preparation-silver-palladium-alloyed-nanoparticles-for-plasmonic

Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular ...

University of Helsinki

Sodium (Na)- and potassium (K)-doped δ-MnO, which presented different band gaps, were synthesized by a hydrothermal method. Then, uniform Au nanoparticles (NPs) were deposited on MnO to form metal-semiconductor nano-heterojunctions (MnO-Au). By comparing their temperature-dependent thermal catalytic performances, p-aminothiophenol to p, p'-dimercaptoazobenzene conversion was used as proof-of-concept transformations. MnO-Au hybrid materials demonstrated better thermal catalytic performances relative to individual Au NPs. Meanwhile, K-doped MnO-Au, with a MnO support displaying a narrower bandgap, displayed superior catalytic activities relative to Na-doped MnO-Au. To get the same catalytic performance by individual Au NPs, it can be ∼50 K less by Na-doped MnO-Au and ∼100 K less by K-doped MnO-Au. The enhancement is mainly attributed to the thermally excited electrons in MnO, which were transferred to Au NPs. The additional electrons in Au NPs increase the electron density and thus contribute to the improvement of thermal catalysis. Our findings show that the establishment of a nano-heterojunction formed by metal NPs on a semiconductor support has a significant impact on thermal catalysis, where a narrower band gap can facilitate thermally excited carriers and thus bring about better catalytic performances. Thus, the results presented here shed light on the design of a nano-heterojunction catalyst to approach reactions with superior performance under moderate conditions.

Tuning Thermal Catalytic Enhancement in Doped MnO-Au Nano-Heterojunctions.

Colloidal particles with a spherical shape and diameters in the range of 0.01-1 μm have been a subject of extensive research, with applications in areas such as photonics, electronics, catalysis, drug delivery, and medicine. For most of these applications, it is of critical importance to achieve monodispersity for the size while expanding the diversity in terms of structure and composition. The uniformity in size allows one to establish rigorous correlations between this parameter and the physicochemical properties of the colloidal particles while ensuring experimental repeatability and measurement accuracy. On the other hand, the diversity in structure and composition offers additional handles for tailoring the properties. By switching from the conventional plain, solid structure to a core-shell, hollow, porous, or Janus structure, it offers immediate advantages and creates new opportunities, especially in the context of self-assembly, encapsulation, and controlled release. As for composition, monodispersed colloidal spheres were traditionally limited to amorphous materials such as polystyrene and silica. For metals and semiconducting materials, which are more valuable to applications in photonics, electronics, and catalysis, they tend to crystallize and thus grow anisotropically into nonspherical shapes, especially when their sizes pass 0.1 μm. Taken together, it is no wonder why chemical synthesis of monodispersed colloidal spheres has been a constant theme of research in areas such as colloidal science, materials chemistry, materials science, and soft matter. In this Account, we summarize our efforts over the past two decades in developing solution-phase methods for the facile synthesis of colloidal spheres that are uniform in size, together with a broad range of compositions (including metals and semiconductors) and structures (e.g., solid, core-shell, hollow, porous, and Janus, among others). We start with the synthesis of monodispersed colloidal spheres made of semiconductors, metals with low melting points, and precious metals. Through chemical reactions, these colloidal spheres can be transformed into core-shell or hollow structures with new compositions and properties. Next, we discuss the synthesis of colloidal spheres with a Janus structure while taking a pseudospherical shape. Specifically, metal-polymer hybrid particles composed of one metal nanoparticle partially embedded in the surface of a polymer sphere can be produced through precipitation polymerization in the presence of metal seed. With these Janus particles serving as templates, other types of Janus structures such as hollow spheres with a single hole in the surface can be obtained via site-selected deposition. Alternatively, such hollow spheres can be fabricated through a physical transformation process that involves swelling of polymer spheres, followed by freeze-drying. All these synthesis and transformation processes are solution-based, offering flexibility and potential for large-scale production. At the end, we highlight some of the applications enabled by these colloidal spheres, including fabrication of photonic devices, encapsulation, and controlled release for nanomedicine.

Synthesis, Transformation, and Utilization of Monodispersed Colloidal Spheres.

Although various efforts have been made to develop effective treatments for alveolar bone defect, alveolar regeneration has been emerging as the one with the most potential Herein, we investigated the potential of gelatin methacrylate (GelMA) hydrogels-encapsulated human periodontal ligament stem cells (hPDLSCs) to regenerate alveolar bone. The easy, rapid, and cost-effective nature of GelMA hydrogels makes them a promising mode of stem cell-delivery for clinically relevant alveolar bone regeneration. More importantly, GelMA hydrogels provide an optimal niche for hPDLSCs proliferation, migration and osteogenic differentiation, which are critical for alveolar bone regeneration. In this study, we examined the microstructure of GelMA hydrogels, and identified a highly porous and interconnected network. Compressive test of GelMA hydrogels showed that the stress reached a maximum value of 13.67 ± 0.03 kPa when the strain reached 55%. The maximum values of swelling ratio were 700 ± 47% at the fifth hour. The proliferation rate of hPDLSCs in the GelMA hydrogels resembled that in 2D culture and gradually increased. We established a critical-sized rat model of alveolar bone defects, and applied Micro-CT to assess new bone formation. Compared to the control group, there was substantial bone regeneration in the GelMA + hPDLSCs group at both 4 and 8 weeks after the operation. Histological analysis results were consistent with Micro-CT results. Our study demonstrates that the GelMA hydrogels-encapsulated hPDLSCs have a significant alveolar regenerative potential, and may represent a new strategy for the therapy of alveolar bone defects.

Investigating the repair of alveolar bone defects by gelatin methacrylate hydrogels-encapsulated human periodontal ligament stem cells.

Solar-to-chemical conversion via photocatalysis is of paramount importance for a sustainable future. Thus, investigating the synergistic effects promoted by light in photocatalytic reactions is crucial. The tandem oxidative coupling of alcohols and amines is an attractive route to synthesize imines. Here, we unravel the performance and underlying reaction pathway in the visible-light-driven tandem oxidative coupling of benzyl alcohol and aniline employing Au/CeO nanorods as catalysts. We propose an alternative reaction pathway for this transformation that leads to improved efficiencies relative to individual CeO nanorods, in which the localized surface plasmon resonance (LSPR) excitation in Au nanoparticles (NPs) plays an important role. Our data suggests a synergism between the hot electrons and holes generated from the LSPR excitation in Au NPs. While the oxygen vacancies in CeO nanorods trap the hot electrons and facilitate their transfer to adsorbed O at surface vacancy sites, the hot holes in the Au NPs facilitate the α-H abstraction from the adsorbed benzyl alcohol, evolving into benzaldehyde, which then couples with aniline in the next step to yield the corresponding imine. Finally, cerium-coordinated superoxide species abstract hydrogen from the Au surface, regenerating the catalyst surface.

Hot Electrons, Hot Holes, or Both? Tandem Synthesis of Imines Driven by the Plasmonic Excitation in Au/CeO Nanorods.

Current time-resolved in situ approaches limit the scope of mechanochemical investigations possible. Here we develop a new, general approach to simultaneously follow the evolution of bulk atomic and electronic structure during a mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based X-ray methods: X-ray absorption spectroscopy (XAS) and X-ray diffraction. We apply this method to investigate the bottom-up mechanosynthesis of technologically important Au micro and nanoparticles in the presence of three different reducing agents, hydroquinone, sodium citrate, and NaBH4. Moreover, we show how XAS offers new insight into the early stage generation of growth species (e.g. monomers and clusters), which lead to the subsequent formation of nanoparticles. These processes are beyond the detection capabilities of diffraction methods. This combined X-ray approach paves the way to new directions in mechanochemical research of advanced electronic materials.

Article	Year
Tuning Thermal Catalytic Enhancement in Doped MnO-Au Nano-Heterojunctions. ACS applied materials & interfaces\| PubMed ID: 31013046	2019
Synthesis, Transformation, and Utilization of Monodispersed Colloidal Spheres. Accounts of chemical research\| PubMed ID: 31793763	2019
Investigating the repair of alveolar bone defects by gelatin methacrylate hydrogels-encapsulated human periodontal ligament stem cells. Journal of materials science. Materials in medicine\| PubMed ID: 31811403	2019
Hot Electrons, Hot Holes, or Both? Tandem Synthesis of Imines Driven by the Plasmonic Excitation in Au/CeO Nanorods. Nanomaterials (Basel, Switzerland)\| PubMed ID: 32759860	2020
Tandem X-ray absorption spectroscopy and scattering for in situ time-resolved monitoring of gold nanoparticle mechanosynthesis. Chemical communications (Cambridge, England)\| PubMed ID: 32760966	2020

Pedro H. C. Camargo

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