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See more from this Session: Environmental Mineralogy
Abstract:
Structural parameters of the ZnIV-TCS and ZnVI-TCS species with single or double occupancy at a Mn vacancy (i.e., ZnIV-TCS; ZnVI-TCS; ZnIV-TCS + ZnIV-TCS; ZnIV-TCS + ZnVI-TCS; or ZnIV-TCS + ZnVI-TCS) obtained by DFT geometry optimization were in excellent agreement with available experimental data on Zn-birnessite. Their total energies, magnetic moments, and electron-overlap populations showed that tetrahedral ZnIV-TCS is stable in birnessite without a need for Mn(III) substitution in the Mn octahedral sheet and that it is more effective at reducing vacancy O undersaturation than is octahedral ZnVI-TCS. Our DFT study also revealed details of structural distortion of a Mn vacancy site: Mn nearest to Zn move toward a vacancy by 0.08 0.11 Å, while surface O bordering a vacancy move away from it by 0.16 0.21 Å, relative to their positions in an ideal vacancy-free MnO2. The structures of the Zn-TCS species in birnessite determined in the present study can serve as unique end-member species of Zn-TCS to facilitate the detailed interpretation of spectroscopic data on Zn sorbed by birnessite.
See more from this Division: Topical Sessions
See more from this Session: Environmental Mineralogy