Adsorption, hydrolysis and coordination change of Zn(II) on the rutile (110) surface: A combined X-ray standing wave, EXAFS, and density functional theory study

COLL 454

James D. Kubicki, kubicki@geosc.psu.edu1, Jorge O. Sofo, sofo@psu.edu2, A. V. Bandura, andrei@ab1955.spb.edu3, Paul Fenter, fenter@anl.gov4, Zhan Zhang4, Michael J. Bedzyk5, Jeffrey G. Catalano, catalano@anl.gov4, Neil C. Sturchio6, and Shelley D. Kelley4. (1) Dept. of Geosciences, The Pennsylvania State University, 335 Deike Building, University Park, PA 16802, (2) Department of Physics, The Pennsylvania State University, 104 Davey Lab, PMB#172, University Park, PA 16802, (3) St. Petersburg State University, St. Petersburg, Russia, (4) Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, (5) Center for Catalysis and Surface Science, Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208, (6) Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL 60607
A combination of X-ray standing wave (XSW), polarized extended absorption fine structure (EXAFS)spectroscopy, and plane-wave periodic density functional theory (DFT) calculations were used to study the details of Zn(II) adsorption onto the (110) surface of rutile (alpha titanium dioxide). The XSW data reveals that Zn(II) adsorbs as an inner-sphere complex at two sites: a monodentate site above an oxygen atom bonded to two titanium atoms (i.e., Ti-O-Ti) and a site between two terminal oxygen atoms (i.e., 2Ti-O groups). EXAFS results indicate a reduction of the Zn coordination number from six in the aqueous phase to either 4- or 5-fold upon adsorption. Decreasing pH from 8 to 6 does not change the structure of the surface complexes, but it does change the relative stability of the sites. The monodentate site is dominant at pH 8, but the two sites have approximately equal concentrations at pH 6. Periodic DFT calculations using the program VASP were used as a basis for models of the polarized EXAFS spectra and to help interpret the XSW results. In addition, the hydrolysis of Zn(II) at the surface was predicted to be the driving force for the reduced coordination change.
 

Environmental Interfaces
8:30 AM-12:40 PM, Wednesday, 13 September 2006 Sir Francis Drake -- Empire Room, Oral

Division of Colloid & Surface Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006