Titanium dioxide nanoreactor
The titanium dioxide nanoparticles crystallize in a polymer network at room temperature.
Tiny particles of titanium dioxide are found as key ingredients in wall paints, sunscreens, and toothpaste; they act as reflectors of light or as abrasives. However with decreasing particle size and a corresponding change in their surface-to-volume ratio, their properties change so that crystalline titanium dioxide nanoparticles acquire catalytic ability: Activated by the UV component in sunlight, they break down toxins or catalyze other relevant reactions.
Now, Dr. Katja Henzler and a team of chemists at the Helmholtz Centre Berlin have developed a synthesis to produce nanoparticles at room temperature in a polymer network. Their analysis, conducted at BESSY II, Berlin's synchrotron radiation source, has revealed the crystalline structure of the nanoparticles. This represents a major step forward in the usage of polymeric nanoreactors since, until recently, the nanoparticles had to be thoroughly heated to get them to crystallize. The last synthesis step can be spared due to the special environment inside the PNIPAM network.
The Henzler team's polymeric nanoreactors consist of a polystyrene core surrounded by a network of PNIPAM chains. A titanium compound was added to an ethanolic solution of the polymer colloids, which did trigger the formation of small titanium dioxide particles within the PNIPAM network. The BESSY II experiments showed that the chemists were able to control the speed of these processes while at the same time affecting the quality of the nanocrystals that had formed.
Using the novel combination of x-ray microscopy and spectroscopy (NEXAFS-TXM, U41-SGM) at BESSY II, Henzler and the microscopy team were able to show that the nanoparticles are homogeneously distributed over the polymeric nanoreactors. The researchers examined their samples in a cryogenic aqueous environment, which prevents artifact formation due to sample drying. Their analysis showed that the nanoparticles have a crystalline structure. "The nanocrystals have a tetragonal anatase structure and this crystalline structure is a key to their catalytic performance. Additionally, our new analytic method allows us to control the quality of the synthesized particles so that we can optimize them for relevant applications," says Katja Henzler.
Nano Letters, 2013, 13 (2), pp 824–828;
DOI: 10.1021/nl3046798
- Perovskite solar cells from the slot die coater - a step towards industrial productionSolar cells made from metal halide perovskites achieve high efficiencies and their production from liquid inks requires only a small amount of energy. A team led by Prof. Dr. Eva Unger at Helmholtz-Zentrum Berlin is investigating the production process. At the X-ray source BESSY II, the group has analyzed the optimal composition of precursor inks for the production of high-quality FAPbI3 perovskite thin films by slot-die coating. The solar cells produced with these inks were tested under real life conditions in the field for a year and scaled up to mini-module size.
- Superstore MXene: New proton hydration structure determinedMXenes are able to store large amounts of electrical energy like batteries and to charge and discharge rather quickly like a supercapacitor. They combine both talents and thus are a very interesting class of materials for energy storage. The material is structured like a kind of puff pastry, with the MXene layers separated by thin water films. A team at HZB has now investigated how protons migrate in the water films confined between the layers of the material and enable charge transport. Their results have been published in the renowned journal Nature Communications and may accelerate the optimisation of these kinds of energy storage materials.
- TU Berlin appoints Renske van der Veen as professorFor the past two years, Dr Renske van der Veen has led a research group in time-resolved X-ray spectroscopy and electron microscopy at HZB. Her research focuses on catalytic processes that enable, for example, the production of green hydrogen. She has now been appointed to a S-W2 professorship at the Institute of Optics and Atomic Physics (IOAP) at the Technische Universität Berlin.