A versatile method to fabricate self-supported aerogels of nanoparticle (NP) building blocks is presented. This approach is based on freezing colloidal NPs and subsequent freeze drying. This means that the colloidal NPs are directly transferred into dry aerogel-like monolithic superstructures without previous lyogelation as would be the case for conventional aerogel and cryogel fabrication methods. The assembly process, based on a physical concept, is highly versatile: cryogelation is applicable for noble metal, metal oxide, and semiconductor NPs, and no impact of the surface chemistry or NP shape on the resulting morphology is observed. Under optimized conditions the shape and volume of the liquid equal those of the resulting aerogels. Also, we show that thin and homogeneous films of the material can be obtained. Furthermore, the physical properties of the aerogels are discussed.

Porous architectures of noble metal nanocrystals are promising for many catalytic as well as for fuel cell applications. Here we present the synthesis of porous, extremely lightweight aerogels of self-supported Pt nanocubes and nanospheres by direct destabilization from nonpolar colloidal solution using hydrazine monohydrate (N 2 H 4 •H 2 O) as gelation reagent. The template-free voluminous lyogels of the Pt nanocrystals are converted to macroscopic solid aerogel monoliths by supercritical drying. The aerogels from Pt nanocubes mostly exhibit (100) as the exposed crystal facets throughout the entire monolithic surface, while the aerogels from quasispherical Pt nanocrystals exhibit many crystal facets such as ( 111) and (100). Furthermore, the aerogels exhibit remarkably low densities of ∼0.19 g cm −3 ± 0.038 g cm −3 (∼0.9% of bulk Pt) and a specific surface area in the range of ∼6400−7000 m 2 mol −1 . The nanocube gels show better catalytic performance than the nanosphere gels when employed for asymmetric hydrogenation reaction, which is exemplarily shown for 4,4-dimethyldihydrofuran-2,3-dione to D-/L-pantolactone conversion with an excess of 9% for the D-enantiomer. Owing to their high specific surface area and certain type of exposed crystal facets, Pt aerogels developed here are highly promising for possible future applications in facet selective catalytic reactions.

We report on a synthesis procedure to achieve site-selective growth of noble metal domains on CdSe nanoplatelets. The novel morphological properties of the resulting metal−semiconductor nanoheteroplatelets are characterized by transmission electron microscopy, UV−vis absorption, photoluminescence emission, X-ray photoelectron spectroscopy, and by X-ray diffractometry. By variation of the synthesis parameters, several different morphologies can be achieved: depending on the noble metal and the type of precursor, the growth of Au, Pt, and Pd domain takes place at the corners or edges, around or only at the two shorter edges of the rectangular sheet. This novel kind of hybrid nanoheterostructure might find future applications in photocatalysis, chemical sensing, or fabrication of photovoltaic devices.

In this work, luminescent CdSe@CdS dot-in-rod nanocrystals, CdSe@CdS/ZnS nanorods as well as CdSe-CdS core-crown nanoplatelets were transferred into aqueous phase via ligand exchange reactions. For this purpose, bifunctional thiol-based ligands were employed, namely mercaptoacetic acid (MAA), 3-mercaptopropionic acid (MPA), 11-mercaptoundecanoic acid (MUA) as well as 2-(dimethylamino)ethanthiol (DMAET). Systematic investigations by means of photoluminescence quantum yield measurements as well as photoluminescence decay measurements have shown that the luminescence properties of the transferred nanostructures are affected by hole traps (induced by the thiol ligands themselves) as well as by spatial insulation and passivation against the environment. The influence of the tips of the nanorods on the luminescence is, however, insignificant. Accordingly, different ligands yield optimum results for different nanoparticle samples, mainly depending on the inorganic passivation of the respective samples. In case of CdSe@CdS nanorods, the highest emission intensities have been obtained by using short-chain ligands for the transfer preserving more than 50% of the pristine quantum yield of the hydrophobic nanorods. As opposed to this, the best possible quantum efficiency for the CdSe@CdS/ZnS nanorods has been achieved via MUA. The gained knowledge could be applied to transfer for the first time 2-dimensional CdSe-CdS core-crown nanoplatelets into water while preserving significant photoluminescence (up to 12% quantum efficiency).