vs nalajala and vs moholkar (poster ntp-10)

8/3/2019 Vs Nalajala and vs Moholkar (Poster NTP-10)

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SonochemicalNanosynthesis:

Principles and Processes

Venkata Swamy Nalajala and V. S. Moholkar

Department of Chemical EngineeringINDIAN INSTITUTE OF TECHNOLOGY GUWAHATI

Guwahati 781039, Assam

E-mail: [email protected]; Phone: 09954604473


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Sonochemistry and Cavitation

SonochemistryUse of ultrasound for enhancing reactions.Infrasonic, sonic and ultrasonic.

Cavitation: Formation, Growth and Collapse of bubble. Types of CavitationHydrodynamic Cavitation: Pressure variation due to change in flow geometryAcoustic Cavitation: Pressure variation due to passage of ultrasound waveOptic Cavitation: High intensity laser to vaporize small quantity of liquid

Particle Cavitation: Use of elementary type particle such as proton

Human hearing 20 Hz 20 kHz

Conventional power ultrasound 20 kHz 500 kHzExtended range of sonochemistry 500 kHz 2 MHz

Diagnostic ultrasound 5 MHz 10 MHz

0 10 102 103 104 105 106 107


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Reaction Zones in a

Cavitation Bubble

Zone 1: Inside the bubble where thermal decompositionoccurs (pyrolysis).

Zone 2: Bubble-liquid interface (pyrolysis and hydrolysis).

Zone 3: Bulk liquid medium (hydrolysis).

Zone 1Zone 2 Zone 3


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Newer Techniques for

Nanosynthesis

The most important factors in nanosynthesis are theprecursorssolvents and reaction conditions.

Temperature and pressure of the reaction reduceswith the change in the reaction medium or thesolvents.

Newer and greener means of nanosynthesis

Supercritical fluidsIonic liquids

Microwave


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Advantages of

Sonochemical Technique

Preparation of amorphous products: No need of addition ofglass-formers.

Insertion of nanomaterials into mesoporous materials:Nanomaterial get deposited on the walls of the mesoporeswithout blocking them. These layers are more smooth anduniform.

Surface deposition or surface coating of nanoparticles on a

surface: Smooth homogeneous coating layer on surfacecreated. Particles form chemical bonds or chemical interactionswith substrate and can not be removed by washing.

The formation of proteinaceous micro and nanospheres: Anyprotein can be converted into sphere after sonication. Spheresare biologically active, with some reduced activity.


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Manifestations of Ultrasound

and Cavitation

Sonochemical decomposition of volatile organometallicprecursors in low-volatilitysolvents produces nanostructured

materials. Nanostuctured metals, alloys, oxides, carbides, sulfides,

nanometer colloids, and nanostructured catalysts can all beprepared by this general route.

It can reduce number ofsteps involved in a multi-stepsynthesis.

It can completelyswitch reaction path way.


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Sonochemical Nanosynthesis

The exact location of the sonochemical reaction depends on thenature of the reactants.

Volatile components evaporates into bubble during expansionphase and reaction occurs in gas phase inside the bubble.

If the precursor is nonvolatile compound, the reaction occurs in

the thin liquid shell surrounding the bubble.


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Physical Mechanisms of

Nanosynthesis

Depending on the nature of precursors, reaction will occur inbulk medium or interfacial region or inside of the bubble.

Volatile precursors will evaporate into bubble and decomposeat extreme conditions reached in the bubble. Products ofsuchsynthesis are generally amorphous.

Non-volatile precursorsstay in bulk medium. They areattacked by OH radicals produced by cavitation bubbles andare hydrolyzed. Hydrolysis is relativelyslow and the productis crystalline.

Precursors like chlorides and nitrates are essentially fragilecompounds. They decompose at low temperatures (~ 200oC)reached at bubble-bulk interface during transient collapse.The product formed has crystalline character.


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Sonochemical Synthesis of

Oxides

Various oxides that have been synthesized sonochemicallyinclude Titania, Strontium titanate, silica, ZnO, ZrO2 and MnOx,iron oxides, PbO, CeO

2, SnO

2, WO

2, MoO

x, MgO.

Solvents used: Decalin, Distilled Water, Ethanol, EthyleneGlycol.

The precursors used for the synthesis were alkoxides, nitrates,acetates, chlorides, sulfates, carbonates, acetylacetonates andacetyl acetonates.

Ganesh Kumar (2003) hassynthesized nano particles ofMn3O4using 6 precursors viz. MnSO4, MnCl2, Mn(No2)2, Mn(oAc)2,Mn(II) acetyl acetonate and MnCo3.

The shapes of the nano crystals, varied from sharp edgedcrystals to smooth particles.


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Sonochemical Synthesis

of Sulfides

Chalcogenidessynthesized sonochemically: ZnS, Sb2S3, SnS2, CdS,PbS, In2S3, CuS, HgS, WS2, Bi2S3, Au2S3, MoS2.

Solvents used: Ethanol, Water, Ethylene diamine, Diphenylmethane, Decalin.

Precursors: Acetates or Chlorides. Acetates hydrolyzed by the OH.

radicals generated by cavitation, while saltssuch as chlorides arethermally dissociated to yield metal ions.

Due to the non-volatile nature of precursors, the reaction alwaysoccurred outside the bubble in the thin liquid shell and the productswere of crystalline nature.

The precursors for sulphur were pure sulfur, thio acetamide, sodiumthioshulphate or thiourea.


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Selenides and Tellurides

For the synthesis ofselenides and tellurides, pure (orpristine)Se and Te were used.

Selenides PbTe, PbSe, Ag2Se, Hg(II)Se, CdSe, Ag2Se, CuSe, MoSe2,

Bi2Se3, Cu3Se2 were prepared sonochemically.

Solvents used: Ethylene diamine, EDTA, Ethylene glycol,Distilled water.

Tellurides Ag2Te, Cu7Te4, Cu4Te3, MoTe2, Bi2Te3 and HgTe were

prepared sonochemically.

Solvents used: Ethylene diamine, Decalin, Distilled water.


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Mn3O4 from MnSO4 and LiOH(a) sonochemical(b) mechanicalstirring

Mn3O4 from MnCl2 and LiOH(sonochemical preparation)


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Mn3O4 from Mn(II) acetate (a)sonochemical preparation(b) mechanical stirring

Mn3O4 from Mn(NO3)2and LiOH (a)sonochemicalpreparation(b) mechanical stirring


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SEM image of variousstages of t-Se wire growth: (a)spherical colloids ofa-Se by reducing selenious acid with hydrazine. (b) colloidal particles recoveredfrom an ethanol dispersion after sonication (c) initial stage of wire growth(d) final product


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SEM image ofsonochemically preparedProtein microspheres from bovine serum albumin

TEM image ofPlatinum particlesdeposited oncarbon nanotubeswith 10, 20, 30wt% of Pt loading

TEM imageofMn3O4with Mn(II)acetyl

acetonate


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References

Ganesh Kumar V, Aurbach D, Gedanken A. A comparison between hot hydrolysisand sonolysis of variousMn(II)salts. Ultrason. Sonochem. 10 (2003) 17-23.

GedankenA. Using sonochemistry for the fabrication of nanomaterials. Ultrason.

Sonochem. 11 (2004) 47-55.

Xing Y. Synthesis and electrochemical characterization of uniformly dispersed highloading Pt nanoparticles on sonochemically treated carbon nanotubes. J. Phys.Chem. B 108 (2004) 19255-19259.

Jennifer AD, Bettyle LSM, James EH. Toward greener nanosynthesis. Chem. Rev.107 (2007) 2228-2269.

Guo W, Lin Z, Wang X, Song G. Sonochemical synthesis of nanocrystalline TiO2 byhydrolysis of titanium alkoxides. Microelectron. Eng. 66 (2003) 95-101.

Avivi S, Palchik O, Palchik V, Slifkin MA, WeissAM, Gedanken A. Sonochemicalsynthesis of nanophase indium sulfide. Chem. Mater. 13 (2001) 2195-2200.

Suslick KS, Price GJ. Applications of ultrasound to materials chemistry. Ann. Rev.Mater. Sci. 29 (1999) 295-326.

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