6 research outputs found
Exploring the Chemical Enhancement of Surface-Enhanced Raman Scattering with a Designed Silver/Silica Cavity Substrate
Silver nanoparticles were assembled onto the bottom of
closed-packed
silica cavity using polystyrene (PS) spheres as template. Charge transfer
between the adsorbed 4-aminothiophenol (PATP) and the silver nanoparticles
was studied using surface-enhanced Raman spectroscopy with 514, 633,
785, and 1064 nm excitation, and compared to that of the immobilized
silver
nanoparticles without the modification of silica cavity. Using the
concept of degree of charge transfer, we directly observed the additional
chemical enhancement without a deliberate distinction between electromagnetic
(EM) enhancement and chemical enhancement. It was demonstrated that
the negative charges of the silica could induce the formation of the
dipole in the nanoparticles, thus enlarging the electron density at
the sites where probe molecules adsorbed, and leading to higher charge
transfer from the metal to the adsorbed PATP molecules. We also proposed
another model to further elucidate the relationship between the electron
density and the charge transfer. The result showed that the reduction
of the electron density of silver nanoparticles will cause the redistribution
of the dipole, thereby reducing the charge transfer degree
Nanoparticle-Mediated, Light-Induced Phase Separations
Nanoparticles
that both absorb and scatter light, when dispersed in a liquid, absorb
optical energy and heat a reduced fluid volume due to the combination
of multiple scattering and optical absorption. This can induce a localized
liquid–vapor phase change within the reduced volume without
the requirement of heating the entire fluid. For binary liquid mixtures,
this process results in vaporization of the more volatile component
of the mixture. When subsequently condensed, these two steps of vaporization
and condensation constitute a distillation process mediated by nanoparticles
and driven by optical illumination. Because it does not require the
heating of a large volume of fluid, this process requires substantially
less energy than traditional distillation using thermal sources. We
investigated nanoparticle-mediated, light-induced distillation of
ethanol-H<sub>2</sub>O and 1-propanol-H<sub>2</sub>O mixtures, using
Au–SiO<sub>2</sub> nanoshells as the absorber-scatterer nanoparticle
and nanoparticle-resonant laser irradiation to drive the process.
For ethanol-H<sub>2</sub>O mixtures, the mole fraction of ethanol
obtained in the light-induced process is substantially higher than
that obtained by conventional thermal distillation, essentially removing
the ethanol-H<sub>2</sub>O azeotrope that limits conventional distillation.
In contrast, for 1-propanol-H<sub>2</sub>O mixtures the distillate
properties resulting from light-induced distillation were very similar
to those obtained by thermal distillation. In the 1-propanol-H<sub>2</sub>O system, a nanoparticle-mediated, light-induced liquid–liquid
phase separation was also observed
Surfactant-Assisted Synthesis of Fe<sub>2</sub>O<sub>3</sub> Nanoparticles and F‑Doped Carbon Modification toward an Improved Fe<sub>3</sub>O<sub>4</sub>@CF<sub><i>x</i></sub>/LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> Battery
A simple
surfactant-assisted reflux method was used in this study
for the synthesis of cocklebur-shaped Fe<sub>2</sub>O<sub>3</sub> nanoparticles
(NPs). With this strategy, a series of nanostructured Fe<sub>2</sub>O<sub>3</sub> NPs with a size distribution ranging from 20 to 120
nm and a tunable surface area were readily controlled by varying reflux
temperature and the type of surfactant. Surfactants such as cetyltrimethylammonium
bromide (CTAB), polyvinylpyrrolidone (PVP), polyÂ(ethylene glycol)-<i>block</i>-polyÂ(propylene glycol)-<i>block</i>-polyÂ(ethylene
glycol) (F127) and sodium dodecyl benzenesulfonate (SDBS) were used
to achieve large-scale synthesis of uniform Fe<sub>2</sub>O<sub>3</sub> NPs with a relatively low cost. A new composite of Fe<sub>3</sub>O<sub>4</sub>@CF<sub><i>x</i></sub> was prepared by coating
the primary Fe<sub>2</sub>O<sub>3</sub> NPs with a layer of F-doped
carbon (CF<sub><i>x</i></sub>) with a one-step carbonization
process. The Fe<sub>3</sub>O<sub>4</sub>@CF<sub><i>x</i></sub> composite was utilized as the anode in a lithium ion battery
and exhibited a high reversible capacity of 900 mAh g<sup>–1</sup> at a current density of 100 mA g<sup>–1</sup> over 100 cycles
with 95% capacity retention. In addition, a new Fe<sub>3</sub>O<sub>4</sub>@CF<sub><i>x</i></sub>/LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> battery with a high energy density of 371
Wh kg<sup>–1</sup> (vs cathode) was successfully assembled,
and more than 300 cycles were easily completed with 66.8% capacity
retention at 100 mA g<sup>–1</sup>. Even cycled at the high
temperature of 45 °C, this full cell also exhibited a relatively
high capacity of 91.6 mAh g<sup>–1</sup> (vs cathode) at 100
mA g<sup>–1</sup> and retained 54.6% of its reversible capacity
over 50 cycles. Introducing CF<sub><i>x</i></sub> chemicals
to modify metal oxide anodes and/or any other cathode is of great
interest for advanced energy storage and conversion devices
Aluminum Nanocrystals: A Sustainable Substrate for Quantitative SERS-Based DNA Detection
Since its discovery in the 1970s,
surface-enhanced Raman scattering
(SERS) has been primarily associated with substrates composed of nanostructured
noble metals. Here we investigate chemically synthesized nanocrystal
aggregates of aluminum, an inexpensive, highly abundant, and sustainable
metal, as SERS substrates. Al nanocrystal aggregates are capable of
substantial near-infrared SERS enhancements, similar to Au nanoparticles.
The intrinsic nanoscale surface oxide of Al nanocrystals supports
molecule–substrate interactions that differ dramatically from
noble metal substrates. The preferential affinity of the single-stranded
DNA (ssDNA) phosphate backbone for the Al oxide surface preserves
both the spectral features and nucleic acid cross sections relative
to conventional Raman spectroscopy, enabling quantitative ssDNA detection
and analysis
Combining Solar Steam Processing and Solar Distillation for Fully Off-Grid Production of Cellulosic Bioethanol
Conventional
bioethanol for transportation fuel typically consumes
agricultural feedstocks also suitable for human consumption and requires
large amounts of energy for conversion of feedstock to fuel. Alternative
feedstocks, optimally those not also in demand for human consumption,
and off-grid energy sources for processing would both contribute to
making bioethanol far more sustainable than current practices. Cellulosic
bioethanol production involves three steps: the extraction of sugars
from cellulosic feedstock, the fermentation of sugars to produce ethanol,
and the purification of ethanol through distillation. Traditional
production methods for extraction and distillation are energy intensive
and therefore costly, limiting the advancement of this approach. Here
we report an initial demonstration of the conversion of cellulosic
feedstock into ethanol by completely off-grid solar processing steps.
Our approach is based on nanoparticle-enabled solar steam generation,
in which high-efficiency steam can be produced by illuminating light-absorbing
nanoparticles dispersed in H<sub>2</sub>O with sunlight. We used solar-generated
steam to successfully hydrolyze feedstock into sugars; we then used
solar steam-distillation to purify ethanol in the final processing
step. Coastal hay, a grass grown for livestock feed across the southern
United States, and sugar cane as a control are successfully converted
to ethanol in this proof-of-concept study. This entirely off-grid
solar production method has the potential to realize the long-dreamed-of
goal of sustainable cellulosic bioethanol production
Aluminum Nanocrystals as a Plasmonic Photocatalyst for Hydrogen Dissociation
Hydrogen dissociation is a critical
step in many hydrogenation reactions central to industrial chemical
production and pollutant removal. This step typically utilizes the
favorable band structure of precious metal catalysts like platinum
and palladium to achieve high efficiency under mild conditions. Here
we demonstrate that aluminum nanocrystals (Al NCs), when illuminated,
can be used as a photocatalyst for hydrogen dissociation at room temperature
and atmospheric pressure, despite the high activation barrier toward
hydrogen adsorption and dissociation. We show that hot electron transfer
from Al NCs to the antibonding orbitals of hydrogen molecules facilitates
their dissociation. Hot electrons generated from surface plasmon decay
and from direct photoexcitation of the interband transitions of Al
both contribute to this process. Our results pave the way for the
use of aluminum, an earth-abundant, nonprecious metal, for photocatalysis