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 © 2010, K. S. Suslick 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) © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Single Bubble Sonoluminescence 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. © 2010, K. S. Suslick 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 © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Lab Scale Sonochemical Rig 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. © 2010, K. S. Suslick Multi-Bubble Sonoluminescence: 85% Sulfuric Acid 1 cm Ti horn 50 µm © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick What Are the Conditions Inside? Sonoluminescence as a Spectroscopic Probe © 2010, K. S. Suslick 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) © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Temperature vs. Calculated Cr Spectra 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) © 2010, K. S. Suslick 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… Suslick et al., Nature, 1999, 401, 772. 2000, 407, 877 2002, 418, 394. 2005, 434, 52. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Islands of Chemistry © 2010, K. S. Suslick What Else Might Bubble Be Good For? © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Sonochemical Synthesis of Nanostructured Heterogeneous Catalysts Goals: Stable High Surface Energy Materials (i.e., highly defected surfaces) Refractory Materials with High Surface Areas Specific Example: Hydrodesulfurization (HDS) © 2010, K. S. Suslick 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. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Sonochemical Synthesis of Nanostructured Materials 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 H2 H2 + © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Scanning Electron Micrographs of MoS2 o Sonicated Mo(CO)6 and S8 in isodurene, Ar, 80 C 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. © 2010, K. S. Suslick Transmission Electron Micrograph of Sonochemically Prepared MoS2 2 nm Inter-lamellar spacing unchanged, but heavily defected. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Catalytic Microreactor Rig 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 CATALYST BED © 2010, K. S. Suslick 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. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Hollow MoS2 • 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. © 2010, K. S. Suslick Hollow MoS2 o TEM hollow MoS2 nanospheres after thermal annealing at 450 C. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick MoS2 Nanospheres: EDX Line Analysis Across a single particle of MoS2/SiO2 Before Etching After Leaching with HF © 2010, K. S. Suslick MoS2 Nanospheres: HDS of Thiophene After 24 hours of catalysis. Aldrich MoS2 ) 1 - Sonochemical MoS2 s . 1 - 2 Hollow MoS2 (150 nm) g . Hollow MoS (50 nm) s 2 e l u c e l o m 8 1 1 0 1 ( y t i v i t c A 0 325 350 375 Temperature (oC) © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick First Hollow Single Crystals (!) TEM of Hollow MoO3 Nanospheres After Leaching with HF. After thermal annealing at 450oC. © 2010, K. S. Suslick What Happens at Surfaces? © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Mechanisms Of Heterogeneous Sonochemistry SURFACE ACTIVATION: Microjet pitting, etc. INCREASED SURFACE AREA: Shock wave fragmentation. ENHANCED MASS TRANSPORT: Surface turbulence. POWDER MODIFICATION: Interparticle Collisions. © 2010, K. S. Suslick Cavitational Collapse Near a Surface © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Cavitation Near Extended Surface 75,000 fps; W. Lauterborn © 2010, K. S. Suslick Cavitation Near an Extended Surface L. A. Crum © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Cavitation Damage to Al Sheet 10 m © 2010, K. S. Suslick Sonochemical Activation of Ni Powder 1 0.1 ))) Ni Ni* 0.01 (10 m) octane Ni* 1-nonene nonane 0.001 H2 Initial Rate (mM/min) Initial 0.0001 0.00001 050 100 150 200 250 Duration of Ultrasonic Irradiation (min) © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick CHO HO-CHCH2CO2C2H5 ))) Reformatsky Rxn.: + Br-CHCH2CO2C H5 + Zn 100 15 m. 80 5 m. ) 60 % ( d l 2.5 m. e i Y 40 1 m. 20 NO u.s. 0 02040 Thermal Reaction Time (min.) © 2010, K. S. Suslick 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.) 50 min. sputter time ~ 1 m depth Sonication of slurries in octane. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Effect of Ultrasound on Particle Morphology: Ni in decane m 100 Before ultrasound 60 min. ultrasound © 2010, K. S. Suslick Effect of Ultrasound on Particle Morphology: Ni in decane m 10 Before ultrasound 15 min. ultrasound 120 min. ultrasound © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Interparticle Collisions Induced by Ultrasound Zn Powder in decane; 20 kHz, 100 W/cm2 © 2010, K. S. Suslick 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 © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Effect of Ultrasound on Particle Morphology: Cr in decane m 10 Before ultrasound 30 min. ultrasound m.p.: 2130 K © 2010, K. S. Suslick Effect of Ultrasound on Particle Morphology: Mo in decane m 60 Before ultrasound 30 min. ultrasound m.p.: 2890 K © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Effect of Ultrasound on Particle Morphology: W in decane m 60 Before ultrasound 30 min. ultrasound m.p.: 3680 K © 2010, K. S. Suslick 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. © 2010, K. S. Suslick © K. S. Suslick, 2007. www.scs.uiuc.edu/suslick Agglomeration vs.