Synthesis,characterization, and electrochemical performance of nitrogen-modified Pt–Fe alloy nanoparticles supported on ordered mesoporous carbons

A method has been demonstrated to synthesize nitrogen-modified Pt–Fe alloyed nanoparticles (9.2–11.3 nm) supported on ordered mesoporous carbon (Pt _x Fe_100?x N/OMC), which is fabricated by a conventional wet chemical synthesis of Pt–Fe alloyed nanoparticles and followed by carbonization of the nanoparticles with tetraethylenepentamine as nitrogen chelating agent. Among these electrocatalysts, the Pt₃₀Fe₇₀N/OMC has highly catalytic activity for the oxygen reduction reaction (ORR) with significantly enhanced methanol tolerance as well. Combining the results from X-ray diffraction and X-ray absorption spectroscopy, it can be observed that Pt metal in the Pt₃₀Fe₇₀N/OMC is present in the outer shell of Pt–Fe alloys with face-centered cubic crystalline structure. By X-ray photoelectron spectroscopy, the nitrogen-modified Pt surface of Pt₃₀Fe₇₀N/OMC exhibits significant selectivity toward the ORR in the presence of methanol. This enhancement of methanol tolerance could be attributed to the inhibition of methanol adsorption resulting from the modification of the Pt surface with nitrogen.     

Uptake of silver nanoparticles by monocytic THP-1 cells depends on particle size and presence of serum proteins

Human health risks by silver nanoparticle (AgNP) exposure are likely to increase due to the increasing number of NP-containing products and demonstrated adverse effects in various cell lines. Unfortunately, results from (toxicity) studies are often based on exposure dose and are often measured only at a fixed time point. NP uptake kinetics and the time-dependent internal cellular concentration are often not considered. Macrophages are the first line of defense against invading foreign agents including NPs. How macrophages deal with the particles is essential for potential toxicity of the NPs. However, there is a considerable lack of uptake studies of particles in the nanometer range and macrophage-like cells. Therefore, uptake rates were determined over 24 h for three different AgNPs sizes (20, 50 and 75 nm) in medium with and without fetal calf serum. Non-toxic concentrations of 10 ng Ag/mL for monocytic THP-1 cells, representing realistic exposure concentration for short-term exposures, were chosen. The uptake of Ag was higher in medium without fetal calf serum and showed increasing uptake for decreasing NP sizes, both on NP mass and on number basis. Internal cellular concentrations reached roughly 32/10 %, 25/18 % and 21/15 % of the nominal concentration in the absence of fetal calf serum/with fetal calf serum for 20-, 50- and 75-nm NPs, respectively. Our research shows that uptake kinetics in macrophages differ for various NP sizes. To increase the understanding of the mechanism of NP toxicity in cells, the process of uptake (timing) should be considered.     

Fabrication high-purity Fe nanochains with near theoretical limit value of saturation magnetization of bulk Fe

High-yield purity chain-like one-dimensional nanostructures consisting of single crystal Fe nanoparticles have been produced by using solution dispersion approach. Room temperature magnetic measurement shows that the as-fabricated Fe nanochains are ferromagnetic with a high saturation magnetization (203 emu/g) whereas the nanoparticles are single magnetic domains, which indicate that the as-synthesized products have superparamagnetism behavior with the saturation magnetization of about 28 emu/g. Maybe this results from the directional alignment of the nanoparticles. The excellent characteristic may have led to the potential applications in spin filtering, high density magnetic recording, and nanosensors.     

Responsive mechanism of 2-(2'-hydroxyphenyl)benzoxazole-based two-photon fluorescent probes for zinc and hydroxide ions

Response theory is used to investigate one- and two-photon absorption(TPA) as well as the emission properties of a series of potential zinc ion and pH sensitive materials containing 2-(2’-hydroxyphenyl)benzoxazole(HPBO) end groups.Special emphasis is placed on the evolution of their optical properties upon combining with zinc ions or deprotonation.Our calculated results indicate that upon combining with zinc ions or deprotonation,these HPBO derivatives show drastic changes in their one-photon absorption(OPA),emission,and TPA properties.Moreover,the mechanisms of the probes are analyzed and found to be an intramolecular charge transfer.These compounds are thus proved to be excellent candidates for two-photon fluorescent zinc and pH probes.     

纵向耦合对垂直腔面发射激光器的影响

考虑到垂直腔面发射激光器中的光子与载流子的纵向耦合,在行波速率方程中引入了纵向耦合因子。利用这个速率方程,讨论了阀值电流与量子阱数目的关系,计算结果表明光子与载流子的纵向耦合是不容忽视的。给出了阀值电流表达式,它表明纵向耦合因子越大,阀值电流越低。     

Black phosphorus saturable absorber for ultrafast mode‐locked pulse laser via evanescent field interaction

Black phosphorus, or BP, has found a lot of applications in recent years including photonics. The most recent studies have shown that the material has an excellent optical nonlinearity useful in many areas, one of which is in saturable absorption for passive mode‐locking. A direct interaction scheme for mode‐locking, however, has a potential to optically cause permanent damage to the already delicate material. Evanescent field interaction scheme has already been proven to be a useful method to prevent such danger for other 2‐dimensional nanomaterials. In this report, we have utilized the evanescent field interaction to demonstrate that the optical nonlinear characteristics of BP is sufficiently strong to use in such an indirect interaction method. The successful demonstration of the passive mode‐locking operation has generated pulses with the pulse duration, repetition rate, and time bandwidth product of 2.18 ps, 15.59 MHz, and 0.336, respectively.     

Polymer electrolytes—relaxation and transport properties

Relaxations in polymer electrolytes were studied in poly(ethylene oxide) and epoxidized natural rubbers both filled with lithium perchlorate. Impedance relaxation was investigated over a wide range of salt concentration at room temperature. Imaginary part of impedance as a function of frequency exhibits generally one maximum and one minimum. These two extreme values rule properties in the DC limit. They can be related to transport properties and degree of dissociation. It turns out that DC conductivity is dominantly ruled by transport coefficient.