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Graphene membrane set to create better water filters and fuel cells
FEATURE/RESEARCH TRENDS
Graphene membrane set to create better water filters and fuel cells An atomically thin membrane with microscopically small holes may prove to be the basis for future hydrogen fuel cells, water filters and desalination membranes, according to a group of theorists and experimentalists, including three theoretical researchers from Pennsylvania State University. The team, led by Franz Geiger of Northwestern University, tested the possibility of using graphene, robust single atomic layer carbon, as a separation membrane in water, and found that naturally occurring defects – essentially a few missing carbon atoms – allowed hydrogen protons to cross the barrier at unprecedented speeds. Whilst many researchers strive to make graphene defect-free to exploit its superior electronic properties, Geiger’s team found that graphene required the vacancies to create water channels through the membrane. Computer simulations carried out at Pennsylvania State University and the University of Minnesota showed the protons were shuttled across the barrier via hydroxylterminated atomic defects, that is, by oxygen hydrogen groups linked at the defect.
Energy barrier ‘Our simulations and experiments showed that you need to have at least four carbon vacancies and some sort of channel to overcome the energy barrier that would normally prevent the protons from crossing to the other side,’ explained Adri van Duin, Associate Professor, Mechanical and Nuclear Engineering, Pennsylvania State University, who used reactive force-field calculations to do dynamical, atomistic scale simulations of the process. ‘If we can learn how to engineer the defects and the defect size, we could make an effective separation membrane. Although it still requires a lot of design work, clearly this looks highly attractive for many applications, including desalination.’
This figure shows the proton-transfer channel across a quad-defect in graphene, as obtained from a ReaxFF (“reactive force field”) molecular dynamics simulation (image courtesy Muralikrishna Raju, Pennsylvania State University).
RESEARCH TRENDS Determination of pore-size distribution and pore fouling
May 2015
of hollow-fibre membranes using Evapoporometry Hollow-fibre(HF) membranes are used in many applications for which characterisation of the pore-size distribution (PSD) is necessary. Current techniques for determining the PSD require relatively expensive dedicated equipment. Moreover, most techniques are
It may also work for a new, less complicated design for fuel cells in the future, Geiger believes. ‘All you need is slightly imperfect single-layer graphene,’ he commented. Contact: Adri C.T. van Duin, Associate Professor, Department of Mechanical and Nuclear Engineering, 136 Research East Building, Pennsylvania State University, University Park, PA 16802, USA. Tel: +1 814 863 6277, Email: [email protected]
The researchers published their results in a paper entitled ‘Aqueous proton transfer across single-layer graphene’, which appears in the journal Nature Communications (6, article number: 6539, doi:10.1038/ ncomms7539). Pennsylvania State University co-authors are former Ph.D. student Muralikrishna Raju, now a post-doc at Stanford; post-doc Weiwei Zhang and Adri van Duin. Other co-authors include Oak Ridge National Laboratory’s Raymond Unocic, Robert Sacci, Ivan Vlassiouk, Pasquale Fulvio, Panchapakesan Ganesh, David Wesolowski and Sheng Dai; Northwestern University’s Jennifer Achtyl and Franz Geiger; and University of Virginia’s Lijun Xu, Yu Cai and Matthew Neurock (all three now at the University of Minnesota).
not applicable to the characterisation of fouled membranes. Evapoporometry (EP) – a recently developed characterisation technique – is based on vapour-pressure depression that can detect the full spectrum of pore sizes in ultrafiltration (UF) membranes. In prior studies, EP was used to determine the PSD of only flat-sheet membranes, using just isopropyl alcohol (IPA) as the volatile wetting
Membrane Technology
9
Graphene membrane set to create better water filters and fuel cells An atomically thin membrane with microscopically small holes may prove to be the basis for future hydrogen fuel cells, water filters and desalination membranes, according to a group of theorists and experimentalists, including three theoretical researchers from Pennsylvania State University. The team, led by Franz Geiger of Northwestern University, tested the possibility of using graphene, robust single atomic layer carbon, as a separation membrane in water, and found that naturally occurring defects – essentially a few missing carbon atoms – allowed hydrogen protons to cross the barrier at unprecedented speeds. Whilst many researchers strive to make graphene defect-free to exploit its superior electronic properties, Geiger’s team found that graphene required the vacancies to create water channels through the membrane. Computer simulations carried out at Pennsylvania State University and the University of Minnesota showed the protons were shuttled across the barrier via hydroxylterminated atomic defects, that is, by oxygen hydrogen groups linked at the defect.
Energy barrier ‘Our simulations and experiments showed that you need to have at least four carbon vacancies and some sort of channel to overcome the energy barrier that would normally prevent the protons from crossing to the other side,’ explained Adri van Duin, Associate Professor, Mechanical and Nuclear Engineering, Pennsylvania State University, who used reactive force-field calculations to do dynamical, atomistic scale simulations of the process. ‘If we can learn how to engineer the defects and the defect size, we could make an effective separation membrane. Although it still requires a lot of design work, clearly this looks highly attractive for many applications, including desalination.’
This figure shows the proton-transfer channel across a quad-defect in graphene, as obtained from a ReaxFF (“reactive force field”) molecular dynamics simulation (image courtesy Muralikrishna Raju, Pennsylvania State University).
RESEARCH TRENDS Determination of pore-size distribution and pore fouling
May 2015
of hollow-fibre membranes using Evapoporometry Hollow-fibre(HF) membranes are used in many applications for which characterisation of the pore-size distribution (PSD) is necessary. Current techniques for determining the PSD require relatively expensive dedicated equipment. Moreover, most techniques are
It may also work for a new, less complicated design for fuel cells in the future, Geiger believes. ‘All you need is slightly imperfect single-layer graphene,’ he commented. Contact: Adri C.T. van Duin, Associate Professor, Department of Mechanical and Nuclear Engineering, 136 Research East Building, Pennsylvania State University, University Park, PA 16802, USA. Tel: +1 814 863 6277, Email: [email protected]
The researchers published their results in a paper entitled ‘Aqueous proton transfer across single-layer graphene’, which appears in the journal Nature Communications (6, article number: 6539, doi:10.1038/ ncomms7539). Pennsylvania State University co-authors are former Ph.D. student Muralikrishna Raju, now a post-doc at Stanford; post-doc Weiwei Zhang and Adri van Duin. Other co-authors include Oak Ridge National Laboratory’s Raymond Unocic, Robert Sacci, Ivan Vlassiouk, Pasquale Fulvio, Panchapakesan Ganesh, David Wesolowski and Sheng Dai; Northwestern University’s Jennifer Achtyl and Franz Geiger; and University of Virginia’s Lijun Xu, Yu Cai and Matthew Neurock (all three now at the University of Minnesota).
not applicable to the characterisation of fouled membranes. Evapoporometry (EP) – a recently developed characterisation technique – is based on vapour-pressure depression that can detect the full spectrum of pore sizes in ultrafiltration (UF) membranes. In prior studies, EP was used to determine the PSD of only flat-sheet membranes, using just isopropyl alcohol (IPA) as the volatile wetting
Membrane Technology
9