Ascorbate Induced Facet Dependent Reductive Dissolution of Hematite Nanocrystals

The interaction between ascorbate and hematite facets was systematically investigated with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, density functional theory (DFT) calculation, and kinetics model. Results of ATR-FTIR spectroscopy and DFT calculation suggested formation of nonprotonated inner-sphere bidentate mononuclear and monodentate mononuclear iron–ascorbate complexes on the hematite {001} and {012} facets, respectively. The estimated reductive dissolution rate constants at pH 5.0 were (4.04 ± 0.16) × 10–4 and (1.59 ± 0.14) × 10–4 min–1 for hematite nanoplates and nanocubes, respectively, indicating that the bidentate mononuclear iron–ascorbate complexes on the {001} facets favored the hematite reductive dissolution process than the monodentate mononuclear iron–ascorbate counterparts on the {012} facets. These results also revealed that the hematite facet reduction with ascorbate was strongly dependent on the iron–ascorbate complexes formed on the hematite facets. This study provides new insights into the reductive interaction between ascorbate and hematite facets and also shed light on the environmental effects of hematite at the atomic level.