Macroscopic materials with nanoscopic properties have recently been synthesized by self-assembling defined nanoparticles to form self-supported networks, so-called aerogels. Motivated by the promising properties of this class of materials, the search for versatile routes toward the controlled assembly of presynthesized nanoparticles into such ultralight macroscopic materials has become a great interest. Overcoating procedures of colloidal nanoparticles with polymers offer versatile means to produce aerogels from nanoparticles, regardless of their size, shape, or properties while retaining their original characteristics. Herein, we report on the surface modification and assembly of various building blocks: photoluminescent nanorods, magnetic nanospheres, and plasmonic nanocubes with particle sizes between 5 and 40 nm. The polymer employed for the coating was poly(isobutylene- alt -maleic anhydride) modified with 1-dodecylamine side chains. The amphiphilic character of the polymer facilitates the stability of the nanocrystals in aqueous media. Hydrogels are prepared via triggering the colloidally stable solutions, with aqueous cations acting as linkers between the functional groups of the polymer shell. Upon supercritical drying, the hydrogels are successfully converted into macroscopic aerogels with highly porous, open structure. Due to the noninvasive preparation method, the nanoscopic properties of the building blocks are retained in the monolithic aerogels, leading to the powerful transfer of these properties to the macroscale. The open pore system, the universality of the polymer-coating strategy, and the large accessibility of the network make these gel structures promising biosensing platforms. Functionalizing the polymer shell with biomolecules opens up the possibility to utilize the nanoscopic properties of the building blocks in fluorescent probing, magnetoresistive sensing, and plasmonic-driven thermal sensing.

5 nm nanocrystals of CoFe Prussian blue analogue totally exempt from any alkali cation were prepared. Their photomagnetic properties were compared to those of the corresponding powder made of 150 nm particles as well as to those of 5 nm nanocrystals of CoFe PBAs embedded in comparable silica matrices, made of Co II Fe III pairs and prepared under various conditions. The photomagnetic investigation of the nanoparticles exempt of any alkali cation clearly shows that they are transformed by light and the comparison of their photomagnetic properties to those of the powder made of particles of bigger size with the same chemical composition suggests that the species involved in the switching properties are surface species. Furthermore, the comparison of the magnetic properties of nanoparticles prepared under various conditions also suggests that the aggregation state of the nanoparticles in the porous channels of the silica matrix, by modulating inter-particle interactions, plays a predominant role in the magnetic properties of the nanoparticles assemblies.

No abstract

Prussian blue analog (PBA) nanoparticles confined in the ordered mesoporosity of silica monoliths with twodimensional hexagonal structure are used as precursors and transformed into metal oxide or metal alloy by thermal treatment under oxidizing or reducing atmosphere. X-ray diffraction and transmission electron microscopy show that, after appropriate thermal treatment, the ordered silica monoliths contain spherical nanocrystals of mixed oxide and metal alloy aligned along the cylindrical pore axis. Their size (4 nm) is controlled by the diameter of the cylindrical pores of the silica monolith and their aggregation state by the structure of the porosity and the synthesis route. Furthermore, the chemical composition of the starting PBA precisely determines that of the oxide or alloy nanocrystals. The magnetic properties of the monoliths, governed by strong interparticle interactions, are very sensitive to chemical composition, size and aggregation state of the nanoparticles. The multi-scale control of the nanocomposite enables producing a light macroscopic permanent magnet, which is attracted to a NdBFe magnet at room temperature.