High-quality graphene foams have been made from the waste gases produced during the high temperature treatment of organic waste. Researchers in China say their pyrolysis-based technique is cheaper and more environmentally friendly than conventional production methods. Graphene foams are porous, 3D versions of the 2D sheet of carbon that is conventional graphene. Like other forms of graphene, they are super strong, have a high electron mobility and are great conductors of heat. The foams have a wide range of potential uses, including in energy storage, environmental purification, chemistry and biosensing.
Chemical vapour deposition is expensive and uses large amounts of hydrogen, methane and other gases – which is why Jiang and colleagues set out to produce graphene using the carbon-rich waste gases from bio-refineries that run off organic waste. These facilities heat biomass to 500 °C or more in the absence of oxygen to produce alternatives to crude oil-based products, such as biofuels. This process, known as pyrolysis, has been used for thousands of years to produce charcoal. The team set up a high-temperature pyrolysis system and produced graphene foams using two different feedstocks: powdered cellulose and powdered lignin – both derived from plants. The powders were pyrolysed at 800 °C and the waste gases filtered to obtain small-molecule gases. These purified gases were then fed into a chemical vapour deposition chamber and deposited on nickel foam.
But powdered cellulose and lignin are not the same as biomass waste. To simulate more conventional organic waste, the researchers next fed their system straw and sawdust. The graphene foams produced showed minor drops in quality compared with those from cellulose and lignin. The researchers say, however, that all the foams they made exhibit uniform structures and excellent performance in environmental or energy-storage applications. As well as graphene foams, Jiang’s process also produces bio-oil. The team say that making a high-value product like graphene alongside such biofuels could make improve the economic viability of biomass pyrolysis and support its wider commercialization.
Source: Physics World
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