Submicrometer Spheres Research Articles

Ru on Modified Carbon Submicrometric Spheres as Novel Catalysts for the Oxidative Cleavage of Oleic Acid with N‐Methylmorpholine‐N‐Oxide as Green Oxidizing Agent

AbstractOxidative cleavage of unsaturated fatty acids involves the rupture of carbon‐carbon double bonds to produce carbonyl compounds of high added value. This reaction is mainly performed using homogenous catalysts which are pollutant and cannot be recovered while current heterogeneous catalysts display poor activity. To solve this issue, an active catalyst was prepared by impregnating Ru ions on carbon spheres synthesized by hydrothermal carbonization of a glucose solution. Carbon spheres were calcined under air atmosphere to create porosity and functionalized with polydopamine to improve their ability to complex Ru ions. The catalyst was fully characterized and completed the oxidative cleavage of oleic acid within 7 h of stirring at room temperature using NaIO4 as oxidizing agent. The addition of N‐methylmorpholine N‐oxide, a green oxidizing agent, allowed >99 % conversion in only 5 h. Therefore, it was possible to conceive an eco‐friendly carbon catalyst for the valorization of oleic acid under mild conditions.

Crystallization of SrAl12O19 Nanocrystals from Amorphous Submicrometer Particles.

Advanced instrumentation and modern analysis tools such as transmission electron microscopy (TEM) have led to phenomenal progress in understanding crystallization, in particular from solution, which is a prerequisite for the design-based preparation of a target crystal. Nevertheless, little has been understood about the crystallization pathway under high-temperature annealing (HTA) conditions. Metal oxide crystals are prominent materials that are usually obtained via HTA. Despite the widespread application of hydro-/solvothermal methods on the laboratory scale, HTA is the preferred method in many industries for the mass production of metal oxide crystals. However, poor control over the morphology and grain sizes of these crystals under extreme HTA conditions limits their applications. Here, applying ex-situ TEM, the transformation of a single amorphous spherical submicrometer precursor particle of SrAl12O19 (SA6) at 1150 °C toward a nanosized thermodynamically favored hexagonal crystal is explored. It is illustrated in real space, step by step, how both kinetic and thermodynamic factors contribute to this faceting and morphology evolution. These results demonstrate a nonclassical nucleation and growth process consisting of densification, crystallite domain formation, oriented attachment, surface nucleation, 2-dimensional (2D) growth, and surface diffusion of the atoms to eventually result in the formation of a hexagonal platelet crystal. The TEM images further delineate a parent crystal driving the crystal lattice and morphological orientation of a network of interconnected platelets.

Number Concentration Measurements of Polystyrene Submicrometer Particles.

The number of techniques to measure number concentrations and size distributions of submicrometer particles has recently increased. Submicrometer particle standards are needed to improve the accuracy and reproducibility of these techniques. The number concentrations of fluorescently labeled polystyrene submicrometer sphere suspensions with nominal 100 nm, 200 nm and 500 nm diameters were measured using seven different techniques. Diameter values were also measured where possible. The diameter values were found to agree within 20%, but the number concentration values differed by as much as a factor of two. Accuracy and reproducibility related with the different techniques are discussed with the goal of using number concentration standards for instrument calibration. Three of the techniques were used to determine SI-traceable number concentration values, and the three independent values were averaged to give consensus values. This consensus approach is proposed as a protocol for certifying SI-traceable number concentration standards.

Size distribution evolution and viscosity effect on spherical submicrometer particle generation process by pulsed laser melting in liquid

Spherical submicrometer particles (SMPs) can be fabricated by pulsed laser melting in liquid (PLML). In this process, raw nanoparticles dispersed in liquid are irradiated by a pulsed laser, heated over the melting point to generate molten droplets, and quenched to form SMPs. The particle size increment is caused by aggregating and merging raw particles in liquid by transient heating. In this study, the viscosity effect on the formation process of SMPs by PLML process is studied by changing aqueous glycerin solution concentration. In highly viscous liquid, smaller SMPs are generated due to the ineffective aggregation process. The temporal evolution of cumulative volume frequency of particles can be simulated, considering the constraints of the non-melting at larger size due to high heat capacity and evaporation for smaller particles by overheating. The SMP size can be controlled by viscosity of the liquid, prior disaggregation time, and liquid temperature.

Nitrogen and sulfur co-doped carbon sub-micrometer sphere-based electrodes toward high-performance hybrid supercapacitors

The splendid electrochemical characteristics of electrode materials are crucial for achieving high-performance hybrid supercapacitors. In this study, homogeneously dispersed nitrogen and sulfur co-doped carbon (NSC) sub-micrometer spheres are synthesized under a facile polymerization reaction and subsequent carbonization treatment. The NSC sub-micrometer spheres deliver a commendable specific capacitance of 254.8F g−1 at 1 A g−1 along with fantastic cyclic capability benefiting from the rich heteroatoms doping and abundant sub-nanometer pores (<1 nm) on the surface. Besides, using the NSC sub-micrometer spheres as substrate, nickel phosphide (Ni2P) lamellas are in-situ grown on NSC by an effective strategy, which exhibit a decent capacity of 819 C g−1 at 1 A g−1 with 83.2% of capacity retention after 10,000 cycles at 10 A g−1. More importantly, the advanced hybrid supercapacitor fabricated by NSC anode and NSC/Ni2P cathode reveals a desirable energy density of 51.3 Wh kg−1 at 757 W kg−1 and maintains 41.9 Wh kg−1 at 18855 W kg−1 in 6 M KOH, demonstrating the great potential for energy storage applications.

Reduction Mechanism of Transition Metal Oxide Particles in Thermally Induced Nanobubbles during Pulsed Laser Melting in Ethanol.

Pulsed laser melting in liquid (PLML) is a technique to fabricate spherical submicrometer particles (SMPs) wherein nanosecond pulsed laser (several tens to several hundreds of mJ pulse-1 cm-2 ) irradiates raw particles dispersed in liquid. Raw particles are transiently heated above the melting point to form spherical particles, which enables pulsed heating of surrounding liquid to form thermally induced bubbles by liquid vaporization. These transient bubbles play an important role as a thermal barrier to rapidly heat the particle. Reduced SMPs are generated from raw metal-oxide nanoparticles by PLML process in ethanol. This reduction cannot be explained by high-temperature thermal decomposition, but by mediation of molecules decomposed from ethanol. Computational simulations of ethanol decomposition by pulsed heating for 100 ns at the temperature 1000-4000 K revealed that ethylene is generated as the main product. Gibbs free energies of oxide reduction reactions mediated by ethylene greatly decreased compared to those without ethylene mediation. This explanation can be applied to reductive SMP formation from various transition metal oxides by PLML.

Shear response of magnetorheological fluid with Zn0.2Fe2.8O4 sub-micron hollow spheres

Magnetorheological (MR) fluids with Fe3O4 particles are widely studied nowadays due to their soft magnetic nature, controllable morphology, and better chemical stability as compared to their metallic counterpart. However, they can be even more advantageous under Zn doping with elevated magnetization and hollow configuration with low density, making them more active, stable, and dispersible in the carrier fluid. Here, we report the preparation of MR fluids with Zn0.2Fe2.8O4 sub-micrometer hollow spheres and their steady-state MR response under the application of a magnetic field. The MR fluid follows the Bingham plastic nature with a yielding behavior. The variation of yield stress with the applied magnetic field is explained in the context of a newly developed dipolar interaction model.

Microwave absorption properties of spheres-assembled flake-like FeNi3 particles prepared by electrodeposition

Flake-like FeNi3 particles based on submicrometre spheres self-assembly were prepared by electrodeposition method using cetyltrimethylammonium bromide (CTAB) as the morphology modifier. To explore the formation mechanism of the novel flaky structures, three different concentrations of CTAB were employed to electrodeposit FeNi3 particles in the experiment. Linear sweep voltammetry were conducted to measure cathodic polarization curves of the corresponding three solutions. The crystal structure, morphology and electromagnetic properties of corresponding three samples were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, vector network analysis. The effects of CTAB on the morphologies and structures of the FeNi3 particles were investigated. When the concentration of CTAB is 1.0 g/L, the prepared sample exhibited the best microwave absorption properties as a consequence of better electromagnetic impedance matching. The effective absorption bandwidth (RL < −10 dB) increases with decreasing thickness, reaching 4.32 GHz (13.2–17.52 GHz) when the absorber thickness is only 1.3 mm. The minimum reflection loss (RL) reaches −50.42 dB at 3.44 GHz. The absorbent with thickness of 1.3–2.5 mm obtains RL values exceeding −10 dB over a wide frequency range of 4.40–17.52 GHz, which covers almost the whole C, X and Ku-band (4–18 GHz). The microwave absorption properties of as-prepared FeNi3 particles possess the advantage of broad absorption bandwidth especially at thin thickness.

Fabrication of Magnetic α-Fe2O3/Fe3O4 Composite Particles by Nanosecond Laser Irradiation of α-Fe2O3 Powder in Water

Magnetic α-Fe2O3/Fe3O4 composite spherical particles were synthesized by nanosecond pulsed laser irradiation to α-Fe2O3 nanoparticle powder suspended in pure water and acetone. It was shown that the laser-induced reduction efficiencies in two solvents were comparable. The obtained submicrometer spheres exhibited a ferromagnetic property having a higher coercivity than that of commercial Fe3O4.

Thiourea linked glycolipid-assisted synthesis of sub-micrometer sized polyaniline spheres for enzyme less sensing of dopamine

A simple methodology of synthesizing sub-micrometer sized polyaniline (PANI) spheres using gold electrodes with thiourea linked glycolipid self-assembly for the selective detection of dopamine (DA) is reported here. The synthesis was carried out using a potentiodynamic polymerization method. The self-assembled thiourea linked glycolipid on the gold electrodes and the same lipid acting as the surface directing agent for the formation of polyaniline microspheres is the highlighting factor in this work. The biocompatible sub-micrometer polyaniline spheres are characterized using scanning electron microscopy and transmission electron microscopy studies. Amperometry and electrochemical impedance spectroscopy were employed to estimate the concentration of dopamine. The amperometric studies reveal a linear range of ~ 1 to 640 μM, sensitivity of 370 μA cm−2 μM−1, a very low detection limit of 10 nM, and a response time of ~ 5 s. The interference from l-Dopa, ascorbic acid and uric acid has been minimized on account of the Nafion (Nf) coating and selectivity of the electrode. Real sample analysis was carried out using standard addition method. Schematic representation for the formation of sub-micrometer PANI spheres using thiourea linked glycolipid on Au electrodes for sensing of dopamine.

GdF3hollow spheres: self-assembly and multiple emission spanning the UV to NIR regions under 980 nm excitation

Monodispersed GdF3:Er3+,Yb3+hollow submicrometer spheres were successfully synthesized by self-assembly of ∼16 nm nanocrystals, and exhibit unique strong emissions spanning from UV to NIR under excitation at 980 nm.

Hydrothermally synthesized Iron Phosphate Hydroxide thin film electrocatalyst for electrochemical water splitting

Hydrogen production is an immediate need to replace the fossil fuels to keep environmental balance, and water splitting is an effective solution in presence of catalyst through oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, for the first time, we have synthesized Iron Phosphate Hydroxide (Fe2.95(PO4)2(OH)2) thin film electrode as a superior electrocatalyst by facile hydrothermal method using binder free approach. The crystallographic properties are studied from X-ray diffraction pattern, and Reitveld refinement analysis shows best fit with the tetragonal Lipscombite structure of Iron Phosphate Hydroxide (Fe2.95(PO4)2(OH)2). Flower like structure consist of agglomerated nanorods on micro and sub-micrometric spheres of Fe2.95(PO4)2(OH)2 exhibits lower overpotential of 281 mV at 10 mA/cm2 current density towards OER in alkaline (1 M KOH) medium and maintains its activity after 12 h catalytic stability test. Moreover, prepared electrode shows HER with overpotential 165.7 mV at current density 10 mA/cm2 in acidic (1 M H3PO4) medium and demonstrates enhanced performance (126.4 mV overpotential) after 12 h catalytic stability. The Fe2.95(PO4)2(OH)2 thin film electrodes show superior performance in OER and HER, compared with its oxide counterpart (Fe2O3).

Structural regulation of NiFe2O4 colloidal nanocrystal assembly and their magnetic and electrocatalytic properties

In-situ assembly of colloidal nanocrystals provides us an effective way to synthesize unique functional assemblies. Submicrometric spheres with tunable structures, which are assembled by nickel ferrite colloidal nanocrystals, were synthesized through solvothermal synthesis. The morphologies and structures of NiFe2O4 colloidal nanocrystal assemblies (CNAs) were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. One of the NiFe2O4 CNAs adopt an inverse spinel structure with a size of around 300 nm from the sodium acetate-contained synthesis system, in which the crystallite size of NiFe2O4 nanocrystals is about 11 nm. However, provided that the urea were added into the synthesis system, the as-prepared NiFe2O4 CNAs has a normal spinel structure, which these clusters assembled by 31 nm nanocrystals are 600 nm in size. The magnetometric measurement results showed that the small NiFe2O4 CNAs displayed nearly superparamagnetic behavior at room temperature while the large NiFe2O4 CNAs performed ferromagnetic behavior mainly owing to the effect of crystallite size. In particular, electrochemical sensing measurements showed that the size of the NiFe2O4 nanocrystals played an important role in the electrochemical reduction of H2O2. Based on the experimental results, the formation mechanisms of both NiFe2O4 CNAs as well as the relationship between their structures and properties were analyzed and discussed in this paper.

Tribological properties of laser-generated hard ceramic particles in a gear drive contact

The lubricant is a central element in the transmission design. It primarily separates the two contact partners through a pressure-induced solidification in the lubrication gap, thus enabling the operation of heavily loaded sliding-rolling contacts. On the one hand, the quality and properties of a lubricant depend on the base oils, which differ by their viscosity and process-technological parameters. The addition of particulate additives gives the lubricants further functional properties that are not contained in the base oil. In this study, the influence of laser-synthesized yttria-stabilized zirconia nano- or submicrometer spheres as dispersed functional elements in the lubricant is studied, and their impact on wear and fatigue on the tooth flank is investigated. The work includes systematic investigations on the influence of the particle’s shape and size by running tests on a FZG gear test rig. Finally, the potential of the laser-generated particles as a lubricant additive is evaluated in a first conclusion.

Polystyrene Opals Responsive to Methanol Vapors.

Photonic crystals (PCs) show reflectance spectra depending on the geometrical structure of the crystal, the refractive index (neff), and the light incident angle, according to the Bragg-Snell law. Three-dimensional photonic crystals (3D-PCs) composed of polymeric sub-micrometer spheres, are arranged in an ordered face cubic centered (fcc) lattice and are good candidates for vapor sensing by exploiting changes of the reflectance spectra. We synthesized high quality polystyrene (PS) 3D-PCs, commonly called opals, with a filling factor f near to the ideal value of 0.74 and tested their optical response in the presence of different concentrations of methanol (MeOH) vapor. When methanol was present in the voids of the photonic crystals, the reflectance spectra experienced energy shifts. The concentration of methyl alcohol vapor can be inferred, due to a linear dependence of the reflectance band maximum wavelength as a function of the vapor concentration. We tested the reversibility of the process and the time stability of the system. A limit of detection (LOD) equal to 5% (v/v0), where v was the volume of methanol and v0 was the total volume of the solution (methanol and water), was estimated. A model related to capillary condensation for intermediate and high methanol concentrations was discussed. Moreover, a swelling process of the PS spheres was invoked to fully understand the unexpected energy shift found for very high methanol content.

Anchoring of Ag nanoparticles on Fe3O4 modified polydopamine sub-micrometer spheres with enhanced catalytic activity

In this study, highly dispersed Ag nanoparticles anchored on Fe3O4 modified polydopamine sub-micrometer spheres (PSS) nanocomposites were fabricated by a facile two-step approach. The catalytic properties of the as-obtained PSS/Fe3O4/Ag ternary nanocomposites were evaluated with the reduction of 4-nitrophenol by NaBH4 as a model reaction. It is shown that the presence of Fe3O4 can significantly decrease the particle size of the in-situ formed Ag nanoparticles on PSS, and optimize the catalytic performance of PSS/Ag nanocomposites. Additionally, the as-synthesized PSS/Fe3O4/Ag ternary nanocomposites exhibit high catalytic stability for recycle. Magnetic study reveals that the ternary nanocomposites display room-temperature superparamagnetic behavior. It is believed that this simple and effective method can be extended for the preparation of other polydopamine-based multicomponent nanocomposites with intriguing property, which would hold great promise for a variety of applications.

Template‐Derived Submicrometric Carbon Spheres for Lithium–Sulfur and Sodium‐Ion Battery Electrodes

AbstractHighly microporous submicrometric carbon spheres were synthesized by etching a sol–gel derived silicon oxycarbide (SiOC) material with aqueous hydrofluoric acid solution. The resulting material shows a large total pore volume of 0.63 cm3 g−1 and thus acts as an ideal host for elemental sulfur. Melt impregnation was used to synthesize a carbon–sulfur composite (50:50 wt %) as a cathode for lithium–sulfur batteries. Characterization by electron microscopy clearly showed that the sulfur is homogeneously distributed within the carbon particles. Electrodes prepared from the composite show good cyclic stability at higher specific currents (e.g., at 500 mA g−1); capacities (related to the active material content) as high as 241 mAh g−1 were retained after 100 cycles and coulombic efficiencies quickly reached values close to 100 %. The material was also tested as an anode in sodium‐ion batteries. Compared to the SiOC precursor, the carbon shows significantly improved electrochemical performance. For instance, at a specific current of 100 mA g−1, a capacity as high as 89 mAh g−1 was retained after 100 cycles, whereas SiOC showed a lower capacity of approximately 70 mAh g−1.

Fe3+ mediated self-assembling of polyarylene ether nitrile block copolymer into cationic dye adsorptive sub-micrometer spheres

Polymeric adsorbents normally need to be chemically crosslinked to be effective in aggressive scenarios, which thus triggers the non-recyclable concern of crosslinked plastics. In this study, we firstly synthesized a novel thermoplastic polyarylene ether nitrile (PEN) block copolymer containing pendant carboxyl and sulfonate groups, which were employed to prepare the sub-micrometer PEN spheres with rough surface and porous morphology via a Fe3+ mediated emulsion self-assembling protocol. Furthermore, the obtained PEN microspheres (MS) demonstrated a maximum adsorption capacity of 738 mg/g towards methylene blue (MB), and more than 90% of MB can be removed at 90 °C for 5 min.

Robust FeCo nanoparticles embedded in a N-doped porous carbon framework for high oxygen conversion catalytic activity in alkaline and acidic media

FeCo alloy nanoparticles were nucleated onto graphitic carbon layers through the pyrolysis of polydopamine (PDA) sub-micrometer spheres to form a highly active electrocatalytic system that exhibits excellent oxygen conversion catalytic activity in both alkaline and acidic media.

Self-Assembly of Peptide-Polyoxometalate Hybrid Sub-Micrometer Spheres for Photocatalytic Degradation of Methylene Blue.

The spontaneous formation of hybrid submicrometer spheres that were composed by a Weakley-type polyoxometalate Na9[EuW10O36]·32H2O (denoted as EuW10) and cationic peptide (K8) through a simple ionic self-assembly method was investigated. The approach presented in this study is an extended research which combined a biomolecule and a functional inorganic polyoxoanion for the fabrication of a multifunctional material. The K8/EuW10 hybrid submicrometer spheres were fully characterized by transmission electron microscopy, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, confocal laser scanning microscopy, and fluorescence spectra. The results indicated that the electrostatic interaction, hydrogen-bonding interaction, and combined hydrophobic interaction between EuW10 and K8 favored the formation of the smooth submicrometer sphere structure. Once the EuW10/K8 submicrometer spheres were forming, the fluorescence of EuW10 was reduced due to the hydrogen bonding between the ammonium group of K8 and the oxygen atom of EuW10 that blocked the hopping of the d1 electron in EuW10. Interestingly, our submicrometer spheres showed excellent decomposition efficiency toward organic pollutants such as the dye of methylene blue (MB), suggesting their promising applications in the treatment of wastewater.