Ultrasmooth, Highly Spherical Monocrystalline Gold Particles for Precision Plasmonics

Ultrasmooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle sizes of 200 nm or more. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances in small clusters. The high monodispersity of the particles we demonstrate should facilitate the self-assembly of nanoparticle clusters with uniform optical resonances, which could in turn be used to fabricate optical metafluids. Narrow size distributions are required to control not only the spectral features but also the morphology and yield of clusters in certain assembly schemes.Engineering and Applied Science

Large-scale Facile Synthesis of Monodisperse Iron Oxide Nanoparticles in Alcohol

The large-scale synthetic method of hydrophobic soluble Fe2O3 and Fe3O4 nanoparticles was developed with the thermal decomposition technique. From the characteristic analysis with a transmission electron microscopy and X-ray diffraction, the obtained iron oxide nanomaterials showed a cubic structure with a size of ca. 2 nm. The oxidation states of the nanoparticles were investigated via X-ray photoelectron spectroscopy analysis. The tetramethylammonium hydroxide treatment might be induced a phase transfer of the iron oxide nanocrystals from a hydrophobic state to a hydrophilic one. The carbon-coated hydrophilic soluble Fe2O3 nanoparticles could be prepared by a solvothermal reaction of the particles, glucose, and H2O

Identification of Spinel Iron Oxide Nanoparticles by 57Fe NMR

We have synthesized and studied monodisperse iron oxide nanoparticles of smaller than 10 nm to identify between the two spinel phases, magnetite and maghemite. It is shown that 57Fe NMR spectroscopy is a promising tool for distinguishing between the two phases

The Nature of Magnetic State of Small Fe3O4 Nanoparticles

We have investigated the nature of the magnetic state of 4 nm and 7 nm magnetite Fe3O4 nanoparticles and show that they form a collective superspin glass state. Magnetic force on the nanoparticles relevant to the tumor targeting application was determined as well

Unraveling the Simultaneous Enhancement of Selectivity and Durability on Single-Crystalline Gold Particles for Electrochemical CO2 Reduction

Electrochemical carbon dioxide reduction is a mild and eco-friendly approach for CO2 mitigation and producing value-added products. For selective electrochemical CO2 reduction, single-crystalline Au particles (octahedron, truncated-octahedron, and sphere) are synthesized by consecutive growth and chemical etching using a polydiallyldimethylammonium chloride (polyDDA) surfactant, and are surface-functionalized. Monodisperse, single-crystalline Au nanoparticles provide an ideal platform for evaluating the Au surface as a CO(2)reduction catalyst. The polyDDA-Au cathode affords high catalytic activity for CO production, with >90% Faradaic efficiency over a wide potential range between -0.4 and -1.0 V versus RHE, along with high durability owing to the consecutive interaction between dimethylammonium and chloride on the Au surface. The influence of polyDDA on the Au particles, and the origins of the enhanced selectivity and stability are fully investigated using theoretical studies. Chemically adsorbed polyDDA is consecutively affected the initial adsorption of CO2 and the stability of the *CO2, *COOH, and *CO intermediates during continuous CO2 reduction reaction. The polyDDA functionalization is extended to improving the CO Faradaic efficiency of other metal catalysts such as Ag and Zn, indicating its broad applicability for CO2 reduction

Percolated Plasmonic Superlattices of Nanospheres with 1 nm-Level Gap as High-Index Metamaterials

Nanophotonics relies on precise control of refractive index (RI) which can be designed with metamaterials. Plasmonic superstructures of nanoparticles (NPs) can suggest a versatile way of tuning RI. However, the plasmonic effects in the superstructures demand 1 nm-level exquisite control over the interparticle gap, which is challenging in a sub-wavelength NPs. Thus far, a large-area demonstration has been mostly discouraged. Here, heteroligand AuNPs are prepared, which are stable in oil but become Janus particles at the oil–water interface, called “adaptive Janus particles.” NPs are bound at the interface and assembled into 2D arrays over square centimeters as toluene evaporates, which distinctively exhibits the RI tunability. In visible and NIR light, the 2D superstructures exhibit the highest-ever RI (≈7.8) with varying the size and interparticle gap of NPs, which is successfully explained by a plasmonic percolation model. Furthermore, fully solution-processable 2D plasmonic superstructures are proved to be advantageous in flexible photonic devices such as distributed Bragg reflectors. © 2022 Wiley-VCH GmbH.11Nsciescopu

Facile synthesis of fully ordered L1(0)-FePt nanoparticles with controlled Pt-shell thicknesses for electrocatalysis

We report a simple one-step approach for the synthesis of similar to 4 nm uniform and fully L1(0)-ordered face-centered tetragonal (fct) FePt nanoparticles (NPs) embedded in similar to 60 nm MCM-41 (fct-FePt NPs@MCM-41). We controlled the Pt-shell thickness of the fct-FePt NPs by treating the fct-FePt NPs@MCM-41 with acetic acid (HOAc) or hydrochloric acid (HCl) under sonication, thereby etching the surface Fe atoms of the NPs. The fct-FePt NPs deposited onto the carbon support (fct-FePt NP/C) were prepared by mixing the fct-FePt NPs@MCM-41 with carbon and subsequently removing the MCM-41 using NaOH. We also developed a facile method to synthesize acid-treated fct-FePt NP/C by using a HF solution for simultaneous surface-Fe etching and MCM-41 removal. We studied the effects of both surface-Fe etching and Pt-shell thickness on the electrocatalytic properties of fct-FePt NPs for the methanol oxidation reaction (MOR). Compared with the non-treated fct-FePt NP/C catalyst, the HOAc-treated and HCl-treated catalysts exhibit up to 34% larger electrochemically active surface areas (ECASAs); in addition, the HCl-treated fct-FePt NP (with similar to 1.0 nm Pt shell)/C catalyst exhibits the highest specific activity. The HF-treated fct-FePt NP/C exhibits an ECASA almost 2 times larger than those of the other acid-treated fct-FePt NP/C catalysts and shows the highest mass activity (1,435 mA.mg(-1) Pt, 2.3 times higher than that of the commercial Pt/C catalyst) and stability among the catalysts tested. Our findings demonstrate that the surface-Fe etching for the generation of the Pt shell on fct-FePt NPs and the Pt-shell thickness can be factors for optimizing the electrocatalysis of the MOR. © Tsinghua University Press and Springer-Verlag Berlin Heidelberg 20173

Ultrasmooth, highly spherical monocrystalline gold particles for precision plasmonics

Ultrasmooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle sizes of 200 nm or more. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances in small clusters. The high monodispersity of the particles we demonstrate should facilitate the self-assembly of nanoparticle clusters with uniform optical resonances, which could in turn be used to fabricate optical metafluids. Narrow size distributions are required to control not only the spectral features but also the morphology and yield of clusters in certain assembly schemes.Fil: Lee, You Jin. Sungkyunkwan University; Corea del Sur. Korea Basic Science Institute; Corea del SurFil: Schade, Nicholas B.. Harvard University; Estados UnidosFil: Sun, Li. Harvard University; Estados UnidosFil: Fan, Jonathan A.. University of Illinois; Estados UnidosFil: Bae, Doo Ri. Korea Basic Science Institute; Corea del SurFil: Mariscal, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Lee, Gaehang. Korea Basic Science Institute; Corea del SurFil: Capasso, Federico. Harvard University; Estados UnidosFil: Sacanna, Stefano. University of New York; Estados UnidosFil: Manoharan, Vinothan N.. Harvard University; Estados UnidosFil: Yi, Gi Ra. Sungkyunkwan University; Corea del Su

Synthesis and Assembly of Colloidal Particles with Sticky Dimples

The preparation of anisotropic colloidal particles by a simple yet versatile temperature-controlled swelling process is described. The resulting polymeric particles feature a surface dimple, the size and shape of which were determined by the amount of oil captured in particles and the interfacial tension between the three phases: polystyrene (PS), decane, and the suspending medium. Following the removal of free or physically adsorbed surfactant from the swollen particles, hydrophobic dimples were produced upon evaporation of the oil phase. We demonstrate the spontaneous assembly of these ‘dimpled particles’ into dumbbell shapes or trimers through a site-selective hydrophobic interaction