Press release -
Swelling of multi-layered graphene oxide materials studied
Graphite oxide is a multilayer hydrophilic material produced by oxidation of graphite. It is a starting point for preparation of many materials for variety of applications. In his thesis in physics defended at Umeå University, Sweden, Artem Iakunkov includes extensive studies of some fundamental properties of graphite oxides, chemical modification and testing for several important applications.
In his research graphite oxide was used to produce graphene oxide and multilayer graphene oxide membranes, converted into graphene-related porous materials for applications in energy storage devices and made into extremely defect form in order to remove dangerous radioactive pollutants from water.
The main property of graphite oxide and graphene oxide membranes related to filtration properties is swelling. Swelling occurs when material sucks water or alcohols into a space between graphene oxide layers thus expanding its structure and providing subnanometer “channels” for diffusion of water and e.g. sea water salt ions. Scientists hope to use these properties for water desalination by making the size of interlayers sufficiently large for water penetration but too small for diffusion of salts.
“Therefore, we have studied the swelling of graphite oxide in different solvents as well as in solutions observing the change of inter-layer distance” says Artem Iakunkov.
Swelling results in strong expansion of material volume and if the expansion occurs under confined conditions swelling pressure develops. Surprisingly, swelling pressure has never been measured for graphite oxide and graphene oxide membranes. Experiments presented in the thesis report the first measurements of swelling pressures for bulk graphite oxides (up to 220 bar) and graphene oxide membranes (up to 20 bar). Swelling pressure is an important parameter which needs to be taken into account in membrane applications of graphene oxide.
Another surprising finding was that swelling of graphene oxide membranes decreases if samples are stored on air for several months and almost completely disappeared after few years. The sample stored on air for 5 years become impermeable for all studied molecules (e.g. alcohols) except water. Some earlier studies suggested that graphene oxide is metastable with chemical composition changing spontaneously after synthesis. The studies presented in the thesis demonstrate that air ageing of graphene oxide membranes is a chemical process, which starts on the membrane surface and with time propagates to sub-surface layers.
“Graphite oxide is reported to be a promising material for sorption applications. We have designed a new defect-rich graphene oxide with an increased number of small holes on the surface. We have demonstrated that the introduction of new defects can significantly enhance the sorption capacity of radionuclides” says Artem Iakunkov.
Finally, graphite oxide can be converted into reduced graphene oxide and activated graphene. Both materials have shown promising properties for supercapacitor application. A supercapacitor is an energy storage device, which can generate significantly more power compared to standard litium batteries.
“The main drawback of supercapacitors is low energy density. We have investigated correlations between different structural parameters and the energy density of graphene-related supercapacitors. We have varied surface area, pore size distribution, oxygen content, and conductivity in order to find out an optimum set of properties required for the best supercapacitor performance” says Artem Iakunkov.
About the dissertation:
On Friday 17 December Artem Iakunkov, Department of Physics, Umeå University defends his thesis titled Materials prepared using graphite oxides: properties and applications. Swedish title: Material framställda med grafitoxider: egenskaper och tillämpningar. The dissertation takes place at 13.00 in room NAT.D.440, Natural Sciences Building, Umeå University. Dr. Josef Breu, Professor, Chair of Inorganic Chemistry, University of Bayreuth, Germany.
For more information, please contact:
Artem Iakunkov, doctoral student, Department of Physics, Umeå University
Phone: +46 76 796 11 05
Email: artem.iakunkov@umu.se
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Umeå University is one of Sweden’s largest institutions of higher education with over 36,000 students and 4,000 faculty and staff. The university is home to a wide range of high-quality education programmes and world-class research in a number of fields. Umeå University was also where the revolutionary gene-editing tool CRISPR-Cas9 was discovered that has been awarded the Nobel Prize in Chemistry.
At Umeå University, distances are short. The university's unified campus encourages academic meetings, an exchange of ideas and interdisciplinary co-operation, and promotes a dynamic and open culture in which students and staff rejoice in the success of others.
