2 research outputs found
Surface-Dependent, Ligand-Mediated Photochemical Etching of CdSe Nanoplatelets
Photochemical etching of CdSe nanoplatelets was studied
to establish
a relationship between the nanocrystal surface and the photochemical
activity of an exciton. Nanoplatelets were synthesized in a mixture
of octylamine and oleylamine for the wurtzite (W) lattice or in octadecene
containing oleic acid for the zinc-blende (ZB) lattice. For photochemical
etching, nanoplatelets were dispersed in chloroform containing oleylamine
and tributylphosphine in the absence or presence of oleic acid and
then irradiated with light at the band-edge absorption maxima. Etching
phenomena were characterized using UV–vis absorption spectroscopy
and transmission electron microscopy. The absorption spectra of both
W and ZB CdSe nanoplatelets showed that the exciton was confined in
one dimension along the thickness. However, the two nanoplatelets
presented different etching kinetics and erosion patterns. The rate
of etching for W CdSe nanoplatelets was much faster than that for
ZB nanoplatelets. Small holes were uniformly perforated on the planar
surface of W nanoplatelets, whereas the corners and edges of ZB nanoplatelets
were massively eroded without a significant perforation on the planar
surface. This suggests that the amine-passivated surface of trivalent
cadmium atoms on CdSe nanoplatelets is photochemically active, but
the carboxylate-passivated surface of divalent cadmium atoms is not.
Hence, the ligand, which induces the growth of W or ZB CdSe nanoplatelets,
mediates the surface-dependent photochemical etching. This result
implies that an electron–hole pair can be extracted from the
planar surface of amine-passivated W nanoplatelets but from the corners
and edges of carboxylate-passivated ZB nanoplatelets
Paper-Based Flow Fractionation System Applicable to Preconcentration and Field-Flow Separation
We
present a novel paper-based flow fractionation system for preconcentration
and field-flow separation. In this passive fluidic device, a straight
channel is divided into multiple daughter channels, each of which
is connected with an expanded region. The hydrodynamic resistance
of the straight channel is predominant compared with those of expanded
regions, so we can create steady flows through the straight and daughter
channels. While the expanded regions absorb a great amount of water
via capillarity, the steady flow continues for 10 min without external
pumping devices. By controlling the relative hydrodynamic resistances
of the daughter channels, we successfully divide the flow with flow
rate ratios of up to 30. Combining this bifurcation system with ion
concentration polarization (ICP), we develop a continuous-flow preconcentrator
on a paper platform, which can preconcentrate a fluorescent dye up
to 33-fold. In addition, we construct a field-flow separation system
to divide two different dyes depending on their electric polarities.
Our flow fractionation systems on a paper-based platform would make
a breakthrough for point-of-care diagnostics with specific functions
including preconcentration and separation