Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry

Abstract

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.

Interactions between Biological Cells and Layered Double Hydroxides: Towards Functional Materials

“…This offers a tremendous range of possibilities to produce LDH materials on demand. By playing on the synthetic parameters, particle sizes can be tuned in a large extend ranging from nanoclusters, to several microns . Thanks to hard and soft templating approaches, phase separation phenomenon and miniemulsion, peculiar LDH morphologies displaying enhanced meso and macroporosity, have been recently described such as microspheres, fibrous structures, inverse opals and macroporous monoliths …”

Preparation of Mesoporous Basic Oxides through Assembly of Monodispersed Mg–Al Layered Double Hydroxide Nanoparticles

“…There have also been reports on the preparation of very small metal hydroxide nanoparticles (particle size: 5–8 nm) using propylene oxide for pH control and organic additives at a low temperature (20–40 °C) . On the basis of this method, single‐component metal hydroxide nanoparticles composed of various metal cations and Ni‐Al LDH nanoparticles have been prepared. However, if this method is applied to the preparation of Mg‐Al LDH nanoparticles, Al(OH) 3 may be produced as an impurity as a result of the gradual increase in pH .…”

Aqueous synthesis of metal hydroxides with controllable nano/macro architectures

“…50) Recently, the author and coauthors reported the synthesis of a soft-templated mesoporous LDH film from LDH nanoclusters and an amphiphilic polymer (Pluronic surfactant). 38) Although the mesophase is less ordered compared to those of the previously-reported oxide systems, better structural ordering of mesophase is further expected by decreasing the size of LDH NBBs; the size of LDH particle used in the report is 7.8 nm, whereas the sizes of NBBs for the oxides are less than 46 nm. 48),51) The mechanism of the formation of LDH nanoclusters is versatile and the process can be extended to CoAl, ZnAl, and LiAl LDHs.…”

“…38) The synthesis was performed via a facile one-pot route. Briefly, NiCl 2 ·6H 2 O, AlCl 3 ·6H 2 O, and acetylacetone (acac) were dissolved in a mixture of ethanol and ultra-pure water.…”