Rapid Photooxidation of As(III) through Surface Complexation with Nascent Colloidal Ferric Hydroxide

Abstract

Contamination of water and soils with arsenic, especially inorganic arsenic, has been one of the most important topics in the fields of environmental science and technology. The interactions between iron and arsenic play a very significant role in the environmental behavior and effect of arsenic species. However, the mechanism of As(III) oxidation in the presence of iron has remained unclear because of the complicated speciation of iron and arsenic. Photooxidation of As(III) on nascent colloidal ferric hydroxide (CFH) in aqueous solutions at pH 6 was studied to reveal the transformation mechanism of arsenic species. Experiments were done by irradiation using light-emitting diodes with a central wavelength of 394 nm. Results show that photooxidation of As(III) and photoreduction of Fe(III) occurred simultaneously under oxic or anoxic conditions. Photooxidation of As(III) in the presence of nascent CFH occurred through electron transfer from As(III) to Fe(III) induced by absorption of radiation into a ligand-to-metal charge-transfer (LMCT) band. The estimated quantum yield of photooxidation of As(III) at 394 nm was (1.023 ± 0.065) × 10(-2). Sunlight-induced photooxidation of As(III) also occurred, implying that photolysis of the CFH-As(III) surface complex could be an important process in environments wherein nascent CFH exists.

Removal of Rhodamine B with Fe-supported bentonite as heterogeneous photo-Fenton catalyst under visible irradiation

“…It indicated the important role of visible light in the heterogeneous Fenton process for the degradation of RhB. The quantum yield ( ) was estimated to examine the photodegradation efficiency [39,64], which was found to be (1.66 ± 0.21) × 10 −2 (see Supplementary Material for detail). In order to explore the contribution of photolysis to the removal of RhB, the dye was irradiated by visible light alone, with the adsorption equilibrium concentration of RhB being selected as the initial dye concentration.…”

“…Compared to conventional light sources, light-emitting diode (LED) lamps are small in size, robust, environmentally friendly, which have relatively low costs but a longer life span [38]. More importantly, the LED lamps are not calorigenic, and then the reactions can be performed at room temperature without the use of cooling water [39]. Therefore, in this study, natural bentonite clay was used as support to synthesize photo-Fenton catalyst (Fe-supported bentonite, denoted as Fe-B) and LED lamps with a central wavelength of 455 nm were employed as visible light sources.…”

Mechanism and products of the photolysis of hexabromocyclododecane in acetonitrile–water solutions under a UV-C lamp

“…The competitive reaction for 1 O 2 was also performed in an LED reactor, which was the same as that used in previous work [22]. The UV-C lamps used for photolysis of HBCD mainly have emission at wavelengths between 224 and 254, 266, 276, 281 and 290 nm as shown in Fig.…”

Solid surface photochemistry of montmorillonite: mechanisms for the arsenite oxidation under UV-A irradiation

“…HO • reacts with As(III) more rapidly than do HO 2 • or H 2 O 2 and mainly oxidizes As(III) to As(IV) in photochemical systems containing iron oxides and iron hydroxides (Wang et al 2013a, b;Xu et al 2013). The intermediate As(IV) can be easily oxidized to As(V) by either Fe(III), O 2 , or HO • , as shown in reactions (4), (5), and (6), respectively.…”

“…The intermediate As(IV) can be easily oxidized to As(V) by either Fe(III), O 2 , or HO • , as shown in reactions (4), (5), and (6), respectively. Additionally, Xu et al (2013) reported a novel pathway of As(III) photooxidation on nascent colloidal ferric hydroxide in aqueous solutions. The surface complex formed by reaction of As(III) and ferric hydroxide can undergo ligand-to-metal charge-transfer from As(III) to As(V) under irradiation (Woods et al 1963;Dutta et al 2005).…”