2014 was a very interesting year for materials science, as researchers made important developments in many materials with applications in different fields, which included environment, defense industry and energy storage.
Here are some highlights, although this list is not (cannot be) exhaustive.
Materials used for Defense/Human Protection
Kevlar ® is a polymer (poly-aramid) made in the form of fibers, and which has a very high tensile strength. Because of this, it is already widely used by military for human body protection, for instance in the manufacture of bullet proof clothing.
Researchers in the US developed a modified Kevlar ® which, in addition to the high tensile strength, also has a much higher cut resistance. This was done by depositing thin layers of titanium dioxide (TiO2) and aluminum oxide (Al2O3) on the surface of the Kevlar ® samples; they used a technique called atomic layer deposition (ALD). Results showed that layers of both oxides 5 nm thick led to cut resistance about 30 % higher than the unmodified material.
In another study performed at the National Institute of Standards and Technology (NIST), scientists discovered a material which could decompose chemical weapons, such as sarin gas (nerve gas). The material is made of single wall carbon nanotubes (SWCNTs) modified with atom of copper (Cu). When tested, Cu-SWCNTs degraded 4-nitrophenol phosphate, a molecule which simulates nerve gas behavior. Although the material has still to be optimized and its inclusion into a fabric has to be studied, it shows real potential for the development of protective clothing.
Energy Storage: More Advanced Batteries
2014 saw some interesting developments for energy storage devices such batteries.
Italian researchers reported a new lithium ion battery which had better performance than the lithium batteries commercially available. These results were achieved by using graphene as an anode, instead of the conventional graphite. The crucial step in the battery manufacture was the anode preparation, which was done using graphene in the form of spreadable ink, basically a suspension containing graphene flakes with dimensions between 30 and 100 nm. The battery showed an energy density of 190 W h kg-1, that is about 25 % higher than commercial lithium batteries.
Chinese scientists, on the other hand, developed a stretchable lithium ion battery. In this battery, the cathode was made of carbon nanotubes and LiMnO2, while the anode was a mixture of carbon nanotubes and Li4Ti5O12. Both the electrodes were prepared in the form of long fibers, which were then wound onto polydimethylsiloxane, a highly stretchable material.
The battery was stretchable by up to 600 % of its original length; moreover, 88 % of its specific capacity (91.3 mA h-1 g-1) was maintained after the stretch.
Greenhouse Gas Mitigation: Carbon Dioxide
Carbon dioxide (CO2) is a greenhouse gas and, according to some people, one of the causes of global warming; moreover, it is undoubtedly linked to ocean acidification. At the moment there are many studies to find ways to reduce CO2 concentration in the atmosphere.
One possible solution is to absorb the CO2 emitted from the industrial plants using appropriate materials. In this field, interesting results were reported within a joint project by UK and US researchers, which developed an innovative material based on a porous organic polymer (hyper-cross-linked benzene). This material showed better performance than those previously reported in literature, as it is very selective (i.e. absorbs just CO2); moreover, it is also resistant to acid, and its activity does not get affected by the presence of water vapor.
An alternative way to decrease CO2 concentration is to convert it into other molecules which could be valuable for our industry/society. To achieve this, however, it is essential to have appropriate catalysts which make the reaction fast, selective and, hence, worth considering.
Researchers from Delaware University (US) published an important study on this topic; they developed a silver-based catalyst to convert CO2 into carbon monoxide (CO) through an electrochemical process. Due to its porous nanostructure, this catalyst had a conversion rate about 3,000 times higher than the standard polycrystalline silver material.
Scientists from Brookhaven National Laboratory (US), on the other hand, found a way to transform CO2 into methanol (CH3OH). The catalyst they developed is a combination of copper, cerium oxide and titanium dioxide. Using this catalyst, the reaction of a CO2/CO mixture with H2 to give methanol was 87 times faster than with other catalysts.
Both CO and methanol are molecules widely used in industry as starting material to make several chemical compounds; producing them in an efficient way from CO2 can therefore have beneficial effect on both the environment and the economy.
Other Remarkable Developments
Other important news from the materials science world are:
- Researchers from Leiden University (the Netherlands) built a microphone device using just a single molecule. The system is based on antrachene, doped with an organic dye (dibenzoterrylene). Scientists detected the vibration of just a single molecule of the dye.
- Researchers from Massachusetts Institute of Technology (MIT) discovered a new two-dimensional material with structure similar to the one of graphene but with better conductive properties. This compound – nickel bonded to an organic complex Ni3(HITP)2 – has a band gap structure and for this it could be used in electronic device fabrication.
- A research group in Australia developed fabrics with excellent antibacterial properties. This was achieved by adding silver nanowires to the fabrics; the key element for the high antimicrobial efficiency was the high aspect ratio of the nanoparticles (> 3000).
Looking Forward to 2015
This summary showed how many important results were achieved in materials science in 2014, with implications in different aspects of our life/society. Surely 2015 will bring us more exciting discoveries, both as new studies and as further developments of current investigations.
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