The impact of semiconductors on the concepts of electrochemistry

Pure ZrO2 and 0.5−5 wt % iron-containing samples have been prepared by a sol−gel technique and thoroughly characterized by several techniques, X-ray diffraction (XRD), differential thermal analyses (DTA), diffuse reflectance spectroscopy (DRS), scanning and transmission electron microscopies (SEM and TEM), X-ray photoelectron spectroscopy (XPS), and other complementary techniques. Introduction of iron in zirconia produced a phase transition from monoclinic to tetragonal. In contrast to generally reported values of zirconia band gap (5 eV), the values of the present samples ranged between 2.3 and 3.8 eV, determined from DRS, depending on the preparation conditions and on the iron content. Preliminary experiments of adsorption of different species (nitrite, ethylenediaminetetraacetic acid (EDTA), and Cr(VI)) are also presented and the results explained by a correlation with the physicochemical properties of the characterized oxides. Oxygen photoadsorption and oxygen isotopic exchange (OIE) results can be co...

Preparation and physicochemical properties of ZrO2 and Fe/ZrO2 prepared by a sol-gel technique

A semiempirical correlation between the optical band gap of binary oxides and the difference of electronegativity between the oxygen and metallic elements (Pauling's extraionic energy) is proposed. In the frame of the proposed correlation an estimate of the repulsive term in the total lattice energy of ionic oxides is obtained in very good agreement with the existing data. An extension of the correlation to the ternary oxides and hydroxides is proposed by using the concept of average cationic or anionic group electronegativity. The usefulness of the proposed correlation for the in situ characterization of passive films on metals and alloys by photocurrent spectroscopy is illustrated by reporting some preliminary experimental results on Sn and AlTi alloy.

Semiempirical Correlation between Optical Band Gap Values of Oxides and the Difference of Electronegativity of the Elements. Its Importance for a Quantitative Use of Photocurrent Spectroscopy in Corrosion Studies

The photocatalytic efficiency of pure and 0.5‐20 wt.% Fe-containing ZrO 2 samples, prepared by a sol‐gel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25). All samples were active, although the efficiency was lower than that of TiO 2. Nevertheless, the presence of iron increased the activity for nitrite photooxidation, with the maximum efficiency at 5 wt.% Fe content. At higher Fe content, the efficiency decreased but it was always higher than that of the undoped sample. For EDTA oxidation and Cr(VI) reduction, the same trend was observed. Remarkably, Cr(VI) reduction in the presence of EDTA was strongly accelerated, all zirconia samples being as active as P-25, although initial rates were lower and somewhat detrimentally affected by the presence of iron. The photocatalytic activity depends on the structural, surface and optical properties of the sample, on the preparation conditions and on the nature of the photocatalytic reaction. ©1999 Elsevier Science S.A. All rights reserved.

Photocatalytic properties of ZrO2 and Fe/ZrO2 semiconductors prepared by a sol-gel technique

A.R. Newmark

Papers

Photoelectrochemical studies of passive films on zirconium and amorphous iron-zirconium alloys

The influence of localized electronic states on the photoelectrochemical behavior of passive films

Photoinduced electron transfer involving localized electronic states

Photoelectrochemical properties of ion-implanted hafnium dioxide films

On the evaluation of the flatband potential from photocurrent measurements