The Chemical Effects of Ultrasound Kenneth S. Suslick Stable Single

The Chemical Effects of Ultrasound Kenneth S. Suslick

School of Chemical Sciences University of Illinois at Urbana-Champaign

• Acoustic Cavitation and Hot Spot Conditions • Sonochemical Synthesis of Nanomaterials • Heterogeneous Sonochemistry • Ultrasonic Spray Pyrolysis

Stable Single Bubble Cavitation ACOUSTIC PRESSURE LIQUID DENSITY

m) 40  IMPLOSION SHOCKWAVE (?) 20 HOT SPOT

BUBBLE RADIUS ( RAPID QUENCHING 0 0 50 100 150 TIME (s)

piezoceramic hydrophone

piezoceramic driver

Photo in full room light for single bubble in H2SO4; glowing bubble clearly visible to the naked eye at 50 m.

Cavitational Collapse of a Single Bubble

Strobed Single Bubble

Rmax ~ 50 µm ~ hair diameter

Rmin < 500 nm ~ large virus size

Pacoustic ~ 1.5 Bar

 = 52 kHz

sbsl ~ 50 ps to 1 ns

Power Supply Suppliers:

Piezoelectric Sonics & Materials, Transducer Branson, Mysonix, ACE Glass, and Titanium Horn even Aldrich! Collar & O-Rings

Gas Inlet/Outlet

Cooling Commercial Scale-up: Glass Cell bath Reaction 2 tons/hr coal gob Solution Lewis Corp. 21 kW, 1800 gal.

Multi-Bubble Sonoluminescence: 85% Sulfuric Acid

1 cm Ti horn

50 µm

MBSL from Cr(CO)6 in Hexadecane

1200 Cr* 1000

800

600 Cr * Cr * Intensity 400

CH * C2 * C2 * 200

background continuum 0

350 400 450 500 550 600 Wavelength (nm)

MBSL of Cr(CO)6 Cr : 4700 K  300 K 2.0 Mo: 4800 K  400 K 6000 K C2 : 4900 K  300 K 5000 K 1.5 Fe : 5100 K  350 K 4000 K

1.0 3000 K Relative Intensity 0.5

0 350 370 390 410 430 450 470 490 510 530 Wavelength (nm)

Hot Spot Conditions during Cavitation

Single Bubble Multi-Bubble Temperature: >15,000 K 1600 to 9000 K (…but, 35 eV plasma) (v.p. controlled)

Pressure: ~1100 atm ~300 atm

Duration: < 1 nsec ~ 1 nsec

Cooling rate: >1013 K/sec >1012 K/sec novel materials…

What Else Might Bubble Be Good For?

Goals:

Stable High Surface Energy Materials (i.e., highly defected surfaces)

Refractory Materials with High Surface Areas

Specific Example: Hydrodesulfurization (HDS)

Why Nanostructured Catalysts? • Nanostructured: 1-10 nm, 100 to 104 atoms. • Properties distinct from either bulk or molecular. • Surface atoms predominate: surface highly defected. • High catalytic activity, often unusual selectivities.

Why Sonochemistry? • Unique interaction of energy and matter. • Every bubble is an isolated 10-18 L (aL) reactor. • Extreme conditions, but extraordinary quench rates. • Easy to produce both in lab and in scale-up.

M(CO)x(NO)y

Supported Nanophase Catalyst Colloids in or zer g ULTRA- SOUND i an bil ic sta ox ide M n Mnn ge su xy lfu o s r ou rce hydro- Nanophase carbon Nanophase Metal Oxides Metal Sulfides Nanophase Metals Powders or Carbides n = 100 - 10,000 © 2010, K. S. Suslick

Why Hydrodesulfurization?

• Sulfur present in all fossil fuels. • Dibenzothiophenes most difficult to remove.

• Fuel burning produces SO2 : major part of acid rain. • Recent decreases in permitted fuel S content. HDS

+ 2 H + H S S 2 catalyst 2

Hydrogenation + H 2 catalyst

1.0 µm 1.0 µm

SEM of Sonochemical MoS2 SEM of Conventional MoS2 Greatly increased edge surface. Limited edge surface, Extremely active HDS Catalyst! limited HDS activity.

Transmission Electron Micrograph of

Sonochemically Prepared MoS2

2 nm

Inter-lamellar spacing unchanged, but heavily defected.

VACUUM He Ar Vac Org. Vac Pressure SYSTEM Gauge Liquid Line Transducer

G.C. M.S.

Flow Controllers

Purifiers TEMP. CONTROL

H CO C H H +CO+Ar NO OVEN 2 226 2 2

Thiophene Hydrodesulfurization

3 MoS2 (conv) )

-1 ReS2 (conv) s * Mo2C (sono) -1

g RuS (conv): PREVIOUS BEST * 2

2 MoS2 (sono) molecules 18 1 Activity (10 Activity

0 325 350 375 Temperature (oC) HDS activity comes from the Mo at edges, not within planes.

Nanostructured MoS2 has more edges.

• Spherical Template: Silica nanospheres (from base hydrolysis of tetraethyl orthosilicate, TEOS)

• Ultrasonic irradiation of slurry:

Mo(CO)6 (1 g), S8 (300 mg), and silica spheres (1 g) in isodurene under Ar flow.

o • MoS2 /silica composite nanospheres annealed 450 C.

• Leach silica with 10% ethanolic aqueous HF.

Hollow MoS2

o TEM hollow MoS2 nanospheres after thermal annealing at 450 C.

Across a single particle of MoS2/SiO2

Before Etching After Leaching with HF

MoS2 Nanospheres: HDS of Thiophene After 24 hours of catalysis.

Aldrich MoS2

)

1 - Sonochemical MoS2

1 - 2 Hollow MoS2 (150 nm)

g . Hollow MoS (50 nm)

s 2

1 1

(

A 0 325 350 375 Temperature (oC)

TEM of Hollow MoO3 Nanospheres

After Leaching with HF. After thermal annealing at 450oC.

What Happens at Surfaces?

SURFACE ACTIVATION: Microjet pitting, etc.

INCREASED SURFACE AREA: Shock wave fragmentation.

ENHANCED MASS TRANSPORT: Surface turbulence.

POWDER MODIFICATION: Interparticle Collisions.

Cavitational Collapse Near a Surface

Cavitation Near an Extended Surface

L. A. Crum

10  m

Sonochemical Activation of Ni Powder

0.1

))) Ni Ni* 0.01 (10 m) octane

Ni* 1-nonene nonane 0.001 H2 Initial Rate (mM/min) Initial

0.0001

100

15 m. 80

5 m. ) 60

(

l 2.5 m.

i Y 40 1 m.

20 NO u.s.

Surface Composition Changes Auger Electron Spectroscopy Depth Profiles

Before Ultrasound After Ultrasound 100 100

Cu 80 80 Cu 60 60

40 O 40 800 nm oxide layer 20 20 O

Atomic Composition (%) C Atomic Composition (%) C 0 0 0204060 0204060 Sputter Time (min.) Sputter Time (min.)

Before ultrasound 60 min. ultrasound

Effect of Ultrasound on Particle Morphology: Ni in decane m  10

Before ultrasound 15 min. ultrasound 120 min. ultrasound

Zn Powder in decane; 20 kHz, 100 W/cm2

Velocity Of Interparticle Collisions

Melted Neck Volume ~ 1 m3 ~ 8 x 10-12 g

Heat of Melting (Fe) ~ 1 m3 ~ 1.6 kJ / g

To melt neck ~ 0.1 erg / neck

Kinetic Energy = ½ mv2 > 0.1 erg

Velocity of Impact ~ 100 to 500 m / s !

Speed of Sound ~ 1100 m / s

Before ultrasound 30 min. ultrasound

m.p.: 2130 K

Effect of Ultrasound on Particle Morphology: Mo in decane m  60

Before ultrasound 30 min. ultrasound

m.p.: 2890 K

Before ultrasound 30 min. ultrasound

m.p.: 3680 K

Effects Of Ultrasound On Metal Powders

METAL MELTING AGGLOME- SURFACE POINT RATION MORPHOLOGY

Sn 505 K ++ ++ Zn 693 K ++ ++ Cu 1358 K ++ ++ Ni 1726 K ++ ++ Cr 2130 K ++ + Mo 2890 K + - W 3680 K - -

20 kHz, 50 W/cm2 , 293 K, 10 micron powder, in decane under Ar.

PR 9 t  v 1exp2  vi 62R n s   o co i t

c u

e s

s d - r X a g g

n i

e r critical velocity c

n i for melting

What About Liquid-Gas Interfaces?

Ultrasonic Humidifier (Sunbeam, $20 eBay) Frequency ~1.7 MHz 2.7 gal of mist / day

Nebulization is due to momentum transfer.

Ultrasonic Fountain and Nebulization

each frame: ~15 x 15 cm.

~1 cm

Ultrasonic Nebulization

Nebulization occurs at capillary standing waves (i.e., ripples).

droplet size  capillary wavelength (Kelvin Eqn.)  1/3 Lang Eqn: D ~ d ()f2

Dd  droplet diameter   surface tension   density f  atomization frequency

At 1.7 MHz, 2 to 5 μm diameter droplets with H2O

Synthetic Methodology: furnace 2 Easy nanoparticle synthesis: droplets as isolated microreactors. product furnace 1 collector One pot encapsulation, polymerization, & drying: in situ template synthesis.

ultrasonic Porous solid synthesis: fountain matrix with pyrolyzable template. carrier gas Continuous and large scale 1.7 MHz production possible. piezoelectric

USP is an easily scalable & versatile synthetic methodology.

How To Make Nanosized Particles with USP

Traditional USP Droplet Solvent evaporates, Agglomeration, Particles form Sintering 1 droplet = 1 particle

Solution: High boiling point solvents instead of water Keep droplet as hot liquid phase; multi-nucleation sites. 1 droplet = 1000s of particles. “Chemical Aerosol Flow Synthesis” (CAFS)

CAFS Droplet Cosolvent Nucleation, particles Final Particles evaporates formation & growth collected

1 droplet = 1000s particles

Why Quantum Dots? • nm size gives quantum confinement, i.e., size-dependent fluorescent color • No photobleaching of inorganic pigments

How Prepared? • High temperature batch reaction at high dilution. • Expensive, high boiling-point solvents. octadecene, hexadecane, isodurene. • Often nasty precursors: dimethyl cadmium originally! Now Cd acetate, oxide thiourea, trioctylphosphine sulfide (selenides/tellurides, too) • Surface stabilizers: acids (oleic, phosphonic, stearic), amines, TOPO (trioctylphosphine oxide)

USP of CdS, CdSe, CdTe Nanoparticles

Conditions: USP, Ar 1.5 L/min

Precursors: Cd(OAc)2, TOP-E (S, Se, Te)

Surface Stabilizer: Stearic acid

Temperatures: 200 to 340°C

XRD: nano-crystals

Diameters: ~3.5 nm

0.8

0.4

Fluorescence 220 240 260 280 300 320 340oC

0 450nm 550 nm 650 nm

Conditions: Cd Ac2, Stearic acid, TOPSe residence time ~2 s.

How to Make Nanoporous Materials

Traditional USP Powder Synthesis

Solution Δ Δ

Solvent Nebulized liquid evaporation/ Particle Product droplet particle formation aggregation densification

Sacrificial Nano-Templates: SiO2, polymer, salt; added or formed in situ. Solution

Δ HF

nano- template Nebulized liquid Template Precursor Porous droplet composite collection material Templates can produce high surface area, porous materials.

initial solvent-free dense porous droplet conglomerate microsphere microsphere initial heating and heating consolidation etching

TiO2 solvent SiO2 precursor SiO2 precursor: bis(ammonium)(lactato)(dihydroxo)TiIV ball-in-ball sacrificial template: silica colloid

hollow ball

Titania Size Distribution

before etching Ti:Si=1:1 Etching with HF/EtOH after etching

500 nm SiO2 200 nm TiO2

Hollow TiO2 microsphere shells with SiO2 ball inside.

Sucrose-Based Porous Carbon via USP

• Scalable production technology: USP • Simple, cheap precursors: sugar, carbohydrates.

Cn(H2O)n  n C + n H2O↑

• No hazardous decomposition byproducts. • Rational design of very high surface area carbons. • Addition of alkali carbonate or nitrate salt to precursor promotes decomposition of sucrose and gas decomposition products create internal pores.

0.1 M NaNO3 0.5 M Na2CO3 solid S. A. ~ 440 m2/g

Characterization of Porosity

Scanning Electron Microscopy Focused Ion Beam

Scanning Transmission Transmission Electron Microscopy Electron Microscopy

TEM and BET shows hierarchical pore structure.

microporous shell

internal macropores

High surface areas indicate microporous shell allows access to internal macropores.

Very narrow micropore distribution at 0.6 nm

Other Applications of Sonochemistry

• Liquid-Solid Reactions (Grignards, Li, KMnO4 …)

• Emulsification (i.e. Liquid-liquid reactions)

• Sonocrystallization of pharmaceuticals

• Microencapsulation (e.g., protein microspheres for imaging and drug delivery)

• Surface modification (e.g., wettable PE, PVC polymers)

• Drinking water remediation (OH• from water sonolysis)

• “Megasonic” cleaning of microelectronics (e.g., Si wafers)

Naval jet engine rebuilding and maintenance facility. (cleaning of whole engines after avian encounters)

21 kW, 1800 gal., immersible magnetostrictive transducers

Conclusions

• Ultrasound does High Energy Chemistry thru Cavitation. Cavitation Clouds: 5000 K, ~300 Atm., ~10-9 sec. Single Bubbles: >15,000K, ~1100 Atm., <10-9 sec.

• Sonochemistry: new tool for nanophased materials. Metals, alloys, carbides, sulfides, oxides all available: as colloids, supported catalysts, nanoporous solids.

• Extremely Active New Nanostructured Catalysts.

• Heterogeneous Systems: diverse & dramatic enhancements

• Metal Surface Activation: Inter-Particle Collisions.

• Ultrasonic Spray Pyrolysis as a versatile synthetic route.

Jin Ho Bang Jamie Oxley Yuri Didenko Tanya Prozorov Arul Dhas Ruslan Prozorov Nathan Eddingsaas Sara Skrabalak Ming Ming Fang Won Hyuk Suh David Flannigan Hangxun Xu Maria Fortunato Richard Helmich UIUC Matl. Res. Lab., Steve Hopkins Center for Microanalysis Taeghwan Hyeon of Materials, supported by DOE. Millan M. Mdleleni William B. McNamara III NSF, DOE, DARPA