Mechanisms of Sb(III) Photooxidation by the Excitation of Organic Fe(III) Complexes

Abstract

Organic Fe(III) complexes are widely distributed in the aqueous environment, which can efficiently generate free radicals under light illumination, playing a significant role in heavy metal speciation. However, the potential importance of the photooxidation of Sb(III) by organic Fe(III) complexes remains unclear. Therefore, the photooxidation mechanisms of Sb(III) were comprehensively investigated in Fe(III)-oxalate, Fe(III)-citrate and Fe(III)-fulvic acid (FA) solutions by kinetic measurements and modeling. Rapid photooxidation of Sb(III) was observed in an Fe(III)-oxalate solution over the pH range of 3 to 7. The addition of tert-butyl alcohol (TBA) as an ·OH scavenger quenched the Sb(III) oxidation, suggesting that ·OH is an important oxidant for Sb(III). However, the incomplete quenching of Sb(III) oxidation indicated the existence of other oxidants, presumably an Fe(IV) species in irradiated Fe(III)-oxalate solution. In acidic solutions, ·OH may be formed by the reaction of Fe(II)(C2O4) with H2O2, but a hypothetical Fe(IV) species may be generated by the reaction of Fe(II)(C2O4)2(2-) with H2O2 at higher pH. Kinetic modeling provides a quantitative explanation of the results. Evidence for the existence of ·OH and hypothetical Fe(IV) was also observed in an irradiated Fe(III)-citrate and Fe(III)-FA system. This study demonstrated an important pathway of Sb(III) oxidation in surface waters.

Influence of environmental and anthropogenic parameters on thallium oxidation state in natural waters

“…It is reported that over 99% of dissolved iron may be complexed to organic matter in natural waters, greatly increasing the solubility of iron and preventing the precipitation of oxyhydroxides (Su et al, 2015). Iron(III) organic complexes, such as Fe-oxalate, Fe-citrate and Fe−fulvic acid (the fraction of humic acids soluble at low pH) can be photolyzed to generate reactive species, such as O2• − , H2O2, •OH (Kong and He, 2016). Thus, we separately added to the Tl(I)+Fe(III) synthetic solution these three organic compounds: citric (1 mmol/L), oxalic (1 mmol/L) and fulvic acid (10 mg/L).…”

Simultaneous separation and determination of thallium in water samples by high‐performance liquid chromatography with inductively coupled plasma mass spectrometry

“…H 2 C 2 O 4 is a dissolved organic matter commonly found in nature water and can form stable complexes with Fe. A previous study has shown that , Fe‐H 2 C 2 O 4 can be photolyzed and produce active products which lead to oxidation of metals. Therefore, in this experiment, we used Fe and H 2 C 2 O 4 to prepare experimental water.…”

TiO2 crystal facet-dependent antimony adsorption and photocatalytic oxidation

“…, were reported to be responsible for Sb (III) oxidation in the TiO 2 /UV system (Table 1) [24,[34][35][36][37]. To evaluate the relative importance between Å OH or O 2 ÅÀ for Sb(III) oxidation on the four TiO 2 facets, the radical trapping technique has been used with certain selective radical scavengers.…”

“…To verify our hypothesis that high-index TiO 2 exhibits excellent performance, three low-index {101}, {001}, {100} TiO 2 samples and one high-index {201} TiO 2 were systematically investigated. Antimony (Sb), an analogue of arsenic, was selected as a probe molecule due to its wide-spread pollution and toxicity [22][23][24]. Also, the effect of TiO 2 facets on Sb adsorption and photooxidation is an uncharted area.…”