Modification of Nanocrystalline TiO2 with Phosphonate- and Bis(phosphonate)-Bearing Macrocyclic Complexes: Sorption and Stability Studies

The first systematic study of chemical adsorption/desorption of phosphonic acid and geminal bis(phosphonic acid) on/from the surface of anatase nanoparticles is reported. Stable TiO2 colloidal nanodispersions were used in the study. The colloidal stability is preserved upon nanoparticle modification. A macrocyclic lanthanide(III) complex, attached through a phosphonic/bis(phosphonic) group to the TiO2 surface allowed precise quantification of sorption parameters by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES). Results show different behavior of phosphonate and bis(phosphonate) groups. For phosphonate, a monomolecular layer formation was observed, and the desorption rate depends on the sorption conditions. It is probably caused by different phosphonate binding modes on the surface. Excess amounts of phosphate in the washing media accelerates the desorption rate of the phosphonate. The bis(phosphonate) is adsorbed on the surface in large quantities forming multilayers that resist desorption even in the presence of phosphate ions and, thus, the bis(phosphonate) moiety is a suitable group for anchoring other molecules on the TiO2 particle surface.