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Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants. Kinetic current density (jk) at certain overpotential calculated by K-L equation is commonly used as the metrics to evaluate the activity of electrocatalysts. However, it is frequently found that the jl is not correctly identified in the literatures. Instead of jK, the measured current density normalized by diffusion limiting current density (j/jL) has also been frequently under circumstance where its validity is not justified. By taking ORR/HER/HOR as examples, we demonstrate that identify the actualjL for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce jk. Our analysis reveals that j/jL is a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same. In addition, if one wants to use j/jL to compare the intrinsic activity, the concentration overpotential should be eliminated.
This work reports the systematic study of surface phenomenon and self-aggregation behavior of cationic surfactant cetyltrymethyl ammonium bromide (CTAB) with ammonium nitrate (NH4NO3) salt. Surface and thermodynamic properties of cationic surfactant CTAB with ammonium nitrate salt were investigated at different temperatures through different techniques like conductometry and surface tensiometery. The surface tension measurement was carried out to find out the critical micelle concentration (CMC), free energy of adsorption (?Gads), free energy of micellization (?Gm), minimum area per molecule (A) and surface excess concentration (Г). The study reveals that the process of micellization is spontaneous and exothermic in nature. Conductance measurement enabled us to determine CMC, degree of ionization (α), degree of counter ion binding (β). Upon addition of NH4NO3 to the surfactant solutions increase the values of α and β, although it lowers the values of CMC showing that the process of micellization is more favorable and spontaneous. The study is very helpful to develop better understanding about interaction between electrolyte and surfactant.
Understanding the influence of nanoparticles on the formation of protein amyloid fibrillation is crucial to extend their application in related biological diagnosis and nanomedicines. In this work, Raman spectroscopy was used to probe the amyloid fibrillation of hen egg-white lysozyme (HEWL) in the presence of silver nanoparticles (AgNPs) at different concentrations, combined with atomic force microscopy (AFM) and Thioflavin T (ThT) fluorescence assays. Four representative Raman indicators were utilized to monitor transformation of the protein tertiary and secondary structures at the molecular level: the Trp doublet bands at 1340 and 1360 cm-1, the disulfide stretching vibrational peak at 507 cm-1, the N-Cα-C stretching vibration at 933 cm-1, and the amide I band. All experimental results confirmed the concentration-dependent influence of AgNPs on the HEWL amyloid fibrillation kinetics. In the presence of AgNPs at low concentration (17 µg/ml), electrostatic interaction of the nanoparticles stabilizes disulfide bonds, and protect the Trp residues from exposure to hydrophilic environment, thus leading to formation of amorphous aggregates rather than fibrils. However, with the action of AgNPs at high concentration (1700 µg/ml), the native disulfide bonds of HEWL are broken to form Ag-S bonds owing to the competition of electrostatic interaction from a great deal of nanoparticles. According to providing functional surfaces for protein to interact with, AgNPs play a bridge role on direct transformation from α-helices to organized β-sheets. The present investigation sheds light on the controversial effects of AgNPs on the kinetics of HEWL amyloid fibrillation.
We report a measurement of electron momentum distributions of valence orbitals of cyclopentene employing symmetric noncoplanar (e, 2e) kinematics at impact energies of 1200 and 1600 eV plus the binding energy. Experimental momentum profiles for individual ionization bands are obtained and compared with theoretical calculations considering nuclear dynamics by harmonic analytical quantum mechanical and thermal sampling molecular dynamics approaches. The results demonstrate that molecular vibrational motions including ring-puckering of this flexible cyclic molecule have obvious influences on the electron momentum profiles for the outer valence orbitals, especially in the low momentum region. For π*-like molecular orbitals 3a'' and 2a''+3a' , the impact-energy dependence of the experimental momentum profiles indicates a distorted wave effect.
Though poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely adopted as hole transport material (HTM) in flexible perovskite solar cells (PSCs), arising from high optical transparency, good mechanical flexibility, and high thermal stability, its acidity and hygroscopicity would inevitably hamper the long-term stability of the PSCs and its energy level does not match well with that of perovskite materials which would lead to a relatively low open-circuit voltage (VOC). In this investigation, p-type delafossite CuCrO2 nanoparticles synthesized through hydrothermal method have been employed as an alternative HTM for triple cation perovskite [(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08 (possessing better photovoltaic performance and stability than conventional CH3NH3PbI3) based inverted architecture PSCs. The average VOC of PSCs has increased from 908 mV of the devices with PEDOT:PSS HTM to 1020 mV of the devices with CuCrO2 HTM. Ultraviolet photoemission spectroscopy measurement demonstrates the energy band alignment between CuCrO2 and perovskite is better than that between PEDOT:PSS and perovskite, the electrochemical impedance spectroscopy indicates CuCrO2 based PSCs exhibit larger recombination resistance and longer charge carrier lifetime, which contribute to the high VOC of CuCrO2 HTM based PSCs.
Fast and accurate quantitative detection of $^{14}$CO$_2$ has important applications in many fields. The optical detection method based on the sensitive cavity ring-down spectroscopy technology has great potential. But currently it has difficulties of insufficient sensitivity and susceptibility to absorption of other isotopes/impurity molecules. We propose a stepped double-resonance spectroscopy method to excite $^{14}$CO$_2$ molecules to an intermediate vibrationally excited state, and use cavity ring-down spectroscopy to probe them. The two-photon process significantly improves the selectivity of detection. We derived the quantitative measurement capability of double-resonance absorption spectroscopy. The simulation results show that the double-resonance spectroscopy measurement is Doppler-free, thereby reducing the effect of other molecular absorption. It is expected that this method can achieve high-selectivity detection of $^{14}$CO$_2$ at the sub-ppt level.
A novel electrochemical non-enzymatic glucose sensor based on three-dimensional Au/MXene nanocomposites was developed. MXenes were prepared using the mild etched method, and the porous foam of Au nanoparticles was combined with the MXene by means of in situ synthesis. By controlling the mass of MXene in the synthesis process, porous foam with Au nanoparticles was obtained. The three-dimensional foam structure of nanoparticles was confirmed by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical performance of the Au/MXene nanocomposites. The Au/MXene nanocomposites acted as a fast redox probe for non-enzymatic glucose oxidation and showed good performance, including a high sensitivity of 22.45 μA mM−1 cm−1 and a wide linear range of 1–12 mM. Studies have shown that MXene as a catalyst-supported material is beneficial to enhance the conductivity of electrons and increase the loading rate of the catalyst materials. The foam structure with Au nanoparticles can provide a larger surface area, increase the contact area with the molecule in the catalytic reaction, and enhance the electrochemical reaction signal. In summary, this study showed that Au/MXene nanoparticles have the potential to be used in non-enzymatic glucose sensors.
N-乙基吡咯是吡咯分子的一个乙基取代衍生物,它的激发态衰变动力学目前为止很少被研究。在本文中,我们利用飞秒时间分辨光电子成像的实验方法研究了N-乙基吡咯分子S1态的衰变动力学。实验上采用了241.9和237.7 nm的泵浦激发波长。在241.9 nm激发下,得到了5.0±0.7 ps, 66.4±15.6 ps 和1.3±0.1 ns三个寿命常数。对于237.7 nm, 得到了2.1±0.1 ps 和13.1±1.2 ps两个寿命常数。我们将所有寿命常数都归属为S1态的振动态。并对不同S1振动态的弛豫机理进行了讨论。 N-ethylpyrrole is one of ethyl-substituted derivatives of pyrrole and its excited-state decay dynamics has never been explored. In this paper, we investigate ultrafast decay dynamics of N-ethylpyrrole excited to the S1 electronic state using a femtosecond time-resolved photoelectron imaging method. Two pump wavelengths of 241.9 and 237.7 nm are employed. At 241.9 nm, three time constants, 5.0±0.7 ps, 66.4±15.6 ps and 1.3±0.1 ns, were derived. For 237.7 nm, two time constants of 2.1±0.1 ps and 13.1±1.2 ps were derived. We assign all these time constants to be associated with different vibrational states in the S1 state. The possible decay mechanisms of different S1 vibrational states are briefly discussed.
The burgeoning two-dimensional (2D) layered materials provide a powerful strategy to realize efficient light-emitting devices. Among them, Gallium telluride (GaTe) nanoflakes, emerging strong photoluminescence (PL) emission from multilayer to bulk crystal, relax the stringent fabrication requirements of nanodevices. However, detailed knowledge on the optical properties of GaTe varied as layer thickness is still missing. Here we perform thickness-dependent PL and Raman spectra, as well as temperature-dependent PL spectra of GaTe nanoflakes. Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in GaTe nanoflakes. To understand the experimental results, we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes. On the basis of temperature-dependent PL spectra, the optical gap of the hexagonal phase is determined to 1.849 eV, which can only survive under a temperature higher than 200 K with the increasing phonon population. Furthermore, the exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 meV/K. Our results prove the coexistence of dual crystalline phases in multilayer GaTe nanoflakes, which may provoke further exploration of phase transformation in GaTe materials, as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.