Sonochemical Reactions Chemical changes/reactions induced by ultrasound No direct interaction of ultrasound field with molecules (in contrast to photochemistry,...) •Liquid phase reactions - chemical reactions driven by cavitation effects • Solid state reactions - introduction of defects = speeding up diffusion Sound Sound = pressure waves = periodic compression/expansion cycles traveling through a medium possessing elastic properties (gas, liqud, solid) Liquids and gases - longitudinal pressure waves - compression/rarefaction Solids - longitudinal and transverse waves The energy is propagated as deformations (tensile/compressive stress) in the media The molecules oscillate about their original positions and are not propagated The propagation of a sound wave = the transfer of vibrations from one molecule to another Longitudinal Pressure Waves Compression Ra/e fraction [III] Compression =la refraction m Compression I Sound In a typical liquid, the speed of sound decreases as the temperature increases, at all temperatures. The speed of sound in water is almost five times greater than that in air (340 m s1) Substance Speed of sound, u [m s_1] Air 343 Helium 965 Water 1482 Lead 1960 Steel 5960 Granite 6000 Speed of Sound The speed of sound (u) u2 = 1/Ksp = [dP/dp]s ~ 1/(<(V)2>) ks = adiabatic compressibility p = density P = pressure 1600 50 100 150 Temperature, °C 200 Sound Intensity Sound Intensity = Power / area = Watts/m2 Source of Sound Intensity (WI ml) Sound level (dB) Jet Airplane 30 m away 102 140 Air-raid Siren, nearby 1 120 Threshold of Pain 101 120 Concert -101 115 Riveter 103 100 Busy Traffic 105 70 Normal Conversations 106 60 Whisper 1010 20 Threshold of Hearing 10~12 0 0 dB (10 12 W/m2) 10 dB = 10 as intense 20 dB = 102 as intense 30 dB = 103 as intense 120 dB = 1012 as intense Pa = PAsin27üft Pa acoustic pressure PA pressure amplitude f sound frequency c = A,f (for 20 kHz, X = 7.5 cm) p = p + p ■total ra rh Ph hydrostatic pressure Acoustic Pressure compression compression displacement (x) graph ^\ A r\ rare1 action Pressure (P) graph \J A K" r Acoustic Pressure i I ■ I I compression compression displacement (x) graph r\ r\ r\ raref action M J \J \J Pressure (P) graph r\ r\ r \ f \j 1 iL Compression and rarefaction (expansion) regions PA=jlIpc PA = driving pressure amplitude [Pa] I = irradiation intensity fW m-2] (500 W system - 1.3 105 W nr2) p = liquid density fkg m-3] c = sound velocity in liquid fm s_1] (Water 1482 m s"1) PA = 620 700 Pa = 6.2 bar Ultrasound Utrasound frequencies from 20 kHz to 50 MHz 10 10 10 _L 6 10 JU 7 10 JL Human hearing ► Conventional povrer ultrasound frequency, Hz 16Hz-18kHz 20kHz-100kHz Extended range for sonochemistry B | 20kHz - 2MHz Diagnostic ultrasound 5MHz-10MHz _ Generation of Ultrasound Transducer -into another gas driven liquid driven electromechanical a device converting one type of energy whistle (F. Galton), liquid atomizer siren liquid whistle homogeniser, a jet of liquid passed through an orifice on a thin metal blade, vibrations, cavitation, mixing of immiscible liquids, ketchup, mayonnaise magnetostrictive, Ni, Co/Fe, Al/Fe, Tb/Dy/Fe alloys shrink when placed in mg. field, solenoid, pulses, upper limit 100 kHz, cooling piezoelectric, oposite charges applied on crystal sides, contraction/expansion, quartz, Pb(Zr/Ti)Os ceramics (PZT), up to MHz Generation of Ultrasound casing containing transducer element upper fixed horn (booster) detachable horn replaceable tip generator screw fitting at null point Sonochemical Reactor Piezoelectric transducer Piezoelectric Ultrasound Generator Ultrasound Processor VCX 500 W Sonochemical Reactor Ultrasound Processor VCX 500 W Frequency 20 kHz 0 to 40 °C Argon (flow rate 62 cm3 mhr1) TIME of ultrasound treatment PULSE irradiation and a dwell time 2:2 TEMP maximum temperature 50 °C AMPL amplitude 50 % I Sonochemical Reactor Ti alloy horn, minimum lenght is a half-wavelength of sound in a material, 26 cm for 20 kHz in Ti, multiples of 13 cm vibration amplitude 5-50 u.m Sonochemical Reactor Sandwich transducer operating at 1-200 kHz Hydrodynamic Cavitation the passage of liquid through an orifice plate the kinetic energy/velocity of the liquid increases at the expense of the pressure throttling causes the pressure to fall (Bernoulli) below the threshold pressure for cavitation (vapor pressure) cavities are generated the liquid jet expands, the pressure recovers energetic collapse of the cavities Hydrodynamic Cavitation Lord Rayleigh for the British Admiralty 1895 cavitation erosion of propeller blades The University of Texas at Austin RR+-R=-[p -P0-P(t)]-4v-- — 2 py' 0 R pR SHEET CAVITATION LEADING EDGE DETACHMENT TIP VO RTEX CAVITATI0 N (developed) CLOUD CAVITATION BUBBLE CAVITATION HUB VORTEX CAVITATION TIP VORTEX CAVITATION (inception, desinence) 0199« S.A. Kinnas FACE SHEET CAVITATION Snapping Shrimp snaps a claw shut to create a water jet -speed of 30 m/s, or 100 km/h a drop of the pressure to below the vapor pressure of water - cavitation bubbles acoustic pressures of up to 80 kPa at a distance of 4 cm The pressure wave is strong enough to kill small fish M. Versluis, B. Schmitz, A. von der Heydt, D. Lohse, How Snapping Shrimp Snap: Through Cavitating Bubbles. Science 289, 2114-2117 (2000) Snapping Shrimp -1.00 -0.75 -0.50 -0.25 -0.00 TIME D. Lohse, B. Schmitz, M.Versluis, Nature 413, 477-478 (2001) cavitation bubbles Snapping Shrimp D. Lohse, B. Schmitz, M.Versluis, Nature 413, 477-478 (2001) Stable vs. Transient Cavitation t.f (adimensional time) l.f (adimensional time) Acoustic Cavitation Cavitation effects = creation, growth, and implosive collapse of bubbles (1-2 jus) in a liquid = implosion HOT SPOT (1 ns) TRANSIENT CAVITATION: THE ORIGIN OF SONOCHEMISTRY Compression ilWWWVWW Expansion E 9 en 9 n - IMPLOSION SHOCKWAVE FORMATION MM T T T 200 300 400 Time { usee) RAPID QUENCHING —I- v .Hi stable cavitation - bubbles oscillate for many cycles transient cavitation - transient cavities expand rapidly collapse violently Acoustic Cavitation Cavitation effects = creation, growth, and implosive collapse of bubbles in a liquid Bubble formation = breakage of liquid during expansion, overcoming tensile strength (pure water 1500 bar, only 6.2 bar available) Weak spots needed = dissolved gas molecules, solid particles, trapped gases Bubble growth (300 jws), energy absorption, size oscillations critical size (170-300 jum) = most efficient energy absorption, rapid growth, inefficient energy absorption, collapse compression compression compression compression Acoustic Cavitation Standing wave Low pressure High pressure Bubble expansion Bubble collapse Light emisssion Acoustic Cavitation Bubbles collapse = spherically symmetrical implosion, shear forces, adiabatic compression, life time 1-2 jus Hot spot = end of the collapse temperature of the gas inside bubble 5 000 - 20 000 °C (for 1 ns) surrounding liquid layer 2000 °C pressure 500 - 1500 bar Extreme cooling rates 1010 K s-1 red hot steel poured into water 2500 K s_1 Homogeneous Sonochemistry Two-Site Mechanism Cavity interior Filled with gases and vapors temperatures 5 000 - 20 000 °C pressure 500 - 1500 bar Surrounding liquid layer temperatures 2000 °C Bulk liquid Shock waves, shear forces Homogeneous Sonochemistry Mechanism •••• SurrdVinding interface layer ■ A-B diffusion of volatile reagents Bulk liquid CD** nonvolatile reagents Shock waves, shear forces » ■ ■ How to Measure the Temperature inside a Bubble ? Sonoluminescence - Light generated during the implosive collapse of bubbles in liquids irradiated with ultrasound Kenneth S. Suslick University of Illinois 95% H2S04(aq.) under Ar 20 kHz (14 W/cm2) Ti horn directly immersed T = 298 K Apparent blackbody temperature Ar emission SO and CK+ emission 8 000 - 15 000 K A 14Wfcm2 22 WJcm2 B 3 14 Watts/cm2 22 Watts/cm2 30 Watts/cm2 680 30 W/cm2 880 Wavelength (nm) Temperature/Pressure inside a Bubble Neppiras Equation T =T 1 max ± 0 fa(y-i) Q 7 P =0 max ^p(r-l)V-i V Pa = acoustic pressure T0 = solution temperature y=cp/cv Q = gas pressure inside a bubble upon initiation of the collapse, at its maximum size Gas Y = Cp/Cv Kr 1.66 Ar 1.66 He 1.63 o2 1.41 Fate of Bubbles under Ultrasonic Irradiation Ultrasound Bubble nuclei Dissolution Coalescence Rectified diffusion Fragmentation «- Buoyancy Resonance Sl/C Collapse VV SL Rectified diffusion - during expansion phase the bubble has larger surface area - more gas diffuses inside than during compression gets out Single Bubble Sonoluminescence SBSL D. F. Gaitan, L. A. Crum, 1990 a method to trap a single sonoluminescing bubble within an acoustic standing wave field Standing acoustic wave field One bubble trapped The bubble oscillates for many cycles Bubble sonoluminescence Single Bubble Sonoluminescence SBSL D. F. Gaitan, L. A. Crum, 1990 Standing acoustic wave field 1 bar One bubble levitates in the acustic field The bubble oscillates for many cycles Bubble sonoluminescence Bjerknes force sound pressure p(x,t) 11 location x t=T/2; ..........--" bubble force at the time t=0: volume V(t) force at the time t=T/2: time-averaged force: C. A. and V. Bjerknes The force on an object in a liquid depends on its volume and the pressure gradient, the time averaged force drives the bubble towards the antinode of sound pressure and keeps it there. Single Bubble Sonoluminescence SBSL Proper conditions for a single sonoluminescing bubble within an acoustic standing wave field 50 Single Bubble Sonoluminescence SBSL Single Bubble Sonoluminescence SBSL Red - MBSL in dodecane Blue - MBSL in water, 16 kHz Green - SBSL in water, 43 kHz Black - blackbody curve for 16200 K Single Bubble Sonoluminescence SBSL Red - bubble radius Green - bubble temperature Blue - acoustic pressure 1.3 bar/25 kHz 8120 6960 -—* 5800 elvin ID 4640 CC Z) RAT 3480 LU Q- LU 2320 1160 290 ,60 2570 2580 TIME (microseconds) 2590 258T5-255TT TIME (microseconds) Multi Bubble Sonoluminescence MBSL Multi-bubble sonoluminescence Spatial and temporal average 250 bar Sonoluminescence Light generated during the implosive collapse of bubbles in liquids irradiated with ultrasound 10-12-; 200 300 85% H2S04 under Xe 400 Wavelength (nm) 500 600 700~ Apparent blackbody temperature (all 4 spectra) 12500 ±1500 K Sonoluminescence 95% H2S04(aq.) blackbody temperature Ar emission an optically opaque plasma core Wavelength hm) Sonoluminescence 95% H2S04(aq.) SO and 02+ emission with vibronic progression _160 i c I & 120 I mm -TTTi=v' 1112 13 14=va V'=0I I I I I I I I I I I v"=A 5 6 7 8 9 1011 121314 SO B3r - X3I" 250 300 350 Wavelength (nm) 200 250 300 Wavelength (nm) 1580 ± 110 K at 3.3 bar 2470 ± 170 K at 4.2 bar 3480 ± 240 K at 5.1 bar Sonofusion Fraud D + D^ 3He(0.82MeV) + n(2.45MeV) D + D ^T(l.01MeV) + H(3.02MeV) Neutron burst from PN LS Time SD, fis ~i 1 3 +3 PMT Microphone - 4 PNG Neutron-Induced Luminescence — -_ _ ; Sonoluminescence 27 Shock Wave from Bubble reaches Wall of Test Section 54 Sonofusion Fraud Degassed deuterated acetone (CD3)2CO, 0 °C 4 105 neutrons s1 Microphone Chamber with test fluid Linear Amp Master Wave Form Generator pzt Slave Wave Form Generator Power Measurement in Sonochemistry Calorimetry P = power, W P el = input power to generator P hf = high-freq. power output s ß P th = power input into liquid Power Measurement in Sonochemistry Calorimetry P = power, W T = temperature, K t = time, s cp = heat capacity, J g1 K1 m = mass, g Volume 50 cm3 Argon atmosphere Error 5% heat capacity, J g1 K1 Water Tetraglyme 4.2 2.08 54 49 o o 19 Calorimetric measurement for water 75% amplitude 20 40 60 80 Time (s) Power Measurement in Sonochemistry Chemical dosimetry The Weissler reaction Volume 50 cm3 Kl 0.1 M CC14 0.2 cm3 Time 30 min ^max = 355 nm 6 = 26303 dm3mol1 cm 1 CC14 + H20 —- Cl2 + CO + 2 HC1 2 KI + Cl2 I2 + 2KC1 h + 2 S20,2" - —- 21 + S4Ofi2- Weissler Reaction ccl4 + H2o —»- Cl2 + CO + 2 HCl 2KI + C12 — —- I2 + 2KC1 I2 + 2 S2032" —- 2r + s4o62- 0.20^ Calorimetrically determined ultrasonic power (W) Power Measurement in Sonochemistry Chemical dosimetry The Fricke reaction Volume 50 cm3 (NH4) Fe(S04)2.6H20 0.001 M H2S04 0.4 M NaCl 0.001 M Time 30 min Fe3+ ^max = 304 nm 6 = 2197 dm3 mol1 cm 1 H20-+OH Fe2+ + OH-^ Fe3+ + OH Fricke Reaction Fe2+ + OH-^ Fe ^ + OH H +OH 3+ 1.0x10" 8.0x10s CO I ■I 6.0x10*5 o E £ 4.0x10"5 - (a) 2.0x10' 0.0 10 -i—i—i—i i i i i 1 ii 11 _i_i_i_■ i ■ ■ ■ ..... 100 Frequency (kHz) 1000 Power Measurement in Sonochemistry Chemical dosimetry Porphyrin decomposition ratio TPPS 3.3 10 6 M Volume 50 cm3 -03S TPPS = 412 nm s = 500000 dm3 mol1 cm 1 Porphyrin Decomposition 0.10 £ 0.05 """(/) CL 0 -1-r-1-1-1—i—i—r (c) 1 1-1-1-1-1—1—1—1—1—1- f J hi1 r _1_1_1_1_1_1_1_l_ j_i_i_i_i_i_i_i_i_i_ 10 100 Frequency (kHz) 1000 Power Measurement in Sonochemistry Temperature [°C] Reactor Optimization cavitating bubbles in the optimised cell (water, 20 kHz, Pus = 10 W) and simulated intensity distribution for the same geometry Heterogeneous Sonochemistry Solid surfaces = implosion, microjets, shock waves 200 jLim minimum particle size at 20 kHz for microjets surface erosion removal of unreactive coatings (oxides, nitrides, carbonaceous) fragmentation of brittle materials, increased surface area Heterogeneous Sonochemistry LARGE PARTICLES SMALL PARTICLES surface cavitation due to delects leading to frag mentation collision can lead to surface erosion or fusion Heterogeneous Sonochemistry Solid particles in liquid = shock waves high speed interparticle collisions (500 km/s) surface smoothing, surface coating removal Ni catalytic activity in hydrogenation increased 105 fold by NiO removal localized melting of metal particles at the impact point fragmentation, increased surface area intercalation rates enhanced 200 fold in layered oxides and sulfides (V2Os, Mo03, MoS2, ZrS2, TaS2) Heterogeneous Sonochemistry Metal powders Cr (mp 2130 K) and Mo (mp 2890 K) agglomerate W (mp 3683 K) does not temperature at the point of impact ~ 3000 °C Before ultrasound 30 min. ultrasound Cavitational Corrosion of the Tip Control of Sonochemical Reactions sound intensity - minimum for cavitation threshold, depends on frequency, optimum intensity for given reaction conditions, at high powers great number of bubbles hinder sound transmission, decoupling of a liquid from the source, breakdown of transducer material, 10 - 100 W cm2 sound frequency - 20 - 100 kHz, the higher the frequency, the higher power needed to actuate cavitation, stronger cavitation effects, rarefaction phase shortens at high frequency sound attenuation - proportional to the frequency, more power needed at high frequencies Effect of Frequency on Cavitation in Water The frequency dependence of the intensity required to produce cavitation for degassed water at room temperature. The intensity required to produce vaporous cavitation above the frequency of 100 kHz rises rapidly. Control of Sonochemical Reactions volatile reactants - primary reaction site inside the bubbles, diameter 200 urn, 5000 °C, easy bubble formation, more reactant vapors inside bubbles, but the cavitation is cushioned Fe(CO)5 Fe(acac)3 FeS04 nonvolatile reactants - reaction in the thin layer (200 nm) surrounding the bubble, 2000 °C, less cushioning, more energetic cavitation (collapse) high boiling solvents - high vapor pressure inside the bubble cushions the implosion, nonvolatile solvents give less cushioning, more energetic cavitation less cavitation in viscous liquids, viscosity resists shear forces low surface tension facilitates cavitation, in water add surfactants Control of Sonochemical Reactions temperature - higher temperature increases vapor pressure of a medium, lowers viscosity and surface tension, many bubbles formed at temperatures close to solvent boiling point, a barrier to sound transmission, reaction rates decrease with increasing temperature, more vapors in bubbles ambient gas energy developed on bubble collapse: monoatomic (Ar) > diatomic (N2) > triatomic (C02) Xe: low thermal conductivity, heat of the collapsing cavity retained He: high thermal conductivity, heat of the collapsing cavity dissipitated, no reaction external pressure - higher pressure suppresses bubble formation but makes cavitation more energetic, optimum pressure for a given frequency Effect of Temperature on Cavitation in Water c o u J5 M(CO)5 (M = V, Nb, Ta) Mo + 6 CO -> Mo(CO)6 r. t, 1 bar, normally needs 300 bar, 300 °C R2SiCl2 + Li -> [-SiR2-SiR2-]n + LiCl monomodal MW distribution Homogeneous Sonochemical Reactions Liquids = heating/cooling by cavity implosions H20 -> H + OH H2 + H202 precursor decomposition: metals Fe(CO)5 -> Fe + 5 CO oxides Ga3+ + H20 -> Ga(0)(OH), diaspore nitrides, carbides, sulfides alkane cracking polymer degradation, lower MW, surface modification emulsification of immiscible liquids (oil-water, Hg-organics, polymer-inorganics) M(acac)n as Precursors Me M(acac)3 • Well studied class of compounds •Many elements form acac complexes • Metal complexes - precursors in CVD, sol-gel, thermolysis routes to oxides • Easily chemically modified • Volatile, organics soluble • Nontoxic Chemistry of M(acac)n Precursors Thermal decompositon pathway H f-hC. ,CH- o o M CH. 200 °C 300 °C 3n4 JVL CHiCOCH MCO- 765 °C - CO? MxOy Ismail, H. M. J. Anal. Appl. Pyrolysis 1991, 21, 315-326. Ligand Removal by Water 180' \ / CVD -OH M M180+ 2 /\ -o o- Pinkas, J.; Huffman, J. C; Baxter, D. V.; Chisholm, M. H.; Caulton, K. G. Chem. Mater. 1995, 7, 1589-1596. Sonochemical Synthesis of Iron Oxide Nanoparticles ))))) / f > Fe203 \ Fe(CO)5 -► 1 amorphous 1 decaline Cao, X.; Prozorov, R.; Koltypin, Y; Kataby, G.; Feiner, I.; Gedanken, A. J. Mater. Res. 1997, 12, 402-406. Cao, X.; Koltypin, Yu.; Prozorov, R.; Kataby a, G.; Gedanken, A. /. Mater. Chem. 1997, 7, 2447-2451. ))))) i Fe203 \ Fe(acac)3 -► ( amorphous 1 hexadecane Amorphous product, by heating to 700 °C converted to a-Fe203 20-40 nm Nikitenko, S. I.; Moisy, Ph.; Seliverstov, A. R; Blanc, P.; Madic, C. Ultrasonics Sonochem. 2003, 10, 95-102. Sonochemical Synthesis of Iron Oxide Nanoparticles Amorphous sono-Fe203 ))))) TG Fe203 maghemite 340 °C w dynam/isothermal T Composite particles (20-30 nm) Amorphous Fe203 particles (2 to 3 nm) Embedded in organic matrix (acetate) Fe203 hematite J. Pinkas, V. Reichlova, R. Zboril, Z. Moravec, P. Bezdicka, J. Matejkova: Sonochemical synthesis of amorphous nanoscopic iron(lll) oxide from Fe(acac)3 Ultrasonic Sonochem. 2008, 15, 256-264 Defect spinel Corundum SEM of Nanoscopic Fe203 Fe(acac)3 Fe203 Particle size 20 - 30 nm Spherical shape Uniform size distribution S.OkV X150.000 100nm WD 3.0mm IR Spectrum of Sono-Fe203 0.7 : as-synthesized Fe203 (red) after calcination to 500 °C (blue) -i-1-1-p 4000 30 00 2000 Wave numbe r (cm-1) 1000 IR Spectrum of Sono-Fe203 Acetate stretching Diketonate vibr. absent 0.65 I 0.60 1 0.55 1 0.50 I 0.45 I 03 0.40 1 8 0^51 < ._ 0.30 1 0.25 1 0.20 I 0.15 I 0.10 I 0.05 1 0.00 3 vas(COO) 1566 cm-1 A = vas(COO) - vs(COO) = 134 cm1 -i—i—i—i—i—i—i—i—i—i—i—r 3000 T vs(COO) 1432 cm-1 -i-1-r 4000 2000 Wavenumber (cm-1) 1000 Decomposition of Acac Ligands Speculation about the nature of residual organic groups Deacon-Phillips Rules A = vas(COO) - vs(COO) A CH3COO- = 164 cm 1 A larger than ionic form = unidentate A smaller than ionic form = bidentate A comparable to ionic form = bridging CH3 CH3 CH3 c/\ c/Sd 0^0 1 \/ 1 1 Fe Fe Fe Fe Deacon, G. B.; Phillips, R. J. Coord. Chem. Rev. 1980, 3, 227-250. TEM proves amorphous character of sono-Fe203 11* T.S.P- Electron diffraction Crystallization of Amorphous Fe203 under TEM Beam Electron diffraction Maghemite or Magnetite -► Time under TEM beam Crystallization induced by heating (300 °C) 5 nm Smaller particle size on calcination - why? 20 nm Specific Surface Area Surface area 48 to 260 m2 g1 (BET) depending on H20 content BET surface area of the Fe203 heated to different temperatures during 12h outgassing periods 220 200 - cn 180 £ < 160 CO 140 - 120 50 100 150 200 250 300 350 400 Temperature, °C The oxide surface area increases as the acetate groups are removed, then the particle size increases because of sintering Composite Particles of Sono-Fe203 SO *rn j Composite Particles of Fe203 10 nm XRD of amorphous Fe203 heated dynamically in air up to 250, 300, and 360 °C Maghemite Y ■ Fe203 24000 16000 8000 4000 = 3000 Sl 1 2000 ^^JJ 6000 4000 2000 20 TEM of Fe203 Calcined at 600 °C Iron oxide particle size 10 to 20 nm 50 nm HT-XRD of Sono-Fe203 280 - 390 °C 10000 9000 8000 7000 < 5000 4000 3000 ľOOO 1000 Hematite Calcination to 1000 °C 20.0 30.0 Pseudo-isothermal 350 330 320 310 300 °C 290 280 y^^vM-^^^^ (pseudo-isothermal heating) provides a different polymorph - Hematite 70.0 2Theta Ramp 1 °C min1, 1 min equilb., 30 min data collect., 10 °C Steps Hematite Particle Size coherence length D (nm) Dependence of the coherence length, D (nm) of a-Fe203 on the crystallization temperature under dynamic-isothermal conditions of the HT-XRD measurement