Resource World Magazine

J U N E / J U L Y 2 0 1 7 www.resourceworld.com 67 GREEN TECHNOLOGIES water and pump it back to shore. Graphene is a candidate for desalination because it acts like a big sponge sitting on the water's surface, drawing water up through it and cleaning it in the process. Graphene-oxide mem- branes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts without affecting the flow of water too much. Until now, however, these membranes couldn't be used for sieving common salts used in desalina- tion technologies, which require even smaller sieves. Previous research at Manchester University found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membranes along with water, but larger ions or molecules are blocked. The Manchester-based group has further developed these graphene membranes and found a strategy to avoid the membrane swelling. The pore size in the membrane is precisely controlled, which can sieve common salts out of salty water and make it safe to drink. Professor Rahul Nair, at Manchester University said, "Realization of scalable membranes with uniform pore size, down to atomic scale is a significant step forward and will open new pos- sibilities for improving the efficiency of desalination technology. This is the first clear-cut experiment in this regime." In a News and Views article accompanying a study in Nature Nanotechnology, Ram Devanathan, from the Pacific Northwest National Laboratory in Richland, WA, said more work must be done to produce gra- phene oxide membranes inexpensively to an industrial scale. He added that scientists also want to demonstrate the durability of the membranes under prolonged contact with seawater and ensure the membrane is resistant to "fouling" by salts and biolog- ical material (which requires existing barriers to be periodically cleaned or replaced). "The selective separation of water molecules from ions by physical restriction of interlayer spacing opens the door to the synthesis of inexpensive membranes for desalination," wrote Dr. Devanathan. "The ultimate goal is to create a filtration device that will produce potable water from seawater or wastewa- ter with minimal energy input." Scientists hope that graphene-oxide membrane systems can be built on a smaller scale, making this technology accessible to countries that do not have the financial infrastructure to fund large plants without compromising the yield of fresh water produced. IRON GENERATES CLEAN ELECTRICITY Scientists at Montreal's McGill University sent an experiment to use iron as an electricity source onboard a European Space Agency research rocket in April 2017. Every few years, the European Space Agency allows researchers to test their experi- ments in space. The agency ranked the McGill experiment No.1 out of 100 submissions, said Andrew Higgins, a professor in the Mechanical Engineering Department, where the team has been studying the idea for five or six years. The rocket, MAXUS 9, was launched from a site north of the Arctic Circle, and travelled up 700 km, twice the height of the International Space Station, to test how burning iron can be used (and reused) to generate electricity without generating green- house gases. The unmanned research rocket travelled outside the atmosphere for 12 to 14 minutes, and data from the capsule was retrieved when the capsule parachuted back to Earth in northern Sweden. Iron was the primary candidate for this purpose because mil- lions of tons of iron powders are already produced annually for the metallurgy, chemical and electronic industries. And, iron is readily recyclable with well-established technologies. Some novel techniques avoid producing the carbon dioxide emissions associ- ated with traditional iron production using coal. The new technique put forward by the McGill team takes advantage of an important property of metal powders: when burned, they react with air to form stable, nontoxic solid-oxide products that can be collected relatively easily for recycling, unlike the CO 2 emissions from burning fossil fuels that escape into the atmosphere. When iron powder burns, it releases more heat than the equivalent volume of gasoline and the exhaust from this combustion, iron oxide, also known as rust, is environmentally benign. The rust is easily collected and recycled back into iron using a renewable energy source. Iron is in many ways a more practical energy carrier than chemical batteries or hydrogen, says the team. But to understand the fundamentals of how metals burn, they wanted to go to the unique environment of weightlessness because in the on-ground laboratory, the metal powders settle too quickly, and the hot com- bustion products rise and disrupt the experiments. The McGill experiment successfully dispersed iron powder in microgravity. They expect results analysis to take some weeks. "It turns out that iron and combustible fuels like this store 10 times the amount of energy that an equivalent battery does," Higgins said. The experiment helps researchers understand whether metal powders, like iron, can be used as a clean energy source in the future, for example, to power generators or to replace batteries in cars, Higgins speculated. n

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