Nearly monodispersed spherical silver nanoparticles (Ag NPs) were synthesized by using tannic acid (TA) as both reductant and stabilizer in a 30 °C water bath. The size of the as-prepared Ag NPs could be tuned in a range of 7-66 nm by changing the molar ratio of TA to silver nitrate and pH of the reaction solutions. UV-vis spectra, TEM observations, and temporal evolution of the monomer concentrations for the reactions carried out at different experimental conditions showed that the improved size distribution and size tunability of the Ag NPs were mainly attributed to the use of TA, which could promote the balance of nucleation and growth processes of the NPs effectively. The size of the Ag NPs was extendable up to 200 nm in one-pot fashion by the multi-injection approach. The size-dependent surface-enhanced Raman scattering (SERS) activity of the as-prepared Ag NPs was evaluated, and the NPs with size around 100 nm were identified to show a maximum enhanced factor of 3.6 × 10(5). Moreover, the as-prepared TA-coated Ag NPs presented excellent colloidal stability compared to the conventional citrate-coated ones.
Homogeneous
platinum alloy nanoparticles (NPs) are of great interest
to the electrocatalytic community for potential use in various fuel
cell electrodes. Increasing the surface area available per unit mass
by decreasing the size of NPs while maintaining or improving activity
is one of the key tasks of fuel cell catalysis. Achieving both in
a synthesis of multielement NPs is still a challenging workup. In
this investigation, we report the use of glycine as a size control
agent to make ultrasmall homogeneous trimetallic PtNiCu NPs within
2–5 nm range. The mechanistic roles of dimethyl formamide (DMF),
formaldehyde, water, and glycine are explored to understand the formation
of these small NPs. Interestingly, it was observed that these PtNiCu
NPs exhibited substantially enhanced mass activities toward the electro-oxidation
of ethanol in comparison to commercial Pt black.
We
report a simple but detailed solution 13C nuclear
magnetic resonance spectroscopic study of atomically precise neutral
Au25(SR)18
0 (SR = alkyl thiolate) clusters. The paramagnetic 13C Knight shift of alkyl chain carbons, which is proportional to the
local electron spin density, exhibits an electron spin delocalization
that exponentially decays along the alkyl chain. The magnitude and
decay constant of the observed electron spin delocalization, although
largely independent of alkyl chain length, depend on where, that is,
“in” versus “out” (vide infra) position, the alkyl chain is bound, in agreement
with density functional theory calculations. Notably, the determined
position-dependent decay constants, 1.70/Å and 0.41/Å for
“in” and “out” ligands, respectively,
not only could have important ramifications in molecular spintronics
but are also comparable to measured decay constants in molecular electrical
conductance of alkyl chains, potentially offering an alternative,
simple method for estimating the latter. Moreover, the negative intercept
temperatures of linear fits of reciprocal 13C (as well
its bound 1H) Knight shift versus temperature
strongly suggest the existence of local ferrimagnetism in individual
Au25(SR)18
0 clusters.
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