Adsorption of bi-isonicotinic acid on rutile TiO2(110)

Bi-isonicotinic acid (2,2'-bipyridine- 4,4'-dicarboxylic acid) is the ligan d of several organometallic dyes, used in photoelectrochemical applications . Therefore the atomic scale understanding of the bonding of this molecule to rutile TiO2(110) should give insight into the crucial dye-surface intera ction. High resolution x-ray photoelectron spectroscopy (XPS), near edge x- ray absorption fine structure (NEXAFS), and periodic intermediate neglect o f differential overlap (INDO) calculations were carried out on submonolayer bi-isonicotinic acid rutile TiO2(110). Data from multilayers is also prese nted to support the submonolayer results. For a multilayer, XPS shows that the carboxyl groups remain in the (pristine) protonated form, and NEXAFS sh ow that the molecular plane is tilted by 57 degrees with respect to the sur face normal. For the submonolayer, the molecule bonds to the rutile TiO2(11 0) surface via both deprotonated carboxyl groups, with a tilt angle of 25 d egrees, and additionally an azimuthal orientation of 44 degrees with respec t to the [001] crystallographic direction. The adsorbant system was also in vestigated by quantum mechanical calculations using a periodic INDO model. The most stable theoretical adsorption geometry involves a twist around the molecular axis, such that the pyridine rings are tilted in opposite direct ions. Both oxygen atoms of each carboxyl group are bonded to five-fold coor dinated Ti atoms (2M-bidentate), in excellent agreement with the experiment al results. (C) 1999 American Institute of Physics. [S0021-9606(99)70509-X] .