Nitrogen dopants on carbon materials play vital roles in metal-free carbon catalysis, while the role of pyridinic nitrogen (N P ) or graphitic nitrogen (N G ) is still on debate. In this work, N-doped carbon nanotubes were employed to catalyze the oxidation of styrene (SOR) with tert-butyl hydroperoxide as oxidant. We observed a significant enhancement of SOR activity caused by the incorporation of nitrogen dopants when the N content was lower than 3.51% but a decline of activity at higher N contents. At N content up to 7.51%, even worse performance than that on N-doped carbon nanotubes with 0.98% N content was observed. This behavior was rationalized by thorough density functional theory calculations. Different catalytic functions of N P and N G were revealed. More significantly, a synergistic effect between N P and N G was demonstrated when they are quite close, which is unbeneficial for the catalytic activity due to the very high energy barriers. The finding may pave a way to the rational design of high-performance metal-free carbon catalysts.
Here
a facile synthesis strategy toward carboxylated leaning tower[6]arene
(CLT6)-mediated gold nanoparticles (CLT6-AuNPs) without external energy
sources and reducing agents has been developed. Due to the cavity
structure of CLT6, CLT6-AuNPs with a controllable particle size show
good stability and excellent performance in label-free detection of
diquat. Significantly, we reveal the reduction mechanism of AuNP formation,
which is the cleavage of some phenyl ether bonds of CLT6 to produce
reductive phenols, thus reducing Au3+ to AuNPs.
Lithium-ion battery anode Hollow nanostructure a b s t r a c t Dual-transition-metal oxide (DTMO) nanostructures are emerging materials for lithium-ion battery (LIB) anodes with improved structural stability, electronic conductivity and electrochemical performance compared to their single-metal counterpart. Herein, composites of graphene with DTMOs (MFeO, M ¼ Co, Mn, Zn) were controllably prepared by harnessing the synthesis atmospheres and the nanoscale diffusion couple. Their composition and morphology were characterized by TEM, EDS mappings, XRD and XPS. The NH 3 treatment resulted in the formation of hollow DTMO nanoparticles on nitrogen-doped graphene, while H 2 and Ar gave graphene-supported hollow and solid DTMO particles, respectively. Electrochemical tests were applied to compare the performance of these composites as LIB anodes. The superior anode performance DTMO electrodes was demonstrated to the corresponding iron oxide composite. CoFe 2 O/RGO composites exhibit excellent rate capability and high-rate cycling stability for lithium storage, due to its stable solid structure. However, the hollowing of DTMO particles cannot elevate the capacity and stability, due to the interfacial resistance and structural changes upon cycling.
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