Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Interlayer distance in graphite oxide gradually changes when water is added

01.07.2014

Physicists from Umeå University and Humboldt University in Berlin have solved a mystery that has puzzled scientists for half a century.

They show with the help of powerful microscopes that the distance between graphite oxide layers gradually increases when water molecules are added. That is because the surface of graphite oxide is not flat, but varies in thickness with "hills" and "valleys" of nanosize. The new findings are published in the scientific journal Nano Letters.


Scanning force microscopy images, which show the relief of a graphene oxide flake. Bright areas are "hills" and dark areas are "valleys". The left image was recorded at low relative humidity, one can say on a dry surface. The right image was recorded at high relative humidity, 65 percent. One can see that new bright spots appear in some regions, which are due to the insertion of water. The overall relief becomes less flat and more curved with more hills while valleys are preserved.

“Now we can better understand the mechanisms of solvent insertion between layers of graphene oxide. It increases our knowledge of the ultrathin membranes and helps to design new types of membranes with permeation properties that can be finely adjusted by adding water and various other solvents,”says Alexandr Talyzin, researcher at the Department of Physics at Umeå University.

Graphite oxide is a unique and useful material, with many unusual properties. It can easily dissolve in water and form single atomic layers of graphene oxide sheets. The super thin flakes can then be arranged in a multilayer membrane with the unique ability to incorporate various solvents between the layers.

... more about:
»Physics »graphene »mechanisms

Already in the 60's such membranes were tested for seawater desalination and filtration applications. Recent studies show that the graphene oxide membranes may also be used to separate liquids and gases. Thin graphene oxide films can separate binary gas mixtures with fairly high efficiency. Even more interesting, the separation characteristics can be finely adjusted by water vapors.

Water molecules easily penetrate between the graphene oxide layers and it has long been known that the distance between the graphene oxide layers depends on the humidity. By simple logic, it means that the distance between the layers is to change in steps corresponding to the size of the water molecules. What has puzzled scientists for half a century is that the distance between the layers, as measured by diffraction methods, is gradually changing proportionally to the humidity change.

“Obviously, we cannot put in quarter molecules or half molecules. So why do we see continuous changes in the distance between the graphene oxide layers? We decided to study the layers of graphene oxide with modern microscopic methods, which strangely enough had not been done before”, says Alexandr Talyzin.

So far the puzzle had been explained with a phenomenon called interstratification - a random stacking of layers with different number of water layers - and what is measured by diffraction data has been an average value related to the different proportions between the number of layers having different degrees of hydration.

The new study conducted by physicists from Humboldt University in Berlin together with Alexandr Talyzin´s research team at Umeå University provides a different explanation. With microscopy of very high resolution, Scanning Force Microscopy, the researchers could measure the absolute distance between two graphene oxide layer and record changes as a function of humidity.

“The distance between two single graphene oxide layers obviously changed gradually again, but the explanation for this effect was revealed as nanometer-sized areas that were not equally filled with water. Of course, the effect of interstratification was excluded in our experiments because we only studied two layers and a single distance”, says Alexandr Talyzin.

The results indicate that picturing graphene oxide as a flat plane is not correct. It is, rather, a relatively thick layer (about two times the thickness of graphene) with a variation of thickness, including "hills" and "valleys" of different size. Adding water molecules increases the thickness of this layer locally, but not necessary by the exact size of the water molecule if some “valleys” are filled first. When all available water adsorption sites (“valleys”) are filled, an additional water layer is added at once. This happens at very high humidity or in liquid water. 

About graphite oxide:

Graphene is a thin film of carbon, only one atom thick. It is a unique adsorptive material because of its extremely large surface. One gram graphene has a surface comparable to a football field. This space would be ideal for adsorption of gases and liquids in applications for gas storage, extraction of impurities from water, and so on, unless the graphene would be hydrophobic, meaning that its surface repels water. Oxidation of graphene results in notable changes of its properties. Graphene oxide is hydrophilic and attracted to water, and is even highly soluble in water. A material consisting of many graphene oxide layers is called graphite oxide. One possible application in the environmental area is purifying contaminated soil and seawater. Graphene oxide functions as a filter that separates all other components in water, except the water molecules.

Original article:

B. Rezania, Nikolai Severin, Alexandr V. Talyzin, and Jürgen P. Rabe: Hydration of Bilayered Graphene Oxide. Nano Letters. DOI: 10.1021/nl5013689
http://pubs.acs.org/doi/abs/10.1021/nl5013689

For more information, please contact:

Alexandr Talyzin, Department of Physics at Umeå University
Telephone: +4690-786 63 20
E-mail: alexandr.talyzin@ physics.umu.se

Alexandr Talyzin | Eurek Alert!

Further reports about: Physics graphene mechanisms

More articles from Physics and Astronomy:

nachricht Spiral arms: not just in galaxies
30.09.2016 | Max-Planck-Institut für Radioastronomie

nachricht Discovery of an Extragalactic Hot Molecular Core
29.09.2016 | National Astronomical Observatory of Japan

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First-Ever 3D Printed Excavator Project Advances Large-Scale Additive Manufacturing R&D

Heavy construction machinery is the focus of Oak Ridge National Laboratory’s latest advance in additive manufacturing research. With industry partners and university students, ORNL researchers are designing and producing the world’s first 3D printed excavator, a prototype that will leverage large-scale AM technologies and explore the feasibility of printing with metal alloys.

Increasing the size and speed of metal-based 3D printing techniques, using low-cost alloys like steel and aluminum, could create new industrial applications...

Im Focus: New welding process joins dissimilar sheets better

Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of light metals.
Scientists at the University of Stuttgart have now developed two new process variants that will considerably expand the areas of application for friction stir welding.
Technologie-Lizenz-Büro (TLB) GmbH supports the University of Stuttgart in patenting and marketing its innovations.

Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of...

Im Focus: First quantum photonic circuit with electrically driven light source

Optical quantum computers can revolutionize computer technology. A team of researchers led by scientists from Münster University and KIT now succeeded in putting a quantum optical experimental set-up onto a chip. In doing so, they have met one of the requirements for making it possible to use photonic circuits for optical quantum computers.

Optical quantum computers are what people are pinning their hopes on for tomorrow’s computer technology – whether for tap-proof data encryption, ultrafast...

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Paper – Panacea Green Infrastructure?

30.09.2016 | Event News

HLF: From an experiment to an establishment

29.09.2016 | Event News

European Health Forum Gastein 2016 kicks off today

28.09.2016 | Event News

 
Latest News

First-Ever 3D Printed Excavator Project Advances Large-Scale Additive Manufacturing R&D

30.09.2016 | Materials Sciences

New Technique for Finding Weakness in Earth’s Crust

30.09.2016 | Earth Sciences

Cells migrate collectively by intermittent bursts of activity

30.09.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>