Beam-induced redox transformation of arsenic during AsK-edge XAS measurements: availability of reducing or oxidizing agents and As speciation

Author:

Han Young-Soo,Jeong Hoon Young,Hyun Sung Pil,Hayes Kim F.,Chon Chul-MinORCID

Abstract

During X-ray absorption spectroscopy (XAS) measurements of arsenic (As), beam-induced redox transformation is often observed. In this study, the As species immobilized by poorly crystallized mackinawite (FeS) was assessed for the susceptibility to beam-induced redox reactions as a function of sample properties including the redox state of FeS and the solid-phase As speciation. The beam-induced oxidation of reduced As species was found to be mediated by the atmospheric O2and the oxidation products of FeS [e.g.Fe(III) (oxyhydr)oxides and intermediate sulfurs]. Regardless of the redox state of FeS, both arsenic sulfide and surface-complexed As(III) readily underwent the photo-oxidation upon exposure to the atmospheric O2during XAS measurements. With strict O2exclusion, however, both As(0) and arsenic sulfide were less prone to the photo-oxidation by Fe(III) (oxyhydr)oxides than NaAsO2and/or surface-complexed As(III). In case of unaerated As(V)-reacted FeS samples, surface-complexed As(V) was photocatalytically reduced during XAS measurements, but arsenic sulfide did not undergo the photo-reduction.

Funder

Basic Research Project of the Korea Institute of Geoscience and Mineral Resources

Basic Science Research Program through the National Research Foundation of Korea

Publisher

International Union of Crystallography (IUCr)

Subject

Instrumentation,Nuclear and High Energy Physics,Radiation

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