8 research outputs found
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
liquidâvapor 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
AuâSiO<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 liquidâliquid
phase separation was also observed
Solar Vapor Generation Enabled by Nanoparticles
Solar illumination of broadly absorbing metal or carbon nanoparticles dispersed in a liquid produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Sunlight-illuminated particles can also drive H<sub>2</sub>Oâethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation. These phenomena can also enable important compact solar applications such as sterilization of waste and surgical instruments in resource-poor locations
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
moleculeâsubstrate 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
Evolution of Light-Induced Vapor Generation at a Liquid-Immersed Metallic Nanoparticle
When an Au nanoparticle in a liquid
medium is illuminated with
resonant light of sufficient intensity, a nanometer scale envelope
of vaporî¸a ânanobubbleâî¸surrounding the
particle, is formed. This is the nanoscale onset of the well-known
process of liquid boiling, occurring at a single nanoparticle nucleation
site, resulting from the photothermal response of the nanoparticle.
Here we examine bubble formation at an individual metallic nanoparticle
in detail. Incipient nanobubble formation is observed by monitoring
the plasmon resonance shift of an individual, illuminated Au nanoparticle,
when its local environment changes from liquid to vapor. The temperature
on the nanoparticle surface is monitored during this process, where
a dramatic temperature jump is observed as the nanoscale vapor layer
thermally decouples the nanoparticle from the surrounding liquid.
By increasing the intensity of the incident light or decreasing the
interparticle separation, we observe the formation of micrometer-sized
bubbles resulting from the coalescence of nanoparticle-âboundâ
vapor envelopes. These studies provide the first direct and quantitative
analysis of the evolution of light-induced steam generation by nanoparticles
from the nanoscale to the macroscale, a process that is of fundamental
interest for a growing number of applications
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
The Surprising <i>in Vivo</i> Instability of Near-IR-Absorbing Hollow AuâAg Nanoshells
Photothermal ablation based on resonant illumination of near-infrared-absorbing noble metal nanoparticles that have accumulated in tumors is a highly promising cancer therapy, currently in multiple clinical trials. A crucial aspect of this therapy is the nanoparticle size for optimal tumor uptake. A class of nanoparticles known as hollow Au (or AuâAg) nanoshells (HGNS) is appealing because near-IR resonances are achievable in this system with diameters less than 100 nm. However, in this study, we report a surprising finding that <i>in vivo</i> HGNS are unstable, fragmenting with the Au and the remnants of the sacrificial Ag core accumulating differently in various organs. We synthesized 43, 62, and 82 nm diameter HGNS through a galvanic replacement reaction, with nanoparticles of all sizes showing virtually identical NIR resonances at âź800 nm. A theoretical model indicated that alloying, residual Ag in the nanoparticle core, nanoparticle porosity, and surface defects all contribute to the presence of the plasmon resonance at the observed wavelength, with the major contributing factor being the residual Ag. While PEG functionalization resulted in stable nanoparticles under laser irradiation in solution, an anomalous, strongly element-specific biodistribution observed in tumor-bearing mice suggests that an avid fragmentation of all three sizes of nanoparticles occurred <i>in vivo</i>. Stability studies across a wide range of pH environments and in serum confirmed HGNS fragmentation. These results show that NIR resonant HGNS contain residual Ag, which does not stay contained within the HGNS <i>in vivo</i>. This demonstrates the importance of tracking both materials of a galvanic replacement nanoparticle in biodistribution studies and of performing thorough nanoparticle stability studies prior to any intended <i>in vivo</i> trial application
Hot Electrons Do the Impossible: Plasmon-Induced Dissociation of H<sub>2</sub> on Au
Heterogeneous catalysis is of paramount importance in
chemistry
and energy applications. Catalysts that couple light energy into chemical
reactions in a directed, orbital-specific manner would greatly reduce
the energy input requirements of chemical transformations, revolutionizing
catalysis-driven chemistry. Here we report the room temperature dissociation
of H<sub>2</sub> on gold nanoparticles using visible light. Surface
plasmons excited in the Au nanoparticle decay into hot electrons with
energies between the vacuum level and the work function of the metal.
In this transient state, hot electrons can transfer into a Feshbach
resonance of an H<sub>2</sub> molecule adsorbed on the Au nanoparticle
surface, triggering dissociation. We probe this process by detecting
the formation of HD molecules from the dissociations of H<sub>2</sub> and D<sub>2</sub> and investigate the effect of Au nanoparticle
size and wavelength of incident light on the rate of HD formation.
This work opens a new pathway for controlling chemical reactions on
metallic catalysts
Impurity-Induced Plasmon Damping in Individual Cobalt-Doped Hollow Au Nanoshells
The
optical properties of plasmonic nanoparticles in the size range
corresponding to the electrostatic, or dipole, limit have the potential
to reveal effects otherwise masked by phase retardation. Here we examine
the optical properties of individual, sub-50 nm hollow Au nanoshells
(Co-HGNS), where Co is the initial sacrificial core nanoparticle,
using single particle total internal reflection scattering (TIRS)
spectroscopy. The residual Co present in the metallic shell induces
a substantial broadening of the homogeneous plasmon resonance line
width of the Co-HGNS, where the full width at half-maximum (fwhm)
broadens proportionately with increasing Co content. This doping-induced
line broadening provides a strategy for controlling plasmon line width
independent of nanoparticle size, and has the potential to substantially
modify the relative decay channels for localized nanoparticle surface
plasmons