Xikun Yang

TD-DFT accuracy in determining excited-state structures and fluorescence spectra of firefly emitter

We analyzed the excited-state structures and emission spectra of firefly emitter, the anionic keto form of firefly oxyluciferin(keto-1), determined by the time dependent-density functional theory(TD-DFT) approach. The analysis is based on a direct comparison with the highly correlated CASSCF(MS-CASPT2) ab initio approach. 49 DFT functionals were considered and applied to the study. Among the tested functionals, mPW3PBE, B3PW91 and B3P86 give the best performance for ground-state geometry, absorption spectrum, excite-state geometry and emission spectrum.

One-pot synthesis of PdM/RGO (M=Co, Ni, or Cu) catalysts under the existence of PEG for electro-oxidation of methanol

The binary PdM (M=Co, Ni, Cu) catalysts were synthesized with one-pot on reduced graphene oxide (RGO) using the sodium borohydride reduction method under the existence of the polyethylene glycol (PEG). And the catalysts were used for the electro-oxidation of methanol in alkaline media. Cyclic voltammetry (CV) and chronoamperometry (i-t) tests indicated that the Pd-based binary systems significantly enhanced electrochemical activities and improved stability compared with the monometallic Pd/RGO and commercial Pd/C (JM) catalysts. The lower onset potentials of PdM/RGO indicated that the prepared PdM/RGO catalysts had the better electrochemical performance than Pd/RGO and Pd/C (JM). Physicochemical properties of the PdM/RGO catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman. These results show that the better electrochemical performance of PdM/RGO can be ascribed to the addition of the second metal and PEG, because M successfully modified the morphology and electronic structure of Pd, and improved dispersibility of PdM on the reduced graphene oxide. And these modifications can be easily carried out under the presence of PEG.

The Enhanced Electro-catalytic Performance of Au@Pd Nanoparticles Self-assembled on Fluorine-Modified Multi-walled Carbon Nanotubes for Methanol Oxidation

Au@Pd nanoparticles (NPs) with different atomic ratios (4:1, 1:1, 1:4) are synthesized via a simple one-step ultraviolet irradiation method, which are self-assembled on the surface of multi-walled carbon nanotubes modified by –F groups (HF−MWCNTs). The morphology, structure and composition of catalysts are characterized by ultraviolet visible spectra (Uv–Vis), transmission electron microscopy (TEM), high-angle annular dark-filed scanning TEM (HAADF-STEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results display Au@Pd (1:4) NPs have a clear core–shell structure. All of Au@Pd NPs can be uniformly dispersed on the HF−MWCNTs. Methanol oxidation performance of the catalysts is measured by cyclic voltammetry (CV) and chronoamperometry (i−t). Electrochemical tests indicate that Au@Pd/MWCNTs (1:1) catalyst exhibits the excellent electrocatalytic activity and best durability toward methanol oxidation in alkaline media, which is 4.4 times higher than that of the commercial Pd/C. This enhanced electro-catalytic performance could be attributed to uniform dispersion, synergetic effect of core–shell structure, strong metal-support interaction (SMSI effect) between –F functional groups and NPs. The –F groups can interact with Au and Pd atoms to form fluorine complexes, which change the electronic structure of Au and Pd atoms so as to enhance the activity and stability of the Au@Pd/MWCNTs (1:1) catalyst.Graphical Abstract

Pd Nanoparticles Self-Assembled on Fluorine-Modified MWCNTs as Electro-Catalysts for Methanol Electro-Oxidation

Multi-walled carbon nanotubes (MWCNTs) were modified by hydrogen fluoride (HF) in a simple method. With the help of fluorine, Pd nanoparticles (3.9nm) synthesized by a one-step photochemical reduction were uniformly self-assembled on the active sites of functionalized MWCNTs and a new catalyst (Pd/HF-MWCNT) was obtained. UV–Vis absorption spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used. The results demonstrated that –F groups were introduced onto the surface of MWCNTs and C–F chemical bonds were formed. In addition, the electronic structure of Pd was changed. Pd–F coordination bond maybe formed between F atom and Pd atom. Cyclic voltammetry and chronoamperometry tests indicated that electro-catalytic activity of Pd/HF-MWCNTs catalyst for methanol in alkaline medium was about 1.6 times higher than that of the commercial Pd/C (JM) catalyst at the same condition. This new functionalized method ha...