The researchers at the University at Buffalo, New York have used a proof-of-concept direct ink writing 3D printing technique and subsequent freeze-drying to prepare graphene-biopolymer aerogels for water treatment.
"The goal is to safely remove contaminants from water without releasing any problematic chemical residue," said study co-author Nirupam Aich, PhD, assistant professor of environmental engineering at the UB School of Engineering and Applied Sciences. "The aerogels we've created hold their structure when put in water treatment systems, and they can be applied in diverse water treatment applications."
The study - 3D printed graphene-biopolymer aerogels for water contaminant removal: a proof of concept – has been published in the Emerging Investigator Series of the journal Environmental Science: Nano.
An aerogel is a light, highly porous solid formed by replacement of liquid in a gel with a gas so that the resulting solid is the same size as the original. Graphene is a nanomaterial formed by elemental carbon and is composed of a single flat sheet of carbon atoms arranged in a repeating hexagonal lattice.
To create the right consistency of the graphene-based ink, the researchers added polydopamine (PDA, a synthetic material similar to the adhesive secretions of mussels), and bovine serum albumin (a protein derived from cows).
In tests, the reconfigured aerogel is said to have removed certain heavy metals, such as lead and chromium, that occur drinking water systems in the US. It also removed organic dyes, such as cationic methylene blue and anionic Evans blue, plus organic solvents like hexane, heptane and toluene.
To demonstrate the aerogel's potential for reuse, the researchers ran organic solvents through it 10 times. Each time, it removed 100 per cent of the solvents. The researchers also reported the aerogel's ability to capture methylene blue decreased by 2-20 per cent after the third cycle.
In a statement, Aich said the aerogels can also be scaled up in size because, unlike nanosheets, aerogels can be printed in larger sizes. This eliminates a previous problem inherent in large-scale production and makes the process available for use in large facilities, such as in wastewater treatment plants, he said. He added the aerogels can be removed from water and reused in other locations, and that they do not leave any kind of residue in the water.
Aich is part of a collaboration between UB and the University of Pittsburgh, led by UB chemistry professor Diana Aga, PhD, to find methods and tools to degrade per- and polyfluoroalkyl substances (PFAS), toxic materials so difficult to break down that they called ‘forever chemicals.’
"We can use these aerogels not only to contain graphene particles but also nanometal particles which can act as catalysts," Aich said. "The future goal is to have nanometal particles embedded in the walls and the surface of these aerogels and they would be able to degrade or destroy not only biological contaminants, but also chemical contaminants."
Aich, plus co-author Chi Zhou, PhD, associate professor of industrial and systems engineering at UB; and lead-author Arvid Masud, PhD, a former student in Aich's lab, hold a pending patent for the graphene aerogel described in the study. Industrial partners are being sought to commercialise this process.