Essentially, the term aerogel describes a special geometric structure of matter. It is neither limited to any material nor to any synthesis procedure. Hence, the possible variety of materials and therefore the multitude of their applications are almost unbounded. In fact, the same applies for nanoparticles. These are also just defined by their geometrical properties. In the past few decades nano-sized materials have been intensively studied and possible applications appeared in nearly all areas of natural sciences. To date a large variety of metal, semiconductor, oxide, and other nanoparticles are available from colloidal synthesis. However, for many applications of these materials an assembly into macroscopic structures is needed. Here we present a comprehensive picture of the developments that enabled the fusion of the colloidal nanoparticle and the aerogel world. This became possible by the controlled destabilization of pre-formed nanoparticles, which leads to their assembly into three-dimensional macroscopic networks. This revolutionary approach makes it possible to use precisely controlled nanoparticles as building blocks for macroscopic porous structures with programmable properties.

Three-dimensional (3D) porous metal nanostructures have been a long sought-after class of materials due to their collective properties and widespread applications. In this study, we report on a facile and versatile strategy for the formation of Au hydrogel networks involving the dopamine-induced 3D assembly of Au nanoparticles. Following supercritical drying, the resulting Au aerogels exhibit high surface areas and porosity. They are all composed of porous nanowire networks reflecting in their diameters those of the original particles (5–6 nm) via electron microscopy. Furthermore, electrocatalytic tests were carried out in the oxidation of some small molecules with Au aerogels tailored by different functional groups. The beta-cyclodextrin-modified Au aerogel, with a host–guest effect, represents a unique class of porous metal materials of considerable interest and promising applications for electrocatalysis.

Hydrogels are fabricated from CdSe/CdS seeded nanorod building blocks by the addition of hydrogen peroxide and converted to aerogels by supercritical drying. The aerogels show higher photoluminescence quantum yields and longer lifetimes than the hydrogels and the nanoparticle solutions. A model for this observation is derived.

Novel assemblies and self-assembly architectures are currently of great interest for nanochemistry and chemical nanotechnology. The assemblies are generally considered as bottom-up alternative to top-down methods (i.e., nanolithography, e-beam epitaxy, and others).Stable, water-soluble, strongly light-emitting thiol-capped CdTe nanocrystals (NCs) [1,2] are promising materials for nanotechnological applications such as bioimaging, [3,4] labeling [5][6][7][8] and coding, [9] light-emitting diodes, [10][11][12][13] nanophotonic devices, [14,15] and energy scavengers. [16] In particular, lightemitting diodes (LEDs) based on thiol-capped NCs are the only known devices that are assembled by utilizing environmentally friendly layer-by-layer (LbL) technology under ambient conditions and show electroluminescence that is visible to the naked eye. This is stable for hours in air with output parameters as high as 0.51% external quantum efficiency, 0.8 lm W À1, and 0.4 cd A À1 luminous efficiency.[13]The aqueous approach to the synthesis of thiol-capped NCs is relatively low-toxic, routinely yields NCs with photoluminescence (PL) quantum efficiencies (QE) of 60% without postpreparative treatment, [17] can be easily scaled up, and is applicable to a variety of II-VI semiconductor NCs (CdTe, [2] ZnSe, [18] CdSe, [19] and HgTe [20] ) with optical activities covering the spectral region from the UV through visible into the near IR. The PL QE, the size distribution, the stability, and the solvent compatibility of these NCs may additionally be improved by post-preparative size-selective precipitation, [1] by photochemical treatment, [18,21] or by capping-agent exchange. [22,23] One of the main tasks of bottom-up nanotechnology is the controllable manipulation and addressing of nano-objects (e.g., nanoparticles, functional molecules) to assure their desired positioning and efficient performance in future devices. Therefore, the development and improvement of assembly approaches is at the focus of current research activities. NCs stabilized with short-chain thiols possessing terminal groups such as amino, carboxy, hydroxy, and others exhibit both specific functionalities and charge, allowing assembly into 1D structures on molecular templates, [24] covalent linkage to surfaces yielding stable 2D layers, [25] and electrostatic assembly into 2D-3D LbL structures. [26] Another attractive feature of this type NCs is their ability to self-assemble, that is, to create superstructures without additional templates or functional molecules. It has been shown that thioglycolic-acid-capped CdTe NCs may self-assemble, yielding brightly emitting and stable nanowires as a result of a gentle destabilization of the colloidal solution by partial removal of the capping agent [27] or by the addition of a specific buffer. [28] CdTe NCs capped with 2-(dimethylamino)ethanethiol may form 2D sheets that are free floating in solution and possess a certain physical integrity, showing remarkable stability during gentle stirring and drying. [29] Very small molecu...

A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods.