Morphology control of the fabricated hydrophobic gold nanostructures in W/O microemulsion under microwave irradiation

The hydrophobic gold nanostructures with different shapes were prepared by using n-butanol situ reduction in cetyltrimethylammonium bromide (CTAB)/n-butanol/n-heptane/HAuCl₄(aq) W/O microemulsion through microwave dielectric heating. The CTAB-stabilized gold nanoparticles and nanowires with a networked structure obtained through this method were characterized and analyzed by ultraviolet visible spectroscopy (UV-vis), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. The morphologies of the hydrophobic gold nanocrystals were successfully controlled through the adjustment of molar ratios of CTAB/HAuCl₄ in the reverse microemulsion. The formation mechanism of anisotropic gold nanostructures was discussed, which demonstrated that CTAB played an important role in forming and stabilizing the shape of gold nanowires.     

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt3Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Pt₃Ni stands as one of the most active electrocatalysts for the oxygen reduction reaction (ORR). The activity varies with the morphology of the nanocrystals with a high activity observed for the octahedral shape where only the high density {111} crystallographic planes are exposed. Herein, the synthesis of 6 nm Pt₃Ni octahedral nanocrystals with a Pt enriched shell or cuboctahedral nanocrystals with a Ni enriched shell is described. Interestingly, the cuboctahedral nanocrystals display a six-pointed star/skeleton of platinum, which features a very uncommon atomic distribution. In the synthesis, a decrease in the oxygen partial pressure induces the transition from octahedral to cuboctahedral morphology. The octahedral and cuboctahedral nanocrystals both demonstrate high ORR activity (1.1 mA cm⁻²_Pt and 1.2 A mg⁻¹_Pt at 0.9 V vs reversible hydrogen electrode (RHE) are the highest values obtained for PtNi-20 and PtNi-15, respectively). After exposure to oxidative conditions in the acidic electrolyte, the cuboctahedral nanoparticles with a pristine Ni-rich skin show a Pt skin and retain their cuboctahedral morphology.     

Synthesis, characterization and mechanism of cetyltrimethylammonium bromide bilayer-encapsulated gold nanosheets and nanocrystals

Single-crystal Au nanosheets and fcc gold nanocrystals of uniform size were synthesized by a novel and simple route. The results of field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated the formation of the single-crystal structure of gold nanosheets and fcc nanocrystals. Energy-dispersive analysis of X-ray (EDAX) showed absorbance of cetyltrimethylammonium bromide (CTAB) molecules onto the surface of gold nanostructures. Moreover, zeta potential measurements showed that CTAB-coated nanostructures were positively charged and the zeta potential remained almost the same upon centrifugation and redispersion of the resulting nanostructures in methanol, confirming the high stability of the surfactant-protected nanocomposites. Evolution of the nanostructures during the reaction was monitored by TEM observations. The results indicated that the formation of the gold nanostructures followed a two-step mechanism with a bilayer CTAB structure on the surface of the gold nanostructures.     

Cooling dynamics of self‐assembled monolayer coating for integrated gold nanocrystals on a glass substrate

Picosecond time‐resolved X‐ray diffraction has been used to study the nanoscale thermal transportation dynamics of bare gold nanocrystals and thiol‐based self‐assembled monolayer (SAM)‐coated integrated gold nanocrystals on a SiO₂ glass substrate. A temporal lattice expansion of 0.30–0.33% was observed in the bare and SAM‐coated nanocrystals on the glass substrate; the thermal energy inside the gold nanocrystals was transported to the contacted substrate through the gold–SiO₂ interface. The interfacial thermal conductivity between the single‐layered gold nanocrystal film and the SiO₂ substrate is estimated to be 45 MW m^?2 K^?1 from the decay of the Au 111 peak shift, which was linearly dependent on the transient temperature. For the SAM‐coated gold nanocrystals, the thermal dissipation was faster than that of the bare gold nanocrystal film. The thermal flow from the nanocrystals to the SAM‐coated molecules promotes heat dissipation from the laser‐heated SAM‐coated gold nanocrystals. The thermal transportation of the laser‐heated SAM‐coated gold nanocrystal film was analyzed using the bidirectional thermal dissipation model.     

Fe3O4 surface electronic structures and stability from GGA + U

The electronic structures, stabilities and magnetic properties of the Fe₃O₄(111), (110) and (001) surfaces have been computed at the level of density functional theory by including the Hubbard parameter (U) for describing the on-site Coulomb interaction of iron 3d electrons. Among the six Fe₃O₄(111) terminations, the Fe_tet1 (exposing tetrahedral coordinated iron) and Fe_oct2 (exposing octahedral coordinated iron) terminations are more stable and have metallic character. For the Fe₃O₄(110) surface, strong surface distortion has been found; the A-layer termination (exposing tetrahedral coordinated iron) has metallic character, while the B-layer termination (exposing tetrahedral and octahedral coordinated iron) has half-metal character. For the Fe₃O₄(001) surface, both A-layer (exposing tetrahedral coordinated iron) and B-layer (exposing octahedral coordinated iron) terminations have half-metal character. The surface stability of (111) > (001) > (110) on the basis of the computed surface energies agrees well with the experimental findings, and explains reasonably the observed diversity and complexity of the experiments.     

Infrared study of triruthenium dodecacarbonyl interactions with gold

We present here a study of the interaction of triruthenium dodecacarbonyl Ru₃(CO)₁₂ with gold surfaces using time-evolved and temperature-programmed infrared reflection absorption spectroscopy (IRAS) and STM. Ru₃(CO)₁₂ exhibits drastically different adsorption/desorption behavior on high-index surfaces of gold in comparison to the smooth Au(111) surface. On the smooth Au(111) surface, the adsorption of Ru₃(CO)₁₂ at 200 K is observed to be molecular and reversible with the molecule's Ru₃-plane oriented essentially perpendicular to the surface in the first and second layer. In the multilayer (> 3 ML), the molecule is oriented parallel (or moderately inclined) to the surface. On high-index gold surfaces, prepared by partial annealing of rough gold films, the molecules dissociate. Vibrational spectra reveal dissociation of carbonyl to Ru and CO at elevated temperature (> 250 K) with the formation of CO covered Ru-islands and the subsequent desorption of CO from Ru-islands. Increasing amounts of CO observed with increasing surface roughness demonstrate that the rate of Ru₃(CO)₁₂ dissociation is related directly to the surface roughness of the gold surface. STM images reveal at low coverage the formation of 2-D islands of carbonyl fragments with lateral sizes of 1 to 1.5 nm and at higher coverage the formation of larger 3-D islands of 1 to 3 layers and lateral sizes above 10 nm.     

Facet‐Dependent Effect of Well‐Defined CeO2 Nanocrystals on the Adsorption and Dephosphorylation of Phosphorylated Molecules

CeO₂ nanocrystals (CN) with different morphologies (i.e., cube, octahedron, and rod) are prepared and the facet‐dependent effect of these CeO₂ nanocrystals on the adsorption and dephosphorylation of phosphorylated molecules is investigated for the first time using the model p‐nitrophenyl disodium orthophorphate (p‐NPP). Due to their different surface atomic configurations, the {111} and {110} facets have much higher adsorption capacity and kinetic catalytic activities than {100} facets. All the CeO₂ nanocrystals can intensely promote the dephosphorylation reaction owing to the strong interaction between Ce cations and phosphoryl oxygens resulting in the cleavage of phosphoester bonds. As was expected, the above facet‐dependent effect can be verified by the practical application results of the CeO₂ nanocrystals on the capture and dephosphorylation of phosphopeptides. Thus, surface engineering could be a useful and feasible strategy for not only fundamentally understanding the interaction between crystal facets and molecules but also effectively developing high‐performance functional materials.     

Optical properties and ferromagnetism of ternary Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te nanocrystals

Cd_1−x Mn _x Te (x = 0, 0.1, 0.2) nanocrystals have been synthesized by mechanical alloying (MA) Cd, Mn, and Se elemental powders. XRD patterns and HRTEM images confirmed the formation of cubic Cd_1−x Mn _x Te nanocrystals. All the diffraction peaks from elemental Cd, Mn, and Te powders disappeared completely in those XRD patterns of as-milled Cd_1−x Mn _x Te nanocrystals for more than 20 h. When the MA process was carried out for 40 h, typical zinc blende structure diffraction mode was exhibited in the XRD pattern. Subsequently, capping the surface of as-milled Cd_1−x Mn _x Te nanocrystals with long chain trioctylphosphine/trioctylphosphine oxide/nitric acid (TOP/TOPO/NA) molecules has achieved colorful dispersion solution, which shows similar optical properties to those CdTe nanocrystals prepared by wet chemical process. The grain size is within the range of 2–8 nm for the capped Cd_1−x Mn _x Te nanocrystals being ball milled for 40 h. The PL excitation peak red shifts to longer wavelength side with increasing Mn concentration. Pure CdTe nanocrystals show ferromagnetism behavior at room temperature, the saturation magnetization value and magnetic hysteresis loop increase with the content of substituting Mn ions within the Cd_1−x Mn _x Te nanocrystals.     

Rapid extra-/intracellular biosynthesis of gold nanoparticles by the fungus <Emphasis Type="Italic">Penicillium</Emphasis> sp.

In this work, the fungus Penicillium was used for rapid extra-/intracellular biosynthesis of gold nanoparticles. AuCl₄ ⁻ ions reacted with the cell filtrate of Penicillium sp. resulting in extracellular biosynthesis of gold nanoparticles within 1 min. Intracellular biosynthesis of gold nanoparticles was obtained by incubating AuCl₄ ⁻ solution with fungal biomass for 8 h. The gold nanoparticles were characterized by means of visual observation, UV–Vis absorption spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The extracellular nanoparticles exhibited maximum absorbance at 545 nm in UV–Vis spectroscopy. The XRD spectrum showed Bragg reflections corresponding to the gold nanocrystals. TEM exhibited the formed spherical gold nanoparticles in the size range from 30 to 50 nm with an average size of 45 nm. SEM and TEM revealed that the intracellular gold nanoparticles were well dispersed on the cell wall and within the cell, and they are mostly spherical in shape with an average diameter of 50 nm. The presence of gold was confirmed by EDX analysis.     

Enhancement of the room temperature oxidation of silicon by very thin predeposited gold layers

The oxidation of Si(111) surfaces covered with very thin layers of gold is studied by Auger and electron energy loss spectroscopies under ultra high vacuum conditions. It is found that by exposing the Au covered surface to an oxidizing atmosphere, formation of silicon dioxide occurs at room temperature on top of the substrate and the presence of SiO₄ tetrahedra is clearly seen on electron energy loss spectra. In contrast, oxidation under the same conditions of a clean Si(111) surface leads to the formation of an oxygen monolayer and no structure corresponding to Si-O bonds in SiO₄ tetrahedra are observed. This enhancement of the oxidation is attributed to a change in the hybridization state of Si atoms in a gold environment.     

Au/Cu2O core/shell nanostructures with efficient photoresponses

Metal/semiconductor nanoscale heterojunctions are of pronounced attention because of their specific structures and properties that vary in their individual counterparts and anticipated applications in photo-driven fields. A modified facile method is reported in this connection for the formation of cuprous-oxide coated gold (Au/Cu₂O) nanostructures including octahedral, cuboctahedral and flower-like structures using cubic and multi-faceted gold nanostructures as the core material. The well-organized shape growth of the Cu₂O-shell is accomplished via an adequate adjustment of the ratio H₂O:NH₂OH^·HCl in the solution. The effect of nanoparticle's shape and thickness of the shell on the optical properties of truncated-octahedra, cuboctahedra and flower-like Au/Cu₂O nanostructures (having sizes within 90–230 nm) shows a bathochromatic shift in the surface plasmon resonance (SPR) band of the Au-core with the increase of shell thickness. A comparative study to correlate the photoluminescence analyses of core/shell nanostructures with their photocatalytic activities shows that truncated-octahedra and nanoflowers, bounded by {111} facets, are photocatalytically more active. On the other hand, cuboctahedra with more {100} catalytically inactive sites reveal a comparatively sharp emission peak. These photoresposes are also appeared to be affected by SPR coupling between plasmonic metal-core and semiconducting-shell.     

Growth of monodisperse nanocrystals of cerium oxide during synthesis and annealing

Monodisperse cerium oxide nanocrystals have been successfully synthesised using simple ammonia precipitation technique from cerium(III) nitrate solution at different temperatures in the range 35–80 °C. The activation energy for growth of CeO₂ nanocrystals during the precipitation is calculated as 11.54 kJ/mol using Arrhenius plot. Average crystal diameter was obtained from XRD analysis, HR-TEM and light scattering (PCS). The analysis of size data from HR-TEM images and PCS clearly indicated the formation of highly crystalline CeO₂ particles in narrow size range. CeO₂ nanocrystals precipitated at 35 °C were further annealed at temperatures in the range 300–700 °C. The activation energy for crystal growth during annealing is also calculated and is close to the reported values. An effort is made to predict the mechanism of crystal growth during the precipitation and annealing.     

Enhancement of second harmonic intensity in thermally poled ferroelectric nanocrystallized glasses in the BaO-TiO2-SiO2 system

The transparent nanocrystallized (heat-treatment: 750 ^°C, 1 h) glasses consisting of ferroelectric Ba₂TiSi₂O₈ nanocrystals (size: 100-200 nm) have been prepared in 40BaO-20TiO₂-40SiO₂ glass, and the effect of a thermal poling (DC electric voltage: 8.8 kV/cm, temperature: 110-300 ^°C, time: 1 h) on the second harmonic (SH) intensity has been examined. It is found that the formation behavior of nanocrystals at the surface differs from that in the interior of glass, giving a new insight into the well-known concept for nanocrystallization or homogeneous nucleation in glass. The Maker fringe patterns with fine structures are observed, indicating a high orientation of the polarization axes of Ba₂TiSi₂O₈ crystals formed at the surface. The prominent enhancement in the SH intensity is observed due to thermal poling, demonstrating that thermal poling is an effective method in enhancing anisotropic polarization of ferroelectric Ba₂TiSi₂O₈ nanocrystals in crystallized glasses. The present study proposes that the Maker fringe pattern for SH intensity of nanocrystallized glasses is very sensitive to the anisotropic polarization of nanocrystals at the surface, indicating the importance of the Maker fringe technique for the characterization of nanocrystals in materials.     

Hyperfine characterization of the crystallization of nanocrystalline NiFe2O4 from the amorphous silica gel

Nanocrystalline NiFe₂O₄ was in‐situ prepared in amorphous silica using tetramethylor‐thosilicate and nickel (iron) nitrate hydrate as the starting materials in a sol‐gel reaction. The magnetic nanocrystals in the amorphous silica glasses grew slowly with increasing temperature. Above 600^○C, nickel ferrite nanoparticles began to precipitate from the amorphous silica matrix. Mössbauer spectroscopy of the nanocomposites suggested that in the silica glasses, Fe ions were present exclusively as Fe³⁺ in octahedral coordination, and the chemical environment of the Fe³⁺ ions appeared to remain unchanged until the crystallization of nickel ferrite nanocrystals. The formation of NiFe₂O₄ nanocrystals was the result of partial transformation of the FeO₆ octahedra to FeO₄ tetrahedra. The nanocrystalline NiFe₂O₄ are characterized by super‐paramagnetic behaviour at room temperature.     

Effect of surfactants on the degradation of perfluorooctanoic acid (PFOA) by ultrasonic (US) treatment

Perfluorooctanoic acid (C₇F₁₅COOH, PFOA) is an aqueous anionic surfactant and a persistent organic pollutant. It can be easily adsorbed onto the bubble-water interface and both mineralized and degraded by ultrasonic (US) cavitation at room temperature. The aim of this study is to investigate whether the effect of US on the degradation of PFOA in solution can be enhanced by the addition of surfactant. To achieve this aim, we first investigated the addition of a cationic (hexadecyl trimethyl ammonium bromide, CTAB), a nonionic (octyl phenol ethoxylate, TritonX-100), and an anionic (sodium dodecyl sulfate, SDS) surfactant. We found the addition of CTAB to have increased the degradation rate the most, followed by TritonX-100. SDS inhibited the degradation rate. We then conducted further experiments characterizing the removal efficiency of CTAB at varying surfactant concentrations and solution pHs. The removal efficiency of PFOA increased with CTAB concentration, with the efficiency reaching 79% after 120 min at 25 °C with a 0.12 mM CTAB dose.     

Combined Facile Synthesis,Purification, and Surface Functionalization Approach Yields Monodispersed Gold Nanorods for Drug Delivery Applications

Synthesizing gold nanorods (AuNRs) by seed-mediated growth method results in the presence of undesired size and shape particles by-products occupying 10–90% of the population. In this study, AuNRs are synthesized by the seed-mediated growth method using cetyltrimethylammonium bromide (CTAB) as a surfactant. AuNRs with redshifted longitudinal localized surface plasmon resonance (LLSPR) peak, localized in the biological “transparency window” (650–1350 nm), are synthesized after optimizing seed solution, silver nitrate solution, and hydrochloric acid solution volumes, based on the published protocols. A two-step purification method, dialysis followed by centrifugation, is applied to remove excess CTAB and collect LLSPR-redshifted AuNRs with high rod purity (>90%). CTAB is subsequently exchanged with polyethylene glycol (PEG) to improve AuNRs biocompatibility. PEGylated AuNRs are confirmed innocuous to both SN4741 cells and B16F10 cells by the modified MTT assay and the modified lactate dehydrogenase (LDH) assay up to 1 nm and 24 h incubation. In this study, a combined facile synthesis, purification, and surface functionalization approach is proposed to obtain water-dispersible monodispersed AuNRs for drug delivery applications.     

Synthesis of hydrophobic gold nanoclusters: growth mechanism study,luminescence property and catalytic application

One-pot synthesis of well dispersed, size-controlled gold nanoparticles with the average size of 10–15 nm and luminescent gold nanoclusters with average size of 1.7–2.0 nm were successfully achieved by thermal decomposition of gold organometallic precursor CH₃AuPPh₃ in the presence of thiol surfactants in o-xylene. Only difference between the preparations of two types of Au nanoparticles is the amount of thiol surfactant employed. The mechanistic study of formation of gold nanoparticles was carried out by analyzing the samples at different reaction time intervals and revealed that two-staged growth process was involved. The nanoclusters showed strong red emission with the maximum intensity at about 600 nm. The maximum room temperature photoluminescence quantum yield was measured as 1.2%. The catalytic ability of the Au nanoclusters to promote Suzuki–Miyaura coupling involving the C–C bond formation was also investigated.     

Core-shell LaF<Subscript>3</Subscript>:Er,Yb nanocrystal doped sol–gel materials as waveguide amplifiers

The oleic acid (OA)-modified LaF₃:Er,Yb and LaF₃:Er,Yb–LaF₃ core-shell nanocrystals are synthesized. The lifetime values could be further improved by incorporating core-shell nanocrystals. A kind of sol–gel derived organic–inorganic hybrid material (SGHM) allows for 50 wt.% or even more of both the two nanocrystals in the matrix, and we give the explanation from scattering analysis. It’s precisely because we use the erbium nanocrystals rather than erbium organic complexes, and avoid the undesirable luminescence quenching by Er–Er clustering with a high Er³⁺ concentration. LaF₃:Er,Yb–LaF₃/SGHM transparent films and optical waveguides are also fabricated. The nanocomposite films show strong 1550 nm luminescence intensity under the excitation of 980 nm after heat treatment below 150 °C and the full-width-at-half-maximum is about 51 nm. The loss and optical gain of the waveguide are measured. A relative gain of about 3.5 dB is measured at 1550 nm in a 1.7 cm long waveguide.     

Polar oxide interface stabilization by formation of metallic nanocrystals

In situ x-ray photoelectron spectroscopy and ex situ transmission electron microscopy and diffraction studies of a model Fe3O4(111)/MgO(111) polar oxide interface exclude stabilization by interface faceting, reconstruction, or by formation of a continuous interfacial layer with altered stoichiometry, and uncover stabilization by dominant formation of metallic Fe(110) nanocrystals. The iron nanocrystals nucleate both at the interface and within the magnetite film and grow in a Nishiyama-Wasserman orientation relationship with a bimodal size distribution related to twinning. Minority magnetite nanocrystals were also observed, growing in the less polar (100) orientation than the magnetite (111) film. Electron transfer and bond hybridization mechanisms are likely at the metal/oxide and oxide/oxide interfaces and remain to be explored.     

Nucleation of Polypropylene Crystallization with Gold Nanoparticles. Part 2: Relation between Particle Morphology and Nucleation Activity

The influence of gold nanoparticle morphology on nucleation of isotactic polypropylene (PP) crystallization was investigated. Previous experiments indicated certain nucleation activity of gold nanoparticles, varying with their size. In this work, eight types of gold micro/nanoparticles were used: vacuum-sputtered nanostructures (nanoparticles, nanoislands, and nanolayers), chemically prepared isometric gold nanocrystals (5, 20, and 100 nm diameters), and two types of gold microcrystals with well-developed crystal facets [with (100) and (111) facets, respectively]. To minimize the effect of particle agglomeration, we used our recently introduced sandwich method, in which the nucleating agent was deposited between thin PP films and the nucleation was evaluated by polarized light microscopy (PLM), X-ray scattering (WAXS), and differential scanning calorimetry (DSC). The nucleation activity of Au particles in PP was lower than it might be expected from the previous studies and depended on their morphology. The nucleation activity of Au microcrystals with well-developed facets was higher than the activity of non-faceted Au nanocrystals.