Photoinduced Degradation of Orange II on Different Iron (Hydr)oxides in Aqueous Suspension:  Rate Enhancement on Addition of Hydrogen Peroxide, Silver Nitrate, and Sodium Fluoride

Abstract

Photoinduced organic oxidation with iron (hydr)oxides in aqueous suspension has been argued with respect to two principal mechanisms: (a) photoinduced ligand-to-metal charge transfer within a surface complex and (b) semiconductor photocatalysis. In this work, the photodegradation of azo dye orange II with UV light (lambda > or = 320 nm) in the aerated aqueous suspensions of haematite, maghemite, magnetite, goethite, lepidocrocite, and feroxyhite at an initial pH of 6.5 has been examined. The results showed that (1) all of the catalysts were effective at initiating dye photodegradation but the iron oxides appeared to be more active than the iron hydroxides; (2) the photodissolution of different iron phases and the dye photolysis in the dissolved iron solutions were very slow; (3) the initial rate of dye loss was proportional to the initial amount of adsorption, implying dye photodegradation on the catalyst surface; and (4) upon addition of H2O2, AgNO3, and NaF to the suspension, the rate of dye photodegradation was significantly enhanced with all the catalysts. In the presence of H2O2, less than 50% of the total rate enhancement was ascribed to the photo-Fenton reaction in solution and the dark Fenton reactions in solution and on the catalyst. In the presence of AgNO3, about 1 mole of silver particles was produced by consuming 3 moles of the dye substrate. In the presence of NaF, hydroxyl radicals were detected by an ethanol scavenger, whereas such radicals were not found in the absence of NaF. Moreover, under visible-light irradiation (lambda > or = 450 nm), the dye degradation was much slower than that under UV irradiation, but the reaction was also accelerated by the addition of NaF and AgNO3. The results suggest that mechanism b, not mechanism a, is operative for dye photodegradation occurring on the iron (hydr)oxides. A detailed discussion of all possible pathways is given in the text.

Preparation of magnetite-based catalysts and their application in heterogeneous Fenton oxidation – A review

“…-FeOOH and its poorly natural counterpart, feroxyhyte ('-FeOOH), have structures based on the CdI 2 and disordered CdI 2 models, respectively [45]. They have received also little attention since Fe oxides (magnetite, maghemite and hematite) have shown to be more active than Fe (hydr)oxides in the studies carried out so far [45,53]. Table 2 summarizes the work done on the application of magnetite-based natural minerals in CWPO up to now.…”

Photoinactivation of virus on iron-oxide coated sand: Enhancing inactivation in sunlit waters

“…To improve the microbial quality of the water, it would be desirable to couple virus adsorption with inactivation. Several studies have shown that the irradiation of iron oxides with sunlight leads to the degradation of organic contaminants, in particular if the contaminants are adsorbed onto the iron oxide surface (Andreozzi et al, 2003;Du et al, 2008).…”

“…Iron oxides are semiconductors capable of producing oxidants when irradiated with sunlight (Andreozzi et al, 2003;Du et al, 2008). They can also participate in photo-Fenton reactions leading to the production of hydroxyl radicals (He et al, 2002), which cause virus inactivation (Nieto-Juarez et al, 2010).…”

Colloidal cubes for the enhanced degradation of organic dyes

“…From these results, together with the low, albeit signicant, degradation speeds, we infer that the degradation reaction is primarily governed by other properties of the hematite cubes. Considering that hematite is a known photocatalyst, 32,35,37,46,47 we investigated the inuence of active illumination with visible and UV light.…”