Photoproduction of Hydroxyl Radicals Under Sunlight by Fe-Zn Oxides for Partial Oxidation Applications

Abstract

Iron-zinc oxide (FZ) photocatalysts with activity in the visible region were designed for the partial oxidation of organic molecules with the least loss of raw material. The FZ materials were synthesized using the sol-gel method with citric acid as a stabilizing agent. From TGA results, 400 °C was observed as the minimum temperature for precursors degradation, then two thermal treatment times were assessed at 60 and 180 min. The powder photocatalysts were comprehensively characterized by TGA, DSC, FTIR, XRD, Raman, Mössbauer, XPS, UV-Vis, and SEM. The production of hydroxyl radicals (•OH) was followed by the fluorescence emission of 2-hydroxy-terephthalic acid (OHTA). The absorbance decrease of methylene blue (MB) and disodium terephthalate (NaTA) was measured by UV-Vis spectroscopy to calculate the total degradation degree. The photocatalytic activity of FZ materials was quantified after 2 h under simulated sunlight radiation at room temperature conditions. All FZ oxides treated for 60 min presented no •OH detection, in which photocatalytic blanks showed an adsorption phenomenon of the probe molecules. FZ7 and FZ8 materials showed the best •OH production and the least MB/NaTA degradation, making them the best candidates for partial oxidation applications.