Researchers from Barcelona, Madrid and Utrecht have managed to construct nanoparticles that spontaneously assemble into well-ordered 3D superstructures with photonic crystal properties. Marjolein Dijkstra, Professor of physics at Utrecht University, carried out computer simulations to predict the self-assembled structures. The discoveries can be applied in the design of novel photonic materials for sensing applications. The collaboration between researchers from Utrecht University, the Catalan Institute of Nanoscience and Nanotechnology and the Institute of Materials Science of Madrid resulted in a publication that appeared on 23 October in Nature Chemistry.
Self-assembly of nanoparticles is an efficient route to fabricating materials with uniform structures. Many studies to date have reported the synthesis of polymeric and metal-based particles that spontaneously self-assemble into ordered 3D superstructures. The current project is the first to work with hybrid metal-organic particles, adding a new family to the list of compounds that can be synthesised for 3D self-assembly: metal-organic frameworks (MOFs).
So far, the formation of well-ordered, well-packed and functional 3D structures had never been achieved for crystalline hybrid compounds like MOFs, even though they have the same geometric properties as their metal-based counterparts.
The resulting 3D superstructures, made up of many billions of identical particles arranged into crystals several millimetres across, present properties typical of photonic crystals, a promising new material that is finding applications in the manipulation of light. As such, the new structures scatter light in a way that provides colour without the use of pigments or dyes, known as structural colour. Furthermore, the colour of the material can be changed by controlling the size and shape of the particles at synthesis.
Built from MOFs, the new structures also boast high porosity, a feature that can be exploited in sensing applications: different substances adsorbed into the pores cause the light to be refracted into different colours. This effect can be tuned such that a given colour indicates the presence of a given substance. The ability to form 3D superstructures from porous units also opens the door to applications based on the alignment of the pores on a large scale, for instance, to produce improved membranes for gas adsorption and catalysis.
Civan Avci, Inhar Imaz, Arnau Carné-Sánchez, Jose Angel Pariente, Nikos Tasios, Javier Pérez-Carvajal, Maria Isabel Alonso, Alvaro Blanco, Marjolein Dijkstra*, Cefe Lopez, and Daniel Maspoch
Self-Assembly of Polyhedral Metal-Organic Framework Particles into Three-Dimensional Ordered Superstructures
Nature Chemistry, 23 October 2017, DOI: 10.1038/nchem.2875
* affiliated with Utrecht University