of purifying our water and trying to target different types of contaminants using just one type of material. Current water purification methods use a lot of different processes, so we're trying to get that down to a single purification process.”
Nanotechnology no doubt has an exciting future ahead, with the ability to revolutionise such a range of industries that it's on the agenda of governments around the world. While many of the potential risks are still being worked out and some applications are still years away from being realised, judging by the trailer the CSIR tour offered, this is one sci-tech indie film everyone should see.
* Look out for the second part of this feature series, which reveals how nanotechnology could enable doctors to directly target cancer cells, and eliminate the need for needles.
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