This page contains a Flash digital edition of a book.
| FEATURES & INNOVATIONS |


“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”


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.


1µm


Porous nanoparticles can remove toxic heavy metals from contaminated water to trace amounts within seconds.


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 1 ppb. Each pore is 10–20 nanometers wide and packed with compounds, known as amines that stick to the metals. By 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 oppor- tunities 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


As the nanofibers form, they trap crude oil in a tangled net that floats above the water. 14 A*STAR RESEARCH


technologies for real-world applications, it will not be long before nanoscience treats the Earth for its many maladies.


ISSUE 5 | OCTOBER – DECEMBER 2016


© 2016 A*STAR Institute of Bioengineering and Nanotechnology


© 2016 A*STAR Institute for High Performance Computing


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52