8 research outputs found
Improving The Catalytic Activity Of Semiconductor Nanocrystals Through Selective Domain Etching
Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of semiconductor nanocrystals. While many nanocrystal architectures can be obtained directly via colloidal growth, other nanoparticle morphologies require alternative processing strategies. Here, we show that chemical etching of colloidal nanoparticles can facilitate the realization of nanocrystal shapes that are topologically inaccessible by hot-injection techniques alone. The present methodology is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle dimer, constructed in a way that both CdSe and CdS semiconductor domains are exposed to the external environment. This structural morphology is highly desirable for catalytic applications as it enables both reductive and oxidative reactions to occur simultaneously on dissimilar nanoparticle surfaces. Hydrogen production tests confirmed the improved catalytic activity of CdSe/CdS dimers, which was enhanced 3-4 times upon etching treatment. We expect that the demonstrated application of etching to shaping of colloidal heteronanocrystals can become a common methodology in the synthesis of charge-separating nanocrystals, leading to advanced nanoparticles architectures for applications in areas of photocatalysis, photovoltaics, and light detection
Enhanced Lifetime Of Excitons In Nonepitaxial Au/cds Core/shell Nanocrystals
The ability of metal nanoparticles to capture light through plasmon excitations offers an opportunity for enhancing the optical absorption of plasmon-coupled semiconductor materials via energy transfer. This process, however, requires that the semiconductor component is electrically insulated to prevent a backward charge flow into metal and interfacial states, which causes a premature dissociation of excitons. Here we demonstrate that such an energy exchange can be achieved on the nanoscale by using nonepitaxial Au/CdS core/shell nanocomposites. These materials are fabricated via a multistep cation exchange reaction, which decouples metal and semiconductor phases leading to fewer interfacial defects. Ultrafast transient absorption measurements confirm that the lifetime of excitons in the CdS shell (tau approximate to 300 ps) is much longer than lifetimes of excitons in conventional, reduction-grown Au/CdS heteronanostructures. As a result, the energy of metal nanoparticles can be efficiently utilized by the semiconductor component without undergoing significant nonradiative energy losses, an important property for catalytic or photovoltaic applications. The reduced rate of exciton dissociation in the CdS domain of Au/CdS nanocomposites was attributed to the nonepitaxial nature of Au/CdS interfaces associated with low defect density and a high potential barrier of the interstitial phase
Ultrafast Photochemistry of Polyhalogenated Methanes and Non-Metals
A molecular level understanding of photodynamics in condensed media is one of the recent challenges to chemical physics. This is because of the intrinsic complexity of liquid-phase photophysical and photochemical singularities arising from competing intra- and intermolecular processes. Such processes often take place on a timescale of a few femtoseconds (10-15 s) to several tens of picoseconds (10-12 s). In this work, the model photochemical processes used to investigate ultrafast photo-induced reaction dynamics in solution. The model compounds are non-metal/metal polyhalogenated small molecules. The gas-phase photochemistry of these small molecules is thoroughly examined, which also enables to establish the connection between liquid and gas phase dynamics. Furthermore, contrary to the scrupulously investigated di- and triatomic molecular systems, more vibrational degrees of freedom are accessible both for the model parent molecules, nascent polyatomic radical species, and isomer photoproducts. Therefore, a detailed mapping of the photochemical reaction paths of these molecular systems can possibly reveal different couplings between the reactive modes and other dark states in a far-from-equilibrium situation. The complexity of the encountered ultrafast events requires the utilization of several experimental and computational approaches. Results of femtosecond transient absorption, picosecond transient resonance Raman, excited state ab initio calculations are discussed in this context
Changing Mechanical Strength in Cr(III)- Metallosupramolecular Polymers with Ligand Groups and Light Irradiation
We
have demonstrated the ability to control the mechanical properties
of metallosupramolecular materials via choice of ligand binding group,
as well as with external light irradiation. These photoresponsive
CrÂ(III)-based materials were prepared from a series of modified hydrogenated
polyÂ(ethylene-<i>co</i>-butylene) polymers linked through
metal–ligand interactions between a CrÂ(III) metal center and
pyridyl ligand termini of the polymers. The introduction of these
CrÂ(III)-pyridine bonds gave rise to new mechanical and optical properties
of the polymer materials. Depending on the type of pyridyl ligand,
density functional theory calculations revealed changes in coordination
to the CrÂ(III), which ultimately led to materials with significantly
different mechanical properties. Electronic excitation of the CrÂ(III)
materials with 450 and 655 nm CW lasers (800 mW/cm<sup>2</sup>) resulted
in generation of excited state photophysical processes which led to
temporary softening of the materials up to 143 kPa (41.5%) in storage
modulus (<i>G</i>′) magnitude. The initial mechanical
strength of the materials was recovered when the light stimulus was
removed, and no change in mechanical properties was observed with
light irradiation where there was no absorbance by the CrÂ(III) moiety.
These materials demonstrate that introduction of metal–ligand
bonding interactions into polymers enables the design and synthesis
of photoresponsive materials with tunable optical-mechanical properties
not seen in traditional polymeric materials
Improving the Catalytic Activity of Semiconductor Nanocrystals through Selective Domain Etching
Colloidal chemistry offers an assortment
of synthetic tools for
tuning the shape of semiconductor nanocrystals. While many nanocrystal
architectures can be obtained directly via colloidal growth, other
nanoparticle morphologies require alternative processing strategies.
Here, we show that chemical etching of colloidal nanoparticles can
facilitate the realization of nanocrystal shapes that are topologically
inaccessible by hot-injection techniques alone. The present methodology
is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle
dimer, constructed in a way that both CdSe and CdS semiconductor domains
are exposed to the external environment. This structural morphology
is highly desirable for catalytic applications as it enables both
reductive and oxidative reactions to occur simultaneously on dissimilar
nanoparticle surfaces. Hydrogen production tests confirmed the improved
catalytic activity of CdSe/CdS dimers, which was enhanced 3–4
times upon etching treatment. We expect that the demonstrated application
of etching to shaping of colloidal heteronanocrystals can become a
common methodology in the synthesis of charge-separating nanocrystals,
leading to advanced nanoparticles architectures for applications in
areas of photocatalysis, photovoltaics, and light detection