Pure and Fe-Doped Mesoporous Titania Catalyse the Oxidation of Acid Orange 7 by H2O2 under Different Illumination Conditions: Fe Doping Improves Photocatalytic Activity under Simulated Solar Light

Francesca Freyria,Gianguido Ramis,Barbara Bonelli,Nicoletta Ditaranto,Matteo Compagnoni,Marco Piumetti,Ilenia Rossetti

doi:10.3390/catal7070213

Abstract

A sample of mesoporous TiO2 (MT, specific surface area = 150 m2·g−1) and two samples of MT containing 2.5 wt.% Fe were prepared by either direct synthesis doping (Fe2.5-MTd) or impregnation (Fe2.5-MTi). Commercial TiO2 (Degussa P25, specific surface area = 56 m2 g−1) was used both as a benchmark and as a support for impregnation with either 0.8 or 2.5 wt.% Fe (Fe0.80-IT and Fe2.5-IT). The powders were characterized by X-ray diffraction, N2 isotherms at −196 °C, Energy Dispersive X-ray (EDX) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance (DR) ultra-violet (UV)-Vis and Mössbauer spectroscopies. Degradation of Acid Orange 7 (AO7) by H2O2 was the test reaction: effects of dark-conditions versus both UV and simulated solar light irradiation were considered. In dark conditions, AO7 conversion was higher with MT than with Degussa P25, whereas Fe-containing samples were active in a (slow) Fenton-like reaction. Under UV light, MT was as active as Degussa P25, and Fe doping enhanced the photocatalytic activity of Fe2.5-MTd; Fe-impregnated samples were also active, likely due to the occurrence of a photo-Fenton process. Interestingly, the Fe2.5-MTd sample showed the best performance under solar light, confirming the positive effect of Fe doping by direct synthesis with respect to impregnation.

Highlights

TiO2 is a widely used semiconductor due to its band gap (3.2–3.0 eV), low toxicity, availability of different polymorphs and the possibility to obtain TiO2 nanoparticles (NPs) with different morphologies and shapes [1,2,3]
The specific surface area (SSA) of the Fe2.5-MTd sample was almost unaffected by Fe doping, whereas a sizeable decrease of SSA occurred with the Fe2.5-MTi sample, probably due to the second annealing treatment following the impregnation and/or to some pores occlusion occurring during such a procedure
The amount of well‐dispersed surface Fe species had a crucial role during the reaction under dark conditions, and the sample obtained by impregnating mesoporous TiO2 (MT) was the most active

Summary

Introduction

TiO2 is a widely used semiconductor due to its band gap (3.2–3.0 eV), low toxicity, availability of different polymorphs and the possibility to obtain TiO2 nanoparticles (NPs) with different morphologies and shapes [1,2,3]. Such physico-chemical properties promote the use of TiO2 mostly as photocatalyst and/or a catalytic support [3,4,5,6,7], it is used in dye sensitized solar cells [8,9,10,11] and, recently, in biomedical applications [12,13]. Different methods have been proposed for azo-dye removal from the environment, including adsorption [27,28], reduction by nanoscale zerovalent iron [25,29], and photocatalytic degradation with TiO2 [25], generally in the presence of an oxidizing agent, such as H2 O2 [23,30]

Methods

Results

Conclusion