Recent Advances in Functional Nanoparticle Assemblies

Assemblies of colloidal nanoparticles (NPs) into various functional superstructures, such as ordered or nonordered, microscopic or macroscopic, and templated or self-supported, have recently attracted a lot of research interest. The continuous development of colloidal nanoparticle synthesis enables a fine-tuning of the structure and properties of such functional superstructures leading to numerous new applications. Herein, it is aimed to summarize a variety of assemblies based on ordered self-assembled NPs, e.g., stacked nanoplatelets, and nonordered self-assembled NPs, e.g., nanoparticle-based aerogels and cryoaerogels, systems ranging from the microscopic to the macroscopic range. Depending on the materials of the nanoparticle building blocks used, e.g., metallic, magnetic, semiconducting, or their combination in hybrid systems, both ordered and nonordered assemblies yield interesting properties for a wide variety of applications, such as catalysis, photocatalysis, or sensing, which are highlighted and discussed

Impact of Hard Magnetic Nanocrystals on the Properties of Hardened Cement Paste

In this work, nano-sized hard magnetic gallium-substituted iron oxide crystals, wherein gallium is used to stabilize the metastable epsilon iron oxide phase, were added to cement-water suspensions at different ratios, which were subsequently hydrated for at least 28 days. It is shown that higher contents of such nanocrystals in the hardened cement paste introduce a magnetic moment, whereas the mechanical properties remain unchanged compared to non-blended hardened cement paste for a wide concentration range

Investigation of the Photocatalytic Hydrogen Production of Semiconductor Nanocrystal-Based Hydrogels

Destabilization of a ligand-stabilized semiconductor nanocrystal solution with an oxidizing agent can lead to a macroscopic highly porous self-supporting nanocrystal network entitled hydrogel, with good accessibility to the surface. The previously reported charge carrier delocalization beyond a single nanocrystal building block in such gels can extend the charge carrier mobility and make a photocatalytic reaction more probable. The synthesis of ligand-stabilized nanocrystals with specific physicochemical properties is possible, thanks to the advances in colloid chemistry made in the last decades. Combining the properties of these nanocrystals with the advantages of nanocrystal-based hydrogels will lead to novel materials with optimized photocatalytic properties. This work demonstrates that CdSe quantum dots, CdS nanorods, and CdSe/CdS dot-in-rod-shaped nanorods as nanocrystal-based hydrogels can exhibit a much higher hydrogen production rate compared to their ligand-stabilized nanocrystal solutions. The gel synthesis through controlled destabilization by ligand oxidation preserves the high surface-to-volume ratio, ensures the accessible surface area even in hole-trapping solutions and facilitates photocatalytic hydrogen production without a co-catalyst. Especially with such self-supporting networks of nanocrystals, the problem of colloidal (in)stability in photocatalysis is circumvented. X-ray photoelectron spectroscopy and photoelectrochemical measurements reveal the advantageous properties of the 3D networks for application in photocatalytic hydrogen production

Recent Advances in Functional Nanoparticle Assemblies

Assemblies of colloidal nanoparticles (NPs) into various functional superstructures, such as ordered or nonordered, microscopic or macroscopic, and templated or self‐supported, have recently attracted a lot of research interest. The continuous development of colloidal nanoparticle synthesis enables a fine‐tuning of the structure and properties of such functional superstructures leading to numerous new applications. Herein, it is aimed to summarize a variety of assemblies based on ordered self‐assembled NPs, e.g., stacked nanoplatelets, and nonordered self‐assembled NPs, e.g., nanoparticle‐based aerogels and cryoaerogels, systems ranging from the microscopic to the macroscopic range. Depending on the materials of the nanoparticle building blocks used, e.g., metallic, magnetic, semiconducting, or their combination in hybrid systems, both ordered and nonordered assemblies yield interesting properties for a wide variety of applications, such as catalysis, photocatalysis, or sensing, which are highlighted and discussed

Semiconductor‐Metal Hybrid Nanoparticle‐Based Hydrogels: Efficient Photocatalysts for Hydrogen Evolution Reaction

Abstract In semiconductor‐metal hybrid nanoparticles, excited charge carriers can be separated efficiently by transferring the electron to the metal, because the Fermi level is located within the bandgap of the semiconductor. Besides charge carrier separation, the catalytically active surface of the metal enables the use of these charge carriers for further reactions. Due to limited colloidal stability, the application of nanoparticles in solution is challenging. To circumvent these difficulties, the destabilization can be used to build monolithic 3D (non‐ordered) gel‐like structures with retained high surface area and an ensured diffusion within the network. Here, the resulting nanoparticle‐based hydrogels of CdSe/CdS/Pt nanoparticles show photocatalytic hydrogen production rates up to 58 (mmol(H2))/(g∙h). Due to the self‐supporting network structure, colloidal stability is unnecessary, and the applicability is improved. By simply mixing semiconductor and semiconductor–metal hybrid nanoparticles before gelation, the synthesis of the gels allows the reduction of the metal content, which further tunes the photocatalyst