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

Significance Statement

Layered double hydroxide as a promising green catalyst candidate has special properties such as surface basicity, adsorption nature, anion exchangeability coupled with biological and environmental capabilities. Despite the tremendous advantages an aqueous synthesis of nano layered double hydroxide offers certain drawbacks such as rapid crystallization kinetics leading to rapid aggregation of embryonic crystals to form an inhomogeneous gel-like state. In order to overcome this scenario, the trade-off of crystallization principle between growth and stabilization of nanocrystals needs important consideration to achieve layered double hydroxides nanomaterials that can be applied in green process.

A family of green nanomaterials, layered double hydroxide nanoclusters in favorable aqueous reaction media was synthesized by Tokudome et al. (2016). The work published in journal, ACS Nano, demonstrated a direct synthesis nano-layered double hydroxide aqueous suspension and layered double hydroxide nanoclusters, LDH NC, by overcoming the trade-off of the crystallization principle between growth and stabilization at higher supersaturation.

Delamination of bulky layered double hydroxide crystals in preparation of its nanomaterials is known to yield 2D nanosheets with thickness around 1nm and with further experiments proving extremely high specific areas of 260-460m2/g-1. However, isolating delaminated layered double hydroxides nanosheets in polar solvent remains a considerable challenge due to aggregation and restacking thereby imposing a need to be highly diluted in a liquid media. Its stability is also reportedly lost in several days at a concentration as low as 10g/L and a high ionic strength or poor solvents involved in its application further decrease the colloidal stability.

For this experiment, Tokudome et al. (2016) typical synthesis of layered double hydroxides nanoclusters was achieved by dissolving nickel (II) chloride hexahydrate (NiCl2.6H2O), aluminum chloride hexahydrate (AlCl3.6H2O, 98%), and acetylacetone (acac) in a mixture of H2O and ethanol followed by propylene oxide addition. Without any additional processes, a green-colored colloidal suspension of layered double hydroxide nanocrystals which exhibits the Tyndall effect was spontaneously formed at room temperature.

Results from X-ray diffraction patterns, field emission scanning electron microscopy, transmission microscopy images showed successful preparation of layered double hydroxides nanoclusters by overcoming the trade-off between the growth and stabilization of nanocrystals in water through a spontaneous gelation−deflocculation process. Small angle X-ray scattering analysis demonstrated an individual crystal with a diameter of 7.8nm isolated in suspension without aggregation. Concentration of layered double hydroxide nanocrystal is 98.7g/L which is multiple time higher than exfoliated layered double hydroxide.

From kinetic plots Knoevenagel condensation, layered double hydroxide nanoclusters properly worked as basic catalyst and no induction period was observed because of homogenous mixing with reactant when compared to those without layered double nanoclusters. Catalytic conversions were 89% and 21% for cases with and without layered double hydroxide nanoclusters respectively.

H3Cit-modified maghemite nanoparticles readily formed a nanocomposite with layered nanoclusters via an electrostatic interaction by simply the two solutions due to inherent positive charge of layered double hydroxides. Hence, magnetically modified layered double hydroxides nanoclusters could be collected by a magnet which is vital for catalytic applications.

The nanocatalytic nature of layered double hydroxide nanoclusters developed in this study show relevance in field of catalysis and biomedicine due to versatility of shape, size and compositional layered double hydroxides.

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

 

About the author

Yasuaki Tokudome is an Associate Professor at Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Japan. He received BE (2005), ME (2007), and PhD Sci. (2010) from Kyoto University, Japan.

He has strong research interests in the science and technology of liquid phase reactions, particularly in developing functional materials, including porous materials, layered materials (clays), organic-inorganic hybrids, green materials, stimuli-responsive materials. 

 

Journal Reference

Yasuaki Tokudome*1, Tsuyoshi Morimoto1, Naoki Tarutani1, Pedro D. Vaz2,3, Carla D. Nunes2, Vanessa Prevot4,5,Gavin B. G. Stenning3, Masahide Takahashi1. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.  ACS Nano, 2016, 10 (5), pp 5550–5559.

[expand title=”Show Affiliations”]
  1. Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan.
  2. Centro de Química e Bioquímica, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Ed. C8,1749-016 Lisboa, Portugal.
  3. ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX,United Kingdom.
  4. Université Clermont Auvergne Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand, France.
  5. CNRS, UMR 6296, ICCF, F-63171 Aubiere, France.
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