Adsorption Configurations and Decomposition Pathways of Boric Acid on TiO2 Rutile (110) Surface: A Computational Study

We have investigated the adsorption and reactions of the monomer and dimer of B(OH)(3) on TiO2 rutile (110) surface by first-principles calculations. The most stable adsorption structure for B(OH)(3) On the surface is a molecular monodentate configuration, with one hydrogen bonded to a neighboring surface bridging oxygen with an adsorption energy of 20.1 kcal/mol. The adsorbed B(OH)(3) molecule can dissociate into the bidentate adsorption configuration, Ti-OB(OH)O-Ti(a), in which the -OB(OH)O- moiety binds to the surface through two Ti-O bonds with the two dissociated H atoms on neighboring bridged surface oxygen atoms following stepwise H-migration. Notably, the adsorption energy for Ti-OB(OH)O-Ti(a) with 2 H on two O-b surface atoms is 134.6 kcal/mol. In the case of dimer there are two identical molecules similar to monodentate configuration of B(OH)(3) adsorbed on two 5-fold-coordinated Ti atoms of the surface with an adsorption energy of 37.9 kcal/mol. Following intramolecular dehydration and successive migrations of protons from two OH groups to neighboring Ob sites, very stable Ti-OB(OH)OB(OH)O-Ti adsorbate can be readily formed with 141.1 kcal/mol binding energy. Both Ti-OB(OH)O-Ti(a) and Ti-OB(OH)OB(OH)O-Ti(a) adsorbates can be ideally employed as linkers between semiconductor quantum dots such as metal nitride or selenides and TiO2 nanoparticles by pretreatment of nanoparticle films with B(OH)(3). A similar study on the adsorption and reactions of B(OH)(3) on anatase (101) surface has been recently reported. The most noticeable difference is that B(OH)(3) and its dimer on the rutile surface have slightly higher binding energies than those on the anatase surface and that the rutile surface is more effective for proton migration from the acid to the surface O-atom.