LAUSR

Hematite nanoparticles are abundant in the photic zone of aquatic environments, where they play a prominent role in photocatalytic transformations of bound organics. Here we examine the photocatalytic degradation of rhodamine B (RhB) by visible light using two different structurally well-defined hematite nanoparticle morphologies. In addition to detailed solids characterization and aqueous kinetics measurements, we also exploit species-selective scavengers in electron paramagnetic spectroscopy (EPR) to sequester specific reaction channels and thereby assess their impact. Photodegradation rates for nanoplates dominated by {001} facets and nanocubes dominated by {012} facets were 0.13 and 0.7 h-1, respectively, and turn over frequencies for the active sites on {001} and {012} were 7.89 × 10-3 and 3.07× 10-3 s-1, yielding apparent activation energies of 17.13 and 24.94 kcal/mol within the energetic span model. Facet-specific differences appear directly linked not with the simple aerial cation site density but instead with their extent of undercoordination. By establishing this linkage, the findings lay a foundation for predicting the photocatalytic degradation efficiency for the myriad of possible hematite nanoparticle morphologies, and more broadly help unveil key reactions at the interface that may govern photocatalytic organic transformations in natural and engineered aquatic environments.