“By 2025 the UN expects that 14% of the world’s population will encounter water scarcity.”
Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved.
New research demonstrates the real-world potential of providing clean drinking water for millions of people who struggle to access adequate clean water sources.
The new findings from a group of scientists at The University of Manchester were published today in the journal Nature Nanotechnology. Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.
Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts. Until now, however, they couldn’t be used for sieving common salts used in desalination technologies, which require even smaller sieves.
Previous research at The University of Manchester found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked.
The Manchester-based group have now further developed these graphene membranes and found a strategy to avoid the swelling of the membrane when exposed to water. The pore size in the membrane can be precisely controlled which can sieve common salts out of salty water and make it safe to drink.
As the effects of climate change continue to reduce modern city’s water supplies, wealthy modern countries are also investing in desalination technologies. Following the severe floods in California major wealthy cities are also looking increasingly to alternative water solutions.
When the common salts are dissolved in water, they always form a ‘shell’ of water molecules around the salts molecules. This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing along with the water. Water molecules are able to pass through the membrane barrier and flow anomalously fast which is ideal for application of these membranes for desalination.
Professor Rahul Nair, at The University of Manchester said: “Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology.
“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”
Mr. Jijo Abraham and Dr. Vasu Siddeswara Kalangi were the joint-lead authors on the research paper: “The developed membranes are not only useful for desalination, but the atomic scale tunability of the pore size also opens new opportunity to fabricate membranes with on-demand filtration capable of filtering out ions according to their sizes.” said Mr. Abraham.
By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. This technology has the potential to revolutionize water filtration across the world, in particular in countries which cannot afford large scale desalination plants.
It is hoped that graphene-oxide membrane systems can be built on smaller scales making this technology accessible to countries which do not have the financial infrastructure to fund large plants without compromising the yield of fresh water produced.
More information: Tunable sieving of ions using graphene oxide membranes, Nature Nanotechnology, nature.com/articles/doi:10.1038/nnano.2017.21
|Harvesting heat produced by a car’s engine which would otherwise be wasted and using it to recharge the car’s batteries or powering the air-conditioning system could be a significant feature in the next generation of hybrid cars.|
Prof Ian Kinloch, Professor of Materials Science The average car currently loses around 70% of energy generated through fuel consumption to heat. Utilising that lost energy requires a thermoelectric material which can generate an electrical current from the application of heat.
Thermoelectric materials convert heat to electricity or vice-versa, such as with refrigerators. The challenge with these devices is to use a material that is a good conductor of electricity but also dissipates heat well.
Currently, materials which exhibit these properties are often toxic and operate at very high temperatures – higher than that produced by car engines. By adding graphene, a new generation of composite materials could reduce carbon emissions globally from car use.
|Scientists from The University of Manchester working with European Thermodynamics Ltd have increased the potential for low cost thermoelectric materials to be used more widely in the automotive industry.|
|The team, led by Prof Ian Kinloch, Prof Robert Freer and Yue Lin, added a small amount of graphene to strontium titanium oxide.|
|The resulting composite was able to convert heat which would otherwise be lost as waste into an electric current over a broad temperature range, going down to room temperature.|
|Prof Freer said: “Current oxide thermoelectric materials are limited by their operating temperatures which can be around 700 degrees Celsius. This has been a problem which has hampered efforts to improve efficiency by utilising heat energy waste for some time.|
|“Our findings show that by introducing a small amount of graphene to the base material can reduce the thermal operating window to room temperature which offers a huge range of potential for applications.|
|“The new material will convert 3-5% of the heat into electricity. That is not much but, given that the average vehicle loses roughly 70% of the energy supplied to it by its fuel to waste heat and friction, recovering even a small percentage of this with thermoelectric technology would be worthwhile.”|
|The findings were published in the journal ACS Applied Materials and Interfaces (“hermoelectric power generation from lanthanum strontium titanium oxide at room temperature through the addition of graphene”). Graphene’s range of superlative properties and small size causes the transfer of heat through the material to slow leading to the desired lower operating temperatures.|
|Improving fuel efficiency, whilst retaining performance, has long been a driving force for car manufacturers. Graphene could also aid fuel economy and safety when used as a composite material in the chassis or bodywork to reduce weight compared to traditional materials used.|
|Source: University of Manchester|
Scientists have moved graphene—the incredibly strong and conductive single-atom-thick sheet of carbon—a significant step along the path from lab bench novelty to commercially viable material for new electronic applications.
Researchers from the University of Manchester, together with BGT Materials Limited, a graphene manufacturer in the United Kingdom, have printed a radio frequency antenna using compressed graphene ink. The antenna performed well enough to make it practical for use in radio-frequency identification (RFID) tags and wireless sensors, the researchers said. Even better, the antenna is flexible, environmentally friendly and could be cheaply mass-produced. The researchers present their results in the journal Applied Physics Letters, from AIP Publishing.
The study demonstrates that printable graphene is now ready for commercial use in low-cost radio frequency applications, said Zhirun Hu, a researcher in the School of Electrical and Electronic Engineering at the University of Manchester.
“The point is that graphene is no longer just a scientific wonder. It will bring many new applications to our daily life very soon,” added Kostya S. Novoselov, from the School of Physics and Astronomy at the University of Manchester, who coordinated the project.
Graphene Gets Inked
Since graphene was first isolated and tested in 2004, researchers have striven to make practical use of its amazing electrical and mechanical properties. One of the first commercial products manufactured from graphene was conductive ink, which can be used to print circuits and other electronic components.
Graphene ink is generally low cost and mechanically flexible, advantages it has over other types of conductive ink, such as solutions made from metal nanoparticles.
To make the ink, graphene flakes are mixed with a solvent, and sometimes a binder like ethyl cellulose is added to help the ink stick. Graphene ink with binders usually conducts electricity better than binder-free ink, but only after the binder material, which is an insulator, is broken down in a high-heat process called annealing. Annealing, however, limits the surfaces onto which graphene ink can be printed because the high temperatures destroy materials like paper or plastic.
The University of Manchester research team, together with BGT Materials Limited, found a way to increase the conductivity of graphene ink without resorting to a binder. They accomplished this by first printing and drying the ink, and then compressing it with a roller, similar to the way new pavement is compressed with a road roller.
Compressing the ink increased its conductivity by more than 50 times, and the resulting “graphene laminate” was also almost two times more conductive than previous graphene ink made with a binder.
The high conductivity of the compressed ink, which enabled efficient radio frequency radiation, was one of the most exciting aspects of the experiment, Hu said.
Paving the Way to Antennas, Wireless Sensors, and More
The researchers tested their compressed graphene laminate by printing a graphene antenna onto a piece of paper. The antenna measured approximately 14 centimeters long, and 3.5 millimeter across and radiated radio frequency power effectively, said Xianjun Huang, who is the first author of the paper and a PhD candidate in the Microwave and Communcations Group in the School of Electrical and Electronic Engineering.
Printing electronics onto cheap, flexible materials like paper and plastic could mean that wireless technology, like RFID tags that currently transmit identifying info on everything from cattle to car parts, could become even more ubiquitous.
Most commercial RFID tags are made from metals like aluminium and copper, Huang said, expensive materials with complicated fabrication processes that increase the cost.
“Graphene based RFID tags can significantly reduce the cost thanks to a much simpler process and lower material cost,” Huang said. The University of Manchester and BGT Materials Limited team has plans to further develop graphene enabled RFID tags, as well as sensors and wearable electronics.
SOURCE: American Institute of Physics