TY - JOUR

T1 - Adsorption of Al 13 -Keggin clusters to sapphire c-plane single crystals

T2 - Kinetic observations by streaming current measurements

AU - Lützenkirchen, J.

AU - Kupcik, T.

AU - Fuss, M.

AU - Walther, Clemens

AU - Sarpola, A.

AU - Sundman, O.

PY - 2010/1/4

Y1 - 2010/1/4

N2 - We have carried out streaming current measurements of sapphire c-plane single crystals in contact with the solutions containing the Al 13 -ε-Keggin ions at different pH values. We followed the evolution of the zeta-potential as a function of time and pH. The Keggin ions were synthesised and characterised by ESI-MS in two different laboratories, and the results showed that nearly 100% of Al was in the form of Al 13 cluster. The streaming current measurements were carried out to investigate whether Al 13 clusters would (i) be adsorbed to the surface and (ii) remain stable. Close to the isoelectric point of the sapphire c-plane (around pH 4) it was found that the Al 13 ions were adsorbed and stable in the systems for an extended period. After some time the conductivity of the solution strongly increased and the zeta-potential declined, indicating that the clusters were destroyed (certainly in solution, as indicated by the conductivity reading, but potentially also at the surface). ESI-MS measurements at various dilution factors or decreased pH also showed disintegration of the clusters resulting in a multitude of smaller Al species, in agreement with the conductivity measurements during the streaming current measurements. Additions at higher pH showed clear adsorption of the clusters but resulted in stability over the complete observation period as inferred from the conductivity measurements.

AB - We have carried out streaming current measurements of sapphire c-plane single crystals in contact with the solutions containing the Al 13 -ε-Keggin ions at different pH values. We followed the evolution of the zeta-potential as a function of time and pH. The Keggin ions were synthesised and characterised by ESI-MS in two different laboratories, and the results showed that nearly 100% of Al was in the form of Al 13 cluster. The streaming current measurements were carried out to investigate whether Al 13 clusters would (i) be adsorbed to the surface and (ii) remain stable. Close to the isoelectric point of the sapphire c-plane (around pH 4) it was found that the Al 13 ions were adsorbed and stable in the systems for an extended period. After some time the conductivity of the solution strongly increased and the zeta-potential declined, indicating that the clusters were destroyed (certainly in solution, as indicated by the conductivity reading, but potentially also at the surface). ESI-MS measurements at various dilution factors or decreased pH also showed disintegration of the clusters resulting in a multitude of smaller Al species, in agreement with the conductivity measurements during the streaming current measurements. Additions at higher pH showed clear adsorption of the clusters but resulted in stability over the complete observation period as inferred from the conductivity measurements.

KW - ESI-MS

KW - Isoelectric point

KW - Sapphire c-plane

KW - Single crystals

KW - Speciation

KW - Zeta-potential

UR - http://www.scopus.com/inward/record.url?scp=77953131294&partnerID=8YFLogxK

U2 - 10.1016/j.apsusc.2009.12.095

DO - 10.1016/j.apsusc.2009.12.095

M3 - Article

AN - SCOPUS:77953131294

VL - 256

SP - 5406

EP - 5411

JO - Applied Surface Science

JF - Applied Surface Science

SN - 0169-4332

IS - 17

ER -