Visible Light-Driven Photocatalytic Activity and Kinetics of Fe-Doped TiO2 Prepared by a Three-Block Copolymer Templating Approach

Abstract

Fe-doped titania photocatalysts (with 1, 2.5, and 3.5 wt. % Fe nominal content), showing photocatalytic activity under visible light, were prepared by a soft-template assisted sol–gel approach in the presence of the triblock copolymer Pluronic P123. An undoped TiO2 photocatalyst was also prepared for comparison. The photocatalysts were characterized by means of X-ray powder Diffraction (XRPD), Quantitative Phase Analysis as obtained by Rietveld refinement, Diffuse Reflectance (DR) UV−Vis spectroscopy, N2 adsorption/desorption at −196 °C, electrophoretic mobility in water (ζ-potential), and X-ray photoelectron spectroscopy (XPS). The physico-chemical characterization showed that all the samples were 100% anatase phase and that iron was present both in the bulk and at the surface of the Fe-doped TiO2. Indeed, the band gap energy (Eg) decreases with the Fe content, with Tauc’s plot determined values ranging from 3.35 (undoped TiO2) to 2.70 eV (3.5 wt. % Fe). Notwithstanding the obtained Eg values, the photocatalytic activity results under visible light highlighted that the optimal Fe content was equal to 2.5 wt. % (Tauc’s plot determined Eg = 2.74 eV). With the optimized photocatalyst and in selected operating conditions, under visible light it was possible to achieve 90% AO7 discoloration together with a TOC removal of 40% after 180 min. The kinetic behavior of the photocatalyst was also analyzed. Moreover, the tests in the presence of three different scavengers revealed that the main reactive species are (positive) holes and superoxide species. Finally, the optimized photocatalyst was also able to degrade phenol under visible light.

Photocatalytic Degradation of Crystal Violet Dye under Visible Light by Fe-Doped TiO2 Prepared by Reverse-Micelle Sol–Gel Method

“…As expected, Fe doping induces a (bathochromic) shift of the onset of adsorption of the studied samples, but also to the formation of a broad absorption at ca. 490 nm (asterisk), likely due to the d-d transitions of Fe 3+ ions [ 57 , 58 , 59 ] in Fe-oxohydroxo clusters at the surface of the NPs, as aleady observed by some of us in other types of systems [ 60 ] and in other Fe-doped TiO 2 powders [ 53 , 61 ].…”

“…According to the QPA results, by increasing the nominal Fe content, the amount of anatase decreases and, correspondingly, the amounts of both brookite and rutile increase (samples RM_2.5Fe and RM_3.5Fe). This effect may be due to the presence of Fe 3+ ions within the micelles’ core, which notoriously give rise to a more acidic environment, a condition favouring the formation of brookite [ 52 ], as already observed to occur by using the same synthesis procedure with other metallic dopants [ 37 , 38 , 53 ]. The formation of rutile, notwithstanding the adopted calcination temperature, can be due to the presence of both brookite, which may favour the anatase-to-rutile thermal transition [ 54 , 55 ], and Fe 3+ ions; indeed, as reported by Hanaor et al [ 56 ], low charge cations (i.e., <+4) can act as anatase-to-rutile transition promoters.…”

“…The mineralization efficiency for RM_0Fe was largely negligible, and this must be remarked upon to understand the selection of the best photocatalyst; indeed, the TOC removal with RM_2.5Fe photocatalyst was the highest, with a mineralization efficiency equal to about 52%, while lower values of TOC removal were found with the other samples. The higher TOC removal of the Fe doped samples with respect to the undoped TiO 2 could be related to the presence of Fe 3+ ions in the crystalline TiO 2 structure that allow enhancing the separation of the photo-generated charge carriers, since Fe 3+ can act as electron acceptor, consequently reducing recombination phenomena of e − /h + pairs [ 53 ]. Conversely, at higher Fe-contents, the formation of surface Fe-containing species can lead to the undesired formation of recombination centers, finally lowering the photocatalytic yield.…”

Synthesis of Fe-TiO2 and Cu-TiO2 Based Materials by Olive Leaves Biotemplating—Application to Hydrogen Production from Glycerol Photoreforming

“…Furthermore, the incorporation of Fe and Cu in the synthesized solids further extends the absorption to the visible part of the spectrum, observing onsets of absorption at longer wavelength for Fe-AOL and Cu-AOL solids. Thus, in the case of Fe-AOL, there is a relevant red shift of the absorption in the 400–650 nm region that is usually ascribed in the literature to the d–d transitions of Fe +3 species [ 38 ]. The band gap for the Fe-AOL solid was 2.00 eV, a very intense decrease which is in agreement with the literature reports of high content iron-doped TiO 2 catalysts [ 39 ].…”

MOF/TiO2 erythrocyte-like heterostructures decorated by noble metals for use in hydrogen photogeneration and pollutant photodegradation

“…6 To overcome these disadvantages, several approaches, such as modification with noble metals or the production of nanocomposites with other photocatalysts, have been developed. 7,8 Recently, there has been a significant increase in interest surrounding photocatalysts based on metal-organic frameworks (MOFs). Specifically, MOFs are materials consisting of metallic centers and organic linkers; they are characterized by high physicochemical stability, highly developed specific surface areas, and large pore sizes.…”