Multibubble sonoluminescence and sonochemistry of f-transition elements

Pflieger R.,1 Virot M.,1 Chave T.,1 Schneider J.,2 Nikitenko S.I.,1

1ICSM, Marcoule, France, 2MPI, Potsdam, Germany

Institute for Separation Chemistry of Marcoule (ICSM), Laboratory of Sonochemistry in Complex Fluids (www.icsm.fr)

August 13-16, 2012, Singapore

Fluorescence of uranyl ions

Uranyl ion UO22+ is a major chemical form of uranium in aqueous solutions

Absorption and emission spectra of UO22+ in 0.1M HClO4

at 25°C (used in analysis)

Why U and lanthanides (Tb)?

U is a principal element of nuclear industry

Ln are the important fission products and also they are widely used in industry (catalysis, optics, medical diagnostics, etc.)

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Multifrequency reactor for MBSL and sonochemistry

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In HClO4 UO22+ exhibits

extremely weak MBSL

MBSL of 0.1M UO22+ in HClO4 and in H3PO at 203 kHz, 10°C, Ar. The inset shows the emission

spectrum of 0.2M UO22+ in 0.2 M HClO4 after photoexcitation at λ = 427 nm.

In H3PO4 MBSL of UO22+ is much

stronger than that in HClO4

Strong effect of acid

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UO22+ SL intensity is strongly influenced by the ultrasonic frequency

The strongest intensity of UO22+ SL is observed at 203 kHz ultrasound

exhibiting the highest total SL (0.5M H3PO4, Ar)

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Ultrabright SL of UO22+ in H3PO4 can be seen by the unaided eye!

30 sec

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The difference between HClO4 and H3PO4 is attributed to UO22+

quenching

Intramolecular quenching with coordinated water: (UO2

2+)* + H2O → UO2+ + H+ + OH•

Intermolecular quenching :

(UO22+)* + H2O2 → UO2

+ + H+ + HO2•

UO2+ + OH• (HO2

•, H2O2) → UO22+

Quenching of UO22+ MBSL with 1•10-2 M

H2O2. 203 kHz, 86 W, 7.2•10-3 M UO22+ 0.5 M

H3PO4, 10°C, Ar.

Stable phosphate complexes UO2Hx(PO4)n+(2-3n+x) strongly decrease both

intra- and intermolecular quenching

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Effect of UO22+ concentration – an effective tool to elucidate the

mechanism of excitation

SL photons are totally absorbed by UO22+

(>10-4 M)

SonophotoluminescenceIn diluted solutions

Contribution of collisional mechanism in concentrated

solutions

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MBSL of Tb(III) in aqueous solutions

There is no SL of Tb(III) in diluted (<0.05 M) solutions

Tb(III) absorption

MBSL spectra of 0.1M TbCl3 in water (11°C, Ar)

Tb(III) emission

________________________f, kHz Pac, W QY, a.u.________________________20 24 0.40203 47 0.17607 41 0.10PL 0.08________________________

In solutions Tb(III) is excited mostly via collisional mechanismCollisional excitation is stronger at low-frequency?

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MBSL of Tb(III) at the extended solid-liquid interface

(Ce0.9Tb0.1)PO4 sintered pellet, water, 20 kHz, Ar, 10°C

Tb(III) at the interface is excited via sonophotoluminescence mechanism

Pellet

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CONCLUSIONS

MBSL of UO22+ is the first observation of SL for radioactive elements

MBSL of UO22+ and Tb(III) is extremely sensitive to ultrasonic frequency

and to the presence of complexing reagents.

Intramolecular and intermolecular quenching strongly influence the intensity of UO2

2+ and Tb(III) MBSL

The mechanism of UO22+ MBSL seems to vary with uranium concentration:

sonophotoluminescence dominates in diluted solutions, and collisional excitation would add its contribution at higher UO2

2+ concentration

MBSL of Tb(III) in solutions is triggered mostly by collisional mechanism and by sonophotoluminescence at the extended solid/liquid interface

==============================This work was supported by French ANR program (ANR-10-BLAN-0810) NEQSON

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