| AVS 56th International Symposium & Exhibition | |
| In Situ Microscopy and Spectroscopy: Interfacial and Nanoscale Science Topical Conference | Thursday Sessions |
| Session IS+SS-ThM |
| Session: | In-Situ Spectroscopy - Interfacial Science & Catalysis |
| Presenter: | S. Kaya, SLAC National Accelerator Lab |
| Authors: | S. Kaya, SLAC National Accelerator Lab F. Mbuga, SLAC National Accelerator Lab T. Kendelewicz, Stanford University J. Newberg, Lawrence Berkeley National Lab H. Bluhm, Lawrence Berkeley National Lab H. Ogasawara, SLAC National Accelerator Lab G.E. Brown, Stanford University A. Nilsson, SLAC National Accelerator Lab |
| Correspondent: | Click to Email |
Natural contamination of groundwater by arsenic has become an important water quality problem in many parts of the world [1]. Arsenite [As(III)] and arsenate [As(V)] are highly toxic inorganic arsenic species that represent a potential threat to the environment and human health. Iron oxides play a significant role in controlling dissolved As concentration and limit the mobility and availability of As(III) and As(V). Arsenic adsorption mechanisms involve exchange of the As species for surface water and surface OH groups therefore in-situ characterizations of iron oxide surfaces in the presence of water are crucial.
We have studied chemical nature of As on Fe3O4(111) and Fe3O4(111)/Fe(OH)x thin films in the presence of water (P<0.5 Torr) using Ambient Pressure Photoemission Spectroscopy (APPES) at Advanced Light Source (ALS) [2]. Hydroxylation of pristine Fe3O4(111) surface commences at low relative humidity (RH) values and is followed by adsorption of molecular water with increasing RH. In 0.5 Torr water H2O:OH ratio at room temperature is about one and all acidic sites are fully hydroxylated. As 3d spectra taken in presence of 0.5 Torr water suggests that oxidation state of arsenic depends on degree of hydroxylation of iron oxide surfaces studied. In addition to the hydroxylation process, increasing RH leads to oxidation of arsenic from As(III) to As (V). Fe2+ surface sites plays an important role in the oxidation states of arsenic and the reasons of which will be discussed based on the changes in formal charges during hydration-dehydration processes.
[1] R. Nickson, et. al., Nature, 395 338 (1998).
[2] H. Bluhm et al., MRS Bulletin, 34 1022 (2007).