Solar Paradigm #5: Generating Singular Nanomaterials

Solar Paradigm #5: Generating
Singular Nanomaterials
Si
MoS2
WIS: Reshef Tenne, Ana Albu-Yaron, Moshe Levy
BGU: Jeffrey Gordon, Daniel Feuermann, Eugene A. Katz
Solar Paradigms 1-4:
1) Solar thermal
2) Solar
photovoltaics
3) Solar biology (photosynthesis)
4) Solar
rectifying
antennas
Solar paradigm 5: Using
concentrated sunlight to
synthesize valued nanomaterials
at the service of science and
technology (rather than
supplanting conventional power
generation systems)
Si
MoS2
R. Tenne et al: Fullerenes and
nanotubes should not be
restricted to Carbon: they could
occur in other layered
compounds, e.g., MoS2 (layered
structure similar to that of
graphite) - also a super lubricant
and super adhesive
Another attractive
candidate
but problematic to
handle in the
lab,
with fullerene-like
structures
remaining
elusive
Cs2O tailors coatings
in photo-emissive and
photo-detecting devices
(but is ultra-reactive)
Limitations of laser ablation:
1. Requirement of oven enhancement - conventional
quartz ovens < 1100 C
2. Typically ultra-small focal regions (e.g., 10-3 mm2)
3. Uniform annealing environment (vs strong
gradients that may favor metastable nanostructures)
Proposal: Highly concentrated direct sunlight
a) Generate reactor temperatures ≈ 2000-3000 K,
over sizable areas (of order mm2),
b) Naturally create a photonically hot, strongly
inhomogeneous annealing environment, and
c) Affordable (as opposed to high-wattage lasers)
The brightest non-coherent (non-laser) light
available to us has been from the surface of the sun.
Irradiance at the fiber tip (1.0 mm diameter):
up to 10,000 suns (10 W/mm2)
Target irradiance after dilution ≈ 4,000 suns
Sample TEM images for Cs2O
Simple, inexpensive, photo-thermal procedure for
synthesizing Cs2O fullerenes with highly
concentrated sunlight: demonstrated and
unambiguously confirmed with TEM and HRTEM
WIS + BGU teams, Advanced Materials 18 (2006) 2993-2996
Solar nanomaterial synthesis of MoS2
MoS2 nanotubes
From pure
crystalline MoS2
only
SiO2 nanofibers and
nanospheres
First-time generation of
SiO2 nanoparticles
directly from quartz
SiO2 nanoparticles
indicate reactor
temperatures
≥ 2000 K
Si nanorods and nanofibers
(from SiO + black absorber, e.g., MoS2 , WS2 , C)
2SiO ® Si + SiO2
MoS2, SiO2 and Si nanostructure findings:
WIS+BGU teams, J. Mater. Chem. 18 (2008) 458-462
Limitation to be surmounted:
Diverging solar fiber optic dilutes target irradiance.
Can we increase power density and power, hence
enlarging the target area and annealing region at
even higher temperatures?
Experimental (optical) modification:
New solar mini-furnace that can attain ~15,000 suns
(15 W/mm2) over a sizable irradiated region (mm2)
(converging Gregorian telescope)
Creation of a favorable hot annealing region via
(a) thermal blackbody radiation from the irradiated
target material and
(b) an extended wide-angle focal region (of order mm2)
quartz ampoule
gradient oven effect from
precursor blackbody radiation
and wide-angle solar input
field of ultra-intense
uniform solar irradiation
Nano-structures from the solar furnace
1. Exfoliated MoS2 (battery electrode applications)
2. Exfoliated graphene-like
nano-structures from pure graphite
Nature’s true inorganic fullerenes:
MoS2 nano-octahedra – the
basic smallness limit.
Already found: large hollow multiwall quasi-spherical MoS2
WIS+BGU teams, Angew. Chem. Int. Ed. 50 (2011) 1810-1814
Can hybrid nano-structures
(nano-octahedral core and
quasi-spherical shells) exist?
Unprecedented (and unpredicted) hybrid MoS2
nano-structures generated by solar ablation
(at ~15,000 suns, with temperatures ≥ 2500°C):
~10 core nano-octahedra surround by ~10 quasispherical layers
+ signatures of simulateneous metallic and semiconducting layers (atomic resolution microscopy)
Massive increases in nanotube yields via Pb catalysis:
for MoS2, MoSe2, WS2, WSe2
[WIS + BGU teams, J. Am. Chem. Soc. 134 (2012) 16379-16386]
Deciphering reaction pathways
via solar ablation of variable duration
Two possibilities for contending with the ephemeral
nature of direct sunlight:
1)
2) Ultra-bright short-arc Xe discharge lamps (sun in a bottle)
+ clever optics
Dual-mirror tailored (aplanatic) optics for
reconstituting the immense power density of ultrabright lamps onto a nanomaterial reactor
Radiative transfer near the thermodynamic limit
Peak target irradiance = 7 W/mm2 (7,000 suns)
Lamp-ablation results: replicating many earlier solar
ablation results, with product that indicate reactor
temperatures ≥ 2500°C:
(1) MoS2 nano-octahedra at the fundamental
smallness limit for nano-structure stability.
(2) Lamp ablation of graphite: carbon nanotubes uncatalyzed
Solar Paradigm #5: Generating
Singular Nanomaterials
Si
MoS2
WIS: Reshef Tenne, Ana Albu-Yaron, Moshe Levy
BGU: Jeffrey Gordon, Daniel Feuermann, Eugene A. Katz