A Combinatorial Study Investigating the Growth of Ultrasmall Embedded Silver Nanoparticles upon Thermal Annealing

Ultrasmall nanoparticles (NPs) with a high active surface area are essential for optoelectronic and photovoltaic applications. However, the structural stability and sustainability of these ultrasmall NPs at higher temperatures remain a critical problem. Here, we have synthesized the nanocomposites (NCs) of Ag NPs inside the silica matrix using the atom beam co-sputtering technique. The post-deposition growth of the embedded Ag NPs is systematically investigated at a wide range of annealing temperatures (ATs). A novel, fast, and effective procedure, correlating the experimental (UV-vis absorption results) and theoretical (quantum mechanical modeling, QMM) results, is used to estimate the size of NPs. The QMM-based simulation, employed for this work, is found to be more accurate in reproducing the absorption spectra over the classical/modified Drude model, which fails to predict the expected shift in the LSPR for ultrasmall NPs. Unlike the classical Drude model, the QMM incorporates the intraband transition of the conduction band electrons to calculate the effective dielectric function of metallic NCs, which is the major contribution of LSPR shifts for ultrasmall NPs. In this framework, a direct comparison is made between experimentally and theoretically observed LSPR peak positions, and it is observed that the size of NPs grows from 3 to 18 nm as AT increases from room temperature to 900 °C. Further, in situ grazing-incidence small- & wide-angle X-ray scattering and transmission electron microscopy measurements are employed to comprehend the growth of Ag NPs and validate the UV + QMM results. We demonstrate that, unlike chemically grown NPs, the embedded Ag NPs ensure greater stability in size and remain in an ultrasmall regime up to 800 °C, and beyond this temperature, the size of NPs increases exponentially due to dominant Ostwald ripening. Finally, a three-stage mechanism is discussed to understand the process of nucleation and growth of the silica-embedded Ag NPs.

MOF-derived CeO2/Au@SiO2 hollow nanotubes and their catalytic activity toward 4-nitrophenol reduction

A hollow CeO₂/Au@SiO₂ sandwiched nanocatalyst with enhanced catalytic activity was prepared by using Ce-MOF as a sacrificial template.

Synthesis and Application of Dendritic Fibrous Nanosilica/Gold Hybrid Nanomaterials

Morphologically unique silica nanoparticles can be used as effective templates to prepare silica-metal hybrid nanomaterials, which are highly applicable in a variety of areas. Mesoporous silica nanoparticles, which have high surface areas and an abundance of pores, can be used to synthesize mesoporous silica core-metal shell nanostructures with catalytically active sites. In this work, dendritic fibrous nanosilica (DFNS) with a high surface area is successfully employed as a template to synthesize DFNS/Au hybrid nanomaterials. Au nanodots are initially synthesized through the selective reduction of Au ions on the surface of the DFNS after surface modification to form DFNS/Au dots. A seed-mediated growth method is used to controllably grow Au nanoparticles on the DFNS/Au dots to generate DFNS core-Au nanoparticles shell nanohybrids (DFNS/Au NPs) and DFNS core-Au layer shell nanohybrids (DFNS/Au layers). The catalytic activities of DFNS/Au NPs and DFNS/Au layers in the 4-nitrophenol reduction reaction are compared.

Platinum Nanoparticle-embedded Porous Diamond Spherical Particles as an Active and Stable Heterogeneous Catalyst

Platinum nanoparticle-embedded porous diamond spherical particles (PtNP@PDSPs), as an active and stable catalyst, were fabricated by spray-drying of an aqueous slurry containing nanodiamond (ND) particles, platinum nanoparticles (PtNP), and polyethylene glycol (PEG) to form ND/PtNP/PEG composite spherical particles, followed by removal of PEG and a short-time diamond growth on the surface. The average diameter of the PtNP@PDSPs can be controlled in the range of 1–5 μm according to the spray-drying conditions. The Brunauer-Emmett-Teller (BET) surface area and average pore diameter of the PtNP@PDSPs were estimated to be ca. 170–300 m² g⁻¹ and ca. 4–13 nm, respectively. When ND with the size of 20–30 nm was used, the size of PtNP in the PtNP@PDSP was almost unchanged at 5–6 nm even after high temperature processes and reuse test for catalytic reaction, showing stable supporting. The catalytic activity of the PtNP@PDSPs for the dehydrogenation of cyclohexane was higher than that for a Pt/C catalyst, which is attributed to the stable PtNP support by the three-dimensional packing of ND and efficient mass transfer via the interconnected through-hole pores in the PDSPs.

Silica-supported Au@hollow-SiO2 particles with outstanding catalytic activity prepared via block copolymer template approach

Catalytically active Au@hollow-SiO₂ particles embedded in porous silica support (Au@hollow-SiO₂@PSS) were prepared by using spherical micelles from poly(styrene)-block-poly(4-vinyl pyridine) block copolymer as a sacrificial template. Drastic increase of the shell porosity was observed after pyrolytic removal of polymeric template because the stretched poly(4-vinyl pyridine) chains interpenetrating with silica shell acted as an effective porogen. The embedding of Au@hollow-SiO₂ particles in porous silica support prevented their fusion during pyrolysis. The catalytic activity of Au@hollow-SiO₂@PSS was investigated using a model reaction of catalytic reduction of 4-nitrophenol and reductive degradation of Congo red azo-dye. Significantly, to the best of our knowledge, Au@hollow-SiO₂@PSS catalyst shows the highest activity among analogous systems reported till now in literature. Such high activity was attributed to the presence of multiple pores within silica shell of Au@hollow-SiO₂ particles and easy accessibility of reagents to the catalytically active sites of the ligand-free gold surface through the porous silica support.

Synthesis and Characterization of Monodisperse Metallodielectric SiO2@Pt@SiO2 Core-Shell-Shell Particles

Metallodielectric nanostructured core-shell-shell particles are particularly desirable for enabling novel types of optical components, including narrow-band absorbers, narrow-band photodetectors, and thermal emitters, as well as new types of sensors and catalysts. Here, we present a facile approach for the preparation of submicron SiO2@Pt@SiO2 core-shell-shell particles. As shown by transmission and scanning electron microscopy, the first steps of this approach allow for the deposition of closed and almost perfectly smooth platinum shells onto silica cores via a seeded growth mechanism. By choosing appropriate conditions, the shell thickness could be adjusted precisely, ranging from ∼3 to ∼32 nm. As determined by X-ray diffraction, the crystalline domain sizes of the polycrystalline metal shells were ∼4 nm, regardless of the shell thickness. The platinum content of the particles was determined by atomic absorption spectroscopy and for thin shells consistent with a dense metal layer of the TEM-measured thickness. In addition, we show that the roughness of the platinum shell strongly depends on the storage time of the gold seeds used to initiate reductive platinum deposition. Further, using polyvinylpyrrolidone as adhesion layer, it was possible to coat the metallic shells with very homogeneous and smooth insulating silica shells of well-controlled thicknesses between ∼2 and ∼43 nm. After depositing the particles onto silicon substrates equipped with interdigitated electrode structures, the metallic character of the SiO2@Pt particles and the insulating character of the SiO2 shells of the SiO2@Pt@SiO2 particles were successfully demonstrated by charge transport measurements at variable temperatures.

The facile ionic liquid-assisted synthesis of hollow and porous platinum nanotubes with enhanced catalytic performances

A facile one-pot synthetic method was developed to synthesize hollow and porous Pt nanotubes (Pt-HPNTs) using silica nanorods as a template, ionic liquid as a precipitator and reductant, and in situ generated KCl as an etching agent.

Silica-supported ultra small gold nanoparticles as nanoreactors for the etherification of silanes

Ultra-small Au–SiO₂ nanoparticles worked as nanoreactors for the etherification of silanes with high selectivity and reusability.

A simple, rapid, one-step approach for preparation of Ag@TiO2 nanospheres with multiple cores as effective catalyst

Novel Ag@TiO₂ nanostructures with multiple Ag nanoparticles as cores and a crystalline TiO₂ as the outer shell have been successfully achieved via a facile and one-step solvothermal route.

Galvanic replacement synthesis of Ag x Au1-x @CeO2 (0 ≤ x ≤ 1) core@shell nanospheres with greatly enhanced catalytic performance

A galvanic replacement strategy has been successfully adopted to design Ag x Au1-x @CeO2 core@shell nanospheres derived from Ag@CeO2 ones. After etching using HAuCl4, the Ag core was in situ replaced with Ag x Au1-x alloy nanoframes, and void spaces were left under the CeO2 shell. Among the as-prepared Ag x Au1-x @CeO2 catalysts, Ag0.64Au0.36@CeO2 shows the optimal catalytic performance, whose catalytic efficiency reaches even 2.5 times higher than our previously reported Pt@CeO2 nanospheres in the catalytic reduction of 4-nitrophenol (4-NP) by ammonia borane (AB). Besides, Ag0.64Au0.36@CeO2 also exhibits a much lower 100% conversion temperature of 120 °C for catalytic CO oxidation compared with the other samples.