Photopotential decay delay on TiO2 surface modified with p‐benzaldehydes: consequences and applications

Abstract

TiO2 (Anatase) surface has been modified with p‐substituted benzaldehydes (p = OCH3, CH3, H, CN, and NO2) and 4‐stilbene carboxaldehyde. Fourier transform infrared spectroscopy attenuated total reflectance spectroscopy, UV–Vis reflectance spectra, and theoretical calculations indicate that the TiO2 surface has been chemically modified and supported acetal formation by means of TiO2–OH reaction with the aldehyde. A steady state photocurrent was obtained during simulated UV light irradiation of the acetal‐TiO2 in aqueous solution. Once the light irradiation is turned off, open‐circuit potential decay measurements were used in order to determine the electron life‐time (tn). Excited electron decay is inhibited down to 1 s when the electron withdrawing delocalization capacity of the modified TiO2 increases. Electron life‐time also depends on the solution reduction capacity. However, the unmodified TiO2 life‐time does not. The TiO2 modification results in a new series of photocatalysts that improve the organic contaminants degradation in solution because slow electron decay also induces retardation of the electron‐hole recombination. Therefore, there is a linear relationship between the electron decay life‐time and degradation rate constant. However, when electron delocalization is further increased in a way that the electron life‐time becomes ca. 7 s, degradation rate is kept constant. Therefore, the extra electron stability compromise degradation in such a way that the modified nanoparticle switches from a useful oxidant agent to a material that favors the charge carriers separation through a stable radical anion formation. Copyright © 2014 John Wiley & Sons, Ltd.