DNA‐Assisted Creation of a Library of Ultrasmall Multimetal/Metal Oxide Nanoparticles Confined in Silica

Abstract

electrical, [3] catalytic, [4] and magnetic [5] properties. To overcome the poor stability and severe aggregation in catalytic processes that remain major problems for UMNPs, MNPs have been immobilized onto/into various supports through postsynthetic and one-pot synthesis methods. [6] With either method, it is critical to control the interaction between the metal ions and supports and interactions between metal ions. Various functional groups have been selected and used to improve metal precursor impregnation rates and metal-support interactions to avoid metal leaching into the liquid phase and to control particle aggregation and growth; for example, P and N ligands constituted with bisphosphinoamino moieties, diphenylphosphinopyridine moieties, dendrimers, small organic molecules (amines, thiols, citrate, etc.), surfactants (hexadecyltrimethylammonium bromide), and silanization reagents (SH, NH 2 , and COOH) have been used. [7] However, these methods are not universally applicable to a large number of metals because of the limit of the coordination selectivity of ligands.DNA is one of the most attractive "building blocks" because of its double-stranded helical structure with well-defined minor and major grooves, well-regulated micrometer length, and a uniform diameter of ≈2 nm. More importantly, the unique chemical composition of DNA provides a variety of binding Supported ultrasmall metal/metal oxide nanoparticles (UMNPs) with sizes in the range of 1-5 nm exhibit unique properties in sensing, catalysis, biomedicine, etc. However, the metal-support and metal-metal precursor interactions were not as well controlled to stabilize the metal nanoparticles on/in the supports. Herein, DNA is chosen as a template and a ligand for the silica-supported UMNPs, taking full use of its binding ability to metal ions via either electrostatic or coordination interactions. UMNPs thus are highly dispersed in silica via self-assembly of DNA and DNA-metal ion interactions with the assistance of a co-structural directing agent (CSDA). A large number of metal ions are easily retained in the mesostructured DNA-silica materials, and their growth is controlled by the channels after calcination. Based on this directing concept, a material library, consisting of 50 mono-and 54 bicomponent UMNPs confined within silica and with narrow size distribution, is created. Theoretical calculation proves the indispensability of DNA with combination of several organics in the synthesis of ultrasmall metal nanoparticles. The Pt-silica and Pt/Ni-silica chosen from the library exhibit good catalytic performance for toluene combustion. This generalizable and straightforward synthesis strategy is expected to widen the corresponding applications of supported UMNPs.

Experiments‐Guided Modeling of MCM‐41: Impact of Pore Symmetry on Gas Adsorption

“…[45] Unfortunately, the few reports on P4mm mesostructured silica we are aware of, do not show any N 2 or other gases adsorption isotherm. [27][28][29][30][31][32][33] From the microscopic point of view, the largest difference between the MCM-41/DFT and tMCM-41/DFT models is the surface density of silanol groups, with that of the former (9.4 µmol m −2 ) lower than the latter (10.4 µmol m −2 ). Figure 5 shows the distribution of the orientation assumed by the N 2 molecules in the first adsorbed layer (described through the θ and φ angles defined in Figure 6) at two selected pressure values.…”

“…[ 45 ] Unfortunately, the few reports on P4mm mesostructured silica we are aware of, do not show any N 2 or other gases adsorption isotherm. [ 27–33 ]…”

“…The present investigation addressed for the first time the effect of changing the symmetry of a mesostructured silica-based material from the typical hexagonal P6mm to the unusual tetragonal P4mm. Although methods to prepare and tailor the latter were already reported in the literature since 2009, [27][28][29][30][31][32][33] this is the first investigation about their performance as gas sorbents in comparison with the most common P6mm materials. The microscopic details of the N 2 adsorption process were correlated with each other to explain the macroscopic adsorption isotherm.…”

“…[28][29][30][31][32] Recently, the confinement of ultrasmall metal/metal oxide nanoparticles within the mesopores was also achieved. [33] However, these materials have not been tested yet for their performance as gas sorbents and molecular sieves. As far as we are aware, not even a single N 2 adsorption isotherm has been reported so far.…”

Stabilization of transition metal heterojunctions inside porous materials for high-performance catalysis

“…Mesoporous silica materials have many fascinating features, such as ordered mesoporous structures, tunable pore sizes, tailorable surface properties and high hydrothermal stability, which have been used for porous hosts to encapsulate transition metal heterojunctions for high-performance catalysis under extreme conditions. [126][127][128][129] Ungureanu et al used metal nitrate aqueous solutions and SBA-15 to prepare a bimetal precursor/silica composite through an incipient wetness impregnation and mild drying (IWI-MD) method, and, followed by calcination and H 2 reduction, to prepare a Ni-Cu/SBA-15 composite for chemoselective hydrogenation of cinnamaldehyde to synthesize hydrocinnamaldehyde (Fig. 10).…”