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A Spectroscopic and Electrochemical Approach to the Study of the Interactions and Photoinduced Electron Transfer between Catechol and Anatase Nanoparticles in Aqueous Solution
journal contribution
posted on 2005-09-14, 00:00 authored by Teresa Lana-Villarreal, Antonio Rodes, Juan M. Pérez, Roberto GómezWe have combined in situ photoelectrochemical and spectroscopic techniques (Attenuated Total
Reflection Infrared, ATR-IR, and Resonance Raman Spectroscopy) for the study of the charge-transfer
complex formed upon adsorption of catechol on anatase nanoparticles in contact with aqueous acidic
solutions. Vibrational spectroscopies reveal the existence of at least two adsorbate configurations:
catecholate in a chelate configuration and molecularly adsorbed catechol, with apparent
values of
−12.3 and −10.5 kJ mol-1, respectively. These values are significantly less negative than the values reported
for anatase colloidal dispersions. The adsorption of both catechol species on the nanoparticulate anatase
thin films follows the Freundlich isotherm. As revealed by resonance Raman spectroscopy, only the adsorbed
chelating catecholate forms the charge-transfer complex. The electron transfer from the adsorbate to the
anatase nanoparticles has been evidenced by the development of a negative photopotential upon 514.5
or 632.8 nm laser illumination of an anatase nanostructured thin film electrode in contact with a catechol
solution. The time evolution of the Raman spectra shows an increasing fluorescence indicating that, upon
electron injection, catechol polymerization occurs on the TiO2 surfaces. This conclusion is confirmed by in
situ ATR-IR measurements, which show a progressive broadening of the catecholate bands together with
the appearance of new signals. This study illustrates the benefits of combining electrochemical, infrared,
and Raman techniques for the elucidation of processes occurring at the semiconductor/solution interface.
Finally, evidence is given on the different adsorption and reactivity behavior found for suspensions and
nanoporous thin films under equivalent experimental conditions.