HR: 09:30h
AN: B31F-06    [Abstracts]
TI: Nature's Semiconductors: Electronic Structure of Biogenic Manganese Oxides
AU: * Kwon, K D
EM: kkwon@nature.berkeley.edu
AF: Lawrence Berkeley National Laboratory, Department of Geochemistry, Berkeley, CA 94720, United States
AU: Refson, K
EM: k.refson@rl.ac.uk
AF: STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, United Kingdom
AU: Sposito, G
EM: gsposito@nature.berkeley.edu
AF: Lawrence Berkeley National Laboratory, Department of Geochemistry, Berkeley, CA 94720, United States
AB: Many bacteria produce Mn(IV) oxides (MnO₂), which are environmental nanoparticles having a layer structure. Biogenic Mn oxide minerals are known to participate importantly in both redox reactions and metal- scavenging in soil and aquatic environments. An important structural characteristic of the oxides is the presence of Mn(IV) cation vacancies whose charge deficit is typically compensated by metal cations or protons. These vacancies have long been identified as strong adsorption sites for heavy metals, but they may also play an important role in redox biogeochemistry, particularly in photo-induced redox reactions occurring in natural waters. Because electronic structure is the key to understanding (photo) redox transformations, we examined the electronic structures of Mn oxides both with and without Mn(IV) vacancies using quantum mechanical density functional theory (DFT) simulations. Our DFT results show that Mn(IV) vacancies compensated with protons effectively narrow the band gap energy of MnO₂, facilitating the formation and transfer of photo-induced electrons and holes. This study also suggests that the photoconductivity of natural and synthetic MnO₂ nanoparticles can be optimized by control of cation vacancies.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0419 Biomineralization
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0463 Microbe/mineral interactions
DE: 1000 GEOCHEMISTRY
SC: Biogeosciences [B]
MN: 2007 Fall Meeting