ABSTRACT
An investigation of EtOAc extract from the roots of Paeonia lactiflora yielded three new 30-noroleanane triterpenoids paeonenoides L-N (1-3) and one new oleanane triterpenoid paeonenoide O (4) together with 7 known compounds (5-11). Extensive spectrographic experiments were applied to identify the structures of 1-4, and their absolute configurations were unambiguously determined by theoretical calculations of ECD spectra, as well as the single-crystal X-ray diffraction analysis. Compounds 8, 9 and 10 were isolated from the Paeonia genus for the first time. Moreover, compounds 8, 9 and 11 showed inhibitory activities against LPS-induced nitric oxide (NO) production in RAW264.7 macrophages with the IC50 values of 72. 17 ± 4.74, 30.02 ± 2.03 and 28.34 ± 1.85 µM, respectively.
ABSTRACT
Binary cobalt and nickel phosphides have been widely developed owing to their remarkable activities for the oxygen reduction reaction (OER) as well as their low cost. However, the OER active sites of binary cobalt and nickel phosphides are still controversial. Here, we use a CoNiP nanocage as a model catalyst and systematically investigate the correlation between the composition and the OER activity, clarifying how the ratio of CoOOH/NiOOH affects the OER activity. With the increase of the atomic ratio of Ni/Co (y/x, 0 < y/x < 3.5), the amount of NiOOH generated during the OER always increases; and the CoOOH initially increases and subsequently decreases, showing a similar changing tendency to the OER activity of CoNiP. When y/x = 1.5, CoNiP has the best OER activity with an overpotential of 278 mV at a current density of 10 mA cm-2 and a low Tafel slope of 67 mV dec-1. All tested CoNiP catalysts show better catalytic activity than pure CoP, indicating that the catalytic activity of CoNiP should be attributed to the synergistic effect of CoOOH and NiOOH rather than exclusively to CoOOH or NiOOH. This study clarifies the origin of the catalytic activities of CoNiP, helpful for designing high-efficiency CoNiP catalysts.
ABSTRACT
Cubic Pd nanocrystals (CPNCs) as one of typical nanostructures are generally fabricated using I- or Br- as capping ions. However, which ion, I- or Br-, exclusively mediates the growth of CPNCs in a given reaction system is not well understood. Herein, regardless of I- or Br- as the capping ion, we successfully achieved CPNCs in the same reaction system simply by adjusting the pH. Based on the Finke-Watzky kinetic model, an increase in pH accelerates the overall reduction rate of Pd2+, and the formation of CPNCs only occurs over the range of specific solution reduction rate constants (k1). This kinetically illuminates that the reduction rate of Pd2+ is the physicochemical parameter that determines which ion, I- or Br-, dictates the growth of CPNCs. Also, density functional theory (DFT) calculations further elucidate the dependence of the reduction rate of Pd2+ on pH and the configuration of the activated Pd2+ complex.
ABSTRACT
Three-dimensional (3D) cubic superstructures of PtPd nanocubes were achieved by spontaneous adjustment of PtIV reduction kinetics, and exhibited enhanced catalytic activity and long-term durability towards methanol oxidation compared with the state-of-the-art Pt/C. This work demonstrates the first example of designing 3D shaped architectures of PtPd nanocubes for methanol electrooxidation.
ABSTRACT
Ultralong (â¼25-30 µm) surface-Pt-rich Au93Pt7 alloy nanowires (ANWs) were achieved by a directional coalescence between spherical nanoparticles. Also, the ANWs exhibit superior electrocatalytic activity and long-term durability towards ethanol oxidation, â¼12 times in the mass activity better than the state-of-the-art commercial Pt/C catalyst.
