2,4-D flips at the anatase surface: an ATR-FTIR study

TAUCHERT E.; MENDIVE C.; BAHNEMANN D.

Jornada; NanoDay 2010; 2010

The spectral bands of adsorbed 2,4-D can be assigned to its different moieties (as depicted on the spectra) suggesting that a surface complex is formed via the carbonyl group and some Cl atoms from the ring. At high concentrations the adsorption sites at the (100) surface are occupied by 2,4-D molecules which closed package is likely stabilized by ring-ring interactions. The surface complex is laterally adsorbed to guarantee these interactions. Free rotations of the rings are therefore sterically hindered and almost unchanged spectral signal are obtained.At a concentration of 2.7 mM the adsorption kinetics is not observed as in the case of a lower concentration. While at 2.7 mM spectral changes upon time are small, at 1.4 mM most of the bands considerably loose intensity with the exception of those in the spectral region under 1200 cm-1. Here, there are two bands assigned to Cl-C and aliphatic C-C stretching modes which increase with time. We suggest that not all sites are covered by adsorbed 2,4-D molecules leaving enough empty space to allow the rings to rotate, for instance, around the Cl-O axis. These rotations alter the stability of the structure to some extent observed in the remarkable decrease in the intensity of the bands, except from those involving Cl atoms which upon rotations can more efficiently contribute to the IR signal.