Nano News: 07/01/15

Bio-inspired catalyst paves the way to gas-to-liquid technologies

A new bio-inspired zeolite catalyst, developed by an international team with researchers from Technische Universität München (TUM), Eindhoven University of Technology and University of Amsterdam, might pave the way to small scale 'gas-to-liquid' technologies converting natural gas to fuels and starting materials for the chemical industry. Investigating the mechanism of the selective oxidation of methane to methanol they identified a copper-oxo-cluster as the active center inside the zeolite micropores.

The zeolite structure with the Cu3O3-cluster as the active center (Cu: turquoise, O: red). (Image: Guanna Li and Evgeny Pidko / TUe) In an era of depleting mineral oil resources natural gas is becoming ever more relevant, even though the gas is difficult to transport and not easily integrated in the existing industrial infrastructure. One of the solutions for this is to apply 'gas-to-liquid' technologies. These convert methane, the principal component of natural gas, to so-called synthesis gas from which subsequently methanol and hydrocarbons are produced. These liquids are then shipped to chemical plants or fuel companies all over the world. This approach, however, today is only feasible at very large scales. Currently there is no 'gas-to-liquid' chemistry available for the economical processing of methane from smaller sources at remote locations. This has spawned many research efforts regarding the chemistry of methane conversion. Of all the conceptually promising smaller scale processes for the direct conversion of methane, the partial oxidation to methanol seems the most viable since it allows for lower operating temperatures, making it more inherently safe and more energy efficient. Bio-inspired catalyst A research team combining the expertise of Moniek Tromp (UvA/HIMS), Evgeny Pidko and Emiel Hensen (Eindhoven University of Technology), Maricruz Sanches-Sanches (Technische Universität München) as well as Johannes Lercher (Technische Universität München and Pacific Northwest National Laboratory) is currently focusing on a bio-inspired method enabling such partial methane oxidation. At the focus of the team is a modified zeolite, a highly structured porous material, developed at Lercher’s research group in Munich. This copper-exchanged zeolite with mordenite structure mimicks the reactivity of an enzyme known to efficiently and selectively oxidize methane to methanol. In their actual publication in ("Single-site trinuclear copper oxygen clusters in mordenite for selective conversion of methane to methanol") the researchers provide an unprecedented and detailed molecular insight in the way the zeolite mimics the active site of the enzyme methane monooxygenase (MMO). Highly selective The researchers show that the micropores of the zeolite provide a perfect confined environment for the highly selective stabilization of an intermediate copper-containing trimer molecule. This result follows from the combination of kinetic studies in Munich, advanced spectroscopic analysis in Amsterdam and theoretical modeling in Eindhoven. Trinuclear copper-oxo clusters were identified that exhibit a high reactivity towards activation of carbon–hydrogen bonds in methane and its subsequent transformation to methanol. “The developed zeolite is one of the few examples of a catalyst with well-defined active sites evenly distributed in the zeolite framework – a truly single-site heterogeneous catalyst,” says Professor Johannes Lercher. “This allows for much higher efficiencies in conversion of methane to methanol than with zeolite catalysts previously reported.” Furthermore, the research showed the unequivocal linking of the structure of the active sites with their catalytic activity. This renders the zeolite a "more than promising" material in achieving levels of catalytic activity and selectivity comparable to enzymatic systems.

New graphene supercapacitor structure inspired by the intricate design of leaves

There was a time during the early development of portable electronics when the biggest hurdle to overcome was making the device small enough to be considered portable. After the invention of the microprocessor in the early 1970s, miniature, portable electronics have become commonplace and ever since the next challenge has been finding an equally small and reliable power source. Chemical batteries store a lot of energy but require a long period of time for that energy to charge and discharge plus have a limited lifespan. Capacitors charge quickly but cannot store enough charge to work for long enough to be practical. One possible solution is something called a solid-state micro-supercapacitor (MSC). Supercapacitors are armed with the power of a battery and can also sustain that power for a prolonged period time. Researchers have attempted to create MSCs in the past using various hybrids of metals and polymers but none were suitable for practical use. In more recent trials using graphene and carbon nanotubes to make MSCs, the results were similarly lackluster. An international team of researchers led by Young Hee Lee, including scientists from the Center for Integrated Nanostructure Physics at the Institute for Basic Science (IBS) and Department of Energy Science at Sungkyunkwan University in South Korea, has devised a new technique for creating an MSC that doesn’t have the shortcomings of previous attempts but instead delivers high electrochemical performance (" Leaf Vein-Inspired Nanochanneled Graphene Film for Highly Efficient Micro-Supercapacitors").

Inspired by natural vein-textured leaves, a 2D nanochanneled graphene film with high packing density and efficient ion transport pathways is proposed to facilitate high rate capabilities while maintaining high energy density. The 2D nanochannels serve as pathways for efficient ion diffusion parallel to the graphene planes in all-solid-state micro-supercapacitors with interdigitated electrode geometry. When designing something new and complex, sometimes the best inspiration is one already found in nature. The team modeled their MSC film structure on natural vein-textured leaves in order to take advantage of the natural transport pathways which enable efficient ion diffusion parallel to the graphene planes found within them. To create this final, efficient shape, the team layered a graphene-hybrid film with copper hydroxide nanowires. After many alternating layers they achieved the desired thickness, and added an acid solution to dissolve the nanowires so that a thin film with nano-impressions was all that remained. To fabricate the MSCs the film was applied to a plastic layer with thin, ∼5µm long parallel gold strips placed on top. Everything not covered by the gold strips was chemically etched away so that only the gold strips on top of a layer of film were left. Gold contact pads perpendicular to the gold strips were added and a conductive gel filled in the remaining spaces and was allowed to solidify. Once peeled from the plastic layer, the finished MSCs resemble clear tape with gold electrical leads on opposite sides. The team produced stunning test results. In addition to its superior energy density, the film is highly flexible and actually increases capacitance after initial use. The volumetric energy density was 10 times higher than currently available commercial supercapacitors and also far superior to any other recent research. The MSCs are displaying electrical properties about five orders of magnitude higher than similar lithium batteries and are comparable to existing, larger supercapacitors. According to Lee, “To our knowledge, the volumetric energy density and the maximum volumetric power density in our work are the highest values among all carbon-based solid-state MSCs reported to date.” In the future, consumers will likely power their devices with MSCs instead of batteries. Applications for light, reliable energy storage combined with a long lifespan and fast charge/discharge time. The team’s MSCs could be embedded into an electronic circuit chip as power sources for practical applications such as implantable medical devices, active radio frequency identification tags, and micro robots. If engineers utilize the material’s incredible flexibility, these MSCs could be utilized in portable, stretchable, and even wearable electronic devices.

Zooming in on the right molecule

Have a look round your living room. Everything around you is made up of molecules - just as you are. When they are put together, the molecules act as the building blocks of life. Every single building block has a very small effect and we normally relate to the finished things. However, there are scientific disciplines that have specialised in looking down at the individual molecules to understand how they work and especially what happens when something goes wrong with the building blocks. Molecular Pacman Research into individual molecules is about understanding the components and using this as a gateway to learning more about the correlations. In figurative terms, it is like observing cats at night. They all appear to be grey, but we have to recognise their colour individually to distinguish them from each other. Researchers all over the world who work with molecular biology, nanoscience, chemistry and physics are carrying out multidisciplinary work in this area. To a great extent, they make use of a measuring method called single-molecule fluorescence resonance energy transfer (smFRET), which takes measurements of distances between molecules right down to 2-10 nanometres. Molecules are not static, but can move, open and close - something like the Pacman game of the 1980s. Their structure and movement patterns have an impact on how they interact with other molecules, which is why the researchers are interested in being able to describe them. Individual molecules provide new knowledge "If we can visualise and characterise a single molecule and see how it interacts with the other molecules, we can understand what is going on in the individual event. Once we understand the mechanisms behind this, we can begin to work on controlling how the molecules work, so that this takes place at the most advantageous times," says Associate Professor Victoria Birkedal, who carries out research into the understanding of individual molecules at the Interdisciplinary Nanoscience Centre (iNANO), Aarhus University. Easy access to better data Associate Professor Birkedal's research group has developed new software that makes it much easier to obtain rapid and precise data following an smFRET analysis. The group has just published an article about the software in ("iSMS: single-molecule FRET microscopy software"). The software provides easier access to data that would otherwise be time-consuming and laborious to obtain. Only a few specialists have previously been able to process the data. However, the program now makes it accessible to a wide circle of researchers. From dot to structure "We used to do data analyses during the night without really knowing whether they'd provide the answers we wanted. The program is so fast that we now get the results within a few minutes," says Associate Professor Birkedal. The program provides an innovative visual approach to data and enables the researchers to carry out faster and more precise data analyses. Seeing the individual molecules and analysing their behaviour gives graphic support that can be used in all research into individual molecules, but the Aarhus group uses it to look at biological processes in the body. "A molecule is very, very small, but it's no longer just a dot. We can see its structure and how it behaves, and try to understand why it does what it does," says Associate Professor Birkedal. The next step is to control the molecule's structure so as to get it to behave in a particular way - something that can be used in targeted medicine. Democratic software The group has decided to make its software freely available to everyone. "We'd like to democratise access to data," says Associate Professor Birkedal, who is pleased that the software opens up for easier opportunities to work together at a distance. The program has been well received wherever it has been presented.