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 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 (340 m s1) Substance Speed of sound, u [m s_1] Air Helium Water Lead Steel Granite 343 965 1482 1960 5960 6000 The speed of sound (u) u2 = 1/Ksp = föP/öp]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 (W/m2) 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 10-io 20 Threshold of Hearing 1012 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 Acoustic Pressure Pa = PA sin 2ti ft Pa acoustic pressure PA pressure amplitude f sound frequency c = Xf (for 20 kHz, X = 7.5 cm) p = p + p rtotal r a rh Ph hydrostatic pressure compression compression displacement (x) graph A A ra ret action M cA J \j \j Pressure (P) graph \J /i ^ 1 A Pa k r Acoustic Pressure compression compression Compression and rarefaction (expansion) regions displacement (*) graph rarefaction A k Pressure (P) graph ! P. \ ! /K /' PA = driving pressure amplitude [Pa] I = irradiation intensity fW m~2] (500 W system - 1.3 105 W m"2) 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 0 10 _l_ 10 _L 10 _L 10 _L 7 10 Human hearing ► Conventional povrer ultrasound frequency, Hz 16Hz-18kHz 20kHz-100kHz Extended range for sonocherristry j | 20kHz - 2MHz Diagnostic ultrasound 5MHz-10MHz Generation of Ultrasound Transducer - a device converting one type of energy into another gas driven liquid driven electromechanical 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 -1—s upper fixed horn (booster) Bsp ■IL liiiiiiiss . ■.-.'.-i.-.-.a:'.:-.; :.;.-o.;.;.i generator detachable horn screw fitting at null point Sonochemical Reactor iezoelectric 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 min1) TIME of ultrasound treatment PULSE irradiation and a dwell time 2:2 TEMP maximum temperature 50 °C AMPL amplitude 50 % 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 \im 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 RR+ — R =-[p -PB-P(Ö]-4v—- — SHEET CAVITATION LEADING EDGE DETACHMENT The University of Texas at Austin TIP VORTEX CAVITATION [developed] CLOUD CAVITATION BUBBLE CAVITATION HUB VORTEX CAVITATIO N TIP VORTEX CAVITATION (inception, desinence] (Q 1996 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) w 0.30 0.20 ■ 0.10- Snapping Shrimp Lohse, B. Schmitz, M.Versluis, Nature 413, 477-478 (2001) -1.00 -0.75 -0.50 -0.25 -0.00 TIME 3 He (ft 82Me V) +11 (2.45MeV} D + D ^T(L01MeV) + H(3.02MeV) Neutron burst from PN LS Time SD, (is H—I 3 +3 PMT Microphone Li.; PNG Neutron-Induced Luminescence oluminescence 27 *t, us Shock Wave from Bubble reaches Wall of Test Section ■^"f, (IS 54 Sonofusion Fraud Degassed deuterated acetone (CD3)2CO, 0 °C 4 105 neutrons s1 Power Measurement in Sonochemistry Calorimetry P = power, W P el = input power to generator P hf = high-freq. power output © ■ ■ P th = power input into liquid Power Measurement in Sonochemistry Calorimetry P = power, W T = temperature, K t = time, s cp = heat capacity, J g -i K-i m = mass, g Volume 50 cm3 Argon atmosphere Error 5% 54 49 heat capacity, J g1 K1 Water Tetraglyme 4.2 2.08 19 Calorimetric measurement for water 75% amplitude y = 0,2284x + 20,76 20 40 60 80 100 120 Time (s) 140 Power Measurement in Sonochemistry Chemical dosimetry The Weissler reaction Volume 50 cm3 KI 0.1 M CC14 0.2 cm3 Time 30 min i CC14 + H20 2 KI + Cl2 |l2 + 2 S2Q; 2- Cl2 + CO + 2 HCll I2 + 2 KC1 21+ S40( 2- A,„,„„ = 355 nm 'max s = 26303 dm3 mol1 cm 1 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 IHiO-+OH Fe3+ + OH H2S04 0.4 M NaCl 0.001 M Time 30 min Fe3+ ^max = 304 nm 8 = 2197 dm3 mol1 cm 1 Power Measurement in Sonochemistry Chemical dosimetry Porphyrin decomposition ratio Cr TPPS 3.3 106 M Volume 50 cm3 TPPS ^max = 412 nm 8 = 500000 dm3 mol1 cm 1 Power Measurement in Sonochemistry ■ ^ 0.2 o CO ■□ □ p ^ ^— O-O-o -0-- -A- o-o-o -o-o- —o— -A.. -°-*o ° "-A "A 10 20 30 40 50 GO Temperature [°C] 70 Si; Reactor Optimization cavitating bubbles in the optimised cell (water, 20 kHz, Pus = 10 W) and simulated intensity distribution for the same geometry H D Heterogeneous Sonochemistry Solid surfaces = implosion, microjets, shock waves 200 urn minimum particle size at 20 kHz for microjets surface erosion removal of unreactive coatings (oxides, nitrides, carbonaceous) fragmentation of brittle materials, increased surface area LARGE PARTICLES SMALL PARTICLES surface cavitation due to defects leading to fragmentation collision can lead to surface erosion or 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 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 The effect of temperature on cavitation and its associated hysteresis effect for tap water. The increase in intensity as the temperature is increased can be observed before it falls away at the boiling point. When the temperature is allowed to fall an increase in intensity is found in the region of 50-60 °C. This is quite a significant effect and appears to occur in all liquids. Sonochemical Reactions Solid surfaces = implosion, microjets, shock waves 200 jum minimum particle size at 20 kHz for microjets surface erosion removal of unreactive coatings (oxides, nitrides, carbonaceous) fragmentation of brittle materials, increased surface area Li, Mg, Zn, Al, Cu react at room temperature MC15 + Na + CO -> 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 M(acac) 1 Well studied class of compounds -Many elements form acac complexes • Metal complexes - precursors in CVD, Me sol-gel, thermolysis routes to oxides Easily chemically modified Volatile, organics soluble Nontoxic Ismail, H. M. J. Anal. Appl. Pyrolysis 1991, 21, 315-326. 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 ))))) / Fe203 > amorphous J 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.; Katabya, G.; Gedanken, A. J. Mater. Chem. 1997, 7, 2447-2451. ))))) / Fe203 \ Fe(acac)3 -► I amorphous 1 hexadecane Amorphous product, by heating to 700 °C converted to a-Fe203 20-40 nm Nikitenko, S. I.; Moisy, Ph.; Seliverstov, A. F.; Blanc, P.; Madic, C. Ultrasonics Sonochem. 2003, 10, 95-102. Sonochemical Synthesis of Iron Oxide Nanoparticles Amorphous sono-Fe203 Fe(acac)3 ))))) 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) Ultrasonic Sonochem. 2008, 15, 256-264 Corundum SEM of Nanoscopic Fe203 IR Spectrum of Sono-Fe203 1.0 0.9 0.8 0.7 0.6 : I 03 o s — ■e 0.5 = o CO |< _ 0.4 0.3 0.2 0.1 0.0 as-synthesized Fe203 (red) after calcination to 500 °C (blue) 4000 30 00 2000 Wave number (cm-1) 1000 IR Spectrum of Sono-Fe203 Acetate stretching /rrirr* Diketonate vibr. absent ^asv^""/ 1566 cnr1 0.65; 0.60 0.55! 0.50 0.45! CD _i c 0.40! co -i -Q ° 0.35! -Q < 0.30 0.25! 0.20 0.15! 0.10 0.05! 0.00 A = vas(COO) - vs(COO) = 134 cm 1 vs(COO) 1432 cm1 4000 3000 2000 Wavenumber (cm-i; 1000 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 CH CH3 CH3 Deacon, G. B.; Phillips, R. J. Coord. Chem. Rev. 1980, 3, 227-250. TEM proves amorphous character of sono-Fe203 Crystallization of Amorphous Fe203 under TEM Beam Electron diffraction Maghemite or Magnetite Time under TEM beam Crystallization induced by heating (300 °C) E nm EM of amorphous Fe203 20 nm TEM Fe203 calcined at 300 °C 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 50 100 150 200 250 300 350 400 Temperature, 2C The oxide surface area increases as the acetate groups are removed, then the particle size increases because of sintering Composite Particles of Sono-Fe203 TEM (5 nm bar) 5 nm Composite Particles of Fe203 TEM (10 nm bar) Iron oxide particle size 2 to 3 nm Embedded in organic matrix Iron oxide particle size 10 to 20 nm Hematite Particle Size coherence length D (nm) 31,0 Dependence of the coherence length, D (nm) of a-Fe203 on the crystallization temperature under dynamic-isothermal conditions of the HT-XRD measurement