Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

Experimental details, XRD patterns, FT-IR spectra, N 2 sorption, SEM and TEM images, Raman spectrum, electrochemical analysis, and detailed structural assignment (PDF)

No abstract

Mesoporous crystalline (hydr)oxides of lowvalence metal ions (M(II) and M(III)) are highly demanded in the context of various applications. In this study, we demonstrate key factors to the successful formation of ordered mesoporous films through the assembly of nanobuilding block (ANBB) approach using a colloidal solution of crystalline M(OH) 2 (M = Mn, Fe, Co, Ni, and Cu). The colloidal system of α-Ni(OH) 2 is presented in depth as a typical example. Crystal growth and aggregation kinetics of the NBB were tuned by synthetic parameters. Nanometer-sized NBBs of tailored size between oligomer scale to over 20 nm were obtained. The films prepared from α-Ni(OH) 2 NBBs with a diameter of ≤7.5 nm showed ordered mesostructures through evaporation-induced self-assembly in the presence of supramolecular templates. Coarse-grained simulations suggest that there is a threshold diameter of NBB toward the formation of well-ordered mesostructures. It was found that, as well as limiting the diameter of NBB, inhibition of an aggregation of NBBs by using coordinative additives or diluting the NBB colloidal solution was essential to control the assembly of NBBs and templates into the ordered mesostructures. The results obtained here open up the synthesis of ordered mesoporous materials with a crystalline wall of variety of chemical compositions containing low-valence metal elements.

Structurally colored coatings composed of colloidal arrays of monodisperse spherical particles have attracted great attention owing to their versatile advantages, such as lowcost, resistance to fading, and low impacts on the environment and human health. However, the weak mechanical stability is considered to be a major obstacle for their practical applications as colorants. Although several approaches based on the addition of polymer additives to enhance the adhesion of particles have been reported, the challenge remains to develop a strategy for the preparation of structurally colored coatings with extremely high robustness using a simple process. Here, we have developed a novel approach to fabricate robust structurally colored coatings by using cathodic electrophoretic deposition (EPD). The addition of a metal salt, i.e., Mg(NO3)2, to the coating dispersion allows SiO2 particles to have a positive charge, which enables the electrophoresis of SiO2 particles toward the cathode. At the cathode, Mg(OH)2 codeposits with SiO2 particles because OHions are generated by the decomposition of dissolved oxygen and NO3ions. The mechanical stability of the colloidal arrays obtained by this process is remarkably improved because Mg(OH)2 facilitates the adhesion of the particles and substrates.The brilliant structural color is maintained even after several cycles of the sandpaper abrasion test. We have also demonstrated the coating on a stainless-steel fork. This demonstration reveals that our approach enables a homogeneous coating on a complicated surface. Furthermore, the high durability of the coating is clarified because the coating did not peel off even when the fork was stuck into a plastic eraser. Therefore, the coating technique developed here will provide an effective method for the pervasive application of structural color as a colorant.