Photoelectrochemical detection and speciation of thallium (I) and thallium (III)

128

An ion-exchange separation technique followed by analysis with atomic absorption spectroscopy was used to study the chemical forms and distribution of thallium in Lakes Michigan, Huron, and Erie. The dominant thallium form found in water samples analyzed was the oxidized Tl(III) which comprised 68 ± 6% of the total dissolved thallium, contrary to thermodynamic prediction that Tl(I) is favored in natural waters. A significant proportion of Tl(III) may be in colloidal form. No definite spatial (horizontal or vertical) pattern was found in the distribution of total dissolved thallium in the water columns of Lakes Michigan, Huron, and Erie. An overall decline of thallium concentration from Lake Michigan to Lake Erie was observed which may be related to rapid scavenging removal from the water column.

Section: Resultsmentioning

confidence: 99%

Thallium Speciation in the Great Lakes

Lin

Nriagu

1999

128

“…The photochemical reaction is an important process impacting the redox state and thus the speciation of Tl. ,− Irradiation via ultraviolet (UV) light could directly induce the redox conversion of Tl(III) to Tl(I) through the charge-transfer absorption of the hydrolyzed Tl(III) species (i.e., TlOH 2+ ) at 254 nm , The reduction is reported to occur with the generation of an unstable intermediate Tl(II) and the highly oxidative hydroxyl radical ( • OH) (eqs and ) . In solutions containing Fe(III), UV or solar irradiation can also induce the conversion of Fe(III) to form Fe(II) and • OH, , which in turn influences the redox cycling of aqueous Tl.…”

Section: Introductionmentioning

confidence: 99%

Light- and H₂O₂-Mediated Redox Transformation of Thallium in Acidic Solutions Containing Iron: Kinetics and Mechanistic Insights

Huang

Huangfu

et al. 2022

The redox transformation between the oxidation states of thallium (Tl(I) and Tl(III)) is the key to influencing its toxicity, reactivity, and mobility. Dissolved iron (Fe) is widely distributed in the environment and coexists at a high level with Tl in acidic mine drainages (AMDs). While ultraviolet (UV) light and H 2 O 2 can directly (by inducing Tl(III) reduction) and indirectly (by inducing Fe(III) to form reactive intermediates) impact the redox cycles of Tl in Fe(III)-containing solutions, the kinetics and mechanism remain largely unclear. This study is the first to investigate the UV light-and H 2 O 2 -mediated Tl redox kinetics in acidic Fe(III) solutions. The results demonstrate that UV light and H 2 O 2 could directly reduce Tl(III) to Tl(I), with the extent of reduction dependent on the presence of Fe(III) and the solution pH. At pH 3.0, Tl(I) was completely oxidized to Tl(III), which can be ascribed to the generation of hydroxyl radicals ( • OH) from the Fe(III) photoreduction or Fe(III) reaction with H 2 O 2 . The kinetics of Tl(I) oxidation were strongly affected by the Fe(III) concentration, pH, light source, and water matrix. Kinetic models incorporating Tl redox kinetics with Fe redox kinetics were developed and satisfactorily interpreted Tl(III) reduction and Tl(I) oxidation under the examined conditions. These findings emphasize the roles of the UV light-and H 2 O 2 -driven Fe cycles in influencing the redox state of Tl, with implications for determining its mobility and fate in the environment.

“…The photochemical reactions are of critical importance for mediating the redox cycling of Tl. ,− In our earlier study, we showed that the conversion of Tl(III) to Tl(I) occurs through a direct charge-transfer process within Tl(OH) 2+ in acidic solutions upon irradiation via ultraviolet light . The photochemical reduction kinetics of Tl(III) is highly dependent on solution pH, with a faster reduction rate obtained at higher pH .…”

Section: Introductionmentioning

confidence: 99%

Sunlight-Mediated Reductive Transformation of Thallium(III) in Acidic Natural Organic Matter Solutions: Mechanisms and Kinetic Modeling

Huang

Huangfu

2023

Thallium (Tl) redox state determines its speciation and fate in aqueous environments. Despite the high potential of natural organic matter (NOM) providing the reactive groups to complex and reduce Tl(III), the kinetics and mechanisms by which NOM influences the Tl redox transformation have remained insufficiently understood. Here, we studied the reduction kinetics of Tl(III) in acidic Suwannee River fulvic acid (SRFA) solutions under dark and solar-irradiated conditions. Our results show that the thermal Tl(III) reduction occurs by the reactive organic moieties in SRFA, with the electron-donating capacities of SRFA increased with pH and decreased with [SRFA]/[Tl(III)] ratios. Solar irradiation promoted Tl(III) reduction in SRFA solutions as a result of ligand-to-metal charge transfer (LMCT) within the photoactive Tl(III) species as well as an additional reduction process mediated by a photogenerated superoxide. We demonstrated that the formation of Tl(III)–SRFA complexes decreased the reducibility of Tl(III), with the kinetics dependent on the nature of the binding component and SRFA concentrations. A “three ligand class” kinetics model has been developed and satisfactorily describes Tl(III) reduction kinetics over a range of experimental conditions. The insights presented here should assist in understanding and predicting the NOM-mediated speciation and redox cycle of Tl in a sunlit environment.