The Precise Synthesis and Growth of Core–Shell Nanoparticles within a Self‐Assembled Spherical Template

Abstract

Nanoparticles with core-shell structures can exhibit unique material properties and promise a variety of applications in materials science, optics, catalysis, and biophysics. [1][2][3][4][5][6][7][8][9][10][11] The precise synthesis of core-shell nanoparticles is of utmost importance as the material properties depend on the constituent elements as well as the size and shape of the nanoparticles. The synthesis of core-shell nanoparticles is typically carried out by coating the surface of the core nanoparticles with metal ions or metal alkoxides in solution, where the controlled growth of the core nanoparticles and the outer shells is achieved by modulating the synthetic conditions (e.g., temperature, concentration, solvent, and pH value). However, the preparation of both the highly monodisperse core nanoparticles and the subsequent coreshell nanoparticles remains difficult. Recently, several groups have utilized hollow assemblies and media, such as reverse micelles, to control the growth of core-shell nanoparticles, in which the hollow interior acts as a template. [12][13][14] Unfortunately, the templating assemblies are themselves not monodisperse and thus the precise control of nanoparticle growth remained elusive. Furthermore, the large size of the template assemblies precludes the synthesis of small (< 10 nm) coreshell nanoparticles.Recently we published the synthesis of monodisperse SiO 2 nanoparticles using structurally exact coordination spheres as templates.[15] The M 12 L 24 spheres self-assembled from 12 Pd 2+ ions (M) and 24 bent bridging ligands (L) [15][16][17][18][19][20][21] and presented a sugar-coated interior that templated the precise synthesis of highly monodisperse SiO 2 nanoparticles with diameters of 2-4 nm using the sol-gel condensation of alkoxysilanes. Herein, we describe the elaboration of monodisperse SiO 2 nanoparticles confined within the template sphere with a metal oxide (MO 2 ; where M = Ti or Zr) layer to generate monodisperse core-shell nanoparticles (Figure 1). The core-shell nanoparticles (SiO 2 /TiO 2 , SiO 2 /ZrO 2 ) have diameters of 3 nm and preserve the highly monodisperse molecular weight distributions (M w /M n < 1.01) as characterized by TEM and MS analyses.Self-assembled nanosphere 1 (nitrate salt unless otherwise noted) with the templating glucose interior lining was prepared from sugar-appended ligand 2 and Pd(NO 3 ) 2 in DMSO. With sphere 1 as a template, silica (SiO 2 ) core nanoparticles were prepared as follows: tetramethoxysilane (TMOS, 100 equiv) was added to sphere 1 (80 mm, CDCl 3 / [D 6 ]DMSO 9:1) and the mixture was stirred at room temperature for four days. Upon hydrolysis and condensation of TMOS inside 1, NMR signals of the sphere framework significantly broadened because of the growth of SiO 2 nanoparticles within the inner cavity (Figure 2 a,b). Under laser desorption ionization mass spectrometry (LDI-MS) conditions, the shell framework of 1 was destroyed and we could directly confirm the formation of highly monodisperse silica nanoparticles with molec...

Ultra-Small Face-Centered-Cubic Ru Nanoparticles Confined within a Porous Coordination Cage for Dehydrogenation

“…[23][24][25][26] There are very few examples of using coordination cages to tailor the size of encapsulated NPs. 27,28 We envision that MOPs may have great potential for catalysis because of their cavity confinement effect and facile functionalization.…”

Synthesis and Applications of Endohedrally Functionalized Metal‐Ligand Cage Complexes

“…Unlike in the examples with silica nanoparticles, the titanium nanoparticles could be removed from the cage by addition of a metal scavenger followed by precipitation. A combination of these concepts allowed the use of the M 12 L 24 cage complex to promote the formation of multilayer core‐shell nanoparticles (Figure ) . After the formation of the previously‐reported silica nanoparticles, active Ti 2+ was added in the form of Ti(thd) 2 (OiPr) 2 (thd=2,2,6,6‐tetramethyl‐3,5‐heptanedionate).…”

Synthesis of Mn2O3 homogeneous core/hollow-shell structures with excellent adsorption performance

“…The design and fabrication of core-shell-structured micro-and nanomaterials have been extensively studied in material research because of the diverse potential applications in catalysis, enhanced luminescence, energy transfer, and waste removal [1][2][3][4][5]. Up to now, the majority of the core/shell structures is heterogeneous and made from more than one type of material, whereas the construction of homogeneous core/shell structures with well-defined shapes is still a significant challenge to materials scientists [6][7][8][9].…”