X-ray studies bridge the molecular and macro length scales during the emergence of CoO assemblies.

The key to fabricating complex, hierarchical materials is the control of chemical reactions at various length scales. To this end, the classical model of nucleation and growth fails to provide sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for assemblies of polyhedrally shaped CoO nanocrystals. Utilizing high energy-resolution fluorescence-detected X-ray absorption spectroscopy, we directly access the molecular level of the nanomaterial synthesis. We reveal that initially Co(acac)3 rapidly reduces to square-planar Co(acac)2 and coordinates to two solvent molecules. Combining atomic pair distribution functions and small-angle X-ray scattering we observe that, unlike a classical nucleation and growth mechanism, nuclei as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final spherical assemblies are smaller than 100 nm, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution.

Organic-inorganic hybrids for CO2 sensing, separation and conversion.

Motivated by the air pollution that skyrocketed in numerous regions around the world, great effort was placed on discovering new classes of materials that separate, sense or convert CO2 in order to minimise impact on human health. However, separation, sensing and conversion are not only closely intertwined due to the ultimate goal of improving human well-being, but also because of similarities in material prerequisites -e.g. affinity to CO2. Partly inspired by the unrivalled performance of complex natural materials, manifold inorganic-organic hybrids were developed. One of the most important characteristics of hybrids is their design flexibility, which results from the combination of individual constituents with specific functionality. In this review, we discuss commonly used organic, inorganic, and inherently hybrid building blocks for applications in separation, sensing and catalytic conversion and highlight benefits like durability, activity, low-cost and large scale fabrication. Moreover, we address obstacles and potential future developments of hybrid materials. This review should inspire young researchers in chemistry, physics and engineering to identify and overcome interdisciplinary research challenges by performing academic research but also - based on the ever-stricter emission regulations like carbon taxes - through exchanges between industry and science.

Resistive pressure sensors based on freestanding membranes of gold nanoparticles.

In this communication the application of gold nanoparticle membranes as ambient pressure sensors with electromechanical signal transduction is demonstrated. The devices were fabricated by sealing microstructured cavities with membranes of 1,6-hexanedithiol cross-linked gold nanoparticles, which were electrically contacted by metal electrodes deposited on both sides of the cavities. Variations of the external pressure resulted in a deflection of the membranes and, thus, increased the average interparticle distances. Therefore, the pressure change could easily be detected by simply monitoring the resistance of the membranes.